vegetation and environmental changes in northern anatolia between 134 and 119 ka recorded in black sea sediments this multiproxy study on se black sea sediments provides the first detailed reconstruction of vegetation and environmental history of northern anatolia between 134 and 119 ka here the glacial interglacial transition is characterized by several short lived alternating cold and warm events preceding a meltwater pulse 130 4 131 7 ka the latter is reconstructed as a cold arid period correlated to heinrich event 11 the initial warming is evidenced at 130 4 ka by increased primary productivity in the black sea disappearance of ice rafted detritus and spreading of oaks in anatolia a younger dryas type event is not identifiable the eemian vegetation succession corresponds to the main climatic phases in europe i the quercus juniperus phase 128 7 126 4 ka indicates a dry continental climate ii the ostrya corylus quercus carpinus phase 126 4 122 9 ka suggests warm summers mild winters and high year round precipitation iii the fagus carpinus phase 122 9 119 5 ka indicates cooling and high precipitation and iv increasing pinus at 121 ka marks the onset of cooler drier conditions generally pollen reconstructions suggest altitudinal latitudinal migrations of vegetation belts in northern anatolia during the eemian caused by increased transport of moisture the evidence for the wide distribution of fagus around the black sea contrasts with the european records and is likely related to climatic and genetic factors

late carboniferous to early permian oceanic subduction in central inner mongolia and its correlation with the tectonic evolution of the southeastern central asian orogenic belt abstract the late paleozoic magmatism in central inner mongolia provides important insights on the tectonic evolution and crustal growth in the central asian orogenic belt caob which formed due to the closure of the paleo asian ocean pao this paper presents new zircon u pb ages and hf isotopic compositions as well as whole rock geochemical data on a suite of volcanic rocks from the late paleozoic baoligaomiao formation and coeval intrusions in the baiyinwula region of the mongolian arc this study revealed that the magmatic sequences evolution includes 1 early andesites 317 311 ma with enrichment in large ion lithophile elements liles depletion in high field strength elements hsfes and positive zircon ehf t values from 9 0 to 15 5 indicating a derivation from enriched mantle 2 felsic rocks emplaced from 306 ma to 292 ma with relatively lower ehf t values from 6 3 to 11 3 implying juvenile crust as the primary magma source and 3 a type igneous rocks 280 278 ma the comparison of palaeontological lithostratigraphical and magmatic evolution in late paleozoic between different tectonic units in the eastern part of caob has displayed that the subduction of paleo asian oceanic crust caused the opening of the hegenshan ocean along the southern margin of mongolian arc in devonian and the baoligaomiao formation volcanic rocks and coeval intrusions have recorded early northwards subduction and subsequent slab rollback of hegenshan oceanic crust

geochemical characteristics of the permian basins and their provenances across the solonker suture zone assessment of net crustal growth during the closure of the palaeo asian ocean abstract the solonker suture zone is commonly recognised as the location of the late permian to early triassic closure of the palaeo asian ocean in the southeastern segment of the central asian orogenic belt however the absence of typical suture related features as a consequence of uncommon collisional geometries gave it a cryptic nature thus the tectonic setting which led to suturing still remains enigmatic a geochemical characterisation of permian sedimentary and volcanic rocks across the suture was carried out supplemented with hf and nd isotopic analyses this approach enables not only a better definition of such regional suture but also estimates on the long controversial issue of net crustal growth in accretionary tectonic environments the results indicate short sedimentary transport distances between the arc basins and their provenances of which the studied volcanic rocks were a major contributor similar enrichment and depletion patterns with respect to n morb and average continental crust further corroborate a close source sediment relationship immobile element provenance analyses indicate that the active continental northern margin of the north china craton was a major source for arc basins to the south of the solonker suture zone to its north arc basins are interpreted to be sourced by a more complex mixture of provenances e g the baolidao volcanic arc suite and the heterogenous precambrian basement of southern mongolia an overall collisional tectonic setting across the suture is recognised the geochemical signature of sedimentary rocks to the south of the suture points at an active continental arc setting whereas the bimodal geochemical distribution of the samples to the north shows a contemporaneous active oceanic island arc as well as a passive margin environment these features favour a double sided subduction of the palaeo asian ocean beneath the north china craton and the mongolian arcs throughout the palaeozoic including back arc basin opening north of the suture in the permian analysis of hf and nd isotopic compositions revealed that magmas to the south were produced involving significant crustal contamination thus having less radiogenic compositions north of the suture however isotopic compositions tend to be more radiogenic implying a more juvenile contribution however the bulk isotopic compositions are close to present day chur suggesting that crustal reworking appears to be equally balanced by juvenile addition during the palaeozoic closure of the palaeo asian ocean across the solonker suture zone

crustal architecture and tectonic evolution of the sergipe alagoas and jacuipe basins offshore northeastern brazil abstract the sergipe alagoas and the jacuipe basins are divergent margin basins located in the south atlantic ocean at the northeastern brazilian margin high quality 18 s two way travel time seismic reflection profiles which extend from the coastline towards the boundary with the oceanic crust were integrated with potential field data and calibrated with the results of several exploratory boreholes when combined these data provide evidence that the deep seismic reflectors in the deep water region are related to the crustal architecture of the basin rather than to sedimentary features arrays of high impedance reflectors previously interpreted as top of basement probably correspond to detachment planes near the base of the crust or to underplated igneous rocks above the moho the extensional processes that were active during rifting resulted in normal crustal faults that apparently detach near the seismic moho in the deep water region these crustal faults control and rotate syn rift sedimentary units along the margin the seaward portion of the rift seems to have been uplifted and highly eroded during a post break up tectonic event the deep seismic reflection profiles also indicate that the deep water province is characterized by wedges of reflectors that dip seawards these features probably correspond to seaward dipping reflectors sdr which are composed of volcanic rocks marking the transition to oceanic crust the sdr wedges are locally associated with volcanic intrusions several volcanic plugs in deep water region are aligned with oceanic fracture zones that apparently penetrate through the whole crust and reach the upper mantle on the other hand there are some diapiric structures located near the boundary between continental and oceanic crust that bear evidence for deep water salt tectonics

early oligocene stratigraphic turnover on the west africa continental margin a signature of the tertiary greenhouse to icehouse transition the post rift stratigraphy on the west african margin is characterized by aggradation of a carbonate ramp during late cretaceous to eocene epochs and progradation of a terrigenous wedge from oligocene to the present such first order structure has been attributed in the past to geodynamic forcing however comparison of the stratigraphic record of the margin with eustasy 18o and 87sr 86sr curves shows a close temporal relationship with the tertiary climate cooling an increase of continental weathering and a long term lowering of sea level we suggest that the transition from low amplitude high frequency sea level changes during the greenhouse period to high amplitude high frequency sea level changes during the icehouse period may account for i the switch from an aggrading carbonate ramp to a prograding clastic wedge and ii the enhanced continental weathering and increased terrigenous influx to the margin

sporormiella fungal spores a palynological means of detecting herbivore density during the historic period spores of the dung fungus sporormiella are abundant in lake and cave sediment where livestock are plentiful in the western united states sporormiella spores occasionally exceed 50 of the upland pollen sum in samples from corral ponds and bed grounds and routinely reach 4 in lake and marsh samples in pastoral areas sporormiella spores are comparatively rare in mid holocene sedimentary records but they reach values of 2 4 in pleistocene samples from lake sediments sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung from bechan cave utah in several sites in the western united states a precipitous decline of sporormiella percentages after ca 10 800 radiocarbon yr b p 12 900 years ago marks a decline of herbivore density probably associated with the north american megaherbivore extinction

field evidence for flank instability basal spreading and volcano tectonic interactions at mt cameroon west africa the mt cameroon volcano is the highest and most active volcano of the cameroon volcanic line little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics after reviewing the tectonic evolution of the region the analysis of a digital elevation model and results from a field campaign dedicated to mapping geological structures in the summit area and at the se base of mt cameroon are presented mt cameroon is a lava dominated volcano with long steep over 30 flanks it is elongate parallel to its well defined rift zone the summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults geological profiles were measured along rivers cutting through a topographic step at the se base of mt cameroon this step is associated with deformed miocene sediments from the douala basin that are overlain by volcanic products weak sediments of this area are deformed by 050 060 and 020 030 trending asymmetrical folds verging toward the se and thrusts faults related to the spreading of the volcano over its mechanically weak substratum combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice repeated dyke intrusions the weak sedimentary substratum and tectonic structures

tectonic implications of paleomagnetic and geochronologic data from the yukon koyukuk province alaska the paleomagnetic and geochronologic record of alaska is complicated by overprints that make it difficult to relate the terranes of northern and southern alaska to each other and to north america to better understand these relationships and the overprinting paleomagnetic and k ar dating samples were analyzed from the three major geologic units of the yukon koyukuk province ykp of central alaska these units consist of a basal jurassic early cretaceous volcanic island arc assemblage albian cenomanian clastic sedimentary rocks and bimodal eocene volcanic rocks k ar age determinations of the early tertiary volcanic rocks form two distinct groups the older group 65 49 ma is mostly felsic and probably represents the maximum inboard penetration of low angle subduction related volcanism these older rocks were deformed during the regional deformation of the ykp the younger group 44 43 ma is post deformational and composed dominantly of basalt these results bracket a time 49 44 ma when deformation ceased in the province this time interval is coincident with a major transition from convergence to strike slip and extensional tectonic style throughout alaska the geologic units of the ykp display two characteristic paleomagnetic signatures primary directions based on positive reversal conglomerate and or bedding tilt stability tests were obtained from the albian cenomanian sedimentary rocks and eocene volcanic rocks the mid cretaceous sedimentary rocks show about 15 of poleward motion between 90 56 ma a time of high rates of convergence between alaska and the pacific and eurasian plates age equivalent rocks from neighboring regions st matthew island and the alaskan north slope also indicate similar amounts of poleward northward motion which suggests that the whole of western and northern alaska may have moved northward about 10 relative to north america as a more or less coherent block paleomagnetic results from the eocene volcanic rocks indicate that the ykp was in place by 56 ma and formed part of the accretionary nucleus that served as a backstop for the accreted terranes of southern alaska secondary remagnetized directions are recorded in the basal island arc assemblage and in albian cenomanian sediments near younger igneous occurrences the clustering of secondary directions in the geographic reference frame indicates that they were acquired after deformation ceased 49 44 ma which is consistent with the coincidence of the mean of these directions and the 54 44 ma north american reference direction

