The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the ...The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence.展开更多
Thus far, our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results. Therefore, in this study,...Thus far, our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results. Therefore, in this study, the ^40Ar/^39Ar and sensitive high resolution ion micro-probe （SHRIMP） U-Pb dating methods were both used and the results compared, particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding, to establish ages that are close to the real emplacements. The results of SHRIMP U-Pb dating for zircon showed a high amount of U, but a very low value for Th/U. The high U amount, coupled with characteristics of inclusions in zircons, indicates that Xuebaoding granites are not suitable for U-Pb dating. Therefore, muscovite in the same granite samples was selected for ^40Ar/^39Ar dating. The ^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding, gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma. The 4^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ^40Ar/^36Ar intercept of 277.0±23.4 （2σ） was very close to the air ratio, indicating that no apparent excess argon contamination was present. These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma, respectively. Through comparison of both dating methods and their results, we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ^40Ar/^39Ar dating without extra Ar. Based on this evidence, as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites, it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma. Moreover, compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt, the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze. Therefore, ^40Ar/^39Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.展开更多
Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the ...Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the South Qinling fold belt might both be a part of the old Yangtze platform. Rifting generated by the Caledonian orogeny in the terminal Early Palaeozoic caused the massif to be disintegrated from the northwestern part of the Yangtze platform. This disintegration, however, was not thorough, and the rift troughs were later gradually closed and filled up. The Emei taphrogeny that was initiated in the Early Permian Maokou' an Stage involved a second disintegration of this massif from the Yangtze platform. The rift line largely goes along the Muli-Pingwu line. This rifting belongs to synchronous extensional rifting at peripheries of the Yangtze platform and in its interior, showing that the posterior, lateral and interior extension resulting from rapid northward shift of the Yangtze platform led to isolation of this massif together with South Qinling from their adjacent areas. During the Ladinian Stage, the Songpan-Garze massif and southern Qinling sank strongly en masse. This subsidence continued till the end of the Late Triassic when the late Indosinian movement caused the sea trough to be closed and Songpan-Garze1 and southern Qinling to be folded and uplifted and become mountains.展开更多
The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laura...The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laurasia and the Cimmerian fragments of Qiangtang (North Tibet) and Yangtze (South China), the Songpan Garzê Fold Belt was shortened by more than 50% during the Indosinian Orogeny c.200Ma. [BW(D(S,,)G2*7][BHDWG2*7,WK*2,WK5,WK15*2,WK17*2,WK*2W] 2000,7(增刊) 地 学 前 缘 [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau [BW(S(S,,)G2*7][BHDWG2*7,WK*2,WK17*2,WK15*2,WK5,WK*2W] [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau 地 学 前 缘 2000,7(增刊)South\|directed Indosinian compression decolléd onlapping basin sediments from the Yangtze Block’s passive margin—reactivating the margin’s tiered geometry and partitioning strain into margin\|normal and margin\|parallel structures on a large scale. Margin\|normal transport of the allochthonous sedimentary pile was accommodated by southeast\|directed nappe propagation in the Longmen Mountains Thrust—Nappe Belt, whilst conjugate, margin\|parallel (southwest\|directed) transport was accommodated by a flat\|lying detachment at the base of the sedimentary pile.The later is characteristic of deformation of the greater Songpan Garzê Fold Belt.展开更多
In the Songpan-Garze fold belt of the northeastern Tibetan Plateau, an Indosinian lithospheric delamination model has been proposed, based on previous investigation of widespread granitoids. However, this model lacks ...In the Songpan-Garze fold belt of the northeastern Tibetan Plateau, an Indosinian lithospheric delamination model has been proposed, based on previous investigation of widespread granitoids. However, this model lacks comparable information from volcanism in the area. During the Indosinian delamination in the Songpan-Garze fold belt, whether partial melting of litho- spheric mantle taken place is debated. This paper reports U-Pb zircon LA-ICP-MS ages, geochemical and Sr-Nd-Hf isotopic compositions from the Aba and Wasai calc-alkaline volcanic rocks in the central Songpan-Garze fold belt. Obtained magma crystallization ages are 210±3 Ma for the Aba andesite and 205±1 Ma for the Wasai andesite. These are consistent with magma crystallization ages of the late Indosinian granitoids in the Songpan-Garze fold belt that formed in a post-collisional tectonic setting. The Aba and Wasai andesites have distinct geochemical singnatures. The former has higher Al2O3, K2O, Rb but lower Na2O, Ba and Sr contents, suggesting differences in their magmatic evolution. The Aba andesites have ISr values of 0.7070-0.7076 and εNd(t) values of -3.9 to -5.3, and the Wasai andesites have ISr values of 0.7075-0.7077 and εNd(t) values of -3.6 to -3.9. Zircons show εHf(t) values of -3.7 to 0.3 for the Aba andesites and -2.7 to 5.5 for the Wasai andesites. Geochemical and Sr-Nd-Hf isotopic compositions indicate that fractional crystallization and crustal assimilation processes are not key roles for their magma evolution, implying that their chemical compositions are those of primary melts. We suggest that the magma of the Aba andesites originated predominantly from a crustal source, with a minor mantle-derived component. The source region of the magma was likely at the crust-mantle boundary. The magma of the Wasai andesites resulted from partial melting of lithospheric mantle, which was probably metasomatized by fluids so that it was amphibole bearing. The petrogenesis of the Aba and Wasai andesites provides an additional evidence for the lithospheric delamination in the the Songpan-Garze fold belt, indicating that this process invoked mantle asthenosphere upwelling and caused the partial melting of remaining lithospheric mantle.展开更多
