Cenozoic potassic-ultrapotassic igneous rocks are widespread in the southeastern Tibetan Plateau.Their petrogenesis and magmatic processes remain subject to debate in spite of numerous publications.Almost all of the C...Cenozoic potassic-ultrapotassic igneous rocks are widespread in the southeastern Tibetan Plateau.Their petrogenesis and magmatic processes remain subject to debate in spite of numerous publications.Almost all of the Cenozoic extrusive and intrusive rocks in the Yao’an area,western Yunnan Province,SW China,are geochemically shoshonitic,collectively termed here the Yao’an Shoshonitic Complex(YSC).The YSC is located in the(south)easternmost part of the ENE-WSW-trending,~550 km-long and~250 km-wide Cenozoic magmatic zone;the latter separates the orthogonal and oblique collision belts of the India-Eurasia collision orogen.Previously published geochronological and thermochronological data revealed that the rocks of the YSC were emplaced over a short timespan of 34-32 Ma.This and our new data suggest that the primary magma of the YSC likely was formed by partial melting of ancient continental lithospheric mantle beneath the Yangtze Block.This part of the continental lithospheric mantle had likely not been modified by any oceanic subduction.Fractionation crystallization of an Mg-and Ca-bearing mineral and TiFe oxides during the magmatic evolution probably account for the variable lithologies of the YSC.展开更多
In order to determine the age of the sedimentary hiatus and its geological significance, a study of the calcareous nannofossil biostratigraphy was carried out. Detailed stratigraphical data of the Late Oligocene-Early...In order to determine the age of the sedimentary hiatus and its geological significance, a study of the calcareous nannofossil biostratigraphy was carried out. Detailed stratigraphical data of the Late Oligocene-Early Miocene diagnostic species thus obtained. The nannofossil zonation of this interval was subdivided and the Oligocene-Miocene boundary was further determined. Several last Late Oligocene events were recognized, indicating a long-term sedimentary hiatus in the uppermost Upper Oligocene. The time span of the hiatus was estimated for about 2.2 Ma, at least from 23.9 to 26.1 Ma. The lithological and geophysical data from Site 1148 indicate some abrupt sedimentary changes that occurred below and above the hiatus. This hiatus at Site 1148 was probably related to the tectonic change, a major ridge jump during the seafloor spreading in the Late Oligocene South China Sea.展开更多
Oil and gas exploration prospect for the Miocene and Late Oligocene strata in Qiongdongnan（琼东南） basin are evaluated.The structural-sedimentary and reservoir characteristics are discussed and helpful conclusions a...Oil and gas exploration prospect for the Miocene and Late Oligocene strata in Qiongdongnan（琼东南） basin are evaluated.The structural-sedimentary and reservoir characteristics are discussed and helpful conclusions are drawn.It was proved that there are mainly two reservoir and capping assemblages in Qiongdongnan basin by drilled wells,i.e.,one assemblage of the second and the third members of Lingshui（陵水） Formation,upper Sanya（三亚） and Meishan（梅山） formations.According to hydrocarbon evaluation from burial history and well data,all source rocks in Yacheng（崖城） and Lingshui formations have reached the mature-overmature stage.High temperature and overpressure provide dynamic conditions for oil and gas migration,while the long-term activity of basin controlling faults is adverse to their accumulation in upheaved areas.However,because the secondary faults in the basin ceased their activities at the end of the Sanya Period,and the Sanya Formation was later covered by the regional overlying layer of the Meishan Formation,the blocks and low uplifts near the secondary faults were favorable for oil and gas accumulation.Furthermore,as another important pointed area for gas migration,the highest position of a structural ridge should reasonably be a range that is covered by marine mudstone or sandy mudstone during the whole subsiding period,and therefore,the reservoir bed should not be in that position but at its inferior eminence or adjacent slope zone.Therefore,we can draw a conclusion that the inferior low uplifts and structural ridges rather than the upheavals or the top of a structural ridge,probably,have huge reservoirs,and should be chief exploration targets in the Qiongdongnan basin.展开更多
The Liupan Mountains,one of the important mountain ranges in western China,are located on the boundary between the northeastern Tibetan Plateau and the Ordos Block.The uplift history of the Liupan Mountains remains co...The Liupan Mountains,one of the important mountain ranges in western China,are located on the boundary between the northeastern Tibetan Plateau and the Ordos Block.The uplift history of the Liupan Mountains remains controversial.Loess deposits are good tracers of regional tectonic and geomorphic changes,because loess is sensitive to erosion and the formation and preservation of loess requires relatively flat highlands and relatively stable tectonic environments.We investigated the distribution of Neogene loess deposits on the western piedmont of the Liupan Mountains and examined a near-continuous loess section(Nanping section)on the piedmont alluvial highlands.Correlation of magnetic susceptibility stratigraphy with the QA-ⅠMiocene loess sequence dates this 56-m section covering the interval from~8.1 to 6.2 Ma.The lower boundary age of this section,together with previously reported Zhuanglang red clay(sand-gravel layers with intercalated loess during~9–8 Ma and near-continuous loess during~8–4.8 Ma)and Chaona red clay(~8.1–2.58 Ma),indicates that the Liupan Mountains were uplifted in the late Miocene(~9–8 Ma)and basically formed by~8 Ma,attesting to no intense mountain building since that time.In addition,based on the information from the Zhuanglang core and the QA-Ⅰsection,we infer that sizable parts of the Liupan Mountains were uplifted during the late Oligocene–early Miocene and did not experience intense uplift during~22–9 Ma.展开更多
基金financially supported by the Ministry of Sciences and Technology of China(Grant No.2022YFF0800901)the Natural Science Foundation of China(Grant Nos.92055206 and 42163007)。
文摘Cenozoic potassic-ultrapotassic igneous rocks are widespread in the southeastern Tibetan Plateau.Their petrogenesis and magmatic processes remain subject to debate in spite of numerous publications.Almost all of the Cenozoic extrusive and intrusive rocks in the Yao’an area,western Yunnan Province,SW China,are geochemically shoshonitic,collectively termed here the Yao’an Shoshonitic Complex(YSC).The YSC is located in the(south)easternmost part of the ENE-WSW-trending,~550 km-long and~250 km-wide Cenozoic magmatic zone;the latter separates the orthogonal and oblique collision belts of the India-Eurasia collision orogen.Previously published geochronological and thermochronological data revealed that the rocks of the YSC were emplaced over a short timespan of 34-32 Ma.This and our new data suggest that the primary magma of the YSC likely was formed by partial melting of ancient continental lithospheric mantle beneath the Yangtze Block.This part of the continental lithospheric mantle had likely not been modified by any oceanic subduction.Fractionation crystallization of an Mg-and Ca-bearing mineral and TiFe oxides during the magmatic evolution probably account for the variable lithologies of the YSC.
