tectonic evolution of sw wales during the upper palaeozoic during the upper palaeozoic the development of several strike faults strongly influenced the deformation history of sw wales this aspect of the deformation is emphasized in this new description of the tectonic evolution of the region after the caledonian orogeny several strike faults caused crustal extension by normal dip slip and partially controlled the subsidence of depositional basins these faults ceased moving before the initiation of variscan deformation in sw wales two of the earlier faults were reactivated with reverse slip translations during variscan deformation when three strike faults were initiated as a result of gravitational spreading two of the new faults formed sole thrusts for northward translating nappes and the other developed as a subsidiary lag fault the sole thrusts transected some of the pre existing faults causing along strike variation in their motion the strike faults in sw wales were therefore initiated at different times and display contrasting displacement histories

oxygen isotope record of fluid rock sio 2 interaction during variscan progressive deformation and quartz veining in the meta volcanosediments of belle ile southern brittany abstract belle ile in the south armorican domain is composed of palaeozoic volcano detrital sequences with sericite phyllites and porphyroids fine banded and folded meta tuffites microquartzites and graphitic quartzites occur in the basal part at plage de bordardoue phengite compositions constrain that variscan metamorphism did not exceed 430 c 4 5 kbar four generations 1 4 of centimeter thick quartz veins were precipitated during variscan progressive deformation and recorded changing fluid compositions values of 26 18osmow in vein 1 quartz exceed high 18osmow in the host rocks decrease of quartz 18osmow from margins to centers can be observed from the syntaxial veins younger veins 4 have lower 18o their inclusions indicate lower salinities and traces of ch4 in the fluid when compared with veins 1 veins 1 were overprinted by shearing and fissuring subgrain rotation recrystallization occurred along briquette structures and subgrain boundaries the initial isotope values have been preserved larger domains with small grained quartz can be identified by lower values of 18o homogeneous isotopic compositions are found in hinges of folded veins 2 with grain boundary migration recrystallization the small scale oxygen isotope variations and the changing fluid compositions point to a locally hosted fluid system with a limited contribution of meteoric water during multiphase deformation and vein formation

vein growth mechanisms and fluid sources revealed by oxygen isotope laser microprobe in situ laser microprobe analyses of millimeter wide quartz veins has revealed the largest 18o gradients 9 mm yet documented in terrestrial samples the systematic isotopic variations indicate a crack seal growth mechanism that variably interleaved 18 o enriched quartzite porphyroclasts with newly precipitated 18 o depleted vein quartz the isotopically light quartz requires open system infiltration of meteoric fluids into the quartzite during its incorporation into the ruby gap duplex central australia documentation of the fluid source in these small veins would not be possible without submillimetre isotopic sampling capabilities application of this laser based technology to other geologic problems should result in similar documentation of large isotopic gradients and provide new insight into fluid rock interactions

estimating thermal conductivity in sedimentary basins using lithologic data and geophysical well logs a method for estimating in situ thermal conductivity profiles in oil and gas wells is advanced to rectify a major shortcoming in thermal analyses of sedimentary basins thermal conductivity estimates are made in a two stage procedure and are based on a model for the conductivity of mixtures and input data from lithological and geophysical logs first rock matrix conductivity for an arbitrary depth interval i e drill cuttings sample interval which is about 3 m is determined from the laboratory calibrated conductivities and volumetric representation of its individual lithologic components using a geometric mean model in situ conductivity is then estimated by a second application of the model correcting for temperature and porosity determined from geophysical logs the method is illustrated for three uinta basin utah wells that penetrate a series of tertiary sandstones shales and muddy carbonates detailed lithologic descriptions together with sonic and neutron logs were digitized and used for estimating in situ conductivity the validity of the method was tested by comparing the prediction against laboratory measurements on 565 samples from the same wells rock matrix thermal conductivity ranges from 1 6 to 6 8 w m k and is predicted within 20 of the actual measurement for 90 of the samples both in situ conductivity values and variations for a given lithologic unit are reduced at increased porosity and increased temperature thermal conductivity nomograms are presented as useful tools to predict directly the in situ thermal conductivit of a formation from a well log signal

