how paleosols influence groundwater flow and arsenic pollution a model from the bengal basin and its worldwide implication in the bengal basin the land surface exposed during the last lowstand of sea level around 20 ka and now buried by holocene sediment is capped by an effectively impermeable clay paleosol that we term the last glacial maximum paleosol lgmp the paleosol strongly affects groundwater flow and controls the location of arsenic pollution in the shallow aquifers of our study site in southern west bengal and by implication in shallow aquifers across the bengal basin and as polluted deltaic aquifers worldwide the presence of the lgmp defines paleointerfluvial areas it is absent from paleochannel areas a paleosol model of pollution proposed here predicts that groundwater in paleochannels is polluted by arsenic while that beneath paleointerfluvial areas is not paleointerfluvial aquifers are unpolluted because they are protected by the lgmp from downward migration of arsenic and from downward migration of organic matter that drives as pollution via reductive dissolution of as bearing iron oxyhydroxides horizontal groundwater flow carries arsenic from paleochannels toward paleointerfluvial aquifers in which sorption of arsenic minimizes the risk of pollution

late cretaceous and cenozoic tectonics of the malay peninsula constrained by thermochronology abstract new thermochronological analyses of granites from the malay peninsula record the region s thermal history during the late mesozoic and cenozoic 40 ar 39 ar and u th sm he analyses are combined with existing fission track data to provide a comprehensive set of temperature and time data fully and partially reset k feldspar and biotite mica 40 ar 39 ar analyses indicate a significant period of thermal perturbation between 100 and 90 ma and a second lesser perturbation between 51 and 43 ma zircon u th sm he analyses and existing fission track data indicate exhumation of the malay peninsula in the cretaceous and renewed localised exhumation in the early paleogene apatite u th sm he and fission track data indicate rapid exhumation of the region in the late eocene and oligocene late cretaceous tectonism is linked to the reversal of a regional dynamic topographic low following the cessation of subduction along the sundaland margin in the late cretaceous causing regional uplift and exhumation and the addition of significant heat into the crust via mantle upwelling early paleogene exhumation may reflect the continuation of cretaceous tectonism or a discrete phase of paleocene exhumation linked to localised transpressional tectonics eocene tectonism is coincident with major subsidence offshore of the malay peninsula interpreted to reflect regional block faulting in response to north south compression driven by the resumption of subduction along the southern margin of sundaland in the eocene

late cretaceous early palaeogene tectonic development of se asia abstract the late cretaceous early palaeogene history of the continental core of se asia sundaland marks the time prior to collision of india with asia when se asia from the tethys in the west to the palaeo pacific in the east lay in the upper plate of subduction zones in myanmar and sumatra subduction was interrupted in the aptian albian by a phase of arc accretion woyla and mawgyi arcs and in java eastern borneo and western sulawesi by collision of continental fragments rifted from northern australia subsequent resumption of subduction in the myanmar thailand sector explains 1 early creation of oceanic crust in the andaman sea in a supra subduction zone setting 95 ma 2 the belt of granite plutons of late cretaceous early palaeogene age starting 88 ma in western thailand and central myanmar and 3 amphibolite grade metamorphism between 70 and 80 ma seen in gneissic outcrops in western and central thailand and 4 accretionary prism development in the western belt of myanmar until glancing collision with the ne corner of greater india promoted ophiolite obduction deformation and exhumation of marine sediments in the early palaeogene the ranong strike slip fault and other less well documented faults were episodically active during the late cretaceous palaeogene time n to nw directed subduction of the palaeo pacific ocean below southern china vietnam and borneo created a major magmatic arc associated with rift basins metamorphic core complexes and strike slip deformation which continued into the late cretaceous the origin and timing of termination of subduction has recently been explained by collision of a large luconia continental fragment either during the late cretaceous or palaeogene evidence for such a collision is absent from the south china sea well and seismic reflection record and here collision is discounted instead relocation of the subducting margin further west possibly in response of back arc extension which created the proto south china sea is preferred lying between the two subduction related arcs the khorat basin is of predominantly late jurassic early cretaceous age but stratigraphic and apatite fission track data also indicates deposition of 1 2 km of late cretaceous sediments the synformal basin geometry probably arose due to the dynamic topography created by converging tethyan and palaeo pacific subduction zones the aptian albian slowing of basin subsidence and onset of evaporite deposition coincides with collision of the mawgyi and woyla island arcs extensive palaeogene deformation and exhumation 3 km in places affected all margins of the khorat plateau deformation includes folds of the phu phan uplift and strike slip faults thrusts and folds on the southern and eastern margins south of the khorat plateau outcrop and seismic reflection data from the ton le sap basin cambodia and the gulf of thailand indicate syn depositional fault controlled subsidence was important during cretaceous deposition the hot thickened crust developed during the late cretaceous palaeogene events follows the weak indosinian crustal scale inthanon and sukhothai zones which persistently guided the location of later structures including cenozoic extensional and post rift basins and influenced the widespread occurrence of low angle normal faults metamorphic core complexes and eastern gulf of thailand super deep post rift basins

slab detachment during continental collision influence of crustal rheology and interaction with lithospheric delamination abstract collision between continents can lead to the subduction of continental material if the crust remains coupled to the downgoing slab a large buoyancy force is generated this force slows down convergence and promotes slab detachment if the crust resists to subduction it may decouple from the downgoing slab and be subjected to buoyant extrusion we employ two dimensional thermo mechanical modelling to study the importance of crustal rheology on the evolution of subduction collision systems we propose simple quantifications of the mechanical decoupling between lithospheric levels and the potential for buoyant extrusion of the crust the modelling results indicate that a variable crustal rheological structure results in slab detachment delamination or the combination of both mechanisms a strong crust provides coupling at the moho low and remains coherent during subduction low it promotes deep subduction of the crust 180 km and slab detachment exhumation occurs in coherent manners via eduction and thrusting slab detachment triggers the development of topography 4 5 km close to the suture a contrasting style of collision occurs using a weak crustal rheology mechanical decoupling at the moho high promotes the extrusion of the crust high disabling slab detachment ongoing shortening leads to buckling of the crust and development of topography on the lower plate collisions involving rheologically layered crust allow decoupling at mid crustal depths this structure favours both the extrusion of upper crust and the subduction of the lower crust such collisions are successively affected by delamination and slab detachment topography develops together with the buoyant extrusion of crust onto the foreland and is further amplified by slab detachment our results suggest that the occurrence of both delamination apennines and slab detachment himalayas in orogens may indicate differences in the initial crustal structure of subducting continental plates in these regions

symmetry during the syn and post rift evolution of extensional back arc basins the role of inherited orogenic structures abstract rheological heterogeneities in the lithosphere have first order control on the topographical expression of tectonic processes pre existing orogenic suture zones localise extensional deformation resulting in asymmetric basins such crustal geometries are often in contrast with the more symmetric regional lithospheric structure observed beneath extensional basins we study such a symmetries and their controlling parameters by conducting a series of 2d thermo mechanical numerical experiments of the extension of an overthickened hot lithosphere that contains a weakness zone the modelling shows that syn rift subsidence is low to moderate creating asymmetric half grabens where extension migrates in space and time grouped in an overall symmetrical appearance on a larger scale the initial lithospheric mantle asymmetry is attenuated by the lateral heat conduction and further dynamic evolution of the thermal anomaly during the post rift phase resulting in differential vertical movements of the crust including additional 2 3 km subsidence in the basin centre the modelling shows that the initial crustal and lithospheric thicknesses rate of extension and surface processes strongly control the thermo mechanical evolution of the extensional system the numerical modelling yields new insights into the mechanics of coupling between near surface kinematics and the evolution of deep lithospheric structure in the pannonian basin and the aegean two of europe s largest back arc systems

