corumbella an ediacaran grade organism from the late neoproterozoic of brazil abstract the morphology and phylogenetic affinities of corumbella werneri hahn g hahn r leonardos o h pflug h d and walde d h g 1982 korperlich erhaltene scyphozoen reste aus dem jungprakambrium brasiliens geologica et paleontologica 16 1 18 type species of the genus is reinterpreted based on new material from the tamengo formation corumba group upper neoproterozoic of western mato grosso do sul brazil corumbella secreted a narrow elongate tetraradially symmetrical tube reinterpretation of tube morphology and new evidence of reproduction by means of budding indicate close affinities with the present day coronate scyphozoan cnidarian stephanoscyphus and possibly the conulariids corumbella species were distributed between the amazon craton and laurentia corumbella is interpreted as a sessile predator and provides evidence of the importance of predation in animal evolution during the late neoproterozoic

west florida continental shelf response to upwelling favorable wind forcing 2 dynamics dynamics analyses are presented for the west florida continental shelf response to upwelling favorable alongshore or offshore winds using a three dimensional time dependent primitive equation model these analyses complement the kinematics analyses of li and weisberg 1999 results are provided on four topics 1 the response evolutions to quasi steady states 2 the across shelf distributions of the vertically integrated alongshore and across shelf momentum balances 3 the three dimensional structures of the terms composing the momentum balance closures and 4 the model sensitivity to vertical friction parameterization the response evolution starts with a local wind driven acceleration and it transitions over the inner shelf into a primary balance between the pressure gradient coriolis and vertical friction terms thus the inner shelf spin up takes a classical ekman geostrophic route the middle shelf takes longer because it also depends on coastal boundary effects notably the partial closure of the domain in the south by the florida keys the outer shelf never achieves a steady state because of topographic wave effects coastline and isobath geometries result in fully three dimensional flow fields thus a two dimensional model that ignores alongshore variations cannot account for the results obtained the inner shelf is the transition region between ekman and ekman geostrophic balances where the surface slope results from mass adjustments through overlapping surface and bottom ekman layers across the inner shelf the vertically integrated momentum balance shows a gradual trade off between the coriolis pressure gradient and bottom friction terms and with the inner shelf frictionally determined its scale is sensitive to vertical friction parameterization

stable isotope and rare earth element evidence for recent ironstone pods within the archean barberton greenstone belt south africa there is considerable debate about the mode and age of formation of large up to 200 m long hematite and goethite ironstone bodies within the 3 2 to 3 5 ga barberton greenstone belt we examined oxygen and hydrogen isotopes and rare earth element ree concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from sea floor vents in the archean ocean or from recent surface and shallow subsurface spring systems goethite d 18 o values range from 0 7 to 1 0 and dd from 125 to 146 which is consistent with formation from modern meteoric waters at 20 to 25 c hematite d 18 o values range from 0 7 to 2 0 which is consistent with formation at low to moderate temperatures 40 55 c from modern meteoric water ree in the goethite and hematite are derived from the weathering of local sideritic ironstones silicified ultramafic rocks sideritic black cherts and local felsic volcanic rocks falling along a mixing line between the eu eu and shale normalized hreeavg lreeavg values for the associated silicified ultramafic rocks and felsic volcanic rocks contrasting positive ce ce of 1 3 to 3 5 in hematite and negative ce ce of 0 2 to 0 9 in goethite provides evidence of oxidative scavenging of ce on hematite surfaces during mineral precipitation these isotopic and ree data taken together suggest that hematite and goethite ironstone pods formed from relatively recent meteoric waters in shallow springs and or subsurface warm springs

elastic properties of high grade metamorphosed igneous rocks from enderby land and eastern dronning maud land antarctica evidence for biotite bearing mafic lower crust

oxygen isotopes in iron iii oxides abstract quartz sio 2 and hematite fe 2 o 3 possess considerably different gram formula weights and different stoichiometric coefficients for their oxygen these differences mean that the numerical values of sio 2 and fe 2 o 3 compositions when reported as weight percent are not the same as the numerical values of x o i e oxygen in the mineral as a mole percent of the total oxygen in a binary quartz hematite system consequently end member quartz and hematite 18 o values which are determined from linear extrapolations of 18 o vs weight percent fe 2 o 3 data from binary mixtures can be in error by as much as several per mil extrapolation to end member 18 o values in binary quartz hematite systems should always be performed using mole fraction of oxygen as the compositional variable the hematite water fractionation curve of yapp and the quartz water curve of knauth and epstein were used together with the kinetic isotope exchange model of criss et al to constrain the depositional environment of the late proterozoic quartz hematite banded iron formation deposits of urucum brazil the depositional temperatures permitted by the model assumptions employed here range from 0 to 35 c or 54 c the permitted range of depositional water 18 o values is from 6 6 or 8 9 to 0 0 while the range of permitted depositional conditions is rather large it does encompass the possible cool temperatures and brackish or fresh waters which are indicated by sedimentologic evidence in these deposits

high resolution seismic velocities and shallow structure of the san andreas fault zone at middle mountain parkfield california a 5 km long high resolution seismic imaging survey across the san andreas fault saf zone and the proposed san andreas fault observatory at depth safod drill site near parkfield california shows that velocities vary both laterally and vertically velocities range from 4 0 km sec probably correspond to granitic rock of the salinian block which is exposed a few kilometers southwest of the saf the depth to the top of probable granitic rock varies laterally along the seismic profile but is about 600 m below the surface at the proposed safod site we observe a prominent lateral low velocity zone lvz beneath and southwest of the surface trace of the saf the lvz is about 1 5 km wide at 300 m depth but tapers to about 600 m wide at 750 m depth at the maximum depth of the velocity model 750 m the lvz is centered approximately 400 m southwest of the surface trace of the saf similar velocities and velocity gradients are observed at comparable depths on both sides of the lvz suggesting that the lvz is anomalous relative to rocks on either side of it velocities within the lvz are lower than those of san andreas fault gouge and the lvz is also anomalous with respect to gravity magnetic and resistivity measurements because of its proximity to the surface trace of the saf it is tempting to suggest that the lvz represents a zone of fractured crystalline rocks at depth however the lvz instead probably represents a tectonic sliver of sedimentary rock that now rests adjacent to or encompasses the saf such a sliver of sedimentary rock implies fault strands on both sides and possibly within the sliver suggesting a zone of fault strands at least 1 5 km wide at a depth of 300 m tapering to about 600 m wide at 750 m depth fluids within the sedimentary sliver are probably responsible for observed low resistivity values

the frictional nearshore response to forcing by synoptic scale winds abstract an analytic barotropic model was used to study the nearshore frictional response to synoptic scale wind forcing the results depend only on the region where the surface and bottom ekman layers interact strongly and the water is consequently well mixed thus the conclusions apply even to shelves where baroclinic effects are not negligible father offshore the main findings are as follows i the blocking of the surface ekman flux which drives the shelf flow is a consequence of the interaction of ekwan layers in the nearshore region the interaction transfers progressively more of the surface stress directly to bottom stress as the depth decreases the consequent decrease in ekman flux toward the shore creates an ekman flux divergence which drives the interior flow ii the region over which the shelf is effectively forced is narrow it extends approximately from where the depth divided by the ekman layer e folding scale is 0 2 to where it is 2 5 iii simple equations for pressure and the

composition and tectonic evolution of the chinese continental crust constrained by poisson s ratio article i nfo we have measured both p and s wave velocities vp and vs and poisson s ratios of 60 typical ultrahigh pressure uhp metamorphic rock samples from the chinese continental scientific drilling ccsd main and pre pilot holes and surface outcrops in the sulu dabie orogenic belt at hydrostatic confining pressures up to 850 mpa the experimental results together with those compiled in handbook of seismic properties of minerals rocks and ores ji s c wang q xia b 2002 handbook of seismic properties of minerals rocks and ores polytechnic international press montreal 630 pp reveal that except for monomineralic rocks such as quartzite serpentinite anorthosite limestone and marble the rest of the rock types have poisson s ratios falling along an upward convex curve determined from the correlations between elastic moduli and density poisson s ratios increase with density as the lithology changes from granite felsic gneiss and schist through diorite syenite intermediate gneiss and metasediment to gabbro diabase amphibolite and mafic gneiss and then decrease as the rocks become ultramafic in composition eclogite has a higher density but a lower poisson s ratio than peridotite the results were applied to constrain the crustal composition and tectonic evolution of the chinese continental crust based on crustal thickness h and poisson s ratio from 248 broadband seismic stations measured using teleseismic receiver function techniques the north china yangtze south china and northeast china blocks and songpan ganzi terrane are dominated by low b0 26 and moderate 0 26 b0 28 values n70 suggesting the dominance of felsic composition in the crust the lhasa terrane qiangtang terrane and indochina block are characterized by high proportions 33 42 of measurements with very high values 0 30 and h is found for the south china block northeast block lhasa block qiangtang terrane and indochina block indicating either tectonic thickening of the felsic upper and middle crust by folding and thrusting or the removal of mafic layers from the lower crust into the upper mantle by delamination