a thin skinned thrust model for variscan pembrokeshire wales abstract the east and west coasts of pembrokeshire sw wales provide two sections through the variscan fold and thrust belt the evolution of these structures is interpreted in terms of a thin skinned tectonic model balanced cross sections are constructed for the high level imbricate sequences and these allow reasonably accurate estimates of shortening to be made basement control on structures developed in the upper carboniferous cover rocks is minimal though some thrust ramp positions may be determined by the location of earlier normal faults the thrust belt may be divided into two parts according to the depth to the decollement horizon in the north imbricate fans developed from a shallow level detachment shortening is heterogeneous and both thrust periodicity and fold style are partly determined by rheology cumulative tectonic displacement increases to the west across pembrokeshire resulting in a net clockwise rotation of about 40

surface deformation related to the 2008 wenchuan earthquake and mountain building of the longmen shan eastern tibetan plateau abstract the 12 may 2008 ms 8 0 wenchuan earthquake china was one of largest continental thrusting events worldwide based on interpretations of post earthquake high resolution remote sensing images and field surveys we investigated the geometry geomorphology and kinematics of co seismic surface ruptures as well as seismic and geologic hazards along the longmen shan fold and thrust belt our results indicate that the wenchuan earthquake occurred along the ne sw trending yingxiu beichuan and guanxian anxian faults in the longmen shan fold and thrust belt the main surface rupture zones along the yingxiu beichuan and guanxian anxian fault zones are approximately 235 and 72 km in length respectively these sub parallel ruptures may merge at depth the yingxiu donghekou surface rupture zone can be divided into four segments separated by discontinuities that appear as step overs or bends in map view surface deformation is characterized by oblique reverse faulting with a maximum vertical displacement of approximately 10 m in areas around beichuan county earthquake related disasters e g landslides are linearly distributed along the surface rupture zones and associated river valleys the wenchuan earthquake provides new insights into the nature of mountain building within the longmen shan eastern tibetan plateau the total crustal shortening accommodated by this great earthquake was as much as 8 5 m with a maximum vertical uplift of approximately 10 m the present results suggest that ongoing mountain building of the longmen shan is driven mainly by crustal shortening and uplift related to repeated large seismic events such as the 2008 wenchuan earthquake furthermore rapid erosion within the longmen shan fold and thrust belt occurs along deep valleys and rupture zones following the occurrence of large scale landslides triggered by earthquakes consequently we suggest that crustal shortening related to repeated great seismic events together with isostatic rebound induced by rapid erosion related unloading is a key component of the geodynamics that drive ongoing mountain building on the eastern tibetan plateau

incipient metamorphism and deformation in the variscides of sw dyfed wales first steps towards isotopic equilibrium incipient metamorphism accompanying thrusting folding and cleavage development has been investigated in a varied sequence of palaeozoic sediments near the variscan front in sw dyfed wales the aim was to evaluate a critical stage in the progression from heterogeneous sediment whose detrital phases are neither in equilibrium with one another nor with pore fluids through indurated sedimentary rock to metamorphic rock comprising newly formed crystals that equilibrated with one another as they grew quartz veins are widely developed in the area especially in the more psammitic lithologies while finer grained rocks became cleaved during tectonic deformation mineralogical constraints and fluid inclusion measurements suggest maximum temperatures around 200 310d c slightly higher in the marloes musselwick thrust sheet than in other parts of the structural succession at depths of the order of 6 13 km quartz veins yield distinctly heavier oxygen isotopic compositions than detrital quartz grains in the adjacent wall rocks although care must be taken in interpreting the data because slivers of detrital grains may become incorporated into veins while matrix detrital grains may incorporate veinlets or rims of newly formed quartz it is concluded that vein quartz grew in isotopic equilibrium with a fluid phase whose isotopic composition was primarily controlled by exchange with phyllosilicates not detrital quartz grains vein and matrix quartzes from the marloes musselwick thrust sheet are distinctly lighter 18oveins 14 to 18 and 18omatrix 11 to 14 than those from other thrust sheets 18o 17 to 20 and 14 to 17 respectively we conclude that vein quartz and phyllosilicate grains in cleavage domains probably attained equilibrium with a locally buffered pore fluid at the peak of metamorphism but many relict grains of different chemical and isotopic composition remained elsewhere in the rock local fluid migration along veins and through cleavage lamellae facilitated the attainment of equilibrium but there is little evidence for large scale infiltration of externally derived fluids with further metamorphism the quartz in these rocks would attain an isotopic composition intermediate between that of the heavy vein material and light detritus which coexist here

