an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

new late cretaceous and paleogene paleomagnetic results from south china and their geodynamic implications 1 to better understand the tectonic evolution of south china block scb in response to the india asia collision we present new paleomagnetic results from late cretaceous and paleogene red bed formations of the hengyang basin of hunan province in the interior part of the scb stepwise thermal demagnetization of the rocks isolated a high temperature component the tilt corrected mean direction from the late cretaceous rocks is d 15 6 i 29 9 with a95 5 7 n 26 sites corresponding to a paleopole at 71 9 n 236 3 e with a95 4 7 which passes reversal tests the tilt corrected mean direction d 358 9 i 35 4 with a95 5 0 n 22 sites from the paleogene rock which passes the reversal test gives a pole at 82 6 n 300 6 e with a95 4 4 the low field anisotropy of magnetic susceptibility results suggest that the red beds have not experienced significant strain due to compaction or tectonic stress while the anisotropy of isothermal remanence results suggest that postdepositional compaction in these red beds produced no more than 3 4 of inclination shallowing these paleomagnetic and rock magnetic tests imply that the remanence is primary on the basis of paleomagnetic results obtained from coeval basalts in mongolia and siberia we suggest that no significant latitudinal motion has taken place between the scb and siberia since the late cretaceous the significant latitudinal discrepancy between the scb and european block could be due to nonrigid behavior of the eurasian plate since the late cretaceous a 16 7 5 0 clockwise rotation of the scb during the late cretaceous to the paleogene could be related to the collision of india and asia in the west and the subduction of the circum pacific plate to eastern asia in the east

paleogene clockwise tectonic rotation of the xining lanzhou region northeastern tibetan plateau 1 to help understand the deformational history of the northeastern tibetan plateau paleomagnetic samples were collected from 177 sites and two magnetostratigraphic sections at 16 localities distributed among upper jurassic lower cretaceous to pliocene sedimentary and subordinate volcanic rocks within the xining lanzhou region 34 37 n 101 105 e a total of 127 sites at 12 localities yielded primary magnetizations confirmed by fold reversal and conglomerate tests age control on sedimentary rocks is provided by regional synthesis of chronostratigraphic data and our own biostratigraphic and magnetostratigraphic analysis presented in the companion paper by horton et al 2004 analysis of paleomagnetic declination combined with results from previous studies yield a remarkably consistent trend of vertical axis tectonic rotations across the studied region whereas 19 0 7 2 to 37 8 10 6 clockwise rotations are recorded consistently in all paleomagnetic localities in lower cretaceous to eocene rocks all paleomagnetic localities in oligocene to pliocene rocks have recorded minor to insignificant rotations indicating that the xining lanzhou region has undergone a wholesale regional clockwise rotation during late paleogene time consistent with regional chronostratigraphic and thermochronologic results this late paleogene tectonic rotation confirms that deformation reached regions of the northern tibetan plateau shortly after the initial collision of india with asia when compared to rotational paleomagnetic results from adjacent regions several mechanisms can be proposed to explain the clockwise rotation on the basis of consistency with geologic data we prefer a model involving clockwise rotation of the xining lanzhou region through right lateral shear and associated shortening related to northward indentation of the qaidam basin index terms 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 8102 tectonophysics continental contractional orogenic belts 9320 information related to geographic region asia 9604 information related to geologic time cenozoic keywords tectonics paleomagnetism tibetan plateau

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

paleomagnetic evidence for 25 15 ma crust fragmentation of north indochina 23 26 n consequence of collision with greater india ne corner

paleomagnetic evidence for clockwise rotation of the simao region since the cretaceous a consequence of india asia collision samples were collected for paleomagnetic analysis from 36 sites from six formations west of the red river fault in southwestern yunnan province china on the simao block 23 4 n 100 8 e in an attempt to examine the effects of the india asia collision on the asian continent paleomagnetic results from rocks ranging from cretaceous to miocene in age indicate a large clockwise rotation of these sites with respect to stable eurasia since the late cretaceous the tectonic corrected data from cretaceous samples mean direction of two formations are d 112 6 i 34 7 95 7 5 k 9 1 n 45 for eocene samples the data are d 84 7 i 38 9 95 7 6 k 12 0 n 32 and for miocene samples they are d 21 1 i 35 5 95 7 1 k 15 3 n 29 the samples from the paleocene and pliocene are either remagnetized or too weak to provide stable directions the cretaceous sites were sampled from folded beds and these sites pass the fold test the amount of rotation seen in this study r 86 1 9 9 as a mean value for the cretaceous r 76 8 11 for the eocene and r 14 7 10 0 for the miocene is significantly larger than that documented in previous studies from the lower cretaceous of northwestern and central yunnan province and may indicate that differential rotation has taken place in the region this rotation can be explained by the northward motion and collision of india with asia in the paleocene which caused continuous deformation of southwestern china in the form of strike slip faulting and clockwise rotation it is concluded that the rotation and deformation resulting from this collision probably continued from the paleocene until at least the miocene

aspects of pre tertiary paleomagnetism of spitsbergen and their tectonic implications abstract paleomagnetic investigations were carried out on cretaceous dolente dykes and sills permian limestones permo carboniferous limestones and lower devonian sandstones from different parts of spitsbergen detailed rock magnetic studies showed that the main magnetic minerals in dolentes limestones and sandstones are titanomagnetite magnetite and hematite respectively the rocks were demagnetized thermally and in alternating fields vector analysis of the demagnetization path separates the different components of nrm and establishes a characteristic remanence the paleomagnetic poles for cretaceous dolentes permo carboniferous limestones and lower devonian sandstones from spitsbergen are respectively 65 n 222 e 34 n 140 e and 12 n 135 e when compared with the european and north american apparent polar wander paths all spitsbergen poles he at a distance from both apwps suggesting that spitsbergen has been rotated and even translated in relation to europe during the opening of the labrador sea and greenland norwegian sea

tertiary deformation and metamorphism se of tibet the folded tiger leap decollement of nw yunnan china the yulong haba xue shan range in the northwestern part of yunnan china is a large n s antiform that folds the paleozoic series of the yangzi platform the upper yangzi river jinsha jiang has cut a 3500 m deep valley hu tiao gorge across this antiform thus exposing folded bedding parallel ductile shear zones decollements with transport toward the ssw in the present geographical coordinates the large finite shear strain implies tens of kilometers of transport pointing to the regional significance of these decollements rb sr radiometric dating of phlogopites that crystallized in marbles within the foliation planes yields the age of the metamorphic and deformation event 35 9 0 3 2 ma the age derives from an internal rb sr isochron made on different size fractions of the same mineral which provides a novel demonstration of the feasibility of such plots transport on the decollement and related shortening occurred prior to or at the onset of extrusion of indochina along the ailao shan red river shear zone 80 km west of the yulong shan the 39ar 40ar age spectra of k feldspar from the core of the yulong shan suggest uplift by antiformal folding around 17 ma as indochina s extrusion came to an end we infer that other large scale cenozoic decollements such as that exhumed in the yulong shan underlie some of the vast folded areas that surround the eastern himalayan syntaxis transport on such decollements first toward the south and then toward the east and folding above them might have occurred during two principal shortening phases whose ages bracket indochina s escape toward the se

