the mesozoic tectono magmatic evolution at the paleo pacific subduction zone in west borneo abstract metamorphic and magmatic rocks are present in the northwestern part of the schwaner mountains of west kalimantan this area was previously assigned to sw borneo swb and interpreted as an australian origin block predominantly cretaceous u pb zircon ages c 80 130 ma have been obtained from metapelites and i type granitoids in the north schwaner zone of the swb but a triassic metatonalite discovered in west kalimantan near pontianak is inconsistent with a swb origin the distribution and significance of triassic rocks was not known so the few exposures in the pontianak area were sampled and geochemical analyses and zircon u pb ages were obtained from two meta igneous rocks and three granitoids and diorites triassic and jurassic magmatic and metamorphic zircons obtained from the meta igneous rocks are interpreted to have formed at the mesozoic paleo pacific margin where there was subduction beneath the indochina east malaya block geochemically similar rocks of triassic age exposed in the embuoi complex to the north and the jagoi granodiorite in west sarawak are suggested to have formed part of the southeastern margin of triassic sundaland one granitoid 118 6 1 1 ma has an s type character and contains inherited carboniferous triassic and jurassic zircons which indicate that it intruded sundaland basement two i type granitoids and diorites yielded latest early and late cretaceous weighted mean ages of 101 5 0 6 and 81 1 1 1 ma all three magmatic rocks are in close proximity to the meta igneous rocks and are interpreted to record cretaceous magmatism at the paleo pacific subduction margin cretaceous zircons of metamorphic origin indicate recrystallisation at c 90 ma possibly related to the collision of the argo block with sundaland subduction ceased at that time followed by post collisional magmatism in the pueh 77 2 0 8 ma and gading intrusions 79 7 1 0 ma of west sarawak

stress state in the cuu long and nam con son basins offshore vietnam abstract the results presented in this paper are the first published estimates of the complete stress tensor in the cuu long and nam con son basins offshore vietnam we analysed in situ stress and pore pressure fields in the sedimentary formations using data from petroleum exploration and production wells to evaluate the stress state in these basins the data were obtained from the seafloor to 4300 m burial depth and include both hydrostatic and overpressured sections minimum horizontal stresses were obtained from extended leak off tests and mini fracture tests maximum horizontal stresses were estimated from drilling induced fracture parameters and borehole breakout widths in twelve wells using rock properties measured in the laboratory or estimated empirically from wireline logs seven data points are located in sediments and seventeen data points in igneous basement rocks at depths greater than 3000 m the estimated magnitudes of h are 70 110 of the v magnitudes considering the errors in the stress magnitude estimates their relative magnitudes suggest that a borderline normal strike slip stress regime presently exists in normally pressured sequences of the nam con son and cuu long basins of the twenty four data points twenty have effective stress ratios at a critical stress state for faulting on the assumption that there are faults present that are optimally oriented for failure with friction coefficients of 0 5 the results suggest that the stress state in these basins is generally critical

the red river fault system in the tonkin gulf vietnam abstract the red river fault system in the tonkin gulf offshore haiphong was studied using seismic profiles calibrated by deep wells well characterised left lateral strike slip occurred continuously within a narrow 30 km wide zone southwest of the vinh minh fault between 30 ma and 5 5 ma however the corresponding amount of offset probably does not exceed a few tens of kilometres no sign of post 5 5 ma right lateral motion can be detected prior to 30 ma there is a widespread extension in a wider 100 km wide zone which could be related to a significant amount of left lateral motion the motion of the fault splays to the northeast of the vinh minh fault prior to 30 ma was absorbed in the rifting of the gulf of beibu a 15 5 ma unconformity separates the transtensional regime from a later transpresional regime this 15 5 ma date coincides with the cessation of sea floor spreading in the south china sea

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

cenozoic paleostress evolution in south central vietnam implication for changing dynamics of faulting along the eastern indochina continental margin abstract the tectonics of the indochina continental margin before and after the neogene quaternary basalt eruption is poorly understood the analysis of 1500 striated faults observed in different rocks mostly from volcano plutonic rocks with ages ranging from cretaceous to quaternary at more than 140 locations in south central vietnam by direct inversion method allowed us to determine four paleostress regimes that affected eastern indochina from oligocene up to present day the first tectonic paleostress regime with oligocene age was responsible for the sinistral and dextral motions along the nw se and ne sw striking faults respectively this stress state is typical for a strike slip tectonic regime with maximum principal stress 1 and minimum principal stress 3 axes oriented nearly in e w and n s direction and both plunging at average angle of 80 and 100 respectively the paleostress ellipsoid shape ratio 2 3 1 3 ranges from 0 23 to 0 77 with an average of 0 50 0 15 the subsequent strike slip tectonic stress state prevailing from the late oligocene to very early miocene was characterized by 1 and 3 axes trending in nnw sse and ene wsw and plunging at 120 90 and 120 130 respectively the paleostress ellipsoid shape ratio ranges from 0 12 to 0 88 with a 0 52 0 23 average under this paleostress regime the n1100 to n1400 and n1600 to n200 striking faults moved with dextral and sinistral movements respectively the third paleostress state with assigned early miocene to late miocene age was responsible for dextral and sinistral motions along n1400 to n1600 and n200 to n400 striking faults coeval with emplacement of n s striking basaltic dykes this pattern shows consistency and homogeneity of the 1 and 3 axes in n s trend plunging at 120 90 and 3 in e w trend plunging at 130 110 respectively the paleostress ellipsoid shape ratio varies from 0 41 to 0 89 with an average of 0 53 0 16 the fourth tectonic stress regime occurring since the late miocene to the present day is characterized by a consistency of sub horizontal nne striking 1 plunging 110 100 and ese striking 3 plunging at 130 11 and an average of ellipsoid shape ratio 0 45 0 24 under the latest tectonic stress state the n s and n450 to n600 striking faults continue to move as dextral and sinistral faults respectively the first three paleostress regimes have evolved clockwise and were induced by the force exerted from the eastern himalayan syntaxis during the northward indian plate motion while the fourth tectonic stress regime is most likely linked to the force originated from the sunda subduction

present day stress field of southeast asia article i nfo it is now well established that ridge push forces provide a major control on the plate scale stress field in most of the earth s tectonic plates however the sunda plate that comprises much of southeast asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field the cenozoic tectonic evolution of the sunda plate is usually considered to be controlled by escape tectonics associated with india eurasia collision however the sunda plate is bounded by a poorly understood and complex range of convergent and strike slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region we compile the first extensive stress dataset for southeast asia containing 275 a d quality 177 a c horizontal stress orientations consisting of 72 stress indicators from earthquakes located mostly on the periphery of the plate 202 stress indicators from breakouts and drilling induced fractures and one hydraulic fracture test within 14 provinces in the plate interior this data reveals that a variable stress pattern exists throughout southeast asia that is largely inconsistent with the sunda plate s approximately ese absolute motion direction the present day maximum horizontal stress in thailand vietnam and the malay basin is predominately north south consistent with the radiating stress patterns arising from the eastern himalayan syntaxis however the present day maximum horizontal stress is primarily oriented nw se in borneo a direction that may reflect plate boundary forces or topographic stresses exerted by the central borneo highlands furthermore the south and central sumatra basins exhibit a ne sw maximum horizontal stress direction that is perpendicular to the indo australian subduction front hence the plate scale stress field in southeast asia appears to be controlled by a combination of himalayan orogeny related deformation forces related to subduction primarily trench suction and collision and intraplate sources of stress such as topography and basin geometry

