Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogenei...Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture,structure, mineral species and geochemical compositions at different scales from small dike to large batholith. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. Although granitic magma has high viscosity because of its elevated SiO2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation,mineral species and its chemical variations, and geochemical compositions. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. On the contrary, flow segregation or dynamic sorting may be more important. Accordingly, granite can be divided into unfractionated, fractionated(including weakly fractionated and highly fractionated) and cumulated types, according to the differentiation degree. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. We proposed that highly fractionated granites are an important sig展开更多
This paper aims at exploring the tectonic characteristics of the South China Continent （SCC） and extracting the universal tec- tonic rules from these characteristics,to help enrich the plate tectonic theory and bett...This paper aims at exploring the tectonic characteristics of the South China Continent （SCC） and extracting the universal tec- tonic rules from these characteristics,to help enrich the plate tectonic theory and better understand the continental dynamic system. For this purpose, here we conduct a multi-disciplinary investigation and combine it with the previous studies to reas- sess the tectonics and evolution of SCC and propose that the tectonic framework of the continent comprises two blocks, three types of tectonic units, four deformation systems, and four evolutionary stages with distinctive mechanism and tectonic characteris- tics since the Neoproterozoic. The four evolutionary stages are： （1） The amalgamation and break-up of the Neoproterozoic plates, typically the intracontinental rifting. （2） The early Paleozoic and Mesozoic intracontinental orogeny confined by plate tectonics, forming two composite tectonic domains. （3） The parallel operation of the Yangtze cratonization and intracontinental orogeny, and multi-phase reactivation of the Yangtze craton. （4） The association and differentiation evolution of plate tectonics and intraconti- nental tectonics, and the dynamic characteristics under the Meso-Cenozoic modem global plate tectonic regime.展开更多
Crustal subduction and continental collision is the core of plate tectonics theory. Understanding the formation and evolution of continental collision orogens is a key to develop the theory of plate tectonics. Differe...Crustal subduction and continental collision is the core of plate tectonics theory. Understanding the formation and evolution of continental collision orogens is a key to develop the theory of plate tectonics. Different types of subduction zones have been categorized based on the nature of subducted crust. Two types of collisional orogens, i.e. arc-continent and continent-continent collisional orogens, have been recognized based on the nature of collisional blocks and the composition of derivative rocks. Arc-continent collisional orogens contain both ancient and juvenile crustal rocks, and reworking of those rocks at the post-collisional stage generates magmatic rocks with different geochemical compositions. If an orogen is built by collision between two relatively old continental blocks, post-collisional magmatic rocks are only derived from reworking of the old crustal rocks. Collisional orogens undergo reactivation and reworking at action of lithosphere extension, with inheritance not only in the tectonic regime but also in the geochemical compositions of reworked products(i.e., magmatic rocks). In order to unravel basic principles for the evolution of continental tectonics at the post-collisional stages, it is necessary to investigate the reworking of orogenic belts in the post-collisional regime, to recognize physicochemical differences in deep continental collision zones, and to understand petrogenetic links between the nature of subducted crust and post-collisional magmatic rocks. Afterwards we are in a position to build the systematics of continental tectonics and thus to develop the plate tectonics theory.展开更多
