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

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

paleomagnetic versus gps determined tectonic rotation around eastern himalayan syntaxis in east asia abstract northward indentation of the indian plate has brought about significant tectonic deformation into east asia a record of long term tectonic deformation in this area for the past 50 m yr particularly the vertical axis rotation is available through paleomagnetic data in order to depict rotational deformation in this area with respect to eurasia we compiled reliable paleomagnetic data sets from 79 localities distributed around eastern himalayan syntaxis in east asia this record delineates that a zone affected by clockwise rotational deformation extends from the southern tip of the chuan dian fragment to as far as the northwestern part of the indochina peninsula a limited zone that experienced a significant amount of clockwise rotation after an initial india asia collision is now located at 23 5 n 101 e far away from an area 27 5 n 95 5 e where an intense rotational motion has been viewed by a snapshot of gps measurements this discrepancy in clockwise rotated positions is attributed to southeastward extrusion of the tectonic blocks within east asia as a result of ongoing indentation of the indian plate a quantitative comparison between the gps and paleomagnetically determined clockwise rotation further suggests that following an initial india asia collision the crust at 30 n 94 e paleoposition was subjected to southeastward displacement together with clockwise rotation which eventually reached to present day position of 23 5 n 101 e implying a crustal displacement of about 1000 km during the past 50 m yr

paleomagnetism of the earliest cretaceous to early late cretaceous sandstones khorat group northeast thailand implications for tectonic plate movement of the indochina block abstract a total of 400 samples 33 sites were collected from the earliest cretaceous to early late cretaceous sandstones of the khorat group in the indochina block for paleomagnetic study to unravel the tectonic evolution of the region the sites were adopted from 3 traverses located in the northern edge of the khorat plateau northeastern thailand results indicate that almost all the sandstones exhibit similar magnetic values with an average declination d 31 7 inclination i 30 3 59 7 190 9 k 54 4 and a95 3 7 at reference point 17 30 n and 103 30 e the calculated paleolatitude points are inferred to deviate from the present latitude point by 1 2 2 3 only the lowermost part of the cretaceous sandstones can pass a positive fold test at 95 confidence level the relationship between the virtual geomagnetic poles vgps of cretaceous rocks of the indochina plate in thailand and those of the south china plate advocate that there is a major displacement of indochina along the northwest trending red river and associated faults by about 950 150 km with a 16 0 17 0 clockwise rotation relative to the south china plate during earliest cretaceous times paleomagnetic results of the early late cretaceous indochina plate point to a 20 25 clockwise rotation relative to the present occurring since very late cretaceous 65 myrs early neogene times which may be due to the collision between india and asia

paleomagnetic data from sarawak malaysian borneo and the late mesozoic and cenozoic tectonics of sundaland paleomagnetic data from 231 samples from 31 sites in rocks of upper jurassic to miocene age in sarawak malaysian borneo reveal a trend of increasing counterclockwise ccw declination deflection with age six sites in tertiary hypabyssal intrusions show 8 to 52 of ccw deflection the intrusion deflected 52 ccw was k ar dated at 26 m y upper oligocene while one deflected 22 ccw gives a 17 m y age lower miocene three sites in the upper eocene to miocene silantek formation show an average 40 of ccw deflection prefolding directions showing 90 of ccw deflection are isolated in 4 sites including two positive fold tests in upper jurassic and cretaceous rocks of the bau limestone and pedawan formations a postfolding cenozoic remagnetization with an average of 60 of ccw deflection is found in five bau limestone sites three sites in the upper jurassic kedadom formation show an average of 50 of ccw deflection ccw declination deflections found in mesozoic and cenozoic rocks as far as 400 km east and 150 km south of sarawak in kalimantan indonesian borneo also fit the trend of deflection versus age on the basis of the regional consistency of declination deflection versus age along with geologic evidence the data are considered to be evidence of a regional rather than a local block or distributed shear rotation the domain of ccw rotation extends into west malaysia suggesting that west borneo and the malay peninsula may have been a stable block during the latest cretaceous and cenozoic west malaysia and borneo may have had different histories in the rest of the mesozoic the data imply up to 108 ccw rotation of borneo with respect to stable eurasia sometime during the cretaceous and cenozoic cenozoic rotation may also have occurred between indochina and borneo the sense of rotation shown by the data does not support the propagating extrusion tectonics model for cenozoic southeast asia

