post rift tectonic history of the songliao basin ne china cooling events and post rift unconformities driven by orogenic pulses from plate boundaries

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

a deforming plate tectonic model of the south china block since the jurassic abstract the south china block has experienced multiple phases of tectonic deformation since the middle jurassic understanding this deformation history helps reveal the driving mechanisms responsible and sheds light on the associated magmatism and mineralization here we construct deformable plate tectonic reconstructions for the south china block from 170 ma to the present using gplates the deformation starts with a nw se oriented shortening phase from 170 to 136 ma subsequently south china experienced two episodes of extension in the cretaceous during 136 118 ma and 100 80 ma respectively the cenozoic extension occurred mostly along the southeast continental margin including the east china sea shelf basin and rift basins in the northern south china sea margin and the taiwan margin segment the rifting was initiated nearly simultaneously along the continental margin at 65 ma and ceased at 34 30 ma the northern portion of the okinawa trough started rifting at 15 ma while the southern portion rifted in the last few million years the luzon volcanic arc thrusting onto the southeasternmost south china block since 6 5 ma caused the still active taiwan orogeny the predicted accumulated deformation at present day is characterized by overall shortening onshore with contraction factors mostly between 0 8 and 1 and extension offshore with stretching factors generally between 1 and 2 the central china orogen and taiwan orogen experienced more intense shortening relative to the interior south china by factors down to 0 6 the okinawa trough experienced intense stretching by factors up to 2 5 in its central part the intraplate deformation in the south china block is closely related to the subduction of the izanagi and pacific plates the jurassic and earliest cretaceous shortening was likely induced by trench advance and the extension during the cretaceous and the cenozoic was mostly driven by subduction retreat

throughgoing crustal faults along the northern margin of the south china sea and their role in crustal extension a study of the rifled northern margin of the south china sea based on new single ship and two ship multichannel seismic data has revealed the presence of highly reflective steeply dipping normal faults which cut through the entire crust these faults with dips of 25 40 are associated with localized crustal thinning of 5 15 km and represent horizontal extension of the order of tens of kilometers a range of 5 20 km of horizontal extension has been measured along individual faults although the relative amount of horizontal extension taken up by these faults is modest compared to the total extension across the margin only about 15 or less the amount of localized crustal thinning which takes place along these fault surfaces is quite significant at one fault location the crustal thickness is reduced by 40 although the faults described have been recognized at three separate locations along the margin their trends appear to differ at each in two examples the faults are oblique to the inferred general north south extension direction of the margin this characteristic taken with the fact that some of the crustal faults also appear to serve as abrupt boundaries between broad regions of differing crustal thickness and reflectivity of the lower crust suggests that at least some of these faults were present prior to rifting such faults are postulated to have been former thrust faults perhaps associated with a triassic suture zone and or cretaceous subduction margin which have been reactivated as normal faults during subsequent rifting alternatively some of the throughgoing faults may represent crustal detachment surfaces that first formed as the result of a simple shear response to crustal extension

miocene to present activity along the red river fault china in the context of continental extrusion upper crustal rotation and lower crustal flow detailed mapping of field relationships along the red river fault reveals information about the distribution and magnitude of slip along the fault about its interactions with other regional fault systems and the relationship between river incision and growth of the eastern margin of the tibetan plateau the red river fault is complex consisting of up to four strands and is dominated by right lateral strike slip displacement evidence for an extensional component of displacement is strongest along the northern part of the fault and decreases to the southeast to zero southeast of a major bend in the fault results of this study indicate dextral displacement on the red river fault is probably at least 40 km 15 16 km of which predates incision of the red river in pliocene time or later and probably also predates plateau growth and development of other regional fault systems long term average slip rate on the red river fault is a minimum of 5 mm yr however regional active tectonics are characterized by rotation of the upper crust around the eastern himalayan syntaxis bounded to the east by the xianshuihe xiaojiang fault system which deflects but does not cut the red river fault the distributed nature of the xianshuihe xiaojiang fault system as it approaches the red river fault is important for accommodating shearing across the strong crustal anisotropy formed by the red river fault and ailao shan shear zone the red river fault appears to terminate in the extending dali fault system in northwest yunnan pliocene surface uplift river incision and rotation around the eastern himalayan syntaxis are inconsistent with the pre pliocene displacement on the red river fault and lateral extrusion along the ailao shan shear zone advocated by the extrusion model this suggests a significant change in crustal conditions on the southeast margin of the tibetan plateau in pliocene time possibly the result of lower crustal flow

kinematics of cenozoic extension on the south china sea continental margin and its implications for the tectonic evolution of the region abstract in the northern south china sea several large sedimentary basins developed during the cenozoic characterized by episodic rifting clockwise rotation of the rifts an eastward aging breakup unconformity and intensifying crustal extension to the east these features may be summarized by a scissors model the maximum rifting occurred north of the maximum thermal subsidence which was in turn north of the seafloor opening in contrast the nansha microcontinent south of the south china sea basin was dominated by compressional deformation during the cenozoic extension was of subordinate significance and manifested mainly by block faulting and tilting in the late early oligocene maximum tilting occurred in the southern part of the nansha microcontinent at distance from the deep sea basin of the south china sea the asymmetric development of extensional structures around the south china sea basin may be explained by the simple shear model proposed by wernicke 1981 the tectonic development of the south china sea was the consequence of various interactions of three major plates and may be summarized into three stages with dominating influences of respectively the retreat of the west pacific subduction zone in the late cretaceous the hard collision and impinging of india to tibet since the late eocene and the fast northward subduction of the indian ocean australian plate since the late early miocene

petrogenesis of andalusite kyanite sillimanite veins and host rocks sanandaj sirjan metamorphic belt hamadan iran quartz rich veins in metapelitic schists of the sanandaj sirjan belt hamadan region iran commonly contain two al2sio5 polymorphs and more rarely three coexisting al2sio5 polymorphs in most andalusite and sillimanite schists the types of polymorphs in veins correlate with al2sio5 polymorph s in the host rocks although vein polymorphs are texturally and compositionally distinct from those in adjacent host rocks e g vein andalusite is enriched in fe2o3 relative to host rock andalusite low grade rocks contain andalusite quartz veins medium grade rocks contain andalusite sillim anite quartz plagioclase veins and high grade rocks contain sillimanite quartz plagioclase veins leucosomes although most andalusite and sillimanite bearing veins occur in host rocks that also contain al2sio5 kyanite quartz veins crosscut rocks that lack al2sio5 e g staurolite schist granite a quartz vein containing andalusite kyanite sillimanite staurolite muscovite occurs in andalusite sillimanite host rocks textural relationships in this vein indicate the crystallization sequence andalusite to kyanite to sillimanite this crystallization sequence conflicts with the observation that kyanite quartz veins post date andalusite sillimanite veins and at least one intrusive phase of a granite that produced a low pressure high temperature contact aureole these relationships imply a sequence of andalusite to sillimanite to kyanite varying crystallization sequences for rocks in a largely coherent metamorphic belt can be explained by p t paths of different rocks passing near slightly above slightly below the al2sio5 triple point and by overprinting of multiple metamorphic events in a terrane that evolved from a continental arc to a collisional orogen