late carboniferous to early permian magmatic pulses in the uliastai continental margin linked to slab rollback implications for evolution of the central asian orogenic belt abstract the paleo asian ocean underwent a protracted closure history during late paleozoic here we investigate the magmatic evolution during this process based on a detailed study in the baiyinwula region along the uliastai continental margin the major rock types in this area are late carboniferous early permian volcanic sequences and coeval intrusions we identified four stages of magmatic evolution based on the diverse assemblages and their precise isotopic ages the first stage is represented by andesites with a zircon 206pb 238u age of ca 326 12 ma these rocks are metaluminous to weakly peraluminous high k calc alkaline and possess high na2o k2o ratios in the range of 1 23 to 2 45 they also display enrichment of large ion lithophile elements lile and depletion of high field strength elements hfse with markedly positive zircon ehf t varying from 8 1 to 15 6 the geochemical features of these andesites are similar to those of typical arc volcanic rocks the second stage includes granodiorites emplaced at 318 6 1 8 ma the rocks are high k calc alkaline with a cnk values ranging from 0 95 to 1 06 and show enrichment in lile and depletion in hfse they show geochemical affinities to adakites with high sr and low y and yb contents indicating magma derivation from thickened lower crust zircon grains from these rocks display positive initial ehf t values ranging from 11 1 to 14 6 with corresponding two stage hf model ages tdm2 of 394 622 ma the third stage consists of syenogranite together with a volcanic suite ranging in composition from rhyolite todacite which formed during 303 4 1 2 to 285 1 2 2 ma they possess elevated silica and alkali contents high feot mgo and ga al ratios low al2o3 mgo and cao contents and high rb y nb ce zr y and ga contents strong negative ba sr and eu anomalies showing i to a type granitic affinities zircons in these rocks show elevated hf isotopic compositions ehf t 9 9 to 14 6 with tdm2 varying from 324 to 673 ma the fourth magmatic pulse is represented by k feldspar granite with zircon u pb ages from 283 2 1 9 ma to 280 0 1 4 ma and typical alkalic a type granite geochemistry these rocks possess positive ehf t values in the range of 9 7 to15 2 and a restricted range of hf model age from 327 to 684 ma the magmatic rocks from the four stages show comparable ehf t and t2dm suggesting that the magmas were derived from the same evolving mantle derived source we propose a tectonic model linking the evolution of the magmatism with the closure of the paleo asian ocean that involved the following stages the andesites were formed during the initial oceanic subduction stage with magma sourced from the metasomatized lithospheric mantle stage 2 adakite like rocks were derived from subduction induced thickened crust subsequent slab rollback resulted in asthenospheric upwelling and melting of residual juvenile crust to generate the i and a type syenogranite rhyolite and dacite suite finally followed by the a type k feldspar granite

late paleozoic early mesozoic southward subduction closure of the paleo asian ocean proof from geochemistry and geochronology of early permian late triassic felsic intrusive rocks from north liaoning ne china abstract many studies have confirmed the existence of late paleozoic early mesozoic accretionary arc and subduction complex belt to the south of the solonker xar moron changchun yanji suture sxcys zone nevertheless since the suture from the east is covered by the songliao basin until now there have been no completed reports focused on the late paleozoic early mesozoic intrusive rocks of this area recently a sequence of granitoid intrusions was identified in the faku area northern liaoning zircon shrimp u pb dating results show that there are eight groups of felsic intrusions in the study area and the intrusions formed at 283 227 ma early permian to late triassic together with study of regional events a four stage tectonic evolution scenario was recommended during permian triassic in the faku area early permian magmatism in an activity continental margin setting 293 274 ma middle late permian magmatism in a setting where subduction is translated into collision 270 255 ma early middle triassic magmatism in a setting where collision is translated into detachment of the oceanic slab 255 242 ma and middle to late triassic magmatism recorded procedure of post collision orogeny transformed into extensional environment 241 215 ma the early permian late triassic felsic intrusions documented the extension collision of the convergent continental margin and the subduction extinction of the paleo asian ocean zircon hf isotopic analyses yield ehf t values of 2 03 15 80 almost all of which are positive with two points being negative indicating the depleted characteristics of the source area according to emplacement time and occurrence location the plutons are interpreted to have been generated by the subduction collision of the paleo asian oceanic crust beneath the north china craton ncc this study provides strong evidence for late paleozoic early mesozoic tectonic evolution and the characterization of the eventual closure of the paleo asian ocean in the songliao basin overlying the northern margin of the ncc

sediment dynamics and hydrologic events affecting small lacustrine systems on the southern central tibetan plateau the example of tt lake a sedimentological geochemical micropaleontological and palynological study of a lacustrine sediment record from the small tt lake southern central tibetan plateau shows that the background sedimentation was frequently interrupted by event related deposits these event related deposits are interpreted as the result of hydrologic events that are triggered by above average precipitation events in total 11 events were recorded in the tt lake sequence two types can be differentiated fluvial runoff events caused by precipitation that carried sediment in suspension into the lake and a sediment mass transport caused by torrential precipitation the hydrologic events appear to be decoupled from long term climate and environmental variations but there is evidence that anthropogenic impact in terms of pastoralism might have favored the runoff events the multi proxy approach proved to be valuable and allowed for a detailed study of sedimentary processes within the lake and its watershed in order to asse

evidence for the diet and habitat of two late pleistocene mastodons from the midwest usa we analyzed intestinal contents of two late glacial mastodons preserved in lake sediments in ohio burning tree mastodon and michigan heisler mastodon a multi proxy suite of macrofossils and microfossils provided unique insights into what these individuals had eaten just before they died and added significantly to knowledge of mastodon diets we reconstructed the mastodons habitats with similar multi proxy analyses of the embedding lake sediments non pollen palynomorphs especially spores of coprophilous fungi differentiated intestinal and environmental samples the burning tree mastodon gut sample originates from the small intestine the heisler mastodon sample is part of the large intestine to which humans had added clastic material to anchor parts of the carcass under water to cache the meat both carcasses had been dismembered suggesting that the mastodons had been hunted or scavenged in line with other contemporaneous mastodon finds and the timing of early human incursion into the midwest both mastodons lived in mixed coniferous deciduous late glacial forests they browsed tree leaves and twigs especially picea they also ate sedge swamp plants and drank the lake water our multi proxy estimates for a spring summer season of death contrast with autumn estimates derived from prior tusk analyses we document the recovered fossil remains with photographs

directional flank spreading at mount cameroon volcano evidence from analogue modeling mount cameroon is characterized by an elongated summit plateau steep flanks and topographic terraces around its base although some of these features can be accounted for by intrusion induced deformation we here focus on the contribution of edifice scale gravitational spreading in the structure of mount cameroon we review the existing geological and geophysical data and morphostructural features of mount cameroon and surrounding sedimentary basins volcanic ridge gravitational spreading is then simulated by scaled analogue models on which fault formation is recorded using digital image correlation three sets of models are presented i models recorded in cross section type i ii models recorded from above with a uniform type iia and iii nonuniform ductile layer type iib type i models illustrate the formation of faults accommodating summit subsidence and lower flank spreading type iia models favor displacement perpendicular to the long axis with formation of a summit graben and basal folds but fail to reproduce the steep flanks type iib models investigate the effect of spatial variations in sediment thickness and or properties consistent with geological evidence directional spreading of the volcano s central part perpendicular to the long axis is accounted for by a sediment layer with restricted lateral extent and increasing thickness away from the volcano axis the later model closely reproduces key features observed at mount cameroon steep upper flanks are accounted for by enhanced lateral spreading of the lower flanks relative to the summit the relevance of these findings for understanding flank instabilities at large oceanic volcanoes is finally highlighted

a rift system in southeastern central asian orogenic belt constraint from sedimentological geochronological and geochemical investigations of the late carboniferous early permian strata in northern inner mongolia china abstract the late carboniferous early permian is the most controversial period for the tectonic evolution of the southeastern central asian orogenic belt caob in this study we performed sedimentological and detrital zircon dating on the clastic sediments as well as zircon u pb age and geochemical analysis on the rhyolitic rocks of the late carboniferous early permian strata from northern inner mongolia china the sedimentological analysis showed that the late carboniferous early permian sediments are composed of continental clastic and volcanic rocks with basal conglomerate overlying the devonian strata the detrital zircon study revealed three age peaks at 300 ma 440 ma and 530 ma indicating that the clastic rocks derived from paleozoic magmatic rocks and pre carboniferous sediments from northern inner mongolia the age data revealed that rhyolitic rocks from northern inner mongolia extruded in two stages at late carboniferous and latest carboniferous early permian the late carboniferous rhyolites show i to a type granitic affinities whereas the latest carboniferous early permian rhyolites have a type granitic characteristics the difference suggests a transition of tectonic setting from post collisional extension to intraplate rift the late carboniferous early permian strata from northern inner mongolia and south mongolia show similar sedimentary facies detrital zircon age distribution and geochemistry features hence they were probably deposited in the same tectonic setting a unified block was finally proposed in northern inner mongolia and south mongolia where a rift system provided an intra continental sedimentary basin and induced intense syn rift magmatic activities the intra continental basin and syn rift magmatism indicate that the xing an airgin sum songliao hunshandake and south mongolia blocks in southeastern caob have been welded into a single continental block before the late carboniferous

an overview of permian marine stratigraphy and biostratigraphy of mongolia this paper summarizes the spatial distribution stratigraphical divisions and biostratigraphical zonation schemes of permian marine deposits in mongolia where appropriate correlations of the various permian marine biostratigraphical units with those of adjacent regions are also reviewed and discussed in general permian marine sequences are developed in two separate basins one in central and northeastern mongolia where the permian stratigraphy and marine faunas bear strong similarities with those of the transbaikal verkhoyansk and kolyma omolon regions of southern and eastern russia and the other in southeastern mongolia where the permian marine faunas and rock sequences are closest to those of northeast china and southern primorye of far east russia

