2012 Vol. 37, No. S1
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2012, 37(S1): 1-10.
doi: 10.3799/dqkx.2012.S1.001
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Abstract:
Paleoenvironment and paleoproductivity variations were constructed, combined with radiocarbon dating, based on 17 geochemical elements, TOC and CaCO3, since 13.7 ka in the Bering Sea. The results show that the sedimentation rate was 34.2 cm/ka and the climate signals such as Younger-Dryas (YD), Bolling-Allerod (BA), and meltwater pulse were also reflected in the B5-4 core. The accumulation of terreginous sediments is controlled by many factors, including climate condition in the sediments source, sea level change and biogenic material dilution. The obvious features are the high paleoproductivity and hypoxia in the bottom water in the Bering Sea during the last deglacial period. The high paleoproductivity are attributed to the meltwater pulse event and the input of warmer Pacific water with the increased temperature. Hypoxia in the bottom water is caused by high productivity in the surface water and subsurface waterbody stratification due to saline gradient. However, the potential factors caused hypoxia in the bottom water also include the decreasing Pacific intermediate water ventilation and bottom-current speed in the Pacific Ocean. In the Holocene, the paleoenvironment and productivity of the Bering Sea were mainly controlled by the Alaskan stream. There are no obvious changes for productivity and paleoenvironment in the Holocene.
Paleoenvironment and paleoproductivity variations were constructed, combined with radiocarbon dating, based on 17 geochemical elements, TOC and CaCO3, since 13.7 ka in the Bering Sea. The results show that the sedimentation rate was 34.2 cm/ka and the climate signals such as Younger-Dryas (YD), Bolling-Allerod (BA), and meltwater pulse were also reflected in the B5-4 core. The accumulation of terreginous sediments is controlled by many factors, including climate condition in the sediments source, sea level change and biogenic material dilution. The obvious features are the high paleoproductivity and hypoxia in the bottom water in the Bering Sea during the last deglacial period. The high paleoproductivity are attributed to the meltwater pulse event and the input of warmer Pacific water with the increased temperature. Hypoxia in the bottom water is caused by high productivity in the surface water and subsurface waterbody stratification due to saline gradient. However, the potential factors caused hypoxia in the bottom water also include the decreasing Pacific intermediate water ventilation and bottom-current speed in the Pacific Ocean. In the Holocene, the paleoenvironment and productivity of the Bering Sea were mainly controlled by the Alaskan stream. There are no obvious changes for productivity and paleoenvironment in the Holocene.
2012, 37(S1): 11-19.
doi: 10.3799/dqkx.2012.S1.002
Abstract:
As two common weathering minerals, hematite and goethite are generally regarded as sensitive indicators for environment. In this paper, suspended particle matter and floodplain sediments from the main stream and major tributaries of the Yangtze River are systemically studied by diffuse reflectance spectroscopy (DRS). The result reveals that the first derivative curve peak for hematite in the Yangtze River sediments occurs at 565 nm, while the first derivative curve main peak for goethite occurs at 505 nm and secondary peak for goethite occurs at 435 nm. It is different from previous studies on loess that the height of goethite's main peak in the Yangtze River sediments is overall higher than its secondary peak. In the Yangtze River catchment, both hematite and goethite are quite homogeneous in the Yangtze River main stream due to the hydrodynamic mixing, while variations in hematite and goethite contents are larger in the tributaries. Clear differences in DRS are observed between the Yangtze River and Huanghe sediments, loess and dust, which implies that the DRS method may shed new light on discriminating sediment provenances.
As two common weathering minerals, hematite and goethite are generally regarded as sensitive indicators for environment. In this paper, suspended particle matter and floodplain sediments from the main stream and major tributaries of the Yangtze River are systemically studied by diffuse reflectance spectroscopy (DRS). The result reveals that the first derivative curve peak for hematite in the Yangtze River sediments occurs at 565 nm, while the first derivative curve main peak for goethite occurs at 505 nm and secondary peak for goethite occurs at 435 nm. It is different from previous studies on loess that the height of goethite's main peak in the Yangtze River sediments is overall higher than its secondary peak. In the Yangtze River catchment, both hematite and goethite are quite homogeneous in the Yangtze River main stream due to the hydrodynamic mixing, while variations in hematite and goethite contents are larger in the tributaries. Clear differences in DRS are observed between the Yangtze River and Huanghe sediments, loess and dust, which implies that the DRS method may shed new light on discriminating sediment provenances.
2012, 37(S1): 20-27.
doi: 10.3799/dqkx.2012.S1.003
Abstract:
This study presents the SHRIMP U-Pb dating results of Archean biotite granitic gneiss found in the Early Precambrian metamorphic basement in Xi Ulanbulang area in northern foot of Daqingshan Mountain in central Inner Mongolia. Zircon characteristic of the rock is consistent and it obviously shows core-mantle-boundary structure from cathodoluminescence images. The core of zircons not only has intensive magmatic zoning but also has a smaller range of age distribution. The weighted average age (2 697±11 Ma) represents the diagenetic age of rock which is the oldest one of all rocks reported in the region. It shows that a magamatism occurred to 2.7 Ga years ago in the region. The mantle and of zirons is considered to be featured with metamorphic recrystallization causes. Both the weighted average age (mantle 2 561±18 Ma; rige 2 539±34 a) and Th, U content features of them are very close except for different cathodoluminescence images. Therefore, we consider that the ages of the mantle and boundary together reflect the tectono-thermal event which occurred to 2.5 Ga ago that has been proved to be an important geological event by substantial evidences during the formation and evolution of the North China craton and a large number of pre-rocks have been strongly transformed.
This study presents the SHRIMP U-Pb dating results of Archean biotite granitic gneiss found in the Early Precambrian metamorphic basement in Xi Ulanbulang area in northern foot of Daqingshan Mountain in central Inner Mongolia. Zircon characteristic of the rock is consistent and it obviously shows core-mantle-boundary structure from cathodoluminescence images. The core of zircons not only has intensive magmatic zoning but also has a smaller range of age distribution. The weighted average age (2 697±11 Ma) represents the diagenetic age of rock which is the oldest one of all rocks reported in the region. It shows that a magamatism occurred to 2.7 Ga years ago in the region. The mantle and of zirons is considered to be featured with metamorphic recrystallization causes. Both the weighted average age (mantle 2 561±18 Ma; rige 2 539±34 a) and Th, U content features of them are very close except for different cathodoluminescence images. Therefore, we consider that the ages of the mantle and boundary together reflect the tectono-thermal event which occurred to 2.5 Ga ago that has been proved to be an important geological event by substantial evidences during the formation and evolution of the North China craton and a large number of pre-rocks have been strongly transformed.