a new model for the indochina and south china collision during the late permian to the middle triassic article i nfo a comparative analysis of indochina and south china during the early paleozoic indicates the former may be extended to include north vietnam part of the qinzhou tectonic zone and southern hainan island these three regions were traditionally regarded as parts of south china separated from indochina by the song ma suture in central north vietnam a new suture called the dian qiong suture is proposed here approximately along the southern margin of the present nanpanjiang basin this suture is linked to its eastern counterpart in hainan island through a nne trending dextral transform fault zone along the eastern margin of the nanpanjiang basin the conventional song ma suture originally constitutes its western extension and was translated to its present location by sinistral displacement along the red river fault zone during the tertiary upper paleozoic deep water turbidites and associated mid oceanic ridge basalts along the suture in the nanpanjiang basin illustrate a coeval ocean between indochina and south china the ocean was consumed by south directed subduction beneath indochina during the late permian to the middle triassic this suture zone was finally re shaped by the indentation between the active margin of indochina and the irregular passive continental margin of south china during the late triassic as well as displacement along the red river fault zone during the cenozoic

a simple model of fjord and coastal circulation interaction abstract the dynamical interaction of a narrow fjord with a wind driven coastal regime is investigated using a linear two layer numerical model the coriolis acceleration is important in the coastal regime but assumed to he unimportant in the fjord dynamical because v 0 for a wide variety of wind conditions bottom topography and model parameters the wind forced coastal circulation with its geostrophic alongshore currants has a strong effect on the circulation within the fjord these geostrophic currents control the free surface and pycnocline displacement at the fjord mouth thereby strongly affecting fjord circulation this mechanism is an alternative to the classical idea of hydraulic control at the mouth by sills or constrictions model simulators also show that the free surface slope is a baroclinic effect and that alongshore and across shore winds affect the fjord differently alongshore winds produce flooding while up and down fjord winds simply sat up the surface we find that offshore win

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

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

satellite observations of tidal upwelling and mixing in the st lawrence estuary satellite thermal images noaa 9 of the st lawrence estuary are used to confirm the existence of a persistent cold spot due to tidal upwelling at the head of the lower st lawrence estuary and to show that cold water may be found episodically up to 100 km downstream of the head this extended cold anomaly may exist in two spatial configurations one confined to near the south shore the other being centered over mid estuary we discuss the various physical agencies likely to contribute to the growth of this anomaly and conclude that wind internal tides and advection of cold water from the head region are the most significant

a mechanism governing the estuarine circulation in deep strongly stratified fjords the estuarine circulation in deep strongly stratified fjords is discussed it is argued that a two layer description of the stratification in the fjord is correct in very wide fjords wide compared to the width of the mouth and possibly also in narrow fjords with high runoff and or weak mixing a theory for the thickness and the salinity of the brackish layer in a wide fjord was earlier developed by the present author and published in swedish 1975 and it is presented here among other findings in that theory we may mention that the thickness of the brackish layer is primarily determined by the internal hydraulic control for high specific runoff runoff unit horizontal surface area of the fjord and weak mixing in the other extreme with low specific runoff and strong mixing the thickness of the brackish layer is found to be proportional to the monin obukhov length the circulation in not very wide fjords is also discussed it is found that recirculation in the brackish layer may be expected whereby a two layer description of the flow field breaks down at least locally a critical rayleigh number that seems to control the recirculation of brackish water within the fjord is found a theory for the density difference between the mouth and the head in the brackish layer in the fjord is developed from the critical rayleigh number condition it is found that this density difference normally is proportional to the density difference between the brackish water at the mouth and the underlying sea water provided that the river runoff is not too heavy and or the mixing is not too weak this prediction is confirmed by extensive measurements from the nordfjord

semidiurnal internal tides in a patagonian fjord abstract the fjords of central chilean patagonia 47 s receive fresh water from both precipitation and the baker river this buoyancy input generates a two layer hydrographic system characterized by strong salinity stratification 30 g kg 1 over a depth range of 7 15 m which favors baroclinic conditions in the fjord hourly current velocity profiles were collected with an acoustic doppler current profiler adcp moored at a depth of 40 m during march april 2009 and complemented by 11 ctd profiles and hourly sea level time series these data allowed the detection of semidiurnal internal tidal waves for the first time in this region wavelength and horizontal phase speeds were determined by the dynamical mode 1 for internal waves maximum wavelength was 52 km travelling at a horizontal phase speed of 1 16 m s 1 wavelet spectral and empirical orthogonal function eof analysis techniques applied to the echo anomaly signal and to the baroclinic velocity showed largest semidiurnal amplitudes near the pycnocline out of three modes obtained from the eof analysis two modes displayed a two or three layer flow structure with flow direction reversing at the pycnocline the semidiurnal internal waves were found as fluctuations near the pycnocline in sporadic packets correlated to high discharge pulses of the baker river r2 0 77 additionally internal froude number calculations at the mouth of the baker river indicated critical flow conditions which allowed for generation of internal waves at the plume front these waves are separated from the river plume after internal wave phase speeds surpassed frontal speeds this suggests that the internal waves were modulated by pulses in high river discharge rather than the interaction of barotropic tide with bathymetry a sill an implication of these internal waves would be to increase vertical mixing of nutrients toward the surface through shear instabilities which would favor primary production

numerical modeling of failed rifts in the northern south china sea margin implications for continental rifting and breakup abstract failed rifts record important information of continental extension and breakup process in the northern south china sea scs margin the tainan southern depression and the baiyun sag to the east are characterized with lower crust high velocity anomalies lchva and intracrust detachment faults whereas the xisha trough to the west develops on a larger scale with crust cutting normal faults and absence of lchva these contrasts indicate different rifting processes between the northeastern and northwestern scs 2d numerical modeling is performed to understand the formation mechanism of these failed rifts two types of mechanisms are proposed i syn rift competitive type and ii rift migration type with a half extension rate of 2 cm yr and 1 5 cm yr respectively in type i two rifts develop initially on the shoulders of the weak zone but they compete with each other during extension one rift becomes dominant to furnish the final breakup whereas the other one is abandoned the crust structure of this type fits the observations in the baiyun sag and the tainan southern depression however in type ii only one rift develops at the beginning the initial rifting center will migrate and the final continental breakup will occur at a place far from the initial rifting location in this type normal faults cut through whole crust and wide extensional margins will form such as observed in the xisha trough our results suggest that the depth dependent extension of the scs is strongly heterogeneous resulting primarily from varying extensional rates

