2020 Vol. 45, No. 6
Display Method:
PDF 320KB
2020, 45(6): 1865-1876.
doi: 10.3799/dqkx.2020.071
Abstract:
Accurate landslide susceptibility map is an important basis for landslide risk assessment. In order to improve the accuracy of landslide susceptibility assessment,Longjuba area in the Three Gorges reservoir area was taken as a case study,10 factors (i.e. slope) were selected and parepared,and the frequency ratio method was used to analyze the relationship between each factor and landslide development quantitatively. 70% landslides were randomly selected as training samples while the 30% were adopted for testing,the radial basis neural network and adaboost ensemble learning coupled model (RBNN-Adaboost),radial basis neural network (RBNN) and logistic regression (LR) model were used to make the assessment of landslide susceptibility,respectively. Results show that factors of distance to river,slope and so on are the main controlling factors of landslide development; RBNN-Adaboost shows the best prediction accuracy (0.820) than logistic regression model (0.748) and RBNN (0.781). The adaboost ensemble learning can further improve the prediction performance of the model. By combining the advantages of RBNN and adaboost,the proposed method achieves the highest prediction accuracy,which is a reliable assessment model of landslide susceptibility.
Accurate landslide susceptibility map is an important basis for landslide risk assessment. In order to improve the accuracy of landslide susceptibility assessment,Longjuba area in the Three Gorges reservoir area was taken as a case study,10 factors (i.e. slope) were selected and parepared,and the frequency ratio method was used to analyze the relationship between each factor and landslide development quantitatively. 70% landslides were randomly selected as training samples while the 30% were adopted for testing,the radial basis neural network and adaboost ensemble learning coupled model (RBNN-Adaboost),radial basis neural network (RBNN) and logistic regression (LR) model were used to make the assessment of landslide susceptibility,respectively. Results show that factors of distance to river,slope and so on are the main controlling factors of landslide development; RBNN-Adaboost shows the best prediction accuracy (0.820) than logistic regression model (0.748) and RBNN (0.781). The adaboost ensemble learning can further improve the prediction performance of the model. By combining the advantages of RBNN and adaboost,the proposed method achieves the highest prediction accuracy,which is a reliable assessment model of landslide susceptibility.
2020, 45(6): 1877-1886.
doi: 10.3799/dqkx.2019.272
Abstract:
As an important component of microbial cell membrane,phospholipid fatty acid (PLFAs) can respond sensitively to environmental changes,PLFAs can be altered by microorganisms changing their cell membrane composition by changing their metabolic or nutrient pathways. The current researches on soil PLFAs mainly focus on how changes in seasons and vegetation community affect microbial community structure. It is still not clear how habitats mediate the structure of soil microbial community revealed by topsoil PLFAs. In this study,soil PLFAs compositions were investigated among different habitats (including Sphagnum peat,herb peat,degraded peat,hygrophyte-mesophyte meadow,mesophyte-xeric meadow,xeric meadow,and deciduous broad-leaved forest) in Dajiuhu,Shennongjia. The results show that totally 26 PLFAs with carbon numbers ranging from C14 to C19 are common in the topsoil of the seven habitats. The concentration of total PLFAs in peats is 3-8 times higher than that in meadows. Because of pH and SWC (soil water content) PLFAs also reveal that microbial community structures are different among habitats. The microbial abundance and microbial community structure are similar and different in topsoil under different habitats. The results in this study shed light to better understand the changes of microbial community structure in regional ecosystem,and to facilitate the study of microbe's role in carbon cycle,paleoecology.
As an important component of microbial cell membrane,phospholipid fatty acid (PLFAs) can respond sensitively to environmental changes,PLFAs can be altered by microorganisms changing their cell membrane composition by changing their metabolic or nutrient pathways. The current researches on soil PLFAs mainly focus on how changes in seasons and vegetation community affect microbial community structure. It is still not clear how habitats mediate the structure of soil microbial community revealed by topsoil PLFAs. In this study,soil PLFAs compositions were investigated among different habitats (including Sphagnum peat,herb peat,degraded peat,hygrophyte-mesophyte meadow,mesophyte-xeric meadow,xeric meadow,and deciduous broad-leaved forest) in Dajiuhu,Shennongjia. The results show that totally 26 PLFAs with carbon numbers ranging from C14 to C19 are common in the topsoil of the seven habitats. The concentration of total PLFAs in peats is 3-8 times higher than that in meadows. Because of pH and SWC (soil water content) PLFAs also reveal that microbial community structures are different among habitats. The microbial abundance and microbial community structure are similar and different in topsoil under different habitats. The results in this study shed light to better understand the changes of microbial community structure in regional ecosystem,and to facilitate the study of microbe's role in carbon cycle,paleoecology.
2020, 45(6): 1887-1904.
doi: 10.3799/dqkx.2020.116
Abstract:
To study the change characteristics of extreme temperature in the Yangtze and Yellow River basins,the output data from 22 general climate models (GCMs) of the coupled model intercomparison project phase 5 (CMIP5) were selected.The data were processed by accuracy evaluation and delta downscaling,then 16 extreme temperature indices were calculated based on these data. The ensemble reliability average (REA) results were selected for historical simulation and future prediction of extreme temperature over the two basins. The results show that the spatial characteristics of the observations are in good agreement with that of the REA values,except for the Sichuan basin. During the three periods(2020s,2050s,2080s) in future,the trends of the indices would continually decrease under the Representative Concentration Pathways (RCP) 4.5 scenario,while the trends of these indices would increase under the RCP8.5 scenario. The variation of the indices is similar before the 1940s under the RCP4.5 and RCP8.5 scenarios,however,the variation characteristics under RCP4.5 and RCP8.5 have a significant difference since the 1940s. In the future,most indices would show upward trends,especially in winter. Moreover,the difference of the cold extreme indices between the two basins are greater than the difference of the warm extreme indices.In general,warm extreme events in the Yangtze and Yellow River basins will be more serious in future.
To study the change characteristics of extreme temperature in the Yangtze and Yellow River basins,the output data from 22 general climate models (GCMs) of the coupled model intercomparison project phase 5 (CMIP5) were selected.The data were processed by accuracy evaluation and delta downscaling,then 16 extreme temperature indices were calculated based on these data. The ensemble reliability average (REA) results were selected for historical simulation and future prediction of extreme temperature over the two basins. The results show that the spatial characteristics of the observations are in good agreement with that of the REA values,except for the Sichuan basin. During the three periods(2020s,2050s,2080s) in future,the trends of the indices would continually decrease under the Representative Concentration Pathways (RCP) 4.5 scenario,while the trends of these indices would increase under the RCP8.5 scenario. The variation of the indices is similar before the 1940s under the RCP4.5 and RCP8.5 scenarios,however,the variation characteristics under RCP4.5 and RCP8.5 have a significant difference since the 1940s. In the future,most indices would show upward trends,especially in winter. Moreover,the difference of the cold extreme indices between the two basins are greater than the difference of the warm extreme indices.In general,warm extreme events in the Yangtze and Yellow River basins will be more serious in future.
2020, 45(6): 1905-1917.
doi: 10.3799/dqkx.2019.171
Abstract:
To investigate the impacts of temperature,precipitation and human activity on the vegetation normalized difference vegetation index (NDVI) variation,in this study,taking Yangtze River basin (YRB) as the study area,temperature,precipitation and vegetation NDVI variation were analyzed using linear regression (LR) analysis and Theil-Sen Median trend analysis. The impacts of temperature,precipitation and human activity on vegetation NDVI variation were analyzed using the Pearson correlation analysis and residuals analysis. The results show that the annual mean temperature significantly increased over the whole basin during 1960—2015. However,the precipitation shows little change. The annual mean NDVI shows a significant increasing trend over the whole study area during 1982—2015. The correlation coefficients between NDVI and temperature are high. However,the mean NDVI has no significant correlation with annual precipitation. The regions where the NDVI increased caused by human activity were mainly located in the northern,southeastern and southwestern YRB,while the regions where the NDVI decreased caused by human activity were mainly located in the small part of mid-western YRB and YRD. This study highlights that the mean air temperature has stronger effects on vegetation NDVI than precipitation and the effects of global warming and human activity on ecological environment at the local scale.
To investigate the impacts of temperature,precipitation and human activity on the vegetation normalized difference vegetation index (NDVI) variation,in this study,taking Yangtze River basin (YRB) as the study area,temperature,precipitation and vegetation NDVI variation were analyzed using linear regression (LR) analysis and Theil-Sen Median trend analysis. The impacts of temperature,precipitation and human activity on vegetation NDVI variation were analyzed using the Pearson correlation analysis and residuals analysis. The results show that the annual mean temperature significantly increased over the whole basin during 1960—2015. However,the precipitation shows little change. The annual mean NDVI shows a significant increasing trend over the whole study area during 1982—2015. The correlation coefficients between NDVI and temperature are high. However,the mean NDVI has no significant correlation with annual precipitation. The regions where the NDVI increased caused by human activity were mainly located in the northern,southeastern and southwestern YRB,while the regions where the NDVI decreased caused by human activity were mainly located in the small part of mid-western YRB and YRD. This study highlights that the mean air temperature has stronger effects on vegetation NDVI than precipitation and the effects of global warming and human activity on ecological environment at the local scale.
2020, 45(6): 1918-1927.
doi: 10.3799/dqkx.2019.205
Abstract:
In order to understand the land cover change of beach in the Dongting Lake since the 1970s, it has been systematically monitored based on various remote sensing images since 1978 in this study. Results show that poplar and reed land have experienced the largest changes of land cover in the past 40 years,showing a complementary relationship with one increased with decrease of the other. After 2007, the distribution area of poplar and reed land has been basically same. Till 2015, the distribution area of poplar land has been substantially reduced,and the distribution area of the reed land has been steadily increased. Before 2002, the beach area of Dongting Lake has been increased,after that,the area tends to be stable. Reed land and lake grass are two most covered categories in the Dongting Lake,which is 2/3 of the total beach area. In Dongting Lake Nature Reserve area,populus nigra is widely distributed in the Nature Protection Zone of South Dongting Lake,reed is widely distributed in the Nature Protection Zone of East and South Dongting Lake. Since 2015, the artificial usage of the beach in the Dongting Lake is decresed to 48.57%,but further control measures are urgently needed.
