The West Junggar of the western Central Asian Orogenic Belt is one of the typical regions in the term of ocean subduction, contraction and continental growth in the Late Paleozoic. However, it is still controversial o...The West Junggar of the western Central Asian Orogenic Belt is one of the typical regions in the term of ocean subduction, contraction and continental growth in the Late Paleozoic. However, it is still controversial on the exact time of ocean-continent transition so far. This study investigates rhyolites with columnar joint in the West Junggar for the first time.Based on zircon U-Pb dating, we determined that the ages of the newly-discovered rhyolites are between 303.6 and 294.5 Ma, belonging to Late Carboniferous–Early Permian, which is the oldest rhyolite with columnar joint preserved in the world at present. Geochemical results show that the characteristics of the major element compositions include a high content of SiO_2(75.78–79.20 wt%) and a moderate content of Al_2O_3(12.21–13.19 wt%). The total alkali content(K_2O +Na_2O) is 6.14–8.05 wt%, among which K_2O is 2.09–4.72 wt% and the rate of K_2O/Na_2O is 0.38–3.05. Over-based minerals such as Ne, Lc, and Ac do not appear. The contents of TiO_2(0.09–0.24 wt%), CaO(0.15–0.99 wt%) and MgO(0.06–0.18 wt%) are low. A/CNK=0.91–1.68, A/NK=1.06–1.76, and as such, these are associated with the quasi-aluminum-weak peraluminous high potassium calc-alkaline and some calc-alkaline magma series. These rhyolites show a significant negative Eu anomaly with relative enrichment of LREE and LILE(Rb, Ba, Th, U, K) and depletion of Sr, HREE and HFSE(Nb, Ta, Ti, P). These rhyolites also have the characteristics of an A2-type granite, similar to the Miaoergou batholith,which indicates they both were affected by post-orogenic extension. Combining petrological, zircon U-Pb dating and geochemical characteristics of the rhyolites, we conclude that the specific time of ocean-continent transition of the West Junggar is the Late Carboniferous–Early Permian.展开更多
Around 71% of the Earth’s surface is covered by oceans with depths that exceed several kilometers, while continents are geographically enclosed by these vast bodies of water. The principle of fluid mechanics stipulat...Around 71% of the Earth’s surface is covered by oceans with depths that exceed several kilometers, while continents are geographically enclosed by these vast bodies of water. The principle of fluid mechanics stipulates that water yields pressure everywhere in the container that holds it, and the water pressure against the wall of container generates force. Ocean basins are naturally gigantic containers of water, in which continents form the walls of the containers. In this study, we present that the ocean water pressure against the walls of continents generates enormous force, and determine the distribution of this force around continents and estimate its amplitude to be of the order of 1017 N per kilometer of continent width. Our modelling suggests that the stresses yielded by this force are mostly concentrated on the upper part of the continental crust, and their magnitudes reach up to 2.0 - 6.0 MPa. Our results suggest that the force may have significantly impacted the dynamics of continent (lithospheric plate) and its evolution.展开更多
Plate motion representing a remarkable Earth process is widely attributed to several primary forces such as ridge push and slab pull. Recently, we have presented that the ocean water pressure against the wall of conti...Plate motion representing a remarkable Earth process is widely attributed to several primary forces such as ridge push and slab pull. Recently, we have presented that the ocean water pressure against the wall of continents may generate enormous force on continents. Continents are physically fixed on the top of the lithosphere that has been already broken into individual plates, this attachment enables the force to be laterally transferred to the lithospheric plates. In this study, we combine the force and the existing plate driving forces (i.e., ridge push, slab pull, collisional, and shearing) to account for plate motion. We show that the modelled movements for the South American, African, North American, Eurasian, Australian, Pacific plates are well agreement with the observed movements in both speed and azimuth, with a Root Mean Square Error (RMSE) of the modelled speed against the observed speed of 0.91, 3.76, 2.77, 2.31, 7.43, and 1.95 mm/yr, respectively.展开更多
