submarginal debris transport and till formation in active temperate glacier systems the southeast iceland type locality abstract exhaustive sedimentological analysis of freshly exposed subglacial surfaces and moraines in southern iceland provides diagnostic sedimentological signatures of a debris transport pathways through active temperate glacier snouts and b till production in subglacial traction zones dominated by deforming layers three till end members are recognised based on stratigraphic architecture 1 thin and patchy tills over eroded bedrock 2 single push moraines and complexes and 3 overridden moraines or outwash fans typical till thicknesses are 0 10 1 40 m with each till relating to a deformation event driven by the seasonally tuned processes of glacier sub marginal shearing freeze on squeezing and bulldozing clast form trends demonstrate progressive modification towards mature forms in subglacial traction zones with till being clearly differentiated from scree and glacifluvial deposits clast macrofabric strengths are variable rarely matching those of laboratory shearing experiments except where obviously lodged clasts are abundant they also consistently record former glacier flow directions but localized variability is introduced by bedrock protuberances cavity infill clast interference and freshly imported plucked clasts within tills macrofabrics strengthen from lower b horizon to upper a horizon tills but at the outer edges of sub marginally thickening till wedges or push moraines seasonally driven cycles of squeezing flowage freeze on melt out and bulldozing give rise to a range of clast macrofabric strengths as well as superimposed deformation signatures this reflects two extremes of till emplacement including the more mobile flowing and often liquefied matrixes in push squeeze moraines and in contrast the lodgement deformation and ploughing at the thin end of sub marginal till wedges

mid silurian back arc spreading at the northeastern margin of gondwana the dapingzhang dacite hosted massive sulfide deposit lancangjiang zone southwestern yunnan china abstract the dapingzhang dacite hosted volcanogenic massive sulfide deposit is located in a late paleozoic collisional zone the sanjiang fold and thrust belt characterized by a collage of gondwana derived terranes at the southern margin of the south china yangtze block this area has experienced repeated paleozoic and mesozoic collisional and extensional events and is overprinted by himalayan strike slip and thrust movements the dapingzhang orebody is strongly sheared into discontinuous ore lenses and blocks and is hosted by a several hundred meter thick volcanic rock sequence of dacite with minor metabasalt spilite rhyolite and chert bulk rock nd isotope data give end 429 ma values of 2 to 5 and indicate a dominantly mantle source or origin from young continental crust tdm 800 1000 ma the dacites have distinctly low abundances of ti nb ta zr th and rees which is typical of subduction related volcanism the base metal mineralization occurs as polymetallic massive sulfide mineralization mainly pyrite sphalerite galena chalcopyrite tetrahedrite tennantite and locally barite and as pyrite chalcopyrite stockworks pervasive hydrothermal alteration is dominantly quartz sericite maximum enrichment in gold bismuth selenium and tellurium is at the interface between the stockwork and massive sulfide mineralization styles deeper parts of the stockwork zone are characterized by elevated molybdenum and rhenium whereas the distal parts to the massive sulfide mineralization have high mercury antimony zinc cadmium arsenic lead and silver the metal association and mineral assemblage are typical of volcanic rock hosted massive sulfides in back arc volcanic settings uranium pb dating on zircon by la icp ms defines an age of 429 3 ma 2 n 19 for the dacite sequence rhenium os isotope data on mo rich bulk ore samples define an isochron of 429 10 ma 2 n 9 mswd 0 21 initial 187os 188os 3 1 1 9 common os is very low and the absolute abundances of 187re and 187os define a model age of 429 4 ma n 9 95 confidence the mid silurian dacite sequence and associated massive sulfide mineralization identify a hitherto unknown early rifting and back arc seafloor spreading event at the northeastern gondwana margin related to the early evolution of the paleotethys ocean

