an unusual high mg garnet spinel orthopyroxenite from southern india evidence for ultrahigh temperature metamorphism at high pressure conditions we report here a garnet spinel orthopyroxenite in close association with an ultrahigh temperature uht granulite from the central part of the madurai granulite block in southern india the garnet spinel orthopyroxenite is almost entirely composed of orthopyroxene spinel and rare garnet in a granular texture spinels in the rock are characterized by high mg x mg 0 69 0 71 with low cr and fe 3 consistent with compositions reported from spinels occurring within xenoliths in kimberlites and high pressure temperature p t alpine complexes the orthopyroxenes have high al content al 2 o 3 up to 4 85 wt typical of equilibration under high p t conditions the p t estimates derived for the garnet spinel orthopyroxenite indicate temperatures of around 1000 c and pressures exceeding 17 kbar the data indicate that uht metamorphism in this locality traversed from above 17 kbar to 11 kbar prior to the final stage of isothermal decompression our study reports the highest pressures obtained by far for extreme crustal metamorphism in southern india and elsewhere in gondwana the multi stage decompression observed in the uht rocks associated with the high p t garnet spinel orthopyroxenite could be correlated to extension of the crust and possibly of the lithospheric mantle and or its delamination with the asthenospheric mantle as the ultimate heat source during the final stage of amalgamation of the gondwana supercontinent

ultrahigh temperature metamorphism and decompression history of sapphirine granulites from rajapalaiyam southern india implications for the formation of hot orogens during gondwana assembly sapphirine bearing mg al granulites from rajapalaiyam in the southern part of the madurai block provide critical evidence for late neoproterozoic cambrian ultrahigh temperature uht metamorphism in southern india poikiloblastic garnet in quartzo feldspathic and pelitic granulites contain inclusions of fine grained subidioblastic to xenoblastic sapphirine associated with quartz suggesting that the rocks underwent t 1000 c peak metamorphism quartz inclusions in spinel within garnet are also regarded as clear evidence for a uht condition inclusions of orthopyroxene within porphyroblastic garnet in the sapphirine bearing rocks show the highest al 2 o 3 content of up to 10 3 wt suggesting t 1050 1070 c and p 8 5 9 5 kbar temperatures estimated from ternary feldspar and other geothermometers t 950 1000 c further support extreme thermal metamorphism in this region xenoblastic spinel inclusions in sapphirine coexisting with quartz suggest that the spinel quartz assemblage pre dates the sapphirine quartz assemblage probably implying a cooling from t 1050 c or an anticlockwise p t path the fmas reaction sapphirine quartz garnet orthopyroxene sillimanite indicates a cooling from the sapphirine quartz stability field after the peak metamorphism corona textures of orthopyroxene cordierite sapphirine orthopyroxene sapphirine cordierite and cordierite spinel around garnet suggest subsequent near isothermal decompression followed by decompressional cooling toward t 650 750 c and p 4 5 5 5 kbar the sapphirine quartz association and related textures described in this study have an important bearing on the uht metamorphism and exhumation history of the madurai block as well as on the tectonic evolution of the continental deep crust in southern india our study provides a typical example for extreme metamorphism associated with collisional tectonics during the late neoproterozoic cambrian assembly of the gondwana supercontinent

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

high pressure and ultrahigh temperature metamorphism at komateri northern madurai block southern india we report for the first time the evidence for prograde high pressure hp metamorphism preceding a peak ultrahigh temperature uht event in the northernmost part of the madurai block in southern india mg al rich grt ged rocks from komateri in karur district contain poikiloblastic garnet with numerous multi phase inclusions although most of the inclusion assemblages are composed of gedrite quartz and secondary biotite rare staurolite sapphirine and spinel quartz are also present the xmg mg fe mg of staurolite 0 45 0 49 is almost consistent with that reported previously from namakkal district in the palghat cauvery shear zone system xmg 0 51 0 52 north of the madurai block the hp event was followed by peak uht metamorphism at t 880 1040 c and p 9 8 12 5 kbar as indicated by thermobarometric computations in the grt ged rock and associated mafic granulite symplectic intergrowth of spinel xmg 0 50 0 59 zno 1 7 wt and quartz a diagnostic indicator of uht metamorphism probably formed by decompression at uht conditions the rocks subsequently underwent retrograde metamorphism at t 720 760 c and p 4 2 5 1 kbar the p t conditions and clockwise exhumation trajectory of the komateri rocks comparable to similar features recorded from the palghat cauvery shear zone system suggest that the madurai block and the palghat cauvery shear zone system underwent similar hp and uht metamorphic history probably related to the continent continent collision during the final stage of amalgamation of gondwana supercontinent

