stacking paleointensity and oxygen isotope data for the last 1 5 myr piso 1500 coupled relative geomagnetic paleointensity rpi and oxygen isotope records are used to construct rpi and oxygen isotope stacks for the last 1 5 myr the coupled correlations are accomplished using the match algorithm lisiecki l e and lisiecki p a 2002 application of dynamic programming to the correlation of paleoclimate records paleoceanography 17 1049 doi 10 1029 2001pa000733 to simultaneously correlate isotope and rpi records the simultaneous match reduces the degree of freedom associated with correlations using rpi or oxygen isotope records alone the overall compatibility of rpi and oxygen isotopes indicates a dominant global but independent component in both signals the local wavelet power spectrum lwps for the rpi stack indicates little significant orbital power although the accompanying oxygen isotope stack has all the lwps characteristics expected of a high resolution oxygen isotope record containing orbital frequencies the piso 1500 stack represents a new stratigraphic template that can be used to correlate among marine sediment records and link them to polar ice cores via variations in cosmogenic nuclide production scaling the stack to values for virtual axial dipole moment vadm indicate maxima at 15 1022 am2 and minima that imply a threshold of 2 5 1022 am2 below which values are associated with either polarity reversals or magnetic excursions

gravity anomalies and the indian lithosphere review and analysis of existing gravity data abstract the upper part of the lithosphere has been actively involved in various exogenic and endogenic processes which have left their imprint on the gravity field on the indian peninsula and the himalaya analysis of the gravity field over the dharwar craton shows that the greenstone belts of this craton have been formed as a result of development of deep fractures in the earth s crust during archaean times precambrian mountain ranges such as the aravallies vindhyans satpura and eastern ghats are located peripheral to archaean cratons most of these mountain belts are characterized by gravity highs suggesting that the underlying crust is of higher than normal density these mountain ranges with the exception of the eastern ghats do not appear to be locally compensated regional compensation seems to prevail over all these areas eastern ghats ranges are also underlain by a crust of higher than normal density relative to the dharwar and bastar cratons and exist with a sharp contact with the cratons in the west isostatic compensation in the eastern ghats appears to have been achieved by thickening of the underlying crust the himalaya has attained a fairly high degree of isostatic compensation

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

iceberg trajectory modeling and meltwater injection in the southern ocean this is the first large scale modeling study of iceberg trajectories and melt rates in the southern ocean an iceberg model was seeded with climatological iceberg calving rates based on a calculation of the net surface accumulation from each snow catchment area on the antarctic continent in most areas modeled trajectories show good agreement with observed patterns of iceberg motion though discrepencies in the weddell sea have highlighted problems in the ocean general circulation model output used to force the iceberg model the coriolis force is found to be important in keeping bergs entrained in the coastal current around antarctica and topographic features are important in causing bergs to depart from the coastal regions the modeled geographic distribution of iceberg meltwater joining the ocean has been calculated and is found in many near coastal regions to be comparable in magnitude to the excess of precipitation over evaporation p e

the present and past bottom current flow regime around the sediment drifts on the continental rise west of the antarctic peninsula throughout the last decade large sediment drifts located on the upper continental rise west of the antarctic peninsula were the target of oceanographic measurements bathymetric mapping seismic investigations shallow sediment coring and deep sea drilling by ocean drilling program odp leg 178 these studies concluded that for most of the late neogene and quaternary a generally sw ward directed bottom current affected the deposition on the drifts in particular during glacial periods the deposition was additionally influenced by nw ward directed transport of terrigenous detritus supplied by turbidity currents from the antarctic peninsula continental slope in a recent study however the palaeomagnetic signal of the drift sediments recovered at two odp leg 178 sites 1095 and 1101 was interpreted to provide spatial and directional information on the physical record of the ne ward flowing antarctic circumpolar current acc here we investigate the link between the clockwise flowing acc and the generally sw wards flowing near bottom contour current we show that at the odp leg 178 sites on the western antarctic peninsula continental margin the acc only affects the ocean circulation above ca 1000 m water depth therefore the signal of acc flow might only be archived in the ice rafted debris ird content of the drift sediments however the ird from the leg 178 sites accounts for only a small proportion of the drift sediments and is dominantly of local origin past variability of bottom water flow around the sediment drifts was reconstructed on the basis of seismic studies and clay mineralogical and grain size analyses these reconstructions provide useful information about both downstream direction and velocity changes of the bottom current and point to its sw ward flow along the upper rise during at least the last 9 4 ma

terrestrial heat flow in botswana and namibia we report terrestrial heat flow measurements from 25 new sites in botswana and namibia twelve sites from the archean kaapvaal zimbabwe craton and the limpopo belt have a mean of 47 4 mw m 2 standard error of the mean but show a trend of increasing heat flow from less than 40 mw m 2 within the cratonic nucleus to about 60 mw m 2 at its edge thirteen sites in the proterozoic and pan african mobile belts that surround the craton have a mean of 66 3 mw m 2 increasing from about 60 mw m 2 at the cratonic margin to more than 70 mw m 2 several hundred kilometers away radiogenic heat production in near surface basement rocks was measured for four sites on the craton and seven sites in the mobile belts the limited heat flow heat production data from the craton are insufficient to establish a correlation heat flow and heat production data from the mobile belts when combined with published data from six sites in zambia exhibit a linear trend with an intercept of 50 3 mw m 2 and a slope of 5 5 1 1 km some but not all of the observed difference in surface heat flow between the mobile belts and the cratonic nucleus may be due to differences in crustal heat production that part of the regional variation in surface heat flow which originates at greater depths implies a fundamental difference in thermal structure of the lithosphere between the craton and the mobile belts in southern africa

unusual lithospheric structure beneath the hyderabad granitic region eastern dharwar craton south india abstract using multiparametric geological and geophysical data the evolutionary history of the lithosphere beneath the late archean early proterozoic hyderabad granitic region hgr of the eastern dharwar craton of south indian shield has been attempted our study reveals that the entire granitic region and the surroundings 200 km 200 km is being neotectonically uplifted possibly due to a major intrusive body situated at sub crustal depth leading to changes in river courses and also erosion of several kilometers 10 km from its upper crustal column beneath this region the moho is elevated 32 33 km the reduced heat flow is of the order of 28 mw m2 and the asthenosphere is located at shallow depths of about 124 km i e far less than 200 400 km depth found in precambrian shield areas of the globe the cratonic mantle lithosphere beneath hgr contains a highly conductive 15 m hydrous and seismically anisotropic metasomatic zone between depth of 90 and 100 km where the estimated temperatures could be in the range of 900 1000 c the surface granitic layer containing unusually high radioactivity 5 25 w m3 appears very thin probably a kilometer or so beneath which the entire crustal column seems to be differentiated and made up of low radioactive granulite facies rocks of acid to intermediate composition persistent episodic thermal reactivations during the last 2 6 gega years and continuous uplifting seems to have played a major role towards making its crustal column unusual

geoelectric structure of the dharwar craton from magnetotelluric studies archean suture identified along the chitradurga gadag schist belt summary broad band magnetotelluric data were collected at 50 stations over a 400 km long approximately east west profile over the granite greenstone terrain of dharwar southern india the tensor decomposed data were interpreted using a 2 d inversion scheme the geoelectric model is suggestive of a suture along the chitradurga gadag schist belt formed by the thrusting of the west dharwar craton beneath its eastern counterpart with an easterly dip of 20 30 the thrust proposed here pre dates the formation of these schists which occurred during the late archean 2600 ma the accretionary wedge of the thrust and the depressed part of the west dharwar craton may have controlled the emplacement of the chitradurga gadag and shimoga dharwar schists the subsequent weathering the several episodes of tectonic activity witnessed during the precambrian and the vertical block movements caused during the passage of the indian plate over the reunion hotspot may have modified the crust leading to the present day geological configuration despite its age and several tectonothermal episodes the signature of this thrust is adequately preserved in the dharwar craton several similarities with younger sutures as is evident from the observed relics of the oceanic rocks present along the chitradurga schist belt suggest that the tectonic processes leading to this archean event may have had a close resemblance to those witnessed in recent times magnetotelluric studies also image a zone of low resistivity at a depth of 40 km beneath the west dharwar craton this seems to be a regional feature extending to the north over a distance of at least 250 km beneath the deccan volcanics the low heat flow values and the high density associated with this feature make partial melting an unlikely explanation for the low resistivity the grain boundary graphites and the sulphides deposited in the form of pyrites may have caused the low resistivity in the lithospheric mantle of the west dharwar craton although the fluids generated and trapped in the mantle during the passage of the indian plate over the reunion hotspot in the waning phase of its outburst could also be a possibility the asthenosphere is delineated at a depth of about 100 km beneath the east dharwar craton

climate change in india inferred from geothermal observations 1 temporal variations in surface ground temperature impart a signal to the subsurface thermal regime that is captured in borehole temperature depth profiles seventy temperature depth profiles in india located between 12 and 28 n are analyzed to infer past changes in ground temperature these profiles exhibit predominantly positive anomalous temperatures relative to the background thermal regime beginning at depths of 75 150 m and increasing toward the surface this pattern is consistent with warming over the past century an interpretation in terms of linear surface temperature change indicates warming of about 0 9 0 1 c over the past 150 years relatively complete surface air temperature sat records from meteorological stations near the boreholes indicate similar rates of warming over the last century a combined analysis of borehole temperatures and sat records yields a long term preobservational mean temperature 0 8 0 1 c lower than the 1961 1990 mean sat when the most recent decade is included directly in the analysis the average total warming in india from the early 1800s to the late 1990s is 1 2 c