2012, 37(S1): 28-42.
doi: 10.3799/dqkx.2012.S1.004
Abstract:
LA-ICP-MS U-Pb age and trace elements composition have been conducted from 111 spots analyses on detrital zircons from the sandstone of the lower Nanhua-Sinian Quanji Group, the unmetamorphosed sedimentary cover on the Quanji massif (a continental fragment separated from the Tarim block). The age spectra from 87 concordant ages records strong ~2.45, ~2.32, ~2.11 and ~1.95 Ga thermal events in the Paleoproterozoic and two weak thermal events in the Neoarchean time, and indicates that sediments of quartzo-sandstone were derived from the basement comprising of the Dakendaban Group and Delingha complex with unexposed Ended-Paleoproterozoic mafic dike swarm in the middle to eastern Quanji massif. CL images and trace elements of the detrital zircons suggest that the ~2.45, ~2.32 and ~2.11 Ga thermal events are characterized by magmatic intrusion along with crustal growth and the ~1.95 Ga event by strong regional metamorphism and anatexis, with magmatic intrusion a possible event that could not be ruled out. Our new data demonstrate that basement of the Quanji massif and its inherited Tarim craton are mainly composed of Paleoproterozoic rocks, however, they regionally developed magmatic intrusions accompanying crustal growth during ~2.32-2.45 Ga, thus share a similar geological evolution history or probably ever interacted with the North China craton in their early history.
LA-ICP-MS U-Pb age and trace elements composition have been conducted from 111 spots analyses on detrital zircons from the sandstone of the lower Nanhua-Sinian Quanji Group, the unmetamorphosed sedimentary cover on the Quanji massif (a continental fragment separated from the Tarim block). The age spectra from 87 concordant ages records strong ~2.45, ~2.32, ~2.11 and ~1.95 Ga thermal events in the Paleoproterozoic and two weak thermal events in the Neoarchean time, and indicates that sediments of quartzo-sandstone were derived from the basement comprising of the Dakendaban Group and Delingha complex with unexposed Ended-Paleoproterozoic mafic dike swarm in the middle to eastern Quanji massif. CL images and trace elements of the detrital zircons suggest that the ~2.45, ~2.32 and ~2.11 Ga thermal events are characterized by magmatic intrusion along with crustal growth and the ~1.95 Ga event by strong regional metamorphism and anatexis, with magmatic intrusion a possible event that could not be ruled out. Our new data demonstrate that basement of the Quanji massif and its inherited Tarim craton are mainly composed of Paleoproterozoic rocks, however, they regionally developed magmatic intrusions accompanying crustal growth during ~2.32-2.45 Ga, thus share a similar geological evolution history or probably ever interacted with the North China craton in their early history.
2012, 37(S1): 43-49.
doi: 10.3799/dqkx.2012.S1.005
Abstract:
The Jianghan plain is the first large-scale offloading basin of the Yangtze River after the formation of the Three Gorges. Its sediment deposits should reflect that the Yangtze River used to flow through. Ti-augite, a characteristic rock of Panxi area, where the formational conditions is unique in the Yangtze River basin, can be used as a tracing mineral to analyze the formation of the Three Gorges. The analysis of the percentage content and the electron microprobe analysis of the pyroxenes in Zhoulao core fine sediments between 0.063 mm and 0.125 mm show that the content of pyroxenes increases after 104 meters and Ti-augites appear. This line of change (104 m) dated of about 1.1 Ma attest a change of sediment provenance. So we conclude that the Three Gorges was formed around the time 1.1 Ma. From that time, materials from upper Three Georges has deposited in the Jianghan basin as a result of the forming of the Yangtze River. The characteristics of the pyroxenes composing the first 45 meters dated around (0.45 Ma) and those of the current Yangtze River are alike, meaning that during that period the Yangtze River already develops to its current pattern.
The Jianghan plain is the first large-scale offloading basin of the Yangtze River after the formation of the Three Gorges. Its sediment deposits should reflect that the Yangtze River used to flow through. Ti-augite, a characteristic rock of Panxi area, where the formational conditions is unique in the Yangtze River basin, can be used as a tracing mineral to analyze the formation of the Three Gorges. The analysis of the percentage content and the electron microprobe analysis of the pyroxenes in Zhoulao core fine sediments between 0.063 mm and 0.125 mm show that the content of pyroxenes increases after 104 meters and Ti-augites appear. This line of change (104 m) dated of about 1.1 Ma attest a change of sediment provenance. So we conclude that the Three Gorges was formed around the time 1.1 Ma. From that time, materials from upper Three Georges has deposited in the Jianghan basin as a result of the forming of the Yangtze River. The characteristics of the pyroxenes composing the first 45 meters dated around (0.45 Ma) and those of the current Yangtze River are alike, meaning that during that period the Yangtze River already develops to its current pattern.
2012, 37(S1): 50-59.
doi: 10.3799/dqkx.2012.S1.006
Abstract:
The stages of the granitoid in the Xiao Hinggan Mountains is the key to the tectonic evolution of Northeast China. Using zircon U-Pb dating results by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS), the granitoids from Yichun-Hegang regional in the east Xiao Hinggan Mountains can be grouped into Cambrian-Ordovician (508-447 Ma), Middle-Late Permian (266-259 Ma), Early-Middle Triassic (244-231 Ma), and Late Triassic (222-200 Ma). Considering the evolution history of Xing'an-Mongolia orogenic belt (XMOB), the granitoids can be divided into different types on the basis of their Sr and Yb contents. The Middle Permian granitoids shows the characteristics of Himalayan-type granite, and was related to collision of North China craton with the Siberian craton. The Early-Middle Triassic granitoids shows the characteristics of Adakite, which originated from the thickened crust. Late Triassic granitoids shows the characteristics of Zhemin-Nanling-type granite. The formations of Triassic granitoids are related to the continued collision and extension after closure of the Paleo-Asian Ocean, respectively.
