nd sr isotopic composition of granulites and constraints on the evolution of the lower continental crust in a statistical study of granulite facies rocks we have analysed 32 samples with ages ranging from 2 900 to 200 myr for sm nd rb and sr and 143nd 144nd and 87sr 86sr ratios the sm nd ratio is found to be constant compared with the highly variable rb sr ratio using the model age formalism we show that in many cases internal differentiation of continental crust follows external differentiation with a large time interval

chronostratigraphy of the 600 000 year old continental record of lake van turkey lake van sediment cores from the ahlat ridge and northern basin drill sites of the icdp project paleovan contain a wealth of information about past environmental processes the sedimentary sequence was dated using climatostratigraphic alignment varve chronology tephrostratigraphy argon argon single crystal dating radiocarbon dating magnetostratigraphy and cosmogenic nuclides based on the lithostratigraphic framework the different age constraints are compiled and a robust and precise chronology of the 600 000 year old lake van record is constructed proxy records of total organic carbon content and sediment color together with the calcium potassium ratios and arboreal pollen percentages of the 174 meter long ahlat ridge record mimic the greenland isotope stratotype ngrip therefore the proxy records are systematically aligned to the onsets of interstadials reflected in the ngrip or synthesized greenland ice core stratigraphy the chronology is constructed using 27 age control points derived from visual synchronization with the gicc05 timescale an absolutely dated speleothem record e g hulu sanbao linzhu cave and the epica dome c timescale in addition the uppermost part of the sequence is complemented with four ages from holocene varve chronology and two calibrated radiocarbon ages furthermore nine argon argon ages and a comparison of the relative paleointensity record of the magnetic field with reference curve piso 1500 confirm the accuracy of the age model also the identification of the laschamp event via measurements of 10be in the sediment confirms the presented age model the chronology of the ahlat ridge record is transferred to the 79 meter long event corrected composite record from the northern basin and supplemented by additional radiocarbon dating on organic marco remains the basal age of the northern basin record is estimated at 90 ka the variations of the time series of total organic carbon content the ca k ratio and the arboreal pollen percentages illustrate that the presented chronology and paleoclimate data are suited for reconstructions and modeling of the quaternary and pleistocene climate evolution in the near east at millennial timescales furthermore the chronology of the last 250 kyr can be used to test other dating techniques

gamma ray measurements in the kirchrode i and ii boreholes abstract the downhole ray logs in the kirchrode i and ii boreholes through the albian southeast of hannover in northwest germany were used a to correlate the two boreholes b to calculate the clay content of the sediments and c to detect cyclicity in changes in sediment composition the cross correlation of the downhole ray logs of the kirchrode i and ii showed that a shift of the kirchrode ii borehole downwards by 89 m provides the best correlation with the kirchrode i borehole a comparison of the ray log of kirchrode ii with that of the nearby prakla 2 borehole for which biostratigraphic data is available also yields a close correspondence using this correlation of the logs and adopting the stratigraphic subdivision of the prakla 2 borehole by kemper 1989 the upper middle albian and middle lower albian boundaries in kirchrode ii are at depths of 152 and 252 m respectively the ray logs were used to calculate the clay content it varies between 30 and 60 indicating only small lithologic changes this result is in agreement with values derived from analysis of the quartz and caco3 contents of core samples the montmorillonite illite and kaolinite contents of the clay fraction determined by kuhn et al 2001 are the basis for an independent calculation of the clay contents of the core using mean literature values for the thorium and potassium contents of these three clay minerals the periodicities identified by spectral analysis of the ray measurements made every 5 cm throughout the recovered albian sequence can be interpreted in terms of milankovitch cycles sliding window spectral analysis shows that the sedimentation rates were relatively constant during the late albian 8 12 cm ka sedimentation rates of 4 cm ka were determined for the middle albian

conjunctive use of spectral gamma ray logs and clay mineralogy in defining late jurassic early cretaceous palaeoclimate change dorset u k abstract detrital clay mineralogy is controlled by weathered source rock climate transport and deposition that in turn influence the spectral gamma ray sgr response of resultant sediments whilst a palaeoclimate signal in clay mineralogy has been established in some ancient successions the sgr response remains contentious largely because the data sets have yet to be collected at the same or appropriate vertical scales to allow comparison in addition the influence of organic matter on sgr is not always considered here we present clay mineralogical total organic carbon toc and sgr analyses from the late jurassic and early cretaceous of the wessex basin a period of previously documented palaeoclimate change the aim of this paper is to estimate the sensitivity of sgr as palaeoclimatic tool sgr and clay mineral data having been collected at the same sample points making this one of the most rigorous comparison of clay mineral and sgr to date overall the correlation between high thorium potassium or thorium uranium and kaolinite associated with a well established palaeoclimate change shows that elevated thorium may be used as a proxy for humid palaeoweathering as suggested by few previous studies

crustal structure and tectonics of the northern part of the southern granulite terrane india deep seismic reflection studies investigating the exposed archean lower continental crust of the southern granulite terrane india yield important constraints on the nature and evolution of the deep crust including the formation and exhumation of granulites seismic reflection images along the kuppam bhavani profile reveal a band of reflections that dip southward from 10 5 to 15 0 s two way time twt across a distance of 50 km the bottom of these reflections beneath the dharwar craton is interpreted as the moho further south another reflection band dipping northward is observed these bands of reflectivity constitute a divergent reflection fabric that converges at the moho boundary observed at the mettur shear zone reflection fabrics that intersect at a steep angle are interpreted as a collisional signature due to the convergence of crustal blocks which we infer resulted in crustal thickening and the formation of granulites anomalous gravity and magnetic signatures are also observed across the mettur shear zone the gravity model derived from the bouguer gravity data corroborates seismic results the tectonic regime and seismic reflection profiles are combined in a 3 d representation that illustrates our evidence for paleo subduction at a collision zone the structural dissimilarities and geophysical anomalies suggest that the mettur shear zone is a suture between the dharwar craton in the north and another crustal block in the south this study contributes significantly to our understanding of the operation of archean plate tectonics here inferred to involve collision and subduction furthermore it provides an important link between the gondwanaland and global granulite evolution occurring throughout the late archean

neoarchean continental growth through arc magmatism in the nilgiri block southern india the formation and growth of continental crust in the archean have been evaluated through models of subduction accretion and mantle plume the nilgiri block in southern india exposes exhumed neoarchean lower crust uplifted to heights of 2500 m above sea level along the north western margin of the peninsula major lithologies in this block include charnockite with or without garnet anorthosite gabbro suite pyroxenite amphibolite and hornblende biotite gneiss ttg all these rock types are closely associated as an arc magmatic suite with diffuse boundaries and coeval nature the charnockite and hornblende biotite gneisses ttg show sio2 content varying from 64 to 73 wt the hornblende biotite gneisses ttg are high al type with al2o3 15 wt whereas the charnockites show al2o3 15 wt the composition of charnockite is mainly magnesian and calcic to calc alkaline the mafic ultramafic rocks show composition close to that of tholeiitic series the low values of k 2 o 3 wt k rb k2o 500 zr ti and trace element ratios like la yb n sr y y nb y nb rb y ta rb yb ta indicate a volcanic arc signature for these rocks the geochemical signature is consistent with arc magmatic rocks generated through oceanic plate subduction the primitive mantle normalized trace element patterns of these rocks display enrichment in large ion lithophile elements lile and comparable high field strength elements hfse in charnockite and hornblende biotite gneisses ttg consistent with subduction related origin primitive mantle normalized ree pattern displays an enrichment in lree in the chamockite and hornblende biotite gneisses ttg as compared to a flat pattern for the mafic rocks the chondrite normalized ree patterns of zircons of all the rock types reveal cores with high hree formed at ca 2700 ma and rims with low hree formed at 2500 2450 ma log transformed la th nb th sm th yb th discrimination diagram for the mafic and ultramafic rocks from nilgiri displays a transition from mid oceanic ridge basalt morb to island arc basalt iab suggesting a morb source the u pb zircon data from the charnockites mafic granulites and hornblende biotite gneisses ttg presented in our study show that the magma generation during subduction and accretion events in this block occurred at 2700 2500 ma together with the recent report on neoarchean supra subduction zone ophiolite suite at its southern margin the nilgiri block provides one of the best examples for continental growth through vertical stacking and lateral accretion in a subduction environment during the neoarchean c 2014 elsevier b v all rights reserved

repetitions and cycles in stratigraphy abstract stratigraphic sections show repetitions of similar or identical conditions on all scales from millimeters to many hundreds of meters representing time intervals from possibly seconds to many millions of years any such repetitions have been called cycles to understand the reason why cycles occur a time scale is essential beds can be with or without time information the latter are known as event stratifications the event which triggers the formation of beds or any succession of sediments could be a random effect or it could be part of a mechanism in which cyclic behaviour is due to an oscillating physical system such systems are dynamic systems which means that they involve the transport of masses over distances and in definite time intervals cycles generated by such systems can be used as time units a special example is the earth solar system which can generate cycles from daily periods to orbital variations of thousands and millions of years orbital variations are known as milankovitch cycles and they are the subject of cyclostratigraphy proper the recognition of milankovitch cycles or of any other cycle associated with oscillating systems rests on the regularity or time periodicity of such patterns the correct ways of analysing such cycles are the methods of time series analysis repetition patterns representing time intervals of millions and possibly many hundreds of millions of years are known from sequence stratigraphy we know as yet very little about the mechanisms which generate such long periods of repetition it has been suggested that the earth s crust has reached a state of self organized criticality bak p 1996 how nature works springer new york 212 pp in which case sequence formation could be part of the complexity which undoubtedly is an attribute of the earth s crust and history

age and tectonic evolution of neoproterozoic ductile shear zones in the southern granulite terrain of india with implications for gondwana studies 1 the high grade rocks of the southern granulite terrain sgt of peninsular india are bounded to the north by the archean dharwar craton another high grade terrane the mesoproterozoic eastern ghats occurs to the northeast of the sgt the tectonic relationship between these crustal domains is complex we present new geochronological and structural data that indicate a continuation of the dharwar craton into the southern granulite terrain as far south as a newly identified neoproterozoic shear zone here named the karur kamban painavu trichur shear zone kkptsz south of the kkptsz mesoproterozoic dates of the sgt are similar to those recorded in the eastern ghats and the two domains may have been conterminous thirty three new u pb th single zircon and monazite dates of samples from six structural transects across the regional shear zones indicate that the sgt has experienced at least seven thermo tectonic events at 2 5 ga 2 0 ga 1 6 ga 1 0 ga 800 ma 600 ma and 550 ma and two distinct episodes of metasomatism charnockitization between 2 50 2 53 and between 0 55 0 53 ga deformation along a number of major shear zones in the sgt is neoproterozoic to earliest paleozoic in age with an early phase d2 concentrated between 700 800 ma and a later phase d3 between 550 and 600 ma major charnockitization 530 550 ma post dates d3 and is in turn overprinted by granitization retrogression and uplift between 525 and 480 ma the kkptsz active between 560 and 570 ma is either a terrane boundary or a tectonized decollement between cover and archean basement rocks represented by predominantly paragneisses to the south and orthogneisses to the north respectively other regional neoproterozoic shear zones do not appear to separate allochthonous terranes as previously suggested on the basis of nd model ages and rb sr biotite whole rock dates the neoproterozoic cambrian tectonothermal history of the sgt and eastern ghats is similar to that recorded in parts of madagascar east africa and antarctica and is used to reconstruct parts of central gondwana here named the deccan continent with more robust confidence

