There has been a long\|term debate about the Paleo\|Tethyan Ocean in South China continent. Based on the geological and geochemical studies, it is suggested that there exist two tectonic belts in SE Yunnan, SW China c...There has been a long\|term debate about the Paleo\|Tethyan Ocean in South China continent. Based on the geological and geochemical studies, it is suggested that there exist two tectonic belts in SE Yunnan, SW China called Ailao Shan zone and Shizong—Mile zone, which separate Yangtze Block, Cathysian Block and Indo\|China Block from each other. The evolutionary history and its geodynamics of these suture zones are correlated with the Paleo\|Tethyan Ocean. Both of the zones are keys to understanding whether the Paleo\|Tethyan Ocean extended from Western Yunnan area to east of the South China continent. The Ailao Shan belt consists of Red River fault, Ailao Shan fault, Shuanggou fault and Huashan—Yayi fault, which are the boundaries of the Ailao Shan basement metamorphic belt, ophiolitic melange belt and Island\|arc volcanic\|sediments belt, respectively.The ophiolitic melange belt is characterized by the existence of the ophiolite in Shuanggou area, which represents the relicts of the oceanic crust of the Ailao Shan Ocean. In addition, there exist volcanic rocks in west of the ophiolitic melange belt in Jingdong area. The geochemical characteristics of basalts in Jingdong are similar to that of the E\|MORB. Synthesized studies on geochemistry and tectonics suggest that the basalts in Jingdong area were formed in an extensional rift setting in Devonian.展开更多
The Mianlue suture extends from Derni-Nanping-Pipasi-Kangxian to the Lueyang-Mianxian area, then traverses the Bashan arcuate structure eastward to the Huashan region, and finally to the Qingshuihe area of the souther...The Mianlue suture extends from Derni-Nanping-Pipasi-Kangxian to the Lueyang-Mianxian area, then traverses the Bashan arcuate structure eastward to the Huashan region, and finally to the Qingshuihe area of the southern Dabie Mountains. From east to west, with a length of over 1500 km, the ophiolitic melange associations are distributed discontinuously along the suture. The rock assemblages include ophiolite, island-arc and oceanic island rock series, indicating that there existed a suture zone and a vanished paleo-ocean basin. The Mianliie paleo-ocean basin experienced its main expansion and formation process during the Carboniferous-Permian and closed totally in the Triassic. It belongs to the northern branch of the eastern paleotethys, separated from the northern margin of the Yangtze block under the paleotethys mantle dynamic system.展开更多
A volcano-platform carbonate sequence ,from Carboniferous to Permian , is widely trapped in the deep water deposits in Changning- Menglian belt .Three components can be roughly recognized in ascending order as :the la...A volcano-platform carbonate sequence ,from Carboniferous to Permian , is widely trapped in the deep water deposits in Changning- Menglian belt .Three components can be roughly recognized in ascending order as :the lava .the volcaniclastic and carbonate rocks .In most cases, the sequence is incomplete due to faulting resulted from the strong orogenic compression. But (he stratigraphic succession is continuous except for the two interruptions of paleokarsts . which extended from middle Late Carboniferous to Late Permian and from late Early Permian to Late Permian respectively .A preliminary study indicates that the stratigraphy, petrology , sedimentation , vokanism geochemistry and fossils in the sequence are quite similar to mat in modern and ancient oceanic islands and there may be the relics of ancient oceanic islands in the paleo-Tethys .The differences among these sequences probably suggest a complex configuration of the islands or island chain These islands were formed under infra oceanic environments of the paleo-Tethys ,far from continent and accreted to Simao continental margin in Late Permian .The occurrence of large number of ancient oceanic islands in orogenic belts , including the paleo Tethys, Cordillera , etc ..suggests mat some ancient oceans .such as the paleo Tethys and proto-Pacific ,were full of archipelagoes as their modem counterparts . It is possible that more oceanic islands will be recongnized when sufficient research is done in orogenic belts over the world .展开更多
Late Paleozoic to Early Mesozoic granites are widespread in the southern Qaidam Basin, northern margin of the eastern Kunlun orogenic belt. Their petrogenesis can provide us insights into the tectonic evolution and cr...Late Paleozoic to Early Mesozoic granites are widespread in the southern Qaidam Basin, northern margin of the eastern Kunlun orogenic belt. Their petrogenesis can provide us insights into the tectonic evolution and crustal growth process in the Qaidam Basin. This paper reports Permian–Triassic granites from the Kunbei area, southwestern Qaidam Basin. Detailed zircon LA-ICP MS U-Pb dating reveals that the granites from the four drilling cores（q404, q406, q1612-8, q1613-8） have identical ages of 251±3, 256±4, 247±2, and 251±6 Ma, respectively, these ages are identical with the Permian–Triassic granites from the eastern Qaidam Basin. Detailed geochemical analyses indicate that these granites display typical affinities of highly-fractionated I-type granites：（1） they have high SiO_2（up to 76.5 wt.