revisiting the lushan taihua complex new perspectives on the late mesoarchean early neoarchean crustal evolution of the southern north china craton abstract the taihua complex in the lushan area was divided into gneisses series and supracrustal rocks the former is mainly composed of ttg gneisses and amphibolites and records the late mesoarchean early neoarchean crustal evolution of the southern north china craton ncc late mesoarchean amphibolites 2 84 ga are enriched in light rare earth elements lrees and large ion lithophile elements liles with negative nb ta and ti anomalies derived from partial melting of a metasomatic mantle source late mesoarchean ttg gneisses 2 81 ga have high la yb and sr y ratios and low mgo cr and ni contents and are interpreted as resulting from partial melting of a thickened lower crust with residual garnet and amphibole in the source early neoarchean amphibolites 2 80 2 73 ga show flat ree patterns but slightly negative nb ta and ti anomalies due to the fractionation of ti rich minerals and have depleted hf nd isotopes and were derived from large degree partial melting of a depleted mantle source most of the early neoarchean ttg gneisses show pronounced positive eu anomalies and have relatively lower trace element concentrations and more depleted nd hf isotopes than the late mesoarchean ttg gneisses resulted from the partial melting of thickened juvenile lower crust with residual garnet and amphibole in the source and subsequent plagioclase accumulation in addition some of the early neoarchean ttg gneisses have high mgo cr and ni contents which were likely derived from partial melting of delaminated lower crust or a thickened lower crust interacting with mafic melt late mesoarchean amphibolites and ttg gneisses are restricted in the center of lushan area denoting an ancient continental nucleus in contrast early neoarchean amphibolites and ttg gneisses outcrop in peripheral of the ancient nucleus exhibiting as an elongated belt along the dangzehe river which is evidence for the subduction overall the lushan amphibolites and ttg gneisses show slightly negative to positive whole rock end t and ehf t values and zircon ehf t values indicating a dominant crustal accretion with subordinate crustal reworking therefore the continental growth recorded in the lushan taihua complex was caused by the subduction accretion process suggesting a convergent margin in the southern ncc during the late mesoarchean and early neoarchean

reply to the discussion by karen johannesson on rare earth element geochemistry of scleractinian coral skeleton during meteoric diagenesis a sequence through neomorphism of aragonite to calcite by webb et al sedimentology 56 1433 1463 webb et al 2009 described a late pleistocenecoral sample wherein the diagenetic stabilization of original coral aragonite to meteoric calcite was halted more or less mid way through the process allowing direct comparison of pre diagenetic and post diagenetic microstructure and trace element distributions those authors found that the rare earth elements rees were relatively stable during meteoric diagenesis unlike divalent cations such as sr and it was thus concluded that original in this case marine ree distributions potentially could be preserved through the meteoric carbonate stabilization process that must have affected many if not most ancient limestones although this was not the case in the analysed sample they noted that where such diagenesis took place in laterally transported groundwater trace elements derived from that groundwater could be incorporated into diagenetic calcite thus altering the initial ree distribution banner et al 1988 hence the paper was concerned with the diagenetic behaviour of rees in a groundwater dominated karst system the comment offered by johannesson 2011 does not question those research results but rather seeks to clarify an interpretation made by webb et al 2009 of an earlier paper johannesson et al 2006

mesoarchean assembly and stabilization of the eastern kaapvaal craton a structural thermochronological perspective 1 understanding the construction and stabilization of archean continental lithosphere has important implications for models of tectonic and thermal regimes in the early earth as well as for the subsequent evolution of continents we provide new constraints for the amalgamation and stabilization of the eastern kaapvaal craton in the vicinity of the barberton greenstone belt circa 3 3 3 1 ga isotope dilution thermal ionization mass spectrometry u pb geochronology and thermochronology are combined with mapping and structural analysis around the margins of this belt in order to constrain movement on major shear zones that separate high grade orthogneiss terranes from low grade supracrustal rocks and to relate this movement to the timing of differential exhumation new and existing data are consistent with accretion at 3 23 ga within an oblique subduction plate boundary manifested in the bgb as an asymmetric flower like structural geometry for 100 ma following terrane assembly transform boundary tectonics manifested partially as transtension on reactivated faults led to large scale juxtaposition of middle to lower crustal basement orthogneiss complexes against upper crustal greenstone sequences and episodic emplacement of granitic batholiths stabilization of this portion of archean lithosphere involved at least a three stage process 1 creation of a thick and rigid mantle lithosphere during crustal growth subduction and terrane assembly from circa 3 30 to 3 23 ga 2 generation of a rigid crust during strike slip and transtensional tectonics coupled with migration of granites and heat producing elements into the upper crust between circa 3 2 and 3 1 ga and 3 erosion and removal of the uppermost crust during regional peneplanation that lasted until circa 2 9 ga

late quaternary climates of the australian arid zone a review abstract aridity in australia has generally been associated with glacial intervals of the last few glacial cycles the causes and nature of aridity varied from north to south over the continent in northern and central australia reduced monsoon rain in global cold stages caused lakes and rivers to dry vegetation to become more sparse sand dunes to become active and dust advection to increase while the monsoon is correlated with warmer global temperatures and high sea levels overall the exact timing of the greatest development of the monsoon in stage 5 remains uncertain in southeastern australia the proxy records give a less clear picture while vegetation seems to have been more sparse in cold stages and sand dune activity and dust flux consequently greater records of runoff in rivers and lakes have mixed or opposite behaviour to northern or central australia the nature of aridity in southeastern australia is not analogous to conditions anywhere on the continent today greatly reduced temperatures over the central and southern interior greater influence of snow and periglaciation on runoff high groundwater tables lower rainfall and reduced atmospheric carbon dioxide levels may all have contributed to and interacted to produce the reconstructed picture of a cold sparsely vegetated arid landscape with large rivers and perennial lakes the largest changes in circulation patterns over the glacial cycle probably occurred in the location and or intensity of summer tropical convergence in northern australia over southern australia changes to the temperature and humidity of the westerly circulation have been more significant than the small fluctuations in latitude of the sub tropical high pressure ridge

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

age origin and significance of the wugang bif in the taihua complex southern north china craton abstract the wugang bif hosted in a neoarchean taihua complex th in the wugang area at the southern margin of the north china craton ncc is one of the important iron ore in central plain in this study we report new data on whole rock compositions of iron ore sample u pb isotopic compositions of detrital zircon from metasedimentary rocks one bif sample and two associated garnet paragneisses in combination with literature data they yielded a minimum age peak of 2 60 ga for 110 detrital zircons of magmatic origin from the tieshanmiao formation dominantly bif bearing strata that we interpret as an upper limit age for the wugang bif depositional age thirty six detrital zircons of metamorphic origin gave a maximum metamorphic age peak of 2 45 ga reflecting the lower limit age thus the depositional ages of wugang bif can constrained at 2 60 2 45 ga the presence of proximal detrital zircons in bif samples river flux contributions and some bif samples have true negative ce anomalies suggest that they were deposited in near shore continental shelf or back arc basin environments coinciding with that they are typically interbedded with marble quartz arenite and other metasedimentary rocks but lack of volcanic material in particular both hanging wall and footwall for tiegukeng bif orebody from tieshanmiao formation are marble except for several diopside dykes 1943 ma orebody is dominantly composed of pyroxene rich bif quartz rich bif and other metasedimentary rocks the wugang bif displayed the weak positive eu eu sn anomalies average 1 74 associated with the low cr 10 ppm and v

geochronology and geochemistry of the ttg and potassic granite of the taihua complex mts huashan implications for crustal evolution of the southern north china craton abstract tonalite trondhjemite granodiorite ttg suite and potassic granite volumetrically expose in the neoarchean to paleoproterozoic taihua complex mts huashan region southernmost segment of the trans north china orogen tnco zircon u pb dating on the trondhjemite granitic gneiss k feldspar granite and coarse grained granite samples show three episodes of magmatism 2 55 2 49 ga 2 33 2 25 ga and 1 87 1 80 ga with distinct geochemical features in this area during the paleoproterozoic the trondhjemite samples have high sio2 67 46 71 73 wt na2o 4 83 5 95 wt low mg 31 40 and hree contents with moderate la yb n values 16 8 to 35 3 and sr y ratios 15 8 to 34 the potassic granite samples show high sio2 65 2 75 43 wt k2o 3 9 8 6 low na2o 1 74 4 17 wt mg 2 46 and hree contents with moderate to high la yb n values 10 3 to 226 and sr y ratios 12 8 to 208 all these granitoid samples are characterized by high sio2 and low mg cr ni with moderate to high la yb n values and sr y ratios the absence of evidence of any pre existing high sr y and la yb sources in this region led to that the granitoids probably generated from partial melting of hydrous mafic rocks with garnet and amphibole in the residue therefore partial melting of thickened lower curst is the most likely origin combined with previous studies the first episodic magmatism 2 55 2 49 ga represented by ttg and granitic gneisses with positive whole rock nd t and zircon hf t values is interpreted as melts from partial melting of juvenile thickened lower crust the second episodic magmatism 2 33 2 25 ga represented by ttg granitic gneisses and k feldspar granite with positive to negative whole rock nd t and zircon hf t values is suggested as the product of partial melting of both juvenile and pre existing crustal material the third episodic magmatism 1 87 1 80 ga is represented by these potassic granites which is synchronism with the metamorphism recorded in this region and probably resulted from partial melting of pre existing crustal materials in a syn orogenic or post orogenic setting during the collision between the eastern and western blocks of the north china craton multistage continental accretion at 2 84 2 72 ga 2 57 2 43 ga and 2 36 2 25 ga and reworking at 2 36 2 25 ga 2 19 2 07 ga and 1 87 1 80 ga occurred in the southern segment of the tnco from neoarchean to paleoproterozoic transformation from an andean type continental margin arc setting on the western margin of the eastern block to continent arc continent collision in the southern tnco during late neoarchean to late paleoproterozoic is suggested in this paper