silica mobility and fluid movement during metamorphism of the connemara schists ireland quartz veins are developed in a wide range of metasediment types in the upper amphibolite facies rocks of connemara and attest to considerable migration of silica contrary to common assumptions there is clear evidence that these veins do not primarily result from movement of fluid to regions of lower p t down the regional geothermal gradient under amphibolite facies conditions a dilute chloride fluid moving down temperature has the potential to alter 60g of plagioclase to muscovite for each gram of vein quartz precipitated while cooling over the temperature interval from 650 to 500 c the absence of significant metasomatic effects in the vein walls effectively precludes a simple origin from such through flowing externally derived fluids the oxygen isotopic composition of matrix quartz shows considerable differences between different rock types quartzite pelite and marble with a range of 18osmow from c 11 5 quartzite to 18 5 marble in each rock type vein quartz compositions closely match those of the matrix quartz these results demonstrate the importance of local segregation processes in the formation of veins and suggest that fluid convection cells were not developed during metamorphism on a scale larger than the individual sedimentary formations if at all both oxygen isotope data and the absence of metasomatism indicate that veins form primarily by segregation of quartz from the host lithologies with only a relatively minor component of through flow of externally derived fluid veins are clearly not the major pathways of metamorphic dewatering it is proposed that abundant veins in the predominantly pelitic ballynakill formation formed during peak metamorphic d3 folding because the formation was embrittled by high fluid pressures but was capped by impermeable marble hence the pelitic formation fractured repeatedly and the pore fluid drained through the fractures to form veins while irreversible loss through the rest of the succession was a much less important process in the central mountains of connemara rather pure unreactive quartzites are cut by widely spaced laterally extensive quartz veins that are axial planar to d3 folds these veins may mark pathways whereby metamorphic fluid made its way through the massive impermeable quartzite from lower parts of the nappe pile but here too oxygen isotope data indicate considerable segregation of locally derived quartz reflecting the importance of pumping of fluid between wail rocks and fractures relative to the component of through flow

real time fluid analysis during drilling of the wenchuan earthquake fault scientific drilling project and its responding features abstract the wenchuan earthquake fault scientific drilling project was established shortly after the wenchuan earthquake several on site laboratories were built to perform the real time fluid analysis during drilling simultaneously the concentrations of argon methane hydrogen carbon dioxide helium nitrogen oxygen and radon in drilling mud gas were determined during the entirely process of drilling the setup for real time fluid analysis was stability for long time the mud gas such as methane and radon yielded low concentrations above the principal slip zone psz whereas yielded high concentrations under the psz the real time fluid data might provide the real time information for identifying and validating of the psz in the deep fault zone the gas concentration showed abnormal fluctuation during the ms 4 0 earthquake on april 27 2010 the abnormality occurred one hour before the earthquake and ended half an hour after the earthquake the real time fluid analysis during drilling might have captured the signal of the ms 4 0 earthquake at a quarter past six on april 27 one strong and nearest aftershock

