zircon u pb chronology of the jianping complex implications for the precambrian crustal evolution history of the northern margin of north china craton abstract the neoarchean to paleoproterozoic jianping complex in the western liaoning province is an important component of the precambrian basement of the north china craton this region connects the neoarchean fengning chengde complex in the west the neoarchean to paleoproterozoic north chaoyang complex in the northeast and the yixian fuxin archean greenstone belt in the east the precambrian jianping complex is dominantly composed of metamorphosed supracrustal sequence and dioritic to granitoid gneisses tonalite trondhjemite granodiorite ttg here we present results from la icpms zircon u pb isotope dating from the various lithological units in this complex which reveal that the magmatic precursors of the metavolcanic rocks associated with the supracrustal sequence were generated during 2555 2550 ma and up to 2615 ma a major magmatic pulse of dioritic to granitic suite occurred during 2538 to 2495 ma this was followed by ca 2485 ma granulite facies metamorphism and a retrograde event at ca 2450 2401 ma our data also reveal a major charnockite emplacement event in this region at ca 1694 ma integrating our new results with the available geologic and previous geochronological data we identify three major growth stages in the crustal evolution history of the northern margin of the eastern continental block of the north china craton at ca 2550 2495 ma ca 2403 2394 ma and ca 1700 ma the la icp ms zircon data provide new insights on the neoarchean to paleoproterozoic tectonothermal evolution history in the northern margin of the eastern continental block of the north china craton

ultrahigh temperature metamorphism under isobaric heating new evidence from the north china craton abstract the khondalite belt within inner mongolia suture zone imsz in the north china craton ncc preserves evidence for extreme crustal metamorphism under ultra high temperature uht conditions at ca 1 92 ga associated with the subduction collision tectonics between the yinshan and ordos blocks here we report a new locality in hongsigou where cordierite and spinel bearing granulites record uht metamorphism the prograde peak and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as bt1 grt1 sil1 kfs1 pl1 ilm qtz1 grt1 sil2 kfs2 pl2 spl ilm qtz2 liq and crd grt2 sil3 kfs2 pl2 ilm qtz2 respectively the peak metamorphic conditions of the pelitic granulite were estimated as 930 1050 c and 6 5 7 5 kbar based on pseudosection analysis in the system nckfmashto suggesting extreme thermal metamorphism we report la icpms zircon u pb data from the granulite which show weighted mean 207pb 206pb age of 1881 6 6 ma marking the timing of uht metamorphism lu hf analyses of the zircons show ehf t values within a restricted range of 4 2 to 0 3 and together with hf model ages a paleoproterozoic arc magmatic source is inferred for the detrital zircons the estimated p t path for the uht granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory different from the anti clockwise p t paths defined in earlier studies for the 1 92 ga uht rocks from the imsz the younger age and the isobaric heating trajectory suggest that the hongsigou uht rocks are related to heat input from underplated mafic magmas following continental collision

multiple mafic magmatic and high grade metamorphic events revealed by zircons from meta mafic rocks in the daqingshan wulashan complex of the khondalite belt north china craton abstract meta mafic rocks in the daqingshan wulashan complex in the central segment of the paleoproterozoic khondalite belt of the north china craton are composed predominantly of garnet bearing mafic granulites mafic granulites and amphibolites they occur mainly as irregular lenses and as a set of deformed dyke sill swarms within dioritic granitic orthogneisses and al rich paragneisses an integrated study involving laser raman and scanning electron microscope analyses of mineral inclusions from zircons cathodoluminescence imaging and la icp ms u pb dating of zircons shows that magmatic zircons in these meta mafic rocks record four age groups of 2500 2450 2300 2100 1970 1930 and ca 1850 ma indicating multiple mafic magmatic events occurred within the daqingshan wulashan complex in addition four groups of metamorphic zircons with ages of ca 2450 ca 1950 ca 1900 and ca 1850 ma are present within these meta mafic rocks zircons of the first oldest group contain medium to low pressure mlp granulite facies mineral inclusions of orthopyroxene clinopyoxene amphibole plagioclase quartz and yield ages of ca 2450 ma representing the timing of the early mlp granulite facies metamorphic event within the daqingshan wulashan reworked basement complex in contrast zircons of the second group are free of mineral inclusions and yield ages of ca 1950 ma which is considered to be the timing of the regional high grade metamorphic and structural event probably caused by the collision of the yinshan and ordos blocks zircons of the third group contain mlp granulite facies mineral inclusions of orthopyroxene clinopyoxene amphibole plagioclase quartz similar to the zircons of the first group but yield younger ages of ca 1900 ma interpreted as the timing of the regional mlp granulite facies metamorphism that most likely occurred during the early stage of post orogenic exhumation of the daqingshan wulashan complex zircons of the fourth group contain mlp amphibolite facies mineral inclusions of clinopyoxene amphibole plagioclase quartz and yield the youngest ages of ca 1850 ma which probably represent the timing of the regional amphibolite facies metamorphism during the late stage of post orogenic exhumation of the daqingshan wulashan complex combined with previous geological data of the khondalite belt it is speculated that the multiple mafic magmatism and contemporaneous high grade metamorphism of the daqingshan wulashan complex from the khondalite belt were most likely generated by an orogenic process involving early subduction collision and late exhumation in an active continental margin arc

metamorphic p t paths and zircon u pb ages of archean ultra high temperature paragneisses from the qian an gneiss dome east hebei terrane north china craton

geochronology and trace element geochemistry of zircon monazite and garnet from the garnetite and or associated other high grade rocks implications for palaeoproterozoic tectonothermal evolution of the khondalite belt north china craton abstract it is well documented that the khondalite belt of the north china craton formed by the collision of the yinshan and ordos blocks during ca 1 95 ga but the onset of the post collisional exhumation stage has not been well dated the garnetite and garnet bearing quartz rich lens that are regarded as residue melt phases occur occasionally in the foliated metasedimentary rocks in the jining terrane of the khondalite belt they are free of regional gneissosity and may be generated during the post collisional exhumation stage zircon u pb dating monazite chemical dating and trace element analyses of zircon monazite and garnet have been carried out on the garnetites and associated other high grade metamorphic rocks the geochronological results reveal a major age group of ca 1890 ma from the zircon grains overgrowths and inclusion type monazites within the garnet poikiloblasts in the garnetites the trace elements analyses show that zircon hosted in the mantle of the garnet poikiloblasts in the garnetite contains the highest hree and y contents whereas zircon hosted in the garnet rims shows higher hree and y contents than matrix zircon grains inclusion type monazite in the garnetite shows higher lan smn ratio than matrix monazite grains large garnet poikiloblasts in the garnetite exhibit bell shaped hree and y zoning profiles attributed to rayleigh fractionation during their growth compared to garnet poikiloblasts coronal garnet shows higher gro cr and li contents but lower xmg sm hree zn and zr contents and weaker eu negative anomalies reflecting their different formation environments based on evidences from microstructural analyses ree concentrations and patterns hree partition coefficients and the ti in zircon thermometer it is proposed that most of the zircon grains overgrowths in the garnetite formed coevally with garnet poikiloblasts consequently ca 1890 ma represents the timing of garnet poikiloblast growth during the partial melting of the protolith coronal garnet or zn rich spinel plus cordierite coupled with the matrix type monazite formed after garnet poikiloblasts growth during near isothermal decompression given the high metamorphic temperature and pressure revealed by the garnetite 820 850 c and up to 950 c 8 5 9 5 kbar it is suggested that the ca 1890 ma age group represents the beginning of extension exhumation event in the khondalite belt which is also recorded in the associated other high grade rocks such as the garnet bearing quartz rich lenses sillimanite garnet bearing quartzo feldspathic gneisses garnet bearing quartzo feldspathic gneisses and a pure quartz vein

a possible new mechanism for northward propagation of boreal summer intraseasonal oscillations based on trmm and merra reanalysis boreal summer intraseasonal oscillations bsisos manifest in the active and break spells and act as the primary building block of the indian summer monsoon although recent research has evolved a basic framework for understanding the scale selection and northward propagation of the bsiso the role of different hydrometeors in modulating these processes remains poorly explored in this study trmm 2a12 retrievals and modern era retrospective analysis for research and applications reanalysis data are examined to establish relationship between cloud hydrometeors and other atmospheric dynamical parameters with the northward propagation of the bsisos the study reveals that the cloud liquid water leads the deep convection during the northward propagation of bsisos in the lower troposphere while the cloud ice slightly lags the convection this distribution indicates the occurrence of a possible mechanism of the lower level moistening through the large scale moisture advection in lower atmosphere and boundary layer pbl convergence followed by triggering of the deep convection the analyses of moisture advection and the dynamical fields with respect to the convection center show that low level moistening is a manifestation of the barotropic vorticity and pbl convergence of moisture anomaly north of the convection center a new internal dynamical thermodynamical mechanism is unraveled to understand the reason behind the middle tropospheric heating maximum and its role on the northward propagation it is shown that the enhanced moisture perturbation in lower levels together with the heat transport by the sub grid scale eddies within the pbl induces lower level instability required to precondition the lower atmosphere for triggering the deep convection vigorous upward motion inside the deep convection uplifts the liquid hydrometeors to upper levels and the formation of precipitable ice leads to the heating maxima in the middle troposphere to check the robustness of the proposed hypothesis similar analysis is performed for the weak northward propagating bsiso cases

duration of igneous activity in the sesia magmatic system and implications for high temperature metamorphism in the ivrea verbano deep crust abstract the ivrea verbano zone and serie dei laghi of northern italy constitute a virtually complete section of the adriatic continental crust which was intruded at different levels by coeval magmas of permo carboniferous age collectively referred to as the sesia magmatic system at the deepest levels of the section the relationship between magmatic underplating and granulite facies metamorphism in the ivrea verbano zone may be studied we present new zircon u pb age data which significantly extend the record of igneous activity in this terrane and which demonstrate that igneous pulses began intruding the deep and middle crust no later than 314 ma an age corresponding to that inferred for regional granulite facies metamorphism and predating by more than 20 m y the well documented main magmatic pulse at about 292 to 282 ma a gap in age information from 316 3 ma to 276 4 ma observed in the deep crustal granulite facies paragneiss of the ivrea verbano zone overlaps a gap from circa 314 to 283 ma between igneous and reset zircons in a closely associated mafic ultramafic sill however zircon ages demonstrate intrusive activity in the middle and upper crust during this time gap we infer that prolonged maintenance of temperatures above zircon saturation in the deep crustal paragneiss could explain the gap in zircon ages in those rocks viewed in this light a gap in a geochronological record within high grade terranes might not necessarily mean an absence of events but instead may record the occurrence and duration of a thermal peak