The South China Block was formed through the collisional orogeny between the Cathaysia Block and the Yangtze Block in the Early Neoproterozoic.The northern,western and southern sides of the South China Block were affe...The South China Block was formed through the collisional orogeny between the Cathaysia Block and the Yangtze Block in the Early Neoproterozoic.The northern,western and southern sides of the South China Block were affected by disappearance of the Paleo-Tethyan Ocean during the Paleozoic.The southern and northern sides of the South China Block were respectively collided with the Indo-China Block and North China Block in the latest Paleozoic to form the basic framework of the Eastern China.The Eastern China has been affected by the westward subduction of the Pacific Plate since the Mesozoic.Therefore,the South China Block was influenced by the three major tectonic systems,leading to a superposed compound tectonics.The comparative study of the Mesozoic geology between the South China Block and its surrounding areas suggests that although the Mesozoic South China Block was adjacent to the subduction zone of the western Pacific,no juvenile arc-type crust has been found in the eastern margin.The main Mesozoic geology in South China is characterized by reworking of ancient continental margins to intracontinental tectonics,lacking oceanic arc basalts and continental arc andesites.Therefore,a key to understanding of the Mesozoic geology in South China is to determine the temporal-spatial distribution and tectonic evolution of Mesozoic magmatic rocks in this region.This paper presents a review on the tectonic evolution of the South China Block through summarizing the magmatic rock records from the compressional to extensional tectonic process with the transition at the three juncture zones and using the deformation and geophysic data from the deep part of the South China continental lithosphere.Our attempt is to promote the study of South China’s geology and to make it as a typical target for development of plate tectonic theory.展开更多
The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with em...The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with emplacement ages mainly at Late Triassic, Late Jurassic and Early Cretaceous. The Late Triassic alkaline rocks and the Late Jurassic granitoids only crop out in the eastern part of the Sulu orogen, whereas the Early Cretaceous magmatic rocks occur as massive granitoids, sporadic intermedi- ate-mafic intrusive and volcanic rocks throughout the Dabie-Sulu orogenic belt. Despite the different ages for their emplacement, the Mesozoic magmatic rocks are all characterized not only by enrichment of LREE and LILE but depletion of HFSE, but also by high initial Sr isotope ratios, low εNd(t) values and low radiogeneic Pb isotope compositions. Some zircons from the Jurassic and Cretaceous granitoids contain inherited magmatic cores with Neoprotozoic and Triassic U-Pb ages. Most of the Cretaceous mafic rocks have zircon δ18O values and whole-rock δ13C values lower than those for the normal mantle. A systematic comparison with adjacent UHP metaigneous rocks shows that the Mesozoic granitoids and mafic rocks have elemental and isotopic features similar to the UHP metagranite and metabasite, respectively. This indicates that these magmatic and metamorphic rocks share the diagnostic features of lithospheric source that has tectonic affinity to the northern edge of the South China Block. Their precursors underwent the UHP metamorphism and the post-collisional anatexis, respectively at different times and depths. Therefore, the Mesozoic magmatic rocks were derived from anatexis of the subducted continental lithosphere itself beneath the collision-thickened orogen; the geodynamic mechanism of the post-collisional magmatisms is tectonic collapse of orogenic roots in response to lithospheric extension.展开更多
The Mianle tectonic zone (Mianle zone), an ancient suture zone in addition to the Shangdan suture in the Qinling-Dabie orogenic belt, marks an important tectonic division geo-logically separating north from south and ...The Mianle tectonic zone (Mianle zone), an ancient suture zone in addition to the Shangdan suture in the Qinling-Dabie orogenic belt, marks an important tectonic division geo-logically separating north from south and connecting east with west in China continent. To de-termine present structural geometry and kinematics in the Mianle tectonic zone and to recon-struct the formation and evolution history involving plate subduction and collision in the Qinling-Dabie orogenic belt, through a multidisciplinary study, are significant for exploring the mountain-building orogenesis of the central orogenic system and the entire process of the major Chinese continental amalgamation during the Indosinian.展开更多
