tide supported gravity flows on the upper delta front fraser river delta canada abstract three anomalous events aes were recorded off the fraser river canada during the freshet of 2008 and are ascribed to quasi continuous gravity flows these flows transport warm low salinity fraser river waters to the upper delta front of the fraser delta to at least 50 m water depth all flows occurred during the freshet and spring ebbing tide and were characterized by deposition of fine grained sand and silt beds with likely high water contents these sediments were susceptible to resuspension by the subsequent flood tide current producing very high near bed suspended sediment concentrations ssc with enough excess density to generate hyper concentrated flows our observations show that these episodic events result from the combination of high river discharge high ssc and strong tides and therefore are likely to occur on the delta fronts of other large tide dominated and tide influenced rivers in shallow water basins

late mesozoic bimodal volcanic rocks in the jinniu basin middle lower yangtze river belt yrb east china age petrogenesis and tectonic implications abstract late mesozoic intrusive and volcanic rocks are widespread in the southeast hubei province middle lower yangtze river belt yrb east china detailed in situ zircon u pb and hf isotope elemental and sr nd pb isotopic data are presented in this paper for late mesozoic volcanic rocks from the jinniu basin yrb aiming to constrain their age petrogenesis and tectonic implications the jinniu volcanic rocks show a bimodal distribution in composition with dominant rhyolite and dacite and subordinate basalt and basaltic andesite new shrimp and la icpms zircon u pb ages indicate that the volcanic rocks of three formations in the jinniu basin were erupted at quite a short age range of about 5 ma during the early cretaceous 130 125 ma the mafic rocks are moderately enriched in large ion lithophile elements lile e g ba th u and pb and light rare earth elements lree and are characterized by negative nb ta and ti anomalies and relatively high tio2 0 72 2 06 and nb 9 20 26 5 ppm contents these analyses indicate that the geochemical characteristics of the mafic rocks in the jinniu basin are similar to worldwide phanerozoic nb enriched basalt and andesites neba new in situ zircon u pb ages and field geological relationships demonstrate that neba in the southeast hubei province are not spatially or temporally associated with high silica adakitic rocks but were most likely derived from an enriched lithospheric mantle with assimilation of minor crustal materials and then fractional crystallization during the evolution of the magma overall the felsic rocks in the jinniu basin have geochemical characteristics and sr nd pb signatures and in situ zircon hf isotopic compositions similar to those of the mafic rocks compared with the mafic rocks the felsic rocks are characterized by enriched and variable concentrations of lile and ree e g ba 33 3 1372 ppm y 11 4 33 6 ppm ybc 5 07 18 7 and negative eu anomalies eu 0 22 0 98 as well as a wide range of radiogenic nd pb isotopic values with end t 10 2 to 2 4 206pb 204pb i 17 659 18 705 207pb 204pb i 15 478 15 663 and 208pb 204pb i 37 654 38 935 and in situ zircon hf compositions of ehf t 12 7 to 1 8 these features indicate that the genesis of felsic magma in the jinniu basin is consistent with extensive fractional crystallization and large amounts of crustal contamination from an evolved mafic magma sio2 55 the bimodal volcanic rocks in this study provide convincing evidence that early cretaceous volcanic rocks in the yrb developed in a back arc extensional tectonic regime

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

coarse clastic barrier environments evolution and implications for quaternary sea level interpretation abstract this paper reviews recent work particularly from eastern canada on the dynamics and evolution of coarse clastic barriers it is argued that an understanding of quaternary coastal changes on paraglacial glacially influenced coasts can only be achieved with a knowledge of gravel barrier morphodynamics and sedimentation gravel barriers are distinctive coastal forms in which morphological inheritance and sediment sorting provide major behavioral controls spatially adjacent gravel barriers may display different depositional tendencies prograde seawards migrate landward or aggrade vertically such inconsistent spatial behaviour must be considered in terms of an erosional front advancing landward under stationary or rising sea level redistribution of sediment across or along the erosional front supplies sediment for the development of gravel barriers which in turn provides environments for fine grained deposition which is favourable for further barrier migration an example of an erosional front is given from chezzetcook inlet nova scotia three stages are recognized in the development of gravel barriers starting with the initiation of small drift aligned forms at the leading edge of the erosional front as sea level rises this is followed by a period of consolidation and stabilization when drift aligned forms may become swash aligned conditions for this transition are discussed under rising sea levels it is difficult to explain the conditions leading to the formation of multiple parallel swash aligned ridges although three hypotheses are advanced all of which may operate in different locations the third stage is associated with the breakdown of barriers as sediment supply fails and or sea level rises drift aligned forms are inherently unstable and show signs of pre breakdown stress in the form of reworking and remobilization of proximal sediments into cells swash aligned barriers may be breached revert to drift alignment become segmented or be overstepped some gravel is re incoporated in barriers farther landward while other material is passed seaward of the erosional front and becomes abandoned on the shoreface gravel barriers may exert a major influence on estuary and back barrier environments especially where they control the depositional record the implications for the reconstruction and interpretation of quaternary environments are summarized

cretaceous ridge subduction along the lower yangtze river belt eastern china the lower yangtze river belt is one of the most important metallogenic belts in china the mechanisms responsible for ore genesis and the formation of related cretaceous igneous rocks such as adakite a type granitoid and nb enriched basalt remain controversial mesozoic granitoids in the lower yangtze river belt were mostly formed in the early cretaceous 140 125 ma and three granitoid belts the inner the south and the north have been defined according to petrological and geochemical characteristics previously based mainly on negative end and high initial sr isotope values the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust both of which require crustal thickening mesozoic crustal thickening however is not supported by the development of extensional basins in the region from the late jurassic to cretaceous eastern china was closely associated with subduction of the pacific plate in the south and the izanagi plate in the north the midocean ridge mor between these two plates was drifting toward and likely subducting under the lower yangtze river belt a ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt partial melting of subducting young hot oceanic slabs close to the ridge formed adakitic rocks the negative end values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle and or crustal materials through afc process a slab window opened during ridge subduction as indicated by a type granitoids in the center of the inner belt nb enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths

submarine canyons and channels in the lower st lawrence estuary eastern canada morphology classification and recent sediment dynamics abstract series of submarine canyons and channels observed in the lower st lawrence estuary lsle provide an opportunity to analyze in great detail the morphology spatial distribution and modern activity of such systems in a relatively shallow 300 m semi enclosed basin based on their geomorphology and physical settings the canyons and channels were classified into four categories according to their feeding sources ancient or recent glacially fed river fed longshore drift fed and sediment starved systems their activity was interpreted based on geomorphological characteristics such as the presence of bedforms related to gravity flows backscatter intensity axial incision and the presence of rapidly deposited layers in surficial sediments river fed deltas were interpreted as inactive mainly because suspended sediment concentrations at river mouths are low preventing the generation of hyperpycnal currents or delta lip failures related to high sediment supply longshore drift fed canyons present where the coastal shelf narrows were found to be episodically active probably due to earthquakes or extreme storm events unlike other longshore drift fed canyons observed elsewhere in the world they are active infrequently because of the modern low rates of sediment supply to their heads the most active canyons are the sediment starved type and were observed near pointe des monts their activity is probably due to slope failures and to the presence of strong hydrodynamic processes therefore sediment supply is not the main mechanism responsible for modern canyon and channel activity in the lsle however sediment supply has been an important factor during the formation of the submarine channels and canyons their quasi exclusive occurrence on the quebec north shore is attributed to its larger watershed and important sedimentary delivery during deglaciation the quebec north shore watershed is 20 times greater than the quebec south shore watershed which favored the transport of greater volumes of sediment during the early holocene moreover the slope proximity to the shore led to the formation of longshore drift fed systems on the north shore when sediment supplied to rivers were transferred on a narrow shelf