sapphirine and corundum bearing granulites from karur madurai block southern india we report new occurrences of sapphirine and corundum bearing granulites intercalated within orthogneisses at lachmanapatti and malappatty in the northern part of madurai block sapphirine in these localities occurs either as needle like intergrowth with cordierite and corundum in symplectites and medium to fine grained euhderal to subhedral crystals associated with cordierite and corundum lachmanapatti or in association with plagioclase corundum and gedrite malappatty the sapphirine from lachmanapatti is highly magnesian xmg 0 87 0 94 with higher cr content up to 0 9 pfu as compared with those in other localities in the madurai block the sapphirine corundum association reported in this study has important bearing on the ultrahigh temperature metamorphism and exhumation history of the northern madurai block as well as on the tectonic evolution of the continental deep crust in southern india

ultrahigh temperature mafic granulites from panrimalai south india constraints from phase equilibria and thermobarometry abstract the panrimalai area constitutes part of the granulite facies rocks of the madurai block in the southern granulite terrain sgt india garnet bearing mafic granulites in panrimalai occur as small enclaves within charnockite the common stable assemblage during peak metamorphism contains hornblende garnet orthopyroxene clinopyroxene quartz and plagioclase the resorption of garnet in various reaction textures and the development of spectacular orthopyroxene plagioclase and hornblende plagioclase symplectites characterize the subsequent stages of metamorphism application of multi equilibrium calculation procedures for mineral core compositions of the early assemblage yields near peak conditions at 900 c at 9 kbar these estimates are the highest yet reported in mafic granulites from the madurai block the post peak p t path is constructed for the mafic granulites based on observed microstructural relations and thermobarometric results is characterized by a steep clockwise decompressional p t segment from 9 to

p t t evolution of sapphirine bearing semipelitic granulites from vadkampatti in eastern madurai domain southern india insights from petrography pseudosection modelling and in situ monazite geochronology abstract migmatitic semipelitic granulites from the eastern madurai domain of southern india preserves reaction textures indicating a clockwise p t evolution with near isothermal decompression the prograde history is recorded by included phases within porphyroblastic garnet and orthopyroxene development of high xmg garnet up to 0 69 orthopyroxene al2o3 up to 9 6 wt assemblage indicates attainment of ultrahigh temperature uht condition at the peak stage subsequent formation of a series of symplectic assemblages opx2 spr2 sil2 pl2 and opx2 crd2 with aluminous orthopyroxene al2o3 up to 9 5 wt at the expense of garnet indicates decompression at ultrahigh temperatures conventional thermobarometry and feldspar thermometry indicate peak metamorphic p t conditions of 970 30 c 10 3 0 4 kbar and formation of symplectites at 960 20 c 9 2 0 3 kbar for opx2 spr2 sil2 and at 890 40 c 7 3 0 6 kbar for opx2 crd2 obtained p t conditions are in agreement with the p t estimates from pseudosection modelling texturally controlled in situ monazite dating shows that the th poor and extremely hree depleted dark cores of matrix monazite with a weighted age of 586 8 ma formed simultaneously with garnet growth during the prograde evolution on the other hand th rich and hree depleted bright rims with a weighted age of 532 7 ma formed from the dissolution reprecipitation due to melt crystallization at or near t max dating the peak of metamorphism the compositionally homogeneous hree y enriched monazite in the symplectite with a weighted age of 475 12 ma formed along with the symplectites during garnet breakdown our results are suggestive of a late neoproterozoic to cambrian long lived ca 55 million years hot orogenic plateau in the madurai block uht conditions were likely achieved by conductive heating before being rapidly uplifted to shallower crustal depth during late cambrian to early ordovician 475 12 ma this is consistent with the hot orogen model for the attainment of uht conditions which demonstrates that crusts that are moderately rich in heat producing elements can reach temperatures 900 c when the duration of orogeny is sufficiently long i e slow erosion rates to allow conductive heating through radioactive decay

