present day crustal deformation characteristics of the southeastern tibetan plateau and surrounding areas by using gps analysis abstract the southeastern tibetan plateau and surrounding areas comprise a typical tectonic belt in mainland china characterized by a complex geological background and intense tectonic activity we study present day crustal deformation characteristics of this region based on gps data for the periods 1999 2007 and 2009 2011 we first analyze the variations in crustal motion and strain rate and then discuss the 3d crustal motion and local sub block activities as well as the correlation between the intensity of crustal activity and the strain rate distribution finally we explain the present day geodynamic characteristics of the region our results indicate that the entire region shows overall clockwise motion with respect to the stable eurasian plate the tectonic boundary belts between this region and the south china block display significant compressional strain accompanied by associated extensional strain relatively high maximum shear strain and the transition zones of the significant plane strain gradients are also mainly concentrated along the ganzi yushu xianshuihe anninghe zemuhe xiaojiang lijiang xiaojinhe and red river faults as well as the western and southern yunnan province 3d crustal velocities further reflect significant differences in tectonic activity between different structural belts we conclude that the regions showing higher shear strain and the transition zones of the significant plane strain gradients correspond to the areas with frequent earthquakes according to the crustal deformation and strain characteristics we infer that the present day geodynamic setting of the region is related to the ongoing india eurasia collision and the associated resistance of the stable alashan ordos and south china blocks resulting in the extrusion of the southeastern tibetan plateau crustal material with an overall clockwise flow around the eastern himalayas and significant compressional strain along the tectonic boundary belts furthermore notable compressional strain and enhanced sub block motions occurred around the longmenshan fault area following the wenchuan earthquake

inclination variation in the late jurassic to eocene red beds from southeast asia lithological to locality scale approach summary shallowpalaeomagneticinclinationshavebeenfrequentlyreportedfromtheredbedsofcentral and southeast asia to trace the origin of this phenomenon inclination variation in southeast asia is examined on lithological to locality scale lithological aspect of this variation has been studied using the early cretaceous bailong and cangxi formations of the bazhong area 32 1 n 106 7 e the northern sichuan basin samples from 36 sites consisting 18 pairs of successive sandstones and mudstones layers were collected for this purpose from a synclinal structure stepwise thermal demagnetization of most samples revealed the presence of stable characteristic remanent magnetization which is generally unblocked by 680 c positive fold and reversal tests suggest a primary origin for this component yielding the early cretaceous palaeomagnetic direction of declination inclination 20 9 26 5 ks 37 2 95 4 4 n 30 10 pairs of sandstone and mudstone layers show almost identical inclinations isandstones 23 3 3 7 and imudstones 24 7 2 4 but 27 shallower than that expected from the eurasian apparent polar wander paths apwps indicating that no lithological variation in inclination has occurred location wise variation in inclination shallowing is examined through palaeomagnetic data from late jurassic to eocene red beds distributed around southeast asia based on these investigations no inclination shallowing is observed in the eastern part of the south china block scb whereas large degree of shallowing is observed in the sichuan and xining ninhe basins variation in inclination shallowing from one sedimentary basin to another could probably be caused by changes in the depositional environment the eastern part of the scb where no inclination shallowing have been observed is characterized by basin and range type tectono geological setting in contrast the foreland basins are bounded to the north by east west striking high altitude orogenic belt swift developmentofthesebasinsasaresultofflexuralsubsidenceisthemostlikelyreasonforinclination shallowing

