Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including: (1) parti...Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including: (1) partial melting of subducted young (〈25 Ma), hot and hydrated oceanic slab; (2) partial melting of thickened lower crust; (3) assimilation and fractional crystallization processes involving basaltic magma; (4) partial melting of delaminated lower crust; and (5) partial melting of hydrous garnet peridotite. The various origins for adakites provide important constraints on crustal growth and evolution throughout the Earth's history.展开更多
At first, the paper reviews, analyses and discusses uplifting mechanism and history, current situation of Tibet plateau. Coal\|bearing strata and coal seam were discovered by surveying and many rocks samples and struc...At first, the paper reviews, analyses and discusses uplifting mechanism and history, current situation of Tibet plateau. Coal\|bearing strata and coal seam were discovered by surveying and many rocks samples and structural samples were collected, which established the foundation for further studying. From all above, the paper has studied strata system, time\|spatial evolution, magma activity and its regularity of continental collision of Tibet plateau and rock’s mechanical features under high temperature and pressure. The paper has also summerized tectonic features, studied geological process by time coordinate and proposed multidisciplinary geological model. The paper has proposed evolutinal model of modern structural stress field in early quaternary, modern structural stress field and crustal deformation and explored geophysical field features and deep structures from man\|mad earthquake, regional gravity field and electrical structures, thus established geophysical field model. In addition, the paper proposed overall dynamic model according to stress field, displacement orientation and velocity restriction condition, indoplate collision to Eurasia.Thoroughly, the paper has studied and stated mechanical system, non\|stability, multibody collision mechanics and mantle plume mechanical model and established mechanical model. Finally, the paper has studied numeral simulation about spheric inter\|acting during continental collision of Tibet plateau, from this, analysed and inferred its evolution history.展开更多
There is a general consensus that Plate Tectonics can explain metallogenesis based on the collisions between oceanic and continental crust. For instance, the large-sized porphyry copper deposits that occur along the C...There is a general consensus that Plate Tectonics can explain metallogenesis based on the collisions between oceanic and continental crust. For instance, the large-sized porphyry copper deposits that occur along the Cordillera of the Andes around the east coast of the Pacific, and in the Phillipines, Malaysia and Indonesia along the western coast of the Pacific that sit upon the massive Pacific plates. They are considered to be typical of deposits resulting from collision between the oceanic and continental crust. Many experts, however, have long held a negative view about whether the collision between continental crusts can lead to metallogenesis. In recent years, Chinese geologists have proposed a new concept for "Continent-Continent Collision Metallogenesis" after many years of studying in the Qinghai--Tibet Plateau. Here we give a brief introduction to this idea.展开更多
Objective The tectonic characteristics and evolution of the Paleoproterozoic Jiao-Liao-Ji belt have been extensively studied in recent decades (Fig. 1 a). Two main models have been proposed for the formation of this...Objective The tectonic characteristics and evolution of the Paleoproterozoic Jiao-Liao-Ji belt have been extensively studied in recent decades (Fig. 1 a). Two main models have been proposed for the formation of this belt: a continental-or arc-continent collisional belt, and the opening and closure of an intra-continental rift. The main reasons for these ongoing debates are own to the complex composition, including metamorphosed volcano-sedimentary rocks, multiple pulses of granitic magmatism, meta-mafic intrusions, and tectono- metamorphic history. In addition, earlier work focused on the geochronology and metamorphic evolution, whereas the source properties, petrogenesis, and tectonic setting of the metamorphosed volcano-sedimentary sequence and meta- mafic intrusions are poorly understood.展开更多
Ample observational evidence shows that there is a northward crustal subduction zone underneath the Yarlung Zangbo suture between India and Eurasia. It penetrates Moho to a depth of about 100 km. There are probably mu...Ample observational evidence shows that there is a northward crustal subduction zone underneath the Yarlung Zangbo suture between India and Eurasia. It penetrates Moho to a depth of about 100 km. There are probably multiple such crustal subductions under the Himalayas. They are different from lithosphere subduction during oceanic collisions. The detected slabs in the upper mantle north of the Yarlung Zangbo suture can be interpreted as remains of the Indian Plate's mantle lithosphere. In contrary to ocean-continent subduction, the mantle lithosphere is de- laminated from the crust as the Indian Plate subducts underneath Eurasia. Existing structural images of the crust and upper mantle of the Tibetan Plateau reveal that there were both northward and southward subductions over different geological period, causing some seismic velocity annmalies around those subduction zones.展开更多