Using the CCM3/NCAR, a series of numerical experiments are designed to explore the effect of ocean-land interlaced distributions of Africa-Arabian Sea-India Peninsula-Bay of Bengal （BOB）-Indo-China Peninsula- South ...Using the CCM3/NCAR, a series of numerical experiments are designed to explore the effect of ocean-land interlaced distributions of Africa-Arabian Sea-India Peninsula-Bay of Bengal （BOB）-Indo-China Peninsula- South China Sea on the formation of the Asian summer monsoon circulation （ASMC）. The results show that the thermal difference between African or Indian Subcontinent and nearby areas including the Indian Ocean, Arabian Sea, and part of BOB is the primary mechanism that maintains the Indian monsoon circulation. In the experiment getting rid of these two continents, the Indian monsoon system （IMS） members, i.e., the Somali cross-equatorial jet （40°E） and the southwesterly monsoon over the Arabian Sea and BOB, almost disappear. Moreover, the Hadley circulation weakens dominantly. It also proves that Africa has greater effect than Indian Subcontinent on the IMS. However, the existence of Indo-China Peninsula and Australia strengthens the East Asian monsoon system （EAMS）. The thermal contrast between Indo-China Peninsula and SCS, Australia and western Pacific Ocean plays an important role in the formation of the tropical monsoon to the south of the EAMS. When the Indo-China Peninsula is masked in the experiment, the cross-equatorial flow （105°E and 125°E） vanishes, so does the southwesterly monsoon usually found over East Asia, and EAMS is enfeebled significantly. In addition, the impacts of these thermal contrasts on the distribution of the summer precipitation and surface temperature are investigated.展开更多
The Indian Ocean and the West Pacific Ocean and their ocean-continent connection zones are the core area of ＂the Belt and Road＂. Scientific and in-depth recognition to the natural environment, disaster distribution,...The Indian Ocean and the West Pacific Ocean and their ocean-continent connection zones are the core area of ＂the Belt and Road＂. Scientific and in-depth recognition to the natural environment, disaster distribution, resources, energy potential of ＂the Belt and Road＂ development, is the cut-in point of the current Earth science community to serve urgent national needs. This paper mainly discusses the following key tectonic problems in the West Pacific and North Indian oceans and their ocean-continent connection zones （OCCZs）： 1. modern marine geodynamic problems related to the two oceans. Based on the research and development needs to the two oceans and the ocean-continent transition zones, this item includes the following questions. （1） Plate origin, growth, death and evolution in the two oceans, for example, 1） The initial origin and process of the triangle Pacific Plate including causes and difference of the Galapagos and West Shatsky microplates; 2） spatial and temporal process, present status and trends of the plates within the Paleo- or Present-day Pacific Ocean to the evolution of the East Asian Continental Domain; 3） origin and evolution of the Indian Ocean and assembly and dispersal of supercontinents. （2） Latest research progress and problems of mid-oceanic ridges： 1） the ridge-hot spot interaction and ridge accretion, how to think about the relationship between vertical accretion behavior of thousands years or tens of thousands years and lateral spreading of millions years at 0 Ma mid- oceanic ridges; 2） the difference of formation mechanisms between the back-arc basin extension and the normal mid-oceanic ridge spreading; 3） the differentials between ultra-slow Indian Ocean and the rapid Pacific spreading, whether there are active and passive spreading, and a push force in the mid-oceanic ridge; 4） mid-oceanic ridge jumping and termination： causes of the intra-oceanic plate reorganization, termination, and spatial jumps; 5） interaction of mantle plume and mid-oc展开更多
Worldwide comparison of lithospheric investigation results achieved from projects of COCORP, BIRPS, DEKORP, LITHOPROBE, ICDP, ECORS and SINOPROBE enables us to expand the classical Wilson cycle, which mainly describes...Worldwide comparison of lithospheric investigation results achieved from projects of COCORP, BIRPS, DEKORP, LITHOPROBE, ICDP, ECORS and SINOPROBE enables us to expand the classical Wilson cycle, which mainly describes evolution of ocean plates, into a complete and detailed cycle that describes generation, development and evolution of both ocean and continent plates. The expanded Wilson cycle presented in this paper introduces the evolution sequences of continental lithospheric processes by adding into the classical Wilson cycle with ocean-continent transition, continental collision and accretion, as well as continental rifting and splitting in details. These mentioned continental lithospheric processes have been presented by the author in a series of recent review papers in detail, and their summary and further deduction is presented in this paper.展开更多