%）, Na_2O＋K_2O（7.91 wt.% to 9.48 wt.%） contents and high FeO^T/MgO values of 4.7 to 9.3, suggesting significant fractional crystallization;（2） their low A/CNK values of 0.54 to 1.03, no normative Al-rich minerals, inconsistent with the per-aluminous S-type granites;（3） their low Ga（14.5 ppm to 20.7 ppm） and 10 000×Ga/Al（2.23 to 3.03, most of them 〈2.6） values are inconsistent with the A-type granites;（4） the high Rb（191 ppm to 406 ppm） contents and Rb/Sr（2.1 to 13.4） ratios, as well as the significant negative Eu anomalies（0.10 to 0.42） also indicate significant fractional crystallization of feldspars;（5） their low P_2O_5 contents（0.02 wt.% to 0.10 wt.%） suggest the limited solubility of phosphorus in primitive metaluminous melts. In combination with the geological background, we propose that the Permian–Triassic highly-fractionated I-type granites resulted from partial melting of intra-crustal mafic rocks, and the primitive I-type granitic melts underwent significant fractional crystallization of feldspars. The occurrence of highly-fractionated I-type granites in the southwestern Qaidam Basin suggests a Permian–Triassic active continental margin in the northern margin of the East Kunlun orogenic belt.展开更多
High-temperature magma generation process and granulite-facies metamorphism can provide important information about mantle-crustal interaction and tectonic evolution. The strongly peralu- minous monzonite pluton, the ...High-temperature magma generation process and granulite-facies metamorphism can provide important information about mantle-crustal interaction and tectonic evolution. The strongly peralu- minous monzonite pluton, the Jinshuikou cordierite granite on the southern margin of the Qaidam Block, can provide important information about the mantle-crustal interaction and constraints on tectonic tran- sition from Proto-Tethys to Paleo-Tethys. This pluton develops enclaves of mafic granulite, amphibolite and quartzofeldspathic rocks, and is cut by massive monzonitic leuco-granite veins. Zircon and monazite U-Pb dating for the cordierite granite, the granulite enclaves and a massive monzonitic leuco-granite vein reveal that the cordierite granitic magma was generated from Mesoproterozoic continental crust with protolith derived from a provenanee that was composed of 〉2.8 Ga old recycled crustal materials and re- corded a -1.7 Ga magmatic event. The continental crust underwent low-pressure granulite-facies metamorphism at -380 Ma ago, whereas the cordierite granite magmas was generated and emplaced during 380 Ma, followed by intrusion of the massive monzonitic leuco-granite vein at circa 370-330 Ma. These data suggest that after the final closure of Proto-Tethys Ocean spreading along the southern Qaidam Block at -420 Ma, break-off of the subducted slab or delamination of the lower crustal base and upwelling of the asthenospheric mantle beneath the southern Qaidam Block occurred before the Mid-Devonian, and that the initiation of the Paleo-Tethys tectonics might initiate near the end of Early-Carboniferous in the East Kunlun-Qaidam region, East Asia.展开更多
The Ceno\|Tethys is a southern branch of the Tethyan ocean and existed in the Mesozoic and early Cenozoic times. The evolution of the Ceno\|Tethys has been discussed based mainly on geological and paleontological data...The Ceno\|Tethys is a southern branch of the Tethyan ocean and existed in the Mesozoic and early Cenozoic times. The evolution of the Ceno\|Tethys has been discussed based mainly on geological and paleontological data obtained from shallow marine sediments on the both sides of the ocean. Pelagic sediments deposited in a deep ocean basin of the Ceno\|Tethys are often incorporated in suture zones. However, geological and paleontological data from the pelagic sediments, which enable us to elucidate the paleoceanography and tectonic evolution of the Ceno\|Tethys, are still limited. The Xialu chert crops out about 30 km south of Xigaze and occupies the southern marginal part of the E—W trending Yarlung Zangbo Suture zone. As a result of radiolarian biostratigraphic research along two continuous sections, we identified seven different aged radiolarian assemblages from pelagic and hemipelagic sediments ranging early Middle Jurassic (Aalenian) to Early Cretaceous. The Aalenian radiolarian fauna is the oldest known record so far for the Xialu chert. It is noteworthy to point out that the fauna came from a chert sample which contains no terrigenous elements other than clay minerals. There is a possibility that radiolarian faunas older than Aalenian age will be discovered from the Xialu chert in the future.展开更多