hybrid collapse mechanism at piton de la fournaise volcano reunion island indian ocean 1 recent studies have shown that hydrothermal alteration in the core of volcanoes may weaken the edifice and trigger sector collapse lopez and williams 1993 day 1996 voight and elsworth 1997 van wyk de vries et al 2000 reid et al 2001 alteration of volcanic products must take place over long periods of times before collapse can occur so this process is considered to be less frequent than volcanic failure generated by magmatic intrusion and flank spreading however acceleration of this slow process may occur along one direction as a result of a weak lateral confinement following outward gravitational sliding of a flank of the volcano we present here evidence that the enclos fouque depression of piton de la fournaise volcano results from such a hybrid mechanism seaward sliding of the grand brule trough on top of an ancient hypovolcanic complex led to a lateral unconfined boundary along which collapse of the altered core of the edifice took place the result is a caldera like structure breached on the grand brule slide scaled experiments to simulate this process of pseudocaldera formation reveal tectonic features remarkably similar to those encountered in the field and demonstrate the mechanical consistency of the model similar processes may have played a role in the evolution of other volcanoes

tracking late quaternary extinctions in interior alaska using megaherbivore bone remains and dung fungal spores one major challenge in the study of late quaternary extinctions lqes is providing better estimates of past megafauna abundance to show how megaherbivore population size varied before and after the last extinctions in interior alaska we use both a database of radiocarbon dated bone remains spanning 25 0 ka and spores of the obligate dung fungus sporormiella recovered from radiocarbon dated lake sediment cores spanning 17 0 ka bone fossils show that the last stage of lqes in the region occurred at about 13 ka ago but the number of megaherbivore bones remains high into the holocene sporormiella abundance also remains high into the holocene and does not decrease with major vegetation changes recorded by arboreal pollen percentages at two sites the interpretation of sporormiella was enhanced by additional dung fungal spore types e g sordaria in contrast to many sites where the last stage of lqes is marked by a sharp decline in sporormiella abundance in interior alaska our results indicate the continuance of megaherbivore abundance albeit with a major taxonomic turnover including mammuthus and equus extinction from predominantly grazing to browsing dietary guilds this new and robust evidence implies that regional lqes were not systematically associated with crashes of overall megaherbivore abundance

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

carboniferous and cretaceous mafic ultramafic massifs in inner mongolia china a shrimp zircon and geochemical study of the previously presumed integral hegenshan ophiolite abstract we present shrimp zircon ages and whole rock geochemical data to identify mafic ultramafic massifs of early carboniferous and early cretaceous ages from northern inner mongolia china the early carboniferous massifs chongenshan xiaobaliang wusnihei comprise predominantly lherzolite and minor gabbroic rocks zircons from a microgabbro e nd t 9 8 and a plagiogranite e nd t 9 yielded weighted mean 206 pb 238 u ages of 354 7 ma and 333 4 ma that we interpret as reflecting the time of zircon and magma crystallization a volcanic breccia resting unconformably on the ultramafic rocks serpentinites has an eruption age of 300 2 ma and provides a younger minimum time limit for the emplacement of the early carboniferous mafic ultramafic massifs in contrast the early cretaceous mafic ultramafic massifs hegenshan chaogenshan consist predominantly of harzburgite a pegmatoid gabbro and a rodingite e nd t 10 6 from the hegenshan massif have magmatic zircon ages of 139 2 ma and 132 7 ma respectively the chaogenshan massif is concentrically zoned with an ultramafic core dominantly harzburgite dunite subordinate lherzolite surrounded by gabbro with minor hornblendite and an outermost volcano sedimentary sequence metabasaltic flows metapelites we dated zircons from a leuocogabbro 125 2 ma e nd t 10 6 a coarse grained gabbro 142 4 ma and a metabasalt 134 2 ma zircon xenocrysts ca 152 492 ma are ubiquitous in these and other associated rocks a coarse grained gabbro and a diabase as in the hegenshan rocks ca 152 468 ma the youngest detrital zircon in outer zone garnet schist i e metapelite has an age of 132 2 ma accordingly we conclude that the northern inner mongolia lherzolite dominant and harzburgite dominant massifs are temporally and genetically unrelated their emplacement is attributed to asthenospheric upwelling and consequent lithospheric extension during periods of orogenic quiescence in the southern central asian orogenic belt

a late carboniferous to early early permian subduction accretion complex in daqing pasture southeastern inner mongolia evidence of northward subduction beneath the siberian paleoplate southern margin abstract a subduction accretion complex is identified from previously defined late carboniferous and early permian strata in daqing pasture southern xiwuqi inner mongolia the subduction accretion complex is composed of a matrix of siltstone and exotic blocks of bioclastic limestone pillow basalt foliated basalt chert and asbestos the pillow basalt possesses the geochemical characteristics of mid ocean ridge basalt n morb whereas the foliated basalt displays the geochemical characteristics of island arc basalt iab indicating that these basalts are of different origins u pb zircon dating indicates that the foliated basalt formed in the late carboniferous 314 5 to 318 4 ma and the bioclastic limestone formed in the early early permian combined with regional geological data the subduction accretion complex and coeval calc alkaline granitic belt to the north constitute the essential elements of the late carboniferous to early early permian subduction zone on the southern margin of the siberian paleoplate the zircon ehf t values of the foliated basalt are positive 14 4 to 23 9 suggesting that this basalt originated directly from depleted mantle the temporal spatial distribution of the subduction accretion complex and ophiolite belts in southeastern inner mongolia indicates that there was significant lateral crustal growth on the southern margin of the siberian paleoplate in the late paleozoic

seismic evidence for crustal underplating beneath a large igneous province the sierra leone rise equatorial atlantic wide angle seismic profiles reveal anomalously thick crust with a high velocity 7 3 km s 1 zone under the sierra leone rise a major mid plate elevation in the atlantic lying between the cape verde platform and the cameroon volcanic line a profile recorded over the crest using an ocean bottom seismometer and surface sonobuoys shows that beneath a 3 km water layer and 1 km of sediments the basement extends to 16 20 km below sea level most velocity depth values fall outside the expected range for mesozoic early cenozoic ocean floor and stretched continental crust the detection of 7 3 7 5 km s 1 material beneath thick lower velocity volcanics suggests that magmatic underplating of the crust has occurred a prominent change in velocity gradient 10 12 km below sea level may mark the transition to underplated material emplaced during the late cretaceous early cenozoic a pronounced change in moho depth lies on the line of a long offset fracture zone extending from the african margin implying underplating was influenced by a pre existing discontinuity in the lithosphere other seismic lines show 7 0 7 2 km s 1 basement above the underplated zone extending into water depths of almost 5 km this is probably the intrusive foundation of early formed crust over a mantle hot spot it is suggested that the development of the sierra leone rise is distinct from other atlantic hot spot features to which it has been linked because of its setting in a region of intense lithospheric shear

the harbour of elaia a palynological archive for human environmental interactions during the last 7500 years abstract elaia the harbour city for ancient pergamon western turkey was investigated using geoarchaeological methods the rise and fall of elaia were closely linked to the flourishing period of pergamon which ruled wide parts of today s western turkey in hellenistic times in the framework of this research the palynological analysis of a 9 m sediment core ela 70 retrieved from the enclosed harbour of the city was carried out to reconstruct the vegetation and environmental history of the wider gulf of elaia region an age depth model based on 11 calibrated radiocarbon ages starting from 7 5 ka bp provides the basis for the high resolution study of sediments from the hellenistic period as well as before and after the lower part of the pollen diagram is characterised by high percentages of deciduous oaks and pines suggesting the dominance of open forests close to the coring site the change from oak forests to a cultural landscape with olive pistachio walnut and grape started around 850 bc reaching a maximum ca 250 bc and continuing to ca ad 800 this period is characterised by increase of fire activity soil erosion intensity and pastoral farming such long lasting intensive land use likely led to the climax ecosystem turnover from open deciduous oak forests to pine stands while salt marshes developed around the coring site the discovery of the dinoflagellate cysts of peridinium ponticum a black sea endemic species in the harbour of elaia evidences maritime trade between the aegean sea and the black sea its first occurrence coincides with the time of the mithridatic wars 1st century bc in conclusion palynological data in addition to historical and archaeological records provide a deeper insight into human environmental interactions as derived from the geoarchaeological archive of the harbour of elaia

seismic reflection character of the cameroon volcanic line evidence for uplifted oceanic crust deep imaging multifold seismic fines across submarine parts of the cameroon volcanic line west africa gulf of guinea show asymmetric uplift of oceanic crust associated with extensive magmatism the main pulse of uplift occurred after creation of a regional sequence boundary believed to be miocene in age the apparent synchroneity of uplift argues against the cameroon line being a simple hotspot trace as previously inferred one plausible theory of origin for the seaward part of the cameroon volcanic line and its asymmetric uplift geometry combines regional asthenospheric upwelling with restriction of magmatic egress to regularly spaced weak spots corresponding to fracture zone crossings horizontal motion and buckling also may have occurred along the cameroon volcanic line

solonker suture in east asia and its bearing on the final closure of the eastern segment of the palaeo asian ocean abstract the location and tectonic nature of the solonker suture in east asia and hence the late palaeozoic to early mesozoic closure of the palaeo asian ocean have notoriously been enigmatic in the past decades due to limited rock exposure and the absence of unambiguous collision related regional features several tectonic models have been proposed since but in many cases these models were derived only from single key exposures or methodologies often being over simplified or interpreted leading to questionable extrapolations on regional and global scales despite the complexity of the palaeozoic accretionary tectonic framework now the regionally consistent availability of geochronological geochemical stratigraphic and palaeo geographic data enables us to integrate these into a highly detailed and coherent palaeozoic tectonic review of the suture the region across the solonker suture can generally be subdivided into three major palaeozoic tectonic provinces e g i a sino cratonic province that resembles the active palaeozoic northern margin of the north china craton to the south of the suture ii a mongolian province that comprises the south eastern margin of the mongolian terrane to the north of the suture and iii an east asian pre pacific province in north east china that accreted with the late permian initiation of pacific plate subduction the sino cratonic province experienced episodic tectonic activity that includes the accretion of the initially ensialic bainaimiao arc onto the passive northern margin of the north china craton at 437 453 ma subsequent southward directed subduction activity beneath the amalgamated margin until at least 400 ma followed by a temporary cessation of magmatic activity accompanied by a switch from north to southward directed continental drift and finally concluded by renewed subduction activity until the final closure of the palaeo asian ocean the mongolian province is suggested to have been more closely associated with the siberian craton before the presumably late devonian opening of the mongol okhotsk ocean the east asian pre pacific province originally rifted away from the eastern margin of gondwana at 600 750 ma recorded early palaeozoic 500 ma orogenic processes along the then northern margin of the siberian craton the baolidao arc system successively developed along the present day south eastern margin of the mongolian province due to continued subduction activity throughout the palaeozoic after the middle carboniferous opening of the hegenshan back arc basin renewed subduction beneath a matured baolidao arc during carboniferous and permian times led to the obduction of the hegenshan ophiolite not earlier than 270 ma shortly after the palaeo asian ocean diachronously closed from west to east along the solonker suture in the late permian to early triassic the east asian pre pacific province re attached itself by the mid mesozoic followed by a change in the regional stress regime controlled by palaeo pacific plate subduction a divergent double sided subduction model for the closure of the palaeo asian ocean provides based on the reviewed data a tectonic model that is not only able to reasonably well explain the absence of typical collision related features in the region but also the abundance of mesozoic a type granitic magmatism in north east china