new insights into the cenozoic lateral extrusion of crustal blocks on the southeastern edge of tibetan plateau evidence from paleomagnetic results from paleogene sedimentary strata of the baoshan terrane in order to characterize the lateral extrusion of crustal material during the cenozoic we conducted a paleomagnetic study of the eocene oligocene zhushan formation and paleocene muguahe formation in the central part of the baoshan terrane bst on the southeastern edge of tibetan plateau a primary magnetic component and a remagentized component with the miocene acquisition age were isolated from the muguahe formation and zhushan formation respectively these data indicate that the bst did not commence clockwise rotation in the period of the paleocene and the oligocene and that the bst experienced 80 clockwise rotation relative to east asia since the miocene combining with the documented history of crustal boundary strike slip faults on the southeastern edge of the tibetan plateau shows that the bst and tengchong terrane tct firstly underwent latitudinal crustal shortening in the oligocene and the eastward extension was the main type of motion of the crustal material during this period which induced the initial strike slip movement of their boundary faults since the miocene the main form of crustal motion of bst tct and simao terrane was gradually transformed into clockwise rotation which possibly indicates that the fold and thrusting fault systems induced crustal shortening and thickening in the southeastern edge of the tibetan plateau have reached extremity and the southeastern part of the tibetan plateau have already been uplifted to the similar elevation with today s elevation in the miocene

a cretaceous pole from south china and the mesozoic hairpin turn of the eurasian apparent polar wander path to contribute to the apparent polar wander path apwp of the south china block and eurasia in general we collected paleomagnetic samples from mesozoic red beds around the city of ya an 30 n 103 e in the western tip of the sichuan basin in this paper we present the results from 373 oriented cores taken from one section representing 3 km of sedimentary rocks the section is dated with continental ostracods and with a magnetostratigraphic correlation between a densely sampled 272 m sequence and the polarity time scale giving an upper jurassic to upper cretaceous or lower tertiary age the remanent direction is remarkably stable throughout the section d 2 0 i 34 2 k 63 1 95 3 6 n 26 28 sites while this fact might suggest that the section has been remagnetized paleomagnetic and rock magnetic tests indicate that the remanence is primary the pole position 78 6 n 273 4 e dp 2 4 dm 4 1 corresponds to a rather low paleolatitude 18 8 2 4 but is consistent with other cretaceous poles from china if one accepts the eurasian apwp of irving and irving 1982 this result would imply that more than 1000 km of shortening took place between south china and eurasia following the acquisition of the remanence however there is no geological evidence for this large shortening we propose that the remanence was acquired within the time corresponding to the tip of the hairpin turn 150 50 ma in the revised apwp of besse and courtillot this issue the local geology suggests that the syncline from which the samples were taken has been rotated by 15 5 counterclockwise which is reflected in a similar discrepancy between the measured paleodeclination and that predicted by the besse and courtillot this issue eurasian apwp after correcting for this rotation the pole position is 70 9 n 225 2 e dp 2 4 dm 6 5 we conclude that eurasia was fully assembled by the end of the jurassic and that the mesozoic eurasian hairpin turn is a real feature

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

paleomagnetic study of permian and mesozoic sedimentary rocks from northern thailand supports the extrusion model for indochina abstract the mode of deformation of southeast asia resulting from the indian collision is still controversial is convergence between stable india and siberia absorbed principally by crustal shortening and thickening and minor strike slip faulting or by a mechanism of extrusion involving crustal thickening and lateral escape of blocks along major strike slip zones in order to test these models we have carried out a paleomagnetic study of sedimentary rocks of jurassic to cretaceous age on the khorat plateau in thailand a large discrepancy between the poles of indochina presented in this paper and a compilation of south china block pole positions both at the triassic jurassic and the jurassic cretaceous boundary imply some 1500 800 km of post middle cretaceous left lateral slip along the red river and xian shui he fault zones and approximately 14 7 of clockwise rotation for the indochina block relative to the south china block such relative motions are in agreement with a model of lateral extrusion of indochina during the india asia collision additional data of permian upper triassic and lower jurassic age collected in indochina indicate a post late permian remagnetization for the upper permian limestones a comparison of these data with those from yunnan south china the north china block and the south china block shows that these blocks have probably been in contact at least since the late triassic

paleomagnetic study of cretaceous rocks from pu er western yunnan china evidence of internal deformation of the indochina block abstract cretaceous red sandstones and siltstones were collected at 31 sties for paleomagnetic investigation from the jingxing and nanxin formation around pu er 23 0 n 101 0 e western part of yunnan province china in order to examine quantitative amount of tectonic deformation of the simao terrane due to collision of india with asia after stepwise thermal demagnetization the high temperature component magnetization with unblocking temperature of around 680 c is isolated positive field tests show that the high temperature component magnetization from 25 sites is primary for the cretaceous formations a tilt corrected mean direction is d 59 9 i 45 2 with 95 5 1 corresponding to a paleopole at 35 8 n 173 1 e with a 95 5 6 comparison with cretaceous paleomagnetic pole of the whole china block indicates that amount of clockwise rotation in the pu er area is evaluated to be 46 9 with respect to the whole china block which is consistent with large amount of rotation in the mengla and jinggu areas 47 and 66 in the central part of the simao terrane clockwise rotation of the central part is larger by more than 20 compared to the yunlong and yongping areas of northern part of the simao terrane suggesting that the simao terrane experienced internal deformation the southward displacement of the pu er area expected from inclination data is 7 5 6 6 with respect to the chuan dian fragment which is a similar estimate to other areas in the simao terrane and the indochina block while the simao terrane displaced southward by 800 km together with clockwise rotation of 30 as a whole further clockwise rotation occurred in the central part

synthetic seismogram and surface wave constraints on crustal models of spitsbergen abstract seismic refraction data collected on spitsbergen in 1978 are used to obtain a crustal model assuming plane horizontal layering the observed travel times and wave forms are compared with those of synthetic seismograms computed for various published crustal models the more detailed models adequately explain some but not all of the features of the synthetics these models are adjusted utilizing travel times and wave form amplitudes until a satisfactory fit is achieved the best fitting model consists of a 4 layer crust having thicknesses of 4 1 10 0 7 4 and 5 8 km and compressional velocities of 4 65 6 21 6 30 and 6 65 km sec with increasing depth the uppermost mantle has a velocity of 7 90 km sec a comparison of observed and synthetic p n waveforms supports the existence of a thin low velocity zone beginning at a depth of about 5 km beneath the moho boundary an inversion of seismic surface wave group velocity data yields a shear wave model which is compatible with the compressional wave model

seismic activity inferred crustal stresses and seismotectonics in the rana region northern norway abstract the seismotectonic significance of the rana region is known both from the fact that this was the location of the largest known earthquake in fennoscandia in recent times the m s 5 8 6 2 earthquake of august 31 1819 and from its relatively high constant seismic activity also in the 20th century in order to study this region in more detail a local seismic network has been in operation there since july 1997 as part of the neonor neotectonics in norway project the network was primarily designed to detect possible activity on the basmoen fault which runs 50 km subparallel to the rana fjord and which shows signs of likely post glacial activity the results have revealed a quite complex spatio temporal distribution of seismic activity and has also shown no activity on the basmoen fault itself during the first 18 months of operation july 1997 january 1999 the network has detected 373 locatable seismic events of which 267 were local earthquakes most of these earthquakes occurred in five groups in the western parts of the network all five groups had similar nnw esw trends in epicenter locations and all have shallow foci 2 12 km similar to what has also been found earlier for other concentrated earthquake zones in northern norway and the magnitude range is between m l 0 1 and 2 8 earthquake focal mechanism solutions within the network reveal a predominance for normal faulting with the tensional stress axis perpendicular do the coastline implying an unusual coast parallel orientation of the principal horizontal compressive stress the earthquakes occur in a region of maximum post glacial uplift gradients which supports deglaciation flexure as a viable explanation for these earthquakes a certain influence from more local factors however tied in general to crustal in homogeneities cannot be ruled out