This paper presents a review on the rock associations, geochemistry, and spatial distribution of Mesozoic-Paleogene igneous rocks in Northeast Asia. The record of magmatism is used to evaluate the spatial-temporal ext...This paper presents a review on the rock associations, geochemistry, and spatial distribution of Mesozoic-Paleogene igneous rocks in Northeast Asia. The record of magmatism is used to evaluate the spatial-temporal extent and influence of multiple tectonic regimes during the Mesozoic, as well as the onset and history of Paleo-Pacific slab subduction beneath Eurasian continent. Mesozoic-Paleogene magmatism at the continental margin of Northeast Asia can be subdivided into nine stages that took place in the Early-Middle Triassic, Late Triassic, Early Jurassic, Middle Jurassic, Late Jurassic, early Early Cretaceous, late Early Cretaceous, Late Cretaceous, and Paleogene, respectively. The Triassic magmatism is mainly composed of adakitic rocks,bimodal rocks, alkaline igneous rocks, and A-type granites and rhyolites that formed in syn-collisional to post-collisional extensional settings related to the final closure of the Paleo-Asian Ocean. However, Triassic calc-alkaline igneous rocks in the Erguna-Xing'an massifs were associated with the southward subduction of the Mongol-Okhotsk oceanic slab. A passive continental margin setting existed in Northeast Asia during the Triassic. Early Jurassic calc-alkaline igneous rocks have a geochemical affinity to arc-like magmatism, whereas coeval intracontinental magmatism is composed of bimodal igneous rocks and A-type granites. Spatial variations in the potassium contents of Early Jurassic igneous rocks from the continental margin to intracontinental region, together with the presence of an Early Jurassic accretionary complex, reveal that the onset of the PaleoPacific slab subduction beneath Eurasian continent occurred in the Early Jurassic. Middle Jurassic to early Early Cretaceous magmatism did not take place at the continental margin of Northeast Asia. This observation, combined with the occurrence of low-altitude biological assemblages and the age population of detrital zircons in an Early Cretaceous accretionary complex,indicates that a strike-slip tectonic regime existed b展开更多
Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemi...Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and87Sr/86Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.展开更多
Continental orogens on Earth can be classified into accretionary orogen and collisional orogen.Magmatism in orogens occurs in every periods of an orogenic cycle,from oceanic subduction,continental collision to orogeni...Continental orogens on Earth can be classified into accretionary orogen and collisional orogen.Magmatism in orogens occurs in every periods of an orogenic cycle,from oceanic subduction,continental collision to orogenic collapse.Continental collision requires the existence of prior oceanic subduction zone.It is generally assumed that the prerequisite of continental deep subduction is oceanic subduction and its drag force to the connecting passive-margin continental lithosphere during continental collision.Continental subduction and collision lead to the thickening and uplift of crust,but the formation time of the related magmatism in orogens depends on the heating mechanism of lithosphere.The accretionary orogens,on the other hand,have no strong continental collision,deep subduction,no large scale of crustal thrusting,thickening and uplift,and no UHP eclogite-facies metamorphic rocks related to continental deep subduction.Even though arc crust could be significantly thickened during oceanic subduction,it is still doubtful that syn-or post-collisional magmatism would be generated.In collisional orogens,due to continental deep subduction and significant crustal thickening,the UHP metamorphosed oceanic and continental crusts will experience decompression melting during exhumation,generating syn-collisional magmatism.During the orogen unrooting and collapse,post-collisional magmatism develops in response to lithosphere extension and upwelling of asthenospheric mantle,marking the end of an orogenic cycle.Therefore,magmatism in orogens can occur during the continental deep subduction,exhumation and uplift after detachment of subducted oceanic crust from continental crust,and extensional collapse.The time span from continental collision to collapse and erosion of orogens(the end of orogenic cycle)is 50–85 Myr.Collisional orogens are the key sites for understanding continental deep subduction,exhumation,uplift and orogenic collapse.Magmatism in collisional orogens plays important roles in continental reworking and net g展开更多
There are large-scale Mesozoic bimodal igneous rock associations on the continental margin of southeastern China. They aroused extensive attention in the 1980s because of their specific tectonic implications, and have...There are large-scale Mesozoic bimodal igneous rock associations on the continental margin of southeastern China. They aroused extensive attention in the 1980s because of their specific tectonic implications, and have been found frequently during recent geological surveys. This paper reviews the studies of regional Mesozoic bimodal rocks, and concludes that they can be subdivided into three stages, i.e., the Early Jurassic (209-170 Ma, the first (Ⅰ) stage), the Late Jurassic-early Early Cretaceous (154-121 Ma, the second (Ⅱ) stage), and the late Early Cretaceous-Late Cretaceous (115-85 Ma, the third (Ⅲ) stage). These three stages of bimodal rocks were formed in different tectonic settings, and are important indicators for regional Mesozoic tectonic evolution.展开更多