granites of the southern mongolia carboniferous arc new geochronological and geochemical constraints the crust in southern mongolia is part of the central asian orogenic belt a vast accretionary orogen that records the opening and closure of the palaeo asian ocean in the late proterozoic to palaeozoic the crustal evolution of the region is revealed in basement inliers that also contain intrusion related porphyry ore bodies that are important mineral exploration targets the saykhandulaan inlier in southeast mongolia is a devonian carboniferous segment of island arc crust which is dominantly composed of extrusive and sedimentary lithologies but which also contains the oyut ulaan i type quartz monzonite intrusion a u pb zircon age for the oyut ulaan monzonite indicates emplacement at 330 0 0 5 ma to the east of the saykhandulaan inlier intrusive complexes dominate the neighbouring mandakh inlier new ages are presented for four of these plutons the bronze fox granodiorite 333 6 0 6 ma the narin hudag monzonite 333 2 0 6 ma the shuteen quartz monzonite 325 5 1 0 ma and the north mandakh granite 292 3 0 5 the intrusive bodies of the saykhandulaan and mandakh inliers have two distinct geochronological and geochemical associations 1 mid carboniferous i type monzonites that constitute the most easterly intrusive expression of the southern mongolia carboniferous arc and 2 early permian a type and peralkaline granites that represent a post orogenic phase of voluminous granite emplacement both groups are significantly younger than the nearby oyu tolgoi and tsagaan suvarga cu porphyry ore bodies which have previously been dated as early and late devonian respectively the new data presented here provide constraints on the timing of the transition from island arc magmatism to post collisional extension related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to cu au mineralisation

eruptive and earthquake activities related to the 2000 eruption of mount cameroon volcano west africa abstract mount cameroon is an active volcano located in the gulf of guinea west of central africa after the march april 1999 eruption on the sw flank another eruption of the volcano occurred in 2000 it took place from three sites on the southwest flank and near the summit the first eruptive site was located 500 m to the southwest of the summit at 3900 m altitude activity on this site was mainly explosive with no lava flow the second site was located between 3220 and 3470 m altitude lava was emitted along nne sse fissures from this site and flew towards buea the main city of the area stopping 4 km from the first houses the last site was located in the south western flank at 2750 m altitude the lava ejected from an old cone near the first 1999 eruptive site was divided into two branches for a total length of around 1 km the location of active volcanic cones in 1999 and 2000 seems to be linked to the local tectonics the pre eruptive period was characterized by a seismic swarm which may be a precursor recorded in march 2000 by an analogue seismic station the main shock was a magnitude 3 2 event and was felt by the population in ekona town located on the eastern flank it had a modified mercalli intensity of iii iv when the eruption started a temporary network of short period 3 component seismic stations was set up around the volcano to improve the monitoring of seismic activity the co eruptive period from late may to september was characterized by sequences of earthquake swarms volcanic tremor and a family of earthquakes having similar waveform and appearing regularly in august and early september some of the earthquakes were felt by the population in buea and its environments the largest seismic event recorded had a magnitude of 4 during the post eruptive period from mid september to december seismicity returned to its background level of 1 3 earthquakes per 3 days hypocenter locations reveal a linear narrow structure under the summit zone which could represent the magmatic conduit of the volcano the frequency magnitude relationship revealed a b value of 1 43 higher than those previously determined but more representative of volcanic media seismic energy release was gradual after the 2000 eruption started

dynamic interactions between the gulf of guinea passive margin and the congo river drainage basin 2 isostasy and uplift 1 the gulf of guinea continental margin is paralleled by a coastal relief that isolates the congo drainage basin and can play a subsequent role in interactions between margin deposits and continental denudation migration of depocenters from the ogooe and kwanza rivers to the congo fan in the oligocene low present day sediment delivery or pleistocene submarine channels instabilities are possible evidences for this interaction in order to test this hypothesis we examine successively margin isostasy regional uplift erosional unloading and flexural bulge created by sediment loads satellite free air gravity and two dimensional thermomechanical modeling including depth of necking are used to determine the structure of continental margin and strength conditions for two selected sections across south gabon and congo fan both verify similar conditions for extension geometry depth of necking 10 20 km and strength equivalent elastic thickness of 20 30 km differences in observed gravity are explained mainly by differences in sediment volumes regional uplift during miocene of at least 450 m is attributed for both continent and margin as evidenced by the elevated base level of the congo drainage basin and the uplift of shelf break and coastal plains topography corrected for regional uplift valley erosion below relics surfaces and corresponding erosion unloading has been determined as a proxy of oligocene topography it shows a typical rift shoulder topography isolating congo drainage basin from margin in such conditions small amplitude flexural uplift related to sediment loads can possibly have negative feedbacks for both oligocene and present time

using palaeoenvironmental dna to reconstruct past environments progress and prospects palaeoenvironmental dna palendna is defined as ancient dna adna originating from disseminated genetic material within palaeoenvironmental samples sources of palendna include marine and lake sediments peat loess till ice permafrost palaeosols coprolites preserved gut contents dental calculus tephras and soils as well as deposits in caves rockshelters and at archaeological sites palendna analysis provides a relatively new tool for quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions testing hypotheses regarding megafaunal extinctions human environment interactions taxonomic studies and studies of dna damage because palendna samples comprise markedly different materials and represent wide ranging depositional and taphonomic contexts various issues must be addressed to achieve robust reproducible findings such issues include climatic and temporal limitations the biological origin and state free versus bound of palendna stratigraphic reliability sterile sampling ability to distinguish modern from adna signals dna damage and pcr amplification dna extraction methods and taxonomic resolution in this review we provide a non specialist introduction to the use of palendna for quaternary and archaeological researchers assess attributes and limitations of this palaeoenvir onmental tool and discuss future prospects of using palendna to reconstruct past environments copyright 2014 the authors journal of quaternary science published by john wiley sons ltd on behalf of quaternary research association

early permian a type granites from central inner mongolia north china magmatic tracer of post collisional tectonics and oceanic crustal recycling abstract a type granitoids constitute volumetrically minor but genetically important building blocks of most post archean continental landmasses on earth and their diversified genesis encapsulates key information for ascertaining critical geodynamic controls on continental crustal formation and differentiation this zircon u pb dating and geochemical study documents the early permian peralkaline granites from central inner mongolia of china eastern central asian orogenic belt caob these granites show an a type magmatic affinity with typical enrichment in alkalis ga zr nb and y depletion in sr and p and fractionated ree patterns showing strong negative eu anomalies they have meaningful initial 87 sr 86 sr ratio of 0 70594 e nd t of 4 25 to 6 05 zircon e hf t from 9 8 to 16 0 and 18 o values from 2 41 to 4 72 these elemental and isotopic characters argue for parental magmas from partial melting of a newly trapped charnockitic lower crustal protolith and their subsequent fractional crystallization with an inherent hydrothermally altered oceanic crustal heritage and possible tectonic linkage to post collisional slab breakoff this kind of a type granites could not only serve as an insightful temporal milestone for monitoring the amalgamation between various constituent terranes in the caob but also present a spatial magmatic proxy for marking the maturation stage of juvenile crustal reworking during the final phase of a large orogenic event

permian stratigraphy and correlation of northeast china a review palaeontological lithostratigraphical data from the permian strata and correlation of the permian successions for different tectonic units in northeast china are reviewed and summarized in this paper permian strata in northeast china are dominated by brachiopods fusulinoideans and land plants with limited ammonoids conodonts and bivalves the cisuralian early permian in the northern margin of the north china block and in the manchuride belt is composed mostly of marine massive limestone with the characteristic pseudoschwagerina zone in the asselian and sakmarian and the misellina claudiae zone in the kungurian the cisuralian in the xing an block and the northeastern part of inner mongolia is dominated by huge terrestrial deposits with fossil plants the guadalupian middle permian in the manchuride altaid and yanbian belts are characterized by bi temperate roadian or early wordian monodiexodina fauna and the late wordian capitanian codonofusiella schwagerina or neoschwagerina yabeina faunas the mixed brachiopod faunas between the boreal antitropical and the palaeoequatorial cathaysian forms the roadian or early wordian solitary coral faunas and the late wordian capitanian compound waagenophyllum wentzelella fauna the nadanhada terrane contains some exotic limestone blocks with a typical cathaysian neoschwagerina yabeina fauna in a late jurassic early cretaceous melange which is related to mesozoic subduction in the western circum pacific region the lopingian late permian in northeast china is mostly characterized by terrestrial molasse deposits with a mixed flora between the boreal angaran and the palaeoequatorial cathaysian provinces indicating the final closure of the palaeo asian ocean c 2005 elsevier ltd all rights reserved

ophiolites in the xing an inner mongolia accretionary belt of the caob implications for two cycles of seafloor spreading and accretionary orogenic events the xing an inner mongolia accretionary belt in the southeastern segment of the central asian orogenic belt caob was produced by the long lived subduction and eventual closure of the paleo asian ocean and by the convergence between the north china craton and the mongolian microcontinent two ophiolite belts have been recognized the northern erenhot hegenshan xi ujimqin ophiolite belt and the southern solonker linxi ophiolite belt most basalts in the northern ophiolite belt exhibit characteristics of normal type to enriched type mid ocean ridge basalt affinities with depleted nd isotopic composition epsilon nd t 5 comparable to modern eastern pacific mid ocean ridge basalts most basaltic rocks in the southern belt show clear geochemical features of suprasubduction zone type oceanic crust probably formed in an arc back arc environment the inferred back arc extension along the solonker linxi belt started at circa 280 ma statistics of all the available age data for the ophiolites indicates two cycles of seafloor spreading subduction which gave rise to two main epochs of magmatic activity at 500 410 ma and 360 220 ma respectively with a gap of similar to 50 million years myr the spatial and temporal distribution of the ophiolites and concurrent igneous rocks favor bilateral subduction toward the two continental margins in the convergence history with final collision at similar to 230 220 ma in the whole belt signals of continental collision and himalayan style mountain building are lacking we thus conclude that the xing an inner mongolia segment of the caob experienced two cycles of seafloor subduction back arc extension and final appalachian type soft collision

influences of climate cattle density and lake morphology on sporormiella abundances in modern lake sediments in the us great plains sporormiella a genus of coprophilous fungus is increasingly used as a qualitative proxy for megafaunal density decreased spore abundances in late pleistocene and holocene sediments are thought t