The main types of intrusive rocks in the Kelameili-Harlik Hercynian orogenic belt include calc-alkaline granites, diabase dykes, kaligranites and alkaline granites. Investigation in field geology, petrology, mineralog...The main types of intrusive rocks in the Kelameili-Harlik Hercynian orogenic belt include calc-alkaline granites, diabase dykes, kaligranites and alkaline granites. Investigation in field geology, petrology, mineralogy and geochemistry shows that the calc-alkaline granites belong to the syntexis-type (or I-type) and were formed in a pre-collisional magmatic arc environment. In consideration of the fact that kaligranites have many features of alkaline granites with higher consolidation temperatures than the calc-alkaline granites and show a discontinuity of minor element and REE evolution in respect to the calc-alkaline granites, they could not have been derived by differentiation of magmas for the calc-alkaline granites, but are likely to have been generated in an environment analogous to that for alkaline granites. The triplet of basic dyke swarms, kaligranites and alkaline granites could be regarded as a prominent indication of the initial stage of post-collisional delamination and extension. These rocks might have originated from underplating and intraplating of mantle-derived magmas at varying levels with varying degrees of partial melting, mixing, and interchange of crustal and mantle materials展开更多
We outline the post-Late Paleozoic (latest Permian to Cenozoic) collisional framework of the southern Great Altai (Central Asia) produced by the convergence between the Tuva-Mongolia and Junggar continental terran...We outline the post-Late Paleozoic (latest Permian to Cenozoic) collisional framework of the southern Great Altai (Central Asia) produced by the convergence between the Tuva-Mongolia and Junggar continental terranes (microplates). The collisional structures in the region classified on the basis of their geometry and deformation style, dynamic metamorphism, and compositions of tectonites are of three main types: (1) mosaic terranes made up of large weakly deformed Paleozoic blocks separated by younger shear zones; (2) contractional deformation systems involving structures formed in post-Late Paleozoic time, parallel faults oriented along collisional deformation systems, and relict lenses of Paleozoic orogenic complexes; and (3) isolated zones of dynamic metamorphism composed mostly of collisional tectonites different in composition and alteration grade.展开更多
This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core.The Himalayan orogeny was divided into three stages.Stage 60–40 Ma...This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core.The Himalayan orogeny was divided into three stages.Stage 60–40 Ma:The Himalayan crust thickened to~40 km through Barrovian-type metamorphism(15–25°C/km),and the Himalaya rose from<0 to~1000 m.Stage 40–16 Ma:The crust gradually thickened to 60–70 km,resulting in abundant high-grade metamorphism and anatexis(peak-P,15–25°C/km;peak-T,>30°C/km).The three sub-sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo-Himalayan thrust,High Himalayan thrust,and Main Central thrust,and the Himalaya rose to≥5,000 m.Stage 16–0 Ma:the mountain roots underwent localized delamination,causing asthenospheric upwelling and overprinting of the lower crust by ultra-high-temperature metamorphism(30–50°C/km),and the Himalaya reached the present elevation of~6,000 m.Underplating and imbricate thrusting dominated the Himalaya’growth and topographic rise,conforming to the critical taper wedge model.Localized delamination of mountain roots facilitated further topographic rise.Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events,contact metamorphism and rare metal mineralization,metamorphic decarbonation and the carbon cycle in collisional belts.展开更多
The Central India Tectonic Zone (CITZ) marks the trace of a major suture zone along which the south Indian and the north Indian continental blocks were assembled through subduction-accretion- collision tectonics in ...The Central India Tectonic Zone (CITZ) marks the trace of a major suture zone along which the south Indian and the north Indian continental blocks were assembled through subduction-accretion- collision tectonics in the Mesoproterozoic. The CITZ also witnessed the major, plume-related, late Cretaceous Deccan volcanic activity, covering substantial parts of the region with continental flood basalts and associated magmatic provinces. A number of major fault zones dissect the region, some of which are seismically active. Here we present results from gravity modeling along five regional profiles in the CITZ, and combine these results with magnetotelluric (MT) modeling results to explain the crustal architecture. The models show a resistive (more than 2000 Ω. m) and a normal density (2.70 g/cm3) upper crust suggesting dominant tonalite-trondhjemite-granodiorite (TTG) composition. There is a marked correlation between both high-density (2.95 g/cm3) and low-density (2.65 g/cm3) regions with high conductive zones (〈80 Ω. m) in the deep crust. We infer the presence of an interconnected grain boundary network of fluids or fluid-hosted structures, where the conductors are associated with gravity lows. Based on the conductive nature, we propose that the lower crustal rocks are fluid reservoirs, where the fluids occur as trapped phase within minerals, fluid-filled porosity, or as fluid-rich structural conduits. We envisage that substantial volume of fluids were transferred from mantle into the lower crust through the younger plume-related Deccan volcanism, as well as the reactivation, fracturing and expulsion of fluids transported to depth during the Mesoproterozoic subduction tectonics. Migration of the fluids into brittle fault zones such as the Narmada North Fault and the Narmada South Fault resulted in generating high pore pressures and weakening of the faults, as reflected in the seismicity. This inference is also supported by the presence of broad gravity lows near these faults, as well as the low velocity in the lower crust beneath regions of recent major earthquakes within the CITZ.展开更多