initiation of the australian summer monsoon 14 000 years ago abstract definitive evidence for the onset of monsoon moisture in northern australia following the arid phase of the last glacial maximum has been elusive in large part due to the lack of long continuous sediment records here we report new evidence from two separate drainage basins in the kimberley region of monsoonal northwestern australia at both sites radiocarbon ages on basal biogenic materials in flood deposits indicate stream flow as high or higher than maximum historic levels began about 14 cal ka bp these results suggest that the australian summer monsoon was fully active several millennia earlier than previously expected the early onset of the monsoon and the widespread evidence for diminished monsoon activity in the late holocene cannot be reconciled with primary forcing of the australian monsoon by changes in low latitude summer insolation over australia

geochemistry of ttg and ttg like gneisses from lushan taihua complex in the southern north china craton implications for late archean crustal accretion the late archean taihua complex mainly composed of amphibolite and ttg and ttg like gneisses is volumetrically most important metamorphic rock suites scattered along the southern margin of the north china craton ncc zircon shrimp u pb dating shows two episodes 2765 13 and 2723 9 ma of archean magmatism in the lushan area with distinct geochemical features the early 2765 13 ma suite ttg like gneisses has low sio2 52 5 66 1 wt high mg 0 47 0 68 low hree ybn 3 0 5 4 and y 8 07 13 9 ppm with low to moderate la yb n 6 7 37 1 and sr y 25 9 119 3 the younger 2723 9 ma suite ttg gneisses has high sio2 63 5 74 3 wt low mg 0 13 0 52 very low ree ybn 1 1 20 2 43 both suites show pronounced negative nb ta and ti anomalies on the primitive mantle normalized spidergram the ttg like gneiss suite has similar bulk rock nd and zircon hf model ages 3 0 ga with end t 0 0 26 1 46 and is interpreted as resulting from melt of mantle interactions with the melts derived from partial melting of subducted ocean crust with a residual assemblage of garnet clinopyroxene rutile amphibole which favors subducted slab model for the late archean ttg the ttg gneiss suite has abundant relic zircons 2 95 2 80 ga with end t 0 1 31 to 0 23 which is best interpreted as derived from partial melting of thickened lower continental crust with a garnet amphibolite residue garnet amphibole rutile significant high pressure fractional crystallization garnet amphibole and accumulation plagioclase are also required in the petrogenesis the lushan amphibolite with nearly flat primitive mantle normalized trace element pattern is interpreted to represent early ocean crust metamorphism these observations suggest a possible model of late archean crustal accretion from ocean crust to continental terrain in the southern north china craton

mesoarchean to paleoproterozoic crustal evolution of the taihua complex in the southern north china craton abstract the taihua complex is exposed mostly in the central western part along the southern margin of the north china craton ncc in this study field geological geochemical la icp ms zircon u pb age dating and lu hf isotopic analysis are applied to the orthorgneisses felsic leucosomes and granites of the taihua complex in order to provide constraints on its crustal evolution from the mesoarchean to paleoproterozoic ca 2 9 1 8 ga the ca 2 90 2 73 ga magmatism was an important episode of contemporaneous crustal growth and crustal reworking among them the ca 2 90 ga granodioritic enclaves have features similar to those of the archean sanukitoids and were generated by the direct partial melting of peridotitic mantle wedge in the subduction processes representing the early continental nucleus the ca 2 84 ga high mg ttgs were derived from the partial melting of subducted oceanic crust after interaction with mantle wedge whereas the ca 2 82 2 77 ga low mg ttgs were originated from the partial melting of underplated basaltic crust pointing to a series of continuous arc magmatic activities the formation of the ca 2 75 2 73 ga crust derived granites and felsic leucosomes in association with the contemporaneous metamorphism indicate the presence of a crustal anatexis which probably was the result of an important magmatic underplating event the magmatism between 2 9 ga and 2 73 ga indicates that the increased crust mantle interaction and crustal differentiation stimulated the crust in the taihua complex to become more matural the ca 2 57 2 43 ga magmatism represents another prominent magmatism in the taihua complex the ttg gneisses and dioritic gneisses aged at ca 2 57 2 50 ga were derived from partial melting of the hydrated basalts under eclogite to garnet amphibolite facies conditions with interaction between initial melts and mantle wedge indicating that incessant subduction led to the amalgamation of micro blocks the intrusion of granitic rocks felsic leucosomes ttg like gneisses accompanied by metamorphism during ca 2 50 2 43 ga indicate that a dominant crustal anatexis event occurred in association with the cratonic stabilization processes the ca 2 36 2 24 ga magmatism was also characterized by reworking of the basement rocks which are represented by the intrusion of calc alkaline monzogneisses a type granitic gneisses and mafic dykes this scenario was coeval with the formation of volcanic sedimentary sequences indicating the presence of an extension event in the taihua complex the ca 1 96 1 85 ga tectono thermal event represented the last phase of compressional deformation and consequent metamorphism leading to reworking of the pre existed basement rocks this event formed a wnw ese trending metamorphic belt that extends over 1000 km along the southern margin of the ncc and was well concordant with the world wide orogeny associated with the amalgamation of nuna supercontinent subsequently widespread a type granites mafic dykes and volcanic rocks aged of ca 1 84 1 74 ga formed marking the final consolidation of the crystalline basement at the taihua complex since then the southern ncc became stable and entered into the stage of development of platform

the source of a type magmas in two contrasting settings u pb lu hf and re os isotopic constraints the sources of post orogenic a type magmas from two distinct geodynamic settings are compared the end of the ca 514 480 ma delamerian orogeny southeastern south australia was marked by 10 myr of bimodal a type magmatism driven by convective removal of thickened lithosphere initial os and hf isotope ratios record a heterogeneous lithospheric mantle source with some input from aesthenospheric mantle mafic parental melts fractionated to produce the granites in contrast initial os isotope ratios of the a type magmas that comprise the ca 1598 1583 ma mesoproterozoic gawler felsic large igneous province central south australia record a dominant evolved lower crust component however initial hf isotope ratios from these samples are depleted indicating a mantle source for lithophile elements this voluminous bimodal magmatism lasted for 15 myr and ended the wartakan orogeny in both cases the homogenisation of chemical rheological heterogeneities inherited from terrain amalgamation and orogenic thickening strengthened the lithosphere the contemporaneous fusion of heterogeneous mantle crust may represent a common stabilising influence on the lithospheric column regardless of tectono magmatic setting

episodic crustal growth in the southern segment of the trans north china orogen across the archean proterozoic boundary abstract the dengfeng and taihua complexes are well exposed neoarchean to paleoproterozoic units in the southern segment of the trans north china orogen tnco zircon u pb dating shows that the dengfeng complex records two episodes 2568 11 ma and 2306 6 ma of tonalite trondhjemite granodiorite ttg magmatism all of the ttg rocks are characterized by high sio2 66 7 75 4 wt na2o 3 20 5 06 wt and relatively low mgo 0 40 1 78 wt the late neoarchean ttg gneisses have very low contents of hree ybn 0 69 2 75 and y 1 73 7 07 ppm with moderate la yb n 24 1 53 8 and high sr y 65 1 291 3 ratios the early paleoproterozoic ttg gneisses have low contents of hree ybn 2 93 6 37 and y 6 7 11 0 ppm with moderate la yb n 10 1 27 0 and sr y 10 6 52 1 ratios both suites show pronounced negative nb ta p and ti anomalies but positive sr and pb anomalies the late neoarchean ttg gneisses all have similar bulk rock nd and zircon hf model ages with mainly positive nd t and are interpreted as resulting from the melting of dominantly juvenile thickened lower crust with residual garnet and amphibole the early paleoproterozoic ttg gneisses have extremely variable nd t 6 23 to 4 23 and heterogeneous zircon hf t 3 3 to 3 1 which are also best interpreted as resulting from the partial melting of thickened lower crust with residual amphibole and garnet the taihua complex in the xiaoqinling area records three episodes of early paleoproterozoic ttg magmatism 2 48 ga at caotan 2 31 ga at houjiacun and 2 16 ga at bayuan younger than the taihua complex in the lushan area 2 85 2 72 ga all rocks have relatively low contents of hree ybn 1 03 8 32 and y 2 84 24 ppm with moderate la yb n 8 7 88 4 and sr y 19 8 125 8 ratios and show negative ta nb and ti anomalies and positive sr and pb anomalies the caotan gneisses at 2 48 ga and the houjiacun ttg gneisses at 2 31 ga have low mg 0 14 0 45 low cr the geochronology of the dengfeng complex in the dengfeng area and the taihua complex in the lushan xiong er and xiaoqinling areas reveals at least four magmatic episodes in the southern segment of the tnco from the late mesoarchean to early paleoproterozoic 2 85 2 72 ga 2 57 2 48 ga 2 34 2 30 ga and 2 20 2 07 ga the rocks of the two early episodes are dominantly of juvenile compositions with mostly positive whole rock nd t and zircon hf t values suggesting two episodes of crustal growth formed in a subduction tectonic setting the magmatic rocks of the third episode consist of both the juvenile and pre existing crustal materials with variable whole rock nd t and zircon hf t values which were generated in a subduction zone during the initial assembly of the ncc within the columbia supercontinent cycle the final episode of magmatism lacks juvenile materials with whole rock nd t and zircon hf t values being consistently negative these may have resulted from the orogenic collapse the episodic continental growth recorded in the southern segment of the tnco was caused by subduction and consequent orogeny consistent with global supercontinent cycles within the late archean and early paleoproterozoic