thermochronological evidence for the movement of the ailao shan red river shear zone a perspective from vietnam in order to explore the timing of strike slip movement along the ailao shan red river shear zone an 40ar 39ar thermochronological study of the day nui con voi metamorphic massif in northern vietnam was undertaken the massif exposed in the southeastern segment of the ailao shan red river shear zone reveals a rapid cooling in the early miocene 25 21 ma after a very slow cooling ca 34 25 ma the slow cooling period most likely resulted from a geothermal perturbation in the lithosphere owing to the late paleogene 40 30 ma extension in eastern tibet and western yunnan china the rapid cooling consistent with evidence of a wider rapid cooling span from 27 to 17 ma compiled from the entire ailao shan red river shear zone constrains the duration of left lateral shearing which eventually offset indochina from south china by about 600 km the time constraints we have established reinforce the argument that the onset of the ailao shan red river shear zone postdates the opening of the south china sea that began ca 30 ma this result highlights the necessity for reevaluating the cenozoic tectonic models of southeast asia

tertiary evolution of the eastern indonesia collision complex abstract eastern indonesia is the zone of interaction between three converging megaplates eurasia the pacific and indo australia the geological basis for interpretations of the tertiary tectonic evolution of eastern indonesia is reviewed and a series of plate tectonic reconstructions for this region at 5 million year intervals covering the last 35 million years is presented the oldest reconstruction predates the onset of regional collisional deformation at this time a simple plate configuration is interpreted consisting of the northward moving australian continent approaching an approximately e w oriented southward facing subduction zone extending from the southern margin of the eurasian continent eastwards into the pacific oceanic domain beginning at about 30 ma the australian continental margin commenced collision with the subduction zone along its entire palinspastically restored northern margin from sulawesi in the west to papua new guinea in the east from this time until ca 24 ma the australian continent indented the former arc trend with the northward convergence of australia absorbed at the palaeo northern boundary of the philippine sea plate the present day palau kyushu ridge at ca 24 ma the present day pattern of oblique convergence between the northern margin of australia and the philippine sea plate began to develop at about this time a large portion of the palaeogene colliding volcanic arc the future eastern philippines began to detach from the northern continental margin by left lateral strike slip from ca 18 ma oblique southward directed subduction commenced at the maramuni arc in northern new guinea at ca 12 ma the sorong fault zone strike slip system developed effectively separating the philippines from the indonesian tectonic domain the sorong fault zone became inactive at ca 6 ma since which time the tectonics of eastern indonesia has been dominated by the anticlockwise rotation of the bird s head structural block by some 30 40 contemporaneously with post 18 ma tectonism the banda arc subduction collision system developed off the northwestern margin of the australian continent convergence between indo australia and eurasia was accommodated initially by northward subduction of the indian ocean and subsequently since ca 8 ma by the development of a second phase of arc continent collision around the former passive continental margin of nw australia

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

acquisition of chemical remanent magnetization during experimental ferrihydrite hematite conversion in earth like magnetic field implications for paleomagnetic studies of red beds abstract hematite bearing red beds are renowned for their chemical remanent magnetization crm if the crm was acquired substantially later than the sediment was formed this severely compromises paleomagnetic records to improve our interpretation of the natural remanent magnetization the intricacies of the crm acquisition process must be understood here we contribute to this issue by synthesizing hematite under controlled earth like field conditions 100 t crm was imparted in 90 oriented samples with varying inclinations the final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides when the magnetic field intensity is 40 t the crm records the field direction faithfully however for field intensities 40 t the crm direction may deviate considerably from that of the applied field during synthesis the crm intensity normalized by the isothermal remanent magnetization crm irm 2 5 t increases linearly with the intensity of growth field implying that crm could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties crm in hematite has a distributed unblocking temperature spectrum from 200 to 650 c while hematite with a depositional remanent magnetization drm has a more confined spectrum from 600 to 680 c because it is usually coarser grained and more stoichiometric therefore the thermal decay curves of crm with their concave shape are notably different from their drm counterparts which are convex these differences together are suggested to be a potential discriminator of crm from drm carried by hematite in natural red beds and of significance for the interpretation of paleomagnetic studies on red beds