The stages of the granitoid in the Xiao Hinggan Mountains is the key to the tectonic evolution of Northeast China. Using zircon U-Pb dating results by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS), the granitoids from Yichun-Hegang regional in the east Xiao Hinggan Mountains can be grouped into Cambrian-Ordovician (508-447 Ma), Middle-Late Permian (266-259 Ma), Early-Middle Triassic (244-231 Ma), and Late Triassic (222-200 Ma). Considering the evolution history of Xing'an-Mongolia orogenic belt (XMOB), the granitoids can be divided into different types on the basis of their Sr and Yb contents. The Middle Permian granitoids shows the characteristics of Himalayan-type granite, and was related to collision of North China craton with the Siberian craton. The Early-Middle Triassic granitoids shows the characteristics of Adakite, which originated from the thickened crust. Late Triassic granitoids shows the characteristics of Zhemin-Nanling-type granite. The formations of Triassic granitoids are related to the continued collision and extension after closure of the Paleo-Asian Ocean, respectively.
2012, 37(S1): 60-79.
doi: 10.3799/dqkx.2012.S1.007
Abstract:
Zoophycos is one of the most widespread but still enigmatic trace fossils, especially with regard to morphology and ethology surrounding its 3-D helically coiled spreite structures. The genus Zoophycos is systematically revised based on the systematic researches of the literature with detailed description and plate from 1855 to 2011. The ichnogenus Zoophycos is revised into 9 ichnospecies, which include Zoophycos cauda-galliVanuxem, 1842 ; Zoophycos curtain Vanuxem, 1842 ; Zoophycos velum Vanuxem, 1842 ; Zoophycos brianteus Massalongo, 1855 ; Zoophycos villae Massalongo, 1855 ; Zoophycos liasinus Fischer-Ooster, 1858 ; Zoophycos flabelliformis Fischer-Ooster, 1858 ; Zoophycos insignis Squinabol, 1890 ; Zoophycos rhodensis Bromley and Hanken, 2003 . The ichnogenus Spirophyton is composed of Spirophyton typum Hall, 1863 and Spirophyton eifeliense Kayser, 1872 . The Zoophycos and Spirophyton are grouped into Zoophycos Group.
Zoophycos is one of the most widespread but still enigmatic trace fossils, especially with regard to morphology and ethology surrounding its 3-D helically coiled spreite structures. The genus Zoophycos is systematically revised based on the systematic researches of the literature with detailed description and plate from 1855 to 2011. The ichnogenus Zoophycos is revised into 9 ichnospecies, which include Zoophycos cauda-galli
2012, 37(S1): 80-92.
doi: 10.3799/dqkx.2012.S1.008
Abstract:
The Jinshuikou cordierite granite (JCG) is the only strong peraluminous granite pluton discovered so far on northwestern margin of the Tibetan plateau. This cordierite granite contains mafic minerals of cordierite, garnet and biotite, characterizing mafic peraluminous granite. However, more comprehensive investigations of its genetic mechanism and implications for affinity and tectonic evolution of the basement of the Qaidam block is needed. This paper studies systematically on major and trace elements and Nd-Sr-Pb isotopic geochemistry of the JCG following the geology and petrographical observation. The JCG pluton shows A/CNK=1.12-2.05, K2O/Na2O=0.44-2.99, Rb/Sr=0.42-1.23, Nb/Ta=11.88-15.30, and is enriched in Rb, Th and U, but depleted in Sr and Ba, significant negative Eu anomalies (δEu=0.41-1.01, average at 0.62), ISr=0.711 4-0.750 3 and εNd(t)=-9.30 to -13.32. These data suggest that magma for the JCG was derived from partial melting of biotite-bearing metagreywacke in the upper continental crust, and that the melting conditions featuring high temperature but shallow depth level suggest existence of an extra heat source, implying that deep processes of subducted plate delamination, asthenospheric mantle upwelling, mafic magma intrusion and underplating might occurred at southern margin of the Qaidam block in the late caledonian. The JCG pluton has Nd model age (TDM2) of 1.9-2.2 Ga and initial Pb isotope ratios 206Pb/204Pb of 18.181-18.389, 207Pb/204Pb values of 15.582-15.632 and 208Pb/204Pb values of 37.914-38.243, suggesting that the basement of the Qaidam block is geochemically akin to that of the Yangtze block.
The Jinshuikou cordierite granite (JCG) is the only strong peraluminous granite pluton discovered so far on northwestern margin of the Tibetan plateau. This cordierite granite contains mafic minerals of cordierite, garnet and biotite, characterizing mafic peraluminous granite. However, more comprehensive investigations of its genetic mechanism and implications for affinity and tectonic evolution of the basement of the Qaidam block is needed. This paper studies systematically on major and trace elements and Nd-Sr-Pb isotopic geochemistry of the JCG following the geology and petrographical observation. The JCG pluton shows A/CNK=1.12-2.05, K2O/Na2O=0.44-2.99, Rb/Sr=0.42-1.23, Nb/Ta=11.88-15.30, and is enriched in Rb, Th and U, but depleted in Sr and Ba, significant negative Eu anomalies (δEu=0.41-1.01, average at 0.62), ISr=0.711 4-0.750 3 and εNd(t)=-9.30 to -13.32. These data suggest that magma for the JCG was derived from partial melting of biotite-bearing metagreywacke in the upper continental crust, and that the melting conditions featuring high temperature but shallow depth level suggest existence of an extra heat source, implying that deep processes of subducted plate delamination, asthenospheric mantle upwelling, mafic magma intrusion and underplating might occurred at southern margin of the Qaidam block in the late caledonian. The JCG pluton has Nd model age (TDM2) of 1.9-2.2 Ga and initial Pb isotope ratios 206Pb/204Pb of 18.181-18.389, 207Pb/204Pb values of 15.582-15.632 and 208Pb/204Pb values of 37.914-38.243, suggesting that the basement of the Qaidam block is geochemically akin to that of the Yangtze block.
2012, 37(S1): 93-100.
doi: 10.3799/dqkx.2012.S1.009
Abstract:
The noble gas isotopes abundance and composition were determined for various layers of a Co-rich Fe-Mn crust from seamount MH in the central Pacific. The He isotopic compositions of this Co-rich crust are similar to those of the abyssal sediments, and are mainly originated from the cosmic dust. 3He contents of the Co-rich crust are nearly constant throughout the section, but the 3He content increases significantly in 8 Ma, which is 4-5 times those of other samples, which responds to the 3He content maximum of the abyssal sediment in 8 Ma. In non-phosphatized Fe-Mn crust layers, the 3He/4He ratios of D4, D5 and D7 are also equivalent to the 3He/4He values n×102 Ra of the abyssal sediments. The 3He/4He ratios in phosphatized layers are relatively low, which resulted from incorporation of carbonate fluorapatite concentrates with enriched 4He, and depleted 3He during phosphatization. The loose layers of the Fe-Mn crust are relatively advantageous to adsorbing of Ar, and the majority of Ar in the crust possibly adsorbs directly from ambient sea water in the crust growth process.