The North Qaidam UHPM（ultra-high pressure metamorphism） belt is a typical continental subduction-collision belt containing continental crust deep subduction metamorphic products and oceanic crust relics, And it is a...The North Qaidam UHPM（ultra-high pressure metamorphism） belt is a typical continental subduction-collision belt containing continental crust deep subduction metamorphic products and oceanic crust relics, And it is an ideal region to study the ocean-continent transition and exhumation mechanism of oceanic UHP rocks during continental deep subduction process. In this paper, we report integrated in situ U-Pb, Lu-Hf and O isotope analyses of zircons from a serpentinized harzburgite as well as U-Pb dating for zircons from a kyanite eclogite from the North Qaidam Dulan UHPM terrane, and use these data to discuss the ocean-continent transition and exhumation mechanisms of oceanic UHP rocks during continental deep subduction. The serpentinized harzburgite was dated at 448±9 Ma, consistent with 455±5 Ma age for the kyanite eclogite within analytical errors. Zircons from the serpentinized harzburgite have uniform 176Hf/177 Hf values ranging from 0.282 842 to 0.282 883 and εHf（t） values from 11.6 to 13.3. Zircon δ^18O values of the serpentinized harzburgite vary from 4.47‰ to 5.29‰, slightly lower than the value of 5.3‰±0.6‰ for the normal mantle zircon. These Hf-O isotopic features indicate that the protolith of the serpentinized harzburgite was derived from depleted-mantle source, and might have experienced high-temperature rock-water interaction. Therefore, the serpentinized harzburgite was possibly located in the lower part of an oceanic section. The serpentinized harzburgite and kyanite eclogite were both formed due to the subduction of oceanic crust. The UHP metamorphism occurred successively from the oceanic crust to continental crust rocks of the North Qaidam UHP terrane. Low-density serpentinized peridotite and continental rocks possibly have negative buoyancy and play a key effect on preservation and exhumation of high-density oceanic eclogite.展开更多
Structural and petrological data suggest that the Xigaze ophiolite from the Yarlung Zangbo Suture Zone(YZSZ)in south Tibet was a typical slow-spreading ridge.A new field,geochemical,mineral,and U-Pb zircon dataset of ...Structural and petrological data suggest that the Xigaze ophiolite from the Yarlung Zangbo Suture Zone(YZSZ)in south Tibet was a typical slow-spreading ridge.A new field,geochemical,mineral,and U-Pb zircon dataset of plagiogranite intrusions were used to constrain the dynamic processes of oceanic accretion in this slow-spreading ridge.Plagiogranites mainly occur as dykes or intrusions intruded into the whole sequence of the ophiolite and have a similar orientation to the dolerite dykes developed in the late stage of detachment faulting.U-Pb zircon ages of 122–123 Ma were obtained for two types of plagiogranites and associated dolerite dykes.Detailed geochemical and mineralogical examinations suggest that the plagiogranites are the product of low-pressure(2–3 kbar)fractional crystallization of midocean ridge basalt-like magma and unlikely to have been derived from the partial melting of hydrous gabbroic rocks.The complex cross-cut relationship between the plagiogranites and ophiolite sequence reflects that they are controlled by small discontinued melt lenses rather than a big magma chamber under the ridge axis and reveals multiple injections during the oceanic crust accretion.The formation of plagiogranites possibly reflects the complex characteristic of oceanic accretion at slow-spreading ridges,time-dependent on structural(external)and magmatic(internal)processes.展开更多
Plate tectonic activity has played a critical role in the development of petrotectonic associations in the Kadiri schist belt. The calc alkaline association of basalt, andesite, dacite and rhyolite （BADR） is the sig...Plate tectonic activity has played a critical role in the development of petrotectonic associations in the Kadiri schist belt. The calc alkaline association of basalt, andesite, dacite and rhyolite （BADR） is the signature volcanic rock suite of the convergent margin. The N-S belt has gone below the unconformity plane of Cuddapah sediments. In the northern part geochemical and structural attributes of the Kadiri greenstone belt is studied along with microscopic observations of selected samples. Harker diagram plots of major elements generally indicate a liquid line of descent from a common source, such that BADR rocks are derived from a common parent magma of basaltic to andesitic composition. These calc-alkaline volcanic rocks are formed at convergent margins where more silicic rocks represent more highly fractionated melt. All the litho-units of this greenstone belt indicate crush and strain effects. The stretched pebbles in the deformed volcanic matrix with tectonite development along with associated greenschist facies metamorphism, alteration and hydration is remarkable. Flow foliation plane with N-S strike and very low angle （5~ to 10~） easterly dip and N-S axial planar schistosity formed due to later phase isoclinal folding can be clearly identified in the field. Basic intrusives are quite common in the surrounding area. All the observations including the field setting and geochemistry clearly demonstrate ocean-continent subduction as the tectonic environment of the study area.展开更多