late quaternary sedimentary environments and landforms in the ganges delta abstract late quaternary sediments deposited since the lowest stand of sea level during the last glacial maximum in the ganges delta and its surrounding region were classified into five units according to their sedimentary facies these are the lowest unit of sandy gravels the lower unit of sand with a few gravels and the middle upper and uppermost units consisting mainly of sand and silt with occasional peat layers the contact between the lower and middle units is fairly sharp and the upper part of the lower unit is oxidized in some places this suggests a period of subaerial exposure after the deposition of the lower unit during the low stand of sea level about the time of the last glacial maximum rivers in the ganges delta and its surrounding region dissected the surfaces of the region and deposited the lowest unit on the valley floors the lower unit was deposited over the lowest unit during an early stage of the post glacial transgression between ca 12 000 yr bp and 10 000 yr bp the surface of the delta was slightly dissected and the top of the lower unit was weathered and oxidized following this period the middle and upper units of alluvial or deltaic sand and silt with occasional peat were deposited the coastline in the early holocene retreated towards the central part of the present ganges delta in the middle and late holocene the silt and clay with occasional peat layers of the uppermost unit indicate that the lowland gradually became marshy and poorly drained as the rate of transgression became slower

the role of strike slip faults in the displacement of the palaeotethys suture zone in southeast thailand abstract six n s tectono stratigraphic belts can be recognized in southeast thailand each with a distinct stratigraphy and igneous history the westernmost belt i is thought to be part of the sibumasu block and the easternmost v to include part of the indochina block between those belt iii comprises acid volcanic rocks volcaniclastics and carboniferous to triassic sedimentary rocks with distinctive faunas interpreted to be a volcanic arc belt iv comprises triassic rocks of back arc basin origin belt v is interpreted as a permian accretionary complex on the western flank of indochina and vi is an unconformable cover of jurassic cretaceous red beds correlating with the khorat group a history of the triassic indosinian orogeny is proposed leading to the cratonization of southeast thailand by the end triassic the apparent absence in southeast thailand of rocks from the devonian triassic palaeotethys ocean the inthanon zone of northern thailand is suggested to have resulted from a phase of post indosinian oblique to longitudinal sinistral strike slip faulting that phase is thought to have included displacement on the mae yuam fault which bounds the inthanon zone in northern thailand then followed a phase of transverse sinistral strike slip faulting which offset the tectono stratigraphic belts and faults of the earlier phase

kinematics of post orogenic extension and exhumation of the taku schist ne peninsular malaysia abstract recent studies imply that the formation and evolution of many se asian basins was driven by extensional detachments or systems of low angle normal faults that created significant crustal exhumation in their footwalls in this context the architecture of the triassic indosinian orogen presently exposed in peninsular malaysia is compatible with significant extension post dating the orogenic event in this study we performed a kinematic analysis based on fieldwork and microstructural observations in the taku schist kemahang granite and the surrounding gua musang sediments of northern peninsular malaysia in order to shed light on processes related to the build up and subsequent demise of the indosinian orogen the first three phases of deformation were related to an overall period of e w oriented contraction and burial metamorphism these phases of deformation are characterized by isoclinal folding with flat lying axial plane cleavages d1 asymmetrical folding top to the w sw shearing d2 and upright folding d3 all are in general agreement with observations of the previously inferred permo triassic indosinian orogeny during these times the taku schist a sequence of paleozoic clastic sediments with mafic intercalations was metamorphosed to amphibolite facies these rocks are most likely equivalent to the ones exposed in the bentong raub suture zone structural relations suggest that the triassic kemahang pluton is syn kinematic which provides important constraints for the timing of these contractional events we demonstrate that the overall shortening was followed by a hitherto undescribed extension in nw se direction resulting in the formation of a large scale detachment the taku detachment in northern peninsular malaysia extension probably reactivated the former subduction plane as a detachment and exhumed previously buried and metamorphosed rocks of similar lithological composition to the neighboring bentong raub suture zone such a mechanism is similar to that observed in other regions such as the aegean apennines dinarides or the betics rif system where exhumation of high pressure metamorphic rocks is largely controlled by detachments or low angle normal shear fault systems

subduction kinematics and dynamic constraints the kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings two reference frames are used here to describe the simple 2d kinematics of subduction zones in the first the upper plate is assumed fixed whereas in the second frame upper and lower plates move relative to the mantle relative to a fixed point in the upper plate u the transient subduction hinge h can converge diverge or be stationary similarly the lower plate l can converge diverge or be stationary the subduction rate vs is given by the velocity of the hinge h minus the velocity of the lower plate l vs vh vl the subduction rate 1 increases when h diverges and 2 decreases when h converges combining the different movements at least 14 kinematic settings can be distinguished along the subduction zones variable settings can coexist even along a single subduction zone as shown for the 5 different cases occurring along the apennines subduction zone apart from few exceptions the subduction hinge converges toward the upper plate more frequently along e or ne directed subduction zone whereas it mainly diverges from the upper plate along w directed subduction zones accompanying backarc extension before collision orogen growth occurs mostly at the expenses of the upper plate shortening along e ne directed subduction zones whereas the accretionary prism of w directed subduction zones increases at the expenses of the shallow layers of the lower plate the convergence shortening ratio is 1 along e or ne directed subduction zones whereas it is 1 along accretionary prisms of w directed subduction zones backarc spreading forms in two settings along the w directed subduction zones it is determined by the hinge divergence relative to the upper plate minus the volume of the accretionary prism or in case of scarce or no accretion minus the volume of the asthenospheric intrusion at the subduction hinge since the volume of the accretionary prism is proportional to the depth of the decollement plane the backarc rifting is inversely proportional to the depth of the decollement on the other hand along e or ne directed subduction zones few backarc basins form e g aegean andaman and can be explained by the velocity gradient within the hangingwall lithosphere separated into two plates when referring to the mantle the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames the subduction hinge is mostly stationary being the slab anchored to the mantle along w directed subduction zones whereas it moves w or sw ward along e or ne directed subduction zones surprisingly along e or ne directed subduction zones the slab moves out of the mantle i e the slab slips relative to the mantle opposite to the subduction direction kinematically this subduction occurs because the upper plate overrides the lower plate pushing it down into the mantle as an example the hellenic slab moves out relative to the mantle i e sw ward opposite to its subduction direction both in the deep and shallow hotspot reference frames in the shallow hotspot reference frame upper and lower plates move westward relative to the mantle along all subduction zones this kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions w directed subduction zones rather provide about 2 3 times larger volumes of lithosphere re entering into the mantle and the slab is pushed down this opposite behavior is consistent with the down dip extension seismicity along e ne directed subduction zones and the frequent down dip compression along the w directed subduction zones subduction kinematics shows that plate velocity is not dictated by the rate of subduction along the w directed subduction zones the rate of subduction is rather controlled i by the hinge migration due to the slab interaction with the easterly trending horizontal mantle wind along the global tectonic mainstream ii by the far field plate velocities and iii by the value of negative buoyancy of the slab relative to the country mantle alternatively e ne nne directed subduction zones have rates of sinking chiefly determined i by the far field velocity of plates and ii by the value of negative buoyancy of the slab relative to the country mantle along this type of subduction the subduction hinge generally advances e ne ward toward the upper plate decreasing the subduction rate but it moves w sw ward relative to the mantle all this indicates that subduction zones have different origin as a function of their geographic polarity and the subduction process is more a passive feature rather than being the driving mechanism of plate motions a rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones

forearc basins types geometries and relationships to subduction zone dynamics forearc basins are one of the fundamental sedimentary basins and they preserve various geological phenomena arising from dynamic interactions between subducting and overriding plates along convergent plate boundaries previous studies have proposed descriptive classification schemes for such basins and performed analog experiments and numerical simulations examining basin formation and evolution however the great variability of forearc basins means that a comprehensive understanding of these features remains elusive this paper proposes a new classification scheme for forearc basins from the viewpoints of material transfer between the two plates accretionary or nonaccretionary and the long term strain field in the basin compressional or extensional by using characteristics of 41 modern forearc basins geometric characteristics were also analyzed in order to reveal the relationship to subduction zone dynamics including material transfer at the plate boundary accretion erosion plate convergence configurations and kinematics and the mechanics of strain and its partitioning compressional accretionary type basins which are characterized by landward tilting strata and the landward migration of depocenters show a constant width thickness ratio indicating self similar growth of the basin as the outer wedge builds up extensional accretionary type basins develop normal faults in the basin probably due to a gravitational instability of the outer wedge an increase of sediment flux at the trench may grow the accretionary prism and thicken the subduction channel faster leading to a reduction of basal and internal shear strengths of the outer wedge subsidence caused by crustal thinning characterizes the nonaccretionary type basins which have thin trench fill sediments large forearc slopes steady widths of the outer wedge and variable width thickness ratios of the basins from these results the sediment flux at the trench and the plate boundary can be considered as a dominant factor that determines accretion or erosion of the outer wedge and uplift or subsidence of the outer arc high and that is also responsible for the style of deposition in the forearc basin an increase or decrease of the sediment flux may change the type geometry and deformation manner of the forearc basin the results of this study provide important clues to further our understanding of dynamic interactions between forearc basins and subduction zone processes

cenozoic rotation history of borneo and sundaland se asia revealed by paleomagnetism seismic tomography and kinematic reconstruction se asia comprises a heterogeneous assemblage of fragments derived from cathaysia eurasia in the north and gondwana in the south separated by suture zones representing closed former ocean basins the western part of the region comprises sundaland which was formed by late permian triassic amalgamation of continental and arc fragments now found in indochina the thai penisula peninsular malaysia and sumatra on borneo the kuching zone formed the eastern margin of sundaland since the triassic to the se of the kuching zone the gondwana derived continental fragments of sw borneo and east kalimantan accreted in the cretaceous south china derived fragments accreted to north of the kuching zone in the miocene deciphering this complex geodynamic history of se asia requires restoration of its deformation history but quantitative constraints are often sparse paleomagnetism may provide such constraints previous paleomagnetic studies demonstrated that sundaland and fragments in borneo underwent vertical axis rotations since the cretaceous we provide new paleomagnetic data from eocene miocene sedimentary rocks in the kutai basin east borneo and critically reevaluate the published database omitting sites that do not pass widely used up to date reliability criteria we use the resulting database to develop an updated kinematic restoration we test the regional or local nature of paleomagnetic rotations against fits between the restored orientation of the sunda trench and seismic tomography images of the associated slabs paleomagnetic data and mantle tomography of the sunda slab indicate that sundaland did not experience significant vertical axis rotations since the late jurassic paleomagnetic data show that borneo underwent a 35 counterclockwise rotation constrained to the late eocene and an additional 10 counterclockwise rotation since the early miocene how this rotation was accommodated relative to sundaland is enigmatic but likely involved distributed extension in the west java sea between borneo and sumatra this late eocene early oligocene rotation is contemporaneous with and may have been driven by a marked change in motion of australia relative to eurasia from eastward to northward which also has led to the initiation of subduction along the eastern sunda trench and the proto south china sea to the south and north of borneo respectively

a detrital heavy mineral viewpoint on sediment provenance and tropical weathering in se asia abstract understanding heavy mineral preservation is important for interpreting generation pathways provenance and geochemistry of sediments despite this many assumptions about heavy mineral stability are based on ancient strata and few studies consider modern sediments particularly those in tectonically active tropical areas such as se asia we report new heavy mineral data on 69 river sand samples from the malay peninsula and sumatra in which one aim was to find provenance indicators specific to these areas identifications were performed using optical microscopy and confirmed with sem eds in the malay peninsula heavy minerals record granitic and contact metamorphic provenance variable amounts of zircon tourmaline hornblende andalusite epidote monazite rutile and titanite and minor amounts of pyroxene apatite anatase garnet diaspore colourless spinel cassiterite and allanite are typical of this source area the composition of assemblages from sumatra indicates contributions from two major sources the modern volcanic arc i and the basement ii abundant pyroxene particularly hypersthene up to 70 is diagnostic of the volcanic arc source vesuvianite garnet andalusite tourmaline chrome spinel rutile anatase and corundum are present only in small amounts

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

formation of forearc basins and their influence on subduction zone earthquakes recent observations of an association between forearc basins and slip during subduction thrust earthquakes suggest a link between processes controlling upper plate structure and seismic coupling on the subduction zone thrust fault we present a mechanism for the formation of these basins where sedimentation occurs on landward dipping segments of the subduction wedge which itself is actively growing through the accretion of material from the subducting plate our numerical simulations demonstrate that sedimentation stabilizes the underlying wedge preventing internal deformation beneath the basin maximum slip during great thrust earthquakes tends to occur where sedimentary basins stabilize the overlaying wedge the lack of deformation in these stable regions increases the likelihood of thermal pressurization of the subduction thrust allows the fault to load faster and allows greater healing of the fault between rupture events these effects link deformation of the subduction wedge to the seismic coupling of the subduction thrust

a middle permian middle triassic accretionary complex and a late triassic foredeep basin forerunners of an indosinian late triassic thrust complex in the thailand malaysia border area abstract the semanggol formation of nw peninsular malaysia is a middle permian late triassic sequence of predominantly radiolarian chert sandstone and mudstone including turbidites and conglomerate the belt of country occupied by this unit extends into thailand where various names including na thawi formation have been applied to its correlatives fossil evidence particularly radiolarian has established its age but also revealed that it is tectonically complex with numerous out of sequence slices interpreted here to be caused by thrusting the model proposed here involves initially in the middle permian accumulation in the oceanward part of an accretionary complex as palaeotethys began subducting beneath indochina east malaya this regime it is proposed continued until about the end of the middle triassic when sibumasu collided with indochina east malaya bringing an end to subduction but as crustal shortening continued into the late triassic a foredeep basin formed in front of the now inactive subduction zone and accretionary complex and the youngest part of the semanggol formation was deposited during this final stage the whole package of rocks comprising those in the accretionary complex and those deposited in the foredeep basin underwent lateral compression resulting in a thrust complex the semanggol formation and its thailand correlatives occupy part of a n s belt of imbricately thrust deeper water sediments which include slope deposited carboniferous and lower permian beds that belt is interpreted as a series of thrust slices juxtaposing rocks of different ages referred to here as the songkhla semanggol terrane its western boundary is a n s line of inferred thrusting which coincides with a major westward facies change to platform carbonates of middle permian to late triassic age called here the rattaphum kodiang tectonic line

