2010 Vol. 35, No. 4
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2010, 35(4): 507-511.
doi: 10.3799/dqkx.2010.065
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Abstract:
A thalattosaur forelimb specimen described here, was collected from the second member of Guanling Formation (the Middle Triassic Anisian Pelsonian) of Xinzai village, Luoping County, Yunnan Province. It is not only the first appearance of Thalattosauria from Luoping Biota, but also the oldest record of long-necked taxon (Askeptosauridea). The incomplete skeleton of zeugopodium and autopodium is featured with the following special characters such as paralleled distolateral margins, expanded distal end of ulna, 11 ossified carpal elements, a transverse process in the proximal end of the third metacarpal and the phalangeal formula 2-3-4-4-4 (?). These characters are not enough to define a new taxon in Thalattosauria, but they show that some thalattosaur taxa preserved some primitive characters when they were divergent to water. Furthermore, these primitive characters indicate that some thalattosaur taxa could have lived on seashore.
A thalattosaur forelimb specimen described here, was collected from the second member of Guanling Formation (the Middle Triassic Anisian Pelsonian) of Xinzai village, Luoping County, Yunnan Province. It is not only the first appearance of Thalattosauria from Luoping Biota, but also the oldest record of long-necked taxon (Askeptosauridea). The incomplete skeleton of zeugopodium and autopodium is featured with the following special characters such as paralleled distolateral margins, expanded distal end of ulna, 11 ossified carpal elements, a transverse process in the proximal end of the third metacarpal and the phalangeal formula 2-3-4-4-4 (?). These characters are not enough to define a new taxon in Thalattosauria, but they show that some thalattosaur taxa preserved some primitive characters when they were divergent to water. Furthermore, these primitive characters indicate that some thalattosaur taxa could have lived on seashore.
2010, 35(4): 512-514.
doi: 10.3799/dqkx.2010.066
Abstract:
Abundant conodont clusters were found after careful sampling, processing and analysis of the specimens in the Daaozi section of the second member of Guanling Formation yielding Luoping Fauna at the centimeter level. And a complete conodont multielement apparatus (P1, S0, S1, S2/3, M) was shown to us by fine identification and detailed analysis, including one pair of P1 elements (Neospathodiform), one S0 element (Cypridodelliform), pairs of S1 (Enantiognathiform), S2/S3 (Hindeodelliform), and M elements (Cypridodelliform).
Abundant conodont clusters were found after careful sampling, processing and analysis of the specimens in the Daaozi section of the second member of Guanling Formation yielding Luoping Fauna at the centimeter level. And a complete conodont multielement apparatus (P1, S0, S1, S2/3, M) was shown to us by fine identification and detailed analysis, including one pair of P1 elements (Neospathodiform), one S0 element (Cypridodelliform), pairs of S1 (Enantiognathiform), S2/S3 (Hindeodelliform), and M elements (Cypridodelliform).
2010, 35(4): 515-525.
doi: 10.3799/dqkx.2010.067
Abstract:
Oxygen and carbon stable isotope records (with an average time resolution of 228 a) were obtained from Core MD05-2904 (19°27.32', 116°15.15', water depth 2 066 m), using the mixed-layer dwelling planktonic foraminifer Globigerinoides ruber (white). The 45 m core spans from end of MIS 8 to the Holocene, representing the sediment record of the last 257 a. Strong precession periods (23.4 ka and 19.8 ka) were found from spectral analysis of both δ18O and δ13C records, following with semi-precession cycles (11.7 ka and 9.9 ka). The high resolution δ18O record of MD05-2904 reveals nearly all the Dansgaard/Oeschger and Heinrich events during MIS 2-4, as defined in the Greenland ice core record. A better correlation between MD05-2904 planktonic δ18O, the Hulu stalagmite δ18O record and previously published planktonic δ18O records from the SCS suggests that the planktonic δ18O record is influenced by monsoon-dominated regional factors, such as rainfall and river discharge related salinity changes. Lighter δ18O values in early MIS 3, early MIS 6 and MIS 7.4, and heavier values in MIS 5.5 are due to changes in precipitation and evaporation affected by monsoon. Sedimentation rates increased to 65-70 cm/ka in LGM, indicating more sediments when the site location was closer to the river mouth during glacial at lower sea level.
Oxygen and carbon stable isotope records (with an average time resolution of 228 a) were obtained from Core MD05-2904 (19°27.32', 116°15.15', water depth 2 066 m), using the mixed-layer dwelling planktonic foraminifer Globigerinoides ruber (white). The 45 m core spans from end of MIS 8 to the Holocene, representing the sediment record of the last 257 a. Strong precession periods (23.4 ka and 19.8 ka) were found from spectral analysis of both δ18O and δ13C records, following with semi-precession cycles (11.7 ka and 9.9 ka). The high resolution δ18O record of MD05-2904 reveals nearly all the Dansgaard/Oeschger and Heinrich events during MIS 2-4, as defined in the Greenland ice core record. A better correlation between MD05-2904 planktonic δ18O, the Hulu stalagmite δ18O record and previously published planktonic δ18O records from the SCS suggests that the planktonic δ18O record is influenced by monsoon-dominated regional factors, such as rainfall and river discharge related salinity changes. Lighter δ18O values in early MIS 3, early MIS 6 and MIS 7.4, and heavier values in MIS 5.5 are due to changes in precipitation and evaporation affected by monsoon. Sedimentation rates increased to 65-70 cm/ka in LGM, indicating more sediments when the site location was closer to the river mouth during glacial at lower sea level.
2010, 35(4): 526-532.
doi: 10.3799/dqkx.2010.068
Abstract:
High-resolution carbon and oxygen isotope analysis for cores NS93-5 and NS97-37 from southern South China Sea (SCS) shows the rapid negative excursion of carbon isotope in the last deglaciation (about 18 ka) and the penultimate deglaciation (about 130 ka). In the same layer, the oxygen isotope also displays similar phenomena. It is found that the Globigerinoides rubber (Pink) died out in midpoint of MIS 5/6 (about 129.84 ka). The change of carbon and oxygen isotope is in consonance with atmospheric methane concentration from the Vostok ice core. The two rapid negative excursions of carbon isotope recorded in SCS are likely related to gas hydrate dissociation, i.e. the changes of temperature and pressure induced gas hydrate dissociation and released methane in SCS and/or other areas, which made the climate warmer, ocean anoxic and further led to the extinction of some marine organism and accelerated glacial termination.