Differences in rare earth elements and other trace elements in bedded chens reflect the deposihonal settings of the sediments. Based on cerium anomaly (Ce/Ce ), total REE (ΣREE) and other trace element abundance var...Differences in rare earth elements and other trace elements in bedded chens reflect the deposihonal settings of the sediments. Based on cerium anomaly (Ce/Ce ), total REE (ΣREE) and other trace element abundance variahons preserved in the bedded cherts in the Paleo-Tethys, Western Yunnan, three deposihonal regimes can be recotwzed: spreading ridge proximal, ocean-basin floor and conhnental margin. This geochemical method of discriminating deposihonal environments for thine marine sedimentary rocks which are physically indistinct provides a powerful new tool for paleotectonic and paleogeographic recondruchons.展开更多
Objective It is still controversial about when,where and how the East Paleotethys Ocean closed due to the lack of reliable paleomagnetic data from the blocks or terranes located in both sides of the suture,which prohi...Objective It is still controversial about when,where and how the East Paleotethys Ocean closed due to the lack of reliable paleomagnetic data from the blocks or terranes located in both sides of the suture,which prohibits our better understanding of a series of key scientific issues such as how major blocks of East Asia collided together。展开更多
Objective The eastern extending range of the Paleo-Tethys Ocean in southwest China has always been focused and controversial. At the beginning of this century some scholars proposed that the Paleo-Tethys Branch Ocean...Objective The eastern extending range of the Paleo-Tethys Ocean in southwest China has always been focused and controversial. At the beginning of this century some scholars proposed that the Paleo-Tethys Branch Ocean may extend to the Babu-Pingxiang and Cengxi areas along the stouthwestern margin of the South China Block （Cai and Zhang, 2009）. However, the pivotal proof of Late Paleozoic ophoilite and magmatic rocks was absent or sporadical in the Guangxi Zhuang Autonomous Region, resulting in insufficient evidence to support this viewpoint. For the first time this work reported the Late Devonian tuff in the Qinzhou area in the south of the Guangxi Zhuang Autonomous Region and conducted zircon U-Pb dating on it in order to constrain the extension of the Paleo-Tethys Ocean in the South China Block.展开更多
The high-pressure metamorphic belt （HPMB） of eclogite-blueschist in Central Qiangtang （羌塘） lies in the Longmu Co （龙木错）-Shuanghu （双湖） suture zone. To the west, the HPMB extends 500 km from Hongjishan （...The high-pressure metamorphic belt （HPMB） of eclogite-blueschist in Central Qiangtang （羌塘） lies in the Longmu Co （龙木错）-Shuanghu （双湖） suture zone. To the west, the HPMB extends 500 km from Hongjishan （红脊山） to Caiduochaka （才多茶卡）, east of Shuanghu; to the east it extends to Baqing （巴青） and Jitang （吉塘） in Qamdo （昌都）, and then bends southward to Yunnan （云南） Province. Including the Lancangjiang （澜沧江） blueschist belt, the entire HPMB is about 2 000 km long. In Central Qiangtang, the belt is mainly composed of blueschist and eclogite, whereas in West Yunnan it contains only blueschist. The Baqing-Jitang segment is dominated by garnet phengite schist. 40Ar-39Ar dating of glaucophane and phengite from the blueschists yielded plateau ages ranging from 223 to 215 Ma, whereas SHRIMP U-Pb dating of zircon from the eclogites gives metamorphic ages of 243-217 Ma. The calculated metamorphic conditions for the blueschists are 410-460 ℃ and 0.67-0.75 GPa, and for the eclogites, 〈500℃ and 1.56-2.35 GPa. The metamorphic ages suggest that the Longmu Co-Shuanghu suture closed in the Late Triassic. The region south of the Longmu Co-Shuanghu- Lancang suture consists of the pan-African basement overlain by Condwana sedimentary and metasedimentary rocks, whereas the region north of the suture is dominated by the Jinning （晋宁） basement and Yangtze sedimentary and metasedimentary rocks. The Qiangtang HPMB marks the closure of the paleo-Tethys Ocean.展开更多
The Yarlung Zangpo Suture Zone(YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys ocean.We report here geochronological and petrological data obtained for newly discove...The Yarlung Zangpo Suture Zone(YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys ocean.We report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a m(?)lange zone of the YZSZ,in Zhongba area, southwestern Tibet.The gabbros are Late Devonian in age and of intra-oceanic Ocean Island Basalt(OIB) affinity.Single-zircon U-Pb analyses from one representative gabbro sample by SIMS(Secondary展开更多
The study of the tectono-sedimentary evolution of the lower Cretaceous series realized in the southern on the tethysian margin in the Tunisian central-Southerner Atlas, shows that the architecture of this field is gov...The study of the tectono-sedimentary evolution of the lower Cretaceous series realized in the southern on the tethysian margin in the Tunisian central-Southerner Atlas, shows that the architecture of this field is governed by a NW-SE compressive phase. This latter has reactivated the old faults to give birth to associated, distensive and compressive structures at the same time simultaneously. It is about a network of combined strike slip fault EW dextral and sinistral NS which divided the cover into four zones of deformation corresponding to the right dihedron of the strike slip fault system. In the compressive dihedron, the deformation develops essentially several folds and in the distensive dihedron, normal faults which delimit horsts and grabens.展开更多