The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system ...The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system in the north and a latest PaleozoicMesozoic collisional orogenic system in the south, it may serve as an ideal place to study the tectonic evolution between the North and South China Blocks. The available literature data in the past 20 years indicate that the tectonic processes of the Tongbai-Hong'an orogen involved four stages during the Phanerozoic:(1) Early Paleozoic(490–420 Ma) oceanic subduction, arc magmatism and arc-continent collision created a new Andean-type active continental margin on the North China Block;(2) Late Paleozoic(340–310 Ma) oceanic subduction and accretion generated separated paired metamorphic belts: a medium P/T Wuguan-Guishan complex belt in the south of the Shandan-Songpa fault and a high P/T Xiongdian eclogite belt in the northern edge of the Mesozoic HP metamorphic terrane;(3) Latest Paleozoic-Early Mesozoic(255–200 Ma) continental subduction and collision formed the Tongbai HP terrane in the west and the Hong'an HP/UHP terrane in the east as a consequence of deep subduction towards the east and syn-subduction detachment/exhumation of the down-going slab;(4) Late Mesozoic(140–120 Ma) extension, voluminous magma intrusion and tectonic extrusion led to the final exhumation of the Tongbai-Hong'an-Dabie HP/UHP terrane and the wedge-shaped architecture of the terrane narrowing towards the west. However, many open questions still remain about the details of each evolutionary stage and earlier history of the orogen. Besides an extensive study directly on the Tongbai-Hong'an orogen in the future, integrated investigation on the "soft-collisional" Qinling orogen in the west and the "hard-collisional" Dabie-Sulu orogen in the east is required to establish a general tectonic model for the whole Qinling-TongbaiHong'an-Dabie-Sulu orogenic 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 Eoce展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 41130313)by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB03010200)
文摘Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture,structure, mineral species and geochemical compositions at different scales from small dike to large batholith. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. Although granitic magma has high viscosity because of its elevated SiO2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation,mineral species and its chemical variations, and geochemical compositions. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. On the contrary, flow segregation or dynamic sorting may be more important. Accordingly, granite can be divided into unfractionated, fractionated(including weakly fractionated and highly fractionated) and cumulated types, according to the differentiation degree. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. We proposed that highly fractionated granites are an important sig
基金supported by the special grant of Ministry of Science and Technology of the People’s Republic of China for State Key Laboratory of Continental Dynamics,Northwest University,the key research project of Sinopec Group(Grant No.YPH08012)the National Natural Science Foundation of China(Grant Nos.41190072,41190073,41190074,41190070)
文摘This paper aims at exploring the tectonic characteristics of the South China Continent （SCC） and extracting the universal tec- tonic rules from these characteristics,to help enrich the plate tectonic theory and better understand the continental dynamic system. For this purpose, here we conduct a multi-disciplinary investigation and combine it with the previous studies to reas- sess the tectonics and evolution of SCC and propose that the tectonic framework of the continent comprises two blocks, three types of tectonic units, four deformation systems, and four evolutionary stages with distinctive mechanism and tectonic characteris- tics since the Neoproterozoic. The four evolutionary stages are： （1） The amalgamation and break-up of the Neoproterozoic plates, typically the intracontinental rifting. （2） The early Paleozoic and Mesozoic intracontinental orogeny confined by plate tectonics, forming two composite tectonic domains. （3） The parallel operation of the Yangtze cratonization and intracontinental orogeny, and multi-phase reactivation of the Yangtze craton. （4） The association and differentiation evolution of plate tectonics and intraconti- nental tectonics, and the dynamic characteristics under the Meso-Cenozoic modem global plate tectonic regime.