In order to understand the land cover change of beach in the Dongting Lake since the 1970s, it has been systematically monitored based on various remote sensing images since 1978 in this study. Results show that poplar and reed land have experienced the largest changes of land cover in the past 40 years,showing a complementary relationship with one increased with decrease of the other. After 2007, the distribution area of poplar and reed land has been basically same. Till 2015, the distribution area of poplar land has been substantially reduced,and the distribution area of the reed land has been steadily increased. Before 2002, the beach area of Dongting Lake has been increased,after that,the area tends to be stable. Reed land and lake grass are two most covered categories in the Dongting Lake,which is 2/3 of the total beach area. In Dongting Lake Nature Reserve area,populus nigra is widely distributed in the Nature Protection Zone of South Dongting Lake,reed is widely distributed in the Nature Protection Zone of East and South Dongting Lake. Since 2015, the artificial usage of the beach in the Dongting Lake is decresed to 48.57%,but further control measures are urgently needed.
2020, 45(6): 1928-1936.
doi: 10.3799/dqkx.2020.015
Abstract:
Based on the historical topographic maps of the 1930s and 1950s, the 1954 aerial photo,the 1968 US KH-4B military satellite imagery,and the 2016 domestic GF-1 satellite imagery,in this paper,it comprehensively analyses the paleo-channel under the Jingjiang River. It evolved characteristics and inverted the historical changes of its 400 years since the Ming Dynasty. The results show that the paleo-channel of the Jingjiang River section is frequently oscillated laterally,and is constrained by the hard bank slope and artificial revetment project,there are 20-32 km space sway zone along the paleo-channel plane,the morphological form are two: lateral gradual swing along the main squall line and sudden migration of river channels,which are the bases for the inversion of the paleo-channel in the Jingjiang River. Historically,the shaping of the Lower Jingjiang River has undergone complicated processes,such as overflow,branching and diversion,formation of a single straight channel and evolution and development of meandering. During the period of Hongzhi in the Ming Dynasty,meandering currents mainly occurred in Jianli-Chenglingji section,while the section from Shishou to Jianli was only slightly curved. In the late Ming and early Qing Dynasties,Donggang Lake bend and Haohe River bend were cut and straightened naturally. The meandering channel of the Lower Jingjiang River had been traced back to Shishou in an all-round way and formed a series of meandering bends. In the middle of the 19th century,the development of the meander of the Lower Jingjiang River was characterized by lateral movement,narrowing of the meandering neck,retreat of the concave bank circulation erosion,and high thrust of the convex bank. Since then,there has been no major change. The evolution mode of modern river bend of Lower Jingjiang River includes deposition-propelled in convex bank,collapse-back in concave bank,cut-bank and thrown-away-elbow in convex bank,cut-bend,combing drifting central bar with the bank,cluster ditch-flow in concave bank.The role of the river itself is the main reason for its evolution,but the artificial construction of the levee and large-scale cofferdams are important external factors.
Based on the historical topographic maps of the 1930s and 1950s, the 1954 aerial photo,the 1968 US KH-4B military satellite imagery,and the 2016 domestic GF-1 satellite imagery,in this paper,it comprehensively analyses the paleo-channel under the Jingjiang River. It evolved characteristics and inverted the historical changes of its 400 years since the Ming Dynasty. The results show that the paleo-channel of the Jingjiang River section is frequently oscillated laterally,and is constrained by the hard bank slope and artificial revetment project,there are 20-32 km space sway zone along the paleo-channel plane,the morphological form are two: lateral gradual swing along the main squall line and sudden migration of river channels,which are the bases for the inversion of the paleo-channel in the Jingjiang River. Historically,the shaping of the Lower Jingjiang River has undergone complicated processes,such as overflow,branching and diversion,formation of a single straight channel and evolution and development of meandering. During the period of Hongzhi in the Ming Dynasty,meandering currents mainly occurred in Jianli-Chenglingji section,while the section from Shishou to Jianli was only slightly curved. In the late Ming and early Qing Dynasties,Donggang Lake bend and Haohe River bend were cut and straightened naturally. The meandering channel of the Lower Jingjiang River had been traced back to Shishou in an all-round way and formed a series of meandering bends. In the middle of the 19th century,the development of the meander of the Lower Jingjiang River was characterized by lateral movement,narrowing of the meandering neck,retreat of the concave bank circulation erosion,and high thrust of the convex bank. Since then,there has been no major change. The evolution mode of modern river bend of Lower Jingjiang River includes deposition-propelled in convex bank,collapse-back in concave bank,cut-bank and thrown-away-elbow in convex bank,cut-bend,combing drifting central bar with the bank,cluster ditch-flow in concave bank.The role of the river itself is the main reason for its evolution,but the artificial construction of the levee and large-scale cofferdams are important external factors.
2020, 45(6): 1937-1947.
doi: 10.3799/dqkx.2020.012
Abstract:
Tuojiang River is one of the most important tributaries among the Upper Reaches of Yangtze River basin. In order to characterize of the water quality variations and the prevention focus of Tuojiang River basin,this paper presents analyses in its four periods of the year,month,quarter and water period using single factor evaluation and rank correlation coefficient method,based on the monitoring data of water quality in 36 monitoring sections in Tuojiang River Basin from 2010 to 2017, the results show that the water quality of Tuojiang River basin was generally in a polluted state,but has a positive trend. Total phosphorus (TP) was the primary pollutant. The standard rate of water quality monitoring sections in basin shows a trend of increasing first,then decreasing and then increasing again. The water quality index changed significantly during the year,which reached its minimum in wet season and reached the maximum in dry season. Besides,the water quality of the main stream was better than that of the tributary. The spatial variability of TP and ammonia nitrogen (NH3-N) concentrations were weak,and the spatial variability of chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) concentrations were strong. Although the water environmental quality of Tuojiang River basin has changed,the pollution problem that Tuojiang River basin faced is still grim. Therefore,it is necessary to attach great importance to the control of pollution source,especially the prevention of TP in future.
Tuojiang River is one of the most important tributaries among the Upper Reaches of Yangtze River basin. In order to characterize of the water quality variations and the prevention focus of Tuojiang River basin,this paper presents analyses in its four periods of the year,month,quarter and water period using single factor evaluation and rank correlation coefficient method,based on the monitoring data of water quality in 36 monitoring sections in Tuojiang River Basin from 2010 to 2017, the results show that the water quality of Tuojiang River basin was generally in a polluted state,but has a positive trend. Total phosphorus (TP) was the primary pollutant. The standard rate of water quality monitoring sections in basin shows a trend of increasing first,then decreasing and then increasing again. The water quality index changed significantly during the year,which reached its minimum in wet season and reached the maximum in dry season. Besides,the water quality of the main stream was better than that of the tributary. The spatial variability of TP and ammonia nitrogen (NH3-N) concentrations were weak,and the spatial variability of chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) concentrations were strong. Although the water environmental quality of Tuojiang River basin has changed,the pollution problem that Tuojiang River basin faced is still grim. Therefore,it is necessary to attach great importance to the control of pollution source,especially the prevention of TP in future.
2020, 45(6): 1948-1955.
doi: 10.3799/dqkx.2020.004
Abstract:
Refined extraction of surface gullies is an important part of topography research. Aiming at the existence of fracture zones and a pseudo-gully zones in the existing gully extraction results,in this paper,it proposes an "expansion-fusion" extraction method based on DEM and high-resolution remote sensing image. The method combines the D8 algorithm,the SOA (slope of aspect) algorithm and the object-oriented classification method to extract the results. Firstly,the distance mapping algorithm is introduced to directional expansion of the initial gully,and then the raster re-classification and algebraic operation are used to merge the gully and eliminate the pseudo-gully. In this study,this method is adopted to extract gully area with GDEM v2 data and GF-2 data covering the area of Juheigou to Mawancun in Shennongjia Forest of Hubei Province. The random point verification method is used to evaluate the accuracy of the gully extraction in the experimental area. The results show that the overall accuracy of the method is 92%,which can effectively bridge the fracture area in the combined data,and eliminate the pseudo-gully area to improve the extraction accuracy of the gully.
Refined extraction of surface gullies is an important part of topography research. Aiming at the existence of fracture zones and a pseudo-gully zones in the existing gully extraction results,in this paper,it proposes an "expansion-fusion" extraction method based on DEM and high-resolution remote sensing image. The method combines the D8 algorithm,the SOA (slope of aspect) algorithm and the object-oriented classification method to extract the results. Firstly,the distance mapping algorithm is introduced to directional expansion of the initial gully,and then the raster re-classification and algebraic operation are used to merge the gully and eliminate the pseudo-gully. In this study,this method is adopted to extract gully area with GDEM v2 data and GF-2 data covering the area of Juheigou to Mawancun in Shennongjia Forest of Hubei Province. The random point verification method is used to evaluate the accuracy of the gully extraction in the experimental area. The results show that the overall accuracy of the method is 92%,which can effectively bridge the fracture area in the combined data,and eliminate the pseudo-gully area to improve the extraction accuracy of the gully.
2020, 45(6): 1956-1966.
doi: 10.3799/dqkx.2020.005
Abstract:
Due to the impacts of climate change and anthropogenic activities, water resource issues are challenging and have been received much attention worldwide. Over the last few decades, the development of satellite altimetry has enabled the monitoring of lake levels over a large spatial extent. In this work, water-level changes from lakes in Dongting Lake basin were derived from ICESat-1 and CryoSat-2 altimetry data during the period of 2003 to 2017. The temporal variation of lake water levels was analyzed to characterize the water level dynamics in different periods. The TRMM satellite precipitation data and human water consumption data were collected to identify the responses of lake water level changes to both climate change and human activities. The results indicate that 80% of the lakes in the basin exhibite a downward trend (-0.18 to -0.09 m/a) in lake water levels in 2003—2009, while 75% of the lakes show a stable or rising trend (0-0.39 m/a) in water levels in 2010—2017. In general, 75% of the lakes show a rising trend (0.02-0.22 m/a) in water levels during the period of 2003 to 2017. The analysis reveals that the change of lake water levels is the result of a combination of multiple factors. Precipitation is the main driving factor for lake water level change. In addition, the operation of reservoirs produced a seasonal variation in the water level of lakes. The continued growth of human water consumption also has a certain impact on the lake water level. Multi-mission altimetry satellite provides a powerful tool for the long-term and large-scale monitoring of lake level variations, which is of great significance to the study of lake level change and its response to climate and environment.
Due to the impacts of climate change and anthropogenic activities, water resource issues are challenging and have been received much attention worldwide. Over the last few decades, the development of satellite altimetry has enabled the monitoring of lake levels over a large spatial extent. In this work, water-level changes from lakes in Dongting Lake basin were derived from ICESat-1 and CryoSat-2 altimetry data during the period of 2003 to 2017. The temporal variation of lake water levels was analyzed to characterize the water level dynamics in different periods. The TRMM satellite precipitation data and human water consumption data were collected to identify the responses of lake water level changes to both climate change and human activities. The results indicate that 80% of the lakes in the basin exhibite a downward trend (-0.18 to -0.09 m/a) in lake water levels in 2003—2009, while 75% of the lakes show a stable or rising trend (0-0.39 m/a) in water levels in 2010—2017. In general, 75% of the lakes show a rising trend (0.02-0.22 m/a) in water levels during the period of 2003 to 2017. The analysis reveals that the change of lake water levels is the result of a combination of multiple factors. Precipitation is the main driving factor for lake water level change. In addition, the operation of reservoirs produced a seasonal variation in the water level of lakes. The continued growth of human water consumption also has a certain impact on the lake water level. Multi-mission altimetry satellite provides a powerful tool for the long-term and large-scale monitoring of lake level variations, which is of great significance to the study of lake level change and its response to climate and environment.