anomalous seismic velocity drop in iron and biotite rich amphibolite to granulite facies transitional rocks from deccan volcanic covered 1993 killari earthquake region maharashtra india a case study 65 ma deccan volcanic province of western india forms one of the largest flood basaltic eruptions on the surface of the earth the nature of the concealed crust below this earthquake prone region which is marked by several low velocity zones at different depths has hardly been understood these low velocity zones have been invariably interpreted as fluid filled zones genetically connected to earthquake nucleation while carrying out detailed geological and petrophysical studies on the late archean basement cores obtained from a 617 m deep klr 1 borehole drilled in the epicentral zone of 1993 killari earthquake region of the southern deccan volcanic province we came across several instances where we observed remarkable drop in measured p wave velocity in a number of high density cores we provide detailed petrographic and geological data on 11 such anomalous samples which belong to mid crustal amphibolite to granulite facies transitional rocks they are associated with a mean p wave velocity of 6 02 km s range 5 82 6 22 km s conforming to granitic upper crust but in contrast have a high mean density of 2 91 g cm3 range 2 75 3 08 g cm3 which characterise mid to lower crust this velocity drop which is as much as 15 in some cores is primarily attributed to feot enrichment up to about 23 wt during the course of mantle fluid driven retrogressive metasomatic reactions caused by exhumation of deep seated mafic rocks presence of iron content mainly magnetite widely seen as opaques in thin sections of the rocks seems to have resulted into sharp increase in density as well as mean atomic weight our study indicates that the measured vp is inversely related to feot content as well as mean atomic weight of the rock

observations and simulation of a bottom ekman layer on a continental shelf a numerical model was used to simulate the bottom ekman layer of a continental shelf region the basis for the model was the mellor and yamada level 2 turbulence closure scheme conservation equations for momentum turbulent kinetic energy and turbulent length scale were utilized in the model the model was used to simulate data taken from a cyclesonde mooring on the peruvian continental shelf in may 1976 as part of the joint ii coastal upwelling ecosystems analysis program the cyclesonde provided mean horizontal velocity temperature salinity and pressure data an intense poleward undercurrent drove the bottom flow regime the most striking feature of the data was the clockwise ekman veering of velocity vectors as the bottom was approached a 48 hour period was chosen for the model simulations the vertical profile of speed 48 hours mean simulated by the model fell within the error bars of the data the corresponding ekman spiral display of the model results also showed good agreement with the observati ons

the relationship between seismic velocity and density in the continental crust a useful constraint summary plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa although a single linear relationship is often assumed in crustal gravity calculations because of the scatter whenever rocks of known seismic velocity are converted to density using this relationship a reduction is made to the resolving power of the resulting gravity calculation if these rocks reach thicknesses of more than a few kilometres then the uncertainties become significant when compared with the size of commonly observed gravity anomalies examples are considered from the north sea mississippi and carolina trough it is concluded that the use of a seismic velocity measurement as the only indication of rock density does not provide a useful constraint when attempting to reproduce observed gravity variations an appropriate model for isostatic compensation is probably the most important factor for successful predictions of crustal structure on the basis of gravity data

an upwelling case study on florida s west coast using a combination of satellite sea surface temperature imagery in situ currents temperature and sea level data and a numerical circulation model we describe an upwelling event observed along florida s west coast although ubiquitous features of continental shelves descriptions of coastal upwellings or downwellings are generally complicated by the continuum of processes in which they occur for the case study presented the winds were light and the baroclinic background currents were steady for several days prior to the event these conditions allow the evolution of a specific winddriven upwelling event to be viewed as an initial value problem the data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical ekman geostrophic one sea level drops due to an offshore ekman transport causing a geostrophic alongshore jet and the associated onshore flow within the bottom ekman layer accounts for the appearance of cold water at the surface this surface manifestation occurs as an elongated feature centered about the 25 m isobath that spans roughly half of the florida peninsula from just north of tampa bay to key west the coldest water is observed offshore from tampa bay and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries

oxygen isotopic composition of ferric oxides from recent soil hydrologic and marine environments low temperature synthesis experiments on ferric oxide water systems have resulted in disparate oxygen isotope fractionation temperature t curves in this study recent ferric oxides mostly goethites of holocene age were collected and analyzed from a variety of modern soil stream and marine environments where formation temperature and the oxygen isotopic composition 18o of the water from which ferric oxides precipitated can be independently measured or estimated this allows comparison of experimental t relationships with data from natural systems selective dissolution methods were refined for the pretreatment of fine grained minerals in order to obtain reliable 18o values for pure and crystalline ferric oxides the difference 18o between the 18o value of goethite and that of local mean meteoric water ranges from 1 5 to 6 3 for soil goethites from new jersey indiana michigan iowa south dakota and taiwan we argue that these variations are largely the result of differences between the 18o of formation water and that of local mean meteoric water induced probably by 18o enrichment of soil waters by evaporation or other processes in soil horizons where ferric oxides are forming a marine goethite sample from scotland and a subaqueous bog iron sample from new jersey which can not be biased by evaporative processes provide crucial natural evidence that the difference in 18o between goethite and formation water is 1 5 at 10 c this result is consistent with our prior laboratory synthesis results bao and koch 1999 but in conflict with other experimental calibrations given the highly variable 18o value of soil or other surface water as well as the potential of initially formed ferric oxides for reequilibration with subsurface burial fluids during maturation to crystalline phases an understanding of formational and diagenetic conditions is absolutely essential when attempting to use the oxygen isotope composition of ferric oxides as a paleoclimatic proxy

west florida shelf response to upwelling favorable wind forcing kinematics the barotropic responses of the west florida continental shelf to idealized upwelling favorable alongshore and offshore wind stresses are studied using the three dimensional time dependent primitive equation princeton ocean model pom when forced with uniform winds the shelf circulation evolves quickly to a quasi steady state a southeastward alongshore wind lowers sea level along the coast and drives a southeastward coastal jet with a relatively weak northwestward return flow farther offshore a southwestward offshore wind lowers sea level along the west florida coast and raises sea level along the panhandle coast two independent circulation gyres are set up in association with these regionally different sea level distributions an anticyclonic gyre off the west florida coast consisting of a southeastward coastal jet and a broad return flow over the middle shelf and a cyclonic gyre off the panhandle coast consisting of a strong northwestward coastal jet and an adjacent narrow southeastward undercurrent these gyres are separated by the big bend region in both cases alongshore and offshore wind forcing the circulations are fully three dimensional with opposing surface and bottom boundary layer flows accounting for the across shelf transports the shapes of the coastline and the isobaths are important determinants of the shelf wide responses several locally maximum upwelling regions are identified for geometrical reasons these include the panhandle coast south of apalachicola bay the west florida coast south of tampa bay along the florida keys and at the shelf break where topographic rossby waves are evident

anomalous crustal and lithospheric mantle structure of southern part of the vindhyan basin and its geodynamic implications abstract tectonically active vindhyan intracratonic basin situated in central india forms one of the largest proterozoic sedimentary basins of the world possibility of hydrocarbon occurrences in thick sediments of the southern part of this basin has led to surge in geological and geophysical investigations by various agencies an attempt to synthesize such multiparametric data in an integrated manner has provided a new understanding to the prevailing crustal configuration thermal regime and nature of its geodynamic evolution apparently this region has been subjected to sustained uplift erosion and magmatism followed by crustal extension rifting and subsidence due to episodic thermal interaction of the crust with the hot underlying mantle almost 5 6 km thick sedimentation took place in the deep faulted jabera basin either directly over the bijawar mahakoshal group of mafic rocks or high velocity high density exhumed middle part of the crust detailed gravity observations indicate further extension of the basin probably beyond nsl rift in the south a high heat flow of about 78 mw m2 has also been estimated for this basin which is characterized by extremely high moho temperatures exceeding 1000 c and mantle heat flow 56 mw m2 besides a very thin lithospheric lid of only about 50 km many areas of this terrain are thickly underplated by infused magmas and from some segments granitic gneissic upper crust has either been completely eroded or now only a thin veneer of such rocks exists due to sustained exhumation of deep seated rocks a 5 8 km thick retrogressed metasomatized zone with significantly reduced velocities has also been identified around mid to lower crustal transition

deep crustal structure of the indian shield from joint inversion of p wave receiver functions and rayleigh wave group velocities implications for precambrian crustal evolution 1 the s wave velocity structure of the crust and uppermost mantle of the indian shield has been investigated by jointly inverting p wave receiver functions and rayleigh wave group velocities at 38 broadband stations in the subcontinent the indian shield is an amalgamation of several terranes of archean and proterozoic age that were partly flooded by deccan trap volcanism during cenozoic times and that make up a natural laboratory for assessing models of precambrian crustal evolution our results reveal significant variations in crustal thickness and deep crustal velocities 45 50 km thick under the archean west dharwar craton and southern granulite terrane with lower crustal velocities around 4 1 km s 32 35 km thick beneath the archean east dharwar and bundelkhand cratons with lower crustal velocities around 3 8 3 9 km s 50 65 km thick under the proterozoic bhandara craton with lower crustal velocities around 4 2 4 3 km s and 55 km thick under the proterozoic aravalli delhi belt with lower crustal velocities around 4 2 km s s velocities in the 4 1 4 3 km s range in the deep crust can be attributed to mafic lithologies suggesting there has been no secular change in the precambrian evolution of the south indian shield moreover pervasive mafic dike swarming throughout the indian shield suggests that the layer of mafic cumulates is 2 5 1 6 ga old and that it delaminated from some archean terranes our interpretation is that mafic underplating of the terranes making up the indian shield occurred in proterozoic times and that a refractory root developed under the archean terranes after the proterozoic event