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

reflection of the internal tide in upper loch linnhe a scottish fjord abstract results from an observational study of the internal tide of upper loch linnhe a fjord on the west coast of scotland are presented between november 1992 and june 1993 moorings containing current meters measuring velocity temperature and salinity were deployed at two sites in the loch observations of the horizontal velocities show the presence of an energetic first mode linear internal tide at the m 2 frequency with surface amplitudes of up to 0 57 m s 1 cf 0 03 m s 1 for the barotropic component independent evidence of the m 2 internal tide is provided by vertical velocities inferred from salinity and temperature variations in june 1993 an undulating ctd was used to study the horizontal propagation of the semi diurnal internal tide the results show that over the inner reaches of the loch the internal tide behaves as a standing wave with a large proportion of the internal tide energy being reflected at the landward end of the loch using the phase relationship between the velocity components from the mooring data it is demonstrated that there is a significant standing wave component present throughout the 7 month observational period closer to the sill the undulating ctd observations show the formation of an intense hydraulic jump on the flood tide suggesting the area immediately landward of the sill to be a region of complicated dynamics and high dissipation

complex accumulation and leakage of yc21 1 gas bearing structure in yanan sag qiongdongnan basin south china sea abstract yc21 1 is a gas bearing structure found within the yanan sag in the qiongdongnan basin south china sea while the structure bears many geological similarities to the nearby yc13 1 gas field it nevertheless does not contain commercially viable gas volumes the main reservoirs of the yc21 1 structure contain high overpressures which is greatly different from those of the yc13 1 structure the pressure coefficients from drillstem tests wireline formation tests and mud weights are above 2 1 based on well log analysis illite content and vitrinite reflectance data of mudstones in well yc21 1 2 combining with tectonic and sedimentation characteristics the timing and causes of overpressure generation are here interpreted the results indicate the existence of two overpressure segments in the yc21 1 structure the first overpressure segment resides mainly within the lower and the middle intervals of the yinggehai formation and is interpreted to have been mainly caused by clay diagenesis while disequilibrium compaction and hydrocarbon generation may also have contributed to overpressure generation the second overpressure segment comprising the sanya formation pressure transition zone and the lingshui and yacheng formations hard overpressure zone is interpreted to owe its presence to kerogen to gas cracking according to petrography homogenization temperature and salinity of fluid inclusions two stages of oil gas charge occurred within the main reservoirs on the basis of overpressure causes and oil gas charge history combining with restored tectonic evolution and fluid inclusion characteristics a complex accumulation and leakage process in the yc21 1 gas bearing structure has been interpreted collective evidence suggests that the first oil charge occurred in the middle miocene circa 16 3 11 2 ma small amount of oil generation and absence of caprocks led to the failure of oil accumulation rapid subsidence in the pliocene and quaternary gave rise to a sharp increase in geotemperature over a short period of time leading to prolific gas generation through pyrolysis and consequently overpressure within the main reservoirs the second overpressure segment during this period the second gas charge occurred in the pliocene and quaternary circa 4 5 0 4 ma the natural gas migrated in several phases consisting of free and water soluble phases in a high pressure environment large amounts of free gas are considered to have been consumed due to dissolution within formation water in highly pressured conditions water soluble gas could not accumulate in high point of structure when the pore fluid pressures in main reservoirs reached the fracture pressure of formation free gas could leak via opened fractures within cracked caprocks a repeated fracturing of caprocks may have consumed natural gas stored in formation water and have made water soluble gas unsaturated therefore the two factors including caprocks fracturing and dissolution of formation water are interpreted to be mainly responsible for the failure of natural gas accumulation in the yc21 1 structure

double diffusive layering and mixing in patagonian fjords abstract double diffusive layering was quantified for the first time in the chilean patagonian fjords region 41 5 56 s approximately 600 temperature and salinity profiles collected during 1995 2012 were used to study water masses quantify diffusive layering and compute the vertical diffusivity of heat development of diffusive layering or simply layering was favored by relatively fresh cold waters overlying salty warm waters fresh waters are frequently derived from glacial melting that influences the fjord either directly or through rivers salty waters are associated with modified subantarctic msaaw and subantarctic water saaw double diffusive convection occurred as layering in 40 of the year round data and as salt fingering in 5 m 2 s 1 diffusive layering events presented a meridional gradient with less layering within the 41 47 s northern region relative to the southern region between 47 and 56 s layering occupied on average 27 and 56 of the water column in the northern and southern regions respectively thermohaline staircases were detected with microprofile measurements in martinez and baker channels 48 s showing homogeneous layers 2 4 m thick below the pycnocline 10 40 m also in this area increased vertical mixing coincided with the increased layering events high values of thorpe scale l t 7 m dissipation rate of tke e 10 5 10 3 w kg 1 and diapycnal eddy diffusivity k 10 6 10 3 m 2 s 1 were associated with diffusive layering implications of these results are that diffusive layering should be taken into account together with other mixing processes such as shear instabilities and wind driven flows in biological and geochemical studies

baroclinic annular variability of internal motions in a patagonian fjord time series of horizontal velocities echo intensity wind velocity and atmospheric pressure were collected for 200 days in a patagonian fjord to explore pycnocline motions produced by the southern hemisphere s baroclinic annular mode bam the bam variability occurs between 20 and 30 days and is associated with fluctuations in atmospheric kinetic energy and in turbulent fluxes of heat spectra of horizontal velocities and normalized echo intensity in the fjord s water showed highest energy between 25 and 30 days this was explained by sustained westerly winds associated with extreme low pressure systems 900 hpa that had periodicity related to the bam wind forcing produced 40 cm s 1 along channel and cross channel currents in the surface layer which in turn created a wind induced setup toward the head of the fjord the setup was accompanied by a deepening of the pycnocline from 5 to 15 m depth with 25 to 30 day periodicity as derived from the normalized echo intensity the dominant empirical orthogonal function mode of the normalized echo intensity profiles explained 70 8 of the variance and also exhibited a 25 30 day periodicity further a wavelet and spectral analysis of 10 years of atmospheric pressure indicated peaks between 25 and 30 days each year indicating that the bam consistently influences weather patterns in chilean patagonia this is the first documented case of baroclinic annular variability in a specific region of the southern hemisphere and of its effects on fjord systems

4 d evolution of rift systems insights from scaled physical models the four dimensional 4 d evolution of brittle fault systems in orthogonal oblique and offset rift systems has been simulated by scaled sandbox models using dry cohesionless fine grained quartz sand extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model the results of these analog model studies are compared with natural examples of rift fault systems rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction segmentation of the rift margin increases with increase in obliquity of the rift axis resulting in a consequent increase in displacement on intrarift fault systems offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone along strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones high relief extension parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults the second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low relief oblique slip zone or grabens these typically are found in highly oblique rift systems 45 degrees and above right steps in offset rift models

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

double diffusive convection in this paper we present a rather personal view of the important developments in double diffusive convection a subject whose evolution has been the result of a close interaction between theoreticians laboratory experimenters and sea going oceano graphers more recently applications in astrophysics engineering and geology have become apparent in the final section we attempt to draw some general conclusions and suggest that further progress will again depend on a close collaboration between fluid dynamicists and other scientists