a 600 000 year long continental pollen record from lake van eastern anatolia turkey abstract lake van is the fourth largest terminal lake in the world 38 5 n 43 e volume 607 km 3 area 3570 km 2 maximum water depth 460 m extending for 130 km wsw ene on the eastern anatolian high plateau turkey the sedimentary record of lake van partly laminated obtains a long and continuous continental sequence that covers multiple interglacial glacial cycles promoted by the potential of the sedimentary sequence for reconstructing the paleoecological and paleoclimate development of the near east a deep drilling operation was carried out in 2010 supported by the international continental scientific drilling program icdp the 219 m long continental pollen record presented here is based on a well dated composite profile drilled on the so called ahlat ridge in water depth of 360 m encompassing the last 600 000 years it is the longest continuous continental pollen record of the quaternary in the entire near east and central asia obtained to date the glacial interglacial cycles and pronounced interstadials are clearly reflected in the vegetation development based on millennial scale time resolution in general the glacial stadial vegetation is characterized by dwarf shrub steppe and desert steppe whereas the climax vegetation of past interglacials can be described as oak steppe forest similar to the present interglacial in this sensitive semi arid region between the black caspian and mediterranean seas by comparing the lake van pollen record with other western asian and southern european long continental pollen sequences as well as marine and ice core records the regional variability of the climate signals is also discussed

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

palaeoclimate analysis using spectral gamma ray data from the aptian cretaceous of southern england and southern france abstract the abundance and half lives of potassium k uranium u and thorium th make these three elements the dominant sources of gamma rays detected in rocks both at outcrop and in the subsurface with the advent of the spectral gamma ray tool sgr the variation shown by these three elements in rocks has been considered to reflect sorting at flooding surfaces and changes in the weathering regime of sediment source lands k and u are considered to be more soluble than th thus elevated th to k or u ratios in soils and eroded clays can reflect hot humid climates and palaeoclimates this study makes an assessment of the usefulness of sgr data to palaeoclimate studies by comparing changing th k and th u ratios from a known period of palaeoclimate change to extensive published and new data from other analytical methods new sgr data from the cretaceous of southern england and southern france compare favourably to outcrop sedimentological facies interpretations and laboratory geochemical data palaeoclimate data from two other sections northern germany northern italy are compared as controls to the study together these analyses suggest that there was a gradual change from semi arid climate in the barremian and early aptian to a semi humid climate in the mid aptian superimposed on this long term rise in humidity were a number of short term ammonite zone length changes in th k and th u ratios and the abundance of climate sensitive materials this study shows that sgr data are more useful than originally thought when problems of overprinting from heavy minerals and diagenesis are overcome outcrop and borehole spectral gamma ray logs from mudstones or the clay rich beds of mixed successions may be used to interpret past patterns of hinterland weathering

cyclostratigraphic studies of sediments from lake van turkey based on their uranium contents obtained from downhole logging and paleoclimatic implications a deep drilling campaign was performed at lake van turkey to enhance the understanding of the paleoenvironmental conditions of the middle east cores were collected and the sediments are mainly composed of clayey silts and tephra deposits spectral gamma ray data were acquired 0 210 m below lake floor and the uranium data were used for cyclostratigraphic studies to estimate the sedimentation rates and the time of deposition detection and analysis of climate cycles require continuous sedimentation and cannot be applied to these sediments which include numerous tephra layers therefore these layers were removed and a synthetic log was created cumulative thickness of the tephra 50 m remaining lacustrine sediments 160 m high amplitudes were detected and correlated to milankovic cycles their evolution was analyzed using the sliding window technique the sedimentation rates varied from 22 to 33 cm ka in the upper section the sediments between the lake floor and a depth of 210 m were deposited over a period of 587 ka our results agree with core interpretations e g correlation of total organic carbon with marine isotope stages which suggest a time span of deposition of 600 ka high frequency cycles were detected and correlated with interstadials from the north greenland 18o record for the past 75 ka the two datasets agreed closely we conclude that climate signals even on sub milankovic scale are imprinted in uranium of these sediments and cyclostratigraphic methods are applicable if event layers are subtracted from the sediment record

facies characterization based on physical properties from downhole logging for the sediment record of lake van turkey abstract lake van turkey is the 4th largest terminal lake in the world and is located at a key position for climatic reconstruction the icdp project paleovan is a deep drilling campaign initiated in the summer of 2010 to enhance the understanding of paleoclimatic and paleoenvironmental conditions in the middle east for a period of 550 000 years multiple coring of two sites northern basin and ahlat ridge at a water depth of up to 360 m has been performed the sedimentary record is mainly composed of clayey silts and tephra deposits that were supplied by four volcanic sources 1 the suphan volcano located on the northern shore 2 the nemrut volcano 15 km west of the westernshore 3 the incekaya volcano on the southwestern shore and 4 intralake eruptive centers the dominant chemical composition of the volcanic sources is known from studies of land deposits high quality downhole logs have been acquired from both sites to construct a continuous lithological profile 180 m of downhole logging data from the ahlat ridge have been analyzed by cluster analysis to improve the differentiation of the sediments two elemental intensity profiles from x ray fluorescence core scanning calcium and zirconium performed on the composite profile core material were added to the cluster analysis five cluster units were derived and transformed into three tephra and two clayey silt units to compare the two clayey silt units with the composite profile from the visual core description vcd that showed 15 lithological units the composite profile was classified into two major groups of lacustrine sediments banded clayey silts interpreted as glacial deposits and laminated clayey silts interpreted as interglacial deposits despite this simplification no correlation between the two clayey silt units derived from cluster analysis and the banded and laminated clayey silts could be found the following reasons are proposed a the comparability of the datasets was limited by significant depth shifts of up to 2 5 m between the composite profile based on the vcd and the downhole measurements in hole 2d of the ahlat ridge b a correlation was difficult to ascertain from the vertical resolution of the downhole logging data and the extremely detailed core description in mm scale c mixed signals were obtained because of prevailing thin layers and intercalations of different lithotypes and d cluster analysis was difficult to perform because the contrast within the input data is too low possibly background sedimentation to distinguish between glacial and interglacial deposits tephra units are characterized by contrasting properties and differ mainly in their magnetic susceptibility spectral gamma ray components uranium thorium and potassium and xrf intensities of calcium and zirconium tephra units have been linked to the dominant volcanic composition of the deposited tephra layers and partly to the volcanic sources depth trends are derived with prevailing basaltic deposits in the bottom part 128 m 210 m below lake floor and are gradually outweighed by the highly differentiated dacitic and rhyolitic trachytic products towards the top of the record

impact of volcanism on the evolution of lake van ii temporal evolution of explosive volcanism of nemrut volcano eastern anatolia during the past ca 0 4ma thirty two new single crystal ages document 400 000 years of widespread explosive volcanism of historically active nemrut volcano towering over huge alkaline lake van eastern anatolia the dated deposits were selected to monitor the volcanic and compositional evolution of nemrut volcano through time and thus to provide a rigorous temporal framework for the tephra record of the paleovan drilling project tephra samples were taken from large volume deposits or those that occur in medial to distal localities well exposed stratigraphic sections or from the initial phase of an eruptive sequence mainly fallout deposits were chosen because most ignimbrites show more complex and corroded feldspar populations owing to compositional zoning and magma mixing moreover fallout deposits held the promise to be more clearly identifiable with and correlatable to 300 tephra layers in the paleovan drill cores even though commonly in amounts marginal or insufficient in thickness to allow well supported single crystal dating the crystals dated are dominantly anorthoclase the main phenoctyst phase in the trachytic to rhyolitic slightly to strongly peralkaline nemrut magmas ages obtained so far range from ca 400 ka to ca 30 ka for nemrut volcano the causes of significant changes in the frequency volume and composition of tephra layers per unit time are discussed in terms of external erosion climate changes geodynamic factors and internal forcing changes in magma supply and composition and incubation periods preceding large volume rhyolitic eruptions for example the low frequency of tephra layers deposited prior to ca 200 ka may be due to low explosive activity severe erosion between mis 9 and mis 11 or both nevertheless the overall frequency of explosive eruptions appears to have increased during the past ca 200 ka we also recognize a slight peak in explosive eruptions during warm periods e g mis 5 and mis 7 and speculate on lithospheric unloading triggering increased partial melting or magma reservoir unloading following massive glacier melting the ages of 5 dated ignimbrites span ca 250 000 years suggesting that nemrut volcano went through a polycyclic evolution with multiple caldera collapses and major pyroclastic flow eruptions the oldest dated so far as 265 ka the widely held view of the impressive nemrut caldera now dated to have formed at ca 30 ka as the main paroxysmal event during the evolution of the volcano is no longer tenable distinct and coherent compositional characteristics especially in trace element concentrations characterize several groups of trachytic tephras we speculate that the growth of nemrut volcano caused the isolation of the lake van basin on account of their mineralogical anorthoclase hedenbergite fayalite aenigmatite and alkalic chemical compositions and large volume dated nemrut fallout tephras are likely to represent excellent markers in lakes and other sites of paleoclimatological or archeological interest in neighboring countries to the northeast of lake van as far as the caspian sea in what may be called the east anatolian tephra province

climato hydrological fluctuations printed in long lacustrine records in lake hovsgol mongolia abstract a provisional age model is proposed for hdp 04 sedimentary records from lake hovsgol on the mongolian plateau of a middle latitude zone during the brunhes epoch the model is established on the basis of two procedures first age model linear age model with some dates c 14 238 u 234 u 230 th and paleomagnetic events and a second age model with auto orbital tuning for the first age model the age model suggests that the mis 1 to mis 7 interval is included in the upper part and the mis 11 to mis 19 is included in the lower part in addition to the missing part of about 100 ky the glacial interglacial cycle is most clearly presented by aridity water level change three milankovitch parameters precession obliquity and eccentricity are detected in most datasets grain size is occasionally large in glacial intervals and small in interglacial ones in the upper part above the hiatus possibly related to material mobility with water level change change in erosion area and wind availability a deep depression cold stage comparable to glacial periods corresponded to an insolation minimum is detected at about the mis 5d in records indicating that this region is highly sensitive to solar insolation another depression found during the mis 11 interval also corresponded to a small insolation minimum showing that the interval was not a simple prolonged interglacial period

isotopic data upb rbsr pbpb and smnd on mafic granulites from finnish lapland abstract a combined approach using several methods pb pb u pb rb sr sm nd on granulitic rocks selected from classic areas in northern finland is presented the results show that the emplacement of igneous rocks and the granulitic metamorphism occurred nearly coevally 1 9 2 0 ga this result which is supported by field observations means that these rocks are not ideal for comparing the response of the various parent daughter pairs to the high grade metamorphism or for checking the special geochronological possibilities of each method nevertheless because of the coherence of results from rocks of different origins a discussion is possible the bulk of the mafic granulite was certainly derived from upper mantle sources or short lived crustal mafic materials granulites of the granulitic belt and anorthosites are thought to have originated from two distinct mantle sources reflecting mantle heterogeneities at that time

