Recently, the Altyn strike\|slip fault in western China has become a hot topic to the research on continental dynamics of Tibetan Plateau. The chronological research is very important to constrain the age of tectono\|...Recently, the Altyn strike\|slip fault in western China has become a hot topic to the research on continental dynamics of Tibetan Plateau. The chronological research is very important to constrain the age of tectono\|thermal event within Altyn fault belt. Many isotopic dating researches, related to the ophiolites, high\|pressure metamorphic rocks and some granitic rocks, have been done by Chinese and foreign geologists in the area. There, however, are only few isotopic dating researches on the syntectonic\|growing minerals within Altyn fault. We collected a sample of Caledonian mylonitized granite (At3a) in the north of Dangjin pass and two samples of Jurassic meta\|sedimentary rocks in Qaidam gate fault\|valley (At37c) and Geshi fault\|valley (At30d). All the samples contain the syntectonic\|growing minerals such as white mica, chlorite, sericite and biotite etc. By dating these minerals, we can constrain the time of the tectonic events occurred in Altyn fault belt.Sample At3a, mylonitized granite, has been strongly deformed with undulating extinction of quartz. The plagioclase and quartz were elongated and surrounded by fine\|grained white micas and chlorites with strain shadow texture. These suggest that the sample has been suffered ductile deformation. The estimation of p\|T condition is 350℃, 180MPa. The isochronal age of (89.2±1.6)Ma has been obtained by laser probe 40 Ar/ 39 Ar dating analyses of six white mica grains.展开更多
As the northern boundary of Tibetan Plateau, the Altyn strike\|slip fault in western China has a very important implication to the tectonic division in the middle Asia continent, and has become a hot topic for the res...As the northern boundary of Tibetan Plateau, the Altyn strike\|slip fault in western China has a very important implication to the tectonic division in the middle Asia continent, and has become a hot topic for the research on continental dynamics of Tibetan Plateau. During the research of our project funded by NSFC, we collected a sample of Caledonian mylonitized granite in the north of Dangjin pass and two samples of Jurassic meta\|sedimentary rocks in Qaidam gate fault\|valley and Geshi fault\|valley. The texture study shows that all samples were reformed by ductile deformation with undulating extinction and elongated quartzes. The metamorphic p\|T condition are estimated to be 350～500℃ and 150～450MPa They contain the syntectonic\|growing minerals such as white mica, chlorite, sericite and biotite etc. By dating these minerals, we obtain a group white mica 40 Ar/ 39 Ar isochronal age of 89 2～91 7Ma and a (46 6±6 4)Ma sericite 40 Ar/ 39 Ar apparent age. These data are very important to determine the strike\|slip age of Altyn fault.The 40 Ar/ 39 Ar age data (91～46Ma), we obtained, are reported for the first time in the researches of Altyn fault belt. The ages of 91～89Ma indicate that Altyn fault began to slip with slight metamorphism around late Jurassic. These ages are consistent with the ages of the collision between Kohistan\|Ladakh massif (northwestern India) and Eurasian continent at 102～85Ma.This suggests that the strike\|slip movement of Altyn fault should be related to the formation of the so\|called“Western tectonic joint" in Nepal\|western Kunlun area. The age of 46Ma should represent the overprint age of the tectono\|thermal event during main collision between Indian and Eurasian continents along the Yarlung Zangbo River. With the continent\|continent collision of Indian and Eurasian Plates, Altyn fault underwent Multi\|phase strike\|slip events in late Paleocene—Oligocene (37～35Ma), Miocene (22～20Ma), Miocene—Pliocene (8～6Ma), Pliocene (2 5Ma) and early Pleistocene (1～0 7Ma), respectively. The eastern extension of Altyn fault has two branches, one to Xar Moron River with around 3500km length, and another to Okhotsk Ocean with about 4500km length. So Altyn fault is the biggest strike\|slip fault in Cenozoic in the Middle Asia continent, it is characterized by sinistral strike\|slip movement. The basins and tectonic belts, formed before late Jurassic, on the both side of Altyn fault should be displaced. Therefore, the tectonic outline of western China should be re\|recognized.展开更多
The east\|west striking Northern Altyn Tagh Fault, about 240km long between Bashkaogong (90°E, 39°25′N) and Lapeiquan (92°15′E, 39°25′N), was previously mapped as a north\|dipping thrust, juxtap...The east\|west striking Northern Altyn Tagh Fault, about 240km long between Bashkaogong (90°E, 39°25′N) and Lapeiquan (92°15′E, 39°25′N), was previously mapped as a north\|dipping thrust, juxtaposing late Archean\|Mesoproterozoic gneisses in the hanging wall over Paleozoic volcanics, plutons, turbidite, and melange complexes in the footwall. In order to estimate the total magnitude of slip along the Cenozoic Altyn Tagh fault, we conducted geologic mapping along four traverses across the Jinyan Shan where the fault lies. Our field observations suggest that the fault is south\|dipping, with dip angles varying from <25° in the east to about 40° in the west. The eastern fault zone exhibits mylonitic fabrics, whereas the western fault zone is characterized by cataclastic deformation. Kinematic indicators in the ductily deformed mylonitic shear zone consistently show a top\|to\|the\|south sense of shear, suggesting that the Northern Altyn Tagh fault is a south\|dipping normal fault, not a north\|dipping thrust.. The ductile shear zone is typically 30～40m thick, consisting of highly sheared metasediments (pelite and marble), granites, and granitic veins.The latter are systematically cut by small\|scale, south\|dipping ductile normal faults with displacements between 10s of cm to several meters, forming spectacular asymmetric boudinages in the sheared meta\|pelite matrix.The minimum displacement along the detachment is about 20km, as measured by the north\|south width of the exposed footwall gneisses. We renamed the Northern Altyn Tagh Fault in the Jinyan Shan region as the Lapeiquan detachment fault to avoid confusion with other east\|west trending Cenozoic faults to the west along the northern edge of the Altyn Tagh range (e.g., the Cenozoic Jianglisai fault near Qiemo), collectively known as the Northern Altyn Tagh fault system (see Cowgill et al., Geology,in press). The lower age bound of the Lapeiquan fault is Ordovician, as the fault cuts Ordovician volcanics and plutons in its hanging wall. As the Ordovician volcanic rocks are folded together with Carboniferous marbles and Jurassic sedimentary strata, it is likely that normal faulting along the Lapeiquan detachment postdates the Jurassic. The Lapeiquan detachment fault is covered by Quaternary sediments of the Tarim basin in the west, and is apparently truncated by the Cenozoic left\|slip Altyn Tagh fault to the east as indicated by regional geologic maps. If true, this relationship implies that the Lapeiquan fault predates the Cenozoic Altyn Tagh fault. The apparent truncational relationship between the Lapeiquan fault and the Altyn Tagh fault posses an important question: where is the counterpart of the Lapeiquan fault south of the Altyn Tagh fault? Preliminary mapping in the Yema Nan Shan south of the Altyn Tagh fault reveals a fragment of a low\|angle mylonitic shear zone, which is interpreted as a detachment fault because it puts lower\|grade meta\|pelite over higher\|grade mylonitic quartzite. The correlation of detachment faults in the Yema Nan Shan and the Lapeiquan area would imply an amount of about 280～300km left slip along the Altyn Tagh fault. Alternatively, movement along the Lapeiquan detachment fault could have been synchronous with the development of the Cenozoic Altyn Tagh fault. This interpretation requires no counterpart of the Lapeiquan fault south of the Altyn Tagh fault. Instead, it implies that a major topographic collapse event occurred in the Cenozoic along the northern edge of the Tibetan plateau during movement along the Altyn Tagh fault. On\|going thermochronologic analysis will provide constraints on the age of the detachment fault and a test for the two distinctive hypotheses.展开更多
The Altyn Tagh fault (ATF) extending in NEE—SWW direction lying at the northwestern boundary of Qinghai—Tibet plateau is the largest strike\|slip fault in Central Asia. On the basis of recent geologic mapping and de...The Altyn Tagh fault (ATF) extending in NEE—SWW direction lying at the northwestern boundary of Qinghai—Tibet plateau is the largest strike\|slip fault in Central Asia. On the basis of recent geologic mapping and detailed study of lithotectonic characteristics for the paleotectonic units at the two sides of the Altyn Tagh Fault ( Altun Mt. to west and the Qilian Mt. to east ) we propose that the paleotectonic units in the Altun Mt. can be correlated with those in the Qilian Mt. assuming 400km left\|lateral displacement for the Altyn Tagh fault. Natural seismic data across the Altun Mt. indicate that the Altyn Tagh fault is a lithospheric shear fault and the lithospheric shearing is probably related to southward intracontinental oblique subduction of the Tarim terrane beneath the Altun Mt.1\ Comparison of the major paleotectonic units at the two sides of the Altyn Tagh fault\;(1) The Alxa\|Dunhuang Massif:The Alxa massif lying at the southern margin of the Sino\|Korean craton consists mainly of an Early Proterozoic basement including high\|grade and middle\|grade metamorphic rocks, which were intruded by granite at 1719Ma. The Paleozoic passive margin sediments is well developed. In the Altun Mt., the Early Proterozoic and late Archean basement of the Duhuang massif includes high\|grade and middle\|grade metamorphic rocks dating 2789Ma (Sm\|Nd method) and 2405Ma (U\|Pb method).展开更多
A 100～500m\|wide mylonite zone in the Altun Group of Lower Proterozoic age was discovered along the Altyn Tagh strike\|slip fault. The zone is mainly composed of amphibolitic and granitic mylonites. The planar joints...A 100～500m\|wide mylonite zone in the Altun Group of Lower Proterozoic age was discovered along the Altyn Tagh strike\|slip fault. The zone is mainly composed of amphibolitic and granitic mylonites. The planar joints of the rocks strike in NE70 and dip steeply (nearly vertical), coincident with the striking of Altyn Tagh fault zone, and their stretched lineations are nearly horizontal. Shear strains are well developed and show sinistral sheared. The amphibolitic and granitic mylonites are most probably the products of deep\|seated melting caused by sinistral strike\|slip shearing as suggested by the evidence below: (1) The migmatization is intensely developed and spatially controlled by the shear zone, and the rock has a set of NNE perspective foliation which is in accord with the direction of the Altyn Tagh strike\|slip fault zone. (2) The recrystallized hornblende aggregate is distributed in band with obvious nebulous texture, indicating the characteristics of anatexis, and the hornblendes are oriented and form the nearly horizontal stretching lineation; some hornblendes have titanite inclusions, and magmatic long\|columnar zircons are in directional arrangement.(3) The banded felsic material is developed, and the plagioclase is characteristic of high\|temperature plastic deformation and shows sinistral shear stain. (4) In mylonites, all the axis C fabric of quartz shows the feature of sinistral shearing and the majority is generally middle to low temperature fabric, but there also exists high temperature fabric, which suggests that high temperature shearing occur in the early stage of strike\|slip deformation and it is characterized by middle to low temperature shearing at the beginning of anatexis or in the late stage of the deformation. (5) On the XZ plane of mylonite and mylonitized rocks, there exists the consistent sinistral shear stain, which suggests the products of the same strike\|slip shearing.Zircons were separated from three samples of mylonitized granitic rocks for age dating. Two groups of zircon were distinguished in morphology: one is elongate prismatic grains, and the other shows slight rounding. Some zoned structure of selected grains were examined by cathodoluminescence. Dating was completed in the SHRIMP laboratory of Stanford University. Fifteen analyses were made on 14 zircon grains. Sample S99\|25 show two obvious two age groups, one is 527～549Ma, and the other is 466～472Ma. Sample S99\|9 contains two age groups either, one is 475～507Ma and the other is 279Ma. Sample S99\|6 shows three groups: ① 528Ma; ② 365Ma and③ 238～243Ma, here the 365Ma is explained as mixture age between the other two age groups according to its exact location in the grain. In summary, from the three samples we found at least three age groups: 507～548Ma; 466～472Ma; 238～243Ma.The ages of 507Ma to 548Ma and 466Ma to 472Ma represent the deformation and metamorphism of Early Paleozoic age, which is most likely correspond to the close of the Qilian Sea and continental subduction and collision reported in recent papers (Yang Jingsui et al., 1998; Zhang Jianxin et al., 1999; Xu Zhiqin et al., 1999). The 238～243Ma most likely represent the formational age of the Altyn Tagh strike\|slip fault, which is consistent with the formational age (200～240Ma) of the large\|scale sinistral strike\|slip fault zone of the South Margin of East Kunlun (Li Haibing et al., 1996), and both can be attributed to the oblique subduction and collision of the Bayan Har terrane with the East Kunlun terrane during Indosinian period.展开更多