evidence of enso mega drought triggered collapse of prehistory aboriginal society in northwest australia the kimberley region of northwest australia contains one of the world s largest collections of rock art characterised by two distinct art forms the fine featured anthropomorphic figures of the gwion gwion or bradshaw paintings and broad stroke wandjina figures luminescence dating of mud wasp nests overlying gwion gwion paintings has confirmed an age of at least 17 000 yrs b p with the most recent dates for these paintings from around the mid holocene 5000 to 7000 yrs b p radiocarbon dating indicates that the wandjina rock art then emerged around 3800 to 4000 yrs b p following a hiatus of at least 1200 yrs here we show that a mid holocene enso forced collapse of the australian summer monsoon and ensuing mega drought spanning approximately 1500 yrs was the likely catalyst of this change in rock art the severity of the drought we believe was enhanced through positive feedbacks triggered by change in land surface condition and increased aerosol loading of the atmosphere leading to a weakening or failure of monsoon rains this confirms that pre historic aboriginal cultures experienced catastrophic upheaval due to rapid natural climate variability and that current abundant seasonal water supplies may fail again if significant change in enso occurs

the timing of linear dune activity in the strzelecki and tirari deserts australia abstract linear dunes occupy more than one third of the australian continent but the timing of their formation is poorly understood in this study we collected 82 samples from 26 sites across the strzelecki and tirari deserts in the driest part of central australia to provide an optically stimulated luminescence chronology for these dunefields the dunes preserve up to four stratigraphic horizons bounded by palaeosols which represent evidence for multiple periods of reactivation punctuated by episodes of increased environmental stability dune activity took place in episodes around 73 66 35 32 22 18 and 14 10 ka intermittent partial mobilisation persisted at other times throughout the last 75 ka and dune activity appears to have intensified during the late holocene dune construction occurred when sediment was available for aeolian transport in the strzelecki and tirari deserts this coincided with cold arid conditions during marine isotope stage mis 4 late mis 3 and mis 2 and the warm dry climates of the late pleistocene holocene transition period and late holocene localised influxes of sediment on active floodplains and lake floors during the relatively more humid periods of mis 5 also resulted in dune formation the timing of widespread dune reactivation coincided with glaciation in southeastern australia along with cooler temperatures in the adjacent oceans and antarctica

geochronology and petrogenesis of gray gneisses from the taihua complex at xiong er in the southern segment of the trans north china orogen implications for tectonic transformation in the early paleoproterozoic the taihua complex in the xiong er area along the southern segment of the trans north china orogen tnco consists of gray gneisses with minor amphibolites zircon u pb dating of the gray gneisses reveals at least two episodes of early paleoproterozoic magmatism 2 30 2 32 ga and 2 07 2 19 ga each with distinct geochemical features the tieluping ttg gneisses of the early suite have very low hree ybn 0 58 4 75 and y contents 2 05 13 2 ppm with moderate to high la yb n 14 3 192 6 and sr y ratios 38 5 220 1 pronounced negative ta nb and ti anomalies but positive sr and pb anomalies the protoliths of these gneisses were most likely derived from partial melting of thickened lower crust with residual garnet and amphibole and underwent garnet amphibole fractionation plagioclase accumulation and or fractionation the tieluping ttg gneisses have variable zircon hf model ages tdm hfc 2 48 3 06 ga and whole rock end t values 4 89 4 98 and the youngest whole rock depleted mantle nd model age tdm 2 32 ga is close to the crystallization age of the ttg 2318 8 ma the protolith of the gneisses formed from a combination of pre existing continental crust and juvenile materials implying an andean type continental margin arc environment it is suggested that crustal thickening was the result of accretionary orogenesis accompanied by basaltic underplating the ganshugou potassium rich gneisses of the later suite have low na2o and high k2o and show fractionated lree and nearly flat hree patterns with strong negative ta nb and ti anomalies they are characterized by negative end t values 5 01 to 2 33 and heterogeneous zircon ehf t values 10 65 2 10 with decoupling of zircon hf model ages tdm hfc 2 64 3 23 ga and whole rock nd model ages tdm 2 55 2 81 ga the protolith of the ganshugou gneisses was a potassium rich igneous rock which was likely the result of partial melting of pre existing crustal materials at shallow depth compatible with a post collisional setting there is therefore a tectonic transformation from an accretionary orogenesis to an extensional regime as a consequence of post collisional uplift in the southern segment of the tnco in the early paleoproterozoic

crustal growth in the north china craton at 2 5ga evidence from in situ zircon u pb ages hf isotopes and whole rock geochemistry of the dengfeng complex abstract the dengfeng complex is located on the southern margin of the north china craton ncc and belongs to the southern portion of the trans north china orogen this terrane is important to understand the formation and evolution of ncc during late neoarchean 2 5 ga the dengfeng complex is well exposed in the junzhao region and comprises two distinct lithologic units supracrustal assemblage and plutonic rocks la icpms magmatic zircon u pb age data shows that the rocks formed within the range of 2547 2504 ma the available hf isotope data indicate that the majority of ca 2 5 ga zircons from the dengfeng complex have high e hf t values close to the initial hf isotope ratios of the contemporaneous depleted mantle these data indicate that the rocks in the dengfeng represent juvenile crust the ttg gneisses in the dengfeng complex display low mg 41 48 mgo 59 69 mgo 3 5 6 6 wt ni 82 130 ppm and cr 148 237 ppm abundances elevated sr 1759 1927 ppm and ba 1742 2289 ppm concentrations and high lree la n 38 487 such geochemical features are similar to archean sanukitoids a two stage model is applied here to explain the genesis of metadiorites of dengfeng complex 1 firstly the mantle is metasomatized either by melts or by aqueous fluids from a subducted slab 2 subsequently sanukitoid magmas were produced by partial melting of the hybridized mantle furthermore the amphibolites of supracrustal rocks have a mixture of morb and arc like geochemical affinities suggesting the development of a back arc in the southern ncc at ca 2 5 ga the contemporary late neoarchean ttgs sanukitoids and morb back arc association may represent a late neoarchean tectonic melange implying a neoarchean subduction accretion process which would suggest that modern style plate tectonics processes was probably initiated in the southern ncc by 2 5 ga

late neoarchean to early paleoproterozoic tectonic evolution of the southern north china craton evidence from geochemistry zircon geochronology and hf isotopes of felsic gneisses from the taihua complex abstract the archean paleoproterozoic taihua complex extending from east to west along the southern margin of the north china craton ncc is an ideal window to understand the tectonic evolution of the early earth here we present new data on petrology zircon geochronology whole rock geochemistry and isotopes of ttgs granitic gneisses and felsic leucosomes of migmatites from the taihua complex in the xiaoqinling area zircon la icp ms analyses of rocks yield the formation ages of 2564 2503 ma for ttgs 2481 2476 ma for felsic leucosomes and 2359 2334 ma for granitic gneisses respectively the zircon lu hf isotopes suggest that crustal growth occurred in the late neoarchean and crustal reworking occurred in the end of neoarchean and the early paleoproterozoic the ttg gneisses are characterized by high na2o k2o la yb sr y and low nb ta ratios and they were likely generated by partial melting of subducted juvenile oceanic crust with garnet or amphibole in residuals a mechanism similar to the slab melting model both the felsic leucosomes and granitic gneisses have high sio2 contents and various hf isotopic compositions and they probably were formed in an extensional setting attributing to partial melting as well as mixing of the preexisting ttg suite statistically we report a major transitional phase in the tectonic milieu of the southern ncc from compression to extension during the late neoarchean ca 2 57 2 42 ga the compressional tectonics can be attributed to amalgamation of micro continental blocks during the late neoarchean ca 2 57 2 5 ga as the leading period of crustal growth and associated multistage ttg magmatism in contrast the extensional phase occurred during the end of neoarchean ca 2 5 2 42 ga that may represent the end of cratonic stabilization period and formation of large amounts of k rich granitic rocks widespread high grade metamorphism and migmatites additionally the formation of a large amount of crust derived granites and mafic dykes during the early paleoproterozoic in southern ncc reflect another stage ca 2 36 2 24 ga of crustal extension which represents an episode of initial worldwide rifting events probably linking to the great oxygen event goe therefore the present study proposes a new profile on multi stage crustal growth reworking and craton stabilization during neoarchean paleoproterozoic period along the southern ncc and provides useful insights on complex and heterogeneous evolutionary processes of early earth