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

sources of continental magmatism adjacent to the late archean kolar suture zone south india distinct isotopic and elemental signatures of two late archean magmatic series conspicuous nd sr and pb isotopic differences exist between the archean gneiss terranes adjoining the suture at the kolar schist belt south india these gneisses which are the deformed equivalents of plutonic and volcanic rocks have known or inferred igneous ages of 2630 to 2530 ma initial isotopic ratios of nd sr and pb suggest that metaplutonic gneisses west of the kolar schist belt were emplaced into and variably contaminated by an evolved continental crust that formed prior to 3200 ma felsic metaigneous gneisses that occur as slivers on the western margin of the schist belt have an isotopic character similar to that of the metaplutonic rocks on the same side of the kolar schist belt on the east side of the kolar schist belt the isotopic evidence suggests that the 2530 ma granitic gneisses were not derived from or contaminated by an older continental crust their source probably evolved with a nd isotopic composition similar to that of typical archean mantle but became light rare earth element enriched after 2900 to 2700 ma the inferred tectonic setting for the west side of the kolar schist belt is an andean continental magmatic arc for the east side of the kolar schist belt a possible phanerozoic analog is an evolved island arc such as japan

smnd pbpb and rbsr geochronology and petrogenesis of the mafic dyke swarm of mahbubnagar south india implications for paleoproterozoic crustal evolution of the eastern dharwar craton abstract the sm nd rb sr and pb pb isotopic systematics of whole rock and separated mineral fractions from four tholeiitic mafic dykes of the mahbubnagar swarm have been investigated this dyke swarm intrudes the granitic basement of the cuddapah basin in the eastern dharwar craton edc the sm nd data on whole rock samples of four gabbros and one dolerite and 15 mineral fractions yielded a linear array with an isochron age of 2173 64 ma and an initial nd value of 0 4 0 3 the sm nd data of a metapyroxenite and its three mineral fractions plot parallel to this array yielding an isochron age of 2189 123 ma with a negative initial nd value of 1 8 1 4 rb sr and pb pb internal isochron ages of three gabbros and a pb pb internal isochron age of a metapyroxenite dyke range between 2031 and 2284 ma and within the limits of experimental error broadly conform to the sm nd isochron age by contrast rb sr internal isochron ages of three other samples range between 1474 and 1952 ma and one sample yields a pb pb internal isochron age of 3446 ma showing the effects of partial isotopic resetting possibly due to hydrothermal alteration these data suggest that mafic dykes of the mahbubnagar swarm were emplaced at c 2170 ma marking an episode of the crustal extension and fracturing which ultimately resulted in the formation of the cuddapah basin different petrological and geochemical variants of mafic dykes seen in the area most probably represent generation and or crystallization of the progressively evolved batches of magma during a relatively short time interval the initial nd values calculated at 2170 ma range from 0 6 to 2 0 and can be explained as reflecting contamination of depleted mantle derived magma by crustal rocks of edc the initial 87 sr 86 sr ratios 0 7027 0 7064 and model 1 values 8 3 8 5 of apparently undisturbed samples are also consistent with this suggestion

neoarchean microblock amalgamation in southern india evidence from the nallamalai suture zone abstract a collage of crustal blocks ranging in age from mesoarchean to neoarchean accreted to the southern margin of the dharwar craton in peninsular india preserve distinct evolutionary history but share a common metamorphic record during archean proterozoic transition here we investigate the tectonic boundary between two of these microblocks the shevaroy block to the west and the madras block to east termed as the nallamalai suture zone nlsz we present integrated field petrological geochemical and zircon u pb and lu hf data from a suite of meta igneous and metasedimentary units along the nlsz and its flanks zircon grains from the meta monzogranite hornblende biotite gneiss amphibolite granodiorite diorite charnockite bif banded iron formation and bmq from this area show magmatic emplacement ages clustering around 2 50 to 2 56 ga except for the meta monzogranite showing ages up to 3 2 ga correlating with long lived convergent margin magmatism through multiple slab melting episodes all the rocks show tightly constrained early paleoproterozoic ca 2 46 2 48 ga metamorphic ages including the metamorphic zircon in the bifs marking the timing of collision of the two continental blocks with consumption of the intervening oceanic lithosphere the ehf t values of magmatic zircon grains from the different rock types range from 4 1 to 5 7 and together with t dm c hf model ages of 2672 3247 ma a dominantly juvenile crust growth is indicated which initiated around 3 3 ga and continued to 2 7 ga followed by crustal reworking in a continental arc towards the end of neoarchean the geochemical data suggest that tholeiitic to calc alkaline parental melts for the mafic intermediate felsic suite were generated by low degree partial melting of a peridotitic mantle wedge metasomatized by subduction derived fluids and sediments and continuous slab melting ensued by intracrustal fractional crystallization of melts with reworking of older continental crust the bif and bmq samples display positive eu anomalies negative to negligible ce anomalies and superchondritic y ho ratios suggesting their formation in an oceanic realm proximal to an active continental margin setting the magmatic and tectonic attributes are consistent with eastward oceanic subduction and ocean closure along the nlsz which is defined here as the trace of a suture welding the shevaroy and madras blocks we envisage that multiple subduction and amalgamation of several microblocks occurred in the dharwar craton and its southern domains amalgamating several microblocks during the archean paleoproterozoic transition

palaeomagnetic and rock magnetic study of a deeply exposed continental section in the charnockite belt of southern india implications to crustal magnetisation and palaeoproterozoic continental nucleii abstract this study has investigated palaeomagnetism and magnetic properties of a tract of continental basement in south india metamorphosed to granulite facies close to the archaean proterozoic boundary 2600 ma at former depths of 20 35 km the metamorphism is characterised by extensive development of charnockite produced by flushing of co2 rich fluids through older crust rock magnetic studies thermomagnetic high and low temperature susceptibility hysteresis and irm show that very low ti metamorphic magnetite is the ubiquitous ferromagnet in all rock types it has predominantly multidomain characteristics but is of high magnetic stability probably due to exsolution precipitation and microfracture filling producing anisotropic grain shapes magnetic susceptibility shows little increase with temperature falling to zero at 550 c implying that induced magnetisation drops to a weak paramagnetic effect near this isotherm susceptibilities and intensities of magnetisation increase from amphibolite to granulite facies and by an order of magnitude within charnockites in the lower dehydrated crust induced magnetisations are able to explain 50 of observed magnetic anomalies of deep origin intensities of magnetisation and qn values are high especially in charnockite where metasomatism has resulted in new magnetite formation and it is concluded this facies is able to explain observed magnetic anomalies provided that viscous remnant magnetisation is enhanced at depth to contribute the remaining magnetisation the magnitude of anisotropy of magnetic susceptibility ams is also increased by charnockite formation as are degrees of lineation and foliation however directions of ams in these anhydrous rocks are essentially random and reflect the static nature of the charnockite metasomatism no appreciable phanerozoic overprinting is evident in this terrane and the dominant feature of the palaeomagnetic record is a west to north shallow swathe of component directions with a minor antiparallel sequence between means summarised by a1 d i 280 8 a2 d i 319 11 and a3 d i 1 10 this swathe is interpreted as an uplift related cooling acquisition following charnockite formation at 2600 ma and a remanence age of 2600 2400 ma is implied by the absence of most of the swathe in early palaeoproterozoic and younger dyke swarms cutting the region a second group of component directions b mean d i 238 87 is similar to magnetisations found in dykes linked to an age of 2370 ma and interpreted as somewhat younger than the a swathe we argue that the entire magnetic record was acquired before final basement uplift prior to 2000 1800 ma collective late archaean early proterozoic palaeopoles from india define a low to high latitude movement of the shield at 2600 2300 ma which is replicated in contemporaneous results from the other ancient gondwana nucleii of southern africa and australia the cratonic nucleii of these three shields have the oldest laterally extensive supracrustal covers and comprise the core of the protocontinent of ur the 2900 2200 ma palaeopoles are consistent with close proximities and subsequent movements between them were apparently limited because continental proximities but not configurations were similar within the palaeozoic supercontinent of gondwana

signal analysis of cyclicity in maastrichtian pelagic chalks from the danish north sea abstract low field bulk magnetic susceptibility has been determined on maastrichtian chalk samples from a drill core from the dan field in the danish north sea fast fourier transformations fft have been used to detect possible cycles in the magnetic susceptibility data power spectra from the complete section and from sub sections of the magnetic susceptibility reveal two cyclicities of ca 0 4 cycles m and ca 1 7 cycles m which are present on a 90 confidence level signal analysis of natural gamma ray wire line log data supports these findings sedimentation rate estimates place the cycles in the milankovitch frequency band artificial time series are used to study the applicability of the fft to identifying cyclicity in chalks expected geological distortions e g hiati and sedimentation rate variations are introduced into the time series to investigate the response of the frequency spectra different methods of handling missing data intervals are also examined

the annual particle cycle in lake van turkey abstract the varved sediments of lake van provide a high quality continental archive of seasonal to decadal scale climate variability in order to read the natural record modern varve formation was studied on the basis of 1 remotely sensed total suspended matter tsm rs concentrations 2 time series of particle flux and water temperatures and 3 turbidity temperature and oxygen profiles tsm rs validated by contemporaneous water column sampling shows great temporal and lateral variations whitings and turbidity plumes from 2006 to 2009 sequential sediment traps recorded high particle fluxes during spring and fall medium fluxes during summer and almost zero flux during winter the mean total mass flux of 403 mg m 2 day 1 comprised 33 seasonally up to 67 calcium carbonate 7 aquatic organic matter 6 biogenic opal and 54 detrital minerals the caco 3 fluxes are controlled by river discharge precipitation and snowmelt during spring by high productivity during summer and by river discharge precipitation before snowfall starts and mixing during fall in november 2007 an anomalously high caco 3 flux occurred as a result of a warm water surface supersaturated with calcite coinciding with an anomalous runoff event the results demonstrate that the couplets of light and dark laminae in the short sediment cores are true varves representing spring summer fall and winter conditions respectively consequently varve formation can be linked to the seasonal climate pattern providing a calibration that can be used to interpret the partially varved paleo record of lake van and related environmental processes