One of the focus views of the uplifting of Tibetan Plateau is the growth history of the plateau. This is an unresolved question because of the poor study in north margin, where the ATF (Altyn Tagh Fault) is acting an ...One of the focus views of the uplifting of Tibetan Plateau is the growth history of the plateau. This is an unresolved question because of the poor study in north margin, where the ATF (Altyn Tagh Fault) is acting an important role in the growth and deformation of the plateau. The fault links two huge contractional belts, e.g. Qilian Nan Shan and West Kunlun, and merges a series of thrusting\|folding arcs in southeast. Mapping of piercing points, such as unconformities between Cenozoic, Mesozoic and Paleozoic strata, and magmatic arcs, shows left slips of ca. 240km and ca. 550km along the middle and western segments of the ATF. About 140～450km of crustal shortening, approximately the same magnitude as the west segment of the ATF, is deduced from balanced sections in West Kunlun foreland thrusting belt. This implies that left\|slip displacement along the west segment of the ATF was absorbed by the contraction in West Kunlun. The ATF system merged bunches of WNW arcuated fold\|fault belts in Qaidam basin, implying anti\|clockwise rotation. Tertiary and some Lower to Middle Pleistocene strata involved in fold\|fault belts, and dip in ESE due to the uplifting of Altyn Tagh. The newest strata involved in the deformation is more and more younger from south to north, that is, from Lower Pliocene to Middle Pleistocene, showing the uplifting trends from south to north in the SE side of the fault.展开更多
The NEE\|striking Altyn Tagh Fault (ATF) has been well known as one major point to know the growth history of the Tibetan plateau. Lots of investigations done since 1970’s were mostly focus on active features, partic...The NEE\|striking Altyn Tagh Fault (ATF) has been well known as one major point to know the growth history of the Tibetan plateau. Lots of investigations done since 1970’s were mostly focus on active features, particularly on determining slip, slip rate and their distribution along the fault. However, Cenozoic slip\|history of this fault remains poorly understood, and the age of initiation and total offset are controversial. Several Cenozoic sedimentary basins develop in Suo’erkulinan to Mangya regions (Fig.1). Their sedimentary processes are closely related with the ATF. The studies of the Neogene sedimentary sequences and the reconstruction of the paleo\|geography are essential to establish the displacement history of the fault during Late Cenozoic.Located at the southern side of the ATF, the Suo’erkulinan basin consists of more than 600\|meter\|thick Pliocene Shizigou Formation below and about 120\|meter\|thick Early to Middle Pleistocene Qigequan Formation above according to the 1∶200000 geological map by Xinjiang Province. An obvious erosional surface can be seen on the top of the lower sequence. Sediments in the Shizigou Formation are characterized by 400\|meter\|thick yellow to red cobble\|sized conglomerates in the bottom, up\|grading to sandstones and grey\|green mudstones. This indicated that the sedimentary facies changed from alluvial fan to fluvial fan and sediments became more and more mature. The upper sequence, the Qigequan Formation, corresponds to an alluvial facies series composed of yellow to white cobble\|sized conglomerates intercalated with lenticular sandstones. Paleo\|current indicators showed that the Shizhigou conglomeratic series were sourced from northwest. Well\|developed syn\|sedimentary faults, normal faults mostly inherited from syn\|sedimentary faults, and some striation lineations on the surface indicated transtensional tectonic environment of the strike\|slip faulting.展开更多
The transform fault is essentially a displacement fault whose terminal part is adjusted by other tectonic types, its displacement component is absorbed by other structures intersected with it by high angles or meet at...The transform fault is essentially a displacement fault whose terminal part is adjusted by other tectonic types, its displacement component is absorbed by other structures intersected with it by high angles or meet at right angles. The main elements of transform fault are the sleep\|dipping displacement faults and the adjusted structures intersected with it at high angles. According to the combination of tectonic features formed by its two ends of displacement fault and the structures intersected with it, the transform fault can be divided into three types, including the adjusted transform fault of extensional normal fault, the adjusted transform fault of compressive fold and thrust fault, and the compound transform fault. The transform fault is different from the displacement fault, its horizontal displacement may be increased or decreased or not be changed at all as the time of fault movement extended, but for parallel displacement the dislocation will be increased. Therefore, the study of transform fault is very important for the recognition of long time disputed displacement components of huge displacement fault. The traditional Altyn fault is the adjusting fault of the compression deformation of the Western Kunlun and Northern Qilian mountains of the northern margin of the Tibetan Plateau since Cenozoic.展开更多