0 INTRODUCTION Subduction of oceanic plate is vital for carbon redistribution and recycling between Earth's surface and mantle,which plays a critical role in shaping carbon budgets and terrestrial habitability thr...0 INTRODUCTION Subduction of oceanic plate is vital for carbon redistribution and recycling between Earth's surface and mantle,which plays a critical role in shaping carbon budgets and terrestrial habitability through geological time(e.g.,Plank and Manning,2019;Sverjensky et al.,2014;Dasgupta and Hirschmann,2010).The long-term subduction of Pacific/Paleo-Pacific Plate from Late Mesozoic to Cenozoic beneath Northeast China makes this area an ideal candidate for exploring ancient carbon recycling and its impact on Earth's surface environment.展开更多
Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experie...Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experienced significant seismic events,particularly along its northern boundary,highlighting the recurrent seismic activity in the Kyrgyz Republic.The Issyk-Ata fault,stretching 120 km from west to east in the northern Tien Shan,bounds from the north a young,growing anticline demarcating the foothills of the Kyrgyz Range and the Chui depression.This region is susceptible to strong earthquakes,posing a significant threat to the Chui region and Bishkek,the capital city with over a million residents.The youngest fault in the area is the Issyk-Ata fault,traversing the southern part of Bishkek,where modern construction has obscured its features.This study integrates remote sensing,detailed fieldwork,and paleoseismological investigations to map and analyze surface ruptures,quantify vertical displacements,and assess seismic hazards along the Issyk-Ata fault.Using optically stimulated luminescence and radiocarbon dating,we determined ages for documented paleoseismic events,placing two ancient earthquakes in the Holocene.Magnitude estimates suggest seismic events with magnitudes ranging from 6.6 to 7.1.In the Dzhal area,geological and geomorphological analysis yielded a longterm fault-slip rate of 1.15 mm/a.The Issyk-Ata fault shows variable rupture behavior,with distinct segments demonstrating different seismic characteristics and histories of activity.This variability necessitates comprehensive seismic hazard modeling to better understand and mitigate potential risks in the region.展开更多
Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy.In the Middle East,particularly in Libya,Tunisia,and Egypt,nummulitids are key constituents of n...Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy.In the Middle East,particularly in Libya,Tunisia,and Egypt,nummulitids are key constituents of nummulitic limestone reservoirs,making the taxonomic identification of this structurally complex group vital for biostratigraphic and petroleum applications.This review focuses on the genus Gaziryina of the nummulitids,clarifying its taxonomic status,biostratigraphic utility,and paleobiogeographic significance using biometric data from published literature.Previously misidentified as Nummulites pulchellus,Gaziryina species have been systematically reassessed based on biometric data from published literature.The findings confirm Gaziryina as a distinct genus comprising two species:Gaziryina basatinensis(late Lutetian-Bartonian,SBZ15-18a) and Gaziryina pulchellus(late Bartonian-Priabonian,SBZ18a/b-20).Morphological characters(test shape,size progression,chamber configuration,protoconch enlargement) and ontogenetic trends(tight to lax) indicate a phylogenetic transition where Gaziryina basatinensis evolved into Gaziryina pulchellus,consistent with Cope's rule.Paleobiogeographic reconstruction indicates a probable origin in the southern NeoTethys,likely the Western Desert of Egypt,with subsequent dispersal across the northern and southeastern Tethys.These findings confirm Gaziryina as a key biostratigraphic marker,necessitating further research on its evolution and biostratigraphic framework.展开更多
This study reconstructs the lithofacies and paleogeographic evolution of North Africa during the Cambrian to Devonian periods,emphasizing the influence of tectonic events,sea-level fluctuations,and climatic changes on...This study reconstructs the lithofacies and paleogeographic evolution of North Africa during the Cambrian to Devonian periods,emphasizing the influence of tectonic events,sea-level fluctuations,and climatic changes on the region's depositional systems and basin development.Integrating seismic,well log,and core data,we identify key depositional patterns and their implications for hydrocarbon exploration.During sedimentation of diverse stages,the source-to-sink systems underwent significant transitions under provenance variation.During the Cambrian-Ordovician periods,intracratonic sag basins dominated,with braided river systems transitioning into glacial deposits in response to climatic cooling and glaciation.Under the control of the source-to-sink system,Silurian