The noble gas isotopes abundance and composition were determined for various layers of a Co-rich Fe-Mn crust from seamount MH in the central Pacific. The He isotopic compositions of this Co-rich crust are similar to those of the abyssal sediments, and are mainly originated from the cosmic dust. 3He contents of the Co-rich crust are nearly constant throughout the section, but the 3He content increases significantly in 8 Ma, which is 4-5 times those of other samples, which responds to the 3He content maximum of the abyssal sediment in 8 Ma. In non-phosphatized Fe-Mn crust layers, the 3He/4He ratios of D4, D5 and D7 are also equivalent to the 3He/4He values n×102 Ra of the abyssal sediments. The 3He/4He ratios in phosphatized layers are relatively low, which resulted from incorporation of carbonate fluorapatite concentrates with enriched 4He, and depleted 3He during phosphatization. The loose layers of the Fe-Mn crust are relatively advantageous to adsorbing of Ar, and the majority of Ar in the crust possibly adsorbs directly from ambient sea water in the crust growth process.
2012, 37(S1): 101-110.
doi: 10.3799/dqkx.2012.S1.010
Abstract:
Based on the case study of Jianshuigou outcrop in Huaying Mountains, the geological and geochemical identifications of Permian-Triassic Boundary (PTB), an unresolved geological problem which has been the focus of debate, are discussed in this paper. Two different types and layers of PTB, biostratigraphical PTB and lithostratigraphical PTB are identified from Jianshuigou PTB section in the present study. The distance between them is 4.56 m, and all of complex geological events, such as sea level drops, biotic mass extinctions, volcanic eruptions and the conversion of Sr content in paleocean from normal to abnormal (with higher Sr content) etc., occurred between the two Permian-Triassic boundaries. Evolution curves of Fe, Mn, Sr content, δ13C and δ18O are established at Jianshuigou PTB section, and their regular changes and related controlling factors are tightly bound with the complex geological events. Therefore, all the complex geological events have good correlation with the geochemical features.
Based on the case study of Jianshuigou outcrop in Huaying Mountains, the geological and geochemical identifications of Permian-Triassic Boundary (PTB), an unresolved geological problem which has been the focus of debate, are discussed in this paper. Two different types and layers of PTB, biostratigraphical PTB and lithostratigraphical PTB are identified from Jianshuigou PTB section in the present study. The distance between them is 4.56 m, and all of complex geological events, such as sea level drops, biotic mass extinctions, volcanic eruptions and the conversion of Sr content in paleocean from normal to abnormal (with higher Sr content) etc., occurred between the two Permian-Triassic boundaries. Evolution curves of Fe, Mn, Sr content, δ13C and δ18O are established at Jianshuigou PTB section, and their regular changes and related controlling factors are tightly bound with the complex geological events. Therefore, all the complex geological events have good correlation with the geochemical features.
2012, 37(S1): 111-124.
doi: 10.3799/dqkx.2012.S1.011
Abstract:
Recognition of multiple metamorphic events can provide essential evidences to constrain the evolution history of a polycyclic orogen. The basic rocks in the Songshugou area have recorded two metamorphic events in Eopaleozoic, which is an important "fingerprint" to study the evolution of North Qinling. The field work and petrology research show that the Songshugou garnet amphibolites are distributed as lens, with increasing retrograde degree transiting to plagioclase amphibole schists towards the edge of the lens. Zoned amphiboles are widely developed in plagioclase amphibole schists and those bearing garnet relics from the highly retrograded belt, with compositions ranging from actinolite in cores to magnesiohornblende in rims, which suggests that metabasic rocks have initially retrograded from granulite to amphibolite to greenschist facies, and then been overprinted by later low amphibolite facies metamorphism. According to petrologic study, zircon U-Pb geochronology reveals that the metabasic rocks record two Eopaleozoic events, too: 1. After having been experienced granulite or amphibolite facies metamorphism at the age of 484±4 Ma, metabasic rocks retrograded to greenschist facies; 2. The growth of amphibole zoning resulted from a later thermal event at the age of 418±5 Ma.
Recognition of multiple metamorphic events can provide essential evidences to constrain the evolution history of a polycyclic orogen. The basic rocks in the Songshugou area have recorded two metamorphic events in Eopaleozoic, which is an important "fingerprint" to study the evolution of North Qinling. The field work and petrology research show that the Songshugou garnet amphibolites are distributed as lens, with increasing retrograde degree transiting to plagioclase amphibole schists towards the edge of the lens. Zoned amphiboles are widely developed in plagioclase amphibole schists and those bearing garnet relics from the highly retrograded belt, with compositions ranging from actinolite in cores to magnesiohornblende in rims, which suggests that metabasic rocks have initially retrograded from granulite to amphibolite to greenschist facies, and then been overprinted by later low amphibolite facies metamorphism. According to petrologic study, zircon U-Pb geochronology reveals that the metabasic rocks record two Eopaleozoic events, too: 1. After having been experienced granulite or amphibolite facies metamorphism at the age of 484±4 Ma, metabasic rocks retrograded to greenschist facies; 2. The growth of amphibole zoning resulted from a later thermal event at the age of 418±5 Ma.
2012, 37(S1): 125-133.
doi: 10.3799/dqkx.2012.S1.012
Abstract:
West equatorial Pacific is the key area of global change, and are important to paleo-ocean and paleo-environment reconstruction. Based on elements geochemistry of sediments of core WP7, recovered from southwest Ontong Java plateau, 4 acidic tephra inputs (2.5-6.4 ka, 57.0-61.2 ka, 79.7-88.4 ka, and 193.7-249.5 ka) and 4 mafic tephra inputs (19.8-24.4 ka, 50.0-62.6 ka, 143.2-150.5 ka, and 160.8-171.1 ka) were deciphered after normalization of Al, Na, K, Be, Ga, Rb, Zr, Nb, Cs, Ce, Hf, Ta, Th, Fe and Mg to Ti. The input of tephra changed the sediment constituents, diluted the biotic CaCO3, darkened the sediment color, and raised the sedimentation rate.