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

cretaceous palaeomagnetic results from hainan island in south china supporting the extrusion model of southeast asia abstract we report the cretaceous palaeomagnetic results from hainan island south china in hainan island we collected the early cretaceous redbeds of the lumuwan formation at eleven sites we also describe the tectonic kinematics for and around hainan island since the cretaceous deduced from our and previous palaeomagnetic results the palaeolatitude of hainan island is 25 9 n 3 4 3 2 implying that hainan island was situated about 7 north from the present position during the cretaceous the palaeopole of hainan island latitude 77 7 n longitude 162 1 e k 65 6 and a95 4 4 suggests 4 0 5 8 counterclockwise rotation and 14 1 5 5 southward translation relative to the suspected coherent part of the south china block scb since the cretaceous the rotation and translation of similar sense 18 8 7 4 and 7 8 6 9 respectively are detected in the existing palaeomagnetic result from the xinlong formation in guangxi which is situated approximately 400 km north northwest from hainan island the southward translation of both areas seems to have been due to the southeastward extrusion of dissected zones within the southwestern part of the scb in a similar pattern to the indochina block which had resulted from the indentation of india into asia this sw part seems to have slightly rotated counterclockwise because its extrusion was probably smaller in scale than the indochina block and therefore it was dragged out by the indochina block this hypothesis is supported by the existence of a northwest southeast trending fault system parallel to the red river fault

a viscoelastic earthquake cycle model for taiwan 1 while recent geophysical measurements including global positioning system gps surveys have clarified the mechanisms of active mountain building in the taiwan arc continent collision the geometry of faults beneath the island remains unclear in this paper we use gps data collected before the 1999 chi chi earthquake to image the geometry of active faults under taiwan and estimate slip rates on these faults we invert the data using kinematic and mechanical earthquake cycle models consisting of faulting in an elastic lithosphere overlying a viscoelastic asthenosphere in the kinematic model uniform slip is prescribed on the faults at a constant rate while in the mechanical model the faults slip in response to shear stresses in the lithosphere these models explain the essential features of both the horizontal and vertical gps velocity fields we find a 27 39 km thick elastic lithosphere overlying a viscoelastic asthenosphere with maxwell relaxation time of 15 80 years or viscosity of 0 5 4 1019 pa s the models produce a combined slip rate of 30 50 mm yr on the frontal thrusts in western taiwan and 60 80 mm yr of slip on the longitudinal valley fault inversion of the data using both models indicates a decollement dipping 10 under western taiwan and increasing in dip by no more than 10 under the central ranges and eastern taiwan

magnetic inclination shallowing problem and the issue of eurasia s rigidity insights following a palaeomagnetic study of upper cretaceous basalts and redbeds from se china

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

anomalously shallow inclination in middle northern part of the south china block palaeomagnetic study of late cretaceous red beds from yichang area summary we present new palaeomagnetic results from late cretaceous red beds of the paomagang formation collected at 42 sites in the yichang area 30 7 n 111 7 e middle northern part of the south china block a high unblocking temperature component around 680 c was isolated from 26 sites by stepwise thermal demagnetization fold tests are positive at the 95 per cent confidence limit for 14 and 11 sites of the paomagang and wangdian areas respectively normal and reversed polarity sequence found in the wangdian area passed a reversal test at the 95 per cent confidence limit the tilt corrected mean direction for yichang area is d 3 8 i 23 3 95 5 1 n 26 corresponding to a palaeopole at 71 5 n 280 0 e with a95 4 3 comparison with the expected inclination from the 80 ma eurasian apwp pole indicates a inclination flattening of 26 3 6 4 middle cretaceous to cenozoic nw se extension tectonics within the scb contributes only 2 0 to the inclination flattening while the massive samples of the paomagang formation show a moderate degree of anisotropy 1 017 pj 1 086 and steeper inclination i 29 3 the laminated samples which form more than 75 per cent of the studied samples show a higher degree of anisotropy 1 052 pj 1 227 and shallower inclination value i 22 7 a good correlation between remanence inclination and facies types indicates that depositional processes produced the observed shallow inclination in the yichang area

