strain heating as a mechanism for partial melting and ultrahigh temperature metamorphism in convergent orogens implications of temperature dependent thermal diffusivity and rheology 1 we explore the importance of strain heating in ductile shear zones for production of leucogranites and high temperature metamorphism in collisional orogens with temperature dependent thermal diffusivity d and rock rheology new measurements on metamorphic rocks from the bohemian massif show that d is 1 3 mm2 s at 25 c and decreases exponentially to as low as 0 4 mm2 s at 600 c this temperature dependence causes model lithospheric geotherms to be straighter compared to geotherms calculated with a constant d using power law parameters for rheology we show that deformation of quartzite at strain rate of 3 10 13 s 1 produces 100 w m3 at 550 c and 7 w m3 at 800 c deformation of stronger clinopyroxenite at this strain rate produces 8 w m3 even at 1050 c when strain heating is introduced by a 3 km thick ductile shear zone with quartz rheology at the depth of 35 km in a lithosphere that has 70 km thick crust and 60 km thick lithospheric mantle the schist solidus is reached by 8 myr in the vicinity of the shear zone deforming at the strain rate of 3 10 13 s 1 for clinopyroxenite rheology ultrahigh temperature uht metamorphic conditions are reached in 40 myr after initiation of strain heating two dimensional models that replicate the exhumation of the greater himalaya crystalline rocks above the main central thrust produce extensive partial melting and an inverted metamorphic field gradient occurrences of leucogranites within crustal shear zone systems may be evidence of the coupling between deformation and heat production in the crust

structure and dynamics of decadal anomalies in the wintertime midlatitude north pacific ocean atmosphere system the structure and dynamics of decadal anomalies in the wintertime midlatitude north pacific ocean atmosphere system are examined in this study using the ncep ncar atmospheric reanalysis hadisst sst and simple ocean data assimilation data for 1960 2010 the midlatitude decadal anomalies associated with the pacific decadal oscillation are identified being characterized by an equivalent barotropic atmospheric low high pressure over a cold warm oceanic surface such a unique configuration of decadal anomalies can be maintained by an unstable ocean atmosphere interaction mechanism in the midlatitudes which is hypothesized as follows associated with a warm pdo phase an initial midlatitude surface westerly anomaly accompanied with intensified aleutian low tends to force a negative sst anomaly by increasing upward surface heat fluxes and driving southward ekman current anomaly the sst cooling tends to increase the meridional sst gradient thus enhancing the subtropical oceanic front as an adjustment of the atmospheric boundary layer to the enhanced oceanic front the low level atmospheric meridional temperature gradient and thus the low level atmospheric baroclinicity tend to be strengthened inducing more active transient eddy activities that increase transient eddy vorticity forcing the vorticity forcing that dominates the total atmospheric forcing tends to produce an equivalent barotropic atmospheric low pressure north of the initial westerly anomaly intensifying the initial anomalies of the midlatitude surface westerly and aleutian low therefore it is suggested that the midlatitude ocean atmosphere interaction can provide a positive feedback mechanism for the development of initial anomaly in which the oceanic front and the atmospheric transient eddy are the indispensable ingredients such a positive ocean atmosphere feedback mechanism is fundamentally responsible for the observed decadal anomalies in the midlatitude north pacific ocean atmosphere system

origin of paired high pressure ultrahigh temperature orogens a ridge subduction and slab window model introductionmetamorphism at elevated pressure temperature conditions and distinct uid regimes generates ultrahigh pres sure uhp high pressure hp andultrahigh temperature uht rocks harley 2004 brown 2006 2007 2009 kelsey 2008 santosh andomori 2008a b santos et al 2009 santosh et al 2009a zhang et al 2009 although previous studies havecorrelated these di erent orogens todistinct tectonic settings recent inves tigations record high pressure anduht conditions from the same tec tonic environment within the sameorogenic belt and in some cases evenwithin the same samples mostoftheseexamples come from major collisionalzones along which continental blocksweresuturedatdi erenttimesinearthhistory including from the neoarch ean hp uht rocks of the limpopobeltinsouthafrica tsunogaeandvanreenen 2006 the palaeoproterozoichp guo et al 2004 obrien et al 2005 and uht santosh et al 2007a b 2008 2009b belts in thenorth china craton and the hp uht belts in the neoproterozoiceastern ghats belt as well as thecambrian gondwana suture in south ern india shimpo et al 2006 tsuno gaeet al 2008a santoshet al 2009c notably the thermal regimes for thesepaired hp and uht rocks are similar 1000 c and they also share acommon uid history characterizedby co

