Chinese Continental Blocks in Global Paleocontinental Reconstruction during Paleozoic and Mesozoic

The Cambrian to Cretaceous paleomagnetic data from Chinese continental and adjacent blocks were collected using principles to obtain reliable and high-precision paleomagnetic data and to pay attention to the similarity of paleobiogeography and the coordination of tectonic evolution.The Chinese continental blocks were laid up on the reconstruction of proposed global paleocontinents with almost the same scale.Thus,it can be clearly recognized that the global continents,including Chinese continental blocks,range along latitudes on the southern side of the equator during the Early Paleozoic. In the Paleozoic,Chinese continental blocks were still located among the Laurentia,Siberia and Gondwana plates,following the fast moving of the Siberia Plate northwards,the amalgamation in a north-south direction at the western parts of the Laurentia and Gondwana plates,and the Iapetus and Rheic Oceans were subducted,eventually to form a uniform Pangea in the Late Paleozoic.The Australian and Indian plates of Eastern Gondwana moved and dispersed gradually southwards, continued to extend the Paleo-Tethys Ocean.The Chinese continental and adjacent blocks were still located in the Paleo-Tethys Ocean,preserved the status of dispersion,gradually moving northwards, showing characteristics of ranging along a north-south orientation until the Permian.In addition,a series of local collisions happened during the Triassic,and consequently most of the Chinese continental blocks were amalgamated into the Pangea,except for the Gangdise and Himalayan blocks. There was a counter-clockwise rotation of the Eastern Asian continent in the Jurassic and northwards migration of the Chinese continent in varying degrees during the Cretaceous,but the Himalayan and Indian plates did not collide into the Chinese continent during this period.

The Tunggurian Stage of the Continental Miocene in China

The Tunggurian Age was nominated in 1984, and the Second National Commission on Stratigraphy of China formally suggested establishing the corresponding chronostratigraphic unit, the Tunggurian Stage, based on the Tunggurian Age in 1999. The name of this stage comes from a lithostratigraphic unit, the Tunggur Formation, and the stratotype section is located at the Tunggur tableland, 15 km southeast of Saihan Gobi Township, Sonid Left Banner, Inner Mongolia. The Tunggurian Age is correlated to the Astaracian of the European land mammal ages, and they share the same definition of the lower boundary at the base of the paleomagnetic Chron C5Bn.1r with an age of 15.0 Ma. In the Tairum Nor section on the southeastern edge of the Tunggur tableland, this boundary is situated within the successive deposits of reddish-brown massive mudstone of the lower part of the Tunggur Formation, with a distance of 7.6 m from the base of the grayish-white sandstones in the middle part of the section. The Tunggurian is approximately correlated to the upper part of the marine Langhian and the marine Serravallian in the International Stratigraphical Chart. The Tunggurian Stage includes two Neogene mammal faunal units, i.e. NMU 6 （MN 6） and NMU 7 （MN 7/8）. The Tairnm Nor fauna from the Talrnm Nor section corresponds to NMU 6, and the Tunggur fauna （senso stricto） from the localities on the northwestern edge of the Tunggur tableland, such as Platybelodon Quarry, Wolf Camp and Moergen, corresponds to NMU 7. Among the Middle Miocene mammalian faunas in China, the Laogou fauna from the Linxia Basin, Gansu, the Quantougou fauna from the Lanzhou Basin, Gansu, the Halamagai fauna from the northern Junggar Basin, Xinjiang, and the Dingjiaergou fauna from Tongxin, Ningxia correspond to NMU 6.

Timing,Displacement and Growth Pattern of the Altyn Tagh Fault:A Review

The Altyn Tagh Fault（ATF） is the longest, lithospheric scale and strike-slip fault in East Asia. In the last three decades, multidisciplinary studies focusing on the timing, displacement of strikeslip and growth mechanics of the ATF have made great progresses. Most studies revealed that the ATF is a sinistral strike-slip and thrust fault, which underwent multiple episodes of activation. The fault is oriented NEE with a length of 1600 km, but the direction, timing of activity and magnitude of its extension eastward are still unclear. The AFT was predominately active during the Mesozoic and Cenozoic, in relation to the Mesozoic collision of the Cimmerian continent（Qiangtang and Lhasa block） and Cenozoic collision of India with Asia. The AFT strike-slipped with a left-lateral displacement of ca. 400 km during the Cenozoic and the displacement were bigger in the western segment and stronger in the early stage of fault activation. The slip-rates in the Quaternary were bigger in the middle segment than in the western and eastern segment. We roughly estimated the Mesozoic displacement as ca. 150-300 km. The latest paleomagnetic data showed that the clockwise vertical-axis rotation did not take place in the huge basins（the Tarim and Qaidam） at both side of ATF during the Cenozoic, but the rotation happened in the small basins along the ATF. This rotation may play an important role on accommodating the tectonic deformation and displacement of the ATF. Even if we have achieved consensus for many issues related to the ATF, some issues still need to be study deeply; such as：（a） the temporal and spatial coupling relationship between the collision of Cimmerian continent with Asia and the history of AFT in the Mesozoic and（b） the tectonic deformation history which records by the sediments of the basins within and at both side of AFT and was constrained by a high-resolution and accurate chronology such as magnetostratigraphy and paleomagnetic data.