tectonic implications of seismic reflectivity pattern observed over the precambrian southern granulite terrain india abstract the southern granulite terrain sgt constitutes a large part of the south indian precambrian shield a study of the crustal reflectivity and tectonic framework of the madurai block of the sgt has been carried out using multifold seismic reflection survey along the vattalkundu kalugumalai transect the seismic stack sections along the profile showing conspicuous changes in reflectivity pattern indicate the presence of several structurally distinct crustal blocks it is apparent from the north dipping reflectors near vattalkundu that the kodaikanal massif extends 5 km further south of vattalkundu where the dip direction changes towards south the reflectivity pattern in the crustal column of central part of the profile between sedapatti and sarvathapuram suggests block uplift accompanied by internal domal deformation of the crust in madurai block the dip on the southern flank of the dome is steeper than that of northern side the south dipping reflections in the southern part of the profile between sivakasi and kalugumalai in the upper crust are strong and continuous the presence of the ultrahigh temperature pressure uht p metamorphic layering reported in the region might be contributing to the increased reflectivity however the relationship between the reflectivity and the uht p is enigmatic and yet to be established in general the region is characterized by distinct upper and mid crustal reflectivity but the reflection moho identifiable at 13 0 13 5 s two way travel time twt is diffuse

biogenic sediments in the west caroline basin the western equatorial pacific during the last 330 000 years abstract primary productivity as well as new production have played an important role in the global carbon cycle during the late quaternary the mean organic carbon nitrogen atomic ratio was 8 3 from the c4402 sediments in the west caroline basin which indicates a limited contribution of terrigenous organic carbon to the organic matter in the sediments the fluctuation of carbonate preservation shows that the accumulation rate of organic carbon has reflected primary productivity the results from sediment trap experiments which were carried out at site c4402 indicate that plankton bloom was characterized by a large influx of siliceous plankton when organic carbon was effectively removed palaeoproductivity estimates calculated by using the formula of sarnthein et al 1988 would be plausible because the fluctuation pattern of such estimates correlates closely with changes in the accumulation rate of biogenic opal in the sediments the primary productivity in the west caroline basin increased during stage 2 stage 3 late stage 6 stage 6 7 boundary and stage 8 at a glance the results are similar to other studies that have reported higher glacial productivity in low latitude regions however some leads and lags are found between the west caroline basin and other areas of the equatorial pacific and atlantic the spectral analysis of mar organic indicates that the western equatorial pacific reaches a maximum in mar organic approximately 7000 years before the maxima in the eastern pacific a regional variation of the response of mar organic to the orbital forcing climatic condition suggests that the efficiency of the organic carbon pump may vary with longitude in the equatorial pacific

co2 rich fluid inclusions in staurolite and associated minerals in a high pressure ultrahigh temperature granulite from the gondwana suture in southern india abstract we report the first detailed fluid inclusion study on mg al rocks from the gondwana suture zone along the palghat cauvery shear zone system in southern india these rocks underwent high pressure p 12 kbar and ultrahigh temperature t 990 c metamorphism during the late neoproterozoic associated with the collisional assembly of the gondwana supercontinent fluid inclusions of texturally primary and pseudosecondary categories occur in plagioclase staurolite and kyanite in these rocks inclusions of secondary nature are found in garnet and apatite all the trapped fluids show melting temperatures in the range of 58 6 to 56 6 c suggesting a dominantly pure co 2 composition the secondary inclusions show high homogenization temperatures t h of 12 9 to 30 0 c indicating low density of 0 59 0 83 g cm 3 although most of the primary and pseudosecondary inclusions also contain moderate to low density fluids 0 67 0 95 g cm 3 t h 3 5 to 27 4 c rare high density inclusions 1 00 1 06 g cm 3 t h 26 1 to 14 1 c were discovered in matrix plagioclase and porphyroblastic staurolite the estimated co 2 isochores for the high density primary and pseudosecondary inclusions intersect the clockwise p t trajectory of the rocks at around 8 3 9 0 kbar at 1000 c which broadly coincide with the peak metamorphic conditions of the area since these fluid inclusions show textural evidence for entrapment during the growth of the host high grade minerals we interpret the high density co 2 fluids to be traces of a co 2 rich synmetamorphic fluid that was present during the peak ultrahigh temperature metamorphism despite the preservation of high density co 2 inclusions in staurolite and plagioclase the primary and pseudosecondary inclusions in most of the other minerals show wide density variation which suggests the fluids in these inclusions underwent significant density reversal density decrease during decompression of the rocks from high pressure through the peak ultrahigh temperature stage along a clockwise p t trajectory the finding of pure co 2 inclusions in these mg al granulites conforms with similar observations from many other granulite facies terrains with the carbonic fluids probably derived from mantle reservoirs and transferred through deep seated shear zones that characterize this gondwana suture