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

structural evolution of malay basin its link to sunda block tectonics abstract the malay basin is located offshore west malaysia in the south china sea within north central region of 1st order sunda block the basin developed partly as a result of tectonic collisions and strike slip shear of the southeast asia continental slabs as the indian plate collided into eurasia and subsequent extrusion of lithospheric blocks towards indochina the sunda block epicontinental earliest rift margins were manifested by the palaeogene w e rift valleys which formed during nw se sinistral shear of the region later eocene nw se dextral shear of 2nd order indochina block against east malaya block rifted open a 3rd order malay basin developed within it is a series of 4th order n s en echelon ridges and grabens the grabens and some ridges sequentially host w e trending 5th order folds of later compressional episodes the malay basin ridge and graben model explains the multi phased structural deformation which started with the a pre rift palaeo mesozoic crystalline metamorphic basement b synrift phase during paleogene c fast subsidence from late oligocene to middle miocene d compressional inversion of first sunda fold during late miocene and e basin sag during plio pleistocene with mild compressional episodes the subsequent mio pliocene folding history of malay basin is connected to the collision of sunda block against subducting indian australian plate this neogene sunda tectonics to some degree after the cessation of south china sea spreading is due to the diachronous collision along the 1st order plate margins between se asia and australia

late cretaceous synorogenic low angle normal faulting along the schlinig fault switzerland italy austria and its significance for the tectonics of the eastern alps abstract the schlinig fault at the western border of theotztal nappe eastern alps previously interpreted as a west directed thrust actually represents a late cretaceous top se to ese normal fault as indicated by sense of shear criteria found within cataclasites and greenschist facies mylonites normal faulting postdated and offset an earlier cretaceous age west directed thrust at the base of theotztal nappe shape fabric and crystallographic preferred orientation in completely recrystallized quartz layers in a mylonite from the schlinig fault record a combination of 1 top east southeast simple shear during late cretaceous normal faulting and 2 later north northeast directed shortening during the early tertiary also recorded by open folds on the outcrop and map scale offset of the basal thrust of theotztal nappe across the schlinig fault indicates a normal displacement of 17 km the fault was initiated with a dip angle of 10 to 15 low angle normal fault domino style extension of the competent late triassic hauptdolomit in the footwall was kinematically linked to normal faulting the schlinig fault belongs to a system of east to southeast dipping normal faults which accommodated severe stretching of the alpine orogen during the late cretaceous the slip direction of extensional faults often parallels the direction of earlier thrusting top w to top nw only the slip sense is reversed and the normal faults are slightly steeper than the thrusts in the western austroalpine nappes extension started at about 80 ma and was coeval with subduction of piemont ligurian oceanic lithosphere and continental fragments farther west the extensional episode led to the formation of austroalpine gosau basins with fluviatile to deep marine sediments west directed rollback of an east dipping piemont ligurian subduction zone is proposed to have caused this stretching in the upper plate

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

determination of the tectonic evolution from fractures faults and calcite twins on the southwestern margin of the indochina block in polyphase tectonic zones integrating a study of fault and fracture with calcite twin analysis can determine the evolving paleostress magnitudes and principle stress directions that affected the area this paper presents the results of the analyses of fractures striated faults and calcite twins collected within the khao khwang fold thrust belt in central thailand se asia here we attempt to reconstruct the orientation of the principal stresses that developed during the tectonic evolution of this highly deformed polyphase orogen tectonic data were collected in the permian carbonates of the khao khad formation of the saraburi group and five successive tectonic stages are determined that are interpreted to have developed before during and after the triassic indosinian orogeny the first three stages predate the main deformation event the first stage is interpreted as a pre indosinian n s extensional stage the second stage described a n s strike slip and compressional regime largely perpendicular to the fold axes of the main structures while the third stage is associated with an e w compressional strike slip phase a further two stages took place after or during the main folding event and correspond to n s compression and to an e w composite strike slip contractional stage the latter which is interpreted to represent cenozoic deformation related to the india asia collision

westward migration of extension in the northern gulf of california mexico interpretation of industry seismic lines indicates that the eastern margin of the northern gulf of california contains the inactive adair tepoca and upper tiburon basins the western margin is active and includes the wagner consag upper delfin and lower delfin basins these basin systems are separated by a wide basement high across which the upper strata in the inactive basins correspond to the middle and lower strata in the active basins recording the westward migration of strain and subsidence during late pliocene time our results illustrate the formation of an abandoned rift margin along the eastern gulf of california

tectonic evolution of the malay peninsula abstract the malay peninsula is characterised by three north south belts the western central and eastern belts based on distinct differences in stratigraphy structure magmatism geophysical signatures and geological evolution the western belt forms part of the sibumasu terrane derived from the nw australian gondwana margin in the late early permian the central and eastern belts represent the sukhothai arc constructed in the late carboniferous early permian on the margin of the indochina block derived from the gondwana margin in the early devonian this arc was then separated from indochina by back arc spreading in the permian the bentong raub suture zone forms the boundary between the sibumasu terrane western belt and sukhothai arc central and eastern belts and preserves remnants of the devonian permian main palaeo tethys ocean basin destroyed by subduction beneath the indochina block sukhothai arc which produced the permian triassic andesitic volcanism and i type granitoids observed in the central and eastern belts of the malay peninsula the collision between sibumasu and the sukhothai arc began in early triassic times and was completed by the late triassic triassic cherts turbidites and conglomerates of the semanggol formation were deposited in a fore deep basin constructed on the leading edge of sibumasu and the uplifted accretionary complex collisional crustal thickening coupled with slab break off and rising hot asthenosphere produced the main range late triassic earliest jurassic s type granitoids that intrude the western belt and bentong raub suture zone the sukhothai back arc basin opened in the early permian and collapsed and closed in the middle late triassic marine sedimentation ceased in the late triassic in the malay peninsula due to tectonic and isostatic uplift and jurassic cretaceous continental red beds form a cover sequence a significant late cretaceous tectono thermal event affected the peninsula with major faulting granitoid intrusion and re setting of palaeomagnetic signatures

variation in apatite fission track length measurement implications for thermal history modelling abstract predictive thermal history modelling using apatite fission track ft data is dependent on an algorithm to describe the time and temperature dependency of ft annealing which in turn relies on the empirical determination of ft length as a measure of the annealing process assessment of variation in ft length measurement is poorly described with few comparisons between analysts and little interlaboratory standardisation using apatites of various compositions containing induced tracks annealed to differing degrees this study has assessed variation in horizontal confined track length measurement for a variety of procedural conditions replicate analysis by a single observer is typically within 3 but increases inversely with track length comparison between observers on the same samples shows significant generally nonsystematic variation between observers for a complex length distribution variation is 12 sources of variation are identified as a variation from track revelation including etching track in track tint vs track in cleavage tincle measurement and use of 252 cf irradiation to produce additional etching channels b bias in measurement including equipment analytical procedures and sample size and c observer bias principally differences in and consistency of personal technique 5 m hno 3 is preferred to weaker etchants although more anisotropic tracks are better defined permitting more rigorous measurement while c axis parallel sections where 2 4 geometry is better defined are more easily identified for all but the longest length distributions tincles are significantly longer than tints with few short tincles at high angles measurement of tincles effectively masks the anisotropy of annealing 252 cf irradiation is effective in increasing the number of tints sampled and measured variation between values measured for unirradiated and cf irradiated aliquots does not exceed that found for a single analyst although a slight systematic shift to longer lengths for cf irradiated samples is seen as reported by other workers track length distributions are anisotropic anisotropy increasing with annealing level track angle exerts a major influence on measured length summing affects from annealing and etching anisotropies with observer bias track angle should be accommodated within the annealing algorithm it is recommended that similar track revelation observation and measurement conditions are used for the analysis of field samples as are used in annealing experiments and subsequently employed in numerical models to predict thermal history a parallel argument can be advanced for using samples of similar composition further we recommend that the ft community should seek as a matter of some urgency a programme of interlaboratory comparison of track length measurement using standard apatite samples containing artificial length distributions typifying various levels of complexity such comparisons would provide a more rigorous baseline for thermal history prediction in geological case studies

