late holocene paleoenvironmental changes inferred from manasbal lake sediments kashmir valley india abstract paleoclimate investigations and reconstruction using the lake sediment cores of kashmir valley have been rarely attempted the basin is influenced by indian summer monsoon westerlies and the local katabatic winds in the present study an 80 cm undisturbed sediment core was retrieved from the manasbal lake situated in north western himalaya sediments were dated using 14c method and the age depth model indicated a depositional history extending from 3345 yrs bp to the present grain size major and trace elements toc om contents c n ratio and diatom assemblages were applied to reconstruct the paleoenvironmental changes around the area the a cn k diagram displays that the weathering intensity of the manasbal lake sediments are moderate to highly weathered and the sediments have been derived from nearby and mixed source origin several wet and cold phases were identified during 3300 yrs bp to 2500 yrs bp and 1800 yrs bp to 1300 yrs bp due to intense precipitation reflect high lake level these wet phases are marked by higher sand and silt content c n ratio and high allochthonous input with less abundance of diatom species clay om toc contents and high cia values consequently low lake level and dry and cold period from 3345 yrs bp to 3300 yrs bp and 2500 yrs bp to 1800 yrs bp is observed these inferences are corroborated with the trace elemental ratios cia and cwi data our data indicate that the westerlies and localised katabtic winds rather than the indian summer monsoons played a major role in controlling the past climate around the manasbal lake kashmir valley

prolonged magmatism juvenile nature and tectonic evolution of the chinese altai nw china evidence from zircon u pb and hf isotopic study of paleozoic granitoids abstract paleozoic granitoid magmatism played an important role in the tectonic evolution of the chinese altai and zircon u pb and hf isotopic compositions have been determined for samples from eleven granitic plutons batholiths the jiadengyu gneissic granitic pluton yielded a zircon u pb age of 479 ma and thus it does not represent precambrian basement as suggested previously our results and published data demonstrate that voluminous granitoids were continuously emplaced over more than 30 area of the chinese altai during the period from 447 ma to 368 ma with a climax at ca 400 ma ages for zircon overgrowth rims demonstrate additional thermal events at ca 360 and 280 ma respectively positive e hf t values 0 to 9 of normal magmatic zircons suggest that the granitoid magmas were derived from juvenile sources xenocrystic zircon cores are 543 421 ma old and also give positive e hf t values 2 5 to 12 suggesting their origin as early crystallized minerals in the magma chambers or as inherited cores from newly accreted meterials the strong magmatism at ca 400 ma significantly changed the hf isotopic composition of the magma source by substantial input of juvenile material in a relatively short period geophysical geological and geochemical data support that ridge subduction was a possible mechanism for the strong magmatism ca 400 ma and the above mentioned change of hf isotopic composition in the magma source

formation and palaeozoic evolution of the gorny altai altai mongolia suture zone south siberia zircon u pb constraints on the igneous record abstract the altai sayan fold belt epitomises how phanerozoic island arc continental crust contributed to the growth of the palaeo eurasian continent its formation is dominated by the closure of the palaeo asian ocean pao when island arc systems and gondwana derived terranes accreted to the siberian margin relics of the pao related tectonic units and associated granitoids occur along the ophiolitic charysh terekta ulagan sayan suture ctuss between gorny altai and altai mongolia zircon la icp ms u pb dating of this igneous record constrains the multi stage geodynamic pao evolution primitive kuznetsk altai island arc crust formed at the siberian margin during the ediacaran early cambrian 525 555 ma this island arc matured during the middle late cambrian 510 ma and was consumed by pao subduction in the late cambrian early ordovician 480 490 ma forming the siberian early caledonian accretion collision belt south of the ctuss granitic magmatism occurred within gondwana derived altai mongolia during the middle late ordovician 450 470 ma palaeo kazakhstan assembly and during a silurian early devonian 400 425 ma andean type collision middle late devonian 360 395 ma granitoids were emplaced as a result of the collision of altai mongolia with siberia during final pangaea amalgamation the suture was strike slip reactivated associated magmatism 295 ma the youngest 220 255 ma sampled granitoids originated in an intra plate setting

