abundant sr rich aragonite in eastern mediterranean sapropel s1 diagenetic vs detrital biogenic origin caco3 contents in eastern mediterranean sapropels are generally lower than in the enclosing marl sediments in sediments of a transect from 650 to 2100 m water depth at the sirte continental slope the opposite feature was observed although the increased sr ca ratios observed in these sediments agree with such feature observed in other eastern mediterranean s1 sediments their absolute magnitude is much higher the enhanced sr ca ratio in these sediments is associated with their aragonite content which for the sirte transect reaches levels of up to 40 wt the aragonite content and sr ca ratios in the s1 sediments of this transect decrease with increasing water depth and decrease with distance to the african coast for all eastern mediterranean cores in view of the lack of a coherent relationship with sedimentary reduced sulphur contents and porosity and considering the major amount of aragonite found specifically in the sediments of the sirte transect authigenic precipitation can contribute only a limited fraction at most sem observation and electron microprobe analyses showed that the needles and needle clusters are morphologically aragonite contain the highest sr ca ratio and are similar to skeleton fragments of the green alga halimeda consequently a detrital biogenic source is the likely mechanism for the major part of the aragonite enrichments found in s1 sediments possibly offshore directed surface water flows related to wind stress and or enhanced run off consistent with enhanced precipitation during sapropel s1 may have assisted in the transport of near coastal aragonitic organisms to more coast remote areas

simulating reef response to sea level rise at lizard island a geospatial approach abstract sea level rise will result in changes in water depth over coral reefs which will influence reef platform growth as a result of carbonate production and accretion this study simulates the pattern of reef response on the reefs around lizard island in the northern great barrier reef two sea level rise scenarios are considered to capture the range of likely projections 0 5 m and 1 2 m above 1990 levels by 2100 reef topography has been established through extensive bathymetric profiling together with available data including lidar single beam bathymetry multibeam swath bathymetry lads and digitised chart data the reef benthic cover around lizard island has been classified using a high resolution worldview 2 satellite image which is calibrated and validated against a ground referencing dataset of 364 underwater video records of the reef benthic character accretion rates are parameterised using published hydrochemical measurements taken in situ and rules are applied using boolean logic to incorporate geomorphological transitions associated with different depth ranges such as recolonisation of the reef flat when it becomes inundated as sea level rises simulations indicate a variable platform response to the different sea level rise scenarios for the 0 5 m rise the shallower reef flats are gradually colonised by corals enabling this active geomorphological zone to keep up with the lower rate of rise while the other sand dominated areas get progressively deeper in the 1 2 m scenario a similar pattern is evident for the first 30 years of rise beyond which the whole reef platform begins to slowly drown to provide insight on reef response to sea level rise in other areas simulation results of four different reef settings are discussed and compared at the southeast reef flat barrier reef coconut beach fringing reef watson s bay leeward bay with coral patches and mangrove beach sheltered lagoonal embayment the reef sites appear to accrete upwards at a rate commensurate with the rate of rise thereby maintaining their original profile and position relative to the sea surface and the leeward and lagoonal sites with a low accretion rate maintain a similar profile but slowly gain depth relative to sea level the result of this variable response is that elevated features of the reef platform such as reef patches and crests tend to become more pronounced

hornblende garnet plagioclase thermobarometry a natural assemblage calibration of the thermodynamics of hornblende calibrations are presented for an independent set of four equilibria between end members of garnet hornblende plagioclase and quartz thermodynamic data from a large internally consistent thermodynamic dataset are used to determine the g of the equilibria then with the known mixing properties of garnet and plagioclase the non ideal mixing in amphibole is derived from a set of 74 natural garnet amphibole plagioclase quartz assemblages crystallised in the range 4 13 kbar and 500 800 c the advantage of using known thermodynamic data to calculate g is that correlated variations of composition with temperature and pressure are not manifested in fictive derived entropies and volumes but are accounted for with non ideal mixing terms the amphibole is modelled using a set of ten independent end members whose mixing parameters are in good agreement with the small amount of data available in the literature the equilibria used to calibrate the amphibole non ideal mixing reproduce pressures and temperatures with average absolute deviations of 1 1 kbar and 35 c using an average pressure temperature approach and 0 8 kbar with an average pressure approach the mixing data provide not only a basis for thermobarometry involving additional phases but also for calculation of phase diagrams in complex amphibole bearing systems

late paleoproterozoic 1900 1800ma nappe stacking and polyphase deformation in the hengshan wutaishan area implications for the understanding of the trans north china belt north china craton abstract the hengshan wutaishan area forms part of the trans north china belt developed in response to the final amalgamation of the north china craton the hengshan wutaishan domain and the adjacent fuping massif constitute the largest and the most representative rock exposure of the belt a structural study allows us to redefine the lithological and tectonic units that compose the architecture of the hengshan wutaishan domain and to propose that the trans north china belt was built up through a polyphase tectonic evolution within the period 1900 1800 ma the first event d1 corresponds to the emplacement of lower and upper nappes herein called the orthogneiss and volcanites unit ovu and the low grade mafic unit lgmu respectively the ovu mainly consists of rocks formed in an arc system and metamorphosed under amphibolite facies conditions whereas the lgmu represents oceanic crust rocks with an arc component that underwent greenschist facies metamorphism the syn metamorphic d1 deformation is characterized by a nw se stretching and mineral lineation with a top to the se sense of shear that corresponds to the sense of nappe motion u th pb epm chemical dating on monazite from three metapelites of the ovu gives isochron ages of 1884 11 ma 1886 5 ma and 1887 4 ma interpreted as the age of the prograde amphibolite facies metamorphism coeval with nappe stacking during the d1 event the d2 event corresponds to a widespread crustal melting of the ovu and underlying basement rocks in hengshan related to the exhumation of deep structures about 20 30 ma after nappe emplacement the migmatite contains blocks of retrograded eclogite or hp granulitic restites and is characterized by the development of a pervasive foliation and lineation a late d2 event represents the folding stage of the migmatitic foliation during the completion of a dome the orthogneiss and volcanics unit and the low grade mafic unit are unconformably covered by weakly metamorphosed to unmetamorphosed sediments belonging to the hutuo supergroup these rocks were deformed by a ductile d3 event characterized by a nw se trending stretching lineation south verging folds associated with an axial planar slaty cleavage and an e w crenulation lineation lastly a left lateral wrenching along the zhujiafang shear zone separates the northern and southern parts of hengshan our structural study shows that there is no significant difference between the southern part of hengshan and the lower part of wutaishan both areas belong to ovu and show a structural continuity we suggest that this polyphase deformation developed in response to a north westward subduction of an old ocean named the luliang ocean beneath the western block followed by collision with a micro continent named the fuping block at 1890 1880 ma

metamorphic evolution and zircon u pb geochronology of the mts huashan amphibolites insights into the palaeoproterozoic amalgamation of the north china craton abstract exposed in the southernmost terminal of the palaeoproterozoic trans north china orogen tnco the garnet bearing amphibolites in the mts huashan metamorphic complex preserve three generations of mineral assemblages including the prograde peak and retrograde metamorphic stages the prograde metamorphic stage m1 is recognized as inclusion type mineral assemblages hornblende plagioclase quartz biotite ilmenite preserved in the garnet porphyroblasts the peak metamorphic assemblages m2 are represented by the garnet porphyroblasts and matrix minerals hornblende plagioclase quartz biotite ilmenite the retrograde metamorphic assemblages m3 are characterized by the symplectitic intergrowth minerals hornblende plagioclase quartz orthopyroxene biotite ilmenite rimming decomposed relict garnet porphyroblasts known as the white eye socket reaction textures calculated by geothermometers and geobarometers the p t conditions of these three metamorphic stages are estimated to be of 5 7 6 0 kbar 660 760 c for the prograde stage m1 6 6 7 7 kbar 700 820 c for the peak stage m2 and 4 5 6 7 kbar 720 760 c for the retrograde stage m3 respectively therefore these three metamorphic stages define clockwise p t paths including nearly isothermal decompression itd processes geochronological studies of zircons from the amphibolites indicate that the protolith of the amphibolites formed at 2 3 ga and the metamorphism occurred at 1 87 1 85 ga and the metamorphic period was further deciphered to be of 1 96 1 80 ga when considering our previous reports it is therefore proposed that the southernmost terminal of the tnco was also involved in the subduction and collision processes between the eastern and western blocks of the north china craton at least as early as 1 96 ga and continued as late as 1 80 ga followed by rapid uplift and exhumation the available data suggest that the palaeoproterozoic tectono metamorphic event of the southernmost terminal of the trans north china orogen not only started earlier but also continued longer than the other terranes in the middle and northern sections elsewhere in the orogen

zircon sims u pb geochronology of the lushan terrane dating metamorphism of the southwestern terminal of the palaeoproterozoic trans north china orogen high resolution sims u pb dating of metamorphic zircons of the ttg gneisses gneissic granitoid and amphibolites of the lushan terrane taihua metamorphic complex suggests that the metamorphism had taken place at least as early as 1 96 1 86 ga these new dates along with reference data demonstrate that the southern and middle terranes of the trans north china orogen had been involved in the continent continent collision between the western block and the eastern block of the north china craton this orogenic process started as early as 1 96 ga and lasted as late as 1 80 ga

