The Altyn Tagh fault (ATF) extending in NEE—SWW direction lying at the northwestern boundary of Qinghai—Tibet plateau is the largest strike\|slip fault in Central Asia. On the basis of recent geologic mapping and de...The Altyn Tagh fault (ATF) extending in NEE—SWW direction lying at the northwestern boundary of Qinghai—Tibet plateau is the largest strike\|slip fault in Central Asia. On the basis of recent geologic mapping and detailed study of lithotectonic characteristics for the paleotectonic units at the two sides of the Altyn Tagh Fault ( Altun Mt. to west and the Qilian Mt. to east ) we propose that the paleotectonic units in the Altun Mt. can be correlated with those in the Qilian Mt. assuming 400km left\|lateral displacement for the Altyn Tagh fault. Natural seismic data across the Altun Mt. indicate that the Altyn Tagh fault is a lithospheric shear fault and the lithospheric shearing is probably related to southward intracontinental oblique subduction of the Tarim terrane beneath the Altun Mt.1\ Comparison of the major paleotectonic units at the two sides of the Altyn Tagh fault\;(1) The Alxa\|Dunhuang Massif:The Alxa massif lying at the southern margin of the Sino\|Korean craton consists mainly of an Early Proterozoic basement including high\|grade and middle\|grade metamorphic rocks, which were intruded by granite at 1719Ma. The Paleozoic passive margin sediments is well developed. In the Altun Mt., the Early Proterozoic and late Archean basement of the Duhuang massif includes high\|grade and middle\|grade metamorphic rocks dating 2789Ma (Sm\|Nd method) and 2405Ma (U\|Pb method).展开更多
Introduction The widespread occurrence of Cenozoic magma of the Tibetan Plateau suggest that they are common to most destructive plate margins and orogenic belts and active faults. In northern Tibet, volcanic rocks ar...Introduction The widespread occurrence of Cenozoic magma of the Tibetan Plateau suggest that they are common to most destructive plate margins and orogenic belts and active faults. In northern Tibet, volcanic rocks are divided into two volcanics subzone, i.e., the Qiangtang subzone and Kunlun subzone.We found most shoshonitic lavas in Kunlun subzone had extruded for 0～17Ma..The sodic volcanics had erupted for 44～60Ma in western Qiangtang subzone and the most potassic lavas had extruded for 18～45Ma, in eastern Qiangtang subzone.The volcanism in Qiangtang starting 60Ma ago, most volcanic rocks dominantly formed between 45 and 18Ma (Fig.1). From 45Ma to 18Ma, there is a trend that the strength of volcanism gradually decreases. The peralkaline volcanism occurred in late Palaeogene and was re\|active at local area in Neogene.展开更多
The Shiyaogou deposit,located in Songxian,Henan Province,China,is a medium-sized Molybdenum deposit newly discovered in the East Qinling molybdenum belt.Occurring in the altered Proterozoic Xionger Group,mineralizatio...The Shiyaogou deposit,located in Songxian,Henan Province,China,is a medium-sized Molybdenum deposit newly discovered in the East Qinling molybdenum belt.Occurring in the altered Proterozoic Xionger Group,mineralization of the deposit consists of molybedenite disseminations and quartz -molybdenite veinlets and stockworks.Hydrothermal alteration is well developed and is composed of potassic alteration,silicification,sericitization,pyriti-展开更多
The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian plate since 50～60Ma, and has sensitivity tracke...The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian plate since 50～60Ma, and has sensitivity tracked and preserved the whole collisional processes. It should depend on the detail geological investigations to establish the deformational accommodate mode, and the uplift history, to elucidate the deep structure and the crust\|mantle interaction of the EHS. The Namjabarwa metamorphic complex indented into the Gangdise arc along the sinistral Pai shear fault and the dextral Aniqiao shear fault on the both sides of the Great Canyon of Yalung Zangbo river since the collision of the NE corner of the Indian plate and the Eurasian Plate at 60～70Ma [1] . The distance between Yarlung Zangbo suture and Bangong—Nujiang suture is shortened more 120km in the EHS area than that of the Lhasa block.展开更多