the mamonia complex sw cyprus revisited remnant of late triassic intra oceanic volcanism along the tethyan southwestern passive margin upper triassic volcanic and sedimentary rocks of the mamonia complex in southwestern cyprus are exposed in erosional windows through the post cretaceous cover where the mamonia complex is tectonically imbricated with the troodos and akamas ophiolitic suites most of these upper triassic volcanic rocks have been considered to represent remnants of triassic oceanic crust and its associated seamounts new nd and pb isotopic data show that the whole mamonia volcanic suite exhibits features of oceanic island basalts oib four rock types have been distinguished on the basis of the petrology and chemistry of the rocks volcanism began with the eruption of depleted olivine tholeiites type 1 and oceanic island tholeiites type 2 associated with deep basin siliceous and or calcareous sediments the tholeiites were followed by highly phyric alkali basalts type 3 interbedded with pelagic halobia bearing limestones or white reefal limestones strongly lree enriched trachytes type 4 were emplaced during the final stage of volcanic activity nd and pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts the trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions this is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes the correlations observed between incompatible elements nb th and varepsilon nd and pb isotopic initial ratios suggest that the mamonia suite was derived from the mixing of a depleted mantle dmm and an enriched component of high 238u 204pb himu type models using both nd and pb isotopic initial ratios suggest that the depleted tholeiites type 1 derived from a dmm source contaminated by an enriched mantle type 2 component em2 and that the oceanic tholeiites type 2 alkali basalts type 3 and trachytes type 4 were derived from the mixing of the enriched mantle source of the depleted tholeiites with a himu component none of the mamonia volcanic rocks show evidence of crustal contamination the upper triassic within plate volcanism likely erupted in a small southerly neotethyan basin located north of the eratosthenes seamount and likely floored by oceanic crust

mjo signals in latent heating results from trmm retrievals abstract four tropical rainfall measuring mission trmm datasets of latent heating were diagnosed for signals in the madden julian oscillation mjo in all four datasets vertical structures of latent heating are dominated by two components one deep with its peak above the melting level and one shallow with its peak below profiles of the two components are nearly ubiquitous in longitude allowing a separation of the vertical and zonal temporal variations when the latitudinal dependence is not considered all four datasets exhibit robust mjo spectral signals in the deep component as eastward propagating spectral peaks centered at a period of 50 days and zonal wavenumber 1 well distinguished from lower and higher frequency power and much stronger than the corresponding westward power the shallow component shows similar but slightly less robust mjo spectral peaks mjo signals were further extracted from a combination of bandpass 30 90 day filtered deep and shallow components largest amplitudes of bo

composite nature of the north china granulite facies belt tectonothermal and geochronological constraints granulite facies rocks are intermittently exposed in a roughly e w trending belt that extends for approximately 2000 km across the north china craton from the helanshan qianlishan wulashan daqingshan guyang and jining complexes in the western block through the huai an hengshan xuanhua and chengde complexes in the trans north china orogen to the jianping western liaoning eastern hebei northern liaoning and southern jilin complexes in the eastern block the belt is generally referred to as the north china granulite facies belt previously interpreted as the lowest part of an obliquely exposed crust of the north china craton recent data indicate that the north china granulite facies belt is not a single terrane instead it represents components of three separate terranes the eastern and western blocks and trans north china orogen each of these units records different metamorphic histories and reflect the complex tectonic evolution of the ncc during the late archean and paleoproterozoic mafic granulites in the eastern block and the yinshan terrane western block underwent medium pressure granulite facies metamorphism at about 2 5 ga with anticlockwise p t paths involving near isobaric cooling following peak metamorphism reflecting an origin related to intrusion and underplating of mantle derived magmas pelitic granulites in the khondalite belt western block underwent medium pressure granulite facies metamorphism at about 2 0 1 9 ga with clockwise p t paths which record the paleoproterozoic amalgamation of the yinshan and ordos terranes to form the western block mafic and pelitic granulites in the trans north china orogen experienced high to medium pressure granulite facies metamorphism at 1 85 ga with clockwise p t paths involving nearly isothermal decompression following peak metamorphism which are in accord with the final collision between the eastern and western blocks to form the north china craton at 1 8 ga the ncgb cannot therefore represent a separate unique terrane instead it reflects the amalgamation of three separate granulite terranes that evolved independently and at different times d 2005 international association for gondwana research published by elsevier b v all rights reserved

role of stratiform heating on the organization of convection over the monsoon trough it has been recently demonstrated that stratiform heating plays a critical role in the scale selection of organized tropical convection in an aquaplanet version of a coarse resolution atmospheric general circulation model coupled to a stochastic multicloud cumulus parameterization scheme it is shown that madden julian oscillation like organization dominates when the model is tuned to produce strong and long lived stratiform heating while it gives rise to mostly convectively coupled waves in the case of weak and short lived stratiform clouds the study is extended here to the case of an asymmetric forcing mimicking the migration of the intertropical convergence zone itcz during summer to understand the impact of changes in stratiform heating on the monsoon dynamics consistent with the equatorial itcz case strong and long lived stratiform heating promotes northward and eastward moving intraseasonal disturbances while weak and short lived stratiform heating yields mostly westward propgating synoptic scale low pressure systems moreover the underlying intraseasonal versus low pressure system activity seems to impact the strength and extend of the monsoon trough mt in the regime with intraseasonal activity the mt is much stronger and extends northward while in the low pressure system case mt is some what weaker in strength but extends further westward in the low pressure dominated regime the background vorticity and zonal wind profiles over the monsoon trough are consistent with the observations

coupling between northward propagating intraseasonal oscillations and sea surface temperature in the indian ocean using a hybrid atmosphere ocean coupled model it is shown that during the boreal summer northwardpropagating intraseasonal oscillations npisos are strongly coupled to the underlying sea surface temperature sst in the indian ocean sector on the one hand the intraseasonal atmospheric convection changes the sst through solar radiation latent heat flux and mixed layer entrainment on the other the induced sst fluctuations feed back to affect the intraseasonal convection the preferential northward rather than southward propagation of boreal summer isos in the indian ocean is partially explained by an interaction among the summer mean climate state the atmospheric disturbances and the ocean surface temperature a solution to an atmosphere only model forced with daily sst produces much stronger npisos than a similar solution forced with monthly mean sst amip type run the atmosphere only model however even when it is forced by daily sst from the coupled model with a small amount of noise in the initial and or boundary conditions is unable to reproduce the npisos in the coupled case in the coupled system intraseasonal sst anomalies are forced by intraseasonal atmospheric convection and hence are in quadrature with the convection in the stand alone atmospheric model however sst acts only as a boundary forcing and the resultant atmospheric convection has almost the same phase with the underlying sst one consequence is that the intensity of the sst forced intraseasonal convection in the stand alone atmospheric model is considerably weaker than in the coupled model finally solutions indicate that the northward movement of the off equatorial convection in the northern indian ocean is more closely related to local intraseasonal sst anomalies than to the equatorial eastward moving madden julian oscillation positive negative sst anomalies in the northern indian ocean lead the active break phases of the intraseasonal convection by about 2 pentads 10 days therefore intraseasonal sst anomalies in the northern indian ocean are potentially a useful index to forecast active break spells of the south asian summer monsoon

the relationship between anomalous presummer extreme rainfall over south china and synoptic disturbances a spectral analysis of daily rainfall data has been performed to investigate extreme rainfall events in south china during the presummer rainy seasons between 1998 2015 excluding 1999 2006 2011 and 2014 the results reveal a dominant frequency mode at the synoptic scale with pronounced positive rainfall anomalies by analyzing the synoptic scale bandpass filtered anomalous circulations 24 extreme rainfall episodes defined as those with a daily rainfall amount in the top 5 are categorized into cyclone 15 and trough 8 types with the remaining events as an anticyclone type according to the the primary anomalous weather system contributing to each extreme rainfall episode the 15 cyclone type episodes are further separated into 11 lower and 4 upper tropospheric migratory anomalies an analysis of their anomalous fields shows that both types could be traced back to the generation of cyclonic anomalies downstream of the tibetan plateau except for two episodes of lower tropospheric migratory anomalies originating over the south china sea however a lower tropospheric cyclonic anomaly appears during all phases in the former type but only in the wettest phase in the latter type with its peak disturbance occurring immediately beneath an upper level warm anomaly the production of extreme rainfall in the trough type episodes is closely related to a deep trough anomaly extending from an intense cyclonic anomaly over north china which in turn could be traced back to a mid latitude rossby wave train passing by the tibetan plateau the results have important implications for understanding the origin structure and evolution of synoptic disturbances associated with the pre summer extreme rainfall in south china

late paleoproterozoic tectono thermal event in the northwestern north china craton evidence from u pb dating and o hf isotopic compositions of zircons from metasedimentary rocks north of hohhot city inner mongolia northern china abstract the khondalite belt is located in the northwestern north china craton and contains late paleoproterozoic metasedimentary rocks that generally underwent high grade metamorphism only a few supracrustal sequences experienced low grade metamorphism such as the meidaizhao sequence in the daqingshan area the erdaowa sequence north of hohhot city inner mongolia is another late paleoproterozoic supracrustal unit showing relatively low grade metamorphism compared with the adjacent metapelitic khondalites it is composed of metavolcanic as well as clastic metasedimentary rocks and marble it was traditionally subdivided into the halaqin and hongshangou formations we undertook an integrated study of u pb zircon dating and o hf isotopic analysis combined with whole rock chemistry on metasedimentary rocks of the erdaowa sequence in order to understand the relationship between the low and high grade rocks and their tectono thermal history in the khondalite belt cores and metamorphic domains of detrital zircons from a two mica schist of the halaqin formation have 207 pb 206 pb ages of 2 0 and 1 86 ga 18 o values of 6 69 9 45 and 6 68 12 15 and hf t values of 7 7 to 16 2 and 3 3 to 20 9 respectively a recrystallized core fir tree domain and altered domain of zircon from a grt st ky two mica gneiss have 207 pb 206 pb ages of 2 0 ga 1 88 ga and 1 86 ga 18 o values of 12 10 12 75 11 57 12 65 and 11 57 12 27 and hf t values of 0 7 to 5 4 2 0 to 4 7 and 2 0 to 0 5 respectively these data limit the time of deposition of the sedimentary rocks between 2 0 and 1 88 ga and show a high maturity similar to khondalites of the same sequence compared with previous studies we infer that the erdaowa sequence consists of rocks of different origins and metamorphic grades including khondalites which were brought up to the same crustal level as tectonic slices due to late paleoproterozoic tectonic processes