2020, 45(6): 1967-1976.
doi: 10.3799/dqkx.2020.159
Abstract:
The deep carbon cycle and surface's carbon cycle together constitute the global carbon cycle. Research on deep carbon cycles is of significance for understanding the long-term climate change of the Earth given that >90% of Earth's carbon is stored in the deep Earth. Research on deep carbon cycles involves many aspects, among which one of the most important scientific issues is how to accurately identify recycled surface carbon in the mantle. Zinc (Zn) is a lithophile element and widely distributed in igneous rocks, mantle and sedimentary carbonates. There is a large Zn isotope difference between marine carbonates and the terrestrial mantle. Also, subduction-related dehydration, partial melting and magmatic differentiation only result in limited Zn isotope fractionation. Thus, Zn isotope has the potential as a novel tracer for deep carbon cycles. In this paper, the principle and potentiality of Zn isotope utilized as a tracer for deep carbon cycle are reviewed and the advances of using Zn isotope to trace deep carbon cycles in previous studies are presented. In addition, the combination between Zn and magnesium (Mg) isotopes is expect to the essential aspect of the deep carbon cycles in the future.
The deep carbon cycle and surface's carbon cycle together constitute the global carbon cycle. Research on deep carbon cycles is of significance for understanding the long-term climate change of the Earth given that >90% of Earth's carbon is stored in the deep Earth. Research on deep carbon cycles involves many aspects, among which one of the most important scientific issues is how to accurately identify recycled surface carbon in the mantle. Zinc (Zn) is a lithophile element and widely distributed in igneous rocks, mantle and sedimentary carbonates. There is a large Zn isotope difference between marine carbonates and the terrestrial mantle. Also, subduction-related dehydration, partial melting and magmatic differentiation only result in limited Zn isotope fractionation. Thus, Zn isotope has the potential as a novel tracer for deep carbon cycles. In this paper, the principle and potentiality of Zn isotope utilized as a tracer for deep carbon cycle are reviewed and the advances of using Zn isotope to trace deep carbon cycles in previous studies are presented. In addition, the combination between Zn and magnesium (Mg) isotopes is expect to the essential aspect of the deep carbon cycles in the future.
2020, 45(6): 1977-1985.
doi: 10.3799/dqkx.2019.285
Abstract:
A high precision zircon Pb isotope ratio measurement method (using 205Pb as spike) was developed with a TRITON Plus thermal ionization mass spectrometer (TIMS) equipped with a multiple ion-counting (MIC) system. With the method, the Pb isotopes were measured with multi-ion counters using a multi-dynamic ion collection method. Compared to the traditional static multi-collection MIC method, the multi-dynamic MIC method can completely eliminate the influence of gain bias between different ion counters on the Pb isotope analytical results. Compared to the traditional zircon ID-TIMS Pb isotopic measurement method using a single secondary electron multiplier (SEM) with five peak jumps, the multi-dynamic MIC method can determine all the Pb isotope ratios of zircon in two peak jumps. Thus, the ion collection efficiency for the Pb isotopes were improved by 2.5 folds. In the meantime, the influences of ion beam stability on the analytical results of Pb isotopes was also reduced. To verify the reliability of the method, NIST981 Pb standards doped with 205Pb spike and Qinghu standard zircons were measured. The analytical precision of 207Pb/206Pb for 5×10-11 g of 205Pb-NIST981 Pb mixture can achieve 0.079% (2RSD, n=20). The analytical 206Pb/238U age result for Qinghu standard zircon was 159.51±0.11 Ma(2SE, n=7; MSWD=1.1), which was consistent with the previously reported values within analytical error.
A high precision zircon Pb isotope ratio measurement method (using 205Pb as spike) was developed with a TRITON Plus thermal ionization mass spectrometer (TIMS) equipped with a multiple ion-counting (MIC) system. With the method, the Pb isotopes were measured with multi-ion counters using a multi-dynamic ion collection method. Compared to the traditional static multi-collection MIC method, the multi-dynamic MIC method can completely eliminate the influence of gain bias between different ion counters on the Pb isotope analytical results. Compared to the traditional zircon ID-TIMS Pb isotopic measurement method using a single secondary electron multiplier (SEM) with five peak jumps, the multi-dynamic MIC method can determine all the Pb isotope ratios of zircon in two peak jumps. Thus, the ion collection efficiency for the Pb isotopes were improved by 2.5 folds. In the meantime, the influences of ion beam stability on the analytical results of Pb isotopes was also reduced. To verify the reliability of the method, NIST981 Pb standards doped with 205Pb spike and Qinghu standard zircons were measured. The analytical precision of 207Pb/206Pb for 5×10-11 g of 205Pb-NIST981 Pb mixture can achieve 0.079% (2RSD, n=20). The analytical 206Pb/238U age result for Qinghu standard zircon was 159.51±0.11 Ma(2SE, n=7; MSWD=1.1), which was consistent with the previously reported values within analytical error.
2020, 45(6): 1986-1998.
doi: 10.3799/dqkx.2020.074
Abstract:
In this paper, it documents for the first time the presence of the distinctive Grt-Ky-Cld assemblage low-temperature/high-pressure (LT-HP) eclogitic metapelites from the Paleoproterozoic Shuiyuesi mélange belt in the Kongling complex, Yangtze craton. The high-pressure metapelites display peak metamorphic mineral assemblages of garnet+kyanite+chloritoid+phengite+rutile+quartz. A near-isothermal decompression (ITD) clockwise P-T path with peak conditions of 571-576 ℃ and 19.2-21.8 kbar were estimated by phase equilibria modelling. The LA-ICP-MS zircon U-Pb dating shows that the metapelite has a metamorphic age of 1 991±20 Ma recorded by zircon rims and ages ranges from 2.1 to 2.2 Ga recorded detrital zircon cores. The sedimentary tectonic setting and metamorphic peak conditions of the Grt-Ky-Cld assemblage in eclogitic metapelites indicate that it has formed in a cold subduction zone with low thermal gradient (dT/dP≈300 ℃/GPa) at the active continental margin. Our study further implies that the modern plate tectonics with "cold subduction" tectonic characteristics has been initiated at least since the Paleoproterozoic.
In this paper, it documents for the first time the presence of the distinctive Grt-Ky-Cld assemblage low-temperature/high-pressure (LT-HP) eclogitic metapelites from the Paleoproterozoic Shuiyuesi mélange belt in the Kongling complex, Yangtze craton. The high-pressure metapelites display peak metamorphic mineral assemblages of garnet+kyanite+chloritoid+phengite+rutile+quartz. A near-isothermal decompression (ITD) clockwise P-T path with peak conditions of 571-576 ℃ and 19.2-21.8 kbar were estimated by phase equilibria modelling. The LA-ICP-MS zircon U-Pb dating shows that the metapelite has a metamorphic age of 1 991±20 Ma recorded by zircon rims and ages ranges from 2.1 to 2.2 Ga recorded detrital zircon cores. The sedimentary tectonic setting and metamorphic peak conditions of the Grt-Ky-Cld assemblage in eclogitic metapelites indicate that it has formed in a cold subduction zone with low thermal gradient (dT/dP≈300 ℃/GPa) at the active continental margin. Our study further implies that the modern plate tectonics with "cold subduction" tectonic characteristics has been initiated at least since the Paleoproterozoic.
2020, 45(6): 1999-2010.
doi: 10.3799/dqkx.2019.193
Abstract:
Zhongdian arc is located in the southern section of the Yidun arc at the Sanjiang Tethys, Southwest China. It is known as the Indosinian porphyry copper deposits and the Yanshanian skarn-hydrothermal quartz vein Mo-W-Cu deposits. In this paper, it was measured the titanite chemical compositions from ore-forming rocks of Pulang, Disuga and Xiuwacu with EMPA and LA-ICP-MS to discuss their implications for petrogenesis and mineralization. The titanites from Pulang, Disuga and Xiuwacu are all of magmatic origin. The titanite formation temperature from Pulang pluton is 743-754 ℃, and 702-753 ℃ from Xiuwacu pluton. Based on the δCe, δEu from titanites, it can be inferred that the order of oxygen fugacity of these plutons is: Pulang > Disuga > Xiuwacu. It requires high magma oxygen fugacity for Cu mineralization, but the Cu contents in titanite are insensitive to the content variations of Cu in magma, which can not be used as an indication of the Cu contents in magma. Mo mineralization does not require high magma oxygen fugacity, and the magma oxygen fugacity and crystalization of molybdenite need to be thought when we use the Mo contents of titanite to determine the Mo fertility in magma. The F contents in magma can reduce magma viscosity and promote Mo mineralization which can be an indication for Mo mineralization. The W and Sn contents in the titanite is a good indication of the Mo-W mineralization, and the W and Sn contents in the Xiuwacu Mo-W deposit are higher than those in the Pulang and Disuga.
Zhongdian arc is located in the southern section of the Yidun arc at the Sanjiang Tethys, Southwest China. It is known as the Indosinian porphyry copper deposits and the Yanshanian skarn-hydrothermal quartz vein Mo-W-Cu deposits. In this paper, it was measured the titanite chemical compositions from ore-forming rocks of Pulang, Disuga and Xiuwacu with EMPA and LA-ICP-MS to discuss their implications for petrogenesis and mineralization. The titanites from Pulang, Disuga and Xiuwacu are all of magmatic origin. The titanite formation temperature from Pulang pluton is 743-754 ℃, and 702-753 ℃ from Xiuwacu pluton. Based on the δCe, δEu from titanites, it can be inferred that the order of oxygen fugacity of these plutons is: Pulang > Disuga > Xiuwacu. It requires high magma oxygen fugacity for Cu mineralization, but the Cu contents in titanite are insensitive to the content variations of Cu in magma, which can not be used as an indication of the Cu contents in magma. Mo mineralization does not require high magma oxygen fugacity, and the magma oxygen fugacity and crystalization of molybdenite need to be thought when we use the Mo contents of titanite to determine the Mo fertility in magma. The F contents in magma can reduce magma viscosity and promote Mo mineralization which can be an indication for Mo mineralization. The W and Sn contents in the titanite is a good indication of the Mo-W mineralization, and the W and Sn contents in the Xiuwacu Mo-W deposit are higher than those in the Pulang and Disuga.