基金supported by funds from the National Basic Research Program of China(Grant No.2015CB856100)the National Natural Science Foundation of China(Grant No.41221062)
文摘Crustal subduction and continental collision is the core of plate tectonics theory. Understanding the formation and evolution of continental collision orogens is a key to develop the theory of plate tectonics. Different types of subduction zones have been categorized based on the nature of subducted crust. Two types of collisional orogens, i.e. arc-continent and continent-continent collisional orogens, have been recognized based on the nature of collisional blocks and the composition of derivative rocks. Arc-continent collisional orogens contain both ancient and juvenile crustal rocks, and reworking of those rocks at the post-collisional stage generates magmatic rocks with different geochemical compositions. If an orogen is built by collision between two relatively old continental blocks, post-collisional magmatic rocks are only derived from reworking of the old crustal rocks. Collisional orogens undergo reactivation and reworking at action of lithosphere extension, with inheritance not only in the tectonic regime but also in the geochemical compositions of reworked products(i.e., magmatic rocks). In order to unravel basic principles for the evolution of continental tectonics at the post-collisional stages, it is necessary to investigate the reworking of orogenic belts in the post-collisional regime, to recognize physicochemical differences in deep continental collision zones, and to understand petrogenetic links between the nature of subducted crust and post-collisional magmatic rocks. Afterwards we are in a position to build the systematics of continental tectonics and thus to develop the plate tectonics theory.
基金financially supported by the China Geology Survey(Grant Nos.1212011121098,1212010611805,12010911012,1212011120120)International Cooperation Program for Chinese Science and Technology(Grant No.2011DFA22460)Department of Science and Technology of Zhejiang Province of China(Grant No.2014C33023)
文摘The South China Block was formed through the collisional orogeny between the Cathaysia Block and the Yangtze Block in the Early Neoproterozoic.The northern,western and southern sides of the South China Block were affected by disappearance of the Paleo-Tethyan Ocean during the Paleozoic.The southern and northern sides of the South China Block were respectively collided with the Indo-China Block and North China Block in the latest Paleozoic to form the basic framework of the Eastern China.The Eastern China has been affected by the westward subduction of the Pacific Plate since the Mesozoic.Therefore,the South China Block was influenced by the three major tectonic systems,leading to a superposed compound tectonics.The comparative study of the Mesozoic geology between the South China Block and its surrounding areas suggests that although the Mesozoic South China Block was adjacent to the subduction zone of the western Pacific,no juvenile arc-type crust has been found in the eastern margin.The main Mesozoic geology in South China is characterized by reworking of ancient continental margins to intracontinental tectonics,lacking oceanic arc basalts and continental arc andesites.Therefore,a key to understanding of the Mesozoic geology in South China is to determine the temporal-spatial distribution and tectonic evolution of Mesozoic magmatic rocks in this region.This paper presents a review on the tectonic evolution of the South China Block through summarizing the magmatic rock records from the compressional to extensional tectonic process with the transition at the three juncture zones and using the deformation and geophysic data from the deep part of the South China continental lithosphere.Our attempt is to promote the study of South China’s geology and to make it as a typical target for development of plate tectonic theory.
基金Supported by the Chinese Academy of Sciences (Grant No. KZCX2-YW-131)the Chinese Ministry of Science and Technology (Grant No. 2009CB825004)National Natural Science Foundation of China (Grant No. 40673009)
文摘The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with emplacement ages mainly at Late Triassic, Late Jurassic and Early Cretaceous. The Late Triassic alkaline rocks and the Late Jurassic granitoids only crop out in the eastern part of the Sulu orogen, whereas the Early Cretaceous magmatic rocks occur as massive granitoids, sporadic intermedi- ate-mafic intrusive and volcanic rocks throughout the Dabie-Sulu orogenic belt. Despite the different ages for their emplacement, the Mesozoic magmatic rocks are all characterized not only by enrichment of LREE and LILE but depletion of HFSE, but also by high initial Sr isotope ratios, low εNd(t) values and low radiogeneic Pb isotope compositions. Some zircons from the Jurassic and Cretaceous granitoids contain inherited magmatic cores with Neoprotozoic and Triassic U-Pb ages. Most of the Cretaceous mafic rocks have zircon δ18O values and whole-rock δ13C values lower than those for the normal mantle. A systematic comparison with adjacent UHP metaigneous rocks shows that the Mesozoic granitoids and mafic rocks have elemental and isotopic features similar to the UHP metagranite and metabasite, respectively. This indicates that these magmatic and metamorphic rocks share the diagnostic features of lithospheric source that has tectonic affinity to the northern edge of the South China Block. Their precursors underwent the UHP metamorphism and the post-collisional anatexis, respectively at different times and depths. Therefore, the Mesozoic magmatic rocks were derived from anatexis of the subducted continental lithosphere itself beneath the collision-thickened orogen; the geodynamic mechanism of the post-collisional magmatisms is tectonic collapse of orogenic roots in response to lithospheric extension.