ultrahigh temperature metamorphism followed by two stage decompression of garnet orthopyroxene sillimanite granulites from ganguvarpatti madurai block southern india the mg al granulites from ganguvarpatti consist of orthopyroxene sillimanite garnet quartz as peak assemblage with a few porphyroblasts of cordierite and sapphirine these assemblages were strongly overprinted by late symplectites and coronas orthopyroxene inclusions in garnet and porphyroblast cores have the highest xmg 0 80 and al2o3 content 10 7 wt the estimated near peak metamorphic conditions 1 000 50 c and 11 kbar using garnet orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid the proposed multi stage evolution process implies an initial decompression deduced from multi phase symplectites followed by cooling during biotite formation further late decompression is explained from the orthopyroxene rims on biotite this proposed p t path thus suggests a unique and complex evolution history for the uht granulites of southern india present results are comparable with similar adjacent terranes in the gondwana supercontinent but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain

from sediment to granite timescales of anatexis in the upper crust abstract granite formation is the culmination of a sequence of events initiated by prograde heating of the protolith and followed by formation of a grain boundary melt melt segregation into a vein network ascent of the melt through the network and finally crystallisation of the melt experimental constraints on the formation of a crustal melt from the incongruent melting of muscovite combined with geochemical studies of anatexis in the high himalaya allow the timescales required for each of these processes to be assessed discordant temperatures determined from monazite and zircon thermometry for himalayan anatectic granites indicate that at least for some intrusives the melt was undersaturated in lree implying that melts have probably been extracted in less than 10 ka experimental studies suggest that some himalayan melts are also undersaturated in zr implying segregation may have occurred within 100 years such short timescales confirm that deformation driven mechanisms are important in extracting these melts from their source the transport distances of himalayan granitic melts of 10 km may be achieved by the ascent of magma through dykes in about 1 day at such rates even the largest granite could theoretically be emplaced in 10 years crystallisation of himalayan melts involves much longer periods if emplaced as thin sheets 100 m wide a timescale of 500 years is required compared with 30 ka for single stage intrusion of the larger laccoliths for composite sheet complexes magma crystallisation rather than melt ascent comprises the rate determining step on the emplacement of the intrusion the overall timescales of melt segregation and emplacement for many orogenic granites are therefore less than 10 ka and possibly less than 1 ka in contrast the timescale required for prograde heating of the protolith is 1 ma since the melt production rate is determined by heat flow into the protolith and not by reaction kinetics for any geologically significant period we conclude that heat flow determined by both the mechanism of heating and the thermal diffusivities of crustal rocks provides the overall rate determining step of crustal anatexis

ultrahigh temperature metamorphism in madurai granulites southern india evidence from carbon isotope thermometry abstract ultrahigh temperature uht metamorphism in the madurai block of the southern indian granulite terrain has been verified using the calcite graphite isotope exchange thermometer carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 c the 13c and 18o values of calcite are homogenous implying equilibration of the isotopes during metamorphism however the 13c values of single graphite crystals show variations in the order of 1 within a hand specimen detailed isotopic zonation studies indicate that graphite preserves either the time integrated crystal growth history or reequilibrium fractionation during its cooling history the graphite cores preserve higher 13c values than the rims the fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 c which matches the petrologically inferred temperature estimates in the high

the enso related west pacific sea surface temperature gradient abstractel nino southern oscillation enso events are accompanied by an anomalous zonal sea surface temperature sst gradient over the west pacific ocean defined here as the west pacific sst gradient wpg the wpg is defined as the standardized difference between area averaged sst over the central pacific ocean nino 4 region and west pacific ocean 0 10 n 130 150 e while the direction of the wpg follows enso cycles the magnitude of the gradient varies considerably between individual el nino and la nina events in this study el nino and la nina events are grouped according to the magnitude of the wpg and tropical sst circulations and precipitation are examined for the period 1948 2011 until the 1980s the wpg showed little trend as the west and central pacific warmed at similar rates however the west pacific has recently warmed faster than the central pacific which has resulted in an increased wpg during la nina events the temporal evolution and distribution of tropical pacific sst as we