Ultrahigh-pressure(UHP) metamorphic rocks are distinctive products of crustal deep subduction,and are mainly exposed in continental subduction-collision terranes. UHP slices of continental crust are usually involved...Ultrahigh-pressure(UHP) metamorphic rocks are distinctive products of crustal deep subduction,and are mainly exposed in continental subduction-collision terranes. UHP slices of continental crust are usually involved in multistage exhumation and partial melting, which has obvious influence on the rheological features of the rocks, and thus significantly affect the dynamic behavior of subducted slices. Moreover,partial melting of UHP rocks have significant influence on element mobility and related isotope behavior within continental subduction zones, which is in turn crucial to chemical differentiation of the continental crust and to crust-mantle interaction.Partial melting can occur before, during or after the peak metamorphism of UHP rocks. Post-peak decompression melting has been better constrained by remelting experiments; however, because of multiple stages of decompression, retrogression and deformation, evidence of former melts in UHP rocks is often erased. Field evidence is among the most reliable criteria to infer partial melting. Glass and nanogranitoid inclusions are generally considered conclusive petrographic evidence. The residual assemblages after melt extraction are also significant to indicate partial melting in some cases. Besides field and petrographic evidence, bulk-rock and zircon trace-element geochemical features are also effective tools for recognizing partial melting of UHP rocks. Phase equilibrium modeling is an important petrological tool that is becoming more and more popular in P-T estimation of the evolution of metamorphic rocks; by taking into account the activity model of silicate melt, it can predict when partial melting occurred if the P-T path of a given rock is provided.UHP silicate melt is commonly leucogranitic and peraluminous in composition with high SiO_2,low MgO, FeO, MnO, TiO_2 and CaO, and variable K_2 O and Na_2 O contents. Mineralogy of nanogranites found in UHP rocks mainly consists of plagioclase + K-feldspar + quartz, plagioclase being commonly albite-rich.Trace element pattern of the melt is characterized by significant enrichment of large ion lithophile elements(LILE), depletion of heavy rare earth elements(HREE) and high field strength elements(HFSE),indicating garnet and rutile stability in the residual assemblage. In eclogites, significant Mg-isotope fractionation occurs between garnet and phengite; therefore, Mg isotopes may become an effective indicator for partial melting of eclogites.展开更多
According to tectono stratigraphical division principle, different units in Kangguertage Huangshan collision zone, Eastern Tianshan, are divided into order and disorder two types of stratum rock associations, which be...According to tectono stratigraphical division principle, different units in Kangguertage Huangshan collision zone, Eastern Tianshan, are divided into order and disorder two types of stratum rock associations, which belong to two kinds of different tectono volcanic activity belts. The collision ororeny and ductile shear zone have a strong space time coupling. Based on the island arc bearing volcanic rock on both sides of the collision zone, time of ore forming and rock forming, characteristics of collision granit, geochemical province, special multistage collision orogeny and intracontinental orogeny basin forming developed features have been found. Gold and copper deposits, with the relation to the collision orogeny, are divided into seven genetic types. The ten metallogenic zones are classified into two kinds of ore forming system of paleo continental margin. Metallogenesis of gold deposits can be classified into five stages. Gold and copper deposits are distributed in belts with the relation to the development of the collision orogeny. The distribution of main large scale copper deposits in the north part of the collision zone and most large middle scale gold deposits in the south part of the collision zone can direct the prospecting for gold and copper deposits. The actual targets are put forward.展开更多
Detailed facies analysis of the Neogene successions of the Pishin Belt (Katawaz Basin) has enabled documentation of successive depositional systems and paleogeographic settings of the basin formed by the collision o...Detailed facies analysis of the Neogene successions of the Pishin Belt (Katawaz Basin) has enabled documentation of successive depositional systems and paleogeographic settings of the basin formed by the collision of the northwestern continental margin of the Indian Plate and the Afghan Block. During the Early Miocene, subaerial sedimentation started after the final closure of the Katawaz Remnant Ocean. Based on detailed field data, twelve facies were recognized in Neogene successions exposed in the Pishin Belt. These facies were further organized into four facies associations i.e. channels, crevasse splay, natural levee and floodplain facies associations. Facies associations and variations provided ample evidence to recognize a number of fluvial architectural components in the succession e.g., low-sinuosity sandy braided river, mixed-load meandering, high-sinuosity meandering channels, single-story sandstone and/or conglomerate channels, lateral accretion surfaces (point bars) and alluvial fans. Neogene sedimentation in the Pishin Belt was mainly controlled by active tectonism and thrusting in response to the oblique collision of the Indian Plate with the Afghan Block of the Eurasian Plate along the Chaman-Nushki Fault. Post Miocene deformation of these formations successively caused them to contribute as an additional source terrain for the younger formations.展开更多