2020, 45(6): 2011-2029.
doi: 10.3799/dqkx.2020.024
Abstract:
Detailed researches on Zircon U-Pb chronology and geochemistry of the Dengshan Group in the eastern Jiangnan orogen have been undertaken in this paper in order to figure out the tectonic setting of the eastern Jiangnan orogen in the Neoproterozoic. SHRIMP zircon U-Pb dating of two samples yielded weighted mean ages of 855.5±8.2 Ma and 798±7.8 Ma, respectively. The sandstone rocks are mostly affiliated with a continental arc, in good agreement with the proposed back-arc basin scenario. These rhyolites display LREE enriched REE patterns, with positive εHf(t) values, and has high values of FeOt/(FeOt+MgO) and Ga/Al, low contents of CaO and MgO, and it is enriched in Ba, Th, U and HFSEs, and depleted in Sr, P, and Ti, thus resembling A-type granitoids. These basalts are of tholeiitic basalt, and display ocean island basalt (OIB)-like geochemical signatures, with the enrichment of LREE and large-ion lithophile element relative to HREE. The bimodal volcanic rocks are suggested to be formed during post-collisional extension setting. Combined with the previously data from the Jiangnan orogen, we propose that the Jiangnan orogen leading to the assembly of the Yangtze and Cathaysia Blocks took place during 855-800 Ma. This was followed by breakup after the orogenesis which was triggered by mantle upwelling.
Detailed researches on Zircon U-Pb chronology and geochemistry of the Dengshan Group in the eastern Jiangnan orogen have been undertaken in this paper in order to figure out the tectonic setting of the eastern Jiangnan orogen in the Neoproterozoic. SHRIMP zircon U-Pb dating of two samples yielded weighted mean ages of 855.5±8.2 Ma and 798±7.8 Ma, respectively. The sandstone rocks are mostly affiliated with a continental arc, in good agreement with the proposed back-arc basin scenario. These rhyolites display LREE enriched REE patterns, with positive εHf(t) values, and has high values of FeOt/(FeOt+MgO) and Ga/Al, low contents of CaO and MgO, and it is enriched in Ba, Th, U and HFSEs, and depleted in Sr, P, and Ti, thus resembling A-type granitoids. These basalts are of tholeiitic basalt, and display ocean island basalt (OIB)-like geochemical signatures, with the enrichment of LREE and large-ion lithophile element relative to HREE. The bimodal volcanic rocks are suggested to be formed during post-collisional extension setting. Combined with the previously data from the Jiangnan orogen, we propose that the Jiangnan orogen leading to the assembly of the Yangtze and Cathaysia Blocks took place during 855-800 Ma. This was followed by breakup after the orogenesis which was triggered by mantle upwelling.
2020, 45(6): 2030-2043.
doi: 10.3799/dqkx.2020.008
Abstract:
Late Jurassic magmatic activity in the Liaodong Peninsula was less and the research degree was lower. In this paper, zircon U-Pb dating, geochemistry and zircon Lu-Hf isotope analysis were carried out to further understand the tectonic dynamics of the Liaodong Peninsula in the Late Jurassic. The U-Pb weighted mean age of magmatic zircons in the Huangdi granite is 161.1±3.6 Ma (MSWD=1.4), indicating that the formation of the Huangdi granite is the Late Jurassic, which is the product of the Yanshanian magmatism. The pluton contains muscovite and other aluminum-rich minerals geochemical data show that the pluton is the peraluminum calcium alkaline series, enriched with LILE such as K, Rb, Cs, and Ba, and depleted HFSE such as Nb, Ti, and P. With the characteristics of light rare earth element enrichment and heavy rare earth element loss, Eu is a moderate negative anomaly (δEu=0.33-0.80).The average A/CNK value of the granite is 1.10, and the corundum molecule (>1%) appears in the CIPW standard mineral. It is considered that the pluton is an S-type granite that has undergone a high degree of crystallization differentiation. The CaO/Na2O ratio of the Huangdi granite is less than 0.3, and the εHf(t) is less than 0 (-36.968 to -23.298), indicating that the rock is formed by the mudstone of the earth's crust. The single-stage Hf mode age is TDM=1 728-2 311 Ma, the two-stage Hf mode age is TDMC = 2 680-3 568 Ma. It is shown that the time when the constituent materials of the source rock of the pluton were separated from the mantle reservoir was Neo-Archean to Ancient Archean.In summary, the pluton is formed in the background of the ancient Pacific plate subduction to the Eurasian continent and the subduction angle becomes larger and submerged deeper.
Late Jurassic magmatic activity in the Liaodong Peninsula was less and the research degree was lower. In this paper, zircon U-Pb dating, geochemistry and zircon Lu-Hf isotope analysis were carried out to further understand the tectonic dynamics of the Liaodong Peninsula in the Late Jurassic. The U-Pb weighted mean age of magmatic zircons in the Huangdi granite is 161.1±3.6 Ma (MSWD=1.4), indicating that the formation of the Huangdi granite is the Late Jurassic, which is the product of the Yanshanian magmatism. The pluton contains muscovite and other aluminum-rich minerals geochemical data show that the pluton is the peraluminum calcium alkaline series, enriched with LILE such as K, Rb, Cs, and Ba, and depleted HFSE such as Nb, Ti, and P. With the characteristics of light rare earth element enrichment and heavy rare earth element loss, Eu is a moderate negative anomaly (δEu=0.33-0.80).The average A/CNK value of the granite is 1.10, and the corundum molecule (>1%) appears in the CIPW standard mineral. It is considered that the pluton is an S-type granite that has undergone a high degree of crystallization differentiation. The CaO/Na2O ratio of the Huangdi granite is less than 0.3, and the εHf(t) is less than 0 (-36.968 to -23.298), indicating that the rock is formed by the mudstone of the earth's crust. The single-stage Hf mode age is TDM=1 728-2 311 Ma, the two-stage Hf mode age is TDMC = 2 680-3 568 Ma. It is shown that the time when the constituent materials of the source rock of the pluton were separated from the mantle reservoir was Neo-Archean to Ancient Archean.In summary, the pluton is formed in the background of the ancient Pacific plate subduction to the Eurasian continent and the subduction angle becomes larger and submerged deeper.
2020, 45(6): 2044-2058.
doi: 10.3799/dqkx.2019.277
Abstract:
The multistage magmatism and metamorphism in the Paleoproterozoic of the southern North China craton (NCC) have recorded the basement and tectonic evolution of the southern NCC. However, the magmatism in Middle-Late Paleoproterozoic were rarely reported. In this paper, it presents a detailed study of petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotope for the Middle-Late Paleoproterozoic granites in the Xinyang area of southern NCC. They include the Panzhuang K-feldspar granite and Chenzhuang biotite K-feldspar granite. The magmatic zircons from them yield the crystallization ages of 1 868 Ma and 1 955 Ma, respectively, indicating that they formed in the Middle-Late Paleoproterozoic. All the studied granites have high SiO2, and total alkaline, but low CaO, P2O5 and MgO contents. Their A/CNK values range from 1.12 to 1.28, suggesting that they are peraluminous rocks. Meanwhile, they show enrichment of LILEs (e.g. Rb, Th and K) but depletion of HFSEs (e.g. Nb, Ta and Ti), Sr and P with moderate to weak negative Eu anomalies. Moreover, the Panzhuang and Chenzhuang plutons have similar zircon εHf(t) values (-0.6-+2.6), with the two-stage Hf model ages (Tcrust) ranging in 2.40-2.64 Ga. All of these evidences indicate that the Late Archean to Early Paleoproterozoic crust in the Xinyang area were strongly modified in Middle-Late Paleoproterozoic. Combined with the records of magmatism and metamorphic events in the southern margin of the NCC, it is suggested that the formation of the granites in the Xinyang area may be related to the collision between the eastern and western blocks of NCC. Furthermore, the frequent Paleoproterozoic magmatic activities (2.24-1.85 Ga) in this area probably resulted from an eastward-directed subduction of an ancient ocean between the eastern and western blocks, and the western block.
The multistage magmatism and metamorphism in the Paleoproterozoic of the southern North China craton (NCC) have recorded the basement and tectonic evolution of the southern NCC. However, the magmatism in Middle-Late Paleoproterozoic were rarely reported. In this paper, it presents a detailed study of petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotope for the Middle-Late Paleoproterozoic granites in the Xinyang area of southern NCC. They include the Panzhuang K-feldspar granite and Chenzhuang biotite K-feldspar granite. The magmatic zircons from them yield the crystallization ages of 1 868 Ma and 1 955 Ma, respectively, indicating that they formed in the Middle-Late Paleoproterozoic. All the studied granites have high SiO2, and total alkaline, but low CaO, P2O5 and MgO contents. Their A/CNK values range from 1.12 to 1.28, suggesting that they are peraluminous rocks. Meanwhile, they show enrichment of LILEs (e.g. Rb, Th and K) but depletion of HFSEs (e.g. Nb, Ta and Ti), Sr and P with moderate to weak negative Eu anomalies. Moreover, the Panzhuang and Chenzhuang plutons have similar zircon εHf(t) values (-0.6-+2.6), with the two-stage Hf model ages (Tcrust) ranging in 2.40-2.64 Ga. All of these evidences indicate that the Late Archean to Early Paleoproterozoic crust in the Xinyang area were strongly modified in Middle-Late Paleoproterozoic. Combined with the records of magmatism and metamorphic events in the southern margin of the NCC, it is suggested that the formation of the granites in the Xinyang area may be related to the collision between the eastern and western blocks of NCC. Furthermore, the frequent Paleoproterozoic magmatic activities (2.24-1.85 Ga) in this area probably resulted from an eastward-directed subduction of an ancient ocean between the eastern and western blocks, and the western block.