Arc magmatism as a window to plate kinematics and subduction polarity:Example from the eastern Pontides belt,NE Turkey

The Eastern Pontides orogenic belt in the Black Sea region of Turkey offers a critical window to plate kinematics and subduction polarity during the closure of the Paleotethys. Here we provide a brief synthesis on recent information from this belt. We infer a southward subduction for the origin of the Eastern Pontides orogenic belt and its associated late Mesozoic--Cenozoic magmatism based on clear spatial and temporal variations in Late Cretaceous and Cenozoic arc magmatism, together with the exis- tence of a prominent south-dipping reverse fault system along the entire southern coast of the Black Sea. Our model is at variance with some recent proposals favoring a northward subduction polarity, and illus- trates the importance of arc magmatism in evaluating the geodynamic milieu associated with convergent margin orocesses.

Early Paleozoic tectonics of Asia:Towards a full-plate model

Asia is key to a richer understanding of many important lithospheric processes such as crustal growth,continental evolution and orogenesis. But to properly decipher the secrets Asia holds, a first-order tectonic context is needed. This presents a challenge, however, because a great variety of alternative and often contradictory tectonic models of Asia have flourished. This plethora of models has in part arisen from efforts to explain limited observations(in space, time or discipline) without regard for the broader assemblage of established constraints. The way forward, then, is to endeavor to construct paleogeographic models that fully incorporate the diverse constraints available, namely from quantitative paleomagnetic data, the plentiful record of geologic and paleobiologic observations, and the principles of plate tectonics. This paper presents a preliminary attempt at such a synthesis concerning the early Paleozoic tectonic history of Asia. A review of salient geologic observations and paleomagnetic data from the various continental blocks and terranes of Asia is followed by the presentation of a new, full-plate tectonic model of the region from middle Cambrian to end-Silurian time(500-420 Ma). Although this work may serve as a reference point, the model itself can only be considred provisional and ideally it will evolve with time. Accordingly, all the model details are released so that they may be used to test and improve the framework as new discoveries unfold.

Late Cenozoic Stratigraphy and Paleomagnetic Chronology of the Zanda Basin,Tibet, and Records of the Uplift of the Qinghai-Tibet Plateau

The characteristics of Late Cenozoic tectonic uplift of the southern margin of the Qinghai- Tibet Plateau may be inferred from fluvio-lacustrine strata in the Zanda basin, Ngari, Tibet. Magnetostratigraphic study shows that the very thick fluvio-lacustrine strata in the basin are 5.89- 0.78 Ma old and that their deposition persisted for 5.11 Ma, i.e. starting at the end of the Miocene and ending at the end of the early Pleistocene, with the Quaternary glacial stage starting in the area no later than 1.58 Ma. Analysis of the sedimentary environment indicates that the Zanda basin on the southern Qinghai-Tibet Plateau began uplift at -5.89 Ma, later than the northern Qinghai-Tibet Plateau. Presence of gravel beds in the Guge and Qangze Formations reflects that strong uplift took place at -5.15 and -2.71 Ma, with the uplift peaking at -2.71 Ma.

拉萨地块和羌塘地块多个二叠纪基性岩及一个古特提斯海山的初步古地磁结果:对模拟东冈瓦纳晚古生代裂解的暗示(英文)

Detachment of the sliver-like Cimmerian terrane from eastern Gondwana in the Early Permian triggered mafic volcanism in many parts of the rift zone.To understand this tectonic episode we have carried out paleomagnetic investigations on

Plate tectonics in the late Paleozoic

As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics--and its influence on the deep Earth and climate-it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ＇full-plates＇ （including oceanic lithosphere） becomes increasingly challenging with age. Prior to 150 Ma ~60% of the lithosphere is missing and re- constructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ＇continental＇ re- constructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding （or only loosely applying） plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geo- dynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic （410-250 Ma） together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