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

multiple metamorphic events recorded in the metamorphic terranes in central inner mongolia northern china implication for the tectonic evolution of the xing an inner mongolia orogenic belt abstract the tectonic evolution of the xing an inner mongolia orogenic belt ximob in the southeastern segment of the central asian orogenic belt is not well understood it is arguable whether the paleo asian ocean was closed in devonian or early mesozoic and whether the tectonic regimes during carboniferous and permian were operated by continuous subduction arc systems or extension after the orogenic process comprehensive studies of metamorphism for four metamorphic terranes including the ondor sum group baoyintu group xilingol complex and early triassic metamorphic sequences in central inner mongolia provide good constraints on the arguable issues about the ximob according to the zircon u pb dating analyses in this study quartz schists of the ondor sum group in the northern and southern orogenic belts nob and sob have a broad detrital zircon age range from late archean to early paleozoic with a similar youngest deposition age of 434 430 ma but have different zircon age populations with a 650 ma peak for the nob but not for the sob biotite gneisses of the xilingol complex have age populations and the youngest deposition age of 436 ma similar to the ondor sum group in the nob amphibolites in the complex have a metamorphic zircon age of 321 3 ma and hornblende 40ar 39ar age of 309 2 ma the early triassic metamorphic sequences metabasites in wulangou and mica schists in shuangjing both have broad zircon age ranges from the late archean to late paleozoic their protoliths are constrained to have formed later than 258 ma and 261 ma respectively and the metamorphism occurred soon afterwards in the early triassic constrained by an actinolite 40ar 39ar age of 241 19 ma in metabasite and a muscovite 40ar 39ar age of 240 2 ma in mica schist combined with the results previously published this study identified four phases of metamorphism in central inner mongolia since paleozoic the silurian 430 426 ma high p t metamorphism of the ondor sum group was related to bidirectional subduction processes the devonian 400 ma medium p t metamorphism of the baoyintu group suggests a crustal thickening orogeny the carboniferous 337 321 ma low p t metamorphism of the xilingol complex is indicative of an extension process of a previous orogen the early triassic 240 ma extensive medium low p t metamorphism along the solonker suture zone was attributed to the closure of limited ocean basins thus an alternative tectonic scenario for the metamorphic terranes in central inner mongolia involves i the early paleozoic trench arc system 500 425 ma ii the devonian collisional orogeny due to closure of the paleo asian ocean 400 360 ma iii the carboniferous and permian extension after the collision 350 250 ma and iv the early triassic within plate orogeny due to the closure of limited ocean basins 240 ma

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

geochronological and hf isotopic variability of detrital zircons in paleozoic strata across the accretionary collision zone between the north china craton and mongolian arcs and tectonic implications the central asian orogenic belt formed by accretion subsequent to the contraction of the paleo asian ocean and its southeastern segment terminated along the solonker suture zone amalgamating the mongolian arcs and the north china craton by the end of the early triassic since typical regional collisional features are absent its tectonic evolution remains speculative an investigation into the variability of detrital zircon u pb ages and hf ratios in permian strata along a southeast northwest transect from the mongolian arcs to the north china craton reveals distinct differences northern basins carry a broad mesoproterozoic to latest precambrian age signature and their sedimentary source terranes are of mixed juvenile to crustal magmatic origin in contrast southern basins contain detritus from the north china craton and their sources are of dominantly crustal contaminated magmatic origin provenance analysis suggests that in the early paleozoic ca 429 ma the paleo asian ocean was consumed along the uliastai arc and the north china craton initiating the formation of the northern and southern accretionary orogens respectively by the end of the middle carboniferous the mongolian arcs were consolidated after the accretion of the uliastai arc in the late carboniferous ca 314 ma the hegenshan back arc basin opened detaching the northern accretionary orogen while subduction continued there it may have temporarily ceased in the south after the accretion of a microcontinent ca 300 ma by the end of the middle permian ca 269 ma back arc basin closure led to the formation and obduction of the suprasubduction zone hegenshan ophiolite eventually the paleo asian ocean closed by double sided subduction such accretionary wedge wedge collision would not involve continental deep subduction unlike other continental collisions the early stages of the sequence likely resembled a pacific type scenario dominated by the subduction of oceanic lithosphere including a japanese sea type back arc basin opening the late stages involved the accretion of large scale continental blocks ultimately leading to final ocean closure which may be similar to the archipelago type setting of present day southeast asia

can we characterise openness in the holocene palaeoenvironmental record modern analogue studies of insect faunas and pollen spectra from dunham massey deer park and epping forest england this paper examines the degree to which tree associated coleoptera beetles and pollen could be used to predict the degree of openness in woodland the results from two modern insect and pollen analogue studies from ponds at dunham massey cheshire and epping forest greater london are presented we explore the reliability of modern pollen rain and sub fossil beetle assemblages to represent varying degrees of canopy cover for up to 1000 m from a sampling site modern woodland canopy structure around the study sites has been assessed using gis based mapping at increasing radial distances as an independent check on the modern insect and pollen data sets these preliminary results suggest that it is possible to use tree associated coleoptera to assess the degree of local vegetation openness in addition it appears that insect remains may indicate the relative intensity of land use by grazing animals our results also suggest most insects are collected from within a 100 200 m radius of the sampling site

major changes in volcano behaviour after a sector collapse insights from stromboli italy in recent years increasing numbers of volcanoes are being recognized as having undergone large sector collapses how far such events can change the succeeding behaviour of the volcano is poorly known despite the importance for natural hazards and economic applications by analysing the last 100 kyr geological history of stromboli italy which has involved multiple collapses this paper illuminates the feedback effect between sector collapse and magma upwelling and emplacement the collapsed zone of stromboli is episodically unbuttressed draining magma preferentially with formation of eruptive centres in the collapse amphitheatre and dyking along the collapse shoulders after a collapse there were no further linear eruptions across the cone on opposing middle lower slopes but these occurred again after rebuilding of the cone the time averaged eruption rate increased immediately before the first collapse and remained higher during the succeeding period of frequent collapses

pollen and sporormiella evidence for terminal pleistocene vegetation change and megafaunal extinction at page ladson florida abstract two cores from the page ladson archaeological site florida were analyzed for pollen and the dung fungus sporormiella the cores contained stratified deposits spanning the pleistocene holocene transition a period characterized by the widespread extinction of pleistocene megafauna and abrupt changes in vegetation type and distribution the disappearance of sporormiella a well established proxy for large herbivore abundance by 12 700 cal bp is consistent with the timing of terminal pleistocene megafaunal extinction elsewhere in north america however a resurgence of sporormiella between 10 750 10 200 cal bp suggests an early holocene incursion of extant megaherbivores such as bison pollen evidence from the site also reflects dramatic vegetation changes which are likely a response to both changing climate and fluctuating herbivore populations prior to 14 500 cal bp the pollen assemblage reflects a relatively cool and dry climate between ca 14 500 12 600 cal bp the sediments are characterized by an increase in hardwood forest and mesic plant taxa indicating an increase in both temperature and precipitation after 12 600 cal bp a decrease in arboreal pollen with the exception of oak alongside an increase in herbaceous pollen indicates drier warmer conditions these results contextualize changes in human behavior at the onset of the holocene

timing and causes of mid holocene mammoth extinction on st paul island alaska relict woolly mammoth mammuthus primigenius populations survived on several small beringian islands for thousands of years after mainland populations went extinct here we present multiproxy paleoenvironmental records to investigate the timing causes and consequences of mammoth disappearance from st paul island alaska five independent indicators of extinction show that mammoths survived on st paul until 5 600 100 y ago vegetation composition remained stable during the extinction window and there is no evidence of human presence on the island before 1787 ce suggesting that these factors were not extinction drivers instead the extinction coincided with declining freshwater resources and drier climates between 7 850 and 5 600 y ago as inferred from sedimentary magnetic susceptibility oxygen isotopes and diatom and cladoceran assemblages in a sediment core from a freshwater lake on the island and stable nitrogen isotopes from mammoth remains contrary to other extinction models for the st paul mammoth population this evidence indicates that this mammoth population died out because of the synergistic effects of shrinking island area and freshwater scarcity caused by rising sea levels and regional climate change degradation of water quality by intensified mammoth activity around the lake likely exacerbated the situation the st paul mammoth demise is now one of the best dated prehistoric extinctions highlighting freshwater limitation as an overlooked extinction driver and underscoring the vulnerability of small island populations to environmental change even in the absence of human influence

juvenile crustal recycling in an accretionary orogen insights from contrasting early permian granites from central inner mongolia north china abstract coeval high k calc alkaline to alkaline granites constitute important components of post collisional to post orogenic igneous suites in most orogenic belts of various ages on earth and their genesis harbors a key to ascertaining critical geodynamic controls on continental crustal formation and differentiation this zircon u pb dating and geochemical study documents three contrasting early permian granites from erenhot of central inner mongolia eastern central asian orogenic belt caob and reveals concurrent high k calc alkaline to alkaline granite association derived from successive partial melting of distinct protoliths the ca 280 ma gancihuduge gcg pluton shows a calc alkaline i type character with initial 87 sr 86 sr ratios of 0 7035 to 0 7039 e nd t of 1 87 to 4 70 zircon e hf t of 8 0 to 13 2 and 18 o from 7 4 to 8 7 the ca 276 ma cailiwusu cls pluton is magnesian and peraluminous with initial 87 sr 86 sr ratios of 0 7036 to 0 7040 e nd t of 1 9 to 2 4 zircon e hf t of 6 5 to 12 1 and 18 o from 9 7 to 10 9 these features are consistent with partial melts of mixed sources composed of newly underplated meta basaltic to andesitic protoliths and variable supracrustal components with distinctively higher proportion of the latter in the cls pluton by contrast the ca 279 ma kunduleng kdl suite exhibits an a type magmatic affinity with typical enrichment in alkalis ga zr nb and y e nd t of 2 39 to 3 55 zircon e hf t from 8 3 to 12 3 and 18 o values from 6 8 to 7 5 these features suggest that they stem from high temperature fusion of dehydrated k rich mafic to intermediate protoliths besides presenting a snapshot into a stratified crustal architecture in 18 o these contrasting granites could not only serve as a temporal marker for monitoring post collisional extension in the aftermath of a retreating subduction zone but also present spatial magmatic proxy for tracing crustal formation and differentiation within back arc basin environments in the caob