geochemistry of sediments of the peninsular rivers of the ganga basin and its implication to weathering sedimentary processes and provenance abstract geochemistry of the himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate among the himalayan rivers the ganga and its himalayan catchment have been studied extensively however the peninsular rivers constituting a significant part of the ganga basin have not received much attention heretofore in the present geochemical study of the peninsular river s sediments we have found that the initial chemical weathering of rocks in the catchment produces texturally mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine grained suspended sediments the overbank sediments possess an intermediate texture and geochemistry but more towards the suspended sediments the sediment geochemistry data indicates that the peninsular river s sediments show an increase in the weathering intensity from the west banas river to the east son river along the climate gradient i e from the arid semiarid to the sub tropical condition the higher chemical index of alteration cia values of the peninsular river s sediments than the yamuna and ganga river sediments reflect the control of weatherable lithology in the tectonically stable low relief and subtropical climate condition the yamuna and ganga river sediments with lower cia values show more physical weathering in the tectonically active himalaya the suspended and overbank sediments of the yamuna and ganga rivers show an increase in their cia values after the confluence of the peninsular rivers indicating the contribution of more weathered materials by the peninsular rivers it has been found that there is a geochemical split between the channel and suspended sediments of the peninsular rivers for sharing different sources i e the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments the weathering geochemistry trace element systematics and ree patterns suggest that the dominant sources of the channel sediments of the peninsular rivers are the felsic crystallines and sedimentary lithologies of the aravalli range bundelkhand and chhotanagpur granite and gneisses and vindhyan sandstones whereas the mafic lithologies such as the deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments within the range of intermediate composition the overbank sediment chemistry reflects more contribution of the mafic sources except for the ken which shows a higher contribution of the felsic sources the geochemical split between the channel and suspended sediments of the peninsular river s sediments for the different provenances indicates differential weathering of the deccan basalts bundelkhand crystalline and vindhyan sedimentary rocks and also the hydrodynamic control of the peninsular rivers during erosion transport and deposition however the himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the himalayan catchment

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

a synthesis of zircon u pb ages and hf isotopic compositions of granitoids from southwest mongolia implications for crustal nature and tectonic evolution of the altai superterrane abstract granitoid magmatism is extensively developed in the altai superterrane but the timing of magmatic events is not so well determined in this study twelve granitoid intrusions from southwest mongolia were dated by the zircon u pb method and analyzed for zircon hf isotopic compositions the new age data indicated three phases of magmatic emplacement middle paleozoic 398 350 ma late paleozoic 317 289 ma and triassic ca 244 211 ma the first phase magmatism is mainly composed of hornblende bearing i type granitoids formed during a long lasting subduction process in the early to middle paleozoic the second phase magmatism was manifested by a few small intrusions primarily distributed along the erqis fault zone and probably formed in a transitional tectonic regime from subduction to post tectonic setting in the late paleozoic the third phase magmatism was represented by post tectonic granitoids emplaced in an intraplate extensional setting model ages that were calculated using the composition of new continental crust are predominantly neoproterozoic to early paleozoic indicating that the protoliths of granitoids were likely dominated by paleozoic juvenile crust with minor neoproterozoic materials the altai superterrane was a huge paleozoic tectonic collage produced by amalgamation of subduction accretion complexes in the margin of the siberian continent and the tuva mongol microcontinent

compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift mesozoic kutch basin western india abstract this study presents a combined petrographical and geochemical investigation to track the compositional changes in the mesozoic sedimentary record during the evolution of the pericratonic rift basin of kutch the mesozoic sequence of the proven petroliferous basin of kutch representing 3000 m thick siliciclastic and carbonate deposition within a time frame of 70 ma consists of jhurio jhumara jhuran and bhuj formations in ascending order of succession the dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks the concentration of individual trace elements such as th sc zr v ni and ratios like th sc cr v y ni th co la sc support the predominantly felsic source rock the lree enrichment and the negative eu anomaly corroborate the predominantly felsic source however concentrations of v ni and ti reveal the mafic input in older stratigraphic units while gdn ybn indicates dominant post archean source across the mesozoic succession younger stratigraphic units reveal contributions from the archean rocks from nagar parkar and aravalli highland regions the cia values suggest intermediate to intense weathering while the icv data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations the high value of zr sc as well a high content of hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks major oxide sio2 na2o and k2o and trace elements la th and hf bear the passive margin setting for the kutch basin during the mesozoic the decrease in feldspar content in sandstones increase in the concentration of zr and hf in shale and a decrease in values of icv from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the kutch basin during the transition from early syn rift to post rift