Late Cenozoic Sedimentary Evolution of Pagri-Duoqing Co graben, Southern End of Yadong-Gulu Rift, Southern Tibet

The north trending rifts in southern Tibet represent the E-W extension of the plateau and confirming the initial rifting age is key to the study of mechanics of these rifts. Pagri-Duoqing Co graben is located at southern end of Yadong-Gulu rift, where the late Cenozoic sediments is predominately composed of fluvio-lacustrine and moraine. Based on the sedimentary composition and structures, the fluviolacustrine could be divided into three facies, namely, lacustrine, lacustrine fan delta and alluvial fan. The presence of paleo-currents and conglomerate components and the provenance of the strata around the graben indicate that it was Tethys Himalaya and High Himalaya. Electron spin resonance(ESR) dating and paleo-magnetic dating suggest that the age of the strata ranges from ca. 1.2 Ma to ca. 8 Ma. Optically stimulated luminescence(OSL) dating showed that moraine in the graben mainly developed from around181-109 ka(late Middle Pleistocene). Combining previous data about the Late Cenozoic strata in other basins, it is suggested that 8-15 Ma may be the initial rifting time. Together with sediment distribution and drainage system, the sedimentary evolution of Pagri could be divided into four stages. The graben rifted at around 15-8 Ma due to the eastern graben-boundary fault resulting in the appearance of a paleolake.Following by a geologically quiet period about 8-2.5 Ma, the paleolake expanded from east to west at around 8-6 Ma reaching its maximum at ca. 6 Ma. Then, the graben was broken at about 2.5 Ma. At last,the development of the glacier separated the graben into two parts that were Pagri and Duoqing Co since the later stages of the Middle Pleistocene. The evolution process suggested that the former three stages were related to the tectonic movement, which determined the basement of the graben, while the last stage may have been influenced by glacial activity caused by climate change.

The northern Qiangtang Block rapid drift during the Triassic Period:Paleomagnetic evidence

As one of the pivotal Gondwana-derived blocks,the kinematic history of the northern Qiangtang Block(in the Tibetan Plateau)remains unclear,mainly because quantitative paleomagnetic data to determine the paleoposition are sparse.Thus,for this study,we collected 226 samples(17 sites)from Triassic sedimentary rocks in the Raggyorcaka and Tuotuohe areas of the northern Qiangtang Block(NQB).Stepwise demagnetization isolated high temperature/field components from the samples.Both Early and Late Triassic datasets passed field tests at a 99%confidence level and were proved to be primary origins.Paleopoles were calculated to be at 24.9°N and 216.5°E with A95=8.2°(N=8)for the Early Triassic dataset,and at 68.1 N,179.9 E with A(95)=5.6°(N=37)for the Late Triassic,the latter being combined with a coeval volcanic dataset published previously.These paleopoles correspond to paleolatitudes of14.3°S±8.2°and 29.9 N15.6°,respectively.Combining previously published results,we reconstructed a three-stage northward drift process for the NQB.(1)The northern Qiangtang Block was located in the subtropical part of the southern hemisphere until the Early Triassic;(2)thereafter,the block rapidly drifted northward from southern to northern hemispheres during the Triassic;and(3)the block converged with the Eurasian continent in the Late Triassic.The^4800 km northward movement from the Early to Late Triassic corresponded to an average motion rate of^11.85 cm/yr.The rapid drift of the NQB after the Early Triassic led to a rapid transformation of the Tethys Ocean.

Phanerozoic Paleomagnetism Characteristics of the Qomolangma Area in Tibet

This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician- Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0~ clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid- Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent- continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate- Himalaya folded structural belt- Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo- Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.

Speleogenesis of Selected Caves beneath the Lunan Shilin and Caves of Fenglin Karst in Qiubei, Yunnan

Yunnan is famous for its attractive karst landscapes especially shilins, fengcong and fenglin. The development of caves beneath the shilins in the vicinity of Lunan is closely connected with the formation of shilins. Most of the waters percolating through shilins run through the caves beneath them and are responsible for their formation. The study of cave speleogenesis deepens knowledge about both the development of shilins and karst structure. In the vicinity of the Lunan Shilin, speleological, morphological and structural geological studies of four karst caves have been accomplished. At Puzhehei, Qiubei, which is characterised by numerous fenglin, fengcong and caves, speleological and morphological studies have been performed. Cave sediments for paleomagnetic analyses have been taken from all studied areas (samples CH 1-9). Karst caves in SE Yunnan are probably much older than the age of the cave sediments (<780,000 years B.P.). The studied areas are located in the vicinity of the Xiaojiang fault (N-S direction I and the Red River fault (NW-SE direction). The general directions of both active faults are assumed to influence the direction of the most frequent fissures as well as the cave passages near the Lunan Shilin. The Xiaojiang fault more strongly influences cave passage orientation, while the more distant Red River fault most strongly influences fissure orientation.

