late paleozoic closure of the ob zaisan ocean along the irtysh shear zone nw china implications for arc amalgamation and oroclinal bending in the central asian orogenic belt the largest accretionary orogen in the world the central asian orogenic belt has evolved through the assembly of various oceanic and continental blocks understanding the processes associated with the development of this orogenic belt relies on precise recognition of the boundaries between various terranes one such major suture zone which records the collisional history of the siberian marginal arc system chinese altai with intra oceanic arc systems east west junggar is the irtysh shear zone in nw china the spatial continuity and the tectonic nature of this shear zone are still poorly understood but its development has supposedly made a significant impact on the architecture of the western central asian orogenic belt and the formation of the kazakhstan orocline here we provide new insight into the evolution of this shear zone based on detrital zircon ages hf isotope composition structural data and ar ar age constraints on the timing of deformation our results show a major discrepancy in detrital zircon populations and hf model ages across the southern chinese altai and the northern east west junggar thus allowing us to map the exact location of the tectonic boundary detrital zircon data constrain the initial closure of the ob zaisan ocean to the late carboniferous 323 ma and new structural and ar ar geochronological data shed light on the subsequent collisional processes we propose that the collisional zone between the chinese altai and the east west junggar was initially subjected to crustal thickening at ca 323 295 ma followed by orogen parallel extension ca 295 ma and transpressional deformation ca 286 253 ma the closure of the ob zaisan ocean in nw china postdates the initial phase of oroclinal bending in the western central asian orogenic belt thus indicating that oroclinal bending initiated during subduction based on our new constraints and other available geological data we suggest that the early stage of oroclinal bending was likely driven by slab rollback

anomalous sulfur poor platinum group element mineralization in komatiitic cumulates mount clifford western australia an unusual occurrence of sulfur poor platinum group element pge mineralization has been discovered at mount clifford in the agnew wiluna belt western australia within the lower part of a 1 000 m thick komatiitic dunite body the host body consists primarily of strongly serpentinized olivine adcumulates with accessory chromite high precision whole rock icp ms data show that the pge mineralization extends over tens of meters whereas the lateral extent is unknown palladium and pt abundances are closely associated with base metal sulfides but show offset distribution patterns with maximum concentrations associated with the relatively sulfide poor base of a disseminated sulfide bearing layer whole rock concentrations range up to 4 100 ppb pd and 920 ppb pt iridium rh and ru follow the trends in pd and pt but are strongly depleted ir 0 4 ppb ru 0 5 ppb rh 0 1 ppb platinum group minerals pgm were located in essentially sulfide free serpentine 2 m below the peak in sulfide abundance and can be categorized into three groups pd antimonides pt dominated pgm and pt bearing ni antimonides the pge mineralization zone is underlain by an interval of strong ni depletion within olivine mesocumulates that is characterized by an unusual negative correlation between ni and the mg number of the rock this relationship is interpreted to be the result of an equilibration of olivine of variable forsterite content with a relatively large mass of magmatic sulfide however there is no direct evidence of this sulfide mass anywhere in the entire mount clifford dunite body the ni depletion is accompanied by strong depletion in ipge ir ru and rh the association of the pge zone with a reversal in the mg fe ratio of the host cumulates and a distinctive offset relationship of multiple pt pd and cu s peaks is suggestive of a primary magmatic origin however this is inconsistent with current models for offset reef pge concentrations which involve the onset of sulfide liquid saturation from a previously sulfur undersaturated pge undepleted magma the association of enriched pt and pd with highly depleted ni and ipge in immediately underlying cumulates conflicts with this model we suggest a combination of processes early sulfide segregation at low r values producing ni and ipge depleted olivine partial redissolution and removal of most of this sulfide component during a major replenishment event and subsequent overprint by a migrating pt pd cu rich fluid

final amalgamation of the tianshan and junggar orogenic collage in the southwestern central asian orogenic belt constraints on the closure of the paleo asian ocean abstract the tianshan and junggar orogenic collage occupies the southwestern part of the central asian orogenic belt and was assembled by collision accretion of several continental blocks and island arcs during late paleozoic early mesozoic time following the consumption of the junggar and south tianshan oceanic basins in the western segment of the paleo asian ocean considerable and continuing controversy has surrounded when where and how this orogenic collage was eventually amalgamated which plays a crucial role in understanding the formation of the central asian orogenic belt this review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains a comprehensive data compilation indicates that the formation of ophiolites along major sutures in the tianshan and junggar region lasted to the early carboniferous for the kalamaili suture zone to the mid carboniferous for the west junggar region and the north tianshan suture zone and to the late carboniferous for the south tianshan suture zone ca 325 310 ma ultra high pressure metamorphism along the western part of the south tianshan suture occurred nearly synchronously with the collision between the tarim craton and the central tianshan yili block the oceanic closure and collision events were sequentially followed by widespread and intensive a type granitic and bimodal magmatism which commenced in the mid carboniferous along the kalamaili belt and in the latest carboniferous to earliest permian in other regions contemporaneously large scale strike slip shearing took place along major faults subparallel to main sutures with a dominant dextral sense and deformation time since the carboniferous permian transition available data and geological evidence support an eastward propagating scissor like closure of the western segment of the paleo asian ocean along the south tianshan and north tianshan suture zones over a period from the mid to end carboniferous with the south tianshan belt representing the final suturing site in the early permian the tarim mantle plume likely merely affected the southwestern part of the assembled tarim and tianshan region as indicated by regional discrepancy in type and geochemistry of early permian a type granitoids the amalgamation of the tianshan and junggar orogenic collage was associated with the tectonic bending of the kazakhstan orocline leaving a piece of trapped oceanic crust in its middle part beneath the present junggar basin

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

paleomagnetic constraints on the paleogeography and oroclinal bending of the devonian volcanic arc in kazakhstan abstract a prominent feature of the central part of the ural mongol orogenic belt is a series of concentric horse shoe shaped volcanic arcs with the youngest arc on the inside this structure was long suspected to be an orocline but unequivocal evidence for this was lacking mainly because paleomagnetic results of suitable age from this area remained sparse but also because their interpretation was not straightforward due to a long history of deformations associated with the protracted late paleozoic assembly of asia our paleomagnetic study of middle devonian basaltic and andesitic flows in southeastern kazakhstan revealed two main components of magnetization the primary nature of a high temperature magnetization tilt corrected dec 286 5 inc 46 4 95 7 8 k 29 2 n 13 sites is supported by the presence of antipodal directions and a baked contact test we also isolated a post folding overprint with an in situ mean direction dec 134 9 inc 43 0 95 4 9 k 71 6 n 13 sites the age of this overprint can be estimated as early permian with a high degree of confidence the declination of the overprint is seen to be deflected counter clockwise by 100 6 relative to the 290 ma reference direction indicating that the studied locality similar to many other localities in the region was affected by late orogenic rotations we use the overprint s deflection to correct the declination of the primary devonian magnetization for these late orogenic block rotations declinations from other silurian and devonian paleomagnetic results in the subduction related devonian volcanic arc of kazakhstan have been corrected for such rotations wherever the latter are reasonably well documented using corrected declinations as passive markers we restored the trend of the volcanic belt to its devonian configuration our analysis indicates that the presently curved belt was nearly straight and nw se trending this 1500 km long volcanic belt characterized the northeastern margin of a landmass in today s central kazakhstan where subduction occurred towards the southwest oroclinal bending of this arc took place in the interval between the middle devonian and the late permian

3d textural evidence for the formation of ultra high tenor precious metal bearing sulphide microdroplets in offset reefs an extreme example from the platinova reef skaergaard intrusion greenland abstract the platinova reef in the skaergaard intrusion east greenland is an example of a type of layered intrusion hosted precious metal enriched stratiform disseminated sulphide deposit referred to as offset reefs these typically show platinum group element pge enrichment immediately below a major increase in the abundance of cu rich sulphides with a prominent peak in au enrichment exactly at that transition between the pge rich and the cu sulphide rich zones the reasons for the relative sequence of offsets in metal peaks and the occasionally very high metal tenors have been subject to great debate here we use an integrated approach of high resolution x ray computed tomography hrxct sem synchrotron and desktop microbeam xrf mapping and thin section petrography to comprehensively classify the textural relations of the precious metal bearing sulphides of the platinova reef as an extreme end member example of an exceedingly high tenor offset deposit our results show that in the zones of pge enrichment precious metal minerals pmms are intimately associated with cu sulphide globules mostly located at or close to silicate and oxide boundaries the textures are identical in zones enriched in pd and au and thus we do not see any evidence for different processes forming the different zones the pmm cu sulphide ratio in each globule varies significantly but overall the size of the globules increases from the pd rich through the au rich and into the cu zone with a significant corresponding decrease in pm tenor as such this records a progression of exceedingly high tenor microdroplets of sulphide which progressively get larger up through the section and decrease in tenor proportionally to their size cumulus droplets of cu sulphide became enriched in metals and were trapped in situ without significant transport from their point of nucleation the transition to larger sulphides represents a change from sulphides nucleated and trapped in situ to larger ones that liquated from magma devoid of crystals and that were able to grow and sink this feature is common in all offset reef deposits and is marked by the major enrichment in au although the metal ratios of pge to au in the pd and au rich offset zones differ the identical textures and comparable mineralogy show the physical mechanisms of concentration are the same indicating a similar physical method of concentration the relative position of the pd au and cu peaks in the platinova reef is essentially the same as that in numerous other offset reefs suggesting that common overarching processes are responsible for the enrichment in metals and relative offsets in peak metal concentrations in all such deposits the most important of these processes are their relative dsul sil values and the diffusivities of the metals which determine the order of offsets and the high tenors of the smallest sulphide droplets the platinova reef therefore records the extreme enrichment via equilibrium and diffusive partitioning into sulphide liquid microdroplets very close to their point of nucleation

thermochronological constraints on the late paleozoic tectonic evolution of the southern chinese altai abstract the chinese altai as an accretionary orogen developing from the cambrian to carboniferous was modified by permian deformation metamorphism and magmatism in response to the collision with the east junggar the tectonic processes of the collision and the timing of related deformation and metamorphism are still enigmatic here we present new 40 ar 39 ar dating results for granitic gneisses and amphibolites exposed in the qiongkuer domain in two areas alahake and fuyun of the southern chinese altai the amphiboles from both aalaheke and fuyun areas yield consistent 40 ar 39 ar plateau ages at 265 9 1 7 ma and 270 1 3 1 ma in contrast the biotites from two areas show distinct 40 ar 39 ar ages of 232 0 2 1 ma and 226 8 1 7 ma for the alahake area and 245 1 1 5 ma and 264 5 2 2 ma for the fuyun area respectively given that 40 ar 39 ar ages are younger than the permian high temperature metamorphism at 299 277 ma as constrained by metamorphic zircons in the qiongkuer domain we interpret these 40 ar 39 ar ages to record the cooling history of two areas compatible amphibole ages in both areas indicate a similar exhumation age along the qiongkuer domain cooling through 550 c at 270 265 ma which may have been associated with the development of the sinistral erqis shear zone during the collision between the chinese altai and the east junggar the subsequent exhumation processes were variable in different areas of the qiongkuer domain as showed by the distinct biotite ages which may indicate along strike variation of cooling processes from 550 c to 300 c in the qiongkuer domain