The studies of continental deep subduction and ultrahigh-pressure metamorphism have not only promoted the development of solid earth science in China, but also provided an excellent opportunity to advance the plate te...The studies of continental deep subduction and ultrahigh-pressure metamorphism have not only promoted the development of solid earth science in China, but also provided an excellent opportunity to advance the plate tectonics theory. In view of the nature of subducted crust, two types of subduction and collision have been respectively recognized in nature. On one hand, the crustal subduction occurs due to underflow of either oceanic crust (Pacific type) or continental crust (Alpine type). On the other hand, the continental collision proceeds by arc-continent collision (Himalaya-Tibet type) or continent-continent collision (Dabie-Sulu type). The key issues in the future study of continental dynamics are the chemical changes and differential exhumation in continental deep subduction zones, and the temporal-spatial transition from oceanic subduction to continental subduction.展开更多
Continental subduction and collision normally follows oceanic subduction,with the remarkable event of formation and exhumation of high-to ultra-high-pressure(HP-UHP)metamorphic rocks.Based on the summary of numerical ...Continental subduction and collision normally follows oceanic subduction,with the remarkable event of formation and exhumation of high-to ultra-high-pressure(HP-UHP)metamorphic rocks.Based on the summary of numerical geodynamic models,six modes of continental convergence have been identified:pure shear thickening,folding and buckling,one-sided steep subduction,flat subduction,two-sided subduction,and subducting slab break-off.In addition,the exhumation of HP-UHP rocks can be formulated into eight modes:thrust fault exhumation,buckling exhumation,material circulation,overpressure model,exhumation of a coherent crustal slice,episodic ductile extrusion,slab break-off induced eduction,and exhumation through fractured overriding lithosphere.During the transition from subduction to exhumation,the weakening and detachment of subducted continental crust are prerequisites.However,the dominant weakening mechanisms and their roles in the subduction channel are poorly constrained.To a first degree approximation,the mechanism of continental subduction and exhumation can be treated as a subduction channel flow model,which incorporates the competing effects of downward Couette(subduction)flow and upward Poiseuille(exhumation)flow in the subduction channel.However,the(de-)hydration effect plays significant roles in the deformation of subduction channel and overriding lithosphere,which thereby result in very different modes from the simple subduction channel flow.Three-dimensionality is another important issue with highlighting the along-strike differential modes of continental subduction,collision and exhumation in the same continental convergence belt.展开更多
Placing precise constraints on the timing of the India-Asia continental collision is essential to understand the successive geological and geomorphological evolution of the orogenic belt as well as the uplift mechanis...Placing precise constraints on the timing of the India-Asia continental collision is essential to understand the successive geological and geomorphological evolution of the orogenic belt as well as the uplift mechanism of the Tibetan Plateau and their effects on climate,environment and life.Based on the extensive study of the sedimentary record on both sides of the Yarlung-Zangbo suture zone in Tibet,we review here the present state of knowledge on the timing of collision onset,discuss its possible diachroneity along strike,and reconstruct the early structural and topographic evolution of the Himalayan collided range.We define continent-continent collision as the moment when the oceanic crust is completely consumed at one point where the two continental margins come into contact.We use two methods to constrain the timing of collision onset:(1) dating the provenance change from Indian to Asian recorded by deep-water turbidites near the suture zone,and(2) dating the age of unconformities on both sides of the suture zone.The first method allowed us to constrain precisely collision onset as middle Palaeocene(59±l Ma).Marine sedimentation persisted in the collisional zone for another 20-25 Ma locally in southern Tibet,and molassic-type deposition in the Indian foreland basin did not begin until another 10-15 Ma later.Available sedimentary evidence failed to firmly document any significant diachroneity of collision onset from the central Himalaya to the western Himalaya and Pakistan so far.Based on the Cenozoic stratigraphic record of the Tibetan Himalaya,four distinct stages can be identified in the early evolution of the Himalayan orogen:(1) middle Palaeocene-early Eocene earliest Eohimalayan stage(from 59 to 52 Ma):collision onset and filling of the deep-water trough along the suture zone while carbonate platform sedimentation persisted on the inner Indian margin;(2) early-middle Eocene early Eohimalayan stage(from 52 to 41 or 35 Ma):filling of intervening seaways and cessation of marine sedimentation;(3) late Eocene-Oligocene late Eohimalayan stage(from 41 to 25 Ma):huge gap in the sedimentary record both in the collision zone and in the Indian foreland;and(4) late Oligocene-early Miocene early Neohimalayan stage(from 26 to 17 Ma):rapid Himalayan growth and onset of molasse-type sedimentation in the Indian foreland basin.展开更多
基金financially supported by the National Nature Science Foundation of China(grant No. 41202037)
文摘Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including: (1) partial melting of subducted young (〈25 Ma), hot and hydrated oceanic slab; (2) partial melting of thickened lower crust; (3) assimilation and fractional crystallization processes involving basaltic magma; (4) partial melting of delaminated lower crust; and (5) partial melting of hydrous garnet peridotite. The various origins for adakites provide important constraints on crustal growth and evolution throughout the Earth's history.