long shelf sediment transport and storm bed formation by cyclone winifred central great barrier reef australia three major sediment facies belts occur on the great barrier reef shelf an inner shelf prism of holocene terrigenous sand and mud a patchy middle shelf veneer of palimpsest muddy shelly calcsand 1 m thick above a weathered pleistocene erosion surface and an apron of modern carbonate mud and sand around reefs of the main reef tract these sediments were mobilized and strongly affected by the passage of severe tropical cyclone winifred central pressure 958 hpa which traversed the central great barrier reef shelf on february 1 1986 re surveys after the passage of cyclone winifred showed that i a storm induced shell lag and or a normally graded bed of terrigenous fine sand mud had been deposited at depths down to 20 m ii middle shelf longitudinal bedforms were widespread at depths of 28 35 m and comprised a furrowed substrate of palimpsest muddy shell gravel surmounted by 40 150 m wide ribbons of quartzose and bioclastic sand up to 15 cm thick iii fields of northward facing 1 2 m wavelength megaripples were present adjacent to zones of ribbons and in the alleys between ribbons iv five days after the cyclone mud was still settling from suspension and large parts of the inner shelf were bathed in muddy hypopycnal river plumes some of which reached 30 km seaward to the inner edge of the reef tract and v suspended mud derived in part by unmixing of the seabed was present throughout the shelf water column and a seaward thinning mud drape up to 40 cm thick had accumulated on and seawards of the inshore sediment prism tapering seawards to a few mm thick only over most of the middle shelf it is inferred that storm waves and currents associated with the passage of cyclone winifred caused widespread unmixing of bottom sediments offshore long shelf transport of bedload sand ribbons and megaripples was affected by powerful shelf parallel currents of velocity 1 3 m s as the storm passed the graded seaward thinning sand mud bed was deposited over the inner middle shelf on the middle shelf bioturbation and downward mixing of the mud drape started immediately after the passage of the cyclone and was well advanced after 3 months in this way the ephemeral seabed features produced by passage of a cyclone are gradually degraded and the storm layer stratigraphy becomes incorporated within a thin middle shelf veneer of muddy shelly calcsand

reef accretion and coral growth rates are decoupled in holocene reef frameworks abstract a central assumption of holocene reef models is that reef accretion rates are directly related to coral growth rates with reefs dominated by faster growing corals having higher accretion rates yet few studies have explicitly tested this assumption particularly in indo pacific region through high precision u th dating and palaeoecological reconstructions of coral community structure this study explores patterns of reef accretion mm yr 1 among late holocene reef frameworks from the inshore central great barrier reef modern assemblages were dominated by either slow growing goniopora 9 6 2 mm yr 1 or rapid growing branching acropora 89 6 mm yr 1 framework building corals despite a nearly 10 fold difference in coral growth rates rates of reef accretion were comparable between frameworks dominated by slow growing goniopora 8 6 1 3 mm yr 1 and rapid growing branching acropora 7 1 1 4 mm yr 1 u th chronologies indicate that accretion rates were continuous throughout the past 750 years r2 0 96 0 98 despite a temporal shift in framework building corals from acropora to goniopora that occurred 250 years ago that coral growth rates are decoupled from reef accretion at holocene scales indicates that previous models of accretion in pacific coral reefs may be based upon inaccurate assumptions the finding that ecological processes are decoupled from geological processes has implications for the management of modern coral reefs and suggests that maintenance of living corals regardless of taxonomic identify is important for accretion of reef frameworks

tectonic switching of the trans north china orogen in the middle paleoproterozoic insights from mafic magmatism in the luliang complex

an improved set of a x parameters for fe mg ca garnets and refinements of the orthopyroxene garnet thermometer and the orthopyroxene garnet plagioclase quartz barometer

zircon u pb geochronology and hf isotopes of major lithologies from the jiaodong terrane implications for the crustal evolution of the eastern block of the north china craton abstract as an important component of the western shandong complex in the eastern block of the north china craton the yishui terrane consists of neoarchean high grade supracrustal rocks granitoid gneisses and charnockites la icp ms zircon u pb dating and hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the neoarchean crustal evolution of the eastern block of the north china craton new zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2 54 2 53 ga and 2 57 2 55 ga respectively and the charnockites were emplaced contemporaneously around 2 56 2 53 ga single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at 2 50 ga suggesting that the yishui terrane experienced a high grade metamorphic event at the end of the neoarchean detrital zircons from pelitic gneisses yield 207pb 206pb ages of 2 89 2 65 ga with a major age peak at 2 53 ga and a subordinate age peak at 2 70 ga implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from 2 53 ga rocks in the yishui terrane and 2 70 ga rocks in the adjacent luxi granite greenstone terrane hf isotopic compositions show that the neoarchean magmatic zircons have positive ehf t values ranging from 1 4 to 7 8 and depleted mantle model ages of 2 92 2 60 ga with a prominent peak at 2 8 2 7 ga suggesting that the neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the yishui area combined with previous data from the adjacent luxi granite greenstone terrane and other complexes in the eastern block it is concluded that the neoarchean was an important period of crust accretion in the eastern block of the north china craton

shrimp u pb zircon ages of granitoid rocks in the luliang complex implications for the accretion and evolution of the trans north china orogen abstract the luliang complex is situated in the central segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of supracrustal and granitoid rocks of which the latter can be subdivided into pre tectonic ttg gneisses including the yunzhongshan guojiazhuang and chijianling guandishan gneisses syn tectonic gneissic granites represented by the huijiazhuang gneissic granite and post tectonic granites including the luyashan charnockite luchaogou porphyritic granite and tangershang guandishan massive granite the pre tectonic ttg gneisses are mostly calc alkaline and considered to have formed in a magmatic arc environment shrimp u pb analyses reveal that the yunzhongshan gneisses were emplaced at 2499 9 ma representing the earliest arc related magmatic event in the luliang complex this was followed by the intrusion of the guojiazhuang gneisses at 2375 10 ma the most widespread arc related magmatic event in the region was the emplacement of the chijianling guandishan granitoid gneisses of which the tonalitic granodioritic and monzogranitic gneisses were emplaced at 2199 11 ma 2180 7 ma and 2173 7 ma respectively metamorphic zircon overgrowth rims from a tonalitic gneiss yielded a weighted mean 207 pb 206 pb age of 1872 7 ma consistent with the metamorphic age range of 1880 1820 ma defined by metamorphic zircons from various high grade rocks in the tnco thus the evolution of the luliang complex involved emplacement of the yunzhongshan granitoids at 2499 ma the guajiazhuang granitoids at 2375 ma and the chijianling guandishan granitoids at 2199 2173 ma with the final collision between the eastern and western blocks in this area occurring at 1872 7 ma the whole series of magmatic events lasting nearly 650 ma this suggests that the trans north china orogen represents a long lived magmatic arc the new shrimp zircon data combined with structural and petrological studies also reveal the existence of both syn and post collisional granites in the luliang complex the former is represented by the huijiazhuang gneissic granite that was emplaced at 1832 11 ma whereas the latter include the 1815 5 ma luyashan charnockite 1807 10 ma luchaogou porphyritic granite 1798 11 ma guandishan massive granite and 1790 14 ma tangershan massive granite

archean to paleoproterozoic evolution of the north china craton preface abstract as one of representative cratons in china the north china craton records a long term and complicated tectonic history including the formation of eoarchean continental nucleus neoarchean continental crustal growth and reworking paleoproterozoic amalgamation of micro blocks and formation of orogenic belts related to the columbia supercontinent and formation of late paleoproterozoic to early neoproterozoic rifts in recent years extensive geochemical geochronological magmatic and metamorphic structural and geophysical investigations have been carried out on the north china craton which have resulted in a series of new achievements and some percussive interpretations of the precambrian continental crustal formation and evolution these new data and results allow us to make a correct judgment for organizing this special issue in which representative and creative experts currently working in the craton exhibit outcomes of their research on the craton thirty nine contributions have been collected in this special issue which provide insightful understanding of the components magmatism and metamorphism metallogeny and tectonic evolution of the north china craton and give an insight into discussion about some key issues on the basis of new data and interpretation such a special issue will not only make a timely addition to the literatures on the precambrian research field but will also open a new window through which the international geological community will adequately understand what major advancements have been obtained in the precambrian geology of the north china craton and what issues are still unresolved and controversial at present

shallow water sclerosponges on jamaican reefs and a criterion for recognition of hurricane deposits we report here that excavation into the acropora palmata rubble on the reef crest at 4 m water depth on discovery bay reefs jamaica revealed the presence of numerous sclerosponges ceratoporella nicholsoni living attached directly to the coral branches 1 2 m below the rubble surface the coral branches excavated were deposited during a storm event in august 1980 and consequently lack the zoned crusts showing a succession from photophilic light loving to sciaphilic shade loving secondary frame builders which normally develop during slow steady incremental coral branch accumulation thus the nature and sequence of encrustations on coral rubble can indicate the speed of its accumulation

