2016 Vol. 41, No. 4
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2016, 41(4): 555-569.
doi: 10.3799/dqkx.2016.046
Abstract:
The study of magmatism can reveal the orogenic tectonic evolution. In this paper, zircon LA-MC-ICPMS U-Pb dating, Hf isotopic compositions and whole rock geochemical data of the Early Paleozoic dioritic rocks from Wulanaobaotu region, central part of the Xing-Meng Orogenic belt are present. The rock suite consists of two major rock types, i.e., quartz-diorite and diorite, with zircon U-Pb ages of 474.0±1.8 Ma and 487.8±1.9 Ma, respectively. In-situ zircon Hf isotopic analysis shows enriched compositions with 176Hf/177Hf ratios varying from 0.282 123 to 0.282 304, negative εHf(t) values and Hf two stage model ages(TDMC) from 1 851 to 2 250 Ma. The results indicate that the intrusive rocks are likely derived from an ancient basement material. Geochemically, these rocks show moderate SiO2 contents (56.52%-66.06%), high and variable Na2O (2.60%-6.81%), Al2O3 (14.69%-18.35%), and CaO (0.57%-6.58%, average 3.97%) contents, but low K2O (0.73%-2.94%), TFeO and MgO contents. Most Na2O/K2O ratios are all higher (0.92-5.66, average 3.19). The trace elemental data of these rocks display enrichment of Rb, Ba, Th, U, K and Sr, but depletion of Nb, Ta, P and Ti. The total REE contents are low with moderate fractionation between LREE and HREE. Meanwhile, weakly negative Eu anormalyies (δEu ranges from 0.76 to 0.99) are observed in all samples. Thus, we propose that the Wulanaobaotu dioritic intrusive rocks were likely formed in an active continental margin setting during Late Cambrian to Early Ordovician, consistent with the existence of Early Paleozoic subduction-related tectonic-magmatic belt in Xing-Meng orogenic belt. The enriched zircon Hf isotopic characteristics further northern suggest the magma originated from a Precambrian basement source.
The study of magmatism can reveal the orogenic tectonic evolution. In this paper, zircon LA-MC-ICPMS U-Pb dating, Hf isotopic compositions and whole rock geochemical data of the Early Paleozoic dioritic rocks from Wulanaobaotu region, central part of the Xing-Meng Orogenic belt are present. The rock suite consists of two major rock types, i.e., quartz-diorite and diorite, with zircon U-Pb ages of 474.0±1.8 Ma and 487.8±1.9 Ma, respectively. In-situ zircon Hf isotopic analysis shows enriched compositions with 176Hf/177Hf ratios varying from 0.282 123 to 0.282 304, negative εHf(t) values and Hf two stage model ages(TDMC) from 1 851 to 2 250 Ma. The results indicate that the intrusive rocks are likely derived from an ancient basement material. Geochemically, these rocks show moderate SiO2 contents (56.52%-66.06%), high and variable Na2O (2.60%-6.81%), Al2O3 (14.69%-18.35%), and CaO (0.57%-6.58%, average 3.97%) contents, but low K2O (0.73%-2.94%), TFeO and MgO contents. Most Na2O/K2O ratios are all higher (0.92-5.66, average 3.19). The trace elemental data of these rocks display enrichment of Rb, Ba, Th, U, K and Sr, but depletion of Nb, Ta, P and Ti. The total REE contents are low with moderate fractionation between LREE and HREE. Meanwhile, weakly negative Eu anormalyies (δEu ranges from 0.76 to 0.99) are observed in all samples. Thus, we propose that the Wulanaobaotu dioritic intrusive rocks were likely formed in an active continental margin setting during Late Cambrian to Early Ordovician, consistent with the existence of Early Paleozoic subduction-related tectonic-magmatic belt in Xing-Meng orogenic belt. The enriched zircon Hf isotopic characteristics further northern suggest the magma originated from a Precambrian basement source.
About 2.5 Ga Tectono-Metamorphic Event in Southern Margin of North China Craton and Its Significance
2016, 41(4): 570-585.
doi: 10.3799/dqkx.2016.047
Abstract:
Linshan Group, located in the southern margin of the central orogenic belt of the North China Craton, is a Precambrian basement. It is important to study the collision era of the central orogenic belt and the distribution of the southern margin of the North China Craton. A study was carried out on the metabasite (plagioclase-amphibole schist) of the Linshan Group for the purpose of constraining the collisional time of the central orogenic belt and its distribution through the zircon U-Pb dating and rock geochemical methods. The results obtained show that most of zircon grains from plagioclase-amphibole schist are long columnar, euhedral to subhedral, and show typical core-rim structure with irregular shape, weak zoning, taxitic zoning and sector zoning structure. Some zircons preserve the inherited cores of the early magma. Zircon rims display characteristics of dissolution texture with low Th/U ratios (most of them less than 0.09), however, zircons' cores show typical oscillatory zoning structure and relatively high Th/U ratios ranging from 0.10 to 9.24. The evidence suggests that the zircons of plagioclase-amphibole schist could be metamorphic origin. Relict cores and rims of the zircons from the plagioclase-amphibole schist yield ages of 2 528±43 Ma (MSWD=1.5, n=10) and 2 474±22 Ma (MSWD=1.3, n=21), respectively. The former data represent residual age of protolith, and the latter indicate a circa 2.5 Ga metamorphic event in the central orogenic belt of the North China Craton. Whole-rock geochemical results show that metabasite samples from the Linshan Group have relatively low contents of SiO2 (47.70%-50.77%, average=48.90%) and K2O (0.56%-1.78%, average=1.13%), and are depleted in high field strength elements (eg., Nb, Th, Ti and Zr) with flat REE patterns. Moreover, the geochemical samples have low content of Zr (less than 130×10-6) and ratios of Zr/Y (less than 4), indicating that the Linshan Group could have been formed in the subducted-related island arc environment. Therefore, the above evidence show that the central orogenic belt that formed by the collision orogenesis between eastern block and western block of the North China Craton experienced late Neoarchean to early Paleoproterozoic subduction-collisional event.