a review of the intracontinental porphyry deposits in the middle lower yangtze river valley metallogenic belt eastern china abstract the middle lower yangtze river valley metallogenic belt mlyb is one of the most important metallogenic belts in eastern china and contains many important porphyry deposits these deposits include the tongshankou cu mo jiguanzui cu au chengmengshan cu mo wushan cu mo fengshandong cu au dingjiashan cu yangjishan au shaxi cu au dongguashan cu au shujiadian cu and anjishan cu deposits etc in this review we summarize the geological characteristics including the stratigraphy structure ore bearing porphyry types vein characteristics and wall rock alteration metallogenic ages and petro geochemistry of representative porphyry deposits in the mlyb we conclude that porphyritic magmatism and metallogeny have occurred in three stages the early ca 149 135 ma and late ca 123 105 ma stages comprise mainly porphyry skarn mineralization whereas the middle ca 133 125 ma stage comprises porphyry mineralization ore bearing porphyries in the mlyb are the high k calc alkaline to calc alkaline series with the majority possess adakitic geochemical signature the ore bearing porphyries with adakitic signature may have originated from magma mixing produced by the delamination of enriched lithospheric mantle and partial melting of the thickened lower crust the enriched mantle derived mafic melts component are very important for generating fertile magma and the 34s and 18o values suggest that ore forming materials were magma derived compared with porphyry deposits in typical magmatic arc settings porphyry deposits in the mlyb do not contain advanced argillic lithocaps or high to intermediate sulfidation systems and the magmatic and ore forming material sources are also very different

palaeogeography of atlantic canada 13 0 kyr abstract we combine isobase maps with a digital terrain model of atlantic canada to map coastlines from 13 14c kyr bp to the present at 13 14c kyr bp there are ridges of high relative sea level rsl values over newfoundland and the maritime provinces and a re entrant of low values in the gulf of st lawrence this pattern persists well into the holocene and reflects crustal response to the slow wasting of ice caps that persisted in newfoundland and the maritime provinces for up to five millennia after the removal of ice from the gulf of st lawrence by a migrating calving embayment the palaeogeographic reconstructions reveal an archipelago on the outer shelf from grand bank to the continent that persisted from 13 14c kyr bp until ca 8 14c kyr bp much of the magdalen shelf was exposed but the magdalen islands were never connected to the mainland prince edward island was initially separated from the mainland became connected after 11 14c kyr bp and was separated again just before 6 14c kyr bp when northumberland strait formed the reconstructions are highly sensitive to relatively small changes in isobase values especially on the shallow banks on the continental shelf

a pseudo adakite derived from partial melting of tonalitic to granodioritic crust kyushu southwest japan arc abstract cretaceous peraluminous granitic intrusions occur in kyushu in the southwest japan arc as batholiths or stocks accompanied by metaluminous tonalite to granodiorite the peraluminous intrusions are classed as adakitic based on sr y y ppm relationships but they contain abundant k feldspar a phase not common in typical adakites to consider their significance in the arc system we investigated the tsutsugatake stock as representative of the intrusions exposed in central kyushu the tsutsugatake rocks are mainly garnet bearing two mica leuco granitoids their sr y ratios and rare earth element concentrations are appropriate for adakite but k 2 o na 2 o ratios 0 53 1 43 and al 2 o 3 13 7 15 0 wt mgo 0 20 0 55 wt sr 207 462 ppm cr 12 ppm and ni 8 ppm contents differ from those of typical adakite geochemical modeling shows that the petrogenesis of the tsutsugatake stock can be explained by partial melting of arc type tonalite or adakitic granodiorite under middle to lower crustal conditions leaving amphibole and plagioclase as residual phases the differences between the tsutsugatake stock and classical adakites lie in their source rocks and melting conditions the tsutsugatake source was not basaltic and the melting pressure was insufficient to stabilize garnet the tsutsugatake rocks are here designated pseudo adakites such pseudo adakites may be found in both modern and ancient arcs and would play an important role in crustal evolution as a member of the recycled constituent

semiannual patterns of erosion and deposition in upper monterey canyon from serial multibeam bathymetry recently acquired 3 m resolution 244 khz multibeam seafloor bathymetry 0 5 m depth precision reveals geomorphology at sufficient detail to interpret small scale features and short term processes in the upper 4 km of monterey canyon california the study area includes the continental shelf and canyon features from 10 m to 250 m depth the canyon floor contains an axial channel laterally bounded by elevated complex terrace surfaces sand waves with 2 m height and 35 m average wavelength dominate the active part of the canyon floor the sand waves are strongly asymmetrical indicating net down canyon sediment transport in this reach terraces including a broad 25 m tall terrace complex near the head of the canyon bear evidence of recent degradation of the canyon floor slump scars and gullies having a variety of sizes and relative ages shape the canyon walls serial georeferenced digital elevation models were analyzed to detect net changes in bathymetry or morphology occurring during both a six month period september 2002 to march 2003 and a 24 h period 24 march to 25 march significant changes over the six month period include 1 complete reorganization of the sand waves on the channel floor 2 local channel degradation creating new 2 m tall erosional terraces on the channel margins 3 local channel widening that laterally eroded older channel margin terraces and 4 60 m extension of one minor gully head on a steep canyon wall there were no discernable changes in morphology during the 24 h study period raster subtraction of serial bathymetric grids provides estimates of sediment erosion and deposition that occurred between the canyon head and a point 2 km down canyon during the six month study erosion of 320 000 m 3 80 000 m 3 of sediment occurred mainly in the tributaries along the margins of the axial channel and in the lowest 700 m of the analyzed reach this eroded volume was approximately balanced by 260 000 m 3 70 000 m 3 of sediment deposition that was concentrated in the nearshore region along the rim of the canyon head there was no measurable sediment gain or loss during the 24 h study period

early cretaceous adakitic granites in the northern dabie complex central china implications for partial melting and delamination of thickened lower crust abstract to date few adakitic rocks have been reported in direct association with contemporary intra continental extensional structures which has cast doubt on genetic models involving partial melting of the lower crust this study presents early cretaceous 143 129 ma new sensitive high resolution ion microprobe shrimp zircon u pb ages adakitic granites which are directly associated with a contemporary metamorphic core complex i e the northern dabie complex in the dabie area these granites exhibit relatively high sr contents negligible to positive eu and sr anomalies high la yb and sr y ratios but very low yb and y contents similar to subducted oceanic crust derived adakites they are also characterized however by very low mgo or mg and ni values and nd sr isotope compositions end t 14 6 to 19 4 and 87sr 86sr i 0 7067 0 7087 similar to triassic continent derived eclogites subducted in the dabie sulu orogen additionally late granitic dikes in the adakitic intrusions exhibit low sr contents clearly negative eu and sr anomalies low la yb and sr y ratios but relatively high yb and y contents similar to 118 105 ma granites in the northern dabie complex based on composition and geochronology data of neoproterozoic amphibolites and orthogneisses triassic high to ultra high pressure metamorphic rocks and early cretaceous mafic ultramafic intrusive rocks and the constraints provided by experimental melt data for tonalites metabasaltic rocks and eclogites we suggest that the adakitic granites were most probably generated by partial melting of thickened amphibole or rutile bearing eclogitic lower crust as a consequence of triassic middle jurassic subduction and thrusting the late dikes probably originated from plagioclase bearing intermediate granulites moreover we suggest that late mesozoic delamination or foundering of thickened eclogitic lower crust is also a more plausible mechanism for the petrogenesis of early cretaceous mafic ultramafic intrusive rocks in the dabie area and probably involved partial melting of a mixed source comprising eclogitic lower crust that had delaminated or foundered into upper lithospheric or asthenospheric mantle peridotite asthenospheric upwelling in response to post collisional delamination of lithospheric mantle was likely to have provided the heat source for the cretaceous magmatism