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

mid late pleistocene glacimarine sedimentary processes of a high latitude deep sea sediment drift antarctic peninsula pacific margin the effects of glaciation on sediment drifts is recognised from marked sedimentary facies variation in deep sea cores taken from the continental rise of the antarctic peninsula pacific margin nineteen sediment cores were visually described logged for magnetic susceptibility and x radiographed about 1000 analyses were performed for grain size clay minerals and biostratigraphy foraminifera nannofossils and diatoms four sediment types associated with distinct sedimentary processes are recognised based on textural compositional analysis 1 hemipelagic mud forms the bulk of the interglacial sediment and accumulated from the pelagic settling of bioclasts and ice rafted wind transported detritus 2 terrigenous mud forms the bulk of the glacial sediment and accumulated from a combination of sedimentary processes including turbidity currents turbid plumes and bottom current reworking of nepheloid layers 3 silty deposits occurring as laminated layers and lenses represent the lateral spillout of low density turbidity currents 4 lastly glacial interglacial gravelly mud layers derive from settling of ice rafted detritus five depositional settings are interpreted within sediment drift 7 each characterised by the dominance interaction of one or several depositional processes the repetitive succession of typical sedimentary facies is inferred to reflect a sequence of four climatic stages glaciation glacial deglaciation and interglacial each one characterised by a distinctive clay mineral assemblage and bioclastic content variations in clay mineral assemblage within interglacial stage 5 core sed 06 suggest minor colder climatic fluctuations possibly correlatable with substages 5a to 5e

environmental magnetism of antarctic late pleistocene sediments and interhemispheric correlation of climatic events abstract recent developments in paleomagnetism and environmental magnetism provide new tools for the detailed correlation of climatically induced magnetic mineralogy changes in sedimentary sequences studies of these changes contribute to the reconstruction of climate history for the glacial interglacial cycles of the late pleistocene and to the delineation of the range of natural variability for global climate during the past hundred thousands years here we show that sharp coercivity minima observed in fine grained sediments from the continental rise of the western antarctic peninsula correlate to the major rapid cooling events of the northern atlantic heinrich layers we interpret such an environmental magnetic signal in terms of variations in deep sea diagenetic processes of sulfide formation which reflect changes in the input of detrital organic matter controlled by sea ice extent with the inherent uncertainties in age controls the sedimentary paleoclimatic markers of the two hemispheres are almost contemporaneous but interhemispheric time lags or leads of the order of 1 2 kyr such as those recently reported from the greenland and antarctic ice cores are also compatible with the data

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

biostratigraphic characterization and quaternary microfossil palaeoecology in sediment drifts west of the antarctic peninsula implications for cyclic glacial interglacial deposition abstract the sedano project recovered 19 gravity cores on sediment drifts from the pacific continental margin of the antarctic peninsula camerlenghi et al 1997a high resolution terrigenous sedimentary record of the sediment drifts on the antarctic peninsula pacific margin in ricci c a ed the antarctic region museo nazionale dell antartide siena pp 705 710 fifteen cores were sampled with the aim of developing an integrated biostratigraphy and palaeoecology based on calcareous nannofossils diatoms planktonic and benthic foraminifera framed in a depositional process reconstruction barren gray laminated and brown bioturbated hemipelagic sediments characterize glacial and interglacial cycles respectively analyses from both intervals allow comparison between microfossil occurrence in glacial and interglacial cycles the unit boundaries were drawn more accurately by means of the microfossil distribution on the basis of micropalaeontological and sedimentological evidence interglacial unit c is correlated to oxygen isotope stage 5 thus dating the unit boundaries at 127 and 70 ka peaks in diatom abundance correlate well with interglacial units and indicate high productivity and an open ocean environment a calcareous nannofossil cold taxa association is present in most cores examined and its consistent distribution within interglacial unit c indicates key environmental relationships the occurrence of calcareous nannofossils has been related to temperature tolerance sea ice cover reduction nutrient availability and factors limiting primary productivity our results confirm that coccolithophorids occurred at southern high latitudes in the western marginal basins of the antarctic peninsula during short periods of the late quaternary a foraminiferal assemblage made up of sinistral neogloboquadrina pachyderma and few benthics occurs only in interglacial units correlation of microfossil occurrences with climatic cycles adds information on their palaeoecology and palaeoproductivity in the southern high latitudes

the nature and thickness of lithosphere beneath the archean dharwar craton southern india a magnetotelluric model abstract the dharwar craton in the southern indian shield region occupies a key position in reconstructions of the earliest supercontinent ur as well as in the global neoarchean configurations of continental assembly here we synthesize the available geophysical data that include heat flow seismic tomography temperature profile derived from xenoliths and magnetotellurics mt from the dharwar craton a thickness of more than 200 km is identified for the lithosphere beneath this craton by magnetotelluric model our inference lends support to the models from recent seismological investigations that argue for the presence of a thick lithosphere as well as the upper mantle structure derived from the analysis of mantle xenoliths a synthesis of recent geophysical and geochemical data together with our magnetotelluric model indicate the existence of a thick lithospheric root beneath the dharwar craton and suggest that not much of the lithosphere has been eroded since precambrian in this region leading to the conclusion that the dharwar craton preserves an archean tectosphere an increase in the lithospheric thickness from east to west in the dharwar craton and the lithosphere asthenosphere boundary lab migration to shallower levels observed from geophysical data towards the east is interpreted as a probable reflection of the mesoproterozoic subduction erosion of the archean cratonic keel

bouguer gravity anomalies and occurrence patterns of kimberlite pipes in narayanpet maddur regions andhra pradesh india the narayanpet kimberlite field that lies southwest of hyderabad the capital city of andhra pradesh india hosts a number of kimberlite pipes these pipes appear to be randomly positioned however based on regional geologic structures revealed by bouguer gravity anomalies especially in a regional gravity map their locations form a definite pattern in the narayanpet maddur region regional bouguer gravity contours exhibit some features of geologic interest 1 the eastward convex regional contours show an increase in convexity from the maddur and kotakonda area on the east to narayanpet on the west 2 convexity is maximum in the vicinity of narayanpet where a large number of kimberlite pipes occur nearly parallel to the regional contour and 3 between narayanpet and the maddur kotakonda region kimberlite pipes occur at intersections of three eastward convex concentric zones with four lineaments one trending northeast southwest and the other three nearly east west these linear trends are be