witnessed the opening of the Paleo-Tethys Ocean,leading to extensive marine transgressions and the deposition of organic-rich shales of the Lower Silurian,a primary hydrocarbon source rock.Regression during the Late Silurian introduced deltaic and fluvial systems,influenced by tectonic uplifting.During the Devonian period,the Hercynian Orogeny significantly impacted basin architecture,facilitating the development of passive margin basins.Braided and meandering river systems transitioned into deltaic and shallow marine environments,with Late Devonian anoxic conditions fostering the formation of additional hydrocarbon source rocks.This research highlights the interplay of tectonics,climate,and sea-level changes in shaping North Africa's sedimentary history.The findings provide critical insights into the distribution of hydrocarbon source and reservoir rocks,offering valuable guidance for exploration and development in the region.展开更多
The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep wate...The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .展开更多
文摘There has been a long\|term debate about the Paleo\|Tethyan Ocean in South China continent. Based on the geological and geochemical studies, it is suggested that there exist two tectonic belts in SE Yunnan, SW China called Ailao Shan zone and Shizong—Mile zone, which separate Yangtze Block, Cathysian Block and Indo\|China Block from each other. The evolutionary history and its geodynamics of these suture zones are correlated with the Paleo\|Tethyan Ocean. Both of the zones are keys to understanding whether the Paleo\|Tethyan Ocean extended from Western Yunnan area to east of the South China continent. The Ailao Shan belt consists of Red River fault, Ailao Shan fault, Shuanggou fault and Huashan—Yayi fault, which are the boundaries of the Ailao Shan basement metamorphic belt, ophiolitic melange belt and Island\|arc volcanic\|sediments belt, respectively.The ophiolitic melange belt is characterized by the existence of the ophiolite in Shuanggou area, which represents the relicts of the oceanic crust of the Ailao Shan Ocean. In addition, there exist volcanic rocks in west of the ophiolitic melange belt in Jingdong area. The geochemical characteristics of basalts in Jingdong are similar to that of the E\|MORB. Synthesized studies on geochemistry and tectonics suggest that the basalts in Jingdong area were formed in an extensional rift setting in Devonian.
基金the National Nature Science Foundation of China(Grant Nos.40234041, 49732080) the Teaching and Research Award Program for Outstanding YoungTeachers in HigherLearning Institutions of the Ministry of Education of China.
文摘The Mianlue suture extends from Derni-Nanping-Pipasi-Kangxian to the Lueyang-Mianxian area, then traverses the Bashan arcuate structure eastward to the Huashan region, and finally to the Qingshuihe area of the southern Dabie Mountains. From east to west, with a length of over 1500 km, the ophiolitic melange associations are distributed discontinuously along the suture. The rock assemblages include ophiolite, island-arc and oceanic island rock series, indicating that there existed a suture zone and a vanished paleo-ocean basin. The Mianliie paleo-ocean basin experienced its main expansion and formation process during the Carboniferous-Permian and closed totally in the Triassic. It belongs to the northern branch of the eastern paleotethys, separated from the northern margin of the Yangtze block under the paleotethys mantle dynamic system.
基金The research is supported by National Nature Science Foundation of China No.49172101the State Education Committee Funds for Doctoral Supervisors
文摘A volcano-platform carbonate sequence ,from Carboniferous to Permian , is widely trapped in the deep water deposits in Changning- Menglian belt .Three components can be roughly recognized in ascending order as :the lava .the volcaniclastic and carbonate rocks .In most cases, the sequence is incomplete due to faulting resulted from the strong orogenic compression. But (he stratigraphic succession is continuous except for the two interruptions of paleokarsts . which extended from middle Late Carboniferous to Late Permian and from late Early Permian to Late Permian respectively .A preliminary study indicates that the stratigraphy, petrology , sedimentation , vokanism geochemistry and fossils in the sequence are quite similar to mat in modern and ancient oceanic islands and there may be the relics of ancient oceanic islands in the paleo-Tethys .The differences among these sequences probably suggest a complex configuration of the islands or island chain These islands were formed under infra oceanic environments of the paleo-Tethys ,far from continent and accreted to Simao continental margin in Late Permian .The occurrence of large number of ancient oceanic islands in orogenic belts , including the paleo Tethys, Cordillera , etc ..suggests mat some ancient oceans .such as the paleo Tethys and proto-Pacific ,were full of archipelagoes as their modem counterparts . It is possible that more oceanic islands will be recongnized when sufficient research is done in orogenic belts over the world .