vertical diabatic heating structure of the mjo intercomparison between recent reanalyses and trmm estimates abstractcapitalizing on recently released reanalysis datasets and diabatic heating estimates based on tropical rainfall measuring mission trmm the authors have conducted a composite analysis of vertical anomalous heating structures associated with the madden julian oscillation mjo because diabatic heating lies at the heart of prevailing mjo theories the intention of this effort is to provide new insights into the fundamental physics of the mjo however some discrepancies in the composite vertical mjo heating profiles are noted among the datasets particularly between three reanalyses and three trmm estimates a westward tilting with altitude in the vertical heating structure of the mjo is clearly evident during its eastward propagation based on three reanalysis datasets which is particularly pronounced when the mjo migrates from the equatorial eastern indian ocean eeio to the western pacific wp in contrast this vertical tilt in heating structure is not readily seen in the three trmm product

halaqin volcano sedimentary succession in the central northern margin of the north china craton products of late paleoproterozoic ridge subduction abstract the halaqin volcano sedimentary succession hvss is tectonically situated on top of the largely late archean to early paleoproterozoic yinshan terrane in the central northern margin of the north china craton it comprises greenschist to amphibolite facies schists quartzites marbles and amphibolites which were originally pelites pebbly sandstones sandstones limestones and volcanic rocks the presence of tight to isoclinal folds and thrusts of the hvss indicates tectonic transport from southeast to northwest present coordinates u pb ages of detrital zircon grains in the clastic rocks suggest provenance from both the fengzhen belt in the south and the yinshan terrane in the north zircon u pb ages of the hvss volcanic rocks e g 1909 10 ma 1894 6 ma 1887 6 ma and 1884 8 ma indicate volcanism in the period 1910 1880 ma detrital zircon age study of the neighbouring majiadian group reveals significant 2700 ma crust growth and 2500 ma metamorphism events in the yinshan terrane the hvss volcanic rocks have a trimodal geochemical distribution demonstrated by sio2 contents of 45 50 wt basalts 53 60 wt andesites and 70 76 wt dacites rhyolites the basalts and andesites are tholeiitic in chemistry and show distinct depletion in high field strength elements hfse e g nb zr ti compared to neighbouring elements in spider diagrams specifically low mg basalts and andesites mgo 5 wt have more or less flat ree patterns la ybn 0 45 1 76 and lile ndt t 1890 ma values of the basalts and andesites vary from 4 8 to 0 4 the rhyolites and dacites have strongly enriched light trace element patterns la ybn 8 49 47 9 and lile but depleted hfse e g nb zr ti the basalts and basaltic andesites most likely originated from the asthenosphere contaminated by melts from the lithosphere whereas the dacites and rhyolites likely originated from the crust we propose that the basalts and andesites are extrusive counterparts of the coeval and geochemically similar xuwujia gabbronorites and the dacites and rhyolites are upper crustal equivalents of the contemporaneous chemically comparable liangcheng granitoids which are in the originally underlying fengzhen belt we suggest that the hvss was most likely generated by ridge subduction below active continental margin just prior to the final amalgamation of the north china craton this ridge subduction contributed to the ultra high temperature metamorphism in this area terminal collision tectonics was responsible for the regional metamorphism and high deformation of the halaqin succession when it was transported northwestwards onto the yinshan terrane

zircon u pb ages of paleoproterozoic mafic granulites from the huai an terrane north china craton ncc implications for timing of cratonization and crustal evolution history abstract the north china craton ncc is considered to have been incorporated into the columbia supercontinent during late paleoproterozoic the huai an terrane located in north central part of the ncc is an important tectonic window to investigate the paleoproterozoic crustal evolution history of this craton particularly due to the wide occurrence of high grade metamorphic rocks including retrograded eclogites and high pressure granulites available data show two controversial peak metamorphic ages of these rocks as 1 95 1 90 or 1 85 1 80 ga thus determining the precise timing of metamorphism of the high pressure granulites is important in reconstructing the collisional history in this study we present zircon u pb ages bulk chemistry and mineral inclusions in zircons and matrix mineral assemblages from the high pressure granulites to evaluate the timing of metamorphism our results reveal ca 2 05 2 0 ga ages from magmatic zircons in these rocks representing the timing of emplacement of mafic magmas the metamorphic zircons yield two groups of ages at 1 95 1 90 and 1 85 1 80 ga clinopyroxene plagioclase titanite and apatite occur as common mineral inclusions within the 1 85 1 80 ga metamorphic zircons the chemical compositions of clinopyroxene and plagioclase occurring as inclusions are very similar to those of the rim compositions of those minerals in the matrix suggesting their formation during retrograde granulite metamorphism and are distinctly different from those of the core domains of the minerals in the matrix which represent high pressure granulite metamorphism these results indicate that the metamorphic zircons formed during retrograde granulite metamorphism dated as 1 85 1 80 ga and the age range of 1 95 1 90 ga corresponds to high pressure granulite metamorphism the dual nature of the geological and geochronological features suggest that the archean gray gneisses in the huai an terrane represent the basement rocks detached from the khondalite belt of the ncc after collision integrating with published data a double side collision with scissor like suturing model is proposed for the paleoproterozoic cratonization of the ncc

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

petrogenesis of late paleoproterozoic liangcheng charnockites and s type granites in the central northern margin of the north china craton implications for ridge subduction abstract the 1930 1890 ma garnet bearing peraluminous liangcheng granitoids are mainly distributed in the fengzhen belt in the north china craton ncc they consist of early porphyritic coarse grained charnockites magmatic orthopyroxene granitic rocks and late medium to coarse grained s type crustal melt granites the charnockites are distinguished from the s type granites by their higher tio 2 al 2 o 3 feo t mgo cao and trace element contents especially the heavy rare earth elements ree the charnockites show varied light ree enrichments la yb n 1 92 18 0 negative eu anomalies eu eu 0 2 0 9 and negative anomalies in high field strength elements hfses e g nb ta ti and in sr compared with the neighbouring elements in spidergrams their 87 sr 86 sr t t 1900 ma ratios vary from 0 704 to 0 707 with one at 0 74 and nd t t 1900 ma values range from 4 to 1 in contrast the liangcheng s type granites show strong light ree enrichments la yb n 13 3 230 positive eu anomalies eu eu 1 1 3 6 negative anomalies in hfses e g nb ta ti and negative or positive anomalies in sr compared with neighbouring elements in spidergrams their 87 sr 86 sr t t 1900 ma ratios vary from 0 703 to 0 712 and nd t t 1900 ma values range from 3 to 1 both the charnockites and s type granites originated by melting of in situ meta sediments with significant charnockites or little s type granites amounts of additional melts from the parental magma of the adjacent xuwujia gabbronorites high mg 19 23 wt samples of the xuwujia gabbronorites have whole rock re contents of 0 16 1 93 ppb os contents of 1 6 9 8 ppb 187 re 188 os ratios of 0 08 1 76 and 187 os 188 os ratios of 0 1168 0 1186 with one exception at 0 1845 these values are comparable with those of typical komatiites and agree with a depleted source for these rocks the charnockites have received 10 30 wt or even larger amounts of melt contribution from the xuwujia gabbronorites whereas the s type granites received only few melts from the gabbronorites and they possibly had lower melting temperature than the charnockites we consider that the charnockites and s type granites had surface counterparts represented by two types of rhyolitic to dacitic volcanics in the halaqin succession which also contains basalts to basaltic andesites that are geochemically comparable to the xuwujia gabbronorites or the charnockites some andesites from their field relations and geochemical and thermal characteristics we propose that the peraluminous charnockites and s type granites were most likely generated by ridge subduction at 1930 ma prior to the final cratonization of the ncc at 1850 ma and that this ridge subduction was also responsible for the regional 1950 1880 ma gabbronorites charnockites s type granites volcanics as well as the 1930 ma ultrahigh temperature metamorphism in the ncc

diabatic heating profiles over the continental convergence zone during the monsoon active spells the present paper aims to bring out the robust common aspects of spatio temporal evolution of diabatic heating during the monsoon intraseasonal active phases over the continental tropical convergence zone ctcz the robustness of spatio temporal features is determined by comparing the two state of the art reanalyses ncep climate forecast system reanalysis and modern era retrospective analysis the inter comparison is based on a study period of 26 years 1984 2009 the study confirms the development of deep heating over the ctcz region during the active phase and is consistent between the two datasets however the detailed temporal evolution of the vertical structure e g vertical tilts of heating differs at times the most important common feature from both the datasets is the significant vertical redistribution of heating with the development of shallow low level heating and circulation over the ctcz region 3 7 days after the peak active phase the shallow circulation is found to be associated with increased vertical shear and relative vorticity over certain regions in the subcontinent this increased vertical shear and relative vorticity in the lower levels could be crucial in the sustenance of rainfall after the peak active phase model experiments with linear dynamics affirm the role of shallow convection in increasing the lower level circulation as observed

texturally controlled u th pb monazite geochronology reveals paleoproterozoic uht metamorphic evolution in the khondalite belt north china craton