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

progressive localisation of strain during the evolution of a normal fault population abstract the evolution of a syn sedimentary normal fault population has been established from the analysis of a high quality 3d seismic reflection survey from the timor sea offshore nw australia growth of the fault population which initiated ca 6 ma ago occurred in three distinct but temporally overlapping stages the initial stage of fault population evolution was characterised by rapid growth of fault length in the first 1 2 ma of extension displacement rates of individual faults were established during this stage and were constant throughout subsequent fault growth the second stage involved amplification of fault displacements on existing fault traces with minimal fault propagation during the third stage shortening of the traces of active faults and high mortality rates for small faults resulted in a net decrease in fault trace length on successively younger horizons this stage was accompanied by a declining extension rate fault throw populations have constant slopes on each syn faulting horizon however an up sequence shallowing of the slope of length and geometric moment populations demonstrates a progressive concentration of strain onto fewer and larger faults through time if extension were to continue beyond the present value of 4 5 this strain localisation might culminate in the formation of a single active through going fault

structural evolution of a quartz sillimanite vein and nodule complex in a late to post tectonic leucogranite western adirondack highlands new york abstract quartz sillimanite veins and nodules within the carapace of a late to post tectonic leucogranite crosscut one another as well as calcsilicate schlieren these relationships document a fracture related and hydrothermal origin of the vein and nodule complex two dominant orientations n50e n20e are observed with the former being the oldest and most deformed both of these sets have undergone deformation including boudinage of veins to produce nodules zircon geochronology fixes the emplacement age of the leucogranite at 1035 1 3 8 ma and late crosscutting pegmatites at 1034 10 ma hence the vein nodule complex must fall within this interval late dikes of leucogranite truncate the complex and document the continued presence of magma during vein nodule formation anisotropy of magnetic susceptibility ams in the leucogranite carapace reveals an approximately horizontal flow direction within a plane striking n49e and dipping moderately to the northwest in this regime quartz sillimanite veins formed initially as tension fractures in subvertical nne orientations either as a result of high fluid pressures or rapid sinistral shear along the n50e contact progressive sinistral shear rotated the veins counterclockwise causing buckling followed by boudinage and rotation of fragments into near parallelism with the n50e contact strain was accommodated by slip between crystals and melt migration with an estimated melt fraction of at least 30 multiple episodes of fracturing and vein formation appear to have occurred final deformation of the carapace and the vein nodule complex is envisioned as a flattening against the contact perhaps as a result of pluton inflation melt was still present after this event as evidenced by post vein granite and pegmatite dikes commonly with sinistral shear along the dike margin

fault linkage patterns and their control on the formation of the petroleum systems of the erlian basin eastern china abstract fault linkage patterns in rift basins are very common while the process of fault linkage may be very short it changes sedimentation patterns before and after linkage and controls the development of half grabens the propagation and growth of boundary faults can be divided into a simple fault propagation pattern and a fault growth linkage pattern based on structural style sedimentation patterns and oil source correlations in the erlian basin three types of grabens and petroleum systems can be identified the abei graben is controlled by a single boundary fault and forms an independent petroleum system the saihantala graben is controlled by several linked faults which also has an independent petroleum system the wuliyasitai depression controlled by two boundary fault segments which results in two petroleum systems as not all half grabens develop one petroleum system they may therefore have two or more systems the relay ramps between fault segments before linkage are the locations of deposition of sands and conglomerates and consequently are the focus areas for stratigraphic lithologic trap exploration

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

sedimentary organic matter geochemistry of clayoquot sound vancouver island british columbia surface sediment samples from three interconnected fjords of clayoquot sound british columbia were density fractionated 1 6 g cm 3 to isolate discrete organic debris od from mineral associated organic matter mom total organic carbon oc values varied greatly ranging from 0 1 to 8 8 by weight with a general decreasing trend from fjord head to the continental shelf within the sediment terrestrial om was present either as vascular plant debris or soil mom down fjord the woody vascular plant material in the od fraction acquires nitrogen which is hypothesized to be due to the bacterial incorporation of nitrogen from the water terrestrial oc in the mom is incompletely replaced by marine oc within the fjords resulting in a 65 net loss of mom sediments deposited under oxic and intermittently anoxic water column conditions have organic carbon to surface area ratios oc sa ranging from 0 4 to 1 2 mg c m 2 similar to that of typical continental margin sediments given that temperate fjords contain an estimated 12 of the continental margin sediment deposited during the last 100 000 yr and that they bury at least a margin equivalent amount of oc either weight or surface area normalized we hypothesize that temperate fjords may contain 12 or more of the sedimentary oc buried during this time

on the nature of the frontal zone of the choctawhatchee bay plume in the gulf of mexico river plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume which ultimately impact spreading and mixing rates with the ambient coastal ocean the degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations a field campaign was conducted in a river plume in the northeast gulf of mexico in december 2013 in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions current velocity density and turbulent kinetic energy values e were obtained using an acoustic doppler current profiler adcp a conductivity temperature depth ctd profiler a vertical microstructure profiler vmp and two acoustic doppler velocimeters advs the frontal region contained e values on the order of 10 5 m2 s 3 which were markedly larger than in the ambient water beneath o 10 9 m2 s 3 an energetic wake of moderate e values o 10 6 m2 s 3 was observed trailing the frontal edge the interfacial region of an interior section of the plume featured opposing horizontal velocities and a e value on the order of 10 6 m2 s 3 a simplified mixing budget was used under significant assumptions to compare contributions from wind tides and frontal regions of the plume the results from this order of magnitude analysis indicated that frontal processes 59 dominated in overall mixing this emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

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

oil and gas fields transfer zone relationships thrace basin nw turkey in the thrace basin oil and gas are produced from carbonate and sandstone reservoirs of eocene and oligocene age detailed geological and geophysical studies reveal that earlier and eocene structures were influenced by basement paleotopography resulting from late cretaceous movements between the arabian and anatolian plates while latest miocene structures were generated by splays of the north anatolian fault in the thrace basin the eocene structures which contain the hamitabat gas and devecatagi and k osmancik oil fields trend in a ne sw direction however miocene structures which are gas producers in the karacaoglan and umurca fields are oriented in a nw se direction parallel to the strike of the main faults which accommodate the transfer zones in the thrace basin the transfer zones occur between faults that dip in opposite directions conjugate and in the same directions synthetic the formation of reservoir zones improvement of reservoir characteristics and generation of oil and gas in the oil window zone were influenced by the timing of faulting and appearance of the transfer zones in the thrace basin