structural anatomy of a dismembered ophiolite suite from gondwana the manamedu complex cauvery suture zone southern india abstract detailed geological and structural mapping of the manamedu ophiolite complex moc from the south eastern part of the cauvery suture zone csz within the gondwana collisional suture in southern india reveals the anatomy of a dismembered ophiolite succession comprising pyroxenite actinolite hornblendite hornblendite gabbro norite gabbro anorthosite amphibolite plagiogranite mafic dykes and associated pelagic sediments such as chert magnetite bands and carbonate horizons the magmatic foliation trajectory map shows inward dipping foliations and a variety of fold structures structural cross sections of the moc reveal gentle inward dips with repetition and omission of different lithologies often marked by curvilinear hinge lines the succession displays imbricate thrust sheets and slices of dismembered ophiolite suites distributed along several localities within the csz the moc can be interpreted as a deformed large duplex structure associated with south verging back thrust system consistent with crustal scale flower structure the nature and distribution of ophiolitic rocks in the csz suggest supra subduction zone setting associated with the lithospheric subduction of the neoproterozoic mozambique ocean followed by collision and obduction during the final stage of amalgamation of the gondwana supercontinent in the end precambrian

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

linking monazite geochronology with fluid infiltration and metamorphic histories nature and experiment migmatised metapelites from the kodaikanal region central madurai block southern india have undergone ultrahigh temperature metamorphism 950 1000 degrees c 7 8 kbar in situ electron microprobe th u pb isochron chime dating of monazites in a leucosome and surrounding silica saturated and silica poor restites from the same outcrop indicates three principal ages that can be linked to the evolutionary history of these rocks monazite grains from the silica saturated restite have well defined inherited cores with thick rims that yield an age of ca 1684 ma this either dates the metamorphism of the original metapelite or is a detrital age of inherited monazite monazite grains from the silica poor restite thick rims from the silica saturated restite and monazite cores from the leucosome have ages ranging from 520 to 540 ma suggesting a mean age of 530 ma within the error bars in the leucosome the altered rim of the monazite gives an age of ca 502 ma alteration takes the form of th depleted lobes of monazite with sharp curvilinear boundaries extending from the monazite grain rim into the core we have replicated experimentally these altered rims in a monazite leucosome experiment at 800 degrees c and 2 kbar this experiment coupled with earlier published monazite fluid experiments involving high ph alkali bearing fluids at high p t helps to confirm the idea that alkali bearing fluids in the melt and along grain boundaries during crystallization were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution reprecipitation c 2015 elsevier b v all rights reserved

partial melting and p t evolution of the kodaikanal metapelite belt southern india abstract the kodaikanal region of the madurai block in southern india exposes a segment of high grade metamorphic rocks dominated by an aluminous garnet cordierite spinel sillimanite quartz migmatite suite designated herein as the kodaikanal metapelite belt kmb these rocks were subjected to extreme crustal metamorphism during the late neoproterozoic despite the lack of diagnostic ultrahigh temperature assemblages the rocks preserve microstructural evidence demonstrating initial heating dehydration melting to generate the peak metamorphic assemblage and later retrogression of the residual assemblages with remaining melt the peak metamorphic assemblage is interpreted to be garnet sillimanite k feldspar spinel fe ti oxide quartz melt which indicates pressure temperature p t conditions around 950 1000 c and 7 8 kbar based on calculated phase diagrams a clockwise p t path is proposed by integrating microstructural information with pseudosections we show that evidence for extreme crustal metamorphism at ultrahigh temperature conditions can be extracted even in the cases where the rocks lack diagnostic ultrahigh temperature mineral assemblages our approach confirms the widespread regional occurrence of uht metamorphism in the madurai block during gondwana assembly and point out the need for similar studies on adjacent continental fragments

structure and evolution of the cauvery shear zone system southern granulite terrain india evidence from deep seismic and other geophysical studies abstract the southern granulite terrain with exposed archean lower crustal rocks is studied using various geophysical tools the crustal structure derived from seismic reflection and refraction wide angle reflection studies is used to understand the tectonic evolution of the region deep seismic reflection section along the kolattur palani segment shows an oppositely dipping reflection fabric near the moyar bhavani shear zone which is interpreted as a signature of collision between the dharwar craton and another crustal block in the south the thickened crust due to collision was delaminated during the orogenic collapse and modified the central part covering the cauvery shear zone system located between the moyar bhavani and karur oddanchatram shear zones the delaminated lower crust is altered by magmatic underplating as evidenced by the high velocity layer just above the moho the velocity model of the region indicates crustal thickening at the boundary of the dharwar craton and moyar bhavani shear zone and thinning further south back scattered seismic wave field with negative moveout and the moho offset indicate the spatial location and strike slip nature of the shear zones present study suggests that the late archean collision and suturing of the dharwar craton with the southern crustal block at the moyar bhavani shear zone may be responsible for the evolution of late archean granulites late neoproterozoic rifting is observed along the paleo fault zones the seismic studies constrained by gravity magnetic and magnetotelluric data suggest that the moyar bhavani and karur oddanchatram shear zones of the cauvery shear zone system mark terrane boundaries suture zones