Whilst the topographic relief of the Tibetan Plateau’s northeast margin reflects recent Himalayan Orogenesis, its position and geometry reflect much older structures that developed during the Indosinian Orogeny c.200...Whilst the topographic relief of the Tibetan Plateau’s northeast margin reflects recent Himalayan Orogenesis, its position and geometry reflect much older structures that developed during the Indosinian Orogeny c.200Ma. The Indosinian Orogeny was responsible for closure and shortening of the Songpan Garzê Basin, a Palaeo\|Tethyan relict, during accretion of the Cimmerian Continental Chain to the southern margin of Laurasia. Sandwiched between Laurasia and the Cimmerian fragments of the Qangtang (North Tibet) and Yangtze (South China) blocks, this basin evolved into the Songpan Garzê Fold Belt—a major accretionary prism which now forms the northeast portion of the Tibetan Plateau.展开更多
A series of Jinning granites are located in the eastern margin of the main part of the Songpan-Ganze Orogenic Belt. The research is focused on Gezong and Donggu granites in the Danba area. From the viewpoint of isotop...A series of Jinning granites are located in the eastern margin of the main part of the Songpan-Ganze Orogenic Belt. The research is focused on Gezong and Donggu granites in the Danba area. From the viewpoint of isotopic chronology, geochemistry and tectonic geology, their formation ages, origins and geneses of source materials, and the influences of Himalayan tectonic thermal events are discussed- It is suggested that they were the products of Jinning tectono-magmatism. The source materials were the poorly matured volcano-sedimentary rocks formed in the middle-late period of the middld-Proterozoic. They represent in fact the basement of the old Yangtze Block. The late Proterozoic erogenic belt of the entire western margin of the Yangtze Block, including the Danba area, should be the key part of the old Yangtze Block.展开更多
基金National Key Research Development Project (No. G1998 040700/sub-project 95-13-02-03).
文摘The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence.
基金funded by the Major State Basic Research Program of China (2009CB421008)the Program for the New Century Excellent Talents in China(NCET-07-0771) +1 种基金the Program for Changjiang Scholars and Innovative Research Team in University,"111"Project(No.B07011)State Key Laboratory of Geological Processes and Mineral Resources(No.GPMR200838,GPMR0736)
文摘Thus far, our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results. Therefore, in this study, the ^40Ar/^39Ar and sensitive high resolution ion micro-probe （SHRIMP） U-Pb dating methods were both used and the results compared, particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding, to establish ages that are close to the real emplacements. The results of SHRIMP U-Pb dating for zircon showed a high amount of U, but a very low value for Th/U. The high U amount, coupled with characteristics of inclusions in zircons, indicates that Xuebaoding granites are not suitable for U-Pb dating. Therefore, muscovite in the same granite samples was selected for ^40Ar/^39Ar dating. The ^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding, gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma. The 4^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ^40Ar/^36Ar intercept of 277.0±23.4 （2σ） was very close to the air ratio, indicating that no apparent excess argon contamination was present. These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma, respectively. Through comparison of both dating methods and their results, we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ^40Ar/^39Ar dating without extra Ar. Based on this evidence, as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites, it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma. Moreover, compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt, the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze. Therefore, ^40Ar/^39Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.
基金This paper is one of the research results of the subject "The Ecostratigraphy of the Indosinian Continental Margins on the Sichuan-Gansu-Qinghai Border"(No.48970080)supported by the National Natural Science Foundation of China
文摘Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the South Qinling fold belt might both be a part of the old Yangtze platform. Rifting generated by the Caledonian orogeny in the terminal Early Palaeozoic caused the massif to be disintegrated from the northwestern part of the Yangtze platform. This disintegration, however, was not thorough, and the rift troughs were later gradually closed and filled up. The Emei taphrogeny that was initiated in the Early Permian Maokou' an Stage involved a second disintegration of this massif from the Yangtze platform. The rift line largely goes along the Muli-Pingwu line. This rifting belongs to synchronous extensional rifting at peripheries of the Yangtze platform and in its interior, showing that the posterior, lateral and interior extension resulting from rapid northward shift of the Yangtze platform led to isolation of this massif together with South Qinling from their adjacent areas. During the Ladinian Stage, the Songpan-Garze massif and southern Qinling sank strongly en masse. This subsidence continued till the end of the Late Triassic when the late Indosinian movement caused the sea trough to be closed and Songpan-Garze1 and southern Qinling to be folded and uplifted and become mountains.
