provenance and tectonic settings of permian turbidites from the beishan mountains nw china implications for the late paleozoic accretionary tectonics of the southern altaids the beishan orogenic belt which connects the tianshan suture on the west and solonker suture on the east contains key evidence for the termination time of the southern altaids critical for evaluating different controversial tectonic models are permian marine volcaniclastic arenites in the liuyuan and heishankou areas which are dominated by greywackes and lenticular pebbly litharenites that contain grading groove marks and erosional bases which provide evidence of turbidity action sandstones from the liuyuan section are dominated by angular basaltic andesitic and feldspar fragments but sandstones from the heishankou section mainly consist of andesitic and felsic volcanic fragments these relations suggest derivation from two different sources major element compositions suggest that the source rocks of the heishankou litharenites were more sio2 rich than those at liuyuan sandstones at heishankou are characterized by lower ni co cr v and slightly higher th and la contents than those at liuyuan this indicates that the litharenites in the liuyuan and heishankou areas were derived from intermediate mafic and intermediate felsic source rocks respectively tectonic setting discrimination plots suggest that the liuyuan sandstones were deposited as detritus from an oceanic island arc but the heishankou sediments from an andean continental margin our petrological and geochemical data from these two types of permian turbidites suggest that an arc continent collision took place in the early permian and this is consistent with the permian termination of the southern altaids

martin brasier s contribution to the palaeobiology of the ediacaran cambrian transition martin brasier s work spanned almost the entire geological column but the origin of animals and the nature of the cambrian explosion were areas of particular interest to him martin adopted a holistic approach to the study of these topics that considered the interplay between multiple geological and biological phenomena and he sought to interpret the fossil record within the broad context of geological biogeochemical and ecological changes in the earth system here we summarize martin s main contributions to this area of research and assess the impact of his findings on the development of this field karl popper would have said that palaeontology is not real science because you can t go out and sample it i think absolutely the opposite i think this is actually where science is it s trying to guess what lies over the hill and map terra incognita when people come in and colonize that s just technology martin brasier 2013 excerpt from a phone interview in moor 2016

mid latitude mesoscale variability neither homogeneous quasi geostrophic turbulence nor the effect of eddies on the interior ocean circulation remains the major focus of mesoscale research as was the case for much of the preceding 20 years following identification of the phenomena concentration on basin wide geographical exploration of eddy properties was rather well established by 1978 over the last few years a promising zero order description and rationalization of the mesoscale field has become available that is eddy energy is largest near strong flows intensification not only in western boundary currents but along their mid latitude open ocean extension roughly as indicated by gyre scale numerical models where eddies develop as a result of instability processes in the mid latitude jet and recirculation regimes and then propagate into the ocean interior our point of view is that mesoscale eddies drive recirculations but do not play a crucial role in the dynamics of the mean flow in the ocean interior in the north atlantic for example the idea is that the downstream increase in transport of the gulf stream is eddy driven but not the flow through the florida straits in addition the fluctuating response to forcing by variable winds may now be widely perceived as forming the horizontally homogeneous background signal in subtropical gyres the time dependent field associated with thermohaline flows at abyssal depths also has a special character

modular construction of early ediacaran complex life forms newly discovered exceptionally preserved soft bodied fossils near spaniard9s bay in eastern newfoundland exhibit features not previously described from ediacaran terminal neoproterozoic fossils all of the spaniard9s bay taxa were composed of similar architectural elements centimeter scale frondlets exhibiting three orders of fracticality in branching frondlets were combined as modules atop semi rigid organic skeletons to form a wide array of larger constructions including frondose and plumose structures this architecture and construction define the rangeomorphs a biological clade that dominated the mistaken point assemblage 575 to 560 million years ago but does not appear to be ancestral to any phanerozoic or modern organisms

mapping climatological seasonal variations of surface currents in the tropical atlantic using ship drifts the seasonal variability of current velocities in the tropical atlantic was studied by grouping ship drift velocity observations into 2 5 boxes and calculating monthly mean velocity values these values were used to calculate and map the annual mean velocity the seasonal variation about the mean the annual and semiannual harmonics and the first two empirical orthogonal functions eofs the seasonal variation is primarily zonal in the equatorial band and in the north equatorial countercurrent necc and primarily alongshore near the coast of south america maxima of seasonal variation of 23 cm s are centered in the necc near 6 n 42 5 w and in the gulf of guinea near 2 n 7 5 w most 80 of the variance in the necc and along the western boundary of the area studied has an annual period most of the variance along the equator in the mid atlantic has a semiannual period over the whole region 49 of the seasonal variance is explained by the annual harmonic and 69 is explained by a combination of the annual and semiannual harmonics the second eof contains 29 of the variance of the data set and shows a simultaneous speeding slowing of the major equatorial currents the south equatorial current sec the north brazil current the necc and the guinea current along their principal axes of variation with a concurrent slowing speeding of the guyana current and the brazil current the pattern of variation resembles a large equatorial gyre centered along 4 n that flows clockwise from may to september and counterclockwise most of the rest of the year the first eof accounts for 35 of the variance and shows a simultaneous speeding slowing of eastward velocity from 5 s to 10 n except in the western sec the western end of the north brazil current and the guinea current the out of phase fluctuations apparent in the western sec near the equator are explained by the slowing and reversal of the south equatorial current near 2 n 40 w between april and june this slowing of the sec is associated with the start up of the necc which accelerates eastward in may june and july and flows eastward across the atlantic from july through december the sec divides seasonally near the eastern tip of brazil where residual alongshore velocities are northward for half the year peaking during may and june and southward for the other half of the year a second division can be seen north of the amazon where the north brazil current continues up the coast into the guyana current during the first half of the year but partially retroflects into the necc during the last half of the year a fast eastward flow in the necc coincides with below average velocities in the guyana current and above average velocities in the western sections of the north brazil current and the sec north of the equator

geochronology and isotope geochemistry of the baogutu porphyry copper deposit in the west junggar region xinjiang china abstract the baogutu copper deposit a newly discovered middle sized porphyry copper deposit is located in the west junggar region of xinjiang nw china baogutu is associated with a late carboniferous intrusive complex that was emplaced into lower carboniferous volcano sedimentary strata the intrusive complex comprises main stage diorites and minor late stage diorite porphyries their intrusive activity occurred in 313 0 2 2 ma to 312 3 2 2 ma based on u pb zircon sims analyses molybdenite separated from ore bearing quartz veins yields re os model ages from 309 4 4 4 ma to 314 1 4 5 ma with a weighted mean age of 312 4 1 8 ma biotites separated from fresh diorite and hydrothermal breccias in main stage diorites yield 40ar 39ar plateau ages of 308 26 1 88 and 305 69 1 76 ma respectively these dates obtained from three independent dating techniques constrain the ore forming age of the baogutu deposit stable isotopes h o s and radiogenic isotope pb have been used to discriminate the sources of the ore forming fluid at baogutu the 18o 1 14 1 74 and d 74 to 98 data indicate that the water of the ore forming fluids was derived from magmatic water the 34s values 0 24 to 0 4 show that the sulfur isotope composition of the ore fluids is characterized by magma sulfur lead isotope compositions 206pb 204pb 17 92 18 89 207pb 204pb 15 45 15 62 208pb 204pb 37 68 38 36 indicate that the lead of the ore fluids is derived from the mantle these data confirm the occurrence of a cu au mo mineralizing event at late carboniferous in the baogutu region and the ore forming fluids are mainly derived from the mantle the event is inferred to be associated with late carboniferous junggar oceanic crust subduction