High-resolution carbon and oxygen isotope analysis for cores NS93-5 and NS97-37 from southern South China Sea (SCS) shows the rapid negative excursion of carbon isotope in the last deglaciation (about 18 ka) and the penultimate deglaciation (about 130 ka). In the same layer, the oxygen isotope also displays similar phenomena. It is found that the Globigerinoides rubber (Pink) died out in midpoint of MIS 5/6 (about 129.84 ka). The change of carbon and oxygen isotope is in consonance with atmospheric methane concentration from the Vostok ice core. The two rapid negative excursions of carbon isotope recorded in SCS are likely related to gas hydrate dissociation, i.e. the changes of temperature and pressure induced gas hydrate dissociation and released methane in SCS and/or other areas, which made the climate warmer, ocean anoxic and further led to the extinction of some marine organism and accelerated glacial termination.
2010, 35(4): 533-541.
doi: 10.3799/dqkx.2010.069
Abstract:
The magnetic susceptibility of loess as a proxy for the intensity of summer monsoon has be used to investigate the periodicity of paleoclimatic changes of aeolian deposits in China.However, previous studies focused most on the southeast monsoon areas. On the basis of magnetostratigraphic study of the Garzê A section on the southeastern margin of the Qinghai-Tibet Plateau, the magnetic susceptibility records during the past 1.16 Ma were subject to an empirical mode decomposition (EMD) to discuss the periodicity of the southwest monsoon evolution at various time scales. The results show that: (1) the significant orbital periodicities do exist including the eccentricity, obliquity and precession periods in our records, which indicates that the southwest monsoon is also controlled by the astronomical factors; (2) The beat frequency periods of the precession are detected, which shows the tropical climatic characteristics of the southwest monsoon; (3) the quasi-200 ka cycle is confirmed in existence but its forming mechanism needs further study; (4) the appearance of quasi-400 ka cycle fluctuation may correspond to quasi-400 ka eccentricity cycle. Therefore, the main forcing of Indian monsoon system may be the solar insolation at low latitude. As for the studies of paleoenvironment evolution of sedimentary records, EMD is superior and has more potentials than the traditional method of spectral analysis.
The magnetic susceptibility of loess as a proxy for the intensity of summer monsoon has be used to investigate the periodicity of paleoclimatic changes of aeolian deposits in China.However, previous studies focused most on the southeast monsoon areas. On the basis of magnetostratigraphic study of the Garzê A section on the southeastern margin of the Qinghai-Tibet Plateau, the magnetic susceptibility records during the past 1.16 Ma were subject to an empirical mode decomposition (EMD) to discuss the periodicity of the southwest monsoon evolution at various time scales. The results show that: (1) the significant orbital periodicities do exist including the eccentricity, obliquity and precession periods in our records, which indicates that the southwest monsoon is also controlled by the astronomical factors; (2) The beat frequency periods of the precession are detected, which shows the tropical climatic characteristics of the southwest monsoon; (3) the quasi-200 ka cycle is confirmed in existence but its forming mechanism needs further study; (4) the appearance of quasi-400 ka cycle fluctuation may correspond to quasi-400 ka eccentricity cycle. Therefore, the main forcing of Indian monsoon system may be the solar insolation at low latitude. As for the studies of paleoenvironment evolution of sedimentary records, EMD is superior and has more potentials than the traditional method of spectral analysis.
2010, 35(4): 542-550.
doi: 10.3799/dqkx.2010.070
Abstract:
The evolution of the shore-normal profile shape of an accretional tidal flat is controlled by the transport of muddy and sandy sediments by tidal currents. To understand the evolution processes, a model is established to simulate the tidal flat profile changes in response to spring-neap tidal cycles, and it is applied to the accretional tidal flat on the central Jiangsu coast to investigate the interrelationships between the initial profile shape of the inter-tidal flat, tidal range, sediment supply, the equilibrium profile shape of the intertidal flat, and the long-term behavior of a prograding profile. The modeling output indicates that: (1) the shape of the accretional tidal flat tends to be convex when reaching its equilibrium state; (2) equilibrium of the intertidal flat morphology is independent of the initial profile shape; (3) if the sediment supply remains stable, then the width of the intertidal flat is positively correlated to tidal range; (4) the width of the intertidal flat increases with sediment supply and the accretion or erosion status of the intertidal flat is determined by sediment supply; (5) there is a need to design an algorithm to treat the area close to high water on springs to simulate long-term growth of the tidal flat; (6) the intertidal flat associated with abundant sediment supply will progradeg towards the sea, and at the same time its equilibrium shape will be maintained; and (7) the width and gradient of the intertidal flat from the model output are consistent with those of the Jiangsu coast, when inputting parameters derived locally for the model.
The evolution of the shore-normal profile shape of an accretional tidal flat is controlled by the transport of muddy and sandy sediments by tidal currents. To understand the evolution processes, a model is established to simulate the tidal flat profile changes in response to spring-neap tidal cycles, and it is applied to the accretional tidal flat on the central Jiangsu coast to investigate the interrelationships between the initial profile shape of the inter-tidal flat, tidal range, sediment supply, the equilibrium profile shape of the intertidal flat, and the long-term behavior of a prograding profile. The modeling output indicates that: (1) the shape of the accretional tidal flat tends to be convex when reaching its equilibrium state; (2) equilibrium of the intertidal flat morphology is independent of the initial profile shape; (3) if the sediment supply remains stable, then the width of the intertidal flat is positively correlated to tidal range; (4) the width of the intertidal flat increases with sediment supply and the accretion or erosion status of the intertidal flat is determined by sediment supply; (5) there is a need to design an algorithm to treat the area close to high water on springs to simulate long-term growth of the tidal flat; (6) the intertidal flat associated with abundant sediment supply will progradeg towards the sea, and at the same time its equilibrium shape will be maintained; and (7) the width and gradient of the intertidal flat from the model output are consistent with those of the Jiangsu coast, when inputting parameters derived locally for the model.