geochronological and geochemical constraints on the luliang group in the luliang complex implications for the tectonic evolution of the trans north china orogen abstract the luliang complex is located at the western margin of the middle segment of the trans north china orogen along which the western and eastern blocks amalgamated to form the basement of the north china craton the complex consists of the late neoarchean to paleoproterozoic granitic plutons and meta supracrustal rocks of which the latter are subdivided into the jiehekou luliang yejishan and heichashan lanhe groups the luliang group is composed mainly of siliciclastic rocks in the lower part and volcanic rocks in the upper part all of which have been metamorphosed from greenschist to amphibolite facies u pb ages of detrital zircons from meta sedimentary rocks in the luliang group yield four populations of 3061 2920 ma 2790 2600 ma 2599 2280 ma and 2211 2202 ma suggesting that their provenances were derived mainly from the luliang and taihua complexes in the trans north china orogen the meta volcanic rocks give igneous zircon u pb ages of 2209 2178 ma and e hf t values of 0 8 to 3 6 geochemically they are subalkaline basalts and andesites that can be classified into two groups of which one group has flat lrees weak enrichment in lrees relative to hrees and flat hrees and displays e morb like spider diagrams with the exception of insignificantly negative nb ta zr hf and ti anomalies in contrast the other group displays stronger lree fractionation stronger enrichment in lrees relative to hrees and mildly fractionated hrees and is characterized by spiky spider diagrams similar to arc volcanic rocks the first group is interpreted to have originated from a neoarchean e morb source whereas the second group shows inputs of newly subduction derived fluids in the mantle source these geochronological and geochemical signatures indicate the existence of an 2 2 2 1 ga continental back arc system in the luliang complex of the trans north china orogen which is consistent with the model that the collision between the eastern and western blocks to form the coherent basement of the north china craton in the paleoproterozoic not at the end of neoarchean

a long lived tectono metamorphic event in the late paleoproterozoic evidence from sims u th pb dating of monazite from metapelite in central south trans north china orogen abstract as a key accessory mineral in metapelite monazite forms in the metamorphic event and therefore places important direct constraint on the timing of the tectono metamorphic event in this study we investigate four representative metapelites from different metamorphic terranes in the central south trans north china orogen tnco applying secondary ion mass spectrometry sims u th pb dating on monazite the dating results reveal that monazite collected from the huashan luoning zanhuang and wutai metamorphic complexes record the metamorphic ages of 1 83 ga 1 95 ga 1 85 ga and 1 91 to 1 83 ga respectively combined with the literature data of metamorphic geochronology on the discrete terranes within the tnco it is suggested that the amalgamation between the western and eastern blocks of the north china craton along the nearly ns trending tnco stared as earlier as 1 97 ga and continued to as late as 1 80 ga which was in fact a long lived tectono metamorphic event

development of a pliocene mixed carbonate siliciclastic reef limon costa rica the miocene to pleistocene limon group of costa rica is a mixed carbonate siliciclastic succession that formed in association with the emergence of the central american isthmus our study focuses on a lower late pliocene reef unit the newly excavated contact cut which is located at the contact between the siliciclastic sediments of the rio banano formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the quebrada chocolate formation the siliciclastic sediments were deposited in a thick deltaic setting sourced by erosion of the cordillera de talamanca deposits of the limon group preserve a sequence of progressively shallowing near shore sediments that were exposed by uplift during the early to middle pleistocene the contact cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of caribbean coral reef predominance in the neogene it shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea level highstand three stages of reef evolution are recognized based on faunal diversity the contact cut reef complex is comparable to the time equivalent reef of the las islas roadcut situated west of limon which shows a rapid burial of the corals by siliciclastics both reefs document a distinct facies diversification during the final stages of the closing of the central american seaway the reefs developed in an environment stressed by siliciclastic input which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs the biotic composition of the patch reefs that occurred during the sea level rise las islas and contact cut did not differ from the reefs that developed during the final highstand in sea level the reefs of the overlying moin formation limon group differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs with a very fast give up scenario for las islas reef and a catch up followed by a give up phase for contact cut reef

two phases of paleoproterozoic metamorphism in the zhujiafang ductile shear zone of the hengshan complex insights into the tectonic evolution of the north china craton abstract the zhujiafang ductile shear zone is located in the central hengshan complex a key area for understanding the paleoproterozoic tectonic evolution of the trans north china orogen north china craton detailed metamorphic and geochronological analyses were carried out on metapelite and garnet amphibolite from the zhujiafang ductile shear zone the metapelite preserves two phases of mineral assemblages early kyanite rutile bearing assemblage and late chlorite staurolite bearing assemblage in garnet mica schist and inclusion type muscovite high si kyanite assemblage and late sillimanite bearing assemblage in sillimanite mica gneiss garnet in the metapelite occasionally exhibits pronounced two stage zoning characteristic of a diffusion core with irregular pyrope xpy and grossular xgr contents and a growth rim with xpy and xgr increasing outwards the isopleths of the maximum xgr in garnet core and si content in inclusion type muscovite in the p t pseudosections suggest that the early mineral assemblages underwent medium high pressure type metamorphism with pressures up to 12 14 kbar at 700 750 c the late assemblages and the growth zoning of garnet rim predict a late separated clockwise p t path with peak conditions of 6 5 0 2 kbar 620 10 c medium low pressure type the garnet amphibolite is mainly composed of garnet hornblende plagioclase ilmenite and quartz without overprinting of late mineral assemblages except for localized corona textures phase modeling suggests that the rock has experienced high amphibolite facies metamorphism with peak conditions of 10 5 0 8 kbar 770 50 c which is broadly consistent with the early phase metamorphism of metapelite zircon u pb dating on metapelite yields two metamorphic age groups of 1 96 1 92 ga and 1 87 1 86 ga which are interpreted to represent the timing of the two separated phases of metamorphism two separated orogenic events may have occurred respectively at 1 95 ga and 1 85 ga in the hengshan wutai area the older phase of orogeny was resulted from continental collision and the younger phase of orogeny may be caused by within plate deformation the final exhumation of the high grade rocks formed in the older i e 1 95 ga orogeny should be related with the younger deformation metamorphic event

carbonate and terrigenous sediment budgets for two inshore turbid reefs on the central great barrier reef abstract inshore turbid zone reefs on the great barrier reef gbr occur within 20 km of the mainland coast under marine environmental conditions with respect to sedimentation rates turbidity and water quality that are generally considered marginal for reef growth despite this data from various benthic habitat assessments report high 30 coral cover in these environments and reef core records show them to be characterised by relatively rapid rates of vertical accretion 2 8 mm year a long term trend indicative of high net carbonate productivity and in situ carbonate framework accumulation however the lack of quantitative data on terrigenous sediment input and flux rates and on carbonate production rates has inhibited understanding of both ecological timescale rates of carbonate production and the aggregated long term net impacts of sediments on reef growth to address this knowledge gap a modern carbonate budget and terrigenous sediment model that quantified allochthonous sediment inputs onto within and off reef was developed at two inshore reefs middle reef and paluma shoals both are located within the central region of the gbr and are subjected to high terrigenous sediment load 11 000 tonnes year and fluctuating turbidity 5 to 100 mg l regimes based on sediment dynamic modelling over 81 of sediments delivered were transported off reef with net sediment accumulation limited to sheltered reef habitats net carbonate production was high 6 9 kg m2 year due to high coral cover 30 high coral calcification rates acropora average 6 3 g cm2 year and low bioerosion rates 0 3 to 5 kg m2 year but varied spatially with highest net carbonate production 10 kg m2 year within deep 2 m at lat windward reef zones high carbonate framework production has enabled middle reef and paluma shoals to vertically accrete rapidly middle reef establishing at depths of 4 m paluma shoals at 3 m depth and both reaching sea level in

zircon u pb and lu hf isotopic and whole rock geochemical constraints on the lanhe and heichashan groups implications for the paleoproterozoic tectonic basin evolution of the luliang complex abstract the luliang complex is located at the western margin of the middle segment of the trans north china orogen along which the western and eastern blocks collided to form the north china craton the complex mainly consists of metamorphosed granitic plutons and supracrustal rocks of which the latter are subdivided into the jiehekou luliang yejishan lanhe and heichashan groups the lanhe group is composed of meta conglomerates quartzites and phyllites with minor meta basalts whereas the heichashan group consists of molasse like meta conglomerates and coarse grained quartzites geochemistry of the yejishan meta sedimentary rocks indicates weak source weathering and dominantly chemical immature features whereas the lanhe and heichashan samples display opposite features u pb ages of detrital zircons from the lanhe groups yield four age peaks at 2180 ma 2370 ma 2520 ma and 2700 ma the former three peaks coincide with ages of the chijianling guandishan ttg gneisses 2199 2151 ma and meta volcanic rocks from the luliang and yejishan groups 2213 2156 ma age of the gaijiazhuang porphyritic gneisses 2375 2364 ma and age of the yunzhongshan ttg gneisses 2499 ma respectively whereas detrital zircons forming the oldest age peak were most likely derived from the early neoarchean crust of the eastern block for the heichashan group the dominant 2 2 2 0 ga detrital zircons were probably recycled from the underlying jiehekou group and the minority is directly derived from the early paleoproterozoic granitoids in the luliang complex the youngest detrital zircon age peaks of 2 17 ga and 1 82 ga place maximum depositional ages on the lanhe and heichashan groups respectively whereas the local 1 81 1 79 ga massive granites place constraint on their minimum depositional ages taking into account the lithostratigraphic features provenance and formation ages we suggest that the lanhe group formed in a shrinked remnant back arc basin and the heichashan group was deposited in a foreland basin conversion of the tectonic basin from the middle paleoproterozoic back arc basin to the late paleoproterozoic foreland basin is well consistent with the model that the single collision to form the basement of the north china craton happened at 1 85 ga