a type granite belts of two chemical subgroups in central eastern china indication of ridge subduction abstract early cretaceous a type granites in the lower yangtze river belt central eastern china with both a 1 and a 2 chemical subgroups formed at 125 2 ma after a cretaceous ridge subduction remarkably a 1 and a 2 group granites are distributed in three zones roughly parallel to each other and to a slightly older adakite belt in general a 1 granites form in intraplate settings whereas a 2 granites near paleo convergent margins the alternate distribution of these two subgroup a type granites is compatible with a proposed cretaceous ridge subduction in the region the subduction of a dry and hot spreading ridge may have only released small amount of fluids so that metasomatism on the overriding lithosphere was undetectable correspondingly resulted in a 1 granites later on in contrast wetter and colder oceanic crust away from the spreading ridge was responsible for mantle metasomatism and consequently the formation of a 2 granites further away from the ridge the subduction angle was much steeper and dehydration of the slab had occurred earlier during the subduction and thus dramatically reduced mantle metasomatism corresponding to a 1 granites again both a 1 and a 2 granites formed within a short period of time due to slab window rollback after the ridge subduction the distribution of the a 1 and a 2 granites together with the adakite belt may be taken as discrimination indice for ancient ridge subduction

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

the hydraulic autogenesis of distinct cyclicity in delta foreset bedding flume experiments abstract we report the experimental discovery of autogenic cyclicity in delta foreset bedding that arises simply from steady water and sediment input under particular hydraulic characteristics this autogenesis is intrinsic to froude supercritical flow associated with a train of upstream migrating hydraulic jumps that delineate cyclic steps upstream migration of hydraulic jumps is associated with discrete packages of sediment accumulation on the foreset slope this synchronism originates from the periodic alternation between supercritical and subcritical flow states on the delta topset just upstream of the shoreline i e the topset foreset break of the delta the alternation in turn depends on the distance from the topset foreset break to the nearest hydraulic jump immediately upstream when the hydraulic jump is still in close proximity to the river mouth delta shore it reworks existing topset deposits and perhaps upper foreset deposits as well as it migrates upstream reworked sediment is then entrained into the subcritical flow between the shore and the hydraulic jump which then emplaces this fine suspended sediment onto the foreset slope as the hydraulic jump moves sufficiently far upstream of the mouth the topset flow becomes supercritical with a flow velocity sufficient to transport fine sediment offshore beyond the foreset under these conditions the sediment emplaced on the foreset tends to be coarser material deposited via avalanching or proximal deposition from suspension the details of this selective sedimentation vary according to the material in the topset bed near the mouth that is available for entrainment into the subcritical flow regardless of the details however distinct cyclic sedimentation of the delta foreset can be sustained as long as the inflow conditions of water and sediment dictate the formation of cyclic steps on the alluvial bed of the topset such hydraulic autogenesis accounts for a set of stratigraphic features that are common in ancient gilbert deltas

sedimentary imprints of former ice sheet margins insights from an end ordovician archive sw libya fromthe proterozoic to the quaternary the evolution of the earthwas characterised by recurrent periods of glaciation however the margins of many ancient ice sheets are poorly defined on palaeogeographic reconstructions the extent and outlines of ancient ice sheets can be better understood through careful documentation of sediments deposited at the ice sheet margin an outstanding example is provided herein based on an end ordovician archive in libya tihemboka area murzuq basin the four sets of structures include i subglacial glaciotectonic structures and soft sediment deformations from flowing glacier ice such as intraformational glacial striae intraformational deformation shear planes sheath folds normal microfaults and large scale glaciotectonic folds and thrusts ii structures resulting from overpressured subglacial meltwater flows such as clastic dykes and tunnel valleys iii proglacial depositional structures and facies related to highmagnitude meltwater floods such as sandstone intraclasts large scale bedforms resulting from supercritical flows climbing dune cross stratification and kettle holes and iv deformation structures resulting from free floating and nonglacier ice such as ice keel scours and ice crystal marks such a set of structures points to an ice marginal essentially continental depositional setting and provides an excellent suite of criteria to identify margins of ancient ice sheets in the stratigraphic record at a regional scale a reconstruction through time and space of the related depositional wedge is proposed this corresponded to a seismic scale n120 m in thickness 40 km in length ice marginal wedge in front of an essentially warm based ice sheet inducing concomitant large scale glaciotectonic deformation glacial basin and tunnel valley downcuttings the related ice front was associated with high energy meltwater flows feeding a network of deeply incised proglacial channels downstream and beyond them a fluvioglacial deltaic system shallow ice marginal permafrost most likely affected the depositional wedge at a larger scale the tihemboka ice marginal wedge is interpreted as related to a stillstand period over the gondwana platform developed over an estimated interval of a few thousands of years based on these data the conditions that arose in a particularly favourable context for the development the preservation and the identification of ice marginal wedges in the geological record are reviewed significant meltwater derived sediment deposition and aggradation in an accommodation space resulting either from preglacial inheritance glacial downcuttings and or glacio isostatic lithospheric flexure or active tectonic subsidence 1 myr are required for their formation and subsequent preservation

geology and geochronology of magnetite apatite deposits in the ning wu volcanic basin eastern china the ning wu volcanic basin is an important part of the middle lower yangtze river valley metallogenic belt in eastern china where magnetite apatite deposits are common these magnetite apatite deposits can be classified into two types the first type includes the washan taocun heshangqiao and dongshan deposits which are hosted in diorite porphyry and adjacent volcanic rocks the second type includes gushan baixiangshan and hemushan deposits developed at the contact between gabbro diorite and sedimentary rocks we used 40ar 39ar dating on phlogopite and u pb la icp ms dating of zircon in ore related diorite porphyry and gabbro diorite to determine the timing of iron mineralization in the basin the ages of the magnetite apatite deposits such as washan taocun heshangqiao gushan baixiangshan hemushan deposits are from 130 ma to 131 ma thus the magnetite apatite deposits in the ning wu volcanic basin all formed at about 130 ma later than the skarn and porphyry cu au deposits in the adjacent fault uplift areas such as edongnan jiu rui anqing guichi and tongling clusters that are between 146 ma and 135 ma based on available petrological and geochemical data the magnetite apatite deposits in the ning wu volcanic basin are interpreted to have formed under regional lithospheric extension and thinning and ore forming elements were derived from basaltic melts sourced from enriched lithospheric mantle and the crust