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

the world stress map database release 2016 crustal stress pattern across scales abstract knowledge of the present day crustal in situ stress field is a key for the understanding of geodynamic processes such as global plate tectonics and earthquakes it is also essential for the management of geo reservoirs and underground storage sites for energy and waste since 1986 the world stress map wsm project has systematically compiled the orientation of maximum horizontal stress shmax for the 30th anniversary of the project the wsm database has been updated significantly with 42 870 data records which is double the amount of data in comparison to the database release in 2008 the update focuses on areas with previously sparse data coverage to resolve the stress pattern on different spatial scales in this paper we present details of the new wsm database release 2016 and an analysis of global and regional stress pattern with the higher data density we can now resolve stress pattern heterogeneities from plate wide to local scales in particular we show two examples of 40 60 shmax rotations within 70 km these rotations can be used as proxies to better understand the relative importance of plate boundary forces that control the long wave length pattern in comparison to regional and local controls of the crustal stress state in the new wsm project phase iv that started in 2017 we will continue to further refine the information on the shmax orientation and the stress regime however we will also focus on the compilation of stress magnitude data as this information is essential for the calibration of geomechanical numerical models this enables us to derive a 3 d continuous description of the stress tensor from point wise and incomplete stress tensor information provided with the wsm database such forward models are required for safety aspects of anthropogenic activities in the underground and for a better understanding of tectonic processes such as the earthquake cycle

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

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

early paleozoic or early middle triassic collision between the south china and indochina blocks the controversy resolved structural insights from the kon tum massif central vietnam abstract in central vietnam the kontum massif is subdivided from north to south into i kham duc ii ngoc linh iii kan nack complexes the kham duc complex consists of metapelite metapsammite paragneiss metagabbro amphibolite serpentinized ultramafic and orthogneiss blocks the southern part of this complex experienced an early paleozoic crustal melting event responsible for migmatites and anatectic granites the ngoc linh complex the largest one is formed by metatexite and granitoid enclosing blocks of eclogite high pressure hp granulite orthogneiss metagabbro amphibolite granodiorite and migmatite the kan nack complex is formed by migmatites with ultra high temperature u ht granulite charnockites and enderbites the three metamorphic complexes are intruded by per aluminous granite and subordinate mafic plutons in spite of local variations the foliation of the ngoc linh complex defines a bulk domal structure and the stretching lineation consistently trends nw se the nw se lineation is also observed in the tectonically overlying the kan nack complex the ngoc linh and kan nack complexes are interpreted here as parts of a metamorphic core complex mcc or ngoc linh mcc exhumed by a top to the nw detachment fault along the northern margin of the ngoc linh mcc upright folds with e w striking axes and e w stretching lineation deform the foliation these structures are developed in a transpressive regime coeval with the activity of plurikilometer scale dextral strike slip faults zircon and monazite u pb radiometric datings document a 250 240 ma age for the crustal melting and the top to the nw ductile shearing coeval with the formation of the ngoc linh mcc this extensional tectonics is followed by a dextral strike slip faulting at ca 240 230 ma before the emplacement of the two mica granitic plutons at ca 240 224 ma furthermore in the ngoc linh and kan nack complexes zircon and monazite yield u pb early paleozoic ages in the kham duc complex a ca 460 ma mp mt garnet biotite staurolite kyanite metamorphism followed by migmatites at ca 450 ma is also recognized the 420 400 ma age of the dai loc plutonic suite and the 450 425 ma age of the dien binh calc alkaline granodiorite document an early paleozoic event the early paleozoic mafic and ultramafic masses of the hiep duc complex are ophiolites included into a metasedimentary matrix thus the kham duc complex is interpreted as a tectonic melange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the migmatites a part of the early paleozoic rocks are enclosed as xenoliths in the triassic migmatite of the ngoc linh mcc these petrologic structural and chronological features allow us to propose the following geodynamic evolution for the kontum massif during the early paleozoic a continental collision which was accommodated by a north directed subduction of a southern block s vietnam or viet cambodia block below a northern block n vietnam or viet lao block occurred along the tam ky phuoc son suture during the early triassic at ca 250 245 ma the s vietnam block experienced a crustal melting giving rise to the ngoc linh mcc that reworked the early paleozoic orogen lastly during the middle triassic the dextral faulting superimposed upon the ngoc linh migmatite the geodynamic significance of the kontum massif is discussed in the general framework of indochina south china relationships the early paleozoic collision in vietnam is viewed as the driving force responsible for the development of the intracontinental orogeny of s china in order to account for the important heat flow required for the formation of uht metamorphic rocks a possible interaction between the scb indochina collision and the emeishan mantle plume is proposed

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

40ar 39ar geochronology of the charnockites and granulites of the kan nack complex kon tum massif vietnam abstract the truong son belt forms the eastern rim of the indochina block in southeast asia the age of the metamorphism mainly along nw se mylonitic shear zones that affects this belt has been formerly determined at about 240 250 ma this age corresponds to the indosinian tectonometamorphic episode the kon tum massif situated to the south of this belt comprises high temperature rocks the kan nack complex including charnockites and granulites the main charnockitic outcrops restricted to the song ba valley establish the intrusive nature of these magmatic rocks within granulite facies material basic charnockitic rocks are mainly quartz enderbites to norites and hornblende pyroxene granulite facies rocks the 40 ar 39 ar age of intrusion cooling of charnockitic magmas is determined from primary magmatic biotites at about 245 ma in the east of the kan nack complex some granulite facies rocks exhibit relicts of primary granulite facies parageneses whereas others show evidence of overprinting by a retrogressive low grade metamorphism ar ar dating confirm this evolution giving ages of 400 ma for primary relict granulite facies phases and 260 270 ma from the most retrogressed samples establishing the youngest limit for the granulite facies metamorphism granulites intruded by charnockites in the song ba valley yield ages of about 250 ma equivalent to the ages of the charnockites and have evidently been completely reset by these high temperature intrusions therefore the kan nack complex of the kon tum massif is not an independent unit with respect to the indosinian orogen but represents the deep crustal part of this belt

preface for the special issue geology geodynamics and mineral resources of se asia insights from geosea xv congress hanoi 2018 se asia is an assembly of gondwana derived crustal blocks and an important piece for the geodynamic understanding of the asian continent since the phanerozoic this area experienced several significant geodynamic events the separation of many continents and microcontinents from gondwana through rifting lead to the opening of oceanic domains the closure of these oceanic basins and the subsequent continental collision is attested by subduction related magmatism accretionary complexes high pressure and high temperature metamorphisms crustal melting and magmatism including volcanism and plutonism the mesozoic tectono magmatism the cenozoic intracontinental tectonics related to the india collision and the recent magmatism and tectonics are also significant events recognized in se asia these geodynamic events represent the general framework for the numerous ore deposits recognized in the area