glacial contourites on the antarctic peninsula margin insight for palaeoenvironmental and palaeoclimatic conditions deep sea finely laminated and barren glacial sediments occur in the sediment drift field offshore the pacific margin of the antarctic peninsula where a weak contour current flows at present to the sw atypical sedimentary facies were related to the coexistence and interaction of different sedimentary processes three end members of radiograph facies were defined to represent the sedimentary sequences controlled by a dominant process as follows 1 direct influence of turbidity currents on sedimentation is observed in the area surrounding the alexander channel system with silty layers interbedded with laminated mud free of ice rafted debris ird 2 distal meltwater turbid flows dominate the more proximal area of the top plateau with structureless and coarser grained sediments containing ird 3 along the crest of the drift persistent weak bottom currents control the deposition of fine grained sediments conveyed into the system through other processes these laminated sediments contain ird and are atypically not bioturbated because of unusual climatically related environmental conditions of suppressed primary productivity and oxygen reduced deep waters these glacial contourites were observed on most of the antarctic margin with the exception of the areas in which polynyas were maintained during the glacial stages glacial contourites can be used as a proxy to define temporal and spatial extension of the antarctic sea ice deep sea sediments of the sediment drifts offshore the pacific margin of the antarctic peninsula were investigated within the sedano sediment drifts of the antarctic offshore and mogam morphology and geology of antarctic margins antarctic peninsula and wilkes land projects of the italian programma nazionale di ricerche in antartide fig 1 the continental shelf of the pacific margin of the antarctic peninsula is dissected by a number of modern u shaped troughs that reflect the neogene path of large ice streams rebesco et al 1998 2002 sediments across the continental shelf were transported mainly by ice streams and delivered to the continental slope and rise during the periods of maximum glacial expansion the continental rise hosts a number of large sediment drifts separated by dendritic deep sea channel systems that originated on the lower continental slope in alignment with the reaches of each glacial trough amblas et al 2006 rebesco et al 2007 two main alternating lithologies related to climatic changes were initially distinguished pudsey camerlenghi 1998 pudsey 2000 interglacial brown bioturbated mud containing sparse icerafted debris ird and glacial grey laminated mud further detailed studies consisting of over 1000 sedimentological compositional and biostratigraphic analyses diatoms foraminifers and nannofossils allowed lucchi et al 2002a to distinguish four distinctive sets of sedimentary facies connected to a sequence of four climatic stages each characterized by the onset of typical sedimentary processes fig 2 as follows 1 strongly bioturbated mud with abundant ird and aeolian sediment input was produced during the interglacial phase fig 2a the increased bioactivity is matched by insignificant downand along slope processes negligible suspended load and sediment transport by the southwesterly flowing bottom currents is occurring at present on the continental rise giorgetti et al 2003 2 terrigenous structureless mud including a series of close spaced ird layers was produced during the deglaciation transition from glacial to interglacial conditions by the disintegration of the retreating grounded ice sheet fig 2b the absence of calcareous microfossils is related to strong carbonate dissolution and rise of the carbonate compensation depth ccd as a result of major meltwater discharge which in turn caused water stratification with less oxygenated and nutrient enriched conditions at the sea bottom 3 a large variety of from viana a r rebesco m eds economic and palaeoceanographic significance of contourite deposits geological society london special publications 276 111 127 0305 8719 07 15 00 the geological society of london 2007

heat flow and heat generation in the archaean dharwar cratons and implications for the southern indian shield geotherm and lithospheric thickness abstract we report terrestrial heat flow density measurements from 11 new sites in the archaean eastern and western dharwar cratons of the southern indian shield the new values together with already published data have yielded a mean heat flow of 40 3 4 s d mw m 2 n 11 for the eastern dharwar craton which is a predominantly gneiss granite terrain the mean heat flow in the archaean supracrustal belts of western dharwar craton which is a granite greenstone terrain is 31 4 1 s d mw m 2 n 4 the observed difference in surface heat flow between the two cratons is ascribed to differences in radiogenic heat production in upper crustal layers inferred to be related to different crust forming processes it has been argued that low heat production appears to be an inherent characteristic of the crust similar to that of the western dharwar craton which evolved during the early archaean and suffered depletion of the lithophile elements of its lower crust prior to the late archaean radiogenic heat production measurements were carried out on borehole core samples for one heat flow site sortur and data have been compiled from the literature on three other sites and on a variety of rocks of the southern indian shield heat flow and radiogenic heat production for sortur when combined with the published data define a linear relation r 0 97 with a slope of 11 5 km and an intercept of 23 mw m 2 the thickness of the thermal lithosphere beneath the dharwar cratons is over 200 km thereby indicating beneath the cratons the existence of deep continental roots a concept which is also supported by teleseismic p wave travel time data the geothermal data has clearly demonstrated that the archaean dharwar cratons of the indian landmass are associated with low mean surface heat flow 37 7 mw m 2 reduced heat flow moho heat flux 12 17 mw m 2 and a cool and thick lithosphere all characteristics of many archaean early proterozoic terrains of other shields it is inferred that the thermal structure of the south indian lithosphere is identical with that of other cratons

geoid anomalies and the structure of continental and oceanic lithospheres geoid anomalies in the wavelength range corresponding to spherical harmonies 6 to 30 are used to bring new constraints on the deep structure of the continental lithosphere on the nature of upper mantle seismic anomalies and on the thermal evolution of the oceanic lithosphere for the shallow lithospheric density anomalies considered here the geoid anomaly is shown to follow approximately the moment law derived from isostasy by a procedure of least squares inversion the geoid over old cratons is found to be equal to that over relatively young 50 myr oceanic lithosphere the oceanic geoid as a function of age follows the expected linear trend with flattening at old ages these results are independent of the degree at which the spherical harmonics are truncated if the tectosphere consisted only of a thick thermal boundary layer marked geoid lows with an amplitude larger than 20 m should be present over cratons in disagreement with the present observation the predicted geoid agrees with the observations if the negative density anomalies associated with a depleted peridotitic layer are present to the bottom of the lithosphere this analysis of the geoid confirms the petrological inferences that the deep roots observed seismically in the top upper mantle form a chemically differentiate reservoir the density of these cold roots is similar to that of mantle material elsewhere because the increase in density resulting from their lower temperature is largely balanced by the decrease in density caused by their depletion analysis in wavelength range corresponding to harmonics 6 to 30 in the oceans confirms that the geoid flattens at old ages and thus supports the view that an important amount of heat is transferred at the base of the lithosphere by small scale convection

use of total grain size distributions to define bed erosion and transport for poorly sorted sediment undergoing simulated bioturbation abstract flume experiments were conducted using poorly sorted beds made to resemble those glacial deposits that blanket the antarctic seafloor today flow within the flume was gradually increased over 2 cm s 1 increments up to 20 cm s 1 an initial run was made without altering the bed and two additional runs were made in which the bed was mechanically mixed in order to simulate bioturbation initial and efficient transport of a given size particle was determined using total grain size distribution data for samples taken from the residual bed from trays placed at different elevations above the floor of the flume and from the water column using this method we were able to measure the current velocities at which initial movement occurred as well as relate different modes of transport for given size ranges to current velocity without mixing the bed current velocities greater than 16 cm s 1 were required to initiate particle movement but because the bed became armored this initial movement was not reflected in the total grain size distribution of the bed with mixing a residual bed containing little silt and clay was produced at velocities of only a few centimeters per second once fines were removed from the bed sand sized material began to move by either traction or saltation a curve relating current velocity to sediment transport by bed load traction and saltation intermittent suspension and suspension is presented the results of our flume experiments demonstrate how sorted sediments are presently being derived from cohesive often overcompacted poorly sorted glacial sediments on high latitude continental shelves where measured current velocities are less than 20 cm s 1 the antarctic seafloor for example furthermore we have gained important information about the true meaning of grain size data as it relates to current velocity mean grain size sorting and skewness reflect not only current velocity but also the efficiency with which the bed was mixed therefore attempts to reconstruct paleovelocity using only these parameters may be meaningless

the southern high grade margin of the dharwar craton the amphibolite facies to granulite facies transition at the southern margin of the dharwar craton has been studied in the krishnagiri satnur halaguru and kushalnagar areas of southern india in all three areas the transition appears to be a progressive metamorphic overprint on cratonal gneisses and their mafic and metasedimentary enclaves without major structural interruption in the kabbal satnur br hills section of karnataka a high grade charnockite massif with pronounced rb depletion is the culmination of an apparently continuous increase of metamorphic grade southward in this and the kushalnagar areas increase of paleopressure from near 6 to near 8 kbar with increasing grade indicates a depth zone relationship of the amphibolite and granulite facies incipient charnockite replacing peninsular gneiss first appears along n s shears parallel to the regional grain of the craton low p h 2 o high co 2 vapors were instrumental in the creation of orthopyroxene introduction from a deep so

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

is the indian shield hotter than other gondwana shields abstract geothermal data on various precambrian terrains from the african australian indian and south american brazil only gondwana landmasses have been compiled synthesised and statistically analysed the results do not support the prevailing notion that the indian shield is hotter than other shields the study clearly shows that the mean surface heat flow values from the various precambrian cratons and mobile belts of the indian landmass for which the data have become available are either equal to or even lower in some cases than that in similar terrains from other gondwana continents further on the basis of available data it is found that the moho and the reduced heat flow values and moho temperatures in the south indian south african western australian and brazilian shields fall within a narrow range thus indicating within the error limits of the estimation the similarity of these shields in terms of these characteristics in conclusion it is shown that the indian landmass is not hotter than the other gondwana landmasses including even the presently immobile african continent and that the super mobility of the indian landmass does not appear to be associated with its thermal characteristics the cause of the latter lies elsewhere