apparent polar wander paths of the major chinese blocks since the late paleozoic toward restoring the amalgamation history of east eurasia abstract high quality paleomagnetic poles a k a paleopoles are essential for quantitative lithospheric plate reconstruction however the current paleomagnetic database of the major chinese blocks including the north china block ncb the south china block scb and the tarim block tb since the late paleozoic era contain outdated and low quality data here we update the database by adding recently published high quality paleopoles and rejecting low quality outdated ones the database includes 288 paleopoles published 1980 2014 90 of them published after 2000 following the van der voo selection criteria 75 paleopoles each with a quality factor q smaller than 4 were rejected in the first round of selection we then removed another 59 paleopoles that have been locally rotated or shallowed since the acquisition of stable remanence eventually 154 paleopoles were selected and adopted to calculate the new apparent polar wander paths apwps for the major chinese blocks we found comparable clastic and igneous paleopoles at intervals when a quantitative comparison was available as such comparison was not possible during most periods epochs our conclusions reflect an unclear extent of inclination errors in chinese clastic paleopoles new models of the chinese apwps with and without inclination error corrections were computed from carefully selected paleopoles version 1 running mean v1rm paths were calculated at the period epoch level version 2 running mean v2rm paths were computed in a set sliding time window of 20 or 30 myr spline paths were calculated with the same time windows along with a smoothing parameter of 50 using a recent global reconstruction model and up to date geological observations new models of the chinese apwps allowed us to re evaluate the coalescence history of east eurasia since the late paleozoic era four major tectonic events were confirmed 1 the tb accreted with the kazakhstan orocline during amalgamation of the west altaids during the middle late permian period ca 265 250 ma 2 the suturing of the ncb and the scb likely occurred in a scissor like pattern and had been accomplished no later than the middle jurassic period ca 180 160 ma 3 the amalgamation between the ncb and the tb along with the microblocks between the two might have been achieved during the late jurassic early cretaceous periods ca 160 140 ma 4 the mongol okhotsk ocean should have been closed no later than the early cretaceous period ca 140 120 ma

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

palaeomagnetic study of eastern tibet deformation of the three rivers region summary a palaeomagnetic study was undertaken for cretaceous red beds and granitic rocks of three geological provinces the lhasa the qiangtang and the sichuan along a road between chengdu and lhasa in eastern tibet in an attempt to determine aspects of deformation of se asia high temperature characteristic directions were isolated from 20 sites the tilt corrected data from the qiangtang terrane at markam 29 7 n 98 6 e exhibit largely clockwise deflected declinations with steep inclinations d 48 2 i 49 0 a95 8 8 whereas the lhasa terrane at basu 3o l0n 96 9 e and the sichuan province at ya an 3o l0n 103 0 e have northerly directions with shallow inclinations d 3 9 i 23 4 a95 19 2 and d 2 lo z 30 7 ag5 11 3 respectively the palaeomagnetic data indicate that the qiangtang terrane was subjected to clockwise rotation through 50 with respect to the neighbouring provinces of the lhasa and sichuan since the cretaceous tectonic deformation occurred later than the cretaceous in the eastern part of the qiangtang terrane and formed the arcuate shape of the orogenic belt in the three rivers region