impact of volcanism on the evolution of lake van i evolution of explosive volcanism of nemrut volcano eastern anatolia during the past 400 000 years the historically active nemrut volcano 2 948 m asl eastern anatolia rising close to the western shore of huge alkaline lake van has been the source of intense plinian eruptions for 530 000 years drilled lake sediments about 40 widespread newly recognized trachytic and less common rhyolitic fallout tephras and ca 12 interbedded ignimbrites sourced in nemrut volcano are documented in stratigraphic traverses throughout an area of 6 000 km2 mostly west of lake van phenocrysts in the moderately peralkaline trachytes and rarer large volume comenditic rhyolites comprise anorthoclase hedenbergite augite fayalite and especially in trachytic units augite minor aenigmatite apatite and quartz and rare chevkinite and zircon dacitic to rhyolitic tephras from nearby calcalkalic suphan volcano 4 058 m asl locally interbedded with nemrut tephras are characterized by disequilibrium phenocryst assemblages biotite augitic clinopyroxene and hypersthene minor olivine common crystal clots and or in some deposits amphibole the magma volume dre of the largest nemrut tephra sheet ap 1 described in detail may exceed 30 km3 extreme facies and systematic compositional changes are documented in the ca 30 ka nemrut formation nf deposits formed from one large and complex eruption thick rhyolitic fallout overlain by ignimbrite welded agglutinate overbank surge deposits and final more mafic fallout deposits common evidence of magma mixing in nemrut ignimbrites reflects eruption from compositionally zoned magma reservoirs several young cekmece formation trachytes overlying ca 30 ka old nf deposits and the late trachytes of the nf deposits show compositional affinities to tephra from suphan volcano possibly due to temporary influx of suphan magmas into the nemrut system following the evacuation of 10 km3 magma dre during the caldera forming nf eruption axes of large fallout fans are dominantly sw ne but w e in the younger sheets resembling the direction of the present dominant wind field growth of nemrut volcanic edifice and its peripheral domes since before 0 5 ma in the hinge area between the van and mus tectonic basins is likely to have been the major factor in isolating lake van basin thus initiating the origin and subsequent alkaline evolution of the lake this alkalinity was later significantly controlled by climate forcing internal forcing mechanisms volcanic and geodynamic may also have contributed to major lake level changes in addition to climate forcing

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

sm nd age of the garhwal bhowali volcanics western himalayas vestiges of the late archaean rampur flood basalt province of the northern indian craton abstract whole rock sm nd isotope dating of the garhwal and bhowali mafic volcanics of the kumaun lesser himalayan sector yield an age of 2 51 0 08 ga and an initial nd 5 1 0 5 this age and initial nd are the same as that of the rampur mandi volcanics which occur to the west in the lesser himalayas in addition to confirming the widespread presence of the late archaean crustal elements in the himalayas these data constrain the age of the oldest rifting event and deposition of supracrustal sediments in the himalayas and set at rest the long standing controversy about the age and inter relationship of these mafic volcanics despite their present day disparate occurrence as a result of the post eruption deformation the area covered by these mafic volcanics is large enough to classify them as flood basalts the rampur flood basalt rfb province rift related volcanism of the same age is known from the contiguous aravalli region of the nw indian shield the orientation of the rifts in the two regions suggests the possibility of a mantle plume setting for the rfb

oldest rocks from peninsular india evidence for hadean to neoarchean crustal evolution abstract the evolution of continental crust during hadean and archean and related geodynamic processes provides important clues to understand the early earth history here we report evidence for hadean and eoarchean crust from the fringe of the coorg block one of the oldest crustal blocks in peninsular india we present geological petrological and geochemical data together with zircon u pb ages and lu hf isotopes from a suite of metaigneous granitoids diorite charnockite metavolcanics and metasedimentary quartz mica schist calcareous schist ferruginous quartzite and bif rocks petrological and geochemical studies indicate that the igneous suite formed from subduction related arc magmatism and that the sedimentary suite represents an imbricated accretionary package of continental shelf sequence and pelagic components mineral thermometry suggests metamorphism under temperatures of 710 730 c and pressures up to 8 kbar magmatic zircons in the metaigneous suite show oscillatory zoning and high th u contents up to 3 72 and record multiple pulses of magmatism at ca 3 5 3 2 2 7 and 2 5 2 4 ga the metasedimentary rocks accreted along the margins of the coorg block show multiple zircon population with mean 207pb 206pb ages at 3 4 3 2 3 1 2 9 2 7 2 6 2 5 2 2 2 0 and 1 3 ga and overprinted by younger thermal event at ca 0 8 0 7 ga zircons in the 3 5 ga dioritic gneiss show positive ehf t values ranging from 0 0 to 4 2 and hf crustal model ages tdmc of 3517 to 3658 ma suggesting that the parent magma was derived from eoarchean juvenile sources the zircons in the 3 2 ga charnockite display ehf t values in the range of 3 0 to 2 9 and hf crustal model ages tdmc of 3345 to 3699 ma the neoarchean metagranites diorites and felsic tuff show both positive and negative ehf t values and a range of tdmc values from 2904 to 3609 ma suggesting magma derivation from meso to eoarchean juvenile and reworked components the tdmc values of the dominant zircon population in the metasedimentary suite range from 3126 to 3786 ma with the oldest value 4031 ma recorded by zircon grain in a ferruginous quartzite the ehf t values of detrital zircons also show both positive and negative values with a dominant crustal source our zircon u pb and lu hf data suggest vestiges of neohadean primordial continental crust in peninsular india with episodic crustal growth during eoarchean mesoarchean and neoarchean building the continental nuclei the results contribute to the understanding of crustal evolution in the early history of the earth

a palaeomagnetic study of charnockites from madras block southern granulite terrain india abstract the south indian craton is composed of low grade and high grade metamorphic rocks across different tectonic blocks between the moyar bhavani and palghat cauvery shear zones and an elongated belt of eastern margin of the peninsular shield the madras block north of the moyar bhavani shear zone which evolved throughout the precambrian period mainly consists of high grade metamorphic rocks in order to constrain the evolution of the charnockitic region of the pallavaram area in the madras block we have undertaken palaeomagnetic investigation at 12 sites chrm directions in 61 oriented block samples were investigated by alternating field af and thermal demagnetization titanomagnetite in cation deficient cd and multi domain md states is the remanence carrier the samples exhibit a chrm with reverse magnetization of d m 148 1 i m 48 6 k 22 2 95 9 0 and a palaeomagnetic pole at 37 5 n 295 6 e dp dm 7 8 11 8 this pole plots at a late archaean location on the indian apparent polar wander path apwp suggesting an age of magnetization in the pallavaram charnockites as 2600 ma the nearby st thomas mount charnockites indicate a period of emplacement at 1650 ma mesoproterozoic thus the results of madras block granulites also reveal crustal evolution similar to those in the eastern ghats belt with identical palaeopoles from both the areas

constraints on the application of carbon isotope thermometry in high to ultrahigh temperature metamorphic terranes nine marble horizons from the granulite facies terrane of southern india were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite the marbles in trivandrum block show coupled lowering of 13c and 18o values in calcite and heterogeneous single crystal 13c values 1 to 10 for graphite indicating varying carbon isotope fractionation between calcite and graphite despite the granulite facies regional metamorphic conditions the stable isotope patterns suggest alteration of 13c and 18o values in marbles by infiltration of low 13c 18o bearing fluids the extent of alteration being a direct function of the fluid rock ratio the carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated recrystallized in the presence of an externally derived co2 rich fluid and that the infiltration had occurred under high temperature and low fo2 conditions during metamorphism the onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining fluid calcite carbon reservoir following a rayleigh type distillation process within fluid rich pockets pathways in marbles resulting in the observed zonation the results suggest that calcite graphite thermometry cannot be applied in marbles that are affected by external carbonic fluid infiltration however marble horizons in the madurai block where the effect of fluid infiltration is not detected record clear imprints of ultrahigh temperature metamorphism 800 1000 c with fractionations reaching 1000 c and would be consistent with uht metamorphism

orbital forcing of continental climate during the pleistocene a complete astronomically tuned climatic record from lake baikal se siberia abstract a new composite bdp 96 biogenic silica record over the entire pleistocene was generated by splicing bdp 96 1 and bdp 96 2 drill cores from lake baikal crosschecked against a similar record from a nearby bdp 98 drill core a new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of september perihelia this target is derived from analysis of regional climate proxy responses during the holocene the last interglacial and around paleomagnetic reversals by resolving virtually every precessional cycle during the pleistocene the new age model represents a major improvement compared with previously reported lake baikal timescales the astronomically tuned ages of the pleistocene paleomagnetic reversals are consistent with published dates the minimal tuning approach we used precession only has also aligned high signal power in a narrow obliquity band confirming the strong presence of orbital forcing there are also strong ca 100 ka scale cycles but these are not aligned with the orbital eccentricity despite the location of lake baikal in a continental interior that is highly sensitive to insolation forcing the tuned biogenic silica record reveals a consistent phase difference of 32 ca 4 ka relative to insolation in the obliquity band an inherent lag embedded in a continental proxy record not driven by global ice volume is an intriguing finding another new observation is that long term changes in sedimentation rates in lake baikal appear to be related to the amplitude of orbital forcing both amplitudes and sedimentation rates undergo significant changes during mis 24 mis 19 interval corresponding to the middle pleistocene transition with potential for linking continental and marine climato stratigraphies the new baikal record serves a new benchmark correlation target in continental eurasia as an alternative to june 65 n insolation and odp correlated timescales

teleseismic tomographic evidence for contrasting crust and upper mantles in south indian archaean terrains abstract we compare the velocity structure of the crust and upper mantle of the archaen granulite terrain of southernmost india with that of the archaean granite greenstone dharwar craton terrain just to the north through p wave teleseismic travel time measurements the teleseismic rays recorded by a coarse network of 11 portable seismic stations show an anomalous pattern of late arrivals delays over the granulite terrain in contrast to fast arrivals on the dharwar craton such a pattern of time residuals amongst these archaean terrains which have remained inert in the last 2 ga may indicate the presence of compositional heterogeneity within the crust and upper mantle beneath them three dimensional p wave velocity tomography using teleseismic rays from a variety of azimuths indicates the existence of contrasting p wave crust and upper mantle velocity patterns 1 in the crust 0 40 km the western dharwar craton and the granulite terrain have lower velocity up to 3 compared with the higher velocity 1 3 observed over the eastern dharwar craton and 2 in the upper mantle 40 177 km there is 2 3 lower velocity beneath the granulite terrain compared with the western dharwar craton the existence of such lateral velocity variation in the crust and upper mantle and its preservation since late archaean times points to the presence of possibly thick and chemically distinct lithospheres that did not participate in mantle convection