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

paleomagnetism of mid paleozoic subduction related volcanics from the chingiz range in ne kazakhstan the evolving paleogeography of the amalgamating eurasian composite continent the tectonic and paleogeographic evolution of the ural mongol belt between the cratons of baltica siberia and tarim is key to the formation of the eurasian composite continent during paleozoic time but the views on this complicated process remain disparate and sometimes controversial a study of three volcanic formations of mid silurian lower to middle devonian and middle devonian age from the southwestern boundary of the chingiz range ne kazakhstan yields what are interpreted as primary paleomagnetic directions that help clarify the evolution of the belt a single polarity characteristic component in mid silurian andesites yields a positive intraformational conglomerate test whereas dual polarity prefolding components are isolated from the two devonian collections post folding reversed polarity overprint directions have also been isolated and are likely of permo triassic age these new data can be evaluated together with previously published paleomagnetic results from paleozoic rocks in the chingiz range and allow us to establish with confi dence the polarity of each result and hence to determine the hemisphere in which the area was located at a given time we conclude that ne kazakhstan was steadily moving northward albeit with variable velocity crossing the equator in silurian time these new paleomagnetic data from the chingiz range also agree with and reinforce the hypothesis that the strongly curved volcanic belts of kazakhstan underwent oroclinal bending between middle devonian and middle permian time a comparison of the chingiz paleolatitudes with those of siberia shows insofar as the sparse data allow similarities between the northward motion of the chingiz unit and that of siberia which imposes important constraints on the evolving paleogeography of the ural mongol belt

major features of glaciochemistry over the last 110 000 years in the greenland ice sheet project 2 ice core major chemical species cl no3 so42 na nh4 k mg2 ca2 and 18o covering the last 110 000 years from the greenland ice sheet project 2 gisp2 ice core were utilized in this study in order to reconstruct the soluble chemistry of the atmosphere over greenland and interpret major climate events that have affected the region during the holocene the major chemical species and 18o do not display any significant relationship however a strong inverse correlation was found between concentrations of the major chemical species and 18o a proxy for temperature during the last glacial period suggesting that in general during periods of decreased temperature there is an increase in atmospheric chemical loading examination of changes in major chemical composition over the last 110 000 years of the gisp2 ice core reveals that during the holocene the atmosphere was acidic during inters t adials the atmosphere was neutral or alkalescent and during stadials the atmosphere was alkaline in addition the relative abundance of major chemical species varied during the holocene stadials and interstadials during the holocene nh4 and no3 are the dominant cations and anions while ca2 and so42 are the dominant cations and anions during the stadials and inters t adials this suggests that source regions or types differed between the holocene and the last glacial period in addition changes in chemical composition and changes in chemical ratios also indicate that source regions differed during the holocene stadials and interstadials twenty four previously identified dansgaard oeschger stadial interstadial events dansgaard et al 1993 were in the gisp2 chemical series the duration of the stadials is inversely correlated with variations in sea level over the last glacial period i e the more extensive the northern hemisphere ice sheet the longer the duration of the stadial there is also a close correspondence between the duration of interstadials and the timing of heinrich events massive icebergs discharged into the ocean in the gisp2 ice core long up to 2000 years warm periods follow each heinrich event suggesting perhaps that enhanced deep water circulation is re initiated following heinrich events

apparent polar wander paths of the major chinese blocks since the late paleozoic toward restoring the amalgamation history of east eurasia abstract high quality paleomagnetic poles a k a paleopoles are essential for quantitative lithospheric plate reconstruction however the current paleomagnetic database of the major chinese blocks including the north china block ncb the south china block scb and the tarim block tb since the late paleozoic era contain outdated and low quality data here we update the database by adding recently published high quality paleopoles and rejecting low quality outdated ones the database includes 288 paleopoles published 1980 2014 90 of them published after 2000 following the van der voo selection criteria 75 paleopoles each with a quality factor q smaller than 4 were rejected in the first round of selection we then removed another 59 paleopoles that have been locally rotated or shallowed since the acquisition of stable remanence eventually 154 paleopoles were selected and adopted to calculate the new apparent polar wander paths apwps for the major chinese blocks we found comparable clastic and igneous paleopoles at intervals when a quantitative comparison was available as such comparison was not possible during most periods epochs our conclusions reflect an unclear extent of inclination errors in chinese clastic paleopoles new models of the chinese apwps with and without inclination error corrections were computed from carefully selected paleopoles version 1 running mean v1rm paths were calculated at the period epoch level version 2 running mean v2rm paths were computed in a set sliding time window of 20 or 30 myr spline paths were calculated with the same time windows along with a smoothing parameter of 50 using a recent global reconstruction model and up to date geological observations new models of the chinese apwps allowed us to re evaluate the coalescence history of east eurasia since the late paleozoic era four major tectonic events were confirmed 1 the tb accreted with the kazakhstan orocline during amalgamation of the west altaids during the middle late permian period ca 265 250 ma 2 the suturing of the ncb and the scb likely occurred in a scissor like pattern and had been accomplished no later than the middle jurassic period ca 180 160 ma 3 the amalgamation between the ncb and the tb along with the microblocks between the two might have been achieved during the late jurassic early cretaceous periods ca 160 140 ma 4 the mongol okhotsk ocean should have been closed no later than the early cretaceous period ca 140 120 ma

paleomagnetism of the siberian traps new data and a new overall 250 ma pole for siberia the flood basalt province in siberia is one of the largest in the world but the number of reliable paleomagnetic data on these volcanics is still limited we studied lava flows and trap related intrusions from two areas in the north and west of the siberian platform a dual polarity characteristic component was isolated from most samples with the aid of stepwise thermal and alternating field demagnetization we then compiled all published paleomagnetic data on the siberian traps that have been obtained according to modern standards also included are presumably trap related overprint directions in paleozoic rocks although these overprints and trap results may locally differ the corresponding mean poles based on remagnetized sediments and volcanics show excellent overall agreement and justify pooling of both data types several ways of data grouping were attempted the trap mean pole proved to be rather insensitive to statistical treatment irrespective of the averaging procedure used the overall mean poles for the siberian traps nsp2 55 1 n 147 0 e n 8 k 123 a95 5 0 or nsp4 57 2 n 151 1 e n 8 k 192 a95 4 0 differ slightly but significantly from the coeval mean poles of baltica torsvik 2001 van der voo r and torsvik t h the quality of the european permo triassic paleopoles and its impact on pangea reconstructions in timescales of the paleomagnetic field j e t channell d v kent w lowrie and j g meert eds agu geophys monogr 2004 135 29 42 we consider possible causes for this difference and conclude that it could be explained either by persistent non dipole terms in the permo triassic geomagnetic field or widespread inclination shallowing in the european data

early silurian to early carboniferous ridge subduction in nw junggar evidence from geochronological geochemical and sr nd hf isotopic data on alkali granites and adakites abstract the central asian orogenic belt caob evolved through a long lived orogeny involving multiple episodes of subduction and accretion marking a major phase of continental growth during the paleozoic the northern part of the western junggar region nw junggar offers a window into these processes particularly to constrain the timing of closure of the paleo asian ocean here we report geochemical geochronological and isotopic data from k feldspar granites and adakitic rocks from the nw junggar region zircon u pb ages suggest that the granites were emplaced during early silurian to the early carboniferous 434 328 ma the granites show geochemical characteristics similar to those of a type granites with high sio2 71 13 76 72 wt na2o k2o 8 00 9 59 wt and al2o3 12 28 14 08 wt but depleted sr nb ta and eu they display moderate to high positive end t and ehf t values 4 26 8 21 and 7 69 14 60 respectively and young nd and hf model ages t2dm nd 489 740 ma and t2dm hf 471 845 ma suggesting magma derivation through partial melting of lower crust in the boshchekul chingiz and zharma saur arcs the adakites are characterized by high sr content 406 5 751 6 ppm and low y 13 8 16 4 ppm and yb 1 5 1 8 ppm content yielding relatively high sr y ratios 25 38 49 41 similar to those of modern adakites they have high positive end t and ehf t values 7 85 8 25 and 13 23 15 97 respectively and young nd and hf model ages t2dm nd 429 535 ma and t2dm hf 355 550 ma indicating that their source magmas were likely derived from partial melting of the oceanic crust beneath the boshchekul chingiz arc the petrogenesis and distribution of the a type granites and adakites as well as the tectonic architecture of the region suggest that a ridge subduction event might have occurred during the early silurian to early carboniferous in combination with previous studies in the chinese altai we suggest a two sided ridge subduction model for the junggar altai region