heat flow in the witwatersrand basin and environs and its significance for the south african shield geotherm and lithosphere thickness the late archaean early proterozoic witwatersrand basin is situated in the center of the kaapvaal craton south africa two new heat flow determinations and 71 new heat flow estimates permit excellent definition of the heat flow pattern nonvertical heat conduction explains much of the observed local heat flow variability regionally the heat flow in the basin is uniform and the overall mean 51 6 mw m 2 is higher than the mean heat flow for archaean cratons published data indicate that heat generated in the basin s strata 7 5 mw m 2 is largely responsible for the excess heat flow the subsediment heat flux is 43 5 mw m 2 seven new heat flow and heat production determinations in archaean granite domes northwest of the basin average 33 2 mw m 2 and 2 3 0 8 w m 3 respectively contrasted with the heat flux across the floor of the basin the lower heat flow in the domes probably reflects a smaller radiogenic contribution from the crystalline crust below the domes published heat production data from upturned granitic basement exposed in the vredefort dome in the center of the basin indicate that the radioactive contribution from the crust below the basin is 26 5 m w m 2 subtracting this value and the contribution from the strata 7 5 mw m 2 from the basin s surface heat flow 51 mw m 2 indicates that the heat flux through the moho is approximately 17 mw m 2 calculated lithospheric temperatures agree closely with pressure temperature regimes inferred from studies of mantle inclusions in kimberlites in the kaapvaal craton both data sets indicate that the cratonic lithosphere is considerably cooler and thicker than that below an equilibrium ocean implications of the cold thick cratonic lithosphere for understanding the distribution of southern african diamondiferous kimberlites and the density and buoyancy of the lithosphere are discussed

thorium and uranium contents of gneisses and trondhjemites in the western dharwar craton india widespread metasomatic addition of u has apparently occurred in archean tonalitic trondhjemitic gray gneisses in the western dharwar craton of southern india gneisses of 3200 3000 ma age near the holenarasipur schist belt contain average concentrations of about 10 ppm th and 3 5 ppm u the u is considerably more abundant than average u 1 5 ppm in archean gray gneisses of the superior province of the canadian shield and consequently the th u ratios are low in the indian gneisses comparatively massive trondhjemitic plutons associated with a 3000 ma event in the dharwar craton are very depleted in both th and u and we propose that the metasomatism of the gneisses occurred while the plutons were being emplaced and were expelling fluids from the magmas there is no evidence for metasomatism 2500 ma ago the age of extensive granulite metamorphism in southern india

geology geochemistry and tectonic setting of archaean greywackes from karnataka nucleus india more than 80 of the area covered by the chitradurga and shimoga schist belts 3 0 2 6 ga of karnataka nucleus india is made up of greywackes feldspathic lithic and quartzose greywackes are deposited respectively along the western northern and the eastern margin of the chitradurga schist belt greywackes of the shimoga schist belt show a large compositional scatter between feldspathic and lithic types compositional differences indicate variable provenance for the different localities tonalite trondhjemite gneisses ttg mafic ultramafic schists basic intermediate acid volcanic rocks sedimentary rocks like banded iron formation quartzites and cherts and k granites in minor quantity were exposed in the source area volcanic debris was also contributed from contemporaneous volcanism in the basin greywackes in this region are invariably interbedded with fine grained biotite rich phyllites and schists marked compositional differences are observed between the greywackes and the interbedded phyllites the greywackes have k2o na2o 1 whereas phyllites show large variation in k2o na2o ratios ranging from 1 5 to 15 0 high cr ni content of the greywackes and phyllites of the chitradurga belt are indicative of an important contribution from ultramafic rocks light ree enrichment and negative eu anomalies are particularly pronounced in the mudpacks of the greywackes represented by phyllite the ree and other chemical data such as la th ti zr and k2 mgo ratios indicate that these greywackes were supplied from a juvenile continental nucleus and were laid down on a simatic and converging active continental margin an archaean miniplate model with low angle subduction and sedimentary basins of moderate size is proposed to explain the geochemical and tectonic features of the schist belts

compositions and sources of metasediments in the upper dharwar supergroup south india texturally mature quartz rich sandstones texturally mature mafic rich sandstones and texturally immature graywackes are abundant in the late archean chitradurga group of the dharwar craton in south india when compared to graywackes of paleozoic age from northeastern north america the chitradurga graywackes have slightly higher average concentrations of na and ferromagnesian elements indicating the existence of a more tonalitic and mafic rich provenance during the late archean in karnataka the regional tonalitic gneiss peninsular gneiss is the predominant source of these sediments although mafic ultramafic volcanic debris from unidentified sources is also important neither intermediate nor felsic volcanics nor an extensive metasedimentary terrane were prominent in the provenance although the composition of the craton was dominantly sialic the presence of abundant ferromagnesian debris in some of the texturally mature sandstones that probably formed in shallow water intracratonic or platform

a comparison of heat flow from the gondwana continents with velocities of gondwana plates geodynamic implications abstract the velocities of the lithospheric plates generally differ from each other and the cause of the super mobility of the indian subcontinent is an unresolved problem as the lithospheric plates and the sub lithospheric mantle form the two key elements of plate tectonic movement the thermal characteristics of the three constituent plates of gondwanaland i e the indian african and australian landmasses have been compared in this study it has been clearly shown that the mean surface heat flow values q s in those gondwana terrains of india which remained unaffected by tectonic and igneous activity during the last 150 m y i e after the break up of gondwanaland are either equal to or mostly lower by 5 22 mw m 2 than those in similar terrains of australia and even the immobile african continent and that q s values for the terrains of these landmasses which were affected by such activity during the last 150 m y are uniformly equal it is inferred that the indian lithosphere is neither hotter nor thinner than that beneath the above mentioned continents and that the sub lithospheric upper mantle beneath the indian peninsula is not hotter or less viscous than that beneath the african and australian shields these results and inferences evidently imply that the thermal regime and the other related parameters of the continental lithosphere do not contribute to the mobility of the plates to which it is attached that the rapid movement of the indian landmass is not coupled with the thermal characteristics of its lithosphere and that the drag force which the present studies have shown to be insignificant would not have been lower on the base of the indian lithosphere than beneath the african and australian landmasses accordingly the earlier reported postulate that the high velocity of the indian landmass is due to its thin and hot continental lithosphere and less viscous upper mantle is not valid the paleo reconstruction indicates the existence of the reunion and kerguelen plumes one on each side of the indian landmass it is likely that these plumes created in the sub lithospheric mantle favourable conditions which worked together with forces that resulted from slab pull and ridge push to give a high velocity to the indian landmass

antarctic peninsula ice sheet evolution during the cenozoic era the antarctic peninsula region is currently undergoing rapid environmental change resulting in the thinning acceleration and recession of glaciers and the sequential collapse of ice shelves it is important to view these changes in the context of long term palaeoenvironmental complexity and to understand the key processes controlling ice sheet growth and recession in addition numerical ice sheet models require detailed geological data for tuning and testing therefore this paper systematically and holistically reviews published geological evidence for antarctic peninsula ice sheet variability for each key locality throughout the cenozoic and brings together the prevailing consensus of the extent character and behaviour of the glaciations of the antarctic peninsula region major contributions include a downloadable database of 186 terrestrial and marine calibrated dates an original reconstruction of the lgm ice sheet and a new series of isochrones detailing ice sheet retreat following the lgm glaciation of antarctica was initiated around the eocene oligocene transition in east antarctica palaeogene records of antarctic peninsula glaciation are primarily restricted to king george island where glacigenic sediments provide a record of early east antarctic glaciations but with modification of far travelled erratics by local south shetland island ice caps evidence for neogene glaciation is derived primarily from king george island and james ross island where glaciovolcanic strata indicate that ice thicknesses reached 500 850 m during glacials this suggests that the antarctic peninsula ice sheet draped rather than drowned the topography marine geophysical investigations indicate multiple ice sheet advances during this time seismic profiling of continental shelf slope deposits indicates up to ten large advances of the antarctic peninsula ice sheet during the early pleistocene when the ice sheet was dominated by 40 kyr cycles glacials became more pronounced reaching the continental shelf edge and of longer duration during the middle pleistocene during the late pleistocene repeated glacials reached the shelf edge but ice shelves inhibited iceberg rafting the last glacial maximum lgm occurred at 18 ka bp after which transitional glaciomarine sediments on the continental shelf indicate ice sheet retreat the continental shelf contains large bathymetric troughs which were repeatedly occupied by large ice streams during pleistocene glaciations retreat after the lgm was episodic in the weddell sea with multiple readvances and changes in ice flow direction but rapid in the bellingshausen sea the late holocene epoch was characterised by repeated fluctuations in palaeoenvironmental conditions with associated glacial readvances however this has been subsumed by rapid warming and ice shelf collapse during the twentieth century