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

astronomical forcing and sedimentary noise modeling of lake level changes in the paleogene dongpu depression of north china abstract challenges in interpreting continental sequence stratigraphy and typically uncertain geochronology hinder the understanding of paleolake evolution and hydrocarbon exploration in terrestrial basins the dongpu depression in north china is a lacustrine basin with abundant hydrocarbon resources an accurate chronology for the paleogene stratigraphy in the dongpu depression is lacking and the mechanism of lake level variation remains unclear in this study we utilize high resolution gamma ray logs to conduct a cyclostratigraphic analysis of the shahejie formation which is a paleogene succession in the dongpu depression characterized by sandstones and dark mudstones interbedded with thin salt rocks time series analysis reveals evidence for 405 kyr eccentricity cycles in the gamma ray series which is supported by statistical modeling of optimal sedimentation rates tuning of the gamma ray data to this 405 kyr eccentricity cyclicity enables a 14 7 myr long astronomical time scale to be constructed this astrochronology is anchored to the astronomical age of the dongying formation shahejie formation boundary 28 86 ma in the bohai bay basin thus providing an absolute timescale for the studied interval that extends from 28 86 ma to 43 59 ma using this anchored astrochronology we show that a recently established sedimentary noise model for inferring sea level change in marginal marine settings can be used to similarly infer lake level fluctuations in terrestrial basins in particular sedimentary noise modeling of the tuned gamma ray series reveals high resolution changes in sedimentary noise that are indicative of lake level variations linked to million year scale i e 4 8 myr 2 4 myr and 1 2 myr astronomical forcing these inferred changes in lake level are supported by previously published sequence stratigraphic interpretations moreover an evolutionary correlation coefficient ecoco analysis of the gamma ray series also indicates recurrent distortions in sedimentation that may be linked to lake level changes this study provides new methods for the assessment of paleolake level variations as well as insights into the connection between astronomical forcing and lake evolution across long timescales in terrestrial basins

metamorphism and isotopic evolution of granulites of southern india reference to neoproterozoic crustal evolution abstract granulites are important component of high grade metamorphic rocks reflecting intense conditions observed for crustal rocks in terms of temperature and pressure this review paper demonstrates how these high grade granulites are critical to understanding the evolution of the lower continental crust with special reference to southern india geothermobarometric traverse across different granulite blocks in southern india shows wide ranging p t conditions of metamorphism 700 1000 c and 5 10 kbar the sapphirine orthopyroxene sillimanite and spinel bearing quartz deficient granulites recognised from parts of southern granulite terrain ganguvarpatti kiranur and palani hill ranges etc show oriented sillimanite aggregates pseudomorph after course twinned kyanite staurolite kyanite assemblages and corroded blebs of gedrite within orthopyroxene suggesting a prograde stage of a clockwise p t evolution evidence of itd history comes from the textures in which an early mg rich garnet xmg 52 60 with orthopyroxene up to 10 al2o3 involving sillimanite breakdown forming variety of symplectites having combinations of orthopyroxene sapphirine cordierite and spinel these spectacular reaction textures and mineralogic sensors from the high grade rocks establish a prograde clockwise p t t path with notable decompressive history itd in the southern granulite terrain the inferred p t t paths have been further integrated with the recent geochronological and isotopic data to constrain the timing and duration of metamorphism emplacement of the magmatic protolith for characterising the evolution of the granulites and their bearing on the geodynamic implications based on the emerging evidence for neoproterozoic tectonothermal imprints in the southern granulite terrain history of the assembly of dispersed fragments is also addressed within the east gondwana framework

alkali granites with pan african affinities from kerala s india in the kerala region of the south indian shield alkali granite plutons ranging in age from 550 to 740 ma intrude precambrian charnockites and migmatites all of them are spatially related to regional fault lineaments their geochemistry is similar to pan african post kinematic plutons from the afro arabian shield they are of granitic to adamellitic composition with high sio 2 k 2 o up to 12 and na 2 o and low cao feo and mgo their major element composition together with a low 87 sr 86 sr i 0 703 from one pluton denote a type affinities however local charnockites have such low rb and radiogenic 87 sr that the granites could have formed by crustal melting their overall trace element characteristics are typical of alkaline granites in general but the details show that most resemble more recent volcanic arc granites and one pluton is typical of a within plate setting the presence of co 2 rich fluid inclusions supports the notion that the enrichment of rare earth an

ductile shearing in attur shear zone and its relation with moyar shear zone south india abstract in the eastern part of southern peninsular india the charnockitic hills of the madras block are cut across by the e w trending attur shear zone asz which is characterised by a thick 1 to 1 5 km phyllonite zone showing intense mylonitisation due to ductile shearing steeply plunging 70 80 stretching lineation on steeply dipping mylonitic foliation within this zone indicates a relative vertical upliftment of the adjacent blocks a dextral shearing event from west to east is envisaged from the kinematic analysis of shear sense indicators such as s c fabric asymmetric folds asymmetric augens and asymmetric porphyroclasts simultaneous development of these features related to vertical and horizontal movements may be explained by the mechanism of transpressional deformation the attur shear zone may be correlated with the moyar shear zone based on distinct lithological and structural similarities

the pan african event in east antarctica a view from sri lanka and the mozambique belt abstract late pan african 580 550 ma high grade deformation of the sri lankan basement gave rise to a fold and thrust belt the resulting axial planes to upright folds and earlier stretching lineations define a large scale syntaxial bend this syntaxis is attributed to e w shortening and simultaneous sinistral strike slip along a n s trending transcurrent zone located west of sri lanka prior to gondwana break up the resulting geometry is consistent with a corner effect brun and burg 1982 produced by westward indenting of the basement underneath eastern sri lanka during collision in gondwana reconstructions the sinistral strike slip zone fits into the late kinematics of the mozambique belt shackleton 1986 these new structural data constrain the position of sri lanka in gondwana and favour reconstructions in which sri lanka is located near the lutzow holm bay in east antarctica a review of data from adjacent gondwana fragments suggests that the tectonometamorphic evolution of the sri lankan basement is closely related to the interplay between two orogenic belts the mozambique belt and the lutzow rayner belt it is argued that a late event of n s shortening gondwana coordinates in the lutzow rayner belt can be attributed to a pan african tectonometamorphic event in this interpretation the lutzow rayner belt developed in part simultaneously with the mozambique belt reworking an older granulitic basement in the rayner complex

carbonic fluid inclusions in south indian granulites evidence for entrapment during charnockite formation field evidence and fluid inclusion studies on south indian incipient charnockites suggest that charnockite formation occurred during a decompressional brittle regime following the peak of metamorphism and regional deformation the most abundant type of inclusions in quartz and garnet grains in these charnockites contain high density carbonic fluids although lower density fluids occur in younger arrays of inclusions discrete fluid inclusion generations optically are observed to decrepitate over well defined temperature intervals and quantitative measurements of co2 abundance released from these inclusions by stepped thermal decrepitation show up to a four fold increase by volume in the incipient charnockites relative to the adjacent gneisses from which they are derived studies based on optical thermometry visual decrepitation and stepped heating inclusion release together indicate that entrapment of carbonic fluids coincided with charnockite formation we confirm that an influx of carbon dioxide rich fluids is associated with the amphibolite granulite transition as recorded by the incipient charnockites the remnants of which are commonly preserved as the earliest generation of high density fluid inclusions

archean granulite gneisses from eastern hebei province china rare earth geochemistry and tectonic implications the granulite gneisses and their retrograded products of the qianxi group from eastern hebei province china have been investigated for their isotope and trace element geochemistry a consistent age of about 2 5 ae has been obtained by the rb sr and sm nd whole rock isochron methods in agreement with the zircon u pb data pidgeon 1980 d y liu unpubl geochemical arguments from initial isotopic ratios isr and ind and elemental distribution patterns have led us to conclude that this age of about 2 5 ae represents the time of granulite facies metamorphism which must have followed closely the primary emplacement of their protoliths previous claims for early archean ages 3 5 ae of these granulites are not substantiated the mineral isotope systematics register an important thermal event at about 1 7 ae roughly corresponding to the time of the widespread luliang orogeny ma and wu 1981 or chungtiao movement huang 1978

multiple tectonothermal events in the granulite blocks of southern india revealed from epma dating implications on the history of supercontinents abstract we report age data on zircon monazite uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern india using an electron microprobe technique the rocks analysed in this study cover all of the major lithounits in these terrains and include garnet bearing and garnet free charnockites garnet biotite gneisses khondalites calc silicate rocks and a suite of orthogneisses biotite gneiss biotite hornblende gneiss two pink metagranites representing the magmatic phase were also analysed zircons from the madras block yield well defined isochrons at 2 5 2 6 ga core to rim analyses of single zircon grains show age zoning with 2 6 2 9 ga igneous cores mantled by 2 4 2 5 ga rims detrital zircons show age up to ca 3 2 ga monazites in this block have cores and rims with 2 5 2 3 ga a suite of 19 samples from the madurai block brings out the multiple tectonothermal events in this terrain zircons from an orthogneiss yield well defined isochrons at 1 7 0 1 ga 0 82 0 05 ga and 0 58 0 04 ga from core inner rim and rim portions respectively zircon grains in other rocks preserve either core or secondary growth ages at 0 8 1 0 ga zircons in a pink metagranite from this block show sharply defined isochrons of 0 68 0 03 ga for the core and 0 57 0 01 ga for the secondary portion a late pan african overprint is observed throughout this block with zircon rims monazite uraninite and huttonite yielding age values in the range of 0 45 0 60 ga zircons from both the trivandrum and nagercoil blocks show a major tectonothermal event at 0 55 ga with faint indications of previous tectonothermal events during 0 8 1 0 and 1 7 2 0 ga monazite data from both the trivandrum and nagercoil blocks are essentially similar to those from the madurai block except for presence of relic monazite in the former our study confirms the notion that the palghat cauvery shear zone marks the major terrain boundary between an archean craton in the north and proterozoic terrains in the south it also strengthens the view of paleoproterozoic accretion and pan african reworking of blocks south of this shear zone the ages of production accretion and reworking in the terrains of southern india yield important information for the histories of columbia 1 8 1 5 ga rodinia 1 1 1 0 ga and gondwana 0 6 0 5 ga supercontinents the southern indian terrains formed part of a worldwide network of orogenic belts that is centered around 1 8 ga and outlines the configuration of columbia accretion of terrains in the madurai block to archean rocks north of the palghat cauvery shear zone at this time is consistent with the ages suggested to be the oldest metamorphic event in the eastern ghats orogen of eastern india and the rayner belt of coastal east antarctica our data confirm earlier evidence that all of southernmost india underwent resetting of isotopic systems during the final accretion of gondwana at the time of the pan african orogeny 0 5 ga the possibility that the trivandrum and nagercoil terrains accreted to the madurai block after 0 7 ga suggests that this pan african zone may also have involved accretion and closure of ocean basins if that happened then this zone may be the long sought suture between east and west gondwana