New Jurassic Paleomagnetic Results from Southeastern China and Their Geological Implication

A paleomagnetic study was carried out on late Jurassic sediments in the Nanjing area. Stepwise thermal demagnetization was used to isolate the characteristic higher temperature component （HTC）（D=354.0°,I=48.5°,a95=7.8°）,which passes the reversal test.A 24.7±8.7°counter-clockwise rotation relative to the Sichuan area is detected through comparing this new pole（84.4°N,7.0°E, A95=7.7°）with other coeval poles reported from South China.This rotation was conducted by sinistral action of slip faults.These cases presenting in several areas of eastern China indicate that deformation of eastern China is under the effect of subduction from the Pacific Ocean plate.The difference on the paleolatitude of several areas across the Tan-Lu fault zone is calculated and suggests about at most 250 km offset distance after the later Jurassic.

Paleomagnetism of late Cretaceous dykes in the Gangdese belt: New constraints on the position and structure of the southern margin of Asia prior to the India-Asia collision

This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.

Paleomagnetic Excursions Recorded in the Yanchi Playa in Middle Hexi Corridor, NW China Since the Last Interglacial

Paleomagnetic determinations on lithological profiles of two paralleled[( )-275(long )]drilling cores covering the past 130 kyr B.P., GT40 and GT60, from the Yanchi Playa in the arid Northwestern China, indicate that a series of pronounced paleomagnetic excursions have been documented. By correlating our results with published regional and worldwide reports, 4 excursion events out of 10 apparent reversal signals (labeled from GT-1 to GT-10) were identified as excursion events coeval with the Mono Lake Event ([(28.4)( )]kyr~[(25.8)( )]kyr), Laschamp Event ([(43.3)( )]kyr^40.5 kyr), Gaotai Event (82.8 kyr~[(72.4)25( )]kyr) and the Blake Event (127.4 kyr^113.3 kyr), respectively. GT-9 correlates with the above-mentioned Gaotai Event, GT-7 and GT-6 correspond to two stages of the Laschamp Event and GT-5 to the Mono Lake Event. It is noteworthy that the so-called Gaotai Event has not been reported as a pronounced paleomagnetic excursion in the Northwestern China. Every magnetic excursion event corresponds to paleointensity minima, anteceding those established abrupt paleoclimatic change events, such as the Younger Drays and the Heinrich Events (H1-H6)[(. )-250( )]Here,[( )-250( )]we tentatively[( )-250( )]propose that these geomagnetic excursions/reversals can be viewed as precursors to climate abruptness. During the transitional stages when the earths magnetic field shifted between a temporal normal and a negative period, the earths magnetic paleointensity fell correspondingly to a pair of minima. Although more precise chronology and more convincing rock magnetic parameter determinations are essentially required for further interpretation of their intricate coupling mechanism, these results may have revealed, to some extent, that the earths incessantly changing magnetic field exerts an strong influence on the onset of saw-tooth shaped abrupt climate oscillations through certain feedback chains in arid Central Asia or even North Hemispheric high latitude regions.

Paleomagnetism and paleoclimate change in the South China Sea since the late Pleistocene

Signal processing techniques of cross-correlation, power spectral analysis and cross-power spectral analysis are used to determine the relationships between paleomagnetic properties and the oxygen isotope record of the South China Sea during the late Pleistocene. On the basis of correlation tests between the δ18O time series of cores V3 and A15 with the paleomagnetic properties of core SCS01, five events of susceptibility and intensity of natural remanent magnetization are identified as glacial events corresponding to δ18O positive events. The magnetic properties of the sediments which are independent of the geomagnetic field are sensitive climatic indicators which have frequencies corresponding to the Milankovitch orbital parameters.