Many evidences including those from magmatism and igneous rocks strongly support the heterogeneity of lithosphere in Tibetan plateau.By estimation, volcanic and plutonic rocks occupy an area of 300000km\+2, equaling t...Many evidences including those from magmatism and igneous rocks strongly support the heterogeneity of lithosphere in Tibetan plateau.By estimation, volcanic and plutonic rocks occupy an area of 300000km\+2, equaling to 10% of total area of the Tibetan Plateau. Temporal and spatial distribution of igneous rocks in the Tibetan Plateau is very inhomogeneous (Mo et al., 1998). Temporarily, most of plutonic and volcanic rocks, which occurred in 60% of total area of igneous rocks in the plateau, formed in the period of 65～45Ma. Spatially, 80% of igneous rocks in the plateau concentrated in the Gangdise—Nyainqentanglha region formed a huge complex granite\|volcanic belt. Petrotectonic assemblage and type of igneous rocks also vary from district to district. While Himalayas (especially High\|Himalayan region) were characterized by well development of muscovite\|bearing granites with no high\|potassium volcanic rocks and other volcanic contemporaries, North Tibet (Qiangtang region) by highly potassic volcanic rock series without muscovite\|bearing granites. Besides wide\|spreading calc\|alkaline igneous rocks, however, both highly potassic volcanic rocks and muscovite\|bearing granites developed in the central portion of Gangdise\|Nyainqentanglha region. It was lack of igneous activities in the Pamirs. Mantle\|derived nodules and their hosted rocks have been found only on northern and eastern margins of the plateau so far. All mentioned above, combined with other evidences from geophysics, geochemistry and structural geology, give us a hint to understand the heterogeneity of the lithosphere in its structure, thermal state and evolution processes underneath Tibetan plateau.展开更多
Volcanism is the direct indication of the upper mantle thermodynamic activities, and it is an efficient path to study the lithosphere tectonic evolution. Cenozoic volcanism in North Tibet is of obviously time circles....Volcanism is the direct indication of the upper mantle thermodynamic activities, and it is an efficient path to study the lithosphere tectonic evolution. Cenozoic volcanism in North Tibet is of obviously time circles. In the space, from south to north, the chemical composition of volcanics changed from Na\|rich alkalic basaltic series formed 44Ma. ago into high\|K calcalkali series formed in about 40～31Ma.in Qiangtang area, into minor amount of leucite basalt and phonolite series of 26Ma., further into shoshonite series aged at 19～7Ma. in Cocoxili basin, until Quaternary shoshonite series in Karakunlun and Qilian Mt.\|Yumen region(Xiaoguo Chi etc.1999).Isotopes of Sr,Nd,Pb and trace elements in volcanic rocks provide wide range of information for the evolution of lithosphere in North Tibet after 45Ma. Present research shows that Na\|rich alkalic basalt series formed 44Ma. ago has the features of a primitive mantle in Sr,Nd,Pb isotopes. Along with the evolutionary tendency to high\|K calcalkali series and phonolite series, isotopes of Sr,Nd,Pb evolve towards EM2\|rich mantle end. The North Tibet is a compound continental mass combined from several terrains of different geological periods and the lithosphere mantle sees a complicated evolutionary history. Hence, the mixing of different rocks in ancient subduction zones and long history of metasomatism in the upper mantle offered excellent and favorable conditions for the formation of EM2 mantle end and for potassic enrichment. Isotopic evolutionary features indicate that the early magma came from the asthenosphere while later magmas were derived from partial remelting of lithosphere mantle.展开更多
As one of the most distinct tectonic blocks on the Earth’s surface, Tibetan Plateau draw great attention of the geoscientists from the world. Many authors have proposed various kinds of the mechanism to try to clarif...As one of the most distinct tectonic blocks on the Earth’s surface, Tibetan Plateau draw great attention of the geoscientists from the world. Many authors have proposed various kinds of the mechanism to try to clarify the evolution of the plateau. While many studies are often restricted to crustal units, the important role of the mantle part of the lithosphere (mantle lithosphere) during and after the collision process has not been appreciated widely. The purpose of the paper is to investigate the dynamic process of the thinning (delamination and convective removal) of the thickened lithosphere and its influence upon the uplift of the plateau.1\ Thickened lithosphere root\;Parsons and McKenzie (1978) proposed that the continental lithosphere could be thought of as consisting of two distinct parts: the mechanical and thermal boundary layers. The lower, and hotter, part is the thermal boundary layer. Its viscosity is sufficiently low that the force of gravity acting on density contrasts between the thermal boundary layer and the underlying mantle lead to the episodic sinking of the