geodynamic regimes of subduction under an active margin effects of rheological weakening by fluids and melts the dynamics of subduction under an active margin are analysed by using a 2d coupled petrological thermomechanical numerical model of an oceanic continental subduction system the model includes spontaneous slab bending dehydration of the subducted crust aqueous fluid transport partial melting of both crustal and mantle rocks as well as melt extraction processes resulting in magmatic arc crust growth based on our models the following five geodynamic regimes of subduction which may potentially form at active margins are identified i stable subduction with no backarc spreading centre and without plumes in the mantle wedge ii retreating subduction with a focused backarc spreading centre and without plumes iii retreating subduction with distributed intra arc extension and trans lithospheric sedimentary plumes iv advancing subduction with underplating laterally extending sub lithospheric plumes and v stable to advancing subduction with stationary laterally limited sub lithospheric plumes transitions between these different regimes are mainly caused by the concurrence of rheological weakening effects of i aqueous fluids percolating from the subducting slab into the mantle wedge and ii melts propagating from the partially molten areas formed in the mantle wedge towards the surface the aqueous fluids mainly affect the forearc region strong fluid related weakening promotes plate decoupling and reduces subduction drag and thus results in stacking of sediments in the accretion prism in contrast reduced weakening by fluids results in strong coupling of the plates and leads to advancing collision like subduction with enhanced subduction erosion thickening of the overriding plate and large sedimentary plumes in the mantle wedge are the consequences on the other hand melts extracted from the hot regions above the slab rheologically weaken the lithosphere below the arc which thus controls overriding plate extension and shortening strong rheological weakening by melts in combination with weak plate coupling trigger retreating subduction with a pronounced backarc spreading centre also weakening of the continental lithosphere by melts extracted from trans lithospheric sedimentary plumes generate a weak channel through which these structures may be emplaced into subarc crust if there is insufficient melt related weakening plumes cannot ascend but extend horizontally and thus underplate the lithosphere

the grenville orogen explained applications and limitations of integrating numerical models with geological and geophysical data numerical models offer powerful insights into tectonic processes especially when their validity can be tested against geological and geophysical observations from natural orogenic belts here we explain some of the criteria for success in integrating orogenic models with data using examples from the grenville orogen model designs must be simplified by comparison with nature to illuminate the first order processes that control orogenic evolution which limits the extent to which model results can reproduce geological observations for the western grenville orogen observed variations in geological properties are represented by lower crustal blocks with strength decreasing from the exterior to the interior of the model go series models with this design reproduce the first order crustal architecture of the georgian bay and montreal val d or lithoprobe transects both constant convergence and stop convergence models produce similar geometries but only stop convergence models produce normal sense shear

petrology and u th pb geochronology of the sapphirine quartz bearing metapelites from rajapalayam madurai block southern india evidence for polyphase neoproterozoic high grade metamorphism abstract strongly migmatitic sapphirine bearing granulites occur as dm to m sized enclaves in garnetiferous leucogranites in the southeastern part of the madurai block mb the largest section of neoproterozoic crust in the southern granulite terrain of india sgt early mineral assemblages biotite sillimanite quartz garnet biotite quartz break down via successive dehydration melting reactions to high t and high p phase assemblages e g garnet melt orthopyroxene sillimanite melt orthopyroxene cordierite melt melt consuming reactions along the retrograde path led to partial resorption of garnet to orthopyroxene sillimanite orthopyroxene sapphirine and or orthopyroxene cordierite as well as orthopyroxene sillimanite assemblages to cordierite biotite quartz symplectites the occurrence of uht metamorphism is indicated by the presence of small inclusions of sapphirine quartz intergrowths in garnet this reaction sequence is interpreted in a kfmash partial petrogenetic grid taking both melt producing and melt consuming reactions into account which yields a clockwise heating cooling decompression p t path culminating at 8 11 kbar and 1000 1100 c in situ u th pb monazite dating has been performed to more precisely constrain the ages given by chemical electron microprobe on monazite in various textural positions monazite inclusions in garnet often yield a bimodal distribution of early 950 850 ma and late neoproterozoic 600 500 ma ages which is in good agreement with the results of u pb and epma zircon dating in other places of the southeastern madurai block by contrast monazite inclusions in other mafic minerals orthopyroxene cordierite biotite or as interstitial phase exclusively yield ages between 550 and 480 ma the early neoproterozoic population is interpreted to reflect the timing of migmatisation and peak uht metamorphism whereas the late neoproterozoic ages are inferred to date cooling and exhumation with granitic magmas to a higher crustal level of the madurai block