thermal history and extension of the lithosphere in the mannar basin and realization its hydrocarbon potential offshore sri lanka abstract data on the structure of the sedimentary blanket and the composition of its rocks measurements of deep temperatures and vitrinite reflectance published in the open press were used for the numerical 1 d reconstructions of the thermal evolution of the mannar basin and the history of its tectonic subsidence near wells pearl 1 dorado north pseudo mannar deep and barracuda analysis of variations in the basin s tectonic subsidence and published geophysical data on the modern depth of the moho boundary made it possible to numerically estimate the degree of stretching of the basin s lithosphere at different stages of its evolution our analysis shows that a significant part of the lithosphere extension occurred before the start of the formation of the basin s sedimentary cover the moderate lithosphere extension with amplitude 1 15 1 25 accompanied the thermal activation of the basin lithosphere during the second stage of the basin rifting in the late cretaceous our modeling suggests a more moderate history of changes in the thermal regime of the basin s lithosphere and lower degree of maturity and realization of hydrocarbon potential in sedimentary sections of the pearl 1 dorado north pseudo mannar deep and barracuda wells than those reconstructed numerically in recent studies of the mannar basin

millennial scale instability of the antarctic ice sheet during the last glaciation records of ice rafted detritus ird concentration in deep sea cores from the southeast atlantic ocean reveal millennial scale pulses of ird delivery between 20 000 and 74 000 years ago prominent ird layers correlate across the polar frontal zone suggesting episodes of antarctic ice sheet instability carbon isotopes 13 c of benthic foraminifers a proxy of deepwater circulation reveal that south atlantic ird events coincided with strong increases in north atlantic deep water nadw production and inferred warming interstadials in the high latitude north atlantic sea level rise or increased nadw production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the weddell sea region of west antarctica

some new measurements of heat flow in the superior province of the canadian shield borehole heat flow measurements are reported from six new sites in the superior province of the canadian shield values adjusted for glaciation effects but not for holocene climatic variations range from 42 to 56 mw m2 when these new values are combined with 21 previously published borehole values the mean is 42 mw m2 with a standard deviation of 11 mw m2 the data for a site on the lac du bonnet batholith suggest that the batholith has a thin veneer less than 3 km of rock of high radiogenic heat production at the surface

stress field and seismicity in the indian shield effects of the collision between india and eurasia intraplate stresses and intraplate seismicity in the indian subcontinent are strongly affected by the continued convergence between india and eurasia the mean orientation of the maximum horizontal compression in the indian subcontinent is subparallel to the direction of the ridge push at the plate boundary as well as to the direction of compression expected to arise from the net resistive forces at the himalayan collision zone indicating that the intraplate stresses in the subcontinent including the shield area are caused by plate tectonic processes spatial distribution of historic and instrumentally recorded earthquakes indicate that the seismic activity is mostly confined to linear belts while the remaining large area of the shield is stable the available conventional heat flow data and other indicators of heat flow suggest hotter geotherms in the linear belts leading to amplification of stresses in the upper brittle crust many of the faults in these linear belts which happen to be 200 80 m y old are being reactivated either in a strike slip or thrust faulting mode the reactivation mechanisms have been analyzed by taking into consideration the amplification of stresses pore pressures geological history of the faults and their orientation with respect to the contemporaneous stress field the seismicity of the indian shield is explained in terms of these reactivation mechanisms

u channel track for susceptibility measurements 1 a lightweight transportable and inexpensive magnetic susceptibility track for u channel samples is described the track utilizes a sapphire instruments 3 3 cm square coil having a response function of shape similar to that of the 2g enterprises u channel magnetometer and a half peak width of 3 cm the instrument has been calibrated using a u channel standard made of manganese dioxide the software incorporates automated track control and measurement drift correction susceptibility measurements on this system compare favorably with the 45 mm circular bartington loop used for u channel samples at the laboratoire des sciences du climat et de l environnement gif sur yvette france and with data from the whole core susceptibility track aboard the ocean drilling program research vessel joides resolution

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

radioactive element distribution in the archean granulite terrane of jequie bahia brazil the radioactive element distribution in the archean granulite facies rocks of jequie brazil has been determined the k rb ratios show a large spread with majority of the values falling within the normal field k rb 300 the th u ratios fall into two groups one group with values in the range of 1 7 to 2 6 whereas the other group show th u values greater than 7 7 to 25 these distributions can be explained on the basis of the presence of accessory minerals apatite and zircon the relatively high concentrations of the radioactive and other elements in jequie granulites probably represents the relict primary geochemical character little modified during metamorphism the radiogenic heat production data for the area are calculated and using the measured regional heat flow value from nearby area an estimate of the relative thickness of the continental lithosphere is made using the model developed by oxburgh 1981

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

geochemical characteristics and possible origins of the southern closepet batholith south india the polyphase closepet batholith in south india intrudes archean tonalitic and granitic gneisses in a terrane that grades from amphibolite to granulite grade at the southern end of the batholith two granite and two granodioritic suites are recognized in the batholith one granite suite from the southern terminus of the batholith has high sr ba la yb and eu eu and low sc y nb ta and total ree and is similar to other granites from along the amphibolite granulite transition zone that have the characteristics of a fractionally crystallized cumulate the other granite suite has lower sr and ba higher sc and y and no distinctive eu anomaly this latter group which is widespread in the southern closepet batholith can be derived by 20 equilibrium partial melting of a tonalite source containing hornblende and garnet that is compositionally similar to south india tonalites near the amphibolite granulite transition the two granite groups may have been produced by separate episodes of co 2 metam

surface heat flow and probable evolution of deccan volcanism abstract in the light of surface heat flow observations as well as other related geological and geophysical data the origin of the deccan basalts has been examined the indian lithosphere after its detachment from gondwanaland apparently traversed a rising plume at la reunion which virtually bored through the lithosphere to emerge as the deccan trap volcanism on the surface subsequent volcanic and plutonic activity appears to have continued not only up to the oligocene as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features the west coast faults the narmada son tapti lineament and the cambay graben but also up to the mio pliocene as indicated by the heat flow and gravity data over the cambay graben the dyke swarms and sills which are mostly post trappean evolved from the lithosphere after the indian plate moved away from the hot spot

3d lithosphere density structure of southern indian shield from joint inversion of gravity geoid and topography data abstract we present the 3d crustal and lithospheric structure and crustal average density distribution of southern indian shield south of 18 n sri lanka and adjoining oceans the model is based on the assumption of local isostatic equilibrium and is derived from joint inversion of free air gravity and geoid anomalies and topography data the derived crustal thickness of 10 25 km in the oceanic region increases to 34 35 km along the coast a crustal thickness of 34 38 km is obtained beneath the eastern dharwar craton and 36 45 km beneath the western dharwar craton and the southern granulite terrain sri lanka has a thinner crust of 30 35 km the lithosphere asthenosphere boundary is located at depths of 70 120 km under oceanic regions and 150 180 km below the dharwar craton and the northern block of southern granulite terrain a notably thinned lithosphere of 130 km near bangalore in the eastern dharwar craton 140 km beneath the southern block of southern granulite terrain and 130 km in sri lanka is observed the thickness of the lithosphere 130 km near bangalore is inferred as the frozen in signature of a small fossil mantle plume and or tectono compositional effect of a rifted margin and a suture considerable stretching and or convective removal of pristine lithosphere in the southern block of southern granulite terrain and adjoining sri lanka before disappearing completely in the archaean northern block of southern granulite terrain and dharwar craton is suggested

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

the arsikere granite of southern india magmatism and metamorphism in a previously depleted crust abstract the arsikere granite is a small diapiric potassic pluton intruded into archean gneisses of the western part of the dharwar craton of southern india a rb sr age of 2563 ma indicates that the granite was formed during a period of granulite development at lower crustal levels at least to the south of the dharwar craton schist belts in the craton were metamorphosed to greenschist or amphibolite facies at this time but gneisses underwent no isotopic or other geochemical effects the arsikere granite contains quartz oligoclase highly perthitic alkali feldspar originally precipitated as a single phase f rich biotite plus primary epidote fluorite and f rich muscovite sphene forms large euhedrons which incorporate nearly all of the ti in the rock leaving pure magnetite as the only opaque phase equilibration parameters include temperatures of 700 from feldspars f o 2 10 12 bar biotite and opaques and f oh 10 3 biotite nearby schist belts were metamorphosed at 5 kbar pressure at the same time as granite emplacement if the granite was emplaced at 5 kbar the magma could not have been water saturated perthite an initial 87 sr 86 sr ratio of 0 7021 in the arsikere granite is too low for the magma to have formed by partial melting of rocks with the rb sr ratios of gneisses currently exposed in the craton apparently the magma formed in a lower crust that had been depleted in rb and probably other lithophilic elements several hundred million years earlier at this time the craton also became water poor and inert to further geochemical activity such as resetting isochrons during later metamorphism