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

the composition of shales from the ordos basin china effects of source weathering and diagenesis abstract the ordos basin situated in northwestern china is the biggest mesozoic terrigenous sedimentary basin developed on the north china platform the geochemical data imply that shales from the ordos basin were mainly derived from a source area with an average archaean granite composition high na2o contents very limited variation of ti zr and ratios of gd yb n higher than 2 0 indicate that ordos shales are less mature than typical post archaean shales such as nasc and paas highly variable cia values chemical index of weathering indicate that most ordos shales are less weathered than nasc and paas ratios of la sm n and total ree contents for the ordos shales are positively correlated with cia whereas those of gd yb n inversely vary with cia these suggest that the weathering of source rocks is responsible for the ree fractionation in the shales of the ordos basin depletion of eu in clay sized fractions of the ordos shales decreases with enhanced crystallinity of illite considering that ratios of fe 3 fe 2 in the shales decrease with the increase of crystallinity of chlorites we propose that eu anomalies are directly related to the reduction of iron during burial diagenesis

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

zircon u pb geochronology and hf isotopic composition of granitiods in russian altai mountain central asian orogenic belt the central asian orogenic belt caob consists of many tectonic terranes with distinct origin and complicated evolutionary history understanding of individual block is crucial for the reconstruction of the geodynamic history of the gigantic accetionary collage this study presents zircon u pb ages and hf isotopes for the granitoid rocks in the russian altai mountain range including gorny altai altai mongolian terrane and ctus suture zone between them in order to clarify the timing of granitic magmatism source nature continental crustal growth and tectonic evolution our dating results suggest that granitic magmatism of the russian altai mountain range occurred in three major episodes including 445 429 ma 410 360 ma and 241 ma zircons from these granitoids yield comparable positive ehf t values and neoproterozoic crustal model ages which favor the interpretation that the juvenile crustal materials produced in the early stage of the caob were probably dominant sources for the paleozoic magmatism in the region the inference is also supported by widespread occurrence of short lived juvenile materials including ophiolites seamount relics and arc assemblages in the northern caob consequently the paleozoic massive granitic rocks maybe do not represent continental crustal growth at the time when they were emplaced but rather record reworking of relatively juvenile proterozoic crustal rocks although mantle derived mafic magma was possibly involved to serve as heat engine during granitic magma generation the early triassic granitic intrusion may be a product in an intra plate environment as the case of same type rocks in the adjacent areas the positive ehf t values 1 81 7 47 and corresponding hf model ages 0 80 1 16 ga together with evidence of petrology are consistent with the interpretation that the magma source of the triassic granitic intrusion was derived from enriched mantle and melted under an usually high temperature condition likely due to basaltic magma that underplated the lower crust our data combined with evidence of the regional geology enable us to conclude that the gorny altai and altai mongolian terranes possibly have similar tectonic natures but represent two separate accretionary systems before devonian collision the accretion and amalgamation processes resulted in the paleozoic granitoid magmatism and caused the two terranes to merge as a composite tectonic domain at the siberian continental margin