thermal boundary layer and its replacement by hot asthenosphere. When continental crust shortens and thickens, the mantle directly beneath it must also be displaced downward. In other words, mountain building process shortens horizontally and thickens vertically the mechanical boundary layer, and presumably the thermal boundary layer. And the process stretches the isotherms vertically, thus reducing the geothermal gradient. Houseman’s numerical experiments (1981) show that thickening of the thermal boundary layer enhances the density contrasts between it and the underlying asthenosphere, and so leads to its removal and replacement with hot asthenosphere. This phenomenon is called the instability of the thickened lithosphere.展开更多
Interest in the ore\|forming histories of basins has grown rapid since 1960 and is now intensive. The main reason behind the acceleration is the increasing awareness that the natural processes responsible for generati...Interest in the ore\|forming histories of basins has grown rapid since 1960 and is now intensive. The main reason behind the acceleration is the increasing awareness that the natural processes responsible for generating metal deposits in the sedimentary basin from the source rocks of the beneath the basin and intensively hydrothermal activity in the basin. Observations made in different continental margin basin systems and superlarge deposits in Chinese Yunnan\|Guizhou\|Guangxi Province on the eastern margin of the Qingzang (Himalaya—Karakoram—Tibet) were investigated in terms of geodynamics of basin formation. Geotectonically, the area is situated in the conjoint between the Tethys—Himalaya and the Marginal\|Pacific tectonic domain, characterized by very complex geological structure, typical basin\|mountain tectonics, abundant Superlarge deposits.展开更多
In this paper,218 long period Rayleigh wave records from 7 seismic station of CDSN are selected.We applied a partitioned waveform inversion to these data in order to construct a 3\|D model of shear velocity down to 40...In this paper,218 long period Rayleigh wave records from 7 seismic station of CDSN are selected.We applied a partitioned waveform inversion to these data in order to construct a 3\|D model of shear velocity down to 400km depth in the crust and upper mantle of Qinghai\|Tibet plateau and Its Adjacent Regions (22°～44°N,70°～110°E).The first step of the waveform inversion used involved the matching of the waveforms of fundamental and highermost Ravleigh waves with waveforms synthesized from stratified models;in the second stage,the 3\|D model was constructed by solve linear constrains equation. The major structural features inferred from the surface waveform inversions can be summarized as follows:(1) There is a great contrast between surface waveform through Qinghai—Thibet plateau and the others.Main frequency of the former is lower than the latter, which indicate the crust depth of Qinghai—Tibet plateau is deeper than the others. In addition,the amplitude of about 30s period and 50s period is lower than both sides,which implied these exist lower velocity layer at about 25km depth and about 50km depth in Qinghai—Tibet plateau Crust.The former is common,the latter was argued because resolution of most method can not prove it.展开更多
文摘The Altyn Tagh fault (ATF) extending in NEE—SWW direction lying at the northwestern boundary of Qinghai—Tibet plateau is the largest strike\|slip fault in Central Asia. On the basis of recent geologic mapping and detailed study of lithotectonic characteristics for the paleotectonic units at the two sides of the Altyn Tagh Fault ( Altun Mt. to west and the Qilian Mt. to east ) we propose that the paleotectonic units in the Altun Mt. can be correlated with those in the Qilian Mt. assuming 400km left\|lateral displacement for the Altyn Tagh fault. Natural seismic data across the Altun Mt. indicate that the Altyn Tagh fault is a lithospheric shear fault and the lithospheric shearing is probably related to southward intracontinental oblique subduction of the Tarim terrane beneath the Altun Mt.1\ Comparison of the major paleotectonic units at the two sides of the Altyn Tagh fault\;(1) The Alxa\|Dunhuang Massif:The Alxa massif lying at the southern margin of the Sino\|Korean craton consists mainly of an Early Proterozoic basement including high\|grade and middle\|grade metamorphic rocks, which were intruded by granite at 1719Ma. The Paleozoic passive margin sediments is well developed. In the Altun Mt., the Early Proterozoic and late Archean basement of the Duhuang massif includes high\|grade and middle\|grade metamorphic rocks dating 2789Ma (Sm\|Nd method) and 2405Ma (U\|Pb method).