文摘The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laurasia and the Cimmerian fragments of Qiangtang (North Tibet) and Yangtze (South China), the Songpan Garzê Fold Belt was shortened by more than 50% during the Indosinian Orogeny c.200Ma. [BW(D(S,,)G2*7][BHDWG2*7,WK*2,WK5,WK15*2,WK17*2,WK*2W] 2000,7(增刊) 地 学 前 缘 [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau [BW(S(S,,)G2*7][BHDWG2*7,WK*2,WK17*2,WK15*2,WK5,WK*2W] [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau 地 学 前 缘 2000,7(增刊)South\|directed Indosinian compression decolléd onlapping basin sediments from the Yangtze Block’s passive margin—reactivating the margin’s tiered geometry and partitioning strain into margin\|normal and margin\|parallel structures on a large scale. Margin\|normal transport of the allochthonous sedimentary pile was accommodated by southeast\|directed nappe propagation in the Longmen Mountains Thrust—Nappe Belt, whilst conjugate, margin\|parallel (southwest\|directed) transport was accommodated by a flat\|lying detachment at the base of the sedimentary pile.The later is characteristic of deformation of the greater Songpan Garzê Fold Belt.
基金supported by National Natural Science Foundation of China (Grant Nos.40773019 and 40821061)Ministry of Education of China and the State Administration of Foreign Expert Affairs of China (Grant No.B07039)
文摘In the Songpan-Garze fold belt of the northeastern Tibetan Plateau, an Indosinian lithospheric delamination model has been proposed, based on previous investigation of widespread granitoids. However, this model lacks comparable information from volcanism in the area. During the Indosinian delamination in the Songpan-Garze fold belt, whether partial melting of litho- spheric mantle taken place is debated. This paper reports U-Pb zircon LA-ICP-MS ages, geochemical and Sr-Nd-Hf isotopic compositions from the Aba and Wasai calc-alkaline volcanic rocks in the central Songpan-Garze fold belt. Obtained magma crystallization ages are 210±3 Ma for the Aba andesite and 205±1 Ma for the Wasai andesite. These are consistent with magma crystallization ages of the late Indosinian granitoids in the Songpan-Garze fold belt that formed in a post-collisional tectonic setting. The Aba and Wasai andesites have distinct geochemical singnatures. The former has higher Al2O3, K2O, Rb but lower Na2O, Ba and Sr contents, suggesting differences in their magmatic evolution. The Aba andesites have ISr values of 0.7070-0.7076 and εNd(t) values of -3.9 to -5.3, and the Wasai andesites have ISr values of 0.7075-0.7077 and εNd(t) values of -3.6 to -3.9. Zircons show εHf(t) values of -3.7 to 0.3 for the Aba andesites and -2.7 to 5.5 for the Wasai andesites. Geochemical and Sr-Nd-Hf isotopic compositions indicate that fractional crystallization and crustal assimilation processes are not key roles for their magma evolution, implying that their chemical compositions are those of primary melts. We suggest that the magma of the Aba andesites originated predominantly from a crustal source, with a minor mantle-derived component. The source region of the magma was likely at the crust-mantle boundary. The magma of the Wasai andesites resulted from partial melting of lithospheric mantle, which was probably metasomatized by fluids so that it was amphibole bearing. The petrogenesis of the Aba and Wasai andesites provides an additional evidence for the lithospheric delamination in the the Songpan-Garze fold belt, indicating that this process invoked mantle asthenosphere upwelling and caused the partial melting of remaining lithospheric mantle.
文摘Whilst the topographic relief of the Tibetan Plateau’s northeast margin reflects recent Himalayan Orogenesis, its position and geometry reflect much older structures that developed during the Indosinian Orogeny c.200Ma. The Indosinian Orogeny was responsible for closure and shortening of the Songpan Garzê Basin, a Palaeo\|Tethyan relict, during accretion of the Cimmerian Continental Chain to the southern margin of Laurasia. Sandwiched between Laurasia and the Cimmerian fragments of the Qangtang (North Tibet) and Yangtze (South China) blocks, this basin evolved into the Songpan Garzê Fold Belt—a major accretionary prism which now forms the northeast portion of the Tibetan Plateau.
基金Project supported by the National Natural Science Foundation of China and the Eighth Five-Year Plan's Key Basic Research Program of the Ministry of Geology and Mineral Resources of China.
文摘A series of Jinning granites are located in the eastern margin of the main part of the Songpan-Ganze Orogenic Belt. The research is focused on Gezong and Donggu granites in the Danba area. From the viewpoint of isotopic chronology, geochemistry and tectonic geology, their formation ages, origins and geneses of source materials, and the influences of Himalayan tectonic thermal events are discussed- It is suggested that they were the products of Jinning tectono-magmatism. The source materials were the poorly matured volcano-sedimentary rocks formed in the middle-late period of the middld-Proterozoic. They represent in fact the basement of the old Yangtze Block. The late Proterozoic erogenic belt of the entire western margin of the Yangtze Block, including the Danba area, should be the key part of the old Yangtze Block.