the leading mode of observed and cmip5 enso residual sea surface temperatures and associated changes in indo pacific climate abstractssts in the western pacific ocean have tracked closely with cmip5 simulations despite recent hiatus cooling in the eastern pacific this paper quantifies these similarities and associated circulation and precipitation variations using the first global 1900 2012 enso residual empirical orthogonal functions eofs of 35 variables observed ssts 28 cmip5 sst simulations simple ocean data assimilation soda 25 70 and 171 m ocean temperatures and sea surface heights sshs and twentieth century reanalysis version 2 20crv2 surface winds and precipitation while estimated independently these leading eofs across all variables fit together in a meaningful way and the authors refer to them jointly as the west pacific warming mode wpwm wpwm sst eofs correspond closely in space and time their spatial patterns form a western v extending from the maritime continent into the extratropical pacific their temporal principal components pcs have increased rapidly since 1990 this increase has be

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

compounding effects of warm sea surface temperature and reduced sea ice on the extreme circulation over the extratropical north pacific and north america during the 2013 2014 boreal winter unprecedented atmospheric circulations with extreme weather were observed in the extratropical northern hemisphere during the winter of 2013 2014 the anomalous circulations were the manifestation of the pacific pattern or the north pacific oscillation western pacific pattern but with extremely large amplitude simulation results suggest that the anomalous atmospheric circulations were constructively induced by anomalous sea surface temperature in the tropical pacific and extratropical north pacific as well as the low sea ice concentration in the arctic natural variability played a major role in inducing the anomaly pattern whereas the anomalously warm sea surface temperature and low arctic sea ice concentration in the bering sea contributed to the intensity if the anthropogenic warming has a significant impact on causing the synchronization of the aforementioned anomalies in sea surface temperature and sea ice concentration and this trend continues severe winters similar to that in 2013 2014 may occur more frequently in the future

near isothermal conditions in the middle and lower crust induced by melt migration simple one dimensional thermal models that include the effects of melt migration have been developed the models show that long lived plutonism results in a quasi steady state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust the thermal structure of the crust strongly influences deformation metamorphism and plutonism1 2 3 models for the geothermal gradient in stable crust predict a steady increase of temperature with depth this thermal structure however is incompatible with observations from high temperature metamorphic terranes exhumed in orogens1 4 5 6 global compilations7 of peak conditions in high temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure for both isothermal decompression and isobaric cooling paths here we develop simple one dimensional thermal models that include the effects of melt migration these models show that long lived plutonism results in a quasi steady state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust the models also predict that the upward advection of heat by melt generates granulite facies metamorphism and widespread andalusite sillimanite metamorphism in the upper crust once the quasi steady state thermal profile is reached the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions thus setting the stage for gravitational collapse8 exhumation and isothermal decompression after the onset of plutonism near isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that in part control the shape of the geotherm

observational analysis of extratropical cyclone interactions with northeast pacific sea surface temperature anomalies abstractthis study examines the interaction between a northeast pacific upper ocean thermal anomaly and individual fall storm events between 2013 2016 in 2013 a large upper ocean thermal anomaly