基金Financial support for this study was jointly provided by the National Natural Science Foundation of China (No.41102037)the foundation for the author of National Excellent Doctoral Dissertation of China (No.201324)+1 种基金the Foundation of Young Excellent Scientists of the Shaanxi Province (No.2014KJXX-60)the MOST Special Fund from the State Key Laboratory of Continental Dynamics
文摘Late Paleozoic to Early Mesozoic granites are widespread in the southern Qaidam Basin, northern margin of the eastern Kunlun orogenic belt. Their petrogenesis can provide us insights into the tectonic evolution and crustal growth process in the Qaidam Basin. This paper reports Permian–Triassic granites from the Kunbei area, southwestern Qaidam Basin. Detailed zircon LA-ICP MS U-Pb dating reveals that the granites from the four drilling cores（q404, q406, q1612-8, q1613-8） have identical ages of 251±3, 256±4, 247±2, and 251±6 Ma, respectively, these ages are identical with the Permian–Triassic granites from the eastern Qaidam Basin. Detailed geochemical analyses indicate that these granites display typical affinities of highly-fractionated I-type granites：（1） they have high SiO_2（up to 76.5 wt.%）, Na_2O＋K_2O（7.91 wt.% to 9.48 wt.%） contents and high FeO^T/MgO values of 4.7 to 9.3, suggesting significant fractional crystallization;（2） their low A/CNK values of 0.54 to 1.03, no normative Al-rich minerals, inconsistent with the per-aluminous S-type granites;（3） their low Ga（14.5 ppm to 20.7 ppm） and 10 000×Ga/Al（2.23 to 3.03, most of them 〈2.6） values are inconsistent with the A-type granites;（4） the high Rb（191 ppm to 406 ppm） contents and Rb/Sr（2.1 to 13.4） ratios, as well as the significant negative Eu anomalies（0.10 to 0.42） also indicate significant fractional crystallization of feldspars;（5） their low P_2O_5 contents（0.02 wt.% to 0.10 wt.%） suggest the limited solubility of phosphorus in primitive metaluminous melts. In combination with the geological background, we propose that the Permian–Triassic highly-fractionated I-type granites resulted from partial melting of intra-crustal mafic rocks, and the primitive I-type granitic melts underwent significant fractional crystallization of feldspars. The occurrence of highly-fractionated I-type granites in the southwestern Qaidam Basin suggests a Permian–Triassic active continental margin in the northern margin of the East Kunlun orogenic belt.
基金supported by the National Natural Science Foundation of China(Nos.40972042,40772041,42072030)the Open Research Program of the Key Laboratory of Continental Dynamics,Northwest University
文摘High-temperature magma generation process and granulite-facies metamorphism can provide important information about mantle-crustal interaction and tectonic evolution. The strongly peralu- minous monzonite pluton, the Jinshuikou cordierite granite on the southern margin of the Qaidam Block, can provide important information about the mantle-crustal interaction and constraints on tectonic tran- sition from Proto-Tethys to Paleo-Tethys. This pluton develops enclaves of mafic granulite, amphibolite and quartzofeldspathic rocks, and is cut by massive monzonitic leuco-granite veins. Zircon and monazite U-Pb dating for the cordierite granite, the granulite enclaves and a massive monzonitic leuco-granite vein reveal that the cordierite granitic magma was generated from Mesoproterozoic continental crust with protolith derived from a provenanee that was composed of 〉2.8 Ga old recycled crustal materials and re- corded a -1.7 Ga magmatic event. The continental crust underwent low-pressure granulite-facies metamorphism at -380 Ma ago, whereas the cordierite granite magmas was generated and emplaced during 380 Ma, followed by intrusion of the massive monzonitic leuco-granite vein at circa 370-330 Ma. These data suggest that after the final closure of Proto-Tethys Ocean spreading along the southern Qaidam Block at -420 Ma, break-off of the subducted slab or delamination of the lower crustal base and upwelling of the asthenospheric mantle beneath the southern Qaidam Block occurred before the Mid-Devonian, and that the initiation of the Paleo-Tethys tectonics might initiate near the end of Early-Carboniferous in the East Kunlun-Qaidam region, East Asia.
文摘The Ceno\|Tethys is a southern branch of the Tethyan ocean and existed in the Mesozoic and early Cenozoic times. The evolution of the Ceno\|Tethys has been discussed based mainly on geological and paleontological data obtained from shallow marine sediments on the both sides of the ocean. Pelagic sediments deposited in a deep ocean basin of the Ceno\|Tethys are often incorporated in suture zones. However, geological and paleontological data from the pelagic sediments, which enable us to elucidate the paleoceanography and tectonic evolution of the Ceno\|Tethys, are still limited. The Xialu chert crops out about 30 km south of Xigaze and occupies the southern marginal part of the E—W trending Yarlung Zangbo Suture zone. As a result of radiolarian biostratigraphic research along two continuous sections, we identified seven different aged radiolarian assemblages from pelagic and hemipelagic sediments ranging early Middle Jurassic (Aalenian) to Early Cretaceous. The Aalenian radiolarian fauna is the oldest known record so far for the Xialu chert. It is noteworthy to point out that the fauna came from a chert sample which contains no terrigenous elements other than clay minerals. There is a possibility that radiolarian faunas older than Aalenian age will be discovered from the Xialu chert in the future.