the evolution of the deep flow regime at soultz sous forets rhine graben eastern france evidence from a composite quartz vein drilling at soultz sous for cflx e ts france conducted as part of the european hot dry rock project intersected a fracture lined with vein quartz and actively producing hot 150h degree c water at 2174 m depth in the granite basement to the rhine graben at least seven generations of quartz are present within the vein but fluid inclusion homogenization temperatures show that temperatures remained within 15h degree c of the present field temperature throughout its development apart from a few rare pulses of hotter water in contrast freezing measurements indicate two distinct fluids the more saline one ranging from 10 to 15 wth percent nacl eq dominated the early stages of vein fill while the second ranging from 0 to 8 wth percent nacl eq become more prominent in later stages oxygen isotope analyses of different quartz generations also show two populations in addition to magmatic relicts in the early stages a population with delta sup 18 o from 14 per thousand to 18 per thousand predominates and is consistent with growth from a sedimentary basin brine later quartz shows lighter values 12 per thousand endash 13 per thousand resulting from precipitation from a fluid isotopically identical to the modern fluid which is in equilibrium with granite feldspar at a temperature approximately 25h degree c higher than the present vein temperature the changemore in delta sup 18 o does not however correlate with that in fluid salinity reflecting the different effects of fluid rock interaction on the two parameters changes in fluid salinity possibly resulting from meteoric inputs into the deep formation waters of the rhine graben occurred early in the flow path of the soultz fluids because there is no decrease in fluid temperature associated with even the most dilute inclusion fluids with time the path by which these fluids from deep in the mesozoic sediments of the graben have made their way to the soultz site has changed resulting in greater interaction with granite as recorded in the oxygen signature copyright 1998 american geophysical union less

evidence from mossbauer spectroscopy for intense localization of metamorphic fluid flow during the formation of spaced cleavage arenites in the low grade metasedimentary rocks of the stirling barren group western australia contain discrete spaced cleavages these in part are pure white mica but up to 30 of the cleavage zones consists of fine grained quartz resulting from crystal plastic deformation a modified gresens analysis shows that the cleavage domains formed by a 50 volume loss associated primarily with sio2 and mgo concentration decreases of 58 and 37 respectively and a 12 decrease in fe2o3 mossbauer spectroscopy shows that the fe2 fe3 ratio from lithon to cleavage changed from 50 so to 15 85 this substantial difference cannot be accounted for by loss of iron the data are best explained by the focusing of a highly oxidizing fluid through the cleavage domains where volumetric fluid rock ratios around 150 to 1 are indicated in this example advectic processes appear to be important in low grade regional metamorphism

interactions between fluvial and eolian geomorphic systems and processes examples from the sahara and australia abstract the remains of once integrated drainage systems are still discernible in many of the hot deserts of the world some of these date back to the mesozoic as in arid western australia where they now form chains of salt lakes others were active in miocene times such as the sahabi rivers that once flowed from chad to the mediterranean a few remained active during quaternary interglacials as in the sahara all contributed sediments that were reworked by wind during drier phases to form desert dunes the desert dunes of australia and of the 9500 km long chain of deserts extending from the sahara through arabia to the thar desert of india originated from sediments eroded from the uplands and deposited in closed interior basins formed during the course of late mesozoic and cenozoic faulting rifting and epeirogenic movements it was the unconsolidated neogene sediments laid down in large subsiding sedimentary basins such as the kufra sirte basin in libya and the chad basin which provided the source material for the late pliocene and quaternary desert dunes of the sahara one effect of the progressive build up of high latitude ice sheets during the neogene was to steepen the temperature and pressure gradients between the equator and the poles resulting in increased trade wind velocities stronger winds were better able to mobilize the alluvial sands of the increasingly dry sahara and adjacent deserts and to fashion them into desert dunes a more subtle form of interaction between eolian and fluvial processes concerns the interplay between desert dust loess accumulation on hill slopes in arid regions and the onset of fine grained valley fill accumulation by sluggish low energy streams in mountain valleys some of these late pleistocene wetlands served as refuge areas for plants reptiles and invertebrates at a time when the surrounding desert plains were very cold and dry as in the flinders ranges of south australia in the arid flinders ranges such valley fills were built up between 35 kyr and 15 kyr ago after which the return of the summer monsoon led to stream channel incision and the formation of a network of gullies often erroneously attributed to human activities understanding the causes of such accelerated erosion can prevent unnecessary and expensive attempts at restoration since the latter are based on the incorrect assumption that overgrazing and present day land use are responsible