modelling global ice and climate changes through the ice ages a global energy balance model has been developed which includes an interactive mixed layer ocean sea ice and snow and ice cover on the land a full annual cycle is included and the model provides a close simulation to the variation of surface temperature through the year over land and over ocean as a function of latitude the present annual variations of sea ice and snow on the ground are also well simulated the model has been used for a wide range of sensitivity tests which include variations of the solar constant surface albedos and the effects of feed back or absence of feed back in the reponse of the snow and ice cover studies have been made of the model s response to the long term variations in the earth s orbital characteristics such as changes in the perihelion the obliquity and the eccentricity as well as various combined changes independent sensitivity studies of the response of the model to the presence of the large ice sheets in the northern hemisphere have also been carried out a series of model runs have been performed to study climatic changes around the globe from 160 000 years p before present to the present an examination is made of the impacts of the orbital changes alone as well as with the feed back from the large ice sheets

kinetic controls on the partitioning of trace elements between silicate and sulfide liquids mass transfer between sulfide and silicate liquids is often discussed elements pge has resulted from liquation immiscible by reference to a mass ratio between hypothetical liquid reservoirs liquid phase separation of sulfide liquid from mafic or at equilibrium defined as r in an open system not at equilibrium ultramafic silicate magma a central assumption of modthe mass of silicate melt from which a growing sulfide droplet els of magmatic sulfide deposit formation is that the base appears to have scavenged chalcophile elements will depend on metals and pge are strongly partitioned into the sulfide diffusivities di and dfes of the element and of the fes component melt previous discussions of the process by which sulfide in the silicate melt respectively on the degree of supersaturation of liquids become enriched in chalcophile metals have fothe melt with fes c o on the radius a of the droplet and on the cused almost exclusively on models in which coexisting velocity v with which the droplet is advected through the melt so bodies of sulfide and silicate melt are considered to be that in equilibrium at all times the intent of this paper is to demonstrate that natural sulfide deposits preserved in igneous rocks will in many r 1 c fes o di 1 2 adiv dfes 1 2 adfesv instances record metal distributions that never attained equilibrium as a result of the kinetic constraints on metal chalcophile elements are expected to show inter element variations partitioning between phases the consequences are that in d spanning several orders of magnitude in some melts leading different elements will seem to show evidence for equito large inter element variations in effective r in a given sulfide libration at different silicate sulfide mass ratios within body these variations in effective r will lead to spatial separations single sulfide bodies i describe the time dependent evolubetween zones of maximum enrichment of chalcophile elements tion of metal distributions in silicate sulfide melt systems produced during fractional segregation of sulfide in layered intrusions starting with analytical solutions for simple boundary whereas it has proven impossible to model the generation of spatially conditions and then adapting them to more complex offset stratiform horizons in the australian munni munni layered systems as numerical models intrusion using equilibrium partition coefficients the present kinetic model reproduces the observed patterns with great fidelity

the santa rita nickel sulfide deposit in the fazenda mirabela intrusion bahia brazil geology sulfide geochemistry and genesis the santa rita ore zone within the fazenda mirabela intrusion is an unusual example of high tonnage magmatic ni cu pge sulfide mineralization developed as a stratiform layer within the main cumulus sequence of a layered intrusion the intrusion as a whole is about 4 2 5 km in outcrop dimensions and at least 3 km in original maximum stratigraphic thickness with an original boat shaped morphology the ore zone comprises a 50 to 200 m thick interval containing up to 5 wt percent disseminated sulfides within a sequence of mostly unaltered harzburgites and orthopyroxenites this orthopyroxene dominated sequence lies between the dominantly olivine rich cumulates that comprise the lower half of the intrusion and the gabbroic cumulates that make up the upper half sulfide tenor variations and silicate host rock compositions have been derived from a very large database of continuous assays of more than 500 diamond drill cores consistent patterns of sulfide tenor gradually decreasing ni from over 20 to about 10 wt percent near constant cu and gradually decreasing pges with cyclically varying pt pd ratios are found within the santa rita ore zone across the entire intrusion and display relatively little lateral variability the position of the sulfide mineralization envelope within the harzburgite orthopyroxenite package migrates to higher stratigraphic levels from the northern to the southern margin of the intrusion maximum grades and thicknesses correlate with the maximum thickness of orthopyroxene bearing cumulates asymmetrically disposed toward the southern margin of the intrusion nickel tenors of the sulfides range from 15 to 25 wt percent exceptionally high for rocks with relatively low values of mgo mgo feo and are closer to the typical values observed in komatiite hosted deposits although cu tenors typically 5 8 wt are much higher than komatiite values sulfide pge tenors range from less than 100 ppb to greater than 10 ppm of both pt and pd with maximum values in s poor rocks at the base of the sulfide bearing interval pges become significantly more depleted toward the top of the santa rita zone we attribute these features along with the localization of the sulfide bearing interval at the contact between ultramafic and mafic cumulates to mixing of an initially s undersaturated moderately ni enriched resident magma with a relatively low ni pge depleted significantly lower temperature replenishing magma charged with suspended sulfide liquid droplets

platinum mineralization in the kapalagulu intrusion western tanzania low grade copper and nickel mineralization was found near the eastern shore of lake tanganyika at kungwe bay in the early part of the twentieth century the mineralization occurs in harzburgite at the base of a layered gabbro complex known as the kapalagulu intrusion emplaced between the paleoproterozoic ubendian basement and overlying neoproterozoic itiaso group metasediments several mining and exploration companies continued the geophysical and drilling exploration for base metals throughout the last century culminating in the discovery of high grade platinum group element pge mineralization associated with chromitite and sulfide bearing harzburgite within the southeastern extension of the kapalagulu intrusion known as the lubalisi zone that is covered by a layer of nickel rich laterite regolith the poorly layered southeastern harzburgite forms part of the 1500 m thick lower ultramafic sequence and resembles a dike like body that flares upwards into a succession of well layered gabbroic rocks of the upper mafic sequence no pge mineralization has been found in the layered gabbro all the mineralization is associated with the chromite and sulfide rich harzburgite of the lower ultramafic sequence and the laterite regolith overlying the mineralized harzburgite the lubalisi zone harzburgite is underlain by basal dunite and overlain by an interval of layered harzburgite and troctolite and this ultramafic sequence is folded into a syncline that plunges towards the northwest that has been modified by major dolerite filled faults orientated subparallel to the fold axial surface extensive deep drilling in the lubalisi zone of the kapalagulu intrusion shows that the folded harzburgite can be subdivided into a lower feldspathic harzburgite a harzburgite containing chromitite seams and intervals of sulfide and chromite mineralization known as the main chromite sulfide succession mcss an overlying sulfide rich harzburgite and an upper feldspathic harzburgite impersistent stratiform pge mineralized horizons occur within the mcss harzburgite from which drill core samples were taken for platinum group mineral pgm characterization from two drill holes where the pge reefs reach the surface there is residual pge mineralization within the laterite regolith from which drill core samples were taken from various laterite lithological units for pgm characterization as the harzburgite pge reefs contain significant concentrations of both sulfide and chromite including chromitite seams they resemble the pge rich chromitite seams of the bushveld complex rather than the pge bearing main sulfide zone of the great dyke and main sulfide layer of the munni munni complex the dominant pd pgm in three pge reef samples varies ranging n 164 relative wt from bismuthides 63 bismuthtellurides 19 and tellurides 6 to tellurides 39 bismuthtellurides 24 stannides 14 and alloys 13 and to antimon arsenides 33 stannides 21 bismuthides 17 tellurides 13 and alloys 10 from 13 5 to 21 0 of the total pd occurs as a solid solution in pentlandite the three samples have similar pt pgm modal distributions n 172 relative wt the dominant pt mineral is sperrylite 79 58 and 47 followed by tellurides 15 17 21 alloys 2 1 1 and sulfides 2 1 0 comparison of pd pt ratios from assays to those calculated from minerals show that the data for the pt and pd pgm are very robust confirming the concentration methodology and characterization study of samples from a shallow drill hole penetrating the laterite regolith shows that the primary pd mineralization has not survived oxidation is mainly dispersed but some was reconstituted to form secondary minerals cabriite unnamed tellurides a selenide a pd te hg mineral alloys and pd bearing secondary sulfides millerite and heazlewoodite the primary pt minerals are more resistant to oxidation and dissolution especially sperrylite and isoferroplatinum but it is likely that other pt alloys tetraferroplatinum and tulameenite are of secondary origin after dissolution of pt tellurides