assemblage palaeoecology of the ediacara biota the unabridged edition fossils of the ediacara biota offer our earliest insight into diverse macroscopic life on this planet in particular given the diversity and range of exquisite soft bodied preservation the potential for unraveling aspects of the paleobiology and paleoecology is great clearly however there can be a taphonomic overprint that dictates how complete the assemblage is new diversity data including richness and evenness from south australia is compared to previously published data from newfoundland and the white sea and is within the range of values for both modern and phanerozoic assemblages however missing from our current understanding of ediacaran ecosystems is a full description and interpretation of the many problematica structures and organic surfaces

a rich ediacaran assemblage from eastern avalonia evidence of early widespread diversity in the deep ocean the avalon assemblage ediacaran late neoproterozoic provides some of the oldest evidence of diverse macroscopic life and underpins current understanding of the early evolution of epibenthic communities however its overall diversity and provincial variability are poorly constrained and are based largely on biotas preserved in newfoundland canada we report coeval high diversity biotas from charnwood forest uk which share at least 60 of their genera in common with ones in newfoundland this indicates that substantial taxonomic exchange took place between different regions of avalonia probably facilitated by ocean currents and suggests that a diverse deepwater biota may already have been widespread at the time contrasts in the relative abundance of prostrate versus erect taxa likely record differential sensitivity to physical environmental parameters hydrodynamic regime substrate and highlight their significance in controlling community structure

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

early paleozoic amalgamation of the songnen zhangguangcai range and jiamusi massifs in the eastern segment of the central asian orogenic belt geochronological and geochemical evidence from granitoids and rhyolites abstract to constrain the early paleozoic tectonic evolution of the songnen zhangguangcai range and jiamusi massifs we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic igneous rocks in the lesser xing an zhangguangcai range of eastern heilongjiang province ne china the zircons from one diorite two rhyolites and four granitoids are euhedral subhedral and display fine scale oscillatory growth zoning indicating a magmatic origin la icp ms zircon u pb age data indicate the occurrence of magmatic events in the late ordovician 443 451 ma and middle silurian 424 430 ma the late ordovician igneous rocks are composed mainly of diorite tonalite and rhyolite whereas the middle silurian igneous rocks consist mainly of monzogranites the early paleozoic igneous rocks have sio2 59 65 76 11 wt mgo 0 13 1 23 wt and na2o k2o 4 68 7 77 wt and are chemically a calc alkaline series they are characterized by enrichment in light rare earth elements and large ion lithophile elements and depletion in heavy rare earth elements and high field strength elements such as nb ta and ti consistent with the chemistry of igneous rocks from an active continental margin setting in situ hf analyses of zircons show that ehf t values of zircons that formed in the early ordovician captured and inherited zircons in late ordovician igneous rocks range from 0 1 to 7 1 those of zircons that formed in the late ordovician including captured and inherited zircons in middle silurian monzogranite vary from 2 6 to 5 6 and those of zircons that formed in the middle silurian vary from 3 0 to 3 2 the progressive decrease in zircon ehf t values from the early ordovician to the middle silurian suggests an increasing involvement of ancient crust in the magma sources corresponding to the transition from subduction to collision take together these data suggest that the formation of late ordovician diorite tonalite and rhyolite in the zhangguangcai range adjacent to the mudanjiang fault may have been related to the westward subduction of an oceanic plate between the songnen zhangguangcai range and jiamusi massifs in contrast coeval rhyolites from the lesser xing an range located far from the mudanjiang fault may have formed in the supra subduction zone the occurrence of a middle silurian monzogranite association combined with geochronological data for detrital zircons from early devonian sedimentary rocks in eastern heilongjiang province suggests that the amalgamation between the songnen zhangguangcai range and jiamusi massifs occurred in the middle silurian

observations of annual and el nino thermal and flow variations at 0 110 w and 0 95 w during 1980 1985 moored measurements of the surface wind and of the current and temperature fields within the uppermost 250 m were recorded from march 1980 to september 1985 at 0 110 w and from july 1981 to november 1983 at 0 95 w at these sites the annual mean thicknesses of the equatorial undercurrent euc and of the surface portion of the south equatorial current sec were about 200 m and 20 m respectively the annual mean euc core speed was 0 9 m s 1 annual cycles of temperature and zonal current at 110 w were most distinctive near the surface at nominal depths of 15 m and 47 5 m the average annual amplitudes were 1 5 c and 0 5 m s 1 at about 100 m the annual amplitudes were about 0 5 c and 0 10 m s 1 at 15 m the annual mean zonal current was 0 05 m s 1 which was not representative of the monthly mean zonal current in april the monthly mean direction was eastward and in october it was westward with speeds of about 0 5 m s 1 in both months warmer water occurred in april and colder water in october the direction of the zonal wind component was westward throughout the year and the annual amplitude of the zonal wind was only about 2 5 times larger than that of the zonal current the average amplitude of the annual cycle of the meridional current component was less than 0 05 m s 1 and not distinguishable from year to year monthly mean variations monthly mean anomalous or el nino currents at 110 w were defined as the difference between the observations and the annual cycle during the august december 1982 onset phase of el nino the strength of the normally westward flowing near surface sec was greatly reduced to near zero speed by an el nino eastward flowing zonal current of about 0 3 m s 1 the largest vertically averaged 15 250 m zonal current anomaly 0 5 m s 1 occurred in january and february 1983 and represented a substantial decrease in the eastward transport of the euc causing a disappearance of the undercurrent the duration of the euc disappearance was longer at 95 w than at 110 w a surface intensified eastward jet with a maximum daily speed of 1 75 m s 1 at 15 m occurred in may 1983 at 110 w but not at 95 w a massive redistribution of heat throughout the mixed layer and thermocline was associated with the 1982 1983 el nino beginning in august 1982 the thermocline at 110 w and 95 w sank 100 m reaching its maximum depth in december 1982 temperatures at 100 m and 150 m which normally were about 15 c and 14 c reached 27 5 c and 22 5 c the time rate of change of the 15 to 200 m heat content was 500 w m 2 during the august december 1982 warming phase and 460 w m 2 during the january february 1983 subsurface cooling phase the euc disappeared during the subsurface cooling phase a second less intensive mixed layer deepening occurred in may 1983 at 95 w but not at 110 w

estimating the basin scale ocean circulation from satellite altimetry part i straightforward spherical harmonic expansion abstract direct estimation of the absolute dynamic topography from satellite altimetry has been confined to the largest scales basically the basin scale owing to the fact that the signal to noise ratio i more unfavorable everywhere else but even for the largest scales the results are contaminated by the orbit error and geoid uncertainties recently a more accurate earth gravity model gem t1 became available thus giving us the opportunity to examine the whole question of direct estimation under a more critical limelight it is found that our knowledge of the earth s gravity field has indeed improved a great deal however it is not yet possible to claim definitively that our knowledge of the ocean circulation has improved through direct estimation yet the improvement in the gravity model has come to the point that it is no longer possible to attribute the discrepancy at basin scales between altimetric and hydrographic results as mostly due to geoid uncertainties a substantial part of the differen