2010, 35(4): 551-562.
doi: 10.3799/dqkx.2010.071
Abstract:
WPD-03 is a sediment core with the Ethmodiscus rex diatom mats recently reported from the low-latitude western Pacific Ocean. Clay mineral assemblages, opal and organic material contents in sediments from Core WPD-03 were measured to trace the formation of diatom mats, based on a multi-approach including X-ray diffraction, inductively coupled plasma optical emission spectrometry (ICP-OES) with wet alkaline digestion and elemental analysis (EA) with high-temperature combustion. Clay minerals at Core WPD-03 are mainly composed of smectite (50%) and illite (39%), with extremely low contents of chlorite (8%) and kaolinite (3%). Provenance studies indicate that most smectite is derived form the chemical alteration of submarine basic volcanic materials, while illite is originated from the dry area of Chinese inland and nearby islands by the transport of wind mainly, the same as chlorite. The analysis of illite/smectite ratio and smectite abundance shows that, at the bottom of diatom mats, it recorded a remarkable strengthened eolian deposition, which imported plentiful silicon and iron to promote the bloom of Ethmodiscus rex probably, resulting in the export of mass biogenic silicon and organic carbon to seafloor and subsequently forming diatom mats. Special ecological characteristics of Ethmodiscus rex and their peculiar demands on marine environments may result in the lag response of Ethmodiscus rex bloom to dust inputs. Therefore, the dust input was considered to favor the formation of diatom mats. The mechanism of "dust input-diatom mats" is significant for comprehensive understanding of the mechanism of diatom mats formation and their role in global carbon cycle and climate changes.
WPD-03 is a sediment core with the Ethmodiscus rex diatom mats recently reported from the low-latitude western Pacific Ocean. Clay mineral assemblages, opal and organic material contents in sediments from Core WPD-03 were measured to trace the formation of diatom mats, based on a multi-approach including X-ray diffraction, inductively coupled plasma optical emission spectrometry (ICP-OES) with wet alkaline digestion and elemental analysis (EA) with high-temperature combustion. Clay minerals at Core WPD-03 are mainly composed of smectite (50%) and illite (39%), with extremely low contents of chlorite (8%) and kaolinite (3%). Provenance studies indicate that most smectite is derived form the chemical alteration of submarine basic volcanic materials, while illite is originated from the dry area of Chinese inland and nearby islands by the transport of wind mainly, the same as chlorite. The analysis of illite/smectite ratio and smectite abundance shows that, at the bottom of diatom mats, it recorded a remarkable strengthened eolian deposition, which imported plentiful silicon and iron to promote the bloom of Ethmodiscus rex probably, resulting in the export of mass biogenic silicon and organic carbon to seafloor and subsequently forming diatom mats. Special ecological characteristics of Ethmodiscus rex and their peculiar demands on marine environments may result in the lag response of Ethmodiscus rex bloom to dust inputs. Therefore, the dust input was considered to favor the formation of diatom mats. The mechanism of "dust input-diatom mats" is significant for comprehensive understanding of the mechanism of diatom mats formation and their role in global carbon cycle and climate changes.
2010, 35(4): 563-571.
doi: 10.3799/dqkx.2010.072
Abstract:
Rare earth elements (REE) in the fine-grained fraction of surface sediments were detected by ICP-MS analysis, to study distribution characters of REE and the influencing factors in the South China Sea. Results reveal that distribution of REE in sediments is mainly related with continental input, biological effects and provision of volcanic materials in the South China Sea. The REE NASC normalization distribution pattern of average fine-grained fraction in the South China Sea is similar to that in Chinese loess, and also those of coastal rivers including the Pearl River and Mekong River, but sharply different from that of Cenozoic basalts from the South China Sea, indicating that fine-grained fraction was mostly derived from the mainland substance. Trend analysis of REE indicates that fine-grained fraction between the Pearl River Mouth and the southern Hainan Island was transported into the slope in the southeastern direction, while sediments between the southwestern Taiwan Island and the Pearl River Mouth were mostly transported southward. Sediments in the western Luzon Island and near the Huangyan Island were mainly conveyed northwestward, which could reach 113°E in the west and 20°N in the north. In the southern South China Sea, sediments were wholly transported towards the northwestern Nansha trough.
Rare earth elements (REE) in the fine-grained fraction of surface sediments were detected by ICP-MS analysis, to study distribution characters of REE and the influencing factors in the South China Sea. Results reveal that distribution of REE in sediments is mainly related with continental input, biological effects and provision of volcanic materials in the South China Sea. The REE NASC normalization distribution pattern of average fine-grained fraction in the South China Sea is similar to that in Chinese loess, and also those of coastal rivers including the Pearl River and Mekong River, but sharply different from that of Cenozoic basalts from the South China Sea, indicating that fine-grained fraction was mostly derived from the mainland substance. Trend analysis of REE indicates that fine-grained fraction between the Pearl River Mouth and the southern Hainan Island was transported into the slope in the southeastern direction, while sediments between the southwestern Taiwan Island and the Pearl River Mouth were mostly transported southward. Sediments in the western Luzon Island and near the Huangyan Island were mainly conveyed northwestward, which could reach 113°E in the west and 20°N in the north. In the southern South China Sea, sediments were wholly transported towards the northwestern Nansha trough.