thrusting in oceanic crust during continental drift offshore niger delta equatorial africa 1 two and three dimensional 3 d seismic reflection data acquired over oceanic crust in the deepwater west niger delta reveal convincing evidence for compressional tectonics during oceanic crustal spreading using the 3 d seismic data set we describe numerous inclined seismic reflections that dissect the entire oceanic crust from the top of the crust to the level of the moho that are interpreted as thrusts thrust propagation results in the development of associated hanging wall anticlines and footwall synclines these structures are orthogonal to and clearly postdate normal faults that formed during the accretion of oceanic crust during continental drift and strike at right angles to them the charcot ridge is located 140 km south of these thrusts and is a significantly larger structure it is a triangular shaped uplifted region of oceanic crust measuring 80 by 150 km and is located along the ne sw oriented charcot fracture zone two interpretations are possible for the role of the fracture zone in the development of the charcot ridge 1 a thin skinned model whereby the oceanic crust west of the fracture zone has been thrust southeastward with detachment occurring close to the level of the moho the ridge forms as a result of translation and folding above a crustal scale ramp flat thrust geometry 2 a thick skinned model where there is no detachment close to the moho with the thrust fault being much steeper penetrating the crust and probably the mantle lithosphere in this interpretation the structure formed owing to the compressional reactivation of the fracture zone approximate dating of onlapping reflections on either side of the ridge constrains the timing of its formation as between 25 and 120 ma ago the charcot ridge represents one of the largest thrust structures to be identified in a passive margin setting many other compressional folds with the same orientation formed to the northeast in the benue trough probably during the santonian as a result of a change in the spreading direction during south atlantic rifting we speculate that the same causal mechanism applies for the formation of the charcot ridge

deformation of oceanic crust in the eastern gulf of guinea role in the evolution of the cameroon volcanic line and influence on the petroleum endowment of the douala rio muni basin

structure of the gabon margin from integrated seismic reflection and gravity data in the south gabon basin deep multi channel seismic reflection and gravity modeling analysis have shed light on key features of the structure of the margin the thinned continental crust beneath the gabon margin appears to be composed of two distinct layers separated by a clear strong and more or less continuous reflector running in the 7 10 s twt window the lower crust is characterized by a higher density intermediate between the lower values of the upper crust and the denser values of the mantle the lower crust is irregularly shaped and presents lateral thickness variations along the direction of thinning and along the coast in the offshore thinned continental domain the lower and upper crust form a 20 25 km thick body crustal thicknesses point to a relatively sharp and narrow transition along a few tens of kilometers between the unthinned and the thinned continental crust the high density layer identified offshore gabon presents similar characteristics in density geometry and spatial distribution as the underplated magmatic bodies observed along volcanic margins e g along the south atlantic namibia margin or the north atlantic voring margin although this lower crustal body could possibly represent ultra mafic serpentinized rocks or high grade metamorphic crustal rocks we suggest that it could be composed of mafic rocks magmas resulting from partial melting during rifting may underplate the crust and or be intruded in the lower crust through a system of dykes and sills in this view the present day crustal thicknesses along rifted margins characterized by magmatic underplating and or intrusion are not representative of the thinning that the crust experienced during rifting results of this study point to relatively shallow sedimentary basins along the south gabon margin the deepest offshore depocenters located under the westernmost side of the continental platform appear to be associated with the deepest syn rift basins these basins seem to extend along 20 to 40 km in the ne sw direction with a present day average thickness of 7 3 km offshore gabon whereas the crustal thinning appears significant the syn rift deposit are not thick we suggest that the area was anomalously uplifted during the rifting phase due to an elevated thermal lithospheric gradient the conclusions derived from our seismic and gravity analysis are consistent with the implications such a thermal anomaly would have on the tectonic evolution of a rifted margin with 1 an underplated high density lower crustal layer 2 shallow depth syn rift basins associated with a relatively thin crust and subsequently 3 elevated recorded subsidence rates in the initial post rift stages research highlights the gabon margin appears characterized by an underplated high density lower crustal layer shallow depth syn rift basins are associated with a relatively thin crust seismic and gravity analysis points to an anomalous uplift of the gabon margin during the rifting phase crustal structure syn rift infill and post rift subsidence are consistent an uplift of the gabon margin during the rifting phase the uplift of the gabon margin is possibly due to an elevated thermal lithospheric gradient

petrogenesis of the middle triassic erenhot granitoid batholith in central inner mongolia northern china with tectonic implication for the triassic mo mineralization in the eastern central asian orogenic belt abstract voluminous post orogenic magmatism holds a key to monitoring important geodynamic processes and crustal evolution within an extensional accretionary orogen the middle triassic erenhot granitoid batholith from central inner mongolia northern china is tectonically located in the eastern central asian orogenic belt this batholith consists of monzogranite syenogranite alkali feldspar granite and albite granite with minor mafic to felsic enclaves and dykes the formation of this composite batholith involved distinct mafic and felsic magma end members concomitant episodic mafic felsic interaction and intra felsic magma evolution mafic diabasic and high mg intermediate dioritic dykes show enrichment in large ion lithophile elements depletion in high field strength elements and heterogeneous isotopic compositions indicative of a metasomatized lithospheric mantle source inherited from prior oceanic slab subduction the monzogranites and aplites have arc like elemental features and variable isotopic compositions isr t 0 706132 end t 0 4 zircon ehf t 2 8 to 7 4 zircon 18o 5 32 to 6 74 clearly suggesting that the felsic magma end member of a dual heritage was derived from dominant newly underplated mafic crust and subordinate ancient lower crust hybridization processes between mantle derived mafic magma and crust derived felsic magma result in the formation of monzonitic enclaves isr t 0 704850 end t 0 1 with an isotopic resemblance to the host granites fractional crystallization of the monzogranitic magmas endows the differentiated syenogranites and alkali feldspar granites with highly evolved elemental characteristics we further deduce that the magmatic immiscibility between k rich and na rich residual melts in a deep reservoir produces albite granites with distinct deformation imprints variable k2o contents and wide range of crystallization temperatures combining with coeval regional igneous episodes as well as concomitant sedimentary and structural events in the northern china mongolia tract the triassic erenhot composite batholith can be considered as post orogenic magmatic products possibly within a coupled geodynamic scenario between lithospheric dripping and concurrent gravitational collapse therefore the documentation of this large scale triassic post orogenic magmatism could not only lead to the characterization of the eventual closure of the paleo asian ocean but also capture a snapshot into the tectonic background for the widespread porphyry type mo mineralization in the eastern central asian orogenic belt during early mesozoic

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

late paleozoic rift related basalts from central inner mongolia china abstract late paleozoic basaltic volcanism widely occurred in central inner mongolia the southeastern part of the central asia orogenic blet caob three volcanic pulses are identified by ion microprobe shrimp ii zircon u pb analysis which are late carboniferous ca 315 ma the latest carboniferous ca 303 ma and early permian ca 284 ma basalts in the earliest stage are characterized by flat hree depletion in nb and ta morb like th yb ratios and depleted mantle dm like hf isotopic ratios these are similar to forearc basalts that have been generated by melting of a fluxed depleted mantle in an extensional environment the latest carboniferous basalts sample d1363 have no zr hf anomalies relatively radiogenic hf isotopic ratios ehf t 12 1 to 19 7 and high 18o values up to 8 5 vsmow these are likely to be magmas originated from decompressional melting of a depleted mantle that interacted with ocean floor pillow basalts during their ascending through the crust the early permian sample d1380 have variable 206pb 238u zircon ages with an interpreted magma crystallization age of 284 4 2 5 ma these zircons have scattered hf isotope ehf t 5 to 14 and 18o 1 8 11 0 vsmow which suggest the involvement of a relatively enriched mantle source overall the temporal evolution of the late paleozoic basaltic volcanism from central inner mongolia suggests a rift related tectonic setting

provenance analysis of the late paleozoic sedimentary rocks in the xilinhot terrane ne china and their tectonic implications abstract the xilinhot terrane is located in the eastern segment of the central asian orogenic belt in ne china and is a key to a hotly debated issue on the paleozoic tectonic evolution of this giant progenic belt to constrain the tectonic evolution of the xilinhot terrane in the late paleozoic we undertook zircon u pb dating and geochemical analyses of the zhesi and benbatu formations in the suolun and xi ujimqin areas in the xilinhot terrane samples of the benbatu formation yield detrital zircon u pb ages ranging from 2659 ma to 316 ma with four age populations at 2659 1826 ma 1719 963 ma 590 402 ma and 396 316 ma whereas samples from the zhesi formation yield detrital zircon u pb ages ranging from 1967 ma to 250 ma with four age populations at 1967 1278 ma 971 693 ma 561 403 ma and 399 250 ma the age groups of both the benbatu and zhesi formations in the xilinhot terrane are similar to those in other parts of the central asian orogenic belt caob this evidence indicates that the xilinhot terrane is a microcontinent and not an accretionary complex as previously thought furthermore the youngest zircon grains in the benbatu and zhesi formations yield weighted mean 206 pb 238 u ages of 322 12 ma msdw 0 12 n 4 and 257 2 8 ma msdw 1 6 n 8 respectively combined with fossil data our new data suggest that the benbatu and zhesi formations in the xilinhot terrane were possibly deposited at 322 ma and 257 ma respectively based on the provenance of the carboniferous permian sandstones came from the blocks of ne china we speculate that the xilinhot terrane is the western part of the songliao block

