A shear-wave velocity model of the crust and uppermost mantle beneath the SE Tibetan plateau was derived by inverting Rayleigh-wave group-velocity mea- surements of periods between 10 and 70 s. Rayleigh-wave group-vel...A shear-wave velocity model of the crust and uppermost mantle beneath the SE Tibetan plateau was derived by inverting Rayleigh-wave group-velocity mea- surements of periods between 10 and 70 s. Rayleigh-wave group-velocity dispersions along more than 3,000 inter- station paths were measured based on analysis of telese- ismic wavelbrm data recorded by temporary seismic stations. These observations were then utilized to construct 2D group-velocity maps in the period range of 10-70 s. Tile new group-velocity maps have an enhanced resolution compared with previous global and regional group-velocity models in this region because of the denser and more uniform data coverage. The lateral resolution across the region is about 0.5° for the periods used in this study. Local dispersion curves were then inverted for a 3D shear-wave velocity model of the region by applying a linear inversion scheme. Our 3D shear-wave model confirms the presence of low-velocity zones （LVZs） in the crust beneath the northern part of this region. Our irnaging shows that the upper-middle crustal LVZ beneath the Tengchong region is isolated from these LVZs beneath the eastern and northern part of this region. The upper-middle crustal LVZ may be regarded as evidence of a rnagma chamber in the crust beneath the Tengchong Volcanoes. Our model also reveals a slow lithospheric structure beneath Tengchong and a fast shield-like mantle beneath the stable Yangtze block.展开更多
We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surfa...We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surface waves. The two profiles cross West Yunnan block （WYB）, the Central Yunnan sub-block （CYB）, South China block （SCB）, and Nanpanjiang basin （NPB）. The profile at -25°N shows that the Moho interface in the CYB is deeper than those in the WYB and the NPB, and the topography and Moho depth have clear correspondence. Beneath the Xiaojiang fault zone （XJF）, there exists a crustal low-velocity zone （LYZ）, crossing the XJF and expanding eastward into the SCB. The NPB is shown to be of relatively high velocity. We speculate that the eastward extrusion of the Tibetan plateau may pass through the XJF and affect its eastern region, and is resisted by the rigid NPB, which has high velocity. This may be the main cause of the crustal thickening and uplift of the topography. In the Tengchong volcanic area, the crust is shown to have alternate high- and low-velocity layers, and the upper mantle is shown to be of low velocity. We consider that the magma which exists in the crust is from the upper mantle and that the complex crustal velocity structure is related to magmatic differentiation. Between the Tengchong volcanic area and the XJF, the crustal velocity is relatively high. Combining these observations with other geophysical evi- dence, it is indicated that rock strength is high and defor- mation is weak in this area, which is why the level of seismicity is quite low. The profile at ~ 23~N shows that the variation of the Moho depth is small from the eastern rigid block to the western active block with a wide range of LVZs. We consider that deformation to the south of the SE Tibetan Plateau is weak.展开更多
The SE Tibetan Plateau,tectonically situated in the eastern India-Eurasia oblique convergence zone,has experienced multiple stages of deformation since the Cenozoic.Three major tectonic boundaries—the Ailaoshan-Red R...The SE Tibetan Plateau,tectonically situated in the eastern India-Eurasia oblique convergence zone,has experienced multiple stages of deformation since the Cenozoic.Three major tectonic boundaries—the Ailaoshan-Red River,ChongshanLincang-Inthanon,and Gaoligong-Mogok shear zones—delineate the first-order tectonic framework in this region.The most striking structural features in the block interiors are a series of NW-and NE-trending fault systems,such as the Dayingjiang,Longlin-Ruili,Nantinghe,Red River,Weixi-Qiaohou,and Lancang-Genma faults,which have conjugate geometric relationships.In this study,we review these structures’geometric and kinematic characteristics and deformation histories.A synthesis of existing geological observations,geomorphological analyses,and chronological data reveals three major Cenozoic tectonothermal events,including crustal shortening,strike-slip shearing,and kinematic reversal.The boundary structures controlled the tectonic extrusion of plateau material during the early Oligocene-early Miocene.In the mid-late Miocene,NW-and NE-trending fault systems mostly experienced diachronous slip-sense inversions.The onset and spatial trend of regional kinematic reversal are constrained by existing chronologic data.Together with geophysical and geodetic observations,the activity and geodynamic drivers of the major fault systems and regional deformation styles are explored,revealing that the SE Tibetan Plateau underwent a transition from discrete(lateral block extrusion)to diffuse deformation in the mid-late Miocene.The intracontinental crustal deformation and its coupling with dynamic processes at depth during the plateau growth are discussed in the context of the IndiaEurasia convergence.展开更多
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
基金supported by the China National Special Fund for Earthquake Scientific Research in Public Interest(201008001)NSFC(41074067)
文摘A shear-wave velocity model of the crust and uppermost mantle beneath the SE Tibetan plateau was derived by inverting Rayleigh-wave group-velocity mea- surements of periods between 10 and 70 s. Rayleigh-wave group-velocity dispersions along more than 3,000 inter- station paths were measured based on analysis of telese- ismic wavelbrm data recorded by temporary seismic stations. These observations were then utilized to construct 2D group-velocity maps in the period range of 10-70 s. Tile new group-velocity maps have an enhanced resolution compared with previous global and regional group-velocity models in this region because of the denser and more uniform data coverage. The lateral resolution across the region is about 0.5° for the periods used in this study. Local dispersion curves were then inverted for a 3D shear-wave velocity model of the region by applying a linear inversion scheme. Our 3D shear-wave model confirms the presence of low-velocity zones （LVZs） in the crust beneath the northern part of this region. Our irnaging shows that the upper-middle crustal LVZ beneath the Tengchong region is isolated from these LVZs beneath the eastern and northern part of this region. The upper-middle crustal LVZ may be regarded as evidence of a rnagma chamber in the crust beneath the Tengchong Volcanoes. Our model also reveals a slow lithospheric structure beneath Tengchong and a fast shield-like mantle beneath the stable Yangtze block.