The ENE\|striking Altyn Tagh Fault (ATF) has been well known as a large, active left\|lateral strike\|slip fault that bounds the thrusting systems in NE Tibet.This fault has been the focal point in the debate between ...The ENE\|striking Altyn Tagh Fault (ATF) has been well known as a large, active left\|lateral strike\|slip fault that bounds the thrusting systems in NE Tibet.This fault has been the focal point in the debate between the discrete extrusion vs. distributed crustal shortening models. Although its active left\|lateralstrike\|slip features have been largely investigated and well documented by both satellite imagery and air\|photo interpretations and field observations, little study has been done upon its Cenozoic displacement history. Questions about the age of initiation and total offset accumulated on the fault remain controversial. A key area to resolve such question is located along the central segment of the fault in the Souerkuli and Mangar regions, where Neogene sedimentary basins well develop and are mostly distributed in three zones, namely from east to west: the Gobiling, Yitunbulak and Yusuale Tagh (Fig.1). Our field investigations were conducted along the ATF cutting the Yitunbulak and Gebiling Neogene sedimentary basins. Two stratigraphic unconformities observed within this Neogene conglomeratic series allow a separation of three major stratigraphic sequences and record the initiation and major deformational episodes of ATF during Cenozoic. An early stratigraphic unconformity occurred between a yellow depositional series below and early Pliocene red\|colored conglomeratic mudstones above. A later stratigraphic unconformities occurred between early and late Pliocene sedimentary series. The lower series below the early stratigraphic unconformities is mainly composed of a conglomeratic rocks containing cobbles and pebbles of basement rock units (mostly mylonitic granites, limestones and quartzes); this series has been poorly mapped and dated; its age could be assigned to late Oligocene to early Miocene; this series tilts to NW with an angle of about 30° and is overlain in angular unconformity by early Pliocene pebble\|sized conglomerates. A weathering zone on top of the lower conglomeratic series is clearly seen, that represents a long period of uplift and erosion. This lacuna occurred between early Miocene and early Pliocene in the west Qaidam basin, which has been documented only locally. Early Pliocene deposits correspond to alluvial to lacustrine facies rocks deposited in strike\|slip basin probably originated at releasing bend of the strike\|slip ATF; late Pliocene deposits is composed by fluviatile conglomerates and fanglomerates lying in unconformity on the upper Pliocene rocks. Early Quaternary deposits are absent along the ATF and have been well documented in the Qaidam basin. Late Quaternary fanglomerates infills active fault valleys.展开更多
he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward disp...he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward displacement of the Tibet plateau relative to the Tarim. The Altyn Tagh fault zone is a typical transpressional fault zone, characterized by blocks rotation and crustal shortening and vertical extrusion of blocks within the Altyn Tagh strike\|slip system. Differences of three\|dimensional deformation and configuration of the active structures are recognized at different segment of the Altyn Tagh fault zone.1\ Structural configuration of the Altyn Tagh fault zone\;In the Altyn Tagh strike\|slip fault zone, the assemblage pattern of the (active) faults is in the form of parallel plumes, especially in the eastern and the western segments of the Altyn Tagh fault zone. These plumes structures in the eastern segment are assembled by string\|like left lateral strike\|slip fault and broom\|like thrusting faults, and in the western segment by arc\|like left lateral strike\|slip faults along with thrusting faults and normal faults. In the middle segment of the Altyn Tagh fault zone, the structures are characterized by the string\|like left lateral strike\|slip faults in the center and reverse thrusting faults on the two sides.展开更多
The age and evolutional history of the Altyn Tagh fault and its role in the formation and uplift of the Qinghai—Tibetan plateau have been focused for years. Many geologists believe that the formation of the fault is ...The age and evolutional history of the Altyn Tagh fault and its role in the formation and uplift of the Qinghai—Tibetan plateau have been focused for years. Many geologists believe that the formation of the fault is a result of the collision between India and Asia. Some people thought that it should have formed earlier than Cenozoic but have no critical evidence. Here we report a preliminary result from our recent investigation on the volcanic rocks at the north end of the Altyn Tagh fault.1 The volcanic rocks on the north end of the Altyn Tagh fault The volcanic rocks are located on the north end of the Altyn Tagh fault, northern Qinghai—Tibetan plateau. The investigated volcano occurs in the Jiuxi basin, a Cretaceous and Tertiary depositional basin. It is about 300m×100m in size and form about a 100m high cliff above the folded Cretaceous strata. It likes relic neck of a volcano rather than a kind of widely distributed lava flow commonly seen in the northern Tibet. The country rocks are Cretaceous sandstone, silt and fine\|grained conglomerate. The cliff formed most likely due to the differing erosion between the hard volcanic rocks and soft rocks.展开更多
Fieldwork along several segments of the Altyn Tagh Fault,between 85 and 95°E,confirms that it ranks as one of the most active faults of Asia.In the East,near Aksay,the active fault trace offsets numerous stream c...Fieldwork along several segments of the Altyn Tagh Fault,between 85 and 95°E,confirms that it ranks as one of the most active faults of Asia.In the East,near Aksay,the active fault trace offsets numerous stream channels,terrace risers and fans tens to hundreds of meters. 14 C dating of organic remains and charcoal within terrace gravels indicates that most of the terraces were emplaced after the beginning of the Holocene,implying a left\|slip rate of about 2cm/a.Large mole tracks attest to the occurrence of great earthquakes.Even larger mole tracks are found north of Lenghu,within the Altun Shan push\|up,a 6000 m high range in a restraining bend of the fault,now sliced by its most active strand.North of Huatougou,at the transition between another push\|up mountain and a recent pull\|apart basin,a spectacular sequence of five flat\|floored,hanging channels,beheaded by the fault from a unique source in the mountain,have been horizontally displaced by up to 1250m.Cosmogenic dating of the abandonment of these channels and of nearby offset terrace risers confirms the slip\|rate at Aksay.Several km to the west,pressure ridges exceeding 10m in height across a large young fan,imply the repeat of several great earthquakes in a relatively short time span.展开更多