post folding magnetization of the triassic rocks from western guizhou and southern yunnan provinces new evidence for large clockwise rotations in the simao terrane abstract thermal demagnetization of the redbed samples collected from the lower triassic feixianguan formation at two localities in western guizhou province reveals that the natural remanent magnetization was dominated by a postfolding component of probably recent origin and the prefolding possibly primary component was barely preserved this confirms that the feixianguan fm in western guizhou and northeastern yunnan provinces was severely remagnetized thermal demagnetization also resolves two postfolding components from the limestone samples of the mid triassic dashuijingshan formation from southern yunnan province a low temperature component acquired in recent times and a high temperature component probably acquired shortly after the india asia collision the mean in situ direction for the high temperature component based on eighteen sites is d 95 4 i 28 4 with 95 6 2 which indicates a clockwise rotation of 86 3 7 3 with respect to stable eurasia this result together with paleomagnetic results previously reported from the jurassic eocene rocks in the same area demonstrates beyond reasonable doubt that the central simao terrane has experienced large clockwise rotations due to the india s collision with and continuing penetration into asia

seismicity and present day tectonics of the svalbard region summary data collected by temporary seismic networks and individual stations over a 7 yr period in the svalbard archipelago are integrated and used to study the seismicity and present day tectonics of the archipelago and surrounding regions most of the continental seismic activity occurs in three concentrated zones one in heer land near the eastern coast of the island of spitsbergen and two in close proximity to one another on the island of nordaustlandet all three zones are in regions which have been devoid of major orogenic activity since the late devonian the heer land zone and at least one of the zones in nordaustlandet define active faulting which has not been identified by surface mapping the other zone in nordaustlandet occurs in the region of a mapped system of faults all branches of which are relatively minor a number of smaller concentrations and individual earthquakes occur throughout much of the archipelago and surrounding continental shelves seismicity is currently low in the region of tertiary orogenic activity in western spitsbergen a roughly linear pattern of minor activity in southern spitsbergen occurs west of the heer land zone and extends at least 50km southward the major n s faults in spitsbergen which are thought to have accomodated large displacements in devonian time are currently inactive except perhaps at the southern termini of the billefjorden and lomfjorden fault zones where they approach the heer land seismic zone earthquakes located near the western continental margin of spitsbergen may occur on segments of rifting and shearing which reflect the opening of the greenland sea during the tertiary the limited extent of the currently active zones of activity their spatial stability over several years and the lack of activity on the major faults of svalbard argue against the existence of plate boundaries along which motion is currently occurring in the svalbard region all fault plane solutions on svalbard are consistent with a stress field characterized by e w compression whereas previously published fault plane solutions for the ridge system west of svalbard indicate e w extension the magnitude of the compressive stress increases from small values near the ridge system to values sufficiently large to dominate the regional seismicity of svalbard over distances of 200 300 km

tectonic amalgamation of the gaoligong shear zone and lancangjiang shear zone southeast of eastern himalayan syntaxis abstract the gaoligong shear zone glgsz and lancangjiang shear zone lcjsz are two major large scale shear zones southeast of eastern himalayan syntaxis ehs and play important roles in the accommodation of the intracontinental deformation in southeast asia the two shear zones which are mainly composed of high grade metamorphic rocks and have long been regarded as the precambrian basement of this area are gradually merged northward and become tectonically amalgamated from fugong to gongshan area structural and kinematic analyses reveal that the amalgamation area has experienced strongly partitioned dextral transpression n s trending tight to isoclinal folds sub vertical foliation and sub horizontal lineation are ubiquitously developed both within the shear zones and the carboniferous flysch sediments of baoshan block in between micro and macro kinematic indicators such as cs structures rotated porphyroclasts asymmetric shear folds sheath folds domino and boudin structures suggest that the shear sense of the glgsz and lcjsz is dextral in the amalgamation area comparative analyses of strata reveal that the baoshan block is aligned with south qiangtang block and the lanping simao block was aligned with north qiangtang block prior to the cenozoic large scale tectonic extrusion and rotation the amalgamation area which has progressively switched positions from northeast of ehs to east and southeast of ehs is just located at the neck of the large scale boudin of south qiangtang baoshan block a boudin model is proposed for the tectonic amalgamation of the glgsz and lcjsz from fugong to gongshan area in response to the continued northward convergence between indian plate and eurasian plate since early eocene resistance of south china block southeastward extrusion and clockwise rotation of baoshan block around ehs

clockwise rotation of the red river fault inferred from paleomagnetic study of cretaceous rocks in the shan thai malay block of western yunnan china more than 150 samples were collected at 23 sites from the lower cretaceous jingxing formation near the city of yongping 25 5 n 99 5 e which is located on the west side of the red river fault sixteen sites have characteristic directions with a high temperature component above 500 c the high temperature component of magnetization from twelve sites is of pre fold origin and reveals clockwise deflection in declination d 42 0 i 51 1 and 95 15 7 the easterly declination of more than 40 at yongping is consistent with the cretaceous paleomagnetic direction d 45 of chuxiong 25 n 101 5 e which is located on the east side of the red river fault both areas were subjected to about 25 clockwise rotation with respect to the eastern part of the yangtze block since cretaceous time we conclude that the red river fault was rotated through25 16 with respect to the eastern part of the yangtze block associated with rotation of the yongping and chuxiong areas removal of the rotation from the red river fault indicates that the latter and the jinsha suture formed a straight line along n55 w s55 e within the asian continent from vietnam to the tibetan plateau in the present coordinate system during the cretaceous the linear feature of the red river fault and jinsha suture was probably deformed to the present curved shape as a result of collision of the indian continent with the asian continent

intraplate earthquakes in northern svalbard abstract a temporary network of microearthquake seismographs deployed in the northern part of svalbard recorded numerous earthquakes during the summer of 1982 most of the earthquakes occurred in concentrated zones in restricted portions of three fault complexes in central nordaustlandet but minor activity also occurred to the east and west of these complexes within the uncertainty of the epicentral locations most earthquakes which occurred on land in regions not covered by glaciers could be associated with segments of mapped faults there are numerous fault segments and even entire faults however along which no recorded earthquake occurred the concentrated spatial locations of these earthquakes along preferred portions of mapped faults and the absence of throughgoing lines of activity suggest that these are intraplate earthquakes occurring along existing faults in response to an applied stress field composite fault plane solutions for the three most active regions each include one nodal plane which can be associated at least roughly with a trend of seismicity and trend of a mapped fault the directions of greatest principle stress for the three fault plane solutions vary between n90 w and n55 w directions which agree approximately with maximum stress directions determined for a region about 200 km to the south the consistency of the directions of maximum principle stress obtained for earthquakes throughout a broad region of svalbard suggests that the earthquakes there occur in response to a stress field which is of plate tectonic origin

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

paleomagnetic study of cretaceous rocks from the yangtze block central yunnan china implications for the india asia collision abstract more than 200 samples for this study were collected at 30 sites from the cretaceous matoushan and puchanghe formations around the city of chuxiong 25 n 101 5 e twenty four sites have characteristic directions with a high temperature component above 350 c paleomagnetic directions from 21 sites of the cretaceous formations reveal clockwise deflection in declination d 44 6 i 41 3 and 95 10 7 the reliability of the direction is ascertained through a positive fold test and the presence of normal and reversed polarities comparison with paleomagnetic data from other areas indicates that the chuxiong area was rotated clockwise through26 17 with respect to the eastern part of the yangtze block whereas it was subjected to more than 44 of clockwise rotation with respect to the neighboring blocks of lhasa 56 21 and western sichuan 44 16 since cretaceous time the clockwise rotation of chuxiong is a reflection of rotational motion of the large region including the southeastern qiangtang terrane and the jinsha suture red river fault paleomagnetic data and tectonic features suggest that the rotation occurred prior to the folding in the central yunnan province probably during the paleogene this large rotation is a spectacular example of the deformation in the southeastern part of the asian continent due to the collision of india