trace elements in shale as indicators of crustal provenance and terrane accretion in the southern canadian cordillera in this study the trace element geochemistry of shale is used to infer the nature of adjacent crustal blocks during terrane amalgamation and accretion in southern british columbia the geochemistry of about fifty shale samples from one of the best dated stratigraphic sections in the north america cordillera is used to 1 infer proximity to source regions characterized by juvenile ocean arcs continental arcs and ophiolites and 2 address a controversy concerning the timing of terrane amalgamation and accretion this study includes analyses of shale from the entire mesozoic stratigraphic section of the cadwallader terrane and overlying tyaughton basin as well as argillites from the structurally adjacent bridge river complex the mid cretaceous albian strata of the upper taylor creek group show light rare earth lree enrichment la n sm n of 3 0 and anomalously high cr and ni older units upper triassic lower cretaceous that stratigraphically underlie the upper taylor creek group have less lree enrichment high ba n la n ratios and no cr or ni anomaly the mid cretaceous strata were probably derived from a continental arc during a period of uplift and erosion of ultramafic rocks probably ophiolites and the co extensive nature of these sediments suggests accretion of many basement terranes to the edge of a continent the trace element geochemistry of the older strata is similar to that of sediment derived from an oceanic arc however lower cretaceous strata of the relay mountain group may record the incipient collision and progressive closure of this ocean basin the bridge river complex which is dominated by oceanic rocks and is interpreted to be an accretionary complex contains two suites of argillites one of which shows significant lree enrichment and isotopic data suggest a jurassic cretaceous age for these argillites that compose the matrix in this complex leitch et al 1991 we suggest that the bridge river complex was a jurassic cretaceous accretionary complex that formed outboard of the methow section of rocks and was not juxtaposed with the cadwallader terrane and tyaughton basin until the albian when these terranes were accreted to north america paleomagnetic data from these rocks maxson et al 1993 indicate that accretion took place at the latitude of central mexico and that subsequent strike slip faulting brought these terranes to their present position by eocene time

diagenetic history and provenance of devonian terrestrial sandstones at the margin of gondwana padeha formation eastern alborz iran abstract the northern margin of gondwana in iran rifted in the devonian forming a passive continental margin to the paleotethys ocean the details of which are obscured by later collision a record of the early phase of opening of paleotethys is preserved in the 600 m thick padeha formation a middle devonian terrestrial rift basin succession the sandstones are quartz arenite sub arkose and arkose and contain minimal detrital matrix 1 bulk rock geochemistry according to major elements suggests a source to the sandstones that was dominated by i type granite but also based on trace elements included small amounts of intermediate or mafic rocks low zr and hree contents suggest little or no sandstone in the source area and thus low abundance of fine grained heavy minerals

petrological and geochemical evidence of the paleoproterozoic and the meso neoproterozoic sedimentary rocks of the bastar craton indian peninsula implications on paleoweathering and proterozoic crustal evolution the petrology and geochemistry of the sandstones and shales of the meso neoproterozoic chattisgarh and indravati basins and the pelites and quartzites of the paleoproterozoic sakoli and sausar basins of the bastar craton have been studied for the paleoweathering tectonic setting and to delineate sediment source components and finally to trace the proterozoic crustal evolution in the bastar craton indian peninsula the geochemical data shows decrease in the abundance of mafic major elements and transition elements and an increase in the large ion lithophile elements liles from the paleoproterozoic pelites to the meso neoproterozoic shales this suggests partial exposure of granitoids in the paleoproterozoic and unroofing of the granitoids by the complete removal of mafic rocks in the provenance as the meso neoproterozoic sedimentation progressed overall the study of the meso neoproterozoic sandstones and shales show homogeneity in the source rock composition with strong felsic component however the paleoproterozoic pelites and quartzites show heterogeneity in the source rock composition with mixture of the felsic and mafic components geological geochemical and petrographic evidences indicate that the sediments in the paleoproterozoic sakoli and sausar basins and the meso neoproterozoic chattisgarh and indravati basins have been deposited in passive margin tectonic settings cratonic basins or intra cratonic rifts the relationship among alkali and alkaline earth elements cia pia and the th u ratio indicate that the source area was affected by moderate to intense weathering history

weathering and sediment generation in the archean an integrated study of the evolution of siliciclastic sedimentary rocks of the 3 2ga moodies group barberton greenstone belt south africa abstract alluvial and braided fluvial deposits of the 3 2 ga moodies group in the barberton greenstone belt south africa are analyzed petrographically and geochemically to identify their source rocks provenance and assess the degree and type s of weathering required to produce the observed moodies sediment compositions conglomerate sandstone and shale data give somewhat differing pictures of provenance and weathering due to derivation from different components within the source terrane and size and compositional fractionation during transport the results suggest that shale geochemistry provides the most accurate estimate provenance although both rare earth element and trace element th sc zr cr and ti data must be used in combination to give the best results the source area for moodies group sediments was dominated by tonalite felsic volcanic rock komatiite basalt and granite based on mineralogical and major element divergence from estimated source area composition the moodies group sediments are remnants of an aggressive weathering environment labile materials such as komatiite basalt and coarse plagioclase grains decomposed almost entirely to clays and solutes and the chemical index of alteration for moodies shale is well above the global average an aggressive weathering environment in the archean may have been achieved by increased rainfall higher temperatures and or higher atmospheric p c o 2 more likely a combination of these conditions worked to offset the inhibitory weathering effects of a plant free environment