sapphirine quartz corona around magnesian xmg 0 58 staurolite from the palghat cauvery suture zone southern india evidence for high pressure and ultrahigh temperature metamorphism within the gondwana suture abstract we report the first finding of equilibrium sapphirine quartz assemblage from the palghat cauvery suture zone pcsz in southern india providing unequivocal evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions associated with the collisional assembly of the gondwana supercontinent in the late neoproterozoic cambrian the sapphirine and quartz occur as coronas around mg rich x mg 0 58 staurolite within poikiloblastic garnet in an mg al rich rock suggesting the progress of the prograde dehydration reaction staurolite garnet sapphirine quartz h 2 o although the occurrence of mg rich staurolite was previously noted from some localities in the pcsz no sapphirine quartz direct association has yet been reported the available experimental studies on mg rich staurolite indicate that the mineral is stable at p 15 kbar and suggest that the complex texture that we report here might correspond to a peak high pressure regime prior to the uht event the symplectic sapphirine quartz around staurolite probably implies decompression from p 15 kbar toward the stability of sapphirine quartz at temperatures of c 1000 c along a clockwise p t path the prograde high pressure metamorphism and following uht event correlate with the subduction collision tectonics associated with the final stage of amalgamation of gondwana supercontinent

proterozoic orogens in southern peninsular india contiguities and complexities abstract the precambrian terranes of southern peninsular india have been central to discussions on the history of formation and breakup of supercontinents of particular interest are the proterozoic high grade metamorphic orogens at the southern and eastern margins of the indian shield skirting the 3 4 ga dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics but also carry imprints of the tectonic framework related to the assembly of the major neoproterozoic supercontinents rodinia and gondwana these proterozoic orogens are described as southern granulite terrane sgt in the southern tip and the eastern ghats mobile belt egmb in the eastern domains of the peninsula the contiguity of these orogens is broken for a distance of 400 km and disappears in the bay of bengal these orogens expose windows of middle to lower crust with well preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems some of which represent collisional sutures the sgt and egmb carry several important features such as fold thrust tectonics regional granulite facies metamorphism of up to ultrahigh temperature conditions in some cases multiple p t paths development of lithospheric shear zones emplacement of ophiolites presence of alkaline and anorthositic complexes development of crustal scale flower structures transpressional strains and reactivation tectonics a heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified both egmb and sgt share a common transpressional deformation history during the latest neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics our synthesis of the spatial distribution geometry kinematics and the transpressional strain of the shear zone systems provides insights into the tectono metamorphic history of the proterozoic orogens of southern india and their contiguity and complexities recent understanding of subduction accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in earth history although the major and common structural architecture was built during the final assembly of the gondwana supercontinent

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

first report of sapphirine bearing rocks from the palghat cauvery shear zone system southern india abstract silica deficient mg al granulites from paramati within the palghat cauvery shear system contain sapphirine in association with corundum spinel and sillimanite gedrite which occurs commonly in this locality coexists with cordierite corundum and sillimanite mineral assemblages and reaction textures indicate peak metamorphism at ultrahigh temperature conditions this new locality provides evidence for extreme crustal metamorphism along the archean proterozoic collision boundary in southern india

first evidence of ultrahigh temperature decompression from the granulite province of southern india sapphirine bearing orthopyroxene sillimanite garnet granulites of the palni hill ranges record evidence of ultrahigh temperature metamorphism during which primary mineral assemblages were partially overprinted by a succession of reaction coronas and symplectites that together suggest decompression model system petrogenetic grids allow constraints to be placed on the evolution of p t conditions as recorded by reaction relationships of successively developed mineral assemblages thermobarometry on garnet bearing assemblages allows minimum constraints to be placed on p t conditions for the primary mineral assemblages primary mineral assemblages suggest p t conditions of c 12 kbar and c 900 1000 c secondary mineral assemblages in reaction textures show a two stage decompression to probable p t conditions of c 5 kbar and c 850 c the inferred p t path is clockwise