invsp gathers of local earthquake seismograms an approach for modelling the upper crustal p and s velocity structure summary a new approach is presented here for obtaining invsp gathers of local earthquake seismograms in regions with adequate seismogenic depth range the inverse vertical seismic profiling invsp geometry is in principle quite similar to the up hole surveys of shallow seismic exploration in which shots fired at various depths in boreholes are recorded on the surface at a fixed offset similarly local earthquake seismograms of selected events at different hypocentral depths can be gathered into constant offset invsp sections for various stations of a mobile seismograph network they can be modelled for p and s velocity structure to upper crustal depths at each of the stations in the network with the aid of synthetic seismogram computations using appropriate source mechanisms of the earthquakes used an invsp gather obtained to a depth range of about 10 km at a station with 28 km constant offset is modelled for the upper crustal p and s velocity structure in the koyna warna seismic region in the western indian shield to demonstrate this approach

elastic wave velocities chemistry and modal mineralogy of crustal rocks sampled by the outokumpu scientific drill hole evidence from lab measurements and modeling the outokumpu scientific deep drill hole intersects a 2500 m deep precambrian crustal section comprising a 1300 m thick biotite gneiss series mica schists at top followed by a 200 m thick meta ophiolite sequence underlain again by biotite gneisses mica schists 500 m thick with intercalations of amphibolite and meta pegmatoids pegmatitic granite from 2000 m downward the dominating rock types are meta pegmatoids pegmatitic granite average isotropic intrinsic p and s wave velocities and densities of rocks were calculated on the basis of the volume fraction of the constituent minerals and their single crystal properties for 29 core samples covering the depth range 198 2491 m the modal composition of the rocks is obtained from bulk rock xrf and mineral chemistry microprobe using least squares fitting laboratory seismic measurements on 13 selected samples representing the main lithologies revealed strong anisotropy of p and s wave velocities and shear wave splitting seismic anisotropy is strongly related to foliation and is in particular an important property of the biotite gneisses which dominate the upper and lower gneiss series at in situ conditions velocity anisotropy is largely caused by oriented microcracks which are not completely closed at the pressures corresponding to the relatively shallow depth drilled by the borehole in addition to crystallographic preferred orientation cpo of the phyllosilicates the contribution of cpo to bulk anisotropy is confirmed by 3d velocity calculations based on neutron diffraction texture measurements for vertical incidence of the wave train the in situ velocities derived from the lab measurements are significantly lower than the measured and calculated intrinsic velocities the experimental results give evidence that the strong reflective nature of the ophiolite derived rock assemblages is largely affected by oriented microcracks and preferred crystallographic orientation of major minerals in addition to the lithologic control c 2009 elsevier b v all rights reserved

west florida shelf mean circulation observed with long term moorings 1 the mean circulation on the west florida continental shelf is described using long term current measurements bounded by the florida peninsula to the east and the gulf of mexico to the west the west florida continental shelf mean flow is oriented approximately along isobath and southward the mean velocity vectors veer systematically with depth shoreward over shallow water and seaward over deeper water this polarization change implies that the mean flow is upwelling over shallow water and downwelling seaward from the inner shelf such a well organized three dimensional coastal ocean circulation pattern revealed by an unprecedented set of observations and explained on the basis of wind forcing and density field adjustment has important implications for both fisheries and red tide occurrences

ultrasonic p and s wave attenuation and petrophysical properties of deccan flood basalts india as revealed by borehole studies petrophysical properties and ultrasonic p and s wave attenuation measurements on 35 deccan basalt core specimens recovered from killari borehole site in western india provide unique reference data sets for a lesser studied deccan volcanic province these samples represent 338 m thick basaltic column consisting four lava flows each of ambenali and poladpur formations belonging to wai subgroup of the deccan volcanic sequence these basalt samples are found to be iron rich average feot 13 4 wt but relatively poor in silica content average sio2 47 8 wt the saturated massive basalt cores are characterized by a mean density of 2 91 g cm3 range 2 80 3 01 g cm3 and mean p and s wave velocities of 5 89 km s range 5 01 6 50 km s and 3 43 km s range 2 84 3 69 km s respectively in comparison saturated vesicular basalt cores show a wide range in density 2 40 2 79 g cm3 as well as p wave 3 28 4 78 km s and s wave 1 70 2 95 km s velocities based on the present study the deccan volcanic sequence can be assigned a weighted mean density of 2 74 g cm3 and a low vp and vs of 5 00 and 3 00 km s respectively such low velocities in deccan basalts can be attributed mainly to the presence of fine grained glassy material high iron contents and hydrothermally altered secondary mineral products besides higher porosity in vesicular samples the measured q values in saturated massive basalt cores vary enormously qp 33 1960 and qs 35 506 while saturated vesicular basalt samples exhibit somewhat lesser variation in qp 6 46 as well as qs 5 49 in general high porosity rocks exhibit high attenuation but we observed the high value of attenuation in some of the massive basalt core samples also in such cases energy loss is mainly due to the presence of fine grained glassy material as well as secondary alteration products like chlorophaeite that could contribute to intrinsic attenuation dominance of weekly bound secondary minerals might also be responsible for the generation of microcracks which may generate squirt flow in saturated samples hence we argue that the deccan basalts attenuate seismic energy significantly where its composition plays a major role

along shelf current variability on the catalan inner shelf nw mediterranean 1 we examine the circulation over the inner shelf of the catalan sea using observations of currents obtained from three acoustic doppler current profilers two at 24 m and one at 50 m during march april 2011 the along shelf current fluctuations during that period are mainly controlled by local wind stress on short time scales and by remote pressure gradients on synoptic time scales different forcing mechanisms are involved in the along shelf momentum balance during storm conditions wind stress sea level gradients and the nonlinear terms dominate the balance during weak wind conditions the momentum balance is controlled by the pressure gradient while during periods of moderate wind in the presence of considerable stratification the balance is established between the coriolis and wind stress terms vertical variations of velocity are affected by the strong observed density gradient the increased vertical shear is accompanied by the development of stratified conditions due to local heating when the wind is not able to counteract and break stratification the occasional influence of the besos river plume is observed in time scales of hours to days in a limited area in near the city of barcelona the area affected by the plume depends on the vertical extent of the fresher layer the fast river discharge peak and the relaxation of cross shore velocities after northeast storm events this contribution provides a first interpretation of the inner shelf dynamics in the catalan sea

seismic measurements of the internal properties of fault zones the internal properties within and adjacent to fault zones are reviewed principally on the basis of laboratory borehole and seismic refraction and reflection data the deformation of rocks by faulting ranges from intragrain microcracking to severe alteration saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity but from borehole measurements densely fractured rocks do show significantly reduced velocities the amount of reduction generally proportional to the fracture density highly fractured rock and thick fault gouge along the creeping portion of the san andreas fault are evidenced by a pronounced seismic low velocity zone lvz which is either very thin or absent along locked portions of the fault thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone high pore pressure within the pronounced lvz may be conductive to fault creep deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated seismically anisotropic mylonites

oxygen and hydrogen isotope variations among goethites α feooh and the determination of paleotemperatures abstract a plot of d vs 18o values from a diverse group of natural goethites defines a data array which is approximately parallel to the meteoric water line the 18o values range from 9 5 to 4 4 per mil while the corresponding d values vary from 202 to 94 per mil there is considerable scatter in the d vs 18o array which can be attributed primarily to different temperatures of mineral formation as determined previously yapp and pedley 1985 and confirmed in this study the goethite water d h fractionation factor is essentially independent of temperature over the range from 25 c to 145 c however the goethitewater 18 o 16 o fractionation factor does vary with temperature as indicated by initial goethite synthesis experiments conducted at 25 c 44 c and 62 c the synthetic goethite 18 g w values suggest that the natural goethites in this study formed at temperatures that may range from about 8 c to 66 c support for the validity of these approximate calculated temperatures is provided by a natural goethite sample from the atlantis ii deep in the red sea these results suggest that goethite can be used as a single mineral low temperature geothermometer perhaps more importantly goethite can be used in low temperature oxygen isotope mineral pair geothermometers such as chert goethite calcite goethite phosphate goethite etc

momentum balances on the inner continental shelf at martha s vineyard coastal observatory 1 the subtidal depth average momentum balances in 12 m and 27 m water depth are investigated using observations from 2001 to 2007 of water velocity temperature and density bottom pressure surface gravity waves and wind stress in the fluctuating across shelf momentum budget the dominant terms are surface wind stress pressure gradient and coriolis acceleration the balance is a combination of 1 the geostrophic balance expected at midshelf sites and 2 the coastal setup and setdown balance driven by the across shelf wind stress expected where surface and bottom boundary layers overlap at the 12 m site the estimated wave radiation stress gradient due to surface gravity wave shoaling is also large but is uncorrelated with the observed pressure gradient a simple model suggests the wave radiation stress gradient is balanced by an across shelf pressure gradient with a spatial scale too small to resolve with this mooring array in the fluctuating along shelf momentum balance the dominant terms are surface wind stress pressure gradient and bottom stress at the shallower site but the other estimated terms are not negligible our results support the grant and madsen 1986 formulation for wave induced bottom stress the fluctuating along shelf pressure gradient is mainly a local sea level response to wind forcing not a remotely generated pressure gradient a strong correlation between along shelf velocity and along shelf wind stress at the shallower site is captured by a simple steady model of imbalance between wind stress and pressure gradient balanced by linear bottom drag