2020, 45(6): 2059-2076.
doi: 10.3799/dqkx.2020.084
Abstract:
In order to understand the formation environment and evolution process of pegmatite magma in Northeast Guangxi, in this paper, the garnet in the pegmatite around the Nb-Ta-Be-Rb rare metal deposit in Mao'antang, Northeast Guangxi, was observed under microscope and studied by EPMA and LA-ICP-MS. The results show that the garnets in pegmatites in Mao'antang area form Northeast Guangxi are magmatic genesis garnets, which belong to the solid solution series of almandine manganese almandine (average Alm49.28-Sps47.09). It can be divided into early iron aluminum garnet (GrtⅠ) and late manganese aluminum garnet (GrtⅡ). Both phases of the garnet with enrichment of heavy rare earth elements (HREE) and high field strength elements (HFSE), loss of light rare earth elements (LREE) and lack of large ion lithophile elements (LILE) as the characteristics of ∑REE distribution pattern show a trend of obvious left-leaning and Eu negative anomaly. The interface reaction rate during the growth of garnet is less than the material migration rate, and the water-rock interaction is weak, ∑REE mainly in the form of surface adsorption and absorption into the garnet stone is responsible for its heavy rare earth elements (HREE), the main cause of light rare earth losses. With the increasing degree of magma differentiation evolution, ∑REE gradually enters and accumulates in the garnet, promoting the evolution of magma from the early low-fractionation (unfractionated) magma melt to the late high-fractionation magma melt. The HREE content in garnet gradually increases with the degree of magma evolution, indicating that late differential evolution of magmatic-hydrothermal fluid is gradually enriched with rare earth and rare metal elements. In the late hydrothermal fluid metasomatism primary minerals, which are rich in metallogenic elements, lead to the development of a large number of metasomatism rare earth and rare metal minerals in the lateral zone and the nuclear granite pegmatite.
In order to understand the formation environment and evolution process of pegmatite magma in Northeast Guangxi, in this paper, the garnet in the pegmatite around the Nb-Ta-Be-Rb rare metal deposit in Mao'antang, Northeast Guangxi, was observed under microscope and studied by EPMA and LA-ICP-MS. The results show that the garnets in pegmatites in Mao'antang area form Northeast Guangxi are magmatic genesis garnets, which belong to the solid solution series of almandine manganese almandine (average Alm49.28-Sps47.09). It can be divided into early iron aluminum garnet (GrtⅠ) and late manganese aluminum garnet (GrtⅡ). Both phases of the garnet with enrichment of heavy rare earth elements (HREE) and high field strength elements (HFSE), loss of light rare earth elements (LREE) and lack of large ion lithophile elements (LILE) as the characteristics of ∑REE distribution pattern show a trend of obvious left-leaning and Eu negative anomaly. The interface reaction rate during the growth of garnet is less than the material migration rate, and the water-rock interaction is weak, ∑REE mainly in the form of surface adsorption and absorption into the garnet stone is responsible for its heavy rare earth elements (HREE), the main cause of light rare earth losses. With the increasing degree of magma differentiation evolution, ∑REE gradually enters and accumulates in the garnet, promoting the evolution of magma from the early low-fractionation (unfractionated) magma melt to the late high-fractionation magma melt. The HREE content in garnet gradually increases with the degree of magma evolution, indicating that late differential evolution of magmatic-hydrothermal fluid is gradually enriched with rare earth and rare metal elements. In the late hydrothermal fluid metasomatism primary minerals, which are rich in metallogenic elements, lead to the development of a large number of metasomatism rare earth and rare metal minerals in the lateral zone and the nuclear granite pegmatite.
2020, 45(6): 2077-2090.
doi: 10.3799/dqkx.2020.030
Abstract:
Sumatra Island is located in the southwestern margin of the Sundaland, and is divided into East/West Sumatra by the Medial Sumatran Zone. While East Sumatran basement affinity and tectonic evolution are not well defined. The Early Paleozoic granitic gneisses have been identified from the East Sumatra Terrane, with providing zircon U-Pb age, in-situ Hf isotopic and geochemical results. Geochronological result yields a 206Pb/238U mean age of 442 ±5 Ma (MSWD = 1.03), representing the crystalline age. Zircon εHf (t) values range from -1.3 to -7.8. The whole-rock geochemical characteristics show that our samples are characterized by high SiO2 (69.97%-74.30%) and Al2O3 (13.90%-15.93%), but poor in TiO2 (0.48%-0.61%), MgO (0.54%-0.93%) and CaO (0.11%-0.25%). These samples have high A/CNK (2.58-3.06) and CIPW-normalized corundum (10.0%-11.4%), similar to those of the S-type granite. They have obvious fractionation between LREEs and HREEs. These samples are characterized by enrichment in LILEs (Rb, Th, U) and depletion in HFSEs (Nb, Ta, Ti). The geochemical results indicate that the Takengon granitic gneisses are originated from the partial melting of the meta-sediments during the evolution of the Prototethyan Ocean. This study confirms the existing of Early Silurian basement rocks in the East Sumatra Terrane, which were related to the Prototethyan evolution.
Sumatra Island is located in the southwestern margin of the Sundaland, and is divided into East/West Sumatra by the Medial Sumatran Zone. While East Sumatran basement affinity and tectonic evolution are not well defined. The Early Paleozoic granitic gneisses have been identified from the East Sumatra Terrane, with providing zircon U-Pb age, in-situ Hf isotopic and geochemical results. Geochronological result yields a 206Pb/238U mean age of 442 ±5 Ma (MSWD = 1.03), representing the crystalline age. Zircon εHf (t) values range from -1.3 to -7.8. The whole-rock geochemical characteristics show that our samples are characterized by high SiO2 (69.97%-74.30%) and Al2O3 (13.90%-15.93%), but poor in TiO2 (0.48%-0.61%), MgO (0.54%-0.93%) and CaO (0.11%-0.25%). These samples have high A/CNK (2.58-3.06) and CIPW-normalized corundum (10.0%-11.4%), similar to those of the S-type granite. They have obvious fractionation between LREEs and HREEs. These samples are characterized by enrichment in LILEs (Rb, Th, U) and depletion in HFSEs (Nb, Ta, Ti). The geochemical results indicate that the Takengon granitic gneisses are originated from the partial melting of the meta-sediments during the evolution of the Prototethyan Ocean. This study confirms the existing of Early Silurian basement rocks in the East Sumatra Terrane, which were related to the Prototethyan evolution.
2020, 45(6): 2091-2102.
doi: 10.3799/dqkx.2019.247
Abstract:
The Bange area is part of North Lhasa terrane. Cambrian magmatism has not been reported in the north Lhasa terrane. In this study, field geological survey and geochemical studies, as well as geochronology, were used to study the firstly discovered gabbro-diorite in Bange and the following conclusions are drawn. The gabbro-diorites belong to the high-K calc-alkaline series. They are rich in large ion lithophilic elements (e.g., Rb and Ba) and light rare earth elements (e.g., La and Ce), and are depleted in high-field strength elements (e.g., Nb, Ta, Zr, Hf and Ti), similar to the Andean island arc magmatic rocks. The rock is interpreted as resulting from partial melting of subduction sediments metasomatized with the overlying mantle wedge. Zircon U-Pb dating demonstrates that the gabbro-diorite formed at 512±3 Ma, which indicates it formed at Cambrian and provides reliable chronological evidence for the existence of Early Paleozoic magmatic events in the North Lhasa terrane. It is confirmed that the North Lhasa terrane is part of northern margin of the Gondwana land. The results provide a new window for further study of the evolution of the tectonic of Tibetan Plateau.
The Bange area is part of North Lhasa terrane. Cambrian magmatism has not been reported in the north Lhasa terrane. In this study, field geological survey and geochemical studies, as well as geochronology, were used to study the firstly discovered gabbro-diorite in Bange and the following conclusions are drawn. The gabbro-diorites belong to the high-K calc-alkaline series. They are rich in large ion lithophilic elements (e.g., Rb and Ba) and light rare earth elements (e.g., La and Ce), and are depleted in high-field strength elements (e.g., Nb, Ta, Zr, Hf and Ti), similar to the Andean island arc magmatic rocks. The rock is interpreted as resulting from partial melting of subduction sediments metasomatized with the overlying mantle wedge. Zircon U-Pb dating demonstrates that the gabbro-diorite formed at 512±3 Ma, which indicates it formed at Cambrian and provides reliable chronological evidence for the existence of Early Paleozoic magmatic events in the North Lhasa terrane. It is confirmed that the North Lhasa terrane is part of northern margin of the Gondwana land. The results provide a new window for further study of the evolution of the tectonic of Tibetan Plateau.
2020, 45(6): 2103-2116.
doi: 10.3799/dqkx.2019.210
Abstract:
The petrogenesis and evolution of Mesozoic complex in the southern Taihang Mountains have been one of hot topics explored since last several decades. Based on field investigation and Electron Probe Microanalysis (EPMA), in the paper, it studies the mineralogy and its significance of Jiaochang diorite. The Jiaochang diorite is mainly composed of plagioclase, amphibole, biotite, and few clinopyroxene and olivine. The SiO2 contents of the rocks range from 52.91% to 53.39% with high Mg# [100×Mg/(Mg+Fe2+)] (60.28-62.39) and Na (Na2O/K2O=1.18-1.40). The plagioclases (about 50%) present An number of 36 to 60 with normal zoning, and belong to andesine and labradorite. The amphiboles (about 30%) has high CaO (>10%) and MgO (>18%), belonging to magnesial amphibole. With [Mg/(Mg+Fe2++Fe3++Mn)] of 0.564-0.582, the biotite (about 12%) is magnesial. The clinopyroxenes (about 5%) belong to Ca-Mg-Fe pyroxene series, which were produced by gradual crystallization of mantle-derived magma during its upwelling from deep to shallow. The olivines (about 2%) as xenocrysts are composed of chrysolite and forsterite with Fo from 76 to 91. The crystallized temperature and pressure of the diorite by clinopyroxene geothermobarometry range from 1 060 ℃ to 1 094 ℃ and from 0.24 GPa to 0.55 GPa respectively. These characteristics suggest that the diorite formed by mantle derived materials from the magma sources. The magma had almost no differentiation during the upward process and the diorite reflects the dual tectonic background of the subduction of the ancient Pacific plate and the extension of North China craton.
The petrogenesis and evolution of Mesozoic complex in the southern Taihang Mountains have been one of hot topics explored since last several decades. Based on field investigation and Electron Probe Microanalysis (EPMA), in the paper, it studies the mineralogy and its significance of Jiaochang diorite. The Jiaochang diorite is mainly composed of plagioclase, amphibole, biotite, and few clinopyroxene and olivine. The SiO2 contents of the rocks range from 52.91% to 53.39% with high Mg# [100×Mg/(Mg+Fe2+)] (60.28-62.39) and Na (Na2O/K2O=1.18-1.40). The plagioclases (about 50%) present An number of 36 to 60 with normal zoning, and belong to andesine and labradorite. The amphiboles (about 30%) has high CaO (>10%) and MgO (>18%), belonging to magnesial amphibole. With [Mg/(Mg+Fe2++Fe3++Mn)] of 0.564-0.582, the biotite (about 12%) is magnesial. The clinopyroxenes (about 5%) belong to Ca-Mg-Fe pyroxene series, which were produced by gradual crystallization of mantle-derived magma during its upwelling from deep to shallow. The olivines (about 2%) as xenocrysts are composed of chrysolite and forsterite with Fo from 76 to 91. The crystallized temperature and pressure of the diorite by clinopyroxene geothermobarometry range from 1 060 ℃ to 1 094 ℃ and from 0.24 GPa to 0.55 GPa respectively. These characteristics suggest that the diorite formed by mantle derived materials from the magma sources. The magma had almost no differentiation during the upward process and the diorite reflects the dual tectonic background of the subduction of the ancient Pacific plate and the extension of North China craton.