seasonal variations of the large scale geostrophic flow field and eddy kinetic energy inferred from the topex poseidon and jason 1 tandem mission data 1 geostrophic surface velocity anomalies are used to analyze the annual variations of the large scale geostrophic currents and of the eddy kinetic energy eke field of the ocean circulation the underlying geostrophic currents were estimated from the jason 1 topex poseidon jtp tandem altimetric sea surface height data using the parallel track approach with a 10 km along track resolution however because of the given separation of the tracks of the two satellites only large mesoscale eddies are resolved by the tandem measurements the analysis covers the entire 3 year period of the tandem mission 109 repeat cycles from september 2002 to september 2005 the analysis of the seasonal flow changes reveals annual changes of all major current systems but especially of the zonal flow field in low latitudes leading to zonal jets on the annual cycle in the southern pacific atlantic and indian oceans in middle and high latitudes indications of a seasonally modulated strength of the sverdrup circulation emerge from the analysis the eke field also shows changes in its amplitude on the annual period in low latitudes those can be rationalized as resulting from seasonally modulated currents in middle and high latitudes changes in the wind driven barotropic circulation loom large which are not represented in other altimetric velocity products results shown suggest that velocity time series of the jtp tandem mission should be continued through similar constellations e g of jason 1 and jason 2

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

garnet spinel corundum quartz bearing titanohematite veins in eclogite from the sulu ultrahigh pressure terrane imprint of a short lived high temperature metamorphic stage abstract eclogite hosted garnet spinel corundum quartz bearing titanohematite veins and lenses 10 20 cm in width are described for the first time in the sulu ultrahigh pressure metamorphic terrane some of the lenses were aligned parallel to the foliation of the host eclogite suggesting that they were the product of ductile deformation of one titanohematite layer a vein composed of titanohematite ilmenite hematite spinel garnet corundum quartz k feldspar albite was studied in detail ti fe oxides account for up to 80 and al rich phases for 15 of the total volume of this vein electron microprobe analyses show that the titanohematite solid solution was made up of 0 75 hematite 0 25 ilmenite the unusual mineral assemblage of garnet spinel corundum quartz implies that this vein could have experienced high temperatures 900 c although the garnets showed well defined mg and mn diffusion zoning in the rim as a result of the high temperature event slight mg and mn growth zoning was preserved in the core thus we suggest that the sulu uhp terrane could have experienced a short lived high temperature 900 c stage during exhumation garnets in the titanohematite vein were characterized by extremely low trace element contents petrological and geochemical features of the veins suggest that they could be metamorphic products of igneous cumulates composed of magnetite plagioclase clinopyroxene

fluid characteristics of high to ultrahigh temperature metamorphism in southern india a quantitative raman spectroscopic study abstract we report the first quantitative compositional data on fluid inclusions in late neoproterozoic to cambrian ultrahigh temperature uht granulites from major crustal blocks and shear zones in southern india fluid inclusions in various high grade minerals such as garnet orthopyroxene plagioclase cordierite and quartz from these rocks were studied in terms of petrography microthermometry and laser raman spectroscopy measured melting temperatures of the inclusions indicate that the trapped fluid phase is dominantly carbonic raman analyses confirmed a co2 rich composition with only minor dilutants such as n2 5 0 mol h2o 0 50 mol and ch4 0 47 mol the range of most co2 isochores computed from density measurements in fluid inclusions from the uht granulites pass below the peak pressure temperature conditions of metamorphism indicating considerable resetting of fluid densities during decompression in contrast garnetiferous granulites from the salem area along the palghat cauvery shear zone system which underwent high pressure prograde metamorphism contain very high density syn metamorphic pure co2 inclusions such dense carbonic fluid inclusions in garnet and plagioclase coexist with carbonate minerals calcite or dolomite indicating probable derivation from deep seated primary magmatic sources although models on the origin of co2 are debatable the ubiquitous association of carbonic fluids in the uht mineral assemblages is in favour of large scale infiltration of co2 rich fluids during extreme crustal metamorphism associated with collisional orogeny and subsequent extensional collapse at the final stage of amalgamation of the gondwana supercontinent