pore fluid and seismogenic characteristics of fault rock at depth on the wasatch fault utah fluid inclusions and structural fabric in fault rock in the exhumed footwall of the wasatch fault allow measurement of fluid pressure temperature and composition and estimation of rheological characteristics of fault behavior hydrothermally altered and deformed oligocene quartz monzonite of the little cottonwood stock forms a partially preserved footwall carapace at the southern end of the salt lake segment of the wasatch normal fault zone cataclasite and phyllonite contain two syndeformational alteration mineral assemblages that formed during progressive faulting and displacement of the footwall an early epidote chlorite sericite magnetite alteration assemblage developed in phyllonite and cataclasite and a later laumontite prehnite hematite alteration assemblage developed during cataclasis fluid inclusions associated with the formation of alteration minerals are preserved in healed fractures in quartz grains fluid inclusions that record the transition temperature from quasi plastic flow to frictional deformation are associated with hydrothermal alteration to chlorite epidote and sericite and were trapped at minimum temperatures of 223 c 353 c and minimum fluid pressures of 1150 2800 bars the fluids average 13 mol co2 and 8 2 wt nacl a radiometric age of hydrothermal sericite suggests that the age of the alteration is 17 6 0 7 m y if maximum fluid pressure is near lithostatic the minimum depth of formation of the alteration was 11 km at 337 c consistent with a thermal gradient of 30 c km the ratio of pore fluid pressure to lithostatic pressure varied from 0 52 to nearly 1 0 and indicates that effective normal stress on the fault at these depths may have approached zero structural fabrics and fluid inclusion characteristics are used to estimate seismogenic characteristics of the fault cleavage lineation and s c bands in the phyllonite indicate that deformation at temperatures above 350 c and depths greater than 11 km was dominated by aseismic creep unstable fracture propagation in cataclasite developed during seismic slip at shallower levels the downdip seismogenic length of the salt lake segment is estimated as 16 km using a fault zone dip of 45 and a minimum depth of 11 km for the quasi plastic frictional transition the segment strike length is 35 km and the seismogenic area is about 600 km2 compatible with generation of m 7 0 earthquakes

metamorphic reactions in the biotite zone eastern scotland high thermal gradients metasomatism and cleavage formation prograde metamorphic reactions involving the growth of phyllosilicates and accompanying cleavage development have been investigated in dalradian metasediments from the biotite zone of eastern scotland crystallization of muscovite within the psammites of the southern highland group is linked to the replacement of plagioclase porphyroclasts this reaction is triggered by significant alkali metasomatism during active deformation and plays an important role in the formation of a prominent spaced cleavage within the psammites the si content of most of these early formed muscovites is partially buffered by the quartz content of the rock although close to the highland boundary fault evidence of greater influence from externally derived fluids on muscovite compositions is preserved locally higher fluid fluxes adjacent to the fault are also indicated by a relatively high 18o smow signature in the rocks the biotite producing reaction in these greenschist facies rocks is linked to the later production of a celadonite poor muscovite which formed as overgrowths around pre existing white micas this reaction is sensitive to the initial composition of muscovite and preferentially occurs in quartz rich metasediments containing a celadonite rich muscovite a systematic increase in the progress of the biotite producing reaction northwards across the biotite zone confirms the presence of high geothermal gradients along the southern margin of the dalradian block adjacent to the highland boundary fault