文摘Differences in rare earth elements and other trace elements in bedded chens reflect the deposihonal settings of the sediments. Based on cerium anomaly (Ce/Ce ), total REE (ΣREE) and other trace element abundance variahons preserved in the bedded cherts in the Paleo-Tethys, Western Yunnan, three deposihonal regimes can be recotwzed: spreading ridge proximal, ocean-basin floor and conhnental margin. This geochemical method of discriminating deposihonal environments for thine marine sedimentary rocks which are physically indistinct provides a powerful new tool for paleotectonic and paleogeographic recondruchons.
基金financially supported by the National Natural Science Foundation of China (grants No. 41190071 and 41702229)
文摘Objective It is still controversial about when,where and how the East Paleotethys Ocean closed due to the lack of reliable paleomagnetic data from the blocks or terranes located in both sides of the suture,which prohibits our better understanding of a series of key scientific issues such as how major blocks of East Asia collided together。
基金financially supported by the National Natural Science Foundation of China(grants No.41602105,41530966,41672106 and 41472086)China Postdoctoral Science Foundation(grant No.2016M590655)the fundamental Research Funds for the Central Universities,Ocean University of China
文摘Objective The eastern extending range of the Paleo-Tethys Ocean in southwest China has always been focused and controversial. At the beginning of this century some scholars proposed that the Paleo-Tethys Branch Ocean may extend to the Babu-Pingxiang and Cengxi areas along the stouthwestern margin of the South China Block （Cai and Zhang, 2009）. However, the pivotal proof of Late Paleozoic ophoilite and magmatic rocks was absent or sporadical in the Guangxi Zhuang Autonomous Region, resulting in insufficient evidence to support this viewpoint. For the first time this work reported the Late Devonian tuff in the Qinzhou area in the south of the Guangxi Zhuang Autonomous Region and conducted zircon U-Pb dating on it in order to constrain the extension of the Paleo-Tethys Ocean in the South China Block.
基金supported by the National Natural Science Foundation of China (Nos. 40872146, 40672147, 40773020)China Geological Survey (No. 1212010818015)
文摘The high-pressure metamorphic belt （HPMB） of eclogite-blueschist in Central Qiangtang （羌塘） lies in the Longmu Co （龙木错）-Shuanghu （双湖） suture zone. To the west, the HPMB extends 500 km from Hongjishan （红脊山） to Caiduochaka （才多茶卡）, east of Shuanghu; to the east it extends to Baqing （巴青） and Jitang （吉塘） in Qamdo （昌都）, and then bends southward to Yunnan （云南） Province. Including the Lancangjiang （澜沧江） blueschist belt, the entire HPMB is about 2 000 km long. In Central Qiangtang, the belt is mainly composed of blueschist and eclogite, whereas in West Yunnan it contains only blueschist. The Baqing-Jitang segment is dominated by garnet phengite schist. 40Ar-39Ar dating of glaucophane and phengite from the blueschists yielded plateau ages ranging from 223 to 215 Ma, whereas SHRIMP U-Pb dating of zircon from the eclogites gives metamorphic ages of 243-217 Ma. The calculated metamorphic conditions for the blueschists are 410-460 ℃ and 0.67-0.75 GPa, and for the eclogites, 〈500℃ and 1.56-2.35 GPa. The metamorphic ages suggest that the Longmu Co-Shuanghu suture closed in the Late Triassic. The region south of the Longmu Co-Shuanghu- Lancang suture consists of the pan-African basement overlain by Condwana sedimentary and metasedimentary rocks, whereas the region north of the suture is dominated by the Jinning （晋宁） basement and Yangtze sedimentary and metasedimentary rocks. The Qiangtang HPMB marks the closure of the paleo-Tethys Ocean.
文摘The Yarlung Zangpo Suture Zone(YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys ocean.We report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a m(?)lange zone of the YZSZ,in Zhongba area, southwestern Tibet.The gabbros are Late Devonian in age and of intra-oceanic Ocean Island Basalt(OIB) affinity.Single-zircon U-Pb analyses from one representative gabbro sample by SIMS(Secondary
文摘The study of the tectono-sedimentary evolution of the lower Cretaceous series realized in the southern on the tethysian margin in the Tunisian central-Southerner Atlas, shows that the architecture of this field is governed by a NW-SE compressive phase. This latter has reactivated the old faults to give birth to associated, distensive and compressive structures at the same time simultaneously. It is about a network of combined strike slip fault EW dextral and sinistral NS which divided the cover into four zones of deformation corresponding to the right dihedron of the strike slip fault system. In the compressive dihedron, the deformation develops essentially several folds and in the distensive dihedron, normal faults which delimit horsts and grabens.