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

composition of the ultramafic mafic contact interval of the great dyke of zimbabwe at ngezi mine comparisons to the bushveld complex and implications for the origin of the pge reefs the great dyke contains the world s second largest platinum resource after the bushveld complex isotopic and trace element data from the interval straddling the contact between the ultramafic and mafic sequences of the great dyke indicate a less enriched composition than in the bushveld complex great dyke sri 0 7024 0 7028 end mostly 1 to 1 ce sm 2 6 bushveld sri 705 0 709 end 5 to 7 ce sm 5 15 these data are interpreted to reflect relatively moderate amounts of contamination of the great dyke parent magma all analyzed isotopes show little variation across the main sulfide zone and the ultramafic mafic contact this corroborates earlier work by other researchers that the great dyke crystallized from a single magma type mixing of compositionally distinct magmas proposed to have caused sulfide melt saturation in the bushveld complex seemingly played little or no role in the formation of the pge mineralization in the main sulfide zone and neither did enhanced crustal contamination of specific magma batches instead sulfide melt saturation of the magma was likely triggered by silicate fractionation the mechanism of concentration of the sulfide melt remains uncertain but theoretical considerations suggest that phase sorting in response to slumping of crystal mushes possibly caused by chamber subsidence played an important role this model is consistent with the highly irregular undulating nature of the contact between the mafic and ultramafic zones of the intrusion in the hanging wall of the main sulfide zone

archean layered mafic ultramafic intrusions in the west pilbara craton western australia a synthesis of some of the oldest orthomagmatic mineralizing systems in the world considerable exploration interest has been generated by the platinum group element pge and ni cu potential of the archean layered mafic ultramafic intrusions in the west pilbara craton western australia the munni munni intrusion contains the largest resource of pge associated with a layered intrusion in australia and the radio hill and mount sholl intrusions host significant resources of ni cu co sulfides titaniferous magnetite layers remobilized sulfides and structurally controlled hydrothermal polymetallic deposits have also been a focus for exploration in recent years the ca 2 9 ga munni munni andover radio hill mount sholl and sherlock layered intrusions are a cogenetic suite of high level 5 kbars bodies that represent some of the oldest mineralizing systems of their type in the world although they display similar field relationships and mineralogical geochemical and isotopic features their contrasting chalcophile metal distribution patterns show that the timing and mechanism of the s saturation event were critical for the development of pge enriched sulfide bearing layers and basal segregations of base metal sulfides the intrusions form thick 5 5 km dikelike bodies or relatively thin 0 5 2 km sheets and sills emplaced at different levels along major lithological discontinuities in the upper crust rhythmically layered ultramafic components are generally thinner than and occur along the northern sides of more massive overlying mafic components the ultramafic zones consist of dunite lherzolite wehrlite olivine websterite clinopyroxenite and websterite inverted pigeonite gabbronorite magnetite gabbro olivine gabbro anorthositic gabbro and anorthosite comprise the mafic sequences olivine and clinopyroxene were generally the first minerals to crystallize except in the andover intrusion where orthopyroxene preceded clinopyroxene and possibly reflects greater contamination of the parent magma by felsic crustal material the crystallization of chromite was inhibited in the ultramafic zones by the partitioning of cr into early crystallizing clinopyroxene thus downgrading the potential for pge chromite associations the pge mineralization in the munni munni intrusion occurs in the upper levels of a porphyritic plagioclase websterite orthocumulate layer directly below the ultramafic gabbroic zone contact mineral compositional trends and nd isotope data indicate that a pd pt au enriched s undersaturated magnesian basaltic magma was frequently injected into a small magma chamber during formation of the ultramafic zone a major influx of more fractionated s saturated tholeiitic gabbroic magma related to the resident magnesian magma rapidly inflated the chamber and induced turbulent magma mixing that resulted in the formation of the pge bearing porphyritic websterite layer in contrast the parent magmas that formed the mount sholl radio hill andover and maitland intrusions were saturated in s before they were emplaced into the magma chambers in these intrusions gravitational and structural controls were important for the concentration of pge poor 5 400 ppb pt pd au massive ni cu co sulfides in depressions and structural embayments along the basal contacts beneath the thickest sequences of mafic ultramafic cumulates the parent magmas to the west pilbara intrusions were siliceous high magnesian basalts of al depleted komatiitic affinity barberton type with 9 to 12 percent mgo 15 to 25 ppm sc 12 to 18 ppm y low al2o3 tio2 ca 11 or half chondrite ratios and light rare earth enrichment chondrite normalized la sm 2 7 la lu 9 0 they were generated with garnet in the residual asthenospheric mantle with probable involvement of a pre 3 0 ga subduction modified lithospheric mantle isotopic and geochemical modeling suggests that the magmas were contaminated by ca 3 0 to 3 3 ga archean tonalitic to granodioritic crust before being emplaced into high level magma chambers

compositional and lithological controls on the pge bearing sulphide zones in the selukwe subchamber great dyke a combined equilibrium rayleigh fractionation model the platinum group element pge bearing main and lower introduction sulphide zones of the selukwe subchamber of the great dyke are an increasing number of mafic layered intrusions are made up of a series of subzones within which the ratios pd pt are reported to have distributions of platinum group elements effectively constant whereas these ratios vary significantly between pge au and base metals characterized by vertically the subzones fractionation of pd with respect to pt varies by a offset profiles offset profiles involve the vertical sepfactor of 10 and cannot be modelled using a sulphide collector aration of metal peaks and were first reported in the phase and constant partition coefficients the link with sulphide is great dyke prendergast keays 1989 wilson et al indisputable and the control is likely to have been the degree of 1989 naldrett wilson 1990 wilson tredoux oversaturation of pge micro nuggets in the magma the apparent 1990 the phenomenon has since been recognized in partition coefficients for pt and pd between silicate and sulphide the munni munni intrusion of western australia barnes liquid are dependent on the degree of oversaturation and thereby et al 1990 the skaergaard intrusion bird et al 1991 exhibit spurious correlation with the pge content of the sulphide and the rincon del tigre complex of eastern bolivia modelling replicates the pt and pd distribution and ratios only by prendergast 2000 pge are also postulated to be transdramatically changing the effective partition coefficients pyroxene ported in fluids emanating from expulsion of intercumulus compositions including tio2 are shown to be strongly dependent liquid from the crystal pile and there is strong evidence on the incompatible element content of the whole rock and specific to support such processes in several gabbroic sections linear arrays relating these variables can be related to the pge of layered intrusions such as the skaergaard intrusion subzones the overall control is rayleigh fractionation but constancy andersen et al 1998 and in the stillwater complex of the ratio pd pt and the initial pyroxene composition before re boudreau mccullum 1986 1992 in contrast the equilibration with trapped liquid within the subzones is indicative mineralized zones in the great dyke and munni munni of equilibrium crystallization this layered structure may have been intrusion are located in pyroxenite and primary magderived from liquid layers in the magma chamber matic processes have been invoked to explain the min

an oxygen isotope study of the lower mafic succession of the darwendale subchamber of the great dyke zimbabwe abstract oxygen isotope values for plagioclase clinopyroxene and orthopyroxene from the upper part of the great dyke are presented the variation in 18 o values in these silicates is narrow and the average values are plagioclase 18 o 6 90 orthopyroxene 18 o 6 clinopyroxene 18 o 6 91 and melt 18 o 6 65 an estimated equilibration isotopic temperature of 1091 c was calculated for this lower mafic succession of the great dyke the oxygen isotope compositions of the silicate minerals are not very close to their magmatic values but they are roughly similar to those from the bushveld complex the stillwater complex and the kiglapait intrusion the clinopyroxene orthopyroxene values can be as high as 0 63 with an average value of 0 33 since the fractionation between these pyroxenes at magmatic temperatures should be approximately zero kyser et al 1981 the high clinopyroxene orthopyroxene values are likely to have been caused by lower temperature crystallisation of both pyroxenes the low clinopyroxene orthopyroxene values in the cumulate rich samples are interpreted as products of high temperature crystallisation while the high clinopyroxene orthopyroxene values are products of low temperature crystallisation associated with postcumulus textures and abundant low temperature phases the slightly 18 o rich silicates from the great dyke acquired additional oxygen up to 59 from the archaean rocks of the zimbabwe craton which has whole rock 18 o values going up to 7 3 barker et al 1976 which occur as roof pendants in the darwendale subchamber of the great dyke

geochemistry and mineralogy of platinum group elements at hartley platinum mine zimbabwe the main sulfide zone msz is the most prominent layer of the great dyke layered intrusion carrying economic platinum group element pge mineralization at the hartley platinum mine the msz is up to some meters thick and is composed of a basal pge rich subzone which overlaps slightly with a base metal sulfide rich subzone on top based on the degree of sulfide mineralization and pge ratios the subzones can be further divided into geochemically distinct layers stratigraphically upwards the msz displays metal profiles characterized by increasing cu ni pt pd and ppge ipge ratios accompanied by a general element decoupling in the order pd pt base metals more specifically ipge pd pt ni cu co s sulfides au te bi the fine structure of the msz is regarded to reflect primary magmatic features of consecutive batches of sulfide accumulation concomitant scavenging of pge and fractionation sulfide deposition was followed by a second limited subsolidus stage of pge redistribution mineralogically most of the pd and rh is hosted in pentlandite whereas pt is dominantly present in the form of discrete platinum group minerals pgm within the msz sequence sperrylite is present throughout the pge subzone of the msz cooperite braggite occur mainly in its basal part and the pt pd bismuthotellurides concentrate at the top these findings indicate that a large proportion of the pge primarily concentrated in sulfide under magmatic conditions was redistributed in the subsolidus stage and formed discrete pgm with available reactant partners chemical gradients and magmatic hydrothermal fluids probably led to small scale redistribution of pge within the msz

horizontal and vertical variations in noble metal distribution in the great dyke of zimbabwe a model for the origin of the pge mineralization by fractional segregation of sulfide abstract a study based largely on diamond drilling undertaken specifically for research purposes has shown that in the darwendale subchamber of the great dyke of zimbabwe there are three principal sulfide zones that are located in subunits 1a and 1b of cyclic unit 1 sulfide zone 1 the main sulfide zone msz is subdivided into three subzones the base of the msz occurs at the top of the main bronzitite layer of cyclic unit 1 extending into the overlying websterite the noble metals are concentrated at the bases of each sulfide zone and subzone and decrease in concentration rapidly upwards whereas variations in the concentrations of base metals such as cu correlate well with variations in the amounts of sulfide across each zone when calculated in terms of their concentration in 100 sulfides it is found that pd decreases upwards most rapidly followed by pt and then au with the cu concentration remaining essentially constant the decrease of the noble metals is interpreted in terms of simple rayleigh fractionation as the consequence of the removal of sulfide the observed correlation between the tops and bottoms of sulfide zones with small variations in the mg number of bronzite is taken to indicate that in zones 2 and 3 sulfide segregation started as a result of crystallization increasing the s content of the resident magma in the chamber until it reached that of sulfide saturation coupled with fresh inputs of sulfide unsaturated more primitive magma causing the resident magma to become unsaturated again this recharge by primitive magma also raised the pge content of the sulfides segregating from the trapped intercumulus liquid indicating that the resident magma was becoming recharged in pge in this way subunits i and ii of sulfide zone 1 are thought to contain too much sulfide to be explicable in this way and it is suggested that mixing with a plagioclase saturated magma possibly generated around the flanks of the intrusion was responsible for these subunits the sulfides of each of the sulfide zones are more concentrated at the margin than at the axis of the great dyke but have a lower tenor of noble metals it is proposed that the axially located sulfides were the consequence of magma sulfide equilibration at a higher r factor magma sulfide ratio than those at the margin the magma sulfide partition coefficients required to explain the percentage difference in the tenors of the different noble metals between axis and margin in this way are the same as those required to explain the vertical variations in noble metal tenor in terms of the fractional segregation model