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

petrogenesis of late mesozoic granitoids and coeval mafic rocks from the jiurui district in the middle lower yangtze metallogenic belt of eastern china geochemical and sr nd pb hf isotopic evidence abstract large scale cu au mineralization is associated with the late mesozoic granitoids in the jiurui district of the middle lower yangtze mineralization belt in eastern china to constrain the petrogenesis of these granitoids and coeval mafic rocks a detailed geochemical and sr nd pb hf isotopic study was performed the jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry these granitoids are characterized by sio 2 and k 2 o contents of 58 8 wt to 68 6 wt and 1 9 wt to 5 7 wt respectively these granitoids show relatively high mgo contents 1 0 wt to 3 1 wt average 2 1 wt and high mg values 39 to 70 average 54 the jiurui granitoids are enriched in light rare earth elements lree large ion lithophile elements lile and compatible trace elements cr ni and v but are relatively depleted in nb ta y and yb these rocks show a negligible negative eu anomaly eu eu 0 76 1 13 average 0 91 and nearly no negative sr anomaly the whole rock initial 87 sr 86 sr ratios range from 0 7060 to 0 7092 and the e nd t values vary from 5 4 to 2 0 the granitoids show radiogenic pb isotopic ratios with values of 206 pb 204 pb 17 93 18 21 207 pb 204 pb 15 55 15 58 and 208 pb 204 pb 38 16 38 56 for the plagioclases the zircon hf isotopic compositions show e hf t values from 11 8 to 2 4 the coeval mafic rocks consist of lamprophyre diabase and fine grained mafic dyke these rocks are characterized by sio 2 contents ranging from 47 6 wt to 54 8 wt with a negative eu anomaly and a positive to negative sr anomaly the whole rock initial 87 sr 86 sr ratios range from 0 7059 to 0 7071 and the e nd t values vary from 3 8 to 1 4 by comparing the geochemical and isotopic compositions of the jiurui granitoids and the coeval mafic rocks we conclude that the granitoids are similar to adakites that were likely related to the delamination processes and the coeval mafic rocks may have originated directly from enriched lithospheric mantle the thickened lower continental crust and underlying enriched lithospheric mantle may have been simultaneously delaminated into the asthenospheric mantle this process led to the partial melting of the thickened lower crust and the enriched lithospheric mantle and the melts experienced an interaction with the asthenospheric mantle during ascension mafic melts could be generated from the enriched lithospheric mantle which was heated by the upwelling asthenospheric mantle the geochemical and isotopic compositions of mafic rocks were most likely controlled by the afc process a geochemical and isotopic comparison of the granitoids in the jiurui district with those of two other districts e g angui and tongling in the same mineralization belt indicates that a significant crust mantle interaction played a crucial role in their petrogeneses and metallogeneses from the southwest to northeast in this metallogenic belt the proportion of mantle component that was involved in the granitic magma shows a decreasing trend from the jiurui to the angui and tongling districts it is suggested that the juirui district has the highest potential for a significant amount of cu au accumulation because the mantle is an important supply for these metals

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

simultaneous measurement of sulfur and lead isotopes in sulfides using nanosecond laser ablation coupled with two multi collector inductively coupled plasma mass spectrometers abstract we herein report the coupling of a nanosecond laser ablation system with a large scale multi collector inductively coupled plasma mass spectrometer nu1700 mc icpms np 1700 and a conventional nu plasma ii mc icpms np ii for the simultaneous laser ablation and determination of in situ s and pb isotopic compositions of sulfide minerals we found that the required aerosol distribution between the two spectrometers depended on the pb content of the sample for example for a sulfide containing 100 3000 ppm pb the aerosol was distributed between the np 1700 and the np ii spectrometers in a 1 1 ratio while for lead contents 3000 and

magmagenesis in a subduction related post collisional volcanic arc segment the ukrainian carpathians abstract calc alkaline magmatism in the south west ukraine occurred between 13 8 and 9 1 ma and formed an integral part of the neogene subduction related post collisional carpathian volcanic arc eruptions occurred contemporaneously in two parallel arcs here termed outer arc and inner arc in the ukrainian part of the carpathians outer arc rocks mainly andesites are characterized by lile enrichment e g k and pb nb depletion low compatible trace element abundances high 87sr 86sr high 18o and low 143nd 144nd isotopic ratios 0 7085 0 7095 7 01 8 53 0 51230 0 51245 respectively inner arc rocks are mostly dacites and rhyolites with some basaltic and andesitic lavas they also show low compatible element abundances but have lower 87sr 86sr 18o and higher 143nd 144nd ratios 0 7060 0 7085 6 15 6 64 0 5125 0 5126 respectively than outer arc rocks both high nb and low nb lithologies are present in the inner arc based on the lile enrichment especially pb a higher fluid flux is suggested for the outer arc magmas compared with those of the inner arc combined trace element and sr nd o isotopic modelling suggests that the factors which controlled the generation and evolution of magmas were complex compositional differences between the inner and outer arcs were produced by introduction of variable proportions of slab derived sediments and fluids into a heterogeneous mantle wedge and by different extents of upper crustal contamination degrees of magmatic fractionation also differed between the two arcs the most primitive magmas belong to the inner arc isotopic modelling shows that they can be produced by adding 3 8 subducted terrigenous flysch sediments to the local mantle wedge source up to 5 upper crustal contamination has been modelled for fractionated products of the inner arc the geochemical features of outer arc rocks suggest that they were generated from mantle wedge melts similar to the inner arc primitive magmas but were strongly affected by both source enrichment and upper crustal contamination assimilation of 10 20 bulk upper crust is required in the afc modelling assuming an inner arc parental magma we suggest that magmagenesis is closely related to the complex geotectonic evolution of the carpathian area several tectonic and kinematic factors are significant 1 hydration of the asthenosphere during subduction and plate rollback directly related to collisional processes 2 thermal disturbance caused by ascent of hot asthenospheric mantle during the back arc opening of the pannonian basin 3 clockwise translational movements of the intracarpathian terranes which facilitated eruption of the magmas

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

an ice contact rhythmite turbidite succession deposited during the november 1996 catastrophic outburst flood jokulhlaup skeiðararjokull iceland abstract this paper presents new evidence of coarse grained deposition from a turbulent suspension within a low energy slack water location during a recent well documented volcanically related high magnitude glacier outburst flood or jokulhlaup skei ararjokull iceland this study uses established spatial and temporal constraints on processes observed during the november 1996 jokulhlaup to interpret resultant flood sediments coarse grained sediments were deposited within flood slack water conditions from suspension load by repeated turbulent flow pulses with durations of seconds minutes depositional processes are thought to be analogous to turbidity currents a minimum thickness of 15 m of rhythmites record suspended sediment dynamics at a conduit mouth during the late rising and early falling stages of the jokulhlaup the morphology and sedimentology of deposits in a large ice walled chamber are consistent with previous models proposed for bar deposition during cataclysmic floods flood flows within subglacial conduits and ice walled open channels were sufficiently powerful to carry material up to boulder size in suspension macro turbulent flows carried huge quantities of suspended sediment to high levels within the main outlet channel high frequency short duration flow pulses entering a complex ice walled channel geometry generated highly unsteady and non uniform flows capable of both erosional and depositional work this study lends support to the deposition of multiple rhythmites per flood under main flow slack water conditions identification of high magnitude jokulhlaups in the ice marginal sedimentary record will depend on the identification and correct interpretation of feeder channel and slack water turbidite sediments the results described here may also have application to rhythmic deposits formed by large turbulent flows in other environmental settings

genesis of chating cu au deposit in the middle lower yangtze river metallogenic belt eastern china implications from magnetite and biotite geochemistry abstract porphyry deposits developed in intracontinental settings have some geological characteristics that differ from those developed in arc related continental margins the chating deposit is a newly discovered cu au deposit in the middle lower yangtze river metallogenic belt mlyb eastern china we carried out detailed petrographic observations and major and trace element analyses of different types of magnetite and biotite from the host quartz diorite porphyry and different alteration zones in chating to elucidate the genesis of chating deposit alteration types in chating include skarn sodic calcic potassic and phyllic and copper mineralization is closely associated with potassic alteration of quartz diorite porphyry the different types of magnetite and biotite at chating show distinctive geochemical characteristics higher ti and al in magmatic magnetites and biotites compared to the hydrothermal minerals indicate higher temperature and pressure in the quartz diorite porphyry higher v in magmatic magnetites and lower xmg in magmatic biotites indicate higher fo2 similar mineral geochemistry from typical worldwide porphyry deposits for example al2o3 tio2 feot mgo na2o iv f and iv cl contents in biotite and ni cr ti al sn and ga in magnetite indicate a predominately magmatic fluid source differences in si ca co ni mg and mn in different types of magnetite and mno cao sio2 differences in two types of biotite from typical porphyry copper deposits show the influence of external fluids moreover high iv f values and low iv cl values in biotites demonstrate that the magmatic hydrothermal system in chating was enriched in cl and lacked f consistent with the importance of cl in the transport of cu based on different discrimination diagrams for magnetite such as ni cr versus ti ni cr mn versus ti v and al mn versus ti v and the geochemical similarities of biotite from chating and other porphyry deposits combined with the similarity of alteration assemblages we conclude that chating has porphyry cu au affinities but the hydrothermal system was affected by external fluids in contrast to more typical subduction related porphyry deposits