episodes of brittle deformation within the dien bien phu fault zone vietnam evidence from k ar age dating of authigenic illite abstract constraining the timing of fault zone origin and movement history is of fundamental geotectonic importance to understand the evolution and processes of the brittle fault structures the authors present in this paper authigenic illite k ar age data from the fault gouge samples collected from the dien bien phu fault dbpf in the dien bien province vietnam as well as in a major strike slip fault zone in south east asia all of which played important roles in the structural formation and geotectonic development of northwestern vietnam the gouge fault samples were separated into four grain size fractions the k ar ages of the fractions were divided into two age groups from 26 to 29 ma and 130 ma the timing of the fault movements is defined at 26 0 24 ma 29 0 61 ma 130 1 1 27 ma and 130 7 1 29 ma this indicates that the dien bien phu fault underwent two movements first in the early cretaceous with an age of about 130 ma and second in the oligocene paleogene with an age of about 26 29 ma the ductile deformation of the dbpf terminated during the early cretaceous these studies also indicate slow exhumation of the dien bien granitoid complex during the cretaceous times the oligocene ages indicate that the dbpf had been reactivated by the se extrusion and clock wise rotation of the indochina block caused by the collision of the indian and eurasian plates this tectonic event led to the dbpf brittle sinistral movement causing the exhumation phase along the fault this movement period ca 26 29 ma is coexistent with 600 700 km sinistral shearing along the red river ailao shan fault this is the first report determining the absolute age constraints of multi activated tectonic events affecting the dien bien phu fault using the k ar dating method for the gouge samples

cenozoic tectonic and stratigraphic development of the central vietnamese continental margin abstract the east vietnam boundary fault zone evbfz forms the seaward extension of the red river shear zone and interacted with the extensional rift systems in basins along the central vietnamese continental margin the structural outline of the central vietnamese margin and the timing of deformation are therefore fundamental to understanding the development of the south china sea and its relation to indochinese escape tectonism and the india eurasia collision this study investigates the structural and stratigraphic evolution of the central vietnamese margin in a regional tectonic perspective based on new 2 d seismic and well data the basin fill is divided into five major oligocene to recent sequences separated by unconformities deposition and the formation of unconformities were closely linked with transtension rifting the opening of the south china sea and late neogene uplift and denudation of the eastern flank of indochina the structural outline of the central vietnamese margin favors a hybrid tectonic model involving both escape and slab pull tectonics paleogene left lateral transtension over the nnw striking evbfz occurred within the song hong basin and the quang ngai graben and over the da nang shelf western phu khanh basin related to the escape of indochina east of the evbfz paleogene ne striking rifting prevailed in the outer phu khanh basin and the hoang sa graben fitting best with a prevailing stress derived from a coeval slab pull from a subducting proto south china sea beneath the southwest borneo palawan region major rifting terminated near the end of the oligocene however late stage rifting lasted to the early miocene when continental break up and seafloor spreading commenced along the edge of the outer phu khanh basin the resulting transgression promoted lower and middle miocene carbonate platform growth on the da nang shelf and the tri ton high whereas deeper marine conditions prevailed in the central part of the basins partial drowning and platform retreat occurred after the middle miocene due to increased siliciclastic input from the vietnamese mainland as a result siliciclastic marine deposition prevailed offshore central vietnam during the pliocene and pleistocene

forty years of paleostress analysis has it attained maturity abstract powerful methods of paleostress analysis from fault slip data have been used since the 1970 s and have demonstrated their capacity for reconstructing stress fields with tectonic significance however in some cases these methods have been applied to samples that do not fulfill basic requirements or developed on the basis of unsound conceptual models most methods of fault slip are based on the wallace bott principle dynamic paradigm while others invoke the necessity of remaining within the alternative kinematic paradigm therefore inferring only finite strain or strain rate axes the scientific community shares neither standard procedures for applying these methods nor standard parameters for assessing the quality of results this indicates that paleostress analysis has not attained maturity it is necessary to see back to the conceptual and methological bases following accurate procedures of data collection using additional field observations and critically assessing the results within the tectonic setting spatial and temporal heterogeneity of stress fields over all scales makes the mean stress tensor obtained from site analysis just an abstract notion though indispensable for understanding lithosphere dynamics

tectonic evaluation of the indochina block during jurassic cretaceous from palaeomagnetic results of mesozoic redbeds in central and southern lao pdr rock magnetic and palaeomagnetic studies were performed on mesozoic redbeds collected from the central and southern laos the northeastern and the eastern parts of the khorat plateau on the indochi

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

frequency and fluid effects on elastic properties of basalt experimental investigations 1 in order to investigate the effects of fluid and frequency on the elastic properties we performed hydrostatic experiments on an icelandic basalt specimen under both dry and saturated conditions this basalt is characterized by a bimodal porosity i e cracks and equant pores the elastic properties bulk moduli in our case were investigated under high pressure through two experimental methods 1 a classical one using ultrasonic p and s waves velocities frequency 106 hz 2 and a new one using oscillation tests frequency 10 2 hz in dry condition experimental data show no significant difference between high hf and low lf frequency bulk moduli however in saturated conditions two effects are highlighted a physico chemical effect emphasized by a difference between drained and dry moduli and a squirt flow effect evidenced by a difference between hf and lf undrained moduli

gps determined eastward sundaland motion with respect to eurasia confirmed by earthquakes slip vectors at sunda and philippine trenches abstract gps measurements acquired over southeast asia in 1994 and 1996 in the framework of the geodyssea program revealed that a large piece of continental lithosphere comprising the indochina peninsula sunda shelf and part of indonesia behaves as a rigid sundaland platelet a direct adjustment of velocity vectors obtained in a eurasian frame of reference shows that sundaland block is rotating clockwise with respect to eurasia around a pole of rotation located south of australia we present here an additional check of sundaland motion that uses earthquakes slip vectors at sunda and philippine trenches seven sites of the geodyssea network are close to the trenches and not separated from them by large active faults two at sumatra trench three at java trench and two at the philippine trench the difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors we first derive a frame free solution that minimizes the upper plate or sundaland motion when corrected for australia eurasia and philippines eurasia nuvel1 a motion the misfit between gps and slip vectors azimuths is significant at 95 confidence indicating that the upper plate does not belong to eurasia we then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of sundaland is a uniform 7 10 mm a eastward velocity however introducing the additional constraint of the fit of the geodyssea sites with the australian igs reference ones or tie with the ntus singapore station leads to a much narrower range of solutions we conclude that sundaland has an eastward velocity of about 10 mm a on its southern boundary increasing to 16 18 mm a on its northern boundary

indosinian nw trending shear zones within the truong son belt vietnam 40ar39ar triassic ages and cretaceous to cenozoic overprints abstract several nw trending ductile and partly mylonitic shear zones cross the truong son belt of central vietnam along the song ma and song ca valleys and north of the kontum block from da nang to aluoi and khe sanh high grade metamorphic rocks of amphibolite facies showing a retrograde evolution and consisting of ortho and paragneisses metavolcanics amphibolites marbles and quartzites are exposed along these structures they display a homogeneous deformation pattern characterized by a generally steeply dipping foliation and a near horizontal to gently plunging mineral stretching lineation indicating a strike slip tectonic regime of deformation along the southernmost fault zone at least various and consistent kinematic indicators including s c structures asymmetric tails of porphyroclasts prove that the strain and metamorphism have been generated by a phase of dominantly non coaxial deformation with a dextral sense of shear 40ar 39ar dating applied on the high grade metamorphic rocks minerals occurring along these zones provide plateau cooling ages closely around 245 ma establishing that this event took place in the lowermost triassic as an early phase of the indosinian orogeny the existence of indosinian movements in vietnam as they have been defined by previous authors during the early century is now accurately confirmed and this is the first insight in the occurrence of ductile strike slip tectonics of indosinian age along nw se fault zones well expressed in central vietnam is a cretaceous thermal and deformational overprint marked by epimetamorphism which took place between 90 and 120 ma as attested by low temperature degassing ages this cretaceous event is not found further north in the song ma zone where younger ages appear as a result of the influence of cenozoic shear movements along the red river fault which displays 20 30 ma ages on the northern flank of song ca in the bu khang phu hoat core complex comparable oligocene lower miocene ages 20 35 ma yielded by biotite and phlogopite reflect a strong overprinting and attest to a rapid uplift of the basement