2010, 35(4): 572-584.
doi: 10.3799/dqkx.2010.073
Abstract:
This paper aims to constrain the starting time of Early Cretaceous large-scale extensional and mantle properties in Dabie orogen. The SHRIMP zircon U-Pb dating results reveal the Yinshafan gabbro dyke from Jinzhai, North Huaiyang region is 125.8±2.7 Ma, the Dongxinxiang lamprophyre dyke from Dawu, West Dabie is 129.6±2.5 Ma. The Early Cretaceous basic dykes from different regions of the Dabie Orogen show similar geochemical features: These samples have SiO2 ranging from 46.13% to 54.42%, Mg# between 42 and 72, mainly belonging to alkaline series, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), evident depletion in high field strength elements (HFSE, e.g., Nb, Zr and Ti), ISr=0.705 5-0.709 4 and highly negative εNd (t) values of about -12.04 to -18.84, TDM=1.60-2.62 Ga. Early Cretaceous crustal extension and large-scale magma eruption in the Dabie orogenic belt began in 130 Ma, and belonged to part of eastern China Late Mesozoic lithospheric thinning extension event. The basic dykes were derived from enriched lithospheric mantle, which originated from North China Craton (NCC) lithospheric mantle contaminated by the deeply subducted Yangtze crust, and maybe have been added in some mantle asthenosphere.
This paper aims to constrain the starting time of Early Cretaceous large-scale extensional and mantle properties in Dabie orogen. The SHRIMP zircon U-Pb dating results reveal the Yinshafan gabbro dyke from Jinzhai, North Huaiyang region is 125.8±2.7 Ma, the Dongxinxiang lamprophyre dyke from Dawu, West Dabie is 129.6±2.5 Ma. The Early Cretaceous basic dykes from different regions of the Dabie Orogen show similar geochemical features: These samples have SiO2 ranging from 46.13% to 54.42%, Mg# between 42 and 72, mainly belonging to alkaline series, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), evident depletion in high field strength elements (HFSE, e.g., Nb, Zr and Ti), ISr=0.705 5-0.709 4 and highly negative εNd (t) values of about -12.04 to -18.84, TDM=1.60-2.62 Ga. Early Cretaceous crustal extension and large-scale magma eruption in the Dabie orogenic belt began in 130 Ma, and belonged to part of eastern China Late Mesozoic lithospheric thinning extension event. The basic dykes were derived from enriched lithospheric mantle, which originated from North China Craton (NCC) lithospheric mantle contaminated by the deeply subducted Yangtze crust, and maybe have been added in some mantle asthenosphere.
2010, 35(4): 585-596.
doi: 10.3799/dqkx.2010.074
Abstract:
The Huaixi copper-gold deposit, located in depression area between the Zhenghe-Dapu and Changle-Nan'ao deep faults in southeastern Zhejiang Province, is a typical hydrothermal vein filling-metasomatic Cu-Au polymetallic deposit. The Caomen K-feldspar granite porphyry pulton is the dominant intrusion in the deposit. Petrography and chemical compositions show that it belongs to shoshonite series characterized by high silicon, and it is enriched in alkali and iron but depleted in phosphorus and titanium. Its SiO2 contents range from 75.64% to 78.00%, while K2O and K2O/Na2O ratios vary from 5.38% to 5.92% and 1.94 to 2.72 respectively. Ga, Rb, Th, U and Pb elements are enriched in the intrusion while Ba, Nb, Sr, P and Ti are depleted. REE is characterized with obvious negative anomalies with Eu/Eu* 0.06-0.13 and exhibits right-dipping "V" patterns with LREE enrichment. Its mineralogy and geochemistry are consistent with those of Late Cretaceous alkaline granites in the coastal areas of Zhejiang-Fujian. This study offers the first highly precise dating of the diagenesis and mineralization in the deposit. The dating of zircon from the Caomen alkaline granite pulton determined by LA-ICP-MS yields age of 102±1 Ma (MSDW=1.3), while Rb and Sr isotopic dating of fluid inclusions in quartz of the Huaixi copper-gold deposit yields isochron age of 101±2 Ma. The results suggest that Cu-Au mineralization was consistent with granite crystallization. The ages of diagenesis and mineralization provide an important chronological constraint for the close genetic relationship of the deposit and the Caomen intrusion. The Huaixi Cu-Au deposit, originated from back-arc extensional tectonic-heat event related to high angle subduction of the ancient Pacific plate, caused by northward movement of the Indian plate, is corresponding to the time of the third large-scale mineralization regionally in the Mesozoic.
The Huaixi copper-gold deposit, located in depression area between the Zhenghe-Dapu and Changle-Nan'ao deep faults in southeastern Zhejiang Province, is a typical hydrothermal vein filling-metasomatic Cu-Au polymetallic deposit. The Caomen K-feldspar granite porphyry pulton is the dominant intrusion in the deposit. Petrography and chemical compositions show that it belongs to shoshonite series characterized by high silicon, and it is enriched in alkali and iron but depleted in phosphorus and titanium. Its SiO2 contents range from 75.64% to 78.00%, while K2O and K2O/Na2O ratios vary from 5.38% to 5.92% and 1.94 to 2.72 respectively. Ga, Rb, Th, U and Pb elements are enriched in the intrusion while Ba, Nb, Sr, P and Ti are depleted. REE is characterized with obvious negative anomalies with Eu/Eu* 0.06-0.13 and exhibits right-dipping "V" patterns with LREE enrichment. Its mineralogy and geochemistry are consistent with those of Late Cretaceous alkaline granites in the coastal areas of Zhejiang-Fujian. This study offers the first highly precise dating of the diagenesis and mineralization in the deposit. The dating of zircon from the Caomen alkaline granite pulton determined by LA-ICP-MS yields age of 102±1 Ma (MSDW=1.3), while Rb and Sr isotopic dating of fluid inclusions in quartz of the Huaixi copper-gold deposit yields isochron age of 101±2 Ma. The results suggest that Cu-Au mineralization was consistent with granite crystallization. The ages of diagenesis and mineralization provide an important chronological constraint for the close genetic relationship of the deposit and the Caomen intrusion. The Huaixi Cu-Au deposit, originated from back-arc extensional tectonic-heat event related to high angle subduction of the ancient Pacific plate, caused by northward movement of the Indian plate, is corresponding to the time of the third large-scale mineralization regionally in the Mesozoic.