tectonic evolution of the tancheng lujiang tan lu fault via middle triassic to early cenozoic paleomagnetic data the north striking tancheng lujiang tan lu fault is a conspicuous and controversial feature of the eastern asian landscape near the southeast extremity of the fault in anhui province we collected paleomagnetic samples at 17 middle triassic t2 and 10 upper cretaceous k2 to lower cenozoic e1 sites t2 remanent magnetizations are interpreted as primary in two of three areas the three areas are rotated 37 to 137 counterclockwise with respect to the south china block scb reference direction k2 e1 remanent magnetization directions pass regional fold and reversals tests and are not rotated with respect to surrounding areas counterclockwise rotation of t2 strata therefore ended before k2 and is attributed to left lateral shear acting along tan lu during the north china block ncb scb collision in shandong province 700 km north of the anhui sites four areas containing 33 upper jurassic j3 and cretaceous sites have negligible declination differences except for one which has dispersed directions the fold test is inconclusive for this latter area and positive for the other three regional concordance of the j3 e1 paleomagnetic data including paleolatitudes together with observed deformation patterns suggest that an extensional regime prevailed in the late cretaceous and cenozoic euler pole positions that constrain the north south china collision and account for tan lu motion suggest at least 500 km of sinistral shear took place along the fault and either 1 subduction and related ultrahigh pressure uhp metamorphism occurred near the present location of the qinling dabieshan and sulu uhp belts while tan lu acted as a transform fault that connected the two subduction zones or 2 tan lu and sulu were parts of the same transform fault system and no uhp rocks formed in situ at sulu in either case uhp rocks originally exhumed near dabieshan could have been transported by plate capture toward sulu along tan lu after north and south china impacted near dabieshan the tan lu fault grew within the scb as the dabieshan corner indented the scb causing folds in scb cover rocks to conform to the ncb margin late cretaceous to cenozoic reactivation of tan lu with both right lateral strike slip and normal fault motion occurred as the scb extruded east relative to the ncb under the influence of the india asia collision

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

timing of the north south china collision from new middle to late mesozoic paleomagnetic data from the north china block we collected paleomagnetic samples from 43 sites of middle and upper jurassic and cretaceous rocks along a 250 km wide east west trending belt located north of the suture between the north and south china blocks in each case laboratory treatment isolates dual polarity antipodal magnetizations that are demonstrably pre folding the paleomagnetic poles show very good coherence with coeval poles from other localities from the north china block ncb suggesting the apparent polar wander path apwp from the ncb is not distorted by post middle jurassic local vertical axis block rotations a comparison of the ncb apwp with that from the south china block suggests that collision continued after the early jurassic and ended no later than the late jurassic a cusp in the ncb apwp coincides with a marked angular unconformity that separates middle jurassic from upper jurassic and younger sediments together these observations indicate that the scissor like collision and associated deformation ceased at the middle to late jurassic boundary 159 ma the time of rapid 1 ma relative angular velocity between the two plates 225 to 190 ma coincides with a peak in u pb and ar ar dates obtained from metamorphic rocks in the suture the combined late jurassic and cretaceous paleomagnetic data from both blocks suggest that the united china plate traveled 2000 km north relative to eurasia during the late jurassic before docking in the cretaceous this younger collision event is also marked by a cusp on the cretaceous part of the eurasian apwp

late mesozoic early cenozoic deformation history of the yuanma basin central south china abstract the yuanma basin situated in central south china with more than 800 km far away from the active plate boundaries is a key region in deciphering the late mesozoic early cenozoic tectonic evolution of south china based on a field analysis of fault slip data collected from different rock units we document polyphase tectonic stress fields and address the changes in the orientation of the principal stresses and finally establish a five phase stress evolution of the basin during the late mesozoic early cenozoic the earliest one with e w compression and n s extension occurred in the mid late jurassic and resulted in regional folding and west directed thrusting along the eastern margin of the basin this deformational event constrains the timing of the significant intracontinental orogeny in south china to be mid late jurassic the subsequent nw se extensional regime was responsible for the initial opening and sedimentary infill of the basin during the earliest cretaceous which occurred coevally with the extensive early cretaceous magmatism volcanism and extensional doming in south china the tectonic regime then changed in the late early cretaceous to a compressional one with nw se compression and ne sw extension causing the inversion of this extensional basin this compression affected the whole south china leading to an apparent magmatic quiescence at 108 117 ma and sinistral strike slip faulting on the nne trending faults the n s extension prevailed in the late cretaceous and activated the east trending normal faults that controlled the late cretaceous subsidence this extensional phase seems to have lasted through the early paleogene and ended in the late paleogene by a compressional regime with ne sw compression and nw se extension as attested by the stratigraphic unconformity at the base of the neogene in the jianghan basin the temporary evolution of these tectonic stress fields documented in the yuanma basin provides a new insight into the influences of different plate tectonics exerting on the south china block over the late mesozoic to early cenozoic time we infer that the yuanma basin was influenced in the middle jurassic early cretaceous by the process of westward subduction of paleo pacific plate and in the late cretaceous early paleogene by a combined effect of the subduction along the west pacific margin and in the tethyan domain and finally in the late paleogene by the far field effects of india asia collision