late paleoproterozoic crustal evolution in the daqingshan area evidences from adakitic and a type granitoids in the guyang changshengqu goldfield khondalite belt north china craton abstract granitic magmatism related to the collisional orogenic belt provides important information for the evolution of continental crust we performed petrological geochemical and zircon u pb hf isotopic studies on four granitoid samples from the guyang changshengqu goldfield daqingshan area khondalite belt north china craton the zircon u pb dating results indicate that the granitoids emplaced at 1950 11 ma 1935 12 ma 1846 11 ma and 1812 8 6 ma represent two periodic granitic magmatism in the daqingshan area the 1 95 and 1 93 ga granites exhibit high sio2 k2o and na2o contents with high sr y and la yb n ratios but low mgo cr and ni contents indicating that they were produced by the partial melting of a thickened lower crust under relatively high pressure conditions the granites show negative dominated zircon ehf t values 5 7 1 9 and their zircon tdm2 hf values range between 2 9 and 2 5 ga indicating an ancient crust source with minor juvenile crustal material involved the 1 85 and 1 81 ga quartz monzonites exhibit high sio2 k2o na2o zr nb ce and y but low mgo cr and ni contents with high ga al and feot feot mgo ratios indicating an a type granite affinity the whole rock geochemistry suggests that they were formed by dehydration re melting of ttg and quartz diorite at high temperatures and shallow depths the quartz monzonites show homogeneous ehf t values 10 6 6 1 and the zircon tdm2 hf values range between 3 0 and 2 8 ga suggesting that they were derived from a neoarchean ancient crust the 1 95 1 93 ga adakitic magmatism is associated with the 1 93 1 92 ga mafic magmatism and uht metamorphic in the eastern part of the khondalite belt this suggests a tectonic transition from collisional compression to post collisional extension the 1 85 1 81ga a type granitic magmatism indicates evident continental crust thinning and asthenospheric upwelling the two unrelated magmatism are possibly induced by two collisional events from the khondalite belt and the trans north china orogen respectively the collision of the western and eastern blocks at ca 1 85 ga may have played an important role in the a type quartz monzonites origin and influenced the crustal evolution as far as the daqingshan area in the khondalite belt

late neoarchean paleoproterozoic arc continent accretion along the khondalite belt western block north china craton insights from granitoid rocks of the daqingshan wulashan area abstract late neoarchean early paleoproterozoic granitoid rocks are widely exposed in the daqingshan wulashan area in the central segment of the khondalite belt kb western block north china craton ncc and are characterized by widespread evidence of ductile deformation and anatexis to improve our understanding of the formation and evolution of the kb in this study we analyzed zircon u pb ages zircon lu hf isotopes and whole rock geochemistry of the granitoid rocks la icp ms u pb analysis of zircons from eight representative granitoid samples indicates the granitoid rocks were emplaced at ca 2 45 and ca 2 50 ga and underwent multi stage metamorphism at ca 1 90 1 95 2 45 and 2 50 ga zircon lu hf isotopic analysis shows that the granitoids have positive zircon ehf t values with an average of 4 36 and two stage depleted mantle zircon hf model ages tdm2 clustering around 2 7 3 0 ga indicative of a juvenile crustal source that formed at ca 2 7 3 0 ga furthermore whole rock geochemical analysis of 34 granitoid samples reveal them to be magnesian low to high k calcic to calc alkalic and metaluminous to weakly peraluminous alumina saturation index asi 0 74 1 17 they are characterized by high total rare earth element ree contents 57 45 346 96 ppm enrichment in light ree and depletion in heavy ree with la yb n ratios of 8 33 224 16 they have weak eu anomalies eu eu 0 37 2 53 average 1 08 high sr contents 300 ppm and relatively low y and yb concentrations average 10 55 and 0 96 ppm respectively primitive mantle normalized trace element diagrams show that the granitoid samples are depleted in high field strength elements nb ta u and ti and enriched in large ion lithophile elements ba k rb and sr in general the samples have geochemical characteristics consistent with cordilleran i type granitoids which form in subduction related magmatic arcs therefore our results together with the occurrence of synchronous mafic rocks and other available geological data indicate the kb contains multiple magmatic arcs and underwent long term deposition and multi phase metamorphism analogous to phanerozoic accretionary orogens such as the cordilleran orogen consequently we infer that the kb underwent long term arc continent accretion along the southern margin of the yinshan block during the late neoarchean paleoproterozoic and late stage continent continent collision between the yinshan and ordos blocks at ca 1 90 1 95 ga

quasi biweekly oscillation over the tibetan plateau and its link with the asian summer monsoon abstract intraseasonal variation isv is especially prominent and unique in the asian summer monsoon region in this work the dominant isv mode over the tibetan plateau tp in the summer monsoon season june august together with its structure and evolution is identified using station observations global precipitation climatology project precipitation data and era interim during 1979 2011 results indicate that quasi biweekly oscillation qbwo is the dominant mode of isv over the tp and is significant in terms of the circulation precipitation and diabatic heating fields in particular the qbwo is closely related to the onset and active break phases of the tp summer monsoon in most cases the qbwo originates from the equatorial western pacific and first propagates northwestward to the bay of bengal and northern india then northward to the southeastern tp and finally eastward to the east asian area showing a clockwise propagation pathway two main mechanisms are responsible for the northward

first application of the revised ti in zircon geothermometer to paleoproterozoic ultrahigh temperature granulites of tuguiwula inner mongolia north china craton the revised titanium in zircon geothermometer was applied to paleoproterozoic ultrahigh temperature uht granulites at tuguiwula inner mongolia north china craton the tuguiwula granulites contain diagnostic uht mineral assemblages such as sapphirine quartz and high alumina orthopyroxene sillimanite quartz suggesting formation under temperatures of ca 1 000 c and pressures of up to 10 kbar here we report detailed petrographic studies and icp ms data on titanium concentration in zircons associated with the uht assemblages the zircons associated with sapphirine spinel sillimanite magnetite assemblages have the highest ti concentration of up to 57 ppm yielding a temperature of 941 c and suggesting that the growth of zircons occurred under ultrahigh temperature conditions the maximum temperatures obtained by the revised ti in zircon geothermometer is lower than the equilibrium temperature of sapphirine quartz indicating an interval of cooling history of the granulites from uht condition to ca 940 c many of the zircons have ti concentrations ranging from 10 to 33 ppm indicating their growth or recrystallization under lower temperatures of ca 745 870 c these zircons are interpreted to have recrystallized during the retrograde stage indicated by microstructures such as cordierite rim or corona between spinel and quartz and orthopyroxene cordierite symplectite around garnet previous geochronological study on the zircons of the tuguiwula uht granulites gave a mean u pb shrimp age of 1 92 ga however based on the ti in zircon geothermometer results reported in this work and considering the relatively slow thermal relaxation of these rocks we infer that the timing of peak uht metamorphism in the tuguiwula area could be slightly older than 1 92 ga

application of ti in zircon and zr in rutile thermometers to constrain high temperature metamorphism in eclogites from the dabie orogen central china abstract ultrahigh pressure uhp eclogites from the northern dabie orogen central china underwent a complex metamorphic evolution during triassic continental deep subduction and subsequent exhumation the eclogites were strongly affected by multiple decompression and re crystallization processes during exhumation thus making the determination of peak metamorphic conditions particularly challenging the recently calibrated ti in zircon and zr in rutile thermometers provide new tools to estimate the peak and post peak temperatures rutiles within uhp mineral bearing domains of zircon have zr contents of 1030 4310 ppm and record a temperature range of 880 1080 c with a peak at 970 c rutiles within high pressure hp mineral bearing domains contain zr contents of 800 5800 ppm and define a temperature range of 780 1030 c with an average value of 873 c rutiles in granulite facies mineral bearing rims of zircon yield a temperature of 845 c in contrast rutile inclusions within garnet have lower zr contents of 100 800 ppm yielding lower temperatures of 600 850 c the uhp and hp mineral bearing mantle domains of zircon have ti contents of 2 15 97 8 ppm yielding ti in zircon temperatures of 620 1020 c ti contents in the rim domains of zircon are low 900 c for the uhp and hp domains of zircon therefore this study combined with the previously published data suggests that the eclogites in the region experienced a protracted high temperature ht metamorphic evolution from uhp eclogite facies to hp granulite facies metamorphic stages this long lived ht evolution coupled with slow cooling and partial melting may explain the rare preservation of uhp traces in the area hp uhp mineral inclusions in garnet and zircon experienced variable degrees of decompression breakdown or retrogression therefore also ti concentrations in zircons and zr concentrations in rutiles within garnet and zircon may have been strongly modified by re crystallization or partial melting as a result only few zircons record their actual crystallization temperatures in comparison the rutile inclusions in zircon generally define higher temperatures we therefore suggest that rutile inclusions in zircon are the most suitable candidates for ht estimates especially in strongly retrogressed eclogites

the timing and duration of high temperature to ultrahigh temperature metamorphism constrained by zircon u pb hf and trace element signatures in the khondalite belt north china craton understanding the timing and duration of metamorphism is fundamental to correctly interpreting the geodynamic evolution of orogenic events metamorphic constraints are still ambiguous in the khondalite belt north china craton so paleoproterozoic orogenic processes remain unclear here we investigate a suite of high grade rocks from the dongpo locality in the daqingshan terrane by integrating zircon trace elements and hf isotopic signatures with u pb ages to track zircon formation events and confidently constrain the timing and duration of metamorphism the application of the ti in zircon thermometer confirms the occurrence of regional ht uht metamorphism linking zircon hree patterns and u pb ages in combination with hree partitioning between zircon and garnet reveals zircon formation during partial melting to thermal peak stage and during the post peak cooling stage local reaction control by garnet breakdown has affected some zircons which show a more radiogenic 176hf 177hf ratio 0 28164 0 28174 relative to unaffected grains 0 28128 0 28156 metamorphic zircon u pb ages combined with results from previous studies constrain partial melting to uht conditions with decompression heating at 1 94 1 90 ga post peak near isobaric cooling at 1 90 1 86 ga and the thermal peak very close to ca 1 90 ga local garnet breakdown occurred during another decompression heating stage to ht uht conditions at 1 86 1 84 ga and further cooling occurred until ca 1 80 ga our work reveals relatively short lived partial melting less than 40 million years in comparison to long lived cooling stages nearly 100 million years in the eastern part of the khondalite belt two pulses of decompression heating to ht uht conditions in the deep crust could result from repeated asthenospheric upwelling driven by lithospheric extension after subduction collision our study sheds new light on zircon behaviour during ht uht metamorphism and elucidates the underlying driver of uht metamorphism in this part of the khondalite belt