holocene deglaciation and climate history of the northern antarctic peninsula region a discussion of correlations between the southern and northern hemispheres holocene deglaciation and climate history of the northern antarctic peninsula region a discussion of correlations between the southern and northern hemispheres

late orogenic large scale rotations in the tien shan and adjacent mobile belts in kyrgyzstan and kazakhstan abstract most of kazakhstan belongs to the central part of the eurasian paleozoic mobile belts for which previously proposed tectonic scenarios have been rather disparate of particular interest is the origin of strongly curved middle and late paleozoic volcanic belts of island arc and andean arc affinities that dominate the structure of kazakhstan we undertook a paleomagnetic study of carboniferous to upper permian volcanics and sediments from several localities in the ili river basin between the tien shan and the junggar alatau ranges in southeast kazakhstan our main goal was to investigate the permian kinematic evolution of these belts particularly in terms of rotations about vertical axes in the hope of deciphering the dynamics that played a role during the latest paleozoic deformation in this area this deformation in turn can then be related to the amalgamation of this area with baltica siberia and tarim in the expanding eurasian supercontinent thermal demagnetization revealed that most permian rocks retained a pretilting and likely primary component which is of reversed polarity at three localities and normal at the fourth in contrast most carboniferous rocks are dominated by postfolding reversed overprints of probably mid permian age whereas presumably primary components are isolated from a few sites at two localities mean inclinations of primary components generally agree with coeval reference values extrapolated from baltica whereas declinations from primary as well as secondary components are deflected counterclockwise ccw by up to 90 such ccw rotated directions have previously also been observed in other tien shan sampling areas and in the adjacent tarim block to the south however two other areas in kazakhstan show clockwise cw rotations of permian magnetization directions one area is located in the kendyktas block about 300 km to the west of the ili river valley and the other is found in the chingiz range to the north of lake balkhash and about 400 km to the north of the ili river valley the timing of the ccw as well as cw rotations is clearly later than the disappearance of any marine basins from northern tarim the tien shan and eastern kazakhstan so that the rotations cannot be attributed to island arc or andean margin plate settings instead we attribute the rotations to large scale east west present day coordinates sinistral wrenching in an intracontinental setting related to convergence between siberia and baltica as recently proposed by natal in and engor natal in b a and engor a m c 2005 late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure tectonophysics 404 175 202 our previous work in the chingiz and north tien shan areas on ordovician and silurian rocks suggested relative rotations of 180 whereas the permian declination differences are of the order of 90 between the two areas thus we assume that about 50 of the total post ordovician rotations are of pre late permian age with the other half of late permian earliest mesozoic age the pre late permian rotations are likely related to oroclinal bending during plate boundary evolution in a supra subduction setting given the calc alkaline character of nearly all of the pre late permian volcanics in the strongly curved belts

permian palaeomagnetism of east kazakhstan and the amalgamation of eurasia summary most of kazakhstan belongs to the ural mongol belt the tectonic evolution of which is poorly understood as demonstrated by disparate tectonic models suggested thus far we undertook a palaeomagnetic study of upper permian basalts and andesites from two localities in east kazakhstan in order to evaluate the final stages of the evolution of this belt and eurasian amalgamation thermal demagnetization revealed a single pre tilting characteristic component of ubiquitously reversed polarity from all samples the mean declination of this remanence from one locality agrees rather well with the permian european palaeomeridian whereas that from the other is clockwise rotated by 28 8 the overall mean inclination of 49 4 differs by 9 7 4 2 from the reference inclination calculated for our localities from the eurasian mean pole for the 245 260 ma interval and is in agreement with 260 275 ma data we account for the observed pattern by either a slightly erroneous rock age lithologies are somewhat older than indicated by geological data or non dipole octopole components of the geomagnetic field because significant relative motion of the study area with respect to eurasia is not demonstrated we conclude that welding of kazakhstan europe and siberia was essentially completed by mid permian time

behavior of the paleosecular variation during the permian carboniferous reversed superchron and comparisons to the low reversal frequency intervals since precambrian times we investigated the paleo latitudinal dependence of angular dispersion sets of virtual geomagnetic poles vgps for the permian carboniferous reversed superchron pcrs 262 318 ma in order to analyze the paleosecular variation during this period we prepared different paleomagnetic datasets from scientific databases and recent literature based on selection criteria which provided high degree of refinement model g of mcfadden et al 1988 was fitted to the vgp dispersion data providing the shape parameters a and b which were further compared with similar results for the cretaceous normal superchron cns and other periods of different geomagnetic reversal rates throughout the last 3 ga our results indicate high similarity between the angular vgp dispersion from the pcrs and cns a low vgp dispersion at low paleolatitudes and strong paleolatitudinal dependence in contrasting difference for periods of higher reversal rates the last 5 ma despite the geodynamic differences related to both phanerozoic superchrons such evidence could point out similar heat flux conditions in the cmb which may favor compatible stability conditions throughout these magnetozones notably two additional observations which arose from the shape parameters relations for both phanerozoic superchrons and precambrian datasets demand further investigation i a pattern of increase for the b a ratio throughout the 0 5 1 6 ga interval was observed which could be partially explained by the maya superchron recently proposed by gallet et al 2012 ii the b a relationship for both phanerozoic superchrons and the 2 45 2 82 ga interval pointed to the presence of one or more long term magnetozones throughout the paleoproterozoic

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

paleomagnetism of paleozoic sedimentary rocks from the karatau range southern kazakhstan multiple remagnetization events correlate with phases of deformation 1 the paleogeography of the altaids and its kinematic and tectonic evolution during the final collision and amalgamation of eurasia is still poorly known addressing this problem a paleomagnetic study has been undertaken on paleozoic sedimentary rocks from the karatau southern kazakhstan stepwise thermal demagnetization reveals the presence of a high temperature component of magnetization in most samples fold tests indicate a syn folding age of magnetic remanence acquisition at three of the five areas studied directional data of devonian and permian rocks yield a positive fold test implying a primary magnetization resulting prefolding paleolatitudes for permian and devonian rocks show the proximity of the karatau to baltica during those times syn and post folding magnetizations result in paleolatitudes for karatau which intersect the paleolatitude curve based on the baltica apparent polar wander path apwp at times which can be correlated to major deformational events at 280 ma 260 ma and 230 ma respectively we interpret this with complicated pattern of remagnetization events accompanying deformation which can include syn folding remagnetization events and areas of primary magnetic signals additionally the differences between reference declinations based on the apwp for baltica and observed declinations suggest successive counterclockwise rotational reorganization of the karatau during the late paleozoic to early mesozoic with maximal rotation values of 65 with respect to baltica the remagnetization events are correlated with latest intracontinental stages of orogenic evolution in the ural mountains and thus the paleozoic amalgamation of the eurasian continent and suggest synchronous and coherent tectonic evolution in the urals and karatau mountains

provenance and tectonic setting of late carboniferous clastic rocks in west junggar xinjiang china a case from the hala alat mountains abstract the late carboniferous palaeo tectonic setting of the west junggar region is comprised of arcs alternating with basins geochemical analysis of the sedimentary rocks associated with these arc related basins was conducted to better constrain the provenance and tectonic setting major and trace element geochemistry data of late carboniferous mudstones and sandstones in the hala alat mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features 1 sediments experienced a simple recycling process 2 a low degree weathering conditions in the source areas 3 compositional immature of the sedimentary rocks 4 dominated by intermediate to felsic provenance with a few intermediate to mafic sediments integrated with the palaeo flow data and previous authors works a fore arc basin model is proposed for the tectonic setting of the sedimentary rocks the sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments the bozchekul chingiz arc and kexia oceanic island arc are the other two secondary sources