late quaternary vegetation climate and fire history of the southeast atlantic coastal plain based on a 30 000 yr multi proxy record from white pond south carolina usa the patterns and drivers of late quaternary vegetation dynamics in the southeastern united states are poorly understood due to low site density problematic chronologies and a paucity of independent paleoclimate proxy records we present a well dated 15 accelerator mass spectrometry 14 c dates 30 000 yr record from white pond south carolina that consists of high resolution analyses of fossil pollen macroscopic charcoal and sporormiella spores and an independent paleotemperature reconstruction based on branched glycerol dialkyl tetraethers between 30 000 and 20 000 cal yr bp open pinus picea forest grew under cold and dry conditions elevated quercus before 26 000 cal yr bp however suggest warmer conditions in the southeast before the last glacial maximum possibly corresponding to regionally warmer conditions associated with heinrich event h2 warming between 19 700 and 10 400 cal yr bp was accompanied by a transition from conifer dominated to mesic hardwood forest sporormiella spores were not detected and charcoal was low during the late glacial period suggesting megaherbivore grazers and fire were not locally important agents of vegetation change pinus returned to dominance during the holocene with step like increases in pinus at 10 400 and 6400 cal yr bp while charcoal abundance increased tenfold likely due to increased biomass burning associated with warmer conditions low intensity surface fires increased after 1200 cal yr bp possibly related to the establishment of the mississippian culture in the southeast

styles of volcano induced deformation numerical models of substratum flexure spreading and extrusion the gravitational deformation of volcanoes is largely controlled by ductile layers of substrata using numerical finite element modelling we investigate the role of ductile layer thickness and viscosity on such deformation to characterise the deformation we introduce two dimensionless ratios a volcano radius ductile layer thickness and b viscosity of ductile substratum failure strength of volcano we find that the volcanic edifice spreads laterally when underlain by thin ductile layers a 1 while thicker ductile layers lead to inward flexure a 1 the deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness increasing a structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself in contrast flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone in addition we show that lower viscosities in the ductile layer low b lead to faster rates of movement and also affect the deformation style considering a thin ductile layer if viscosity is high compared to the failure strength of the volcano high b then deformation is coupled and spreading is produced however if the viscosity is low low b substratum is effectively decoupled from the volcano and extrudes from underneath it in this latter case evidence is likely to be found for basement compression but corresponding spreading features in the volcano will be absent as the cone is subject to a compressive stress regime similar to that produced by flexure at volcanoes where basement extrusion is operating high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse an analysis of deformation features at a volcano can provide information about the type of basement below it a useful tool for remote sensing and planetary geology also knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes where features have not yet become well developed or are obscured

spores of the dung fungus sporormiella increased abundance in historic sediments and before pleistocene megafaunal extinction abstract spores of the dung fungus sporormiella become abundant following the historic introduction of grazing herbivores at seven sites in the western united states during the holocene they are generally rare but at six sites sporormiella spores are abundant before the extinction of pleistocene megaherbivores ca 11 000 yr b p sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung preserved in bechan cave southern utah their abundance in late glacial sediments may reflect the abundance of megaherbivores during quaternary thereby indicating the age of pleistocene extinctions where other indicators are absent

sedimentological and geochronological constraints on the carboniferous evolution of central inner mongolia southeastern central asian orogenic belt inland sea deposition in a post orogenic setting handling editor s j liu keywords central asian orogenic belt central inner mongolia carboniferous sedimentary detrital zircon sedimentological and geochronological analyses were performed on carboniferous strata from central inner mongolia china to determine the tectonic setting of the southeastern central asian orogenic belt caob sedimentological analyses indicate that the widespread late carboniferous strata in central inner mongolia were dominated by shallow marine clastic carbonate deposition with basal conglomerate above the precambrian basement and early paleozoic orogenic belts based on lithological comparison and fossil similarity five sedimentary stages were used to represent the carboniferous deposition the depositional stages include from bottom to top 1 basal molassic 2 first carbonate platform 3 terrigenous with coeval intraplate volcanism 4 second carbonate platform and 5 post carbonate terrigenous these five stages provide evidence for an extensive transgression in central inner mongolia during the late carboniferous detrital zircon geochronological studies from five samples yielded five main age populations 310 ma 350 ma 400 450 ma 800 1200 ma and some meso proterozoic to neoarchean grains the detrital zircon geochronological studies indicate that the provenances for these late carboniferous strata were mainly local magmatic rocks early paleozoic arc magmatic rocks and carboniferous intrusions with subordinate input of precambrian basement combining our sedimentological and provenance analyses with previous fossil comparison and paleomagnetic reconstruction an inland sea was perceived to be the main paleogeographic feature for central inner mongolia during the late carboniferous the inland sea developed on a welded continent after the collision between north china craton and its northern blocks

lithospheric instability and the source of the cameroon volcanic line evidence from rayleigh wave phase velocity tomography the cameroon volcanic line cvl is a 1800 km long volcanic chain extending sw ne from the gulf of guinea into central africa that lacks the typical age progression exhibited by hot spot related volcanic tracks this study investigates the upper mantle seismic structure beneath the cvl and surrounding regions to constrain the origin of volcanic lines that are poorly described by the classic plume model rayleigh wave phase velocities are measured at periods from 20 to 182 s following the two plane wave methodology using data from the cameroon seismic experiment which consists of 32 broadband stations deployed between 2005 and 2007 these phase velocities are then inverted to build a model of shear wave velocity structure in the upper mantle beneath the cvl results show that phase velocities beneath the cvl are reduced at all periods with average velocities beneath the cvl deviating more than 2 from the regional average and 4 beneath the congo craton this distinction is observed for all periods but is less pronounced for the longest periods measured inversion for shear wave velocity structure indicates a tabular low velocity anomaly directly beneath the cvl at depths of 50 to at least 200 km and a sharp vertical boundary with faster velocities beneath the congo craton these observations demonstrate widespread infiltration or erosion of the continental lithosphere beneath the cvl most likely caused by mantle upwelling associated with edge flow convection driven by the congo craton or by lithospheric instabilities that develop due to the nearby edge of the african continent

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

zircon ages and hf isotopic compositions of ordovician and carboniferous granitoids from central inner mongolia and their significance for early and late paleozoic evolution of the central asian orogenic belt abstract we present zircon ages and hf in zircon isotopic data for plutonic rocks and review the evolution of central inner mongolia china in the early and late paleozoic zircons of a granodiorite yielded a 206 pb 238 u age of 472 3 ma that reflects the time of early paleozoic magmatism zircon ages were also obtained for a tonalite 329 3 ma quartz diorite 320 3 ma and granite vein 297 2 ma our results in combination with published zircon ages and geochemical data document distinct magmatic episodes in central inner mongolia the dated samples are mostly granodiorite tonalite and quartz diorite in composition with intermediate to high silica high na 2 o 3 08 4 26 wt low k 2 o 0 89 2 86 wt and high na 2 o k 2 o and sr y ratios their chondrite normalized ree patterns are characterized by lree enrichment in mantle normalized multi element variation diagrams they show typical negative nb and ta anomalies and all samples display positive e hf t and e nd t values and low i sr the ordovician rocks however show higher sr y and la yb ratios than the carboniferous samples implying that the older granitoids represent adakitic granitoids and the carboniferous granitoids are typical subduction related arc granitoids but also with adakite like compositions the results are compatible with the view that the central asian orogenic belt caob in inner mongolia evolved through operation of several subduction systems with different polarities an early middle paleozoic subduction and accretion system along the northern margin of the north china craton and the southern margin of the mongolian terrane and late paleozoic northward subduction along the northern orogen and exhumation of a high pressure metamorphic terrane on the northern margin of the north china craton

supra subduction zone ophiolites from inner mongolia north china implications for the tectonic history of the southeastern central asian orogenic belt abstract the recently discovered diyanmiao ophiolite in the eastern part of the erenhot hegenshan ophiolite belt forms part of the southeastern domain of the central asian orogenic belt caob the ophiolite suite is composed of the northern baiyinbulage ophiolite and the southern naolaiketu ophiolite each extending for nearly 100 km and a width of around 6 km the suite preserves a well exposed and a nearly complete ophiolite stratigraphy and includes from bottom to top harzburgite bedded gabbro isotropic gabbros anorthosite spilite pillow basalt keratophyre baschtauite with overlying chert and plagiogranite veins locally intruding the pillow basalt and gabbro the pillow basalts possess the geochemical characteristics of hahajima island arc tholeiite iat indicating that the diyanmiao ophiolite formed in the incipient arc setting of the supra subduction zone la icp ms u pb dating of zircon grains from three gabbro samples yield ages of 361 13 ma 356 7 3 8 ma and 340 14 ma indicating an early carboniferous age for the diyanmiao ophiolite we suggest that the intra oceanic subduction initiation of the erenhot hegenshan paleo ocean during the early carboniferous resulted in the formation of an incipient arc oceanic crust and that the diyanmiao ophiolite represents an important north dipping subduction event of the paleo asian oceanic crust beneath the southern margin of the siberian plate after early carboniferous and early permian our study provides further insights into the evolution of the paleo asian ocean and eventual construction of caob the globe s largest phanerozoic orogen

late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block constraints on the composition and evolution of the lithospheric mantle abstract the late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block ncb are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the late mesozoic zircon u pb ages show that emplacement of the mafic ultramafic complexes occurred in at least three stages middle devonian ca 395 ma late carboniferous early permian 308 276 ma and triassic 250 220 ma most of the middle devonian complexes display low initial 87sr 86sr ratios of 0 70467 0 70492 weak to moderate negative end t values from 6 3 to 1 5 and weakly negative to weakly positive zircon ehf t values from 11 5 to 5 5 indicating that the parent magma was derived from slightly enriched lithospheric mantle the late carboniferous early permian complexes are characterized by low initial 87sr 86sr ratios of 0 70521 0 70604 significant negative end t values from 14 1 to 9 3 and zircon ehf t values from 17 0 to 10 5 and were probably derived from metasomatized lithospheric mantle the early triassic complexes exhibit initial 87sr 86sr ratios of 0 70656 0 70825 and significant negative end t values from 17 1 to 8 2 indicating their derivation from enriched lithospheric mantle however the late triassic mafic ultramafic complexes display weakly negative to weakly positive end t values of 4 4 to 0 5 and zircon ehf t values from 2 9 to 1 7 indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle zircon ages geochemistry and sr nd hf isotopic studies suggest that the lithospheric mantle beneath the northern ncb had a slightly enriched signature during the middle devonian but it became significantly enriched during the late carboniferous to early permian due to metasomatism of lithospheric mantle during the southward subduction of the paleo asian oceanic plate after final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern ncb in the latest permian to earliest triassic enriched lithospheric mantle still existed beneath the northern ncb during the early triassic however in the late triassic involvement of asthenospheric mantle became significant owing to strong upwelling of asthenospheric mantle and post collisional lithospheric delamination in the early late triassic these results suggest that the cratonic lithospheric mantle beneath the northern ncb underwent multiple stages of modification prior to its destruction and thinning initiation of lithospheric destruction and thinning in the northern ncb likely occurred during the early late triassic which is much earlier than in other parts of the ncb where it occurred in the late mesozoic it appears likely that lithospheric destruction and thinning of the ncb initially started at the northern and eastern margins of the craton as a result of post collisional lithospheric delamination and then spread to the interior of the craton