Linshan Group, located in the southern margin of the central orogenic belt of the North China Craton, is a Precambrian basement. It is important to study the collision era of the central orogenic belt and the distribution of the southern margin of the North China Craton. A study was carried out on the metabasite (plagioclase-amphibole schist) of the Linshan Group for the purpose of constraining the collisional time of the central orogenic belt and its distribution through the zircon U-Pb dating and rock geochemical methods. The results obtained show that most of zircon grains from plagioclase-amphibole schist are long columnar, euhedral to subhedral, and show typical core-rim structure with irregular shape, weak zoning, taxitic zoning and sector zoning structure. Some zircons preserve the inherited cores of the early magma. Zircon rims display characteristics of dissolution texture with low Th/U ratios (most of them less than 0.09), however, zircons' cores show typical oscillatory zoning structure and relatively high Th/U ratios ranging from 0.10 to 9.24. The evidence suggests that the zircons of plagioclase-amphibole schist could be metamorphic origin. Relict cores and rims of the zircons from the plagioclase-amphibole schist yield ages of 2 528±43 Ma (MSWD=1.5, n=10) and 2 474±22 Ma (MSWD=1.3, n=21), respectively. The former data represent residual age of protolith, and the latter indicate a circa 2.5 Ga metamorphic event in the central orogenic belt of the North China Craton. Whole-rock geochemical results show that metabasite samples from the Linshan Group have relatively low contents of SiO2 (47.70%-50.77%, average=48.90%) and K2O (0.56%-1.78%, average=1.13%), and are depleted in high field strength elements (eg., Nb, Th, Ti and Zr) with flat REE patterns. Moreover, the geochemical samples have low content of Zr (less than 130×10-6) and ratios of Zr/Y (less than 4), indicating that the Linshan Group could have been formed in the subducted-related island arc environment. Therefore, the above evidence show that the central orogenic belt that formed by the collision orogenesis between eastern block and western block of the North China Craton experienced late Neoarchean to early Paleoproterozoic subduction-collisional event.
2016, 41(4): 586-604.
doi: 10.3799/dqkx.2016.048
Abstract:
It is a valid approach to explore the tectonic evolution and origin by comparative chronological research of the rocks in the northern margin of Qaidam basin characterized by outcropped basement rocks and frequent magmatic activities. Dakendaban Rock Group (DRG) is one of the dominant crystal basement rocks of Oulongbuluke block. A study was carried out on material composition, deformation and metamorphism of the banded migmatitic gneiss, biotite plagioclase gneiss, two-mica plagioclase quartz schist sampled from the DRG, and the gneissic quartz diorite that intruded the DRG. The zircons from DRG samples yield nearly unanimous two peak age of about 460 Ma and peak age of about 430 Ma by LA-ICP-MS zircon U-Pb isotopic analyses. Combined with the regional tectonic processes, we maintain that the age of about 460 Ma is the geological response to the tectono-magmatism caused by ultradeep continental subduction in the North Qaidam. The metamorphic age about 430 Ma is consistent with the crystallization age (429.0±4.1 Ma) of the gneissic quartz diorite. Combined the chronolgical data with geochronological analyses on the gneissic quartz diorite, and the zircon REE data from DRG samples, it proves that the metamorphism of about 430 Ma is closely related to the homochronous tectono-thermal event. The obvious depletion of HFSE, including Nb, Ta, Zr, Hf, and the Pb enrichment demonstrate that the characteristics of the gneissic quartz diorite are related to the plate subduction which formed the active continental margin. This study provides important information for further revealing the tectonic properties and the evolution of the tectono-thermal event at Early Paleozoic in western Oulongbuluke bolck.
It is a valid approach to explore the tectonic evolution and origin by comparative chronological research of the rocks in the northern margin of Qaidam basin characterized by outcropped basement rocks and frequent magmatic activities. Dakendaban Rock Group (DRG) is one of the dominant crystal basement rocks of Oulongbuluke block. A study was carried out on material composition, deformation and metamorphism of the banded migmatitic gneiss, biotite plagioclase gneiss, two-mica plagioclase quartz schist sampled from the DRG, and the gneissic quartz diorite that intruded the DRG. The zircons from DRG samples yield nearly unanimous two peak age of about 460 Ma and peak age of about 430 Ma by LA-ICP-MS zircon U-Pb isotopic analyses. Combined with the regional tectonic processes, we maintain that the age of about 460 Ma is the geological response to the tectono-magmatism caused by ultradeep continental subduction in the North Qaidam. The metamorphic age about 430 Ma is consistent with the crystallization age (429.0±4.1 Ma) of the gneissic quartz diorite. Combined the chronolgical data with geochronological analyses on the gneissic quartz diorite, and the zircon REE data from DRG samples, it proves that the metamorphism of about 430 Ma is closely related to the homochronous tectono-thermal event. The obvious depletion of HFSE, including Nb, Ta, Zr, Hf, and the Pb enrichment demonstrate that the characteristics of the gneissic quartz diorite are related to the plate subduction which formed the active continental margin. This study provides important information for further revealing the tectonic properties and the evolution of the tectono-thermal event at Early Paleozoic in western Oulongbuluke bolck.