seismic evidence of hyper stretched crust and mantle exhumation offshore vietnam abstract we study the evolution of the eocene recent phu khanh basin opened during the rifting of the south china sea scs this sub basin formed when continental crust ruptured along the east vietnam boundary fault evbf at the western edge of the scs using high quality long streamer seismic lines we interpret structures that highlight the different phases of the scs rifting and processes related to crustal boudinage extreme crustal thinning and mantle uplift that sometimes places sediments in contact with the moho discontinuity mark the central part of the basin the mantle is shallowest there and marks the final rupture of the continental crust during an intense phase of mantle upwelling there a low angle detachment fault separates several crustal blocks from the moho the cylindrical axis of the moho rise is roughly parallel to the trend of the south china sea propagator above the mantle the upper and lower crusts form large crustal boudins the network of normal faults is dense in the upper crust and occasionally propagates into the lower crust however the lower crust is missing at some places the seismic facies above the moho rise is poorly stratified and might have been affected by a certain degree of metamorphism at the apex of mantle uplift there are frequent indications of fluid circulations including volcanic edifices and gas escapes features three stages of extension are clearly identifiable with ages of the two youngest constrained by well calibration the first and oldest rift sequence is situated between the tilted pre rift basement and the oligocene horizons 32 ma the second is delimited by the oligocene to the mid miocene 15 5 ma horizons and the third is bound by the mid miocene and the upper miocene before 10 5 ma horizons these three rift episodes formed in at least two extension directions the first n s and the second nw se the distinct mid miocene 15 5 ma horizon is tilted and the above layers show a diverging reflection these are in turn sealed by an erosional unconformity before 10 5 ma although tectonic activity appears diachronous from north to south we suggest that cessation of rifting did not occur before 12 10 5 ma this differs from models derived from magnetic anomalies observed in the south china sea 15 5 to 20 ma

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

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

u pb dating of high temperature metamorphic episodes in the kon tum massif vietnam abstract in vietnam recent studies demonstrated that the kon tum massif was part of the indosinian mountain system together with the truong son belt one sector of the kon tum massif song ba valley is a granulite facies terrain for which ar ar and u pb ages cluster around 245 250 ma in the area of song bien river also metamorphosed under granulite facies conditions ar ar ages of 410 ma are displayed by biotite in this study u pb dating of monazite and zircon has been used to understand the reason for these two groups of ages taking into account the metamorphic mineral assemblages related to granulite facies metamorphism in the two districts for granulites of song ba valley ages of 245 250 ma are confirmed from monazites in the song bien district ages of 465 470 ma displayed by monazites are interpreted to correspond to the metamorphic climax zircons from one of these samples record the age of anatexis that has affected the granulitic rocks the younger age recorded in the song ba valley is considered to reflect high temperature related to charnockitic intrusions emplaced near the end of the indosinian orogeny overprinting the earlier formed granulites and resetting the u pb and ar ar ages for the first time two ht events are dated in the kon tum massif one occurring during the ordovician and the other during the permo triassic

indochina peninsula and the collision of india and eurasia the collision of india with asia results in a rapidly changing stress pattern around both himalayan syntaxes the maximum compressive stress which is north south north of the indenter fans radially through nearly 180 around the syntaxes to accommodate the necessary strike slip motion on the edges of the indenter thus the whole indochina peninsula was swept by the migrating stress and associated strain pattern as the eastern syntaxis moved to the north as a result the maximum horizontal component of the stress field is predicted to have been first oriented east west then north south we propose that this changing stress field controlled the opening of the sedimentary basins and of the south china sea as well as the direction of motion of the major strike slip faults

major unconformities termination of extension events and associated surfaces in the south china seas review and implications for tectonic development abstract the distribution of unconformities and end of cenozoic rifting events in the south china seas scs reflects both the modes of rift development and the effects of driving mechanisms continental rifting began in the eastern basins during the paleocene and propagated westwards to the vietnam basin margin in the late eocene continental breakup around 32 28 ma caused a regional reduction or cessation in extensional activity particularly affecting basins furthest from the spreading centre basins in the slope and deepwater area north of the spreading centre exhibit reduced fault activity until 21 20 ma propagation of oceanic crust westwards between 25 and 23 ma and termination of seafloor spreading sometime between 20 5 and 16 ma affected fault activity in the qiongdongnan and nam con song basins in the phu khanh basin and south in the dangerous grounds area extension continued until about 16 ma ending at the red unconformity the end of seafloor spreading around 20 5 ma reflects loss of extensional driving force as thinned continental crust entered the nw borneo subduction zone controversially a key component of the driving force maybe attributed to slab pull a transitional period of about 5 7 my between the onset of subduction of continental crust and final jamming of the subduction zone deep regional unconformity dru is inferred the last pulse of extension was focussed in the western scs and terminated around 10 5 ma detailed understanding of proto south china seas development remains uncertain and controversial

late cenozoic and modern stress fields in the western fars iran implications for the tectonic and kinematic evolution of central zagros 1 the zagros iran developed during mio pliocene times in response to arabia eurasia convergence the western fars highlights a major bend of the deformation front and displays a remarkable set of nearly n s right lateral strike slip faults the kazerun borazjan karebass sabz pushan sarvestan faults oblique at high angle to the belt the region likely plays a major kinematic role by accommodating the change in shortening modes from partitioned in the western central zagros to nonpartitioned in the eastern zagros the inversion of focal mechanisms from small and moderate earthquakes shows a consistent n020 030 compression with a low ratio between differential stresses this regime accounts for the combination of strike slip and thrust type mechanisms through likely 2 3 permutations fault slip analysis reveals two successive late cenozoic regional compressional trends ne sw then n020 the latter is in good agreement with the present day stress the significance of the ne sw compression is discussed alternatively in terms of stress deviations or block rotations in relation to the strike slip fault system fieldwork and satellite imagery suggest that these faults behave first as transfer faults during folding of the cover and later as strike slip faults in agreement with the succession of stress regimes and the evolution of the dominant deformation style from thin skinned to thick skinned the first order stability of the collision related state of stress since 5 ma supports that the arabia eurasia convergence did not give rise to partitioning in the western fars but rather was and is still accommodated by distributed deformation involving both shortening and strike slip motion throughout the cover and the basement