isotopic evidence for channeled fluid flow in low grade metamorphosed jurassic accretionary complex in the northern chichibu belt western shikoku japan the low grade metamorphosed jurassic accretionary complex of the northern chichibu belt hijikawa area western shikoku is divided into two units the hijikawa and kanogawa units that are separated by an out of sequence thrust oost the ozu kawabegawa fault the kanogawa unit south of the ozu kawabegawa fault consists mainly of sandstone shale broken formation of alternating sandstone and shale greenstone chert and pelitic melange while the hijikawa unit is characterized by a stack of subunits separated by small scale thrusts the subunits are mainly made up of basic pelitic and psammitic semischists schistose pelitic melange and chert petrological and mineralogical constraints suggest peak metamorphic conditions of 204 247 c at 1 3 kbar in the kanogawa unit and 228 289 c at 3 5 6 kbar in the hijikawa unit quartz and quartz calcite veins are widely developed in the study area especially in the hijikawa unit regional variations in stable isotopic data show that the 18oquartz and 18ocalcite values in veins tend to increase towards the ozu kawabegawa fault the 18owhole rock values are remarkably high in some subunits close to oosts within the hijikawa unit oxygen isotopic compositions from vein quartz indicate that a higher 18o fluid migrated upward from depth along the ozu kawabegawa fault within the accretionary prism during prehnite pumpellyite facies metamorphism the fluid source is inferred to be pelitic rocks at higher temperatures and greater depths within the accretionary prism

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

thermal conductivity of water saturated rocks from the ktb pilot hole at temperatures of 25 to 300 c the conductivitites of selected gneiss two and amphibolite one core samples have been measured under conditions of elevated temperature and pressure with a needle probe water saturated thermal conductivity measurements spanning temperatures from 25 to 300 c and hydrostatic pressures of 0 1 and 34 mpa confirm the general decrease in conductivity with increasing temperature but deviate significantly from results reported from measurements on dry samples over the same temperature range the thermal conductivity of water saturated amphibolite decreases with temperature at a rate approximately 40 less than the rate for dry amphibolite and the conductivity of water saturated gneiss decreases at a rate approximately 20 less than the rate for dry gneiss the available evidence points to thermal cracking as the primary cause of the more rapid decrease in dry thermal conductivity with temperature the effects of thermal cracking were also observed in the water saturated samples but resulted in a net decrease in room temperature conductivity of less than 3 these results highlight the importance of duplicating in situ conditions when determining thermal conductivity for the deep crust

late cenozoic denudation by large magnitude landslides in the eastern edge of tibetan plateau abstract eastern edge of the tibetan plateau is marked by the longmen shan which experienced pronounced denudation in late cenozoic and was previously attributed to river erosion our recent work however demonstrated that the landsliding must have played an important integral role in the surface processes various scale landslides are present in the peripheral zone of the southern longmen shan which were interpreted as overthrust related klippen in previous works we revisited these exotic blocks and demonstrated that they were actually gravity driven landslides in origin the landslides are composed mostly of thick bedded marine limestone and sandstone of paleozoic early triassic ages and were detached along some weak zones like lower silurian phyllite and unconformities three types of landslides can be categorized distributed stacked and coherent and their differential occurrence is considered to bear upon both uplift rates of the longmen shan and foreland topography outward flow of lower crustal materials from the tibetan plateau interior provides a feasible mechanism for initiating the uplift of its eastern flank in cenozoic positive feedbacks are believed to have existed between extrusion of lower crustal channel flow and surface denudation processes rapid denudation by large magnitude landslides in conjunction with coeval river erosion in the southern longmen shan might have led to predominant sub vertical extrusion of lower crustal flow channel as evidenced by nearly symmetric exhumation of the pengguan massif the northern longmen shan was comparatively less denuded with few basement rocks cropping out and landslides are absent in its front as well differential denudation between the southern and northern longmen shan might have in large part resulted from the lower crustal flow that presumably moved to the southeast and had less impact on the northern longmen shan