基金supported by the National Natural Science Foundation of China(Nos.42130310 and 41972055)。
文摘0 INTRODUCTION Subduction of oceanic plate is vital for carbon redistribution and recycling between Earth's surface and mantle,which plays a critical role in shaping carbon budgets and terrestrial habitability through geological time(e.g.,Plank and Manning,2019;Sverjensky et al.,2014;Dasgupta and Hirschmann,2010).The long-term subduction of Pacific/Paleo-Pacific Plate from Late Mesozoic to Cenozoic beneath Northeast China makes this area an ideal candidate for exploring ancient carbon recycling and its impact on Earth's surface environment.
基金financial support of the Faculty Research Grant project of the American University of Central Asia(AUCA)supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea(NRF-2023S1A5B5A16080131)。
文摘Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experienced significant seismic events,particularly along its northern boundary,highlighting the recurrent seismic activity in the Kyrgyz Republic.The Issyk-Ata fault,stretching 120 km from west to east in the northern Tien Shan,bounds from the north a young,growing anticline demarcating the foothills of the Kyrgyz Range and the Chui depression.This region is susceptible to strong earthquakes,posing a significant threat to the Chui region and Bishkek,the capital city with over a million residents.The youngest fault in the area is the Issyk-Ata fault,traversing the southern part of Bishkek,where modern construction has obscured its features.This study integrates remote sensing,detailed fieldwork,and paleoseismological investigations to map and analyze surface ruptures,quantify vertical displacements,and assess seismic hazards along the Issyk-Ata fault.Using optically stimulated luminescence and radiocarbon dating,we determined ages for documented paleoseismic events,placing two ancient earthquakes in the Holocene.Magnitude estimates suggest seismic events with magnitudes ranging from 6.6 to 7.1.In the Dzhal area,geological and geomorphological analysis yielded a longterm fault-slip rate of 1.15 mm/a.The Issyk-Ata fault shows variable rupture behavior,with distinct segments demonstrating different seismic characteristics and histories of activity.This variability necessitates comprehensive seismic hazard modeling to better understand and mitigate potential risks in the region.
文摘Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy.In the Middle East,particularly in Libya,Tunisia,and Egypt,nummulitids are key constituents of nummulitic limestone reservoirs,making the taxonomic identification of this structurally complex group vital for biostratigraphic and petroleum applications.This review focuses on the genus Gaziryina of the nummulitids,clarifying its taxonomic status,biostratigraphic utility,and paleobiogeographic significance using biometric data from published literature.Previously misidentified as Nummulites pulchellus,Gaziryina species have been systematically reassessed based on biometric data from published literature.The findings confirm Gaziryina as a distinct genus comprising two species:Gaziryina basatinensis(late Lutetian-Bartonian,SBZ15-18a) and Gaziryina pulchellus(late Bartonian-Priabonian,SBZ18a/b-20).Morphological characters(test shape,size progression,chamber configuration,protoconch enlargement) and ontogenetic trends(tight to lax) indicate a phylogenetic transition where Gaziryina basatinensis evolved into Gaziryina pulchellus,consistent with Cope's rule.Paleobiogeographic reconstruction indicates a probable origin in the southern NeoTethys,likely the Western Desert of Egypt,with subsequent dispersal across the northern and southeastern Tethys.These findings confirm Gaziryina as a key biostratigraphic marker,necessitating further research on its evolution and biostratigraphic framework.
基金financially supported by the National Natural Science Foundation of China(Grant No.92255302).
文摘This study reconstructs the lithofacies and paleogeographic evolution of North Africa during the Cambrian to Devonian periods,emphasizing the influence of tectonic events,sea-level fluctuations,and climatic changes on the region's depositional systems and basin development.Integrating seismic,well log,and core data,we identify key depositional patterns and their implications for hydrocarbon exploration.During sedimentation of diverse stages,the source-to-sink systems underwent significant transitions under provenance variation.During the Cambrian-Ordovician periods,intracratonic sag basins dominated,with braided river systems transitioning into glacial deposits in response to climatic cooling and glaciation.Under the control of the source-to-sink system,Silurian witnessed the opening of the Paleo-Tethys Ocean,leading to extensive marine transgressions and the deposition of organic-rich shales of the Lower Silurian,a primary hydrocarbon source rock.Regression during the Late Silurian introduced deltaic and fluvial systems,influenced by tectonic uplifting.During the Devonian period,the Hercynian Orogeny significantly impacted basin architecture,facilitating the development of passive margin basins.Braided and meandering river systems transitioned into deltaic and shallow marine environments,with Late Devonian anoxic conditions fostering the formation of additional hydrocarbon source rocks.This research highlights the interplay of tectonics,climate,and sea-level changes in shaping North Africa's sedimentary history.The findings provide critical insights into the distribution of hydrocarbon source and reservoir rocks,offering valuable guidance for exploration and development in the region.
文摘The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .
