large scale three dimensional gravity analysis of the lithosphere below the transition zone from western europe to the east european platform abstract large scale three dimensional gravity modelling using data averaged on a 1 grid has been carried out for the transition area from western europe to the east european craton the model consists of two regional layers of variable thickness the sedimentary cover and the crystalline crust with lateral variation of average density removal of the calculated gravity effect of the crustal model from the observed gravity field reveals residual anomalies of mantle origin this is confirmed by the correlation between mantle gravity anomalies and upper mantle velocity heterogeneities imaged by seismotomographic studies the tornquist teisseyre zone ttz marked in general by a gradient zone of mantle gravity anomalies is considered as a deep density section traced in the upper mantle down to a depth of 200 km across this suture zone a dramatic change of the structure physical properties and composition of the lithosphere of the continent occurs the different characters of the mantle gravity anomalies over the two main parts of the ttz the danish scandinavian and polish segments are explained by the peculiarities of their evolution and the different character of the prevailing tectonic regimes during the proterozoic cenozoic

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

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

the cenozoic evolution of the roer valley rift system integrated at a european scale the roer valley rift system rvrs is located between the west european rift and the north sea rift system during the cenozoic the rvrs was characterized by several periods of subsidence and inversion which are linked to the evolution of the adjacent rift systems combination of subsidence analysis and results from the analysis of thickness distributions and fault systems allows the determination of the cenozoic evolution and quantification of the subsidence during the early paleocene the rvrs was inverted laramide phase the backstripping method shows that the rvrs was subsequently mainly affected by two periods of subsidence during the late paleocene and the oligocene quaternary time intervals separated by an inversion phase during the late eocene during the oligocene and miocene periods the thickness of the sediments and the distribution of the active faults reveal a radical rotation of the direction of extension by about 70 80j counter clockwise integration of these results at a european scale indicates that the late paleocene subsidence was related to the evolution of the north sea basins whereas the oligocene quaternary subsidence is connected to the west european rift evolution the distribution of the inverted provinces also shows that the early paleocene inversion laramide phase has affected the whole european crust whereas the late eocene inversion was restricted to the southern north sea basins and the channel area finally comparison of these deformations in the european crust with the evolution of the alpine chain suggests that the formation of the alps has controlled the evolution of the european crust since the beginning of the cenozoic

tectonic implications of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china 1 a paleomagnetic study has been carried out in the east of the tan lu fault in liaoning province ne china to understand the timing of tan lu fault activity samples aging from early paleozoic to late mesozoic from 51 sites have been analyzed paleozoic and late permian early triassic rocks are remagnetized by the recent geomagnetic field however late cretaceous between 118 and 83 ma red tuffaceous sandstone passes a positive fold test shows no present earth field characteristic remanent magnetization carried by both magnetite and hematite presents a solo normal polarity and thus provides the only reliable paleomagnetic data in this study the paleomagnetic pole calculated from these rocks p 59 4 n p 205 5 e and a95 7 3 is statistically undistinguishable from all available cretaceous paleomagnetic data from eastern liaoning korean peninsula indicating that these areas may belong to a single tectonic unit here named the east liaoning korea elk block at least since the late cretaceous conversely a significant discrepancy between the elk block and chinese block i e north and south china blocks characterized by a differential rotation 22 5 10 2 with a negligible latitudinal displacement 0 8 6 1 is demonstrated this result indicates first that the left lateral displacement along the tan lu fault if any must have occurred before the late cretaceous and second that the korean block can not be considered as a rigid part of north china block sedimentological and structural evidence show that the meso cenozoic triangle shaped plain consisting of songliao xialiaohe sanjiang zeya and other smaller basins developing in northeast china and southeast russia south of the mongol okhotsk belt experienced a heterogeneous rifting from the late jurassic to tertiary the variable amount of extension larger in the northeast 300 km than in the southwest 80 km is probably related to the clockwise rotation of the elk block centered at the south of the bohai bay basin this result shows that a significant segment of the east eurasian margin more than 1000 km long experienced differential rotation in cenozoic times

vertical axis block rotations in southwestern china since the cretaceous new paleomagnetic results from hainan island a paleomagnetic study of early cretaceous redbeds from hainan island south china reveals a pre folding remanence from six sites with a mean direction of d 4 3 i 41 8 k 51 5 95 9 4 the results suggest that hainan island may have been rotated 10 counterclockwise about a vertical axis since the early cretaceous this rotation is likely to have occurred during the mid tertiary when large scale left lateral motion occurred along the red river fault as a result of the indentation of the indian plate into eurasia causing extrusion of the indochina block and opening of the south china sea a comparison of early cretaceous paleomagnetic results from south china indicates that local rotations are widespread in the western part of the south china block such rotations have to be taken into account when examining pre cenozoic tectonic kinematics of south china and constructing apparent polar wander path s for the 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

a paleomagnetic study of tertiary formations from the kyrgyz tien shan and its tectonic implications as part of a general investigation of cenozoic deformation in central asia we studied the paleomagnetism of tertiary red beds and lava flows from intermontane basins in the tien shan region of kyrgyzstan we collected 532 cores and hand samples from 78 sites at 12 localities and progressively demagnetized them thermally or with alternating fields for most sites there are magnetic components with unblocking temperatures higher than 600 c we infer that the magnetic carriers are mainly hematite and magnetite for most localities the high temperature component appears to predate tectonic folding for all localities mean inclinations are shallower than expected from apparent polar wander paths inclination anomalies range from 16 5 for the issyk kul basin to 26 7 for the fergana basin if due to changes in latitude these anomalies imply at least 2000 km of northward displacement of the tien shan during the tertiary for which there is no tectonic evidence we thus consider that the paleomagnetic reference directions cannot be directly compared with our tertiary data we explored other possible reasons for this anomaly which has also been reported from other parts of the alpine belt but we could not find a satisfactory explanation absolute rotations cannot be accurately determined because of problems with the reference direction nevertheless the mean declination for the fergana basin lies counterclockwise by 20 11 from the mean declination of the issyk kul basin this result is consistent with the counterclockwise rotation inferred for the fergana basin from the pattern of cenozoic faults and folds it suggests a cenozoic right lateral displacement of 110 60 km on the talas fergana fault

jurassic paleomagnetic constraints on the collision of the north and south china blocks this paper reports a paleomagnetic study of jurassic rocks from the ordos basin in the north china block ncb a recent remagnetization and a high temperature and or high coercivity component with dual polarities have been isolated the middle jurassic pole 74 n 233 e a95 5 is roughly consistent with previous results and the lower jurassic pole 82 n 286 e a95 7 is located between the late triassic and middle jurassic poles these results combined with paleomagnetic results from adjacent blocks suggest that 1 the pole for the ncb suffered an angular displacement of 47 8 between the late triassic and middle jurassic 2 the scb underwent final accretion to the ncb in the middle jurassic and 3 accretion of the ncb to siberia was not complete until the late jurassic and possibly even until the early cretaceous

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

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

new paleomagnetic data from the huanan block china and cretaceous tectonics in eastern china abstract a total of 72 grey green fine grained sandstone and siltstone core samples from 10 sites were collected from the early cretaceous jieshan and hekou formations at yongan in the huanan block of southeastern china fujian province after removal of an erratic soft magnetic component in fields of 10 20 mt stable magnetizations were retrieved from both rock units which are carried mainly by single domain pseudo single domain sd psd magnetite or titanomagnetite as suggested by isothermal remanent magnetization coercivity measurements and microscopic observations the hekou formation yields a tilt corrected pole at 66 9 n 221 4 e n 5 sites k 203 3 a 95 5 4 a fold test on this result suggests that the magnetization was acquired before tilting which occurred shortly after deposition between early and late cretaceous this magnetization is related to a primary sedimentary fabric as indicated by the low field anisotropy of magnetic susceptibility ams measurements the positive fold test and occurrence of a primary sedimentary fabric suggest a depositional origin for the stable magnetization the jieshan formation gives a pole at 70 8 n 228 7 e n 5 sites k 47 7 a 95 11 2 in geographic coordinates which is statistically indistinguishable from the tilted pole for the hekou formation the associated stable magnetization corresponds to a secondary fabric these features indicate that the jieshan formation has been remagnetized during cretaceous time the predominance of sd psd magnetite or titanomagnetite and igneous activities in eastern fujian during the cretaceous suggest a viscous thermal remanent magnetization origin for the secondary magnetization the early cretaceous pole from the hekou formation is similar to those for the yangzi block suggesting that the huanan block has been accreted to the yangzi block at least since early cretaceous time a high consistency of cretaceous poles from the sino korean yangzi and huanan blocks as well as hainan island indicates that eastern china has been a coherent tectonic unit since cretaceous time although there might have been a small amount of northward displacement of the sampling area with respect to the yangzi block during the early late cretaceous period as a result of the overthrust of the huanan block onto the yangzi carbonate platform comparison of cretaceous poles for eastern china with the eurasian apparent polar wander path apwp suggests that no paleomagnetically detectable relative motion has taken place since the cretaceous the cretaceous poles of eastern china however display a paleomagnetically significant westward motion about 9 in angular distance which is not observed in the eurasian apwp this difference may be indicative of a younger age corresponding to the cretaceous tertiary boundary for all late cretaceous poles from eastern china or more probably may imply a minor error in the definition of the eurasian apwp