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

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

late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean rea d k and janecek t r 1981 late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean palaeogeogr palaeoclimatol palaeoecol 36 55 67 eolian dust preserved in deep sea sediment can provide a direct historical record of global atmospheric circulation data from a reasonably complete upper cretaceous section of pelagic sediments recovered at dsdp site 463 in the central north pacific provides a good record of eolian activity during the time period between about 112 hnd 66 m y ago we have isolated the eolian component from these sediments determined its mass accumulation rate and combined these data with the mineralogy of the inorganic fraction determined by others to construct a record of eolian deposition volcanic input is significant during aptian albian and maastrichtian times otherwise continentally derived minerals dominate mass accumulation rates of the continental eolian component range from over 500 mg cm 103yr during the late albian to a low of 5 mg cm2 10 yr during coniacian time for comparison the upper miocene to pleistocene rate averages about 20 mg cm2 103yr the temporal pattern of late cretaceous eolian accumulation of site 463 generally matches known changes in sea level suggesting that source availability is the dominant control of eolian sedimentation during that time

mineralogy of aeolian dust reaching the north pacific ocean 1 sampling and analysis the mineral composition of the 2 m clay and 2 to 20 m silt size fractions of aerosol particles collected near the margins of the north pacific ocean was determined by x ray diffraction analysis although the same mineral phases are present in the two size fractions there are significant differences in the quartz plagioclase and kaolinite concentrations north pacific aerosols are primarily composed of illite in both size fractions in addition to kaolinite in the 2 m size class and quartz and plagioclase in the 2 to 20 m size class quartz and plagioclase are present in significantly higher amounts in the 2 to 20 m size fraction while kaolinite is greater in the 2 size class western north pacific aerosol particles contain significantly higher 2 m quartz than samples collected in the east and eastern north pacific aerosols have significantly higher concentrations of 2 m smectite than those from the west

paleomagnetism of ca 2 3 ga mafic dyke swarms in the northeastern southern granulite terrain india constraints on the position and extent of dharwar craton in the paleoproterozoic abstract the pole positions reported for the mafic dykes occurring in the northeastern southern granulite terrain and easterly trending dykes of dharwar craton are alike while their ages differ by ca 700 ma confounding tectonic reconstruction to resolve the discordance and to constrain the position of the indian continent in the proterozoic paleomagnetic and geochronological studies have been carried out on the mafic dyke swam in the northeastern southern granulite terrain two distinct pole positions are obtained one from the group of tiruvannamalai dykes as 27 7 s 231 5 e dp dm 12 14 with corresponding mean declination dm and inclination im as 125 and 73 8 95 22 7 6 respectively and second from the east coast dykes as 2 32 s 188 2 e dp dm 5 8 with corresponding mean dm and im as 88 9 and 33 8 95 48 7 1 respectively the remanent efficiency of magnetization values between 0 01 and 0 08 suggest that the dykes have been cooled through curie temperature of magnetite which is the carrier of magnetization the baked contact test confirms that the characteristic remanent magnetization is the primary magnetization the sm nd mineral whole rock isochron from one of the tiruvannamalai dykes yielded an age of 2318 60 ma mswd 1 9 this age is the time of intrusion of the tiruvannamalai dykes and is similar within errors to the age of dykes in the dharwar craton thus the contiguity of dharwar craton with the northern block of southern granulite terrain as early as 2 3 ga ago is established the pole position thus obtained corresponds to a high latitudinal position of dharwar craton during early paleoproterozoic

first report of sapphirine quartz assemblage from southern india implications for ultrahigh temperature metamorphism we report here for the first time the occurrence of sapphirine quartz assemblage in textural equilibrium from quartzo feldspathic and pelitic granulites from southern india the sapphirine bearing rocks occur as layered gneisses associated with pink granite within massive charnockite in rajapalaiyam area in the southern part of madurai block sapphirine occurs in three associations i fine grained subhedral mineral associated with quartz enclosed in garnet ii intergrowth with al rich orthopyroxene up to 9 7 wt al2o3 and iii in symplectitic intergrowth with orthopyroxene al2o3 5 9 6 7 wt and cordierite surrounding garnet the sapphirine in association with quartz is slightly magnesian xmg 0 79 0 80 and low in si content 1 55 1 56 pfu as compared with those associated with orthopyroxene and cordierite xmg 0 77 0 79 si 1 59 1 63 pfu the sapphirine quartz assemblage suggests that the granulites underwent t 1050 c peak metamorphism cores of porphyroblastic orthopyroxene in the sapphirine bearing rocks shows high al2o3 content of up to 9 7 wt suggesting t 1040 1060 c and p 8 kbar fmas reaction of sapphirine quartz garnet sillimanite cordierite indicates a cooling from sapphirine quartz stability field after the peak ultrahigh temperature metamorphism slightly lower temperature estimates from ternary feldspar and sapphirine spinel geothermometers t 950 1000 c also support a post peak isobaric cooling corona textures of orthopyroxene cordierite sapphirine orthopyroxene sapphirine and cordierite spinel around garnet suggest subsequent decompression the sapphirine quartz association and related textures reported in this study have important bearing on the ultrahigh temperature metamorphism and exhumation history of the madurai block as well as on the tectonic evolution of the continental deep crust in southern india