heat flow and crustal thermal structure in the late archaean closepet granite batholith south india the late archaean closepet granite batholith in south india is exposed at different crustal levels grading from greenschist facies in the north through amphibolite and granulite facies in the south along a 400 km long segment in the dharwar craton two areas pavagada and magadi located in the main mass of the batholith best represent the granitoid of the greenschist and amphibolite facies crustal levels respectively heat flow estimates of 38 mw m 2 from pavagada and 25 mw m 2 from magadi have been obtained through measurements in deep 430 and 445 m and carefully sited boreholes measurements made in four boreholes of opportunity in pavagada area yield a mean heat flow of 39 4 s d mw m 2 which is in good agreement with the estimate from deep borehole the study therefore demonstrates a clear cut heat flow variation concomitant with the crustal levels exposed in the two areas the mean heat production estimates for the greenschist facies and amphibolite facies layers constituting the main mass of the batholith are 2 9 and 1 8 w m 3 respectively the enhanced heat flow in the pavagada area is consistent with the occurrence of a radioelement enriched 2 km thick greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented in the magadi area the crustal heat production models indicate similar mantle heat flow estimates in the range 12 14 mw m 2 consistent with the other parts of the greenstone granite gneiss terrain of the dharwar craton

distribution of clay minerals and proxies for productivity in surface sediments of the bellingshausen and amundsen seas west antarctica relation to modern environmental conditions surface sediments from the antarctic continental margin in the bellingshausen and amundsen seas pacific sector of the southern ocean were investigated in order to decipher their capability to record modern environmental conditions spatial distribution of terrigenous sand and mud reflect regional differences in current induced redeposition of glaciogenic debris clay mineral assemblages in the shelf sediments are controlled by the supply of terrigenous detritus from source rocks in the adjacent hinterland suggesting the occurrence of yet unknown sedimentary rocks in the hinterland of the amundsen sea clay mineral distribution on the continental rise in the bellingshausen sea points to the continuation of a bottom current from the antarctic peninsula rise to at least 94 w foraminifer bearing and opal poor deposits prevail on the continental margin in the western bellingshausen sea and the amundsen sea whereas diatom bearing and carbonate free sediments characterize the eastern bellingshausen sea different modes of biological production which were deduced from accumulation rates of biogenic barium during marine isotope stage 1 and recent productivity measurements obviously control the spatial pattern of opal and carbonate bearing sediments in the study area

precambrian tectonics and crustal evolution in south india about 3 4 ga ago voluminous calc alkaline magmas represented by the granitoid gneisses of southern india were emplaced into a now poorly preserved non continental crust unstable ensialic basins initiated at about 3 0 ga were filled with volcanic and sedimentary rocks up to about 2 6 ga this basement cover sequence was deformed at the close of the archaean first by northward accretion and thickening of several crustal slabs formerly separated by prisms of stable shelf sediments structures produced by this episode were refolded and dislocated by large n s strike slip shear belts to impart intense steep planar fabrics to large volumes of the crust fluids rich in co possibly derived from sedimentary material driven beneath the crustal slabs by the thickening mechanism purged the deep crust of h o to form granulites upward migration of hot h o rich fluids encouraged partial melting at intermediate crustal levels these late archaean tectonic and thermal events began soon after the close of basin f

lateral variations in upper mantle thermal structure inferred from three dimensional seismic inversion models global shear wave velocity variations in the upper mantle woodhouse and dziewonski 1984 are employed as a basis for inferring lateral heterogeneities in temperature or composition at a depth of 150 km using experimentally determined elastic moduli for the olivine solid solution and hashin shtrikman bound theory vs and its partial derivatives with respect to temperature or composition iron content are calculated for the depth of interest based on these results the observed seismic vs variations are interpreted as temperature and compositional deviations relative to a spherically symmetric reference model if it is assumed that the vs variations primarily represent lateral temperature changes then the present results can be used to construct a global surface heat flow map from the geotherm families of pollack and chapman 1977 our inferred heat flow patterns calculated independently of actual heat flow data show clear agreement with the surface heat flow maps proposed by chapman and pollack 1975 and chapman 1985 this result is consistent with and supports thermal structure as the primary governing factor in the generation of upper mantle lateral velocity variations compositional changes appear to correlate with temperature but affect velocity structure to a lesser extent

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

evolution of temperature maturation level and realization of hydrocarbon potential in subtrappean sedimentary complex of the bombay offshore results of 1 d basin modeling abstract the modified galo program package for basin modeling is used to calculate the temperature and vitrinite reflectance distributions with depth at any time before during and after the decan trap formation an assessment of hydrocarbon generation by kerogen of type iii is carried out for burial history of probable source rocks in the subtrappean sedimentary complex of the western passive margin of india near the bombay offshore duration of trap formation is most critical and indefinite parameter in construction of maturity aureole in the subtrappean sedimentary complex the analysis in the frame of the model of continuous formation of traps suggests that a maturation level of organic matter in sedimentary rocks under the trap depends strongly on duration of the trap formation even for traps thickness of 1 5 km or more maturity level of organic matter in the rocks located on the 100 500 m below the base of the trap can be rather moderate if the trap has been formed over fairly a long time

radioelements and heat production of an exposed archaean crustal cross section dharwar craton south india the dharwar craton dc in south india exposes a tilted f30 km thick crustal section equivalent to upper middle and lower archaean continental crust the dc is composed of poly magmatic metamorphic terrains such as the western dharwar craton wdc and eastern dharwar craton edc whose contact is marked by the closepet granite batholith cg in situ gamma ray spectrometric analysis has been carried out to measure k u and th abundance at 1023 sites covering all major rock formations of the dc the data show that the greenschist and amphibolite facies tonalite trondhjemite granodioritic ttg gneisses of the wdc are poorer in radioelements compared to granodioritic gneisses of the edc similarly the wdc granites of the amphibolite facies region have lower abundance indicating their derivation from a depleted lower crust which had suffered an earlier crustal differentiation the elemental data on the gneisses in the wdc and edc do not show a difference between the greenschist and amphibolite facies but there is a marked depletion in the granulite facies the depletion reaches a maximum in the high p granulites in the southernmost part of the dc the elongate cg is an i type calc alkaline metaluminous granite which exposes a f12 km thick batholith where k is remarkably uniform but u and th show several fold increase with decreasing crustal levels heat production was calculated from the radioelemental data for estimating the radiogenic heat contribution of crust to heat flow we arrive at a present day crustal configuration comprising four northerly dipping metamorphic facies layers greenschist amphibolite metasomatized granulite and depleted granulite gross heat production of each layer is computed from heat production of constituent rocks and their abundance the crustal contribution is found to decrease from greenschist to granulite facies regions from 23 to 18 mw m 2 in the wdc 27 to 7 mw m 2 in the edc surface heat flow and the crustal contribution models indicate that mantle heat flow of the wdc is lower 7 10 mw m 2 compared to the edc 17 24 mw m 2 in the greenschist and amphibolite facies regions high mantle heat flow of 29 mw m 2 beneath the depleted granulite facies region of the edc appears anomalous in the dharwar craton

extensive microbial modification of formation water geochemistry case study from a midcontinent sedimentary basin united states the upper devonian antrim shale in the michigan basin is an economically significant source of microbially produced methane along the basin margins where meteoric recharge has been focused oxygen and hydrogen stable isotope compositions of antrim formation waters show that fresh waters recharged from pleistocene glaciation and modern precipitation suppressed basinal brine salinity to great depths and enhanced methanogenesis this paper presents results of integrated elemental and isotope analyses of antrim shale formation waters from the margins and center of the michigan basin focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis cl br na systematics reveal that salinity is controlled not only by mixing between variable amounts of basinal brine and meteoric water but also by halite dissolution where fluids recharged through underlying devonian carbonate aquifers with localized evaporite deposits divalent cations carbonate system parameters and carbon isotope compositions of dissolved inorganic carbon have been systematically and profoundly altered by microbial methanogenesis large decreases in formation water ca mg and ca sr ratios accompany increasing carbonate alkalinity values in areas with high rates of microbial gas production thermodynamic and reaction path modeling show that these changes are consistent with calcite precipitation during progressive microbial methanogenesis similar variations in fluid chemistry are evident in databases from other sedimentary basins containing black shales and coal beds associated with microbial gas microbial methanogenesis may play an important role in the geochemical evolution of divalent cation relationships in crustal fluids and should be considered in models of formation water origin and evolution

exhumation history of a section of the sikkim himalayas india records in the metamorphic mineral equilibria and compositional zoning of garnet the exhumation history of pelitic migmatite samples from the high himalayan crystalline complex hhc near the south tibetian detachment system in the sikkim darjeeling section has been determined on the basis of thermo barometric analyses retrograde breakdown reactions and compositional zoning of garnet the peak metamorphic condition is estimated to be 10 4 kbar 800 c from thermo barometric and phase equilibrium constraints the observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and hence extremely rapid 15 mm yr exhumation up to the depth of 15 km numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process 2 mm yr up to at least 5 km depth to lead to the development of the observed compositional zoning of garnet the dramatic change of the exhumation velocity vz might reflect a process of tectonic thinning followed by erosion and or horizontal flow at shallow depth assuming that the vz did not change significantly below 5 km depth these results suggest that the hhc samples studied in this work exhumed from a depth of 34 km within 8 ma