West equatorial Pacific is the key area of global change, and are important to paleo-ocean and paleo-environment reconstruction. Based on elements geochemistry of sediments of core WP7, recovered from southwest Ontong Java plateau, 4 acidic tephra inputs (2.5-6.4 ka, 57.0-61.2 ka, 79.7-88.4 ka, and 193.7-249.5 ka) and 4 mafic tephra inputs (19.8-24.4 ka, 50.0-62.6 ka, 143.2-150.5 ka, and 160.8-171.1 ka) were deciphered after normalization of Al, Na, K, Be, Ga, Rb, Zr, Nb, Cs, Ce, Hf, Ta, Th, Fe and Mg to Ti. The input of tephra changed the sediment constituents, diluted the biotic CaCO3, darkened the sediment color, and raised the sedimentation rate.
2012, 37(S1): 134-142.
doi: 10.3799/dqkx.2012.S1.013
Abstract:
The petrographic characteristics, types of reservoir spaces and diagenesis of volcanic rocks, and formation mechanism of volcanic reservoir in Kalagang Formation of Malang sag in Santanghu basin were studied, by combining core, core wafer, scanning electron microscope log data, electric logging and geochemical analysis data. The results show that: (1) The hydrocarbon bearing volcanics in this region is mainly composed of lava (basalt and andesite) and volcanoclastic rock; (2) The volcanic phase contain mainly effusive facies, explosive facies and volcanic sedimentary facies; (3) The alkali metasomotism in the reservoir is obvious, the typical marks of which are albitization, arfvedsonization, laumontitization and pore-fracture filled with quartz by multi-stage; (4) The volcanics in Kalagang Formation was formed in alkaline environment, the reservoir space of which is mainly secondary dissolution porosity. The solution pore layers of laumontite in the reservoir are good reservoir, which reflects volcanic reservoir formation mechanism of "alkali before acid" in Kalagang Formation; (5) The interaction by layers of laumontite and layers of quartz-cementing, while the former ones are always distributed under the latter ones, is the favorable evidence of the upward migration and discharging silicon after the hydrocarbon alkali fluid metasomatized the volcanic rocks, which reflects the volcanic reservoir formation mechanism of "metasomatism the lower layers and discharging in the upper layers" in Kalagang Formation. The research shows that alkali metasomotism is pervasive in Kalagang Formation, and it also reveals that the characteristics of hydrocarbon alkali fluid participation in the formation and development of volcanic reservoir, which is significant in further acquaintance of the formation mechanism in volcanic reservoir.
The petrographic characteristics, types of reservoir spaces and diagenesis of volcanic rocks, and formation mechanism of volcanic reservoir in Kalagang Formation of Malang sag in Santanghu basin were studied, by combining core, core wafer, scanning electron microscope log data, electric logging and geochemical analysis data. The results show that: (1) The hydrocarbon bearing volcanics in this region is mainly composed of lava (basalt and andesite) and volcanoclastic rock; (2) The volcanic phase contain mainly effusive facies, explosive facies and volcanic sedimentary facies; (3) The alkali metasomotism in the reservoir is obvious, the typical marks of which are albitization, arfvedsonization, laumontitization and pore-fracture filled with quartz by multi-stage; (4) The volcanics in Kalagang Formation was formed in alkaline environment, the reservoir space of which is mainly secondary dissolution porosity. The solution pore layers of laumontite in the reservoir are good reservoir, which reflects volcanic reservoir formation mechanism of "alkali before acid" in Kalagang Formation; (5) The interaction by layers of laumontite and layers of quartz-cementing, while the former ones are always distributed under the latter ones, is the favorable evidence of the upward migration and discharging silicon after the hydrocarbon alkali fluid metasomatized the volcanic rocks, which reflects the volcanic reservoir formation mechanism of "metasomatism the lower layers and discharging in the upper layers" in Kalagang Formation. The research shows that alkali metasomotism is pervasive in Kalagang Formation, and it also reveals that the characteristics of hydrocarbon alkali fluid participation in the formation and development of volcanic reservoir, which is significant in further acquaintance of the formation mechanism in volcanic reservoir.
2012, 37(S1): 143--1.
doi: 10.3799/dqkx.2012.S1.014
Abstract:
Based on the comprehensive analysis of previous research, detailed interpretation of the 2D seismic data, and combined with the analysis of basin petroleum geological conditions, the structural and tectonic features of Papuan basin and its relationship with hydrocarbon accumulation have been studied in this paper. The results show that: (1) There are significant differences between the eastern and western parts of the Papuan basin in structural-tectonic styles. In the western part of the basin, the thin-skinned structure occupies the main deformation style, and the large-scale thrust-fold tectonics are formed, which can be divided into four deformation zones—thrust belt, fold-thrust belt, broad fold belt and stable platform from north to south. While in the eastern part of the Papuan basin, the foreland basin structure is formed. (2) Attributed to the differences in structural-tectonic styles, significant differences of hydrocarbon accumulation and potential also presents between the eastern and western parts of the Papuan basin. The western part of the basin is dominated by the Mesozoic petroleum system and thrust-controlled structural traps. And the Mesozoic source rock turns into mature stage because of the overlying thickening strata, caused by the overthrust sheet. Meanwhile in the eastern part of the Papuan basin, the Neogene petroleum system is the main petroleum system. The overlying huge thick strata sedimentation in foreland basin stage causes the Neogene source rock become mature. And the thrust-controlled structural traps only present in Aure thrust-fold belt. (3) The presence or absence of the Mesozoic incompetent beds is the key factor which causes the differences between the eastern and western parts of the Papuan basin in structural-tectonic styles.
Based on the comprehensive analysis of previous research, detailed interpretation of the 2D seismic data, and combined with the analysis of basin petroleum geological conditions, the structural and tectonic features of Papuan basin and its relationship with hydrocarbon accumulation have been studied in this paper. The results show that: (1) There are significant differences between the eastern and western parts of the Papuan basin in structural-tectonic styles. In the western part of the basin, the thin-skinned structure occupies the main deformation style, and the large-scale thrust-fold tectonics are formed, which can be divided into four deformation zones—thrust belt, fold-thrust belt, broad fold belt and stable platform from north to south. While in the eastern part of the Papuan basin, the foreland basin structure is formed. (2) Attributed to the differences in structural-tectonic styles, significant differences of hydrocarbon accumulation and potential also presents between the eastern and western parts of the Papuan basin. The western part of the basin is dominated by the Mesozoic petroleum system and thrust-controlled structural traps. And the Mesozoic source rock turns into mature stage because of the overlying thickening strata, caused by the overthrust sheet. Meanwhile in the eastern part of the Papuan basin, the Neogene petroleum system is the main petroleum system. The overlying huge thick strata sedimentation in foreland basin stage causes the Neogene source rock become mature. And the thrust-controlled structural traps only present in Aure thrust-fold belt. (3) The presence or absence of the Mesozoic incompetent beds is the key factor which causes the differences between the eastern and western parts of the Papuan basin in structural-tectonic styles.