the interpretation of inverted metamorphic isograds using simple physical calculations several zones of major thrust faulting exhibit a juxtaposition of rocks of higher metamorphic grade over rocks of lower grade this configuration may indicate but does not require that temperature gradients were temporarily inverted near the fault we examine the physical conditions under which such a temperature inversion could occur the overthrusting of hotter rock on colder rock can cause a temporarily inverted gradient both above and below the fault only if the time taken to underthrust rock from the land surface to a given depth z on the fault is less than times the characteristic time for diffusion of heat through the block above the fault where is thermal diffusivity an inverted gradient cannot form without heat generation in the fault zone unless v z sin 100 where v is the rate of underthrusting in millimeters per year z is in kilometers and is the dip of the fault this simple criterion is sufficient to demonstrate that several examples of inverted metamorphic gradients cannot be explained simply by the thrusting of hot on cold rock without heat sources in the fault zone dissipative heating accompanying deformation can cause an inverted temperature gradient within and beneath the thrust zone but whereas the overthrusting of hot upon cold rocks cools the fault zone dissipation heats it thus the overthrusting of hot on cold rock and dissipative heating affect the temperature gradient and the maximum temperatures differently we show that the magnitudes of the inverted temperature gradient and of the maximum temperature above the inverted gradient yield independent estimates of the rate of dissipative heating discrepancy between these estimates implies that some additional process must have occurred such as the post thrusting disruption of the isograds if there is such a discrepancy the maximum temperature probably provides the more reliable estimate of the rate of heating at the fault we illustrate this analysis by applying it to reported inverted metamorphic zonation in the pelona schist the st anthony complex the mt everest region of the main central thrust and the olympos thrust petrological inferences of maximum temperatures depths of metamorphism and magnitudes of apparent inverted gradients imply that shear stresses of about 100 mpa accompanied thrust faulting in some of these regions and that some zones of inverted metamorphism have been tectonically thinned after the metamorphism occured

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

isolating the atmospheric circulation response to arctic sea ice loss in the coupled climate system abstractin this study coupled ocean atmosphere land sea ice earth system model esm simulations driven separately by sea ice albedo reduction and by projected greenhouse dominated radiative forcing are combined to cleanly isolate the sea ice loss response of the atmospheric circulation a pattern scaling approach is proposed in which the local multidecadal mean atmospheric response is assumed to be separately proportional to the total sea ice loss and to the total low latitude ocean surface warming the proposed approach estimates the response to arctic sea ice loss with low latitude ocean temperatures fixed and vice versa the sea ice response includes a high northern latitude easterly zonal wind response an equatorward shift of the eddy driven jet a weakening of the stratospheric polar vortex an anticyclonic sea level pressure anomaly over coastal eurasia a cyclonic sea level pressure anomaly over the north pacific and increased wintertime precipitation over the west coast of north america many

geochemistry of granitic melts produced during the incongruent melting of muscovite implications for the extraction of himalayan leucogranite magmas granites formed from the incongruent melting of muscovite preserve evidence of chemical disequilibrium both between restite and melt and within individual phases during crystallization miocene leucogranites from the himalayas exemplify melt formation from a pelitic source through muscovite breakdown trace elements rb sr and ba reside almost entirely in micas and feldspars in the protolith and therefore are appropriate for quantitative modeling equilibrium between melt and restite was established for sr under fluid phase absent conditions but some disequilibrium is suggested by rb abundances consistent with known diffusion rates for these elements abundances of zr and ce in the granites which provide essential structural constituents of the accessory phases zircon and monazite indicate that the himalayan granite melts were saturated in these elements if formed at temperatures of 670 700 c but slightly undersaturated if formed at somewhat higher temperatures ion microprobe traverses of y and heavy rare earth element abundances across single garnets from himalayan leucogranites provide evidence for disequilibrium between melt and phenocryst during garnet growth thus constraining the evolution of magmatic compositions during melt formation and crystallization in some cases progressive melting of the protolith and crystallization of garnet from the melt appear to have been concomitant indicating that minimum solidus temperatures were maintained throughout the melting event this suggests that thermal buffering rather than melt extraction provided the rate determining step in magma evolution

pacific sea surface temperature and the winter of 2014 it is shown from historical data and from modeling experiments that a proximate cause of the cold winter in north america in 2013 2014 was the pattern of sea surface temperature sst in the pacific ocean each of the three dominant modes of sst variability in the pacific is connected to the tropics and has a strong expression in extratropical sst and weather patterns beginning in the middle of 2013 the third mode of sst variability was two standard deviations positive and has remained so through january 2015 this pattern is associated with high pressure in the northeast pacific and low pressure and low surface temperatures over central north america a large ensemble of model experiments with observed ssts confirms that sst anomalies contributed to the anomalous winter of 2014