the oxygen isotope fractionation behaviour of kyanite in experiment and nature the oxygen isotope fractionation between kyanite and calcium carbonate has been investigated experimentally at four temperatures in the range between 625 and 775 c at 13 kbar because of low exchange rates the isotopic reaction was enhanced by polymorphic transformation of andalusite to kyanite with this experimental modification a close approach to equilibrium was reached in all runs the temperature dependence of the equilibrium fractionation is described by the equation 1000 ln ky cc 2 62 106 t 2 application of the experimental results to natural quartz kyanite garnet assemblages indicates the preservation of the oxygen isotope composition of kyanite acquired during its formation reflecting its extremely low oxygen diffusivity this refractory behaviour restricts the use of kyanite for thermometry but opens the possibility to use its o isotope composition as an indicator for recognition of polymetamorphic rock histories and reconstruction of the prograde evolution of a metamorphic sequence

long term temperature records following the mw 7 9 wenchuan china earthquake are consistent with low friction this is the publisher s final pdf the published article is copyrighted by the geological society of america and can be found at http geology gsapubs org

geothermal study at the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 borehole temperature thermal conductivity and well log data abstract the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 offers a unique opportunity for studying the faulting behavior and the thermal regime of the longmen shan fault zone lmfz east margin of tibetan plateau thermal conductivity of fault rocks within main fault zone shows strong negative interrelations with the porosity the gamma ray and the p wave slowness as well as a positive interrelation with the density here we attribute these correlations to the fractures and the rock fluid reaction generated from the earthquake which will increase the porosity the radioactivity and the p wave slowness as well as decrease the density and the thermal conductivity synchronously 15 continuous temperature profiles were summarized in this paper based on integrated studies of temperature variations and thermal gradients local temperature anomalies were detected at three depth ranges of 480 510 m 580 610 m and 625 755 m respectively these anomalies seem to correspond to different fracture zones and may be attributed to fluid flow in the fractures in addition the non uniform vertical distribution of these temperature anomalies was observed across the co seismic slip surface at 589 2 m in the below 200 m borehole depth a prominent thermal anomaly zone was developed implying more factures were generated in the footwall than the hanging wall during the wenchuan earthquake the heat flow ranges from 69 mw m2 to 72 mw m2 for different logs the persistence of elevated heat flow in the lmfz appears to rule out frictional heating on the yingxiu beichuan fault ybf as the source of the wfsd 1 value but is probably related to the regional tectonic evolution

stable isotope evidence for fluid present and fluid absent metamorphism in metapelites from the damara orogen namibia a large difference of about 5 in the o isotopic composition of quartz characterizes the transition from very low grade or even anchimetamorphic slates to pelites metamorphosed at greenschist facies conditions a further increase in temperature does not result in systematic isotopic shifts mean around 15 5 however immediately at the isograds marking the transition from greenschist to amphibolite facies and amphibolite facies to higher amphibolite facies the quartz 18o values are significantly higher by 1 this increase is restricted to the area immediately at the isograds

palaeomagnetic studies of fold development and propagation in the pembrokeshire old red sandstone abstract the geometry of two folds in lower devonian old red sandstone in pembrokeshire deformed in the hercynian has been defined at intermediate stages during their evolution by this preliminary palaeomagnetic study this is possible because remagnetization appears to have occurred in discrete episodes during deformation and the shape can be reconstructed by restoring the fold limbs to an angle at which the remagnetization directions coincide the plunge of the folds is shown to vary considerably during evolution one fold having an early easterly plunge which changed to the present westerly plunge the other fold having an early plunge which was more steeply to the west than its present attitude clockwise rotation of the whole of southern pembrokeshire by 40 towards the end of or since the hercynian deformation is indicated by the palaeomagnetic data and a structural model for this is proposed