The Altun and North Qaidam Mountains at the northern margin of Qinghai\|Tibet plateau are separated by the Altyn Tagh sinistral strike\|slip fault, which is one of the largest strike\|slip fault systems in the world a...The Altun and North Qaidam Mountains at the northern margin of Qinghai\|Tibet plateau are separated by the Altyn Tagh sinistral strike\|slip fault, which is one of the largest strike\|slip fault systems in the world and was considered as the key element in the escape tectonics model for Euraisa\|India continent\|continent collision.Recently,the eclogites within quratzifeldspathic gneisses or pelitic gneisses characterized by amphibolite\|facies paragenesis were discovered in the Altun and the North Qaidam Mountains(Fig.1). They occur as lens or boundins within the Altun Group and Dakendaban Group respectively which previously were considered as metamorphic basement of Tarim block and Qaidam block. Our studies indicate that the eclogites outcrop in both the Altun and North Qaidam Mountains show similar occurrences, associated country rocks, rock and mineral assemblages, p\|T\% estimates, geochemistryand protolith feature and ages of peak metamorphism (see table) . The garnet\|omphacite\|phengite geothermobarometer gave equilibrium condition of \%p\%=2 8～3 0GPa and t =820～850℃ for the Altun eclogite and p =2 8GPa and \%t\%=730℃ for North Qaidam eclogite respectively(Fig..2). These p\|T conditions are in the coesite stability field. Moreover, Po lycrystalline quartz pseudomorphs after coesite have been identified in the Dulan area, North Qaidam Mountains (Song et al, in review). Therefore, these features suggest that both eclogites of Altun and North Qaidam Mountains probably are a same HP\|UHP metamorphic belt formed from the same of Early Paleozoic age deep subduction and collision, and subsequently displaced by the Altyn Tagh fault.The case is similar to the Dabie\|Sulu HP\|UHP metamorphic zone which was truncated by the Tanlu sinistral strike\|slip fault and splitted it into two distincts, the Dabie region and Sulu region. These correlations support an about 350～400km displacement of the Altyn Tagh sinistral strike\|slip fault (Fig.1).展开更多
基金theNationalNaturalScienceFundCommittee (NO .4 9772 157)
文摘Recently, the Altyn strike\|slip fault in western China has become a hot topic to the research on continental dynamics of Tibetan Plateau. The chronological research is very important to constrain the age of tectono\|thermal event within Altyn fault belt. Many isotopic dating researches, related to the ophiolites, high\|pressure metamorphic rocks and some granitic rocks, have been done by Chinese and foreign geologists in the area. There, however, are only few isotopic dating researches on the syntectonic\|growing minerals within Altyn fault. We collected a sample of Caledonian mylonitized granite (At3a) in the north of Dangjin pass and two samples of Jurassic meta\|sedimentary rocks in Qaidam gate fault\|valley (At37c) and Geshi fault\|valley (At30d). All the samples contain the syntectonic\|growing minerals such as white mica, chlorite, sericite and biotite etc. By dating these minerals, we can constrain the time of the tectonic events occurred in Altyn fault belt.Sample At3a, mylonitized granite, has been strongly deformed with undulating extinction of quartz. The plagioclase and quartz were elongated and surrounded by fine\|grained white micas and chlorites with strain shadow texture. These suggest that the sample has been suffered ductile deformation. The estimation of p\|T condition is 350℃, 180MPa. The isochronal age of (89.2±1.6)Ma has been obtained by laser probe 40 Ar/ 39 Ar dating analyses of six white mica grains.
文摘As the northern boundary of Tibetan Plateau, the Altyn strike\|slip fault in western China has a very important implication to the tectonic division in the middle Asia continent, and has become a hot topic for the research on continental dynamics of Tibetan Plateau. During the research of our project funded by NSFC, we collected a sample of Caledonian mylonitized granite in the north of Dangjin pass and two samples of Jurassic meta\|sedimentary rocks in Qaidam gate fault\|valley and Geshi fault\|valley. The texture study shows that all samples were reformed by ductile deformation with undulating extinction and elongated quartzes. The metamorphic p\|T condition are estimated to be 350～500℃ and 150～450MPa They contain the syntectonic\|growing minerals such as white mica, chlorite, sericite and biotite etc. By dating these minerals, we obtain a group white mica 40 Ar/ 39 Ar isochronal age of 89 2～91 7Ma and a (46 6±6 4)Ma sericite 40 Ar/ 39 Ar apparent age. These data are very important to determine the strike\|slip age of Altyn fault.The 40 Ar/ 39 Ar age data (91～46Ma), we obtained, are reported for the first time in the researches of Altyn fault belt. The ages of 91～89Ma indicate that Altyn fault began to slip with slight metamorphism around late Jurassic. These ages are consistent with the ages of the collision between Kohistan\|Ladakh massif (northwestern India) and Eurasian continent at 102～85Ma.This suggests that the strike\|slip movement of Altyn fault should be related to the formation of the so\|called“Western tectonic joint" in Nepal\|western Kunlun area. The age of 46Ma should represent the overprint age of the tectono\|thermal event during main collision between Indian and Eurasian continents along the Yarlung Zangbo River. With the continent\|continent collision of Indian and Eurasian Plates, Altyn fault underwent Multi\|phase strike\|slip events in late Paleocene—Oligocene (37～35Ma), Miocene (22～20Ma), Miocene—Pliocene (8～6Ma), Pliocene (2 5Ma) and early Pleistocene (1～0 7Ma), respectively. The eastern extension of Altyn fault has two branches, one to Xar Moron River with around 3500km length, and another to Okhotsk Ocean with about 4500km length. So Altyn fault is the biggest strike\|slip fault in Cenozoic in the Middle Asia continent, it is characterized by sinistral strike\|slip movement. The basins and tectonic belts, formed before late Jurassic, on the both side of Altyn fault should be displaced. Therefore, the tectonic outline of western China should be re\|recognized.