polymetamorphic relations in iron ores from the iron quadrangle brazil the correlation of oxygen isotope variations with deformation history this study deals with the oxygen isotope composition of hematite rich ore bodies in the iron quadrangle brazil the area studied can be divided into two different regions a western w zone of greenschist facies assemblages and an eastern e zone of amphibolite facies with transitions into granulite facies assemblages

contrasting behavior of oxygen and iron isotopes in banded iron formations revealed by in situ isotopic analysis abstract in situ o and fe isotope measurements of magnetite and hematite in banded iron formations bifs from the 2 5 ga dales gorge member of the brockman iron formation hamersley group western australia document distinct fine scale isotopic zonation for hematite o 18 values vsmow range from 7 1 to 0 6 and fe 56 values range from 0 50 to 1 53 magnetite has a o 18 range of 5 6 to 7 0 and a fe 56 range of 0 76 to 1 33 notably magnetite shows significant o isotope variability at a o 18 values exists between low si core and si rich overgrowth iron isotope compositions are homogeneous to 0 2 in fe 56 values within individual grains or layers hematite is always isotopically heavier than co existing magnetite by 0 1 0 4 in fe 56 within individual samples and there is a large variation 2 in fe 56 values between bif samples at the m scale e g between meso or macro bands of the dales gorge member in situ isotopic results highlight the distinct behavior of o and fe isotopes during interaction with post deposition diagenetic or metamorphic fluids the large variations in o 18 values of iron oxides likely reflect exchange with fluids during post depositional events at temperatures up to ca 280 c and the lower o 18 values of fe oxides are interpreted to reflect less isotopic modification and lower temperatures o 18 variations support a model where initial fe oh 3 precipitates that formed in the photic zone were converted to hematite during very early diagenesis followed by production of magnetite over a range of temperatures during later diagenesis metamorphism in contrast magnetite and hematite seem to have preserved the initial fe 56 values of early fe oh 3 precipitates despite significant changes in o isotope compositions in magnetite the consistency in apparent fe isotope fractionation between co existing hematite and magnetite suggests that they share a common precursor where magnetite was formed in soft sediment through in situ reduction by microbial processes and possibly including reaction with aqueous fe ii combined in situ fe o isotope analyses allow distinctions to be made between near primary and post depositional signatures in bifs which bears on the use of bifs as paleo environmental proxies and recorders of microbial processes

seismogenesis of the lower crustal intraplate earthquakes occurring in kachchh gujarat india abstract large intraplate continental earthquakes like the 1811 12 new madrid m w 8 0 and the 2001 bhuj mw7 7 were highly destructive because they occurred in strong crust but the mechanisms underlying their seismogenesis are not understood here we show using local earthquake velocity tomography and joint inversion of receiver functions and surface wave group velocity dispersion that the crust and uppermost mantle beneath the 2001 bhuj earthquake region of western india is far more complex than hitherto known through previous studies a new image of the crust and underlying mantle lithosphere indicates the presence of a 18 km thick high velocity vp 7 15 8 11 km s differentiated crustal and mantle magmatic layer above a hot and thin lithosphere only 70 km in the epicentral region of 2001 bhuj earthquake this magmatic layer begins at the depth of 24 km and continues down to 42 km depth below this region brittle ductile transition reaches as deep as the moho 34 km due to the possible presence of olivine rich mafic magma our 1 d velocity structure envisages an initial phase of plume activity deccan plume at 65 m y ago resulting in basaltic magma in the eclogitic layers at sub lithospheric levels wherein they were subjected to crystallization under ultra high pressure conditions our study also delineates an updoming of moho 4 7 km as well as asthenosphere 6 10 km below the kachchh rift zone relative to surrounding areas suggesting the presence of a confined body of partial melts below the lithosphere asthenosphere boundary restructuring of this warm and thin lithosphere may have been caused due to rifting at 184 and 88 m y ago and tholeiitic and alkalic volcanism related to the deccan traps k t boundary event at 65 m y ago recent study of isotopic ratios proposed that the alkalic basalts found in kachchh are generated from a co 2 rich lherzolite partial melts in the asthenosphere that ascended along deep lithospheric rift faults into the lithosphere it appears that such kind of crust mantle structure deepening of brittle ductile transition and a high input of volatiles containing co 2 emanating from mantle control the seismogenesis of lower crustal earthquakes in the kachchh continental rift zone

composition and origin of hydrothermal ironstones from central pacific seamounts abstract ironstones recovered from five late cretaceous seamounts in the central pacific region probably formed during late stage edifice building volcanism ironstones are dense and compact with the appearance of brown chert the ironstones are characterized by a goethite mineralogy with feooh contents up to 88 extreme fractionation of fe and mn low trace element and rare earth element abundances low co zn ratios and isotopic equilibration temperatures of about 20 45 c these characteristics indicate that the ironstones formed from hydrothermal fluids ironstones probably formed below the seawater seafloor interface as indicated by their occurrence as a proximal hydrothermal deposit presence of primary goethite cement pervasive replacement of rocks by goethite and absence of interbedded pyro clastic beds

permo pennsylvanian palaeotemperatures from fe oxide and phyllosilicate δ18o values abstract the oxygen isotope composition of fossil roots that have been permineralized by hematite are presented from eight different stratigraphic levels spanning the upper pennsylvanian and lower permian strata of north central texas hematite 18o values range from 0 4 to 3 7 the most negative 18o values occur in the upper pennsylvanian strata and there is a progressive trend toward more positive 18o values upward through the lower permian strata this stratigraphic pattern is similar in magnitude and style to 18o values reported for penecontemporaneous authigenic palaeosol phyllosilicates and calcites suggesting that all three minerals record similar paragenetic histories that are probably attributed to temporal palaeoenvironmental changes across the late pennsylvanian and early permian landscapes palaeotemperature estimates based on paired 18o values between penecontemporaneous hematite and phyllosilicate samples suggest these minerals co precipitated at relatively low temperatures that are consistent with a supergene origin in a low latitude soil forming environment hematite phyllosilicate 18o pairs indicate 1 relatively low soil temperatures 24 3 c during deposition of the upper pennsylvanian strata followed by 2 a considerable rise in soil temperatures 35 37 3 c during deposition of the lowermost permian strata significantly d and 18o values of contemporaneous phyllosilicates provide single mineral palaeotemperature estimates that are analytically indistinguishable from temperature estimates based on hematite phyllosilicate oxygen isotope pairs the results between the two temperature proxy methods suggest that the inferred large temperature change across the upper pennsylvanian lower permian boundary might be taken seriously if real such a significant climate change would have undoubtedly had far reaching ecological effects within this region of pangaea notably there are important lithological and palaeobotanical changes such as disappearance of coal and coal swamp floras across the upper pennsylvanian early permian boundary of north central texas that may be consistent with major climatic change toward warmer conditions

wind driven currents on the west florida shelf abstract three weeks of current meter wind and sea level data off cedar key florida are analyzed currents and sea level are found to be coherent with alongshore wind stress in the synoptic band 0 05 0 25 cycle per day and to lag it by approximately half a day little coherence is found with cross shelf wind stress at the inshore mooring 22 m depth currents are nearly barotropic for these winter 1978 data a linear parameterization of bottom stress in the barotropic alongshore current leads to a bottom friction parameter r of 0 01 0 02 cm s 1 using coastal wind stress no significant steady alongshore slope is found during this short interval the dominant momentum balance in the alongshore direction is between wind and bottom stress the offshore frictional length scale csanady 1978 is estimated to be 75 100 km which implies a seaward extent to a depth of about 30 m at the offshore mooring 44 m depth there is vertical shear between the currents at 9 and 39 m the upper cross shelf compon

upwarped high velocity mafic crust subsurface tectonics and causes of intraplate latur killari m 6 2 and koyna m 6 3 earthquakes india a comparative study abstract a unique attempt is made to understand the genesis of intraplate seismicity in the latur killari and koyna seismogenic regions of india through derived crustal structure by synthesizing active and passive seismic magnetotelluric gravity and heat flow data it has indicated presence of relatively high velocity density intermediate granulite and amphibolite facies rocks underneath the deccan volcanic cover caused mainly due to a continuous geodynamic process of uplift and erosion since precambrian times these findings have been independently confirmed by detailed borehole geological geochemical and mineralogical investigations the crystalline basement rock is found to contain 2 wt of carbon di oxide fluid components the presence of geodynamic process associated with thermal anomalies at subcrustal depths is supported by a high mantle heat flow 29 36 mw m2 beneath both regions although some structural and compositional variations may exist as evidenced by p and s wave seismic velocities we suggest that the stress caused by ongoing uplift and a high mantle heat flow is continuously accumulating in this denser and rheologically stronger mafic crust within which earthquakes tend to nucleate these stresses appear to dominate over and above those generated by the india eurasia collision the role of fluids in stress generation as advocated through earlier studies appears limited