crustal melting and magma mixing in a continental arc setting evidence from the yaloman intrusive complex in the gorny altai terrane central asian orogenic belt abstract granitoids and their hosted mafic enclaves may retain important information on crust mantle interaction and thus are significant for study of crustal growth and differentiation an integrated petrological geochronological and geochemical study on the granitoid plutons of the yaloman intrusive complex from the gorny altai terrane northwestern central asian orogenic belt was conducted to determine their source nature petrogenesis and geodynamics mafic enclaves are common in the plutons and a zircon u pb age 389 ma 4 ma indicates that they are coeval with their granitoid hosts ca 393 387 ma petrographic observations reveal that these mafic enclaves probably represent magmatic globules commingled with their host magmas the relatively low sio2 contents 46 0 60 7 wt and high mg 38 9 56 5 further suggest that mantle derived mafic melts served as a crucial component in the formation of these mafic enclaves the granitoid hosts including quartz diorites and granodiorites are i type in origin possessing higher sio2 contents 60 2 69 9 wt and lower mg 32 0 44 2 their zircon hf and whole rock nd isotopic compositions indicate that the magmas were dominated by remelting of neoproterozoic 0 79 1 07 ga crustal materials meanwhile the geochemical modeling together with the common occurrence of igneous mafic enclaves and the observation of reversely zoned plagioclases suggests that magma mixing possibly contributed significantly to the geochemical variation of the granitoid hosts our results imply that mafic magmas from the mantle not only provided substantial heat to melt the lower crust but also mixed with the crust derived melts to form the diverse granitoids the oxidizing and water enriched properties inferred from the mineral assemblages and compositions imply that the granitoid plutons of the yaloman intrusive complex were possibly formed in a continental arc related setting which is also supported by their geochemistry the devonian granitoids from the gorny altai terrane show remarkable temporal spatial petrogenetic affinities to the counterparts from the altai mongolian terrane indicating that these two terranes were possibly under subduction of the same oceanic plate i e the ob zaisan ocean the voluminous granitoids signify significant crustal recycling and growth as a response to the underplating of extensive mantle derived basaltic melts

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

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

late carboniferous high end t ehf t granitoids enclaves and dikes in western junggar nw china ridge subduction related magmatism and crustal growth abstract we report results of petrologic geochronological and geochemical investigation of the late carboniferous diorites granodiorites amphibole am bearing granites and associated dioritic and monzonitic enclaves and mafic and granitic dikes in the keramay area of the western junggar region of central asian orogenic belt caob zircon u pb dating suggests that they were generated in the late carboniferous 316 304 ma the diorite and granodiorite compositions extend over a wide range of sio2 53 70 wt sr 240 602 ppm and mg 41 58 values and are characterized by moderately fractionated rare earth element ree patterns nb ta depletion and relatively low y and yb contents the mafic dikes consist of dolerites diorite porphyries and minor granodiorite porphyries and have variable sio2 51 59 wt and high mg cr and ni values with the exception of two samples with relatively high heavy ree hree contents the mafic dikes exhibit trace element characteristics similar to diorites and granodiorites the am bearing granites and a granite porphyry dike sample have high levels of sio2 73 77 wt hrees e g yb 3 46 15 7 ppm and low mg cr and ni contents along with clearly negative eu ba and sr anomalies similar to typical a type granites all granitoids enclaves and dikes in this region have high positive end t 7 13 to 9 74 and zircon ehf t 10 to 16 values and moderate initial 87sr 87sr ratios 0 7004 0 7049 mineral composition data suggest that the parental magmas for mafic dikes are similar to cenozoic sanukitoids in the setouchi arc area japan and were possibly generated under water rich and high oxygen fugacity nno 1 5 to nno 2 7 conditions they most likely originated from partial melting of a mantle source variably modified by subducted oceanic crust derived melts and minor fluids and subsequently underwent fractional crystallization the diorites and granodiorites were possibly generated by magma mixing between enriched lithospheric mantle and juvenile lower crust derived magmas coupled with minor crystal fractionation the am bearing granites and granite porphyry dike were produced by partial melting of juvenile crustal materials at shallow crustal levels taking into account widespread contemporaneous magmatism including morb type basalts and slab derived adakites in western junggar we suggest that the keramay intrusive rocks were generated in a special arc setting related to ridge subduction and resultant slab window which played an important role in the crustal growth of the caob