Former studies show that the Muztag ophiolite, outcropped in the East Kunlun area of Xinjiang, formed in a supra-subduction zone environment. This study is to gain more information about the type of subduetion zone. T...Former studies show that the Muztag ophiolite, outcropped in the East Kunlun area of Xinjiang, formed in a supra-subduction zone environment. This study is to gain more information about the type of subduetion zone. Through field work, thin section observation and microprobe analysis, petrological and mineralogical characteristics of the metamorphic peridotites of this ophiolite are obtained. Although the olivines of metamorphic peridotites appear in three textures of metamorphic relict, metamorphic recrystallizations and orthopyroxene-melting crystallizations by thin-section observations, they have stable and low Fo range of 87.8- 89.5 by microprobe analysis. The orthopyroxenes show metamorphic relict and melting relict textures, with a low En of 88-90 and a wide range of Al2O3 content, from 2.90 wt% to 5. 13 wt%. The spinels develop anhedral-subhedral textures, with Cr^# （=Cr/（Cr＋AI）） focusing on two ranges of 0. 508-0. 723 and 0. 100-0. 118, respectively. Based on these petrological and mineralogical observations, and combined with the era and tectonic setting for the Muztag ophiolite, it can be concluded that the ophiolite formed in a supra-subduction zone where the oceanic crust subducted down to the continental are with a thick continental crust, and resulted from ocean-continent subducion within the Paleotethyan arehiopelagic ocean in the East Kunlun area of Xinjiang.展开更多
The northwestern sub-basin of South China Sea(SCS)is a unique tectonic unit formed in the early spreading of the SCS.The northwestern Sub-basin has a series of complex geological structures such as seamounts and fault...The northwestern sub-basin of South China Sea(SCS)is a unique tectonic unit formed in the early spreading of the SCS.The northwestern Sub-basin has a series of complex geological structures such as seamounts and fault zones surrounded by the Xisha Trough,the Zhongsha Massif,and the Pearl River Valley.These extensional structures and magmatic activity in the northwestern sub-basin are closely related to the lithospheric structure and its deformation.However,details of the deep lithosphere structure are still poorly known.Here,we obtained detailed data of water and Moho depth using sonar buoys,Extended Spread Profiles(ESP),Ocean Bottom Seismometer(OBS),both Multi-beam and land-sea joint seismic surveys in the northwestern sub-basin and its surrounding areas.Then we adopted a thermal isostasy method to calculate the depth of the Lithosphere-Asthenosphere Boundary(LAB)in the northwestern sub-basin of the SCS and its surrounding regions.Results show that the range of LAB depth is~25–110 km.The shallowest burial depth is 25–60 km occurring in the ocean basin.The depth increases to 60–110 km toward the continental margin.The lithospheric structure on the north and south sides of the Xisha Trough is symmetrical and shows the deep structure and thermal features of aborted rifts.The LAB depth in the Zhongsha Trough and the Zhongsha Massif increased from 60 to 70 km southwestwards,consistent with the trend of surface morphology.The LAB depth to the west side of the Pearl River Valley is 60–80 km,and the thinning of the lithosphere is related to the distribution of faults,depressions and the magmatic activity.The LAB depth in the northwestern sub-basin and the eastern subbasin is less than 60 km with the thinnest part being less than 46 km.Combining ocean drilling,seismic investigation,and seafloor topography,we show that the ocean basin of the northwestern sub-basin of the SCS locates within the 46 km isobath of the LAB.The formation of the rifted valleys and discrete blocks surrounding the ocean basins is both cont展开更多
The ophiolites that crop out discontinuously along the;000 km Yarlung Zangbo Suture zone（YZSZ）between the Nanga Parbat and Namche Barwa syntaxes in southern Tibet represent the remnants of Neotethyan oceanic lithosp...The ophiolites that crop out discontinuously along the;000 km Yarlung Zangbo Suture zone（YZSZ）between the Nanga Parbat and Namche Barwa syntaxes in southern Tibet represent the remnants of Neotethyan oceanic lithosphere（Fig.1a）.We have investigated the internal structure and the geochemical makeup of mafic-ultramafic rock assemblages that are exposed in the westernmost segment of the YZSZ where the suture zone architecture displays two distinct sub-belts of ophiolitic and mélange units separated by a continental Zhongba terrane（Fig.1b）.These two sub-belts include the Daba–Xiugugabu in the south（Southern sub-belt,SSB）and the Dajiweng–Saga in the north（Northern sub-belt,NSB）.We present new structural,geochemical,geochronological data from upper mantle peridotites and mafic dike intrusions occurring in these two sub-belts and discuss their tectonomagmatic origin.In-situ analysis of zircon grains obtained from mafic dikes within the Baer,Cuobuzha and Jianabeng massifs in the NSB,and within the Dongbo,Purang,Xiugugabu,Zhaga and Zhongba in the SSB have yielded crystallization ages ranging between130 and 122 Ma.Dike rocks in both sub-belts show N-MORB REE patterns and negative Nb,Ta and Ti anomalies,reminiscent of those documented from SSZ ophiolites.