文摘In order to determine the age of the sedimentary hiatus and its geological significance, a study of the calcareous nannofossil biostratigraphy was carried out. Detailed stratigraphical data of the Late Oligocene-Early Miocene diagnostic species thus obtained. The nannofossil zonation of this interval was subdivided and the Oligocene-Miocene boundary was further determined. Several last Late Oligocene events were recognized, indicating a long-term sedimentary hiatus in the uppermost Upper Oligocene. The time span of the hiatus was estimated for about 2.2 Ma, at least from 23.9 to 26.1 Ma. The lithological and geophysical data from Site 1148 indicate some abrupt sedimentary changes that occurred below and above the hiatus. This hiatus at Site 1148 was probably related to the tectonic change, a major ridge jump during the seafloor spreading in the Late Oligocene South China Sea.
基金supported by the Key Project of the National Eleventh Five-Year Plan of China (No. 2008ZX05023-004)
文摘Oil and gas exploration prospect for the Miocene and Late Oligocene strata in Qiongdongnan（琼东南） basin are evaluated.The structural-sedimentary and reservoir characteristics are discussed and helpful conclusions are drawn.It was proved that there are mainly two reservoir and capping assemblages in Qiongdongnan basin by drilled wells,i.e.,one assemblage of the second and the third members of Lingshui（陵水） Formation,upper Sanya（三亚） and Meishan（梅山） formations.According to hydrocarbon evaluation from burial history and well data,all source rocks in Yacheng（崖城） and Lingshui formations have reached the mature-overmature stage.High temperature and overpressure provide dynamic conditions for oil and gas migration,while the long-term activity of basin controlling faults is adverse to their accumulation in upheaved areas.However,because the secondary faults in the basin ceased their activities at the end of the Sanya Period,and the Sanya Formation was later covered by the regional overlying layer of the Meishan Formation,the blocks and low uplifts near the secondary faults were favorable for oil and gas accumulation.Furthermore,as another important pointed area for gas migration,the highest position of a structural ridge should reasonably be a range that is covered by marine mudstone or sandy mudstone during the whole subsiding period,and therefore,the reservoir bed should not be in that position but at its inferior eminence or adjacent slope zone.Therefore,we can draw a conclusion that the inferior low uplifts and structural ridges rather than the upheavals or the top of a structural ridge,probably,have huge reservoirs,and should be chief exploration targets in the Qiongdongnan basin.
基金supported by the National Natural Science Foundation of China(Grant No.42488201)the Strategy Priority Research Program(Category B)of Chinese Academy of Sciences(Grant No.XDB0710000)。
文摘The Liupan Mountains,one of the important mountain ranges in western China,are located on the boundary between the northeastern Tibetan Plateau and the Ordos Block.The uplift history of the Liupan Mountains remains controversial.Loess deposits are good tracers of regional tectonic and geomorphic changes,because loess is sensitive to erosion and the formation and preservation of loess requires relatively flat highlands and relatively stable tectonic environments.We investigated the distribution of Neogene loess deposits on the western piedmont of the Liupan Mountains and examined a near-continuous loess section(Nanping section)on the piedmont alluvial highlands.Correlation of magnetic susceptibility stratigraphy with the QA-ⅠMiocene loess sequence dates this 56-m section covering the interval from~8.1 to 6.2 Ma.The lower boundary age of this section,together with previously reported Zhuanglang red clay(sand-gravel layers with intercalated loess during~9–8 Ma and near-continuous loess during~8–4.8 Ma)and Chaona red clay(~8.1–2.58 Ma),indicates that the Liupan Mountains were uplifted in the late Miocene(~9–8 Ma)and basically formed by~8 Ma,attesting to no intense mountain building since that time.In addition,based on the information from the Zhuanglang core and the QA-Ⅰsection,we infer that sizable parts of the Liupan Mountains were uplifted during the late Oligocene–early Miocene and did not experience intense uplift during~22–9 Ma.