climatic implications of surface domains in arrays of δd and δ18o from hydroxyl minerals goethite as an example abstract paired d h and 18o 16o analyses of natural goethites range from 224 to 93 for d and from 15 5 to 2 8 for 18o the isotopic systematics of these goethites seem to be most closely mimicked by the goethite water d h and 18o 16o fractionation curves of yapp 1987 yapp 1990 most of these goethites are of unknown age but the large range of their isotopic compositions illustrates the possible paleoenvironmental significance of surface domains calculated for hydroxyl minerals a modern surface domain msd for goethite in coordinates of d and 18o was calculated from the following information a scatter in the modern relationship between surface temperatures and 18o of meteoric water rozanski et al 1993 b average annual surface air temperatures from 0 c to 30 c for the meteoric water sample sites c the meteoric water line mwl of craig 1961 and d the goethite water isotopic fractionation factors of yapp 1987 yapp 1990 goethites that had formed in continental environments in approximate thermal equilibrium with the earth s modern atmosphere would be expected to lie within the msd and 16 of 31 goethites do so the remaining 15 are outliers of the 16 msd samples 12 including the three samples from active soil or bog environments are concordant the calculated isotopic temperatures of the concordant goethites range from 6 c to 27 c and are the same within analytical uncertainty as the modern average surface air temperatures at the respective sites calculated temperatures of the four discordant msd samples range from 7 c to 25 c and are higher than corresponding modern surface temperatures a warm earth surface domain wesd was calculated with an assumed temperature of 35 c for the tropics eight of the 15 outlier samples plot within the portion of the wesd that does not overlap the msd thus these eight goethites may have formed at times when the earth s global climate was warmer than at present temperatures calculated from the eight wesd samples range from 20 c to 33 c and suggest lower latitudinal temperature gradients as predicted by climate models of a warmer earth calculated temperatures of the seven samples that lie outside both the msd and the wesd non sd samples range from 19 c to 69 c the non sd status of these seven samples suggests that they formed in environments dominated by subsurface heat sources surface domains can be calculated for any hydroxyl mineral for which both the hydrogen and oxygen isotope mineral water fractionation factors are known the concept of surface domains provides a criterion for assessing the likelihood that a particular sample records information on ancient climatic temperature

new evidence on magnetite oxygen isotope geothermometers at 175 and 112 c in wairakei steam pipelines new zealand abstract millimeter deep surface layers of magnetite occur in the steam pipelines of the wairakei geothermal power station as part of serious corrosion discovered after 15 years of service these quasi experimental growths provide the following oxygen isotope calibration points of magnetite and h 2 o below the previously available experimental range 175 c 7 9 0 5 and 112 c 3 7 0 5 the data support the earliest proposed magnetite h 2 o fractionation curve by j r o neil and r n clayton with an isotopic cross over near 50 c and could indicate a relatively low temperature origin for some precambrian iron formations

very high18o enrichment in archean cherts from south india implications for archean ocean temperature stable carbon and oxygen isotopic compositions of essentially unmetamorphosed archean 2 6 gyr old cherts and carbonates of the dharwar sequence of southern india from the northernmost part of the dharwar shimoga supracrustal belt kalche and nagargali have been determined the cherts from the nagargali area which preserve oolitic texture and cryptocrystalline silica show highly enriched 18 o values ranging from 28 to 31 4 o relative to smow such values are the highest yet reported from archean nondetrital sediments but are similar to those of modern marine cherts on the assumption of a seawater 18 o of 0 0 calculation of temperature based on the maximum 18 o value of 31 4 0 yields a value of 40 c this is significantly less than 70 80 c reported for the archean oceans based on cherts and chert phosphate pairs diagenetically recrystallized microcrystalline chert dolomite pairs of kalche area exhibit a range of oxygen isotopic ratios similar to those reported for archean cherts and carbonates from other parts of the world the temperature of diagenesis is estimated to be about 68 c

numerical model studies of the winter storm response of the west florida shelf abstract the wintertime wind driven ocean circulation on the west florida continental shelf is studied within the framework of a linearized storm surge model the model bathymetry incorporates a realistic shelf extending from new orleans to the southern tip of florida and a deep ocean region the boundary condition at the coast is that there is no normal flow at the open boundaries located off the shelf in deep water the adjusted sea level is fixed at zero it is found that 1 a coastally trapped response is achieved within one local inertial period following the imposition of the wind 2 the curved coast forces a mass exchange between the coastal water and the deep ocean 3 this exchange leads to the generation of a series of mesoscale eddies along the shelf edge and 4 these eddies give rise to long period shelf wide oscillations that persist beyond the local spin up time a hindcast of the wind driven flow on the west florida shelf for a particular period 11 25 march 1978 that contains the

urucum neoproterozoic cambrian manganese deposits ms brazil biogenic participation in the ore genesis geology geochemistry and depositional environment abstract the urucum region mato grosso do sul brazil contains neoproterozoic cambrian manganese ore in the layers mn 1 mn 2 and mn 3 which are interbedded with iron formations ifs from the santa cruz formation jacadigo group and surrounded by carbonate rocks from the bocaina and tamengo formations corumba group these rocks fill an ancient graben with sediments from the santa cruz formation overlying fluvial deposits from the urucum formation and limestones from the bocaina and tamengo formations deposited in the shallow marginal regions as the graben deepened it was flooded with microbe rich seawater and hydrothermalism began iron and manganese precipitated within the pores in arkosic sandstones thereby forming the clastic lower mn 1 ore layer the remaining manganese was simultaneously deposited on the basin floor with clastic clay and silt from turbidity currents thereby forming the upper mn 1 clastic chemical ore layer the sedimentation of mn 1 and its host ifs was controlled by seawater saturation and homogeneous oxidation which caused manganese and iron sedimentation and the death of microorganisms generating mangano ferriferous sediments with high p co and ni contents mn 2 formed during periods of tectonic quiescence through water influxes that carried abundant microbes fe ii mn ii and sio 2 under uv radiation these microbes oxidized mn ii and fe ii to form hydroxides and died thereby forming biomass that was enriched in p co and ni and minor carbonate adjacent to and below the oxycline these microbes also formed kremydilites oblate structures that resemble manganese stromatolites within the biomass and produced ch 4 and or h 2 gas bubbles during early diagenesis wormlike organisms inhabited the biomass and probably separated iron from manganese to produce cryptomelane microbialites which agglutinated to form manganese micronodules that coalesced to form the massive layer mn 2 this process ended with the disappearance of microorganisms and the sedimentation of the ifs and a new water influx generated layer mn 3 via the same process the final seawater upwelling precipitated ifs in the basin depocenter whereas limestone from the tamengo formation was deposited along the basin s edges the diagenesis initially transformed the manganese oxides into cryptomelane and then into hollandite

inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline 1 the role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments different scenarios include constant versus variable wind forcing and variations in bottom friction the three dimensional response of the shelf within the domain embayment enclosed by capes is associated with the generation of a velocity pycnocline disturbance at the upstream cape and its subsequent downstream advection this disturbance is more pronounced under variable wind conditions its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape when inertia dominates the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore the separation occurs at a low rossby number ro 0 15 which is attributed to the positive curvature of the coastline forming the cape when friction dominates the advection path is constrained along the coastline resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast isobaths simulations with spatially variable bottom friction with higher friction toward the coast result in the generation of eddy like features the numerical results are in agreement with both observations and surface temperature imagery from long bay south carolina an embayment enclosed by two capes and emphasize the role that coastline and associated shelf morphology can play in enhancing cross shelf transport and exchange

stratigraphy and mineralogy of the manganese ores of urucum mato grosso brazil preliminar results of geological mapping and microscopic studies are presented the mineral deposits of urucum are clearly different from the rest of the banded iron formations in brazil urucum is essentially younger and probably late proterozoic the sequence is unmetamorphic two main types of manganese ore exist in urucum namely

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

late diagenetic changes in manganese ores of the upper proterozoic penganga group india sedimentary manganese oxide ores occur interstratified with chert and minor calcareous shale and enclosed in limestone in the transgressive upper proterozoic marine sequence of the penganga group andhra pradesh india this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed the manganeseoxide ores show unusual coexistence of the primary sedimentary minerals todorokite and birnessite with their diagenetic conversion products manganite braunite and bixbyite the mineralogical characters and chemical compositions of the important phases as well as their texture are discussed braunite occurs in two generations one earlier or contemporaneous with bixbyite and the other later than bixbyite the different stages of conversion of todorokite and birnessite to braunite and todorokite to manganite are preserved the general observations suggest that bixbyite was also produced by conversion of todorokite birnessite pyrolusite and cryptomelane conventionally considered as diagenetic products of mn oxide hydroxide precursors deposited as primary sediments are here rarely present and then only as supergene derivatives this documentation of diagenetic transformation of primary todorokite and birnessite directly to braunite and bixbyite should be considered while extrapolating the progenitor mineralogy of the metamorphosed manganese oxide ores that abound in the precambrian

wind influence on water exchange between the ria of ferrol nw spain and the shelf abstract the wind induced water exchange between the ria of ferrol nw spain and the adjacent shelf is analyzed by means of a three dimensional hydrodynamic model mohid2000 since thermohaline measurements indicate that the estuary can be considered vertically homogeneous a barotropic version of the model has been used real in situ wind measurements have been used for model calibration and further analysis the approach to study the wind effect on water exchange through the ria strait consisted in subtracting the signal calculated with only tidal forcing t s from the one with wind and tidal forcing wt s this shows the existence of a residual circulation with water flowing in wind direction along surfaces layers and a counter current flowing in the opposite direction at bottom layers the flux across the strait of ferrol has shown to increase linearly on wind strength with a correlation larger than 96 and reaching values close to 20 m 3 s 1 under real wind forcing