first application of titanium in zircon thermometry to ultrahigh temperature metamorphism titanium in zircon thermometry has been applied to evaluate the temperatures of metamorphism for two ultrahigh temperature uht granulite localities the neoproterozoic anapolis itaucu complex in central brazil and lower crustal xenoliths from the neo archean kaapvaal craton in south africa uht metamorphism in the anapolis itaucu complex occurred ca 640 ma ti in zircon thermometry on metamorphic zircon yields temperatures of 965 811 c a population of late zircon that formed from ilmenite and rutile breakdown records temperatures of 780 c maximum temperatures are less than those inferred from quantitative phase equilibria modeling based on textural setting inclusions in peak phases and as matrix grains these zircons likely record growth during the pro grade and or postpeak evolution in contrast the kaapvaal xenoliths record two phases of zircon growth during uht metamorphism at 2720 2715 ma followed by growth during isobaric cooling in kyanite bearing leucosomes ca 2690 ma temperatures recorded by the two phases of growth are 1024 878 c and 936 839 c respectively suggesting that zircon growth occurred during uht conditions and continued throughout the postpeak evolution over a 200 c interval these examples demonstrate that the ti in zircon thermometer is a powerful new tool with the potential to determine crystallization temperatures of zircon during granulite facies metamorphism throughout the prograde to postpeak evolution of such terranes

cloud regime evolution in the indian monsoon intraseasonal oscillation connection to large scale dynamical conditions and the atmospheric water budget we examine the intraseasonal oscillation iso of the indian summer monsoon to establish the connections of cloud regimes to large scale dynamical states defined by dynamical convergence and moisture advection over the indian subcontinent the developing phase toward iso peaks rainfall maximum is associated with positive anomalies of moisture advection leading in 4 6 days to positive anomalies of dynamical convergence triggering abrupt transitions from shallow cumulus to deep convections in 1 2 days the decaying phase toward iso troughs rainfall minima is associated with negative anomalies of moisture advection and decreasing dynamical convergence accompanying opposite transitions in cloud regimes due to northward propagation of anomalies processes over the indian ocean are similar but lead those over the subcontinent by 10 days during the transitions cirrus clouds always accompany but lag deep convective clouds by 10 days over the equatorial indian ocean cirrus clouds are modulated by equatorial waves

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

paleoproterozoic granulites from the xinghe graphite mine north china craton geology zircon u pb geochronology and implications for the timing of deformation mineralization and metamorphism abstract the xinghe graphite deposit is located in the north central part of the north china craton ncc where archean gray gneiss metasedimentary rocks khondalites and mafic high pressure granulites constitute the dominant rock types in this study we report results of detailed geological and structural mapping around the xinghe graphite mine we identify three stages of deformation d 1 d 3 and the graphite mineralization is correlated with d 1 or between d 1 and d 2 the first stage of deformation represented by rootless intrafolial folds whose axial surface cuts across the regional penetrative gneissosity s 2 of d 2 was constrained at ca 1 95 1 90 ga by u pb age of zircon grains from a mafic high pressure granulite the second stage of deformation is represented by tight folds with formation of regional penetrative foliation and strong ductile shearing when garnet broke down to plagioclase pyroxene this stage is dated as ca 1 85 ga from u pb analysis of zircons in leucosome from a migmatitic gneiss the third stage of deformation is represented by large scale folding which probably formed between 1 85 and 1 80 ga as constrained from the ca 1 80 ga emplacement age of an undeformed pegmatite that cuts across the host metasediments prior to the high pressure granulite metamorphism voluminous ca 2 15 2 0 ga granites were emplaced within the khondalites the graphitization postdates the emplacement of these granites as deduced from the presence of flaky graphites in the metagranites the protolith of the mafic high pressure granulite dike that intruded the khondalite at ca 2 0 ga was also metamorphosed at 1 95 1 90 ga and is part of the exploited graphite ore body we therefore constrain the timing of graphite mineralization to be between ca 1 95 and 1 85 ga our geological and geochronological data indicate that all the rock units in the xinghe graphite mine were subjected to high pressure granulite facies metamorphism at ca 1 95 1 90 ga

the hydrodynamic and sedimentary setting of nearshore coral reefs central great barrier reef shelf australia paluma shoals a case study the great barrier reef gbr shelf contains a range of coral reefs on the highly turbid shallow inner shelf where interaction occurs with terrigenous sediments the modern hydrodynamic and sedimentation regimes at paluma shoals a shore attached turbid zone coral reef and at phillips reef a fringing reef located 20 km offshore have been studied to document the mechanisms controlling turbidity at each reef waves currents and near bed turbidity were measured for a period of 1 month bed sediments were sampled at 135 sites on the inner shelf muddy sands are widespread with admixed terrigenous and carbonate gravel components close to the reefs and islands except on their relatively sheltered sw side where sandy silty clays occur at paluma shoals the coral assemblage is characteristic of inner shelf or sheltered habitats on the gbr shelf dominated by galaxea fascicularis up to 50 coral cover and is broadly similar to that at phillips reef further offshore and in deeper water the sediments of the paluma shoals reef flats consist of mixed terrigenous and calcareous gravels and sands with intermixed silts and clays whereas the reef slope is dominated by gravelly quartz sands the main turbidity generating process is wave driven resuspension and turbidity ranges up to 175 nephelometric turbidity units ntu in contrast at phillips reef turbidity is 40 ntu probably occurs for a total of 40 days each year and relatively little time is spent at intermediate turbidities 15 50 ntu the extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning autotrophy and heterotrophy in response to different levels of turbidity sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux btf of sediment to the sea floor i e 10 000 btf over three orders of magnitude greater than the holocene average for halifax bay of 3 btf as elsewhere along the nearshore zone of the central gbr dry season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments the location of modern nearshore coral reefs is controlled by the presence of suitable substrates which in halifax bay are pleistocene and early holocene coarse grained and relatively stable alluvial deposits

the stability of sapphirine quartz and hypersthene sillimanite quartz assemblages an experimental investigation in the system feo mgo al 2 o 3 sio 2 under h 2 o and co 2 conditions phase relations and mineral chemistry involving the phases garnet gt spinel sp hypersthene hy sapphirine sa cordierite cd sillimanite sil and quartz qz have been experimentally determined in the system fmas feo mgo al2o2 sio2 under low fo2 and for various h2o co2 conditions several compositions were studied with 100 mg mg fe ratio ranging from 64 to 87 with excess quartz and sillimanite our data do not show any differences in gt cd stability and composition as a function of h2o co2 and h2o co2 ch4 content in good agreement with a previous experimental study at lower temperature aranovich and podlesskii 1983 at 1 000 c and 11 kbar under co2 saturated conditions cordierite grew from a crystalline mix unseeded with cordierite thus under water absent conditions cordierite will have a high p stability field in the presence of co2 if water has a pressure stabilizing effect on cordierite then our results would indicate that the effects of h2o and co2 are of the same magnitude at high temperature our data support the theoretical p t grid proposed by hensen 1986 for high t metapelites and are largely consistent with the high temperature experimental data of hensen and green 1973 the univariant boundary gt cd hy sil qz which marks the disappearance of hy sil qz assemblages has a negative dp dt slope above 1 000 c and a positive one below this temperature extrapolation of our data to iron free systems shows that the high p breakdown limit of mg cordierite has a negative slope in the range 1 025 1 300 c and probably positive below 1 000 c this indicates a maximum of stability for mg cordierite at around 1 000 c and 13 kbar because of the curvature of the univariant reactions en sil py qz mg cd en sil qz and gt cd hy sil qz the iron free invariant point involving the phases py en cd sil and qz probably does not exist sapphirine qz bearing assemblages are stable only at temperatures above 1 050 c at 1 075 c the joint gt sa is stable up to 11 kbar at higher pressure garnet sapphirine and quartz react according to the reaction gt sa qz hy sil reequilibrated sapphirines are more aluminous than the theoretical endmember mg2al4sio10 due to alal mgsi substitutions 100 al2o3 al2o3 feo mgo in experimental sapphirines ranges from 50 5 to 52 2 sapphirine in the assemblage sa cd sil qz shows a decrease in al content with decreasing temperature and pressure such that the alumina isopleths for sapphirine have a slight negative dp dt slope a similar decrease in al content of sapphirine with temperature is also observed in sa sil qz assemblages

p t t evolution of pelitic gneiss from the basement underlying the northwestern ordos basin north china craton and the tectonic implications abstract using petrography phase equilibria modeling and in situ u th pb monazite geochronology we show that pelitic gneiss from close to the bottom of the qitan1 borehole in the northwest of the ordos basin records a four stage metamorphic evolution the m1 m3 stages which were suprasolidus are represented by rutile relicts in the matrix and biotite k feldspar plagioclase sillimanite quartz inclusions in the cores of garnet porphyroblasts m1 inclusion free mantles on garnet with ilmenite partially replacing rutile and biotite k feldspar plagioclase sillimanite quartz in the matrix m2 and the appearance of cordierite in the assemblage biotite k feldspar plagioclase sillimanite ilmenite quartz m3 the final subsolidus mineral assemblage is garnet biotite k feldspar plagioclase sillimanite cordierite ilmenite quartz m4 the p t conditions for the mineral assemblage evolution m1 m4 are constrained by a p t pseudosection constructed in the na 2 o cao k 2 o feo mgo al 2 o 3 sio 2 h 2 o tio 2 o 2 chemical system the p t t path is clockwise involving slight heating during near isothermal decompression from 8 8 kbar at 769 c to 5 5 kbar at 785 c followed by close to isobaric cooling across the solidus two cores of monazite and three unzoned grains that have similar populations of dates yield robust ages of 1 96 1 94 ga interpreted to date the timing of late prograde to peak metamorphism m1 m2 in addition one rim and two unzoned monazite grains with similar populations of dates yield robust ages of 1 90 1 88 ga interpreted to date the timing of post decompression slow cooling across the solidus m3 m4 on the basis of these results the pelitic gneiss is interpreted to have formed by crustal thickening m1 during collision between the yinshan and ordos terranes the latter with the khondalite belt protoliths along its northern margin present co ordinates this collision culminated at ca 1 95 ga and was followed by decompression m2 m3 and slow cooling m4 to ca 1 89 ga during post collisional extension the similarity between the p t t path determined in this study and those from hp mp granulites in the khondalite belt confirms that they experienced a common tectono metamorphic history the p t t path records an evolution from an apparent thermal gradient of 75 c kbar at peak pressure to 150 c kbar after decompression together with the occurrence of mid paleoproterozoic magmatism in the basement of the ordos basin these features indicate that the ordos terrane was the upper plate at a convergent margin with the khondalite belt representing the forearc sediments along its northern edge collision with the yinshan terrane part of the subducting plate led to shallow slab breakoff and the development of a two sided hot collision and formation of a wide plateau like hot orogen similar to those in the numerical models of sizova et al 2014