*Harzburgitic host rocks of the mafic dike intrusionsmainly display geochemical compositions of abyssal peridotites（Fig.2）,with the exception of the Dajiweng harzburgites,which show the geochemical signatures of forearc peridotites（Lian et al.,2016）.Extrusive rocks that are spatially associated with these peridotite massifs in both sub-belts also have varying compositional and geochemical features.Tithonian to Valanginian（150–135 Ma）basaltic rocks in the Dongbo massif have OIB-like geochemistry and 138 Ma basaltic lavas in the Purang massif have EMORB-like geochemistry（Liu et al.,2015）.Tuffaceous rocks in the Dajiweng massif are140 Ma in age and show OIB-like geochemistry.We interpret these age and geochemical data to reflect a rif展开更多
基金supported by the China Geological Survey (grant numbers DD20160083 and DD20160344-05)the National Key Research and Development Program of China (grant numbers 2018YFC0603701)Fundamental Research Funds for Central Public Welfare Research Institutes (grant numbers CAGS-YWF201706)
文摘The West Junggar of the western Central Asian Orogenic Belt is one of the typical regions in the term of ocean subduction, contraction and continental growth in the Late Paleozoic. However, it is still controversial on the exact time of ocean-continent transition so far. This study investigates rhyolites with columnar joint in the West Junggar for the first time.Based on zircon U-Pb dating, we determined that the ages of the newly-discovered rhyolites are between 303.6 and 294.5 Ma, belonging to Late Carboniferous–Early Permian, which is the oldest rhyolite with columnar joint preserved in the world at present. Geochemical results show that the characteristics of the major element compositions include a high content of SiO_2(75.78–79.20 wt%) and a moderate content of Al_2O_3(12.21–13.19 wt%). The total alkali content(K_2O +Na_2O) is 6.14–8.05 wt%, among which K_2O is 2.09–4.72 wt% and the rate of K_2O/Na_2O is 0.38–3.05. Over-based minerals such as Ne, Lc, and Ac do not appear. The contents of TiO_2(0.09–0.24 wt%), CaO(0.15–0.99 wt%) and MgO(0.06–0.18 wt%) are low. A/CNK=0.91–1.68, A/NK=1.06–1.76, and as such, these are associated with the quasi-aluminum-weak peraluminous high potassium calc-alkaline and some calc-alkaline magma series. These rhyolites show a significant negative Eu anomaly with relative enrichment of LREE and LILE(Rb, Ba, Th, U, K) and depletion of Sr, HREE and HFSE(Nb, Ta, Ti, P). These rhyolites also have the characteristics of an A2-type granite, similar to the Miaoergou batholith,which indicates they both were affected by post-orogenic extension. Combining petrological, zircon U-Pb dating and geochemical characteristics of the rhyolites, we conclude that the specific time of ocean-continent transition of the West Junggar is the Late Carboniferous–Early Permian.
文摘Around 71% of the Earth’s surface is covered by oceans with depths that exceed several kilometers, while continents are geographically enclosed by these vast bodies of water. The principle of fluid mechanics stipulates that water yields pressure everywhere in the container that holds it, and the water pressure against the wall of container generates force. Ocean basins are naturally gigantic containers of water, in which continents form the walls of the containers. In this study, we present that the ocean water pressure against the walls of continents generates enormous force, and determine the distribution of this force around continents and estimate its amplitude to be of the order of 1017 N per kilometer of continent width. Our modelling suggests that the stresses yielded by this force are mostly concentrated on the upper part of the continental crust, and their magnitudes reach up to 2.0 - 6.0 MPa. Our results suggest that the force may have significantly impacted the dynamics of continent (lithospheric plate) and its evolution.
文摘Plate motion representing a remarkable Earth process is widely attributed to several primary forces such as ridge push and slab pull. Recently, we have presented that the ocean water pressure against the wall of continents may generate enormous force on continents. Continents are physically fixed on the top of the lithosphere that has been already broken into individual plates, this attachment enables the force to be laterally transferred to the lithospheric plates. In this study, we combine the force and the existing plate driving forces (i.e., ridge push, slab pull, collisional, and shearing) to account for plate motion. We show that the modelled movements for the South American, African, North American, Eurasian, Australian, Pacific plates are well agreement with the observed movements in both speed and azimuth, with a Root Mean Square Error (RMSE) of the modelled speed against the observed speed of 0.91, 3.76, 2.77, 2.31, 7.43, and 1.95 mm/yr, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 40375014 and 40475029.