layering and precious metals mineralization in the rincon del tigre complex eastern bolivia geologic investigations supporting recent technically successful platinum exploration of the rincon del tigre complex a ca 4 6 km thick layered sill have provided significant new understandings of the layering development and precious metals mineralization of one of south america s largest mafic ultramafic intrusions three macrocyclic units are recognized from the base up basal unit unit 1 and unit 2 each most likely the product of a major replenishment with mafic magma of one compositional type the ultramafic rocks of all three macrocyclic units largely comprise repeated minor cyclic units of poikilitic harzburgite granular harzburgite olivine bronzitite each a few meters thick with occasional development of bronzitite at the top mafic rocks absent from unit 1 and present only locally in the basal unit form a well developed norite gabbro magnetite gabbro sequence in the upper half of unit 2 associated with the base of the magnetite gabbro is the precious metals zone a persistent zone of low grade subeconomic sulfide and precious metals mineralization 80 to 185 m thick the precious metals zone comprises an upper cu sulfide rich portion its base the sulfide phase boundary about 23 to 70 m above the magnetite phase boundary and a lower precious metals rich portion the lower part straddling the magnetite phase boundary the individual precious metals are concentrated in separate sulfide poor subzones each up to many tens of meters thick in the stratigraphic order rh pt pd au with peak offsets at the same scale modal layering of silicates and magnetite is well developed in the mafic rocks as is modal and cryptic precious metals layering of the sulfides in the precious metals zone all at three different superimposed scales from about 3 m to several tens of meters a possible interpretive framework for the cryptic layering and perhaps for much of the other layering including the meter scale layering of the ultramafic rocks is provided by the likely compositional stratification of the resident magma initiated by the fluid dynamics of the replenishment and mixing processes and in the magnetite gabbro by repeated convective overturns caused by the onset of magnetite precipitation the characteristics of the precious metals zone fit an orthomagmatic model the composition stratigraphic relations and modal correlation with magnetite of the sulfides all imply that s saturation was induced by loss of feo to magnetite precipitation this took place after prolonged closed system fractionation following the last major magma injection at the base of unit 2 during which crystallization of olivine pyroxene plagioclase and finally magnetite precipitation led to overall s cu and precious metals enrichment and ni and finally fe depletion of the magma the development of the mineralization and its complex layering was controlled by sulfide segregation rayleigh fractionation the different but generally very high partition coefficients dsilicate sulfide for each precious metal and repeated convective overturns at three different superimposed scales the decoupled metals distribution is analogous and similar in origin to that of the main sulfide zone of the great dyke zimbabwe and of the main sulfide layer offset portion of the munni munni complex western australia but the stratigraphic order of metal enrichment peaks is different pt pd au vs pd pt au this suggests a reversal in the relative magnitudes of the partition coefficients dpt and dpd that was possibly brought about by changes in the temperature and o s and fe activities of the magmas between the middle and late stages of crystallization constancy of d values during fractionation of mafic magma should not be assumed the precious metals zone is one of several skaergaard type strata bound precious metals zones associated with magnetite gabbros in the upper levels of many layered intrusions and the origin of the skaergaard mineralized zone itself including the potentially economic platinova reefs can be explained in terms of the precious metals zone model presented here the very low grade great thickness and wide separation of individual metal subzones in the precious metals zone are similar to those of the subeconomic axial facies of the main sulfide zone in the wider parts of the great dyke cf the economic more compact marginal facies on the basis of the lateral and vertical thermal model of the great dyke magma chamber the subeconomic status of the precious metals zone may be in large part a function of the specific fluid dynamics of the rincon del tigre magma chamber

ophiolitic melanges in crustal scale fault zones implications for the late palaeozoic tectonic evolution in west junggar china the baijiantan and darbut ophiolites in west junggar are exposed in steep fault zones 70 containing serpentinite melange in contact on either side with regionally distributed upper devonian lower carboniferous ocean floor peperitic basalts and overlying sedimentary successions the ophiolitic melanges show classic structural features created by strike slip faulting and consistent shear sense indicators of left slip kinematics sandstone blocks within the melanges resemble the surrounding sediments in lithology and age indicating that the ophiolitic melanges consist of locally derived rocks the ophiolitic melanges therefore originated from left slip fault zones within a remnant basin and are not plate boundaries nor subduction suture zones sandstone is the youngest lithology involved in the melange and provides a maximum age for the melange of 322 ma whereas stitching plutons are younger than 302 ma multiple clusters in zircon ages from single gabbro blocks in the melange at 375 360 354 and 340 ma are inconsistent with accretionary incorporation of subducting ocean crust but rather suggest that episodic movement of the faults provided pathways for magma from the mantle into magma chambers late paleozoic tectonic evolution of west junggar involved late devonian to carboniferous relative motion between the junggar block and west junggar ocean basin which triggered the left slip fault zones within a remnant ocean basin along which the oceanic crust was disrupted to form linear ophiolitic melanges final filling of this remnant ocean basin and its dismemberment by strike slip faulting occurred in the late carboniferous followed by crustal thickening by juvenile granites at the carboniferous permian boundary

magmatic nickel sulfide mineralization in zimbabwe review of deposits and development of exploration criteria for prospectivity analysis significant magmatic nickel sulfide deposits in zimbabwe occur in archean greenstone belts and archean to proterozoic mafic ultramafic intrusions such as madziwa and the great dyke here we review exploration criteria for magmatic nickel sulfide deposits taking into account nickel sulfide mineral systems in general zimbabwe s cratonic evolution and the geological setting of the deposits we propose that the essential ingredients for nickel sulfide mineral systems in zimbabwe are i proximity to greenstone belts craton margins and orogenic belts ii large mafic ultramafic intrusions and their feeders iii crustal contamination of basic ultrabasic magma with sulfidic crustal lithologies and iv the vicinity to major fault zones that allowed fertile magma to ascend into the upper crust we suggest that there is potential for new nickel sulfide discoveries both within and outside the greenstone belts including the karoo flood basalt province the mashonaland dolerites and the limpopo magondi and zambezi orogenic belts

geometry kinematics and tectonic models of the kazakhstan orocline central asian orogenic belt abstract the central asian orogenic belt caob is one of the largest accretionary orogens on earth and is characterized by the occurrence of tight oroclines kazakhstan and tuva mongolian oroclines the origin of these large scale orogenic curvatures is not quite understood but is fundamentally important for understanding crustal growth and tectonic evolution of the caob here we provide an outline of available geological and paleomagnetic data around the kazakhstan orocline with an aim of clarifying the geometry kinematics and geodynamic origin of the orocline the kazakhstan orocline is evident in a total magmatic image and can be traced by the continuation of high magnetic anomalies associated with the devonian volcanic belt and the late devonian to carboniferous balkhash yili arc paleomagnetic data show 112 126 clockwise rotation of the northern limb relative to the southern limb in the late devonian to early carboniferous as well as 15 28 clockwise rotation of the northern limb and 39 40 anticlockwise rotation of the southern limb relative to the hinge of the orocline during the late carboniferous to permian we argue that the kazakhstan orocline experienced two stage bending with the early stage of bending late devonian to early carboniferous 112 126 driven by slab rollback and the later stage late carboniferous to permian 54 68 possibly associated with the amalgamation of the siberian tarim and baltic cratons this new tectonic model is compatible with the occurrence of rift basins the spatial migration of magmatic arc and the development of large scale strike slip fault systems during oroclinal bending

devonian paleomagnetism of the north tien shan implications for the middle late paleozoic paleogeography of eurasia the ural mongol belt umb between siberia baltica and tarim is widely recognized as the locus of asia s main growth during the paleozoic but its evolution remains highly controversial as illustrated by the disparate paleogeographic models published in the last decade one of the largest tectonic units of the umb is the kokchetav north tien shan domain kntd that stretches from tarim in the south nearly to the west siberian basin the kntd comprises several precambrian microcontinents and numerous remnants of early paleozoic island arcs marginal basins and accretionary complexes in late ordovician time all these structures had amalgamated into a single contiguous domain its paleogeographic position is of crucial importance for elucidating the paleozoic evolution of the umb in general and of the urals in particular the aral formation located in kyrgyzstan in the southern part of the kntd consists of a thick upper devonian frasnian basalt andesite sequence paleomagnetic data show a dual polarity characteristic component dec inc 286 56 95 9 k 21 n 15 sites the primary origin of this magnetization is confirmed by a positive test on intraformational conglomerates we combine this result with other paleozoic data from the kntd and show its latitudinal motion from the late ordovician to the end of the paleozoic the observed paleolatitudes are found to agree well with the values extrapolated from baltica to a common reference point 42 5 n 73 e in our sampling area for the entire interval hence coherent motion of the kntd and baltica is strongly indicated for most of the paleozoic this finding contradicts most published models of the umb evolution where the kntd is separated from baltica by a rather wide ural ocean containing one or more major plate boundaries an exception is the model of engor and natal in a m c engor b a natal in paleotectonics of asia fragments of a synthesis in a yin and m harrison eds the tectonic evolution of asia cambridge university press cambridge 1996 486 640 in which coherent paleolatitudinal motion of baltica and the kntd is hypothesized the latter as part of the kipchak arc we suggest a parallel hypothesis which explains coherent motion of the kntd and baltica in particular we argue that if a basin with oceanic crust ever existed between the kntd and baltica it was a narrow one without significant active spreading in middle to late paleozoic time notably the paleogeographic position of siberia during the middle paleozoic and hence the width of the khanty mansi ocean between siberia on the one hand and baltica kntd on the other hand remains largely unconstrained because of the paucity of high quality silurian devonian and carboniferous paleomagnetic results from siberia

primary carboniferous and permian paleomagnetic results from the yili block nw china and their implications on the geodynamic evolution of chinese tianshan belt in order to better understand the tectonic role of the yili block on the paleozoic evolution of the chinese tianshan belt we performed a primary paleomagnetic study on carboniferous and permian rocks from different areas in the yili block nw of china more than 320 sedimentary and volcanic samples were collected from 39 sites except for the ordovician samples showing a weak and unstable magnetic remanence the majority of this collection presents characteristic remanent magnetization carried by magnetite and hematite in the study area though positive fold test has been observed on the early carboniferous rocks a general remagnetization of these rocks has been identified and attributed to the late carboniferous magmatism moreover all early and late carboniferous samples from the interior of the yili block yield stable and coherent magnetic directions with exhaustively reverse magnetic polarity the late carboniferous c2 is considered as the magnetic remanence age since these rocks are covered or intruded by synchronous magmatic rocks of the yili arc which lasted until to 310 ma the c2 paleomagnetic pole is therefore calculated at 68 6 n 290 6 e with 95 6 4 and n 15 the late carboniferous rocks located close to a deformation zone present a consistentmagnetic inclination but significant different declination with respect to other areas and are suspected to have probably experienced a local rotation although no fold test can be performed due to the monoclinal bedding stable magnetic components are isolated from late permian p2 red beds in the interior of the yili block with also a solo reverse magnetic polarity the p2 paleomagnetic pole of the yili block has been therefore calculated from the characteristic remanent magnetization 79 7 n 172 0 e with 95 11 3 and n 5 keeping important uncertainties in mind comparisons of the c2 and p2 paleomagnetic poles of the yili block with available coeval poles of junggar tarim and siberia indicate 1 no significant relative motion between the yili and junggar blocks since the late carboniferous 2 no significant or weak latitudinal relative motion occurred since the late carboniferous among these blocks but 3 the 46 2 15 1 and the 31 6 15 1 counterclockwise rotations of the yili junggar blocks with respect to tarim and siberia took place during c2 to p2 these rotations are accommodated by the permian dextral strike slip faults along the northern and southern sides of tianshan belt and sinistral strike slip faulting along the erqishi fault of altay belt resulting in about 1000 km and 600 km lateral displacements in the tianshan and altay belts respectively