simulation of monsoon intraseasonal oscillations in a coarse resolution aquaplanet gcm the skill of the global climate models gcms to realistically simulate the monsoon intraseasonal oscillations misos is related to the sensitivity of their convective parameterization schemes here we show that by coupling a simple multicloud parameterization to a coarse resolution aquaplanet gcm realistic misos can be simulated we conduct three different simulations with a fixed nonhomogeneous sea surface temperature mimicking the indian ocean western pacific warm pool wp centered at the three latitudes 5 n 10 n and 15 n respectively to replicate the seasonal migration of the tropical convergence zone tcz this results in the generation of mean circulation resembling the monsoonal flow pattern in boreal summer succession of eastward propagating madden julian oscillation mjo disturbances with phase speed amplitude and structure similar to summer mjos are simulated when the wp is at 5 n when the wp is located over 10 n northward and eastward propagating misos are simulated this case captures the meridional seesaw of convection between continental and oceanic tcz observed during boreal summer over south asia westward propagating rossby wave like disturbances are simulated when the wp is over 15 n congruous with the synoptic disturbances seen over the monsoon trough the initiation of intraseasonal oscillations in the model can occur internally through organization of convective events above the wp associated with internal dynamics

lithotectonic elements and geological events in the hengshan wutai fuping belt a synthesis and implications for the evolution of the trans north china orogen the hengshan wutai fuping belt is located in the middle segment of the trans north china orogen a palaeoproterozoic continental collisional belt along which the eastern and western blocks amalgamated to form the north china craton the belt consists of the medium to high grade hengshan and fuping gneiss complexes and the intervening low to medium grade wutai granite greenstone terrane and most igneous rocks in the belt are calc alkaline and have affinities to magmatic arcs previous tectonic models assumed that the hengshan and fuping gneiss assemblages were an older basement to the wutai supracrustal rocks but recent studies indicate that the three complexes constitute a single long lived neoarchaean to palaeoproterozoic magmatic arc where the wutai complex represents an upper crustal domain whereas the hengshan and fuping gneisses represent the lower crustal components forming the root of the arc the earliest arc related magmatism in the belt occurred at 2560 2520 ma marked by the emplacement of the wutai granitoids which was followed by arc volcanism at 2530 2515 ma forming the wutai greenstones extension driven by widespread arc volcanism led to the development of a back arc basin or a marginal sea which divided the belt into the hengshan wutai island arc japan type and the fuping relict arc at 2520 2480 ma subduction beneath the hengshan wutai island arc caused partial melting of the lower crust to form the hengshan tonalitic trondhjemitic granodioritic ttg suites whereas eastward directed subduction of the marginal sea led to the reactivation of the fuping relict arc where the fuping tonalitic trondhjemitic granodioritic suite was emplaced in the period 2360 2000 ma sporadic phases of isolated granitoid magmatism occurred in the hengshan wutai fuping region forming 2360 ma c 2250 ma and 2000 2100 ma granitoids in the hengshan complex the c 2100 ma wangjiahui and dawaliang granites in the wutai complex and the 2100 2000 ma nanying granitoids in the fuping complex atc 1920 ma the hengshan wutai island arc underwent an extensional event possibly due to the subduction of an oceanic ridge leading to the emplacement of pre tectonic gabbroic dykes that were subsequently metamorphosed together with their host rocks to form medium to high pressure granulites at 1880 1820 ma the hengshan wutai fuping arc system was juxtaposed intensely deformed and metamorphosed during a major and regionally extensive orogenic event the l uliang orogeny which generated the trans north china orogen through collision of the eastern and western blocks the hengshan wutai fuping belt was finally stabilized after emplacement of a mafic dyke swarm at 1780 1750 ma

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

the paleoproterozoic north hebei orogen north china craton s collisional suture with the columbia supercontinent abstract understanding the geologic history and position of the north china craton in the paleoproterozoic columbia supercontinent has proven elusive paleoproterozoic orogenic episodes 2 00 1 85 ga are temporally associated with ultimate stabilization of the north china craton ncc followed by the development of extensive craton wide rift systems at 1 85 1 80 ga the age difference between the sedimentary cover and the metamorphic basement is up to 500 700 ma suggesting that uplift and doming of cratonic basement occurred in the latest paleoproterozoic mafic dike swarms 1 80 1 77 ga and anorogenic magmatism 1 80 1 70 ga record the extensional breakup and dispersal of the north china craton during this stage the late paleoproterozoic tectonic framework and geological events documented provide important constraints for reconstruction of the ncc within the late paleoproterozoic supercontinent of columbia an east west striking thousand kilometer long belt of khondalites granulite facies metapelites stretches along the northern margin of the north china craton on the cratonward side of the northern hebei orogenic belt this granulite belt includes mg al sapphirine bearing granulites that reached ultrahigh temperature peak metamorphic conditions of 1000 c at 10 kbars at 1927 11 ma following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and these trajectories are interpreted to be part of an overall anti clockwise p t evolution indicating that the northern margin of the craton experienced continental collision at 1 93 1 92 ga the position of the khondalite belt south of the northern hebei orogenic belt makes it analogous to tibet a continental collision related plateau characterized by double crustal thicknesses and granulite facies metamorphism at depth we suggest that the tectonic evolution of the ncc during this period was closely related to the assembly and break up of the columbia supercontinent and that the ncc was adjacent to the baltic and amazonian cratons in the period 2 00 1 70 ga craton wide extension occurred within 100 150 ma of collision along the northern margin of the craton at 1 93 1 92 ga it is concluded that mantle upwellings are chiefly responsible for the breakup of the ncc from the paleoproterozoic supercontinent

revised cloud and convective parameterization in cfsv2 improve the underlying processes for northward propagation of intraseasonal oscillations as proposed by the observation based study the performance of revised climate forecast system version 2 cfsv2 are evaluated on the simulation of the underlying cloud and convective processes associated with the strong and weak boreal summer intraseasonal oscillations bsisos events the revised version of the cfsv2 consists of a six class weather research forecasting single moment wsm6 cloud microphysics scheme and the default version has zhao and carr zc cloud microphysics scheme both the version uses revised simplified arakawa schubert rsas convection scheme the study reveals that the revised version of cfsv2 rsas wsm is able to better simulate the northward propagation of bsisos and associated dynamical and thermodynamical mechanism put forward by earlier observation based studies it is found that the large scale organized northwest southeast tilted structure of rain band is better captured in rsas wsm simulation as compared to the default version of cfsv2 rsas zc during strong bsiso events further the reasonable large scale or stratiform rainfall associated with the northward propagating strong bsiso events is seen in rsas wsm while it is completely missing in rsas zc simulation the pressure latitude profiles of cloud liquid water clw and cloud ice cli show more realistic steady northward propagation in rsas wsm simulation consistent with the clw and cli distribution and their influence on the large scale heating structure the large scale condensation heating shows quasi periodic northward propagation in rsas wsm whereas such type of distribution is not captured in rsas zc simulation the realistic representation of cloud processes in wsm leads to simulate reasonable dynamical and thermodynamical processes associated with the strong bsiso events which follows the observation based hypothesis proposed by earlier studies

genesis of the hengling magmatic belt in the north china craton implications for paleoproterozoic tectonics abstract the 2200 1880 ma igneous rocks in the central and eastern parts of the north china craton ncc constitute a new hengling magmatic belt hmb which includes the 2147 ma hengling mafic sill dyke swarm the 2060 ma yixingzhai mafic dyke swarm and the 1973 ma xiwangshan mafic dyke swarm the three swarms are contiguous and have experienced variable degrees of metamorphism from greenschist to low amphibolite facies hengling medium granulite facies yixingzhai and medium high pressure granulite facies xiwangshan they are all tholeiitic in composition typically with 47 52 wt sio 2 and 4 10 wt mgo and all show light rare earth element enrichments and nb and ta depletion their nd t dm ages are in the range of 2 5 3 0 ga specifically the hengling and yixingzhai dykes sills are depleted in th u zr hf and ti whereas the xiwangshan dykes are enriched in u and weakly depleted in other elements variable sr anomalies indicate significant feldspar accumulation positive anomalies or fractionation the end t values of the three swarms are 3 2 3 0 hengling 1 7 1 8 yixingzhai and 1 4 1 0 xiwangshan these mafic representatives of the hmb originated from the 2 5 ga sub continental lithospheric mantle of the ncc and with a type granites and other igneous associations in this belt they likely evolved in an intra continental rift the progressive changing compositions of the three swarms are interpreted in terms of their source regions at different depths i e shallower and shallower through time and the decrease in scale and size of the intrusions and their magma volumes indicate the progressive weakening of magmatism in this rift the rocks in this belt are different chronologically petrologically and chemically from those in the xuwujia magmatic belt xmb we propose that the two magmatic belts represent two different magmatic systems in different blocks of the ncc i e an eastern block with the hmb and a western block with the xmb terminal collision was possibly a result of ridge subduction between the two blocks which led to exhumation of the igneous rocks in the two belts from different crustal levels distinguishable by their different grades of metamorphism

role of stratiform rainfall in modifying the northward propagation of monsoon intraseasonal oscillation 1 the stratiform and convective rain rate measurement from the tropical rainfall measuring mission trmm satellite data can give a realistic idea of the latent heating distribution in the tropics the vertical profile of diabatic heating related to the convective and the stratiform rain is known to modulate the dynamical response of atmosphere and also the vertical structure of madden julian oscillation in this study the contribution of the stratiform and convective rain rate to the total rain rate during different phases of the northward propagating boreal summer monsoon intraseasonal oscillation iso is examined using the trmm data two new insights have emerged from this analysis first unlike conventional wisdom the convective component shows weak northward propagation and grows and decays in situ during the evolution of active and break phases while the northward propagation of the monsoon iso is largely achieved by organized movement of the stratiform component second the trademark meridional dipole pattern of total rainfall between the monsoon trough zone and the southern equatorial indian ocean also arises largely from the contribution of stratiform anomalies as the northward propagation of the monsoon iso is known to be due to the anomalous response of the atmosphere to heating in the presence of mean easterly vertical shear modification of the vertical profile of heating due to a contribution from stratiform rain could influence the northward propagation of the monsoon iso this hypothesis is tested using a simple global atmospheric circulation model to study the response of the convective and stratiform heating profiles on the modification of the mean condition modification in the large scale response of the atmosphere as a result of proper specification of convective and stratiform heating anomalies indicates that the presence of stratiform heating favors the northward propagation of the heat source thereby facilitating the positive feedback leading to northward propagation of the monsoon iso these results underline the importance of simulating the partitioning of convective and stratiform rain by cumulus parameterization in climate models if they have to get the space time structure of the summer isos correct