文摘Using the CCM3/NCAR, a series of numerical experiments are designed to explore the effect of ocean-land interlaced distributions of Africa-Arabian Sea-India Peninsula-Bay of Bengal （BOB）-Indo-China Peninsula- South China Sea on the formation of the Asian summer monsoon circulation （ASMC）. The results show that the thermal difference between African or Indian Subcontinent and nearby areas including the Indian Ocean, Arabian Sea, and part of BOB is the primary mechanism that maintains the Indian monsoon circulation. In the experiment getting rid of these two continents, the Indian monsoon system （IMS） members, i.e., the Somali cross-equatorial jet （40°E） and the southwesterly monsoon over the Arabian Sea and BOB, almost disappear. Moreover, the Hadley circulation weakens dominantly. It also proves that Africa has greater effect than Indian Subcontinent on the IMS. However, the existence of Indo-China Peninsula and Australia strengthens the East Asian monsoon system （EAMS）. The thermal contrast between Indo-China Peninsula and SCS, Australia and western Pacific Ocean plays an important role in the formation of the tropical monsoon to the south of the EAMS. When the Indo-China Peninsula is masked in the experiment, the cross-equatorial flow （105°E and 125°E） vanishes, so does the southwesterly monsoon usually found over East Asia, and EAMS is enfeebled significantly. In addition, the impacts of these thermal contrasts on the distribution of the summer precipitation and surface temperature are investigated.
基金financially supported by the National Key Research and Development Program of China (Nos.2017YFC0601401)National Science and Technology Major Project (No.2016ZX05004001-003)+2 种基金NSFC projects (grant nos. 41702206, 41190072)some by the Taishan Scholar Program to Li Sanzhongfinancial support of the Aoshan Elite Scientist Plan of Qingdao National Laboratory for Marine Science and Technology to Prof. Li Sanzhong and his research group
文摘The Indian Ocean and the West Pacific Ocean and their ocean-continent connection zones are the core area of ＂the Belt and Road＂. Scientific and in-depth recognition to the natural environment, disaster distribution, resources, energy potential of ＂the Belt and Road＂ development, is the cut-in point of the current Earth science community to serve urgent national needs. This paper mainly discusses the following key tectonic problems in the West Pacific and North Indian oceans and their ocean-continent connection zones （OCCZs）： 1. modern marine geodynamic problems related to the two oceans. Based on the research and development needs to the two oceans and the ocean-continent transition zones, this item includes the following questions. （1） Plate origin, growth, death and evolution in the two oceans, for example, 1） The initial origin and process of the triangle Pacific Plate including causes and difference of the Galapagos and West Shatsky microplates; 2） spatial and temporal process, present status and trends of the plates within the Paleo- or Present-day Pacific Ocean to the evolution of the East Asian Continental Domain; 3） origin and evolution of the Indian Ocean and assembly and dispersal of supercontinents. （2） Latest research progress and problems of mid-oceanic ridges： 1） the ridge-hot spot interaction and ridge accretion, how to think about the relationship between vertical accretion behavior of thousands years or tens of thousands years and lateral spreading of millions years at 0 Ma mid- oceanic ridges; 2） the difference of formation mechanisms between the back-arc basin extension and the normal mid-oceanic ridge spreading; 3） the differentials between ultra-slow Indian Ocean and the rapid Pacific spreading, whether there are active and passive spreading, and a push force in the mid-oceanic ridge; 4） mid-oceanic ridge jumping and termination： causes of the intra-oceanic plate reorganization, termination, and spatial jumps; 5） interaction of mantle plume and mid-oc
文摘Worldwide comparison of lithospheric investigation results achieved from projects of COCORP, BIRPS, DEKORP, LITHOPROBE, ICDP, ECORS and SINOPROBE enables us to expand the classical Wilson cycle, which mainly describes evolution of ocean plates, into a complete and detailed cycle that describes generation, development and evolution of both ocean and continent plates. The expanded Wilson cycle presented in this paper introduces the evolution sequences of continental lithospheric processes by adding into the classical Wilson cycle with ocean-continent transition, continental collision and accretion, as well as continental rifting and splitting in details. These mentioned continental lithospheric processes have been presented by the author in a series of recent review papers in detail, and their summary and further deduction is presented in this paper.