phase equilibria of the lyngdal granodiorite norway implications for the origin of metaluminous ferroan granitoids the proterozoic 950 ma lyngdal granodiorite of southern norway belongs to a series of hornblende biotite metaluminous ferroan granitoids hbg suite coeval with the post collisional rogaland anorthosite mangerite charnockite amc suite this granitoid massif shares many geochemical characteristics with rapakivi granitoids yet granodiorites dominate over granites to constrain both crystallization p t fo2 h 2o in melt and magma generation conditions we performed crystallization experiments on two samples of the lyngdal granodiorite with 60 and 65 wt sio2 at 4 2 kbar mainly at fo2 of nno nickel nickel oxide to nno 1 and under fluid saturated conditions with various h2o co2 ratios for each temperature comparison between experimental phase equilibria and the mineral assemblage in the lyngdal granodiorite indicates that it crystallized between 4 and 2 kbar from a magma with 5 6 wt h2 oa t an fo2 of nno to nno 1 these oxidized and wet conditions sharply contrast with the dry and reduced conditions inferred for the petrogenesis of the amc suite and many other rapakivi granites worldwide the high liquidus temperature and h2o content of the lyngdal granodiorite imply that it is not a primary magma produced by the partial melting of the crust but is derived by the fractionation of a mafic magma lyngdal type magmas appear to have volcanic equivalents in the geological record in particular our results show that oxidized high silica rhyolites such as the bishop tuff could be derived via fractionation of oxidized intermediate magmas and do not necessarily represent primary crustal melts this study underlines the great variability of crystallization conditions from anhydrous to hydrous and reduced to oxidized and petrogenetic processes among the metaluminous ferroan magmas of intermediate compositions granodiorites quartz mangerites quartz latites suggesting that there is not a single model to explain these rocks

use of multi proxy approaches to determine the origin and depositional processes in modern lacustrine sediments carajas plateau southeastern amazon brazil abstract geochemical and isotopic compositions of surficial sediments from a plateau lake in carajas southeastern amazon region were investigated to understand the spatial distribution of major and trace elements 13 c 15 n and c n ratio depositional processes and the origin of inorganic and organic fractions the 13 c 15 n and c n ratio indicate mainly an autochthonous source with siliceous sponge spicules and algae being the major source of organic matter in the center of the lake sector 3 while an allochthonous source mainly derived from c3 vascular forest plants dominates in the shallowest portion of the lake sector 1 consequently there was an apparent dilution of c4 plants montane savanna in the sediment water interface among major elements fe 2 o 3 is highly enriched in sector 3 which is controlled by the erosion of catchment laterites and underwater topography while al 2 o 3 and p 2 o 5 enrichment near the northern border of the lake is controlled by the weathering of mafic rocks similar spatial distribution of sio 2 with total organic carbon toc and isotopic evidence indicate that si distribution is partially controlled by organic components such as siliceous sponge spicules and algae the occurrence of most of the trace and rare earth elements ree is independent of fe 2 o 3 and toc but controlled by detrital aluminum silicates and heavy minerals indicating a lack of post depositional diagenetic control on their distribution the distribution of as and mo are possibly controlled by organic matter mineralization during early diagenesis and subsequently precipitation of fe phases the values of the chemical index of alteration cia in the sediments are very high 94 99 and similar to those of the source rocks suggesting that sediment composition is mainly controlled by mechanical weathering rather than chemical weathering geochemical indices al k ti k al ti la th ti zr zr hf hf nb la al co th ba sr and th sc together with the a cn k plot suggest that the provenance of the inorganic sediments remained relatively uniform or constant during the depositional period and that they were mainly derived from laterite crusts and subordinately from mafic soils this inference was further substantiated by the chondrite normalized ree patterns and discrimination plots geochemical indices such as u th authigenic u mo al and v cr indicate that the sediments were deposited under an oxic environment