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

active faults in eurasia general remarks abstract the database and map of active faults of eurasia 1 5 000 000 have been compiled according to the ilp project ii 2 world map of major active faults the map shows the complicated distribution of active faulting the major faults group in broad mobile belts between relatively weakly faulted parts of the main plates the faults form the plates microplates and crustal blocks boundaries there and are accompanied by deformation of the boundary areas using active fault data for the seismic hazard assessment estimation of maximum possible magnitudes of earthquakes in fault zones it is necessary to take into account the total neotectonic activity of the territory and average rate and sense of motion on the fault because trenching gives a possibility to determine only vertical earthquake offset on a fault it is necessary to make corrections for strike slip faults to estimate the earthquake magnitude by using this parameter

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

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

basalt platforms in inner mongolia and hebei province northeastern china new k ar ages geochemistries and revision of palaeomagnetic results summary k ar ages were determined for the basalt samples from northeastern china of which palaeomagnetic results were reported in zheng et al 1991 geophys j int 104 29 40 samples used for dating were collected at 42 sites from 12 basalt platforms near chifeng in inner mongolia and 9 sites from 3 platforms near zhangjiakou in hebei province all of which were stratigraphically dated to the neogene period in the previous study k ar dating showed that most of the platforms with a supposed age of neogene were formed in either the miocene or the oligocene except one platform which turned out to be about 90 ma in age hence minor revision was made to the palaeomagnetic data by discarding the relevant cretaceous palaeodirections and updated palaeomagnetic poles were reported differences in the new and previous poles are not significant for both tertiary and late cretaceous but some of the site mean directions were combined due to their similarity providing a new data set to be used for the study of palaeosecular variation chemical compositions of major and trace elements were measured in some of the tertiary basalt samples secular variation was observed in both the incompatible element concentrations and the normative compositions the secular variation occurred in a similar trend before and after the volcanic hiatus of 10 25 ma it is suggested that the observed secular variation in chemical compositions could be caused by differences both in degrees of partial melting and depths of magma segregation

paleomagnetic evidence for post cretaceous internal deformation of the chuan dian fragment in the yangtze block a consequence of indentation of india into asia abstract paleomagnetic samples of paleocene eocene red sandstones were collected at 36 sites from the jiangdihe 4 and zhaojiadian formations around the yongren 26 1 n 101 7 e and dayao areas 25 7 n 101 3 e these areas are located in the chuxiong basin of the chuan dian fragment southwestern part of the yangtze block after stepwise thermal demagnetization a high temperature component with unblocking temperature of about 680 c is isolated from 26 sites the primary nature of this magnetization is ascertained through positive fold and reversal tests at 95 confidence level the tilt corrected mean paleomagnetic directions for the yongren and dayao areas are d 17 2 i 26 6 with 95 5 8 and d 16 5 i 31 1 with 95 4 8 respectively easterly deflected declinations from this study are consistent with those reported from other areas of the chuxiong basin indicating its wide presence in the cretaceous eocene formations of the said basin comparison with declination values expected from the cretaceous eocene apwp of eurasia indicates that the magnitude of clockwise rotation systematically increases toward the southeast within the chuxiong basin as well as in the chuan dian fragment this trend of the differential tectonic rotation in the chuan dian fragment is consistent with curvature of the xianshuihe xiojiang fault system deformation of the chuxiong basin can fairly be associated with the formation of eastward bulge in the southern part of the chuan dian fragment during southward displacement the chuan dian fragment was probably subjected to tectonic stresses as a result interaction with the yangtze and indochina blocks which resulted into east west extension and north south shortening