文摘Introduction The widespread occurrence of Cenozoic magma of the Tibetan Plateau suggest that they are common to most destructive plate margins and orogenic belts and active faults. In northern Tibet, volcanic rocks are divided into two volcanics subzone, i.e., the Qiangtang subzone and Kunlun subzone.We found most shoshonitic lavas in Kunlun subzone had extruded for 0～17Ma..The sodic volcanics had erupted for 44～60Ma in western Qiangtang subzone and the most potassic lavas had extruded for 18～45Ma, in eastern Qiangtang subzone.The volcanism in Qiangtang starting 60Ma ago, most volcanic rocks dominantly formed between 45 and 18Ma (Fig.1). From 45Ma to 18Ma, there is a trend that the strength of volcanism gradually decreases. The peralkaline volcanism occurred in late Palaeogene and was re\|active at local area in Neogene.
文摘The Shiyaogou deposit,located in Songxian,Henan Province,China,is a medium-sized Molybdenum deposit newly discovered in the East Qinling molybdenum belt.Occurring in the altered Proterozoic Xionger Group,mineralization of the deposit consists of molybedenite disseminations and quartz -molybdenite veinlets and stockworks.Hydrothermal alteration is well developed and is composed of potassic alteration,silicification,sericitization,pyriti-
基金TheNationalNaturalSciencesFoundationofChina (No .49732 10 0 )andNationalKeyProject (No .19980 40 80 0 )forBasicResearchofTibet
文摘The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian plate since 50～60Ma, and has sensitivity tracked and preserved the whole collisional processes. It should depend on the detail geological investigations to establish the deformational accommodate mode, and the uplift history, to elucidate the deep structure and the crust\|mantle interaction of the EHS. The Namjabarwa metamorphic complex indented into the Gangdise arc along the sinistral Pai shear fault and the dextral Aniqiao shear fault on the both sides of the Great Canyon of Yalung Zangbo river since the collision of the NE corner of the Indian plate and the Eurasian Plate at 60～70Ma [1] . The distance between Yarlung Zangbo suture and Bangong—Nujiang suture is shortened more 120km in the EHS area than that of the Lhasa block.
文摘Many evidences including those from magmatism and igneous rocks strongly support the heterogeneity of lithosphere in Tibetan plateau.By estimation, volcanic and plutonic rocks occupy an area of 300000km\+2, equaling to 10% of total area of the Tibetan Plateau. Temporal and spatial distribution of igneous rocks in the Tibetan Plateau is very inhomogeneous (Mo et al., 1998). Temporarily, most of plutonic and volcanic rocks, which occurred in 60% of total area of igneous rocks in the plateau, formed in the period of 65～45Ma. Spatially, 80% of igneous rocks in the plateau concentrated in the Gangdise—Nyainqentanglha region formed a huge complex granite\|volcanic belt. Petrotectonic assemblage and type of igneous rocks also vary from district to district. While Himalayas (especially High\|Himalayan region) were characterized by well development of muscovite\|bearing granites with no high\|potassium volcanic rocks and other volcanic contemporaries, North Tibet (Qiangtang region) by highly potassic volcanic rock series without muscovite\|bearing granites. Besides wide\|spreading calc\|alkaline igneous rocks, however, both highly potassic volcanic rocks and muscovite\|bearing granites developed in the central portion of Gangdise\|Nyainqentanglha region. It was lack of igneous activities in the Pamirs. Mantle\|derived nodules and their hosted rocks have been found only on northern and eastern margins of the plateau so far. All mentioned above, combined with other evidences from geophysics, geochemistry and structural geology, give us a hint to understand the heterogeneity of the lithosphere in its structure, thermal state and evolution processes underneath Tibetan plateau.