evolutionary relationships within the avalonian ediacara biota new insights from laser analysis abstract we report new high resolution laser scanning of the type material for the earliest complex ediacaran genera charnia bradgatia charniodiscus and ivesheadia from charnwood uk and compare these with beothukis mistakensis gen et sp nov and the recently described taxa charnia wardi charnia antecedens and fractofusus spp from broadly coeval strata in newfoundland we use the laser and other techniques to map the similarities and differences in morphology between these ediacaran rangeomorphs key features are suggested to include the number of growth axes the number and placement of growth tips the presence of radiating or subparallel axes for the first and higher order branches the extent of displayed or undisplayed leaf like rangeomorph9 architecture and the extent of furling of the margins of these leaf like elements these features are then used to propose suggested homologies between these taxa leading to a preliminary phylogenetic hypothesis for the evolution of the avalonian ediacara biota

the nature and thickness of lithosphere beneath the archean dharwar craton southern india a magnetotelluric model abstract the dharwar craton in the southern indian shield region occupies a key position in reconstructions of the earliest supercontinent ur as well as in the global neoarchean configurations of continental assembly here we synthesize the available geophysical data that include heat flow seismic tomography temperature profile derived from xenoliths and magnetotellurics mt from the dharwar craton a thickness of more than 200 km is identified for the lithosphere beneath this craton by magnetotelluric model our inference lends support to the models from recent seismological investigations that argue for the presence of a thick lithosphere as well as the upper mantle structure derived from the analysis of mantle xenoliths a synthesis of recent geophysical and geochemical data together with our magnetotelluric model indicate the existence of a thick lithospheric root beneath the dharwar craton and suggest that not much of the lithosphere has been eroded since precambrian in this region leading to the conclusion that the dharwar craton preserves an archean tectosphere an increase in the lithospheric thickness from east to west in the dharwar craton and the lithosphere asthenosphere boundary lab migration to shallower levels observed from geophysical data towards the east is interpreted as a probable reflection of the mesoproterozoic subduction erosion of the archean cratonic keel

wrinkle structures microbially mediated sedimentary structures common in subtidal siliciclastic settings at the proterozoic phanerozoic transition sedimentary structures produced by microbial activity are well known from ancient carbonate facies but little is known about equivalent microbial structures in ancient siliciclastic facies wrinkle marks and kinneyia ripples are closely related sedimentary structures that are commonly found in ancient siliciclastics and they may represent microbial activity to evaluate this possibility these structures were studied in vendian cambrian strata of north america and compared to structures formed by modern microbial mat communities in redfish bay texas striking similarities in sedimentologic petrographic and morphologic characteristics of modern and ancient occurrences suggest that the enigmatic but widespread ancient structures could have been formed by microbial processes the relative abundance of these structures in siliciclastic facies of this interval further suggests that prior to the onset of relatively intense bioturbation in the ordovician microbial mats could have played a significant role in the evolution and diversification of early life in a broad variety of sea floor environments

circulation from a joint gravity field solution determination of the general ocean with the development of satellite altimetry it is possible to infer the geostrophic velocity of the surface ocean currents if the geoid and the position of the satellite are known accurately errors in current geoid models and orbit computations both due primarily to errors in the earth s gravity field model have limited the use of altimeter data for this purpose the objective of this investigation is to demonstrate that altimeter data can be used in a joint solution to simultaneously estimate the quasi stationary sea surface topography and the model for the gravity field satellite tracking data from twelve satellites were used along with seasat altimeter data for the solution the estimated model of compares well at long wavelengths with the hydrographic model of covariance analysis indicates that the geoid is separable from up to degree 9 at which point geoid error is comparable to the signal of

characteristics of surface current flow inferred from a global ocean current data set a seasonal global ocean current data set ocds digitized on a 5 sup 0 grid from long term mean shipdrift derived currents from pilot charts is presented and described annual zonal means of v component currents show subtropical convergence zones which moved closest to the equator during the respective winters in each hemisphere net annual v component surface flow at the equator is northward zonally average u component currents have greatest seasonal variance in the tropics with strongest westward currents in the winter hemisphere an ensemble of ocean currents measured by buoys and current meters compares favorably with ocds data in spite of widely varying time and space scales the ocds currents and directly measured currents are about twice as large as computed geostrophic currents an analysis of equatorial pacific currents suggests that dynamic topography and sea level change indicative of the geostrophic flow component cannot be relied on solely to infer absolute strength of surface currents which include a strong ekman component comparison of ocds v component currents and meridional transports predicted by ekman theory shows agreement in the sign of transports in the midlatitudes and tropics in both hemispheres ekman depths required to scale ocds v component currents to computed ekman transports are reasonable at most latitudes withmore layer depths deepening closer to the equator less

ediacaran epifaunal tiering epifaunal tiering the subdivision of vertical space within a community is a fundamental attribute of phanerozoic suspension feeding communities this paper documents tiering including the presence of meter tall organisms in neoproterozoic ediacaran communities ediacaran tiering was studied from three exceptionally preserved deep water communities at mistaken point newfoundland which contain in situ census populations of hundreds to thousands of organisms tiering consists of overlapping populations of dominant organisms and is characterized by gradational rather than abrupt tier boundaries at least three tiers are apparent a lower level 0 8 cm above the seafloor an intermediate level between 8 22 cm above the seafloor and an upper level that extends as high as 120 cm tier boundaries are relatively consistent between communities but the constituent organisms in each level are variable suggesting that some ediacaran taxa could fill different tiers interchangeably development of a tiered epifaunal structure is consistent with suspension feeding or absorbing dissolved nutrients directly from seawater despite the common occurrence of tall organisms all communities share a similar population structure in which biomass is concentrated in the basal 10 cm above the seafloor comparison with shallow water ediacaran localities suggests that the observed tiering structure is typical of ediacaran communities ediacaran tierers also show the fundamental subdivision between organisms and or colonies that fed along their entire length and those that developed a specialized feeding apparatus implying that the features of phanerozoic tiered skeletal ecosystems were first initiated in soft bodied communities in the late neoproterozoic

u pb zircon chronology of the pangidi kondapalle layered intrusion eastern ghats belt india constraints on mesoproterozoic arc magmatism in a convergent margin setting abstract the pangidi kondapalle layered intrusion is emplaced within high grade supracrustal rocks in the southern sector of the eastern ghats granulite belt proximal to the south eastern periphery of the indian plate this layered complex consists mainly of anorthosites and gabbronorites with pyroxenite cumulates containing orthopyroxenites and chromitites in a regressive intrusive sequence here we report laser ablation icp ms data and ree geochemistry of zircons from three co spatial anorthositic bodies in this complex our results show mean 207 pb 206 pb ages of 1634 18 ma mswd 0 55 for the anorthosite from pangidi two anorthosite samples from kondapalle yield mean 207 pb 206 pb ages of 1628 36 ma mswd 0 54 and 1693 110 ma mswd 5 5 the zircons from all the anorthosite samples show high ree contents prominent hree enrichment and a conspicuous positive eu anomaly suggesting a common melt source the prominent mesoproterozoic ages revealed from our u pb dating of zircons from these layered complexes suggest subduction related magmatic underplating in a convergent margin setting associated with the amalgamation of the columbia derived fragments within the neoproterozoic supercontinent

vendobionta and psammocorallia lost constructions of precambrian evolution the non availability of biomineralized skeletons and low levels of predation led vendian evolution along strange avenues the ediacara type vendobionta appear to represent a kingdom in which foliate shapes large sizes and the necessary compartmentalization were achieved by quilting of the skin rather than by multicellularity psammocorallia in contrast are interpreted as coelenterates that constructed an internal sand skeleton both were immobile soft bottom dwellers that had high population densities and both became preserved by obrutional accidents thus they render fossil snap shots in which the original distributional patterns age structures and standing biomasses of populations are accurately recorded