文摘The North Qaidam UHPM（ultra-high pressure metamorphism） belt is a typical continental subduction-collision belt containing continental crust deep subduction metamorphic products and oceanic crust relics, And it is an ideal region to study the ocean-continent transition and exhumation mechanism of oceanic UHP rocks during continental deep subduction process. In this paper, we report integrated in situ U-Pb, Lu-Hf and O isotope analyses of zircons from a serpentinized harzburgite as well as U-Pb dating for zircons from a kyanite eclogite from the North Qaidam Dulan UHPM terrane, and use these data to discuss the ocean-continent transition and exhumation mechanisms of oceanic UHP rocks during continental deep subduction. The serpentinized harzburgite was dated at 448±9 Ma, consistent with 455±5 Ma age for the kyanite eclogite within analytical errors. Zircons from the serpentinized harzburgite have uniform 176Hf/177 Hf values ranging from 0.282 842 to 0.282 883 and εHf（t） values from 11.6 to 13.3. Zircon δ^18O values of the serpentinized harzburgite vary from 4.47‰ to 5.29‰, slightly lower than the value of 5.3‰±0.6‰ for the normal mantle zircon. These Hf-O isotopic features indicate that the protolith of the serpentinized harzburgite was derived from depleted-mantle source, and might have experienced high-temperature rock-water interaction. Therefore, the serpentinized harzburgite was possibly located in the lower part of an oceanic section. The serpentinized harzburgite and kyanite eclogite were both formed due to the subduction of oceanic crust. The UHP metamorphism occurred successively from the oceanic crust to continental crust rocks of the North Qaidam UHP terrane. Low-density serpentinized peridotite and continental rocks possibly have negative buoyancy and play a key effect on preservation and exhumation of high-density oceanic eclogite.
基金supported by grants from the National Natural Science Foundation of China(Grant Nos.41720104009 and 41772231)the China Geological Survey Project(Grant No.DD20190060).
文摘Structural and petrological data suggest that the Xigaze ophiolite from the Yarlung Zangbo Suture Zone(YZSZ)in south Tibet was a typical slow-spreading ridge.A new field,geochemical,mineral,and U-Pb zircon dataset of plagiogranite intrusions were used to constrain the dynamic processes of oceanic accretion in this slow-spreading ridge.Plagiogranites mainly occur as dykes or intrusions intruded into the whole sequence of the ophiolite and have a similar orientation to the dolerite dykes developed in the late stage of detachment faulting.U-Pb zircon ages of 122–123 Ma were obtained for two types of plagiogranites and associated dolerite dykes.Detailed geochemical and mineralogical examinations suggest that the plagiogranites are the product of low-pressure(2–3 kbar)fractional crystallization of midocean ridge basalt-like magma and unlikely to have been derived from the partial melting of hydrous gabbroic rocks.The complex cross-cut relationship between the plagiogranites and ophiolite sequence reflects that they are controlled by small discontinued melt lenses rather than a big magma chamber under the ridge axis and reveals multiple injections during the oceanic crust accretion.The formation of plagiogranites possibly reflects the complex characteristic of oceanic accretion at slow-spreading ridges,time-dependent on structural(external)and magmatic(internal)processes.
文摘Plate tectonic activity has played a critical role in the development of petrotectonic associations in the Kadiri schist belt. The calc alkaline association of basalt, andesite, dacite and rhyolite （BADR） is the signature volcanic rock suite of the convergent margin. The N-S belt has gone below the unconformity plane of Cuddapah sediments. In the northern part geochemical and structural attributes of the Kadiri greenstone belt is studied along with microscopic observations of selected samples. Harker diagram plots of major elements generally indicate a liquid line of descent from a common source, such that BADR rocks are derived from a common parent magma of basaltic to andesitic composition. These calc-alkaline volcanic rocks are formed at convergent margins where more silicic rocks represent more highly fractionated melt. All the litho-units of this greenstone belt indicate crush and strain effects. The stretched pebbles in the deformed volcanic matrix with tectonite development along with associated greenschist facies metamorphism, alteration and hydration is remarkable. Flow foliation plane with N-S strike and very low angle （5~ to 10~） easterly dip and N-S axial planar schistosity formed due to later phase isoclinal folding can be clearly identified in the field. Basic intrusives are quite common in the surrounding area. All the observations including the field setting and geochemistry clearly demonstrate ocean-continent subduction as the tectonic environment of the study area.
文摘Former studies show that the Muztag ophiolite, outcropped in the East Kunlun area of Xinjiang, formed in a supra-subduction zone environment. This study is to gain more information about the type of subduetion zone. Through field work, thin section observation and microprobe analysis, petrological and mineralogical characteristics of the metamorphic peridotites of this ophiolite are obtained. Although the olivines of metamorphic peridotites appear in three textures of metamorphic relict, metamorphic recrystallizations and orthopyroxene-melting crystallizations by thin-section observations, they have stable and low Fo range of 87.8- 89.5 by microprobe analysis. The orthopyroxenes show metamorphic relict and melting relict textures, with a low En of 88-90 and a wide range of Al2O3 content, from 2.90 wt% to 5. 13 wt%. The spinels develop anhedral-subhedral textures, with Cr^# （=Cr/（Cr＋AI）） focusing on two ranges of 0. 508-0. 723 and 0. 100-0. 118, respectively. Based on these petrological and mineralogical observations, and combined with the era and tectonic setting for the Muztag ophiolite, it can be concluded that the ophiolite formed in a supra-subduction zone where the oceanic crust subducted down to the continental are with a thick continental crust, and resulted from ocean-continent subducion within the Paleotethyan arehiopelagic ocean in the East Kunlun area of Xinjiang.