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

fault linkage in continental rifts structure and evolution of a large relay ramp in zavarotny lake baikal russia abstract the internal structure of a large 10 40 km relay ramp has been described between two border faults of the baikal rift zone the relay ramp which is located partly onshore and partly offshore has been investigated using a dense grid of high resolution seismic profiles and a digital terrain model containing topographic as well as bathymetric data the structure of the relay ramp in zavarotny is characterised by the development of secondary faults striking approximately parallel to the main faults in combination with this breaching occurred through the development of a new connecting fault the breaching in zavarotny has not lead to the destruction of the relay ramp but a clear further evolution has been observed e g a similar morphology of the lake floor and the basement inside the relay ramp as well as the development of a second connecting fault the strike direction of the secondary faults in the relay ramp has likely been influenced by the pre existing basement fabric in the area

onset timing of left lateral movement along the ailao shan red river shear zone 40ar 39ar dating constraint from the nam dinh area northeastern vietnam left lateral motion along the ailao shan red river asrr shear zone has been widely advocated to be the result of the collision between the indian and eurasian plates and to account for sea floor spreading in the south china sea our new 40 ar 39 ar data on the south easternmost outcrop of the day nui con voi metamorphic massif northern vietnam suggest that the exhumation of metamorphic massif by shearing along the asrr zone began 027 ma and lasted until 022 ma a perfect correlation between location and cooling path for the samples along the shear zone suggests that the transtensional deformation may have propagated northwestward at a rate of 0 6c m y 1 such a good correlation also indicates that the onset of the leftlateral movement of the shear zone may have occurred later than 027 5 ma this conclusion is consistent with our previous interpretation that collision induced southeastward extrusion of indochina along the asrr shear zone postdates the opening of the south china sea and that extrusion tectonics in se china may not be responsible for the opening of the south china sea 2000 elsevier science ltd all rights reserved

seasonal mixing processes in an arctic fjord system abstract studies of water movement in the aafardlikavs qaumarujuk fjord system in west greenland have barn carried out in order to understand the movement of mine tailings discharged into agfardlikavs fjord observations are explained in terms of resonance of the internal tide deep convection associated with sea ice growth and basin water exchange occurring at the time of ice breakup in early summer mixing processes are dominated by these events illustrating the limitations of any seasonal description based on conventional diffusive processes

an early miocene transition in deformation regime within the red river fault zone yunnan and its significance for indo asian tectonics recent work has tended to support the view that lateral extrusion of indochina along the red river fault zone was a significant factor in accommodating the convergence of india with asia to better understand the nature and timing of this feature 40ar 39 ar age spectrum analyses were undertaken on minerals from the ailao shan red river metamorphic belt in southern yunnan china interpreted using diffusion domain theory these results yield thermal histories in the temperature range 550 150 c discontinuities in cooling rates observed from these results suggest a transition in deformation style in the shear zone during the early miocene at least in the vicinity of our samples left lateral strike slip ductile deformation appears to have ceased by about 20 ma the mylonitic gneisses in the shear zone were subsequently obliquely unroofed probably due to a component of normal faulting along the eastern edge of the shear zone causing a brief locally 100 c m y cooling episode this transition may have resulted from a component of northeast southwest extension attributable to greater clockwise rotation of indochina relative to south china after 20 ma than that consistent with pure strike slip along the fault k ar ages on clay minerals from gouge within the normal faults bounding the ailao shan and diancang shan yield a range of ages between 20 and 185 ma but show a significant clustering at 20 25 ma these results suggest that early miocene movement on a precursor to the range front normal fault in the ailao shan caused oblique unroofing of the shear zone this early miocene event corresponds in time with a transition from low to very high denudation rates throughout the himalaya and southern tibet this coincidence may reflect that once left lateral strike slip motion on the red river fault zone slowed or was terminated accommodation of much of the continued northward convergence of india occurred on the main central thrust resulting in rapid uplift in the tethyan himalaya and gangdese belt

age and origin of magmatism along the cenozoic red river shear belt china to decipher the geodynamic significance of cenozoic magmatism along the red river shear belt geochemical analyses u pb and rb sr dating and pb sr nd isotope tracing were undertaken zircon monazite titanite and a ti u oxide from foliated granitoid intrusions in the shear belt gneisses yield u pb emplacement ages of 33 1 0 2 2 31 9 0 3 25 8 0 2 and 24 7 0 2 ma and an age of 35 0 0 3 ma was obtained for the roughly 100 km long adjacent jinping phan si pang alkali granite together with our previous data the new ages suggest that magmatism and left lateral strike slip movements occurred coevally during latest eocene oligocene times from 33 to 22 ma the rb sr dating of muscovite and biotite from the northernmost gneisses indicates that cooling to 500 c occurred at 52 6 1 1 ma pre dating the onset of magmatism whereas further cooling to 300 c took place at 28 9 0 6 this shows that unroofing in the north took place almost 9 million years earlier than in the central gneiss segments of the shear zone geochemical data substantiate two types of magmas 1 amphibole bearing intrusions of alkaline trend which are derived from sources with isr 0 7065 0 7089 and i nd 3 7 to 6 6 2 leucogranitic layers and bodies having isr 0 7084 0 7354 and i nd 3 3 to 13 4 the former type of intrusion is found in both the gneisses and the adjacent unmetamorphosed cover rocks whereas leucogranites are restricted to the shear belt gneisses source signatures of the alkaline intrusions lie adjacent to the those of oib plotting at the lower end of the mantle array contamination of these melts by continental material seems to be very limited on the other hand the leucogranitic layers are essentially crustal derived but none of the them has country rock isotope signatures requiring melting of crust different from the actually exposed gneisses magma sources similar to those of ocean island basalt indicate magmatism to involve melting of light rare earth element and large ion lithophile element enriched mantle domains most likely present in the lithosphere underneath the region since lithospheric thickening or subduction can be ruled out to produce both types of magmas the presence of an important thermal anomaly is required which is coevally active with left lateral strike slip shear adiabatic decompression and melting within the rising anomaly is the most plausible mechanism to produce the mantle magmas which successively migrate through the crust to induce anatectic melting at 20 15 km crustal depth alkaline magmas largely dominate the volume of magmatism along the belt being continuously present in the shear zone for millions of years such lubrication potentially explains how very large amounts of displacement can be absorbed in surprisingly narrow shear zones such as the red river belt possibly also playing a role for where and when zones of plate scale lateral extrusion develop

the structure and evolution of deepwater basins in the distal margin of the northern south china sea and their implications for the formation of the continental margin abstract although it is generally accepted that the south china sea margin can be classified as a magma poor rifted margin little is known about the structural style of the distal margin and how the distal deep basins evolved observations and data from the northern south china sea margin suggest that the deepwater basins distal margin domain are commonly underlain by a highly extended continental crust and detachment fault systems have been interpreted in places we have interpreted a large seismic data set covering deepwater basins in the northern south china sea the interpreted moho on reflection seismic profiles indicates that the crustal thickness varies along sections perpendicular to the coast which is the first order criterion to divide the whole margin into a proximal domain necking zone and distal domain furthermore the underlying extremely stretched crust