oligo miocene magnetostratigraphy and rock magnetism of the xishuigou section subei gansu province western china and implications for shallow inclinations in central asia magnetostratigraphy of 222 remanent directions together with late oligocene to early miocene mammal and charophyte paleontology suggest that 2179 m of the xishuigou section subei gansu province china were deposited from 26 to 19 ma stratigraphic patterns of bulk susceptibility anisotropy of magnetic susceptibility parameters and natural and anhysteretic remanent magnetization intensities demonstrate that 1 faulting does not significantly affect the record 2 sediment deposition was relatively continuous 3 sediment source changed around 23 ma and 4 rapid uplift near subei occurred at 21 ma subei rotated 27 5 counterclockwise with respect to the 20 ma pole from the eurasian synthetic apparent polar wander path folding and rotation of the section took place after 19 ma the paleolatitude of subei is 14 less than at present and 19 3 less than predicted from the reference pole both rock magnetic and paleomagnetic data sets suggest that the unusually low paleolatitude is the result of synsedimentary inclination shallowing a phenomenon which has likely affected other paleomagnetic data from central asia

discrepant cretaceous paleomagnetic poles between eastern china and indochina a consequence of the extrusion of indochina abstract a paleomagnetic study of cretaceous and paleocene red beds has been carried out in the yunlong area yunnan province of china of the northern indochina block a high temperature component with dual polarities was isolated from both lower cretaceous and paleocene rocks and of solely polarity for upper early cretaceous and lower late cretaceous rocks thirteen magnetic polarity zones are found along the pijiang section the primary nature of cretaceous magnetic remanence is ascertained by positive and reversal fold tests these results combined with previous cretaceous results from the yunlong and yongping areas of the lanping basin indicate that these areas behaved as a relatively rigid block and rotated 37 2 17 clockwise relative to eurasia since the paleocene comparing available early cretaceous paleomagnetic results obtained both from indochina and eastern china a statistically significant paleolatitude difference of 9 6 5 7 is inferred this difference is consistent with an estimated 1000 400 km extrusion of indochina relative to south china through a counter clockwise rotation of 14 of indochina around a finite rotation pole inferred from the stage poles of rotation derived from the magnetic isochrons in the south china sea the reconstruction is fully consistent between the cretaceous pole obtained from the khorat basin of the stable core of the indochina block and the coeval pole of eastern china

magnetic polarity stratigraphy of the neogene siwalik group at khutia khola far western nepal the middle miocene pliocene siwalik group was deposited in the himalayan foreland basin in response to uplift and erosion in the himalayan fold thrust belt results of thermal demagnetization experiments on samples from the siwalik group in central and western nepal demonstrate that laminated siltstones yield paleomagnetic data useful for tectonic and magnetostratigraphic studies sandstones and paleosols of the siwalik group however generally display highly erratic paleomagnetic behavior during thermal demagnetization on the basis of these observations siltstones from a well exposed 2423 m thick section of the siwalik group in khutia khola far western nepal were sampled for magnetic polarity stratigraphy the siwalik group is composed of informal lower middle and upper members correlation of the resulting polarity stratigraphy with the geomagnetic polarity timescale indicates that the exposed section spans 13 30 to 7 65 ma the lower middle siwalik boundary occurs at 11 05 ma near the beginning of chron c5n the rate of sediment accumulation increases upsection similar to rate changes previously observed in the pakistan siwalik group and probably in response to increasing proximity of the himalayan thrust belt in the khutia khola section a discordant declination indicates that this region has rotated about a vertical axis 16 6 counterclockwise with respect to the indian subcontinent measurements of 13 c in paleosol carbonate indicate the predominance of c 3 plants until 7 65 ma and the clear presence of c 4 plants higher in the undated portion of the section

resolving the problem of shallow magnetizations of tertiary age in asia insights from paleomagnetic data from the qiangtang kunlun and qaidam blocks tibet china and a new hypothesis we present new paleomagnetic results obtained at 39 sampling sites from five sections of tertiary red bed formations two eocene formations from the qiangtang block of tibet xialaxiu locality 32 8 n 96 6 e and the xining basin of qaidam xining locality 36 5 n 102 0 e and three neogene formations from the xining basin jungong locality 34 7 n 100 7 e and the kunlun block tuoluo lake and west yushu localities 35 3 n 98 6 e and 33 2 n 96 7 e respectively thermal demagnetization of the rocks isolated a high temperature component that we interpret as the primary magnetization in four localities the paleopoles lie at 52 6 n 352 e dp dm 6 0 10 7 for xialaxiu 61 6 n 211 3 e dp dm 9 7 16 1 for xining 66 0 n 228 6 e dp dm 3 6 6 9 for jungong and 53 9 n 205 4 e dp dm 5 6 10 0 for west yushu as in previous studies of tertiary formations from asia the inclinations we obtained are shallower by 18 to 26 than the magnetic field computed from the eurasian apparent polar wander path apwp at 10 and 20 ma for neogene rocks and at 40 and 60 ma for eocene rocks on the basis of a compilation of eocene data from the south china block tibet central asia and kyrgyzstan we conclude that this inclination anomaly reflects erroneous predictions of positions of the siberian craton when based on the apwp of eurasia the main reason for this discrepancy might be nonrigid behavior of the eurasian plate in the tertiary combination of this with intracontinental shortening of asia under the penetration of india provides a full explanation for the anomaly verification of this new interpretation of the inclination anomaly will require new geologic and paleomagnetic data from the northern parts of these remote regions in mongolia and siberia

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

new cretaceous paleomagnetic poles from the tarim basin northwestern china most paleomagnetic studies of the tarim have been focused on the paleozoic with little data published for mesozoic rocks however the ancient configuration of this part of asia has been affected by the indian eurasian collision during the second french chinese karakorum expedition from kashkar to kunjerab in the autumn of 1990 we sampled about 500 cores from 53 sites of upper and lower cretaceous red sandstones from three areas near uytak yingjisha and wuqia 38 5 39 5 n 75 76 5 8 isothermal remanent magnetization acquisition indicates the presence of minerals with high magnetic coercivity stepwise thermal demagnetization confirms that hematite is the dominant carrier and allowed the separation of low temperature components ltc 600 c in most samples the mean direction of ltcs is aligned with that of the present earth field normal and reversed polarities have been found for the htcs of each age group htcs show positive fold tests for at least one sub study where the attitudes of bedding were sufficiently different to allow the test to be performed more important the four sub studies from yingjisha and wuqia give fully compatible results results from the uytak area show a wide dispersion in declinations as could be expected from the rather severe deformation and proximity to major thrust and strike slip faults data obtained in the kuche area from northern tarim by li and co workers and in southern junggar by chen and co workers are statistically identical to the new data from yingjisha and wuqia data from paicheng in northern tarim appear to have been subject to local rotation excluding those sites which appear from paleomagnetic study to have been significantly rotated we calculated a mean cretaceous pole for the tarim basin at 69 1 n 223 88 ass 3 5 n 5 this result indicates that the total post cretaceous rotation of tarim relative to junggar and to eurasia has been negligible 2 6 6 1 and 0 4 4 6 respectively continental shortening and rotation between tarim and junggar within the tien shan are not resolved by paleomagnetism although the values obtained 400 t 600 km 3 6 are compatible with tectonic models of the range a major discrepancy warranting further geological investigation is that between the tarim and north china block poles which would imply some 1400 1060 km of north south relative displacement

entrainment at cold glacier beds here we present measurements of the gas content and isotopic composition of debris rich basal layers of a polar glacier meserve glacier antarctica which has a basal temperature of 17 c these measurements show that debris entrainment has occurred without alteration of the glacial ice and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers without bulk freezing of water entrainment at subfreezing temperatures may have formed the u shaped trough containing meserve glacier in addition to possibly allowing some cold based glaciers to be important geomorphic agents entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets which are rheologically distinct and can limit the time span of ice core analyses furthermore accumulating evidence suggests that geomorphologists should abandon the assumption that cold based glaciers do not slide and abrade their beds

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