does burial diagenesis reset pristine isotopic compositions in paleosol carbonates abstract sedimentological study of early oligocene continental carbonates from the fluvial dagshai formation of the himalayan foreland basin india resulted in the recognition of four different types namely soil palustrine pedogenically modified palustrine and groundwater carbonates stable oxygen and carbon isotopic 18 o and 13 c analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep burial diagenesis complete isotopic homogenization does not occur 18 o and 13 c analyses of 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with 18 o of more robust bioapatite fossil vertebrate tooth phase show that dense micrites 70 carbonate invariably preserve the pristine 18 o value mean of 9 8 while altered carbonates show much lower 18 o value 13 8 such inhomogeneity causes large intra sample and intra soil profile variability as high as 5 suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains a simple fluid rock interaction model suggests active participation of clay minerals to enhance the effect of fluid rock ratio in local domains during diagenesis this places an upper limit of 70 micrite concentration above which the effect of diagenetic alteration is minimal careful sampling of dense micritic part of the soil carbonate nodules therefore does provide pristine isotopic composition and it is inappropriate as proposed recently to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis based on pristine 13 c value of 8 8 0 2 in soil carbonates an atmospheric co 2 concentration between 764 and 306 ppmv is estimated for the early oligocene 31 ma dagshai time these data show excellent agreement between two independent proxy records viz soil carbonate and marine alkenone and support early oligocene survival of the antarctic ice sheet

high and low density fluids in a quartz vein from the irish variscides abstract combined microstructural and fluid inclusion studies on a multiple quartz vein from the irish variscides reveal a kinematic history consisting of three separate dynamically distinct extensional opening events the first of these is characterized by trapped fluid at densities of 0 87 0 98 g cm 3 indicative of pressures approximating the estimated lithostatic load while fluid densities associated with the following two events 0 76 0 91 g cm 3 clearly indicate sub lithostatic fluid pressures the combined evidence suggests that these later two opening events were extensional fractures occurring well below the critical depth for tensional 3 least effective principal stress it is argued here that the preservation of such low density fluids in an environment that conventionally requires supra lithostatic fluid pressures for hydraulic failure is due to i the influence of a preexisting material anisotropy in the rock that would result in hybrid extensional failure ii the effect of stress heterogeneities associated with the development of crude boudins in the vein

chemistry source and behavior of fluids involved in alpine thrusting of the central pyrenees quartz veins occupying extensional fractures that formed relatively late in the alpine thrusting history of the pyrenees contain abundant inclusions of hypersaline brines small amounts of bitumen also occur a range of brine compositions is apparent from the freezing behavior of fluid inclusions from different samples with large variations in na ca ratio but many individual samples contain only one brine composition all brine types display a bimodal distribution of homogenization temperature which is interpreted as the result of fluctuation in fluid pressure from a maximum value equal to lithostatic at 5 7 km depth and around 270 c to a value up to 700 bars lower this is ascribed to dilatancy pumping chemical analyses of brines leached from two samples yields balanced analyses for 14 elements both analyses appear to represent sedimentary formation waters and are closely analogous to oil field brines a basement origin is precluded by the presence of bitumens and the low k ca ratios differences between the analyses probably reflect different source bed mineralogy including the presence or absence of dolomite but triassic red beds are likely to be a major source the occurrence of these brines in the fault planes provides constraints on both the sources and movement of the fluids involved in thrusting significant infiltration of either surface waters or metamorphic water of dehydration can be ruled out because of the high salinities typically 20 25 wt dissolved salts hence although permeability was locally high due to fracturing around the faults fluids were pumped into these fractures from sedimentary formations adjacent to the fault individual fluid pathways were short lived relative to the duration of the deformation event so that different fluids were pumped into the faults at different times in response to local fault propagation