2016, 41(4): 605-611.
doi: 10.3799/dqkx.2016.049
Abstract:
The desert and Gobi deposition are prevailing in the west edge of the middle Helan Mountain, which is subject to the frangibility of eco-environment. It is important to explore the relationship between the climate change and deposition response of Gobi desert since the Last Glacial, a pluvial profile of late Late Pleistocene on the east edge of Tengger desert is employed to rebuild the palaeoenvironmental change based on the phytolith analysis. On the basis of regional geological survey, geomorphology pattern and Quaternary sediment distribution in the west of middle Helan Mountain and east edge of Tengger desert were investigated in detail. Based on the AMS14C dating and phytolith records, paleovegetation and paleoclimate changes are reconstructed in detail. Relatively abundant phytolths are found in the pluvial sediments of Qp3-Qh profile at the Yaoba, including the following morphotypes: parallelepipedal bulliform cells (including square-and rectangle-shaped) and cuneiform bulliform cells (fan-shaped), bilobate, rondel, trapeziform sinuate, elongate and unciform hair cell (point-shaped), elongate smooth, elongate echinate, elongate protuberant, and prism, etc. In addition, there are abundant charcoals and burnt phytoliths in the sediments, indicating the history of ancient human activities. Phytolith assemblages with the warmth index analysis have rebuilt the history of paleovegetation and paleocliamte changes in the past 26 ka, showing 7 evident stages as follows: cool-dry, warm-dry, warm-humid, cold-humid, cold-dry, warm-dry, and warm-humid. Our results demonstrate that the sedimentary environment of pluvial fan margin has a good response to the drought and wetness change of climate. The variation of the drought and wetness has a close relation with the regional desertification and ancient human activities.
The desert and Gobi deposition are prevailing in the west edge of the middle Helan Mountain, which is subject to the frangibility of eco-environment. It is important to explore the relationship between the climate change and deposition response of Gobi desert since the Last Glacial, a pluvial profile of late Late Pleistocene on the east edge of Tengger desert is employed to rebuild the palaeoenvironmental change based on the phytolith analysis. On the basis of regional geological survey, geomorphology pattern and Quaternary sediment distribution in the west of middle Helan Mountain and east edge of Tengger desert were investigated in detail. Based on the AMS14C dating and phytolith records, paleovegetation and paleoclimate changes are reconstructed in detail. Relatively abundant phytolths are found in the pluvial sediments of Qp3-Qh profile at the Yaoba, including the following morphotypes: parallelepipedal bulliform cells (including square-and rectangle-shaped) and cuneiform bulliform cells (fan-shaped), bilobate, rondel, trapeziform sinuate, elongate and unciform hair cell (point-shaped), elongate smooth, elongate echinate, elongate protuberant, and prism, etc. In addition, there are abundant charcoals and burnt phytoliths in the sediments, indicating the history of ancient human activities. Phytolith assemblages with the warmth index analysis have rebuilt the history of paleovegetation and paleocliamte changes in the past 26 ka, showing 7 evident stages as follows: cool-dry, warm-dry, warm-humid, cold-humid, cold-dry, warm-dry, and warm-humid. Our results demonstrate that the sedimentary environment of pluvial fan margin has a good response to the drought and wetness change of climate. The variation of the drought and wetness has a close relation with the regional desertification and ancient human activities.
2016, 41(4): 612-618.
doi: 10.3799/dqkx.2016.050
Abstract:
A large number of macrofossils were preserved in-situ as carbonaceous compressions in black shales of the Lower Cambrian Niutitang Formation in Weiganping area of Fuquan, Guizhou Province. The microstructure characters of these fossils are not clear. It is difficult to catalogue most fossils, which belong to some problematic fossils. The fossil assemblages mainly include worm-like fossils, rhabdopleurid-like fossils, tubular fossils and trace fossils, and a small amount of other fossils such as hyolithys, sponge spicules etc. The worm-like fossil assemblages are dominated by worm-like fossils and rhabdopleurid-like fossils, whose size is large. The fossil-bearing bed is located proximately on the nickel-molybdenum multi-metals layer. The worm-like fossil assemblage from the Niutitang Formation in Fuquan is equivalent to that of Zunyi biotas (lower biota of the Niutitang Formation), but different in predominant groups. The discovery of the worm-like fossil assemblage in Fuquan enriches the Cambrian Niutitang biota, and provides new information and materials for the study of evolution of early metazoans. Further studies of the worm-like fossil assemblage will surely provide more favorable evidences of paleontology for the ancient environment recovery and taphonomy research.
A large number of macrofossils were preserved in-situ as carbonaceous compressions in black shales of the Lower Cambrian Niutitang Formation in Weiganping area of Fuquan, Guizhou Province. The microstructure characters of these fossils are not clear. It is difficult to catalogue most fossils, which belong to some problematic fossils. The fossil assemblages mainly include worm-like fossils, rhabdopleurid-like fossils, tubular fossils and trace fossils, and a small amount of other fossils such as hyolithys, sponge spicules etc. The worm-like fossil assemblages are dominated by worm-like fossils and rhabdopleurid-like fossils, whose size is large. The fossil-bearing bed is located proximately on the nickel-molybdenum multi-metals layer. The worm-like fossil assemblage from the Niutitang Formation in Fuquan is equivalent to that of Zunyi biotas (lower biota of the Niutitang Formation), but different in predominant groups. The discovery of the worm-like fossil assemblage in Fuquan enriches the Cambrian Niutitang biota, and provides new information and materials for the study of evolution of early metazoans. Further studies of the worm-like fossil assemblage will surely provide more favorable evidences of paleontology for the ancient environment recovery and taphonomy research.