first report of pan african sm nd and rb sr mineral isochron ages from regional charnockites of southern india mineral and whole rock isotope data for a massive charnockite from kottaram in the nagercoil block at the southern tip of peninsular india yield sm nd and rb sr ages of 517 26 ma and 484 15 ma respectively the nd model age calculated for the charnockite is c 2100 ma our study reports the first pan african mineral isochron ages from regional charnockites of peninsular india which are in good agreement with the recently obtained ages of incipient charnockites in the adjacent blocks as well as alkaline plutons within the same block our results indicate that the pan african tectonothermal event in the granulite blocks south of the palghat cauvery shear zone was regional with terrain wide rejuvenation these results correlate with similar pan african tectono thermal events reported from sri lanka and east antarctica and have an important bearing on gondwana reconstructions

age of younger tonalitic magmatism and granulitic metamorphism in the south indian transition zone krishnagiri area comparison with older peninsular gneisses from the gorur hassan area abstract a major episode of continental crust formation associated with granulite facies metamorphism occurred at 2 55 2 51 ga and was related to accretional processes of juvenile crust dating of tonalitic trondhjemitic granitic gneisses and charnockites from the krishnagiri area of south india indicates that magmatic protoliths are 2550 2530 5 ma as shown by both u pb and 207pb 206pb single zircon methods monazite ages indicate high temperatures of cooling corresponding to conditions close to granulite facies metamorphism at 2510 10 ma these data provide precise time constraints and sr nd isotopes confirm the existence of late tonalitic granodioritic juvenile gneisses at 2550 ma pb single zircon ages from the older peninsular gneisses gorur hassan area are in agreement with some previous sr ages and range between 3200 20 and 3328 10 ma these gneisses were derived from a 3 3 3 5 ga mantle source as indicated from nd isotopes they did not participate significantly in the genesis of the 2 55 ga juvenile magmas all these data together with previous work suggest that the 2 51 ga granulite facies metamorphism occurred near the contact of the ancient peninsular gneisses and the 2 55 2 52 ga juvenile tonalitic trondhjemitic terranes during synaccretional processes subduction mantle plume rb sr biotite ages between 2060 and 2340 ma indicate late cooling probably related to the dextral major east west shearing which displaced the 2 5 ga juvenile terranes toward the west

climatically induced lake level changes at lake van turkey during the pleistocene holocene transition sediment core k10 from lake van eastern turkey provides a continuous varve record back to 14 570 calendar years b p before present 1950 the longest unbroken and non floating lake varve sequence yet described the underlying sediment is unvarved and hard changes in the aragonite calcite ratio the presence of protodolomite and magnesite in certain profile sections the annual record of the sedimentation rate the water content of the sediment the concentrations of organic carbon and opal and the texture of the sediments from this core provide a record of the lake level history the new chronology enabled us to redate the old pollen profile van zeist and woldring 1978a b and to establish an accurate timescale for the reconstructed lake level change carbon 14 dates show that the highest lake terrace corresponds to high lake level at around 19 000 years b p during the last glacial 70 m above its present level before 15 000 years b p the lake must have been completely dry marking a reduction of lake level by 500 m in maximum 4000 years beginning at 14 600 years b p and ending at 12 040 years b p the lake level recovered by 250 m to fall again during the next 1400 years by 10 600 years b p the lake began to rise and reached following another regression between 9000 and 8100 years b p the holocene highstand by about 7500 years b p dropping to today s level at about 3000 years b p

pan african charnockite formation in kerala south india sm nd mineral ages of gneisses and associated granulites from the ponmudi incipient charnockite locality south india indicate that granulite metamorphism occurred at or shortly after 558 ma proterozoic ages recorded by garnet separates reflect a detrital age or an earlier metamorphic event preserved by inclusions within garnet the age of post metamorphic uplift 440 460 ma is constrained by sr isotope equilibration between biotite and plagioclase since charnockite formation and subsequent uplift north of the palghat cauvery shear zone had terminated by earliest proterozoic time these results confirm two distinct periods of granulite formation in south india and suggest that the palghat cauvery shear zone represents the boundary between two blocks of strongly contrasting geological histories both incipient charnockite formation and subsequent uplift at ponmudi may be correlated with the tectonothermal evolution of the highlands group in sri lanka the similarity between nd and sr model ages for charnockites and gneisses from ponmudi indicates that no significant rb sr fractionation has occurred during the crustal history of these incipient charnockites pb isotopic ratios suggest that th u ratios were fractionated during charnockite formation at about 500 ma in contrast to charnockites found north of the palghat cauvery shear zone fractionation of u pb during the archaean did not occur in the ponmudi granulites

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

plate tectonics 2 5 billion years ago evidence at kolar south india the archean kolar schist belt south india is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accrted amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint mantle sources the amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago ma along a zone marked by the kolar schist belt this history of accretion of discrete crustal terranes resembles those of phanerozoic convergent margins and thus suggests that plate tectonics operated on earth by 2500 ma

metamorphic fluids in the deep crust most of the inferences about fluid action in the deep crust are drawn from field petrographic and geochemical studies in the granulite facies terrains deductions on the nature of fluids are made from major and minor element distributions and isotopic patterns in metamorphic rocks calculations of fluid mineral equilibria based on observed assemblages fluid inclusions and field evidence of fluid pathways discussion of these features has focused attention on several major problems concerning the timing flow mechanisms and origin of the fluids a key issue concerns episodicity versus secular activity of fluids there are strong arguments that most fluid action in the deep crust is linked to thermal deformational events including magmatism and regional meta morphism discrete radiometric ages of high grade terrains often define relatively short periods of crystallization or recrystallization the late archean granulite facies metamorphism of southern india is an example where u pb systems of zircons buhl et al 1983 whole rock u pb data peucat et al 1 987 and sm nd systems of whole rocks and minerals bernard griffiths et al 1 987 all show a major high temperature recrys tallization event inferred by several workers to have involved pervasive fluid action centered closely around 2 5 ga another geochemical indi cation of episodic fluids comes from stable isotope studies of progressive metamorphic sequences as in the damara orogen namibia where whole rock b 180 increases slightly at isograds representing arrested dehydration events but is monotonous between isograds hoernes hoffer 1 985

smnd isotopic systematics of enderby land granulites and evidence for the redistribution of sm and nd during metamorphism measurements of143nd 144nd and147sm 144nd are reported for whole rocks and mineral separates from granulites of the napier complex at fyfe hills charnockites leuconorites and gabbros yield a whole rock smnd isochron age of3060 160m y and an initial143nd 144nd ratio of0 50776 10 nd 3060m y 2 0 1 8 the negative nd value and the presence of geologically induced dispersion in the data suggest that the isochron age does not represent the time of primary crystallization of the complex but instead indicates a time of later redistribution of sm and nd and partial re equilibration of143nd 144nd ratios this probably occurred during the upper granulite facies metamorphism which has also been dated at 3100m y by rbsr and upb zircon studies 1 coexisting clinopyroxene apatite and total rock fractions in two adjacent samples define an approximately linear array corresponding to an age of 2300 300 m y this array indicates that redistribution of sm and nd and re equilibration of143nd 144nd ratios occurred on an intermineral scale during the upper amphibolite to lower granulite facies metamorphism at 2450m y due to the resetting of the smnd system on both whole rock and mineral scales the primary crystallization age of the igneous protolith is not well constrained by the present data although it is clearly3100m y if it is assumed that the complex was derived initially from a depleted mantle reservoir nd t 2 evolution of the negative nd value of 2 0 with the observed sm nd ratios requires a prehistory of 380m y this implies a primary age of 3480m y however substantially older primary ages can be inferred if the source reservoirs had nd t 2 and or substantial reductions in the sm nd ratio occurred in whole rocks during the granulite facies metamorphism at 3100 m y such an inferred reduction in the sm nd ratio may have been the result of preferential loss of sm relative to nd or introduction of a low sm nd fluid with nd 0 during granulite facies metamorphism

stochastic resonance in the north atlantic large abrupt changes between warm and cold modes of north atlantic climate exhibit spectral power at 1500 years yet some climatic changes were linked to outburst floods and other events that are unlikely to have been truly periodic we hypothesize that a weak periodic forcing has combined with noise from ice sheet related events to cause the observed mode switches this stochastic resonance hypothesis predicts a recurrence pattern between warmings that is distinct from the predictions of simple periodic and stochastic models and at least some other models the ice isotopic data from central greenland ice cores are consistent with the stochastic resonance hypothesis but not with other models we have tested we thus support arguments for the existence of a periodicity of 1500 years in the north atlantic climate system and for the importance of ice sheet events in forcing north atlantic changes

major and trace element geochemistry and crustal evolution of archaean granodioritic rocks from eastern finland in the eastern part of central finland vast areas of granodioritic gneisses surround the ca 2 65 ga greenstone belts these granodioritic gneisses can be divided into two chronological and lithological units 1 grey gneisses 2 86 ga old with a typical archaean ttg tonalite trondhjemite granodiorite composition 2 augen gneisses 2 51 ga old with a granodioritic to granitic composition the sr and nd isotopic data preclude derivation of the grey gneisses from very much older continental material the highly fractionated ree distribution patterns la yb n 37 103 with few or no eu anomalies militate against a direct mantle origin the data suggest that the grey gneisses have most likely been derived by partial melting of short lived basaltic crustal material garnet bearing amphibolite it is estimated that the basaltic protoliths were separated from a mantle source no more than 150 ma before the melting such an early basaltic crust might have been completely destroyed or might have left some remnants which are now represented by mafic inclusions in the grey gneisses the augen gneisses have a relatively high isr value 0 705 which suggests an origin by recycling of pre existing crustal material grey gneisses their ree patterns are less fractionated than those of the grey gneisses and sometimes have negative eu anomalies using the sr isotopic and trace element data a model calculation suggests that the augen gneisses could have been derived by partial melting 50 of mixed protoliths with ttg greenstone belt volcanics in a proportion of 70 30 by volume followed by fractional crystallisation