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

determination of the ocean circulation using geosat altimetry a spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the earth s geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using geosat altimeter data and tracking data from 14 different satellites the sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data currently errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower corresponding to a minimum wavelength of 4 000 km error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0 2 indicating good separation of the geoid and the sea surface topography at wavelengths of 4 000 km or longer estimates of the scale factor for the significant wave height h sub 1 3 which is used to compute the electromagnetic bias correction and the bias for the geosat altimeter are obtained the estimate of the h sub 1 3 correction is 3 6 plus minus 1 5 and the height bias estimate is zero

geochronology and isotopic geochemistry of the a type granites from the huanggang sn fe deposit southern great hinggan range ne china implication for their origin and tectonic setting abstract the huanggang sn fe deposit inner mongolia is located in southern great hinggan range metallogenic belt la icp ms zircon u pb dating show that the k feldspar granite and granite porphyry in the huanggang mine were formed at 136 7 1 1 ma and 136 8 0 57 ma respectively sr nd pb isotope of the rocks and in situ zircon hf isotopic systematics show that 87 sr 86 sr i values range from 0 70211 to 0 70729 close to the 87 sr 86 sr i of oceanic basalts and lower than those of continental crust the e nd t values and nd model ages t dm vary from 0 8 to 0 9 and 855 to 993 ma respectively the pb isotopic compositions are also variable with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of 18 974 26 107 15 554 15 914 and 38 894 39 890 respectively suggesting that the lead is derived from a mixed source the 176 hf 177 hf values range from 0 282744 to 0 282922 with corresponding e hf t values ranging from 1 9 to 18 3 and two stage hf model ages t dm2 of between 561 and 888 ma the isotope composition shows that huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle perhaps contaminated by small amounts of ancient continental crust younger nd hf isotope model ages imply that an important crustal growth event took place in this area during the neoproterozoic integrating our data with previously published results and the late mesozoic regional tectonic setting we conclude that the huanggang granites were generated in an intraplate tectonic magmatic setting asthenospheric mantle upwelling due to lithospheric delamination and magma underplating caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle this resulted in remelting differentiation and a continued evolution of the mafic juvenile crust producing a large quantity of granitic magma the tectonic setting for these processes may be linked to the nnw subduction of the pacific plate izanagi in the mesozoic which affected most of eastern china

mesoproterozoic ophiolitic melange from the se periphery of the indian plate u pb zircon ages and tectonic implications abstract the kanigiri melange within the proterozoic nellore khammam schist belt in southern peninsular india includes ophiolitic fragments that represent the remnants of an oceanic plate the ophiolitic units were accreted along a ne trending suture that juxtaposes the proterozoic eastern ghats granulite belt eggb against the archean nellore schist belt of the dharwar craton the ophiolite components in the kanigiri melange include plagiogranites and gabbros which show mutually intrusive relations indicating their coeval nature we report laser ablation icp ms age data and ree geochemistry of zircons from the gabbro and granite the zircons from both gabbro and granite show high ree contents prominent hree enrichment and a conspicuous negative eu anomaly suggesting a common melt source zircon ree abundances and normalized patterns show little intersample and intrasample variations u pb dating of the zircons reveals prominent mesoproterozoic ages for the plagiogranite with the ca 1 33 ga age of the kanigiri ophiolitic melange offering important clues for arc continent collision during the final stages of amalgamation of the columbia derived fragments within the neoproterozoic supercontinent assembly

the possible link between net surface heating and el nino three diagnostic analyses are described which strongly suggest the importance of local net surface heating in the life history of the large scale air sea phenomenon centered in the eastern tropical pacific ocean commonly called el nino these analyses rely upon monthly marine weather summaries for the period 1957 to 1976 in the first correlations and coherence spectra were calculated which show a strong link between the net surface heat flux and sea surface temperature variations over the eastern equatorial pacific the second analysis also based upon the use of coherence spectra indicates a sea temperature precursor in the eastern ocean near 25 degrees s which precedes sea temperature changes near the el nino focus near 5 degrees s since the link between the two regions would require ocean advective velocities that appear to be unreasonably large this analysis also suggests the importance of atmospheric forcing through the surface heat flux in the third analysis a proxy variable is described that seems to be a reasonable indicator of the overall effect of ocean dynamics on the temperature of the el nino core region a composite analysis of the four el nino events of 1957 1965 1972 and 1976 suggests that local surface heating is important during the early part of an event whereas dynamical factors dominate later

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

detection of 17 5 day period meridional current oscillations in the equatorial western pacific ocean during 1985 the first long term near equatorial near surface moored current measurements recorded in the pacific ocean west of 160 w were made at 0 150 e during 2 august 1985 1 february 1986 these data revealed 17 5 day period oscillations of the meridional current prior to these measurements these waves had only been observed eastward of about 165 w which also was the westernmost extent of their appearance in ocean general circulation model simulations the 17 5 day period waves also occurred in simultaneous current measurements at 140 w where the wave amplitude was 3 times greater at both sites the 17 5 day period wave amplitude was more than 50 of the record length standard deviations of the meridional current component a wider spectral bandwidth and a smaller tendency towards rectilinear motion occurred at 150 e than at 140 w

worldwide ship drift distributions identify missing data the geographical and temporal distributions of worldwide ship drift velocities were plotted in order to see where and when the observations were made and to identify what appear to be major gaps in the data curiously large areas of the north atlantic north pacific and south pacific were found to be devoid of observations in some months during the years 1920 1934 when the number of yearly observations is large an estimated 700 000 observations are missing these would significantly enhance the usefulness of the data set if they could be found and added to it especially in the pacific where the data density is low

field and laboratory tests for recognition of ediacaran paleosols abstract not a single paleosol had been described from rocks of ediacaran age until 2011 but 354 ediacaran paleosols have been described by 20 different authors since then some of these newly recognized paleosols have proven controversial so this paper reviews 20 distinct tests to determine whether a particular ediacaran bed could be a paleosol or not one problem has been that ediacaran paleosols are not precisely like modern soils because they lack root traces a diagnostic feature of silurian and geologically younger paleosols the principal problem for recognition of some ediacaran paleosols is the occurrence in them of megafossils assumed to have been marine although most of these fossils remain problematic for both biological and ecological affinities not all the tests discussed here are diagnostic of paleosols some are ranked permissive or persuasive permissive conditions for paleosols include ripple marks hummocky bedding pyritic limestones acritarchs or thalloid fossils low strontium isotopic ratios high 26 mg ratios and red color persuasive tests include loessites tsunamites desert playa minerals low boron content high 10 b isotopic ratios high carbon sulfur ratios and very low total reactive iron ratios diagnostic tests include matrix supported lapilli or crystal tuff parent materials ice wedges and other cryoturbation sepic birefringence fabrics evaporitic sand crystals and negative geochemical strain and mass transfer and highly correlated 13 c and 18 o like other geological periods the ediacaran is known from a variety of marine and non marine paleoenvironments