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

geochronological and geochemical constraints on genesis of the adakitic rocks in outang south tan lu fault belt northeastern yangtze block abstract the outang intrusion was newly found near the south tan lu fault belt stlf of the northeastern margin of yangtze block due to the excavating construction of the beijing shanghai high speed railway observations show that lithology of the outang intrusion is intermediate rock series mainly composed of monzodiorite and quartz monzonite major and trace elements zircon u pb dating and hf isotope were analyzed two ages of 124 6 2 9 ma mswd 0 60 n 29 and 129 2 4 1 ma mswd 1 5 n 21 are obtained showing that the regional igneous activity was in early cretaceous being consistent with the massive yanshanian magmatic events in eastern china the quartz monzonite was identified as a high mg adakitic rocks showing geochemical features of high si high k and low sr which indicates that the igneous genesis may be results of partial melting of the delaminated lower crust the negative e hf t values with much older t dm2 ages indicate that the original magma may derive from remelting of ancient continental crust a tectonic model has been proposed to account for the massive subduction of the pacific plate beneath eastern china in jurassic with effect of delamination and thinning from which we conjecture that the archean materials could compose the basement of the stlf caused by massive subduction of the pacific plate beneath the eastern china continent

ridge collision slab window formation and the flux of pacific asthenosphere into the caribbean realm mantle wedge derived arc volcanism ceased in southern costa rica after ca 8 ma because of subduction of the aseismic cocos ridge beneath the central american arc and the subsequent opening of a slab window geochemical and isotopic compositions of small volumes of adakitic and alkalic backarc lavas erupted between 5 8 and 2 ma identify a source derived from the galapagos plume the presence of this source is explained by an influx of pacific upper mantle into the caribbean mantle wedge through a slab window where the alkalic rocks form by melting of the upwelling mantle and the adakites result from melting of the leading edge of the subducted cocos ridge by using geochemical and isotopic signatures we trace this upper mantle flow beneath central america from southern costa rica northward at a rate of 40 mm yr

upslope migrating bedforms in a proglacial sandur delta cyclic steps from river derived underflows abstract backstepping cross strata on steep foresets of a gilbert type proglacial fluviodeltaic system are ascribed to cyclic steps and other associated supercritical bedforms they provide insight into how sandur river flows transition into the marine realm these sedimentary structures are located on steep foresets up to 17 with corresponding top lying flat based topsets in an upper pleistocene delta on the north shore of the gulf of st lawrence quebec canada packages of backstepping cross strata of sand and gravel lying in the lower part of the delta front outcrop are organized in 10 20 m spaced pseudo foresets with a mean slope of 11 12 seawards backstepping strata include frequent internal erosion surfaces that onlap upslope on pseudo foresets and are interpreted as cyclic steps narrow deep and asymmetrical scours and upslope climbing cross beds are interpreted as chutes and pools and antidunes respectively very shallow 15 m depositional paleo bathymetry is inferred from the preservation of the delta brink the well organized stratal pattern in cyclic step to antidune deposits indicates relatively steady and uniform flow patterns there is insufficient distance for a headscarp large enough to transform to the volume of observed accreted sands or for a flow transformation from a gravitational collapse to net depositional cyclic steps these deposits are sandier than the topsets beds and are thus not derived from them but rather correspond to topset erosional surfaces the development of cyclic steps from hyperpycnal flows was likely enhanced by tidal drawdown processes the resulting sediment laden supercritical flows plunged inertially and evolved into an underflow that generated the cyclic steps on the upper foresets the cyclic steps have a high aspect ratio and represent an end member of coarse grained sediment deposited on steep slopes in contrast to low gradient low aspect ratio muddy deposits

zircon ce4 ce3 ratios and ages for yulong ore bearing porphyries in eastern tibet yulong ore bearing porphyries along the northwestern extension of the red river ailao shan fault system in eastern tibet consist of five porphyry deposits containing a total of more than 8 million tons of copper resources u th pb laser inductively coupled plasma mass spectrometry dating of zircon shows that the porphyries were emplaced in early tertiary 41 2 36 9 ma covering a period of 4 3 ma with formation ages decreasing systematically from northwest to southeast the start of porphyry magmatism coincided with the onset of transpressional movement along the red river ailao shan fault system implying a close link between these two events age sequence in intrusions can be plausibly explained by assuming that a region of melting in the lower northwestern plate moved southeasternward along the tuoba mangkang fault relative to the upper plate zircon grains from the yulong ore bearing porphyries have higher ce4 ce3 than those from barren porphyries in the region this suggests that the ore bearing porphyries crystallized from a relatively oxidized magma which has important implications for future ore exploration in the region and other cu deposits in convergent margin environments in general

sediment waves in a modern high energy glacilacustrine environment a 4 7 km2 field of sediment waves occurs in front of the slims river delta in kluane lake the largest lake in the yukon territory slims river heads in the kaskawulsh glacier part of the st elias ice field and discharges up to 400 m3 s 1 of water with suspended sediment concentrations of up to 7 g l 1 the 19 km long sandur of slims river was created in the past 400 years since kaskawulsh glacier advanced and dammed the lake and the sandur has advanced into kluane lake at an average rate of 48 m a 1 however this rate is decreasing as flow is diverted from slims river because of the retreat of the kaskawulsh glacier the sandur and a road constructed on the delta remove coarse grained sediment so the river delivers dominantly mud to the lake inflow during summer generates quasi continuous turbidity currents with velocities up to 0 6 m s 1 the front of the delta consists of a plane surface sloping lakeward at 0 0188 1 08 a field of sediment waves averaging 130 m in length and 2 3 m in amplitude has developed on this surface slopes on the waves vary from 0 067 3 83 i e sloping in the opposite direction to the regional slope to 0 135 7 69 the internal structure of the sediment waves as documented by seismic profiling shows that sedimentation on the stoss portion of the wave averages 2 7 times that on the lee portion rates of sediment accumulation in the wave field are about 0 3 m a 1 so these lacustrine waves have formed in a much shorter period of time less than 200 years and are advancing upslope towards the delta much more quickly 1 to 2 m a 1 than typical marine sediment waves these waves formed on the flat surface of the lake floor apparently in the absence of pre existing forms and they are altered and destroyed as the wave field advances and the characteristics of the turbidity currents change

early pleistocene palaeoenvironments at the time of the homo antecessor settlement in the gran dolina cave atapuerca spain hominin remains unearthed from level td6 2 of gran dolina have been dated to slightly more than 0 8 ma owing to the importance of this discovery every effort is being made to reconstruct the environment where these hominins once lived in this paper the mutual climatic range and habitat weighting methods are applied to the herpetofaunal assemblages in order to estimate climatic and environmental parameters td6 2 is thus characterized by a warm and humid climate mean annual temperature is estimated at 2 1 c higher than at present in burgos with a greater increase in temperature during summer 3 1 c than during winter 1 4 c rainfall was more abundant than at present 407 2 mm occurring as at present principally during spring and autumn humid meadows and riparian woody habitats were common the association between warm climatic conditions and the not fully developed forest suggests that the several episodes of high intensity occupation in td6 2 may correspond to a recolonization by homo antecessor of the high inland plateaus of the iberian peninsula from the mediterranean seashore using the ebro valley as a savannah type corridor after a cold glacial period copyright 2013 john wiley sons ltd