intraplate tectonics in asia a precise age for large scale miocene movement along the ailao shan red river shear zone china tertiary left lateral movement along the 1000 km long ailao shan red river shear zone appears to have played an important role in absorbing post collisional northward penetration of india into asia crustal strike slip shear along this zone caused the formation of a gneiss belt metamorphosed to amphibolite grade including anatectic melting both metamorphism and melting were induced by ductile deformation yielding the possibility to date the major tectonometamorphic event that shaped the ailao shan red river belt 17 u pb isotope analyses were performed on small size fractions of zircon monazite and xenotime extracted from two different leucogranitic layers the two samples are located about 50 km apart in the central segment of ailao shan in structurally well controlled settings where the melts crystallized within the strongly foliated gneisses during late stages of deformation all mineral u pb analyses had to be corrected for excess or deficit amounts of radiogenic 206 pb originating from initial 230 th disequilibrium in the 238 u decay series in monazite such disequilibrium 206 pb reaches 20 of total radiogenic 206 pb the corrected u pb ages of monazite and xenotime lie between 22 1 and 23 9 ma whereas zircon yields significantly discordant u pb ages between 30 5 and 33 9 ma pointing to precambrian material in the magma source region inherited components could also be detected in monazite the set of u pb data shows that monazite and xenotime formed simultaneously in both localities substantiating an early miocene age of 23 0 0 2ma for late kinematic crystallization of anatectic melts in the metamorphic belt of the ailao shan red river shear zone

fabrics and 40ar 39ar ages of metamorphic rocks in the gaoligong tectonic belt implications for cenozoic metamorphism and deformation in the se tibetan plateau abstract as one of the major tectonic belts in the southeastern tibetan plateau the gaoligong tectonic belt plays important roles in accommodating the indian eurasian plate collision in this belt medium high grade metamorphic rocks are preserved in this study we selected three cross sections from the northern to the southern segment of the gaoligong tectonic belt for detailed structural macro and micro observations and quartz fabric analysis quartz c axis fabrics reflect three ranges of metamorphic temperature in the metamorphic rocks range 1 650 700 c corresponding to granulite facies range 2 550 650 c amphibolite facies and range 3 400 500 c greenschist facies mineral separates amphibole muscovite and biotite from five samples taken from the lushui pianma section were selected for 40ar 39ar study yielding plateau ages of 30 ma amphibole 17 ma biotite and 15 ma muscovite respectively combined with the previous geochronological data it is suggested that there are three stages of metamorphism deformation of the gaoligong tectonic belt during cenozoic the early stage of metamorphism occurred at high temperature conditions 650 700 c corresponding to granulite facies during 50 34 ma coeval with the cenozoic collision of the indian plate and tengchong block the subsequent stage of metamorphism occurred at medium to low temperatures 550 650 c 400 500 c respectively during 34 10 ma and is the result of a non coaxial progressive deformation showing dextral shear along the gaoligong strike slip fault the latest stage represents rapid exhumation and cooling during 10 3 ma

lower middle jurassic paleomagnetic data from the mae sot area thailand paleogeographic evolution and deformation history of southeastern asia we have carried out a paleomagnetic study 12 sites 85 samples of early middle jurassic limestones and sandstones from the mae sot area of western thailand this area is part of the shan thai malay stm block and its geological characteristics have led some authors to suggest a late jurassic accretion of this region against the rest of indochina along the changning menglian zone the latter sometimes being interpreted as a mesozoic suture the high temperature or high coercivity component isolated yields a paleodirection at d 359 8 i 31 4 95 5 0 the primary nature of the magnetization acquisition is ascertained at a site with reversed polarity and a positive fold test at the 95 confidence level comparison of the mae sot paleolatitude and another one from the stm with those recently published for the simao and khorat blocks show no significant difference at the 95 level showing that the stm was situated close to or had already accreted with the simao or khorat blocks in the early middle jurassic comparison of the latitudes from these blocks with those from china indicates a relative southward motion of 8 4 of indochina as a single entity relative to china most rotations of these regions relative to china are found to be clockwise between 14 and 75 these rotations and most prominently the 1200 500 km post cretaceous left lateral motion inferred for the red river fault provide quantitative estimates of the large amount of extrusion of indochina with respect to the rest of asia

duration of strike slip movements in large shear zones the red river belt china abstract sixty four size fractions of zircon monazite xenotime and titanite were dated by the u pb method to temporally and spatially constrain left lateral movements in the red river shear zone between the depths of 15 and 20 km the shearing led to the formation of the high grade metamorphic gneisses that form the bulk of the 4200 m high diancang shan and 3100 m high ailao shan mountain ranges the omnipresence of melt layers and pockets in these gneisses shows that temperatures associated with tectonometamorphism lie at and above the solidus of continental crust and deformation patterns are very homogeneous over the entire length of the belt north of the gneisses subvolcanic bodies intrude unmetamorphosed cover rocks in particular eocene red beds along the projected trend of the red river shear zone for a leucogranitic layer in the diancang shan gneisses an age of 24 2 0 2 ma 2 is obtained for monazite and 22 4 0 2 ma is obtained for xenotime whereas zircon formed through two growth stages at 24 23 ma these ages record solidification of the anatectic melts over a period of at least 1 8 0 4 ma during which left lateral shear was continuously active in the ailao shan gneisses zircon and titanite ages are 26 3 0 3 and 26 1 0 2 ma for two monzonitic bodies and 24 1 0 2 and 22 4 0 2 ma for two pegmatitic layers that occur within the monzonitic intrusions these results show that zircon monazite titanite and probably also xenotime are closed systems for u and pb under melting conditions 650 c therefore the ages date mineral formation in the melt rather than cooling below certain closure temperatures a significantly older age of 35 0 0 1 ma is obtained for a monzonitic subvolcanic intrusion north of the diancang shan gneisses because these intrusions follow the trend of the shear zone they most likely represent the surface expression of early activity along that zone indicating that strike slip movement had already occurred in latest eocene time the total set of u pb ages shows that magmatic and metamorphic activity occurred from 35 to 20 ma strengthening the idea that the red river shear zone absorbed most of the intraplate movements required to compensate the opening of the south china sea between 32 and 16 ma the existence of monzonitic syenitic intrusions along the red river zone implies that melting affected source rocks other than the diancang shan and ailao shan gneiss protoliths potential sources to produce such rocks lie in the deep crust possibly including melts from the mantle consequently the red river shear zone must be a deep rooted structure along which melts migrated to the surface moreover the contemporaneity of shear motion and magma generation suggests that melting occurred in direct relation to strike slip activity

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

new cretaceous and early tertiary paleomagnetic results from xining lanzhou basin kunlun and qiangtang blocks china implications on the geodynamic evolution of asia we present the results of a paleomagnetic study of 360 cores drilled at three different areas from the tibetan plateau 13 sites from lower cretaceous red beds in the xining lanzhou basin around xining and lanzhou cities southwest of the qilian mountains 36 2 n 103 5 e 13 sites from cretaceous red beds in the kunlun block near maqin 34 5 n 100 1 and 9 sites from paleocene lower eocene red beds in the qiangtang block near fenghuoshan 34 5 n 92 8 e thermal demagnetization of the samples allowed us to isolate a high temperature component which passes both positive reversal and fold tests for all formations the corresponding paleopoles lie at 50 3 n 195 5 e a95 4 6 for xining lanzhou 80 1 n 281 2 e dp 7 8 dm 12 7 for maqin and 62 6 n 210 5 e dp 3 9 dm 6 8 for fenghuoshan we discuss these in the frame of a new paleogeographic reconstruction of the cretaceous paleoposition of the blocks forming the asian mosaic we conclude that the xining lanzhou area could not be part of the north china block but rather was associated with the tarim qaidam assemblage paleomagnetic data argue in favor of a qaidam kunlun tarim junggar assemblage in the cretaceous significantly to the south of its current position with respect to the asian continent siberia mongolia and north china the large n s convergence 800 500 km implied since the cretaceous appears to be far larger than could be absorbed in the altay range to the north and qilian shan to the east of the order of 300 km part of this motion could have occurred along a large left lateral strike slip fault system which may connect with the mongol okhotsk suture to the northeast verifying this hypothesis will require new geologic and paleomagnetic data from these remote regions

role of lithospheric strength heterogeneities in the tectonics of tibet and neighbouring regions unlike rigid oceanic plates continents show diffuse deformation for example the tibetan plateau that has accommodated much of the convergence of india with asia we interpret the tertiary deformation of asia as the three dimensional strain of a non linear viscous continental lithosphere lateral strength contrasts modify this deformation stress concentration around the relatively strong tarim basin gives rise to local crustal thickening in the tien shan to the north and to strike slip in the altyn tagh along its southern margin