modelling the variability of heat flow due to the random thermal conductivity of the crust summary analytical solutions for the mean heat flow and its error bounds have been obtained by solving the steady state heat conduction equation following a stochastic analytical approach incorporating gaussian uncertainties in the thermal conductivity this study on the uncertainty analysis to quantify the variability in the heat flow along with its associated error statistics has been applied to the latur earthquake region of the indian shield results obtained show that the mean heat flow and its error bounds are highly dependent on the random components of the thermal conductivity such as its coefficient of variability and its correlation length scale hence the study can be used to quantify the error statistics in the heat flow field for any given region

stochastic modeling of the thermal structure to decipher the lithospheric thickness application to dharwar craton a wide range of speculation regarding lithospheric thermal thickness in a region calls for quantifying the uncertainties associated with model parameters in this paper we present an attempt to decipher it by solving the differential equations governing the heat transfer through the lithosphere adequately quantifying the temperature field is very important since it is highly dependent on the controlling thermal parameters thermal conductivity is modeled as a random parameter with a known mean value and correlation structure we compute the temperatures in the crust and lithospheric mantle along with their error bounds using an analytical solution to the steady state heat equation and the adomian method of decomposition we apply these solutions in the archean dharwar craton which is divided into western dharwar craton wdc and eastern dharwar craton edc we obtain a moho temperature estimate of 304 58 c in wdc whilst in edc it is 375 74 c for a 20 coefficient of variability in thermal conductivity the range of lithospheric thickness obtained for wdc is 150 280 km and 110 160 km for the edc these values are in agreement with other geophysical and geological findings in the region the thermal lithosphere obtained from this study is based on the mantle solidus and the surface wave seismological studies considering radial anisotropy reveal that the lithosphere is characterized by higher shear wave velocities and decrease at the lithosphere asthenosphere boundary average shear velocity model for two different cratonic blocks edc and wdc is used to show the lab thickness for the eastern and western dharwar craton the two independent studies show a correlation in the lithospheric thickness

high velocity anomaly under the deccan volcanic province abstract tomographic modelling of p wave residuals at 22 vertical component seismograph stations operated in the deccan volcanic province dvp in west central india and the dharwar craton point to the existence of a large deep at least 300 km high velocity anomaly 1 3 faster directly beneath most of the dvp and dharwar craton there is also marginal evidence that the westernmost part of the dvp may be characterised by low velocity up to 1 5 to a depth of about 200 km this coherent high velocity anomaly under the dvp and its extension into the south indian shield is viewed as a lithospheric root an architecture characteristic of precambrian shields

thermal evolution of cratons in china abstract craton s thermal state is one of the main gateways to understand the craton dynamics three cratons in china the tarim north china and yangtze cratons are in different thermal states and differ in their stabilities low heat flow usually corresponds to stable craton but not vice versa the tarim craton is cold 44 mw m2 and still keeps its stability now the western north china craton and the upper yangtze craton are not too cold 50 60 mw m2 but also remain stable the eastern north china craton and the middle lower yangtze craton are relatively hot with heat flow of 60 70 mw m2 both have been heated and destroyed in the mesozoic all these cratons have experienced complex tectonothermal events since their formation some tectonothermal events only thin and heat craton but others can destroy craton several sedimentary basins are developed in these cratons which recorded individual thermal histories these thermal records could help to understand the thermal evolution of these cratons and provide constraints on craton dynamics including stability or destruction the thermal results indicate parts of craton in western china tarim and sichuan have secular cooling histories which were locally disturbed by mantle plume activities in the permian the middle lower yangtze craton has undergone similar thermal evolution as the eastern north china craton all parts of cratons in eastern china might all have been destroyed due to subduction and dehydration of the pacific plate during the mesozoic

the nature of the crust in southern india implications for precambrian crustal evolution 1 we present crustal thickness and poisson s ratio determinations from receiver function analyzes at 32 sites on the archaean and proterozoic terrains of south india the crustal thickness in the late archaean 2 5 ga eastern dharwar craton varies from 34 39 km similar crustal thickness is observed beneath the deccan volcanic province and the cuddapah basin the most unexpected result is the anomalous present day crustal thickness of 42 51 km beneath the mid archaean 3 4 3 0 ga segment of the western dharwar craton since the amphibolite grade metamorphic mineral assemblages 5 7 kbar paleopressures in this part of western dharwar craton equilibrated at the depths of 15 20 km our observations suggest the existence of an exceptionally thick 57 70 km crust 3 0 ga ago beneath the exhumed granulite terrain in southernmost india the crustal thickness varies between 42 60 km the poisson s ratio ranges between 0 24 0 28 beneath the precambrian terrains indicating the presence of intermediate rock type in the lower crust these observations of thickened crust suggest significant crustal shortening in south india during the archaean

crustal heterogeneities and the thermal structure of the continental crust the observed linear relationship between surface heat flow q0 and the radiogenic heat production of near surface rocks a0 discovered almost two decades ago has been a primary tool used to infer the distribution of heat production in the continental crust recent evidence on the nature of compositional heterogeneities in the continental crust has led us to reexamine the q0 a0 relationship and the likely implications for the thermal structure of the lower continental crust numerical simulations of crustal thermal models indicate that some interpretations derived from this relation may be flawed in particular the length scale determined from the q0 a0 function normally thought to describe the depth distribution of crustal heat sources is significantly affected by the horizontal scale of crustal heterogeneity as a consequence most estimates of lower crustal heat flow and lower crustal temperatures obtained using heat flow data with the q0 a0 relationship are overestimates this overestimation is proportionally largest in areas of low mantle heat flux such as cratons where basal heat flux may be overestimated by more than a factor of two

evidence for thick continental roots beneath south indian shield teleseismic p wave arrivals recorded at south indian seismological stations have been used to construct a 3 d velocity image of the upper mantle beneath this region analysis of a suite of models lead us to conclude that an anomalously high velocity region 1 6 contrast exists in the upper mantle beneath the whole of south indian shield including the deccan traps in the depth range of 60 300 km in contrast the westernmost part of the deccan traps and its subjacent mantle in the northwest is characterised by a relatively low velocity this observed low velocity zone may be a still warm remnant of the spreading centre offset eastwards from the carlsberg ridge which might have been the dominant source of the flood basalts that flowed over the deccan plateau 65 ma ago the high velocity upper mantle of the entire south indian shield is viewed as a continental root formed by a process of geochemical reordering which happens to be more stable

palaeoenvironmental records from the west antarctic peninsula drift sediments over the last 75 ka we present results of a multi proxy study on marine sediment core jr179 pc466 recovered from the crest of a sediment drift off the west antarctic peninsula at approximately 2300 m water depth the 10 45 m long core consists dominantly of glaciomarine terrigenous sedi ments with only traces of calcium carbonate 1 wt despite the very low abundance of calcar eous foraminifera planktonic shell numbers are suf cient for stable isotope analyses in two thirds of the samples studied the core chronology is based on oxygen isotope stratigraphy and corre lation of its relative palaeomagnetic intensity rpi with a stacked reference curve according to the age model core pc466 spans the last 75 ka with average sedimentation rates of between about 4 and 25 cm ka 21 planktonic foraminifera abundances uctuate between 0 and 30 individ uals per gram throughout the core with minima observed during marine isotope stage mis 2 14 29 ka before present bp and mis4 57 71 ka bp planktonic foraminifera are present in the holocene but more abundant in sediments deposited during mis3 29 57 ka bp owing to less dilution by terrigenous detritus and or better carbonate preservation during mis3 forami nifera maxima correlate with antarctic warming events as recorded in the d 18 o signal of the epica dronning maud land edml ice core they indicate higher planktonic foraminifera production and better carbonate preservation west of the antarctic peninsula during that time the abundance of ice rafted detritus ird in core pc466 increased during the last deglaciation between about 19 and 11 ka bp when numerous icebergs drifted across the core site thereby releasing ird during this time sea level rise destabilized the antarctic peninsula apis and west antarctic wais ice sheets that had advanced onto the shelf during the sea level low stand of the last glacial maximum lgm c 19 23 ka bp overall our results demonstrate that it is possible to establish an age model and reconstruct palaeoceanographical and climatic changes at high temporal resolution from sedimentary sequences recovered at 2300 m water depth from a west antarctic drift