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

genetic relationship between granitic magmatism and w mineralization recorded in the nanling scientific drilling sp nlsd 2 in the pangushan w mining district south china abstract the nanling region in south china hosts numerous w dominated polymetallic deposits that are related to mesozoic granites although considerable amounts of age data have been obtained the genetic relationship between granitic magmatism and w mineralization remains unclear the nanling scientific drilling sp nlsd 2 in the pangushan w deposit has penetrated upper devonian sedimentary rocks 4 1 721 9 m sinian sedimentary rocks 721 9 1287 9 m and mesozoic granite 1287 9 2012 1 m the drill hole clearly reveals a zonation including exocontact w bearing quartz veins alkali autometasomatic zone and primary k feldspar granite the k feldspar granite at the depth of 1880 m and rocks of potassium autometasomatic zone at 1414 m and greisenized zone at 1288 m have magmatic zircon grains with u pb ages of 164 8 1 4 ma 161 7 1 6 ma and 153 8 1 2 ma respectively molybdenite re os ages of endocontact mineralization at the depths of 1302 m and 1291 m are 155 9 3 1 ma and 155 0 2 3 ma respectively muscovite ar ar ages of exocontact mineralization at the depths of 1050 and 885 m are 154 9 1 5 ma and 154 0 3 0 ma respectively and molybdenite re os age of exocontact quartz vein type mineralization at 860 m is 152 0 2 6 ma these new ages indicate that the granite emplacement potassium autometasomatism greisenization and w mineralization occurred at 164 8 ma 161 7 ma 153 8 ma and 155 9 152 ma respectively the w mineralization was approximately 9 13 myr younger than the hosting granite the whole rock and feldspar chemical compositions of k feldspar granite potassium autometasomatic zone greisenized zone and feldspar quartz veins indicate the sequence of metal transportation and concentration to form the zonation the granite crystallized from high k calcalkaline metaluminous to peraluminous highly differentiated magmas that were enriched in w and bi during crystallization the magmas underwent potassium autometasomatism caused by post magmatic fluids which were rich in k fe w and rare earth elements ree but poor in na and ca and formed the potassium autometasomatic zone the evolved post magmatic fluids became rich in k si ca ree and w but poor in na and fe and initiated greisenization to generate the greisenized zone which almost exhausted ca ree na and fe of the fluids the later crystallization of feldspar quartz veins exhausted k and caused the residual post magmatic fluids to be rich in si and w the fluids formed w bearing quartz veins with decreasing temperature and pressure the main reason for w enrichment in the hydrothermal fluids was due to the successive crystallization of minerals rather than autometasomatism

a modern vs permian black shale the hydrography primary productivity and water column chemistry of deposition the sediment currently accumulating in the cariaco basin on the continental shelf of venezuela has an elevated organic carbon content of approximately 5 is accumulating under o2 depleted bottom water conditions so42 reduction is composed dominantly of foraminiferal calcite diatomaceous silica clay and silt and is dark greenish gray in color upon lithification it will become a black shale recent studies have established the hydrography of the basin and the level of primary productivity and bottom water redox conditions these properties are used to model accumulation rates of cd cr cu mo ni v and zn on the seafloor the model rates agree closely with measured rates for the uppermost surface sediment the model is applied to the meade peak phosphatic shale member of the phosphoria formation a phosphate deposit of permian age in the northwest united states it too has all of the requisite properties of a black shale although the deposit is a world class phosphorite it is composed mostly of phosphatic mudstone and siltstone chert limestone and dolomite it has organic carbon concentrations of up to 15 is strongly enriched in several trace elements above a terrigenous contribution and is black the trace element accumulation defines a mean primary productivity in the photic zone of the phosphoria basin as moderate at 500 g m 2 year 1 organic carbon comparable to primary productivity in the cariaco basin the source of nutrient enriched water that was imported into the phosphoria basin upwelled into the photic zone and supported primary productivity was an o2 minimum zone of the open ocean the depth range over which the water was imported would have been between approximately 100 and 600 m the mean residence time of bottom water in the basin was approximately 4 years vs 100 years in the cariaco basin the bottom water was o2 depleted but it was denitrifying or no3 reducing rather than so42 reducing