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

cenozoic clockwise rotation of the tengchong block southeastern tibetan plateau a paleomagnetic and geochronologic study abstract paleomagnetic data from 50 35 ma likely 40 ma mafic dykes in yunnan southeastern tibetan plateau cutting 115 ma granitoids record the rotation of the tengchong lhasa block around the east himalayan syntaxis ehs ti rich titanomagnetite and magnetite carry a primary magnetic component group1 a magnetic overprint resides in magnetite group2 likely induced by low grade metamorphism between 30 and 10 ma the tilt corrected overall mean directions are d i 89 8 35 1 for group1 and d i 33 3 41 4 for group2 these data imply a clockwise rotation of 87 87 3 12 5 of the tengchong block since remanence acquisition at 40 ma with respect to stable eurasia the average rotation rate of 2 18 0 31 myr is at the upper limit of the present day rotation rates around the ehs obtained from gps velocities and quaternary strain rates the remagnetized group2 indicates a poorly defined rotation of 31 31 2 32 9 our key results the detection of 87 clockwise rotation with high rotation rates following the india asia collision and a decrease in rotation rates during the miocene suggest that first the tengchong block rotated rapidly around the ehs synchronous with eastward tectonic escape of lithospheric blocks the later slower clockwise rotation similar to those recorded geodetically may be related to viscous flow of tibetan crust

magnetostratigraphy of the xiaolongtan formation bearing lufengpithecus keiyuanensis in yunnan southwestern china constraint on the initiation time of the southern segment of the xianshuihe xiaojiang fault the late cenozoic extensional basins in yunnan province southwestern china which are kinematically linked with the regional strike slip faults can provide meaningful constraints on the fault activity history and tectonic evolution of the southeast margin of the tibetan plateau semtp and further on the geodynamic evolution of the tibetan plateau however this has been severely impeded by the lack of precise age constraints on the timing of fault activity to better constrain the timing of fault activity and the tectonic rotation of semtp we undertook a high resolution magnetostratigraphic study on the xiaolongtan formation in the xiaolongtan basin which is located at the southern tip of the xianshuihe xiaojiang fault and is well known by the presence of hominoid lufengpithecus keiyuanensis rock magnetic experiments indicate that magnetite is the main remanence carrier correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and biostratigraphic data our correlation suggests that the xiaolongtan formation sedimentary sequence spans from chron c5ar 1r to chron c5n 2n which indicates that the age of the xiaolongtan formation ranges from 10 ma to 12 7 ma and that the ages of the two sedimentary layers possibly bearing the hominoid l keiyuanensis are 11 6 ma or 12 5 ma the basal age of the sediments is 12 7 ma which indicates that the activation of the southern xianshuihe xiaojiang fault was initiated at this time the overall mean paleomagnetic direction d 353 2 i 34 2 95 2 1 n 166 documents a counter clockwise vertical axis rotation of 8 3 with respect to eurasia which is the response to the activity of the left lateral xianshuihe xiaojiang fault

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

apparent paleomagnetic rotations reveal pliocene holocene internal deformation of the tengchong block southeastern tibetan plateau abstract we present new paleomagnetic data from early pliocene to holocene volcanic rocks of the tengchong volcanic field and mangbang basin of the tengchong lhasa block yunnan along the eastern margin of the india asia collision zone two remanent magnetization components occur a higher coercive one carried by ti rich titanomagnetite and magnetite and likely of primary origin and a lower coercive one residing in magnetite and representing a more recent overprint the pleistocene holocene rocks of the tengchong volcanic field yield an in situ overall mean direction of d i 352 5 25 4 indicating a southeastward tilt we attribute the tilting to block rotation above listric normal faults that cut the tengchong volcanic field the in situ overall mean direction derived from pliocene volcanic rocks of the mangbang basin is d i 330 5 54 2 we explain this apparent counterclockwise rotation by northeastward tilting due to half graben formation during normal faulting along the nuangdeng fault zone along the eastern basin margin

paleomagnetism of cretaceous to lower tertiary rocks from southwestern sichuan a revisit abstract a re study has been carried out on the cretaceous to lower tertiary rocks from southwestern sichuan province on the south china block the characteristics remanent magnetization chrm resolved from the paleocene eocene leidashu formation is of dual polarity and very shallow inclination the anomalouslylow paleolatitude 6 9 6 3 n indicated by the inclination is not supported by geological evidence from this region and is probably due to inclination error related to depositional and or post depositional processes a positive fold test as well as the prevalence of normal polarity suggests that the chrm of the mid upper cretaceous xiaoba formation might be acquired during the cretaceous long normal superchron clns the tilt corrected mean direction of the xiaoba formation d i 8 1 38 8 95 6 6 n 18 sites is not significantly different from a preliminary result d i 357 6 31 6 95 8 6 n 12 samples we reported earlier for the collective xiaoba and leidashu formations the resultant paleopole 81 5 n 220 9 e a95 7 1 is coincident with other cretaceous poles for the chinese blocks comparison with the eurasian apparent polar wander path apwp indicates neither significant rotation nor latitudinal translation of the study area relative to eurasia the newly obtained mean direction for the xiaoba formation is believed to be more reliable than our earlier result since it is based on a larger sample size and is apparently free from effects of the shallow inclination observed in the leidashu formation and should supercede our previous preliminary result the paleopole derived from sevenentes of the lower cretaceous feitianshan formation 69 0 n 204 6 e a95 4 3 deviates from the track from the late jurassic to late cretaceous poles the deviation might be reduced by further sampling

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

internal deformation of the shan thai block inferred from paleomagnetism of jurassic sedimentary rocks in northern thailand abstract paleomagnetic samples of red sandstones were collected at 16 sites from the lower to upper jurassic phu kradung formation and the upper jurassic phra wihan formation around nan city 19 2 n 101 0 e in the southern region of the shan thai block after stepwise thermal demagnetization a high temperature component with an unblocking temperature of about 680 c is isolated from 11 sites we interpret this to be a prefold characteristic remanent magnetization because of a positive fold test at the 95 confidence level the tilt corrected mean paleomagnetic direction from 11 sites is d 32 3 i 33 3 95 12 2 k 15 0 which gives a paleomagnetic pole for this area of 60 1 n 186 5 e with a95 11 7 compared with a jurassic paleopole for the stable part of the yangtze block we observe a clockwise tectonic rotation of 12 8 which is similar to the observed rotation 18 28 of the northern region of the shan thai block this amount contrasts with a large rotation of more than 45 that is estimated from the narrow zone extending from luxi to mengla in the central region of this block this declination aspect suggests that a coherent whole block rotation by about 20 of the shan thai block took place in an earlier phase during indentation of india into asia and that an internal deformation with additional local rotation between 25 and 77 followed within a limited zone in the central part the internal deformation of the shan thai block absorbed the stress on the asian continent induced by indentation of india as well as its coherent whole block motions of clockwise rotation and southward displacement

reduced seismic velocities in the source zone of new madrid earthquakes a three dimensional inversion of p wave travel time residuals from local earthquakes reveals a remarkable pattern of low seismic velocities in crustal rocks immediately adjacent to the active portions of the new madrid fault system seismic velocities are lowest in regions of greatest concentration of earthquake activity near two intersections of linear trends in seismicity the maximum reduction in compressional wave velocity is at least 7 per cent in the upper 5 km of the crust and at least 4 per cent in the depth range of 5 to 14 km the reductions are consistent with a velocity decrease which would be expected if crustal rocks in the source zone contain fluid filled cracks in which pore pressure is a substantial fraction of external pressure the presence or absence of such fluids may explain why some portions of the faults in and surrounding the upper mississippi embayment are active while others are not

paleomagnetic study of middle cretaceous rocks from yunlong western yunnan china evidence of southward displacement of indochina middle cretaceous red sandstones and siltstones were collected at 20 sites for paleomagnetic study from the nanxin formation around yunlong 25 8 n 99 4 e western part of yunnan province china after stepwise thermal demagnetization high temperature component magnetization with unblocking temperature of about 675 c is isolated a positive fold test at the 99 confidence limit shows that the high temperature component magnetization is primary for the middle cretaceous nanxin formation a tilt corrected formation mean direction is d 40 2 i 49 9 with 95 3 9 corresponding to a paleopole at 54 6 n 171 8 e with a95 4 4 comparison with previously reported cretaceous paleomagnetic directions indicates that the yunlong area has been subjected to southward displacement by 11 9 7 5 corresponding to 1300 800 km with respect to the stable yangtze craton since cretaceous time as well as clockwise rotation through 36 3 13 6 this study elucidates that indochina was squeezed out of the asian continent due to collision of india accompanied with clockwise rotation

reappraisal of the jianchuan cenozoic basin stratigraphy and its implications on the se tibetan plateau evolution abstract we present a new stratigraphy of the jianchuan basin one of the largest cenozoic sedimentary basins in southeastern tibet this basin was regarded as recording sedimentation from the eocene up to the pliocene and as such has been the focus of several studies aiming at constraining the environmental tectonic and topographic evolution of the area within the shuanghe and jianchuan formations thirteen new zircon u pb ages and one biotite 40 ar 39 ar age of interbedded and cross cutting ultrapotassic magmatic rocks show that a brief magmatic event occurred from 35 7 to 34 5 ma 35 2 0 4 ma on average the uppermost formation jianchuan fm supposedly pliocene in age is related to this magmatic event and is 35 4 0 8 ma old all sedimentary formations are thus eocene in age with neither oligocene nor miocene sediments the coal bearing shuanghe formation yields a fossil of a large amynodontid typical of the upper eocene ergilian interval 37 2 to 33 9 ma sedimentation of the shuanghe formation took place in a short time interval at 35 9 0 9 ma after a large scale drainage reorganization that induced the abandonment of a large braided river system this reorganization was possibly linked with the initiation of the left lateral ailao shan red river fault and or to widespread magmatism in the jianchuan basin previous high paleoaltitude estimates for the jianchuan basin are thoroughly re evaluated and yield a value of 1200 1200 m a s l for the upper eocene

paleomagnetism of cretaceous rocks from eastern qiangtang terrane of tibet thermal demagnetization has successfully isolated high unblocking temperature characteristic directions from paleomagnetic samples of lower and middle cretaceous redbed formations from eastern qiangtang terrane tibet the tilt corrected mean direction for the lower cretaceous is d i 57 7 50 2 with 95 10 9 and n 12 sites and that for the middle cretaceous is d i 39 7 51 6 with 95 8 5 and n 11 sites both formations pass the fold test and the latter possesses two polarities the magnetization predates the eocene and was probably acquired during cretaceous time comparison of the mean directions with expected directions from the stable interior of eurasia indicates significant clockwise rotation but little paleolatitudinal change for the sampling area deformation and rotation of these rocks are presumably related to the collision of india with asia and its subsequent northward indentation into asia existing paleomagnetic data from tibet and its environs seems to be compatible with a crustal shortening thickening model dewey et al 1988 in that the continental crust directly north of the indian indenter was substantially shortened north south whereas in the vicinity of the western and eastern syntaxes latitudinal displacement was minimal but tectonic rotation was very important more data are needed to further differentiate between this model and the lateral eastward crustal extrusion model molnar and tapponier 1975

evolution sedimentaire et tectonique du bassin proterozoique superieur de comba congo stratigraphie sequentielle du supergroupe ouest congolien et modele d amortissement sur decrochements dans le contexte de la tectogenese panafricaine abstract the comba trough infilled by the upper proterozoic west congolian supergroup trends n60 e and cuts across the congo zaire archean craton the trough is perpendicular to the nyanga niari basin which itself represents the foreland of the pan african mayombe belt moreover the comba trough was connected to other troughs extending further east beneath the mesozoic cenozoic of the congolian basin the tectono sedimentary evolution of the comba basin was initiated between 950 and 700 ma the trough was formed by a nw se extension it was filled up by periglacial fluvio lacustrine sediments which correspond to the deltaic formations of the bouenza group and the upper diamictite tillite superieurerd respectively then a general climatic warm up produced a rise of the eustatic sea level which flooded the lake of comba as well as the lakes and shelves of the congo zaire craton this marine sedimentation is represented by the schisto calcaire group which in terms of sequence stratigraphy we interpret as a transgressive system tract red marls of the lower part of the scia facies a condensed section pink dolomite of the upper part of the scia facies a highstand system tract deposited along a carbonate ramp the latter corresponds to a lateral facies variation and not a vertical facies succession as it was classically assumed this highstand system tract was composed of an external shelf scib facies a barrier scic facies a lagoon scii facies a beach kisantu oolithe of the sciiia facies and sciiib facies a tidal flat sciiic facies with fluvial sciv facies and tidal niari breccia facies channels between 700 and 600 ma a first compressive phase was responsible further west for the eastward pan african mayombian thrusting this phase was accompanied by the deposition of a thick molassic formation mpioka formation on the foreland belt and extending into the comba basin a late shortening phase of the mayombian belt propagated into the comba basin which was affected by strike slip deformation along its southern edge this strike slip deformation induced important disruptions of the regional mayombian tensor and a particular structural pattern of the comba basin characterized by strike slip damping structures sections of these structures are interpreted as positive negative and dual flowers this particular structural pattern provides an explanation of the combian structures as they reflect local deviation of the pan african shortening axes as a conclusion the evolutionary stages of the comba basin are discussed in the wider context of the upper proterozoic of the congo zaire craton

tectonic deformation of the southwestern part of the yangtze craton inferred from paleomagnetism abstract upper cretaceous red sandstones have been sampled at 21 sites from the jiangdihe formation in yuanmou 25 9 n 101 7 e the northern part of yunnan china characteristic directions with unblocking temperature of 680 c have been isolated from all the sites and provide a positive fold test which is significant at the 99 probability level remanent magnetization of the prefolding origin represents a characteristic direction of the jiangdihe formation d 26 9 i 35 6 and 95 3 6 this paleomagnetic direction confirms the fairly large easterly declination of the cretaceous time for the southern part of the yangtze craton incorporating this result into previous data from the areas along the longitude of 102 e in the southwestern part of yangtze craton the declination value in the cretaceous paleomagnetic direction monotonously decreases from 45 to 2 as latitude increases from 25 0 to 30 1 n the tectonic rotation expected from the apparent polar wander path of eurasia shows that the clockwise rotation decreases gradually from 30 to 10 whilst increasing in latitude the systematically differential rotation along the longitude in the southwestern part of the yangtze craton is a part of the deformation mode of the asian continent due to the collision with india the yangtze craton behaved as a unit continuum material with a ductile nature during deformation

an integrated stratigraphic record from the paleocene of the chijiang basin jiangxi province china implications for mammalian turnover and asian block rotations new paleomagnetic and isotopic results from a similar to 1000 meter thick paleocene stratigraphic section in the chijiang basin of china s jiangxi province provide chromostratigraphic constraints on the shanghuan nongshanian asian land mammal age boundary and allow for a more accurate determination of an early paleogene paleomagnetic pole for the south china block paleomagnetic analysis of 121 sites 326 samples reveals that the shanghuan nongshanian boundary lies close to a normal to reverse polarity change stable carbon isotope analysis of dispersed organic matter and paleosol carbonates indicate a secular increase of similar to 1 5 superimposed on higher frequency variations correlation of this magnetochemostratigraphic pattern to the global timescale suggests that the polarity reversal near the shanghuan nongshanian boundary likely represents the chron c27n c26r transition the torrejonian tiffanian north american land mammal age boundary is closely correlated to this same polarity transition indicating nearly synchronous global mammalian turnover at this time because both land mammal age boundaries are thought to record turnover of mostly endemic taxa it is unlikely that the synchroneity of faunal change is due to intercontinental dispersal as documented for other early paleogene faunal transitions e g paleocene eocene boundary instead these mammalian faunal transitions may represent independent ecological or evolutionary responses to environmental changes that have been interpreted from marine records at this time e g top chron 27n event these new paleomagnetic results from the chijiang basin are also used to augment other published data and to calculate a paleocene paleomagnetic pole for the south china block the new pole shows no significant vertical axis rotation compared to the paleocene reference pole for eurasia indicating that much of the clockwise rotation that has been documented for the south china block from cretaceous deposits cannot be the result of extrusion tectonics associated with the early paleogene india asia collision observed cretaceous rotations of the south china block may be the result of late cretaceous early paleocene rifting in the backarc of the kula pacific subduction zone c 2008 elsevier b v all rights reserved

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

to what extent is the present seismicity of norway driven by post glacial rebound abstract the seismicity of scandinavia is low to intermediate in intensity and with magnitudes that rarely exceed 5 5 even so the seismicity is characterized by a great diversity in space and time related to the fact that its driving forces or sources of stress are multiple and also diverse in nature the dominant driving forces range from plate related such as ridge push through regional to local ones such as topography all however are somehow related to lateral inhomogeneities in lithospheric structure whereas it was earlier assumed that the post glacial uplift was the main cause for the seismicity of scandinavia we now conclude that the uplift may at most be playing a minor role along the coastal stretch of northern norway there are still some indications that the seismicity which is often shallow normal faulting and swarm related may be related to the still remaining glacial isostatic adjustment the flexuring that is needed to explain such behaviour could however also be related to erosion and sedimentation processes it will take more work to separate these potential driving forces

passive crustal clockwise rotational deformation of the sichuan basin since the miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the tibetan plateau

the changning menglian suture zone a segment of the major cathaysian gondwana divide in southeast asia abstract in southwest china the major cathaysian gondwana divide the palaeo tethyan suture is very well delineated by a narrow north south zone of oceanic siliceous sedimentary rocks and dismembered ophiolite complexes including probable remains of reef capped oceanic islands the location of this zone the changning menglian suture is not well appreciated in the english language literature probably because of the failure to recognise the approximately 600 400 km simao terrane which lies to the east of the suture many analyses mistakenly include the simao element in the sibumasu terrane thus placing a terrane of distinct cathaysian affinities on the gondwana side of the major palaeogeographic divide a measure of the size and time span of palaeo tethys is contained in the changning menglian suture zone sedimentary rocks deep marine cherts are dated between early devonian and middle permian and limestones interpreted as caps to seamounts extend the age range of the ocean to late permian these data agree with recent views of cathaysian elements rifting from gondwana in the silurian or devonian followed by a major rifting event on the north gondwana margin early in the permian subduction created an active continental margin on the western edge of the simao terrane throughout much of the triassic and the closure of this branch of palaeo tethys is marked by the cessation of this activity in the early late triassic

internal crustal deformation in the northern part of shan thai block new evidence from paleomagnetic results of cretaceous and paleogene redbeds in order to describe the internal deformation of the northeast part of the shan thai block resulting from the penetration of the indian plate into asia a paleomagnetic study was carried out on the cretaceous and paleogene strata in the southern part of the simao terrane high temperature magnetic components with unblocking temperatures around 680 degrees c were isolated and positive fold test shows its primary nature of magnetization the tilt corrected site mean directions of the lower cretaceous and upper cretaceous from the menglun area are d s 46 2 degrees i s 45 9 degrees k 11 0 alpha 95 10 6 degrees and d s 33 2 degrees i s 30 9 degrees k 68 4 alpha 95 8 2 degrees respectively the site mean directions of the upper cretaceous and lower paleogene for the mengban area are d s 50 5 degrees i s 31 0 degrees k 207 6 alpha 95 6 4 degrees and d s 43 5 degrees i s 23 0 degrees k 26 1 alpha 95 13 4 degrees respectively the results of the lower cretaceous and upper paleogene from the mengla area are d s 46 9 degrees i s 42 2 degrees k 27 3 alpha 95 7 7 degrees and d s 41 8 degrees i s 23 8 degrees k 38 9 degrees alpha 95 5 8 degrees respectively in comparison with previous paleomagnetic data of the simao terrane the rotational deformation can be divided into four stages the cretaceous and paleocene sediments of the simao terrane experienced intensive folding before the early oligocene during the early oligocene to early miocene the shan thai and indochina blocks experienced southeastward extrusion with similar to 20 degrees clockwise rotation relative to the south china block during the middle to late miocene the shan thai blocks experienced more 15 degrees clockwise rotation since the late miocene the activity of strike slip faults surrounding the simao terrane enhanced the internal differential rotations of the terrane these deformation processes finally resulted in a complex internal deformation of the simao terrane c 2013 elsevier b v all rights reserved

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

paleomagnetic results from cretaceous and jurassic rocks of south and southwest yunnan evidence for large clockwise rotations in the indochina and shan thai malay terranes abstract cretaceous and jurassic redbeds have been sampled from south and southwest yunnan china for paleomagnetic study the paleomagnetic directions resolved from the cretaceous rocks indicate that the xiaguan area which is located on the red river fault has not been rotated with respect to stable eurasia since at least late cretaceous times and that the jinggu mengla area 200 400 km farther south has been rotated by 46 65 clockwise the jurassic results reveal the same rotation pattern at face value the differences between the observed cretaceous paleolatitudes and those predicted from the eurasian apparent polar wander path apwp indicate a southward extrusion of the region but the amount of extrusion is not large enough to be resolved by paleomagnetic methods comparison with mesozoic paleomagnetic data from central yunnan northern thailand and northwestern borneo suggests that the red river fault is not a demarcation between unrotated and significantly rotated regions and that sundaland did not respond to the india asia collision as a single coherent unit the existing paleomagnetic data from east asia appear to indicate that the crust in central tibet and tien shan north of tarim directly in front of the indian indentor has been substantially shortened and thickened whereas the crust in the syntaxial areas has probably been largely squeezed out to further evaluate the relative importance of crustal thickening and extrusion in the tectonic evolution of the tibetan plateau paleomagnetic investigation should be intensified in the bounding zones to the indian indentor and be expanded into the cenozoic sedimentary rocks in tibet and surrounding regions