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

duration of strike slip movements in large shear zones the red river belt china abstract sixty four size fractions of zircon monazite xenotime and titanite were dated by the u pb method to temporally and spatially constrain left lateral movements in the red river shear zone between the depths of 15 and 20 km the shearing led to the formation of the high grade metamorphic gneisses that form the bulk of the 4200 m high diancang shan and 3100 m high ailao shan mountain ranges the omnipresence of melt layers and pockets in these gneisses shows that temperatures associated with tectonometamorphism lie at and above the solidus of continental crust and deformation patterns are very homogeneous over the entire length of the belt north of the gneisses subvolcanic bodies intrude unmetamorphosed cover rocks in particular eocene red beds along the projected trend of the red river shear zone for a leucogranitic layer in the diancang shan gneisses an age of 24 2 0 2 ma 2 is obtained for monazite and 22 4 0 2 ma is obtained for xenotime whereas zircon formed through two growth stages at 24 23 ma these ages record solidification of the anatectic melts over a period of at least 1 8 0 4 ma during which left lateral shear was continuously active in the ailao shan gneisses zircon and titanite ages are 26 3 0 3 and 26 1 0 2 ma for two monzonitic bodies and 24 1 0 2 and 22 4 0 2 ma for two pegmatitic layers that occur within the monzonitic intrusions these results show that zircon monazite titanite and probably also xenotime are closed systems for u and pb under melting conditions 650 c therefore the ages date mineral formation in the melt rather than cooling below certain closure temperatures a significantly older age of 35 0 0 1 ma is obtained for a monzonitic subvolcanic intrusion north of the diancang shan gneisses because these intrusions follow the trend of the shear zone they most likely represent the surface expression of early activity along that zone indicating that strike slip movement had already occurred in latest eocene time the total set of u pb ages shows that magmatic and metamorphic activity occurred from 35 to 20 ma strengthening the idea that the red river shear zone absorbed most of the intraplate movements required to compensate the opening of the south china sea between 32 and 16 ma the existence of monzonitic syenitic intrusions along the red river zone implies that melting affected source rocks other than the diancang shan and ailao shan gneiss protoliths potential sources to produce such rocks lie in the deep crust possibly including melts from the mantle consequently the red river shear zone must be a deep rooted structure along which melts migrated to the surface moreover the contemporaneity of shear motion and magma generation suggests that melting occurred in direct relation to strike slip activity

morphotectonic evolution of rifted continental margins inferences from a coupled tectonic surface processes model and fission track thermochronology we use a numerical model to study the topographic evolution and erosional history of rifted continental margins the model combines a kinematic description of lithospheric extension tectonic model with a surface processes model that includes short range hillslope and long range fluvial transport the tectonic model predicts the evolution of the lithospheric temperature and strength elastic thickness distribution as well as the tectonic uplift through time this is input into the surface processes model which calculates the degradation of topography and associated isostatic rebound modeled denudation histories across the margin are used to predict apatite fission track age and length patterns modeling results indicate that depending on the adopted parameters an uplifted rift flank should degrade by erosion within 50 100 m y without significant retreat of the topographic elevation maximum the development of an escarpment system at rifted continental margins is in itself not an indication of tectonic rift flank uplift but results from the existence of a high elevation interior plateau erosional base level lowering as a consequence of rifting and regional isostatic response to erosion of the margin however apatite fission track thermochronology reveals that the areas seaward of the escarpment at a number of rifted margins have been exhumed from several kilometers depth such amounts of denudation cannot be accommodated with isostatic rebound alone and require additional tectonic uplift of the rift flanks modeling of apatite fission track patterns suggests that fission track thermochronology dates the onset of rapid erosion which coincides with the initiation of strong relief i e initiation of rifting fission track ages which are younger than the age of rifting thus cannot be unambiguously interpreted as excluding prerift uplift the timing of margin uplift can be established only by careful track length analysis and integration with regional stratigraphic data the model is applied to the saudi arabian red sea margin and the southeastern australian highlands where it is constrained by present day topography and apatite fission track data as well as seismic and gravity data for the saudi arabian red sea margin synrift regional plateau uplift with a magnitude of approximately 1 km is inferred possibly as a result of asthenospheric upwelling flexurally induced tectonic uplift of the rift flank with a magnitude of 2 km is superimposed on this regional uplift the relatively high elevation of the southeastern australian highlands their steep front and the relatively high amounts of erosion suggest that apart from mesozoic synrift flexural uplift tertiary rejuvenation of topography has occurred possibly as a result of renewed lithospheric thinning and underplating the low elevation of the australian interior would inhibit the evolution of a major escarpment in the absence of such renewed uplift

zircon u pb ages and ree composition constraints on the provenance of the continental slope parallel submarine fan western qiongdongnan basin northern margin of the south china sea abstract the ledong submarine fan in the western qiongdongnan basin runs parallel to the continental slope with an area of over 10 000 km2 and maximum thickness of greater than 2000 m using bulk rare earth element ree compositions of the sediments and detrital zircon u pb age data we analysed the provenance of the ledong submarine fan and its regional tectonic implications the zircon grains in the ledong submarine fan show a wide range of shapes from prismatic crystals to oval grains with mostly rounded corners indicating the long transport distance of these zircon grains prior to deposition the zircon ages have a wide range from 27 to 3006 ma with five major age peaks at ca 27 ma 88 ma 256 ma 415 ma and 785 ma along with a number of subordinate age peaks at ca 1024 ma 1376 ma 1879 ma and 2374 ma these age distribution patterns are similar to those from the red river at yen bai the total ree content range is between 87 72 and 210 38 mg g in the ledong submarine fan the chondrite normalized ree patterns show light ree lree enrichment and weakly negative eu anomalies which are similar to those in the red river at hanoi the evidence from zircon u pb ages and ree geochemistry indicates that the provenance of the ledong submarine fan is the red river system the development of the ledong submarine fan indicates that a rapid subsidence occurred in the western qiongdongnan basin during the late miocene and the strike slip reversal of the red river fault from sinistral to dextral motion was the key factor that induced gravity flow to form the ledong submarine fan

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

petrologic and geochemical links between the post collisional proterozoic harney peak leucogranite south dakota usa and its source rocks abstract the proterozoic terrane of the black hills south dakota includes the composite harney peak leucogranite and associated pegmatites that were emplaced into metamorphosed pelites and graywackes available dates indicate that granite generation post dated regional metamorphism and deformation that have been attributed to collision of the wyoming and superior cratons at 1760 ma previous radiogenic and stable isotope work indicates that the exposed metasedimentary rocks are equivalent to sources of the leucogranites in this study whole rock and mineral compositions of the metasedimentary rocks were used to calculate the likely average residue mineralogies and melt fractions that would be generated by muscovite dehydration melting of the rocks these were then used to model observed trace element compositions of the granites using published mineral melt distribution coefficients model trace element melt compositions using pelitic and graywacke protoliths yield similar results the models reproduce well the observed depletion of transition metals and ba in the granites relative to metasedimentary protoliths the depletion is due mainly to high proportion of biotite with variable amounts of k feldspar in the model residue sr is also depleted in the granites compared to source rocks but to a lesser relative extent than ba this is because of the low biotite melt distribution coefficient for sr and because high proportion of plagioclase in the residue is compensated by high sr concentrations in protoliths rubidium cs and ta behaved as slightly compatible to incompatible elements and therefore were not strongly fractionated during melting of the considered elements only b appears to have been highly incompatible relative to residue during melting the protoliths had sufficient b to allow tourmaline crystallization in those parts of the harney peak granite in which ti concentration was sufficiently low not to enhance crystallization of biotite the reproducibility of observed trace element concentrations in the harney peak granite by the models supports the often made proposition that metapelites and metagraywackes are common sources for leucogranites this argues against mass input from the mantle into metagraywacke and metapelitic crustal sources or melting of amphibolites to generate the post collisional harney peak and other similar peraluminous granite suites