variability of current temperature and bottom pressure across the west florida continental shelf winter 1981 1982 observations are analyzed from four current meter moorings deployed on the broad continental shelf in the northeastern gulf of mexico from november 29 1981 to february 8 1982 71 days consistent with recent modeling studies the shelf circulation responds within an inertial period to the alternating up and down coast synoptic scale wind forcing average response to a 0 5 dyn cm 2 alongshore wind stress as measured at the coast is 20 cm s 1 off cedar key and 40 cm s 1 in the north where the shelf narrows off cape san bias lower layer currents veer counterclockwise with depth as in a bottom ekman layer e folding scale 8 m the pressure field decays offshore e folding scale 160 km and yields a geostrophic current in good agreement with the observed alongshelf flow cross shelf and vertical variations of the tidal signals compare nicely with results from barotropic theory calculations indicate that most of the shoreward propagating tidal energy must be dissipated in depths of 20 m within 50 km of shore

oxygen and hydrogen isotope compositions of permian pedogenic phyllosilicates development of modern surface domain arrays and implications for paleotemperature reconstructions abstract mineralogic chemical and oxygen and hydrogen isotope compositions of 15 different phyllosilicate samples from permo pennsylvanian age paleosols of the eastern shelf of the midland basin of texas and the southern anadarko basin are presented mixtures of 2 1 phyllosilicates and kaolinite dominate most samples although some samples consist of relatively pure 2 1 phyllosilicates chemical and mineralogic data are used in conjunction with published thermodynamic data to calculate hydrogen and oxygen isotope fractionation factors for each sample in turn application of measured oxygen and hydrogen isotope compositions of the phyllosilicates to temperature dependent fractionation equations are used to calculate paleotemperatures of crystallization the d values of the phyllosilicates range from 69 to 55 the 18 o values range from 19 5 to 22 7 if these samples preserve a record of equilibrium with paleo meteoric waters the isotopic compositions of the phyllosilicates correspond to paleotemperatures of phyllosilicate crystallization ranging from 22 3 c to 35 3 c in particular the stratigraphic trend of calculated temperatures from midland basin samples suggests that early permian surface temperatures may have been up to 10 c warmer than those of the latest pennsylvanian

intensified upwelling over a widened shelf in the northeastern south china sea 1 observational and three dimensional modeling studies reveal that the intensified upwelling in the northeastern south china sea nscs is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf the strongest advection occurs over the converging isobaths near the head of the widened shelf as these dense deep waters advance shoreward they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape dynamically the shoreward cross isobath transport over the widened shelf is geostrophically enhanced by a quasi barotropic negative westward along isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf a negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion induced by the respective widened shelf and the coastal promontory the along isobath variations of cross isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the nscs

a loop current intrusion case study on the west florida shelf the gulf of mexico loop current intruded upon the west florida continental shelf in june 2000 in situ currents and hydrography along with satellite temperature and altimetry measurements are used to describe this event and its effects on the shelf a strong southward current is observed to flow along the shelf slope seaward of the intruded water boundary this current transported cold nutrient rich water from the north thereby producing anomalous hydrographic features near the shelf break 80 m isobath an array of moored velocity profilers reveals that the currents landward of the intruded water are independent of the loop current and primarily driven by local winds a series of idealized numerical model simulations inclusive of forcing by both the loop current and local winds confirm the observational findings that the shelfbreak currents are largely loop current controlled while the shelf currents are largely controlled by the local winds

using oxygen isotope chemistry to track hydrothermal processes and fluid sources in itabirite hosted iron ore deposits in the quadrilatero ferrifero minas gerais brazil the quadrilatero ferrifero brazil is presently the largest accumulation of single itabirite hosted iron ore bodies worldwide detailed petrography of selected hypogene high grade iron ore bodies at e g the aguas claras conceicao pau branco and pico deposits revealed different iron oxide generations from oldest to youngest magnetite martite hematite pseudomorph after magnetite granoblastic recrystallised microplaty fine grained 100 m hematite laser fluorination oxygen isotope analyses of selected iron ore species showed that the 18o composition of ore hosted martite ranges between 4 4 and 0 9 and is up to 11 depleted in 18o relative to hematite of the host itabirite during the modification of iron ore and the formation of new iron oxide generations e g microplaty and specular hematite an increase of up to 8 in 18o values is recorded calculated 18o values of hydrothermal fluids in equilibrium with the iron oxide species indicate 1 the involvement of isotopically light fluids e g meteoric water or brines during the upgrade from itabirite hosted hematite to high grade iron ore hosted martite and 2 a minor positive shift in 18ofluid values from martite to specular hematite as result of modified meteoric water or brines with slightly elevated 18o values and or the infiltration of small volumes of isotopically heavy metamorphic and or magmatic fluids into the iron ore system the circulation of large fluid volumes that cause the systematic decrease of 18o 16o ratios from itabirite to high grade iron ore requires the presence of e g extensive faults and or large scale folds

assessing the previous activity at the source zone of the 2001 bhuj earthquake based on the near source and distant paleoseismological indicators 1 the m w 7 7 2001 bhuj kachchh earthquake was not associated with any primary surface rupture but it produced secondary faulting folding and liquefaction this study highlights the potential of a secondary rupture and proxies like lateral spreads and sandblows in unraveling the past activity related to the 2001 source chronological constraints of an older lateral spread and far field paleoliquefaction features combined with archeological data provide evidence for occurrences of two previous earthquakes at the 2001 source zone about 4000 and 9000 years ago distinct stratigraphic evidence for at least one previous offset dated at 4424 656 years could be detected at a stepover zone associated with a dextral secondary fault reactivated during the 2001 earthquake the studies imply longer interseismic intervals for the 2001 source zone in comparison with the source zone of the 1819 earthquake located toward the northwestern part of the rann of kachchh the spatial and temporal correlation of previous events derived on the basis of the available paleoseismic data from the region suggest not only repeated activity at the 2001 source but possibility for additional potential sources in parts of kachchh and cambay basins although we infer a longer recurrence interval for the 2001 bhuj earthquake source our study points to the fact that these additional sources may have the potential to rupture in the future considering the long elapsed time

oxygen isotope exchange kinetics of mineral pairs in closed and open systems applications to problems of hydrothermal alteration of igneous rocks and precambrian iron formations the systematics of stable isotope exchange between minerals and fluids are examined in the context of modal mineralogical variations and mass balance considerations both in closed and in open systems on mineral pair 18 o plots samples from terranes that have exchanged with large amounts of fluid typically map out steep positively sloped non equilibrium arrays analytical models are derived to explain these effects these models allow for different exchange rates between the various minerals and the external fluids as well as different fluid fluxes the steep arrays are adequately modelled by calculated isochron lines that involve the whole family of possible exchange trajectories these isochrons have initially steep near vertical positive slopes that rotate toward a 45 equilibrium slope as the exchange process proceeds to completion the actual data point array is thus analogous to the hand of an isotopic clock that measures the duration of the hydrothermal episode the dimensionless ratio of the volumetric fluid flux to the kinetic rate parameter u k determines the shape of each individual exchange trajectory in a fluid buffered system u k 1 the solutions to the equations 1 are independent of the mole fractions of the solid phases 2 correspond to taylor s open system water rock equation and 3 yield straight line isochrons that have slopes that approach 1 f where f is the fraction reacted of the more sluggishly exchanging mineral the isochrons for this simple exchange model are closely congruent with the isochrons calculated for all of the more complex models thereby simplifying the application of theory to actual hydrothermal systems in nature in all of the models an order of magnitude of time in units of kt separates steep non equilibrium arrays e g slope 10 from arrays approaching an equilibrium slope of unity on a diagram because we know the approximate lifetimes of many hydrothermal systems from geologic and heat balance constraints we can utilize the 18 o 16 o data on natural mineral assemblages to calculate the kinetic rate constants k s and the effective diffusion constants d s for mineral h 2o exchange these calculated values k qtz 10 14 k feld 10 13 10 12 agree with experimental determinations of such constants in nature once the driving force or energy source for the external infiltrating fluid phase is removed the disequilibrium mineral pair arrays will either 1 remain frozen in their existing state if the temperatures are low enough or 2 re equilibrate along specific closed system exchange vectors determined solely by the temperature path and the mineral modal proportions thus modal mineralogical information is a particularly important parameter in both the open and closed system scenarios and should in general always be reported in stable isotopic studies of mineral assemblages these concepts are applied to an analysis of 18 o 16 o systematics of gabbros plagioclase clinopyroxene and plagioclase amphibole pairs granitic plutons quartz feldspar pairs and precambrian siliceous iron formations quartz magnetite pairs in all these examples striking regularities are observed on and plots but we point out that plots have many advantages over their equivalent diagrams as the latter are more susceptible to misinterpretation using the equations developed in this study these regularities can be interpreted to give semiquantitative information on the exchange histories of these rocks subsequent to their formation in particular we present a new interpretation indicating that precambrian cherty iron formations have in general undergone a complex fluid exchange history in which the iron oxide magnetite precursor has exchanged much faster with low temperature 400 c fluids than has the relatively inert quartz