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

cenozoic deformation in western yunnan china myanmar border in the present paper we describe ductile and brittle deformation styles in western yunnan and ne myanmar using field data and landsat 7 imagery we show that this complex area located at the northern termination of sunda plate three rivers area was wedged during the tertiary between the left lateral ailao shan chong shan metamorphic belts to the east and the right lateral shan scarp gaoligong metamorphic belt in west this triangular region therefore underwent the effects of these continental size ductile strike slip faults separating major blocks with a dominant ew to ene compression since the late miocene date of the reversal of motion along the rrf the incipient eastward motion of the sunda block and the persisting right lateral motion along its western boundary sagaing fault created n s compression and e w to wnw extension underlined by left lateral transtension along the wanding nanting fault zones at the same time the diangcan shan situated along strike the ailao shan metamorphic belt was slightly impinged by the blocks extruded from the syntaxis and exhumed again from the early pliocene in accordance with this late and still active state of stress q 2004 elsevier ltd all rights reserved

palaeomagnetic evidence for southward displacement of the chuan dian fragment of the yangtze block summary cretaceous red sandstones of the feitianshan formation and the xiaoba formation were sampled at 33 sites from the dadeli and mishi synclines of xichang 27 9 n 102 3 e the study area is a part of the chuan dian fragment bounded by the xianshuihe xiaojiang and the red river fault systems which in turn constitute the southwestern part of the yangtze block almost all the samples give a characteristic palaeomagnetic direction with unblocking temperatures up to 680 c the primary nature of magnetization is ascertained by a positive fold test with a 99 per cent confidence level for the dadeli syncline the tilt corrected overall mean direction of the 33 sites is d 3 7 i 41 5 95 3 4 with a corresponding palaeopole at 85 2 n 241 7 e a95 3 5 this pole occupies the near sided position with respect to the estimate of the cretaceous pole of the sichuan basin indicating that the xichang area experienced a significant southward displacement combined with earlier reported palaeomagnetic data from the chuan dian fragment a significant southward displacement of 6 7 3 5 in latitude is estimated for the whole fragment with respect to the sichuan basin since the late cretaceous extrusion dynamics in the asian continent due to its collision with india brought about the southward displacement of the chuan dian fragment declination data indicate that the southern part of the chuan dian fragment was subjected to clockwise sense rotation of up to 45 this significantly large tectonic rotation probably occurred during extrusion of this

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

concentrated earthquake zones in svalbard abstract data from a network of seven telemetered and three portable seismic stations operating in the summer of 1979 delineate two concentrated east west trending zones of seismicity in the svalbard archipelago one zone in heer land spitsbergen which has been described previously shows left lateral strike slip movements along a vertical wnw ese striking fault another zone in nordaustlandet reported here for the first time has similar strike direction and dimensions as the heer land zone but differs significantly with regard to its recurrence pattern zones of concentrated intraplate earthquakes appear to be prevalent on the landward side of continental margins in arctic regions the seismicity in these zones can be explained as the interaction of a regional stress field of plate tectonic origin with local zones of weakness

tectonics and paleomagnetic rotation pattern of yunnan 24 n 25 n china gaoligong fault shear versus megablock drift

tertiary paleomagnetic data from northwestern yunnan china further evidence for large clockwise rotation of the indochina block and its tectonic implications abstract eocene red sandstones were collected at 15 sites for paleomagnetic study from two areas lanping and yunlong of the western part of yunnan province china in the northern part of indochina the high temperature magnetization component with an unblocking temperature of around 680 c is isolated after stepwise thermal demagnetization characteristic directions from nine accepted sites reveal a positive fold test at the 99 confidence limit indicating that the high temperature magnetization component is possibly of eocene age a tilt corrected mean direction from nine accepted sites is d 266 1 i 39 8 with 95 11 2 corresponding to a paleopole at 14 5 n 169 7 e with a95 10 9 a comparison with previously reported tertiary paleomagnetic data indicates that the lanping basin of the northern part of the indochina block rotated clockwise through 91 15 with respect to the yangtze craton this large magnitude clockwise rotation is probably caused by the superimposition of regional and local rotations our previous middle cretaceous paleomagnetic results from the yunlong area indicate that about 40 of clockwise rotation out of 90 is explained by tectonic rotation due to a relatively rigid body rotation of the simao terrane during indentation of india the remaining component of rotation is probably ascribed to further eocene post eocene rotational motion of the tectonically independent small blocks within the lanping basin associated with fault movement

the cenozoic rotational extrusion of the chuan dian fragment new paleomagnetic results from paleogene red beds on the southeastern edge of the tibetan plateau abstract paleomagnetic studies were conducted on the eocene and oligocene strata at the western part of the chuan dian fragment in order to describe the crustal deformation induced by continuous penetration of the indian plate into eurasia during the late cenozoic high temperature magnetic components with unblocking temperatures of 680 c were isolated and positive fold and or reversal tests reveal the primary nature of the magnetization the tilt corrected site mean directions obtained from the oligocene and middle early eocene strata are respectively ds 200 9 is 31 3 k 52 8 95 7 7 and ds 29 7 is 32 0 k 44 9 95 5 6 comparison of these results with previous paleomagnetic data from the chuan dian fragment shows that the western and central parts of the chuan dian fragment experienced 20 integral clockwise rotation relative to east asia since the middle miocene however the eastern part of the chuan dian fragment has experienced different rotational deformation relative to east asia since the pliocene because of the intense regional crustal deformation and activity on fault systems the eastern boundary of the chuan dian fragment was bounded by the yuanmou luezhijiang left lateral strike slip fault prior to the pliocene and then substituted by the xiaojiang left lateral strike slip fault since the pliocene due to the eastwards spreading of the clockwise rotational movement of the chuan dian fragment the evolutionary characteristics of the ailaoshan red river and xianshuihe xiaojiang strike slip faults were controlled by the difference between the clockwise rotational extrusion velocities of the chuan dian fragment and the indochina block

nested strike slip duplexes and other evidence for late cretaceous palaeogene transpressional tectonics before and during india eurasia collision in thailand myanmar and malaysia the late cretaceous palaeogene structural and tectonic events in the northern region of sundaland represent a poorly known but potentially important orogenic development in se asia extensive late cretaceous s type granites extending from malaysia through thailand to myanmar have long been used to infer an episode of crustal thickening an inference supported by the presence of late cretaceous eocene ophiolites in myanmar however structural evidence for a well developed associated fold and thrust belt has been lacking apatite and zircon fission track studies of thailand indicate a broad regional uplift from about 80 ma to 40 ma suggesting an episode of crustal thickening but the uplift amount is modest and not that expected for a major fold and thrust belt left lateral motion on major nw se trending strike slip fault zones mae ping and three pagodas faults in myanmar and thailand has been attributed to himalayan tibetan escape tectonics this paper demonstrates that the fault zones are considerably more complicated than just nw se trends they are a network of branching faults with important north south trends as well as nw se trends they form large scale nested strike slip duplex structures and affect a region over 1000 km long and up to 250 km wide this diffuse branching network of strike slip fault trends may represent a substantial late cretaceous palaeogene transpressional belt himalayan escape tectonics represent later increments of deformation with both oligocene sinistral and late oligocene recent dextral reactivation

the origins of the mengye potash deposit in the lanping simao basin yunnan province western china abstract the lanping simao basin lsb is a mesozoic cenozoic continental margin rift basin in western china it formed during the opening and closing of the tethys ocean this basin is also known as a metal belt as it hosts several metal deposits besides the mengye potash deposit however the exact dates of the formation either in the paleocene or the cretaceous and thus the origins of the marine continental or mixed origins of the mengye deposits remain disputed based on the basin s evolution materials of marine origin and or remnant seawater should be present but instead the salt layers of the mengye potash deposit present typically continental lithological features this study examines and reviews evaporative minerals br cl and i cl molar ratios and isotopes of s b and sr i and i cl data for this area has not been previously reported the basin s evaporative minerals are dominated by halite and sylvite the amounts of anhydrite chlorocalcite langbeinite glaserite tachyhydrite and glauberite are small all of these form in both marine and continental environments the values of i and the i cl molar ratios of halite and sylvite are from 0 07 to 0 27 ppm and from 0 03 to 0 11 10 6 respectively dependent on organic substances br and molar br cl values are from 89 08 to 555 45 ppm and from 0 06 10 3 to 0 38 10 3 respectively all of the br cl molar ratios are lower than those of seawater and most of them are 34 s 11 b and 87 sr 86 sr values for evaporative minerals indicate a continental origin for the mengye potash deposit however materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit thus the mengye potash deposit could be of continental origin with a remnant seawater trace