2016, 41(4): 619-632.
doi: 10.3799/dqkx.2016.051
Abstract:
Palaeo-uplift is an important tectonic unit in the petroleum basin. The Research of palaeo-uplift distribution, its evolution and statement its influence on the development of sediment have important study significance for oil and gas exploration. Based on the comprehensive research of core, logging data, seismic data and outcrop, the sequence stratigraphy framework of Kapushaliang Group was established, which was divided into four third-order sequences internally. Then the palaeo-uplift distribution and its evolution in each sequence developmental stages of Kapushaliang Group were reconstructed. In SQ1 period, palaeo-uplift was EW trending, across the entire work area, widening from the middle to east and west, with an erosion area of 1 946 km2. In SQ2 period, the palaeo-uplift area was decreased and submerged in the central uplift, 2 small eroded areas remained in the east and bigger eroded area in the west, with a total area of approximately 1 365 km2. In SQ3 period, the palaeo-uplift area was further decreased, the east was submerged overall and the northwest residual palaeo-uplift was 899 km2, and the palaeo-uplift disappeared to SQ4. According to the core observation, combined with rock combination and logging data, four kinds of sedimentary system types are identified: the brainded river delta, oxidized shallow delta, beach-and-bar facies and shore-shallow lake. Finally the configuration relationship between palaeo-uplift and source-to-sink system is revealed, based on seismic data, logging, core and other analysis data, using the idea of basin analysis, and studying the factors of structure, palaeo-uplift, facies comprehensively. It is found that there are two source systems developed in the research area: the source from the palaeo-uplift to the north and south sides and source from distant southern source. The northern side near the erosion uplift area developed short provenance, which formed braided river delta deposition. With the decrease of erosion area, the braided river delta distribution decreases, while the long axis provenance in the south formed the oxidized delta sedimentary system, with a trend gradually from northeast to northwest direction, and the scope expanded. In addition to supply sediment, the development of palaeo-uplift also conducive to the development of lithological and stratigraphic traps, and the sand beach-and-bar of shore-shallow lake in the south also had good potential as a lithological trap.
Palaeo-uplift is an important tectonic unit in the petroleum basin. The Research of palaeo-uplift distribution, its evolution and statement its influence on the development of sediment have important study significance for oil and gas exploration. Based on the comprehensive research of core, logging data, seismic data and outcrop, the sequence stratigraphy framework of Kapushaliang Group was established, which was divided into four third-order sequences internally. Then the palaeo-uplift distribution and its evolution in each sequence developmental stages of Kapushaliang Group were reconstructed. In SQ1 period, palaeo-uplift was EW trending, across the entire work area, widening from the middle to east and west, with an erosion area of 1 946 km2. In SQ2 period, the palaeo-uplift area was decreased and submerged in the central uplift, 2 small eroded areas remained in the east and bigger eroded area in the west, with a total area of approximately 1 365 km2. In SQ3 period, the palaeo-uplift area was further decreased, the east was submerged overall and the northwest residual palaeo-uplift was 899 km2, and the palaeo-uplift disappeared to SQ4. According to the core observation, combined with rock combination and logging data, four kinds of sedimentary system types are identified: the brainded river delta, oxidized shallow delta, beach-and-bar facies and shore-shallow lake. Finally the configuration relationship between palaeo-uplift and source-to-sink system is revealed, based on seismic data, logging, core and other analysis data, using the idea of basin analysis, and studying the factors of structure, palaeo-uplift, facies comprehensively. It is found that there are two source systems developed in the research area: the source from the palaeo-uplift to the north and south sides and source from distant southern source. The northern side near the erosion uplift area developed short provenance, which formed braided river delta deposition. With the decrease of erosion area, the braided river delta distribution decreases, while the long axis provenance in the south formed the oxidized delta sedimentary system, with a trend gradually from northeast to northwest direction, and the scope expanded. In addition to supply sediment, the development of palaeo-uplift also conducive to the development of lithological and stratigraphic traps, and the sand beach-and-bar of shore-shallow lake in the south also had good potential as a lithological trap.
2016, 41(4): 633-643.
doi: 10.3799/dqkx.2016.052
Abstract:
The formation and evolution of the Dongting basin are important for understanding the geological environmental evolution of the middle Yangtze drainage and even central China. However, Quaternary chronostratigraphy is still controversial in the area. In this study, one continuous borehole S3-7 with a depth of 255.1 m was taken from the Yuanjiang depression, the deposition center of the Dongting basin. Based on detailed stratigraphic and lithological interpretations, the borehole was dated by paleomagnetism, ESR and AMS14C, to establish its chronostratigraphic sequence. Compared with other two typical boreholes, the Quaternary chronostratigraphic sequence of the Dongting basin was established. The results suggest that the Plio-Pleistocene and Early-Middle Pleistocene boundaries of the central Dongting basin are located at the depths of 240-300 m and 90-95 m, respectively, and the boundaries of Middle-Late Pleistocene and Pleistocene/Holocene are located at the depths of 28-50 m and 1.5-3.1 m, respectively. Average deposition rate and piecewise linear equation show that the timing of lithological units in coverage area are as follows: 2 590-1 600 ka BP for the Huatian Formation, 1 600-920 ka BP for the Xiangyin Formation, 920-120 ka BP for the Dongtinghu Formation, 120-11 ka BP for the Anxiang Formation and younger than 11 ka BP for the Holocene.