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

oriented multiphase needles in garnet from ultrahigh temperature granulites connecticut u s a this study investigates distinctive oriented needle shaped multiphase inclusions found within cores of garnets from felsic granulites of the upper member of the bigelow brook formation and the brimfield schist northeastern connecticut u s a the rocks crop out in the southern end of the central maine terrane and thus are a part of the acadian neoacadian orogen the typical mineral assemblage is garnet sillimanite k feldspar plagioclase quartz cordierite biotite spinel the sillimanite is commonly pseudomorphous after kyanite the multiphase needle inclusions and associated exsolved needles of rutile and ilmenite are mostly oriented parallel to of garnet the multiphase needles contain various combinations of quartz micas chlorite rutile graphite a siliceous compositionally variable phase phase cv zn spinel apatite zircon and rare ilmenite we hypothesize that they represent inclusions of fluid that adhered to exsolving ti fe oxide needles mostly rutile or extended along zones of weakness in garnet this requires that multiphase needle formation occurred in response to cooling and or decompression the needles ultimately decrepitated during retrogression we note that micaceous needle shaped multiphase inclusions are rarely described the closest analogs of which we are aware are found in uhp garnets of the erzgebirge perchuk 2008 the brimfield schist in this area underwent ultrahigh temperature metamorphism uhtm of 1000 c at a minimum pressure of 1 gpa ague et al 2013 here we provide new temperature estimates for the adjacent upper member of the bigelow brook formation ternary feldspar reintegration using the activity model of benisek et al 2004 and zr in rutile thermometry tomkins et al 2007 give average temperatures of 990 and 1010 c respectively at 1 gpa for this unit therefore the recently discovered uht zone in the brimfield schist of northeastern connecticut extends to the east to include the upper member of the bigelow brook formation consequently the first confirmed regional uht locality in the united states is larger than initially recognized and is at least 25 km long and 5 10 km wide the oriented elongate multiphase inclusions and petrographically obvious oriented ti fe oxide needles may be useful indicators of extreme temperature and or pressure rocks in other field areas

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

paleoproterozoic ultrahigh temperature granulite facies metamorphism in the sulu orogen eastern china evidence from zircon and monazite in the pelitic granulite abstract because of their essential information for constraining the timescales of high temperature processes zircon and monazite are the two most important minerals for understanding crustal processes zircon and monazite are common accessory minerals in pelitic granulites sulu orogen eastern china the pelitic granulites have a peak mineral assemblage of garnet sillimanite antiperthite plagioclase quartz rutile biotite zircons from the granulite have low th u ratios

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

extreme crustal metamorphism during columbia supercontinent assembly evidence from north china craton abstract a vast supracrustal belt of khondalites granulite facies metapelites occur along the northern margin of the north china craton we report here for the first time spinel quartz equilibrium assemblage from these rocks in two textural settings 1 high zno up to 14 47 wt spinel with quartz as inclusions within garnet porphyroblasts defining pressure above 12 kbar and temperature of 900 c and 2 low zno down to 1 2 wt spinel in association with quartz in the matrix assemblage formed during peak ultrahigh temperature conditions ca 975 c and 9 kbar we present a unique case of decompression where the metamorphic conditions of the rocks traversed mostly through the spinel quartz extended stability field monazite grains in textural association with both types of spinel quartz textures were analysed for age determination and the data define two age peaks at 1927 11 ma and 1819 11 ma since the peak thermal regime of the khondalites was close to or exceeded the theoretical closure temperature of pb in monazite we infer the 1819 11 ma age as the timing of ultrahigh temperature event in this craton our data lend support to the idea of ca 1 9 1 8 ga e w collisional orogen at the northern margin of the north china craton we correlate the extreme crustal metamorphism with tectonics associated with the assembly of the north china craton within the columbia supercontinent

exsolution of rutile or apatite precipitates surrounding ruptured inclusions in garnet from uht and uhp rocks this study describes halos of rutile apatite needles and or plates centred on quartz inferred former coesite inclusions or multiphase inclusions in garnet both types of central inclusions are surrounded by cracks the multiphase inclusions contain mica or carbonate minerals and are interpreted to represent decrepitated fluid inclusions examples from two localities are examined i ultrahigh temperature uht metapelitic gneisses from the southern end of the central maine terrane in northeastern connecticut usa rutile only and ii ultrahigh pressure uhp diamondiferous saidenbachite from the saxonian erzgebirge rutile and apatite the needles of apatite or rutile are typically oriented in three directions within garnet chemical zonation in garnet shows clear ti or p depletion halos corresponding spatially with the rutile or apatite inclusion halos the radii of the inclusion halos when measured from the centre of the central inclusions are about two to several times the radii of the central inclusions we propose that the inclusion halos of rutile apatite formed by exsolution out of ti bearing and or p bearing garnet during retrogression because of its strength garnet can internally maintain higher pressures than the surrounding matrix nonetheless if the inclusion pressure is significantly greater than the confining lithostatic pressure then deformation of the host garnet can occur during exhumation high internal pressures relative to the matrix can result from retention of fluid entrapment pressure or a phase change with a large positive volume increase e g coesite quartz the differential stress imposed on the garnet adjacent to the central inclusion preceding and during mechanical failure would create dislocations and other crystalline defects which are ideal sites for exsolved precipitates to nucleate and grow the strain induced exsolution hypothesis is consistent with observations i the radii of the halos are roughly consistent with the pressure vessel model or the multi anvil model for an inclusion which predict that differential stress will drop off sharply away from the boundary of the central inclusion into the host garnet ii the rutile or apatite inclusions formed in ti or p bearing garnet adjacent to ruptured central inclusions rutile or apatite are rare or absent elsewhere in garnet even in areas of high ti or high p concentration in addition rutile is absent in areas surrounding the central inclusion that were depleted in ti prior to rupturing e g garnet rims that lost ti during retrogression thus both elevated ti p concentrations and proximity to inclusions which deformed the host garnet were necessary for halo formation iii reintegrated garnet ti or p contents in and adjacent to the halos obtained using wide beam electron probe microanalysis are consistent with local derivation of the ti or p necessary to form rutile and apatite from garnet elevated ti p concentrations in aluminous garnet are mostly found in uht hp uhp granulite and mantle environments consequently the phenomena described will most likely occur in such settings

timing of two separate granulite facies metamorphic events in the helanshan complex north china craton constraints from monazite and zircon u pb dating of pelitic granulites abstract this study presents the results of monazite and zircon u pb dating of garnet biotite gneiss and recently discovered spinel bearing ultrahigh temperature uht pelitic granulites from the paleoproterozoic helanshan complex of the north china craton and considers implications for the formation of the complex and the tectonic history of this region shrimp monazite u pb dating of the garnet biotite gneiss yielded a weighted mean 207pb 206pb age of 1944 4 4 2 ma which is the same within error as a weighted mean laser ablation inductively coupled plasma mass spectrometry la icp ms 207pb 206pb age of 1959 18 ma obtained from metamorphic zircons within the same unit the age of 1959 18 ma is similar to the published metamorphic ages of ca 1 96 1 95 ga from high temperature tmax

deformation history of the qianlishan complex khondalite belt north china structures ages and tectonic implications abstract the qianlishan complex is a multiply deformed granulite terrane of the khondalite belt that represents a paleoproterozoic continent continent collisional orogen in the western block of the north china craton two major stages of deformation d1 and d2 were identified in the qianlishan complex d1 mainly produced nww trending overturned to recumbent intrafolial isoclinal folds f1 sub horizontal penetrative foliations s1 nne ssw mineral lineations l1 associated with top to the ssw thrust shear reflecting crustal thickening due to the nne ssw compression d1 was developed with the prograde m1 and peak m2 granulite facies metamorphism d2 successively superposed the d1 structures and was characterized by nww see trending doubly plunging open to tight upright folds f2 and minor sub vertical axial planar foliations cleavages s2 d2 was accompanied by post peak near isothermal decompression m3 probably related to exhumation following the crustal thickening sims u pb zircon ages of deformation related leucocratic dykes demonstrate that d1 broadly occurred at 1976 1936 ma and d2 subsequently happened at 1936 1854 ma these results indicate that the khondalite belt underwent long term 100 myr polyphase deformation and high grade metamorphism associated with magmatism timing constraints and kinematic compatibility suggest that the deformation sequence resulted from the nne ssw collision between the yinshan and ordos blocks to form the western block at 1 95 ga

intraseasonal convection and air sea fluxes over the indian monsoon region revealed from the bimodal iso index the present study aims to elucidate the intraseasonal oscillations iso of atmospheric convection and air sea fluxes over the indian region during summer monsoon season to accomplish this the study employs the extended empirical orthogonal function based bimodal iso index developed by kikuchi et al clim dyn 38 9 10 1989 2000 2012 the propagation of deep convective anomalies and air sea fluxes are explored during the different phases p1 p8 of the bimodal index this is achieved by examining the tropical rainfall measuring mission satellite rainfall outgoing long wave radiation olr sea surface temperatures sst downward shortwave radiation dsr and reanalysis products of 850 hpa winds potential vorticity and latent heat fluxes lhfs composite analysis of the anomalies depicts the strong weak northward eastward propagation of convective anomalies over the indian region equatorial indian ocean over the indian region active suppressed or weak convection is evident during the phases of p4 and p5 p1 p2 and p7 p8 enhanced deep convection is lead by a phase of 850 hpa westerly winds and negative sst anomalies signatures of iso during different phases are examined from research moored array for african asian australian monson analysis and prediction rama buoy observations over the bay of bengal rainfall sst and lhf anomalies from rama buoy measurements are in concurrence with the spatial composites of bimodal iso phases plausible drivers for the variability of intraseasonal convection and air sea fluxes were reviewed using published observational and modelling studies findings from the present study advocate the applicability of kikuchi bimodal index clim dyn 38 9 10 1989 2000 2012 over the indian region and have practical application for the validation of ocean atmospheric coupled models

mechanism of the northward propagating intraseasonal oscillation insights from a zonally symmetric model abstract the propagation and initiation mechanisms of the boreal summer intraseasonal oscillation bsiso in the south asian summer monsoon are examined with a zonally symmetric atmospheric model in the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded the model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere the two vertical modes are coupled by the time mean vertical wind shear the model atmosphere produces a 15 20 day oscillation which is characterized by northward propagation of convection from south of the equator to the indian monsoon trough region and a reinitiation of convection in the region between 10 s and the equator the northward propagation in the model is produced by the free troposphere barotropic divergence which leads convection by about a quarter of a cycle the vertical advection of summer mean easterly vertical wind shear by perturbation vertical motion inside the con