文摘At first, the paper reviews, analyses and discusses uplifting mechanism and history, current situation of Tibet plateau. Coal\|bearing strata and coal seam were discovered by surveying and many rocks samples and structural samples were collected, which established the foundation for further studying. From all above, the paper has studied strata system, time\|spatial evolution, magma activity and its regularity of continental collision of Tibet plateau and rock’s mechanical features under high temperature and pressure. The paper has also summerized tectonic features, studied geological process by time coordinate and proposed multidisciplinary geological model. The paper has proposed evolutinal model of modern structural stress field in early quaternary, modern structural stress field and crustal deformation and explored geophysical field features and deep structures from man\|mad earthquake, regional gravity field and electrical structures, thus established geophysical field model. In addition, the paper proposed overall dynamic model according to stress field, displacement orientation and velocity restriction condition, indoplate collision to Eurasia.Thoroughly, the paper has studied and stated mechanical system, non\|stability, multibody collision mechanics and mantle plume mechanical model and established mechanical model. Finally, the paper has studied numeral simulation about spheric inter\|acting during continental collision of Tibet plateau, from this, analysed and inferred its evolution history.
文摘There is a general consensus that Plate Tectonics can explain metallogenesis based on the collisions between oceanic and continental crust. For instance, the large-sized porphyry copper deposits that occur along the Cordillera of the Andes around the east coast of the Pacific, and in the Phillipines, Malaysia and Indonesia along the western coast of the Pacific that sit upon the massive Pacific plates. They are considered to be typical of deposits resulting from collision between the oceanic and continental crust. Many experts, however, have long held a negative view about whether the collision between continental crusts can lead to metallogenesis. In recent years, Chinese geologists have proposed a new concept for "Continent-Continent Collision Metallogenesis" after many years of studying in the Qinghai--Tibet Plateau. Here we give a brief introduction to this idea.
基金supported by the National Science Foundation of China(grants No.41572169 and 41202136)China Geological Survey(grant No. 12120114021601)the Outlay Research Fund of the Institute of Geology,CAGS(grants No.J1507 and J1301)
文摘Objective The tectonic characteristics and evolution of the Paleoproterozoic Jiao-Liao-Ji belt have been extensively studied in recent decades (Fig. 1 a). Two main models have been proposed for the formation of this belt: a continental-or arc-continent collisional belt, and the opening and closure of an intra-continental rift. The main reasons for these ongoing debates are own to the complex composition, including metamorphosed volcano-sedimentary rocks, multiple pulses of granitic magmatism, meta-mafic intrusions, and tectono- metamorphic history. In addition, earlier work focused on the geochronology and metamorphic evolution, whereas the source properties, petrogenesis, and tectonic setting of the metamorphosed volcano-sedimentary sequence and meta- mafic intrusions are poorly understood.
基金National Natural Science Foundation of China (49374207 and 49974021).
文摘Ample observational evidence shows that there is a northward crustal subduction zone underneath the Yarlung Zangbo suture between India and Eurasia. It penetrates Moho to a depth of about 100 km. There are probably multiple such crustal subductions under the Himalayas. They are different from lithosphere subduction during oceanic collisions. The detected slabs in the upper mantle north of the Yarlung Zangbo suture can be interpreted as remains of the Indian Plate's mantle lithosphere. In contrary to ocean-continent subduction, the mantle lithosphere is de- laminated from the crust as the Indian Plate subducts underneath Eurasia. Existing structural images of the crust and upper mantle of the Tibetan Plateau reveal that there were both northward and southward subductions over different geological period, causing some seismic velocity annmalies around those subduction zones.
基金This rescarch was jointly supported by the NationalNatural Science Foundation of China Grant No.4917-2094National Key Project No.305with additionalsuppor for the analyses from the Modern AnalysisCentre of Nanjing University.