2010, 35(4): 597-610.
doi: 10.3799/dqkx.2010.075
Abstract:
LA-ICP-MS zircon U-Pb dating of the Kubusunan granodiorite and its enclaves in the Kalamaili area of the eastern Junggar indicates that the isotopic age of the granodiorite is 287±2 Ma (MSWD=0.15), and that of its enclaves is 286±3 Ma (MSWD=0.22). The fact that they are the same in error range, showing that granodiorite and enclaves were formed at the same age, ruling out the possibility that the dark microgranule enclaves came from the solid metamorphic rock melt remaining in deep crust, or xenoliths from wall rock in the upper crust, at the same time, ruling out the possibility that the basic magma invaded solidified ganite magma. It presents strong evidence for the crust and mantle magma hybrid. Petrological and geochemical studies reveal the relationship between the enclaves and the host rock and it is found that they are related and restricted with each other. The enclaves are rich in basic ingredients HFSE(such as Ti, Zr, Nb and Hf) and REE, Kubusunan granodiorite characteristics of low 87Sr/86Sr initial values and high εNd(t) values, indicating that granites originated partly from mantle magma. The large number of microgranular dioritic enclaves is direct evidence of crust-mantle magma hybrid. Kubusunan granodiorite was formed later than the Ulungur river and Kalamaili alkali granite (300 Ma±) resulting from post-collision magma activity surrounding eastern Junggar, whose formation and evolution stands for continental crust growth caused by post-collision magma underplating in eastern Junggar.
LA-ICP-MS zircon U-Pb dating of the Kubusunan granodiorite and its enclaves in the Kalamaili area of the eastern Junggar indicates that the isotopic age of the granodiorite is 287±2 Ma (MSWD=0.15), and that of its enclaves is 286±3 Ma (MSWD=0.22). The fact that they are the same in error range, showing that granodiorite and enclaves were formed at the same age, ruling out the possibility that the dark microgranule enclaves came from the solid metamorphic rock melt remaining in deep crust, or xenoliths from wall rock in the upper crust, at the same time, ruling out the possibility that the basic magma invaded solidified ganite magma. It presents strong evidence for the crust and mantle magma hybrid. Petrological and geochemical studies reveal the relationship between the enclaves and the host rock and it is found that they are related and restricted with each other. The enclaves are rich in basic ingredients HFSE(such as Ti, Zr, Nb and Hf) and REE, Kubusunan granodiorite characteristics of low 87Sr/86Sr initial values and high εNd(t) values, indicating that granites originated partly from mantle magma. The large number of microgranular dioritic enclaves is direct evidence of crust-mantle magma hybrid. Kubusunan granodiorite was formed later than the Ulungur river and Kalamaili alkali granite (300 Ma±) resulting from post-collision magma activity surrounding eastern Junggar, whose formation and evolution stands for continental crust growth caused by post-collision magma underplating in eastern Junggar.
2010, 35(4): 611-620.
doi: 10.3799/dqkx.2010.076
Abstract:
Neoproterozoic magmatic rocks are widespread in western margin of the Yangtze block, and their genesis and tectonic setting have been an issue in hot debate at the present time. SHRIMP U-Pb zircon age, petrology, geochemical and Nd isotopic data are reported for the Neoproterozoic Shimian granite in the Kangdian rift of western Sichuan. This pluton is of metaluminous high-K calc-alkalic I-type granite and emplaced at 818±7 Ma. Petrology, geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (Late Mesoproterozoic to Early Neoproterozoic) island arc crust, with contamination of old crust materials during magma ascending and emplacement. The Shimian granite is the product of the tectonic transition from compression to introplate extension in western margin of the Yangtze block. Their arc-like geochemical features (such as Nb-Ta depletion) should have been inherited from the protoliths, rather than reflection of their tectonic setting when the pluton formed.
Neoproterozoic magmatic rocks are widespread in western margin of the Yangtze block, and their genesis and tectonic setting have been an issue in hot debate at the present time. SHRIMP U-Pb zircon age, petrology, geochemical and Nd isotopic data are reported for the Neoproterozoic Shimian granite in the Kangdian rift of western Sichuan. This pluton is of metaluminous high-K calc-alkalic I-type granite and emplaced at 818±7 Ma. Petrology, geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (Late Mesoproterozoic to Early Neoproterozoic) island arc crust, with contamination of old crust materials during magma ascending and emplacement. The Shimian granite is the product of the tectonic transition from compression to introplate extension in western margin of the Yangtze block. Their arc-like geochemical features (such as Nb-Ta depletion) should have been inherited from the protoliths, rather than reflection of their tectonic setting when the pluton formed.
2010, 35(4): 621-636.
doi: 10.3799/dqkx.2010.077
Abstract:
The Shagou Ag-Pb-Zn vein-type deposit, located in the Luoning county of Henan Province, is hosted in amphibolite facies metamorphic rocks of the Archean Taihua Group and consists of four stages of mineralization: the quartz-siderite stage (Ⅰ), the quartz-sphalerite stage (Ⅱ), the quartz-silver minerals-galena stage (Ⅲ), and the quartz-carbonate stage (Ⅳ), with stages Ⅱ and Ⅲ being the main mineralization stages. Scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and electron microprobe (EMP) analysis suggests that both visible and invisible Ag are present in the ores. Invisible Ag occurs mainly as sub-micron inclusions (< 1 μm) within chalcopyrite, sphalerite and other sulphide minerals, whereas visible Ag occurs as silver minerals that replaced galena, chalcopyrite and other sulphides, or fills microfractures in sulphides and quartz. Combined with existing fluid inclusion data, our results indicate that Ag+, Pb+, Zn+ and other metal ions were transported as chloride complexes at the early high-temperature stage. When temperature and oxygen fugacity of the fluids descended, coupled with increasing pH, chloride complexes started to decompose to liberate Ag+, Pb+, Zn+ to form HS- complexes. Continuous drop of temperature and likely degassing of ore fluids, led to separation of Pb+ and Zn+ from HS- to form galena and sphalerite, into which some amounts of Ag+ were incorporated, forming sub-microscopic to microscopic silver inclusions. With the changes of composition and property of ore-forming fluids caused by precipitation of voluminous sulfide, Ag+ was released from HS- complex to combine with Cu+ and Sb3+, forming silver minerals (e.g. polybasite, jalpaite and native silver).