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

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

the direction correction tilt test an all purpose tilt fold test for paleomagnetic studies abstract the tilt or fold test in paleomagnetism is used to infer whether paleomagnetic remanence was acquired before or after tectonic tilting while several tilt test formulations have been proposed none fully satisfies the requirements of statistical validity applicability to all bedding geometries and ease of use this paper introduces the direction correction dc test which examines the relationship between the paleomagnetic site mean directions and their corresponding bedding tilt corrections the dc test is similar to mcfadden s correlation test because both test whether or not the site directions contain information about the bedding tilts however the dc test gives greater weight to sites with greater counter bedding the dc test is similar to watson s numerical tilt tests because they determine the degree of untilting which gives optimal concentration of site directions however the dc test uses analytical rather than numerical methods graphical output aids the researcher in recognizing problem sites using both real and simulated data the dc test is demonstrated to be more discriminating than other tilt test formulations for all bedding geometries the simulations show that the power of the tilt test is inversely proportional to the 95 confidence interval 95 of the overall mean as a rule of thumb paleomagnetists should attempt to sample sufficient sites to obtain an 95 less than 1 6 of the bedding attitude difference

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

paleomagnetic constraints on the extent of the stable body of the south china block since the cretaceous new data from the yuanma basin china abstract we undertook a paleomagnetic investigation of cretaceous red sandstones at 30 sites within the yuanma basin in western hunan central south china block scb china the aim of this study is to further constrain the extent of the scb that has been stable since the cretaceous we isolated the characteristic directions of higher temperature components htcs with an unblocking temperature of 650 to 690 c by progressive thermal demagnetization and principal component analysis the optimal concentrations of global mean htc directions calculated using the direction correction tilt test were achieved at 92 7 59 1 87 9 25 0 and 93 3 19 7 untilting indistinguishable from 100 untilting for early cretaceous k1 13 sites late cretaceous k2 17 sites and k site groupings k1 k2 30 sites respectively this treatment yielded positive tilt tests and the htcs are considered to be primary magnetic components acquired before tilting of the sedimentary layers early k1 and late k2 cretaceous paleomagnetic poles calculated using the site mean directions untilted completely are located at similar positions this suggests the absence of local rotations linked to cretaceous strain within the study area the cretaceous k1 k2 mean paleomagnetic pole calculated using virtual geomagnetic poles from all sites is in agreement with previously reported cretaceous paleomagnetic poles from the eastern and western scb this indicates that the hunan region has been part of the stable body of the scb since the cretaceous and that the tectonic influence of the india asia collision did not extend to within the stable body of the scb the reference cretaceous pole position latitude 80 1 n longitude 204 1 e a 95 2 5 calculated using eight cretaceous poles from the stable body of the scb is similar to those determined from stable eurasia and the north china block ncb this result indicates that the india asia collision caused no relative motion as detected by paleomagnetic analysis among stable eurasia ncb and the stable body of the scb

late cretaceous climbing erg systems in the western xinjiang basin palaeoatmosphere dynamics and east asia margin tectonic forcing on desert expansion and preservation abstract this study reassesses the terrestrial deposits of the late cretaceous tangbian formation in the western xinjiang basin of the south china block originally considered to be aqueous deposits we reinterpret these strata as representing an extensive aeolian system in a desert environment this paper suggests that the development of aeolian deposits in the tangbian fm represents the culmination of the late cretaceous desertification that followed the relatively humid early late cretaceous epoch in the interior of south china the area was dominated by subtropical high pressure systems on a planetary scale combined with coastal mountains caused by sustained orogenic activity the interaction between subtropical high pressure systems and topographic conditions ultimately caused the development of a tropical desert climate characterized by an extensive dry climbing aeolian dune system we propose that the coastal mountains not only blocked moisture transport from the ocean and led to the aridification of south china interior but also exerted a control and transformed the original prevailing surface wind pattern