文摘The main types of intrusive rocks in the Kelameili-Harlik Hercynian orogenic belt include calc-alkaline granites, diabase dykes, kaligranites and alkaline granites. Investigation in field geology, petrology, mineralogy and geochemistry shows that the calc-alkaline granites belong to the syntexis-type (or I-type) and were formed in a pre-collisional magmatic arc environment. In consideration of the fact that kaligranites have many features of alkaline granites with higher consolidation temperatures than the calc-alkaline granites and show a discontinuity of minor element and REE evolution in respect to the calc-alkaline granites, they could not have been derived by differentiation of magmas for the calc-alkaline granites, but are likely to have been generated in an environment analogous to that for alkaline granites. The triplet of basic dyke swarms, kaligranites and alkaline granites could be regarded as a prominent indication of the initial stage of post-collisional delamination and extension. These rocks might have originated from underplating and intraplating of mantle-derived magmas at varying levels with varying degrees of partial melting, mixing, and interchange of crustal and mantle materials
基金supported by V.S. Sobolev Institute of Geology and Mineralogy Siberian Branch of Russian Academy of Sciences (basic project)
文摘We outline the post-Late Paleozoic (latest Permian to Cenozoic) collisional framework of the southern Great Altai (Central Asia) produced by the convergence between the Tuva-Mongolia and Junggar continental terranes (microplates). The collisional structures in the region classified on the basis of their geometry and deformation style, dynamic metamorphism, and compositions of tectonites are of three main types: (1) mosaic terranes made up of large weakly deformed Paleozoic blocks separated by younger shear zones; (2) contractional deformation systems involving structures formed in post-Late Paleozoic time, parallel faults oriented along collisional deformation systems, and relict lenses of Paleozoic orogenic complexes; and (3) isolated zones of dynamic metamorphism composed mostly of collisional tectonites different in composition and alteration grade.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research program(Grant No.2019QZKK0703)the National Natural Science Foundation of China(Grant Nos.41972065 and 41888101)+1 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2022065)the State Key Laboratory of Lithospheric Evolution(Grant No.E152510201).
文摘This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core.The Himalayan orogeny was divided into three stages.Stage 60–40 Ma:The Himalayan crust thickened to~40 km through Barrovian-type metamorphism(15–25°C/km),and the Himalaya rose from<0 to~1000 m.Stage 40–16 Ma:The crust gradually thickened to 60–70 km,resulting in abundant high-grade metamorphism and anatexis(peak-P,15–25°C/km;peak-T,>30°C/km).The three sub-sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo-Himalayan thrust,High Himalayan thrust,and Main Central thrust,and the Himalaya rose to≥5,000 m.Stage 16–0 Ma:the mountain roots underwent localized delamination,causing asthenospheric upwelling and overprinting of the lower crust by ultra-high-temperature metamorphism(30–50°C/km),and the Himalaya reached the present elevation of~6,000 m.Underplating and imbricate thrusting dominated the Himalaya’growth and topographic rise,conforming to the critical taper wedge model.Localized delamination of mountain roots facilitated further topographic rise.Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events,contact metamorphism and rare metal mineralization,metamorphic decarbonation and the carbon cycle in collisional belts.
文摘The Central India Tectonic Zone (CITZ) marks the trace of a major suture zone along which the south Indian and the north Indian continental blocks were assembled through subduction-accretion- collision tectonics in the Mesoproterozoic. The CITZ also witnessed the major, plume-related, late Cretaceous Deccan volcanic activity, covering substantial parts of the region with continental flood basalts and associated magmatic provinces. A number of major fault zones dissect the region, some of which are seismically active. Here we present results from gravity modeling along five regional profiles in the CITZ, and combine these results with magnetotelluric (MT) modeling results to explain the crustal architecture. The models show a resistive (more than 2000 Ω. m) and a normal density (2.70 g/cm3) upper crust suggesting dominant tonalite-trondhjemite-granodiorite (TTG) composition. There is a marked correlation between both high-density (2.95 g/cm3) and low-density (2.65 g/cm3) regions with high conductive zones (〈80 Ω. m) in the deep crust. We infer the presence of an interconnected grain boundary network of fluids or fluid-hosted structures, where the conductors are associated with gravity lows. Based on the conductive nature, we propose that the lower crustal rocks are fluid reservoirs, where the fluids occur as trapped phase within minerals, fluid-filled porosity, or as fluid-rich structural conduits. We envisage that substantial volume of fluids were transferred from mantle into the lower crust through the younger plume-related Deccan volcanism, as well as the reactivation, fracturing and expulsion of fluids transported to depth during the Mesoproterozoic subduction tectonics. Migration of the fluids into brittle fault zones such as the Narmada North Fault and the Narmada South Fault resulted in generating high pore pressures and weakening of the faults, as reflected in the seismicity. This inference is also supported by the presence of broad gravity lows near these faults, as well as the low velocity in the lower crust beneath regions of recent major earthquakes within the CITZ.