episodic mantle melting crustal reworking in the late neoarchean of the northwestern north china craton zircon ages of magmatic and metamorphic rocks from the yinshan block abstract the yinshan block in the northwestern north china craton comprises late neoarchean greenstones high grade metamorphic rocks granulite charnockite enderbite and amphibole gneiss diorites sanukitoid and mg adakite and granitoids predominantly trondhjemite tonalite a greenstone terrane comprises a volcanic sequence of predominant basalt and dacite with minor andesite zircons from a high mg andesite and an andesite have weighted mean 207pb 206pb ages of 2533 5 ma and 2510 7 ma respectively which reflect the timing of two distinct volcanic episodes these two either predated or postdated a major volcanic episode that formed a basalt dacite bimodal suite during 2515 10 basalt to 2516 10 ma dacite magmatic zircons from the high grade metamorphic rocks yielded weighted mean 207pb 206pb ages of 2544 5 ma for a mafic granulite 2521 6 ma for a garnetiferous gneiss 2535 5 ma for a charnockite and 2526 5 ma for an amphibole gneiss these ages reflect the minimum emplacement time of rocks that make up the protoliths of the high grade metamorphic complex the metamorphic ages of the high grade complex were determined at 2515 18 ma for mafic granulite and 2503 12 ma for garnetiferous gneiss zircons from a high mg diorite i e sanukitoid have a weighted mean age of 2520 6 ma which is significantly younger than the 2556 14 ma age of a magnesian diorite mg adakite from the same diorite massif these ages reflect distinctive magmatic pulses that generated the diorite massif a tonalite has a zircon age of 2516 7 ma indistinguishable from the 2520 9 ma age of a trondhjemite from the same trondhjemite tonalite dominated batholith a granitic compositional layer in the 2516 7 ma tonalite has zircon ages of 2515 6 ma high u zircon domains and 2512 22 ma low u zircon domains which reflect an intracrustal melting event the presence of an older crustal remnant ca 2600 ma prior to the formation of the yinshan block is indicated by a 2594 4 ma leucogranite xenolith in the diorite massif and by the widespread presence of ca 2583 3485 ma mostly ca 2700 ma zircon xenocrysts in a variety of volcanic and plutonic rocks an undeformed pegmatite dike in high mg andesite has an emplacement age of 2508 17 ma zircon an undeformed trondhjemite dike that cuts the supracrustal greenstone sequence yielded a zircon age of 2502 6 ma similar to that of the pegmatite dike and representing the latest archean magmatic event in the yinshan block these ages of undeformed granitoid dikes delimit the termination of thermo tectonic development of the yinshan block based on these new ages and published geological and geochronological data we conclude that the yinshan block is a typical neoarchean cratonic block not a segment of the so called paleoproterozoic inner mongolia north hebei orogen episodic mantle melting and resultant crustal reworking account for the thermo tectonic development of the yinshan block in a brief period ca 2556 2502 ma in the late neoarchean and based on their regional chronological correlations we argue for their craton scale significance

secular changes in tonalite trondhjemite granodiorite composition as markers of the progressive cooling of earth archean tonalite trondhjemite granodiorite associations ttg are classically thought to generate through partial melting of hydrous metabasalts however the chemical composition of the least differentiated ttg parental magmas evolved from 4 0 to 2 5 ga during this interval the mg as well as the ni and cr contents increased which is interpreted as reflecting increased interactions between felsic melts generated by metabasalt melting and mantle peridotite similarly cao na2o and sr also increased over time thus reflecting an increase in the abundance of plagioclase in the melt residue the presence or absence of residual plagioclase is interpreted in terms of melting depth the demonstrated interaction between ttg parental magmas and the mantle rules out their genesis by fusion of previously underplated metabasalt and favors the melting of subducted slab material at 4 0 ga earth s geothermal gradient was sufficiently high to allow slab melting at shallow depths where plagioclase was stable consequently due to the small thickness of the overlying mantle wedge felsic magmas interacted little with the mantle at 2 5 ga however owing to lower geothermal gradients the melting depth was greater and plagioclase became no longer stable in the thick mantle wedge overlying the subducted slab as a result felsic magmas reacted strongly with the mantle peridotite the changes of ttg composition during archean time can be thus interpreted as reflecting the progressive cooling of earth

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

shrimp u pb zircon geochronology of the huai an complex constraints on late archean to paleoproterozoic magmatic and metamorphic events in the trans north china orogen the huai9an complex is situated in the northern segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete archean eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of six distinct lithologic units the huai9an ttg gneisses the manjinggou high pressure mafic granulites the khondalite series the dongjiagou granitic gneiss the huai9an charnockite and the dapinggou k feldspar granite shrimp u pb geochronology combined with th and u data and cathodoluminescence cl imaging of zircons enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the tnco cl images reveal the coexistence of magmatic and metamorphic zircons in most lithologies of the huai9an complex of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating oscillatory zoned magmatic zircon cores shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic protoliths of the huai9an ttg gneisses were emplaced at 2515 20 ma 2499 19 ma and 2440 26 ma respectively much earlier than the emplacement of the dongjiagou granitic gneiss dated at 2036 16 ma however their metamorphic zircons yield similar concordant 207pb 206pb ages of 1847 17 ma 1842 10 ma and 1847 11 ma for the tonalitic trondhjemitic and granodioritic gneisses respectively and 1839 46 ma for the dongjia granitic gneiss these ages demonstrate that the huai9an complex underwent a regional metamorphic event at 1850 ma which is further supported by a mean 207pb 206pb age of 1848 19 ma for metamorphic zircons in the manjinggou high pressure mafic granulite and 1849 10 ma and 1850 17 ma for igneous zircons in the anatectic huai9an charnockite and dapinggou garnet bearing s type granite respectively the timing of late archean to paleoproterozoic magmatism and regional metamorphism in the huai9an complex is in general agreement with recent shrimp zircon data for other metamorphic complexes in the tnco these data prove that the high grade gneiss complexes were not the basement to the low grade granite greenstone terranes in the tnco furthermore the lithologies of the orogen are considered to have developed as a long lived magmatic arc that was subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western blocks at 1 85 ga leading to final assembly of the north china craton

a paleoproterozoic drowned carbonate platform on the southeastern margin of the wyoming craton a record of the kenorland breakup abstract the nash fork formation in the upper part of the early paleoproterozoic snowy pass supergroup medicine bow mountains of wyoming was deposited on a mature passive margin along the southern flank of the wyoming craton and straddles the end of the ca 2 2 2 1 ga carbon isotope excursion two drowning events marked by black shales subdivide the carbonate platform into three parts the lower nash fork formation consists of outer shelf to supratidal deposits represented by massive and stromatolitic dolomites heterolithic siliciclastics carbonates large silicified domal digitate stromatolites nodular dolomites and stromatolitic dolomites molds after evaporite crystals are pervasive in the heterolithic siliciclastics carbonates large silicified domal digitate stromatolites formed biostromes and bioherms following flooding events the middle nash fork formation comprises two intervals of black shale separated by inner shelf heterolithic siliciclastics nodular carbonates black shales are organic and pyrite rich contain turbidites and developed in response to drowning of the platform overlying massive dolomite of the upper nash fork formation was deposited in an unprotected intertidal setting and displays an upward shallowing trend terminated by a prominent karstic surface in the middle of the unit the nash fork formation is open marine with no evidence for restricted circulation on the carbonate platform the two drowning events on the carbonate platform are likely related to dissection of the mature passive margin associated with the breakup of kenorland the younger drowning event is associated with the end of the carbon isotope excursion the main building elements of the lower and middle nash fork carbonate platform are dolomitic mudstones and stromatolites macroscopic seafloor precipitates are volumetrically negligible with the exception of tufa deposits and domes in the massive and stromatolitic dolomites and possibly digitate stromatolites within domal digitate stromatolites the upper nash fork formation comprises dolomitic mudstones relatively rare stromatolites and inorganic precipitates that are more common than in the underlying carbonates styles of carbonate deposition on this early paleoproterozoic platform differ from those documented on late archean carbonate platforms there are fewer macroscopic seafloor precipitates and more dolomitic mudstones this pattern is considered to be related to a rise of the atmospheric oxygen level that led to a decrease in bicarbonate saturation in the ocean

environmental history of northwest australia based on phytolith analysis at carpenter s gap 1 examination of a phytolith assemblage from the archaeological site of carpenter s gap 1 provides an hitherto unrecognised source of vegetation history for the tropical savannah region of north western australia two predominant mechanisms contributed to the formation of the phytolith assemblage firstly the introduction of phytoliths in plant materials brought in by humans and secondly the introduction of phytoliths contained in faecal pellets deposited by animals separating the effects of both mechanisms enables local vegetation patterns and by inference climatic conditions to be reconstructed the period ca 40 000 years bp was probably wetter than today allowing the southerly expansion of palms beyond their present day distribution grassland compositional changes occurred by ca 33 000 years bp probably resulting from a combination of lowered rainfall decreased temperatures and possibly aboriginal firing activities a reduction in palm at a similar time followed by its complete disappearance in association with the loss of ulmaceae prior to the last glacial maximum lgm indicates a continued trend in decreasing water availability an abundance of cyperaceae sponge spicules and diatoms during the lgm when considered in conjunction with the other evidence possibly represents altered human behaviour in response to increased aridity