The formation and evolution of the Dongting basin are important for understanding the geological environmental evolution of the middle Yangtze drainage and even central China. However, Quaternary chronostratigraphy is still controversial in the area. In this study, one continuous borehole S3-7 with a depth of 255.1 m was taken from the Yuanjiang depression, the deposition center of the Dongting basin. Based on detailed stratigraphic and lithological interpretations, the borehole was dated by paleomagnetism, ESR and AMS14C, to establish its chronostratigraphic sequence. Compared with other two typical boreholes, the Quaternary chronostratigraphic sequence of the Dongting basin was established. The results suggest that the Plio-Pleistocene and Early-Middle Pleistocene boundaries of the central Dongting basin are located at the depths of 240-300 m and 90-95 m, respectively, and the boundaries of Middle-Late Pleistocene and Pleistocene/Holocene are located at the depths of 28-50 m and 1.5-3.1 m, respectively. Average deposition rate and piecewise linear equation show that the timing of lithological units in coverage area are as follows: 2 590-1 600 ka BP for the Huatian Formation, 1 600-920 ka BP for the Xiangyin Formation, 920-120 ka BP for the Dongtinghu Formation, 120-11 ka BP for the Anxiang Formation and younger than 11 ka BP for the Holocene.
2016, 41(4): 644-654.
doi: 10.3799/dqkx.2016.053
Abstract:
The Linglong and Jiaojia goldfields are the two most famous goldfields in the Northwest Jiaodong with voluminous publication focused on gold mineralization. Whereas it is still a barren land as far to pay attention to the post-mineralization exhumation. Utilizing the latest low-temperature thermochronological technique, this work carries out a tentative research on the exhumation degree in the two goldfields. The results show that the zircon (U-Th)/He ages in Linglong goldfield vary predominantly between 80 and 100 Ma, while they are of significant concentration between 90 and 105 Ma in Jiaojia goldfield. These ages yielded in this work are different from those of the previous obtained by other methods, they are not the geochronological ages in respond to magmatic-hydrothermal mineralization events, instead they must have recorded the thermochronological ages of the post-mineralization exhumation of the granitoid rocks. Based on the constrain of the zircon (U-Th)/He ages, it can be concluded that the degree of exhumation in this area is roughly in agreement with that from the statistics of the global orogenic gold deposits, about 60 m/Ma. The amount of post-mineralization exhumation in the Linglong goldfield is overall ca. 600-900 m more than that in the Jiaojia goldfield, so the prospecting potential at deep part is larger in the Jiaojia goldfield than that in the Linglong goldfield.
The Linglong and Jiaojia goldfields are the two most famous goldfields in the Northwest Jiaodong with voluminous publication focused on gold mineralization. Whereas it is still a barren land as far to pay attention to the post-mineralization exhumation. Utilizing the latest low-temperature thermochronological technique, this work carries out a tentative research on the exhumation degree in the two goldfields. The results show that the zircon (U-Th)/He ages in Linglong goldfield vary predominantly between 80 and 100 Ma, while they are of significant concentration between 90 and 105 Ma in Jiaojia goldfield. These ages yielded in this work are different from those of the previous obtained by other methods, they are not the geochronological ages in respond to magmatic-hydrothermal mineralization events, instead they must have recorded the thermochronological ages of the post-mineralization exhumation of the granitoid rocks. Based on the constrain of the zircon (U-Th)/He ages, it can be concluded that the degree of exhumation in this area is roughly in agreement with that from the statistics of the global orogenic gold deposits, about 60 m/Ma. The amount of post-mineralization exhumation in the Linglong goldfield is overall ca. 600-900 m more than that in the Jiaojia goldfield, so the prospecting potential at deep part is larger in the Jiaojia goldfield than that in the Linglong goldfield.
2016, 41(4): 655-663.
doi: 10.3799/dqkx.2016.054
Abstract:
High resolution magnetic survey and borehole triple-component magnetometry are the effective magetic prospecting methods, especially much more significative for the exploration of banded iron formation (BIF) type iron deposits around coverage region. The Shanzhuang iron deposit, located in the covered regions of north of the Yellow River in Shandong Province, is a medium-to large-scale magnetite-quartzite type iron deposit. The deposit includes more than 20 iron bodies, which occur in the Shancaoyu Formation of the Neoproterozoic Taishan Group. The iron bodies dip to the southwest at 56°-70°. Average grade is about 28% for the total iron, and 22% for the magnetic iron. Taking the prospecting of the Shanzhuang iron deposit as an example, it aims to introduce an integrated prospecting method for BIF iron deposits in covered regions. Based on regional geological and geophysical characteristics, such as aeromagnetic anomaly, a high-resolution magnetic survey and profile measurement in favorable prospecting places were carried out, and the best drilling spot is chosen. It is found in the study that the borehole triple-component magnetometry during drilling and right before ending of drilling should be paid special attention, which could not only help find blind ore bodies, but also indicate abnormity around the borehole.
High resolution magnetic survey and borehole triple-component magnetometry are the effective magetic prospecting methods, especially much more significative for the exploration of banded iron formation (BIF) type iron deposits around coverage region. The Shanzhuang iron deposit, located in the covered regions of north of the Yellow River in Shandong Province, is a medium-to large-scale magnetite-quartzite type iron deposit. The deposit includes more than 20 iron bodies, which occur in the Shancaoyu Formation of the Neoproterozoic Taishan Group. The iron bodies dip to the southwest at 56°-70°. Average grade is about 28% for the total iron, and 22% for the magnetic iron. Taking the prospecting of the Shanzhuang iron deposit as an example, it aims to introduce an integrated prospecting method for BIF iron deposits in covered regions. Based on regional geological and geophysical characteristics, such as aeromagnetic anomaly, a high-resolution magnetic survey and profile measurement in favorable prospecting places were carried out, and the best drilling spot is chosen. It is found in the study that the borehole triple-component magnetometry during drilling and right before ending of drilling should be paid special attention, which could not only help find blind ore bodies, but also indicate abnormity around the borehole.
2016, 41(4): 664-674.
doi: 10.3799/dqkx.2016.055
Abstract:
The common mechanisms of coalbed fracturing assisted with cryogenic gases, such as liquid nitrogen, have been relatively clear, but the impact of low-temperature characteristics of cryogenic gases on coalbed physical properties and its mechanism of improving the fracturing performance have not yet attracted wide attentions, and lack of theoretical understanding. The mechanisms of cold shock of cryogenic gases to the coal rock are summarized first. Then based on the freezing condition of formation water and the thermal properties of cryogenic gases, the cold shock performance of liquid nitrogen to the coal rock was verified by laboratory experiments, and the behavoirs of the cooled coalbed around the wellbore after liquid nitrogen injection were predicted by numerical simulation method. Then the application potential of cold shock was analyzed. The results show that injecting cryogenic gases, such as liquid nitrogen, during coalbed fracturing, can cause a cold shock to the coal rock around wellbore, which will induce the coal matrix shrinking and the formation water freezing. A large number of new microcracks will generate in the coal rock. The mechanical strength of the coal rock will decrease by 10%-30%. These phenomena are favorable for the ice temporary blocking and the improvement of coalbed fracturing. Taking the coalbed of layer 3 in the Fanzhuang block in the Qinshui basin as example, when a amount of liquid nitrogen with a volume of 30-120 m3 is injected underground, a good cooling and shock performance in the coalbed will be obtained within 3-5 m around wellbore. The porosity of the nearby coalbed will increase about 1.5 times and the permeability will increase 4 times. A stretching and squeezing damage may also occur in the coal rock around wellbore. The cold shock of cryogenic gases and its induced ice temporary blocking can be used for the improvement of hydraulic fracturing techniques in coalbed methane and shale gas wells.
The common mechanisms of coalbed fracturing assisted with cryogenic gases, such as liquid nitrogen, have been relatively clear, but the impact of low-temperature characteristics of cryogenic gases on coalbed physical properties and its mechanism of improving the fracturing performance have not yet attracted wide attentions, and lack of theoretical understanding. The mechanisms of cold shock of cryogenic gases to the coal rock are summarized first. Then based on the freezing condition of formation water and the thermal properties of cryogenic gases, the cold shock performance of liquid nitrogen to the coal rock was verified by laboratory experiments, and the behavoirs of the cooled coalbed around the wellbore after liquid nitrogen injection were predicted by numerical simulation method. Then the application potential of cold shock was analyzed. The results show that injecting cryogenic gases, such as liquid nitrogen, during coalbed fracturing, can cause a cold shock to the coal rock around wellbore, which will induce the coal matrix shrinking and the formation water freezing. A large number of new microcracks will generate in the coal rock. The mechanical strength of the coal rock will decrease by 10%-30%. These phenomena are favorable for the ice temporary blocking and the improvement of coalbed fracturing. Taking the coalbed of layer 3 in the Fanzhuang block in the Qinshui basin as example, when a amount of liquid nitrogen with a volume of 30-120 m3 is injected underground, a good cooling and shock performance in the coalbed will be obtained within 3-5 m around wellbore. The porosity of the nearby coalbed will increase about 1.5 times and the permeability will increase 4 times. A stretching and squeezing damage may also occur in the coal rock around wellbore. The cold shock of cryogenic gases and its induced ice temporary blocking can be used for the improvement of hydraulic fracturing techniques in coalbed methane and shale gas wells.
2016, 41(4): 675-682.
doi: 10.3799/dqkx.2016.056
Abstract:
CO2 will rapidly migrate toward the up-tilt direction of the formation under buoyancy when CO2 is stored in the sloping aquifers. This phenomenon is not conducive to the storage security. In this paper, we are proposed setting water injection wells at a certain distance from the CO2 injection well in the up-tilt direction of the formation. Then hydraulic barrier is created to retard upward CO2 migration. The numerical model is set up to investigate the effectiveness of this approach, and to analyze the effects of some factors, for instance, the injection position, the injection distance and the injection rate. The results show that the hydraulic barrier caused by injecting water can effectively retard upward CO2 migration and enhance CO2 dissolution. Pumping water can significantly reduce the formation pressure. To ensure that CO2 is completely retarded, the length of the injection water needs to be greater than the thickness of the CO2 plume, even injecting water through all thickness of the formation. The rate of the injection water is the key factor affecting the effectiveness of the hydraulic barrier. The effectiveness is better when the injection water well is closer to the CO2 injection well. The water can be injected just before the arrival of CO2 plume to reduce the amount of injected water and energy consumption.
CO2 will rapidly migrate toward the up-tilt direction of the formation under buoyancy when CO2 is stored in the sloping aquifers. This phenomenon is not conducive to the storage security. In this paper, we are proposed setting water injection wells at a certain distance from the CO2 injection well in the up-tilt direction of the formation. Then hydraulic barrier is created to retard upward CO2 migration. The numerical model is set up to investigate the effectiveness of this approach, and to analyze the effects of some factors, for instance, the injection position, the injection distance and the injection rate. The results show that the hydraulic barrier caused by injecting water can effectively retard upward CO2 migration and enhance CO2 dissolution. Pumping water can significantly reduce the formation pressure. To ensure that CO2 is completely retarded, the length of the injection water needs to be greater than the thickness of the CO2 plume, even injecting water through all thickness of the formation. The rate of the injection water is the key factor affecting the effectiveness of the hydraulic barrier. The effectiveness is better when the injection water well is closer to the CO2 injection well. The water can be injected just before the arrival of CO2 plume to reduce the amount of injected water and energy consumption.
2016, 41(4): 683-691.
doi: 10.3799/dqkx.2016.057
Abstract:
The influence of dissolved organic matters as metal chelators on the bio-available iron input to the ocean has been widely reported by several studies. However, natural dissolved organic matters, especially the phenolics originated from peatlands and geochemical interactions with iron remains poorly understood. Hani peatland, as the national nature reserve in Jilin Province, is located in the central Longgang Mountain on the west side of Changbai Mountains. Physiochemical characteristics of water samples collected from rivers in Hani, including total dissolved iron, ferrous iron, dissolved organic carbon and pH etc., were detected in the field. Inner connections of these indexes were demonstrated through multivariate statistical analysis and simulation experiments on geochemical interactions between iron and phenolic acids were conducted in laboratory. Results show that total dissolved phenol plays an important role in the existence and transportation of ferrous iron. Ten phenolic acid, including protocatechuic acid, caffeic acid, gallic acid, gentisic acid, syringic acid, ferulic acid, p-hydroxybenzoic acid, p-coumaric acid, salicylic acid and vanillic acid, were detected by high performance liquid chromatography. Simulation experiments reveal that phenolics bearing either catechol or galloyl moiety groups (protocatechuic acid, caffeic acid and galllic acid) could chelate ferrous iron, which is the geochemical cause of high concentration of dissolved iron and is crucial for iron transport in peatland. Reducing action of phenolics to Fe(Ⅲ) is also responsible for maintaining high concentration of Fe(Ⅱ) and Fe(Ⅲ) in rivers drained from peatland. Considering the wide distribution of peatlands globally, the higher concentration of Fe in peatlands, and the enhancement of marine organisms by Fe, the complexation and reductive actions between iron and phenolics originated from peatlands are of important significance to global iron cycle coupled with other element cycles, such as carbon and sulfur, which can significantly influence global ecological balance.
The influence of dissolved organic matters as metal chelators on the bio-available iron input to the ocean has been widely reported by several studies. However, natural dissolved organic matters, especially the phenolics originated from peatlands and geochemical interactions with iron remains poorly understood. Hani peatland, as the national nature reserve in Jilin Province, is located in the central Longgang Mountain on the west side of Changbai Mountains. Physiochemical characteristics of water samples collected from rivers in Hani, including total dissolved iron, ferrous iron, dissolved organic carbon and pH etc., were detected in the field. Inner connections of these indexes were demonstrated through multivariate statistical analysis and simulation experiments on geochemical interactions between iron and phenolic acids were conducted in laboratory. Results show that total dissolved phenol plays an important role in the existence and transportation of ferrous iron. Ten phenolic acid, including protocatechuic acid, caffeic acid, gallic acid, gentisic acid, syringic acid, ferulic acid, p-hydroxybenzoic acid, p-coumaric acid, salicylic acid and vanillic acid, were detected by high performance liquid chromatography. Simulation experiments reveal that phenolics bearing either catechol or galloyl moiety groups (protocatechuic acid, caffeic acid and galllic acid) could chelate ferrous iron, which is the geochemical cause of high concentration of dissolved iron and is crucial for iron transport in peatland. Reducing action of phenolics to Fe(Ⅲ) is also responsible for maintaining high concentration of Fe(Ⅱ) and Fe(Ⅲ) in rivers drained from peatland. Considering the wide distribution of peatlands globally, the higher concentration of Fe in peatlands, and the enhancement of marine organisms by Fe, the complexation and reductive actions between iron and phenolics originated from peatlands are of important significance to global iron cycle coupled with other element cycles, such as carbon and sulfur, which can significantly influence global ecological balance.
2016, 41(4): 692-700.
doi: 10.3799/dakx.2016.058
Abstract:
The heterogeneity of karst water system is the key challenge for water prevention and control in metal mineral deposits with karst water in southern China. Taking Makeng iron mine as the subject, the distribution heterogeneity characteristics of hard structural factors including faults, karst, igneous rocks are identified by data mining of all the hydrogeological information available in this paper. In addition, the characteristics of karst water system in natural condition and dewatering conditions are analyzed by drawing the water level contour maps of 7 different periods. It is concluded that the fault and karst, which control the concentrated runoff zone of karst water, can be used as the main target of advanced water detection and dewatering. Karst water system shows strong heterogeneity under the influence of igneous local impermeable belt. The ore body of Makeng Iron Mine can be liberated effectively and its production can be increased rapidly by multi-phase prevention and control of the karst water in the mining area, utilizing the local igneous impermeable belt, which can ensure its sustainable development.
The heterogeneity of karst water system is the key challenge for water prevention and control in metal mineral deposits with karst water in southern China. Taking Makeng iron mine as the subject, the distribution heterogeneity characteristics of hard structural factors including faults, karst, igneous rocks are identified by data mining of all the hydrogeological information available in this paper. In addition, the characteristics of karst water system in natural condition and dewatering conditions are analyzed by drawing the water level contour maps of 7 different periods. It is concluded that the fault and karst, which control the concentrated runoff zone of karst water, can be used as the main target of advanced water detection and dewatering. Karst water system shows strong heterogeneity under the influence of igneous local impermeable belt. The ore body of Makeng Iron Mine can be liberated effectively and its production can be increased rapidly by multi-phase prevention and control of the karst water in the mining area, utilizing the local igneous impermeable belt, which can ensure its sustainable development.
2016, 41(4): 701-710.
doi: 10.3799/dqkx.2016.059
Abstract:
A hydropower station located on Dadu River of Sichuan Province is under construction now. The construction of its impervious walls have been completed basically, however, the discharge of water is still large in the foundation pit of hydropower station. In order to evaluate the performance of impervious walls, two pumping tests was conducted between the two impervious walls. According to the boundary conditions of this area, the comprehensive well function was used to obtain the hydrogeological parameters. On the basis, numerical model is established by using GMS (groundwater modeling system) software to obtain the aquifer parameters after identifying and verifying the model. The results indicate that the hydraulic conductivity of aquifer is between 19.13-32.24 m/d by analytical method, and 26.00 m/d by numerical simulation. In addition, the hydraulic conductivity of impervious walls is very small (0.01-0.02 m/d), it is found that the performance of impervious walls is good.
A hydropower station located on Dadu River of Sichuan Province is under construction now. The construction of its impervious walls have been completed basically, however, the discharge of water is still large in the foundation pit of hydropower station. In order to evaluate the performance of impervious walls, two pumping tests was conducted between the two impervious walls. According to the boundary conditions of this area, the comprehensive well function was used to obtain the hydrogeological parameters. On the basis, numerical model is established by using GMS (groundwater modeling system) software to obtain the aquifer parameters after identifying and verifying the model. The results indicate that the hydraulic conductivity of aquifer is between 19.13-32.24 m/d by analytical method, and 26.00 m/d by numerical simulation. In addition, the hydraulic conductivity of impervious walls is very small (0.01-0.02 m/d), it is found that the performance of impervious walls is good.
2016, 41(4): 711-717.
doi: 10.3799/dqkx.2016.060
Abstract:
Curves of cumulative displacement vs. time of the landslide generally include the stages of the initial deformation, constant speed deformation and accelerated deformation. Different deformation stages have their own different acceleration characteristics. Now the evolution of landslide can be divided by analyzing the characteristics of acceleration curve. But it lacks theoretical basis and quantitative calculation. To the above problems, the rainfall of current month and reservoir level fluctuation of current month are selected as influencing factors, and the multivariate time series model is adopted to predict the cumulative displacement. Taking the maximum points of F statistic and log-likelihood ratio statistic of the multivariate time series model as segmentation points divides the evolution stages of landslide based on the theory of Chow breakpoint test. This model is used to deal with the data of cumulative displacement, rainfall and reservoir level fluctuation of Xintan landslide and Baishuihe landslide in the Three Gorges reservoir area. The results indicate that the Chow breakpoint test on the multivariate time series prediction model based on the inducing factors and the landslide displacement has certain validity and application value. This division of the landslide evolution stage can provide an important criterion for the early-warning prediction of landslide.
Curves of cumulative displacement vs. time of the landslide generally include the stages of the initial deformation, constant speed deformation and accelerated deformation. Different deformation stages have their own different acceleration characteristics. Now the evolution of landslide can be divided by analyzing the characteristics of acceleration curve. But it lacks theoretical basis and quantitative calculation. To the above problems, the rainfall of current month and reservoir level fluctuation of current month are selected as influencing factors, and the multivariate time series model is adopted to predict the cumulative displacement. Taking the maximum points of F statistic and log-likelihood ratio statistic of the multivariate time series model as segmentation points divides the evolution stages of landslide based on the theory of Chow breakpoint test. This model is used to deal with the data of cumulative displacement, rainfall and reservoir level fluctuation of Xintan landslide and Baishuihe landslide in the Three Gorges reservoir area. The results indicate that the Chow breakpoint test on the multivariate time series prediction model based on the inducing factors and the landslide displacement has certain validity and application value. This division of the landslide evolution stage can provide an important criterion for the early-warning prediction of landslide.
2016, 41(4): 718-728.
doi: 10.3799/dqkx.2016.061
Abstract:
Cobalt-rich ferromanganese crusts are mainly distributed around the top brim and on the slope of Mid-Pacific seamounts and West Pacific seamounts. Calcium-pelagic sediment, carbonate rock and debris flow driven by gravity process are main seafloor sediment types of seamounts, which control the distribution of cobalt-rich ferromanganese crusts. In this paper, multibeam backscatter intensity data from EM122 multibeam system are first used in China to recognize seafloor geological types of Qianyu seamount on Mid-Pacific seamounts. Backscatter data are processed and classified statistically with verification of sub-bottom profile and ground-truthing data to identify four seafloor geological types including cobalt-rich crust, calcium-pelagic sediment, carbonate rock and debris flow. Different backscatter intensities are represented by different seafloor geological types, cobalt-rich crust area shows as uniform strong backscatter intensity representing, and calcium-pelagic sediment area shows as uniform weak backscatter, their backscatter difference is about 20 dB. The top of Qianyu seamount is mostly outcropped by carbonate rock, and locally covered by calcium-pelagic sediment, and cobalt-rich crust distribute around the top brim and southern and eastern slope ridges. Furthermore, three gravity slide areas are recognized on the Qianyu seamount, which are of debris flows.
Cobalt-rich ferromanganese crusts are mainly distributed around the top brim and on the slope of Mid-Pacific seamounts and West Pacific seamounts. Calcium-pelagic sediment, carbonate rock and debris flow driven by gravity process are main seafloor sediment types of seamounts, which control the distribution of cobalt-rich ferromanganese crusts. In this paper, multibeam backscatter intensity data from EM122 multibeam system are first used in China to recognize seafloor geological types of Qianyu seamount on Mid-Pacific seamounts. Backscatter data are processed and classified statistically with verification of sub-bottom profile and ground-truthing data to identify four seafloor geological types including cobalt-rich crust, calcium-pelagic sediment, carbonate rock and debris flow. Different backscatter intensities are represented by different seafloor geological types, cobalt-rich crust area shows as uniform strong backscatter intensity representing, and calcium-pelagic sediment area shows as uniform weak backscatter, their backscatter difference is about 20 dB. The top of Qianyu seamount is mostly outcropped by carbonate rock, and locally covered by calcium-pelagic sediment, and cobalt-rich crust distribute around the top brim and southern and eastern slope ridges. Furthermore, three gravity slide areas are recognized on the Qianyu seamount, which are of debris flows.