基金supported by a National Natural Science Foundation of China (Grant No. 41374097)China National Special Fund for Earthquake Scientific Research in Public Interest (Grant No. 201008001)
文摘We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surface waves. The two profiles cross West Yunnan block （WYB）, the Central Yunnan sub-block （CYB）, South China block （SCB）, and Nanpanjiang basin （NPB）. The profile at -25°N shows that the Moho interface in the CYB is deeper than those in the WYB and the NPB, and the topography and Moho depth have clear correspondence. Beneath the Xiaojiang fault zone （XJF）, there exists a crustal low-velocity zone （LYZ）, crossing the XJF and expanding eastward into the SCB. The NPB is shown to be of relatively high velocity. We speculate that the eastward extrusion of the Tibetan plateau may pass through the XJF and affect its eastern region, and is resisted by the rigid NPB, which has high velocity. This may be the main cause of the crustal thickening and uplift of the topography. In the Tengchong volcanic area, the crust is shown to have alternate high- and low-velocity layers, and the upper mantle is shown to be of low velocity. We consider that the magma which exists in the crust is from the upper mantle and that the complex crustal velocity structure is related to magmatic differentiation. Between the Tengchong volcanic area and the XJF, the crustal velocity is relatively high. Combining these observations with other geophysical evi- dence, it is indicated that rock strength is high and defor- mation is weak in this area, which is why the level of seismicity is quite low. The profile at ~ 23~N shows that the variation of the Moho depth is small from the eastern rigid block to the western active block with a wide range of LVZs. We consider that deformation to the south of the SE Tibetan Plateau is weak.
基金supported by the Natural Science Foundation of Guangdong Province(Grant Nos.2021A1515011631,202102020490 and 2019B1515120019)the National Natural Science Foundation of China(Grant Nos.U1701641 and41802213)+1 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(STEP,Grant No.2019QZKK0703)Guangdong Province Introduced Innovative and R&D Team of Geological Processes and Natural Disasters around the South China Sea(Grant No.2016ZT06N331)。
文摘The SE Tibetan Plateau,tectonically situated in the eastern India-Eurasia oblique convergence zone,has experienced multiple stages of deformation since the Cenozoic.Three major tectonic boundaries—the Ailaoshan-Red River,ChongshanLincang-Inthanon,and Gaoligong-Mogok shear zones—delineate the first-order tectonic framework in this region.The most striking structural features in the block interiors are a series of NW-and NE-trending fault systems,such as the Dayingjiang,Longlin-Ruili,Nantinghe,Red River,Weixi-Qiaohou,and Lancang-Genma faults,which have conjugate geometric relationships.In this study,we review these structures’geometric and kinematic characteristics and deformation histories.A synthesis of existing geological observations,geomorphological analyses,and chronological data reveals three major Cenozoic tectonothermal events,including crustal shortening,strike-slip shearing,and kinematic reversal.The boundary structures controlled the tectonic extrusion of plateau material during the early Oligocene-early Miocene.In the mid-late Miocene,NW-and NE-trending fault systems mostly experienced diachronous slip-sense inversions.The onset and spatial trend of regional kinematic reversal are constrained by existing chronologic data.Together with geophysical and geodetic observations,the activity and geodynamic drivers of the major fault systems and regional deformation styles are explored,revealing that the SE Tibetan Plateau underwent a transition from discrete(lateral block extrusion)to diffuse deformation in the mid-late Miocene.The intracontinental crustal deformation and its coupling with dynamic processes at depth during the plateau growth are discussed in the context of the IndiaEurasia convergence.
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.