文摘The east\|west striking Northern Altyn Tagh Fault, about 240km long between Bashkaogong (90°E, 39°25′N) and Lapeiquan (92°15′E, 39°25′N), was previously mapped as a north\|dipping thrust, juxtaposing late Archean\|Mesoproterozoic gneisses in the hanging wall over Paleozoic volcanics, plutons, turbidite, and melange complexes in the footwall. In order to estimate the total magnitude of slip along the Cenozoic Altyn Tagh fault, we conducted geologic mapping along four traverses across the Jinyan Shan where the fault lies. Our field observations suggest that the fault is south\|dipping, with dip angles varying from <25° in the east to about 40° in the west. The eastern fault zone exhibits mylonitic fabrics, whereas the western fault zone is characterized by cataclastic deformation. Kinematic indicators in the ductily deformed mylonitic shear zone consistently show a top\|to\|the\|south sense of shear, suggesting that the Northern Altyn Tagh fault is a south\|dipping normal fault, not a north\|dipping thrust.. The ductile shear zone is typically 30～40m thick, consisting of highly sheared metasediments (pelite and marble), granites, and granitic veins.The latter are systematically cut by small\|scale, south\|dipping ductile normal faults with displacements between 10s of cm to several meters, forming spectacular asymmetric boudinages in the sheared meta\|pelite matrix.The minimum displacement along the detachment is about 20km, as measured by the north\|south width of the exposed footwall gneisses. We renamed the Northern Altyn Tagh Fault in the Jinyan Shan region as the Lapeiquan detachment fault to avoid confusion with other east\|west trending Cenozoic faults to the west along the northern edge of the Altyn Tagh range (e.g., the Cenozoic Jianglisai fault near Qiemo), collectively known as the Northern Altyn Tagh fault system (see Cowgill et al., Geology,in press). The lower age bound of the Lapeiquan fault is Ordovician, as the fault cuts Ordovician volcanics and plutons in its hanging wall. As the Ordovician volcanic rocks are folded together with Carboniferous marbles and Jurassic sedimentary strata, it is likely that normal faulting along the Lapeiquan detachment postdates the Jurassic. The Lapeiquan detachment fault is covered by Quaternary sediments of the Tarim basin in the west, and is apparently truncated by the Cenozoic left\|slip Altyn Tagh fault to the east as indicated by regional geologic maps. If true, this relationship implies that the Lapeiquan fault predates the Cenozoic Altyn Tagh fault. The apparent truncational relationship between the Lapeiquan fault and the Altyn Tagh fault posses an important question: where is the counterpart of the Lapeiquan fault south of the Altyn Tagh fault? Preliminary mapping in the Yema Nan Shan south of the Altyn Tagh fault reveals a fragment of a low\|angle mylonitic shear zone, which is interpreted as a detachment fault because it puts lower\|grade meta\|pelite over higher\|grade mylonitic quartzite. The correlation of detachment faults in the Yema Nan Shan and the Lapeiquan area would imply an amount of about 280～300km left slip along the Altyn Tagh fault. Alternatively, movement along the Lapeiquan detachment fault could have been synchronous with the development of the Cenozoic Altyn Tagh fault. This interpretation requires no counterpart of the Lapeiquan fault south of the Altyn Tagh fault. Instead, it implies that a major topographic collapse event occurred in the Cenozoic along the northern edge of the Tibetan plateau during movement along the Altyn Tagh fault. On\|going thermochronologic analysis will provide constraints on the age of the detachment fault and a test for the two distinctive hypotheses.
文摘The Altyn Tagh fault (ATF) extending in NEE—SWW direction lying at the northwestern boundary of Qinghai—Tibet plateau is the largest strike\|slip fault in Central Asia. On the basis of recent geologic mapping and detailed study of lithotectonic characteristics for the paleotectonic units at the two sides of the Altyn Tagh Fault ( Altun Mt. to west and the Qilian Mt. to east ) we propose that the paleotectonic units in the Altun Mt. can be correlated with those in the Qilian Mt. assuming 400km left\|lateral displacement for the Altyn Tagh fault. Natural seismic data across the Altun Mt. indicate that the Altyn Tagh fault is a lithospheric shear fault and the lithospheric shearing is probably related to southward intracontinental oblique subduction of the Tarim terrane beneath the Altun Mt.1\ Comparison of the major paleotectonic units at the two sides of the Altyn Tagh fault\;(1) The Alxa\|Dunhuang Massif:The Alxa massif lying at the southern margin of the Sino\|Korean craton consists mainly of an Early Proterozoic basement including high\|grade and middle\|grade metamorphic rocks, which were intruded by granite at 1719Ma. The Paleozoic passive margin sediments is well developed. In the Altun Mt., the Early Proterozoic and late Archean basement of the Duhuang massif includes high\|grade and middle\|grade metamorphic rocks dating 2789Ma (Sm\|Nd method) and 2405Ma (U\|Pb method).
文摘A 100～500m\|wide mylonite zone in the Altun Group of Lower Proterozoic age was discovered along the Altyn Tagh strike\|slip fault. The zone is mainly composed of amphibolitic and granitic mylonites. The planar joints of the rocks strike in NE70 and dip steeply (nearly vertical), coincident with the striking of Altyn Tagh fault zone, and their stretched lineations are nearly horizontal. Shear strains are well developed and show sinistral sheared. The amphibolitic and granitic mylonites are most probably the products of deep\|seated melting caused by sinistral strike\|slip shearing as suggested by the evidence below: (1) The migmatization is intensely developed and spatially controlled by the shear zone, and the rock has a set of NNE perspective foliation which is in accord with the direction of the Altyn Tagh strike\|slip fault zone. (2) The recrystallized hornblende aggregate is distributed in band with obvious nebulous texture, indicating the characteristics of anatexis, and the hornblendes are oriented and form the nearly horizontal stretching lineation; some hornblendes have titanite inclusions, and magmatic long\|columnar zircons are in directional arrangement.(3) The banded felsic material is developed, and the plagioclase is characteristic of high\|temperature plastic deformation and shows sinistral shear stain. (4) In mylonites, all the axis C fabric of quartz shows the feature of sinistral shearing and the majority is generally middle to low temperature fabric, but there also exists high temperature fabric, which suggests that high temperature shearing occur in the early stage of strike\|slip deformation and it is characterized by middle to low temperature shearing at the beginning of anatexis or in the late stage of the deformation. (5) On the XZ plane of mylonite and mylonitized rocks, there exists the consistent sinistral shear stain, which suggests the products of the same strike\|slip shearing.Zircons were separated from three samples of mylonitized granitic rocks for age dating. Two groups of zircon were distinguished in morphology: one is elongate prismatic grains, and the other shows slight rounding. Some zoned structure of selected grains were examined by cathodoluminescence. Dating was completed in the SHRIMP laboratory of Stanford University. Fifteen analyses were made on 14 zircon grains. Sample S99\|25 show two obvious two age groups, one is 527～549Ma, and the other is 466～472Ma. Sample S99\|9 contains two age groups either, one is 475～507Ma and the other is 279Ma. Sample S99\|6 shows three groups: ① 528Ma; ② 365Ma and③ 238～243Ma, here the 365Ma is explained as mixture age between the other two age groups according to its exact location in the grain. In summary, from the three samples we found at least three age groups: 507～548Ma; 466～472Ma; 238～243Ma.The ages of 507Ma to 548Ma and 466Ma to 472Ma represent the deformation and metamorphism of Early Paleozoic age, which is most likely correspond to the close of the Qilian Sea and continental subduction and collision reported in recent papers (Yang Jingsui et al., 1998; Zhang Jianxin et al., 1999; Xu Zhiqin et al., 1999). The 238～243Ma most likely represent the formational age of the Altyn Tagh strike\|slip fault, which is consistent with the formational age (200～240Ma) of the large\|scale sinistral strike\|slip fault zone of the South Margin of East Kunlun (Li Haibing et al., 1996), and both can be attributed to the oblique subduction and collision of the Bayan Har terrane with the East Kunlun terrane during Indosinian period.