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

overview of the meso to neoproterozoic evolution of the vindhyan basin central india abstract despite its origin in a stable intracratonic basin the vindhyan supergroup central india embodies tectonic driven depositional cycles of various orders a marked change in sedimentation pattern was coupled with a transient plate margin compression in the otherwise extensional regime an unconformity laterally correlatable with a conformity that divides the supergroup in two sequences arose in consequence maximum flooding surfaces mfs within the sequences can generally be correlated with intrabasinal volcanism that drastically diminished through the initial rift to later sag stage of basin evolution concomitantly with the change in tectonic milieu paleoseismic deformation structures and related deposits also became drastically reduced in scale nevertheless metre and decametre scale depositional cycles correlate well with the subtle record of paleoseismicity intermittent tilting of the depositional substratum is demonstrable in systematic bed dip changes in metre scale fining upward depositional cycles in the rift stage in the sag stage it is reflected merely in consistent deflection of paleocurrent directions at the top of the decametre scale parasequence sets towards the top of the supergroup progressive thickening and decreasing frequency of parasequences indicates a declining rate of basin subsidence progradation despite punctuation thus resulted in basin filling

geochemical records of qionghai lake sediments in southwestern china linked to late quaternary climate changes abstract knowledge of the chemical weathering history under the subtropical monsoonal climate will help to resolve the discrepancies regarding how climate conditions constrain chemical weathering major element and rare earth element ree compositions of the qionghai lake sediments in sichuan province southwestern china were analyzed aiming to provide information on sediment source discrimination and history of chemical weathering intensities and its responses to variations of indian summer monsoon ism and paleoclimate conditions as revealed by the a cn k diagram and other provenance proxies including tio2 zr ratio th sc vs zr sc and la th vs hf diagrams as well as the ree characteristics the source of qionghai lake sediments was felsic rocks additionally these sediments were subjected to small changes in provenance sedimentary sorting and recycling and weak diagenesis after deposition and or metasomatism indicating original signals were maintained on the intensity of chemical weathering of source area the chemical weathering intensities inferred from cia chemical index of alteration values have significantly fluctuated over the past 28 kyr reflecting three stages of paleoclimate evolution which is consistent with grain size characteristics carbonate contents low frequency magnetic susceptibilities toc and biomarker proxy paq the cia values changed significantly during the typical warm and cold climate events including the last glacial maximum heinrich 1 cold event younger dryas and holocene climatic optimum and generally exhibited an increasing trend in amplitude correspondingly in concert with the climate shifting from cold and dry to warm and humid conditions generally warm and humid climate conditions suggest enhanced chemical weathering intensity whereas weak chemical weathering denotes cold and dry climate in the ism region in addition sequential variations of the cia values during the past 28 kyr may reflect changing chemical weathering processes in responses to the varying intensities of indian summer monsoon and the climate conditions forced by the northern hemisphere solar insolation

pb pb age of earliest megascopic eukaryotic alga bearing rohtas formation vindhyan supergroup india implications for precambrian atmospheric oxygen evolution abstract though considered to be the earliest known well preserved megascopic body fossil of an eukaryotic alga grypania spiralis has not yet been dated directly and reliably in any of its four known locations in the world we report a pb pb isochron age of 1599 48 ma for the grypania bearing rohtas formation of the vindhyan supergroup central india besides being about 500 myears older than the previously inferred age for this formation this pb pb age together with close age constraints on the same fossil bearing horizons in jixian china and montana usa indicates that grypania bloomed on a global scale between 1 6 and 1 5 ga being an obligate aerobe the appearance of a much older grypania within one of the principal bif deposits near michigan usa has been linked to a significant jump in atmospheric oxygen between 2200 and 1900 ma inferred from geochemical evidence the long gap of 400 myears between the older and younger grypania occurrences could be due to reduction of atmospheric oxygen below the grypania survival threshold as a result of extensive bifs between about 1950 and 1850 ma