reactivation of a collisional suture by miocene transpressional domes associated with the red river and song chay detachment faults northern vietnam abstract elongate miocene gneissose and granitic domes in northern vietnam formed in a dextral transpressional ductile shear regime possibly associated with large scale restraining step overs along dextral faults initial anticlinal d1 doming involved folding of both basement and hanging wall rocks with d1 secondary folds that verge toward the anticlinal axes such folds reflect dome scale flexural slip folding with continued shortening d2 detachment faults developed on the flanks of the anticlines along the hanging wall basement interface so that the basement was extruded vertically into the overlying hanging wall rocks the detachment faults were associated with d2 drag folds that verge away from the anticlinal axes the hanging wall assemblage lacks a well ordered stratigraphy displaying primarily block in matrix fabric we identified bedded cherts associated with umbers and alkalic basaltic intrusions within these hanging wall rocks a first report of such rocks from vietnam the association of cherts umbers and basaltic intrusions and extrusions with block in matrix units with clastic rocks strongly suggest that the hanging wall rocks comprise part of a subduction complex because the base of a subduction complex is a former subduction megathrust horizon the hanging wall basement interface represents a reactivated collisional suture such a suture was probably associated with the indosinian orogeny and the basement should be the indochina continental block this structure may have influenced the position of miocene dextral faulting in addition to controlling the position of the dome detachments the well known red river fault marks the boundary of one of the domes but in this region it appears to be a detachment normal fault rather than a dextral strike slip fault however the association with the dome evolution with large scale restraining step overs suggests that dextral faulting associated with dome development may lie further away from the dome axes than the detachment

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

the early triassic indosinian orogeny in vietnam truong son belt and kontum massif implications for the geodynamic evolution of indochina new structural field data at various scale and 40ar 39ar geochronological results from the basement rocks in the truong son belt and kontum massif of vietnam confirm that ductile deformation and high temperature metamorphism were caused by the early triassic event of the indosinian orogeny in the range of 250 240 ma a compilation of isotopic data obtained in other countries along the sibumasu indochina boundary broadly indicates same interval of ages this tectonothermal event is interpreted as the result of a synchronous oblique collision of indochina with both sibumasu and south china inducing dextral and sinistral shearing along e w to nw se and n s fault zones respectively the collision along song ma follows the northwards subduction of indochina beneath south china and the subsequent development of the song da zone which in turn was affected by the late triassic indosinian phase of shortening within the indochina plate internal collisions occurred coevally in the early triassic as along the poko suture at the western border of the kontum massif

characterization of stress perturbations near major fault zones insights from 2 d distinct element numerical modelling and field studies jura mountains abstract we consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations based on 2 d distinct element modelling we reconstruct the local stress field around a vertical discontinuity in various geological contexts the resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 we establish simple relationships controlling stress changes around a pre existing fault zone as a function of 1 the remote differential stress magnitude 1 3 2 the friction coefficient on the discontinuity and 3 the strike of the discontinuity relative to the far field stress as a geological example we present the morez fault zone in the internal jura paleostress reconstruction in forty two sites indicates that the trends of the mio pliocene compression are n110 on average near the fault whereas they are n130 in the surrounding areas a comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 counterclockwise deviation is directly related to the reactivation of this large weak zone we thus evaluate the role of mechanical decoupling along pre existing zones of weakness especially with consideration to the accommodation of the alpine deformation in the jura belt

the red river fault zone in the yinggehai basin south china sea abstract the red river fault a major strike slip fault of onshore southeast asia is suggested to be closely related to the formation of the south china sea and uplift of the tibetan plateau yet published documentation of the offshore segment of the red river fault is sparse high resolution seismic reflection and borehole data obtained by the petroleum industry along the northwestern margin of the south china sea permit mapping of the offshore segment of the red river fault in the yinggehai basin as well as demonstration of the timing of its shear movement and slip reversal two boundary faults and two basin center faults are mapped three successive deformation phases for the offshore red river fault zone include sinistral movement from 30 to16 ma slip reversal between 16 and 5 5 ma and dextral movement with low rates after 5 5 ma although no robust piecing points were observed for the sinistral movement period the horizontal displacement of dextral movement is estimated to be tens of kilometers this study supports a two stage model for the evolution of the india asia collisional orogen before the middle miocene sinistral movement of the red river fault likely was linked to spreading of the south china sea consistent with the concept of continental extrusion after the middle miocene distributed shortening better explains a low rate of dextral accommodation of the red river fault in response to the continuing india asia collision

tectonic deformation of the southeastern tip of the indochina peninsula during its southward displacement in the cenozoic time abstract the terminal collision of india with asia brought about significant tectonic deformation into the asian continent in order to depict these deformational features in the southeastern margin of the indochina peninsula late cretaceous red beds of the dak rium formation were sampled from da lat area 11 7 n 108 3 e the kontum massif vietnam thermal demagnetization procedure revealed the presence of characteristic remanent magnetization with unblocking temperatures around 680 c in most samples primary nature of this magnetization is ascertained through positive fold test a tilt corrected mean direction calculated for the dak rium formation is dec inc 11 4 35 4 ks 331 7 95 1 7 n 21 with a corresponding paleopole at 76 5 n 161 2 e a95 1 7 compared with the european apwp a negative inclination flattening 15 2 4 9 is observed indicating southward displacement of the kontum massif by 9 2 4 9 since late cretaceous since comparable amount of southward displacement has been reported from 16 localities of the indochina and shan thai blocks it seems a reasonable assumption to predict that the indochina peninsula underwent a southward displacement of 5 1 2 4 570 km 270 km as a composite unit including the shan thai block indochina block and kontum massif on the contrary 27 0 9 8 counter clockwise rotation of the kontum massif with respect to the indochina block indicate a significant amount of internal deformation along the tip of south moving indochina peninsula this rotation of the kontum massif is attributed to 32 17 ma left lateral motion along the east vietnam boundary fault which makes up the 1000 km long seaward continuation of the ailao shan red river shear zone tectonic deformation of the indochina peninsula was thus partly accommodated by local block rotation e g counterclockwise rotation of the kontum massif and to some extent by internal tectonic deformation of the shan thai block

crustal motion and block behaviour in se asia from gps measurements results acquired using global positioning system gps data taken over a large part of se asia indicate that sundaland i e indochina along with the western and central part of indonesia constitutes a stable tectonic block moving approximately east with respect to eurasia at a velocity of 12 3 mm yr 31 with respect to india and australia this block moves due south significant motion has not been detected along the northern boundary to south china i e along the red river fault whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between india and sundaland in the andaman burma region fl 2001 elsevier science b v all rights reserved