基金financially supported by the National Basic Research Program of China (Grant No. 2015CB856104)the National Natural Science Foundation of China (Grant No. 41273036)
文摘Ultrahigh-pressure(UHP) metamorphic rocks are distinctive products of crustal deep subduction,and are mainly exposed in continental subduction-collision terranes. UHP slices of continental crust are usually involved in multistage exhumation and partial melting, which has obvious influence on the rheological features of the rocks, and thus significantly affect the dynamic behavior of subducted slices. Moreover,partial melting of UHP rocks have significant influence on element mobility and related isotope behavior within continental subduction zones, which is in turn crucial to chemical differentiation of the continental crust and to crust-mantle interaction.Partial melting can occur before, during or after the peak metamorphism of UHP rocks. Post-peak decompression melting has been better constrained by remelting experiments; however, because of multiple stages of decompression, retrogression and deformation, evidence of former melts in UHP rocks is often erased. Field evidence is among the most reliable criteria to infer partial melting. Glass and nanogranitoid inclusions are generally considered conclusive petrographic evidence. The residual assemblages after melt extraction are also significant to indicate partial melting in some cases. Besides field and petrographic evidence, bulk-rock and zircon trace-element geochemical features are also effective tools for recognizing partial melting of UHP rocks. Phase equilibrium modeling is an important petrological tool that is becoming more and more popular in P-T estimation of the evolution of metamorphic rocks; by taking into account the activity model of silicate melt, it can predict when partial melting occurred if the P-T path of a given rock is provided.UHP silicate melt is commonly leucogranitic and peraluminous in composition with high SiO_2,low MgO, FeO, MnO, TiO_2 and CaO, and variable K_2 O and Na_2 O contents. Mineralogy of nanogranites found in UHP rocks mainly consists of plagioclase + K-feldspar + quartz, plagioclase being commonly albite-rich.Trace element pattern of the melt is characterized by significant enrichment of large ion lithophile elements(LILE), depletion of heavy rare earth elements(HREE) and high field strength elements(HFSE),indicating garnet and rutile stability in the residual assemblage. In eclogites, significant Mg-isotope fractionation occurs between garnet and phengite; therefore, Mg isotopes may become an effective indicator for partial melting of eclogites.
文摘According to tectono stratigraphical division principle, different units in Kangguertage Huangshan collision zone, Eastern Tianshan, are divided into order and disorder two types of stratum rock associations, which belong to two kinds of different tectono volcanic activity belts. The collision ororeny and ductile shear zone have a strong space time coupling. Based on the island arc bearing volcanic rock on both sides of the collision zone, time of ore forming and rock forming, characteristics of collision granit, geochemical province, special multistage collision orogeny and intracontinental orogeny basin forming developed features have been found. Gold and copper deposits, with the relation to the collision orogeny, are divided into seven genetic types. The ten metallogenic zones are classified into two kinds of ore forming system of paleo continental margin. Metallogenesis of gold deposits can be classified into five stages. Gold and copper deposits are distributed in belts with the relation to the development of the collision orogeny. The distribution of main large scale copper deposits in the north part of the collision zone and most large middle scale gold deposits in the south part of the collision zone can direct the prospecting for gold and copper deposits. The actual targets are put forward.
文摘Detailed facies analysis of the Neogene successions of the Pishin Belt (Katawaz Basin) has enabled documentation of successive depositional systems and paleogeographic settings of the basin formed by the collision of the northwestern continental margin of the Indian Plate and the Afghan Block. During the Early Miocene, subaerial sedimentation started after the final closure of the Katawaz Remnant Ocean. Based on detailed field data, twelve facies were recognized in Neogene successions exposed in the Pishin Belt. These facies were further organized into four facies associations i.e. channels, crevasse splay, natural levee and floodplain facies associations. Facies associations and variations provided ample evidence to recognize a number of fluvial architectural components in the succession e.g., low-sinuosity sandy braided river, mixed-load meandering, high-sinuosity meandering channels, single-story sandstone and/or conglomerate channels, lateral accretion surfaces (point bars) and alluvial fans. Neogene sedimentation in the Pishin Belt was mainly controlled by active tectonism and thrusting in response to the oblique collision of the Indian Plate with the Afghan Block of the Eurasian Plate along the Chaman-Nushki Fault. Post Miocene deformation of these formations successively caused them to contribute as an additional source terrain for the younger formations.