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

the link between tectonics and sedimentation in back arc basins new genetic constraints from the analysis of the pannonian basin the architecture of sedimentary basins reflects the relationship between accommodation space and sediment supply their rates and localization being variable during basin evolution the mechanisms driving the interplay between tectonics and sedimentation in extensional back arc basins overlying rheological weak zones inherited from an earlier orogenic evolution are less understood a typical example is the pannonian back arc basin of central europe it is floored by continental lithosphere and was affected by large amounts of extension driven by the subduction rollback that took place in the carpathians and or dinarides a novel kinematic and seismic sequence stratigraphic interpretation calibrated by wells allows the quantification of the link between the formation of half grabens and coeval sedimentation in the great hungarian plain part of the basin while the lower order tectonic induced cycles characterize the main phases of extension in various subbasins the higher order cyclicity and associated unconformities define individual moments of fault re activation our novel interpretation of a temporal and spatial migration of extension during miocene times explains the contrasting present day strike of various subbasins as a result of their gradual clockwise rotation incorporating the observed asymmetry in particular the associated footwall exhumation infers that the amount of extension is much larger than previously thought the quantitative link between tectonics and sedimentation has allowed the definition of a novel model of sedimentation in asymmetric basins that can be ported to other natural scenarios of similarly hyperextended back arc basins observed elsewhere

sand petrology and focused erosion in collision orogens the brahmaputra case abstract the high relief and tectonically active himalayan range characterized by markedly varying climate but relatively homogeneous geology along strike is a unique natural laboratory in which to investigate several of the factors controlling the composition of orogenic sediments coupling of surface and tectonic processes is most evident in the eastern namche barwa syntaxis where the tsangpo siang brahmaputra river draining a large elevated area in south tibet plunges down the deepest gorge on earth here composition of river sands changes drastically from lithic to quartzofeldspathic after confluence with the lohit river draining the transhimalayan equivalent mishmi arc batholiths sediment composition remains remarkably constant across assam indicating subordinate contributions from himalayan tributaries independent calculations based on petrographical mineralogical and geochemical data indicate that the syntaxis representing only 4 of total basin area contributes 35 6 to the total brahmaputra sediment flux and 20 of total detritus reaching the bay of bengal such huge anomalies in erosion patterns have major effects on composition of orogenic sediments which are recorded as far as the bengal fan in the brahmaputra basin in spite of very fast erosion and detrital evacuation chemical weathering is not negligible sand sized carbonate grains are dissolved partially in mountain reaches and completely in monsoon drenched assam plains where clinopyroxenes are selectively altered plagioclase instead is preferentially weathered only in detritus from the shillong plateau which is markedly enriched in microcline most difficult to assess is the effect of hydraulic sorting in bangladesh where quartz garnet and epidote tend to be sequestered in the bedload and trapped on the coastal plain whereas cleavable feldspars and amphiboles are concentrated in the suspended load and eventually deposited in the deep sea high resolution petrographic and dense mineral studies of fluvial sands provide a basis for calculating sediment budgets for tracing patterns of erosion in mountain belts and for better understanding the complex dynamic feedback between surface processes and crustal scale tectonics

combined escape tectonics and subduction rollback back arc extension a model for the evolution of tertiary rift basins in thailand malaysia and laos the tertiary rift basins of thailand and adjacent countries show considerable variability in the timing of rift initiation termination the timing and magnitude of thermal subsidence and the timing and intensity of inversion episodes the rift basins developed on continental blocks that were extruded southeastwards hence their development must be tied into himalayan extrusion tectonics current tectonic models propose that the tertiary basins opened up as pull apart basins associated with strike slip faults published geochronology of strike slip fault zone rocks mapping of fault patterns in the tertiary basins and mapped releasing restraining bend geometries all indicate that in thailand major sinistral strike slip motion ceased at about 30 ma prior to the formation of most rift basins the thailand the effects of later dextral slip were minor and probably a result of reactivation during episodes of inversion during nw se to ne sw himalayan compression dextral slip was not responsible for opening most of the rift basins in thailand an alternative mechanism to open the rift basins is subduction rollback of the indian plate to the west of thailand it is proposed that subuction rollback can help explain some of the characteristics of the rift basins such as non uniform lithospheric extension deep sag basins and the diachronous onset and termination of rifting

characteristics of collisional orogens with low topographic build up an example from the carpathians sequence stratigraphy in the hinterland kinematic analysis of thin skinned thrusting in the foreland and thermochronological tracking of exhumation in the orogenic core are combined to quantify the mechanics of an orogen with low topographic build up the carpathian system demonstrates that collisional deformation can couple and thicken the lower orogenic plate along reverse faults that dip more steeply than the subduction zone defining a foreland coupling type of collision near the surface this is expressed by wide antiforms in the upper plate and the thin skinned orogenic wedge a sequence stratigraphic analysis of the back arc transylvanian basin demonstrates that the sedimentary architecture records orogenic uplift pulses with both short and long wavelengths these correspond to the activation of individual thrust sheets in the thin skinned wedge and to lower plate coupling events respectively

why do model tropical cyclones grow progressively in size and decay in intensity after reaching maturity abstractthe long term behavior of tropical cyclones in the prototype problem for cyclone intensification on an f plane is examined using a nonhydrostatic three dimensional numerical model after reaching a mature intensity the model storms progressively decay while both the inner core size characterized by the radius of the eyewall and the size of the outer circulation measured for example by the radius of the gale force winds progressively increase this behavior is explained in terms of a boundary layer control mechanism in which the expansion of the swirling wind in the lower troposphere leads through boundary layer dynamics to an increase in the radii of forced eyewall ascent as well as to a reduction in the maximum tangential wind speed in the layer these changes are accompanied by changes in the radial and vertical distribution of diabatic heating as long as the aggregate effects of inner core convection characterized by the distribution of diabatic heating are able to draw absolute angula