文摘One of the focus views of the uplifting of Tibetan Plateau is the growth history of the plateau. This is an unresolved question because of the poor study in north margin, where the ATF (Altyn Tagh Fault) is acting an important role in the growth and deformation of the plateau. The fault links two huge contractional belts, e.g. Qilian Nan Shan and West Kunlun, and merges a series of thrusting\|folding arcs in southeast. Mapping of piercing points, such as unconformities between Cenozoic, Mesozoic and Paleozoic strata, and magmatic arcs, shows left slips of ca. 240km and ca. 550km along the middle and western segments of the ATF. About 140～450km of crustal shortening, approximately the same magnitude as the west segment of the ATF, is deduced from balanced sections in West Kunlun foreland thrusting belt. This implies that left\|slip displacement along the west segment of the ATF was absorbed by the contraction in West Kunlun. The ATF system merged bunches of WNW arcuated fold\|fault belts in Qaidam basin, implying anti\|clockwise rotation. Tertiary and some Lower to Middle Pleistocene strata involved in fold\|fault belts, and dip in ESE due to the uplifting of Altyn Tagh. The newest strata involved in the deformation is more and more younger from south to north, that is, from Lower Pliocene to Middle Pleistocene, showing the uplifting trends from south to north in the SE side of the fault.
基金theprogramsof ( 1)theYoungGeologistsFoundationoftheMGMR (No .Qn979812 ) ( 2 )theNational(No .G19980 4 0 80 0 ) and ( 3)the
文摘The NEE\|striking Altyn Tagh Fault (ATF) has been well known as one major point to know the growth history of the Tibetan plateau. Lots of investigations done since 1970’s were mostly focus on active features, particularly on determining slip, slip rate and their distribution along the fault. However, Cenozoic slip\|history of this fault remains poorly understood, and the age of initiation and total offset are controversial. Several Cenozoic sedimentary basins develop in Suo’erkulinan to Mangya regions (Fig.1). Their sedimentary processes are closely related with the ATF. The studies of the Neogene sedimentary sequences and the reconstruction of the paleo\|geography are essential to establish the displacement history of the fault during Late Cenozoic.Located at the southern side of the ATF, the Suo’erkulinan basin consists of more than 600\|meter\|thick Pliocene Shizigou Formation below and about 120\|meter\|thick Early to Middle Pleistocene Qigequan Formation above according to the 1∶200000 geological map by Xinjiang Province. An obvious erosional surface can be seen on the top of the lower sequence. Sediments in the Shizigou Formation are characterized by 400\|meter\|thick yellow to red cobble\|sized conglomerates in the bottom, up\|grading to sandstones and grey\|green mudstones. This indicated that the sedimentary facies changed from alluvial fan to fluvial fan and sediments became more and more mature. The upper sequence, the Qigequan Formation, corresponds to an alluvial facies series composed of yellow to white cobble\|sized conglomerates intercalated with lenticular sandstones. Paleo\|current indicators showed that the Shizhigou conglomeratic series were sourced from northwest. Well\|developed syn\|sedimentary faults, normal faults mostly inherited from syn\|sedimentary faults, and some striation lineations on the surface indicated transtensional tectonic environment of the strike\|slip faulting.
基金theNationalNaturalScienceFoundationofChina (No .4 980 2 0 19)
文摘The transform fault is essentially a displacement fault whose terminal part is adjusted by other tectonic types, its displacement component is absorbed by other structures intersected with it by high angles or meet at right angles. The main elements of transform fault are the sleep\|dipping displacement faults and the adjusted structures intersected with it at high angles. According to the combination of tectonic features formed by its two ends of displacement fault and the structures intersected with it, the transform fault can be divided into three types, including the adjusted transform fault of extensional normal fault, the adjusted transform fault of compressive fold and thrust fault, and the compound transform fault. The transform fault is different from the displacement fault, its horizontal displacement may be increased or decreased or not be changed at all as the time of fault movement extended, but for parallel displacement the dislocation will be increased. Therefore, the study of transform fault is very important for the recognition of long time disputed displacement components of huge displacement fault. The traditional Altyn fault is the adjusting fault of the compression deformation of the Western Kunlun and Northern Qilian mountains of the northern margin of the Tibetan Plateau since Cenozoic.
文摘The ENE\|striking Altyn Tagh Fault (ATF) has been well known as a large, active left\|lateral strike\|slip fault that bounds the thrusting systems in NE Tibet.This fault has been the focal point in the debate between the discrete extrusion vs. distributed crustal shortening models. Although its active left\|lateralstrike\|slip features have been largely investigated and well documented by both satellite imagery and air\|photo interpretations and field observations, little study has been done upon its Cenozoic displacement history. Questions about the age of initiation and total offset accumulated on the fault remain controversial. A key area to resolve such question is located along the central segment of the fault in the Souerkuli and Mangar regions, where Neogene sedimentary basins well develop and are mostly distributed in three zones, namely from east to west: the Gobiling, Yitunbulak and Yusuale Tagh (Fig.1). Our field investigations were conducted along the ATF cutting the Yitunbulak and Gebiling Neogene sedimentary basins. Two stratigraphic unconformities observed within this Neogene conglomeratic series allow a separation of three major stratigraphic sequences and record the initiation and major deformational episodes of ATF during Cenozoic. An early stratigraphic unconformity occurred between a yellow depositional series below and early Pliocene red\|colored conglomeratic mudstones above. A later stratigraphic unconformities occurred between early and late Pliocene sedimentary series. The lower series below the early stratigraphic unconformities is mainly composed of a conglomeratic rocks containing cobbles and pebbles of basement rock units (mostly mylonitic granites, limestones and quartzes); this series has been poorly mapped and dated; its age could be assigned to late Oligocene to early Miocene; this series tilts to NW with an angle of about 30° and is overlain in angular unconformity by early Pliocene pebble\|sized conglomerates. A weathering zone on top of the lower conglomeratic series is clearly seen, that represents a long period of uplift and erosion. This lacuna occurred between early Miocene and early Pliocene in the west Qaidam basin, which has been documented only locally. Early Pliocene deposits correspond to alluvial to lacustrine facies rocks deposited in strike\|slip basin probably originated at releasing bend of the strike\|slip ATF; late Pliocene deposits is composed by fluviatile conglomerates and fanglomerates lying in unconformity on the upper Pliocene rocks. Early Quaternary deposits are absent along the ATF and have been well documented in the Qaidam basin. Late Quaternary fanglomerates infills active fault valleys.