tectonic evolution of high grade metamorphic terranes in central vietnam constraints from large scale monazite geochronology abstract several metamorphic complexes in southeast asia have been interpreted as precambrian basement characterized by amphibolite to granulite facies metamorphism in this paper we re evaluate the timing of this thermal event based on the large scale geochronology and compositional variation of monazites from amphibolite to granulite facies metamorphic terranes in central vietnam most of the samples in this study are from metamorphic rocks n 38 and granitoids n 11 in the kontum massif gneisses n 6 and granitoids n 5 from the hai van migmatite complex and the truong son belt located to the north of the massif were also studied two distinct thermal episodes 245 230 ma and 460 430 ma affected kontum massif gneisses while a single dominant event at 240 220 ma is recorded in the gneisses from the hai van complex and the truong son belt monazites from granitoids commonly yield an age of 240 220 ma mesoproterozoic ages 1530 1340 ma were obtained only from monazite cores that are surrounded by c 440 ma overgrowths thermobarometric results combined with concentrations of y 2 o 3 ce 2 o 3 and heavy rare earth elements in monazite and recently reported pressure temperature paths suggest that triassic ages correspond to retrograde metamorphism following decompression from high to medium pressure temperature conditions ordovician silurian ages reflect low pressure temperature metamorphism accompanied by isobaric heating during prograde metamorphism some samples were affected by both metamorphic events we conclude that high grade metamorphism observed in so called precambrian basement terranes in central vietnam occurred during both the permian triassic and the ordovician silurian while peraluminous granitoid magmatism is triassic additionally our preliminary analyses for u pb zircon age and whole rock chemistry of granitic gneisses from the truong song belt suggests the presence of the ordovician silurian volcanic arc magmatism in the region based on the pressure temperature time protolith evolutions metamorphic rocks from central vietnam provide a continuous record of subduction accretion collision tectonics between the south china and indochina blocks in the ordovician silurian the region was characterized by active continental margin tectonics followed by continental collision during the late permian to early triassic and subsequent exhumation during the late triassic the results also suggest that the timing of metamorphism and protolith formation as well as the geochemical features in other southeast asian terranes should be verified to achieve a better understanding of the precambrian to early mesozoic tectonic history in asia

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

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

denudation history of onshore central vietnam constraints on the cenozoic evolution of the western margin of the south china sea abstract apatite fission track analysis is used to monitor the timing and rate of upper crustal cooling and denudation across central vietnam in response to rifting of the south china sea results show regional denudation in the syn and post rift phases of the south china sea occurred at a similar rate 40 10 m myr consistent with the sedimentation record in adjacent offshore basins this suggests that extension was not the dominant factor controlling cenozoic denudation probably because the study area was sufficiently distant from the actively rifted continental margin a significant change in regional cooling rate during the upper miocene inferred denudation rates also shift from 34 m myr to 390 500 m myr is linked to enhanced erosion and deposition of prograding sediments in adjacent offshore basins this shift in denudation is associated and contemporaneous with initiation of regional basaltic magmatism and development of topography

exhumation history of the red river shear zone in northern vietnam new insights from zircon and apatite fission track analysis abstract a new set of zircon and apatite fission track ages from the ailao shan and day nui con voi dncv metamorphic massifs of the red river shear zone rrsz and neighboring rocks in northern vietnam is presented a complex along strike diachronous denudation history is revealed the southern sector of the dncv cooled to about 100 c by the late oligocene whereas its central compartment was affected by the later thermotectonic evolution of the song chay dome to the e of the rrsz whose final exhumation occurred during the early miocene the northern sector of the rrsz is characterized by the 35 ma phan si pang pre to synkinematic intrusion fission track ages from a vertical section within the phan si pang granite indicate rapid exhumation and cooling the paleozoic tectonic block to the west of the rrsz fission track ages between 40 and 30 ma was exhumed and cooled earlier than the fault mylonite belt fission track ages of 30 ma and younger and also than the eastern block its structural level is consistent with field observations that suggest the rrsz in northern vietnam to be a transtensional system with a regional ne sw oriented extension component

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

tectonic evolution and regional setting of the cuu long basin vietnam abstract the cuu long basin is situated off the southeastern coast of vietnam this study utilizes all available seismic data in the cuu long basin vinh chau basin and coastal mekong delta to constrain the tectonic history of the area the linkage between the mae ping fault zone and deformation in the cuu long basin is also examined in detail two major deformational events are observed a transtensional rifting event from the mid eocene to mid early oligocene 40 31 ma followed by transpression from mid early oligocene to mid late oligocene 31 25 ma the data strongly suggest that all the very straight major tributaries of the mekong river delta follow northwest trending faults that link into to the southwestern end of the cuu long basin fault system and that the basin opened between where the mekong delta faults enter and a point of zero extension at the ne termination of the basin the mekong delta fault zone exhibited left lateral displacement during extension in the cuu long basin and right lateral displacement during younger transpression the orientation age and sense of displacement of the mekong delta fault zone are consistent with slip on the mae ping fault zone in thailand and cambodia and hence are considered to be part of the same regional fault system based on a chainat duplex analogue and other data the mekong delta and mae ping fault zones appear to be linked by a nnw striking step over zone referred to here as the mekong ton le sap step over zone this zone follows the eastern boundary of the paleocene to early eocene kampot fold belt based on structural and stratigraphic similarities it appears the adjacent vinh chau basin shares a common tectonic history with the cuu long basin but the linkage to the mekong delta fault zone is less clear

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

improved understanding of velocity saturation relationships using 4d computer tomography acoustic measurements a recently developed laboratory method allows for simultaneous imaging of fluid distribution and measurements of acoustic wave velocities during flooding experiments using a specially developed acoustic sample holder that combines high pressure capacity with good transparency for x rays it becomes possible to investigate relationships between velocity and fluid saturation at reservoir stress levels high resolution 3d images can be constructed from thin slices of cross sectional computer tomography scans ct scans covering the entire rock core volume and from imaging the distribution of fluid at different saturation levels the x ray imaging clearly adds a new dimension to rock physics measurements it can be used in the explanation of variations in measured velocities from core scale heterogeneities computer tomography gives a detailed visualization of density regimes in reservoir rocks within a core this allows an examination of the interior of core samples revealing inhomogeneities porosity and fluid distribution this mapping will not only lead to an explanation of acoustic velocity measurements it may also contribute to an increased understanding of the fluid flow process and gas liquid mixing mechanisms in rock immiscible and miscible flow in core plugs can be mapped simultaneously with acoustic measurements the effects of core heterogeneity and experimentally introduced effects can be separated to clarify the validity of measured velocity relationships

a plea for more caution in fault slip analysis abstract the analysis of fault slip data is a widely used tool in structural geology this method consists of three major steps a data acquisition by measurements in outcrops b data separation into homogeneous subsets and calculation of the principal stress or strain axes with one of several available methods and c data interpretation in a regional tectonic context which includes the assignment of ages and the derivation of regional patterns each one of these three steps may introduce artefacts and misinterpretations the major problem during step a is sampling bias due to unfavourable outcrop geometry or due to neglecting faults with subtle slip sense indicators step b contains numerous possibilities to influence the calculation results e g by arbitrary separation of data into subsets choice of the analysis method and uncritical use of software age assignment in step c can in most cases be made only indirectly e g by the assumption that measured outcrop scale faults have the same age as parallel map scale faults or by the inference that subsets from different sites with parallel oriented principal axes are syngenetic neither assumption is necessarily valid with this paper we want to sharpen researchers awareness of the problems related to fault slip analysis

oligocene miocene bu khang extensional gneiss dome in vietnam geodynamic implications a large oligocene miocene extensional gneiss dome in vietnam has implications for the kinematics of the ailao shan red river shear zone and rifting of the south china sea a major northeast dipping extensional shear zone separates the bu khang dome from less metamorphosed units above shearing deformation occurred during the exhumation of high pressure rocks 40 ar 39 ar ages on micas reveal oligocene miocene ages from 36 to 21 ma after a high pressure episode of probable oligocene age the area was subjected to northeast southwest extension during the opening of the south china sea a kinematic model involving left lateral shear and block rotation within a north south dextral shear zone integrates our observations in the bu khang dome with south china sea rifting

paleomagnetism of late jurassic to early cretaceous red beds from the cardamom mountains southwestern cambodia tectonic deformation of the indochina peninsula abstract late jurassic to early cretaceous red beds of the phuquoc formation were sampled at 33 sites from the sihanoukville and koah kong areas of the phuquoc kampot som basin southwestern cambodia two high temperature remanent components with unblocking temperature ranging 650 670 c and 670 690 c were identified the magnetization direction for the former component d 5 2 i 18 5 with 95 3 1 in situ reveals a negative fold test that indicates a post folding secondary nature however the latter component carried by specular hematite is recognized as a primary remanent magnetization a tilt corrected mean direction of d 43 4 i 31 9 95 3 6 was calculated for the primary component at 11 sites corresponding to a paleopole of 47 7 n 178 9 e a 95 3 6 when compared with the 130 ma east asian pole a southward displacement of 6 0 3 5 and a clockwise rotation of 33 1 4 0 of the phuquoc kampot som basin as a part of the indochina block with respect to east asia were estimated this estimate of the clockwise rotation is 15 larger than that of the khorat basin which we attribute to dextral motion along the wang chao fault since the mid oligocene the comparison of the herein estimated clockwise rotation with the counter clockwise rotation reported from the da lat area in vietnam suggests the occurrence of a differential tectonic rotation in the southern tip of the indochina block during the southward displacement of the indochina block the non rigid lithosphere under its southern tip moved heterogeneously while the rigid lithosphere under the khorat basin moved homogeneously

crustal anatexis and formation of two types of granitic magmas in the kontum massif central vietnam implications for magma processes in collision zones abstract asia grew in the late permian by the collision of a number of micro continents syn to post collisional magmatism occurred along the continental collision zones in this study we report two types of granitic rocks garnet granite grt granite and orthopyroxene granite opx granite from the kontum massif central vietnam which is situated on the continental collision zone between the south china and indochina cratons these granitic rocks were formed at ca 250 ma when high temperature ht and ultrahigh temperature uht metamorphism took place in the same zone based on the petrological and geochemical features compared with previously reported experimental results garnet bearing granite is derived from pelitic gneisses by partial melting whereas orthopyroxene bearing granite is produced by the partial melting of garnet bearing mafic granulites we inferred that a significantly high geothermal gradient is required to produce vietnamese granitic magmatism and related ht to uht metamorphism this geotherm may be attributed to upwelling mantle plume beneath the kontum massif during the late permian

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

high temperature metamorphism in a major strike slip shear zone the ailao shan red river people s republic of china abstract petrographic and thermobarometric analysis provides constraints on thept path of the mylonitic gneisses of the left lateral ailao shan red river shear zone which has accommodated the lateral extrusion of indochina during the tertiary two different paragenesis p1 and p2 are coeval with this deformation and correspond respectively to the amphibolite and greenschist facies microprobe analysis reveals that p1 garnets bear a chemical zonation from core to rim this zonation indicates a temperature increase during garnet growth conditions of formation of garnet rims p1b which are estimated using biotite garnet and plagioclase garnet thermobarometers are close to the granitic solidus 710 70 c and4 5 1 5 kbar p2 conditions are estimated to be approximately 500 c and

jurassic dextral movement along the dien bien phu fault nw vietnam constraints from 40ar 39ar geochronology abstractthe nne ssw trending dien bien phu fault which dextrally displaces the nw se trending song ma suture in northwestern vietnam is widely considered one of the most seismically active faults in indochina in order to better understand the fault s activity this study reports new 40ar 39ar geochronological data for mica schists and mylonites from several areas along the dien bien phu fault showing 40ar 39ar ages of 194 212 ma for mica schists and 158 198 ma for mylonites these ages suggest that after the collision of the south china and indochina blocks dextral shearing deformation initiated along the dien bien phu fault in the jurassic significantly earlier than previously thought in light of the relevant tectonic events in indochina the successive suturing collision of the indochina simao and sibumasu blocks may have been responsible for the initiation of dextral shearing along the dien bien phu fault which in turn resulted in offset of the song ma suture

triassic tectonics of the ailaoshan belt sw china early triassic collision between the south china and indochina blocks and middle triassic intracontinental shearing in se yunnan the ailaoshan belt has been extensively studied for the ductile shearing coeval with the left lateral cenozoic activity of the red river fault however the late triassic unconformity of the continental red beds upon metamorphic and ductilely deformed rocks demonstrates that the ailaoshan belt was already built up by early mesozoic tectonics from west to east the belt is subdivided into western central eastern ailaoshan and jinping zones the western ailaoshan and central ailaoshan zones correspond to a carboniferous permian magmatic arc and an ophiolitic melange respectively the eastern ailaoshan and the jinping zones consist of deformed proterozoic basement and paleozoic to early triassic sedimentary cover series both belonging to the south china block this litho tectonic zonation indicates that the ailaoshan belt developed through a sw directed subduction followed by the collision between indochina and south china blocks crustal thickening triggered per aluminous magmatism dated at ca 247 240 ma field and microscope scale top to the ne ductile shearing observed only in the pre late triassic formations but never in late triassic or younger formations complies with this geodynamic polarity furthermore the late collisional two mica granitoids and felsic per aluminous volcanites record a ductile deformation that argues for a continuing crustal shearing deformation after the early triassic collision up to the middle triassic therefore a two stage tectonic evolution accounts well for the documented structural and magmatic features the triassic architecture of the ailaoshan belt and its geodynamic evolution correlate well to the south and north with the north vietnam orogens and the jinshajiang belt respectively

depositional environment and reservoir quality of miocene sediments in the central part of the nam con son basin southern vietnam shelf abstract the nam con son basin is a rift basin that formed offshore southern vietnam at the time of opening of the east vietnam sea south china sea the cenozoic stratigraphy in the basin is subdivided into four megasequences based on the main tectonic stages of basin evolution syn rift 1 inter rift syn rift 2 and post rift this study investigates the depositional environment and reservoir quality of the miocene sediments in the central part of the basin and thus discusses the later part of the inter rift the second syn rift and the post rift megasequences we focus on seismic interpretation sediment core analysis biostratigraphy and well log analysis the lower miocene depositional succession is dominated by stacked coarsening upward progradational packages possibly related to the interplay between high sediment supply and fluctuating sea levels the depositional environment is fluvio deltaic to paralic the middle miocene depositional succession is characterized by an upward deepening trend which seems related to northeast southwest rift propagation during this time several intra rift packages demonstrate increasing rift forming activities that resulted in deposition of footwall derived turbidite deposits in the central grabens half grabens and non deposition erosion on structural highs shallow marine facies dominated in the west while the deep marine settings occurred in most of the eastern part of study area carbonate platforms were initiated and widely developed on the structural highs in the southeast and north as a result of overall marine transgression and backstepping of the clastic shoreline toward the west the upper bounding surface of this succession is a regional unconformity marking the boundary between the syn rift 2 and the post rift megasequences during the late miocene deep marine facies extended across the entire study area with extensive submarine fan deposits and submarine channels downcutting w e and s ne which extended across the shelf and slope the miocene sandstones comprise mostly fine to very fine grained feldspathic litharenite to lithic arkose deep marine turbidite sandstones of the upper miocene succession exhibit the best reservoir qualities both porosity and permeability of all the sedimentary facies examined paralic sandstones of the lower miocene succession and footwall derived turbidite sandstones of the middle miocene succession have similar reservoir qualities relatively good reservoir quality sandstones of the middle and upper miocene successions were deposited as thick massive turbidites however parallel laminated turbidites and slumps debris flows often show poor to moderate reservoir qualities precipitation of carbonate cement during burial diagenesis has destroyed the reservoir quality of the miocene sandstones

new tectono geochronological constraints on timing of shearing along the ailao shan red river shear zone implications for genesis of ailao shan gold mineralization abstract several world class gold deposits are located along the ailao shan als belt in eastern tibet china the genesis of gold mineralization along the belt however has been the subject of debates in the last decades which highlights the importance of dating shearing magmatism and mineralization along the ailao shan red river shear zone asrr through detailed field observations and microscopic analysis a group of leucocratic intrusions from within and outside the shear zone along the als belt are investigated in the present paper pre syn and post shearing intrusions are grouped based on structural and microstructural analysis la icp ms and sims dating of the intrusions revealed the existence of two age populations a group of ages older than 30 ma and the other younger than 28 ma the former are distributed both within and outside the shear zone and the latter in contrast occur only within the shear zone our new results show that the ductile shearing along the asrr shear zone initiated since ca 30 ma ago the dating results place major constraints on timing of shearing along the asrr shear zone and have profound implications on the genesis of gold mineralization along the als belt the present study reveals that ductile shearing along the asrr shear zone was resulted from extrusion of the indochina block late during the indian eurasian plate collision meanwhile we conclude that the gold mineralization took place prior to the shearing but in close relation to an early magmatism 30 ma ascribed to post collisional extension collapse involving mantle processes early during the plate collision

geological evolution regional perspectives and hydrocarbon potential of the northwest phu khanh basin offshore central vietnam abstract seismic stratigraphic and structural analyses of the northwest phu khanh basin offshore central vietnam based on 2 d seismic data indicate that the initial rifting began during the latest cretaceous or palaeogene controlled by left lateral transtension along the east vietnam boundary fault zone evbfz and northwest southeast directed extension east of the evbfz rifting stopped due to transpression during middle oligocene times but resumed by left lateral transtension during the late oligocene thick sequences of lacustrine and alluvial sediments were deposited during the palaeogene rift periods the late oligocene rifting ended due to inversion triggered by right lateral wrenching near the palaeogene neogene boundary following the onset of this inversion regional uplift and volcanism took place in the southern half of the study area and contemporaneous subsidence and transgression took place farther north leading to widespread carbonate deposition as the right lateral wrenching decreased during the early neogene thermal subsidence and siliciclastic sedimentation became dominant resulting in the buildup and southward propagation of the shelf slope sediment accumulation and subsidence rates increased after the middle miocene times due to eastward tilting of central vietnam and the adjacent offshore area potential direct hydrocarbon indicators dhis in the phu khanh basin include common amplitude anomalies gas chimney like features and seafloor gas seeps in addition oil seeps are found at dam thi nai immediately landward of the basin geochemical analyses of the oil seeps indicate the existence of at least two early to peak mature source rocks maturation modelling combined with the seismic analysis suggests the likely presence of oil kitchens 40 50 km downdip in the basin and a fairly simple oil migration route the basin is probably charged from lacustrine syn rift mudstones humic coals and fore reef marls potential reservoirs are turbidite lowstand delta shelf and coastal sandstones as well as platform and reef carbonates and fractured basement various structural and stratigraphic traps formed during the palaeogene and early neogene prior to the main stage of petroleum generation

keys and pitfalls in mesoscale fault analysis and paleostress reconstructions the use of angelier s methods whereas most of the stress inversion methods using fault slip data only minimize the angle between the measured striation and a computed shear stress to find the best fitting reduced stress tensor angelier 1990 proposed an alternative method named invd that also takes into account the relative shear stress magnitude which allows the fault to move using artificial datasets and particular fault geometries we compare this method with one of the classical methods based on the minimization of the shear slip angles r4dt angelier 1984 and we show that in most cases the new method has improved the quality of the results furthermore as proposed by angelier we point out that the quality of the stress inversion primarily depends on the quality of the field data we give advice and warn about some pitfalls concerning determination of sense of slip on fault planes recognition of successive faulting events and their chronology drawer or wedge faults stress permutations faults in vertical bedding we also argue that in case of tilted sequences fault diagrams should not be presented without bedding planes but we show that stress inversions when realized with caution and with the correct method can havemuch more applications than reconstructing stress fields like for determining the paleo horizontal the nature and the sense of motion of large faults the chronology and age of large structures

constraints on the left lateral shearing and crustal melting of the ailaoshan massif yunnan province southwest china abstract the ailaoshan red river shear zone asrr in se tibet accommodated about 20 convergence of the cenozoic india asia continental collision which resulted in complicated thermal history during paleocene to miocene the ailaoshan massif in the middle part of asrr is characterized by extensive mylonitization and migmatization but the exact timing of the large scale left lateral shearing and whether the crustal partial melting occurred prior to or coeval with the left lateral shearing remain controversial the detailed structural observation suggests the pre kinematic nature of the ailaoshan corundum with respect to the left lateral shearing la icp ms u pb dating of metamorphic zircon and monazite inclusions in the pre kinematic ailaoshan corundum obtained a weighted 206pb 238u ages of 28 0 0 5 ma mswd 3 3 n 27 and 28 3 0 3 ma mswd 1 8 n 18 respectively which gave an upper limit on the initiation of the left lateral shearing in the ailaoshan massif moreover the presence of protogenetic siliceous melt inclusions in the pre kinematic corundum indicates that the cenozoic crustal anatexis of the ailaoshan massif has occurred before the left lateral shearing along with available geochronological data the crustal partial melting of the ailaoshan massif was attributed to joint results which at least include the neoproterozoic convergence the triassic indosinian orogeny and the cenozoic evolution as a response to the india asia continental collision

late neogene structural inversion around the northern gulf of tonkin vietnam effects from right lateral displacement across the red river fault zone continental extrusion may take up much of the deformation involved in continental collisions major strike slip zones accommodate the relative extrusion displacement and transfer deformation away from the collision front the red river fault zone rrfz accommodated left and right lateral displacements when indochina and south china were extruded during the indian eurasian collision the northern song hong basin onshore and offshore in the gulf of tonkin delineates the direct extension of the rrfz and thus records detailed information on the collision induced continental extrusion we assess the rapidly evolving kinematics of the fault zone buried within the basin based on seismic analysis contrary to previous studies we do not identify indications for latest miocene left lateral motion across the rrfz we tentatively consider the shift from left to right lateral motion to have occurred already during the middle late miocene as indicated by inversion of ne sw striking faults in the bach long vi area right lateral displacement terminated around the end of the miocene in the song hong basin however continued inversion in the bach long vi area and nnw sse striking normal faulting suggests a stress regime compatible with right lateral motion across the onshore part of the rrfz continuing to the present inversion around the bach long vi island may have accommodated up to a few kilometers of right lateral displacement between the indochina and south china blocks comparable ne sw striking fault zones onshore may have accommodated a larger fraction of the right lateral slip across the rrfz thus accounting for the restricted transfer of lateral displacement to the offshore basins