The Shagou Ag-Pb-Zn vein-type deposit, located in the Luoning county of Henan Province, is hosted in amphibolite facies metamorphic rocks of the Archean Taihua Group and consists of four stages of mineralization: the quartz-siderite stage (Ⅰ), the quartz-sphalerite stage (Ⅱ), the quartz-silver minerals-galena stage (Ⅲ), and the quartz-carbonate stage (Ⅳ), with stages Ⅱ and Ⅲ being the main mineralization stages. Scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and electron microprobe (EMP) analysis suggests that both visible and invisible Ag are present in the ores. Invisible Ag occurs mainly as sub-micron inclusions (< 1 μm) within chalcopyrite, sphalerite and other sulphide minerals, whereas visible Ag occurs as silver minerals that replaced galena, chalcopyrite and other sulphides, or fills microfractures in sulphides and quartz. Combined with existing fluid inclusion data, our results indicate that Ag+, Pb+, Zn+ and other metal ions were transported as chloride complexes at the early high-temperature stage. When temperature and oxygen fugacity of the fluids descended, coupled with increasing pH, chloride complexes started to decompose to liberate Ag+, Pb+, Zn+ to form HS- complexes. Continuous drop of temperature and likely degassing of ore fluids, led to separation of Pb+ and Zn+ from HS- to form galena and sphalerite, into which some amounts of Ag+ were incorporated, forming sub-microscopic to microscopic silver inclusions. With the changes of composition and property of ore-forming fluids caused by precipitation of voluminous sulfide, Ag+ was released from HS- complex to combine with Cu+ and Sb3+, forming silver minerals (e.g. polybasite, jalpaite and native silver).
2010, 35(4): 637-644.
doi: 10.3799/dqkx.2010.078
Abstract:
The Mid-West Pacific region is featured with the oldest oceanic crust, the most complicated magnetic anomaly lineation, the densest seamounts, the most peculiar geological feature and the strongest tectonic activity. To research tectonic genesis of these intraplate seamounts, this paper calculates the effective elastic thickness of the lithosphere (Te) with the elastic plate flexure based on the plate tectonic theory in the Mid-West Pacific. As a whole, Te slowly drops from the northwest part to the southeast part in the region. Te of the MST is higher in the middle of the trail than that in the north and the south parts. Te of the MPM is higher in the west part of the mountains than that in the east part. Furthermore, Te of these two typical areas is close to that of the present French Polynesia region. Thus, these seamounts were formed by the large volcanism which was produced by several hotspots during Cretaceous in the present French Polynesia region. And then these seamounts underwent some tectonic activities.
The Mid-West Pacific region is featured with the oldest oceanic crust, the most complicated magnetic anomaly lineation, the densest seamounts, the most peculiar geological feature and the strongest tectonic activity. To research tectonic genesis of these intraplate seamounts, this paper calculates the effective elastic thickness of the lithosphere (Te) with the elastic plate flexure based on the plate tectonic theory in the Mid-West Pacific. As a whole, Te slowly drops from the northwest part to the southeast part in the region. Te of the MST is higher in the middle of the trail than that in the north and the south parts. Te of the MPM is higher in the west part of the mountains than that in the east part. Furthermore, Te of these two typical areas is close to that of the present French Polynesia region. Thus, these seamounts were formed by the large volcanism which was produced by several hotspots during Cretaceous in the present French Polynesia region. And then these seamounts underwent some tectonic activities.
2010, 35(4): 645-656.
doi: 10.3799/dqkx.2010.079
Abstract:
Study of geothermal regime of sedimentary basin is not only vital for understanding the formation and evolution of the basin, but also is of significance for oil and gas generation and preservation in the basin. Temperature data from about 120 exploration wells and measured values of thermal conductivity of 296 rock samples from Tarim basin are used to calculate the present-day geothermal gradient, subsurface formation temperature at the depths of 1 000-5 000 m and the top of source rocks concerned, respectively. The results show that thermal regime of the area is relatively lower with an average geothermal gradient of 23.3 ℃/km and heat flow of 47.3 mW/m2; suggesting that the Permian intensive magmatism in the Tarim basin has no obvious effect on the present-day temperature field. The general pattern of subsurface temperature distribution at different depths is similar to that of the geothermal gradient and heat flow and is featured by higher parameters in the uplift areas and lower ones in the depressions, indicating the influence of base topography configuration on the temperature field. The source rocks of the Bachu Formation, Kalashayi Formation and Lianglitage Formation in the area are predicted to be within favorable hydrocarbon preservation condition now, while the middle and lower Cambrian source rocks are in the Bachu uplift, northwestern Katake uplift and eastern Guchengxu uplift areas, and the unfavorable preservation condition is inferred in other left region. Particularly, it is found that the discovered oil and gas fields are usually accompanied by anomalous high temperature, and the upward migration and accumulation of hot fluid below is speculated to explain this perfect coincidence. The finding of temperature pattern and distribution of oil and gas field can provide some insights for future exploration.
Study of geothermal regime of sedimentary basin is not only vital for understanding the formation and evolution of the basin, but also is of significance for oil and gas generation and preservation in the basin. Temperature data from about 120 exploration wells and measured values of thermal conductivity of 296 rock samples from Tarim basin are used to calculate the present-day geothermal gradient, subsurface formation temperature at the depths of 1 000-5 000 m and the top of source rocks concerned, respectively. The results show that thermal regime of the area is relatively lower with an average geothermal gradient of 23.3 ℃/km and heat flow of 47.3 mW/m2; suggesting that the Permian intensive magmatism in the Tarim basin has no obvious effect on the present-day temperature field. The general pattern of subsurface temperature distribution at different depths is similar to that of the geothermal gradient and heat flow and is featured by higher parameters in the uplift areas and lower ones in the depressions, indicating the influence of base topography configuration on the temperature field. The source rocks of the Bachu Formation, Kalashayi Formation and Lianglitage Formation in the area are predicted to be within favorable hydrocarbon preservation condition now, while the middle and lower Cambrian source rocks are in the Bachu uplift, northwestern Katake uplift and eastern Guchengxu uplift areas, and the unfavorable preservation condition is inferred in other left region. Particularly, it is found that the discovered oil and gas fields are usually accompanied by anomalous high temperature, and the upward migration and accumulation of hot fluid below is speculated to explain this perfect coincidence. The finding of temperature pattern and distribution of oil and gas field can provide some insights for future exploration.