文摘he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward displacement of the Tibet plateau relative to the Tarim. The Altyn Tagh fault zone is a typical transpressional fault zone, characterized by blocks rotation and crustal shortening and vertical extrusion of blocks within the Altyn Tagh strike\|slip system. Differences of three\|dimensional deformation and configuration of the active structures are recognized at different segment of the Altyn Tagh fault zone.1\ Structural configuration of the Altyn Tagh fault zone\;In the Altyn Tagh strike\|slip fault zone, the assemblage pattern of the (active) faults is in the form of parallel plumes, especially in the eastern and the western segments of the Altyn Tagh fault zone. These plumes structures in the eastern segment are assembled by string\|like left lateral strike\|slip fault and broom\|like thrusting faults, and in the western segment by arc\|like left lateral strike\|slip faults along with thrusting faults and normal faults. In the middle segment of the Altyn Tagh fault zone, the structures are characterized by the string\|like left lateral strike\|slip faults in the center and reverse thrusting faults on the two sides.
文摘The age and evolutional history of the Altyn Tagh fault and its role in the formation and uplift of the Qinghai—Tibetan plateau have been focused for years. Many geologists believe that the formation of the fault is a result of the collision between India and Asia. Some people thought that it should have formed earlier than Cenozoic but have no critical evidence. Here we report a preliminary result from our recent investigation on the volcanic rocks at the north end of the Altyn Tagh fault.1 The volcanic rocks on the north end of the Altyn Tagh fault The volcanic rocks are located on the north end of the Altyn Tagh fault, northern Qinghai—Tibetan plateau. The investigated volcano occurs in the Jiuxi basin, a Cretaceous and Tertiary depositional basin. It is about 300m×100m in size and form about a 100m high cliff above the folded Cretaceous strata. It likes relic neck of a volcano rather than a kind of widely distributed lava flow commonly seen in the northern Tibet. The country rocks are Cretaceous sandstone, silt and fine\|grained conglomerate. The cliff formed most likely due to the differing erosion between the hard volcanic rocks and soft rocks.
文摘Fieldwork along several segments of the Altyn Tagh Fault,between 85 and 95°E,confirms that it ranks as one of the most active faults of Asia.In the East,near Aksay,the active fault trace offsets numerous stream channels,terrace risers and fans tens to hundreds of meters. 14 C dating of organic remains and charcoal within terrace gravels indicates that most of the terraces were emplaced after the beginning of the Holocene,implying a left\|slip rate of about 2cm/a.Large mole tracks attest to the occurrence of great earthquakes.Even larger mole tracks are found north of Lenghu,within the Altun Shan push\|up,a 6000 m high range in a restraining bend of the fault,now sliced by its most active strand.North of Huatougou,at the transition between another push\|up mountain and a recent pull\|apart basin,a spectacular sequence of five flat\|floored,hanging channels,beheaded by the fault from a unique source in the mountain,have been horizontally displaced by up to 1250m.Cosmogenic dating of the abandonment of these channels and of nearby offset terrace risers confirms the slip\|rate at Aksay.Several km to the west,pressure ridges exceeding 10m in height across a large young fan,imply the repeat of several great earthquakes in a relatively short time span.
文摘The Altun and North Qaidam Mountains at the northern margin of Qinghai\|Tibet plateau are separated by the Altyn Tagh sinistral strike\|slip fault, which is one of the largest strike\|slip fault systems in the world and was considered as the key element in the escape tectonics model for Euraisa\|India continent\|continent collision.Recently,the eclogites within quratzifeldspathic gneisses or pelitic gneisses characterized by amphibolite\|facies paragenesis were discovered in the Altun and the North Qaidam Mountains(Fig.1). They occur as lens or boundins within the Altun Group and Dakendaban Group respectively which previously were considered as metamorphic basement of Tarim block and Qaidam block. Our studies indicate that the eclogites outcrop in both the Altun and North Qaidam Mountains show similar occurrences, associated country rocks, rock and mineral assemblages, p\|T\% estimates, geochemistryand protolith feature and ages of peak metamorphism (see table) . The garnet\|omphacite\|phengite geothermobarometer gave equilibrium condition of \%p\%=2 8～3 0GPa and t =820～850℃ for the Altun eclogite and p =2 8GPa and \%t\%=730℃ for North Qaidam eclogite respectively(Fig..2). These p\|T conditions are in the coesite stability field. Moreover, Po lycrystalline quartz pseudomorphs after coesite have been identified in the Dulan area, North Qaidam Mountains (Song et al, in review). Therefore, these features suggest that both eclogites of Altun and North Qaidam Mountains probably are a same HP\|UHP metamorphic belt formed from the same of Early Paleozoic age deep subduction and collision, and subsequently displaced by the Altyn Tagh fault.The case is similar to the Dabie\|Sulu HP\|UHP metamorphic zone which was truncated by the Tanlu sinistral strike\|slip fault and splitted it into two distincts, the Dabie region and Sulu region. These correlations support an about 350～400km displacement of the Altyn Tagh sinistral strike\|slip fault (Fig.1).