wave overtopping of sea dikes with very shallow foreshores abstract wave overtopping is one of the key parameters for designing coastal structures the crest level is usually determined using admissible overtopping discharges several formulae already exist for wave overtopping assessment that predict the average overtopping discharge per meter width of the coastal defence generally for deep or intermediate water depths at the toe of the dike however the process of wave overtopping on sea dikes with shallow and very shallow foreshore is not yet fully understood gentle foreshores in combination with very shallow water conditions lead to heavy wave breaking and a significant change of the wave spectra from offshore to the toe of the dike the wave steepness is assumed as one of the main criteria to identify cases of severe wave breaking on shallow and very shallow foreshores for these conditions van gent s formula generally used for wave overtopping with shallow foreshores has been implemented and validated against experimental data it is the purpose of this paper to show that van gent s formula overestimates the average overtopping discharge for cases of very shallow foreshores moreover the existing formula cannot be applied to cases with an emergent toe the present work therefore introduces a new equivalent slope concept to obtain an estimation of average wave overtopping discharges on sea dikes with shallow and very shallow foreshores this study uses data from clash database and experimental campaigns specifically carried out at flanders hydraulics research belgium in order to validate this approach results indicate that this concept shows better performance compared to other empirical formulae which suggests that the influence of the very shallow foreshore on the average wave overtopping discharge should be included

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

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

structural and stratigraphic development of the newark extensional basin eastern north america evidence for the growth of the basin and its bounding structures the newark basin is a half graben bounded on its northwestern margin by a system of mostly normal slip faults many of which are reactivated paleozoic thrust faults and were active at least sporadically during the deposition of the entire basin fill as a result of along strike variations in displacement on the border fault system subsidence increased from the lateral edges toward the center of the basin and from the hinged margin toward the border fault system some intrabasinal faults also formed during the deposition of units currently preserved in their hanging walls along strike variations in the density of intrabasinal faults probably reflect changes in the dip angle of the border fault system variations in the amount of extension accommodated on these intrabasinal faults resulted in the formation of a transfer fault along strike variations in fault displacement probably produced the transverse folds in the hanging walls immediately adjacent to border faults and major intrabasinal normal faults some folds formed syndepositionally progressively younger strata onlap basement rocks along the hinged margin of the basin and younger splays of the border fault system propagated into the footwall the basin therefore grew deeper wider and longer through time

cretaceous and tertiary paleomagnetic results from southeast china and their tectonic implications abstract we report cretaceous and tertiary paleomagnetic data from fujian guangxi and guangdong provinces in south china in guangxi province we sampled early cretaceous redbeds of the xinlong formation at eight localities separated by up to 100 km the high temperature component obtained by thermal demagnetization is of dual polarity and passes the fold test and implies 18 8 counterclockwise rotation and insignificant poleward displacement with respect to cratonic localities in sichuan province a tertiary basin lying in a southeast trending fault zone is also rotated counterclockwise by 40 8 both results can be explained very well by a simple block rotation model for the cenozoic tectonic evolution of western guangxi province that is driven by left lateral shear on southeast trending faults the timing and sense of shear are the same as for india asia collision models involving the extrusion of indochina along the red river fault zone which lies several hundred kilometers to the southwest but the magnitude of fault displacement in guangxi is much less in the coastal provinces of fujian and guangdong we find late cretaceous directions that are rotated clockwise with respect to sichuan province combined with similar clockwise rotations found by two other studies of coeval rocks from the same region the mean rotation for the coastal provinces is 12 8 this could indicate a coherent block rotation of the region driven by extrusion tectonics however the limited number of sampling localities also allows the possibility that the directions reflect local rotations due to dextral shearing driven by circum pacific tectonics