mantle derived fluids in the basement of the deccan trap evidence from stable carbon and oxygen isotopes of carbonates from the killari borehole basement maharashtra india we report here for the first time geochemical mineralogical and stable carbon and oxygen isotopic data on the crystalline basement rocks of the 1993 killari earthquake region of maharashtra india which is covered by a thick suite of deccan volcanics our results revealed the hitherto unknown amphibolite granulite nature of the 2 5 ga basement which contains 2 00 2 28 wt of co2 the stable carbon 13c and oxygen 18o isotopic measurements on carbonates separated from two basement samples kil 13 440 5 m depth and kil 20 499 6 m depth collected from the klr 1 borehole drilled in the epicentral region showed the respective values of 6 23 and 6 22 versus pdb for 13c and 7 94 and 8 11 versus smow for 18o the samples plot in the primary igneous carbonatite field indicating the mantle origin of the carbonates derived through the process of mantle metasomatism from the deep mantle carbon reservoir this would suggest large scale crust mantle thermal fluid interaction beneath the killari seismogenic region which is characterized by massive upwarping of the high velocity mafic crust and retrograde metamorphism

west florida shelf response to local wind forcing april 1998 we compare west florida shelf velocity and sea level data with a model simulation for april 1998 responses for three upwelling and three downwelling favorable wind events are documented along shelf jets accompanied by oppositely directed upper and lower layer across shelf flows with connecting vertical velocity comprise the fully three dimensional inner shelf responses which are sensitive to stratification with an initial density field representative of april 1998 the model simulates velocity and sea level variations in general agreement with the observations whereas substantial mismatches occur without stratification despite the winds being the primary motive agent for the inner shelf the stratification dependence requires that model density fields be maintained through a combination of adequate initial conditions surface offshore and land derived buoyancy inputs and data assimilation dynamical analyses define the inner shelf as the region where the surface and bottom boundary layers are important in the momentum balance kinematically this is where surface ekman layer divergence fed by the bottom ekman layer convergence or conversely sets up the across shelf pressure gradient stratification causes a response asymmetry wherein the offshore scale and magnitude of the upwelling responses are larger than those for the downwelling responses this asymmetry is attributed to thermal wind effects across the bottom ekman layer buoyancy torque by isopycnals bending into the bottom adds constructively destructively with planetary vorticity tilting under upwelling downwelling favorable winds and this may have important implications for nutrients and other material property distributions on the shelf

directional dependence of p and s wave propagation and polarization in foliated rocks from the kola superdeep well evidence from laboratory measurements and calculations based on tof neutron diffraction we have measured p and s wave velocities on two amphibolite and two gneiss samples from the kola superdeep borehole as a function of pressure up to 600 mpa and temperature up to 600 degrees c the velocity measurements include compressional vp and shear wave velocities vs1 vs2 propagating in three orthogonal directions which were in general not parallel to inherent rock symmetry axes or planes the measurements are accompanied by 3d velocities calculations based on lattice preferred orientation lpo obtained by tof time of flight neutron diffraction analysis which allows the investigation of bulk volumes up to several cubic centimetres due to the high penetration depth of neutrons the lpo based numerical velocity calculations give important information on the different contribution of the various rock forming minerals to bulk elastic anisotropy and on the relations of seismic anisotropy shear wave splitting and shear wave polarization to the structural reference frame foliation and lineation comparison with measured velocities obtained for the three propagation directions that were not in accordance with the structural frame of the rocks foliation and lineation demonstrate that for shear waves propagating through anisotropic rocks the vibration directions are as important as the propagation directions the study demonstrates that proper measurement of shear wave splitting by means of two orthogonal polarized sending and receiving shear wave transducers is only possible when their propagation and polarization directions are parallel and normal to foliation and lineation respectively c 2005 elsevier b v all rights reserved

ancient geochemical cycling in the earth as inferred from fe isotope studies of banded iron formations from the transvaal craton variations in the isotopic composition of fe in late archean to early proterozoic banded iron formations bifs from the transvaal supergroup south africa span nearly the entire range yet measured on earth from 2 5 to 1 0 in 56fe 54fe ratios relative to the bulk earth with a current state of the art precision of 0 05 for the 56fe 54fe ratio this range is 70 times analytical error demonstrating that significant fe isotope variations can be preserved in ancient rocks significant variation in fe isotope compositions of rocks and minerals appears to be restricted to chemically precipitated sediments and the range measured for bifs stands in marked contrast to the isotopic homogeneity of igneous rocks which have 56fe 0 00 0 05 as well as the majority of modern loess aerosols riverine loads marine sediments and proterozoic shales the fe isotope compositions of hematite magnetite fe carbonate and pyrite measured in bifs appears to reflect a combination of 1 mineral specific equilibrium isotope fractionation 2 variations in the isotope compositions of the fluids from which they were precipitated and 3 the effects of metabolic processing of fe by bacteria for minerals that may have been in isotopic equilibrium during initial precipitation or early diagenesis the relative order of 56fe values appears to decrease in the order magnetite siderite ankerite similar to that estimated from spectroscopic data although the measured isotopic differences are much smaller than those predicted at low temperature in combination with on going experimental determinations of equilibrium fe isotope fractionation factors the data for bif minerals place additional constraints on the equilibrium fe isotope fractionation factors for the system fe iii fe ii hematite magnetite fe carbonate 56fe values for pyrite are the lowest yet measured for natural minerals and stand in marked contrast to the high 56fe values that are predicted from spectroscopic data some samples contain hematite and magnetite and have positive 56fe values these seem best explained through production of high 56fe 54fe reservoirs by photosynthetic fe oxidation it is not yet clear if the low 56fe values measured for some oxides as well as fe carbonates reflect biologic processes or inorganic precipitation from low 56fe ferrous fe rich fluids however the present results demonstrate the great potential for fe isotopes in tracing the geochemical cycling of fe and highlight the need for an extensive experimental program for determining equilibrium fe isotope fractionation factors for minerals and fluids that are pertinent to sedimentary environments

a numerical modeling study of low frequency circulation on the west florida shelf abstract a numerical model using the linearized diagnostic primitive equations was applied to the west florida shelf to provide estimates of low frequency the model results coupled with the available data suggest 1 the inner shelf region shoreward of the 50 m isobath is primarily wind driven 2 the deeper southern section of the shelf is strongly influenced by shelf edge processes and intrusions from the loop current 3 the deeper northern section of the shelf is primarily wind driven and 4 modeling of shelf edge processes must include the baroclinic component

multivariate reconstruction of missing data in sea surface temperature chlorophyll and wind satellite fields 1 an empirical orthogonal function based technique called data interpolating empirical orthogonal functions dineof is used in a multivariate approach to reconstruct missing data sea surface temperature sst chlorophyll a concentration and quikscat winds are used to assess the benefit of a multivariate reconstruction in particular the combination of sst plus chlorophyll sst plus lagged sst plus chlorophyll and sst plus lagged winds have been studied to assess the quality of the reconstructions the reconstructed sst and winds have been compared to in situ data the combination of sst plus chlorophyll as well as sst plus lagged sst plus chlorophyll significantly improves the results obtained by the reconstruction of sst alone all the experiments correctly represent the sst and an upwelling downwelling event in the west florida shelf reproduced by the reconstructed data is studied

petrophysical properties of the deccan basalts exposed in the western ghats escarpment around mahabaleshwar and koyna india abstract we present petrophysical properties density p and s wave velocity porosity and poisson s ratio of the deccan basalts from the western ghats escarpment around mahabaleshwar and koyna and characterize the dhawar basement rocks around goa the petrophysical properties of basaltic lava flows show significant variation in the bushe poladpur ambenali and mahabaleshwar formations that are widespread in the deccan volcanic province the bushe formation stands out distinctly from other formations because of its lower density and p and s wave velocity the porosity vesicles and amygdales plays a major role in controlling the variation of the petrophysical properties of the basalts the poisson s ratio of the deccan basalts is largely affected by the vesicular porosity aspect ratio of the amygdales and zeolite content the dharwar basement rocks greywackes and granites are found to be lower in density p and s wave velocity and poisson s ratio than the basaltic rocks the variation of the petrophysical properties with elevation in the western ghats sections roughly follows the geochemical stratigraphy high porosity of the bushe and mahabaleshwar formations constitute a multi layered aquifer system in the deccan volcanic province in the koyna earthquake zone these formations may provide an effective groundwater connectivity between the reservoir and earthquake focal areas the new petrophysical data of the deccan basalts and dharwar basement rocks will help to refine the geophysical models of the southwestern deccan basalt province