the stability and origin of sodicgedrite in ultrahigh temperature mg al granulites a case study from the gondwana suture in southern india mg al rich rocks from the palghat cauvery shear zone system pcsz within the gondwana suture zone in southern india contain sodicgedrite as one of the prograde to peak phases stable during t 900 990 c ultrahigh temperature metamorphism gedrite in these samples is mg rich mg fe mg x mg 0 69 0 80 and shows wide variation in na2o content 1 4 2 3 wt naa 0 33 0 61 pfu gedrite adjacent to kyanite pseudomorph is in part mantled by garnet and cordierite the gedrite proximal to garnet shows an increase in naa and aliv from the core naa 0 40 0 51 pfu aliv 1 6 1 9 pfu to the rim naa 0 49 0 61 pfu aliv 2 0 2 2 pfu suggesting the progress of the following dehydration reaction ged ky na ged grt crd h2o this reaction suggests that as the reactants broke down during the prograde stage the remaining gedrite became enriched in na to form sodicgedrite which is regarded as a unique feature of high grade rocks with mg al rich and k si poor bulk chemistry we carried out high p t experimental studies on natural sodicgedrite and the results indicate that gedrite and melt are stable phases at 12 kbar and 1 000 c however the product gedrite is na poor with only 0 13 wt na2o naa 0 015 0 034 pfu in contrast the matrix glass contains up to 8 5 wt na2o suggesting that with the progressive melting of the starting material na was partitioned into the melt rather than gedrite the results therefore imply that the occurrence of sodicgedrite in the uht rocks of the pcsz is probably due to the low h2o activity during peak p t conditions that restricted extensive partial melting in these rocks leaving na partitioned into the solid phase gedrite the occurrence of abundant primary co2 rich fluid inclusions in this rock which possibly infiltrated along the collisional suture during the final amalgamation of the gondwana supercontinent strengthens the inference of low water activity

anticlockwise evolution of ultrahigh temperature granulites within continental collision zone in southern india abstract we report three new localities of corundum and sapphirine bearing hyper aluminous mg rich and silica poor ultrahigh temperature granulites formed during late neoproterozoic cambrian times within the palghat cauvery shear zone system in southern india from petrologic characteristics mineral chemistry and petrogenetic grid considerations the peak metamorphic conditions of these rocks are inferred to lie around 950 1000 c as suggested by al in orthopyroxene thermometer at pressures above 10 kbar as indicated by the equilibrium orthopyroxene sillimanite gedrite quartz assemblage these rocks preserve several remarkable reaction textures the most prominent among which is the triple corona of spinel sapphirine cordierite on corundum with the whole textural assembly embedded within the matrix of gedrite suggesting the reaction ged crn spl spr crd the formation of sapphirine sillimanite assemblage symplectite associated with relict corundum and porphyroblasitc cordierite is explained by the reaction crd crn spr sil the association of sapphirine cordierite symplectite with gedrite sillimanite assemblage as well as with aluminosilicate boundaries indicates the gedrite consuming reaction ged sil spr crd extensive growth of sapphirine cordierite observed on the rim of gedrite porphyroblasts with spinel occurring as relict inclusions within the sapphirine indicates the reaction ged spl spr crd the pressure temperature p t path defined from the observed mineral assemblages and reaction texture is characterized by anticlockwise trajectory with a prograde segment of initial heating and subsequent deep burial followed by retrograde near isothermal decompression such an anticlockwise trajectory is being reported for the first time from southern india and has important tectonic implications since these rocks were developed at the leading edge of the crustal block that was involved in collisional orogeny and subsequent extension during the final phase of assembly of the gondwana supercontinent we propose that the rocks were subjected to deep subduction and rapid exhumation and the extreme thermal conditions were attained either through input from underplated mantle derived magmas or convective thinning or detachment of the lithospheric thermal boundary layer during or after crustal thickening