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

observations of intratidal variability of flows over a sill contraction combination in a chilean fjord underway velocity measurements were carried out for the first time in a chilean fjord using an acoustic doppler velocimeter with the purpose of elucidating the intratidal variability of flows through a pass paso galvarino the pass included a sill where the bottom sloped by roughly 30 and a coastline contraction of 90 the relatively small dimensions of the pass allowed for rapid sampling of the flow evolution throughout the tidal cycle the backscattered sound signal from the velocimeter and from an echo sounder were used to describe the vertical excursions of the pycnocline throughout the domain and to identify regions of enhanced vertical mixing within the pass the spatial variability of the flow in the pass was consistent with uniform two layer flow at the narrowest section of the contraction the pycnocline dropped sharply around both maximum flood and maximum ebb while the flow accelerated downstream relative to the tidal flow the slope of the pycnocline changed sign from flood to ebb which was atypical of other fjord observations but could be explained by the transitions from subcritical to supercritical flow these transitions switched location at either side of the narrowest section of the contraction leeward of this section increased sound backscatter suggested intensified turbulence that extended over a greater area during ebb than during flood because the distance between the point of pycnocline drop and the end of the pass was longer during ebb enhanced vertical mixing within the pass was reflected in the tidally averaged fields by a three layer flow that consisted of near surface and near bottom flow converging toward the pass and flow around the pycnocline diverging away from the pass

quartz sillimanite leucosomes in high grade schists black hills south dakota a perspective on the mobility of al in high grade metamorphic rocks in the black hills south dakota anatectic migmatites that formed above the second sillimanite isograd comprise mesosomes dominated by quartz biotite sillimanite plagioclase and sporadic poikiloblasts of k feldspar melanosomes dominated by biotite and sillimanite and leucosomes some leucosomes have near minimum granite composition but many lack alkali elements and have fibrolitic sillimanite instead of feldspar the proportion of si al is the same in both leucosome types the sillimanite containing leucosomes include fluorapatite which indicates high activity of f the lack of alkali feldspar in these leucosomes is attributed to its instability relative to sillimanite quartz in the presence of fluids with high a h a k ratios that evolved from the crystallizing leucosomes it is suggested that quartz aluminosilicate segregations and veins in other high grade terranes may also represent pegmatitic melts in which alkali feldspar crystallization was inhibited by high activities of hydrogen resulting in loss of alkali elements

b and li in proterozoic metapelites from the black hills u s a implications for the origin of leucogranitic magmas the abundance and distribution of b and li in metasedimentary rocks and in the harney peak granite hpg in the black hills south dakota u s a elucidate the behavior of these two elements during 1 regional metamorphism that began at 1760 ma 2 subsequent contact metamorphism associated with emplacement of the hpg and associated pegmatites at 1715 ma and 3 anatexis leading to production of the granite there is no clear evidence for changes in b and li concentrations with progressive regional metamorphism of the metapelites from chlorite biotite grade up to staurolite grade rocks outside the pegmatite aureole that surround the hpg have average b contents of 80 ppm there is no correlation of b with other elements in the pelitic schists which indicates that none of the major phases is the dominant host for b boron content is mainly controlled by small amounts of randomly distributed tourmaline that was identified in alpha track maps of thin sections in the aureole of the granite b concentrations are depleted in many samples the depletion is attributed to consumption of tourmaline during interaction of the rocks with alkalic fluids the average li contents in metapelites far away from the hpg are also 80 ppm near the hpg li concentrations reach roughly 190 ppm indicating significant metasomatism by fluids that emanated from the granite and pegmatites the concentrations of b and li in the low grade metapelites are sufficient to explain their abundances in the hpg if the granite formed by partial melting of the metapelites and if there was total breakdown of tourmaline stabilization of tourmaline in leucogranites is not necessarily related to sources enriched in b but may be related to its competition for fe and mg with biotite

vertical mixing rates in fjords determined using radon and salinity as tracers excess radon profiles were measured in several washington state and british columbia fjords generally exponential profiels were observed during periods of bottom water stagnation values of the vertical eddy diffusivity were estimated from the exponential excess radon profiles and from salinity changes in the stagnant bottom water these values ranged from 0 16 to 36 cm2 s 1 among fjords and the variation could be explained by different inputs of tidal energy into vertical mixing for the different fjords excess radon was also observed in surface water of several fjords the source of this excess radon was the freshwater runoff entering the fjords values of the vertical eddy diffusivity were estimated for the near surface water of narrows inlet from these profiles to be 0 32 to 0 47 cm2 s 1 across the freshwater saltwater interface and 0 9 to 3 1 cm2 s 1 between 5 and 35 m depth

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

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

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

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

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

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

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

hydrothermal alteration of late to post tectonic lyon mountain granitic gneiss adirondack mountains new york origin of quartz sillimanite segregations quartz albite lithologies and associated kiruna type low ti fe oxide deposits quartz sillimanite segregations quartz albite lithologies ab95 98 and kiruna type low ti iron oxide deposits are associated with late to post tectonic c 1055 ma leucogranites of lyon mountain gneiss lmg in the adirondack mountains new york state most recent interpretations of these controversial features which are global in occurrence favour hydrothermal origins in agreement with results presented here field relations document that quartz sillimanite veins and nodules cut and therefore post date emplacement of host lmg leucogranites veins occur in oriented fracture networks and aligned trains of nodules are interpreted as disrupted early veins late dykes of leucogranite cut veins and nodules demonstrating formation prior to terminal magmatism veins and nodules consist of sillimanite surrounded by quartz that commonly embays wall rock feldspar indicating leaching of na and k from lmg feldspar by acidic hydrothermal fluids subsequent and repeated ductile flow disrupted earlier veins into nodular fragments but produced little grain shape fabric geochemical and petrographic studies of quartz albite rock indicate that it formed through metasomatic replacement albitization of lmg microperthite by sodic hydrothermal fluids that resulted in diagnostic checkerboard albite low ti iron oxide ores are commonly associated with the quartz albite sub unit and it is proposed that hydrothermal fluids related to albitization transported fe as well the regional extent of sodic alteration suggests large quantities of surface derived hydrothermal fluids fluid inclusion and oxygen isotope data are consistent with high temperature regionally extensive fluids consisting primarily of evolved surface derived brines enriched in na and cl quartz sillimanite veins and nodules which are significantly more localised phenomena and require acidic fluids were most likely formed from local magmatic fluids in the crystallizing carapaces of lmg plutons