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

a geodynamic model for extension in the shuswap core complex southeastern canadian cordillera the shuswap core complex records mesozoic and paleocene crustal shortening with superimposed eocene extension during the shortening phase the crust was thickened and slowly uplifted within at most 20 ma of the climax of compression the crustal welt was rapidly uplifted and tectonically denuded shortening of the continental crust may be balanced in the underlying lithosphere by thickening or underplating forming in either case a lithospheric root beneath the crustal welt we consider a model whereby tertiary crustal extension in the shuswap core complex and possibly also in other segments of the north american cordillera is accounted for by the detachment of this root both the time frame and the stress field resulting from the detachment are compatible with geological and geophysical observations far field stresses played an accommodating role but the potential energy required for extension of the shuswap complex was induced by lithospheric thickening

the bentong raub suture zone abstract it is proposed that the bentong raub suture zone represents a segment of the main devonian to middle triassic palaeo tethys ocean and forms the boundary between the gondwana derived sibumasu and indochina terranes palaeo tethyan oceanic ribbon bedded cherts preserved in the suture zone range in age from middle devonian to middle permian and melange includes chert and limestone clasts that range in age from lower carboniferous to lower permian this indicates that the palaeo tethys opened in the devonian when indochina and other chinese blocks separated from gondwana and closed in the late triassic peninsular malaysia segment the suture zone is the result of northwards subduction of the palaeo tethys ocean beneath indochina in the late palaeozoic and the triassic collision of the sibumasu terrane with and the underthrusting of indochina tectonostratigraphic palaeobiogeographic and palaeomagnetic data indicate that the sibumasu terrane separated from gondwana in the late sakmarian and then drifted rapidly northwards during the permian triassic during the permian subduction phase the east malaya volcano plutonic arc with i type granitoids and intermediate to acidic volcanism was developed on the margin of indochina the main structural discontinuity in peninsular malaysia occurs between palaeozoic and triassic rocks and orogenic deformation appears to have been initiated in the upper permian to lower triassic when sibumasu began to collide with indochina during the early to middle triassic a type subduction and crustal thickening generated the main range syn to post orogenic granites which were emplaced in the late triassic early jurassic a foredeep basin developed on the depressed margin of sibumasu in front of the uplifted accretionary complex in which the semanggol formation rocks accumulated the suture zone is covered by a latest triassic jurassic and cretaceous mainly continental red bed overlap sequence

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

structural evolution of mesozoic peninsular malaysia field evidence from upper palaeozoic and mesozoic strata exposed in peninsular malaysia demonstrates that the structural style degree and orientation of folding axial plane cleavage and faulting in the triassic jurassic and cretaceous rocks of the central basin are remarkably similar in contrast the upper palaeozoic strata especially the carboniferous rocks exposed in the eastern part of the peninsula show multiple phase folding and regional metamorphism unlike anything seen in the mesozoic rocks these observations demonstrate that two important compressional events affected peninsular malaysia one in late permian times and the other in the mid to late cretaceous the late palaeozoic compressional event was a major orogenic mountain building phase with associated emplacement of major permo triassic granite plutons that form the eastern and main ranges no indications were found of the widely reported triassic orogenic compression the palaeotectonic and palaeogeographical implications of these discoveries are important for interpreting the evolution of eastern gondwana and tethys the raub bentong line was an important fault zone active during the mesozoic but does not appear to have been a major tectonic suture since the late palaeozoic we postulate that the permo triassic granites of the eastern belt and those presently exposed in the main range were originally about 30 50 km apart and that triassic and jurassic crustal attenuation and subsidence led to the separation of these two granitic belts by more than 100 km

cenozoic tectonic evolution of southeastern thailand derived from low temperature thermochronology low temperature thermochronological techniques specifically apatite u th he and apatite fission track dating were used to reconstruct the thermal history of southeastern thailand this area is intersected by vast and complex fault networks related to the cenozoic mae ping and three pagodas faults these were identified from satellite imagery and confirmed by field observations new apatite fission track and apatite u th he data were collected from crystalline basement blocks within these fault networks ages obtained range from 48 to 24 ma with most of the samples clustering between 36 and 24 ma thermal history modelling indicates late eocene oligocene exhumation of the exposed granitic and metamorphic basement rocks in southeastern thailand exhumation was regional and was contemporaneous with sinistral fault activity during the late eocene early oligocene along the mae ping fault and three pagodas fault moreover this exhumation occurred coevally with a synrift phase of intracontinental offshore rift basin and half graben basin development in the eastern gulf of thailand the phase of exhumation ended in the early miocene as a result of the changing plate tectonic forces along the complex plate boundaries of sundaland supplementary material aft data radial plots and the detailed procedure of thermal history modelling are available at https doi org 10 6084 m9 figshare c 4633064

on the size distribution of atlantic tropical cyclones 1 the size of a tropical cyclone is known to vary considerably across storms though little is understood about the environmental and internal factors that modulate it making use of newly available extended tropical cyclone records that include information about storm structure we examine the size distribution of atlantic tropical cyclones using as a metric the radius of vanishing storm winds normalized by the theoretical upper bound given by the ratio of the potential intensity to the coriolis parameter we find that the distribution of this normalized outer radius is closely log normal

a quikscat climatology of tropical cyclone size 1 quikscat data of near surface wind vectors for the years 1999 2008 are used to create a climatology of tropical cyclone tc size defined as the radius of vanishing winds the azimuthally averaged radius of 12 ms 1 wind r12 is calculated for a subset of tcs n 2154 whose centers of circulation were clearly identifiable via subjective analysis of the quikscat analyzed wind field the outer radius r0 is determined from r12 using an outer wind structure model that assumes no deep convection beyond r12 the global median values of r12 and r0 are 197 km and 423 km respectively with statistically significant variation across ocean basins the global distribution of r12 is found to be approximately log normal the distribution of r0 is quantitatively much closer to log normal and the improvement in fit between r12 and r0 is attributed to the combined effect of the nature of the model employed and the paired distributions of r12 and f moreover the normalization employed by dean et al 2009 is found to weaken rather than improve the log normal fit finally within a given storm both r12 and r0 tend to expand very slowly with time early in the storm lifecycle and then becomes quasi constant though significant variance exists across storms

syn deformation temperature and fossil fluid pathways along an exhumed detachment zone khao khwang fold thrust belt thailand abstract shale detachment zones their influence on deformational style and their internal mechanisms of deformation are an understudied aspect of fold thrust belts properties such as deformational temperature lithology and mineralogy are often recognized as having a key influence on the rheology and deformational style of detachment zones and overlying fold thrust belts however little work has been conducted on rock properties of known detachment zones a recently described upper level detachment zone in the exhumed khao khwang fold thrust belt of central thailand provides an ideal natural laboratory for investigation of the deformation conditions of the detachment zone and association with its complex deformational style the low grade metamorphic indicator illite crystallinty is used to broadly constrain deformational temperatures while oxygen and carbon stable isotope analysis provides insight into fluid flow history and fluid rock interaction illite crystallinity data indicate deep diagenetic to low anchizonal conditions and temperatures of 160 210 c in the shale detachment interpreted as reflecting peak metamorphic conditions during the triassic indosinian orogeny no trend between the intensity spacing complexity of structures and illite crystallinty is observed however shale shear zones of continuous style deformation and inferred higher finite strain display uniformly higher illite crystallinty than surrounding packages of discontinuously faulted shales we also note a positive association between total organic carbon content in the shales and the spacing and complexity of deformational structures data from limestones and syn tectonic vein fills detail the history of fluid rock interaction during early mesogenesis through to orogenesis the early covariant trend of increasingly negative 13 c and 18 o values is attributed to increasing burial while a divergent orogenic trend of increasingly negative 18 o values is interpreted as the result of a loss of matrix permeability and interruption of fluid rock re equilibration these hottest fluids were concentrated along large thrusts which facilitated fluid movement during orogenesis