文摘Volcanism is the direct indication of the upper mantle thermodynamic activities, and it is an efficient path to study the lithosphere tectonic evolution. Cenozoic volcanism in North Tibet is of obviously time circles. In the space, from south to north, the chemical composition of volcanics changed from Na\|rich alkalic basaltic series formed 44Ma. ago into high\|K calcalkali series formed in about 40～31Ma.in Qiangtang area, into minor amount of leucite basalt and phonolite series of 26Ma., further into shoshonite series aged at 19～7Ma. in Cocoxili basin, until Quaternary shoshonite series in Karakunlun and Qilian Mt.\|Yumen region(Xiaoguo Chi etc.1999).Isotopes of Sr,Nd,Pb and trace elements in volcanic rocks provide wide range of information for the evolution of lithosphere in North Tibet after 45Ma. Present research shows that Na\|rich alkalic basalt series formed 44Ma. ago has the features of a primitive mantle in Sr,Nd,Pb isotopes. Along with the evolutionary tendency to high\|K calcalkali series and phonolite series, isotopes of Sr,Nd,Pb evolve towards EM2\|rich mantle end. The North Tibet is a compound continental mass combined from several terrains of different geological periods and the lithosphere mantle sees a complicated evolutionary history. Hence, the mixing of different rocks in ancient subduction zones and long history of metasomatism in the upper mantle offered excellent and favorable conditions for the formation of EM2 mantle end and for potassic enrichment. Isotopic evolutionary features indicate that the early magma came from the asthenosphere while later magmas were derived from partial remelting of lithosphere mantle.
文摘As one of the most distinct tectonic blocks on the Earth’s surface, Tibetan Plateau draw great attention of the geoscientists from the world. Many authors have proposed various kinds of the mechanism to try to clarify the evolution of the plateau. While many studies are often restricted to crustal units, the important role of the mantle part of the lithosphere (mantle lithosphere) during and after the collision process has not been appreciated widely. The purpose of the paper is to investigate the dynamic process of the thinning (delamination and convective removal) of the thickened lithosphere and its influence upon the uplift of the plateau.1\ Thickened lithosphere root\;Parsons and McKenzie (1978) proposed that the continental lithosphere could be thought of as consisting of two distinct parts: the mechanical and thermal boundary layers. The lower, and hotter, part is the thermal boundary layer. Its viscosity is sufficiently low that the force of gravity acting on density contrasts between the thermal boundary layer and the underlying mantle lead to the episodic sinking of the thermal boundary layer and its replacement by hot asthenosphere. When continental crust shortens and thickens, the mantle directly beneath it must also be displaced downward. In other words, mountain building process shortens horizontally and thickens vertically the mechanical boundary layer, and presumably the thermal boundary layer. And the process stretches the isotherms vertically, thus reducing the geothermal gradient. Houseman’s numerical experiments (1981) show that thickening of the thermal boundary layer enhances the density contrasts between it and the underlying asthenosphere, and so leads to its removal and replacement with hot asthenosphere. This phenomenon is called the instability of the thickened lithosphere.
文摘Interest in the ore\|forming histories of basins has grown rapid since 1960 and is now intensive. The main reason behind the acceleration is the increasing awareness that the natural processes responsible for generating metal deposits in the sedimentary basin from the source rocks of the beneath the basin and intensively hydrothermal activity in the basin. Observations made in different continental margin basin systems and superlarge deposits in Chinese Yunnan\|Guizhou\|Guangxi Province on the eastern margin of the Qingzang (Himalaya—Karakoram—Tibet) were investigated in terms of geodynamics of basin formation. Geotectonically, the area is situated in the conjoint between the Tethys—Himalaya and the Marginal\|Pacific tectonic domain, characterized by very complex geological structure, typical basin\|mountain tectonics, abundant Superlarge deposits.
文摘In this paper,218 long period Rayleigh wave records from 7 seismic station of CDSN are selected.We applied a partitioned waveform inversion to these data in order to construct a 3\|D model of shear velocity down to 400km depth in the crust and upper mantle of Qinghai\|Tibet plateau and Its Adjacent Regions (22°～44°N,70°～110°E).The first step of the waveform inversion used involved the matching of the waveforms of fundamental and highermost Ravleigh waves with waveforms synthesized from stratified models;in the second stage,the 3\|D model was constructed by solve linear constrains equation. The major structural features inferred from the surface waveform inversions can be summarized as follows:(1) There is a great contrast between surface waveform through Qinghai—Thibet plateau and the others.Main frequency of the former is lower than the latter, which indicate the crust depth of Qinghai—Tibet plateau is deeper than the others. In addition,the amplitude of about 30s period and 50s period is lower than both sides,which implied these exist lower velocity layer at about 25km depth and about 50km depth in Qinghai—Tibet plateau Crust.The former is common,the latter was argued because resolution of most method can not prove it.