ediacaran fossil preservation taphonomy and diagenesis of a discoid biota from the amadeus basin central australia abstract aspects of the preservation of the enigmatic soft bodied ediacara biota in relatively coarse grained siliciclastic sediments remain unresolved the taphonomic model proposed by gehling in 1999 is here validated through examination of previously unpublished discoid fossils from the shallow marine deltaic arumbera sandstone in the amadeus basin within the flinders style preservation the model predicts stalked frondose organisms attached by a discoid holdfast to a microbial mat encrusted sea bed with sedimentation as periodic storm event beds during a terminal neoproterozoic taphonomic window a pyrite sole veneer provided critical fossil rigidity during burial the sequence of sedimentation events presented here advances a slightly modified gehling model no direct evidence of pyrite is detected instead a thin haematite clay coating covers fossil hyporelief surfaces nevertheless an original pyrite sole veneer is indirectly validated by tracing its diagenetic history through to today s haematite detailed petrography demonstrates reducing conditions during eodiagenesis that remained anoxic mildly alkaline through mesodiagenesis thus the pyrite sole veneer survived deepest burial meteoric water penetrated the deep regolith during prolonged telodiagenesis creating oxic mildly acidic pore water so pyrite oxidised and hydrolised to haematite the applicability of gehling s model is higher where marine shelf sediments subsided continuously in shallower or eroded areas that experienced intermittent meteoric eodiagenesis diagenetic history was different and ediacaran fossil preservation unlikely diagenetic history therefore has crucial implications for ediacaran fossil preservation

dickinsonia from ediacara a new look at morphology and body construction abstract during groundbreaking fieldwork on the taphonomy and sedimentology of the famous fossil deposits at the ediacara sheep station goldring r currnow c n 1967 the stratigraphy and facies of the late precambrian at ediacara south australia journal of the geological society of australia 14 195 214 roland goldring formed one of the few collections of original ediacara fossil materials that can still be accessed outside of australia this material collected from the type locality at ediacara is now housed in the natural history museum at oxford and includes excellent specimens of the enigmatic fossil dickinsonia costata sprigg r c 1949 early cambrian jellyfishes of ediacara south australia and mount john kimberly district western australia transactions of the royal society of south australia 73 72 99 this first detailed description of the oxford dickinsonia material and its associated wrinkle structures is discussed with relevance to some wider problems facing ediacaran taxonomy serial photographic reconstruction techniques are used to produce high resolution analyses of these fossils attention is drawn to features such as relief inversion of the upper surface in which a spatulate b segment is typically preserved in positive hyporelief while the rest of the fossil is mainly preserved in negative hyporelief segments can also appear to bifurcate and merge a feature which together with the glide plane of symmetry is inconsistent with the bilaterian model often argued for this taxon controversial and conflicting claims for the presence of circular muscles a rigid outer cuticle an axial gut and even radial tentacles can all be explained by a single hypothesis that involves a simple possibly coelenterate grade organism which had a distinctive hydraulic body structure that underwent stretching strain collapse and contraction as the internal turgor pressure in the segments changed especially during death and burial

remnants of a cretaceous intra oceanic subduction system within the yarlung zangbo suture southern tibet extensive field investigations along the yarlung zangbo suture zone in southern tibet reveal the presence of now fragmented remnants of a south facing intra oceanic subduction system this system developed within tethys during the cretaceous the associated arc forearc ophiolite and subduction complex were emplaced onto the leading edge of india at the end of the cretaceous rapid sedimentation in oblique slip basins and disruption of water saturated sediments into melange was widespread and concomitant with ophiolite emplacement we describe the tectonic entities that developed during this previously unrecognized phase of tethys tibet evolution and present a new model for the evolution of this portion of tibet

active intracontinental transpressional mountain building in the mongolian altai defining a new class of orogen abstract mountain ranges that are actively forming around the western and northern perimeter of the indo eurasia collisional deformational field such as the mongolian altai comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens late cenozoic uplift and mountain building in the mongolian altai is dominated by regional scale dextral strike slip faults that link with thrust and oblique slip faults within a 300 km wide deforming belt sandwiched between the more rigid junggar basin block and hangay precambrian craton dominant orogenic elements in the mongolian altai include double restraining bends terminal restraining bends partial restraining bends single thrust ridges thrust ridges linked by strike slip faults and triangular block uplifts in areas of conjugate strike slip faults the overall pattern is similar to a regional strike slip duplex array however the significant amount of contractional and oblique slip displacement within the range and large number of historical oblique slip seismic events renders the term transpressional duplex more accurate intramontane and range flanking basins can be classified as ramp basins half ramp basins open sided thrust basins pull apart basins and strike slip basins neither a classic fold and thrust orogenic wedge geometry nor a bounding foredeep exists the manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown however crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late cenozoic regional epeirogenic uplift in the russian altai and sayan regions

geometry and timing of mesozoic deformation in the western part of the xuefeng tectonic belt south china implications for intra continental deformation abstract the xuefeng tectonic belt is an important intraplate structural system in the south china block its west margin is up to 1300 km away the present day continental margin and the mesozoic structural trends in this belt are perpendicular to and have no correlation with the triassic qinling dabie orogenic belt this belt provides important clues for understanding the mechanism of intraplate deformation and the tectonic history of south china we identified two generations of folding with different strike directions in the xuefeng tectonic belt based on the youngest folding involved strata and their overprinting relationship the early one is ne striking overprinted by the n s striking folds both during late jurassic and late cretaceous thrust faults in the xuefeng tectonic belt mainly show top to west thrust movement which is approximately coeval with the n s striking folding the thrust fault system can be divided into three zones the root zone with steep thrusts the middle zone characterized by imbricate thrusts and the frontal zone with a few shallow thrusts in addition two generations of strike slip faults with different structural trends have been identified e w striking strike slip faults showing dextral transpression and ne striking strike slip faults with sinistral offset and controlling the upper cretaceous basins according to regional geological relationship and structural overprinting we interpret that the e w trending strike slip faults formed in the first stage whereas the ne striking strike slip faults formed later during an e w oriented compressional event therefore the principal stress direction varies from nw se to e w

a new ecological model for the 565 ma ediacaran biota of mistaken point newfoundland abstract ediacaran macrofossils immediately precede the first animal ecosystems of the cambrian period and have excited much attention for potentially containing ancestors of the modern animal phyla ediacaran fossil surfaces have been variously interpreted as vertically tiered census populations comparable to animal ecosystems or as osmotrophic ecosystems exploiting turbulent flow regimes these hypotheses are highly dependent upon the taphonomic interpretation of mistaken point newfoundland as a consensus population representing the associations of the organisms in life reanalyses of these surfaces however indicate that this taphonomic model is inconsistent with the range of preservation states seen in each taxon we present a new taphonomic model for mistaken point surfaces in newfoundland canada and describe it using an index of decay this reveals a complex history of life death and decay at these sites data gathered from large scale casting projects in newfoundland show that only 15 40 of individuals were killed by ash flows rather than the whole population as previously interpreted this shows that ediacaran organisms at mistaken point newfoundland had a diverse range of ecological relationships with the microbial mat system frondose organisms are engaged in chemical exchange with the sediment and the water column with the stem penetrating through the microbial mat reclining forms such as fractofusus lived exclusively above the microbial mat and drew nutrients from the dead organisms on which they typically grew the ecology is based on organism interaction with the sediment water interface quite unlike that of modern vertically tiered metazoan communities that have developed since the start of the cambrian period