ambient redox and hydrothermal environment of the wolverine volcanogenic massive sulfide deposit yukon insights from lithofacies and lithogeochemistry of mississippian host shales the wolverine volcanogenic massive sulfide vms deposit is a polymetallic felsic siliciclastic deposit hosted by 352 to 347 ma volcanic and sedimentary rocks of the yukon tanana terrane yukon canada shales are located at various stratigraphic levels and in various mineralized zones within the wolverine deposit area e g fisher puck and sable zones shales present along the mineralized horizon near the immediate hanging wall and footwall were deposited under anoxic conditions e g low mn anoxic v cr mo u systematics whereas in the stratigraphically deeper footwall and uppermost hanging wall the redox signatures imply deposition under suboxic to oxic conditions the mo u systematics of the shales suggest that during the time of sulfide mineralization the ambient basin was periodically euxinic with aqueous h2s present in the water column that this h2s contributed to the sulfur budget of the deposit furthermore the mo u and corg ni systematics favor deposition in a restricted basin i e nutrient trap where restriction of the water column led to h2s formation via sulfate reduction associated with excess organic carbon preservation there is also evidence of a progressive shift upward in the stratigraphy to more oxygenated conditions in the uppermost hanging wall the shift from euxinic to oxic suboxic conditions is consistent with regional tectonic models that indicate a change from rifting during wolverine deposit formation where the basin was partially restricted with minimal circulation i e restricted depocenter to an incipient back arc basin accompanied by extension and likely ingress of oxygenated seawater the rare earth element and y rey systematics in wolverine shales illustrate that proximal to the mineralized horizon shales have higher y ho 27 and ce ce 1 and negative ce anomalies indicative of oxygenated seawater the ce ce values in the wolverine shales have an inverse correlation with p2o5 content and suggest partial control by detrital apatite it is envisioned that apatite formed in the upper oxygenated portion of the water column inherited the ree signature of oxygenated seawater i e ce ce 1 and was subsequently deposited into deeper waters as detrital grains the ce ce and y ho also correlate with co2 and carbonate content of the shales moreover the shales that have the strongest rey signature of oxygenated seawater also coincide with the strongest euxinic signatures this paradox can be reconciled by enhanced deposition of apatite coincident with deposit formation coupled with a late hydrothermal overprint on the shales from low temperature co2 rich oxygenated hydrothermal fluids i e high y ho and ce ce 1 in a vent proximal environment this model is consistent with the geology stratigraphy and hydrothermal alteration in the immediate footwall and hanging wall of the deposit prospective shales in the wolverine basin and similar sediment rich hydrothermal basins globally should exhibit evidence for deposition under anoxic conditions i e mn 1 000 ppm high v mo u uef moef hydrothermal fe al mn systematics i e high fe al and evidence for hydrothermal alteration i e high ciw values high molar sericite and chlorite identification of samples having these features is useful in targeting prospective vms environments in shale dominated successions and potential targets within shale rich basins

using detrital zircons from river sands to constrain major tectono thermal events of the cathaysia block se china abstract detrital zircons from the minjiang and zhujiang rivers in se china have been analyzed for u pb ages and lu hf isotopic compositions to constrain their provenance and the growth history of the continental crust of the cathaysia block zircon u pb ages show five major populations at 90 250 ma 400 500 ma 0 7 1 2 ga 1 6 2 0 ga and 2 3 2 6 ga proterozoic zircons have hf isotopic signatures consistent with the remelted ancient crust and the involvement of juvenile crust however phanerozoic zircons have hf isotopic signatures indicative of reworked or recycled ancient crust crustal growth rates based on the two stage hf model ages of the detrital zircons indicate that 30 and 90 of present crust in the northeastern cathaysia block was formed by 2 5 ga and 1 6 ga respectively whereas