2020, 45(6): 2117-2134.
doi: 10.3799/dqkx.2019.271
Abstract:
The Au-Sb-Pb-Zn-Ag Polymetallogenic Metallogenic belt in South Tibet, also known as the North Himalayan Metallogenic belt, is an important part of the Tethyan Himalayan Metallogenic Region. Although Kangma area is in an advantageous metallogenic location where the SN-trending faults cross the EW- trending faults, few breakthroughs have been made in exploration prediction for a long time due to the lack of clear ore-controlling regularities, feasible prospection methods, and effective prediction examples for reference, which caused by high altitude and thick coverage. In recent years, the discovery of a group of deposits such as Buzhu gold (antimony) deposit has filled the gap of exploration in this area. However, due to the lack of in-depth understanding of the internal architecture and ore-controlling styles of the fault zones, the exploration of Buzhu deposit is seriously restricted. Based on detailed geological survey, the internal architectures of NW- (and EW-) and SN- trending fault zones in this deposit have been systematically dissected here. It is identified that both sets of fault zones were composed of the fault core in the central part and the damage zone in the peripheral. In the NW- (and EW-) trending fault zones, the crumpled pyrite-bearing quartz veins were controlled by the fault core and the straight and steep quartz veins bearing multiple sulfide phases and quartz veins bearing abundant arsenopyrite filled in the joints of the damage zone. In the SN-trending fault zones, the fault core consisting of cleavage zone and breccia zone is barren. While, the bedding tension fractures in the damage zone were filled by high grade veins characterized by obvious limonite and clay alteration. Combined with regional tectonic evolution, a three-stage evolution model depicting the formation, development and ore-controlling of the major fault zones in Buzhu deposit is established in this paper. Under the guidance of this model, 6 prospecting targets were delineated according to the geological facts combined with the prospecting information such as synthetic anomalies of 1:10 000 soil geochemical exploration, wall rock alteration and ore outcrops. And each of the 2 targets was finally selected in the 3 levels of A, B and C, comprehensively considering various factors. Through the above studies on the internal architecture, ore-controlling regularities and evolution model of the fault zones, as well as the delineation of the targets combined with synthetic anomalies, the authors hope to provide useful reference for the ore genesis research and prospection in the Buzhu deposit and Kangma areas.
The Au-Sb-Pb-Zn-Ag Polymetallogenic Metallogenic belt in South Tibet, also known as the North Himalayan Metallogenic belt, is an important part of the Tethyan Himalayan Metallogenic Region. Although Kangma area is in an advantageous metallogenic location where the SN-trending faults cross the EW- trending faults, few breakthroughs have been made in exploration prediction for a long time due to the lack of clear ore-controlling regularities, feasible prospection methods, and effective prediction examples for reference, which caused by high altitude and thick coverage. In recent years, the discovery of a group of deposits such as Buzhu gold (antimony) deposit has filled the gap of exploration in this area. However, due to the lack of in-depth understanding of the internal architecture and ore-controlling styles of the fault zones, the exploration of Buzhu deposit is seriously restricted. Based on detailed geological survey, the internal architectures of NW- (and EW-) and SN- trending fault zones in this deposit have been systematically dissected here. It is identified that both sets of fault zones were composed of the fault core in the central part and the damage zone in the peripheral. In the NW- (and EW-) trending fault zones, the crumpled pyrite-bearing quartz veins were controlled by the fault core and the straight and steep quartz veins bearing multiple sulfide phases and quartz veins bearing abundant arsenopyrite filled in the joints of the damage zone. In the SN-trending fault zones, the fault core consisting of cleavage zone and breccia zone is barren. While, the bedding tension fractures in the damage zone were filled by high grade veins characterized by obvious limonite and clay alteration. Combined with regional tectonic evolution, a three-stage evolution model depicting the formation, development and ore-controlling of the major fault zones in Buzhu deposit is established in this paper. Under the guidance of this model, 6 prospecting targets were delineated according to the geological facts combined with the prospecting information such as synthetic anomalies of 1:10 000 soil geochemical exploration, wall rock alteration and ore outcrops. And each of the 2 targets was finally selected in the 3 levels of A, B and C, comprehensively considering various factors. Through the above studies on the internal architecture, ore-controlling regularities and evolution model of the fault zones, as well as the delineation of the targets combined with synthetic anomalies, the authors hope to provide useful reference for the ore genesis research and prospection in the Buzhu deposit and Kangma areas.
2020, 45(6): 2135-2151.
doi: 10.3799/dqkx.2019.211
Abstract:
The Hejiao iron deposit in Inner Mongolia, which is located in the Yinshan block on the northern margin of western block of the North China craton, is a medium-sized BIF-type iron deposit in the Guyang greenstone belt. Geochronology and petrogeochemistry of amphibolite and iron ore were studied in this paper. LA-ICP-MS U-Pb dating of zircons from the amphibolites interlayer shows that cores of the zircons characterized by core-rim texture and with a Th/U ratio of higher than 0.1(0.27-1.00) have an upper intercept age of 2 549±29 Ma(MSWD=0.51), which is approximately the depositional age of the Hejiao BIF-type iron deposit, during which widespread tectonic-tectonothermal event and most BIFs occurrence took place at the Early Cambrian of North China craton. A protolith reconstruction shows that the protolith of amphibolites is basalt, indicating that Hejiao iron deposit belongs to Algoma-type BIF closely related to volcanic activities. The chondrite-normalized REE pattern of amphibolites is nearly flat, similar to those of E-MORB and back-arc basin basalts (BABB). Primitive mantle-normalized trace element pattern of amphibolites is similar to back-arc basin basalts (BABB), showing enrichment in LILEs such as Rb, Ba, Sr, K, and depletion in HFSEs such as Nb, Ta, U, Th, similar to the characteristics of island arc magmatic rocks. Combining the model of island arc-mantle plume interaction for the Guyang greenstone belt, it is speculated that the amohibolites were formed in a tectonic setting of back-arc basin, accompanied by mantle plume, which implies the tectonic environment of the Hejiao BIF. The characteristics of the iron ores include the depletion of LREE, enrichment of HREE[(La/Yb)PAAS=0.29-0.50], slightly positive La anomaly(La/La*=1.00-1.13), strongly positive Eu anomaly (Eu/Eu*=1.54-2.27), positive Y anomaly(Y/Y*=1.07-1.42), and no distinct Ce anomalies(Ce/Ce*=0.90-0.95).Based on the similar signatures to the komatiite at bottom of the Guyang greenstone belt and the mixture of high-temperature hydrothermal fluid and seawater, it is inferred that Fe of the Hejiao BIF-type iron deposit was supplied through the high-temperature hydrothermal leaching of komatiites.
The Hejiao iron deposit in Inner Mongolia, which is located in the Yinshan block on the northern margin of western block of the North China craton, is a medium-sized BIF-type iron deposit in the Guyang greenstone belt. Geochronology and petrogeochemistry of amphibolite and iron ore were studied in this paper. LA-ICP-MS U-Pb dating of zircons from the amphibolites interlayer shows that cores of the zircons characterized by core-rim texture and with a Th/U ratio of higher than 0.1(0.27-1.00) have an upper intercept age of 2 549±29 Ma(MSWD=0.51), which is approximately the depositional age of the Hejiao BIF-type iron deposit, during which widespread tectonic-tectonothermal event and most BIFs occurrence took place at the Early Cambrian of North China craton. A protolith reconstruction shows that the protolith of amphibolites is basalt, indicating that Hejiao iron deposit belongs to Algoma-type BIF closely related to volcanic activities. The chondrite-normalized REE pattern of amphibolites is nearly flat, similar to those of E-MORB and back-arc basin basalts (BABB). Primitive mantle-normalized trace element pattern of amphibolites is similar to back-arc basin basalts (BABB), showing enrichment in LILEs such as Rb, Ba, Sr, K, and depletion in HFSEs such as Nb, Ta, U, Th, similar to the characteristics of island arc magmatic rocks. Combining the model of island arc-mantle plume interaction for the Guyang greenstone belt, it is speculated that the amohibolites were formed in a tectonic setting of back-arc basin, accompanied by mantle plume, which implies the tectonic environment of the Hejiao BIF. The characteristics of the iron ores include the depletion of LREE, enrichment of HREE[(La/Yb)PAAS=0.29-0.50], slightly positive La anomaly(La/La*=1.00-1.13), strongly positive Eu anomaly (Eu/Eu*=1.54-2.27), positive Y anomaly(Y/Y*=1.07-1.42), and no distinct Ce anomalies(Ce/Ce*=0.90-0.95).Based on the similar signatures to the komatiite at bottom of the Guyang greenstone belt and the mixture of high-temperature hydrothermal fluid and seawater, it is inferred that Fe of the Hejiao BIF-type iron deposit was supplied through the high-temperature hydrothermal leaching of komatiites.
Progress and Prospect on Exploration and Development of Shale Gas in the Yangtze River Economic Belt
2020, 45(6): 2152-2159.
doi: 10.3799/dqkx.2020.061
Abstract:
Shale gas is a clean and unconventional natural resource and it has attracted widespread attention from all over the world. China's shale gas resources are abundant, and about 70% of the resources are distributed in the regions along the Yangtze River economic belt. In addition, commercial development has been realized in the Fuling area of Chongqing city in the upper Yangtze River, and in the Changning-Weiyuan areas of Sichuan Province. The Middle Yangtze River region (i.e., West Hubei region) has achieved breakthroughs, and the Lower Yangtze River region has made some progress. The corresponding exploration theory and technical system are initially formed, and the mining equipment can be made in China. The development of shale gas can accelerate development of the Yangtze River economic belt and is of great significance for optimizing energy consumption makeup, achieving green development, and ensuring national energy supply. However, there are still some problems with shale gas exploration and development. For instances, the ratio of shale gas resource exploration is low, and the enrichment and accumulation of shale gas in complex geological conditions needs further study.The cost of shale gas exploration and development is high, and key technical equipment has yet to be developed. In terms of the market-driven mechanism, the market-oriented pattern in which multiple entities participate together has not yet fully formed. In this study, it analyzes the development of shale gas in terms of shale gas resources, exploration and development, theoretical technology, standard systematic technology and equipment of the Yangtze River economic belt. Finally, it points out the main problems that restrict the rapid development of shale gas exploration and development in China, and propose the related suggestions to solve these problems. To build a new pattern of shale gas exploration and development in the Yangtze, it is necessary to increase exploration and development efforts, to strengthen scientific and technological innovation, to underline the green exploration and development, to strengthen policy support and take coordiuated measures.