2012, 37(S1): 151-162.
doi: 10.3799/dqkx.2012.S1.015
Abstract:
To reveal the nature gas accumulation regularity of Late Paleozoic in Ordos basin, based on the datum of field outcrops, drilling core, well log, seismic inversion, and sample analysis, this paper analyzes the coupling of "provenance-transportation-aggregation" and sandy accumulation in the sedimentary filling process, which shows that there were multi-provenances and several river systems during Late Paleozoic in the north of Ordos intercontinental basin and the broad and gentle slope palaeogeography and frequently migrating shallow water delta resulted in the stereoNET-blanket sand body. What's more, the sequence division of the Upper Paleozoic stratigraphy is proposed, and the history of basin evolution and sedimentary filling is analyzed, on basis of which is concluded that the stereoNET-blanket sand body formed by the distributary channels of braided river delta system or meandering river delta system benefited the gas migration and accumulation deposited in the period SLSC3-SLSC4 of Ordos basin transforming from marine to land, the mudstone of anastomosed river delta and shallow lake system founded the regional cover, and the coal of Taiyuan Formation and Shanxi Formation is the source rock. They formed the source-reservoir-cap rock association of natural gas reservoir together, resulting in such striking features as "gas generated in the whole basin, gas bearing in transitional stratum, gas enriched in ramp region, and gas controlled by lithology".
To reveal the nature gas accumulation regularity of Late Paleozoic in Ordos basin, based on the datum of field outcrops, drilling core, well log, seismic inversion, and sample analysis, this paper analyzes the coupling of "provenance-transportation-aggregation" and sandy accumulation in the sedimentary filling process, which shows that there were multi-provenances and several river systems during Late Paleozoic in the north of Ordos intercontinental basin and the broad and gentle slope palaeogeography and frequently migrating shallow water delta resulted in the stereoNET-blanket sand body. What's more, the sequence division of the Upper Paleozoic stratigraphy is proposed, and the history of basin evolution and sedimentary filling is analyzed, on basis of which is concluded that the stereoNET-blanket sand body formed by the distributary channels of braided river delta system or meandering river delta system benefited the gas migration and accumulation deposited in the period SLSC3-SLSC4 of Ordos basin transforming from marine to land, the mudstone of anastomosed river delta and shallow lake system founded the regional cover, and the coal of Taiyuan Formation and Shanxi Formation is the source rock. They formed the source-reservoir-cap rock association of natural gas reservoir together, resulting in such striking features as "gas generated in the whole basin, gas bearing in transitional stratum, gas enriched in ramp region, and gas controlled by lithology".
2012, 37(S1): 163-173.
doi: 10.3799/dqkx.2012.S1.016
Abstract:
The evolution of the hydrocarbon charging fluids of the Ordovician reservoir, Halahatang depression and the Tarim basin, was studied by the evidence of inclusion petrography, transmitted light-incident fluorescence, homogenization temperature and Micro-FTIR of the petroleum inclusions. The experiments data show that: firstly, two hydrocarbon charging stages were determined, the peak homogenization temperature of associated saline inclusions were 72.5-78.5 ℃ and 92.1-99.7 ℃ respectively; secondly, the Micro-FTIR data confirm that there generally exist H2O in the petroleum inclusion; furthermore, the ratio of H2O/(CH2+CH3) in the primary hydrocarbon inclusions is larger (4.6-2.1) than the ratio (1.1-0.4) in the secondary hydrocarbon inclusions, and the maturity of the primary hydrocarbon inclusions (CH2/CH3 ratio is 7.3-4.5) is lower than the maturity of the secondary hydrocarbon inclusions (CH2/CH3 ratio is 2.9-1.9); lastly, sulf-alcohols compounds generally exist in the primary hydrocarbon inclusions, but do not exist in the secondary hydrocarbon inclusions. Compared with geochemistry data of the Ordovician hydrocarbon, sulf-alcohols compounds were the product of the early reservoir biodegradation having occurred in early-Hercynian, and in the late-Hercynian, the higher maturity hydrocarbon largely generated charges and mixes with the early hydrocarbon, which causes the content of the sulf-alcohols decreased. At the same time, part of the sulf-alcohols cracks to generate H2S.
The evolution of the hydrocarbon charging fluids of the Ordovician reservoir, Halahatang depression and the Tarim basin, was studied by the evidence of inclusion petrography, transmitted light-incident fluorescence, homogenization temperature and Micro-FTIR of the petroleum inclusions. The experiments data show that: firstly, two hydrocarbon charging stages were determined, the peak homogenization temperature of associated saline inclusions were 72.5-78.5 ℃ and 92.1-99.7 ℃ respectively; secondly, the Micro-FTIR data confirm that there generally exist H2O in the petroleum inclusion; furthermore, the ratio of H2O/(CH2+CH3) in the primary hydrocarbon inclusions is larger (4.6-2.1) than the ratio (1.1-0.4) in the secondary hydrocarbon inclusions, and the maturity of the primary hydrocarbon inclusions (CH2/CH3 ratio is 7.3-4.5) is lower than the maturity of the secondary hydrocarbon inclusions (CH2/CH3 ratio is 2.9-1.9); lastly, sulf-alcohols compounds generally exist in the primary hydrocarbon inclusions, but do not exist in the secondary hydrocarbon inclusions. Compared with geochemistry data of the Ordovician hydrocarbon, sulf-alcohols compounds were the product of the early reservoir biodegradation having occurred in early-Hercynian, and in the late-Hercynian, the higher maturity hydrocarbon largely generated charges and mixes with the early hydrocarbon, which causes the content of the sulf-alcohols decreased. At the same time, part of the sulf-alcohols cracks to generate H2S.
2012, 37(S1): 174-178.
doi: 10.3799/dqkx.2012.S1.017
Abstract:
Thermochemical sulfate reduction (TSR) has modified the role of the gas reservoir. Selecting kinetics model on the basis of the high pressure thermal simulation experiment, we have obtained the dynamic parameters and reproduced rock reaction of methane with sulfate in the geological conditions by considering the burial and thermal evolution history of the Puguang area. It is concluded in this study that TSR of CH4 of Feixianguan Formations began from 130 Ma, at paleo 210 ℃, and terminated 30 Ma ago; The cumulative amount of methane consumed by the TSR only amounted to 2.4%, which indicates that Feixianguan TSR in the late lost less methane without affecting the later storage of methane. So, it is of exploration significance for deep carbonate reservoirs.