基金This work was supported by the National Natu-ral Science Foundation of China (Grant Nos. 49732080, 40234041).
文摘The Mianle tectonic zone (Mianle zone), an ancient suture zone in addition to the Shangdan suture in the Qinling-Dabie orogenic belt, marks an important tectonic division geo-logically separating north from south and connecting east with west in China continent. To de-termine present structural geometry and kinematics in the Mianle tectonic zone and to recon-struct the formation and evolution history involving plate subduction and collision in the Qinling-Dabie orogenic belt, through a multidisciplinary study, are significant for exploring the mountain-building orogenesis of the central orogenic system and the entire process of the major Chinese continental amalgamation during the Indosinian.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41330206 & 41702051)the National Key Research and Development Project (Grant No. 2016YFC0600403)the China Postdoctoral Science Foundation (Grant Nos. 2017T100204 & 2017M611314)
文摘This paper presents a review on the rock associations, geochemistry, and spatial distribution of Mesozoic-Paleogene igneous rocks in Northeast Asia. The record of magmatism is used to evaluate the spatial-temporal extent and influence of multiple tectonic regimes during the Mesozoic, as well as the onset and history of Paleo-Pacific slab subduction beneath Eurasian continent. Mesozoic-Paleogene magmatism at the continental margin of Northeast Asia can be subdivided into nine stages that took place in the Early-Middle Triassic, Late Triassic, Early Jurassic, Middle Jurassic, Late Jurassic, early Early Cretaceous, late Early Cretaceous, Late Cretaceous, and Paleogene, respectively. The Triassic magmatism is mainly composed of adakitic rocks,bimodal rocks, alkaline igneous rocks, and A-type granites and rhyolites that formed in syn-collisional to post-collisional extensional settings related to the final closure of the Paleo-Asian Ocean. However, Triassic calc-alkaline igneous rocks in the Erguna-Xing'an massifs were associated with the southward subduction of the Mongol-Okhotsk oceanic slab. A passive continental margin setting existed in Northeast Asia during the Triassic. Early Jurassic calc-alkaline igneous rocks have a geochemical affinity to arc-like magmatism, whereas coeval intracontinental magmatism is composed of bimodal igneous rocks and A-type granites. Spatial variations in the potassium contents of Early Jurassic igneous rocks from the continental margin to intracontinental region, together with the presence of an Early Jurassic accretionary complex, reveal that the onset of the PaleoPacific slab subduction beneath Eurasian continent occurred in the Early Jurassic. Middle Jurassic to early Early Cretaceous magmatism did not take place at the continental margin of Northeast Asia. This observation, combined with the occurrence of low-altitude biological assemblages and the age population of detrital zircons in an Early Cretaceous accretionary complex,indicates that a strike-slip tectonic regime existed b
基金The authors are grateful to Dr. Lu Huayu from the State Key Laboratory of Loess and QuaternaryGeology for his assistance in field work. This work was supported by NKBRSF (G1999043400), National Natural Science Foundation of China (Grant No. 49725307) a
文摘Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and87Sr/86Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.