how was the carboniferous balkhash west junggar remnant ocean filled and closed insights from the well tacan 1 strata in the tacheng basin nw china abstract the balkhash west junggar remnant ocean is a conspicuous tectonic feature that had an important effect on the paleozoic tectonic evolution of the central asian orogenic belt how the carboniferous balkhash west junggar remnant ocean was filled and closed is poorly understood in this study we focus on the integrated tectonic sedimentary evolution of the tacheng basin which is located in the eastern part of the balkhash west junggar remnant ocean using high resolution seismic reflection well line geochronological and geochemical data to establish the filling of the basin by sediments and its evolution the carboniferous balkhash west junggar remnant ocean basin was filled with early carboniferous deep marine mudstone and interbedded sandstone with minor andesite basalt and tuff and late carboniferous basalt andesite breccia and tuff and shallow marine mudstone and sandstone the carboniferous igneous assemblage mainly consists of basalt with high nb content and nb la pm values and concomitant magnesian andesites with adakite geochemical characteristics of high sr and low y and yb suggesting a subduction related tectonic setting zircons in the tuff that underlies the basalts and magnesian andesites were dated to ca 315 ma by la icp ms u pb the identified unconformity between the carboniferous and lower permian from seismic reflection profile in well tacan 1 subdivided the carboniferous early permian strata into two tectonostratigraphic units the lower permian sequences overlap the carboniferous strata and the facies transition from the submarine carboniferous to the terrigenous lower permian indicates that the balkhash west junggar remnant ocean closed during the early permian these new data suggest that the sedimentary filling of the basin was in response to subduction and accretionary processes and that oceanic subduction was an important mechanism that led to the shrinking filling and closure of the balkhash west junggar remnant ocean because of compression therefore lateral crust growth through subduction accretionary processes still played an important role in the carboniferous construction of western junggar

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure abstract a number of en echelon arranged southwest facing arc fragments of palaeozoic to jurassic ages sandwiched between two fairly straight east northeast trending boundaries constitute the basement of the scythian and the turan platforms located between the laurasian and tethyside units they have until now largely escaped detection owing to extensive jurassic and younger cover and the inaccessibility of the subsurface data to the international geological community these units are separated from one another by linear gently curved faults of great length and steep dip those that are exposed show evidence of strike slip motion the arc units originally constituted parts of a single silk road arc located somewhere south of the present day central asia for much of the palaeozoic although by the late carboniferous they had been united into a continental margin arc south of the tarim basin and equivalent units to the west and east they were stacked into their present places in northern afghanistan turkmenistan caucasus and the northern black sea by large scale right lateral strike slip coastwise transport along arc slicing and arc shaving strike slip faults in the triassic and medial jurassic simultaneously with the subductive elimination of palaeo tethys this gigantic dextral zone the silk road transpression was a trans eurasian structure and was active simultaneously with another similar system the gornostaev keirogen and greatly distorted eurasia the late palaeozoic to jurassic internal deformation of the dniepr donets aulacogen was also a part of the dextral strain in southern europe when the emplacement of the scythian and turan units was completed the elimination of palaeo tethys had also ended and neo tethyan arcs were constructed atop their ruins mostly across their southern parts the western end of the great dextral zone that emplaced the turan and scythian units horsetails just east of north dobrudja and a small component goes along the tornquist teisseyre lineament

lateral and vertical distribution of platinum group elements and petrogenetic controls on the sulfide mineralization in the p1 pyroxenite layer of the darwendale subchamber of the great dyke zimbabwe the great dyke of zimbabwe is a major resource of platinum group elements pge and represents the world9s second largest deposit after the bushveld complex the darwendale subchamber contains more than 75 percent of all the pge mineralization in the great dyke and is the subject of this investigation the mineralization is closely associated with sulfide bearing zones located in pyroxenites toward the top of the ultramafic sequence this environment contrasts with many other mineralized layered intrusions in that substantial plagioclase crystallization did not occur prior to the formation of the pge enriched sulfide layers several sulfide layers occur within the bronzitites of the topmost cyclic unit rather than at the base suggesting that a major mixing event of residual magma with a new influx of primitive liquid was not the primary control of the mineralization the lower sulfide zones are disseminated over 10 to 20 m and contrast with the uppermost sulfide zone s1 which is highly mineralized and generally less than 1 5 m in thickness in the s1 zone values for pt are as high as 8 ppm over a narrow interval with pt pd close to 2 the maximum enrichment of pge occurs at the first appearance of sulfide as a result of the high partitioning of these elements into sulfide liquid the order of enrichment in the sulfide is ir pd pt raquo au cu ni and as the abundance of sulfide increases this phase becomes highly depleted in these elements the enrichment pattern is consistent with fractional segregation of sulfide repetition of the mineralization results from periodic disturbance of the magma system which is related to relatively small pulses of new magma and overturns within the stratified magma column the stratified magma was sustained by the repeated influxes of new magma entering as fountains a series of peaks for pt pd and the base metals occurs in the s1 zone contrasting patterns in the vertical profile for pt and pd are attributed to the differences in the effective partition coefficients of these two elements in an environment of rapidly changing sulfide proportions marked lateral variations in the degree and style of mineralization are observed from axis to margin of the subchamber whole rock concentrations of pt are highest nearest to the margin in the very narrow and highly mineralized sulfide zone s1 but these fall to low values in the axis where the zone is more disseminated in any given vertical section the maximum concentration of pge in sulfide is similar in each of the sulfide zones the total amount of pt for the entire mineralized zone and the concentration of pt in sulfide are however significantly higher in the axial facies compared to the margin there are also major lateral variations in maximum values of cu ni and ni cu ni these lateral variations are attributed to a difference in the thermal regimes arising from the flared shape of the great dyke in cross section and its influence on the fluid dynamics of the magma chamber extensive borehole drilling has permitted detailed two dimensional contour patterns to be deduced for the distribution of pt and pd and the base metals in the s1 suboutcrop over a large area of the darwendale subchamber

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

the eocene southern vancouver island orocline a response to seamount accretion and the cause of fold and thrust belt and extensional basin formation abstract a deflection of the fault controlled southwestern coastline of vancouver island suggests the presence of a minor orocline with a southern crustal block south of barkley sound alberni inlet rotated 20 counterclockwise relative to a northern fixed crustal block about a pole of rotation located northeast of port alberni in this paper two models of orocline development one of pure block rotation and one of pure bending are proposed the predictions of these models are tested against available geological maps structural orientation data identified regions of extension and contraction and paleomagnetic data structural orientation and paleomagnetic data are consistent with 18 of post late cretaceous counter clockwise rotation of the southern crustal block relative to the northern fixed crustal block a southward increase in the magnitude of rotation evident in the structural orientation data argues for a model of bending both bending and block rotation models predict the development of a zone of contraction along the northeast margin of the southern crustal block coincident with the location of the eocene cowichan fold and thrust belt that diminishes northward toward the pole of rotation as predicted the fold and thrust belt is characterized by a northerly decrease in the amount of shortening from 30 at the south end of the thrust belt to 0 shortening north of port alberni the northerly decrease in shortening is complemented by a north to south change in structural style from cylindrical to conical folds and finally to planar undeformed strata the model of block rotation predicts the presence of a zone of extension extending southwest from the zone of rotation coincident with the location of eocene extensional structures within barkley sound and with horst and graben structures in the offshore eocene to miocene tofino basin extension is less than predicted by a model of pure block rotation and suggests that much of the oroclinal rotation was accommodated by bending timing constraints indicate that orocline development was coeval with and resulted from the eocene accretion of seamounts of the crescent terrane these findings demonstrate that oroclinal orogeny the buckling of a linear crustal beam about vertical axes of rotation can significantly impact the geometry structure and character of an orogenic belt even where the buckles are minor

comment on the combined analysis of remagnetization circles and direct observations in paleomagnetism by p l mcfadden and m w mcelhinny

the neoproterozoic evolution of the western siberian craton margin u pb hf isotopic records of detrital zircons from the yenisey ridge and the prisayan uplift abstract we present new la icp ms u pb hf detrital zircon data from neoproterozoic sedimentary basins located along the south western margin of the siberian craton in the yenisey ridge the taseeva basin siliciclastic sedimentary units contain abundant 2 7 2 5 ga 2 0 1 75 ga and 0 95 0 57 ga detrital zircon populations whereas for the prisayan uplift slightly different detrital zircon ages of 3 0 2 5 ga 2 2 1 8 ga and 0 95 0 65 ma are common mid neoproterozoic sandstones were deposited in a rift setting or along a rifted cratonic margin facing a back arc basin whereas the immature to submature upper ediacaran to lower cambrian fluvial successions were probably deposited in the foredeep setting at the expense of proximal neoproterozoic igneous suites and the underlying metasedimentary basement a range of ehf values from 10 to 14 indicates intense mixing between juvenile and evolved magma components in a continental arc setting at ca 950 570 ma geological evidence persistent input of detrital zircon material derived from ancient crustal units of western siberian cratonic margin and evolution of hf isotopic compositions suggest that the neoproterozoic arc system of the yenisey ridge and partly sayan orogens developed along the active margin of siberia in the neoproterozoic the arc system probably extended along the periphery of rodinia into the taimyr orogen of northern siberia and valhalla orogen of north eastern laurentia