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

new mesozoic apparent polar wander path for south china tectonic consequences a new paleomagnetic study in the south sichuan basin south china block has been carried out on sediments of early triassic to middle jurassic age detailed stepwise thermal and alternating field demagnetizations allowed us to isolate two to three components a low temperature component component a falls close to the local present earth field direction a middle temperature component component b is found both in limestone and red beds of early triassic age in limestones of middle triassic age and finally in red beds of jurassic age the component b directions failed the fold test but show a significant increase of the ks kg ratio at 60 when a progressive stepwise unfolding is applied the directions obtained at 60 unfolding are grouped best and yield a pole position at 76 5 n 174 1 e a95 3 7 that is close to the late cretaceous pole of the south china block scb or the early tertiary pole of the eurasian plate characteristic directions are finally obtained component c for early triassic and early to middle jurassic sediments only both with reversal and fold tests they yield pole positions at 44 1 n and 217 2 e a95 4 9 and 79 n and 227 e a95 4 5 respectively the early triassic result well fits other data of the same age from the scb the revised late permian to cretaceous paleopole data provide a new mesozoic apparent polar wander path for south china the successive pole positions from late permian to early triassic indicate motion of the south china block as a whole rather than local rotations linked to important strain within the block the early to middle jurassic pole is statistically indistinguishable from the compiled north china block ncb poles and indicates that final suturation between the two blocks occurred by the end of the triassic which is coherent with the age of ultra high pressure metamorphism in the dabie sulu areas of eastern china the asian plate including the mongol central asian block ncb and scb however was probably separated from siberia by the mongol okhotsk ocean during jurassic time

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

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

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

new paleomagnetic constraints on the extrusion of indochina late cretaceous results from the song da terrane northern vietnam abstract samples were collected for paleomagnetic investigations from the upper cretaceous yen chau formation in the song da terrane 21 7 n 103 9 e bounded by the ailao shan red river fault system and song ma fault in an attempt to examine extrusion tectonics of east asia primary nature of the high temperature 600 690 c component of magnetization from 13 sites is supported by a positive fold test the tectonic corrected data provides the characteristic late cretaceous paleomagnetic direction for the song da terrane d 6 4 i 32 0 with 95 8 5 n 13 sites corresponding to a paleopole lying at 82 9 n 220 7 e a95 6 9 comparison with coeval paleomagnetic poles for the neighboring tectonic blocks indicates no latitudinal translation of the son da terrane with respect to the south china block whereas the shan thai block and the southern part of the indochina block revealed a southward displacement of 10 5 9 5 in latitude with respect to the song da terrane we conclude that the southeastern segment of the ailao shan red river fault system to the east of the dien bien phu fault is not a demarcation of the extruded indochina peninsula the indochina block extruded probably along some faults between the song da terrane and the khorat plateau

new palaeomagnetic data supporting the extent of the stable body of the south china block since the cretaceous and some implications on magnetization acquisition of red beds summary previous palaeomagnetic studies have demonstrated that a large part of the south china block scb has behaved as a stable body since the cretaceous we undertook a palaeomagnetic investigation of lower cretaceous red sandstones at 24 sites within the ganzhou and xingguo basins in southern jiangxi province in china the aim of this study was to further constrain the extent of the scb which has been stable since the cretaceous we isolated the characteristic directions of higher temperature components htcs with an unblocking temperature from 650 to 700 c by progressive thermal demagnetization and principal component analysis the optimal concentration of site mean htc directions calculated using the direction correction tilt test was achieved at 51 2 32 4 per cent untilting indicating syntilting magnetization suggesting that the remanences were not acquired immediately after sedimentation most cretaceous sedimentary basins on the eastern part of the scb were controlled by fault movement extensional basins most tilting in such an extensional basin is thought to have progressed contemporaneously with the structural and stratigraphic development of the basin we concluded that the remanence acquisition of red sandstones on the ganzhou and xingguo basins occurred during synsedimentary tilting we adopted 51 2 per cent untilted directions of the htcs as the palaeomagnetic field directions during the early cretaceous the mean palaeomagnetic pole 76 3 n 224 3 e 95 3 3 calculated using virtual geomagnetic poles from 23 sites excluding site 20 which has an insufficient number of samples showing a stable magnetic component is in good agreement with the late cretaceous palaeomagnetic poles from the same region and also with most of cretaceous poles previously reported from the stable body of the scb this agreement indicates that the jiangxi region has been part of the stable body of the scb since the cretaceous this result also demonstrates that the tectonic influence of the india asia collision did not destroy the rigidity of most of the scb the global mean pole position 78 8 n 214 4 e 95 2 6 calculated using sixteen cretaceous poles from the stable body of the scb is suitable for use as the reference cretaceous palaeomagnetic pole of the stable scb

the stationary cretaceous paleomagnetic pole of sichuan south china block upper jurassic to lower tertiary sites have been sampled from three localities separated by up to 150 km in the sichuan basin 30 n 103 e of the south china block each locality has at least one stability test but none alone gives a fully reliable result when taken together however identical directions are found with a global average d 12 7 i 34 2 k 42 9 95 3 3 n 44 sites and corresponding pole 73 9 n 234 4 e dp 2 2 dm 3 8 paleolatitude 18 8 there is no significant apparent polar wander apw with age which is consistent with an acquisition of magnetization during the period of the stable tip of the eurasian apw loop 130 70 ma as defined with poles from other continents transferred onto eurasia this age range is compatible with the available paleontological and magnetostratigraphic age constraints but is shorter than that suggested by the assigned formation ages the paleolatitude of sichuan is significantly lower 8 0 4 0 at 90 ma than that predicted by the reference apw path either because of northward shortening during the tertiary or because of errors in the apw path cretaceous poles from other chinese blocks are consistent with the sichuan pole but there is evidence that these blocks have suffered local rotations up to 10 during the tertiary probably as a result of the india eurasia collision

cretaceous paleomagnetism of the eastern south china block establishment of the stable body of scb abstract a paleomagnetic investigation was performed on the cretaceous red sandstones collected at the eastern side of the south china block scb china and attempted to establish the stable part of the scb since the cretaceous paleomagnetic specimens were collected at 39 25 and 14 sites from three independent parts the northern central and southern regions of eastern scb respectively characteristic directions of higher temperature components htcs with an unblocking temperature of 680 c were isolated from 69 78 sites the optimal concentrations of global mean htc directions calculated using the direction correction tilt test were achieved at 79 19 95 27 71 37 and 117 98 untilting for the early cretaceous sites from the northern part late cretaceous sites from the northern central and southern parts respectively this treatment gives positive tilt tests or brings the optimal concentration not far from being indistinguishable from positive tilt tests although this observation can be due to imperfect separation of a primary component htc from a secondary one lower temperature component we adopted completely 100 untilted directions of the htcs as the paleomagnetic field directions during the cretaceous because the mean directions after complete untilting were almost equal to each mean direction after incomplete untilting showing the optimal concentration the mean paleomagnetic poles for three independent parts were located at almost the same positions and were indistinguishable from that for sichuan the western side of scb at the 95 confidence level this observation indicates that there is no relative movement between the eastern and western sides of scb and implies that a large part of the scb excluding a 400 km wide swath along the red river fault has behaved as its coherent stable body since the cretaceous the cretaceous paleomagnetic pole for the stable body of the scb latitude 80 0 n longitude 206 7 e a 95 2 5 is worth using as a reference cretaceous paleomagnetic pole of the scb and agrees strongly with the reference eurasian paleomagnetic pole during the cretaceous period