evolution of the continental crust in the proterozoic eastern ghats belt india and new constraints for rodinia reconstruction implications from sm nd rb sr and pb pb isotopes abstract for this study nd sr and pb isotope compositions were analyzed for ortho and paragneisses from the eastern ghats belt of india in order to determine its crust formation and crustal evolution this belt represents a proterozoic orogen that extends along the east coast of peninsular india and forms part of the mobile belts in east gondwana and rodinia the eastern ghats belt was affected by mesoproterozoic granulite facies metamorphism in the western segment western charnockite zone and a grenvillian regional scale high grade event in the central and eastern segments western khondalite zone charnockite migmatite zone and eastern khondalite zone as well as a local pan african overprint the results of the isotope studies are used for the large scale reconstruction of the indo antarctic part of the rodinia supercontinent based on nd model ages and pb isotope ratios from leached feldspars four crustal domains can be distinguished in the eastern ghats belt these domains can in part be correlated with the lithological division of the belt 1 the western charnockite zone south of the godavari graben is characterized by nd model ages between 2 3 and 2 5 ga for orthogneisses and 2 6 and 2 8 ga for metasediments domain 1 the pb isotopes are primitive indicating reworking of dominantly archean and mixing with minor proterozoic material 2 north of godavari graben nd model ages for orthogneisses are significantly higher with values ranging from 3 2 to 3 9 ga the pb isotopes are strongly retarded 3 the north eastern parts of the charnockite migmatite zone and western khondalite zone form a distinct and almost homogeneous crustal domain domain 3 with nd model ages between 1 8 and 2 2 ga 4 between the isotopically homogeneous terranes stretches a broad transition zone domain 2 enclosing parts of the western khondalite zone charnockite migmatite zone and eastern khondalite zone the nd model ages for metasediments 2 1 2 5 ga are younger than paragneiss ages of the adjoining western charnockite zone the nd model ages for orthogneisses 1 8 3 2 ga display a large spread which is consistent with the pb isotope signatures that indicate mixing of archean with proterozoic material the border zone between domain 3 and the archean eastern indian craton forms a second transition zone domain 4 characterized by metasediments with nd model ages between 2 2 and 2 8 ga and orthogneisses with model ages around 3 2 ga reworking of archean crustal material is most intense along the border zones of the belt and juvenile material is more dominant away from the orogenic front this scenario is indicative of an active continental margin setting for the two proterozoic episodes of orogenesis in the eastern ghats belt a correlation of domain 3 with the rayner complex and the prydz bay region antarctica for the early crustal evolution is supported by the similarity of the isotope signatures the napier complex is very different to the eastern ghats belt and an early joint evolution of these terranes is ruled out on the basis of the pb pb and sm nd systematics

high frequency cyclicity in a miocene sequence of the vienna basin established from high resolution logs and robust chronostratigraphic tuning abstract a high resolution chronostratigraphic record established by w e paulissen s m luthi p grunert s coric m harzhauser geol carp 2011 that takes into account variations in sedimentation rates and temporal gaps caused by unconformities and faulting in a research borehole in the vienna basin was used to investigate the possible presence of orbital millennial and centennial periodicities the sedimentary sequence covers middle to late miocene shallow marine fluvio deltaic and lacustrine shales silt and sandstones deposited during the transition from a pull apart basin to the final infill in a compressional regime spectral analysis was performed on gamma ray logs and high resolution electrical borehole images using three different analytical methods over six suitable intervals where continuous and constant sedimentation was identified the significant periods were found to closely match the orbital cycles of precession obliquity and short eccentricity providing a solid basis for the analysis of potential sub milankovitch cycles the significant frequencies encountered at the millennial to centennial scale fell for 75 within a relatively narrow time period of 0 25 to 5 kyr with a concentration of peaks between 1 and 2 kyr 29 and 500 to 800 years 17 these periodicities relate closely to the millennial dansgaard oeschger and bond cycles and centennial scale climate cycles documented from the quaternary it is suggested that the high frequency cycles observed in the miocene of the vienna basin represent differences in grain size related to cyclic variations in regional precipitation

sedimentary evolution and environmental history of lake van turkey over the past 600 000 years the lithostratigraphic framework of lake van eastern turkey has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years the lithostratigraphy and chemostratigraphy of a 219 m long drill core from lake van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity an age model was established based on the climatostratigraphic alignment of chemical and lithological signatures validated by 40ar 39ar ages the drilled sequence consists of ca 76 lacustrine carbonaceous clayey silt ca 2 fluvial deposits ca 17 volcaniclastic deposits and 5 gaps six lacustrine lithotypes were separated from the fluvial and event deposits such as volcaniclastics ca 300 layers and graded beds ca 375 layers and their depositional environments are documented these lithotypes are i graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations ii varved clayey silts reflecting strong seasonality and an intralake oxic anoxic boundary for example lake level highstands during interglacials interstadials iii caco3 rich banded sediments which are representative of a lowering of the oxic anoxic boundary for example lake level decreases during glacial inceptions iv caco3 poor banded and mottled clayey silts reflecting an oxic anoxic boundary close to the sediment water interface for example lake level lowstands during glacials stadials v diatomaceous muds were deposited during the early beginning of the lake as a fresh water system and vi fluvial sands and gravels indicating the initial flooding of the lake basin the recurrence of lithologies i to iv follows the past five glacial interglacial cycles a 20 m thick disturbed unit reflects an interval of major tectonic activity in lake van at ca 414 ka bp although local environmental processes such as tectonic and volcanic activity influenced sedimentation the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes making lake van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years

a geological study of lake van eastern turkey lake van is a lake with a volume of 607 km3 and a maximum depth of 451 m in a tectonically active zone in eastern anatolia it may be divided into three physiographic provinces lacustrine shelf sublacustrine slope and lake basin the shelf is largely made up of submerged fluvial valleys and alluvial plains as evidenced by the local occurrence of karst like topography buried leveed river valleys and sediment wedges interpretable as relict deltas the shelf and basinal deposits are characterized by an alternating succession of well stratified and chaotically reflecting layers consisting of turbidites and slump deposits respectively this thick sequence of unconsolidated to consolidated sediments is underlain by a paleozoic metamorphic or upper cretaceous limestone basement

crustal trajectory of sapphirine bearing granulites from ganguvarpatti south india evidence for an isothermal decompression path abstract ganguvarpatti is part of a precambrian terrane characterized by granulite facies rocks including charnockites mafic granulites sapphirine bearing granulites leptynites and gneisses a sequence of reactions deduced from the multiphase reaction textures provide information on the metamorphic history of this area as they formed in response to decompression during uplift geothermobarometry and constraints from reaction textures define a segment of a p t path traversed by the granulites of ganguvarpatti near peak metamorphic conditions of c 800 c and 8 kbar were succeeded by a symplectitic stage at a significantly lower pressure c 700 c and 4 5 kbar documenting a nearly isothermal decompression p t path and rapid uplift c 12 km followed by cooling the presence of many fluid inclusions of extremely low density in the charnockites is consistent with a nearly isothermal uplift path attainment of a maximum pressure of c 8 kbar indicates c 27 km depth of burial during metamorphism this would imply a total crustal thickness of c 65 70 km at 2 6 2 5 ga such a profound crustal thickness and a clockwise decompressive p t path is interpreted as a consequence of tectonic thickening of crust accomplished by collision tectonics of the southern granulite terrane against the dharwar craton along the palghat cauvery shear zone via northward subduction

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

high resolution chronostratigraphy from downhole susceptibility logging tuned by palaeoclimatic orbital frequencies abstract high resolution magnetic records have been obtained by downhole measurement with the geological high resolution magnetic logging tool ghmt in a well drilled in the north sea for hydrocarbon exploration this tool enables a continuous measurement of the polarity of the magnetic remanence and of the magnetic susceptibility throughout the drilled formations a high resolution magnetic chronostratigraphy between 2 6 and 1 6 ma is deduced from the tie points given by the downhole magnetostratigraphy and from a detailed spectral analysis of climatically influenced variations of susceptibility the orbital frequencies identified by spectral analysis of the magnetic susceptibility in the depth domain allow a refined estimation of the sedimentation rate and determination of a high resolution chronology of the sequence characteristic features of the onset of northern hemisphere glaciation and its fluctuations during the late pliocene are identified through this analysis of the susceptibility record our analysis indicates that massive discharge events of non pelagic deposits similar but with a higher amplitude to heinrich events that are observed during the last glaciation occurred between 2 5 and 2 0 ma and were probably related to instabilities of the laurentide ice sheet the relative power of the orbital forcing factors is compared with that documented at other north atlantic ocean sites comparison with an insolation model does not indicate direct correlation but suggests a strong influence of the northern hemisphere ice cover and its local variations

inorganic geochemistry of albian sediments from the lower saxony basin nw germany palaeoenvironmental constraints and orbital cycles abstract within the international albicore project upper albian sediments from a 245 m core kirchrode i drilled in hannover were studied by inorganic geochemical methods more than 650 samples minimum sample spacing 0 5 m were analysed for major and minor element concentrations this chemical database was used to reconstruct the depositional environment and to investigate the influence of high frequency milankovitch cycles on the chemical composition of the sediments the chemical composition of the sedimentary sequence is primarily controlled by variations in carbonate content corresponding to ca al ratios variations in both ti al and si al ratios are interpreted as fluctuations in detrital composition resulting from increases in smectite and quartz content in the upper section of the core high amounts of reactive iron but low pyrite concentrations the lack of enrichment of redox sensitive trace elements v cr and high mn concentrations indicate oxic bottom water conditions and the absence of an oxygen minimum zone for the upper albian at the kirchrode site the nutrient related trace elements ba p zn suggest a generally oligotrophic setting with slightly elevated productivity only in the uppermost upper albian only one layer was identified as containing volcanogenic material at 87 20 m this layer is characterised by elevated montmorillonite zr and nb mass balance calculations for the entire core suggest that the high mn values cannot be explained by riverine input alone therefore a coastal oxygen minimum zone south of the kirchrode site is postulated as an additional mn source cyclic variations in both carbonate content and al normalised concentrations of predominantly detrital elements like si and ti are seen in a 60 m interval 40 100 m where sedimentological palaeontological and geochemical data suggest stable depositional conditions although carbonate cyclicity cyclicity in detrital input and nutrient related element abundances do not correlate with each other three strong peaks in the results of spectral analysis of these chemical data for this interval appear to correspond to milankovitch frequencies in the eccentricity obliquity and precession bands