using in situ monazite and xenotime u pb geochronology to resolve the fate of the missing banded iron formation hosted high grade hematite ores of the north china craton

internally consistent recalibrations of mineral equilibria for geothermobarometry involving garnet orthopyroxene plagioclase quartz assemblages and their application to the south indian granulites abstract three reactions are calibrated as geothermobarometers for garnet orthopyroxene plagioclase quartz assemblages namely 1 2 ferrosilite 1 3 pyrope 1 2 enstatite 1 3 almandine a ferrosilite anorthite 2 3 almandine 1 3 grossularite quartz b and enstatite anorthite 2 3 pyrope 1 3 grossularite quartz c the internally consistent geothermobarometers based on reactions a b and c are calibrated from experimental data only the thermodynamic parameters of reaction a are derived from published experimental data in the fmas system n 104 in the range 700 1400 c and 5 50 kbar while those for reaction b are derived by summation of the existing reversed experimental data of the mineral equilibria ferrosilite fayalite quartz d and anorthite fayalite 2 3 almandine 1 3 grossularite e the retrieved thermodynamic parameters for reactions a b and c are respectively h0 cal 3367 209 2749 350 and 3985 545 s0 cal k 1 1 634 0 163 8 644 0 298 and 5 376 0 391 and v01 298 cal bar 1 0 024 0 60946 and 0 5614 on a one cation basis the derived margules parameters of the ternary ca fe mg in garnet are wfe mg 1256 1 0 0 23 t k wmg fe 2880 1 7 0 13 t k wca mg 4047 77 1 5 t k wmg ca 1000 77 1 5 t k wca fe 723 0 332 0 02 t k wfe ca 1090 cal and the ternary constant c123 4498 1 516 0 265 t k cal subregular solution model of non ideal mixing and fe mg al in orthopyroxene wfe mg 948 200 0 34 0 10 t k wfe al 1950 500 and wmg al 0 cal regular solution model of non ideal mixing the anorthite activity in plagioclase is calculated by the al avoidance model of subregular ca na mixing commonly used for geobarometry based on reactions b and c when the geothermobarometers are applied to garnet orthopyroxene plagioclase quartz assemblages n 45 of wide compositional range from the precambrian south indian granulites temperature ranges of 690 860 c x 760 45 c and pressure ranges of 5 10 kbar were obtained the p t values were estimated simultaneously and there is no difference in the pressure calculated from pmg reaction c and pfe reaction b in the existing calibrations this difference is 1 kbar or more furthermore there is no compositional dependence of the ln k of the experimental data in the fmas n 104 and the cfmas n 78 systems at different temperatures and the estimated temperatures of the south indian granulites

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

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

quaternary atoll development new insights from the two dimensional stratigraphic forward modelling of mururoa island central pacific ocean knowledge about the quaternary evolution of mid ocean atolls comes mainly from drilling and field observations carried out on a number of pacific carbonate islands however little is known about the early to mid pleistocene atoll development history especially at margin and foreslope settings using previous field and subsurface data from mururoa atoll and a process based modelling software dionisos a two dimensional forward stratigraphic model of atoll development is proposed for the past 1 8 million years myr observational data from vertical to inclined coring seismic and bathymetric surveys indicate that from approximately 0 45 to 0 40 million years before present ma carbonate deposition at mururoa atoll resulted in a series of mostly prograding reef units the model is first constrained at the base by the shape and topography of the pre quaternary basement a number of sensitivity tests were performed to define the respective influence of variant parameters the best fit development scenario that accounts for the overall geometry and stratigraphic architecture of the quaternary sediment packages is obtained by using the sea level curve by miller et al 2005 uniform subsidence rate of 105 m myr 1 and carbonate production rates gradually increasing from 0 50 to 8 mm yr 1 between 1 80 ma and the present additional controlling parameters include subaerial erosion at a constant rate of 0 25 m kyr wave energy and sediment transport processes the stratigraphic forward model predicts a succession of three distinct types of carbonate systems that have developed since the earliest pleistocene toe of slope systems from 1 80 ma to about 0 80 ma open platform systems from 0 80 ma to 0 50 ma and framework reef systems from about 0 50 ma to the present the development of these different systems is most likely to be controlled by climate and changes in sea level cycles during the low amplitude 41 kyr cycle periods of the earliest pleistocene ambient conditions were not conducive to framework reef growth shallow water carbonate sedimentation was dominantly gravity driven operating along the platform foreslopes only during the mid pleistocene climate transition narrow open platform units have developed at the upper parts of the pre quaternary basement flanks with the onset of the high amplitude 100 kyr sea level modes and climate restoration reef frameworks started to be generated these models from mururoa agree with a number of previous studies suggesting that most of the true framework reefs were not initiated prior to 0 50 ma mururoa atoll is demonstrated to be a robust analogue for providing more realistic interpretations of the development history of pacific atolls further modelling with three dimensional dionisos could generate better predictions by taking into account hydrodynamic and transport parameters more accurately

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

shrimp u pb zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton the fuping complex is situated in the central part of the north china craton and consists of four major lithological assemblages fuping tonalitic trondhjemitic granodioritic gneisses longquanguan augen gneisses wanzi supracrustal assemblage and nanying granitic gneisses shrimp u pb geochronology combined with u th and cathodoluminescence cl imaging of zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the fuping complex cl images reveal the coexistence of magmatic and metamorphic zircons in nearly all rock types of the fuping complex the metamorphic zircons occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores and are all characterized by nebulous zoning or being structureless with extremely high luminescence and very low th contents these features make them distinct from magmatic zircons that are characterized by concentric oscillatory zoning comparatively low luminescence and high th and u contents shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic plutons of the fuping gneisses were emplaced at 2523 14 ma 2499 10 ma and 2486 8 ma respectively whereas the monzogranitic and granitic plutons of the longquanguan augen gneisses were intruded respectively at 2510 22 ma and 2507 11 ma prismatic and oscillatory zoned zircons dominate in the pelitic rocks of the wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks the concordant and discordant u pb ages of 2502 5 ma and 2507 14 ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than 2507 ma ago in addition a zoned zircon grain in one pelitic rock sample has a near concordant age of 2109 5 1 ma which may provide a maximum depositional age for the wanzi supracrustal rocks shrimp results also reveal that granitic magmatism assigned to the nanying granitic gneisses occurred over a protracted interval from 2077 13 ma to 2024 21 ma the nebulously zoned zircon grains and overgrowth recrystallization zircon rims from different rocks yielded similar concordant 207pb 206pb ages in the range 1875 to 1802 ma interpreted as approximating the age of regional metamorphism of the fuping complex timing of primary zircon crystallization and regional metamorphism of the fuping complex is in general agreement with recent u pb zircon ion probe results for the wutai and hengshan complexes that bound the fuping complex to the northwest these areas are characterized by the emplacement of major granitoid bodies at around 2 50 ga to 2 48 ga ago deposition of supracrustal rocks in the paleoproterozoic intrusion of paleoproterozoic granitic bodies at 2 1 to 2 0 ga and regional metamorphism at 1 875 to 1 802 ga these data indicate that the fuping and hengshan complexes do not represent an older crystalline basement to the wutai complex as suggested in previous tectonic models but together with the wutai complex represent elements of a single late archean to paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western north china blocks at 1 85 ga which resulted in the final assembly of the north china craton

sm nd and shrimp u pb zircon geochronology of high pressure granulites in the sanggan area north china craton timing of paleoproterozoic continental collision abstract high pressure hp mafic granulites are widely distributed as sheet like and lenticular bodies within highly deformed tonalitic gneisses in the sanggan area north china craton they have clockwise isothermal decompression and isobaric cooling p t paths implying continental collision tectonics whole rock analyses of 15 samples define a sm nd isochron yielding an age of 2547 87 ma with e nd t 2 7 corresponding nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites a combined sm nd mineral whole rock isochron from one of these samples yields an age of 1813 23 ma taken to represent the metamorphic age at an early stage on the cooling path shrimp u pb zircon analyses of three hp mafic granulite samples give uniform weighted mean 207 pb 206 pb ages of 1817 12 1817 12 and 1819 16 ma these ages are interpreted to date metamorphism of the hp granulites and with the sm nd mineral whole rock result strongly suggest that the time of continental collision was at ca 1 82 ga an additional sample records two age populations one at 1803 9 ma and an older one at 1872 16 ma the latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at 1 82 ga these results confirm the paleoproterozoic age for assembly of the north china craton

structural evolution and 40ar 39ar dating of the zanhuang metamorphic domain in the north china craton constraints on paleoproterozoic tectonothermal overprinting abstract the zanhuang domain in the hinterland of the north china craton consists of archaean paleoproterozoic mesoproterozoic and palaeozoic rocks and was previously considered a mesozoic metamorphic core complex our reappraisal of regional structural history and mineral 40 ar 39 ar geochronology shows that the domain was subjected to a number of deformation events and had a heterogeneous uplift cooling history during the paleoproterozoic four primary deformation events have been recognized in the domain the first event reflects the earliest deformation in the region however only closed and rootless folds are preserved d2 was dominated by wnw ese shortening and top to ese thrusting in a collisional environment d3 was a divergent extensional and ductile shearing event driven by the post collisional extensional collapse and exhumation of the thickened crust in the domain d4 was characterized by localized ductile shearing with the development of three nne trending ductile shear zones the 40 ar 39 ar plateau ages derived from the thermochronology analyses of the biotite concentrates from the metamorphic rocks are interpreted as cooling ages through biotite 40 ar 39 ar closure temperature 300 c and this allows us to constrain the timing of deformation events in conjunction with the evidence from structural analyses and previous geochronological data we conclude that 1870 and 1870 1826 ma define the timing of d1 and d2 events respectively while 1826 1793 ma represents the age of d3 the last event d4 occurred at 1689 1633 ma as constrained by 40 ar 39 ar plateau ages of biotite concentrates from the mylonites within the ductile shear zones these data together with k feldspar 40 ar 39 ar geochronology allows us to depict the cooling history of the region during the paleoproterozoic and mesoproterozoic it appears that the uplift cooling rate varies temporally and spatially in the region

u pb and hf isotopic study of detrital zircons from the luliang khondalite north china craton and their tectonic implications two types of metasedimentary rocks occur in the trans north china orogen of the north china craton one type consists of highly metamorphosed supracrustal rocks with protoliths of mature cratonic shale called khondalites as found in the luliang complex rocks of the other type are also highly metamorphosed but less mature as represented by the wanzi supracrustal assemblage in the fuping complex u pb isotopic data for detrital zircons from khondalites show a provenance dominated by 1 9 2 1 ga palaeoproterozoic rocks these detrital zircons display a wide range of e hf values from 16 0 to 9 2 and give hf isotopic model ages mostly around 2 3 ga the high positive e hf values approach those for the depleted mantle at 2 1 ga highlighting a juvenile crustal growth event in palaeoproterozoic times hf isotopic data also imply that c 2 6 ga old crustal material was involved in the palaeoproterozoic magmatic event these data are similar to those for the khondalitic rocks from the interior of the western block of the north china craton suggesting a common provenance in contrast other metasedimentary rocks in the trans north china orogen such as the wanzi supracrustal assemblage in the fuping complex have a source region with both palaeoproterozoic and archaean rocks their detrital zircon hf isotopic data indicate reworking of old crustal material and a lack of significant juvenile palaeoproterozoic magmatic input these rocks are similar to the coevally deposited meta sedimentary rocks in the interior of the eastern block we propose that the luliang khondalites were deposited on the eastern margin of the western block in a passive continental margin environment and were thrust eastward later during collision with the eastern block other metasedimentary rocks in the trans north china orogen were deposited on the western margin of the eastern block in a continental arc environment our data support the eastward subduction model for the palaeoproterozoic tectonic evolution of the north china craton

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

the importance of quaternary records in reducing risk from tropical cyclones numerous late holocene records of tropical cyclones have been collected from north east queensland australia they are in the form of multiple sedimentary ridges paralleling the shore the ridges are composed of coral fragments or shell and sand or pure sand a method to determine the intensity of the tropical cyclone responsible for deposition of the ridges at each site has been applied and the results suggest that in the majority of cases these features were deposited by very high magnitude events the results suggest that extrapolations of long term cyclone magnitude and frequencies from the 30 to 40 year long instrumental record which is the method commonly used to assess risk from this hazard substantially underestimate the risk from this hazard this is confirmed for the cairns region by an 800 year long high resolution isotope record of tropical cyclones preserved in a limestone stalagmite together the sedimentary and isotope records suggest that tropical cyclone activity in north east queensland has been in a phase of quiescence since before european settlement of the region in approximately ad 1870 it is suggested that the incorporation of the palaeo record into risk assessments will provide a more realistic guide to the magnitude frequency relationship of tropical cyclones and help reduce risk from this hazard as a consequence

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

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

metamorphic p t t paths retrieved from the amphibolites lushan terrane henan province and reappraisal of the paleoproterozoic tectonic evolution of the trans north china orogen abstract garnetiferous amphibolites preserving prograde inclusion assemblages m1 within garnet porphyroblasts metamorphic peak assemblages m2 and post peak symplectitic assemblages m3 have been found in the lushan terrane henan province taihua metamorphic complex southernmost section of the ns striking palaeoproterozoic trans north china orogen tnco geothermobarometric computation shows that the m1 m2 and m3 assemblages were formed under the p t conditions of 650 730 c 4 9 8 1 kbar 740 810 c 9 10 8 kbar and 750 760 c 5 0 7 7 kbar respectively suggesting that these amphibolites record clockwise p t paths including nearly isothermal decompression itd segments similar to the west alpine type p t paths indicative of being resulted from an orogenic process high resolution sims u pb dating of metamorphic zircons suggests that the metamorphism took place at ca 1 95 1 75 ga these data imply that the palaeoproterozoic collision between the eastern and western blocks of the north china craton along the southernmost terminal of the tnco not only started earlier but also continued longer than the middle and north sections of the tnco

from platform top to adjacent deep sea new source to sink insights into carbonate sediment production and transfer in the sw indian ocean glorieuses archipelago abstract over the past ten years a huge amount of source to sink studies have aimed to unravel the tectonic climatic and other processes that shape the landscape from mountains to the deep ocean interestingly these studies have been mainly dedicated to siliciclastic or mixed systems for which the connection between drainage basins continental shelves slope and basin environments are often well constrained here we present a study focusing on a source to sink study dedicated to a pure carbonate system located in the sw indian ocean glorieuses archipelago extensive field sampling and geophysical acquisition across the carbonate platform have allowed us to estimate the composition the lateral variability and volumes of neritic sands deposited on the platform top additional seismic and bathymetric surveys across the platform interior illustrate the presence of plurimetric sandy bodies deposited along the leeward platform edge corresponding to the export of carbonate sediments from the platform top toward the platform edge under the influence of dominant currents and wind driven processes high resolution seismic bathymetric data and sediment cores acquired along the leeward slope and basin adjacent to the carbonate platform highlight the presence of channel levee complexes and turbiditic lobes which have accumulated on the seafloor on top of a 250 m thick sedimentary basin at 2000 3400 m water depth our study points out that carbonate sands and aragonitic mud produced on the platform top during the holocene have been shed to the adjacent basin we also demonstrate that this routing system was active at least throughout the last three glacial interglacial cycles this study has important consequences for our understanding of carbonate sedimentation processes occurring in the vicinity of isolated carbonate platforms 1 it highlights the role of oceanographic conditions in the distribution of sediment on a platform top and its export along the platform edge and the adjacent basin 2 it contributes to quantify the productivity of a carbonate platform as well as its sediment storage capacity 3 a first estimate of a carbonate source to sink system is proposed demonstrating that 0 57 km3 of sediments have been produced during the holocene 0 3 km3 being presently stored on the platform and the remaining having been exported to the deep basin

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

thermal evolution of two textural types of mafic granulites in the north china craton evidence for both mantle plume and collisional tectonics mafic granulites from the north china craton can be divided into two textural types referred to as a and b types a type mafic granulites display garnet quartz symplectic coronas and outcrop in the eastern and western zones of the craton whereas b type mafic granulites exhibit orthopyroxene plagioclase clinopyroxene symplectites or coronas and are mainly exposed in the central zone of the craton most a type mafic granulites preserve the prograde m 1 peak m 2 and post peak near isobaric cooling m 3 assemblages which are represented respectively by inclusions of hornblende plagioclase quartz a peak mineralogy of orthopyroxene clinopyroxene plagio clase quartz garnet and overprinted by garnet quartz symplectic coronas these mineral assem blages and their p t pressure temperature estimates define anticlockwise p t evolutionary paths the b type mafic granulites preserve the peak m 1 post peak near isothermal decompression m 2 and cooling m 3 assemblages which are represented by the peak assemblage of orthopyroxene clinopyroxene plagioclase quartz garnet hornblende post peak orthopyroxene plagioclase clinopyroxene symplectites or coronas and later hornblende plagioclase magnetite symplectites respectively these mineral assemblages and their p t estimates define clockwise p t paths the anticlockwise p t paths of the a type mafic granulites in the eastern and western zones of the north china craton are consistent with a model of underplating and intrusion of mantle derived magmas in combination with lithological structural and geochronological data the eastern and west ern zones of the north china craton are considered to represent two continental blocks that devel oped through the interaction of mantle plumes with the lithosphere from the palaeoarchaean to the neoarchaean era the b type mafic granulites and associated rocks in the central zone represent a magmatic arc that was metamorphosed and deformed during amalgamation of the eastern and west ern continental blocks in the late palaeoproterozoic era the mineral reaction relations and clockwise p t paths of the b type mafic granulites from the central zone record the tectonothermal history of the collision that resulted in the final assembly of the north china craton at c 1800 ma

discovery of mafic granulite in the guandishan area of the luliang complex north china craton age and metamorphic evolution abstract mafic granulite and amphibolite occur as boudinaged lenses in felsic and metapelitic gneiss in the guandishan area of the southern luliang metamorphic complex peak assemblages recorded by large granoblastic minerals yield pressure temperature p t conditions of 790 c and 9 4 kbar in granulite and 750 c and 6 2 kbar in amphibolite based on standard thermobarometric techniques retrogression produced fine grained resorptive rims in garnet symplectitic hornblende orthopyroxene and plagioclase that record p t conditions of 560 775 c and 2 8 7 5 kbar in granulite and 740 c and 5 7 kbar in amphibolite mineral inclusion patterns and major element zoning are consistent with a clockwise p t path that ended with nearly isothermal decompression uranium pb dating of metamorphic zircons from the granulite and host metapelite reveal two discrete meaningful age groups of metamorphism in the guandishan area most metamorphic zircon grains exhibit peak metamorphic growth at 1935 1920 ma whereas a smaller younger group exhibit growth during retrogression between 1860 and 1815 ma regional metamorphism in the luliang metamorphic complex was related to the amalgamation of the north china craton along the trans north china orogen between c 1 95 and 1 80 ga

the late paleoproterozoic i and a type granites in luliang complex north china craton new evidence on post collisional extension of trans north china orogen abstract the late paleoproterozoic granitoids from luliang complex can provide pivotal constraints on the amalgamation process between eastern and western blocks of north china craton along the trans north china orogen la icp ms zircon dating gives emplacement ages of 1854 20 ma for the huijiazhuang granite 1830 21 ma for the xiyupi granite vein and 1760 20 ma for the dacaoping porphyritic granite respectively the huijiazhuang granite and xiyupi granite dyke have variable sio2 66 71 74 31 wt high k2o 5 09 6 35 wt low p2o5 0 02 0 16 wt al2o3 13 92 15 31 wt right inclined ree patterns with medium negative eu anomalies enrichment in lile depletion in hfse especially nb ta consisting to high k i type granite in a post collisional setting the sr y 7 36 59 95 end t 5 7 to 4 1 with tdm 2381 ma to 2570 ma from whole rock sm nd isotope and ehf t 9 6 to 2 3 with tcdm 2360 ma to 3070 ma from zircon lu hf isotope suggest that they are produced by partial melting of slightly thickened neoarchean paleoproterozoic basement materials including both meta sedimentary and meta igneous rocks the dacaoping porphyritic granites are characterized by high sio2 70 83 74 30 wt k2o 4 84 5 60 wt feot feot mgo 0 86 0 92 seagull type ree pattern with strong negative eu anomaly eu 0 16 0 35 and higher 10000 ga al 2 99 3 36 hfse zr nb ce y 378 583 ppm showing an affinity of a2 type granite they have low sr y 1 17 8 62 end t 6 1 to 6 4 with tdm 2690 ma to 2776 ma from whole rock sm nd isotope and ehf t 7 9 to 5 2 with tcdm 2775 2938 ma from zircon lu hf isotope indicating a result from the melting of thinned neoarchean calc alkaline intermediate basement taking into account the temporal spatial distributions of late paleoproterozoic rocks in the trans north china orogen it suggests a post collisional extension occurred during 1 89 1 76 ga and the crust is thinned visibly since 1 82 ga

distribution of fe2 and mg between coexisting garnet and hornblende in synthetic and natural systems an empirical calibration of the garnet hornblende fe mg geothermometer abstract multiple regression analysis of a compilation of the fe2 mg distribution between garnet and hornblende from experimental runs on basaltic to intermediate compositions n 22 and coexisting garnet clinopyroxene hornblende from natural intermediate to basaltic rocks n 43 has been performed to define ln kd fe2 mg grt hbl as a function of temperature and garnet composition the regression of data covering a large span in pressure 5 16 kbar temperature 515 1025 c and composition yields the ln kd fe2 mg grt hbl p t compositional relationship r2 0 93 t c 1504 1784 x ca grt x mn grt ln k d fe 2 mg grt hbl 0 720 273 where k d fe 2 mg grt hbl fe 2 mg grt fe 2 mg m 1 m 3 hbl x ca grt ca ca mn fe 2 mg in garnet x mn grt mn ca mn fe 2 mg in garnet application of this expression to natural garnet hornblende pairs in intermediate to basaltic and semipelitic rock types from various settings gives temperatures that are consistent with other methods

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

metamorphic records in the luliang metapelites of the jiehekou group implications for the tectonic evolution of the trans north china orogen north china craton abstract to further understand the metamorphic evolution of the trans north china orogen tnco a combined study of petrography pseudosection modeling and conventional thermobarometry was completed on garnet sillimanite bearing metapelitic rocks of the jiehekou group from the southern luliang metamorphic complex in the central segment of the tnco the luliang metapelitic rocks preserve peak assemblages of garnet biotite sillimanite plagioclase and quartz with or without k feldspar that reflect c 750 c and 7 0 kbar garnet has mostly homogeneous grain cores with sparse mineral inclusions enclosed successively by 1 rims of higher spessartine and lower pyrope content and 2 symplectitic intergrowths of cordierite biotite and plagioclase that present a spectacular white eye socket reaction microstructure quantitative phase equilibria modeling and traditional thermobarometric calculation results are consistent with this retrograde microstructure having developed during decompression to t 650 c and p

a detrital sediment budget of a maldivian reef platform abstract sediment dynamics are an important control on the morphology and development of reef systems by actively removing and redistributing excess detrital sediment this study presents quantitative data from direct point measurements of sediment transport on the platform surface and fore reef slope of vabbinfaru reef north male atoll maldives a suite of sediment traps were used to construct actual rates of platform sediment fluxes and off reef export over different spatial and temporal seasonal scales to establish key sediment transport pathways findings showed that high sediment fluxes occur on vabbinfaru platform in the absence of major storm activity up to 1905 g m 1 d 1 with 95 of annual transport occurring during the southwest monsoon as a result of increased wave energy climate driven changes in the platform process regime caused a reversal of net sediment transport pathways between each monsoon season off reef export rates were high reaching a maximum of 12 58 kg m 1 y 1 for gravel and 407 g m 1 d 1 for sand sized sediment an estimated 127 120 kg is exported from the platform annually equating to a significant loss from the reef sediment budget and contributing to the long term geomorphic development of the fore reef slope and atoll basin detrital sediment reservoirs on vabbinfaru are not purely depositional carbonate sinks but rather temporary stores that are important in the transfer of sediment between reef zones

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

u pb and hf isotopic study of detrital zircons from the yejishan group of the luliang complex constraints on the timing of collision between the eastern and western blocks north china craton abstract the trans north china orogen is a recently recognized continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the coherent basement of the north china craton however there is a hot debate on the timing of the collision between the two blocks with one school of thought arguing the collision occurred at 2 5 ga whereas others believe it took place at 1 85 ga u pb ages and hf isotopic data of detrital zircons from foreland basins in the trans north china orogen can provide rigorous constraints on this controversial issue one of such foreland basins is represented by the yejishan group in the luliang complex in the middle sector of the western margin of the trans north china orogen the group consists of conglomerates quartz wackes sandstones and minor limestones most of which contain large amounts of detrital zircons cl images reveal that nearly all detrital zircons from the yejishan group possess oscillatory zoning with th u ratios of 0 2 2 34 typical of an igneous origin the 207 pb 206 pb ages of detrital zircons range between 3 24 and 1 81 ga with most having paleoproterozoic ages of which the youngest group ages are around 1 87 1 81 ga this indicates that the foreland basin in which the yejishan group was deposited must have formed not earlier than 1 87 1 81 ga thus supporting the collision between the eastern and western blocks at 1 85 ga not at 2 5 ga

geochemical ar 40 ar 39 geochronological and sr nd isotopic constraints on the origin of paleoproterozoic mafic dikes from the southern taihang mountains and implications for the ca 1800 ma event of the north china craton abstract the wide occurrence of paleoproterozoic mafic dikes in the basement of the trans north china orogen provides important constraints on the major 1800 ma tectonothermal event of the north china craton these mafic dikes form a tholeiitic series dominated by basalts and basaltic andesites and can be geochemically classified into three groups the groups 1 and 2 rocks are characterized by high total feo contents 12 69 15 61 of which the group 1 rocks are more enriched in lile and lree contents and depleted in hfse th nb n 2 5 3 8 la yb cn 3 0 5 8 nb la n 0 27 0 38 and have more radiogenic nd isotopic ratios nd t 3 40 to 5 14 than the group 2 rocks th nb n 0 8 1 2 la yb cn 1 5 2 1 nb la n 0 65 0 87 nd t 0 60 to 1 67 in contrast the group 3 rocks are typified by low feot 7 86 11 04 and high mgo 5 62 9 56 contents higher la yb cn 4 22 7 13 ratios less radiogenic nd isotopic ratios nd t 2 75 to 5 52 and more significant th u and nb ta depletion are also apparent features 40ar 39ar geochronology of three representative samples from each group yielded plateau ages of 1780 7 0 5 ma 1765 3 1 1 ma and 1774 7 0 7 ma respectively these elemental and isotopic data suggest that the geochemical variations of these rocks cannot be simply explained by crystallization from a common parental magma involving crustal contamination during emplacement instead they most likely originated from variable sources under different degrees of partial melting the group 1 rocks were derived from relatively low degrees of partial melting of a refractory lithospheric mantle previously metasomatised by subduction related fluids whereas the group 2 rocks originated from a hybridized source involving ca 40 subduction modified lithospheric mantle similar to the group 1 and ca 60 n morb component in contrast the group 3 rocks show significant th u depletion that may mark the involvement of portions of gabbroic lower crust trapped in the source region during subduction based on all the available data we propose a tectonic model of a full subduction syncollision postcollision rifting cycle for the evolution of the ncc between 1870 and 1765 ma a variety of source regions beneath the southern taihang mountains initially developed during the period of subduction collision and subsequent extension rifting resulted in the melting of the subduction modified lithospheric mantle which produced widespread paleoproterozoic mafic dikes on the trans north china orogen in response to upwelling of convective mantle

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

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

deglaciation chronology sea level changes and environmental changes from holocene lake sediments of germania havn so sabine o northeast greenland abstract germania havn so is located at the outermost coast of northeastern greenland according to radiocarbon dating the lake basin was deglaciated in the early holocene around 11 000 cal yr bp at that time the lake was a marine bay but the lake was isolated soon after deglaciation at 10 600 cal yr bp the marine fauna was species poor indicating harsh conditions with a high sedimentation rate and lowered salinity due to glacial meltwater supply the pioneer vegetation around the lake was dominated by mosses and herbs deposition of relatively coarse sediments during the early holocene indicates erosion of the newly deglaciated terrain remains of the first woody plant salix herbacea appear at 7600 cal yr bp and remains of other woody plants salix arctica dryas octopetala cassiope tetragona and empetrum nigrum appear around one millennium later declining concentrations of d octopetala and the caddis fly apatania zonella in the late holocene probably imply falling summer temperatures only moderate changes in the granulometric and geochemical record during the holocene indicate relatively stable environmental settings in the lake which can probably be explained by its location at the outer coast and the buffering effect of the neighboring ocean

metamorphic evolution and u pb geochronology of metapelite northeastern wutai complex implications for paleoproterozoic tectonic evolution of the trans north china orogen abstract the wutai complex lies in the middle part of the trans north china orogen mainly consisting of metamorphosed volcanic sedimentary rocks named as wutai group and late archean ttg gneisses garnet biotite schist from the northeastern part of the wutai group lower shizui subgroup mainly consists of garnet porphyroblast plus biotite staurolite kyanite sillimanite fibrolite plagioclase quartz as well as accessory minerals including ilmenite magnetite hematite apatite monazite and zircon petrographic observation and mineral chemistry indicate that these metapelites underwent the sequential prograde m1 peak m2 and retrograde m3 metamorphic stages geothermobarometry computation and phase equilibrium modelling show that the representative samples record clockwise p t paths passing from 3 7 kbar 570 630 c m1 through 9 10 kbar 615 660 c m2p to 6 9 kbar 655 680 c m2t and finally to a speculated exhumation stage m3 indicative of orogenic metamorphism srhimp and la icp ms u pb dating on inherited detrital zircons yielded three age peaks of 2 7 ga 2 5 ga and 2 1 ga the youngest 207pb 206pb age of 2064 21 ma of detrital zircon possibly constrains the maximum depositional age of the shizui subgroup sims and shrimp u pb dating of metamorphic monazite and zircon constrain the metamorphic age of the garnet bearing mica schist to be 1853 1823 ma combined with previous data the wutai complex was demonstrated to have been involved in a prolonged subduction collision process 1 97 1 82 ga between the western and eastern blocks in the paleoproterozoic

neoarchean paleoproterozoic terrane assembly and wilson cycle in the north china craton an overview from the central segment of the trans north china orogen abstract the north china craton ncc is one of the important precambrian nuclei of the globe as well as an integral component of the paleoproterozoic supercontinent columba the ncc is considered in popular models as an assembly of two major crustal blocks the eastern and western blocks which were sutured along the trans north china orogen tnco which represents a major paleoproterozoic collisional orogen the central segment of the tnco preserves important keys to unravel the tectonic history of amalgamation and cratonization of the ncc here we present an overview on the lithology geochemistry geochronology lu hf isotopes and metamorphic history of the neoarchean to paleoproterozoic rocks in the major basement terranes from the central segment of the tnco the available data allow us to re construct the major precambrian events from the heart of the ncc as follows 1 2 58 2 48 ga amalgamation of three microblocks ordos qianhuai and xuchang along the wutai granite greenstone belt and its branch at the zanhuang area together with the convergence of major microblocks along other 2 5 ga granite greenstone belts leading to the initial cratonization of the ncc 2 2 50 2 45 ga post collisional extension as represented by undeformed mafic dykes and granitoid dykes or plutons resulting in the opening of an oceanic basin along the hengshan and huai an xuanhua complexes 3 2 45 2 12 ga subduction in the hengshan huai an xuanhua and luliang complexes and simultaneous rifting in the fuping wutai and zanhuang complexes 4 2 12 1 98 ga opening of oceanic basins in the wutai and fuping areas followed by double subduction of the oceanic lithosphere and arc magmatism in the fuping wutai and luliang complexes with coeval rifting in the northern part as represented by the hengshan and huai an xuanhua complexes and the southern side as represented by the zanhuang complex 5 1 96 1 80 ga the assembly of the separated terranes or complexes driven by the amalgamation of the western and eastern blocks the collisional event may have occurred at 1 96 1 90 ga and the 1 88 1 80 ga metamorphic ages might represent the retrograde cooling during exhumation 6 termination of the collisional event represented by post collisional intrusions of granitoids charnockites and pegmatites until ca 1 74 ga thus the central segment of the tnco records a prolonged wilson cycle following the initial cratonization of the ncc during neoarchean and involved multiple rift subduction and collisional processes in the paleoproterozoic resulting in the unified ncc and its incorporation into the supercontinent columbia

p t t paths and tectonic history of an early precambrian granulite facies terrane jining district south east inner mongolia china abstract the widespread khondalite series of south east inner mongolia consists largely of biotite sillimanite garnet gneiss and quartzo feldspathic gneiss with some marble and mafic granulite layers it has experienced two metamorphic events at c 2500 and 1900 2000 ma a pre peak stage of the first metamorphism at t 600 700 c and p 6 7 kbar is recognized by the relict amphibolite facies assemblage ky grt bt pl qtz and protected inclusions of biotite hornblende sodic plagioclase and quartz in garnet or orthopyroxene the peak stage with t c 800 50 c and p 8 10 kbar is characterized by the widespread granulite facies assemblages sil grt bt kfs pl qtz in gneiss and opx cpx pl hbl grt in granulite the p t t path suggests that the supracrustal sequence was buried in the lower crust by tectonic thickening during d1 d2 the beginning of the second metamorphism is characterized by further temperature rise to 700 c or more at lower pressure this stage is manifested by the appearance of cordierite after garnet fibrolite sil2 after biotite in gneiss and transformation of hbl1 into opx2 and cpx2 in granulite coronas of symplectitic opx2 pl2 surrounding grt1 and cpx1 in mafic granulite are interpreted as products of near isothermal decompression the p t t path may be related tectonically to waning extension of the crust by the end of the early proterozoic

off reef transport of coral fragments at lizard island australia abstract the generation and movement of coral rubble is important to the sedimentary budget of a reef in sediment facies development and in the promotion of reef growth this study examined the rate of down slope transport of live and dead coral fragments from shallow reef fronts at lizard island on the great barrier reef australia ten large 1 m2 collecting trays were deployed and cleared annually for 4 years at each of two sites at the base 8 12 m depth of the steeply sloping fringing reef the rate of export of coral fragments down the reef slope was very high an average of 132 fragments weighing 1 87 kg was recorded each year per meter of reef front a mean of 2 25 of the fragments representing 43 species was alive in the trays at each annual census yielding an average rate of colonization onto the reef slope of 2 7 live fragments per meter of reef front per year reworking of hard calcareous substrates towards the slope promotes reef growth by two mechanisms 1 passive dispersal of live coral fragments to peripheral soft sediment habitats that are unsuitable for larval settlement and 2 subsequent colonization of rubble by coral larvae there were no major storms during the course of the study indicating that significant down slope transport of fragments can occur even in the absence of cyclones

zircon geochronology and metamorphic evolution of mafic dykes in the hengshan complex of northern china evidence for late palaeoproterozoic extension and subsequent high pressure metamorphism in the north china craton abstract magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the hengshan complex of the north china craton these dykes now occur as boudins and deformed sheets within migmatitic tonalitic trondhjemitic granodioritic and granitic gneisses and are conspicuous due to relics of high pressure granulite or even former eclogite facies garnet pyroxene bearing assemblages shrimp ages for magmatic zircons from two dykes reflect the time of dyke emplacement at 1915 ma whereas metamorphic zircons dated by both shrimp and evaporation techniques are consistently in the range 1848 1888 ma the youngest granitoid gneiss yet dated in the hengshan has an emplacement age of 1872 17 ma these results complement recent geochronological studies from the neighbouring wutai and fuping complexes to the se of the hengshan showing that a crustal extension event occurred in the late palaeoproterozoic this preceded a major high pressure collision type metamorphic event in the central part of the north china craton that occurred in the palaeoproterozoic and not in the late archaean as previously thought our data support recent suggestions that the north china craton experienced a major craton wide orogenic event in the late palaeoproterozoic after which it became cratonized and acted as a stable block

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

metamorphic p t paths of the zanhuang amphibolites and metapelites constraints on the tectonic evolution of the paleoproterozoic trans north china orogen garnet bearing metapelites and amphibolites are exposed in the south and middle parts of the zanhuang complex which is located in the central segment of the nearly ns striking trans north china orogen these rocks preserve three metamorphic mineral assemblages forming at the prograde peak and post peak decompression stages the prograde metamorphic stage m1 is represented by mineral inclusions within garnet porphyroblasts the peak metamorphic stage m2 is represented by garnet rims and matrix minerals whereas the retrograde stage m3 is represented by amphibole plagioclase symplectite rimming garnet porphyroblasts in the amphibolites and biotite plagioclase symplectite rimming garnet porphyroblasts in the metapelites all garnet porphyroblasts in the metapelites preserve prograde chemical zoning except for the ubiquitous quite narrow zones from the underwent post peak decompression it has been determined through thermobarometric computation that the metamorphic conditions are 650 710 c at 8 2 9 2 kbar for the m1 inclusion assemblages 810 c at 12 5 kbar for the metamorphic peak m2 matrix assemblages and 660 680 c at 4 4 4 5 kbar for the retrograde m3 symplectite assemblages these rocks are thus determined to have undergone metamorphism with clockwise p t paths involving nearly isothermal decompression itd segments which is inferred to be related to the amalgamation of the eastern and western blocks to form the coherent basement of the north china craton along the trans north china orogen in the late paleoproterozoic 1 88 1 85 ga

carbonate sediment production transport and supply to a coral cay at raine reef northern great barrier reef australia a facies approach abstract coral cays are low lying typically 2 mm grain size and the relative abundances of foraminifera and coral grains gravelly coral dominated sediment is concentrated at the reef margins whereas facies on and around the leeward cay are dominated by the sand size tests of benthic foraminifera mud is absent in reef sediments and reflects the prevailing high energy wave dominated setting as well as a paucity of mud producers benthic foraminifera tests are the major sediment component constituting an average proportion of 39 range 2 77 sediment derived from the skeletal remains of corals 24 1 65 mollusks 15 3 30 halimeda 14 4 36 and coralline algae 6 0 20 are present in lesser volumes foraminifera content is highest 40 on tidally emergent algal pavement where they live in greatest abundance and on the cay shorelines where their tests are deposited and comprise the bulk of beach sand 36 63 a comparison of the raine island data with other exposed modern reefs and platforms of the central and western pacific shows that occurrence and distribution of facies types is broadly consistent beyond these sedimentological data the taphonomy of foraminifera at raine island indicates that tests are vulnerable to destruction due to abrasion when transport and reworking is prolonged therefore the foraminifera rich facies adjacent to and on the cay disjunct from the source zones as well as taphonomic evidence imply that transport from the outer reef flat to the cay must be relatively quick these short temporal links between ecological source zones and depositional landforms are likely to have important ramifications for the contemporary management of reef associated landforms e g cays in the future

coral indicators of past sea level change a global repository of u series dated benchmarks fossil corals provide valuable data for reconstructing past sea levels as they are often well preserved in the fossil record and can be dated with u series methods here we present a global and internally consistent database of usingle bondth dated fossil coral sea level indicators including full consideration of all known associated uncertainties both vertical and chronological we include carefully determined taxon specific depth distributions rather than blanket depth uncertainty terms as used in most previous work this is based on a synthesis of extensive modern ecological information on depth ranges these ranges are found to be spatially variable between ocean basins between regions and on sub regional scales because depth itself is not limiting instead depth distributions arise from complex physical chemical and biological interactions with coral reef growth distribution and composition one of the main causes for recognition of the greater depth variability of coral taxa has been the routine inclusion of deep diving and rov surveys in coral ecological studies over the past few decades which has broken through the shallow water bias of early surveys by adding frequent observations on deeper occurrences although more are needed it is also clear from our assessment that coral habitat depth distributions must be determined on the species level to reduce uncertainties in reconstructions of past sea levels and that application to sea level studies then requires these studies also to identify fossil corals to the species level samples identified only to the genus level give rise to wide uncertainties in habitat depth and hence sea level our database contains extensive metadata to assist evaluations of dating quality as well as geomorphic and stratigraphic metadata we demonstrate with examples how such metadata can help to evaluate sea level reconstructions for example by identifying outlier points one example discusses the last interglacial lig where we use the available data with their uncertainties to assess probabilistically the time at which local sea levels exceed that of the present which yields a mean age of 124 6 ka with 95 probability bounds at 118 5 and 129 5 ka we conclude with identification of key outstanding issues relating to i current incomplete understanding of tectonic setting including the current lack of independent verification of uplift subsidence rates and reliance of somewhat unsatisfactory and circular use of the elevation of last interglacial deposits ii the depth distributions of coral taxa and iii the complete documentation of stratigraphic geomorphological and other contextual information with suggestions for strategies to address these issues

late quaternary shedding of shallow marine carbonate along a tropical mixed siliciclastic carbonate shelf great barrier reef australia the north east australian margin is the largest modern example of a tropical mixed siliciclastic carbonate depositional system with an outer shelf hosting the great barrier reef gbr and an inner shelf dominated by fluvially sourced siliciclastic sediment wedges the long term interplay between these sediment components and sea level is recorded in the queensland trough a 1 2 km deep n s elongate basin situated between the gbr platform and the queensland plateau in this paper 154 samples from 45 surface grabs and six well dated piston cores were analysed for total carbonate content carbonate mineralogy and sr concentration to establish spatial and temporal patterns of carbonate accumulation in the queensland trough over the last 300 kyr surface carbonate contents are lowest on the inner shelf 5 and in the trough axis 60 because of siliciclastic dilution carbonate on the shelf is mostly sr rich aragonite and high mg calcite hmc whereas that in the basin is mostly low mg calcite once normalized to remove the effects of siliciclastic dilution surface sr rich aragonite and hmc abundances decrease linearly to background levels 100 km seaward of the shelf edge core samples show that over time normalized aragonite and sr abundances are greatest during periods of shelf flooding and lowest when sea level drops below the shelf edge this is consistent with changes in the production of coral and calcareous algae and the shedding of their debris from the shelf interestingly normalized hmc concentrations on the slope peak during periods of major transgression perhaps because of maximum off shelf transport from inter reef areas or intermediate water dissolution after accounting for siliciclastic dilution there are strong similarities in both spatial and temporal patterns of carbonate minerals between slopes and basins of the north east australian margin and those of pure carbonate margins such as the bahamas a limited set of basic processes including the formation and breakdown of carbonate on the shelf the transport of carbonate off the shelf and eustatic sea level probably controls carbonate accumulation in slope and basin settings of tropical environments irrespective of proximal siliciclastic sediment sources

unsupported radiogenic pb in zircon a cause of anomalously high pb pb u pb and th pb ages ion microprobe u th pb isotopic analyses of zircons from a granodioritic orthogneiss from the napier complex mount sones enderby land antarctica have identified an unambiguous example of unsupported radiogenic pb in a 3 950 ma old crystal at one 40 m spot on the crystal an unusually large heterogeneity in pb content was found the concentration of radiogenic pb ranging from 5 to 50 percent higher than could have been generated in 3 950 ma by radioactive decay of the co existing u and th this relative excess of radiogenic pb is attributed to pb gain rather than to u and th loss because first the pb content varied by more than the u or th contents and secondly changes in the pb u pb th and pb isotopic composition correlated directly with changes in the pb concentration the individual 207pb 206pb apparent ages ranged from 4 000 ma to 4 145 ma all greater than the inferred age of the crystal a correlation between 207pb 206pb and pb u shows that the pb excess has not resulted from recent pb movement the spot apparently gained radiogenic pb about 2 500 ma ago at the same time as the majority of the other zircons in the rock suffered substantial pb loss the pb movement occurred in response to a discrete geologic event reverse discordance is a phenomenon that must be considered when interpreting zircon u pb ages especially 207pb 206pb ages of single crystals or portions of crystals

palaeoproterozoic metamorphic evolution and geochronology of the wugang block southeastern terminal of the trans north china orogen abstract amphibolites of the wugang block in the taihua metamorphic complex which is located in the southeastern terminal of the palaeoproterozoic trans north china orogen tnco preserve three generations of metamorphic mineral assemblages i e the prograde m 1 peak m 2 and retrograde m 3 assemblages forming during the palaeoproterozoic tectono metamorphic event these amphibolites record metamorphic p t conditions of 4 8 6 7 kbar 720 750 c m 1 9 0 10 6 kbar 710 780 c m 2 and 7 1 8 5 kbar 700 780 c m 3 which define clockwise p t paths involving isothermal decompression itd the metamorphic peak reached upper amphibolite facies and high resolution in situ sims u pb dating of metamorphic zircons suggests that the peak metamorphism took place at 1 96 1 92 ga in the wugang block the present new data suggest that the wugang block was also involved in the continental collision between the eastern and western blocks of the north china craton ncc in the palaeoproterozoic combining metamorphic and geochronological data concerning the tnco obtained by previous scholars it may be anticipated that the middle and southern sections of the tnco were involved in a long lived continental collision and the collision event can be possibly traced back to as early as 1 96 ga and lasted to as late as 1 80 ga

shrimp u pb zircon geochronology of the huai an complex constraints on late archean to paleoproterozoic crustal accretion and collision of the trans north china orogen

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