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

tropical pacific high latitude south atlantic teleconnections as seen in δ18o variability in antarctic coastal ice cores 1 we use a network of eight ice cores from coastal dronning maud land dml antarctica to examine the role of the tropical enso el nino southern oscillation in the temporal variability of 18o in annual accumulation the longest record from the s100 ice core covering the period 1737 1999 is used to analyze the teleconnections between the tropical pacific and coastal dml on decadal scales and longer a shorter stacked coastal dml 18o series spanning 1955 1999 is constructed to assess the variability of enso teleconnection on interannual scales results suggest that on typical enso timescales of 2 6 years the strength of the teleconnection varies in time being stronger for years with generally negative phase of the southern annular mode sam on the timescales of approximately two decades bidecadal positive isotope anomalies are associated with oceanic warming and a westward sea surface temperature sst gradient in the equatorial pacific bidecadal variability in sam forced by the tropical pacific is proposed as a critical element in the teleconnection our analysis suggests that a multidecadal positive trend in the annual mean 18o values from the analyzed cores can be indicative of the atmospheric warming that begun in this part of the dml already in the 1910s the trend in 18o quantified in terms of long term surface air temperature sat changes is consistent with the instrumental data yet we speculate that the accurate estimation of sat trends requires an assessment of the potential role of secular sam and sea ice extent changes in shaping the isotopic signal

spatial and temporal characterization of sea surface temperature response to tropical cyclones abstractthe spatial structure and temporal evolution of the sea surface temperature sst anomaly ssta associated with the passage of tropical cyclones tcs as well as their sensitivity to tc characteristics including tc intensity and translation speed and oceanic climatological conditions represented here by latitude are thoroughly examined by means of composite analysis using satellite derived sst data the magnitude of the tc generated ssta is larger for more intense slower moving and higher latitude tcs and it occurs earlier in time for faster moving and higher latitude storms the location of maximum ssta is farther off the tc track for faster moving storms and it moves toward the track with time after the tc passage the spatial extension of the cold wake is greater for more intense and for slower moving storms but its shape is quite independent of tc characteristics consistent with previous studies the calculations show that the mean ssta over a tc centered box nearly linearly corre

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

structural controls on polyphase hydrothermal dolomitization in the kinta valley malaysia paragenesis and regional tectono magmatism abstract in the eastern side of the malay peninsula thick successions of limestone formations preserve important records of the mesozoic and cenozoic tectonic events here we investigate the strata and fracture bound hydrothermal dolomites in the palaeozoic carbonates of the kinta valley western peninsular malaysia based on their textural and morphologic characteristics structural relationships with the host rock different facies types and associations with hydrothermal calcite and low grade metamorphic marble we attempt to trace their polyphase origin and relationship with thermo tectonic events of the region a detailed evaluation of the nature of brecciation and crystallization of polyphase dolomites dolomitic limestones limestones and marble under the influences of episodic faulting is associated with the regional structural geology with emphasis on pre existing fault reactivations granitic emplacement and progressive thermal influence supply of mg2 from the host rock for dolomitization limited and episodic influx of circulating fluids and cessation of thermo tectonic evolution with progressive cooling are also inferred correlating the geological events in western peninsular malaysia with regional structural dynamics reveals that the major deformation episodes exerted first order controls on the loci of dolomite occurrences the occurrence geometry and structural relationships of the dolomites were controlled by successive magmatic events whereas the intensity of replacement dolomitization was controlled by host rock texture and varied bulk chemistry together with the nature of circulating fluids

controls on facies distribution and stratigraphic preservation in the ganges brahmaputra delta sequence abundant sediment supply and accommodation space in the bengal basin have led to the development of a major late quaternary delta sequence this sequence has formed in a tectonically active setting and represents an important example of a high energy marine and fluvial high yield continental margin deposit recent studies have detailed the delta s stratigraphy and development noting that tectonics and sediment supply control the ganges brahmaputra more significantly than in many other delta systems these ideas are developed here through a discussion of the effects that spatial and temporal variations in tectonics and sediment supply have had on deltaic processes and sequence character unique and differing stratigraphies are found within thedeltasystem suchthatfine grainedsedimentpreservationisfavoredinareasofactivetectonicprocessessuchasfolding block faulting and subsidence coarse grained deposits dominate the stratigraphy under the control of high energy fluvial processes and mixed fine coarse stratigraphies are found in areas dominantly influenced by eustatic sea level change overlaid upon these spatially varying stratigraphic patterns are temporal patterns related to episodic events e g earthquakes and rivers avulsions and long termchangesinclimate andsediment supply modelingisalsousedtoinvestigatethe influenceofavariable sedimentsupply on sequence character results show that the timing and magnitude of sediment input relative to sea level rise is a significant control on the subaerial extent of the delta and the relative dominance of alluvial and marine facies within the sequence d 2002 elsevier science b v all rights reserved

discussion of tectonic models for cenozoic strike slip fault affected continental margins of mainland se asia abstract understanding the roles of cenozoic strike slip faults in se asia observed in outcrop onshore with their offshore continuation has produced a variety of structural models particularly pull apart vs oblique extension escape tectonics vs slab pull driven extension to explain their relationships to sedimentary basins key problems with interpreting the offshore significance of major strike slip faults are 1 reconciling conflicting palaeomagnetic data 2 discriminating extensional and oblique extensional fault geometries from strike slip geometries on 2d seismic reflection data and 3 estimating strike slip displacements from seismic reflection data focus on basic strike slip fault geometries such as restraining vs releasing bends and strongly splaying geometries approach the gulfs of thailand and tonkin suggest major strike slip faults probably do not extend far offshore splays covering areas 10 000 s km2 in extent are characteristic of the southern portions of the sagaing mae ping three pagodas and ailao shan red river faults and are indicative of major faults dying out the areas of the fault tips associated with faults of potentially 100 km displacement scale appropriately with global examples of strike slip faults on log log displacement vs tip area plots the fault geometries in the song hong yinggehai basin are inappropriate for a sinistral pull apart geometry and instead the southern fault strands of the ailao shan red river fault are interpreted to die out within the nw part of the song hong yinggehai basin hence the fault zone does not transfer displacement onto the south china seas spreading centre the strike slip faults are replaced by more extensional oblique extensional fault systems offshore to the south the sagaing fault is also superimposed on an older paleogene early miocene oblique extensional rift system the sagaing fault geometry is complex and one branch of the offshore fault zone transfers displacement onto the pliocene recent andaman spreading centre and links with the west andaman and related faults to form a very large pull apart basin

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

late cretaceous extension and exhumation of the stong and taku magmatic and metamorphic complexes ne peninsular malaysia fragmentation of large continental areas by post orogenic extension requires favourable geodynamic conditions and frequently occurs along pre existing suture zones or nappe contacts as exemplified by the stong and taku magmatic and metamorphic complexes of northern peninsular malaysia for this case we have employed a field and microstructural kinematic study combined with low temperature thermo chronology to analyse the tectonic and exhumation history the results show that the late palaeozoic triassic indosinian orogeny created successive phases of burial related metamorphism shearing and contractional deformation this orogenic structure was subsequently dismembered during a cretaceous thermal event that culminated in the formation of a large scale late santonian early maastrichtian extensional detachment genetically associated with crustal melting the emplacement of syn kinematic plutons and widespread migmatisation the emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range represented by amphibolite and greenschist facies mylonites and as well as brittle structures such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment the formation of this detachment and a first phase of late cretaceous cooling was followed by renewed eocene oligocene exhumation as evidenced from our fission track ages we infer that an initial cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults these cretaceous processes played a critical role in the establishment of the presently observed crustal structure of peninsular malaysia