Shale gas is a clean and unconventional natural resource and it has attracted widespread attention from all over the world. China's shale gas resources are abundant, and about 70% of the resources are distributed in the regions along the Yangtze River economic belt. In addition, commercial development has been realized in the Fuling area of Chongqing city in the upper Yangtze River, and in the Changning-Weiyuan areas of Sichuan Province. The Middle Yangtze River region (i.e., West Hubei region) has achieved breakthroughs, and the Lower Yangtze River region has made some progress. The corresponding exploration theory and technical system are initially formed, and the mining equipment can be made in China. The development of shale gas can accelerate development of the Yangtze River economic belt and is of great significance for optimizing energy consumption makeup, achieving green development, and ensuring national energy supply. However, there are still some problems with shale gas exploration and development. For instances, the ratio of shale gas resource exploration is low, and the enrichment and accumulation of shale gas in complex geological conditions needs further study.The cost of shale gas exploration and development is high, and key technical equipment has yet to be developed. In terms of the market-driven mechanism, the market-oriented pattern in which multiple entities participate together has not yet fully formed. In this study, it analyzes the development of shale gas in terms of shale gas resources, exploration and development, theoretical technology, standard systematic technology and equipment of the Yangtze River economic belt. Finally, it points out the main problems that restrict the rapid development of shale gas exploration and development in China, and propose the related suggestions to solve these problems. To build a new pattern of shale gas exploration and development in the Yangtze, it is necessary to increase exploration and development efforts, to strengthen scientific and technological innovation, to underline the green exploration and development, to strengthen policy support and take coordiuated measures.
2020, 45(6): 2160-2171.
doi: 10.3799/dqkx.2019.248
Abstract:
The Cambrian marine shales are currently over-matured in the Middle-Upper Yangtze region. Several phases of geofluids are detected within these shale reservoirs. However, the impacts and relevant mechanisms of geofluids on the occurrence of nanopores within these shale reservoirs are still unclear. A series of pyrolysis experiments were conducted on the highly matured Cambrian shale from the Shuijingtuo Fm. in the Huangling anticline within a closed hydrous system. The measurements of C-S, XRD, N2 adsorption and FE-SEM were done on these pyrolyzed shale samples with thermal maturity of Ro=2.26%-4.01%. The results demonstrate no obvious change of TOC, continuous decrease of sulfur, inorganic carbon and clays and increase of feldspar throughout the experiments as well as the significant decrease of quartz and increase of diopside at Ro≥2.7% with increasing thermal maturity, which indicates the slight hydrocarbon generation and expulsion, the dissolution of pyrite, carbonate, clays and quartz to varying levels and the formation of feldspar and diopside under the experimental conditions. The nanopore formation within highly matured shale reservoirs is regulated mainly by the mineral dissolution with the addition of geofluids, it is feasible for the occurrence of mesopores and macropores as indicated by the strong negative correlations between the mineral contents versus the total pore and macropore volumes; the formation of feldspar and diopside restricts the occurrence of micropores and promotes the development of mesopores and macropores, further implying the predominant effects of mineral dissolution on nanoporosity under the experimental circumstances; hydrocarbon generation and expulsion have the minor impacts on nanopore development due to the limited capability of petroleum generation and expulsion at the over-mature stage. With increasing mineral dissolution or thermal maturity, the abundance, volumes and specific surface areas of micropores gradually decrease and evolve into mesopores and macropores subsequently as suggested by the negative correlations of pore volumes and specific surface areas of micropores versus those of mesopores and macropores. This study should be helpful in the better understanding of the occurrence mechanisms and relevant controlling factors of nanopores within highly matured shale reservoirs with the presence of geofluids in nature.
The Cambrian marine shales are currently over-matured in the Middle-Upper Yangtze region. Several phases of geofluids are detected within these shale reservoirs. However, the impacts and relevant mechanisms of geofluids on the occurrence of nanopores within these shale reservoirs are still unclear. A series of pyrolysis experiments were conducted on the highly matured Cambrian shale from the Shuijingtuo Fm. in the Huangling anticline within a closed hydrous system. The measurements of C-S, XRD, N2 adsorption and FE-SEM were done on these pyrolyzed shale samples with thermal maturity of Ro=2.26%-4.01%. The results demonstrate no obvious change of TOC, continuous decrease of sulfur, inorganic carbon and clays and increase of feldspar throughout the experiments as well as the significant decrease of quartz and increase of diopside at Ro≥2.7% with increasing thermal maturity, which indicates the slight hydrocarbon generation and expulsion, the dissolution of pyrite, carbonate, clays and quartz to varying levels and the formation of feldspar and diopside under the experimental conditions. The nanopore formation within highly matured shale reservoirs is regulated mainly by the mineral dissolution with the addition of geofluids, it is feasible for the occurrence of mesopores and macropores as indicated by the strong negative correlations between the mineral contents versus the total pore and macropore volumes; the formation of feldspar and diopside restricts the occurrence of micropores and promotes the development of mesopores and macropores, further implying the predominant effects of mineral dissolution on nanoporosity under the experimental circumstances; hydrocarbon generation and expulsion have the minor impacts on nanopore development due to the limited capability of petroleum generation and expulsion at the over-mature stage. With increasing mineral dissolution or thermal maturity, the abundance, volumes and specific surface areas of micropores gradually decrease and evolve into mesopores and macropores subsequently as suggested by the negative correlations of pore volumes and specific surface areas of micropores versus those of mesopores and macropores. This study should be helpful in the better understanding of the occurrence mechanisms and relevant controlling factors of nanopores within highly matured shale reservoirs with the presence of geofluids in nature.
2020, 45(6): 2172-2185.
doi: 10.3799/dqkx.2020.055
Abstract:
Petrology and diagenesis of low permeability sandstone reservoirs in Zhuhai Formation were studied by means of thin sections identification, scanning electron microscopy (SEM), physical property, X-ray diffraction (XRD) analysis and carbon and oxygen isotope. The research of Wenchang A sag, Zhuhai Group of low permeability sandstone reservoir petrology characteristics and characteristics of diagenesis and the quantitative analysis was carried out on the rock strength, compaction, cementation, dissolution, the impact on the reservoir pore evolution. Quantitative analysis of diagenetic strength was carried out to evaluate the effects of compaction, cementation and dissolution on reservoir pore evolution. The results show as follows. (1) The Zhu-3 south fault zone is mainly composed of lithic sandstone and feldspar lithic sandstone with high content of medium and coarse sandstone. However the 6th fault zone is mainly feldspar lithic sandstone and lithic quartz sandstone with high fine sandstone content. The storage space is dominated by secondary dissolution pores, and the physical properties change greatly and show obvious zonation in both longitudinal and plane. (2) Mechanical compaction caused a large number of loss of primary intergranular pores in Zhuhai Formation. Iron-bearing carbonate, authigenic illite and siliceous cement further reduced the intergranular pores, while early chlorite inhibited quartz overgrowth. The dissolution improves the physical properties of deep reservoirs and two secondary dissolution zones developed in the Zhuhai Formation. According to the diagenetic facies prediction, the subaqueous distributary channel with thick layers, coarse-grained sandstones is a high-quality reservoir development zone in the study area.(3) Through quantitative analysis of porosity evolution, it is concluded that diagenesis has different effects on the porosity evolution of coarse and fine-medium grained sandstones.
Petrology and diagenesis of low permeability sandstone reservoirs in Zhuhai Formation were studied by means of thin sections identification, scanning electron microscopy (SEM), physical property, X-ray diffraction (XRD) analysis and carbon and oxygen isotope. The research of Wenchang A sag, Zhuhai Group of low permeability sandstone reservoir petrology characteristics and characteristics of diagenesis and the quantitative analysis was carried out on the rock strength, compaction, cementation, dissolution, the impact on the reservoir pore evolution. Quantitative analysis of diagenetic strength was carried out to evaluate the effects of compaction, cementation and dissolution on reservoir pore evolution. The results show as follows. (1) The Zhu-3 south fault zone is mainly composed of lithic sandstone and feldspar lithic sandstone with high content of medium and coarse sandstone. However the 6th fault zone is mainly feldspar lithic sandstone and lithic quartz sandstone with high fine sandstone content. The storage space is dominated by secondary dissolution pores, and the physical properties change greatly and show obvious zonation in both longitudinal and plane. (2) Mechanical compaction caused a large number of loss of primary intergranular pores in Zhuhai Formation. Iron-bearing carbonate, authigenic illite and siliceous cement further reduced the intergranular pores, while early chlorite inhibited quartz overgrowth. The dissolution improves the physical properties of deep reservoirs and two secondary dissolution zones developed in the Zhuhai Formation. According to the diagenetic facies prediction, the subaqueous distributary channel with thick layers, coarse-grained sandstones is a high-quality reservoir development zone in the study area.(3) Through quantitative analysis of porosity evolution, it is concluded that diagenesis has different effects on the porosity evolution of coarse and fine-medium grained sandstones.
2020, 45(6): 2186-2198.
doi: 10.3799/dqkx.2019.217
Abstract:
Quantitative petrographic analysis of sand and sandstone is an important way of petrology and it contributes to study the source area and background of sediments and the characteristic of sedimentary basin. In the past few decades, geologists have made a lot of progresses on quantitative debris particle statistics and its potential geological significance, such as the relationships between sedimentary debris and source rock, the effects of sedimentary process on debris compositions, the correlations between debris composition and tectonic setting. However, the systematic summary of quantitative petrographic analysis and classifications are scarce, which leads to misunderstandings or even mistakes in practice. Based on the previous literature, in the paper, it systematically describes the quantitative petrographic analysis of sand and sandstone and recommends the best classification naming scheme. This study intends to establish a uniform standard to promote the reliability of debris particle statistics and comparability of the data. Meanwhile, it also discusses applicability of sandstone tectonic background discrimination diagram. Although the diagrams are an effective way to show statistical results of sandstone debris components, it should be used with caution when applied to discriminate the tectonic setting. The best way to discriminate the tectonic setting is to conduct a comprehensive discussion based on the characteristics of the rock itself and other data.