a 100 000 year record of annual and seasonal rainfall and temperature for northwestern australia based on a pollen record obtained offshore pollen recovered from core tops of deep sea cores from offshore northwestern western australia were used to build climatic transfer functions applied to sediment samples from major rivers bordering the ocean in the same region and a deep sea core offshore northwest cape results show for the last 100 000 years with a gap in the record spanning the 64 000 to 46 000 years interval that from about 100 000 to 82 000 yr bp climatic conditions represented by rainfall temperature and number of humid months were significantly higher than today s values for the entire record the coldest period occurred about 43 000 to 39 000 yr bp but it was wetter than today whereas the last glacial maximum saw a significant reduction in summer rainfall interpreted as a result of the absence of monsoonal activity in the region the holocene can be divided into two distinct phases one peaking around 6000 cal yr bp with highest rainfall and summer temperatures the second one commencing at 5000 cal yr bp and showing a progressive decrease in summer rainfall in contrast to an increase in winter rainfall paralleled by a progressive decrease in temperatures copyright 2006 john wiley sons ltd

petrogenesis of the archean tonalite trondhjemite granodiorite ttg and granites in the lushan area southern margin of the north china craton implications for crustal accretion and transformation abstract tonalite trondhjemite granodiorite ttg assemblages and abundant high k calc alkaline magmatism are considered to be closely related to craton stabilization and usually record a tectonic transition three episodes of granitic magmatism are identified in the lushan area at the southern margin of the north china craton ncc on the basis of new la icp ms zircon u pb ages and whole rock geochemical data they are ttg gneisses sodic potassic granite spg suite and potassic granite dated at 2840 ma 2760 ma and 2570 ma respectively the ttg gneisses have high sio 2 variable mg cr and ni contents with high la yb n and sr y ratios suggesting that the parental magmas were derived by partial melting of subducted oceanic crust they show no obvious correlations between sr y and dy yb or la yb n and dy yb and all have negative nb and ta but positive zr and hf anomalies and variable dy yb nb ta zr hf and zr sm ratios suggesting melting of a deep source 45 km with rutile eclogite and garnet amphibolite in the residue the ttg samples have positive hf t values 2 6 to 7 0 with the youngest t dm c 2896 ma close to the crystallization age indicating that they were produced by partial melting of juvenile crustal materials in an arc setting rocks of the spg suite have high sio 2 contents variable na 2 o k 2 o ratios 0 41 10 91 and low y and yb contents with high sr y ratios indicating an affinity to i type granites they display depleted and concave upward ree patterns between middle and heavy rees and higher zr sm than ttg gneisses possibly resulting from amphibole removal by fractional crystallization or as a residual phase during melting meanwhile the rocks have a large variation of dy yb without obvious correlations between sr y and dy yb and la yb n and dy yb in combination with variable but uniformly low y contents therefore we suggest that the spg samples were derived from partial melting with garnet in the residue magmatic zircons have hf t values from 4 3 to 4 2 with t dm c ages from 3200 ma to 2877 ma indicative of older mafic lower crustal sources the rocks formed within a short time interval with the ttg and their emplacement was accompanied by regional granulite and amphibolite metamorphism implying that they may also have formed in an arc setting the potassic granite has high sio 2 74 79 wt and k 2 o na 2 o 9 22 wt contents with a low 10 000ga al 1 89 ratio and t zr 670 c magmatic zircons have a narrow range of hf t values 2 0 to 4 1 with t dm c ages 2942 2692 ma older than the formation age but consistent with the formation age ca 2760 ma of the lushan spg suite the potassic granite has a hf isotope composition identical to that of the spg suite and is enriched in lree and depleted in y with a positive eu anomaly suggesting that the spg suite is the main source one zircon yielded an inherited age of 2837 36 ma consistent with the age of the ttg gneisses indicating that the gneisses could also be the source of the potassic granite the two types of source rocks indicate a shallow crust depth hence the heat required for partial melting of granodioritic rocks to form the potassic granite could have been provided by the upwelling of mantle or mantle derived melts in an extensional setting therefore the ttg gneisses spg suite and potassic granite in the lushan area record a tectonic transition from a compressive to an extensional setting in the southern margin of the ncc between 2 85 and 2 50 ga

zircon u pb dating and hf isotope analysis on the taihua complex constraints on the formation and evolution of the trans north china orogen abstract precise age determination and source tracing of the granitic and pegmatitic gneisses of the taihua complex in the xiaoqinling area are important to address the debates on the timing and processes of the amalgamation of the western and eastern blocks along the trans north china orogen this paper conducted zircon dating of metamorphic rocks from the xiaoqinling area the results demonstrate that the collision between the western and eastern blocks occurred in the paleoproterozoic laser ablation inductively coupled plasma mass spectrometry la icpms zircon uranium lead u pb analyses yielded consistent results the early paleoproterozoic the first period age of 2346 28 ma was determined for granitic gneiss in the taihua complex and 2328 14 ma for the xiaohe granite pluton that intruded into the granitic gneiss the gneissose pegmatitic granite and granitic veins that intruded into the granitic gneiss yielded la icp ms zircon ages of 1881 24 and 1866 19 ma respectively these paleoproterozoic ages strongly indicate that the ocean between the eastern and western blocks were completely subducted at 1 85 ga the hf t values of the zircons from the granitic gneiss can be divided into a positive group 0 44 to 3 77 and a negative group 3 11 to 1 27 the two stage hafnium hf model ages tdm2 hf corresponding to the positive values are between 2672 and 2887 ma the hf t values of the zircons from the xiaohe granite range from 2 49 to 2 58 with the hf isotope model ages ranging from 2742 to 3022 ma thus the xiaohe granite could have resulted from the partial melting of the late archean lower crust caused by subduction and the presence of juvenile mantle material the primary magma of the granitic gneiss of the paleoproterozoic taihua complex was derived from the differentiation of the depleted late archean mantle source with a small portion derived from the remelting of the subducted lower crust

age and evolution of a late archean to paleoproterozoic upper to lower crustal section in the wutaishan hengshan fuping terrain of northern china abstract the taihangshan wutaishan area forms part of the central north china craton and consists of three main components the hengshan and fuping complexes containing predominantly ductilely deformed late archean to paleoproterozoic high grade granitoid orthogneisses intruded by mafic dykes of gabbroic composition and the low grade late archean wutai greenstone belt developed between the high grade terrains and consisting of bimodal volcanic rocks and metasediments associated with coeval granitoids zircon dating shows that both the hengshan and fuping complexes were intruded by major granitoid bodies between 2 52 and 2 48 ga with rare occurrences of 2 7 ga gneisses wutai granitoids adjacent to the fuping complex also contain 2 7 ga xenocrysts all possibly reflecting the same older basement rare granitic gneisses in the hengshan have emplacement ages of 2 35 ga and show the same structural features as the older rocks indicating that the main deformation occurred after 2 3 ga deposition of supracrustal rocks and emplacement of mafic dykes occurred in the paleoproterozoic together with intrusion of granitic bodies at 2 1 2 0 ga and all underwent regional metamorphism at 1 88 1 85 ga we interpret the hengshan and fuping granitoid gneisses as the lower plutonic part of a late archean to early paleoproterozoic japan type magmatic arc with the upper volcanic part represented by the wutai complex components of this arc may have evolved at a continental margin as indicated by the 2 7 ga zircons virtually all magmatic events are recorded in all three complexes however the 1 85 ga metamorphic event is only recorded in the higher grade portions of the wutai since low grade and presumably high crustal level precluded metamorphic zircon growth shear zones in the hengshan are interpreted as major lower crustal discontinuities post dating the peak of high pressure granulite metamorphism we suggest that they formed during orogenic collapse and uplift of the hengshan complex in the late paleoproterozoic 1800 ma

the composite archaean grey gneisses petrological significance and evidence for a non unique tectonic setting for archaean crustal growth abstract the geodynamic context of formation of the archaean continental crust is a matter of debate the crust is largely made of grey gneiss complexes a composite rock assemblage dominated by granitoids that are generally regarded as belonging to the ttg tonalite trondhjemite granodiorite series using a large database of published ttg and grey gneiss compositions it is possible to show that the granitoids forming grey gneiss complexes actually belong to at least four main geochemical groups i a potassic component made of granodiorites and formed by melting of existing crustal lithologies and ii three sodic groups ttg proper that comprise low medium and high pressure groups the geochemistry of the low pressure group is consistent with derivation from a plagioclase and garnet amphibolite the medium pressure group was formed in equilibrium with a garnet rich plagioclase poor amphibolite whereas the high pressure group derived from a rutile bearing eclogite as the temperature of melting of metamafic rocks is largely independent from pressure this corresponds to melting along a range of contrasting geothermal gradients in turn reflecting a range of tectonic sites for the formation of the archaean continental crust

geochronology and geochemistry of the late paleoproterozoic aluminous a type granite in the xiaoqinling area along the southern margin of the north china craton petrogenesis and tectonic implications abstract the occurrence of extensional related a type granites with a high k nature in some early precambrian blocks hints a possible link with the orogeny and may imply the ending of the orogenic processes and the beginning of craton stabilization the newly recognized late paleoproterozoic a type granite the guijiayu pluton composed of monzogranites in the xiaoqinling area of the southern margin of the north china craton ncc is a promising locus to investigate the late paleoproterozoic tectonic evolution of the ncc la icp ms zircon u pb dating shows that the guijiayu pluton was emplaced at 1 80 ga petrologically the guijiayu granites contain perthite annite and calcic amphibole but are lack of alkali mafic minerals geochemically all the rocks are enriched in silicon and total alkali and depleted in mgo cao and p2o5 with high feot mgo tio2 mgo and 10 000 ga al ratios and high hfses i e zr nb ce y concentrations as well as negative eu sr p and ti anomalies they are also characterized by high melting temperatures and metaluminous to weakly peraluminous natures taken together the guijiayu granites show an affinity to aluminous a type granite their geochemical characteristics e g obviously negative eu and sr anomalies along with the low zircon ehf t values 13 9 to 7 0 and whole rock end t values 5 81 to 5 65 indicate that the guijiayu aluminous a type granite was derived from partial melting of the crustal calc alkaline granitoids dominated by the granodiorite of the taihua group in the study area combined with the regional data especially for the identification of the clockwise p t paths of paleoproterozoic metamorphism in the southern margin of the ncc even coeval granites and regional retrograde metamorphism in other areas in the ncc it is most likely that the peak of continent continent collision had finished in the study area at least before 1 80 ga and that the generation of the guijiayu aluminous a type granite was related to the underplating of mafic magmas in a post collisional regime

diversity of late neoarchean k rich granitoid rocks derived from subduction related crust mantle interactions in the jiaobei terrane north china craton abstract the appearance of voluminous k rich granitoids within nearly all ancient cratons represents one major characteristic of late archean earth which hold the key to understand the transitional geodynamic regimes globally during this period the genetic regimes and links among different k rich granitoids and their implications for crustal growth and evolution remain controversial a series of late neoarchean k rich granitoids including quartz dioritic granodioritic and monzogranitic gneisses occur in the jiaobei terrane of north china craton zircon u pb isotopic data reveal that they emplaced during 2544 2494 ma coeval with regional 2530 2470 ma high grade metamorphism the quartz dioritic granodioritic gneisses are magnesian rocks and they show low si and ti but high k and mg similar to archean low ti sanukitoids the sr y and la yb n are high mostly 59 99 119 32 and 8 56 61 42 with moderate to high nb up to 11 79 ppm geochemical modeling combined with depleted zircon ehf t2 0 5 7 2 and the presence of minor xenocrystic zircons indicate that these low silica samples were derived from a metasomatized depleted mantle source with inputs of slab derived fluids and melts and minor contamination by ancient crustal materials the monzogranitic rocks are ferroan rocks showing high si k and fe but low mg they are divided into two subgroups the first displays low tree of 44 00 127 00 ppm and positive eu anomalies eun eu n 1 06 1 60 whereas the second shows high tree of 85 76 819 02 ppm but negative eu anomalies eun eu n 0 51 0 62 geochemical modeling and depleted zircon ehf t2 of 2 6 8 4 suggest their formation by partial melting of juvenile crustal sources involving tonalitic and some metasedimentary rocks at diverse crustal levels combined with regional geological data these late neoarchean k rich granitoids were generated by coupled melting of metasomatized depleted mantle and dominantly juvenile crustal materials during crustal stabilization furthermore the jiaobei terrane experienced 2 6 2 5 ga crustal growth under a subduction accretion setting

anthracology and taphonomy from wood gathering to charcoal analysis a review of the taphonomic processes modifying charcoal assemblages in archaeological contexts abstract a discussion on the representativeness of charcoal from archaeological contexts and their potential for palaeoecological reconstruction is presented the charcoal deposits studied are the result of human activities and natural processes difficult to separate on the basis of their effects only this is why taphonomy should not be limited to the study of charcoal after the extinction of fire as a result our questioning has been widened to include the entire succession of processes from past vegetation to the anthracological diagram we propose a review of the taphonomic processes affecting anthracological assemblages in archaeological contexts from wood gathering to the analysis of charcoal results human practices appear clearly as the first filter determining or conditioning the assemblage the combustion process can induce a double filter by limiting the taxonomic information and by falsifying the initial quantity of burned wood post depositional agents represent a third level of filters between the vegetation and the anthracological assemblage finally sampling and quantification methods can also induce a distortion of the assemblage the aim of this paper is to present the state of the discipline today the problems already solved and the questions that remain to be studied

late quaternary palaeoenvironmental change in the australian drylands in this paper we synthesise existing palaeoenvironmental data from the arid and semi arid interior of the australian continent for the period 40 0 ka moisture is the predominant variable controlli

neoarchean to paleoproterozoic continental growth in the southeastern margin of the north china craton geochemical zircon u pb and hf isotope evidence from the huoqiu complex abstract the huoqiu complex in the southeastern margin of the north china craton ncc is dominated by neoarchean gray gneisses amphibolites and voluminous metasediments here we report the occurrence of neoarchean to paleoproterozoic rocks from drill core samples the gneisses are similar to ttg tonalite trondhjemite granodiorite in composition and show close spatial association with amphibolites geochemical characteristics such as high sr y and la yb n with steep ree patterns and trace element modeling suggest that these rocks were generated by partial melting of hydrous meta basalts amphibolites at the base of a thickened mafic continental crust leaving a rutile bearing eclogite residue la mc icp ms u pb age data from magmatic zircon grains show protolith emplacement ages of 2 76 2 71 ga subsequently widespread migmatization took place at 1 91 1 82 ga generating voluminous migmatites and high k granites hf isotopic compositions of zircon grains from the amphibolite and gneiss show ehf t values of 2 4 15 5 and 3 0 1 5 respectively the tdm2 hf model ages of the gneisses range from 2 87 to 3 14 ga and are identical to the tdm1 hf ages of amphibolites 2 84 3 16 ga within analytical uncertainty suggesting that the gneisses formed by partial melting of amphibolite and attest to large scale reworking of the ancient continental crust during neoarchean the zircon grains from the granites define two groups with regard to their hf isotopic composition the older group 1916 42 ma has ehf t values and tdm2 hf ages of 10 5 2 4 and 2 40 3 20 ga respectively whereas the younger one 1823 41 ma shows a large variation in ehf t values ranging from 18 1 to 12 5 with tdm2 hf model ages of 1 70 3 59 ga a couple of zircon grains from the younger group display consistent u pb ages and tdm2 indicating accretion of juvenile crust from depleted mantle sources during 1 82 to 1 91 ga however the dominant hf isotope features are consistent with the reworking of preexisting continental crust we therefore infer that only limited accretion of juvenile crust occurred during this time and that the paleoproterozoic 1 82 to 1 91 ga tectonics in the southeastern margin of the ncc witnessed extensive reworking of older continental crust

geochronology and geochemistry of the paleoproterozoic yinyugou group in the southern north china craton implications for provenance and tectonic evolution abstract the paleoproterozoic yinyugou group in the southern north china craton is a littoral facies sedimentary sequence which is mainly composed of feldspar quartzites and mica schists with minor carbonate rocks u pb isotopic dating of detrital zircons bracket the depositional age of the yinyugou group at 2 43 2 30 ga chemical index of alteration cia values of most feldspar quartzite and schist samples are lower than 75 indicating generally weak to moderate source weathering conditions for the yinyugou rocks the majority of the studied yinyugou samples give a large range of index of compositional variability icv values of 0 93 2 59 revealing a chemically immature source which deposited in an active continental margin setting chondrite normalized ree patterns and discrimination diagrams involving la th hf co and sc reveal that the yinyugou group dominantly received detritus from felsic sources with minor contribution from mafic igneous rocks u pb ages of detrital zircons from the yinyugou group can be divided into two groups 2 90 2 40 ga and 3 50 3 20 ga with a predominant age peak at 2 50 ga the 3 50 3 20 ga detrital zircons have negative ehf t values ranging from 11 2 to 3 8 and old crustal model ages tdmc of 4246 to 3909 ma indicating a mature crustal source most 2 50 ga zircons show sub depleted mantle positive ehf t values and tdmc ages mainly ranging from 3 10 to 2 70 ga representing the time when juvenile materials were extracted from the depleted mantle taking all these data into account the yinyugou group was most likely deposited in a back arc setting in combination with previous studies on other paleoproterozoic volcanic sedimentary sequences and magmatic rocks in the ncc a cycle of subduction collision extension rift subduction processes is proposed to explain the tectonic evolution of the ncc during paleoproterozoic

wood charcoal analysis at riwi cave gooniyandi country western australia abstract wood charcoals excavated from archaeological sites provide a useful tool for palaeoenvironmental reconstruction particularly in arid and semi arid zones where suitable catchments for palynological archives are often limited preservation of organic material in northern australia is characteristically poor and wood charcoal analysis provides a viable alternative to understand shifts in woody vegetation in the past the analysis of charcoal from matrix contexts at riwi cave located in the southern kimberley region of northern western australia has allowed a reconstruction of the local woody vegetation during occupation over the last 45 000 years the wood charcoal assemblage from the holocene stratigraphic units reflects the composition of the modern vegetation and illustrates that people were occupying the site during periods of relative humidity the pleistocene stratigraphic units show a shift in vegetation composition from eucalyptus spp to corymbia sp dominated savanna with an understory of secondary shrub associated with a late mis 3 arid event observed in both terrestrial and marine archives suggesting that activities continued at riwi during this arid event further anthracological analysis of other sites in the kimberley will help to build a regional picture of woody vegetation change and will further disentangle local and regional climatic signals particularly in relation to phases of occupation

discrimination and origin of the sanukitoid series geochemical constraints from the neoarchean western karelian province finland abstract neoarchean late to post tectonic sanukitoid intrusions are found in the western part of the karelian province in finland variable sized even grained to k feldspar porphyritic intrusions form a series of diorites tonalites and granodiorites that are calc alkaline to alkali calcic magnesian and mostly peraluminous the major and trace element geochemistry of the intrusions show typical sanukitoid affinities a mantle signature high content of mg ni cr and high mg and enrichment in lile especially k ba and sr the intrusions form a distinctive series that can be distinguished from the ttg series of the karelian province by their high ba sr signature low na 2 o k 2 o ratio and uniform hree pattern the sanukitoid series can be compositionally constrained as follows sio 2 55 70 wt na 2 o k 2 o 0 5 3 mgo 1 5 9 wt mg 45 65 k 2 o 1 5 5 0 wt ba sr 1400 ppm and gd er n 2 6 the probable source was enriched subcontinental lithosphere mantle with high lile concentrations in phlogopite and or sanidine the accumulation of k ba and sr in the mantle source may have occurred as a consequence of two separate metasomatic events 1 by subduction related fluids melts and 2 by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff the slab breakoff at the end stage of subduction is also a viable trigger for the sanukitoid magmatism

metamorphism and geochronology of the luoning metamorphic terrane southern terminal of the palaeoproterozoic trans north china orogen north china craton abstract garnet bearing amphibolites and metapelites of the luoning metamorphic terrane taihua metamorphic complex southern terminal of the palaeoproterozoic trans north china orogen tnco preserve different metamorphic mineral assemblages formed at three metamorphic stages in the palaeoproterozoic the prograde mineral assemblages m1 comprise of hornblende plagioclase quartz biotite inclusions preserved in the garnet porphyroblasts in the amphibolites or quartz biotite plagioclase inclusions preserved in the garnet porphyroblasts in the metapelites the metamorphic peak mineral assemblages m2 are represented by the garnet porphyroblasts as well as the matrix minerals plagioclase hornblende biotite quartz in the amphibolites or quartz biotite plagioclase hornblende in the metapelites respectively the retrograde mineral assemblages m3 are the worm like fine grained white eye socket symplectitic assemblages formed between the relict garnet porphyroblasts and the matrix minerals consisting of plagioclase hornblende biotite intergrowths in the amphibolites or plagioclase biotite quartz intergrowths in the metapelites respectively geothermobarometric computation shows that the luoning terrane records clockwise p t trajectories including near isothermal decompression itd processes from 630 790 c 5 3 8 9 kbar through 720 820 c 8 9 10 7 kbar to 690 740 c 7 1 7 7 kbar sims u pb dating of zircons separated from the amphibolites and metapelites presents that the age of the protolith of the amphibolites is 2 32 ga and the metamorphism occurred during 1 97 1 94 ga suggesting that the subduction collision and the subsequent exhumation occurred in the late palaeoproterozoic combined with the literature data of the different discrete terranes within the trans north china orogen it is further deciphered that the tectono metamorphic event of the trans north china orogen started as early as 1 97 ga and lasted as late as 1 80 ga suggesting that the tectono metamorphic event of the orogen is a long and complex history

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

age and tectonic setting of late archean greenstone gneiss terrain in henan province china as revealed by single grain zircon dating the authors report precise u pb zircon ages for single grains of a metarhyodacite from the late archean dengfeng greenstone belt in henan province china near the southern margin of the north china craton most grains belong to an igneous population whose u pb isotopic systematics define a straight line intersecting concordia at 2512 12 ma and this is interpreted as the time of crystallization of the original greenstone volcanics several grains are distinctly older between 2576 9 and 2945 44 ma and the authors interpret the older grains as xenocrysts of pre greenstone continental crust that provide evidence for crustal derivation or crustal contamination of the original rhyodacitic lava the xenocrysts suggest evolution of the dengfeng greenstone belt in a continental environment that may be represented by the taihua high grade gneisses bordering the dengfeng greenstones and for which the authors obtained ages of 2806 7 and 2841 6 ma the data add evidence to the now widely held concept that most archean greenstones developed on or near older continental crust and were therefore prone to crustal contamination in such cases conventional zircon dating may not always record the precise age of rock formation

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

a review of charcoal analysis as a tool for assessing quaternary and tertiary environments achievements and limits abstract identification of charcoal fragments 2 mm using reflected light microscopy is routinely carried out to study former natural ecosystems assess changes in vegetation communities over time and identify the influence and patterns of behaviour of human populations on vegetation material studied comes either from archaeological horizons or soil profiles despite undeniable limits informative results have been obtained in the last 25 years mostly in southwestern europe where charcoal analysis has been widely applied in quaternary studies examples of these achievements are provided focusing on the major vegetation trends since the upper palaeolithic to the middle ages the techniques used for charcoal analysis in the reconstruction of quaternary vegetation are now being used to study tertiary charcoal and lignites the study of fossil charcoal can be a highly informative method for interpreting ancient ecosystems as species easily degraded may be preserved by charcoalification some results from the lower rhine embayment germany are presented here

three tier transition of neoarchean ttg sanukitoid magmatism in the beit bridge complex southern africa abstract neoarchean ttg sanukitoid associations of contrasting scales occur within the beit bridge complex terrane of the limpopo complex in southern africa these include the smaller 2 65 2 63 ga avoca granitoid and the voluminous 2 73 2 64 ga alldays granitoid this study characterizes the wide compositional spectrum preserved in these two granitoids the elliptical avoca pluton consists of a biotite amphibole orthopyroxene clinopyroxene bearing core that is dominantly trondhjemite with less dominant tonalite and granodiorite variants and a thin amphibole biotite bearing granite rim with local occurrence of two pyroxene bearing metabasite boudins while both the core and rim rocks exhibit a linear fabric the granite in addition preserves a penetrative foliation field relations of granite enclaves in the core rocks together with available ages indicate that the core rocks intruded the granite the foliated biotite amphibole bearing alldays granitoid contains inclusions of older supracrustals and rocks of the messina layered intrusion and is widely distributed compositionally it include tonalites and granodiorites and to a lesser extent trondhjemites both the avoca core and rim rocks are characterized by difference in mineral chemistry with the mafic minerals mg rich in the ttg core while they are fe rich in the granite and metabasite in comparison biotite is mg rich and amphibole is fe rich in the alldays granitoid two groups of alldays ttg can be delineated in terms of whole rock geochemical characteristics and are comparable to the low to medium pressure ttg groups delineated by moyen 2011 while the avoca ttg is similar to the high pressure ttg group the lowest silica samples from each group of granitoid have geochemical characteristics comparable to archean sanukitoids with those from the avoca granitoid similar to low ti sanukitoids and those from the alldays granitoid similar to low ti and high ti sanukitoids separate petrogenetic models are suggested for different phases of the avoca core with the trondhjemite tonalites considered as high pressure melts of metabasalt while the granodiorite with lower sio2 content higher k2o and mgo contents and higher incompatible element contents than the trondhjemite tonalites is a product of hybridization of earlier ttg melts and peridodite granite from the avoca rim are low pressure melts of pre existing crustal lithologies the two groups of alldays ttg with lower sr y ratios than the avoca ttg are considered as low to medium pressure melts of metabasalt whose progressive interaction with peridotitic mantle at shallower angles account for the unique composition of alldays low ti and high ti sanukitoids taken together with their spatial and temporal transition from southeastern 2 73 2 72 ga low pressure ttg low ti sanukitoid to central 2 65 2 64 ga medium pressure ttg high ti sanukitoid to northwestern 2 63 ga high pressure ttg low ti sanukitoid parts of the beit bridge complex the three tier transition of ttg sanukitoid magmatism argues for the southern margin of the beit bridge complex to represent an active arc in the neoarchean

late quaternary vegetation change and the extinction of black flanked rock wallaby petrogale lateralis at tunnel cave southwestern australia abstract quaternary vertebrate extinctions attract wide interest because of the role ascribed to humans as agents of extinction through either over hunting or altering habitat this paper examines faunal and floral records from the archaeological site at tunnel cave leeuwin naturaliste region southwestern australia which are relevant to the mid holocene local extinction of black flanked rock wallaby petrogale lateralis possible factors causing the population decline include inter species competition over hunting by humans or other predators or vegetation habitat change caused by climate change or changes in human firing practices identification of macroscopic charcoal excavated at tunnel cave shows that changes in canopy trees began from 10 000 bp consistent with post glacial rainfall increases and probably causing the encroachment of closed habitats and loss of grazing areas these changes are consistent with other faunal shifts at tunnel cave and with faunal and identified charcoal records from the nearby devil s lair deposit there is little evidence for changes in competitor or predator behaviour although increasing geographic isolation of petrogale habitats possibly exacerbated predator impacts the timing of human occupations at tunnel cave in relation to vegetation change suggests that human firing was a minor influence on forest composition or structure petrogale s mid holocene disappearance from the region is therefore attributable to climatically driven encroachment of closed habitat

evaluating human responses to enso driven climate change during the holocene in northwest australia through macrobotanical analyses the holocene is recognised as a period through which a number of climatic fluctuations and environmental stresses occur associated with intensifying el nino southern oscillation enso climatic con

geochronology and petrogenesis of the neoarchean paleoproterozoic taihua complex ne china implications for the evolution of the north china craton abstract the north china craton ncc preserves important records of archean paleoproterozoic crustal evolution here we present results from petrology geochemistry zircon u pb dating and lu hf isotopes of the taihua complex thc from the southern part of the ncc zircon u pb dating of the amphibolite yields the ages of 2776 2771 ma representing the formation age marking a major phase of late archean crustal growth in the ncc the 1922 1915 ma ages represent the paleoproterozoic metamorphism associated with the collisional assembly between the eastern and western blocks the amphibolites are characterized by low sio2 na2o k2o and nb y indicating a sub alkaline basaltic protolith these rocks show relatively high lile hfse and lree hree ratios similar to e morb low nb la pm negative nb ta anomalies and positive ehf t values indicating partial melting of a metasomatic mantle source the ttg gneisses are characterized by high sio2 sr y la yb n nb ta zr sm and zr hf ratios and low mgo cr ni y gd yb and dy yb ratios with positive eu anomalies indicating partial melting of juvenile lower crust with garnet amphibolite residue our data are consistent with a tectonic setting within a volcanic arc in a convergent margin our study on the thc contributes to the archean paleoproterozoic crustal accretion and reworking history along the southern margin of the ncc

redefinition of depositional ages of neoarchean supracrustal rocks in western shandong province china shrimp u pb zircon dating abstract western shandong province is an important terrane in the eastern part of the north china craton where 2 75 2 5 ga tectono thermal events are well recognized supracrustal rocks named the taishan group experienced greenschist to amphibolite facies metamorphism and occur as lenses and strips in granitoids and are subdivided into the yanlingguan shancaoyu and liuhang formations the yanlingguan formation is mainly composed of amphibolite but also contains fine grained biotite hornblende gneiss komatiitic rocks and schist the liuhang formation is similar in rock association to the yanlingguan formation but contains more metasedimentary rocks the shancaoyu formation is mainly composed of fine grained biotite gneiss leptynite preserving bedding and is interlayered with schist its protoliths are mainly sedimentary rocks with some mafic to felsic volcano sedimentary varieties we undertook shrimp zircon dating on eighteen metasedimentary and volcanic samples mainly from the shancaoyu formation and the upper part of the liuhang formation ages of detrital and volcanic zircons vary from 2 75 to 2 54 ga and 2 55 to 2 525 ga respectively and the age distribution patterns vary in different samples we conclude that the shancaoyu formation and the upper part of the liuhang formation were deposited in the late neoarchean 2 55 2 525 ga and not in the early neoarchean 2 8 2 7 ga as thought before western shandong is the only terrane in the north china craton where both early and late neoarchean supracrustal rocks have been identified a magmatic arc model may be applied to explain the tectono thermal evolution at the end of the neoarchean

wood charcoal from an inland dune complex at joldelund northern germany information on holocene vegetation and landscape changes abstract the charcoal content of an inland dune complex close to joldelund in northern germany was analysed as part of a project which aims to reconstruct holocene aeolian activity in high spatial and temporal resolution the eleven investigated profiles contained numerous charcoal enriched layers providing evidence for the potential of inland dunes as palaeoarchives for anthracology earlier studies have found late roman iron age settlement activity and iron ore productions in the research area and in its vicinity charcoal assemblages date to roman iron age as well as early high and late medieval times according to radiocarbon dating of single species identified charcoal fragments and the stratigraphic correlation of sedimentary units the dominance of quercus oak and significant proportions of ericaceae charcoal probably calluna vulgaris heather especially in the early and high medieval samples indicate the presence of a heathland with quercus trees which was managed by fire in the younger layers of sand a greater diversity of taxa were found including the dominant quercus fagus beech alnus alder betula birch corylus hazel fraxinus ash salix willow populus salix poplar willow type acer maple pinus pine maloideae apple subfamily tilia lime as well as some ericaceae the diversity of species indicates that some charcoals were transported by wind together with the sand from the surrounding areas and do not represent the local vegetation on the dunes but rather a nonspecific regional input the differences in the charcoal assemblages and thus the possible correlation of aeolian units support the stratigraphic correlation of the sedimentary aeolian units the comparison with the available pollen data from nearby mires showed a good agreement of the proportions of woody taxa with only few exceptions

deformation history of the hengshan complex implications for the tectonic evolution of the trans north china orogen structural analysis indicates that the hengshan complex underwent five distinct episodes of deformation d1 d5 the d1 episode formed small isoclinal folds f1 penetrative axial planar foliations s1 and mineral stretching lineations l1 d1 fabrics were reworked by following d2 deformation associated with d2 was the development of nw verging asymmetric folds and accompanying thrust faults both d1 and d2 resulted from crustal thickening and coherent with prograde and peak metamorphism d2 deformation was followed by transpressional dextral shearing d3 including top to nw oblique slip shearing and nne ssw dextral strike slip shearing ongoing collision led to development of the zhujiafang ductile shear zone d4 a near e w trending high strain belt across the hengshan complex d5 deformation is characterized by f5 open folds and associated normal faults probably related to exhumation of the complex structural patterns of the hengshan complex can place important insights into a recently proposed tectonic model suggesting that an ocean between the eastern and western blocks underwent eastward directed subduction beneath the western margin of the eastern block and closure of this ocean finally led to collision between the two blocks to form the coherent north china craton

petrogenesis of mantle derived lile enriched archean monzodiorites and trachyandesites sanukitoids in southwestern superior province reply in southwestern superior province diorite monzodiorite and trachyandesite sanukitoids occurring within syn to post tectonic intrusive complexes and within greenstone belts have the following chemical characteristics 55 60 wt sio2 mgo 6 wt mg 0 60 ni and cr both 100 ppm na2o k2o 6 wt sr and ba both 600 1800 ppm and rare earth element ree patterns that are strongly light rare earth element lree enriched cen 80 250 ybn 4 10 and show no eu anomalies sanukitoids and their granodioritic derivatives constitute at least 5 of the exposed crust in the study area the sanukitoids cannot be derived by melting fractionation or crustal contamination of basalts or lamprophyres that are coeval with the sanukitoids crustal contamination of komatiites fails to explain the high large ion lithophile element lile contents of the sanukitoids rather we suggest that the sanukitoids were derived by hydrous melting of lile enriched mantle peridotite at pressures between 10 and

climate variability and land ocean interactions in the indo pacific warm pool a 460 ka palynological and organic geochemical record from the timor sea climatic conditions in the western timor sea and the adjacent northwestern part of australia are reconstructed for the last 460 ka based oil geochemical and palynological proxy records of paleoproductivity and land vegetation precipitation from images core md01 2378 reduced precipitation and elevated productivity characterize glacial stages whereas enhanced precipitation and reduced productivity are typical of interglacial stages a long term reduction in precipitation over the last 320 ka occurred in two steps at approximately 300 ka and 180 ka bp that are clearly recognizable in the pollen record variations in paleoproductivity and paleoclimate in the timor sea and adjacent landmasses appear to be driven by similar mechanisms that are related to the precession control led australian monsoon system c 2005 elsevier b v all rights reserved

combined u pb hafnium and oxygen isotope analysis of zircons from meta igneous rocks in the southern north china craton reveal multiple events in the late mesoarchean early neoarchean abstract we report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from lushan in the far south of the trans north china orogen of the north china craton that reveal the oldest rocks yet dated from the orogen a detailed investigation of the internal structures of zircons combined with targeted sims u pb and oxygen isotope analyses and icp ms hf zircon analyses has resulted in the discovery of previously unknown geological events in the north china craton magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829 18 ma to 2832 11 ma in the tonalites and from 2838 35 ma to 2845 23 ma in amphibolite hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination oxygen isotope ratios in zircons range from 5 1 to 7 3 vsmow with high 18 o results recorded only from metamorphic domains the earliest stage of metamorphic zircon growth present in all four samples analyzed in this study occurred between 2772 17 22 in the tonalites and 2776 20 and 2792 12 ma in the amphibolites a younger metamorphic event at 2638 61 in the tonalite and between 2671 13 and 2651 13 ma in the amphibolites is recognized in zircons from three of the four samples investigated this is the first time that metamorphic events at either of these times have been recorded in the north china craton importantly there is no evidence for the 1 8 ga high grade metamorphic event that is manifest in the northern and central parts of the trans north china orogen

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered

geochemical constraints on the growth of the continental crust several lines of evidence indicate that the archean upper crust was considerably more mafic than the present day upper crust there has been no significant change in ree and th abundances in post archean clastic sedimentary rocks suggesting that there has been no change in the composition of the upper crust during the post archean this indicates that if there have been any additions to the post archean upper crust they must have had similar composition to the upper crust itself geochemical modelling of ree and th abundances in sedimentary rocks suggests that the minimum ratio of post archean to archean upper crustal composition required to eliminate the archean upper crustal trace element signature within analytical uncertainty is about 4 1 such a model also is supported by isotopic data using plausible assumptions regarding the volume of archean crust isostatic relations and extreme models of the earth s degassing history it is proposed that approximately 65 75 of the continental crust formed