Magnetostratigraphy and paleoenvironmental significance of sediments from ANT29-P7-09 core in Prydz Bay,Antarctica

Due to the unique geographical location and sensitive response to global climate changes,the Antarctic region plays an important role in paleoclimate researches,and attracts great attentions from various scholars.One 324 cm long sediment core(ANT29-P7-09)was obtained from Prydz Bay,Antarctica,during the 29th Chinese National Antarctic Research Expedition.Based on sediment particle size,TOC,δ13C analyses and magnetism data,the authors show that the dominant magnetic minerals are ferrimagnetic pseudo single domain(PSD)-multi domain(MD)magnetite.Variations in the paleoenvironmental records allow us to define 4 zones in the core.These zones outline the climatic variations in the region since the late Early Pleistocene,including a warm period,a transitional period,and a cold period.The magnetic particle assemblage varies with glacial-interglacial cycles.Abrupt changes in particle size,TOC content,and geomagnetism occur at 102–90 cm deep in the core,indicating a sudden warming in the Antarctic region,signaling the onset of the Holocene.The authors identified 3 additional climatic signals in the middle part of the core(232–162 cm)that show unexpected cooling events during the warm period in Prydz Bay,Antarctica.

PALAEOMAGNETIC AND STRUCTURAL INVESTIGATIONS ON BLOCK ROTATIONS AND CRUSTAL SHORTENING IN CENTRAL TIBET

As a part of INDEPTH 3/GEODEPTH geological surface investigations were carried out during two field campaigns in 1998 and 1999. The working area covers a roughly N\|S (30～36°N) tren ding, 200km wide belt through the Lhasa Terrane and Qiangtang Terrane at a longitude of 88～90°E. Field geology was focused on geological mapping, structural measurements, and extensive sampling for the purpose of fission track geochronology. Additionally a total number of 742 orientated palaeomagnetic samples were drilled at 73 sites. Most of the samples were taken in fine\|grained sediments of Cretaceous, Eocene, and Neogene age. Five sites were drilled in acid to intermediate volcanics.A first sequence of measurements has been applied on a set of specimen. Most of the chosen formations (>80%) have acquired stable remanences which are carried by hematite and magnetite. As an example for the characteristic demagnetising behaviour of fine\|grained probable Cretaceous sandstones see Fig.1a. The unblocking temperature of 650℃ allows to identify hematite as remanence carrier.. Although single sites show well\|defined mean directions (e.g. site 76B: α 95 =3 8; k =185 8) the distribution among several site means of one formation could scatter (Fig.1b). It has to be checked carefully if rotations of single crustal elements are responsible for this effect. There is evidence to assume the detected characteristic remanences to be primary—further analysis including fold tests will be performed after the data set has increased.

黑濑川地体源于亚洲大陆东缘何处?(英文)

The point at issue:The Kurosegawa Terrane is composed of continental fragments transecting Mesozoic terranes of accretionary complex in Southwest Japan(Fig.1).It is an attenuated tectonic sliver and considered to be allochthonous with respect to the main part of Southwest Japan.The problem of which continental block in the East Asian continental margin is the source of the Kurosegawa Terrane has puzzled Japanese geologists for many years.Firstly,we try to approach this issue based on the analysis of fusulinacean assemblage in accreted terranes composed of subduction complex in the Pacific Rim.Secondly,by applying the result of this analysis we try to locate the source of the continental fragments of the Kurosegawa Terrane.Thirdly,we try to prove its validity with a new paleomagnetic study.

PALEOMAGNETIC STUDY OF IGNEOUS ROCKS OF GUPIS—SHAMRAN AREA,KOHISTAN ARC, PAKISTAN,NW HIMALAYA

Kohistan Sequence has been considered as island arc formed during the subduction of oceanic lithosphere at the leading edge of northward moving Indian continent.. Sedimentary sequences indicate that formation of the intra\|oceanic Kohistan arc began in early Cretaceous time. The isotopic data demonstrate the involvement of enriched, DUPAL type mantle, suggesting that Kohistan arc was formed at or south of the present equator (Khan et al., 1997). The Intra oceanic phase of Kohistan lasted until sometime between 102 and 85 Ma, when Kohistan collided with Asia. From this time until collision with India about 50 Ma ago, Kohistan existed as Andean\|type margin. This paleomagnetic study is from the volcanic and plutonic rocks exposed in Gupis\|Shamran area (west of Gilgit) in northern part of the Kohistan arc. According to geochronological data these rocks were formed 61～55Ma ago (Treloar et al., 1989), when Kohistan was existing as Andean\|type margin. Seven to nine samples were collected from nine sites of Shamran volcanics (58±1)Ma and from five sites of Pingal, Gupis, and Yasin plutons (Ar\|Ar hornblende ages ranges from 61～52Ma). On the basis of one Rb\|Sr age of (59±2)Ma from these plutons, the above\|mentioned Ar/Ar ages may be regarded as reasonable intrusion ages of these plutons (Searle, 1991).