Quantitative petrographic analysis of sand and sandstone is an important way of petrology and it contributes to study the source area and background of sediments and the characteristic of sedimentary basin. In the past few decades, geologists have made a lot of progresses on quantitative debris particle statistics and its potential geological significance, such as the relationships between sedimentary debris and source rock, the effects of sedimentary process on debris compositions, the correlations between debris composition and tectonic setting. However, the systematic summary of quantitative petrographic analysis and classifications are scarce, which leads to misunderstandings or even mistakes in practice. Based on the previous literature, in the paper, it systematically describes the quantitative petrographic analysis of sand and sandstone and recommends the best classification naming scheme. This study intends to establish a uniform standard to promote the reliability of debris particle statistics and comparability of the data. Meanwhile, it also discusses applicability of sandstone tectonic background discrimination diagram. Although the diagrams are an effective way to show statistical results of sandstone debris components, it should be used with caution when applied to discriminate the tectonic setting. The best way to discriminate the tectonic setting is to conduct a comprehensive discussion based on the characteristics of the rock itself and other data.
2020, 45(6): 2199-2209.
doi: 10.3799/dqkx.2019.250
Abstract:
The Xijiang sag is located in the Pearl River Mouth basin, the northern margin of the South China Sea. As one of the Cenozoic sags developed along the northern margin of the South China Sea, this sag recorded the clockwise rotation process of extension stress of the northern margin of the South China Sea. Thus, the study on the geological structure and evolution of this sag would provide robust evidence to this phenomenon. Based on the 2-D and 3-D seismic data, in this paper, it analyzes the Early Cenozoic evolution of the fault system in Xijiang sag. As part of the South China block, the basement of the Xijiang sag experienced several stages of complex evolutions, such as the Indo-China-Asian collision during Triassic, the subduction of Izenaqi plate and Pacific plate, which induced the formation of NE- and NW- striking faults in the basement. During Early to Middle Eocene, the pre-existing NE-striking faults reactivated under the control of the NE-SE-directed extension, and this extension was derived from the NNW-direction subduction of the Pacific plate under the Asian plate. During Late Eocene to Early Oligocene, the extension direction clockwise rotated from NW-SE to N-S, which induced the formation of large amount of EW-striking normal faults and the reactivation of the pre-existing NW-striking fault. This rotation resulted from the direction change of the subduction direction of the Pacific plate from NNW to NWW, the India-Asian collision and the southern ward movement of the Proto-South China Sea block. The analogue experiments are used to investigate the mechanism of the fault evolution. The results show that: (1) under the N-S direction extension, a large amount of EW-striking normal faults formed along the pre-existing NE-striking faults; (2) under the N-S direction extension, a group of pre-existing NW-striking strike-slip faults reactivated, and a small group of EW-striking extensional fault formed.
The Xijiang sag is located in the Pearl River Mouth basin, the northern margin of the South China Sea. As one of the Cenozoic sags developed along the northern margin of the South China Sea, this sag recorded the clockwise rotation process of extension stress of the northern margin of the South China Sea. Thus, the study on the geological structure and evolution of this sag would provide robust evidence to this phenomenon. Based on the 2-D and 3-D seismic data, in this paper, it analyzes the Early Cenozoic evolution of the fault system in Xijiang sag. As part of the South China block, the basement of the Xijiang sag experienced several stages of complex evolutions, such as the Indo-China-Asian collision during Triassic, the subduction of Izenaqi plate and Pacific plate, which induced the formation of NE- and NW- striking faults in the basement. During Early to Middle Eocene, the pre-existing NE-striking faults reactivated under the control of the NE-SE-directed extension, and this extension was derived from the NNW-direction subduction of the Pacific plate under the Asian plate. During Late Eocene to Early Oligocene, the extension direction clockwise rotated from NW-SE to N-S, which induced the formation of large amount of EW-striking normal faults and the reactivation of the pre-existing NW-striking fault. This rotation resulted from the direction change of the subduction direction of the Pacific plate from NNW to NWW, the India-Asian collision and the southern ward movement of the Proto-South China Sea block. The analogue experiments are used to investigate the mechanism of the fault evolution. The results show that: (1) under the N-S direction extension, a large amount of EW-striking normal faults formed along the pre-existing NE-striking faults; (2) under the N-S direction extension, a group of pre-existing NW-striking strike-slip faults reactivated, and a small group of EW-striking extensional fault formed.
2020, 45(6): 2210-2220.
doi: 10.3799/dqkx.2019.222
Abstract:
The whole Shahejie Formation has not been treated as one target for reservoiring research. So in this study, fluid inclusion systematic analysis conducted on samples from Shahejie Formation in Pucheng area, Dongpu depression, combined with the crude oil data, indicates that the vertical distribution of oil maturity is under control of petroleum generation of multiple sets of source rocks. The pressure evolution process considered to be a driving factor was in agreement with the reservoiring stages. Three reservoiring stages were identified in Pucheng area: the first was from 30.9-25.3 Ma, the second was from 22.3-14.8 Ma, the third was from 3.2-1.4 Ma. The source rocks with huge vertical thickness produced crude oil with different maturities at the same time. Moreover, different maturities of oil were generated from the same set of source rock over time, which made the Shahejie Formation in Pucheng area had characteristics of simultaneous reservoiring of crude oil with different maturity. The results of paleopressure simulation show that the first stage was driven by overpressure, the second stage was driven by pressure relief and the third stage had the combined features of the former two stages.
The whole Shahejie Formation has not been treated as one target for reservoiring research. So in this study, fluid inclusion systematic analysis conducted on samples from Shahejie Formation in Pucheng area, Dongpu depression, combined with the crude oil data, indicates that the vertical distribution of oil maturity is under control of petroleum generation of multiple sets of source rocks. The pressure evolution process considered to be a driving factor was in agreement with the reservoiring stages. Three reservoiring stages were identified in Pucheng area: the first was from 30.9-25.3 Ma, the second was from 22.3-14.8 Ma, the third was from 3.2-1.4 Ma. The source rocks with huge vertical thickness produced crude oil with different maturities at the same time. Moreover, different maturities of oil were generated from the same set of source rock over time, which made the Shahejie Formation in Pucheng area had characteristics of simultaneous reservoiring of crude oil with different maturity. The results of paleopressure simulation show that the first stage was driven by overpressure, the second stage was driven by pressure relief and the third stage had the combined features of the former two stages.
2020, 45(6): 2221-2231.
doi: 10.3799/dqkx.2019.270
Abstract:
Hydrogeochemical reaserch of geothermal fluids is an effective method to understand the formation mechanism, occurrence environment and circulation process of geothermal resources. Xiongan New Area, one of the typical low-temperature geothermal systems in the North China plain, is selected as the study area. In this study it is based on the analysis of water chemistry and isotopes, and aims: (1) to discuss the geochemical origin of main components in geothermal fluids, (2) to estimate the deep reservoir temperatures of geothermal waters, (3) to figure out the heat source beneath geothermal area and its genetic mechanism. The hydrochemical evidences imply that the main components in Xiongan geothermal waters are contributed by meteoric waters input and intense fluid-rock interactions at high reservoir temperatures, and several components of Wumishan Formation geothermal waters are from the dissolution of evaporation salt formed during the diagenetic process. The Ca-Mg and quartz geothermometer are suitable for estimating the reservoir temperature of Wumishan Formation geothermal waters, while that for Guantao Formation geothermal waters, the quartz geothermometer is much more appropriate. The calculated temperatures range from 76.4 to 90.6 ℃ and 66.2 to 71.3 ℃, respectively. The geothermal anomaly beneath Xiongan is likely to result from decay of radioactive elements in a specific tectonic setting.
Hydrogeochemical reaserch of geothermal fluids is an effective method to understand the formation mechanism, occurrence environment and circulation process of geothermal resources. Xiongan New Area, one of the typical low-temperature geothermal systems in the North China plain, is selected as the study area. In this study it is based on the analysis of water chemistry and isotopes, and aims: (1) to discuss the geochemical origin of main components in geothermal fluids, (2) to estimate the deep reservoir temperatures of geothermal waters, (3) to figure out the heat source beneath geothermal area and its genetic mechanism. The hydrochemical evidences imply that the main components in Xiongan geothermal waters are contributed by meteoric waters input and intense fluid-rock interactions at high reservoir temperatures, and several components of Wumishan Formation geothermal waters are from the dissolution of evaporation salt formed during the diagenetic process. The Ca-Mg and quartz geothermometer are suitable for estimating the reservoir temperature of Wumishan Formation geothermal waters, while that for Guantao Formation geothermal waters, the quartz geothermometer is much more appropriate. The calculated temperatures range from 76.4 to 90.6 ℃ and 66.2 to 71.3 ℃, respectively. The geothermal anomaly beneath Xiongan is likely to result from decay of radioactive elements in a specific tectonic setting.
2020, 45(6): 2232-2244.
doi: 10.3799/dqkx.2019.280
Abstract:
Groundwater is one of the most important water supply resources in Yongcheng City, but the pollution of shallow groundwater seriously restricts the economic development and the improvement of living standards in the city. On the basis of groundwater investigation and sampling, hydrogeochemical diagram method and multivariate statistics method and geochemical simulation method were comprehensively used to analyze the hydrochemical characteristics and formation mechanism, as well as the pollution source and the main affecting factors. With the change of aquifer medium and the intensity of human activities, the concentrations of K+, Ca2+, NO3-, Cl-, SO42- and COD (chemical oxygen demand) gradually decreased, while the concentrations of Na+, F-, Mg2+, HCO3- and TDS (total dissolved solids) gradually increased with the increase of depth, the former comes from human activities, while the latter comes from the original sedimentary environment. The concentration of SO42- in the areas of coal mine and coal chemical industry is higher than 250 mg/L, which is much higher than that in other regions. The concentration of NO3- is higher than 30 mg/L in agricultural areas. Integrated analyses implies that wastewater discharge of coal mine and chemical industry, leakage of household waste leachate and discharge of sewage, excessive application of pesticides and fertilizers are the main factors affecting the water quality of shallow groundwater.
Groundwater is one of the most important water supply resources in Yongcheng City, but the pollution of shallow groundwater seriously restricts the economic development and the improvement of living standards in the city. On the basis of groundwater investigation and sampling, hydrogeochemical diagram method and multivariate statistics method and geochemical simulation method were comprehensively used to analyze the hydrochemical characteristics and formation mechanism, as well as the pollution source and the main affecting factors. With the change of aquifer medium and the intensity of human activities, the concentrations of K+, Ca2+, NO3-, Cl-, SO42- and COD (chemical oxygen demand) gradually decreased, while the concentrations of Na+, F-, Mg2+, HCO3- and TDS (total dissolved solids) gradually increased with the increase of depth, the former comes from human activities, while the latter comes from the original sedimentary environment. The concentration of SO42- in the areas of coal mine and coal chemical industry is higher than 250 mg/L, which is much higher than that in other regions. The concentration of NO3- is higher than 30 mg/L in agricultural areas. Integrated analyses implies that wastewater discharge of coal mine and chemical industry, leakage of household waste leachate and discharge of sewage, excessive application of pesticides and fertilizers are the main factors affecting the water quality of shallow groundwater.