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

paleomagnetism of the middle late jurassic to cretaceous red beds from the peninsular thailand implications for collision tectonics abstract jurassic to cretaceous red sandstones were sampled at 33 sites from the khlong min and lam thap formations of the trang syncline 7 6 n 99 6 e the peninsular thailand rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620 690 c an easterly deflected declination d 31 1 i 12 2 95 13 9 n 9 in stratigraphic coordinates is observed as pre folding remanent magnetization from north trang syncline whereas westerly deflected declination d 342 8 i 22 3 95 12 7 n 13 in geographic coordinates appears in the post folding remanent magnetization from west trang syncline these observations suggest an occurrence of two opposite tectonic rotations in the trang area which as a part of thai malay peninsula received clockwise rotation after jurassic together with shan thai and indochina blocks between the late cretaceous and middle miocene this area as a part of southern sundaland block experienced up to 24 5 11 5 counter clockwise rotation with respect to south china block this post cretaceous tectonic rotation in trang area is considered as a part of large scale counter clockwise rotation experienced by the southern sundaland block including the peninsular malaysia borneo and south sulawesi areas as a result of australian plate collision with southeast asia within the framework of sundaland block the northern boundary of counter clockwise rotated zone lies between the trang area and the khorat basin

early precambrian crustal development changing styles of mafic magmatism the work of sutton watson 1951 was one of the cornerstones in the interpretation of the evolution of early precambrian archaean and early proterozoic gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted archaean cratons since then the concept of geological terranes and terrane accretion has been extended back to the archaean and different events can be distinguished by increasingly precise isotopic dating techniques there is growing evidence that with certain clear provisos the principle of uniformitarianism can be applied as equally to the early precambrian as it can through the rest of the geological record in terms of mafic magmatism there are similarities between some ancient and modern suites both intrusive and extrusive but there are also some major differences such as the presence of komatiites in the archaean and the formation of large scale layered intrusions and extensive dyke swarms at the end of the late archaean and in the early proterozoic the mantle has evolved continuously with the progressive extraction of mafic magmas but allowing for this continental tholeiites appear to have changed little with time ancient mid ocean ridge basalts are elusive because of their poor preservation record the geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present day arc systems the relative abundance of early precambrian intrusive mafic suites parallels the crustal growth curve reflecting the global crustal accretion differentiation superevent towards the close of the archaean bimodal tholeiitic noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle mafic crust continental crust system this in turn gives a possible link between the respective evolutions of archaean to recent komatiitic noritic and boninitic suites

seismic reflection evidence for a dangerous grounds miniplate no extrusion origin for the south china sea the collision of india and asia has caused large strike slip faults to form in east asia resulting in the extrusion of crustal blocks toward the southeast since the eocene as a result of the indentation of rigid india into asia it has been suggested that the south china sea opened as a result of relative motion between a rigid indochina sundaland block and china alternative models propose that rifting and seafloor spreading were driven by trench forces to the south we test these competing models by analysis of seismic reflection profiles across the boundary between sundaland and the southern rifted margin known as the dangerous grounds we show that the southern boundary of the dangerous grounds is a subduction zone that jammed in the middle miocene to the west the dangerous grounds are bounded by a strike slip zone also active until similar to 16 ma that becomes diffuse south of the now inactive south china sea seafloor spreading center we place the western edge of the dangerous grounds just to the east of the natuna arch lupar line the west baram line is confirmed as originating as a major strike slip fault within the dangerous grounds and is continuous with the red river fault zone because the dangerous grounds were independent of sundaland until similar to 6 ma its motion cannot have been constrained by motion of this block making extrusion impossible as a mechanism to rift the south china sea se motion by both the dangerous grounds and sundaland suggests subduction forces were the primary trigger for plate motions our reconstruction places a similar to 280 km upper limit on the motion on the red river fault and a similar to 1400 km width to the paleo south china sea

janet watson an appreciation and bibliography with the passing of professor janet vida watson frs the earth sciences in the u k and throughout the world lost one of its most distinguished and well known personalities for while janet watson spent most of her academic career in london at imperial college after graduation with a first class general honours degree at reading university in 1943 she was known throughout the world not only for her exceptional gift of clear and persuasive exposition both at the lecture bench and the committee table but also as a major contributor to the advancement of the earth sciences her death on 29 march 1985 at the age of 61 brought to an untimely end a distinguished career which had seen many honours showered on her the geological society of london which had elevated her to the office of president in 1982 84 had previously awarded her jointly with her husband professor john sutton frs both the lyell fund 1954 and the bigsby medal 1965 they also honoured her with the lyell medal 1973 as they had her father professor d m s watson frs nearly 40 years previously the edinburgh geological society 9 awarded her the clough medal 1980 she was president of section c of the british association for the advancement of science 1972 elected a fellow of the royal society of london 1979 and a member of its council and vice president 1983 until her death to the various offices she held janet brought the directness the precision and the liveliness of mind she had shown in one of the very first offices she had held as an earth scientist that of a steward at the 18th international geological congress held in london at imperial college in 1948 tell john later to be her husband 1 2 and 3 with each part of the message clearly and precisely stated yet perhaps it was not in the professional societies congresses and committees where she received most recognition but in the student societies throughout the country they consistently put her at the top of their lists of speakers to be invited and she consistently responded by using her talent of clear precise and persuasive exposition to excite as well as instruct many a budding earth scientist it was scotland that provided janet with the outdoor laboratory that she loved the most the initial choice was that of her teacher mentor and co author of a number of books professor h h read frs who first set her to study one of his favourite topics the migmatites of sutherland an aspect of which was the subject of her first publication he then directed her and her contemporary as a research student john sutton to parts of the lewisian complex of nw scotland where there were abundant migmatitic and igneous rocks this together with the research being done by professor w s pitcher and others at imperial college on the granitic rocks of donegal was to test and apply the concepts of place and time in plutonism enunciated by professor read in his presidential addresses to the geological society of london in 1948 and 1949 the young research workers went to the rocks of nw scotland from which b n peach j horne c t clough and other members of a distinguished team from the geological survey had developed ideas that had made such a big impact on geological thinking at the turn of the century however despite such a daunting prospect both ph d theses were accepted in the summer of 1949 just in time for a wedding and a honeymoon in the channel islands a venue that accounts for a publication about the isle of sark that does not appear to be cognate to the i r main body of published work for the next three decades there flowed from their pens a succession of publications that had a profound impact on geological thinking and the direction of research particularly in basement complexes both in the uk and abroad many were under the authorship of j sutton and j watson but in 9 years as her husband progressively became more involved in administrative matters more of janet s publications were her own or with other authors including a succession of research students and officers of the british geological survey with whom she worked on a number of projects the initiation of the partnership both scientific and personal had really taken place in 1948 when after separate field studies at scourie loch laxford j w and torridon j s and joint studies in the former area with their supervisor they set off by bicycle on roads that seemed to consist largely of blocks of torridonian conglomerate to look at other parts of the lewisian complex particularly around gruinard bay they tested their conclusions that the complex contained the products of two separate orogenic episodes scourian and laxfordian and that chronological subdivision could be made using basic dykes as time markers

timing of india asia collision geological biostratigraphic and palaeomagnetic constraints 1 a range of ages have been proposed for the timing of india asia collision the range to some extent reflects different definitions of collision and methods used to date it in this paper we discuss three approaches that have been used to constrain the time of collision the time of cessation of marine facies the time of the first arrival of asian detritus on the indian plate and the determination of the relative positions of india and asia through time in the qumiba sedimentary section located south of the yarlung tsangpo suture in tibet a previous work has dated marine facies at middle to late eocene by far the youngest marine sediments recorded in the region by contrast our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50 6 52 8 ma in broad agreement with the timing of cessation of marine facies elsewhere throughout the region double dating of detrital zircons from this formation by u pb and fission track methods indicates an asian contribution to the rocks thus documenting the time of arrival of asian material onto the indian plate at this time and hence constraining the time of india asia collision our reconstruction of the positions of india and asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early eocene we conclude the paper with a discussion on the viability of a recent assertion that collision between india and asia could not have occurred prior to 35 ma

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

tectonic evolution of the malay peninsula inferred from jurassic to cretaceous paleomagnetic results abstract a primary remanent magnetization is identified in the jurassic cretaceous red bed sandstones of the tembeling group in peninsular malaysia this high temperature magnetic component is unblocked at 680 690 c revealing a clockwise deflected direction of d s 56 8 i s 31 6 where k s 8 5 95 11 3 and n 22 in stratigraphic coordinates the primary origin of this component is ascertained by a positive fold test and a geomagnetic polarity reversal in the kuala wau section secondary remanent magnetizations are identified in the rocks of the tembeling and bertangga basins which indicate a counter clockwise deflection in the geographic coordinates d g 349 1 i g 15 3 where k g 11 8 95 5 1 n 72 the comparison with the expected paleomagnetic directions from the 130 ma and 40 ma eurasian poles indicates two stages of tectonic movement in the southern malay peninsula 1 a clockwise rotation of 61 1 11 9 accompanied by a 13 3 8 1 southward displacement after the cretaceous and 2 a subsequent counter clockwise rotation of 18 5 5 0 to the present day position the first stage of rotation is ascribed to tectonic deformation caused by the indentation of india into asia after 55 ma while the second stage is attributed to the collision of the australian plate with se asia after 30 20 ma the present paleomagnetic results from the jurassic cretaceous tembeling group thus reveal impacts of both of these collisions on se asia in general and on peninsular malaysia in particular