vegetation history since the last glacial maximum in the ozark highlands usa a new record from cupola pond missouri abstract the timing and drivers of vegetation dynamics and formation of no analog plant communities during the last deglaciation in the unglaciated southeastern us are poorly understood we present a multi proxy record spanning the past 19 800 years from cupola pond in the ozarks mountains consisting of replicate high resolution pollen records 25 ams radiocarbon dates and macrofossil charcoal and coprophilous spore analyses full glacial pinus and picea forests gave way to no analog vegetation after 17 400 yr bp followed by development of quercus dominated holocene forests with late holocene rises in pinus and nyssa vegetation transitions replicated in different cores are closely linked to hemispheric climate events rising quercus abundances coincide with increasing northern hemisphere temperatures and co 2 at 17 500 yr bp declining pinus and picea at 14 500 yr bp are near the bolling allerod onset and rapid decline of fraxinus and rise of ostrya carpinus occur 12 700 yr bp during the younger dryas the cupola no analog vegetation record is unusual for its early initiation 17 000 yr bp and for its three vegetation zones representing distinct rises of fraxinus and ostrya carpinus sporormiella was absent and sedimentary charcoal abundances were low throughout suggesting that fire and megaherbivores were not locally important agents of disturbance and turnover the cupola record thus highlights the complexity of the late glacial no analog communities and suggests direct climatic regulation of their formation and disassembly

how reliable are non pollen palynomorphs in tracing vegetation changes and grazing activities study from the darjeeling himalaya india abstract in spite of their demonstrated implications as ecological indicators modern analogue studies of non pollen palynomorphs npps from the mountainous regions are still meagre we present here the results of a study on modern npp assemblages recovered from surface samples soils sediments from lake surface and bog etc along a c 130 3600 m a s l elevation gradient in the darjeeling eastern himalaya to test their efficacy in distinguishing different vegetation zones and correlating grazing activities we also used these data to check which of the variables i e elevation vegetation type and grazing pressure is are most influential for deposition of npps and to obtain a npp modern analogue model that may assist future regional paleoecological interpretations we subjected frequency data of 69 npps consisting of algal fungal and zoological remains each identified up to a certain taxonomic rank and some other plant remains like phytoclasts hair bases and wood elements etc to multivariate statistical methods like discriminant da and redundancy rda analyses to assess their ecological indicative values da results showed that npps might be efficient predictors that correctly classified 72 6 of the samples to their correct vegetation zones along the elevation rda results further proved elevation and grazing pressure as the most significant variables influencing npp deposition in the darjeeling himalaya considering the ecological requirements of the studied npps this study also links some npps to their corresponding vegetation zones along the rising elevation as well as different grazing pressure and emphasizes the use of modern analogue studies in palaeoecological interpretations

historical context and chronology of bronze age land enclosure on dartmoor uk the upland of dartmoor southwest england is one of the flagship prehistoric landscapes within britain owing to the excellent survival of extensive prehistoric coaxial field systems archaeological surveys and rescue excavations during the 1970s and 1980s did much to further the understanding of this landscape however much remains to be explored in particular the chronology of enclosure the nature of the pre enclosure landscape and the relationship between bronze age communities and their environment reconsideration of this landscape is important given the place it holds in our understanding of subdivision of the landscape across northwest europe during prehistory this paper presents new palaeoecological data recovered as part of an integrated archaeological and palaeoecological project on northeast dartmoor the sequences detailed here include the first dated neolithic period palaeoenvironmental data from within the prehistoric enclosed land on the moor providing a longer term context for enclosure neolithic groups are implicated in the first establishment of heathland in the study area at around 3630 3370 cal bc during the early bronze age reestablishment of hazel scrub in the study area implies reduced use of the upland although it is not clear whether this is local or indicative of the wider landscape a combination of pollen and fungal spore data indicates a substantial shift to species rich grassland with grazing animals at c 1480 cal bc in a phase that lasted 400 years the later bronze age and early iron age are characterised by low intensity use of the upland these data provide new chronological data for land cover change on dartmoor and whilst they broadly confirm existing models of upland land use in later prehistory their proximity to the standing archaeology affords a more nuanced interpretation of local change

geochronology petrogenesis and tectonic implication of late paleozoic volcanic rocks from the dashizhai formation in inner mongolia ne china abstract in this paper we present geochemical zircon u pb and hf isotopic data on the late paleozoic volcanic rocks of the dashizhai formation which are exposed along the northwestern margin of the songnen terrane in eastern inner mongolia our aim is to constrain the petrogenesis and tectonic setting of the volcanic rocks and to unravel the late paleozoic tectonic evolution of the northwestern part of the songnen terrane along the eastern segment of the central asian orogenic belt lithologically the dashizhai formation is composed mainly of rhyolitic tuff rhyolite dacite andesite basaltic andesite and basalt with minor basaltic trachyandesite the zircons separated from these rocks are euhedral subhedral have high th u ratios 0 2 1 6 and display broad oscillatory growth zoning indicating a magmatic origin the results of zircon u pb dating indicate the volcanic rocks formed during the early permian 295 283 ma geochemically these volcanic rocks belong to the mid k to high k calc alkaline series and are characterized by an enrichment in large ion lithophile elements liles and a depletion in high field strength elements hfses such as nb ta and ti similar to igneous rocks that form in active continental margin settings most magmatic zircons of the rhyolites show positive e hf t values 3 65 to 13 0 and two stage model ages t dm2 of 1396 551 ma these geochemical characteristics indicate that the acidic volcanic rocks of the dashizhai formation were most likely derived from the partial melting of dominantly juvenile crustal components with a possible addition of old materials in contrast the basic to intermediate volcanic rocks were derived from the partial melting of a depleted lithospheric mantle that had been metasomatized by fluids derived from a subducted slab these data together with regional geological investigations suggest that the generation of the early permian volcanic rocks of the dashizhai formation was related to the southward subduction of the paleo asian oceanic plate beneath the songnen terrane this also implies that the terminal collision between the songnen and xing an terranes did not occur before the early permian

the oyut ulaan volcanic group stratigraphy magmatic evolution and timing of carboniferous arc development in se mongolia abstract the palaeozoic mesozoic tectonic evolution of central asia including the vast terrane collage that makes up mongolia has been a topic of considerable debate the oyut ulaan volcanic group is a sequence of volcanic and sedimentary rocks in se mongolia that forms the southern part of the devonian permian saykhandulaan inlier fieldwork traverses and mapping have established four distinct formations in the oyut ulaan volcanic group that record the nature of arc activity in part of the central asian orogenic belt during the carboniferous physical volcanological and sedimentological characteristics of the four formations suggest three clear eruptive styles 1 periodic andesite volcanism in an actively eroding arc setting that also contained large rivers and swamps 2 highly effusive plateau andesite volcanism 3 explosive rhyolitic effusion geochemical analyses of volcanic lithologies suggest that the group represents subduction related mature continental arc volcanism geochemical results document an evolving magma system to which surface processes of the volcano sedimentary model may be linked magma pulses and replenishments are identified from variations in chemostratigraphy newly obtained zircon ages from the volcanic succession fix its emplacement eruption at 323 0 0 7 ma mid carboniferous or late mississippian a granite cobble from the lower part of the oyut ulaan volcanic group gives a u pb zircon age of 338 9 0 4 ma indicating that arc plutons were emplaced 10 ma prior to the oyut ulaan volcanism and were eroded soon after our work provides timing constraints for final accretion and continental assembly in se mongolia and also sheds light on the petrological development of a magmatic arc system within an evolving accretionary orogen

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

permian alkaline granites in the erenhot hegenshan belt northern inner mongolia china model of generation time of emplacement and regional tectonic significance abstract the central asian orogenic belt caob is known to be the earth s largest phanerozoic accretionary orogenic belt its southern margin particularly in the southern mongolia and inner mongolia smim shows an extensive distribution of alkaline granites study of these granites could shed light on long debated hypotheses on the late paleozoic tectonic evolution of this region in this work we performed a detailed zircon age determination and whole rock geochemical analysis on alkaline granites from four granitic plutons in northern inner mongolia hongol saiyinwusu baolag and baiyinwula u pb zircon dating yielded early permian ages ca 280 ma for the four plutons whole rock geochemical analyses show chemical characteristics typical of alkaline granites coeval alkaline granites from southern mongolia to northern inner mongolia constitute a gigantic 900 km permian 292 275 ma alkaline granite belt in the southern caob furthermore these alkaline granites have whole rock e nd t varying between 3 6 and 6 4 and zircon e hf t from 4 9 to 20 3 the geochemical and nd hf isotopic signatures suggest derivation by partial melting of a protolith assemblage dominated by metasomatised mantle and followed by fractional crystallization in a post collisional extensional environment

holocene history of lac des lauzons 2180 m a s l reconstructed from multiproxy analyses of coleoptera plant macroremains and pollen hautes alpes france a 1 70 m core extracted from the lac des lauzons haut champsaur french alps at 2180 m altitude provided a detailed holocene record of beetles pollen and plant macrofossils enabling the reconstruction of local palaeoenvironmental changes during the last 10 000 years after an early phase of colonization by plants and insects corresponding to the lateglacial interstadial a long phase of relative stability of the ecosystems at least in the vicinity of the lake is recorded strikingly there is no evidence from beetle and plant macrofossils that the treeline reached the altitude of lauzons during the holocene climate optimum although this period is characterized by major forest expansion in many high altitude sites in the southern french alps the uppermost part of the record is blurred by the infilling of the lake progressively turning into a peat bog this sequence also provides an opportunity to compare the records of coprophilous fungal spores and coprophilous beetles and to improve the interpretation of these proxies in terms of their significance as proxies for pastoralism