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

occurrence of hyperpycnal flows and hybrid event beds related to glacial outburst events in a late ordovician proglacial delta murzuq basin sw libya abstract a late ordovician glacially related delta is documented based on architecture and facies from outcrops in the western murzuq basin libya sandstone megabeds highlight clinoform geometries of a proglacial low angle shallow water delta the progradational wedge extends over 25 km from the sse to the nnw and is about 100 m thick two types of clinothems have been distinguished and eleven facies sequences are characterized in relation with their along slope positions sand prone facies sequences in type 1 clinothems relate to high magnitude low frequency glacial outburst floods generating a freshwater highly concentrated plunging hyperpycnal flow at the river mouth during the waxing stage the slope adjustment of an out of grade profile causes significant erosion the resulting additional sediment charge involves along foresets a downslope flow transformation into a co genetic sandy debris flow and high density turbidity flow hybrid event beds including linked debrites and turbidites are the resulting deposits in the lower slope decreasing sediment concentration of the high density turbidity flow leads to sediment lofting and to a second flow transformation resulting in a lower density turbidity flow and a concomitant rising sediment plume deposition results in crude ripple cross stratification debrite deposition is temporally restricted to an early segment of the rising limb of the flood hydrograph during the ensuing waxing stage uninterrupted sustained flow conditions maintain up to the peak flow permitting the aggradation of thick sandstone successions with crude ripple cross stratification during the waning stage backstepping of the whole depositional system leads to prevailing sedimentation in the delta plain setting mouth bar development and channel plugs are characterized by climbing dune cross stratification cdcs shale prone sedimentation in type 2 clinothems essentially corresponds to background ablation related sedimentation but also includes minor debrite bearing outburst related event beds this study documents the links between glacial outbursts hyperpycnal flows and hybrid beds in low angle delta settings and illustrates a type of proximal sand dominated hyperpycnite dam failure of subglacial lakes is inferred for the outburst generation comparison with modern and pleistocene examples may suggest that outburst events were days to several years in duration type 1 clinothem with a 1 40 ky recurrence period type 2 clinothem

origin of mesozoic adakitic intrusive rocks in the ningzhen area of east china partial melting of delaminated lower continental crust to the best of our knowledge modern adakites have not been documented in a nonarc environment we report geochemical and isotopic data for early cretaceous anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction the anjishan adakitic intrusive rocks which are exposed in the ningzhen area of east china have high sr y and la yb ratios coupled with low yb and y as well as relatively high mgo contents and mg numbers mg 0 4 0 6 similar to products from slab melting however low n d t values 6 8 to 9 7 and high 8 7 sr 8 6 sr i 0 7053 0 7066 are inconsistent with an origin by slab melting the tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust high sr y and la yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting implying that the crustal thickness exceeded 40 km in the early cretaceous the present thickness of the crust in the ningzhen area is only 30 km and therefore the crust appears to have been thinned by at least 10 km since the early cretaceous the relatively high mgo contents and mg of the anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks possibly coinciding with lower crustal delamination which would also account for the observed thinning

structureless coarse tail graded bouma ta formed by internal hydraulic jump of the turbidity current abstract turbidity currents are commonly super critical if they travel on slopes steeper than 0 001 hence upon deceleration such flows must pass a hydraulic jump it is therefore surprising that sedimentary features related to the hydraulic jump are so poorly known and not clearly related to the bouma sequence to study this missing link a stability diagram of bed forms generated by decelerating initially super critical turbidity currents is presented here to sketch the position of hydraulic jump deposits relative to super and sub critical bed forms observed in turbidites the axes of the diagram are formed by the densiometric froude number the grain size and the particle fall out rate experimental evidence shows that the hydraulic jump is hardly manifested in the deposit if turbidity currents pass the jump as a low concentration single phase suspension flow only those turbidity currents that develop two phase suspension flow with a super critical flowing traction carpet cause vigorous erosion and liquefaction of the substrate at the jump locality to produce rip up of the substrate rip up clasts and flame structures which are trapped in structureless coarse tail graded deposits characteristic of the classic bouma ta unit the location of the jump is sensitive to density velocity variations of the traction carpet and can shift rapidly up and down the slope this would explain why structureless coarse tail graded deposits such as bouma ta develop sheet like

morphological evolution of a well constrained subaerial subaqueous source to sink system wabush lake since 1964 the iron ore company of canada has deposited iron tailings resulting from mining operations into wabush lake western labrador canada this activity has resulted in a continuous hyperpycnal flow flowing over the lake floor bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental iron ore company of canada plans to maintain safe disposal strategies of tailings into the lake here this dataset is used to study the evolution of different channels present in wabush lake and their link with knickpoints found at the head of most of these channels the channels show notable evolution from one survey to the next some knickpoints and channels may be followed throughout more than one survey the evolution of these knickpoints is the process responsible for the creation of erosional channels the context in which they appear as well as the evolution of some of the subaqueous channels is analysed cyclic steps and sediment waves are also found in the lake these rhythmic bedforms also created by the passage of turbidity currents are analysed sediment waves found in wabush lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment

lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows from cyclic steps to humpback dunes abstract the preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record although these bedforms are known from a variety of depositional environments this field based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps chutes and pools antidunes and humpback dunes from three dimensional outcrops the well exposed middle pleistocene successions from northern germany comprise glacilacustrine ice contact subaqueous fan and glacial lake outburst flood deposits the studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high energy depositional environments such as fluvial settings coarse grained deltas or turbidite systems deposits of cyclic steps occur within the glacial lake outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets cyclic steps formed due to acceleration and flow thinning when the glacial lake outburst flood spilled over a push moraine ridge these bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes and pools and antidunes the subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms which are interpreted as deposits of aggrading stationary antidunes which require quasi steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation humpback dunes are characterised by downflow divergent cross stratification displaying differentiation into topsets foresets and bottomsets and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common the absence of planar parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions the large scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows which was strongly affected by the occurrence of hydraulic jumps small scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge bed topography and pulsating unstable flows

partial melting of thickened or delaminated lower crust in the middle of eastern china implications for cu au mineralization abstract field relations isotope systematics and plate tectonic reconstructions require that felsic adakites in the yangtze block and the dabie orogen eastern china were not derived from a subducting slab despite the signature of a mantle component in the contemporaneous mafic adakite hosts of cu au deposits in the same areas the apparently contradictory requirements are accounted for by a a deep crustal melting origin for barren adakites and b a crustal delamination origin followed by ascent through lithospheric mantle for adakites associated with mineralization the crustal delamination process associated with the prospective porphyries duplicates the metallogenically essential aspects of the subduction environment the importance of adakitic magmas in the genesis of porphyry style cu au deposits is affirmed by these findings but the range of prospective tectonic environments is extended to include an important intraplate postsubduction setting the porphyries of eastern china demonstrate

geochemistry and nd sr isotopic studies of late mesozoic granitoids in the southeastern hubei province middle lower yangtze river belt eastern china petrogenesis and tectonic setting abstract a geochemical and isotopic study was carried out for the mesozoic yangxin tieshan and echeng granitoid batholiths in the southeastern hubei province eastern china in order to constrain their petrogenesis and tectonic setting these granitoids dominantly consist of quartz diorite monzonite and granite they are characterized by sio 2 and na 2 o compositions of between 54 6 and 76 6 wt and 2 9 to 5 6 wt respectively enrichment in light rare earth elements lree and large ion lithophile elements lile and relative depletion in y concentrations ranging from 5 17 to 29 3 ppm and yb 0 34 2 83 ppm with the majority of the granitoids being geochemically similar to high sio 2 adakites hsa their initial nd e nd 12 5 to 6 1 and sr 87 sr 86 sr i 0 7054 0 7085 isotopic compositions however distinguish them from adakites produced by partial melting of subducted slab and those produced by partial melting of the lower crust of the yangtze craton in the late mesozoic the granitoid batholiths in the southeastern hubei province exhibit very low mgo ranging from 0 09 to 2 19 wt with an average of 0 96 wt and large variations in negative to positive eu anomalies eu eu 0 22 1 4 especially the tieshan granites and yangxin granite porphyry eu eu 0 22 0 73 geochemical and nd sr isotopic data demonstrate that these granitoids originated as partial melts of an enriched mantle source that experienced significant contamination of lower crust materials and fractional crystallization during magma ascent late mesozoic granitoids in the southeastern hubei province of the middle lower yangtze river belt were dominantly emplaced in an extensional tectonic regime in response to basaltic underplating which was followed by lithospheric thinning during the early cretaceous