spindle shaped ediacara fossils from the mistaken point assemblage avalon zone newfoundland the mistaken point assemblage of the ediacara fossils is dominated by rangeomorphs with homologous fractal branching elements the most distinctive are the fusiform fossils herein named fractofusus misrai n gen and n sp and fractofusus andersoni n gen and n sp although endemic to the newfoundland portion of the avalonia terrane they dominated deep sea floor communities below the photic zone in the mid ediacaran period ca 575 560 ma their biological affinities remain uncertain but their architecture suggests a phylogenetic position near the base of the metazoa

re os sulfide chalcopyrite pyrite and molybdenite systematics and fluid inclusion study of the duobaoshan porphyry cu mo deposit heilongjiang province china abstract the duobaoshan porphyry deposit located in the northwestern part of the lesser hinggan range is one of the biggest porphyry cu mo deposits in the central asian orogenic belt in china the duobaoshan porphyry deposit occurs in granodiorite and volcanic rocks of the middle ordovician duobaoshan formation six types of veins have been identified in three ore forming stages as follows a quartz potassic feldspar vein in the early ore forming stage an early stage quartz molybdenite vein late stage quartz molybdenite and quartz chalcopyrite pyrite veins in the middle ore forming stage and quartz pyrite and calcite quartz veins in the late ore forming stage the following four types of fluid inclusions are distinguished from various quartz veins two phase aqueous pure gas phase co 2 bearing and daughter mineral bearing inclusions the ore forming fluid for the early ore forming stage belongs to the h 2 o co 2 nacl system which is characterized by high temperatures 550 c intermediate salinities 16 2 18 1 wt nacl eqv and high co 2 content the ore forming fluid from the middle ore forming stage evolved to the h 2 o co 2 nacl system which is characterized by intermediate to high temperatures 230 450 c and high low salinities 0 8 to 65 3 wt nacl eqv and is also rich in co 2 and metals the ore forming fluid finally reached cool temperatures 110 200 c low salinities 3 9 8 4 wt nacl eqv and was co 2 poor intensive fluid immiscibility or boiling occurred when the ore forming fluid with temperatures of 230 450 c and pressures of 10 41 mpa ascended to 4 1 km inducing the escape of co 2 depressing the solubility of fluid and depositing abundant metal sulfides the total re and os concentrations of chalcopyrite and pyrite range from 0 15 to 2 95 g g and 0 74 to 15 01 ng g respectively analyses of seven chalcopyrite and pyrite samples yielded isochron ages of 482 486 ma and the model age of one molybdenite sample is 485 6 3 7 ma the mineralization age of the duobaoshan deposit is between 482 and 486 ma and mantle fluid and materials were involved in the mineralization process the duobaoshan deposit is a classic porphyry cu mo deposit that formed in an early palaeozoic island arc tectonic setting

stratified oceans and oxygenation of the late precambrian environment a post glacial geochemical record from the neoproterozoic of w mongolia the late neoproterozoic 750 545 ma was a time of revolutionary environmental change recurrent glaciation and tectonic upheaval which culminated in the evolution of metazoans and animal biomineralization geochemical data are presented for a post glacial 700 ma limestone succession from w mongolia 87 sr 86 sr is used to constrain the timing of early diagenetic exchange stratigraphic trends to high d 13 c carb and d 13 c org mirror sea level fluctuations which we argue is consistent with the hypothesis that late precambrian ocean chemistry was controlled by vertical stratification repeated establishment of stratification 700 545 ma would have led to greater oxygen availability in the surface environment a causal link between this oxygenation and the further evolution of animals is proposed

a neoarchean dismembered ophiolite complex from southern india geochemical and geochronological constraints on its suprasubduction origin abstract ophiolites the remnants of ancient oceanic lithosphere have been described from collisional sutures of various ages with only few examples from archean terranes here we report the discovery of a neoarchean ophiolite suite from the southern margin of the dharwar craton in india tectonically intercalated within a neoproterozoic suture zone the metamorphosed and variably dismembered ophiolite suite exposed around devanur comprises altered ultramafic units websterite gabbros mafic dykes amphibolites trondhjemites and pegmatites associated with ferruginous metachert structural and petrographic studies indicate that the rocks represent a highly sheared and metamorphosed suite emplaced as a thrust sheet the major and trace element geochemistry of the mafic dykes indicate derivation from basaltic andesitic magmas with tholeiitic to calc alkaline characteristics the rocks display negative nb anomalies with enrichment of lile k rb ba th and depletion in hfse ti nb hf tb the tectonic discrimination of these rocks based on various geochemical plots suggests that they were generated in a suprasubduction zone setting we present new shrimp zircon u pb data for two trondhjemite samples from this complex which yield 238u 206pb ages of 2528 61 and 2545 56 ma the neoarchean age from the trondhjemites obtained in our study is closely comparable to similar ages obtained in recent studies from magmatic zircons in charnockites and orthogneisses in the area the suprasubduction zone assemblages and arc magmas suggest a neoarchean ocean closure along the southern margin of the dharwar craton

charnia and sea pens are poles apart c harnia from the ediacara biota is here examined in terms of its growth and development the ediacara biota comes from the critical period of evolution just before the cambrian explosion and is key to our understanding of the origin of animal life we show that charnia cannot be related to the modern cnidarian group the sea pens pennatulacea with which it has for so long been compared as generative zones cannot be homologized between these forms

paleozoic early mesozoic gold deposits of the xinjiang autonomous region northwestern china the late paleozoic early mesozoic tectonic evolution of xinjiang autonomous region northwestern china provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major eastern asia cratonic blocks these sutures are now represented by the altay shan tian shan and kunlun shan ranges with the former two separated by the junggar basin and the latter two by the immense tarim basin in northernmost xinjiang final growth of the altaid orogen southward from the angara craton is now recorded in the remote mid to late paleozoic altay shan accreted early to middle devonian oceanic rock sequences contain typically small precious metal bearing fe cu zn vms deposits e g ashele orogenic gold deposits are widespread along the major irtysh e g duyolanasayi saidi taerde kabenbulake akexike shaerbulake and tuergen hongshanzui e g hongshanzui fault systems as well as in structurally displaced terrane slivers of the western junggar e g hatu and eastern junggar areas geological and geochronological constraints indicate a generally late carboniferous to early permian episode of gold deposition which was coeval with the final stages of altaid magmatism and large scale right lateral translation along older terrane bounding faults the tian shan an exceptionally gold rich mountain range to the west in the central asian republics is only beginning to be recognized for its gold potential in xinjiang in this easternmost part to the range northerly and southerly directed subduction accretion of early to mid paleozoic and mid to late paleozoic oceanic terranes respectively to the precambrian yili block central tian shan was associated with 400 to 250 ma arc magmatism and carboniferous through early permian gold forming hydrothermal events the more significant resulting deposits in the terranes of the southern tian shan include the sawayaerdun orogenic deposit along the kyrgyzstan border and the epithermal and replacement deposits of the kanggurtag belt to the east in the chol tagh range gold deposits of approximately the same age in the yili block include the axi hot springs epithermal deposit near the kazakhstan border and a series of small orogenic gold deposits south of urumqi e g wangfeng gold rich porphyry copper deposits e g tuwu define important new exploration targets in the northern tian shan of xinjiang the northern foothills of the kunlun shan of southern xinjiang host scattered small placer gold deposits sources for the gold have not been identified but are hypothesized to be orogenic gold veins beneath the icefields to the south they are predicted to have formed in the tianshuihai terrane during its early mesozoic accretion to the amalgamated tarim qaidam kunlun cratonic block

metasedimentary rocks of the angara kan granulite gneiss block yenisey ridge south western margin of the siberian craton provenance characteristics deposition and age abstract the angara kan granulite gneiss block yenisey ridge is one of the main basements uplift within the south western margin of the siberian craton the major part of the angara kan block is composed of early precambrian high grade metamorphic rocks metasedimentary association of the kan granulitic complex is composed of garnet bearing garnet orthopyroxene and orthopyroxene bearing gneisses garnet and orthopyroxene bearing gneisses with cordierite and sillimanite studied paragneisses were formed at the expense of granulite metamorphism of terrigenous rocks ranging from graywacke to pelitic rock or mudstone to estimate the time of sedimentation and metamorphism of the terrigenous deposits the u pb zircon dating has been performed using the shrimp ii ion microprobe detrital zircon cores from the biotite orthopyroxene and high alumina gneisses yield ages of 2 6 1 94 and 2 4 1 94 ga respectively together with the age of the magmatic zircons formed during high grade metamorphism and partial melting 1 89 ga and metamorphic rims 1 87 ga it defines the time of sedimentation between 2 0 1 94 and 1 89 1 87 ga detrital zircon ages indicate both archean and paleoproterozioc rocks in provenance source that agrees with the nd model ages of metasediments ranging in interval 2 4 2 8 ga potential source of the archean detrital zircons was the exposed basement of the southwestern siberian craton whereas the paleoproterozoic juvenile crustal source seems to be buried basement of the tungus province of the siberian craton deposition of the kan terrigeneous rocks was coeval with sedimentation in the southeastern part of the sharyzhalgay uplift where ages of detrital zircon cores and metamorphic rims from paragneisses bracket sediment deposition between 1 95 and 1 85 ga

middle paleozoic paleomagnetism of east kazakhstan post middle devonian rotations in a large scale orocline in the central ural mongol belt abstract in order to test different hypotheses concerning the paleozoic evolution of the ural mongol belt umb and the amalgamation of eurasia we studied middle devonian basalts from two localities 11 sites and lower silurian volcanics redbeds and intra formational conglomerates from three localities 20 sites in the chingiz range of east kazakhstan the devonian rocks prove to be heavily overprinted in the late paleozoic and a high temperature presumably primary southerly and down component is isolated at only four sites from a homoclinal section most silurian redbeds are found to be remagnetized in the late paleozoic in contrast a bipolar near horizontal remanence isolated from silurian volcanics is most probably primary as indicated by positive tilt and conglomerate tests analysis of paleomagnetic data from the chingiz range shows that southward pointing directions in ordovician silurian and devonian rocks are of normal polarity and hence indicate large scale rotations after the middle devonian the chingiz paleomagnetic directions can be compared with paleozoic data from the north tien shan and with the horseshoe shaped distribution of subduction related volcanic complexes in kazakhstan both paleomagnetic and geological data support the idea that today s strongly curved volcanic belts of kazakhstan are an orocline deformed mostly before mid permian time despite the determination of nearly a dozen new paleozoic paleopoles in this study and other recent publications by our team significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late paleozoic however the paleomagnetic results from the chingiz range and the north tien shan indicate that these areas show generally coherent motions with siberia and baltica respectively

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

glacial south atlantic surface temperatures interpolated with a semi inverse ocean model 1 to drive an atmospheric general circulation model sea surface temperatures ssts are needed as lower boundary condition these are well known for the modern ocean but for other time slices the database is very sparse and often complete global sst fields are not available to circumvent this problem the simple ocean model has been developed which estimates surface currents in a diagnostic manner from surface winds horizontal heat transports by advection and diffusion and surface heat fluxes are used to calculated ssts the unknown transports from the deep ocean are inversely estimated from sparse sst data the model can be understood as a method to estimate a global sst field from a sparse data set where it takes into account the wind driven surface circulation the simple model is applied to a set of last glacial maximum ssts reconstructed from a new south atlantic core data set the resultant completed sst field exhibits more structure than the climap reconstruction with larger glacial cooling in the central equatorial atlantic and off the shore of angola namibia and less cooling in the central south atlantic

low al and high al trondhjemites in the huai an complex north china craton geochemistry zircon u pb and hf isotopes and implications for neoarchean crustal growth and remelting abstract voluminous tonalite trondhjemite granodiorite ttg magmas were emplaced in the huai an complex of north china craton ncc during the neoarchean here we present the geochemical characteristics of these rocks and identify low al lal and high al hal types of trondhjemites within the ttg suite the lal group displays high silica sio2 77 80 wt and low al2o3 contents 11 06 11 89 wt a strongly peraluminous a cnk 1 16 and 1 19 composition and enrichment in hree lan ybn 4 and 5 gdn ybn 0 35 and 0 9 their low rb 13 and 28 ppm th 0 3 and 7 0 ppm relatively high na2o k2o values 3 6 and 4 1 and mgo 0 63 and 0 68 wt with moderately high mg 36 and 53 suggest crystallization from a primitive source the hal group is characterized by relatively low sio2 67 22 71 57 wt and high al2o3 contents 16 35 16 41 wt with trace element contents and distribution patterns closely comparable to those of archean high al ttgs our geochemical data do not favor a direct genetic link between the lal and hal trondhjemite groups the zircon u pb data reveal that the lal and hal groups represent coeval intrusions at ca 2 55 2 5 ga in situ analysis of hf isotopes in the zircons ehf 5 6 to 10 and tdm 2462 2595 ma together with the geochemical features of the low al trondhjemites suggest that they were generated under relatively low pressure

intracontinental deformation in a frontier of super convergence a perspective on the tectonic milieu of the south china block abstract since mesozoic the south china region has been located at the center of a triangular area surrounded by westward subduction of the pacific plate northward subduction of the india plate beneath the eurasia plate and collision of the north and south china blocks along the central china orogen this region thus marks the frontier of a super convergent regime within the super convergence domain the compressional structures in the center of the south china block are mainly characterized by shortening thrusting and decollement the block underwent inhomogeneous rejuvenation of the pre existing crust and lithospheric structures through reactivation of late stage activities the surface deformation of the xuefeng intracontinental tectonic system within the south china block is possibly derived from intraplate tectonics particularly the distinct magmatism between the west and east limbs of the xuefeng precambrian uplift is a possible response of the rheological structure of the lithosphere the deep structures as revealed from tomographic studies show marked difference of lithosphere architecture between the eastern and western sub blocks of the south china block these data illustrate the long term mosaic of multi block convergence which led to present day inhomogeneity in the continental lithosphere in south china a comparison of the intensive contraction of the south china block with the distinct features of rifting of the north china block brings out the contrasting structural and tectonic signatures developed in the same frontier of one of the largest super convergent systems on the globe during the mesozoic to cenozoic

post fossilization processes and their implications for understanding ediacaran macrofossil assemblages fossil assemblages from newfoundland s avalon peninsula preserve diverse examples of the enigmatic ediacaran macrobiota offering some of the earliest evidence for large and complex multicellular life these fossils are exposed on extensive coastal bedding planes in extraordinary abundances permitting palaeoecological studies based on census data from spatially extensive palaeocommunities such studies have been used to constrain the reproductive strategy and phylogenetic placement of ediacaran organisms geological mapping and stratigraphic correlation in the mistaken point ecological reserve reveal that some fossil bearing surfaces can be tracked over distances of several kilometres these laterally extensive surfaces reveal that the modern processes by which the sediment overlying a fossil surface is removed may impose important controls on the observed composition of fossil assemblages weathering and erosion along with factors associated with tectonics metamorphism and discovery are here grouped as post fossilization processes and introduce biases that are often not explicitly accounted for in palaeoecological studies specifically post fossilization processes may differentially influence the preservational fidelity of individual specimens on a given surface and generate features that could be mistaken for original morphological characters we therefore recommend that post fossilization processes must be considered when undertaking palaeoecological studies in ediacaran successions in newfoundland and potentially elsewhere

oceanic surface conditions recorded on the sea floor of the southwest pacific ocean through the distribution of foraminifers and biogenic silica over 180 surface sediment samples from the southwest pacific ocean were investigated for their planktonic foraminiferal 149 m opaline and terrigenous sediment content with the aim to determine the oceanic conditions at the sea surface above the sampling sites high concentrations of biogenic opal are related to high productivity levels recognised in tropical surface waters the abundance of this biogenic opal found within the sediments on the ocean floor shows a slight decrease as one approaches the australian landmass and also poleward from the equatorial belt the distribution of major species of planktonic formainifers reflects different surface water masses q mode factor analysis of planktonic foraminiferal percentage data from 63 core tops permits identification of several characteristic formainiferal assemblages for the southwest pacific ocean four factors explain up to 95 5 of the total variance factor 1 66 is dominated by the tropical subtropical species globigerinoides sacculifer and globigerinoides ruber the transitional to subpolar species globorotalia inflata is important in factor 2 12 the temperate cool factor 3 13 is characterised by turborotalia quinqueloba and globigerinita glutinata factor 4 which explains 3 of the total variance and which is represented by several species is assigned to the high productive equatorial and coastal waters off the australian continental margin palaeoecological equations permitting an estimate of sea surface temperatures and salinities are presented the correlation coefficients between modern data adapted from literature and estimated by transfer function fp 4 transfer function for planktonic formainifers are 0 95 for temperature and 0 77 for salinity

temporal evolution of the permian large igneous province in tarim basin in northwestern china abstract the temporal relations of different types of rocks in the tarim large igneous province tlip are studied using stratigraphic correlation lithologically spatial distribution and isotopic ages the tlip covers an area 250 000 km2 in the western and central part of the tarim basin the lithological units of the tlip include basalt diabase layered intrusive rock breccia pipe mica olivine pyroxenite olivine pyroxenite gabbro ultramafic dyke quartz syenite quartz syenite porphyry and bimodal dyke this is the first report for the spatial distribution of the tlip from the spatial section lines which shows the stratigraphic correlation among basaltic lava tuff interlayered mudstone siltstone and sandstone and the thicknesses of the basaltic lavas from different field sections and drill holes and the basalts from the kupukuziman and kaipaizileike formations were subdivided in the drill hole sections this indicates that the basaltic lavas were widely distributed in the tarim basin combined with previous study of geochemical and sr nd pb isotopic characterization from the basalts and their genetic link with mantle plume activity and large diabase swarms developments the permian igneous units constitute a tarim large igneous province zircon shrimp u pb dating firstly yields 284 3 2 8 ma for the quartz syenite porphyry recent shrimp and la icp ms zircon u pb and 40ar 39ar ages are used to discuss temporal relations of different rock units in the tlip formed between 290 and 274 ma and these data are more reliable than the k ar ages of 220 310 ma reported previously the sequence of magmatism of the tlip in the central and western parts of the tarim basin are basaltic lava in the kupukuziman and kaipaizileike formations 285 290 ma layered mafic ultramafic rock mica olivine pyroxenite breccia pipe diabase and ultramafic dyke quartz syenite quartz syenite porphyry and bimodal dyke 274 284 ma

geochronology and tectonic evolution of karimnagar and bhopalpatnam granulite belts central india abstract the karimnagar granulite belt kgb and the bhopalpatnam granulite belt bgb occur along both flanks of the pranhita godavari pg rift basin we present a state of the art overview on the geochronological and tectonic aspects of these belts and surrounding geologic domains and report new age data on zircon monazite and uraninite recovered from granulite facies assemblages from kgb and bgb based on electron microprobe analyses epma zircons from kgb charnockites show core ages of up to 3 1 ga mantled by rims of 2 6 ga zircons from bgb have 1 9 ga cores mantled by 1 7 ga rims zircons with core ages of 1 6 to 1 7 ga in bgb rocks suggest new growth at this time monazites and uranitite from kgb show clear peaks with well defined ages in the narrow range between 2 42 0 08 ga and 2 47 0 03 ga rims of monazite show mean age of 2 21 0 08 ga monazites from bgb define sharp linear trend in pbo vs tho2 diagram delineating a clear isochron with age of 1 59 0 03 ga age data from kgb and bgb presented in this report negate current models linking these terrains to godavari granulite belt and considering them as single and contemporaneous entity the mid archaean to early palaeoproterozoic signature recognized from kgb is totally missing in bgb on the other hand kgb rocks do not record any evidence for major mesoproterozoic thermal regime the two granulite belts shouldering the pg rift basin have therefore evolved in different times under distinct p t conditions and thermal regimes our results have important implications in evaluating models of supercontinent assemblies particularly the older assemblies of ur columbia and rodinia while tectonothermal events in kgb broadly match with those of east dharwar we propose that bgb represents a 1 6 ga collisional mobile belt between the bastar and the dharwar cratons the 1 6 ga collisional mobile belt at the southern margin of the bastar craton was superposed by rift activity along the pg basin at 1 5 ga this sequence of events goes against the existence of a 3 0 ga old contiguous assembly of ur but closely matches with the history of accretion and break up of the columbia further parts of the pg basin located away from the influence of the eastern ghats mobile belt neither recorded any grenville ages 1 0 ga corresponding to the rodinia accretion nor late pan african ages ca 550 ma relating to the gondwana amalgamation indicating that the region did not witness any of these younger tectonic events

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

an inverse model for seasonal circulation over the southern brazilian shelf near surface velocity from the heat budget abstract an inverse model was developed of the seasonal upper layer circulation in the region adjacent to the coast of southern brazil between 30 and 35 s 50 and 55 w near the boundary of the brazil malvinas confluence in this region there are no in situ data on circulation while a large array of data on sea surface temperature and surface heat fluxes acquired through the last 30 years is available the model is based on the joint analysis of observed seasonal changes of sst along with observed fields of insolation and surface heat fluxes from the equation of heat conservation integrated over the variable depth of the mixed layer the residual flux fields required to explain the observed temperature changes between seasons were computed generally this residual flux accounts for advection diffusion and entrainment diffusion has been neglected based on scaling estimates of term sizes while entrainment was parameterized through observed changes of the mixed layer depth with the assumption that