kinematics of the southern rhodope core complex north greece the southern rhodope core complex is a wide metamorphic dome exhumed in the northern aegean as a result of large scale extension from mid eocene to mid miocene times its roughly triangular shape is bordered on the sw by the jurassic and cretaceous metamorphic units of the serbo macedonian in the chalkidiki peninsula and on the n by the eclogite bearing gneisses of the sideroneron massif the main foliation of metamorphic rocks is flat lying up to 100 km core complex width most rocks display a stretching lineation trending ne sw the kerdylion detachment zone located at the sw controlled the exhumation of the core complex from middle eocene to mid oligocene from late oligocene to mid miocene exhumation is located inside the dome and is accompanied by the emplacement of the synkinematic plutons of vrondou and symvolon since late miocene times extensional basin sediments are deposited on top of the exhumed metamorphic and plutonic rocks and controlled by steep normal faults and flat ramp type structures evidence from thassos island is used to illustrate the sequence of deformation from stacking by thrusting of the metamorphic pile to ductile extension and finally to development of extensional plio pleistocene sedimentary basin paleomagnetic data indicate that the core complex exhumation is controlled by a 30 dextral rotation of the chalkidiki block extensional displacements are restored using a pole of rotation deduced from the curvature of stretching lineation trends at core complex scale it is argued that the rhodope core complex has recorded at least 120 km of extension in the north aegean since the last 40 my

effects of a temperature dependent rheology on large scale continental extension the influence of a temperature dependent rheology on large scale continental extension is investigated using a thin viscous sheet model a vertically averaged rheology is used that is consistent with laboratory experiments on power law creep of olivine and that depends exponentially on temperature the behavior of the model depends principally on two parameters the peclet number which describes the relative rates of advection and diffusion of heat and a dimensionless activation energy which controls the temperature dependence of the rheology numerical calculations of such a thin sheet subjected to an extensional boundary condition show the following results at short times following the beginning of extension deformation occurs with negligible change in temperature so that only small changes in lithospheric strength occur due to attenuation of the lithosphere and maximum rates of deformation are located close to the extensional boundary however after a certain time interval thermal diffusion results in lowered temperatures in the lithosphere strongly increasing lithospheric strength and slowing the rate of extension this critical time depends principally on the peclet number and is short compared with the thermal time constant of the lithosphere the changes in strength cause the locus of high extensional strain rates to shift with time from regions of high strain to regions of low strain results of the calculations are compared with observations from the aegean where maximum extensional strains are found in the south near crete but the largest present day extensional strain rates occur about 300 km further north the comparisons support the hypothesis that the observed separation of the loci of maximum strain and maximum present day strain rates in the aegean may be the consequence of changes in lithospheric strength arising from the temperature dependent mechanical properties of lithospheric materials

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

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

late quaternary sedimentary record and holocene channel avulsions of the jamuna and old brahmaputra river valleys in the upper bengal delta plain abstract the first holocene stratigraphic record of river channel occupation and switching between the brahmaputra jamuna and old brahmaputra paleovalleys is presented here motivated by the brahmaputra river s historic avulsion from the old brahmaputra channel to its present day jamuna course we have obtained sediment and radiocarbon samples from 41 boreholes along a 120 km transect crossing these two braided river valleys the stratigraphy along this transect reveals sand dominated holocene channel systems each bound by remnant mud capped pleistocene stratigraphy using sediment lithology and bulk strontium concentration as a provenance indicator we define the geometry and channel occupation history of each paleovalley the western brahmaputra jamuna valley is broad and somewhat deeper compared with the old brahmaputra valley the latter actually comprising a composite of two narrower sub valleys bifurcated by an antecedent topographic remnant the gently sloped valley margins slope 0 002 to 0 007 and high width to thickness ratio w t 1000 of the brahmaputra jamuna valley suggest that it was filled primarily through lateral channel migration and the reworking of braidbelt and overbank deposits conversely the two old brahmaputra sub valleys have comparatively steeper valley margins slope 0 007 to 0 022 and lower width to thickness ratios w t 125 and 250 indicating that these were filled primarily through vertical aggradation of channel sands we attribute this disparity in valley geometry and fill processes to the different occupation histories for each valley in this case the much larger brahmaputra jamuna valley represents the principal if not singular river course during the last lowstand of sea level with a prominent gravel lag underlying the valley in contrast the smaller old brahmaputra valleys do not appear to have been present or at least well developed at the last lowstand rather these courses were first occupied during the early holocene transgression and we infer that the river had been previously excluded from this region by the relatively higher elevation between the madhupur terrace and the shillong massif we also demonstrate that the brahmaputra river experienced 3 4 major avulsions during the holocene with considerably longer occupation times within the principal brahmaputra jamuna valley together these observations indicate that occupation history and antecedent topography have been important controls on river course mobility and avulsion behavior

tectonic evolution of the sibumasu indochina terrane collision zone in thailand and malaysia constraints from new u pb zircon chronology of se asian tin granitoids three principal granite provinces are defined across se asia as follows 1 the western thailand myanmar burma province consists of hornblende biotite i type granodiorite granites and felsic biotite k feldspar garnet tourmaline granites associated with abundant tin mineralization in greisen type veins new ion microprobe u pb dating results from phuket island show zircon core ages of 212 2 and 214 2 ma and a thermal overprint with rims of 81 2 1 2 and 85 75 ma 2 the north thailand west malaya main range province has mainly s type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the sibumasu plate with indochina during the mid triassic biotite granites around kuala lumpur contain extremely u rich zircons up to 38000 ppm that yield ages of 215 7 and 210 7 ma 3 the east malaya province consists of dominantly permian triassic i type hornblende biotite granites but with subordinate s type plutons and a type syenite gabbros biotite k feldspar granites from tioman island off the east coast of malaysia also yield a zircon age of 80 1 ma showing cretaceous magmatism in common with province 1 geological and u pb geochronological data suggest that two east dipping in present day coordinates subduction zones are required during the triassic one along the bentong raub palaeo tethyan suture and the other west of the phuket burma province 1 belt supplementary material a full description of u pb analytical methods used and data tables are available at www geolsoc org uk sup18523

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

gondwana and cathaysian blocks palaeotethys sutures and cenozoic tectonics in south east asia the triassic indosinian orogeny followed extinction of the palaeotethys ocean resulting in suturing of gondwana affinity and cathaysian blocks

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

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t

exhumation of west sundaland a record of the path of india abstract the indian plate commenced its northward migration towards eurasia in the early cretaceous the lateral effect of this migration on the western edge of the sunda plate in southeast asia still remains equivocal in order to assess this effect we evaluate several key sectors characterized by deep crustal exhumation along a n s transect from the southern malay peninsula to the east himalayan syntaxis the evaluation is aided by a structural analysis of vertical movements and basin development five major metamorphic domes with similar geodynamic evolution maximum p t burial conditions and exhumation are studied exhumation of these domes migrated with time between late cretaceous in the stong complex north malaysia in the south and late miocene in the gaoligong shear zone south china in the north as documented by published work and our new fission track data presented herein deformation is characterized by a n s oriented extension that followed the more regional e w oriented plate tectonic shortening creating local core complexes and syn kinematic magmatism in the footwall of crustal scale detachments which displays a consistent temporal northward migration the n s extension was associated with the onset of hanging wall deposition in the sedimentary basins of western sundaland e g malay sumatra and thai basins during continuous exhumation of the footwall to upper brittle levels our multifaceted analysis of structural and thermochronological data shows a similar succession of tectonic thermal and sedimentary events in west sundaland that was driven by the gradual northward migration of india starting from cretaceous times we infer that the principal mechanism was driven by the subduction of an excess topography of greater india rifted continental margin during its underplating resulting in uplift thermal anomalies extensional exhumation and associated subsidence