on the role of tropical ocean forcing of the persistent north american west coast ridge of winter 2013 14a abstractthe causes of the high pressure ridge at the north american west coast during winter 2013 14 the driest winter of the recent california drought are examined the ridge was part of an atmosphere ocean state that included anomalies defined relative to a 1979 2014 mean of circulation across the northern hemisphere warm sea surface temperatures ssts in the tropical western and northeastern pacific and the south indian ocean and cool ssts in the central tropical pacific the sst anomalies differ sufficiently between datasets that when used to force atmosphere models the simulated circulation anomalies vary notably in realism recognizing uncertainty in the sst field the authors use idealized tropical sst anomaly experiments to identify an optimal combination of sst anomalies that forces a circulation response that best matches observations the optimal sst pattern resembles that observed but the associated circulation pattern is much weaker than observed suggesting an important but limited

hot orogens and supercontinent amalgamation a gondwanan example from southern india abstract the southern granulite terrane in southern india preserves evidence for regional scale high to ultrahigh temperature metamorphism related to the amalgamation of the supercontinent gondwana here we present accessory mineral zircon and monazite geochronological and geochemical datasets linked to the petrological evolution of the rocks as determined by phase equilibria modelling the results constrain the duration of high to ultrahigh temperature 900 c metamorphism in the madurai block to be c 40 ma with peak conditions achieved c 60 ma after the formation of an orogenic plateau related to the collision of the microcontinent azania with east africa at c 610 ma a 1d numerical model demonstrates that the attainment of temperatures 900 c requires that the crust be moderately enriched in heat producing elements and that the duration of the orogenic event is sufficiently long to allow conductive heating through radioactive decay both of these conditions are met by the available data for the madurai block our results constrain the length of time it takes for the crust to evolve from collision to peak p t i e the prograde heating phase then back to the solidus during retrogression this evolution illustrates that not all metamorphic ages date sutures

aftershocks triggered by fluid intrusion evidence for the aftershock sequence occurred 2014 in west bohemia vogtland the west bohemia vogtland region central europe is well known for its repeating swarm activity however the latest activity in 2014 although spatially overlapping with previous swarm activity consisted of three classical aftershock sequences triggered by ml3 5 4 4 and 3 5 events to decode the apparent system change from swarm type to mainshock aftershock characteristics we have analyzed the details of the major ml4 4 sequence based on focal mechanisms and relocated earthquake data our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane unfavorably oriented to the regional stress field most of its intense aftershock activity occurred in plane with classical characteristics such as i the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and ii the decay can be well fitted by the omori utsu law however the absolute number of aftershocks and the fitted omori utsu c and p parameters are much larger than for typical sequences by means of the epidemic type aftershock sequence model we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log t thus we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks the migration patterns and the exponential decrease of the aseismic signal

remote linkages to anomalous winter atmospheric ridging over the northeastern pacific severe drought in california between 2013 and 2016 has been linked to the multi year persistence of anomalously high atmospheric pressure over the northeastern pacific ocean which deflected the pacific storm track northward and suppressed regional precipitation during california s winter rainy season multiple hypotheses have emerged regarding why this high pressure ridge near the west coast of north america was so resilient including unusual sea surface temperature patterns in the pacific ocean reductions in arctic sea ice random atmospheric variability or some combination thereof here we explore relationships between previously documented atmospheric conditions over the north pacific and several potential remote oceanic and cryospheric influences using both observational data and a large ensemble of climate model simulations our results suggest that persistent wintertime atmospheric ridging similar to that implicated in california s 2013 2016 drought can at least partially be linked to unusual pacific sea surface temperatures and that pacific ocean conditions may offer some degree of cool season foresight in this region despite the presence of substantial internal variability

ultrahigh temperature stability of sapphirine and kornerupine in ganguvarpatti granulite madurai block southern india

causes of extreme ridges that induce california droughts abstractcalifornia droughts are often caused by high amplitude and persistent ridges near and off the west coast of north america without apparent connections with enso here with a hierarchy of climate models it is demonstrated that extreme ridges in this region are associated with a continuum of zonal wavenumber 5 circumglobal teleconnection patterns that originate from midlatitude atmospheric internal dynamics although tropical diabatic heating anomalies are not essential to the formation and maintenance of these wave patterns certain persistent heating anomalies may double the probability of ridges with amplitudes in the 90th percentile occurring on interannual time scales those heating anomalies can be caused by either natural variability or possibly by climate change and they do not necessarily depend on enso the extreme ridges that occurred during the 2013 14 and 2014 15 winters could be examples of ridges produced by heating anomalies that are not associated with enso this mechanism could p