the north lhasa terrane in tibet was attached with the gondwana before it was drafted away in jurassic evidence from detrital zircon studies abstract it was commonly accepted that the north lhasa terrane of the present day central tibetan plateau in asia came from the northern gondwana but the timing of its northward drifting away from the gondwana remains controversial here we present for the first time u pb age and hf isotope data on detrital zircons from the cambrian metasedimentary rocks in the north lhasa terrane the detrital zircons display age peaks at ca 505 548 926 and 1104 ma and are interpreted to have gondwanan source regions these metasedimentary rocks were probably deposited in a collisional tectonic setting e g foreland basin related to the cambrian collisional accretion of microcontinents along the gondwanan proto tethyan margin the cambrian and carboniferous late triassic sedimentary rocks in the north lhasa terrane share the similar precambrian cambrian detrital zircon age and ehf t distributions indicating constant source accretion during the cambrian triassic time by contrast the precambrian cambrian detrital zircon age distribution of the late jurassic early cretaceous sedimentary rocks in the north lhasa terrane is distinctive from that of the adjacent cambrian triassic sedimentary rocks suggesting that the northward drifting of this terrane occurred in the jurassic

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

fabric signature of subglacial till deformation breidamerkurjokull iceland the foreland of breidamerkurjokull iceland is the only locality where tills known to have undergone subglacial deformation are exposed till on the foreland has a two tiered structure consisting of a dilatant upper horizon c 0 5 m thick and a compact lower till these horizons correspond to the ductile deforming a horizon and the brittle ductile b horizon observed below the glacier by g s boulton and co workers the relationship between known strain history and a variety of macrofabric elements is examined for these two genetic facies of deformation till the upper horizon exhibits variable a axis fabrics and abundant evidence for clast re alignment reflecting ductile flow and rapid clast response to transient strains in contrast the lower horizon has consistently well organized a axis fabrics with a narrow range of dip values recording clast rotation into parallel with strain axes during brittle or brittle ductile shear the data indicate that till strain history imparts identifiable macrofabric signatures providing important analogues to guide the interpretation of pleistocene tills

middle upper ordovician radiolarians in hunan and jiangxi provinces south china implications for the sedimentary environment and nature of the nanhua basin abstract the yanxi and duiershi formations of the middle upper ordovician in south china are composed of black grayish black and dark gray thin bedded cherts and siliceous slates rich in carbonaceous materials and pyrite horizontal beddings are developed the strata contain randomly distributed fossils radiolarians are discovered in the loudi yongzhou hengyang ji an and ganzhou sections the radiolaria from two sections are identified as protoentactinia sp abundances of radiolarian in the central area of hunan and jiangxi provinces are higher than in the southern area the strata become thickened while the amounts of siliceous materials are decreased and argillaceous contents are increased from northwest to southwest for the yanxi and duiershi formations the lithology gradually changes from carbonate rocks in the north to clastic rocks in the south 30si values of chert and siliceous slate range from 0 6 to 1 18 with al2o3 al2o3 fe2o3 mno tio2 lan cen ce ce and la yb n ratios of 0 65 0 97 0 01 0 16 0 99 1 27 0 85 1 10 and 0 91 1 66 respectively the sio2 and tio2 average contents are 89 08 and 0 27 the sio2 contents decrease while the tio2 increase from northwest to southeast they have similar the ree concentration with no obvious eu anomalies the yanxi and duiershi formations were deposited predominately in a bathyal environment on the continental slope basin and the seawater was stagnant in the middle early late ordovician the nanhua basin occupied a rather large area and sedimentary rocks in the region around hengyang ji an were deposited in the basin center with terrigenous source derived from the southeast

late paleozoic sedex deposits in south china formed in a carbonate platform at the northern margin of gondwana abstract sedex sulfide deposits hosted in black shale and carbonate are common in the south china block the dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 ma pyrite from the orebodies has a re os isochron age of 389 62 ma indicative of formation of the hosting strata and syngenetic pyrite ores in the mid late devonian the hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part the ore hosting black shales have high toc total organic carbon mo as pb zn and cd indicating an anoxic euxinic deep basin origin the high redox proxies v v ni 0 6 and v cr 1 and the positive correlations of toc with mo and v in black shales are also consistent with an anoxic depositional environment the dajiangping deposit is located close to the ne trending wuchuan sihui fault which was active during the devonian the mid late devonian mineralization age and the anoxic euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault bounded basin that developed in a carbonate platform of the south china block the regional distribution of many devonian stratiform carbonaceous sediment hosted sulfide deposits along the ne trending fault bounded basins in south china similar to the dajiangping deposit indicates that these deposits formed at a basin developed in the passive margin setting of the south china block during the devonian this environment was caused by the break up and northward migration of the south china block from gandwana