基金supported by NSFC-Guangdong Joint Fund(Grant No.U20A20100)the Major Projects for Talent Research Team Introduction of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(Grant Nos.GML2019ZD0104,GML2019ZD0204)+2 种基金the Fund of Youth Innovation Promotion Association CAS,the Innovative Development Fund projects of the Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences(Grant No.ISEE2018PY02)the National Natural Science Foundation of China(Grant Nos.41506063,91958212,91428205,42076077)Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2020A1515010502,2017A030312002)。
文摘The northwestern sub-basin of South China Sea(SCS)is a unique tectonic unit formed in the early spreading of the SCS.The northwestern Sub-basin has a series of complex geological structures such as seamounts and fault zones surrounded by the Xisha Trough,the Zhongsha Massif,and the Pearl River Valley.These extensional structures and magmatic activity in the northwestern sub-basin are closely related to the lithospheric structure and its deformation.However,details of the deep lithosphere structure are still poorly known.Here,we obtained detailed data of water and Moho depth using sonar buoys,Extended Spread Profiles(ESP),Ocean Bottom Seismometer(OBS),both Multi-beam and land-sea joint seismic surveys in the northwestern sub-basin and its surrounding areas.Then we adopted a thermal isostasy method to calculate the depth of the Lithosphere-Asthenosphere Boundary(LAB)in the northwestern sub-basin of the SCS and its surrounding regions.Results show that the range of LAB depth is~25–110 km.The shallowest burial depth is 25–60 km occurring in the ocean basin.The depth increases to 60–110 km toward the continental margin.The lithospheric structure on the north and south sides of the Xisha Trough is symmetrical and shows the deep structure and thermal features of aborted rifts.The LAB depth in the Zhongsha Trough and the Zhongsha Massif increased from 60 to 70 km southwestwards,consistent with the trend of surface morphology.The LAB depth to the west side of the Pearl River Valley is 60–80 km,and the thinning of the lithosphere is related to the distribution of faults,depressions and the magmatic activity.The LAB depth in the northwestern sub-basin and the eastern subbasin is less than 60 km with the thinnest part being less than 46 km.Combining ocean drilling,seismic investigation,and seafloor topography,we show that the ocean basin of the northwestern sub-basin of the SCS locates within the 46 km isobath of the LAB.The formation of the rifted valleys and discrete blocks surrounding the ocean basins is both cont
文摘The ophiolites that crop out discontinuously along the;000 km Yarlung Zangbo Suture zone（YZSZ）between the Nanga Parbat and Namche Barwa syntaxes in southern Tibet represent the remnants of Neotethyan oceanic lithosphere（Fig.1a）.We have investigated the internal structure and the geochemical makeup of mafic-ultramafic rock assemblages that are exposed in the westernmost segment of the YZSZ where the suture zone architecture displays two distinct sub-belts of ophiolitic and mélange units separated by a continental Zhongba terrane（Fig.1b）.These two sub-belts include the Daba–Xiugugabu in the south（Southern sub-belt,SSB）and the Dajiweng–Saga in the north（Northern sub-belt,NSB）.We present new structural,geochemical,geochronological data from upper mantle peridotites and mafic dike intrusions occurring in these two sub-belts and discuss their tectonomagmatic origin.In-situ analysis of zircon grains obtained from mafic dikes within the Baer,Cuobuzha and Jianabeng massifs in the NSB,and within the Dongbo,Purang,Xiugugabu,Zhaga and Zhongba in the SSB have yielded crystallization ages ranging between130 and 122 Ma.Dike rocks in both sub-belts show N-MORB REE patterns and negative Nb,Ta and Ti anomalies,reminiscent of those documented from SSZ ophiolites.*Harzburgitic host rocks of the mafic dike intrusionsmainly display geochemical compositions of abyssal peridotites（Fig.2）,with the exception of the Dajiweng harzburgites,which show the geochemical signatures of forearc peridotites（Lian et al.,2016）.Extrusive rocks that are spatially associated with these peridotite massifs in both sub-belts also have varying compositional and geochemical features.Tithonian to Valanginian（150–135 Ma）basaltic rocks in the Dongbo massif have OIB-like geochemistry and 138 Ma basaltic lavas in the Purang massif have EMORB-like geochemistry（Liu et al.,2015）.Tuffaceous rocks in the Dajiweng massif are140 Ma in age and show OIB-like geochemistry.We interpret these age and geochemical data to reflect a rif