40ar 39ar constraints on the age and thermal history of the urucum neoproterozoic banded iron formation brazil urucum is one of the youngest banded iron formations bifs yet its exact age remains uncertain 40 ar 39 ar geochronology on late diagenetic to early metamorphic cryptomelane from the urucum sequence reveals a minimum depositional age of 587 7 ma metamorphic braunite age spectra yield flat segments defining apparent ages of 547 3 ma to 513 4 ma interpreted as recrystallization or cooling ages metamorphic muscovite grains from a meta arkose interbedded with the bif yield reproducible plateau ages of 513 3 ma cryptomelane ages are interpreted to record the minimum timing of the extensional tectonic events that generated the graben systems at the southeastern border of the amazon craton including the chiquitos tucavaca aulacogen and the jacadigo basin which hosts the urucum banded iron formation structurally controlled hydrothermal alteration resulted in crystallization of braunite and muscovite during the interval between 547 and 513 ma coeval with post collisional decompression that resulted in granite emplacement e g sao vicente granite in the paraguay belt subsequent uplift and erosion of the precambrian sequence possibly succeeded metamorphism a chemically distinct cryptomelane generation identified in surface samples yield ca 60 ma results these ages provide evidence for supergene recrystallization after exhumation in the mesozoic cenozoic 40 ar 39 ar systematics implies that the oldest cryptomelane samples experienced ar loss probably via thermally induced diffusion this suggests that the urucum bif was buried and heated to significant temperatures in the late proterozoic consistent with present mineralogy and isotopic composition that do not reflect the original characteristics of the depositional environment

a method for estimating wind driven frictional time dependent stratified shelf and slope water flow abstract friction the alongshore pressure gradient and time dependent effects are all of lowest order importance in the dynamics of wind driven fluctuating currents and sea levels on continental shelves previous work has shown that when all these effects are included the ocean response can be described by an infinite sum of coastal trapped waves whose amplitudes satisfy a fully coupled infinite set of forced first order wave equations we present a practical method for solving this coupled set of equations for general low frequency large scale wind stress forcing as input convergence properties of the solution are examined analytically for the same accuracy more modes are required to describe alongshore currents than sea level and fewer modes are required to describe barotropic than depth dependent motion as an example numerical calculations were carried out for a model of the west florida shelf the sea level field was effectively described by one mode but the alongshore velocity field was not

isotopic evidence for holocene climate change in the northern rockies from a goethite rich ferricrete chronosequence abstract climate proxy records often show regional heterogeneity due to the complex interplay of large scale atmospheric circulation patterns and local topographic features this is especially prevalent in the mountainous regions of the western united states where the interaction of two seasonally distinct weather systems can result in locally abrupt climate boundaries here we establish oxygen isotope ratios of goethite from ferricrete chronosequences formed by natural acid rock drainage as a new source of spatially small scale holocene climate information systematic study of these deposits may prove useful in understanding regional variations in response to global holocene climate change oxygen isotope ratios of goethites from the mountainous northeastern yellowstone region show an increase of 3 over the past 9000 years we attribute this isotopic change to a local increase of isotopically heavier summer precipitation since the early holocene possibly augmented by seasonal temperature differences brought on by orbitally forced insolation changes over the past 9000 years our interpretation is compatible with palynology studies as well as holocene climate simulations which indicate a decrease in monsoon intensity from 9000 years b p to the present unlike the southwestern united states this change may have resulted in wetter summers in our study area

patterns of ocean current variability on the west florida shelf using the self organizing map 1 patterns of ocean current variability are examined on the west florida shelf by a neural network analysis based on the self organizing map som using time series of moored velocity data that span the interval october 1998 september 2001 three characteristic spatial patterns are extracted in a 3 4 som array spatially coherent southeastward and northwestward flow patterns with strong currents and a transition pattern of weak currents on the synoptic weather timescale the variations of these patterns are coherent with the local winds on the seasonal timescale the variations of the patterns are coherent with both the local winds and complementary sea surface temperature patterns the currents are predominantly southeastward during fall winter months from october to march and northwestward during summer months from june to september the spatial patterns extracted by the nonlinear som method are asymmetric a feature that is not captured by the linear empirical orthogonal function method thus we find for the synoptic weather and longer timescales that 1 southeastward currents are generally stronger than northwestward currents 2 the coastal jet axis is located further offshore for southeastward currents than for northwestward currents and 3 the velocity vector rotations with depth are larger in shallower water when the currents are southeastward relative to when the currents are northwestward

2 d crustal velocity structure along hirapur mandla profile in central india an update the 2 d crustal velocity model along the hirapur mandla dss profile across the narmada son lineament in central india murty et al 1998 has been updated based on the analysis of some short and discontinuous seismic wide angle reflection phases three layers with seismic velocities of 6 5 6 7 6 35 6 40 and 6 8 km s 1 and upper boundaries located approximately at 8 17 and 22 km depth respectively have been identified between the basement velocity 5 9 km s 1 and the uppermost mantle velocity 7 8 km s 1 the layer with 6 5 6 7 km s 1 velocity is thin and is less than 2 km deep between the narmada north at katangi and south at jabalpur faults the upper crust shows a horst feature between these faults which indicates that the narmada zone acts as a ridge between two pockets of mafic intrusion in the upper crust the moho boundary at 40 44 km depth and the intra crustal layers exhibit an upwarp suggesting that the narmada faults have deep origins involving deep seated tectonics a smaller intrusive thickness between the narmada faults as compared to those beyond these faults suggests that the intrusive activities on the two sides are independent this further suggests that the two narmada faults may have been active at different geological times the seismic model is constrained by 2 d gravity modeling the gravity highs on either side of the narmada zone are due to the effect of the high velocity high density mafic intrusion at upper crustal level

ocean currents and sea surface heights estimated across the west florida shelf abstract the across shelf structures of the ocean circulation and the associated sea surface height ssh variability are examined on the west florida shelf wfs for the 3 yr interval from september 1998 to december 2001 five sets of characteristic circulation patterns are extracted from 2 day low pass filtered data using the self organizing map extreme upwelling and downwelling structures with strong currents asymmetric upwelling and downwelling structures with moderate currents and a set of transitional structures with weak currents the temporal variations of these structures are coherent with the local winds on synoptic weather time scales on seasonal time scales they are related to both the local winds and the water density variations the circulation is predominantly upwelling during autumn to spring months october april and downwelling during summer months june september coastal sea level fluctuations are related to both the dynamical responses of the inner shelf circulation to meteorol

trace rare earth element and oxygen isotopic systematics for the genesis of banded iron formations evidence from kushtagi schist belt archaean dharwar craton india abstract the ree distribution pattern shapes free 5 92 and 27 87 ppm in chert and hematite respectively positive eu anomalies eu eu 3 25 and 2 1 and la n yb n ratios 0 75 and 0 87 of the chert and hematite layers of the oxide facies bifs of kushtagi schist belt indicate that these constituents were derived from hydrothermal solutions generated and emplaced at an archaean ocean ridge however their oxygen isotopic composition have been modified by mixing with the ambient ocean water and diagenetic reactions 18o values 13 9 17 4 c and 8 6 to 3 3 in chert and hematite respectively yield 150 250 c temperature in the diagenetic and lowest greenschist facies field the mixing model of hydrothermal solutions with ocean water of 1 1000 ratio will not significantly change the oxygen isotope ratio of the ambient ocean water therefore while the trace element data have retained hydrothermal signatures oxygen isotopic signatures are imprinted by diagenetic processes

elastic properties of amphibolite and granulite facies mid crustal basement rocks of the deccan volcanic covered 1993 latur killari earthquake region maharastra india and mantle metasomatism abstract present study provides a new data set of p and s wave velocities and density of metasomatized mid crustal amphibolite and granulite facies basement rocks of the 1993 latur killari earthquake region of maharashtra india which is concealed below a thick suite of deccan volcanics this includes laboratory tests geochemical analysis and petrographic examination on 29 fresh cored samples selected from the depths between 351 7 m and 616 8 m of the klr 1 borehole drilled in the earthquake epicentral zone these samples show a wide range in sio2 content from 52 2 to 70 0 wt majority of these samples are characterized by intermediate composition with a mean density of 2 85 g cm3 range 2 72 3 06 g cm3 and average p and s wave velocities of 6 23 km s 5 83 6 61 km s and 3 56 km s 3 21 3 96 respectively they also contain quite high amount of feot and cao with respective means of 9 76 and 6 59 wt average poisson s ratio is 0 25 together with respective values of young s bulk and rigidity modulus at 90 8 gpa 62 0 gpa and 36 3 gpa inspite of having higher densities some of the biotite and feo rich samples exhibit unusually low velocities consequent to metasomatic activity our study demonstrates that the mantle metasomatic alteration and retrogression of the underlying high velocity mafic crust under the latur killari earthquake region accompanied by geodynamic process of uplift and erosion during the geologic past has led to severe changes in the petrophysical and elastic properties of the studied rocks

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

the southern border of the guapore shield in western brazil and bolivia an interpretation of its geologic evolution abstract the geology of the southeastern and southwestern margins of the guapore shield is described the shield rocks comprise high grade granulite and low grade greenschist sequences these rocks are poorly known oldest recorded ages include transamazonian datings 2 ma the margins of the shield show the development of a mobile belt formed by rocks of upper proterozoic to cambrian age within this mobile belt the cuiaba group of uncertain but possibly upper proterozoic age outcrops to the east and shows tectonic contacts with younger rocks that span the vendian upper proterozoic to cambrian age the rocks of vendian to cambrian age form three isolated elongated basins which show evidence of fault control the axes of these basins are equally separated by angles of 120 and meet at a triple junction near corumba the stratigraphy of the vendian to cambrian basins is correlated from bolivia to brazil based on tectonic continuity sedimentological similarity and fossil content the central location at corumba shows instability since the middle proterozoic when important igneous activity is recorded at rincon del tigre bolivia and in brazil this igneous activity is interpreted as being related to hot spot activity in an intercratonic setting from which the younger upper proterozoic basins originated