2010, 35(4): 657-662.
doi: 10.3799/dqkx.2010.080
Abstract:
Based on the fluorescence property of petroleum, conventional fluorescence spectroscopy was employed to quantify the fluorescence spectra of petroleum inclusions. According to the characteristics of the main peak wavelength (λmax), the maximum fluorescence intensity (Imax), the red-green quotient (Q650/500), and the relationship between them, the hydrocarbon charging events can be identified easily and effectively. The study of 15 fluid inclusion samples from the Es3 Member of the Shahejie Formation in Minfeng sag indicates that the main peak wavelength of fluorescence spectra for petroleum inclusions with yellow fluorescence colors is consistent, and that of petroleum inclusions with white bluish fluorescence colors falls into two types: one is the same as that of the yellow fluorescence petroleum inclusions, and the other is obviously blue shifted. In addition, the relationship between λmax and Imax, and the relationship between λmax and Q650/500 both display 3 specific types, which indicates that the lithologic reservoirs of the Es3 Member of the Shahejie Formation in Minfeng sag underwent 3 hydrocarbon charging events in the geological history.
Based on the fluorescence property of petroleum, conventional fluorescence spectroscopy was employed to quantify the fluorescence spectra of petroleum inclusions. According to the characteristics of the main peak wavelength (λmax), the maximum fluorescence intensity (Imax), the red-green quotient (Q650/500), and the relationship between them, the hydrocarbon charging events can be identified easily and effectively. The study of 15 fluid inclusion samples from the Es3 Member of the Shahejie Formation in Minfeng sag indicates that the main peak wavelength of fluorescence spectra for petroleum inclusions with yellow fluorescence colors is consistent, and that of petroleum inclusions with white bluish fluorescence colors falls into two types: one is the same as that of the yellow fluorescence petroleum inclusions, and the other is obviously blue shifted. In addition, the relationship between λmax and Imax, and the relationship between λmax and Q650/500 both display 3 specific types, which indicates that the lithologic reservoirs of the Es3 Member of the Shahejie Formation in Minfeng sag underwent 3 hydrocarbon charging events in the geological history.
2010, 35(4): 663-673.
doi: 10.3799/dqkx.2010.081
Abstract:
The origin and accumulation mechanism of the marine oils in the Tarim basin has long been a disputed issue. Compound specific isotope, fluid inclusion technique and age-indicating biomarkers have been used in investigating hydrocarbons generation and migration in this study. It is observed that most of the oils in the Tazhong and Lunnan uplifts correspond well with the Middle-Upper Ordovician source rocks according to biomarkers, suggesting their good genetic relationship. However, the compound specific isotope of n-alkanes shows that the oils are primarily mixed oils from both the ∈-O1 and the O2+3 strata, which is further proved by chemical components in fluid inclusions. It is predicated by δ13C of n-alkanes that, the ∈-O1 genetic affinity oils mixed in the Tazhong oils range in 11%-100% (average of 45%), and about 11%-70% (average of 36%) in the Lunnan oils, which suggests that both the ∈-O1 and the O2+3 are the main source intervals for the oils in the Tarim basin. A comprehensive study of migration fractionations of biomarkers and geological conditions shows that, No.1 fault and the associated faults played an essential role in hydrocarbons migration with several main charging points observed where strike slip faults cutting across the No.1 fault. However, lateral migration is an important pattern for the Lunnan oils. Several oil-mixing models are concluded including adjusting type with oil mixing during hydrocarbons re-migration and re-accumulation, multiple-charging type with hydrocarbons from different episodes, and primary type with oil mixed during secondary migration pathway even during primary migration. Our opinion of intensive oil mixing in the Tarim basin suggests great deep petroleum potential in the basin, and unraveling hydrocarbons-accumulation mechanism is significant for further petroleum exploration.
The origin and accumulation mechanism of the marine oils in the Tarim basin has long been a disputed issue. Compound specific isotope, fluid inclusion technique and age-indicating biomarkers have been used in investigating hydrocarbons generation and migration in this study. It is observed that most of the oils in the Tazhong and Lunnan uplifts correspond well with the Middle-Upper Ordovician source rocks according to biomarkers, suggesting their good genetic relationship. However, the compound specific isotope of n-alkanes shows that the oils are primarily mixed oils from both the ∈-O1 and the O2+3 strata, which is further proved by chemical components in fluid inclusions. It is predicated by δ13C of n-alkanes that, the ∈-O1 genetic affinity oils mixed in the Tazhong oils range in 11%-100% (average of 45%), and about 11%-70% (average of 36%) in the Lunnan oils, which suggests that both the ∈-O1 and the O2+3 are the main source intervals for the oils in the Tarim basin. A comprehensive study of migration fractionations of biomarkers and geological conditions shows that, No.1 fault and the associated faults played an essential role in hydrocarbons migration with several main charging points observed where strike slip faults cutting across the No.1 fault. However, lateral migration is an important pattern for the Lunnan oils. Several oil-mixing models are concluded including adjusting type with oil mixing during hydrocarbons re-migration and re-accumulation, multiple-charging type with hydrocarbons from different episodes, and primary type with oil mixed during secondary migration pathway even during primary migration. Our opinion of intensive oil mixing in the Tarim basin suggests great deep petroleum potential in the basin, and unraveling hydrocarbons-accumulation mechanism is significant for further petroleum exploration.
2010, 35(4): 674-680.
doi: 10.3799/dqkx.2010.082
Abstract:
Due to the pressure difference between borehole and reservoirs, drilling mud invades the original reserviors while drilling for petroleum, changing the formation resistivity, which has a negative effect on resistivity logging. Based on the theoretical model of two-phase flow equation, convection-diffusion equation and Archie formula, finite difference method is adopted to discretize mud invasion models in the way of two dimensions. Parameters of the reservoir in Mahuangshan area, Ordos basin, north-central China, with the mud invasion time of 24, 48 hours respectively are input for the model, and the vertical and radial distributions of pressure, water saturation, salinity and formation resistivity in the designated time are worked out. The computing results are consistent with fact instance, and can be used for correcting resistivity logging values for mud invasion reservoirs. A case of low invasion is computed and the results prove to conform to the theoretical analysis. This method can be used in mud invasion of vertical inhomogeneous medium.
Due to the pressure difference between borehole and reservoirs, drilling mud invades the original reserviors while drilling for petroleum, changing the formation resistivity, which has a negative effect on resistivity logging. Based on the theoretical model of two-phase flow equation, convection-diffusion equation and Archie formula, finite difference method is adopted to discretize mud invasion models in the way of two dimensions. Parameters of the reservoir in Mahuangshan area, Ordos basin, north-central China, with the mud invasion time of 24, 48 hours respectively are input for the model, and the vertical and radial distributions of pressure, water saturation, salinity and formation resistivity in the designated time are worked out. The computing results are consistent with fact instance, and can be used for correcting resistivity logging values for mud invasion reservoirs. A case of low invasion is computed and the results prove to conform to the theoretical analysis. This method can be used in mud invasion of vertical inhomogeneous medium.
2010, (4): 681-690.
doi: 10.3799/dqkx.2010.083
Abstract:
Sedimentary characteristics of Baiyun sag in Oligocene and Miocene play an important role in deep-water oil and gas exploration in South China Sea, among which there is a special three-order "source to sink" relationship between shelf-edge delta and slope sedimentary systems. Based on recent cores and exact 3D seismic interpretation, we find out how shelf-edge delta formed and how it evolved, and we also find out that the "source" of the shelf-edge delta controled deep-water gravity flow. The shelf-edge delta generated in late of LST in Oligocene, and delta front is the main component, shelf-edge fault controled its development and delta progressed as "S". On the other hand, between outer shelf and upper slope the sedimentation mechanism changed from tractive current to gravity flow in Miocene. Slope complex channels and gravity flow settings accumulated in Baiyun sag, meanwhile, proximal carbonate rocks from Dongsha uplift blended, so clastic rocks and carbonate rocks mixed. This kind of sedimentary characteristic is controlled by the development of shelf-edge delta and shelf-edge fault, which dominates the distribution of shelf-edge delta and deep-water reservoirs. Therefore, we should pay more attention to formation, evolution and distribution of shelf-edge delta, and its three-order "source to sink" response to deep-water sediment in oil and gas exploration of Baiyun sag.
Sedimentary characteristics of Baiyun sag in Oligocene and Miocene play an important role in deep-water oil and gas exploration in South China Sea, among which there is a special three-order "source to sink" relationship between shelf-edge delta and slope sedimentary systems. Based on recent cores and exact 3D seismic interpretation, we find out how shelf-edge delta formed and how it evolved, and we also find out that the "source" of the shelf-edge delta controled deep-water gravity flow. The shelf-edge delta generated in late of LST in Oligocene, and delta front is the main component, shelf-edge fault controled its development and delta progressed as "S". On the other hand, between outer shelf and upper slope the sedimentation mechanism changed from tractive current to gravity flow in Miocene. Slope complex channels and gravity flow settings accumulated in Baiyun sag, meanwhile, proximal carbonate rocks from Dongsha uplift blended, so clastic rocks and carbonate rocks mixed. This kind of sedimentary characteristic is controlled by the development of shelf-edge delta and shelf-edge fault, which dominates the distribution of shelf-edge delta and deep-water reservoirs. Therefore, we should pay more attention to formation, evolution and distribution of shelf-edge delta, and its three-order "source to sink" response to deep-water sediment in oil and gas exploration of Baiyun sag.
2010, 35(4): 691-696.
doi: 10.3799/dqkx.2010.084
Abstract:
In order to study the effect of lithological background of carbonate rock on spatio-temporal evolution of karst rocky desertification (RD) land, 1∶100 000 scale digital RD distribution maps of Guizhou in 1986, 1995 and 2000 were obtained by RS, GIS and GPS (3S) technology and user-computer interactive interpreting method from Landsat remote sensing images. On the basis of spatial analysis and statistics, in association with digital-distribution map of carbonate rock assemblages' type, the following findings were obtained: (1) The evolution mode of RD land is related to carbonate rock types and is obviously uncorrelated with its purity. (2) Significant positive correlation was observed between evolution scale, evolution speed, evolution frequency and carbonate rock purity. (3) No RD land evolves easily to moderate RD in limestone rock combination type area, yet it evolves easily to light RD in dolomite combination type area. (4) Whatever the purity and component of the carbonate rocks are, the variation of the strong RD and extremely strong RD is not significant in the long-term evolution process, whereas the variation of the light RD and moderate RD is remarkable. In conclusion, the evolution process of RD land is constrained obviously by lithological background of carbonate rock.
In order to study the effect of lithological background of carbonate rock on spatio-temporal evolution of karst rocky desertification (RD) land, 1∶100 000 scale digital RD distribution maps of Guizhou in 1986, 1995 and 2000 were obtained by RS, GIS and GPS (3S) technology and user-computer interactive interpreting method from Landsat remote sensing images. On the basis of spatial analysis and statistics, in association with digital-distribution map of carbonate rock assemblages' type, the following findings were obtained: (1) The evolution mode of RD land is related to carbonate rock types and is obviously uncorrelated with its purity. (2) Significant positive correlation was observed between evolution scale, evolution speed, evolution frequency and carbonate rock purity. (3) No RD land evolves easily to moderate RD in limestone rock combination type area, yet it evolves easily to light RD in dolomite combination type area. (4) Whatever the purity and component of the carbonate rocks are, the variation of the strong RD and extremely strong RD is not significant in the long-term evolution process, whereas the variation of the light RD and moderate RD is remarkable. In conclusion, the evolution process of RD land is constrained obviously by lithological background of carbonate rock.