thermally induced phase changes lateral heterogeneity of the mantle continental roots and deep slab anomalies pressure induced solid solid phase changes are responsible for most of the increase of density and seismic velocity with depth in the upper mantle lateral variations in temperature cause a similar effect abrupt changes of density and seismic velocity due to phase changes are superposed on smaller changes associated with thermal expansion temperature induced isobaric phase changes are as important in explaining various recent geophysical data as are the more familar pressure induced phase changes in cold slabs the equilibrium mineral assemblage contains high density high velocity phases which are not stable in hotter mantle in particular the ilmenite form of mgsio 3 and the spinel form of mg 2sio 4 have broad stability fields in cold mantle which increase the density and velocity of deep slabs to values in excess of those which have been used in geoid and seismic travel time modeling recent arguments for slab penetration into the lower mantle and whole mantle convection are based on thermal models of the slab which ignore the large density and seismic velocity anomalies associated with temperature induced phase changes when these effects are taken into account the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and layered models of mantle convection the seismicity cutoff and evidence for slab thickening at 670 km also favor this style of convection mantle seismic velocities between 200 and 400 km depth in tectonic and young oceanic regions are lower than in shield regions and this is due to the presence of a melt phase and lower velocity high temperature phase assemblages deep 200 km long lived continental roots differing in chemistry from normal mantle are not required when isobaric phase changes are taken into account high velocity subshield mantle is closer to normal subsolidus mantle than is suboceanic mantle which is affected by the presence of high temperature phase assemblages the whole mantle convection thick continental root and deep slab penetration hypotheses are not supported by seismic and geoid data when isobaric phase changes are included in the analysis phase changes are more effective in changing density and seismic velocity than are lateral variations in temperature and composition the lack of correlation of the geoid with ridges shields heat flow and upper mantle velocity variations suggests a low geoid sensitivity to the upper mantle consistent with layered convection

the dharwar craton and the assembly of peninsular india peninsular india can be separated into five discrete crustal areas the bhandara singhbhum and aravalli bundelkhand cratons the eastern ghats and a block in southern india containing the dharwar craton and adjoining granulite terrain these areas are separated by four major joins eastern ghats front godavari rift mahanadi rift sukinda thrust and narmada son lineament and associated thrusts all joins except the godavari rift are former orogenic belts where thrusts juxtapose rocks of different metamorphic grade these thrusts and the absence of clear correlation of suites among different cratons suggest that the indian shield formed by accretion of separate continental fragments epicontinental late archean early pro terozoic sediments throughout india however may indicate that the joins are intracontinental formed within a coherent block the term dravidian shield is used for the southernmost of the five crustal blocks including all of india south of the deccan basalts and godavari rift

heat production and thermal conductivity of rocks from the pikwitonei sachigo continental cross section central manitoba implications for the thermal structure of archean crust the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust in cross section the upper to mid level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses both of which are intruded by granitoid plutons this crustal structure persists downward into the granulite facies where keels of the greenstone belts can be found to constrain thermal models of the crust we measured heat production and thermal conductivity in 60 rocks from this terrain using standard gamma ray spectrometry and divided bar techniques large vertical and lateral heterogeneities in heat production in the upper crust are evident heat production is high in granites and metasedimentary rocks intermediate in tonalite gneisses and low in the portions of greenstone belts dominated by mafic meta igneous rocks in the deeper granulite facies rocks heat production decreases by a factor of two in the tonalitic gneisses and remains low in the high grad

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

heat flow in the bastar craton central indian shield implications for thermal characteristics of proterozoic cratons measurements of surface heat flow density in various lithologies from the central parts of the proterozoic bastar craton of the central indian shield have yielded heat flow values ranging from 51 to 64 mw m 2 with a mean value of 56 mw m 2 standard deviation 6 1 mw m 2 these values are considerably higher than in the archaean and archaean to early proterozoic cratons of many precambrian shields but are compatible with the heat flow data from the proterozoic gawler craton central australian shield it is inferred that 1 the contrast in surface heat flow between the archaean and proterozoic cratons is a consequence of the difference in the radiogenic heat production in their upper 10 20 km thick crustal layers and 2 the proterozoic cratons as these could also have enclaves of basic archaean rocks show a wide range of surface heat flow values controlled mainly by the varying amounts of upper crustal radiogenic heat source

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

sedimentation on the continental rise west of the antarctic peninsula over the last three glacial cycles abstract the continental rise west of the antarctic peninsula includes a number of large sediment mounds interpreted as contourite drifts cores from six sediment drifts spanning some 650 km of the margin and 4 of latitude have been dated using chemical and isotopic tracers of palaeoproductivity and diatom biostratigraphy interglacial sedimentation rates range from 1 1 to 4 3 cm ka glacial sedimentation rates range from 1 8 to 13 5 cm ka and decrease from proximal to distal sites on each drift late quaternary sedimentation was cyclic with brown biogenic burrowed mud containing ice rafted debris ird in interglacials and grey barren laminated mud in glacials foraminiferal intervals occur in interglacial stages 5 and 7 but not in the holocene processes of terrigenous sediment supply during glacial stages differed meltwater plumes were more important in stages 2 4 turbidity currents and ice rafting in stage 6 the terrigenous component shows compositional changes along the margin more marked in glacials the major oxides al2o3 and k2o are higher in the southwest and cao and tio2 higher in the northeast there is more smectite among the clay minerals in the northeast magnetic susceptibility varies along and between drifts these changes reflect source variations along the margin interglacial sediments show less clear trends and their ird was derived from a wider area downslope processes were dominant in glacials but alongslope processes may have attained equal importance in interglacials the area contrasts with the east antarctic continental slope in the se weddell sea where ice rafting is the dominant process and where interglacial sedimentation rates are much higher than glacial the differences in glacial setting and margin physiography can account for these contrasts

heat production in an archean crustal profile and implications for heat flow and mobilization of heat producing elements we have measured concentrations of heat producing elements th u and k in 58 samples representative of the main lithologies in a 100 km transect of the superior province of the canadian shield from the michipicoten wawa greenstone belt near wawa ontario through a domal gneiss terrane of amphibolite grade to the granulite belt of the kapuskasing structural zone near foleyet this transect has been interpreted as an oblique cross section through some 25 km of crust uplifted along a major thrust fault and thus provides an opportunity to examine in detail a continuous profile into deep continental crust of archean age mean heat production values for these terranes based on aereal distribution of major rock types and calculated from their th u and k concentrations are michipicoten greenstone belt 0 72 w m 3 wawa domal gneiss terrane amphibolite grade 1 37 w m 3 kapuskasing granulites 0 44 w m 3 among the silicic plutonic rocks tonalites granites and their derivative gneisses the relatively large variation in heat production correlates with modal abundances of accessory minerals including allanite sphene zircon and apatite we interpret these variations as primary pre metamorphic the relatively high weighted mean heat production of the domal gneiss terrane can be accounted for by the larger proportion there of late stage th u and k rich granitoid plutons these may have been derived from the underlying kapuskasing granulite terrane leaving it slightly depleted in heat producing elements transport of th u and k therefore could have taken place in silicate melts rather than in aqueous or carbonic metamorphic fluids this conclusion is supported by the lack of a statistically significant difference in heat production between tonalites tonalite gneisses and mafic rocks of amphibolite versus granulite grade the pre metamorphic radioactivity profile for this crustal section is likely to have been uniformly low with a mean heat production value less than 1 w m 3 this result is distinctly different from measured profiles in more silicic terranes which show decreasing heat production with depth this implies fundamental differences in crustal radioactivity distributions between granitic and more mafic terranes and may be an important factor in selective reactivation of lithologically different terranes possibly resulting in preferential stabilization of basic terranes in the geological record our results indicate that a previously determined apparently linear heat flow heat production relationship for the kapuskasing area does not relate to the distribution of heat production with depth low but significant heat production 0 4 0 5 w m 3 continues to lower crustal depths with no correlation to the depth parameter from the linear relationship this low heat production may be a minimum average granulite heat production and suggests that in general heat flow through the moho is 8 10 mw m 2 lower than the reduced heat flow calculated from the heat flow heat production regression

geothermal studies in the hyderabad granitic region and the crustal thermal structure of the southern indian shield based on temperature measurements in three boreholes one specially drilled for the purpose and thermal conductivity determinations heat flow density values were determined for three sites in the archaean hyderabad granitic batholith a mean heat flow density value of 40 1 s d mw m 2 has been obtained the heat generation in its rocks 5 57 w m 3 is significantly higher than in average crustal rocks it has been proposed that the hyderabad batholith has a layered structure with a thin 1 km surface layer of high radioactivity these results together with the already reported data have been used to estimate the conductive steady state temperature within and at the base of the crust of the southern indian shield yielding values of the same order as found in the western australian shield