rapid climate change from north andean lake fuquene pollen records driven by obliquity implications for a basin wide biostratigraphic zonation for the last 284 ka this paper compares a new super high resolution pollen record from a central location in lake fuquene 4 n with 3 pollen records from marginal sites from the same lake basin located at 2540 m elevation in the eastern cordillera of colombia we harmonized the pollen sum of all records and provided previously published records of climate change with an improved age model using a new approach for long continental pollen records we dissociated from subjective curve matching and applied a more objective procedure including radiocarbon ages cyclostratigraphy and orbital tuning using the new 284 ka long fuquene basin composite record fq bc as the backbone groot et al 2011 we showed that a common 9 m cycle in the arboreal pollen percentage ap records reflects obliquity forcing and drives vegetational and climatic change the ap records were tuned to the 41 kyr component filtered from standard benthic 18o lr04 record changes in sediment supply to the lake are reflected in concert by the four records making frequency analysis in the depth domain an adequate method to compare records from the same basin we calibrated the original 14c ages and used where necessary biostratigraphic correlation i e for records shorter than one obliquity cycle pollen records from the periphery of the lake showed changes in the abundance of alnus and weinmannia forests more clearly while centrally located record fq 9c shows a more integrated signal of regional vegetation change the revised age models show that core fq 2 reflects the last 44 ka and composite record fq 7c the last 85 5 ka marginally located core fq 3 has an age of 133 ka at 32 m core depth and the lowermost 11 m of sediments appear of older but unknown age the longest record fq bc shows 60 yr resolution over the period of 284 27 ka all pollen records are in support of a common regional vegetation development leading to a robust reconstruction of long series of submillennial climate oscillations reflecting dansgaard oeschger do cycles reconstructed climate variability in the tropical andes since marine isotope stage mis 8 compares well with ngrip 18o based epica dome c d based and the mediterranean sea surface temperature record md01 2443 44 uk 37 based underpinning the global significance of the climate record from this tropical andean lake a basin wide biostratigraphy is presented and we concluded although with varying robustness that each core is representative of regional vegetational and climatic change

lewisian gneiss geochemistry and archaean crustal development models abstract the geochemistry of lewisian amphibolite facies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulite facies gneisses the results show that there are no significant differences between laxfordian amphibolite facies and scourian granulite facies gneisses in terms of ree and other immobile trace elements at equivalent silica levels although the mobile radioactive heat producing elements k rb th u are significantly lower in the granulites in both types the basic gneisses have moderately fractionated ree patterns while the intermediate and acid gneisses have strongly fractionated ree patterns with low heavy ree abundances and decreasing levels of total ree with increasing sio 2 the most silicic gneisses develop large positive europium anomalies these gross chemical similarities between gneisses from intermediate amphibolite facies and lower granulite facies crustal levels constrain models for the evolution of the archaean crust the depletion of k rb cs th and u in granulites but not other incompatible trace elements cannot be explained by magmatic processes the positive eu anomaly in the more siliceous gneisses of both facies is a function of the primary processes of crustal generation and not secondary processes such as intracrustal melting or fractional crystallisation fractionation of radioactive heat producing elements from other trace elements is a result of granulite facies metamorphism with these elements being removed by an active fluid phase the apparent lack of partial melting in lower crustal granulites suggests a model for archaean crustal growth largely through underplating by primary tonalitic magmas

smnd isotopes and ree geochemistry of madras granulites india an introductory statement abstract major and trace elements including ree as well as sm nd isotope analyses of eight granulite samples from the madras area are presented the data provide evidence for the origin of some of the granulites but in other cases demonstrate metasomatic changes in major and trace element contents including lree the data furthermore demonstrate that the analysed granulites are not cogenetic however when plotted in a sm nd isochron diagram the samples yield a linear array which corresponds to an age t 2555 140 ma and nd t 1 1 4 this age of 2555 140 ma could represent the time of granulite facies metamorphism immediately preceded by the formation of the protolith the nd t 1 value may be indicative of a near chondritic mantle source or alternatively of mixing between a depleted mantle and a crustal component

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

discrimination between different water bodies from a multilayered aquifer kaluvelly watershed india trace element signature in the multilayered aquifer of kaluvelly india comprising various sedimentary layers overlying a charnockitic basement concentrations of trace elements were measured in aquifer formations and in groundwaters to identify geochemical tracers for water bodies the two main sandstones cuddalore and vanur originate from the charnockites and the cuddalore sandstone has experienced lateritization in the studied area two charnockite end members were identified a dioritic and a granitic one mineralogical composition and whole rock ti concentrations confirmed the charnockite which displayed the granitic composition as the parent rock of the two sandstones titanium distribution indicates that the cuddalore sandstone originates from a more intense weathering of the parent material than the vanur sandstone despite extensive differences in trace element contents recorded in aquifer formations only a few trace elements were suitable to distinguish the water bodies among soluble elements li in the vanur aquifer and ba in the charnockite and carbonaceous aquifers can be used as tracers as the input of these elements in solution is mainly regulated by the available stock for a given mineralogical origin there is a direct link between the aquifer formation composition and water signature with the exception of as concentrations of redox sensitive elements were not preserved during pumping because of oxidation preventing their use as tracers low mobility elements such as la ce th zr nb hf or ta were too insoluble to be detected in waters and or to record the aquifer formation signature their input in solution was not regulated by the available stock but by the dissolution rate of rock forming minerals only ti can be used to distinguish between two out of the three aquifers charnockite and vanur the specific behavior of ti recorded in these waters may be linked to rutile inclusions within plagioclases and to the influence of climate on ti solubility

chemical th u total pb dating by electron microprobe analysis of monazite xenotime and zircon from the archean napier complex east antarctica evidence for ultra high temperature metamorphism at 2400 ma abstract the chemical th u total pb isochron method chime of dating was carried out on monazite xenotime zircon and polycrase in six samples of ultra high temperature uht granulites and one of pegmatite from five localities in the napier complex enderby land east antarctica despite the chronological heterogeneity in many grains the chime ages overall show strong evidence for a major event near 2420 ma analyzed monazite and xenotime grains except monazite from mt riiser larsen have a narrow range of chime ages 2412 42 ma from beaver island and 2429 36 2421 18 and 2431 22 ma from reference peak these ages are indistinguishable from chime ages on zircon 2436 17 and 2420 20 ma and on central older domains of monazite 2404 54 ma from mt riiser larsen and on a zircon rim 2430 15 ma from mt cronus we conclude that the ca 2420 ma ages relate to the uht metamorphism but we do not exclude the possibility that lead loss has lowered the ages by some 50 ma this interpretation is consistent with a preponderance of ages obtained by other methods on the napier complex particularly the ca 2475 25 ma age for a generation of pegmatites coeval with the uht event and containing the uht mineral assemblage beryllian sapphirine khmaralite quartz events prior to 2500 ma and after 2420 ma have also left their imprint on the chime ages for example a 3646 ma chime age suggests that a zircon core is inherited whereas ca 2200 and 2000 ma chime ages in zoned monazite could be due to further lead loss during post uht activity the much younger chime age of 1094 67 ma for monazite from a pegmatite at zircon point casey bay confirms 1000 1100 ma lead loss ages reported for this region and could result from fluid activity in an outlier of rayner activity near the boundary between the rayner and napier complexes approximately 2500 ma ages have been reported from granulite facies but not uht rocks in the madras and nilgiri blocks in south india these blocks and the napier complex could have constituted a single structural unit by late archean time

palaeomagnetic and rock magnetic study of charnockites from tamil nadu india and the ur protocontinent in early palaeoproterozoic times abstract palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the wsw ene granulite belt of south india magnetite is the dominant ferromagnet identified by rock magnetic and optical study it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval 2500 2100 ma several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions in the northern pallavaram sector these are p1 33 n 99 e dp dm 8 9 and p2 79 n 170 e dp dm 3 6 and in the southern vandallur sector they are v1 23 n 116 e dp dm 8 9 and v2 26 s 136 e dp dm 5 10 these magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences p1 p2 and v1 v2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 ma palaeomagnetic poles from the cratonic nuclei of africa australia and india all identify motion from higher to lower palaeolatitudes in early palaeoproterozoic times and this is dated 2400 and 2200 ma in the former two shields the corresponding apparent polar wander apw segments match the magnetization record within the charnockite basement terranes of southern india to yield a preliminary reconstruction of the ur protocontinent the oldest surviving continental protolith with origins prior to 3000 ma although subject to later relative movements these nuclei seem to have remained in proximity until the mesozoic break up of gondwana

3 5 ga old amphibolites from eastern hebei province china field occurrence petrography sm nd isochron age and ree geochemistry amphibolite blocks frequently occur in association with grey gneisses within a small area near the villages of caozhuang and huangbaiyu in eastern hebei they are interpreted as remnants of an earlier bimodal suite now engulfed in late archaean k rich granitic magma and are further cut by pegmatite dykes they are considered together as giant enclaves within late archaean granite plutons u pb zircon ages 2 5 2 6 ga the amphibolites have been dated by the sm nd isochron method the results yielded t 3470 107 ma ind 0 50827 11 and nd t 2 7 0 6 this age represents the time of protolithic basalt eruption and possibly suggests a period of formation of primitive mafic crust this is the oldest reliable age so far obtained for the archaean rocks of china the sm nd results of grey gneiss samples yielded model ages tdm of about 3 24 ga it is not clear whether this younger age in comparison with that of the amphibolites indicates the intrusive nature of these rocks or is a result of contamination by later granite about 2 5 ga ago the rb sr and common pb isotopic systems have been highly disturbed and no isochron ages could be established the common pb data show retarded growth of radiogenic pb and hence imply reduction of u pb ratios in the past this is consistent with the petrographic study which suggests that the amphibolites have undergone an earlier period of granulite facies metamorphism and were subsequently retrogressed to the present amphibolite facies mineral assemblages the positive nd t value of 2 7 for the amphibolites implies that the protolithic basalt magmas were generated from mantle sources which had undergone long term depletion in light rare earth elements lree the depletion event must have taken place prior to 4 ga ago if their source had a chemical nature similar to the modern oceanic mantle it could have occurred as early as 4 5 ga ago if their source was less impoverished in lree if the mantle depletion was related to extraction of continental or sialic material the sm nd data of the caozhuang amphibolites lend support to the existence of sialic crust if not of a continental size before 4 ga ago

paleovan international continental scientific drilling program icdp site survey results and perspectives lake van is the fourth largest terminal lake in the world volume 607 km 3 area 3570 km 2 maximum depth 460 m extending for 130 km wsw ene on the eastern anatolian high plateau turkey the sedimentary record of lake van partly laminated has the potential to obtain a long and continuous continental sequence that covers several glacial interglacial cycles ca 500 kyr therefore lake van is a key site within the international continental scientific drilling program icdp for the investigation of the quaternary climate evolution in the near east paleovan as preparation for an icdp drilling campaign a site survey was carried out during the past years we collected 50 seismic profiles with a total length of similar to 850 km to identify continuous undisturbed sedimentary sequences for potential icdp locations based on the seismic results we cored 10 different locations to water depths of up to 420 m multidisciplinary scientific work at positions of a proposed icdp drill site included measurements of magnetic susceptibility physical properties stable isotopes xrf scans and pollen and spores this core extends back to the last glacial maximum lgm a more extended record than all the other lake van cores obtained to date both coring and seismic data do not show any indication that the deepest part of the lake tatvan basin ahlat ridge was dry or almost dry during past times these results show potential for obtaining a continuous undisturbed long continental palaeoclimate record in addition this paper discusses the potential of paleovan to establish new results on the dynamics of lake level fluctuations noble gas concentration in pore water of the lake sediment history of volcanism and volcanic activities based on tephrostratigraphy and paleoseismic and earthquake activities c 2009 elsevier ltd all rights reserved