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

tectonic evolution of the chinese tianshan orogen from subduction to arc continent collision insight from polyphase deformation along the gangou section central asia the central asian orogenic belt as the largest accretionary orogen on earth is an ideal candidate to study the geodynamics of convergent plate boundaries through a prolonged period the evolution of this orogen has been explained by different tectonic models which incorporated one or a combination of the following mechanisms lateral stacking of arc systems along major shear zones arc amalgamation oroclinal bending and trench migration here we elucidate major mechanisms responsible for the tectonic evolution of the central asian orogenic belt focusing on the chinese tianshan orogen in the southern central asian orogenic belt structural observations from the 50 km long gangou section show evidence of polyphase deformation the earliest episode of orogen parallel sinistral shearing constrained to the early devonian ca 399 ma by syn deformational intrusions was possibly controlled by oblique subduction this was followed by an episode of ne sw contractional deformation dated at ca 356 ma 40ar 39ar age of syn deformational hornblende and likely associated with an episode of trench advance the third stages of deformation during the latest carboniferous and permian involved ne sw contraction orogen parallel extension and dextral transpression our new geochronological data constrain the timing of orogen parallel extension to ca 303 293 ma and confirm that dextral activation along shear zones occurred during the permian the results highlight the role of trench migration oblique tectonics and syn collisional orogen parallel extension in the build up of the central asian orogenic belt and contribute to the pre collisional reconstruction of this orogenic system

trace element and platinum group element distributions and the genesis of the merensky reef western bushveld complex south africa the merensky reef of the bushveld complex is one of the world s largest resources of platinum group elements pge however mechanisms for its formation remain poorly understood and many contradictory theories have been proposed we present precise compositional data major elements trace elements and platinum group elements pge for 370 samples from four borehole core sections of the merensky reef in one area of the western bushveld complex trace element patterns incompatible elements and rare earth elements exhibit systematic variations including small scale cyclic changes indicative of the presence of cumulus crystals and intercumulus liquid derived from different magmas ratios of highly incompatible elements for the different sections are intermediate to those of the proposed parental magmas critical zone and main zone types that gave rise to the bushveld complex mingling but not complete mixing of different magmas is suggested to have occurred during the formation of the merensky reef the trace element patterns are indicative of transient associations between distinct magma layers the porosity of the cumulates is shown to affect significantly the distribution of sulphides and pge a genetic link is made between the thickness of the merensky pyroxenite the total pge and sulphide content petrological and textural features and the trace element signatures in the sections studied the rare earth elements reveal the important role of plagioclase in the formation of the merensky pyroxenite and the distribution of sulphide

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

the bushveld complex south africa formation of platinum palladium chrome and vanadium rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large relatively slowly cooling subsiding magma chamber platinum group element pge deposits in the bushveld complex and other layered intrusions form when large incompletely solidified magma chambers undergo central subsidence in response to crustal loading resulting in slumping of semi consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides oxides olivine and pyroxene and less dense layers enriched in plagioclase the most economic pge cr and v reefs form in large multiple replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification the depth of emplacement has to be relatively shallow as otherwise ductile crust would not be able to flex and collapse in smaller intrusions cooling rates are faster subsidence is less pronounced and where it occurs the cumulate may be largely solidified resulting in insignificant mush mobility and mineral sorting layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower but the reefs can be relatively thicker an additional factor controlling the pge cr and v prospectivity of intrusions is their location within cratons intra cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large layered igneous bodies furthermore intrusions sited within cratons are more readily preserved because cratons are underlain by thick buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust

palaeomagnetism of east siberian traps and kimberlites two new poles and palaeogeographic reconstructions at about 360 and 250 ma summary we studied basalt sills and dykes and kimberlite pipes from the eastern part of the siberian platform these are spread out over a few hundred kilometres and are divided into two age groups late permian early triassic mir aikhal and olenyek regions and late devonian early carboniferous viluy and markha basins aikhal region the palaeomagnetic poles determined for each sill or dyke are statistically different from each other but averaging all corresponding directions from these sills and dykes with those from kimberlites of different generations yields results with acceptable statistics this is probably due to the averaging out of secular variation and or changes in magnetic polarity the resulting palaeomagnetic poles allow one to reconstruct the palaeopositions of siberia during the two large flood basalt events at about 360 and 250 ma a significant rotation of the siberian platform during the devonian and carboniferous is suggested the new data are in general agreement with some earlier palaeomagnetic poles for the late permian early triassic traps of the tungusska basin and significantly reduce uncertainties for previous late devonian early carboniferous siberian poles which were very scattered together with geological and absolute age data the palaeomagnetic data support the hypothesis that kimberlite magmatism and trap intrusions were both rapid and relatively close in time the 360 ma event is emerging as a magmatic event with considerable extent over the russian and siberian platforms related to incipient continental break up and triple junction formation possibly at or near the time of the frasnian famennian mass extinction

first report of coupled early permian paleomagnetic and geochronologic data from the dunhuang block nw china and implications for the tectonic evolution of the paleo asian ocean abstract in order to better understand the tectonic relationship between the dunhuang block dhb and its adjacent blocks and to constrain the timing of the closure of the paleo asian ocean a combined geochronologic and paleomagnetic investigation has been undertaken on early permian tuff basalt flows and sandstones from the shuangbaotang formation in the northwestern part of the dhb u pb zircon dating indicates that the age of the strata is between 280 6 2 9 ma and 291 4 2 6 ma thermal demagnetization of a three component isothermal remanent magnetization irm and curie point experiment suggest that magnetite dominates in the rock samples analyzed in addition there is a minor amount of hematite in some sandstones stepwise thermal demagnetization successfully isolated stable characteristic remanent magnetization chrm from 11 tuff layers two lava flows and nine sandstone beds two components were isolated from all samples a lower temperature component ltc and a higher temperature component htc the ltc is near the direction of the present day geomagnetic field and produced a negative fold test indicating it is a viscous remanent magnetization in the present day geomagnetic field most of the htc are reverse polarity normal 4 reverse 158 which is in accordance with the kiaman reversed superchron that spans the late carboniferous permian interval in addition the htc of all studied sites passed the fold and reverse tests suggesting that they likely represent primary remanent magnetization the tilt corrected mean direction from all sites tuff basalts and sandstones is ds 1 7 is 43 1 ks 403 95 1 5 n 22 the mean paleopole of the site mean direction corresponded vgps lies at 74 5 n 268 5 e with a95 1 6 considering the consistent inclination values recorded among the studied tuff basalts and sandstones and the low degrees of anisotropy within all samples we suggest that there is no significant inclination shallowing caused by depositional compaction in the sedimentary layers of the studied section taking into account the results from this study as well as previous late paleozoic paleomagentic studies from adjacent tectonic blocks we conclude that the dhb formed part of the amalgamated dunhuang north china alxa qaidam mega block during the early permian but was separated from the tarim block by a small ocean here named the qiemo xingxingxia paleo ocean at this time a comparison of the early permian paleolatitudes of these and other adjacent blocks suggest that the paleo asian ocean sensu lato was still open at this time combined with other geological evidence a paleogeographic reconstruction of the paleo asian ocean has been reconstructed for the early permian

the role of the kazakhstan orocline in the late paleozoic amalgamation of eurasia article i nfo the kazakhstan orocline a horseshoe shaped belt with volcanic arcs of devonian external and late paleozoic internal age is thought to have formed as a result of convergence between the cratons of siberia baltica and tarim leading to the amalgamation of eurasia paleomagnetic and geologic data indicate that in the middle devonian the arc which is now strongly curved was nearly straight near the northwest southeast trending volcanic margin of a kazakhstania continent to constrain the age of oroclinal bending we conducted a paleomagnetic study of late carboniferous to late permian subduction related volcanics from the middle nw and north eastern ne limbs of the orocline our new results indicate that the rotation of the middle arm of the orocline was essentially completed by the earliest permian while the ne arm probably was still 50 short of its final orientation with respect to baltica the rotation of or rotation within the ne arm was completed by the late permian the paleomagnetic data constraining the timing and rotation patterns lead us to propose the following scenario for the bending of the kazakhstan orocline the orogenic deformation scenario began in the late devonian when an initial collision with tarim pinned kazakhstania s southern corner while a dextral shear motion and a considerable clockwise rotation of siberia dragged its northern end relative convergence between siberia and tarim caused initial buckling of the kazakhstania continental element trapped between them subdividing the belt into three sw nw ne segments continued subduction under the established limbs of the orocline with an estimated outward directed subduction velocity of well less than 1 cm yr gradually led to closure of the intervening junggar balkhash oceanic basin and tightening of the orocline 2008 elsevier b v all rights reserved

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

late devonian palaeomagnetism of the north tien shan kyrgyzstan can secular variation vary on a short timescale summary we studied more than 80 lava flows from a 600 m thick pile of upper devonian frasnian basalts and andesites of the aral formation in the north tien shan kyrgyzstan central asia with the aid of stepwise thermal demagnetization a high temperature dual polarity component was reliably isolated from most flows the primary origin of the high temperature component is demonstrated by positive reversal conglomerate and fold tests the most prominent and intriguing feature of this late devonian data set involves a clear distinction in angular dispersion between the lower and upper parts of the studied section a rather low concentration parameter k 13 and several directional anomalies characterize the lower section in contrast a much better grouping k 46 and a lack of directional outliers is observed for the dual polarity vectors from the upper flow sequence of the formation we analysed different mechanisms to account for this directional pattern and found that it is possible in just two ways one is to assume that secular variation sv in the upper sequence is strongly underrepresented and it is a coincidence that the mean directions of both polarities are statistically antipodal and the corresponding concentration parameters are statistically equal the other explanation is to hypothesize that the magnitude of sv can vary several fold at the same palaeolatitude and over time intervals estimated as 10 5 10 6 yr this is in sharp contrast with other models of sv where this magnitude has been assumed to be rather time independent for a givenlatitude ourhypothesisaccountsfortheobservedirregularitiesinpalaeomagneticdata but makes attempts to establish a correlation between sv and other parameters geographic latitude reversal frequency age etc more difficult we are aware however that more data are needed to refute or confirm it

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete