reconciling subduction dynamics during tethys closure with large scale asian tectonics insights from numerical modeling we use three dimensional numerical models to investigate the relation between subduction dynamics and large scale tectonics of continent interiors the models show how the balance between forces at the plate margins such as subduction ridge push and far field forces controls the coupled plate margins and interiors evolution removal of part of the slab by lithospheric break off during subduction destabilizes the convergent margin forcing migration of the subduction zone whereas in the upper plate large scale lateral extrusion rotations and back arc stretching ensue when external forces are modeled such as ridge push and far field forces indentation increases with large collisional margin advance and thickening in the upper plate the balance between margin and external forces leads to similar convergent margin evolutions whereas major differences occur in the upper plate interiors here three strain regimes are found large scale extrusion extrusion and thickening along the collisional margin and thickening only when negligible far field forces ridge push and larger far field forces respectively add to the subduction dynamics the extrusion tectonics develops a strong asymmetry toward the oceanic margin driven by large scale subduction with no need of preexisting heterogeneities in the upper plate because the slab break off perturbation is transient the ensuing plate tectonics is time dependent the modeled deformation and its evolution are remarkably similar to the cenozoic asian tectonics explaining large scale lithospheric faulting and thickening and coupling of indentation extrusion and extension along the asian convergent margin as a result of large scale subduction process

a possible mechanism for the initiation of the yinggehai basin a visco elasto plastic model abstract the yinggehai basin lying along the trace of the red river fault zone in the south china sea has been related to the movements of the red river fault zone and the rotation of the indochina block however the tectonic origin of the yinggehai basin remains unclear this paper explores the initiation of the yinggehai basin using a visco elasto plastic model this model concentrates on two main aspects lateral viscosity variations mainly controlled by temperature in the lithosphere and internal friction angles of the pre existing fault zone modeling results show that 1 for a layered viscosity en echelon faults would likely form when there is no pre existing strike slip fault whereas the basin would be narrow and deep if any when there is a pre existing fault 2 for moderate lateral viscosity variations a large basin forms even without a pre existing fault zone and 3 for strong lateral viscosity variations a major rift could form over geologic time our results indicate that the initiation of the yinggehai basin requires moderate lateral viscosity variations i e a pre existing gentle upwelling of the mohorovicic discontinuity but no pre existing fault in addition the initial extension predicted is ne sw and is generated by the rotation of the indochina block this differs from the nw se extension that resulted from the movements of the red river fault zone this indicates that the left lateral displacements of the red river fault zone and the spreading of the south china sea only influence the basin evolution after its initiation

geomorphic context of the prehistoric huastec floodplain environments lower panuco basin mexico abstract the huasteca of eastern mexico is the northern extent of prehistoric mesoamerican complex culture in comparison to other major mesoamerican culture regions much less is known about the physical environment of the huasteca this paper examines the structure scale and dynamics of floodplain environments in the lower panuco basin the major physical setting in which prehistoric huastec resided data sources included total station surveying topographic and historic maps particle size of floodplain deposits and analysis of air photos and satellite imagery study results illustrate the geoarchaeological significance of spatial changes in floodplain environments valley profiles grade from concave to planar in the upper portions of the study area where the rio moctezuma exits the mountains and are characterized by low floodplain relief and active floodplain reworking thus the narrow valley and dynamic fluvial environment would not have been suitable for sustained habitation the lower moctezuma and panuco valleys have a convex profile with low rates of floodplain reworking relict meander belts and floodplain environments that are more prone to flooding the panuco valley would have represented a stable environment suitable for habitation along wide natural levees which are perched above extensive flood prone backswamps with buried relict channels the absence of multiple oxbow lakes coupled with the association of older huastec material culture along the active channel suggests that low rates of floodplain reworking have persisted since the late holocene and help to constrain the age of a meander belt for a major river system study results provide a framework for future geoarchaeological research within the huasteca

modelling of hydrocarbon generation in the cenozoic song hong basin vietnam a highly prospective basin abstract the cenozoic song hong basin situated on the northern part of the vietnamese shelf has been only sporadically explored for hydrocarbons a review of the results of the exploration efforts so far shows that the distribution of potential source rocks and their time of hydrocarbon generation are the critical risks for finding commercial amounts of hydrocarbons in the song hong basin including the hanoi trough the rocks most likely to have source potential are 1 oil prone eocene lower oligocene lacustrine mudstones and coals 2 oil and gas prone middle miocene coal beds 3 gas prone upper oligocene lower miocene coals and 4 gas and oil prone miocene marine mudstones to assess the time of hydrocarbon generation from these units relative to the formation of traps the generation history was modelled at 32 well and pseudo well locations the modelling demonstrates that the two first mentioned source rock units are especially important in the northern and northeastern part of the basin and along its western margin traps may have been charged by eocene lower oligocene source rocks in the hanoi trough the excellent middle miocene coal beds have probably generated hydrocarbons within the last few million years thus the huge and still underexplored song hong basin provides attractive areas for further exploration

impact of india asia collision on se asia the record in borneo abstract borneo occupies a central position in the sundaland promontory of se asia it has a complex cenozoic geological history of sedimentation and deformation which began at about the same time that india is commonly suggested to have started to collide with asia some tectonic reconstructions of east and se asia interpret a large se asian block with borneo at its centre which has been rotated clockwise and displaced southwards along major strike slip faults during the cenozoic due to the indentation of asia by india however the geological history of borneo is not consistent with the island simply forming part of a large block extruded from asia the large clockwise rotations and displacements predicted by the indentor model for borneo are incompatible with palaeomagnetic evidence and there is no evidence that the major strike slip faults of the asian mainland reach borneo seismic tomography shows there is a deep high velocity anomaly in the lower mantle beneath se asia interpreted as subducted lithosphere but it can be explained just as well by alternative tectonic models as by the indentor model very great thicknesses of cenozoic sediments are present in borneo and circum borneo basins and large amounts of sediment were transported to the crocker turbidite fan of north borneo from the eocene to the early miocene but all evidence indicates that these sediments were derived from local sources and not from distant sources in asia elevated by india asia collision the cenozoic geological history of borneo records subduction of the proto south china sea and miocene collision after this ocean lithosphere was eliminated and a variety of effects resulting from long term subduction beneath se asia there is little to indicate that india asia collision has influenced the cenozoic geological record in borneo

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

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

paleomagnetic constraints from the baoshan area on the deformation of the qiangtang sibumasu terrane around the eastern himalayan syntaxis the sibumasu block in se asia represents the eastward continuation of the qiangtang block here we report a detailed rock magnetic and paleomagnetic study on the middle jurassic and paleocene rocks from northern sibumasu to document the crustal deformation during the india asia collision since the paleocene and reconstruct the overall strike of the qiangtang sibumasu elements before the india asia collision although the fold test is inconclusive based solely on our data a positive reversal test a positive regional fold test with previous paleomagnetic results and a detrital origin of hematite in the red beds as indicated by scanning electron microscopy suggest that the magnetizations obtained from the jurassic and paleocene rocks are most likely primary showing an 80 clockwise rotation since paleocene these results together with previously published paleomagnetic data suggest that the northern sibumasu and northern simao elements experienced a 60 80 clockwise rotation since paleocene this large clockwise rotation is also consistent with the surface gps velocity field and ne sw fault networks suggesting a rotational motion of crustal material from southeastern tibet during late cenozoic we infer that the large clockwise rotation is a sum of rotation in the eocene to middle miocene time associated with indochina extrusion and rotation after the middle miocene associated with the e w extension in central tibet this suggests that the eastward motion of tibetan crustal material along the xianshuihe xiaojiang fault after middle miocene is transmitted to the southwest toward myanmar jurassic and cretaceous paleomagnetic results suggest that the qiangtang northern sibumasu was originally a curved structure with an orientation of n60 w in tibet and changes to n10 w in southern sibumasu

regional scale paleobathymetry controlled location but not magnitude of tidal dynamics in the late cretaceous western interior seaway usa despite extensive outcrop and previous sedimentologic study the role of tidal processes along sandy wave and river dominated shorelines of the north american cretaceous western interior seaway remains uncertain particularly for the extensive mid campanian c 75 77 5 ma tidal deposits of utah and colorado usa herein paleotidal modelling paleogeographic reconstructions and interpretation of depositional process regimes are combined to evaluate the regional scale 100 1000km basin physiographic controls on tidal range and currents along these regressive shorelines in the utah bight southwestern western interior seaway paleotidal modelling using a global and astronomically forced tidal model combined with paleobathymetric sensitivity tests indicates the location of stratigraphic units preserving pronounced tidal influence only when the seaway had a deep center 400 m and southern entrance 100 m maximum tidal velocity vectors under these conditions suggest a dominant south easterly ebb tide within the utah bight consistent with the location and orientation of paleocurrent measurements in regressive tide influenced deltaic units the modelled deep paleobathymetry increased tidal inflow into the basin and enhanced local scale 10 100 km resonance effects in the utah bight where an amphidromic cell was located however the preservation of bidirectional mudstone draped cross stratification in fine to medium grained sandstones requires tides in combination with fluvial currents and or local tidal amplification below the maximum resolution of model meshes c 10 km these findings suggest that whilst regional scale controls govern tidal potential within basins localized physiography exerts an important control on the preservation of tidal signatures in the geologic record

geologic evolution of the cuu long and nam con son basins offshore southern vietnam south china sea rifting and regional subsidence characterize the cuu long and nam con son basins offshore southern vietnam initial rifting began in the eocene early oligocene followed by the uplift and rotation of the crustal blocks in the late oligocene the erosion of the uplifted blocks marked the transition from rifting to regional subsidence in the cuu long basin a second phase of rifting began in the nam con son basin lasting until the late miocene parts of the nam con son basin experienced inversion in the middle to late miocene the synrift and postrift units in the cuu long basin consist of nonmarine deposits and paralic to shallow marine sediments respectively the synrift deposits in the nam con son basin can be divided into the early synrift unit corresponding to the initial rifting phase and the late synrift unit deposited during the second rifting phase the early synrift and late synrift units consist of nonmarine sediments and nonmarine to shallow marine sediments respectively the postrift unit is composed of shelf and deeper marine deposits the data compiled from the published reports suggest that the cuu long basin is oil prone with the oil reservoired mainly in fractured basement highs whereas the nam con son basin is generally gas prone with the gas trapped in miocene sands and late miocene carbonates these distinct trends may be attributed to differences in timing of trap formation and the disruption of trap integrity caused by prolonged rifting and inversion in the nam con son basin gwang h lee is associate professor at kunsan national university korea his research interests include application of seismic reflection to basin research and sequence stratigraphy he received his b s and m s degrees in oceanography from seoul national university korea in 1981 and 1983 respectively and a ph d in geological geophysical oceanography from texas a m university in 1990 from 1991 to 1994 he worked for shell offshore inc in new orleans keumsuk lee received a b s degree in mathematics 1994 and an m s degree in geological oceanography 1999 from kunsan national university kunsan korea he is currently attending florida atlantic university boca raton florida his main research interest is application of geophysical methods to various geological and environmental problems joel s watkins is the earl f cook professor department of geology and geophysics texas am co chief scientist on dsdp leg 66 middle america trench and project director manager and vice president with gulf oil 1977 1985 he is the author or co author of more than 130 scientific publications and senior editor of aapg memoirs 29 34 and 53 his interests are structure and stratigraphy of small ocean basins and seismic reservoir characterization

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

paleogene structural development of the northern song hong basin and adjacent areas implications for the role of extrusion tectonics in basin formation in the gulf of tonkin abstract the song hong basin situated at the distal part of the ailaoshan red river shear zone asrrsz holds important information on the role of extrusion tectonics in the marginal basin development in the south china sea based on an extensive dataset of 2 and 3 d seismic and stratigraphic information from 27 exploration wells the paleogene structural evolution of the northern song hong basin and adjacent areas has been studied in detail this study proposes a new paleogene structural development model of the study area eocene oligocene rifting in the northern song hong basin was driven by left lateral shearing from the asrrsz associated with a combined motion of clockwise rotation and translation of the indochina block which allowed extension along the restraining bend geometry of the basin s eastern margin a structural high separates the song hong basin from the beibuwan basin inhibiting significant strike slip displacement transfer from the asrrsz into rifting in the beibuwan basin strike slip displacement from the asrrsz is maintained further south to the east vietnam boundary fault segment thus extension of the beibuwan qiongdongnan and phu khanh basins were the result of the interplay between extrusion and slab pull tectonics during the end of the oligocene reduced extrusion of indochina caused minimal rotation of the block and the remaining left lateral displacement along the asrrsz was absorbed into inversion around the junction between the song hong and beibuwan basins

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

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

sta cruz atizapan a 22 ka lake level record and climatic implications for the late holocene human occupation in the upper lerma basin central mexico abstract the upper lerma is a high altitude basin with three water bodies linked by the lerma river this basin has a long archaeological history characterised by the establishment of settlements within the lacustrine ecosystem itself man made islands during the late classic to epiclassic ad 550 900 which were abandoned by the end of the epiclassic the upper lerma is an ideal site to study climatic and environmental conditions during the period of human occupation as well as during the last full glacial interglacial cycle two sediment cores stcrz 9 54 m and almoloya del rio 5 12 m were recovered from the highest lake in the system chignahuapan ten radiocarbon dates provide chronologies for these sequences in which the tres cruces tephra c 8500 yr bp and the upper toluca pumice c 11 600 yr bp serve as stratigraphic markers magnetic properties loss on ignition and diatom analyses were used to infer lake level fluctuations during the last c 22 000 yr bp the late pleistocene environment was characterised by a freshwater lake high sediment input and variable lake levels are recorded during the last glacial maximum c 19 000 16 000 yr bp while slightly higher water levels and reduced sediment input are recorded during the late glacial c 16 000 11 000 yr bp a short episode of shallow conditions is inferred by c 12 400 yr bp holocene lake levels were generally shallower and three episodes of very shallow slightly alkaline waters are identified the first dates to the early holocene c 11 000 7000 yr bp the second is centred at c 4600 4500 yr bp the third occurred between c 2000 and 800 yr bp c 200 bc ad 1100 calibrated ages with very shallow water after c 1400 yr bp ad 550 calibrated age lake level increased after c 800 yr bp these three shallow water events are also recorded at other sites in central mexico indicating regional climatic trends rather than local events a deeper water phase occurred between 7000 and 6400 6200 yr bp the last shallow water phase correlates with the classic and epiclassic periods ad 200 900 and shallowest conditions occurred in the late classic to epiclassic c ad 550 900 when the construction of man made islands reached a peak an increase in lake level after c 800 yr bp ad 1100 calibrated age may have led to the abandonment of this life strategy

enhancing rescue archaeology using geomorphological approaches archaeological sites in paredes asturias nw spain abstract palaeolithic remnants a necropolis roman villa and another minor archaeological site were discovered in paredes spain these sites were the focus of multidisciplinary research during the construction of a large shopping centre in asturias nw spain the aims of this study are 1 to contribute to archaeological prospection in the sites and 2 to develop evolutionary models of the sites based on geomorphological inferences detailed archaeological prospection 103 trenches geomorphologic mapping stratigraphic studies 36 logs and ground penetration radar gpr surveys on five profiles indicate that the location of the settlement source of the necropolis is outside the construction perimeter farther to the southeast the pre holocene evolution of the fluvial landscape is marked by the development of two terraces t1 and t2 that host the early palaeolithic remains in the area ca 128 71 ka the holocene evolution of the landscape was marked by the emplacement of the nora river flood plain covered by alluvial fans after ca 9 ka bp cal bc 8252 7787 subsequently neolithic pebble pits dated ca 5 3 ka bp cal bc 4261 3963 and 4372 4051 were constructed on t2 at the area reoccupied as a necropolis during the late roman period 1590 45 years bp cal ad 382 576 coeval human activity during the late roman period at 1670 60 years bp cal ad 320 430 is also recorded by channel infill sediments in a minor site at the margin of an alluvial fan located to the southeast this work shows that a rescue archaeological study can be significantly enhanced by the implementation of multidisciplinary scientific studies in which the holistic view of geomorphologic settings provide key insights into the geometry and evolution of archaeological sites

full fit reconstruction of the south china sea conjugate margins although the south china sea margins have been well studied there are no full fit reconstructions that document the complex rifting history in a regional geodynamic context we restored conjugate margins to their original late cretaceous unstretched geometries and generated the first full fit reconstructions of the south china sea conjugate margins the impact of magmatic underplating on restoration and full fit reconstruction was estimated quantitatively the full fit reconstruction model includes restoration uncertainties and results in minimum gaps and overlaps between the restored conjugate margin geometries based on our restoration the full fit reconstruction and the continental basement thickness distribution we estimate that there was more extension of continental basement on the western part of the conjugate margins compared with the eastern margin prior to the initiation of seafloor spreading therefore the mid ocean ridge initially formed in the east and propagated westward to open the south china sea seafloor spreading propagated along the xisha trough during nw sub basin formation but continental breakup occurred along the southern side of the zhongsha xisha islands where the lithosphere was probably weaker than along the xisha trough consistent with the geometry and evolution of the nw sub basin and the southward jump of the mid oceanic ridge c 2015 elsevier b v all rights reserved

direct dating of left lateral deformation along the red river shear zone china and vietnam 1 exposures of high grade midcrustal rocks within the red river shear zone rrsz which separates the indochina and south china blocks exhibit clear evidence of left lateral ductile deformation assuming that the south china sea represents a pull apart basin formed at the southeastern termination of the rrsz it has been argued that seafloor magnetic anomalies constrain the timing of sinistral slip accommodated by the rrsz between 32 and 17 ma at a rate of 4 cm yr while 40ar 39ar thermochronometry indicates that left lateral slip occurred along the rrsz between 25 and 17 ma the timing of earlier high temperature deformation has not been directly constrained in situ th pb ion microprobe dating of monazite inclusions in garnets allows direct assessment of the timing of amphibolite grade metamorphism and synchronous left lateral shearing results from northern segments of the rrsz in yunnan china indicate that synkinematic garnet growth occurred between 34 and 21 ma and are the first to document late oligocene metamorphism and left lateral shearing data from the southern rrsz within vietnam are complicated by tertiary overprinting of rocks that experienced amphibolite facies metamorphism during the indosinian orogeny 220 ma the period during which sinistral deformation is now constrained to have occurred along the rrsz i e 34 17 ma is essentially coincident with spreading of the south china seafloor 32 17 ma this temporal and kinematic link between left lateral shearing along the rrsz and opening of the south china sea supports the view that indochina was extruded from asia as a block along lithospheric scale strike slip faults

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

flood delineation in a large and complex alluvial valley lower panuco basin mexico determining the extent of flooding is an important role of the hydrological research community and provides a vital service to planners and engineers for large river systems located within distant settings it is practical to utilize a remote sensing approach this study combines a remote sensing and geomorphic approach to delineate the extent of a large hurricane generated flood event in the lower panuco basin 98 227 km2 the seventh largest river system draining into the gulf of mexico the lower panuco basin is located within the coastal plain of eastern mexico and has a complex alluvial valley data sources included a landsat 5tm and landsat 7etm scene and topographic and particle size data from fieldwork and laboratory analysis the landsat 5tm image was acquired after the peak of a large flood event in 1993 whereas the landsat 7etm scene was acquired during the dry season in 2000 the increasing number of days between flood crest and the date of flood image acquisition along the river valley provided the opportunity to examine several methods of flood delineation and to consider differences in floodplain geomorphology backswamp environments were easily delineated in flooded reaches within the panuco and tamuin valleys whereas in the moctezuma valley more sophisticated methods were required because of the greater time between image acquisition and flood peak and the complex floodplain topography this included principal component pc analysis and image classification within the floodplain residual holocene terraces complicated flood mapping classification of both images allowed consideration of the influence of permanent standing water although the flooded areas were greater in the lower reaches of the study area because this portion of the valley contained large floodplain lakes the amount of inundation was actually lower remote sensing offers the ability to examine large alluvial valleys in distant settings but does not imply that geomorphic criteria should be excluded indeed because of heterogeneous floodplain topography this study illustrates the importance of including field based geomorphic analysis so that the complexity of distinct floodplain environments are considered the findings from this study are significant because most remote sensing data obtained for the purpose of flood mapping will not coincide with the flood crest thus this study provides an appropriate method for mapping flood inundation in large and complex floodplain settings after flood crest recession

finite extension across the south vietnam basins from 3d gravimetric modelling relation to south china sea kinematics abstract we derive a crustal thickness map over the south vietnam basins from a 3d inversion of gravity data that takes into account the sedimentary infill and its density variation with depth this map is used to estimate the total amount of stretching across these basins that varies from 190 km to the east at 111 e to 30 km to the west at 107 e comparison with south china sea kinematics amount and timing of oceanic opening implies large decoupling with respect to the indochina block and supports the hypothesis of formation of the south china sea in upper oligocene to lower miocene by southward subduction of the proto south china sea

the sedimentary and tectonic evolution of the yinggehai song hong basin and the southern hainan margin south china sea implications for tibetan uplift and monsoon intensification 1 the yinggehai song hong basin is one of the world s largest pull apart basins lying along the trace of the red river fault zone in the south china sea south of hainan island this basin crosscuts the rifted margin of the northern south china sea in this paper we present for the first time a regional compilation of multichannel seismic reflection data from both the strike slip and rifted margins the basins started to open after similar to 45 ma especially after similar to 34 ma the yinggehai basin was folded and inverted in the middle miocene after 21 ma in the north and 14 ma in the south before rapidly subsiding again after similar to 5 ma because of continued tectonism this subsidence has caused shale diapirism especially driven by associated sedimentation in the late pliocene 2 6 2 0 ma extension along the adjacent south hainan margin shows preferential lower crustal extension suggestive of lower crustal flow increasing toward the continent ocean transition during breakup sediment supply is reconstructed to peak in the middle miocene then falls between 14 and 10 3 ma to reach a low in the late miocene however rates rose again in the pliocene pleistocene the red river sediment budget is incompatible with climate models that propose stronger monsoon rains starting at 8 ma or with large scale river capture away from the red river after similar to 10 ma both lines of evidence point to major uplift in the red river drainage being middle miocene or older the recent preindustrial red river carried much more sediment than the average pleistocene accumulation rate indicating modest sediment buffering onshore at least in recent geologic time

event sequence and sediment exhaustion in the lower panuco basin mexico abstract although large tropical river systems transport the majority of the world s runoff and sediment few studies have examined the dynamics of suspended sediment transport in this setting this includes mexico which contains two of the larger river basins draining into the gulf of mexico this study provides a detailed analysis of discharge q and suspended sediment transport dynamics for the lower panuco basin 98 227 km2 of eastern mexico including the lower moctezuma lower tamuin and panuco rivers daily values of discharge and suspended sediment concentration ssc are examined for three stations spanning from the late 1950s to early 1990s although the panuco is a large basin the relationship between discharge and suspended sediment concentration represents a departure from the oft reported study by heidel trans am geophys union 37 1956 56 instead of sediment lagging discharge the sediment wave precedes discharge by an average of 1 7 days displaying pronounced clockwise positive hysteresis this may be due to the sources of runoff and sediment which are derived primarily in the lower reaches of the basin because of precipitation patterns geology and basin morphometry the distinct differences in lithology between the tamuin and moctezuma basins which join in the coastal plain to form the rio panuco allow the influence of geologic setting to be considered q ssc relations display positive hysteresis where the sediment is derived from erodible tertiary shale deposits in the moctezuma basin in contrast q ssc relations in the rio tamuin which transports less suspended sediment because of its karstic setting are more linear due to these relations being dependent on the entrainment of bed material consideration of the sequence of events during the rainy season suggests that much of the hillslope derived sediment is flushed through the system by early events which would occur because of exhaustion of hillslopes sediments q ssc relations are increasingly linear during later events in the rio panuco which is likely due to these events transporting a higher proportion of sediment entrained from the channel this is manifest by a reduction in lead times as the number of days between peak ssc and peak q for early and late events significantly decreases from 2 6 to 0 9 respectively large events 750 m3 s in the latter part of summer and early fall having high suspended sediment concentrations could be due to the replenishment of hillslope sediments or due to the contribution of sediment from source areas that were not previously exhausted the findings from this study are likely common to most drainage systems having seasonal bimodal streamflow regimes whereas the seasonal signature of q ssc relations is likely enhanced in those settings where agriculture is a major component of the landscape

a sedimentological explanation for the distribution of archaeological sites in a meander belt as stated by the relict channel rule archaeological surveys performed for the u s army corps of engineers within the lower mississippi river and red river valleys have noted that archaeological deposits found on the natural levees of relict river channels consist only of surficial sites that postdate the abandonment of the associated river channel from the results of these surveys richard weinstein and david kelley proposed the relict channel rule in 1989 their rule states that the archaeological deposits associated with the natural levees of an abandon river channel will consist only of surficial sites that postdate the abandonment of the river channel the relict channel rule has been explained as the result of preferences by prehistoric cultures to avoid the occupation of natural levees of active river channels archaeologists have suggested that the lack of rich biotic resources associated with an active channel and the hazards created by periodic flooding caused prehistoric cultures to avoid settling the natural levees of active river channels rather it has been proposed that prehistoric cultures settled around oxbow lakes within abandoned channel segments in addition archaeological studies of the red river within arkansas have speculated that the danger posed by rapidly eroding cut banks was another factor that discouraged the settlement of the natural levees of active river channels sedimentological processes provide an alternative explanation for the relict channel rule while active a typical meandering river channel rapidly migrates back and forth across its meander belt during this time its channel would rapidly migrate away from any archaeological deposits that formed adjacent to an active point bar simultaneously overbank processes would quickly bury them also an actively laterally migrating channel would consume the sites that form on the natural levee of a rapidly migrating cutbank if a river cutbank was to migrate up to and stop at a preexisting site that site would by that time be buried beneath natural levee deposits finally archaeological sites formed during the initial establishment of a river course would eventually be either deeply buried by aggradation of natural levees or destroyed by lateral migration as a result only those archaeological deposits that date to a few tens of years prior to and postdate the abandonment of the channel will occur as surface sites therefore regardless of whether the natural levees of a channel of an actively meandering river were used before or after its abandonment the rapid lateral migration of its channel while active will produce the distribution of surface sites noted by the relict channel rule an active segment of the mississippi river between donaldsonville and port allen louisiana is an exception to the relict channel rule along this segment numerous surface and scattered buried sites containing transitional coles creek and plaquemine components have been recorded from the natural levees along both sides of the currently active mississippi river these sites which include several mounds occur most commonly on the cutbank side of a meander loop along one twenty mile segment at least one prehistoric site is associated with each meander loop preexisting archaeological deposits are present along this active segment of the mississippi river because of the slow rate of lateral migration of its river channel the slow rate of lateral migration has permitted the preservation of archaeological deposits that faster rates of lateral migration would have destroyed also historic maps show that historic native american villages heavily occupied the natural levees of this active segment of the mississippi river thus this study strongly indicates that the distribution of archaeological sites as expressed by the relict channel rule is a result of fluvial rather then cultural processes it is concluded that the rapid lateral migration of a channel within a meander belt badly biases the temporal distribution of both surficial and buried archaeological deposits within it first the formation of a meander belt destroys any archaeological deposits that predate it second rapid lateral migration of a river will destroy many of the archaeological deposits contemporaneous with its activity a few archaeological deposits contemporaneous with an active river course might survive destruction along the outer edge of the meander belt as buried or surface sites associated with the natural levees of abandoned meander loops finally any archaeological deposits that formed after the abandonment of a river course will occur as surface sites because of the extensive destruction and burial of sites by meander belt processes reconstructing settlement patterns from the distribution of recorded sites can be difficult if not impossible for the archaeological deposits of many cultural groups 140 wylie dr apt 5 baton rouge louisiana 70808

the aeromagnetic method as a tool to identify cenozoic magmatism in the west antarctic rift system beneath the west antarctic ice sheet a review thiel subglacial volcano as possible source of the ash layer in the waiscore abstract the west antarctic ice sheet wais flows through the volcanically active west antarctic rift system wars the aeromagnetic method has been the most useful geophysical tool for identification of subglacial volcanic rocks since 1959 64 surveys particularly combined with 1978 radar ice sounding the unique 1991 97 central west antarctica cwa aerogeophysical survey covering 354 000 km 2 over the wais 5 km line spaced orthogonal lines of aeromagnetic radar ice sounding and aerogravity measurements still provides invaluable information on subglacial volcanic rocks particularly combined with the older aeromagnetic profiles these data indicate numerous 100 1000 nt 5 50 km width shallow source magnetic anomalies over an area greater than 1 2 10 6 km 2 mostly from subglacial volcanic sources i interpreted the cwa anomalies as defining about 1000 volcanic centers requiring high remanent normal magnetizations in the present field direction about 400 anomaly sources correlate with bed topography at least 80 of these sources have less than 200 m relief at the wais bed they appear modified by moving ice requiring a younger age than the wais about 25 ma exposed volcanoes in the wars are the present rapid changes resulting from global warming could be accelerated by subglacial volcanism

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

evaluation of relative tectonic activity in the tehran basin central alborz northern iran abstract recent deformations in the area studied control structural expansions influenced by tectonic activities causing transformations of geologic features and morphological landforms the tehran basin is located at the southern edge of the central alborz and is the result of the arabian eurasian convergence and clockwise rotation of the south caspian basin with respect to eurasia hence assessment of the drainage pattern permutations and mountain fronts appears necessary we used six significant morphometric indices for this evaluation stream length gradient sl drainage basin asymmetry af hypsometric integral hi ratio of valley floor width to valley height vf drainage basin shape bs and mountain front sinuosity smf the combined analyzed indices represented the relative active tectonics iat the study area was divided into four regions according to the values of iat these classes include class 1 very high activity class 2 high class 3 moderate and class 4 low the regions with high relative tectonic activity mostly correspond with the active structures in the basin the tectonic activity classes 1 and 2 coincide with the fault mountain fronts in the southern edge of the central alborz especially the north tehran fault the parts of the central mosha fault and the regions in the east the southeast and the west of the basin indicate the moderate class of tectonic activity class 3 the low elevation plain in the south and southwest of the area shows the lowest relative tectonic activity class 4

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

seismic sequence stratigraphy and hydrocarbon potential of the phu khanh basin offshore central vietnam south china sea the phu khanh basin offshore central vietnam is the only undrilled basin on the vietnam margin of the south china sea analysis of multichannel seismic data indicates that the phu khanh basin follows a typical rift margin development faulted basement synrift sedimentation a breakup unconformity and postrift sedimentation initial rifting probably began during the late cretaceous or paleogene rifting and uplift appear to have resumed or continued locally during the late oligocene and early miocene the later part of basin development was dominated by subsidence postrift sedimentation evolved from a transgressive ramp phase to a regressive shelf slope phase during the transgressive phase rising sea level provided favorable conditions for carbonate buildup development the regressive interval contains a number of sequences composed of seismically resolvable lowstand highstand and rarely transgressive systems tracts these sequences are interpreted as third order sequences superposed on second order eustatic cycles principal potential source rocks are believed to be synrift lacustrine sediments the synrift sediments may lie below the oil floor and probably are gas prone in the postrift section the transgressive interval and the starved basinward portion of transgressive and highstand systems tracts within the regressive interval also may have source rock potential carbonate complexes weathered basement shallow water sands and basin floor fans all have the potential to provide reservoirs potential traps include carbonate complexes basement hills and associated anticlines fault traps and coastal sand traps hydrocarbon indicators such as flat spots amplitude anomalies and gas chimneys with seeps occur at a number of locations

constraints on strike slip motion from seismic and gravity data along the vietnam margin offshore da nang implications for hydrocarbon prospectivity and opening of the east vietnam sea

remote sensing of damavand volcano iran using landsat imagery implications for the volcano dynamics abstract remote sensing techniques are applied to retrieve land surface temperature lst radiative heat flux rhf geothermal heat flux ghf and to map hydrothermal alteration zones around the damavand stratovolcano iran landsat enhanced thematic mapper plus etm day and nighttime images are used and merged to available geological data to identify thermal anomaly areas rhf is determined using the stefan boltzmann equation after preprocessing geometric radiometric and atmospheric correction and processing emissivity calculation and lst retrieval of thermal infrared bands in order to estimate ghf from daytime image solar radiation and albedo maps are generated to minimize these effects the ghf values are derived from nighttime image using the background subtraction technique using boolean operation only those pixels with the ghf values greater than 30 w m 2 obtained from daytime image and the ghf values greater than 10 w m 2 estimated from nighttime image are identified as thermal anomalies the geothermal areas are identified by combining the thermal anomaly map and other geological information thermal anomalies have close spatial correlation to faults thermal springs and high heat flow measurements from subsurface data and lithology some of the thermal anomalies and hydrothermal alteration areas also overlap active deformation areas this suggests role of heat and hydrothermal alteration on flank instability processes the thermal anomaly areas show an arc shaped pattern this pattern and the concentration of higher ghf areas in the eastern sector of the volcano are consistent with a release of fluids in a transition zone between a transpressional and a transtensional tectonic regime the combination of thermal infrared data with other geological information layers can be used to detect geothermal areas as well as to analyze the complex relationships among geothermal activity active tectonics and gravity instability processes on volcanoes

crustal stretching style variations in the northern margin of the south china sea linking deep seismic profiles with regional scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution here we map upper and lower crustal thicknesses of the northern south china sea scs margin in order to investigate the occurrence of depth dependent crustal extension from the proximal to the distal margin by comparing upper and lower crustal stretching factors we find that the northern margin of the scs is segmented in three parts 1 sedimentary basins where upper crust is stretched more than lower crust 2 distal margin where lower crust is stretched more than upper crust 3 mostly proximal margin regions where the two layers have similar stretching factors our results suggest that sedimentary basins and distal margin prominently feature depth dependent extension however accommodated by different processes while differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow we suggest the distal margin to be affected by a combination of mantle flow induced lower crustal shearing and sequential fault activity during crustal hyper extension

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

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

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

paleomagnetism of borneo abstract the paleomagnetism of borneo remains controversial although the preponderance of results both from the island itself and from the surrounding regions suggest that counterclockwise ccw rotation has taken place ccw rotations are seen in minor intrusions in sarawak sabah and kalimantan which increase systematically with the age of the intrusion to a maximum value of 51 8 3 7 the rotation can be no older than 25 ma which is the age of the intrusion showing the maximum rotation the rotation appears to have neared completion by 10 ma similar ccw rotations are seen in sites from peninsular malaysia through borneo to sulawesi the celebes sea and palawan in the philippines but the ages of these rotations are for the most part unknown in mesozoic rocks in kalimantan and sarawak a stronger declination rotation of nearly 90 ccw is recorded at seven sites including sites which pass fold and reversal tests this strong rotation is no older than youngest cretaceous and although seen over a wide region in borneo it is not seen in peninsular malaysia nor in the celebes sea or palawan where only the weaker ccw rotation is seen the widespread occurrence of this strong rotation in western borneo suggests that it is essentially a rigid plate or microplate rotation and not a series of local rotations caused by distributed shear in limited deformation zones the rotation of borneo appears to be a consequence of convergence between the australian and eurasian plates which is accommodated by subduction along the northwest margin of borneo

cenozoic plate reconstruction of the south china sea region abstract reconstructions of the south china sea region at 60 ma 40 ma 30 ma 20 ma 10 ma and 5 ma are presented we have attempted to place the south china sea basin in a regional tectonic framework the tectonic evolution of the major blocks surrounding the south china sea were analyzed as well as the relative motions of the indian and australian plates we have tried to correct the tectonic models available in this region a 3 d graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self consistency when the model conflicted with previous interpretations the input data were evaluated for alternative explanations at least two and possibly three stages of extension can be recognized in this region the earliest one active in the late cretaceous to eocene involved nw se extension the second one active from the late eocene to early miocene involved north south extension the third stage of extension which probably trended nw se can be dated as post oligocene the first extensional event produced the ne sw trending proto south china sea and a series of sedimentary basins along the south china margin following the southeastward extrusion of indochina the proto south china sea was mostly consumed at the palawan trough renewed north south extension in the south china continental margin started the present day south china sea spreading in the oligocene the southeastward extrusion of indochina blocked by sundaland resulted in the nw se trending opening of the south china sea basin in the early miocene collision of the north palawan microcontinental block with the west philippines block stopped the opening of the south china sea at the end of early miocene spreading activity switched to the sulu sea basin in the middle miocene but collision between the sulu ridge and the west philippines at mindanao halted the opening of the sulu sea at the end of the middle miocene in the late miocene greater india continued its northward path and seems to have ripped open the andaman sea in the pliocene subduction along the northern manila trench placed the north luzon arc on a collision path with the east asia continental margin at taiwan our reconstructions along with detailed geological and geophysical information may be used as a predictive tool for basin evolution models and block interactions in this region the development of the south china sea basin the gulf of thailand the malay basin and the central thailand basins are the result of collision induced extensional forces the sulu celebes and sumatra basins were formed as a consequence of prolonged subduction the opening of the pearl river mouth west natuna south china sea sulu and possibly celebes basins were terminated by various plate collisions during the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution

evidence of multiphase deformation in the rajang crocker range northern borneo from landsat imagery interpretation geodynamic implications comment 1 abstract landsat imagery structural analysis and nannoplankton dating of the rajang crocker belt in northern borneo defines the geometry style and timing of the development of various tectonostratigraphic units these data are integrated with a review of the formations of the area in order to to emphasize the palaeogeographic environments of the units in sarawak the trends are essentially e w with a first event being characterized by strong deformation and schistosity which affects upper cretaceous lower eocene terrigeneous units prior to the deposition of the middle upper eocene a second event is marked by the northward thrusting of eocene rocks over the oligocene prior to the deposition of the middle miocene succession in the crocker belt of sabah two oblique generations of structures can be observed these deformations occurred prior to the deposition of the upper middle miocene tight or even reverse folds with n s trending axes are deformed by large folds with associated thrusts the axes of these last structures trend n s in the brunei area n60e in northern sabah and bend towards n130e in the sandakan area this complex pattern has been affected by late n60e trending normal faults in central sabah

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

extension across the laptev sea continental rifts constrained by gravity modeling the laptev shelf is the area where the gakkel ridge an active oceanic spreading axis approaches a continental edge causing a specific structural style dominated by extensive rift structures from the latest cretaceous to the pliocene extension exerted on the laptev shelf created there several deep subsided rifts and high standing basement blocks to understand syn rift basin geometries and sediment supply relationships across the laptev shelf accurate extension estimates are essential therefore we used 2 d gravity modeling and 3 d gravity inversion to constrain the amount of crustal stretching across the north america eurasia plate boundary in the laptev shelf the latest cretaceous cenozoic extension in that area is partitioned among two rift zones the laptev rift system and the new siberian rift these rifts were both overprinted on the eurasian margin that had been stretched by 190 250 km before the late cretaceous while the laptev rift system connected to the gakkel ridge reveals increasing extension toward the shelf edge 190 380 km the new siberian rift is characterized by approximately uniform stretching along strike 110 125 km the architecture of the laptev rift system shows that the finite extension of about 500 km is sufficient to entirely eliminate crystalline continental crust in the most stretched rift segment continental mantle is exhumed at the base of the late mesozoic basement the example of the laptev rift system shows that extension driven by divergent plate movement is a sufficient cause to produce almost complete continental breakup without an increased heat input from the asthenospheric mantle

mapping crustal thickness using marine gravity data methods and uncertainties crustal thickness is a critical parameter for understanding the processes of continental rifting and breakup and the evolution of petroleum systems within passive margins however direct measurements of crustal thickness are sparse and expensive highlighting the need for methodologies using gravity anomaly data jointly with other geophysical data to estimate crustal thickness we evaluated alternative gravity inversion methodologies to map crustal thickness variations at rifted continental margins and adjacent oceanic basins and we tested our methodology in the south china sea scs different strategies were investigated to estimate and remove the gravity effect of density variations of sediments and the temperature and pressure variations of the lithospheric mantle from the observed free air gravity anomaly data sediment density was calculated using a relationship between sediment thickness porosity and density we found that this method is essential for crustal thickness inversion in the presence of a thick sedimentary cover by comparing the moho depths obtained from gravity inversion and seismic interpretation in the yinggehai basin where sediments are up to 13 km thick the inversion accuracy depended on the parameters of the exponential equation between porosity and the buried depth we modeled the lithospheric mantle temperature field based on oceanic crustal age continental crustal stretching factors and other boundary conditions we tested three different methods to calculate the thermal expansion coefficient which is either held constant or is a linear polynomial function of temperature for applying a thermal correction and found that the inversion results were relatively insensitive to alternative methods we compared inversion results with two recent deep seismic profiles that image the rifted continental edge at the northern margin of the scs and the continental liyue bank reed bank at the southern margin and we found that the inversion accuracy was improved considerably by removing sediment thermal and pressure gravity effects

large river offsets and plio quaternary dextral slip rate on the red river fault yunnan china using multispectral spot images and 1 100 000 topographic data we present an improved map of the active red river fault zone between midu yunnan china and hanoi vietnam the fault zone is composed of parallel strands one of which the yuanjiang fault was previously undetected there also appears to be a component of extension all along the fault zone such extension increases toward the se from yunnan to the south china sea coast and the vector describing the motion of south china relative to indochina points within the n45 135 e quadrant we attempt to assess the plio quaternary dextral slip rate on the red river fault rrf by restoring large river offsets and searching for the largest plausible one across much of yunnan the fault is perpendicular to local catchments that drain into the red river from precise mapping of the river courses on spot satellite images and on 1 100 000 topographic maps numerous multiple offsets along the fault can be detected and reconstructed the lack of correlation between the apparent offsets and the lengths of the rivers upstream from the fault suggests either that the drainage system was in large part established prior to the onset of dextral slip along the fault or that frequent captures have occurred we thus try to find the best fit between series of river channels upstream and downstream from the fault by progressively restoring the dextral displacement in increments of 500 m up to an offset of 50 km for each increment we measure the misfits root mean squares rms between the upstream and downstream channels the best fit and smallest rms are obtained for an offset of 25 0 5 km that we interpret to represent the clearest large right lateral displacement recorded in the geomorphology along the active red river fault since dextral motion is likely to have started around 5 myr the most probable average plio quaternary slip rate on the fault is of order of 5 mm yr we attribute the apparent lack of seismic activity on a large stretch of the fault to millennial recurrence times between great earthquakes our study shows that relatively small drainage systems can keep a good record of fairly large cumulative fault offsets

reappraisal of the jianchuan cenozoic basin stratigraphy and its implications on the se tibetan plateau evolution abstract we present a new stratigraphy of the jianchuan basin one of the largest cenozoic sedimentary basins in southeastern tibet this basin was regarded as recording sedimentation from the eocene up to the pliocene and as such has been the focus of several studies aiming at constraining the environmental tectonic and topographic evolution of the area within the shuanghe and jianchuan formations thirteen new zircon u pb ages and one biotite 40 ar 39 ar age of interbedded and cross cutting ultrapotassic magmatic rocks show that a brief magmatic event occurred from 35 7 to 34 5 ma 35 2 0 4 ma on average the uppermost formation jianchuan fm supposedly pliocene in age is related to this magmatic event and is 35 4 0 8 ma old all sedimentary formations are thus eocene in age with neither oligocene nor miocene sediments the coal bearing shuanghe formation yields a fossil of a large amynodontid typical of the upper eocene ergilian interval 37 2 to 33 9 ma sedimentation of the shuanghe formation took place in a short time interval at 35 9 0 9 ma after a large scale drainage reorganization that induced the abandonment of a large braided river system this reorganization was possibly linked with the initiation of the left lateral ailao shan red river fault and or to widespread magmatism in the jianchuan basin previous high paleoaltitude estimates for the jianchuan basin are thoroughly re evaluated and yield a value of 1200 1200 m a s l for the upper eocene

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

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

intracrustal detachment within zones of continental deformation geologic mapping of active to recently active geologic structures in panamint valley western united states and in the haiyuan region and northern tibetan plateau china suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres detachment occurs similarly in predominantly extensional panamint valley and in predominantly compressional china environments it involves structures with displacements of more than 10 km and displacement rates of more than 3 mm yr perhaps more than 10 mm yr the steeply dipping strike slip faults present in all three areas hunter mountain fault haiyuan fault and altyn tagh fault zone terminate in zones of extension or compression and geometric relations indicate that all structures including strike slip faults are thin skinned and restricted to the upper crust in panamint valley and in the haiyuan region deformation within these systems can be reconstructed in three dimensions displacement on the strike slip faults is absorbed by extension or compression occurring at the termination of the faults so strike slip displacement is roughly equal to and in the same direction as shortening or extension we propose that left slip on the altyn tagh fault zone in northern tibet is similarly absorbed by shortening southeast of the fault zone within the qaidam basin and the nan shan

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

origin of marginal basins of the nw pacific and their plate tectonic reconstructions abstract geometry of basins can indicate their tectonic origin whether they are small or large the basins of bohai gulf south china sea east china sea japan sea andaman sea okhotsk sea and bering sea have typical geometry of dextral pull apart the java makassar celebes and sulu seas basins together with grabens in borneo also comprise a local dextral transform margin type basin system similar to the central and southern parts of the shanxi basin in geometry the overall configuration of the philippine sea resembles a typical sinistral transpressional pop up structure these marginal basins except the philippine sea basin generally have similar or compatible rift history in the cenozoic but there do be some differences in the rifting history between major basins or their sub basins due to local differences in tectonic settings rifting kinematics of each of these marginal basins can be explained by dextral pull apart or transtension these marginal basins except the philippine sea basin constitute a gigantic linked dextral pull apart basin system formation of the gigantic linked dextral pull apart basin system in the nw pacific is due to nne to ene ward motion of east eurasia this mainly was a response to the indo asia collision which started about 50 ma ago the displacement of east eurasia can be estimated using three aspects 1 the magnitude of pull apart of the dextral pull apart basin system 2 paleomagnetic data from eastern eurasia and the region around the arctic and 3 the shortening deficits in the large tibetan plateau all the three aspects indicate that there was a large amount 1000 to 1200 km of northward motion of the south china block and compatible movements of other blocks in eastern eurasia during the rifting period of the basin system such a large amount of motion of the eastern eurasia region contradicts any traditional rigid plate tectonic reconstruction but agrees with the more recent concepts of non rigidity of both continental and oceanic lithosphere over geological times based on these three estimates the method developed for restoration of diffuse deformation of the eurasian plate and the region around the arctic and the related kinematics of the marginal basins we present plate tectonic reconstructions of these marginal basins in global plate tectonic settings at the four key times 50 35 15 and 5 ma the plate tectonic reconstructions show that the first order rift stage and post rift stage of the marginal basins are correlated with the first order slow uplift stage and the rapid uplift stage of the tibetan plateau respectively the proto philippine sea basin was trapped as a sinistral transpressional pop up structure at a position that was 20 south of its present position at about 50 ma ago or earlier while the japan arc migrated eastward during the rifting period of the japan sea basin the shikoku basin opened and the parece vela basin widened

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

perspectives on the geoarchaeology of the lower mississippi valley abstract the impact of harold n fisk s work on the archaeology and geoarchaeology of the lower mississippi valley lmv has been monumental as a result of his landmark publications on the geology of the alluvial valley of the mississippi river our comprehension of the interplay between geological geomorphic and human actions is relatively well developed however geologists and archaeologists still need to work together more closely to appreciate and understand the contributions each field has to offer examination of the interplay between geologists and archaeologists in the realm of dating and landscape evolution provides the basis for an investigation of the state of geoarchaeology in the lmv today integration of research demands an appreciation of scale which must be approached from an historical perspective humans have both in the past and the present impacted the natural environment of the mississippi river and its floodplain only when this fact is fully appreciated by archaeologists and geologists alike will it be possible to forge a new synthesis of the relationship between the dynamic alluvial valley and its human occupants

the na duong basin north vietnam a key for understanding paleogene basin evolution in relation to the left lateral cao bang tien yen fault abstract the cao bang tien yen fault northern vietnam is subparallel to the red river fault zone the fault controlled cao bang that khe lang son and na duong basins along the cao bang tien yen fault are filled with thick series of terrestrial deposits the investigations conducted in the present study focused on the sedimentary infill of the na duong basin sedimentological observations were made from four geological sites in this basin including an open air coalmine and samples collected for standard palynological petrographical and geochemical analysis seven lithofacies were recognized and their respective depositional mechanisms were interpreted sedimentation in the na duong basin was initially dominated by fluvial and peat forming processes na duong formation followed by lacustrine deposition rinh chua formation these formations were deposited in the early oligocene under a warm temperate to subtropical climate the sedimentary infill of the basin is petrographically mature and was deposited in a relatively long lasting fluvial lacustrine sedimentary system the na duong basin was compared to the cao bang basin the na duong basin is filled with mature sandy and silty deposits of fluvial and lacustrine origin while the cao bang basin is filled with a wide variety of immature or submature clastic deposits from coarse grained alluvial fan through sandy fluvial to fine organic rich lacustrine deposits paleogene basins along the cao bang tien yen fault zone are interpreted as belonging to an associated extensive terrestrial drainage system this system is proposed as a main oligocene feeder system for the beibuwan basin south china sea

role of the red river shear zone yunnan and vietnam in the continental extrusion of se asia the 1000 km long nw se striking left lateral ailao shan red river shear zone runs from the southeastern corner of tibet to the gulf of tonkin and the south china sea it has been used as the prime example of a lithospheric scale strike slip fault that has accommodated between 500 and 1000 km of southeastwards extrusion of indo china away from the indian plate indentor central to the model of continental extrusion is that such faults cut through the entire lithosphere that shear heating resulted in high grade metamorphism and local anatexis and that the ages of sheared granites along the fault also date the timing of strike slip shearing however structural data from the red river shear zone clearly show that vertical strike slip faulting post dated metamorphism and granite emplacement most granites along the shear zone are mantle related granodiorites or within plate alkali granites formed prior to shearing along the red river shear zone left lateral kinematic indicators are ubiquitous within the red river mylonites but they are always lower temperature fabrics formed after peak sillimanite metamorphism and after granite crystallization it is suggested that left lateral strike slip shearing along the red river shear zone started after 21 ma not at 35 ma as previously thought and the fault was purely a crustal structure none of the geological features used to propose the 500 1000 km offsets are robust and the total finite offset remains unknown

symmetry of the south china sea conjugate margins in a rifting drifting and collision context abstract the symmetry of conjugate rifted margins is a first order observable feature reflecting the geodynamic processes acting during and after continental rifting the symmetry of the south china sea scs rifted margins can be deduced from comprehensive geophysical datasets on a continental margin scale here we combine three key approaches 1 lateral fault distributions are delineated according to free air gravity anomalies 2 crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles and 3 total extension of conjugate margins is estimated according to margin restorations and tectonic settings we infer a predominantly symmetric rifting style caused by pure shear extension with only narrow domains of asymmetric deformation in continent ocean transition cot regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup however our analysis also suggests that this symmetry has been modified by post rift geodynamic processes southward lower crustal flow which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting proto scs plate during seafloor spreading shifted the crustal stretching styles from symmetric to asymmetric the collision between the southern margin and borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin this event had a large impact on the se margin but a small impact on the sw margin we conclude that 1 for the se and ne margins the crustal stretching styles shifted from asymmetric to approximately symmetric and the total extension shifted from symmetric to asymmetric 2 for the sw and nw margins the crustal stretching and total extension remained asymmetric and symmetric respectively

three dimensional gravity inversion for moho depth at rifted continental margins incorporating a lithosphere thermal gravity anomaly correction summary this paper describes a method for determining moho depth lithosphere thinning factor 1 1 and the location of the ocean continent transition at rifted continental margins using 3 d gravity inversion which includes a correction for the large negative lithosphere thermal gravity anomaly within continental margin lithosphere the lateral density changes caused by the elevated geotherm in thinned continental margin and adjacent ocean basin lithosphere produce a significant lithosphere thermal gravity anomaly which may be in excess of 100 mgal and for which a correction must be made in order to determine moho depth accurately from gravity inversion we describe a method of iteratively calculating the lithosphere thermal gravity anomaly using a lithosphere thermal model to give the present day temperature field from which we calculate the lithosphere thermal density and gravity anomalies for continental margin lithosphere the lithosphere thermal perturbation is calculated from the lithosphere thinning factor 1 1 obtained from crustal thinning determined by gravity inversion and breakup age for thermal re equilibration time for oceanic lithosphere the lithosphere thermal model used to predict the lithosphere thermal gravity anomaly may be conditioned using ocean isochrons from plate reconstruction models to provide the age and location of oceanic lithosphere a correction is made for crustal melt addition due to decompression melting during continental breakup and seafloor spreading we investigate the sensitivity of the lithosphere thermal gravity anomaly and the predicted moho depth from gravity inversion at continental rifted margins to the methods used to calculate and condition the lithosphere thermal model using both synthetic models and examples from the north atlantic

structure and shearing conditions in the day nui con voi massif implications for the evolution of the red river shear zone in northern vietnam 1 the day nui con voi massif bears a record of the red river shear zone rrsz activity in north vietnam it forms a large scale antiformal core complex type structure bounded by the song hong and song chay faults the kinematics of both faults are identical and reflect transtensional shear initiated under upper amphibolite facies conditions and propagated into greenschist facies microfabric analysis establishes that both extensional and strike slip shearing initiated between 700 and 500 c the rrsz evolved from a single subvertical fault which due to strike perpendicular extension underwent progressive dilation the created space was intruded by already metamorphosed and deformed ductile middle crust in the form of a gneissic dome both strike slip and extensional shearing were accommodated in the limbs of the antiform while its core was uplifted from midcrustal level bearing only a minor record of sinistral shear

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

displacement along the red river fault constrained by extension estimates and plate reconstructions significant e w extension and or compression must have been generated by displacements along the red river fault rrf since its curvature does not match a small circle centered at the euler pole for the indochina south china plate pair the amount of extension perpendicular to the rrf offshore vietnam depends on the magnitude of left lateral displacement along the rrf in general the larger the left lateral displacement along the fault the smaller the amount of e w extension all purely strike slip models of the opening of the south china sea that assume large displacements 250 km along the rrf encounter major problems because they imply little extension or even considerable shortening offshore east vietnam this is inconsistent with the presence of large elongated basins offshore vietnam using a plate tectonic model we compare continental extension values implied by different magnitudes of displacement along the rrf with crustal stretching estimates derived from 2 d profiles modeled from gravity data we utilize 2 d gravity forward models to restore the extended continental margin crust to its original position prior to extension we find that substantial amounts of extension for offshore vietnam can only be modeled assuming moderate displacements along the rrf compatible with the presence of a southward subducting proto south china sea the total amount of ene wsw extension offshore northern vietnam constrained by our 2 d gravity profiles and gravity inversion increases southward from 36 to 89 km along the yinggehai basin these values of ene wsw extension are consistent with 250 km of left lateral displacement along the rrf

oligo miocene midcrustal subhorizontal shear zone in indochina new structural observations of oligo miocene deformation in north vietnam along the red river shear zone suggest that left lateral strike slip shear was restricted to the upper and middle crust above a horizontal shear zone left lateral shear deformation is associated with low pressure low temperature parageneses high temperature deformation is restricted to zones where the foliation has a low dip in the core of the dai nui con voi antiformal dome these observations complete those made earlier in the bu khang extensional dome farther south above the horizontal shear zone left lateral transpression was active during the first stage and changed to transtension some 33 myr ago purely extensional metamorphic domes bu khang or transtensional domes dai nui con voi were exhumed during this younger stage our observations plead for caution when interpreting strike slip structures at lithospheric scale

paleomagnetic constraints on the mesozoic cenozoic paleolatitudinal and rotational history of indochina and south china review and updated kinematic reconstruction abstract paleomagnetic data have long been used to hypothesize that the cenozoic extrusion of the indochina block along the left lateral ailao shan red river fault as a result of the india asia collision may have been associated with a major southward paleolatitude shift of as much as 10 15 and a vertical axis rotation of as much as 25 40 however although numerous paleomagnetic studies have been conducted in the southeast margin of the tibetan plateau and in the indochina region during the last few decades the detailed rotation as well as the latitudinal displacement of the indochina block remain controversial because of apparently contradicting paleomagnetic results geological constraints also yield contrasting estimates on the amount of displacement along different segment of the ailao shan red river fault 700 200 km in the northwest but only 250 km in the southeast in this paper the available paleomagnetic data from the southeast margin of the tibetan plateau and indochina as well as the south china block from jurassic and younger rocks are compiled and critically reviewed using the new paleomagnetic toolkit on paleomagnetism org our results show that 1 the south china block has declinations that reveal no significant rotations relative to eurasia since latest jurassic inclinations are consistently shallower than expected which is likely the result of inclination shallowing in sedimentary rocks 2 there is no paleomagnetically resolvable southward motion of the indochina block with respect to eurasia based on the paleomagnetic data paleomagnetic inclinations are in fact lower than expected probably due to inclination shallowing in sediments 3 paleomagnetic declinations reveal large more or less coherently rotating blocks in the northern indochina domain and the se tibetan margin that rotated up to 70 clockwise much more than the 10 15 rotation of the stable se part of the indochina block these blocks are bounded by fold thrust belts and strike slip faults which we interpret to have accommodated these block rotations during the cenozoic we designed a new tool on the online open access portal paleomagnetism org that allows testing whether euler rotations in a kinematic reconstruction fulfill paleomagnetic data using this tool we built a first order kinematic reconstruction of rotational deformation of northwest indochina in cenozoic we show that the northwestern part of indochina extruded 350 km more along the ailao shan red river fault than the southeastern part accommodated by internal northwest indochina rotation and deformation estimates of 250 km of extrusion of the southeastern part of the indochina then predicts 600 km of left lateral motion along the northwestern part of the ailao shan red river fault which reconciles the small and large estimates that prevail in the literature of extrusion of indochina from the tibetan realm during the cenozoic india asia collision

sinkholes subsidence and subrosion on the eastern shore of the dead sea as revealed by a close range photogrammetric survey abstract ground subsidence and sinkhole collapse are phenomena affecting regions of karst geology worldwide the rapid development of such phenomena around the dead sea in the last four decades poses a major geological hazard to the local population agriculture and industry nonetheless many aspects of this hazard are still incompletely described and understood especially on the eastern dead sea shore in this work we present a first low altitude our analysis reveals a kilometer scale sinuous depression bound partly by flexure and partly by non tectonic faults the estimated minimum volume loss of this subsided zone is 1 83 106 m3 with an average subsidence rate of 0 21 m yr 1 over the last 25 years sinkholes in the surveyed area are localized mainly within this depression the sinkholes are commonly elliptically shaped mean eccentricity 1 31 and clustered nearest neighbor ratio 0 69 their morphologies and orientations depend on the type of sediment they form in in mud sinkholes have a low depth to diameter ratio 0 14 and a long axis azimuth of nne ne in alluvium sinkholes have a higher ratio 0 4 and are orientated nnw n from field work we identify actively evolving artesian springs and channelized sediment laden groundwater flows that appear locally in the main depression consequently subrosion i e subsurface mechanical erosion is identified as a key physical process in addition to dissolution behind the subsidence and sinkhole hazard furthermore satellite image analysis links the development of the sinuous depression and sinkhole formation at ghor al haditha to preferential groundwater flow paths along ancient and current wadi riverbeds