3 d architecture and sequence stratigraphic evolution of a forced regressive top truncated mixed influenced delta cretaceous wall creek sandstone wyoming u s a abstract ground penetrating radar gpr is used to delineate the 3 d facies architectural elements and examine the evolution of a top truncated forced regressive mixed influenced delta front in the cretaceous wall creek member of the frontier formation wyoming the gpr data provide a bridge between outcrop facies architecture and recently published high resolution 2 d seismic studies of quaternary delta systems the gpr data were integrated with outcrops photomosaics cores and gps data two orthogonal grids of 2 d gpr profiles provide information on the 3 d facies architecture and stratigraphy of the deltaic deposits three main gpr architectural elements are identified within the delta front 1 mouth bars are characterized by seaward dipping reflections foreset beds in dip view and mounded bidirectionally downlapping reflections in strike view 2 shallow delta slope channels show truncation and onlap and also show low angle landward northwest dipping reflections the mouth bars are locally interrupted by 3 sub horizontal radar reflections that are interpreted as tidally modulated bars within the mouth bar radar facies both top preserved proximal and top truncated distal examples are observed top preserved proximal bars show evidence of mounded bar crests and landward accretion as is observed in the upstream end of mouth bars on the modern atchafalaya delta in the gulf of mexico distal bar deposits primarily comprise the top truncated seaward dipping foresets the gpr interpretation shows two laterally overlapping delta lobes interpreted to represent autocyclic delta switching the older lower lobe forms a fan shaped delta lobe composed of top truncated coalesced mouth bars the second phase of bars is largely top preserved building over the older bars the presence of thicker bedsets and upstream accretion suggests that the younger lobe was quickly abandoned as seen in the overlying transgressive ravinement although marine erosion during transgression was less effective on these later stage bar deposits ravinement increased landward a comparison of the architectural elements at a more regional scale in two separate wall creek delta lobes murphy creek and raptor ridge 30 km apart indicates that the bar complexes were deposited on the delta fronts as accretionary forced regressive deposits during a relative sea level fall the older river dominated deltaic deposits at the murphy creek site prograded southeastward 124 whereas the younger and more tidally influenced raptor ridge bar deposits expanded southward 171 before final abandonment and regional transgression the most distal lowstand lobe sediments within the offlapping parasequence at raptor ridge are more completely preserved and also show the greatest tidal influence compared to the more severely top truncated murphy creek which is in an otherwise more landward location this challenges the notion that tidal facies are predominantly associated with transgressive or highstand systems tracts greater preservation of deltaic facies in forced regressive and lowstand deltas as shown here has also been documented in quaternary shelf edge deltas such as the lagniappe in the gulf of mexico and the mahakham in kalimantan

direct sediment transfer from land to deep sea insights into shallow multibeam bathymetry at la reunion island abstract submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins this contribution offers a detailed picture of canyon heads off la reunion island with high resolution multibeam bathymetry in the water depth range of 4 220 m the present feeding of the cilaos turbidite system one of the largest modern volcaniclastic systems in the world is deduced from morphological and sedimentological interpretations of newly acquired data the study highlights small scale sedimentary features indicating hydrodynamic and sedimentary processes a direct connexion between the saint etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar this direct connection supplied by river torrential floods cyclonic floods every two or three years suggests the continuity of high density fluvial flows to submarine gravity flows forming hyperpycnal flows in the canyon the initiation of secondary submarine gravity flows by storm waves large austral waves and cyclonic waves is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar bedforms in active canyon axis are considered as an indicator of the frequent activity of high density turbidity currents moreover a morphological record of last glacial and deglacial sea level variations is preserved and particularly the last glacial maximum sea level with the presence of small vertical cliffs observed in this bathymetric data which likely corresponds to a paleo shoreline or paleo reefs

os os dating of copper and molybdenum deposits along the middle and lower reaches of the yangtze river china the 186 os 187 os and 188 os 187 os dating techniques were modified and applied to molybdenites from two cu vein deposits and three mo skarn deposits along the middle and lower reaches of the yangtze river china the results show that these deposits formed at 138 to 133 ma identical to the ages of 140 to 130 ma for the host granitoids re os and os os ages of two of the samples agree within analytical uncertainties the close temporal relationship between the granitoid intrusions and the formation of the deposits supports a magmatic model for the origin of these deposits the results show that the novel os os dating technique is capable of resolving geologic problems although the accuracy obtained by the present work 1 2 is lower than that of the re os method

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

temporal relationship between granite cooling and hydrothermal uranium mineralization at dalongshan in china a combined radiometric and oxygen isotopic study abstract a combined study using multi radiometric dating and oxygen isotopic geothermometry was carried out for mesozoic quartz syenite alkali feldspar granite and associated hydrothermal uranium mineralization at dalongshan in the middle lower yangtze valley of east central china radiometric dating of the quartz syenite yields a whole rock rb sr isochron age of 135 6 4 3 ma a zircon u pb isochron age of 132 9 2 2 ma and k ar ages of 126 2 118 3 and 94 4 ma for hornblende biotite and orthoclase respectively the alkali feldspar granite yields a whole rock rb sr isochron age of 117 3 3 3 ma a zircon u pb isochron age of 114 7 2 1 ma and k ar ages of 112 2 109 3 and 88 4 ma for hornblende biotite and orthoclase respectively oxygen isotope thermometry for both granites gives temperatures of 685 to 720 555 to 580 435 to 460 and 320 to 330 c for hornblende magnetite biotite and orthoclase respectively when paired with quartz the systematic differences among the ages by the different techniques on the different minerals are used to reconstruct the cooling history of the granite the results yield rapid cooling rates of 27 4 to 58 6 c ma from 800 to 300 c in the early stage but slow cooling rates of 6 3 to 7 2 c ma from 300 to 150 c in the late stage the regular sequence of oxygen isotope temperatures for the different quartz mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of both radiometric and o isotopic systems during granite cooling pitchblende u pb isochron dating yields an uranium mineralization age of 106 4 2 9 ma which is younger than the age of the granite emplacement and thus considerably postdates the time of magma crystallization but is close to the closure time of the k ar system in the biotite this points to a close relationship between granite cooling and ore forming process it appears that hydrothermal mineralization took place in the stage of slow cooling of the granite whereas the rapid cooling of the granite was concurrent with the migration of hydrothermal fluids along fault structures therefore the activity of the ore forming hydrothermal system is temporally dictated by the cooling rates of the granite and may lag about 25 to 30 ma behind the crystallization timing of associated granite