Thermochemical sulfate reduction (TSR) has modified the role of the gas reservoir. Selecting kinetics model on the basis of the high pressure thermal simulation experiment, we have obtained the dynamic parameters and reproduced rock reaction of methane with sulfate in the geological conditions by considering the burial and thermal evolution history of the Puguang area. It is concluded in this study that TSR of CH4 of Feixianguan Formations began from 130 Ma, at paleo 210 ℃, and terminated 30 Ma ago; The cumulative amount of methane consumed by the TSR only amounted to 2.4%, which indicates that Feixianguan TSR in the late lost less methane without affecting the later storage of methane. So, it is of exploration significance for deep carbonate reservoirs.
2012, 37(S1): 179-187.
doi: 10.3799/dqkx.2012.S1.018
Abstract:
In support of GIS (geographical information system) technology, this study takes Heigou glacier No.8, Bogda-peak region, Tianshan as an example to analyze ice thickness, ice volume and their changes, based on GPR(ground penetrating radar) ice thickness data and high accuracy RTK-GPS(global positioning system) surveying data in 2009. Results indicate that the mean ice thickness in the tongue of Heigou glacier No.8 is 58.7 m with the ice volume of 115.1×106 m3 (103.5×106 m3 water equivalent). During 1986-2009, the ice tongue thinned by 13±6 m, with the mean thinning rate of 0.57±0.26 m·a-1, corresponding to the loss in ice volume of (25.5±11.8)×106 m3 ((22.9±10.6)×106 m3 water equivalent), which directly resulted from the rapid increase in temperature. By comparison of IDW (inverse distance weighted), RBF (radial basis functions) and OK (ordinary kriging) interpolation methods, the precision of OK interpolation method is higher (Mean: -0.166 5; RMS: 2.822), suitable to the study of ice thickness of the mountain glaciers, such as Heigou glacier No.8. Moreover, the thinning rate of Heigou glacier No.8 is approximately consistent with those of the other monitored glaciers in western China. Integrated use of GPR, GPS and GIS technology in the field of glaciology can effectively facilitate the data capture, precise positioning, and spatial analysis, which has a promisting prospect for multi-applications.
In support of GIS (geographical information system) technology, this study takes Heigou glacier No.8, Bogda-peak region, Tianshan as an example to analyze ice thickness, ice volume and their changes, based on GPR(ground penetrating radar) ice thickness data and high accuracy RTK-GPS(global positioning system) surveying data in 2009. Results indicate that the mean ice thickness in the tongue of Heigou glacier No.8 is 58.7 m with the ice volume of 115.1×106 m3 (103.5×106 m3 water equivalent). During 1986-2009, the ice tongue thinned by 13±6 m, with the mean thinning rate of 0.57±0.26 m·a-1, corresponding to the loss in ice volume of (25.5±11.8)×106 m3 ((22.9±10.6)×106 m3 water equivalent), which directly resulted from the rapid increase in temperature. By comparison of IDW (inverse distance weighted), RBF (radial basis functions) and OK (ordinary kriging) interpolation methods, the precision of OK interpolation method is higher (Mean: -0.166 5; RMS: 2.822), suitable to the study of ice thickness of the mountain glaciers, such as Heigou glacier No.8. Moreover, the thinning rate of Heigou glacier No.8 is approximately consistent with those of the other monitored glaciers in western China. Integrated use of GPR, GPS and GIS technology in the field of glaciology can effectively facilitate the data capture, precise positioning, and spatial analysis, which has a promisting prospect for multi-applications.
2012, 37(S1): 188-194.
doi: 10.3799/dqkx.2012.S1.019
Abstract:
Based on the data of temperature and rainfall recorded by automatic weather stations at different altitudes in the eastern slope of Yulong Snow Mountain from Oct. 2008 to Sep. 2009, the inter-annual variations of temperature and precipitation gradient have been systematically analyzed. The results show that the monthly variation of temperature gradient is significant. Between 2 400 m to 3 046 m, the maximum absolute value of the temperature gradient is 1.01 ℃/100 m in April, the minimum is 0.39 ℃/100 m in December, and the difference is 0.62 ℃/100 m; and the maximum absolute value of the temperature gradient is 0.60 ℃/100 m between 2 400 m to 3 046 m in April, the minimum is 0.32 ℃/100 m in January, both differ by 0.28 ℃/100 m; whereas the maximum absolute value of the temperature gradient is 0.80 ℃/100 m in February, the minimum is 0.46 ℃/100 m in August, and the difference is 0.32 ℃/100 m between 3 046 m to 4 300 m. The precipitation at 2 400, 3 046, 4 300 and 4 800 m above sea level in the eastern slope during May-October is 788.4, 1 884.3, 435.3 and 1 980.7 mm respectively. What's more, with the rise of elevation, there are two precipitation peaks and precipitation gradient display variations from positive to negative to positive to negative. The first higher rainfall belt is between 2 800 m and 3 200 m above sea level, may supply plenty moisture to the forest area; the second largest precipitation zone is in the glacier covered area between 4 800 m and 5 000 m above sea level, providing mass accumulation for glacier formation.
Based on the data of temperature and rainfall recorded by automatic weather stations at different altitudes in the eastern slope of Yulong Snow Mountain from Oct. 2008 to Sep. 2009, the inter-annual variations of temperature and precipitation gradient have been systematically analyzed. The results show that the monthly variation of temperature gradient is significant. Between 2 400 m to 3 046 m, the maximum absolute value of the temperature gradient is 1.01 ℃/100 m in April, the minimum is 0.39 ℃/100 m in December, and the difference is 0.62 ℃/100 m; and the maximum absolute value of the temperature gradient is 0.60 ℃/100 m between 2 400 m to 3 046 m in April, the minimum is 0.32 ℃/100 m in January, both differ by 0.28 ℃/100 m; whereas the maximum absolute value of the temperature gradient is 0.80 ℃/100 m in February, the minimum is 0.46 ℃/100 m in August, and the difference is 0.32 ℃/100 m between 3 046 m to 4 300 m. The precipitation at 2 400, 3 046, 4 300 and 4 800 m above sea level in the eastern slope during May-October is 788.4, 1 884.3, 435.3 and 1 980.7 mm respectively. What's more, with the rise of elevation, there are two precipitation peaks and precipitation gradient display variations from positive to negative to positive to negative. The first higher rainfall belt is between 2 800 m and 3 200 m above sea level, may supply plenty moisture to the forest area; the second largest precipitation zone is in the glacier covered area between 4 800 m and 5 000 m above sea level, providing mass accumulation for glacier formation.
2012, 37(S1): 195-202.
doi: 10.3799/dqkx.2012.S1.020
Abstract:
Taking the seafloor as datum, the high resolution seismic reflecting data acquired in Shenhu area are divided into two parts for the imaging of water column and strata respectively. Two apparent echoes shaped like plume show in the water column and the particular geomorphology such as vents and depressions of seafloor suggests the existence of the gas seepage occurred opposite them on the seismic reflecting section. Moreover, a classical bottom simulating reflector which indicates the presence of gas hydrates appears at the depth less than 100 m. The detailed velocity field reveals that acoustic velocity of sediments decreases beneath both the seep sites and bottom simulating reflector and the seismic reflecting characteristics seem to be related to the gas-bearing of strata. It can be concluded that geophysical anomalies (plumes, acoustic velocity reverse, BSR (bottom simulating reflector)) and the expressions of particular geomorphology of seabed (vents and depressions or craters) should have been resulted from the migration of free gas into the sediments of subsurface and then the formation of gas hydrates or the direct seepage into the seawater. This study indicates that high resolution multi-channel seismic reflecting data has great potential for characterizing the anomalies and then detecting the seepage gas hydrates reservoir.
Taking the seafloor as datum, the high resolution seismic reflecting data acquired in Shenhu area are divided into two parts for the imaging of water column and strata respectively. Two apparent echoes shaped like plume show in the water column and the particular geomorphology such as vents and depressions of seafloor suggests the existence of the gas seepage occurred opposite them on the seismic reflecting section. Moreover, a classical bottom simulating reflector which indicates the presence of gas hydrates appears at the depth less than 100 m. The detailed velocity field reveals that acoustic velocity of sediments decreases beneath both the seep sites and bottom simulating reflector and the seismic reflecting characteristics seem to be related to the gas-bearing of strata. It can be concluded that geophysical anomalies (plumes, acoustic velocity reverse, BSR (bottom simulating reflector)) and the expressions of particular geomorphology of seabed (vents and depressions or craters) should have been resulted from the migration of free gas into the sediments of subsurface and then the formation of gas hydrates or the direct seepage into the seawater. This study indicates that high resolution multi-channel seismic reflecting data has great potential for characterizing the anomalies and then detecting the seepage gas hydrates reservoir.
2012, 37(S1): 203-212.
doi: 10.3799/dqkx.2012.S1.021
Abstract:
After thinning of the North China craton, the magmatism was widely distributed, and, the mantle mafic basalt intruded and reconstructed the wall rock, which formed large scale granite. This paper establishes a proper geophysics model and use the finite element method to numerically simulates the the mantle mafic basalt underplating. If we ignore the convection inside the basalt and only consider the conduction, we inversion calculate the formation of granite required how much intrusion of basaltic magma. The results indicate: (1) under 1 GPa condition, the pure melting volume of tonalite rock and pure crystallization volume of underplating basalt ratio is about 0.161; on the assumption that only 25% magma can dissociate, the total ratio of separated out of basalt lava is about 0.040 25. (2) The numerical results demonstrate the phase transition zone is from -50.285 to -36.867 km to the end. It is close to the results that the present crust and crust-mantle transition zone is about 33-40 and 40-50 km, which is obtained by previous researchers. Hence our conclusion has been verified by petrology.
After thinning of the North China craton, the magmatism was widely distributed, and, the mantle mafic basalt intruded and reconstructed the wall rock, which formed large scale granite. This paper establishes a proper geophysics model and use the finite element method to numerically simulates the the mantle mafic basalt underplating. If we ignore the convection inside the basalt and only consider the conduction, we inversion calculate the formation of granite required how much intrusion of basaltic magma. The results indicate: (1) under 1 GPa condition, the pure melting volume of tonalite rock and pure crystallization volume of underplating basalt ratio is about 0.161; on the assumption that only 25% magma can dissociate, the total ratio of separated out of basalt lava is about 0.040 25. (2) The numerical results demonstrate the phase transition zone is from -50.285 to -36.867 km to the end. It is close to the results that the present crust and crust-mantle transition zone is about 33-40 and 40-50 km, which is obtained by previous researchers. Hence our conclusion has been verified by petrology.
2012, 37(S1): 213-222.
doi: 10.3799/dqkx.2012.S1.022
Abstract:
The Three Gorges located in northern margin of Yangtze plate, is surrounded by four different geotectonic units: Qinling orogenic belt in north, Sichuan basin in west, North China plate in northeast and South China fold belt in southeast. In history, there are so many kinds of tectonic movements occurred. Utilizing Bouguer gravity anomaly in the Three Gorges area, and based on the technology of 3D gravity inversion, the 3D density structure of the upper and middle crust of Three Gorges reservoir area is obtained. The results show that Huangling anticline is a high density area, with a maximum depth of about 15 km. The distribution of regional faults around the Huangling anticline is lozenge-shaped, and those faults cut to the top of the middle crust with a depth of about 10-15 km, controlling the tectonic evolution and earthquake distributions in this area. Along Yangtze River, there is a low density stratum in the middle of Huangling anticline, which presumably is the result of the low density materials intruded along Wuduhe fault. Furthermore, Zigui basin in west has low density values, and its deposit stratum is nonuniform in thickness, that is, becoming thicker and thicker from Badong to Zigui.
The Three Gorges located in northern margin of Yangtze plate, is surrounded by four different geotectonic units: Qinling orogenic belt in north, Sichuan basin in west, North China plate in northeast and South China fold belt in southeast. In history, there are so many kinds of tectonic movements occurred. Utilizing Bouguer gravity anomaly in the Three Gorges area, and based on the technology of 3D gravity inversion, the 3D density structure of the upper and middle crust of Three Gorges reservoir area is obtained. The results show that Huangling anticline is a high density area, with a maximum depth of about 15 km. The distribution of regional faults around the Huangling anticline is lozenge-shaped, and those faults cut to the top of the middle crust with a depth of about 10-15 km, controlling the tectonic evolution and earthquake distributions in this area. Along Yangtze River, there is a low density stratum in the middle of Huangling anticline, which presumably is the result of the low density materials intruded along Wuduhe fault. Furthermore, Zigui basin in west has low density values, and its deposit stratum is nonuniform in thickness, that is, becoming thicker and thicker from Badong to Zigui.