基金supported by the National Basic Research Program of China(Grant No.2015CB856105)the National Natural Science Foundation of China(Grant Nos.41372060,41430207,41130314,41121062)the Basic Geological Survey Programs of China Geological Survey(Grant No.1212011121258)
文摘Continental orogens on Earth can be classified into accretionary orogen and collisional orogen.Magmatism in orogens occurs in every periods of an orogenic cycle,from oceanic subduction,continental collision to orogenic collapse.Continental collision requires the existence of prior oceanic subduction zone.It is generally assumed that the prerequisite of continental deep subduction is oceanic subduction and its drag force to the connecting passive-margin continental lithosphere during continental collision.Continental subduction and collision lead to the thickening and uplift of crust,but the formation time of the related magmatism in orogens depends on the heating mechanism of lithosphere.The accretionary orogens,on the other hand,have no strong continental collision,deep subduction,no large scale of crustal thrusting,thickening and uplift,and no UHP eclogite-facies metamorphic rocks related to continental deep subduction.Even though arc crust could be significantly thickened during oceanic subduction,it is still doubtful that syn-or post-collisional magmatism would be generated.In collisional orogens,due to continental deep subduction and significant crustal thickening,the UHP metamorphosed oceanic and continental crusts will experience decompression melting during exhumation,generating syn-collisional magmatism.During the orogen unrooting and collapse,post-collisional magmatism develops in response to lithosphere extension and upwelling of asthenospheric mantle,marking the end of an orogenic cycle.Therefore,magmatism in orogens can occur during the continental deep subduction,exhumation and uplift after detachment of subducted oceanic crust from continental crust,and extensional collapse.The time span from continental collision to collapse and erosion of orogens(the end of orogenic cycle)is 50–85 Myr.Collisional orogens are the key sites for understanding continental deep subduction,exhumation,uplift and orogenic collapse.Magmatism in collisional orogens plays important roles in continental reworking and net g
基金the NationalNatural Science Foundation of China(Grant 40002005)the 1:250,000-scale Regional Survey Program-theShengxian sheet(No.20001300006141) the ChinaGeological Survey Comprehensive Research Program(No.200113000053).
文摘There are large-scale Mesozoic bimodal igneous rock associations on the continental margin of southeastern China. They aroused extensive attention in the 1980s because of their specific tectonic implications, and have been found frequently during recent geological surveys. This paper reviews the studies of regional Mesozoic bimodal rocks, and concludes that they can be subdivided into three stages, i.e., the Early Jurassic (209-170 Ma, the first (Ⅰ) stage), the Late Jurassic-early Early Cretaceous (154-121 Ma, the second (Ⅱ) stage), and the late Early Cretaceous-Late Cretaceous (115-85 Ma, the third (Ⅲ) stage). These three stages of bimodal rocks were formed in different tectonic settings, and are important indicators for regional Mesozoic tectonic evolution.
基金supported by the National Basic Research Program of China(Grant Nos.2015CB856104,2009CB825006)the National Natural Science Foundation of China(Grant Nos.41472064,40672047)the Geological Investigation Project of China Geological Survey(Grant No.1212010711812)
文摘The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system in the north and a latest PaleozoicMesozoic collisional orogenic system in the south, it may serve as an ideal place to study the tectonic evolution between the North and South China Blocks. The available literature data in the past 20 years indicate that the tectonic processes of the Tongbai-Hong'an orogen involved four stages during the Phanerozoic:(1) Early Paleozoic(490–420 Ma) oceanic subduction, arc magmatism and arc-continent collision created a new Andean-type active continental margin on the North China Block;(2) Late Paleozoic(340–310 Ma) oceanic subduction and accretion generated separated paired metamorphic belts: a medium P/T Wuguan-Guishan complex belt in the south of the Shandan-Songpa fault and a high P/T Xiongdian eclogite belt in the northern edge of the Mesozoic HP metamorphic terrane;(3) Latest Paleozoic-Early Mesozoic(255–200 Ma) continental subduction and collision formed the Tongbai HP terrane in the west and the Hong'an HP/UHP terrane in the east as a consequence of deep subduction towards the east and syn-subduction detachment/exhumation of the down-going slab;(4) Late Mesozoic(140–120 Ma) extension, voluminous magma intrusion and tectonic extrusion led to the final exhumation of the Tongbai-Hong'an-Dabie HP/UHP terrane and the wedge-shaped architecture of the terrane narrowing towards the west. However, many open questions still remain about the details of each evolutionary stage and earlier history of the orogen. Besides an extensive study directly on the Tongbai-Hong'an orogen in the future, integrated investigation on the "soft-collisional" Qinling orogen in the west and the "hard-collisional" Dabie-Sulu orogen in the east is required to establish a general tectonic model for the whole Qinling-TongbaiHong'an-Dabie-Sulu orogenic 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 Eoce