initiation of turbidity currents outcrop evidence for eocene hyperpycnal flow turbidites abstract the most widely used although not as widely documented explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites such instantaneous sediment failures generate short lived surge type flows that deposit turbidite beds described as bouma sequences in this communication we present data from the eocene central basin of spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds deposited by gradual aggradation from sustained flows sustained flows are long lived and more or less continuous they can be generated by a variety of mechanisms e g 1 instability during volcanic eruptions and the consequent remobilisation of unconsolidated material 2 seismically triggered subaerial sliding within the drainage 3 storm surges 4 retrogressive slope failure 5 breaching and 6 hyperpycnal flows our database shows that in the eocene central basin the sustained flows were generated by hyperpycnal flows i e by direct river effluent the hyperpycnal flow turbidites have been recognized on the basis of 1 physical connection between fluvial and turbidite channels at the shelf edge 2 abundance of thick turbidite sandstone beds 3 sand prone nature of the turbidite systems 4 downslope changes of individual thick sandy turbidite beds and their collapsed pinch out segments 5 great abundance of continental material leaves coal fragments in turbidite beds 6 low abundance of associated slumped or debris flow beds and 7 the occurrence of turbidites in systematically accreted shelf margins these features strongly suggest that hyperpycnal flow generated by direct river effluent deposited significant number of turbidite beds in the documented slope and basin floor turbidite successions we also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level the turbidite beds were studied in the context of seismic scale 1 15 km dip oriented outcrops by measuring detailed vertical sections following individual beds and packages of beds downslope for distances over 5 km lateral mapping and helicopter taken photomosaics

supercritical and subcritical turbidity currents and their deposits a synthesis common facies models of turbidite deposits are based on idealized sequences of turbidite units which are assumed to reflect the depositional processes of a decelerating turbidity current we show how suites of turbidite units i e distinct turbidite facies associations that are easily described from core and outcrop may characterize the entire range of large scale dynamics of turbidity currents enabling estimates of their densimetric froude number fr subcritical versus supercritical and suspension fall out rate stratified versus nonstratified flows the linking of facies associations with large scale flow dynamics resolves process facies links that were hitherto unresolved by the common turbidite facies models

geochemical and zircon u pb geochronological study of the yangshan a type granite insights into the geological evolution in south anhui eastern jiangnan orogen abstract the early cretaceous yangshan granite is an a type granitic intrusion that was emplaced along the eastern jiangnan orogen in southern anhui province south china the yangshan intrusion mainly consists of syenite porphyry 127 0 0 6 ma and alkali feldspar granite porphyry 126 0 1 0 ma as a part of qingyang jiuhuashan complex intrusion the yangshan a type granites have lower mgo cao co sr and higher rb nb th and hree contents with enrichment in large ion lithophile elements lile and light rare earth elements lree and slightly negative eu anomalies however the syenite porphyry and the alkali feldspar granite porphyry differ in terms of zircon ehf t values small variations in the syenite porphyry from 5 5 to 3 7 corresponding to hf model ages tdmc between 1 42 ga and 1 53 ga and large variations in the alkali feldspar granite porphyry from 6 4 to 4 4 yielding tdmc of 0 90 1 59 ga while both rocks also have similar end t values ranging from 7 02 to 5 47 corresponding nd model ages tdmc are 1 37 1 49 ga falling within the hf model ages we take these features to indicate that the qingyang i type granites which are isotopically similar and yangshan a type granites were originated from partial melting of mesoproterozoic neoproterozoic crust with minor juvenile crust input for the alkali feldspar granite porphyry followed by fractional crystallization in combination with previous studies we propose that the cretaceous a type granitic rocks formed between 135 ma and 122 ma implying an important mesozoic extensional event in eastern jiangnan orogen which facilitated underplating of mantle derived magma and crustal heating this may have occurred in a back arc extension in response to the drift of subduction direction of the paleo pacific plate which started as early as 135 ma ago

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

an examination of froude supercritical flows and cyclic steps on a subaqueous lacustrine delta lake chelan washington u s a density driven submarine flows including turbidity currents play an important role in the transfer of sediment into deep water these bottom hugging flows often produce flow transverse bedforms along their path a sedimentological and geophysical survey of the stehekin river delta in lake chelan washington reveals a downslope elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the stehekin river an analysis of the bedform morphologies delta geometry and density contrast between lake and river water suggests that these hyperpycnal flows are froude supercritical the bedforms are likely cyclic steps flow transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes the ability to examine the three dimensional bed configuration produced by natural density driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes

supercritical flow structures on a late carboniferous delta front sedimentologic and paleoclimatic significance deposits of fluvial systems in highly seasonal tropical climates possess unique architectural and facies characters owing to a flood prone regime alternating with lengthy periods of ineffective discharge distally linked deltaic successions should also feature distinctive attributes with great potential to preserve the stratigraphic evidence of exceptional discharge events we describe late carboniferous delta front valley confined sandstones from the pennine basin uk originally deposited at paleoequatorial latitudes during final assembly of the pangean megacontinent and characterized by giant sedimentary structures with repetitively sigmoidal geometry facies traits indicate geologically instantaneous deposition of a large sediment volume from a density current at sustained supercritical flow conditions leading to aggradation of cyclic steps recently identified bedforms developing in high energy flows and of which this is the first complete outcrop example the lack of unconformable erosional surfaces and absence of different associated facies point to a single aggradational event during which the structures attained dimensions comparable to those indicated by seismic data sets from which they are remotely detected on modern seafloors cyclic step formation in a deltaic setting suggests that pangean megamonsoons could have triggered hydrologic events capable of imprinting sedimentologic signatures on shallow marine deposits

genesis of cretaceous igneous rocks and its related large scale porphyry cu au mineralization in chating the middle lower yangtze river metallogenic belt the geochemical constrains abstract the newly discovered large chating porphyry cu au deposit is associated with early cretaceous intrusive rocks in the middle lower yangtze river belt mlyrb eastern china two types of intrusive rocks in the chating area have been identified i e the quartz diorite porphyry related to the cu au mineralization and the diorite porphyry that is ore barren zircon la icp ms u pb dating yields 145 136 ma for the chating intrusions they both belong to high k calc alkaline series with enrichments of large ion lithophile elements liles and light rare earth elements lrees depletions of high field strength elements hfses and heavy rare earth elements hrees and no or slightly negative eu anomalies the quartz diorite porphyry shows high sr contents and sr y ratios low mgo cr and ni contents medium la yb n and mg 34 6 54 6 and low k2o na2o

analysis and study on maoshan nappe tectonic zone in jiangsu stride over the stratigraphic regions of yangzi and the south of the lower reaches of the yangtze river the borderline of stratigraphic regionalism between lishui and yixing liyang areas is the deep fault in the south of the lower reaches of the yangtze river the distribution of mesozoic and cenozoic strata and mesozoic volcanic complex are characteristic of control effect of the deep fault for strata structure and volcanic magmatic activities in yixing and liyang areas the analysis and study on maoshan nappe tectonic zone showed that the sphenoidal thrust tectonic belt of maoshan belonged to climbing nappe structure formed by twice mountain building movements of nappe structure maoshan movement in the late yanshanian movement the characters of neocathaysian tectonic system were reflected fully during the mountain building movement of maoshan nappe structure firstly the regional unconformity pukou movement was caused by pukou formation k2p in late cretaceous and underlying early cretaceous gecun formation k1g as well as other pre cretaceous strata secondly the regional unconformity taizhou movement was caused by taizhou formation e1t in cenozoic paleogene and underlying late cretaceous chishan formation k2c as well as other pre cretaceous strata so the influence range of neocathaysian structural system was very wide especially taking jiangnan deep fault as a background neocathaysian structural system was of far reaching structural significance