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

zircon u pb ages and hf isotopic analyses of migmatite from the paired metamorphic belt in chinese sw tianshan constraints on partial melting associated with orogeny abstract a paired metamorphic belt with ubiquitous migmatites and rare granulites in its high dt dp part formed due to oceanic subduction in chinese southwestern sw tianshan although several geochronological studies have addressed it in recent years the exact timing of the high grade metamorphism and partial melting is still controversial for this study we selected nine samples obtained from three valleys transecting the sw tianshan migmatite complex for u pb geochronology and lu hf isotope analysis to provide constraints on partial melting and the mid crustal evolution during oceanic subduction and subsequent continental collision on the basis of internal morphology th u ratios and ree patterns three types of zircons are discriminated dating them reveals five age groups 1 inherited zircons either are detrital with ages scattering from 432 ma to 3261 ma or yield ages concentrated at 406 410 ma reflecting early devonian magmatism 2 recrystallized zircon has been transformed from pre existing zircon under subsolidus conditions at 400 ma and 360 ma 3 metamorphic rims have grown on zircons at 400 ma 290 ma and 270 ma corresponding to three phases of anatexis the partial melting phase at 400 ma is probably related to the emplacement of voluminous mafic to felsic magmas in a continental arc region above the subduction zone consuming the south tianshan paleo ocean that triggered the most extensive regional scale thermal event however the two subsequent partial melting phases at 290 ma and 270 ma representing post collisional stages were not penetrative p t conditions of the studied migmatites estimated by hb pl thermobarometry and ti in zircon thermometry are 682 763 c 4 7 8 0 kbar together with composite kfs q pl kfs q and kfs q ab inclusions representing entrapped melt and kfs inclusions with ab exsolution lamellae in zircon rims the p t estimates support the occurrence of anatexis zircon lu hf isotope analysis indicates that zircon rims formed under high grade metamorphic conditions and during partial melting by dissolution precipitation of pre existing zircons in a close system zircon two stage hf model ages constrain the development of the protoliths of the migmatites at four major crustal formation periods 1871 ma 1368 1426 ma 1099 1276 ma and 743 ma combined with previous researches in this area we conclude that the main crustal formation of the yili and central tianshan plates has mostly occurred in proterozoic times but not or only subordinately during the archean

application of the two feldspar geothermometer to ultrahigh temperature uht rocks in the khondalite belt north china craton and its implications the paleoproterozoic khondalite belt in the north china craton preserves evidence for ultrahigh temperature uht crustal metamorphism associated with the collision of the yinshan and ordos blocks here we apply two feldspar geothermometry to uht granulites from two localities newly reported in this study tuguishan and xuwujia and another two localities from previous studies dajing tuguiwula and dongpo in the khondalite belt the presence of abundant perthite mesoperthite in these rocks reflects post peak slow cooling the minimum estimated peak metamorphic temperatures are 832 998 819 952 844 1037 and 966 1019 c computed at 8 kbar for the dajing tuguiwula dongpo tuguishan and xuwujia areas respectively these results confirm the previous report of extreme metamorphism at dajing tuguiwula and dongpo and reveal similar conditions in the new localities reported here suggesting that uht metamorphism is widespread in the khondalite belt of the north china craton our study demonstrates that uht metamorphism can be recognized using the two feldspar geothermometry in rocks that do not possess other key uht assemblages

paleoproterozoic ultrahigh temperature granulites in the north china craton implications for tectonic models on extreme crustal metamorphism abstract ultrahigh temperature uht metamorphic rocks associated with the khondalite belt within the inner mongolia suture zone imsz provide robust evidence for extreme thermal metamorphism in the north china craton ncc the imsz marks the collisional suture between the yinshan block to the north and the ordos block to the south as the ncc was incorporated within the columbia supercontinent amalgam during paleoproterozoic here we present a synthesis of the salient features of the uht rocks from the ncc including petrologic indicators fluid characteristics and monazite and zircon chronometry on the extreme crustal metamorphism the granulites carry diagnostic uht mineral assemblages including sapphirine quartz low zn fe3 spinel quartz high alumina orthopyroxene sillimanite quartz and high temperature mesoperthite the stability fields of the typical mineral assemblages conventional geothermobarometry and phase equilibria modeling using pseudosections as reported in a number of recent studies converge to indicate that these uht rocks experienced metamorphic temperatures up to or in excess of 1000 c at ca 10 kbar followed by an isobaric cooling segment the rocks were exhumed along a near isothermal decompression path microstructures mineral reactions and phase equilibria modeling suggest an anti clockwise p t path similar to those displayed by metamorphic orogens developed in subduction collision settings the dominant category of fossil fluids preserved within the major uht minerals is co2 consistent with the stability of the broadly anhydrous mineral assemblage in these rocks both chemical and radiogenic isotopic ages from monazite and zircon chronometry suggest the timing of the uht event as around 1 92 ga the paleoproterozoic high grade metamorphism younging from 1 95 ga in the western domain to 1 92 ga in the eastern domain of the khondalite belt might suggest a scissor like closure of oblique collision between the yinshan and the ordos blocks the salient features of the uht metamorphism in the ncc include 1 extreme metamorphic temperatures at moderate pressures 2 dominantly anhydrous nature of the mineral assemblages typically the stability of orthopyroxene 3 common presence of co2 rich fluid inclusions as the trace of the ambient fluid 4 regional extent of the uht granulites and 5 the association of the uht orogen with an accretionary belt in a continental collisional suture we evaluate the diverse models on the generation of uht orogens including their formation in thickened and inverted back arcs orogen self heating through heat producing elements heat and co2 input by plume impingement below a carbonated tectosphere and asthenospheric upwelling through ridge subduction and slab window process or during post collisional slab break off the ultra hot and dry uht rocks in the ncc provide one of the well preserved examples from the paleoproterozoic globe for investigating extreme metamorphism and related tectonic processes within the plate tectonic paradigm

role of north indian ocean air sea interaction in summer monsoon intraseasonal oscillation abstractair sea coupling processes over the north indian ocean associated with the indian summer monsoon intraseasonal oscillation miso are investigated observations show that miso convection an

the first microbialite coral mounds in the cenozoic uppermost paleocene from the northern tethys slovenia environmentally triggered phase shifts preceding the petm abstract upper thanetian microbialite coral mounds from the adriatic carbonate platform sw slovenia are described herein for the first time representing an important case study of extensively microbially cemented boundstones in the early paleogene the mounds are constructed primarily by microbialites associated to small sized coral colonies forming metric bioconstructions in a mid ramp setting detailed macroscopic and microscopic studies show that microbes are the major framework builders playing a prominent role in the stabilization and growth of the mounds with corals being the second most important component microbial carbonates represent up to 70 of the mounds forming centimetric thick crusts alternating with coral colonies the microbial nature of the crusts is demonstrated by their growth form and internal microfabrics showing accretionary binding and encrusting growth fabrics often with gravity defying geometries thin sections and polished slabs reveal a broad range of mesofabrics with dense structureless micrite leiolite laminated crusts stromatolites and clotted micritic masses thrombolites a first layer of micro encrusters including leiolites and thrombolites occurs in cryptic habitats whereas discontinuous stromatolites encrust the upper surface of corals a second encrustation the major mound construction phase follows and is dominated by thrombolites encrusting corals and other micro encrusters this sequence represents the basic constructional unit horizontally and vertically interlocked in an irregular pattern to form the mounds the processes which favored the deposition of these microbial carbonates were mainly related to in situ precipitation with minor evidences for grain agglutination and trapping processes scleractinian corals comprise moderately diversified community of small centimetric colonial massive platy encrusting and branching forms coral colonies are distributed uniformly throughout the mounds without developing any ecological zonation these features indicate that coral development remained at the pioneer stage throughout the mound growth the spatial relationships between corals and microbialites as well as the characteristics of microbial crusts and coral colonies indicate a strong ecological competition between corals and microbes a model for the evolution of the trophic structures during the mound growth is proposed with changes in the paleoecology of the main bioconstructors triggered by frequent environmental perturbations turbidity and nutrient pressure interpreted here as related to frequent recurrences of wet phases during the warm humid climate of the uppermost thanetian might have promoted temporary dominance of microbes over corals causing rapid environmentally driven phase shifts in the dominant biota

application of zr in rutile thermometry a case study from ultrahigh temperature granulites of the khondalite belt north china craton zr in rutile thermometry was applied to ultrahigh temperature uht granulites from three localities dongpo tuguishan and dajing tuguiwula of the khondalite belt north china craton zr concentrations of analyzed rutiles were detected by la icp ms and emp which display a mutative composition zoning a large inter grain variation a bimodal distribution at around 1 500 and 6 000 ppm and no relationship with the textural setting matrix vs inclusion these characteristics were likely caused by post peak diffusional resetting associated with slow cooling rates and the presence of a co2 rich fluid the grains with lower zr concentrations 500 to 3 000 ppm and temperature estimates 650 to 850 c occur close to or in contact with zircon which was easily affected by post peak processes for example diffusion dissolution reprecipitation the lowest temperatures 650 to 700 c we obtained represent the closure temperature of zr in rutile rutiles with higher zr concentrations 3 000 to 8 000 ppm and calculated temperatures 850 to 1 000 c were least affected by late resetting giving near peak metamorphic temperatures these temperature results higher than 900 c even in excess of 1 000 c from the three localities reconfirm the presence of uht metamorphism our results also suggest that zr in rutile thermometry is valid for ultrahigh temperature estimates in addition there are positive correlations between concentrations of zr and hf nb and ta of the investigated rutiles but the correlations weaken as the concentrations increase especially for nb and ta implying fractionation of nb and ta