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

contrasting styles of phanerozoic and precambrian continental collision abstract there are differences in the style of collisional orogens between the phanerozoic and the precambrian most notably the appearance of blueschists and ultrahigh pressure metamorphic uhpm rocks in the geological record since the late neoproterozoic whereas these rocks are absent from older orogens understanding collisional orogenesis in the context of present day values for ambient upper mantle temperature and radiogenic heat production provides a reference from which to extrapolate back to conditions in the precambrian to evaluate differences in the way phanerozoic and precambrian collisional orogens develop a series of experiments was run using a 2 d petrological thermomechanical numerical model in which the collision of spontaneously moving continental plates was simulated for values of ambient upper mantle temperature and radiogenic heat production increasing from those appropriate to the present day thus models of modern collisional orogens involving different modes of exhumation of uhpm rocks were extrapolated back to conditions appropriate for the precambrian based on these experiments an increase of the ambient upper mantle temperature to 80 100 k above the present day value leads to two distinct modes of collision that are different from the modern collision regime and for which the terms truncated hot collision regime strong mafic lower continental crust and two sided hot collision regime weak felsic lower continental crust are proposed some proterozoic orogens record post extension thickening to generate counter clockwise metamorphic p t paths followed by slow close to isobaric retrograde cooling such as occurred in the paleoproterozoic khondalite belt in the north china craton and the late mesoproterozoic early neoproterozoic eastern ghats province part of the eastern ghats belt of peninsular india these orogens have similarities with the truncated hot collision regime in the numerical models assuming subsequent shortening and thickening of the resulting hot lithosphere other proterozoic orogens are characterized by clockwise looping metamorphic p t paths and extensive granite magmatism derived from diverse crustal and subcontinental lithospheric mantle sources these orogens have similarities with the two sided hot collision regime in the numerical models both regimes are associated with shallow slab breakoff that precludes the formation of uhpm rocks the temperature of the ambient upper mantle where this transition in geodynamic regimes occurs corresponds broadly to the neoproterozoic era

orogeny and metamorphism a model for deformation and pressure temperature time paths with applications to the central and southern appalachians a model is presented for deformation uplift and exhumation in convergent orogens based on the following premises 1 foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen 2 the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton on the seaward side of this transition up to 20 km of overthrusts can be accumulated without creating topography 3 critical shape theory can be applied to orogens as a whole allowing predictions to be made concerning dynamic balance between mass addition and loss uplift exhumation and growth of topography and 4 pressure temperature time p t t data can be used to reconstruct particle paths within the deforming orogen three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition as monitored by the foreland rapid exhumation of metamorphic terranes is most likely in the steady state where erosion balances accretion a constructive state where mass addition is greater than mass loss results in crustal thickening and initially little exhumation a destructive state where mass loss outweighs mass addition results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension p t t data on peak metamorphism pluton emplacement uplift exhumation and cooling can be used in conjunction with data from the foreland to distinguish among these various states the topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen application of this model to the central and southern appalachians suggests that during the constructive phases of the taconian and acadian orogenies overthrust loads accumulated mainly on the seaward side of the ocean continent transition as marked by the bouguer gravity gradient between the acadian and alleghanian orogenies the appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton the constructive stage of the alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton this resulted in widespread uplift and westward transport of older metamorphic rocks post orogenic unroofing of the southern appalachians is compatible with the predictions of flexural models the post orogenic unroofing history of the central appalachians and ouachitas probably reflects mesozoic extension in these areas

models of large hot orogens containing a collage of reworked and accreted terranes we describe a classification scheme for orogens using temperature magnitude t m diagrams and use this framework for modelling large hot orogens that evolve in continents comprising cratonic nuclei bordered by a series of juvenile accreted reworked and metamorphosed terranes modelling the complete evolution of an orogen is difficult particularly large orogens with multiple orogenic phases early phases during which a continent is assembled produce a tectonic and metamorphic fabric that needs to be taken into account when modelling the main collisional orogeny this inherited fabric is represented in a simple way in models described here by a series of lower crustal blocks that are arranged to be systematically stronger toward the cratonic continental interiors we investigate how this fabric influences the development of the model orogen during the main collisional phase using upper mantle scale ums and crustal scale cs finite element models the models exhibit a diachronous three phase evolutio