redox controls on arsenic enrichment and release from aquifer sediments in central yangtze river basin abstract more than 100 million people in asia are presently exposed to groundwater with arsenic as concentrations exceeding the world health organization standard of 10 g l 1 arsenic contaminated groundwater within basins of the central portion of the yangtze river has recently been reported but the processes controlling arsenic concentrations have yet to be resolved we examined the hydrologic and geochemical factors controlling arsenic within the jianghan plain an inland sedimentary basin of the yangtze river where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing schaefer et al 2016 hydrologic fluctuations alter redox conditions in the aquifer leading to oscillations between arsenic iron reduction and oxidation here we investigate the depth distribution of solid and aqueous phase iron and arsenic species and through a series of laboratory manipulations constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations in sediment incubations from 20 m below the surface where solid phase arsenic concentrations exceed 100 mg kg 1 both unamended and glucose amended sediment samples result in arsenic release to the aqueous phase in situ carbon was capable of promoting as release in the sediment in contrast sediment batch incubations from other depths resulted in limited as release solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods in sediments below the as enriched zone glucose amendment resulted in arsenic reduction but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the jianghan plain aquifer leads to rapid release of as to groundwater arsenic release from sediments at 20 m depth is sufficient to explain arsenic concentrations throughout the aquifer and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

hydrothermal venting and basin evolution devonian south china constraints from rare earth element geochemistry of chert this paper presents rare earth element ree geochemistry of siliceous deposits from which hydrothermal activity and basin evolution are elucidated in the late devonian in the yangshuo basin south china where siliceous deposits widely occurred as nodular chert in the deep water limestones and bedded chert interbeded with tuffaceous chert in the early late devonian both nodular and bedded cherts are characterized by very low la abundances avg 2 07 and 2 49 ppm respectively intermediate negative ce anomalies ce ce avg 0 69 and 0 61 slight to intermediate positive eu anomalies eu eu avg 1 33 and 1 57 and low to intermediate shale normalized lan ybn values avg 0 86 and 0 52 and intermediate lan cen values avg 1 61 and 1 72 these suggest both nodular and bedded cherts formed in the open marine basin of south china rather than in the intracontinental rift basin as previously assumed with involvement both with seawaters as indicated by intermediate negative ce anomalies and generally lree depleted patterns and hydrothermal vent fluids as indicated by convex less lree depleted patterns with apparent positive eu anomalies in comparison with nodular and bedded chert the tuffaceous chert has the highest la abundances avg 17 11 ppm similar ranges of ce anomalies avg 0 63 and lan cen values avg 1 77 but lower lan ybn values avg 0 48 and no apparent positive eu anomalies avg 0 97 this suggests that the tuffaceous fallouts were also significantly modified by the hydrothermal fluid and seawater rapid spatial variations of eu eu values and degree of lree depletions in the studied basin are recognized characterizing a spatially differential hydothermal activity that is not well discriminated by major element features such a difference in hydrothermal activity is interpreted as having been related to the intensity and depth of syndepositional tectonic activity reconciling the structural pattern unraveled by stratigraphic packages d 2005 elsevier b v all rights reserved

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

intertidal boulder pavements in the northeastern gulf of alaska and their geological significance abstract striated boulder pavements consisting of planar concentrations of clasts having striated upper surfaces are a common feature of glacigenic deposits but their origin is not well understood laterally extensive pavements are currently forming in the intertidal zone west of icy bay in the gulf of alaska pavements comprise armoured layers of interlocking boulders one clast thick that have been eroded from underlying outcrops of late cenozoic glaciomarine diamictites they originate essentially as lag surfaces along a high energy storm dominated mesotidal shoreline boulder pavements are either flat or show a nucleated plan form where successively smaller boulders have been accreted around a large core boulder nucleation imparts a hummocky surface topography to the pavements and suggests that some form of size sorting of clasts has occurred packing is promoted by repeated tamping of the clast lag by floating masses of glacier ice which become grounded across the intertidal zone at low tide repeated abrasion of the pavement surface by debris contained within ice blocks produces smooth flattened clast upper surfaces and short randomly oriented striations data from icy bay can be used to constrain the origin of laterally extensive boulder pavements exposed in late cenozoic glaciomarine sediments on middleton island the significance of such pavements in the geologic record is that they form along erosional unconformities and may identify sequence boundaries

arsenic incorporation into authigenic pyrite bengal basin sediment bangladesh abstract sediment from two deep boreholes 400 m approximately 90 km apart in southern bangladesh was analyzed by x ray absorption spectroscopy xas total chemical analyses chemical extractions and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the bengal basin authigenic framboidal and massive pyrite median values 1500 and 3200 ppm as respectively is the principal arsenic residence in sediment from both boreholes although pyrite is dominant ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment bound arsenic between approximately 20 and 100 m which is the depth range of wells containing the greatest amount of dissolved arsenic the lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources the ability of deeper aquifers 150 m to produce ground water with low dissolved arsenic in southern bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis

reflections on soft subglacial beds as a mosaic of deforming and stable spots abstract much discussion regarding subglacial processes is centred around the question of how soft beds respond to ice overriding in particular how widespread and penetrative is their deformation how does it affect the ice stability and what are the consequences for large scale sediment redistribution patterns contrasting views have been proposed which are difficult to verify and reconcile in the light of scarcity of agreed criteria to identify deforming beds here we suggest that soft beds under warm based glaciers can be envisaged as a mosaic of deforming and stable spots transient in time and space according to changes in the control parameters at the ice bed interface the subglacial mosaic model is consistent with field data showing heavily deformed beds interspersed with largely undisturbed beds it is suggested that deformation found in tills is a cumulative effect of strain within a relatively thin ephemeral deforming spots under the ice sole affecting the till as it accretes during ice overriding in accord with the coulomb plastic rheology the role of clast ploughing in bed deformation is emphasised

geochronology and petrogenesis of the early paleozoic i type granite in the taishan area south china middle lower crustal melting during orogenic collapse abstract the early paleozoic wuyi yunkai orogeny represents the first extensive tectonothermal event in south china since the neoproterozoic break up of the rodinia supercontinent the early paleozoic igneous rocks in the south china block scb are important for understanding the processes responsible for the orogeny the taishan batholith in the inner cathaysia block consists dominantly of granodiorite and hornblende bearing granite zircon u pb dating of four samples gives a consistent crystallization age of ca 436 ma synchronous with widespread late orogenic s type granitic intrusions in the wuyi yunkai orogen the taishan granitoid rocks are metaluminous or peraluminous a cnk 0 94 1 15 and have variable sio 2 61 5 74 9 wt mgo 0 4 2 4 wt fe 2 o 3 1 8 7 4 wt and cao 1 1 5 5 wt with gradually decreasing p 2 o 5 from mafic to felsic components thus the taishan batholith displays the petrological and geochemical characteristics of i type granites additionally all samples have strongly negative e nd t values 11 to 9 suggesting an overall ancient source the early paleozoic i type granitoid rocks in the taishan area were derived from partial melting of ancient middle to lower crust at a high thermal gradient 35 c km and underwent extensive fractional crystallization of hornblende plagioclase and biotite the wuyi yunkai orogenic collapse may have been responsible for middle to lower crustal melting of the cathaysia block the early paleozoic i and s type granitoid magmatism lack significant input of a juvenile component indicating that the processes accompanying orogenic collapse such as asthenosphere upwelling and basaltic underplating contributed heat to trigger widespread early paleozoic felsic magmatism in the scb an intraplate orogenic event instead of continental or arc collision may be the preferred model for the wuyi yunkai orogeny

crustal contamination versus an enriched mantle source for intracontinental mafic rocks insights from early paleozoic mafic rocks of the south china block abstract several recent studies have documented that the silicic rocks sio 2 65 wt comprising silicic large igneous provinces are derived from partial melting of the crust facilitated by underplating intraplating of hidden large igneous province scale basaltic magmas the early paleozoic intracontinental magmatic rocks in the south china block scb are dominantly granitoids which cover a combined area of 22 000 km 2 in contrast exposures of mafic rocks total only 45 km 2 these mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched whole rock initial 87 sr 86 sr 0 7041 0 7102 e nd t 8 4 to 1 8 weighted mean zircon e hf t 7 4 to 5 2 show low ce pb and nb u ratios 0 59 13 1 and 3 5 20 9 respectively and variable th la ratios 0 11 0 51 the high mgo mafic rocks mgo 10 wt tend to have lower e nd t values nd t values 4 and sm nd ratios 0 255 the differences in geochemistry between the high mgo and low mgo mafic rocks indicate greater modification of the compositions of high mgo mafic magmas by crustal material in addition generally good negative correlations between e nd t and initial 87 sr 86 sr ratios mgo and k 2 o along with the presence of inherited zircons in some plutons indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination rather than an enriched mantle source the results show that high mgo mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source and it is more likely that the lithospheric mantle beneath the scb during the early paleozoic was moderately depleted than enriched by ancient subduction processes

basement structures underneath the northern south yellow sea basin east china implications for the collision between the north china and south china blocks abstract the south yellow sea basin sysb as the eastern part of the yangtze block has undergone multiple tectonic events since the formation of its basement the north china south china collision affected intensely the structures of the basin the relationship between the deep structures in the basement and collisional orogeny has long been a matter of debate in this paper 2d seismic magmatic gravity and drilling data were integrated to unravel the basement structures in the interpreted seismic sections the basement can be subdivided into three seismic facies the seismic facies i and iii correspond to two basement layers the seismic facies ii is interpreted as shear zones that were formed during the mesozoic collision and exhumation the influence of the north china south china collision propagated from north to south in the sysb according to observations from drill holes and seismic sections the northern part of the basin the yantai depression uplifted during the earlier stage of the collision resulting in the erosion of the upper paleozoic and triassic strata in the middle and southern parts the laoshan uplift and qingdao depression the compression was obviously after that in the yantai depression the exhumation of the qianliyan basement metamorphic complex of the yangtze block occurred gradually the shear zones were initially developed during the collision during early mesozoic the exhumation process of metamorphic rocks lasted till late mesozoic and the jurassic cretaceous strata were deposited in the hanging wall of the northern boundary fault

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

issues associated with the distinction between climatic and tectonic controls on permian alluvial fan deposits from the kotzen and barnim basins north german basin abstract facies analysis focussing on coarse grained sediments has been carried out on more than 2500 m of drill cores from seven wells from southern margins of the north german basin ngb the ngb forms a central element of the southern permian basin spb the wells exposed conglomerates and sandstones of the rotliegend gruneberg and parchim formations deposited in the kotzen basin and the barnim basin 17 lithofacies types have been grouped into six lithofacies associations the studied successions are dominated by fluid gravity flow deposits hyperconcentrated flows and stream flows of alluvial fan and alluvial plain systems maximum particle size bed thickness plots mps bth support the interpretation as fluid gravity flow deposits the mps and bth data have also been used to differentiate coarsening thickening and fining thinning trends of the fan systems the dominance of water rich mass flow processes together with sedimentary structures such as dewatering structures and outwashed tops suggests the presence of wet type fans and plains under semi humid to semi arid seasonal climates in the central spb the investigated sediments show variation in clast composition subsequent to deep erosion processes on basin margins and changes of source areas synsedimentary normal faults and clastic dykes have been interpreted as indicators of tectonic activity of grabens itself and its frames on a larger scale then evolution from a half graben to a graben is apparent for the tuchen sub basin at least the progradational retrogradational cycles of the studied alluvial fan systems document combined local tectonic movements and influences of climatic changes however our data did not allow for a clear distinction between climatic and tectonic signals furthermore a one to one correlation of fan cycles with depositional trends in the ngb basin centre would appear to be oversimplistic

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member