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

extreme channelization of fluid and the problem of element mobility during barrovian metamorphism geochemical profiles across chemically altered zones selvages surrounding amphibolite facies quartz kyanite veins were investigated to determine major minor and trace element mass transfer and volume strain due to channelized fluid flow the three profiles are perpendicular to two veins cutting the wepawaug schist connecticut u s a which underwent barrovian style metamorphism during the acadian orogeny selvages are highly aluminous with considerably more kyanite staurolite and garnet and less quartz plagioclase and mica than surrounding wallrocks kyanite crystals increase in size toward veins and reach several centimeters in length within veins mass balance analysis indicates 50 silica loss and 34 volume loss from selvages on average silica transferred locally from selvages to veins accounts for 40 to 80 of the vein silica the remainder must have been precipitated from fluids that flowed through the veins during regional devolatilization fluid flow also transported elements into the rock mass which were concentrated in the selvages gains of fe mn y and hree were due to the growth of selvage garnet fe zn and li were sequestered into staurolite kyanite staurolite and garnet growth resulted in al mass gains destruction of mica particularly muscovite and of plagioclase in the selvages resulted in losses of k na ba pb sn and volatiles and losses of na sr and eu respectively thin na and sr enrichment zones associated with increased modal plagioclase are found along the margins between selvages and less altered wallrock and may represent either chemical self organization produced during diffusive mass transfer and reaction or are relics from a possible earlier period of na enrichment in the selvages simple two dimensional numerical modeling of flow in a fractured porous medium indicates that fluxes vary significantly over short distances 1 m adjacent to veins fluids channelized into the high permeability fracture conduits carry the bulk of the fluid flow mass transfer to and from selvages adjacent to the conduits occurred by some combination of diffusion and flow in contrast areas distal to the conduits are impoverished in fluid and undergo much more limited infiltration as a consequence different workers can come to vastly different conclusions about the magnitude of fluid fluxes and element transfer depending on the part of a fractured outcrop studied this extreme spatial variability due to channelization can largely explain contrasting views that have arisen in the literature regarding the nature and intensity of non volatile element mass transfer during barrovian metamorphism determining average time integrated fluid fluxes and levels of element transport across outcrops remains as important research challenges due to the spatial variability of flow

mechanical controls on fault geometry abstract faults inevitably become non planar because of how they grow and how they are affected during slip by mechanical heterogeneities inherent in the earth some faults acquire a non planar geometry because of non uniform tectonic deformation or because they grow by the linkage of originally discontinuous structures however even faults that are originally planar are unlikely to remain so elastic analyses show that as a fault slips it rotates with the surrounding rock it rotates uniformly and remains planar if a the shear stress drop along the fault is uniform b the rock surrounding the fault is uniform and isotropic and c the far field stress state is uniform variation in stress drop or in fault strength heterogeneity in host rock stiffness and interaction with other faults cause non uniform rotation along a fault that slips and the fault geometry deforms mechanical and geometrical heterogeneities are inherent in the earth so all natural faults will tend to become non planar to some degree as they slip even if they were initially planar information on fault shape can illuminate the mechanics of faulting and in conjunction with slip data help locate contacts between rock bodies of different elastic moduli in uniform isotropic rocks fault curvature is proportional to the rate at which the stress drop varies as a function of position along a fault whereas the slip profile reflects a weighted average of the stress drop

modern sedimentary processes at the heads of martinez channel and steffen fjord chilean patagonia abstract chilean fjord sediments constitute high resolution archives of climate and environmental change in the southern andes to interpret such records accurately it is crucial to understand how sediment is transported and deposited within these basins this issue is of particular importance in glaciofluvial martinez channel and steffen fjord 48 s due to the increasing occurrence of glacial lake outburst floods glofs originating from outlet glaciers of the northern patagonian icefield hence the bathymetry of the head of martinez channel and steffen fjord was mapped at high resolution and the grain size and organic carbon content of grab sediment samples were examined results show that the subaquatic deltas of baker and huemules rivers at the head of martinez channel and steffen fjord respectively are deeply incised up to 36 m by sinuous channels the presence of sediment waves and coarser sediments within these channels imply recent activity and sediment transport by turbidity currents although several triggering mechanisms are possible we argue that elevated river discharge and the associated relatively high suspended sediment loads is the main cause of the occurrence of turbidity currents at the head of these fjords and are of key importance in shaping the fjord s subaquatic morphology this study shows that the heads of martinez channel and steffen fjord are dynamic sedimentary environments with rapidly migrating channels it highlights the importance of site selection and multi coring in any future project aimed at reconstructing environmental change using the sediments of either fjord

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

impact of channel geometry and rotation on the trapping of internal tides the generation and propagation of internal tides has been studied with an isopycnic three dimensional ocean model the response of a uniformly stratified sea in a channel which is forced by a barotropic tide on its open boundary is considered the tide progresses into the channel and forces internal tides over a continental slope at the other end the channel has a length of 1200 km and a width of 191 25 km the bottom profile has been varied in a series of four experiments it is shown how the cross channel geometry affects the propagation and trapping of internal tides and the penetration scale of wave energy away from the continental slope is discussed in particular it is found that a cross channel bottom slope constrains the penetration of the internal tidal energy most internal waves refract toward a cross channel plane where they are trapped the exception is formed by edge waves that carry part of the energy away from the continental slope in the case of rotation near the continental slope the poincare waves that arise in the absence of a cross channel slope no longer bear the characteristics of the wave attractor predicted by 2d theory but are almost completely arrested while the right bound kelvin wave preserves the 2d attractor in the cross channel plane which is present in the nonrotating case the reflected barotropic right bound kelvin wave acts as a secondary internal wave generator along the cross channel slope

the tectonic evolution of the qiongdongnan basin in the northern margin of the south china sea abstract qiongdongnan basin is a cenozoic rift basin located on the northern passive continental margin of the south china sea due to a lack of geologic observations its evolution was not clear in the past however recently acquired 2 d seismic reflection data provide an opportunity to investigate its tectonic evolution it shows that the qiongdongnan basin comprises a main rift zone which is 50 100 km wide and more than 400 km long the main rift zone is arcuate in map view and its orientation changes from ene wsw in the west to nearly e w in the east it can be divided into three major segments the generally linear fault trace shown by many border faults in map view implies that the eastern and middle segments were controlled by faults reactivated from ne to ene trending and nearly e w trending pre existing fabrics respectively the western segment was controlled by a left lateral strike slip fault the fault patterns shown by the central and eastern segments indicate that the extension direction for the opening of the rift basin was dominantly nw se a semi quantitative analysis of the fault cut offs identifies three stages of rifting evolution 1 40 4 33 9 ma sparsely distributed ne trending faults formed mainly in the western and the central part of the study area 2 33 9 28 4 ma the main rift zone formed and the area influenced by faulting was extended into the eastern part of the study area and 3 28 4 20 4 ma the subsidence area was further enlarged but mainly extended into the flanking area of the main rift zone in addition estimates of extensional strain along nw se trending seismic profiles which cross the main rift zone vary between 15 and 39 km which are generally comparable to the sinistral displacement on the red river fault zone offshore implying that this fault zone in terms of sinistral motion terminated at a location near the southern end of the yinggehai basin finally these observations let us to favour a hybrid model for the opening of the south china sea and probably the qiongdongnan basin

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

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

a tide generated internal waveform in the western approaches to the strait of gibraltar aircraft expendable bathythermograph radar infrared scanner and visual data collected in october 1982 1984 and 1985 as well as space shuttle photographs indicate that an internal waveform depending on flow conditions either an internal hydraulic jump or a lee wave is a semipermanent feature over the camarinal sill in the western approaches to the strait of gibraltar comparison of these data with both historic and recent current meter mooring data indicates that the waveform generated at the interface between the atlantic and mediterranean waters undergoes periodic changes wrought by interaction of the tidal current and the flow of the atlantic and mediterranean waters we believe that the waveform is a major mixing mechanism between the two water masses