基金Supported by the Chinese Academy of Sciences (Grant No. kzcx2-yw-131)Ministry of Science and Technology of China (Grant No. 2009CB825000)
文摘The studies of continental deep subduction and ultrahigh-pressure metamorphism have not only promoted the development of solid earth science in China, but also provided an excellent opportunity to advance the plate tectonics theory. In view of the nature of subducted crust, two types of subduction and collision have been respectively recognized in nature. On one hand, the crustal subduction occurs due to underflow of either oceanic crust (Pacific type) or continental crust (Alpine type). On the other hand, the continental collision proceeds by arc-continent collision (Himalaya-Tibet type) or continent-continent collision (Dabie-Sulu type). The key issues in the future study of continental dynamics are the chemical changes and differential exhumation in continental deep subduction zones, and the temporal-spatial transition from oceanic subduction to continental subduction.
基金supported by the Start-up Research Fund from Institute of Geology of CAGS(Grant No.J1219)National Natural Science Foundation of China(Grant No.40921001)China Geological Survey Projects(Grant Nos.1212011121275,1212011120161)and Sinoprobe Project
文摘Continental subduction and collision normally follows oceanic subduction,with the remarkable event of formation and exhumation of high-to ultra-high-pressure(HP-UHP)metamorphic rocks.Based on the summary of numerical geodynamic models,six modes of continental convergence have been identified:pure shear thickening,folding and buckling,one-sided steep subduction,flat subduction,two-sided subduction,and subducting slab break-off.In addition,the exhumation of HP-UHP rocks can be formulated into eight modes:thrust fault exhumation,buckling exhumation,material circulation,overpressure model,exhumation of a coherent crustal slice,episodic ductile extrusion,slab break-off induced eduction,and exhumation through fractured overriding lithosphere.During the transition from subduction to exhumation,the weakening and detachment of subducted continental crust are prerequisites.However,the dominant weakening mechanisms and their roles in the subduction channel are poorly constrained.To a first degree approximation,the mechanism of continental subduction and exhumation can be treated as a subduction channel flow model,which incorporates the competing effects of downward Couette(subduction)flow and upward Poiseuille(exhumation)flow in the subduction channel.However,the(de-)hydration effect plays significant roles in the deformation of subduction channel and overriding lithosphere,which thereby result in very different modes from the simple subduction channel flow.Three-dimensionality is another important issue with highlighting the along-strike differential modes of continental subduction,collision and exhumation in the same continental convergence belt.
基金supported by the National Natural Science Foundation of China(Grant No.41525007)the Stratigraphic Pilot Science and Technology Projects of the Chinese Academy of Sciences(Class B)(Grant No.XDB03010400)
文摘Placing precise constraints on the timing of the India-Asia continental collision is essential to understand the successive geological and geomorphological evolution of the orogenic belt as well as the uplift mechanism of the Tibetan Plateau and their effects on climate,environment and life.Based on the extensive study of the sedimentary record on both sides of the Yarlung-Zangbo suture zone in Tibet,we review here the present state of knowledge on the timing of collision onset,discuss its possible diachroneity along strike,and reconstruct the early structural and topographic evolution of the Himalayan collided range.We define continent-continent collision as the moment when the oceanic crust is completely consumed at one point where the two continental margins come into contact.We use two methods to constrain the timing of collision onset:(1) dating the provenance change from Indian to Asian recorded by deep-water turbidites near the suture zone,and(2) dating the age of unconformities on both sides of the suture zone.The first method allowed us to constrain precisely collision onset as middle Palaeocene(59±l Ma).Marine sedimentation persisted in the collisional zone for another 20-25 Ma locally in southern Tibet,and molassic-type deposition in the Indian foreland basin did not begin until another 10-15 Ma later.Available sedimentary evidence failed to firmly document any significant diachroneity of collision onset from the central Himalaya to the western Himalaya and Pakistan so far.Based on the Cenozoic stratigraphic record of the Tibetan Himalaya,four distinct stages can be identified in the early evolution of the Himalayan orogen:(1) middle Palaeocene-early Eocene earliest Eohimalayan stage(from 59 to 52 Ma):collision onset and filling of the deep-water trough along the suture zone while carbonate platform sedimentation persisted on the inner Indian margin;(2) early-middle Eocene early Eohimalayan stage(from 52 to 41 or 35 Ma):filling of intervening seaways and cessation of marine sedimentation;(3) late Eocene-Oligocene late Eohimalayan stage(from 41 to 25 Ma):huge gap in the sedimentary record both in the collision zone and in the Indian foreland;and(4) late Oligocene-early Miocene early Neohimalayan stage(from 26 to 17 Ma):rapid Himalayan growth and onset of molasse-type sedimentation in the Indian foreland basin.