geochemistry and sedimentary petrology of archean clastic sedimentary rocks at mt goldsworthy pilbara craton western australia evidence for the early evolution of continental crust and hydrothermal alteration abstract geochemical and petrological analyses of archean clastic metasedimentary rocks at mt goldsworthy in the pilbara craton western australia reveal the early evolution of continental crust and the earth s surface environment the succession correlative to the ca 3 4 ga strelley pool chert is composed dominantly of silicified medium grained to very coarse grained sandstone siltstone and shale with minor chert and precipitative beds of nahcolite and barite the sandstone is generally rich in detrital quartz with the coarse grained sandstone containing abundant very well rounded mono crystalline quartz that is assumed to be derived from older sedimentary rocks the recycled detritus is mixed with first cycle detrital material such as feldspar and barite that is sourced from reworked precipitative beds the sandstone also contains zircon fe ti oxides sulfides and lithic fragments of various origins including mafic ultramafic volcanic rocks sedimentary and possibly metamorphic rocks al ti zr systematics indicates that the source area for the mt goldsworthy clastic metasedimentary rocks was locally subjected to hydrothermal alteration reaction with the acid solution resulted in al dissolution and the formation of zr and ti enriched residual detrital material the enrichment in heavy rare earth elements and low al 2 o 3 tio 2 values of mt goldsworthy samples reflects the inflow of the residual zircon and ti oxides enriched detritus th sc la sc and eu eu ratios that are unaffected by contamination by the residual detritus indicate a mixed provenance with a significant contribution from granitoid rocks the presence of detrital zircon older than 3 5 ga was also demonstrated in this study

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

provenance studies and mudrocks abstract provenance studies based on the mineralogy of sandstones seem to be falling rapidly into disrepute as a result of the increasing emphasis on the effects of diagenesis on the original detrital mineral composition feldspars in sandstones commonly are dissolved altered to clay minerals and albitized by widely occurring diagenetic processes accessory minerals all too frequently are confined in ancient sandstones to ztr mudrocks in contrast have the potential of greater preservation of feldspars and accessory minerals because of their lesser permeabilities few studies have attempted to use the nonclay mineralogy of mudrocks for provenance work and these few have had promising but mixed results mudrocks deserve more attention in provenance studies than they have received

mesoproterozoic neoproterozoic transition geochemistry provenance and tectonic setting of clastic sedimentary rocks on the se margin of the yangtze block south china abstract the se margin of the yangtze block south china is composed of the mesoproterozoic lengjiaxi group and the neoproterozoic banxi group with sinian and post sinian cover a geochemical study was undertaken on the mesoproterozoic neoproterozoic clastic sediments in order to delineate the characteristics of the sediment source and to constrain the tectonic development and crustal evolution of south china our results show that the mesoproterozoic clastic sediments have a dominant component derived from a metavolcanic plutonic terrane with a large of mafic component there is a minor contribution of mafic rocks and older upper crustal rocks to the provenance strong chemical weathering in the source area occurred before transport and deposition the provenance for the neoproterozoic clastic sediments was most likely old upper continental crust composed of tonalite granodiorite dominated tonalite granodiorite granite source rocks which had undergone strong weathering and or recycling a minor component of older k rich granitic plutonic rocks and younger volcanogenic bimodal rocks is also indicated based on the regional geology the geochemical data and the inferred provenance the mesoproterozoic group is interpreted as a successive sedimentary sequence deposited in an extensional rifting back arc basin adjacent to a 1 80 ga continental margin arc terrane the progressive extension rifting of the back arc basin was followed by increasing subsidence and regional uplift during continental marginal arc continent the cathaysian block collision at 1 0 ga caused the deposition of the neoproterozoic group into back arc to retro arc foreland basin therefore the depositional setting of the proterozoic clastic sediments and associated volcanic rocks within the back arc basin reflected basin development from an active continental margin back arc basin with extension or rifting of the back arc basin to a passive continental margin

paleoclimatic control on the composition of the paleoproterozoic serpent formation huronian supergroup canada a greenhouse to icehouse transition unlike other feldspathic arenites in the 12 km thick huronian supergroup strata of the 250 350 m thick serpent formation contain abundant plagioclase deposited in a distal alluvial setting the serpent formation consists of arenites with minor shale and siltstone the plagioclase abundance could reflect unroofing of a unique source relative to other huronian units or could be due to less intense chemical weathering major trace and rare earth element ree geochemistry of the serpent formation are used to evaluate these two possibilities serpent formation source rocks form part of the archean superior province which mainly consists of tonalitic granitic and supracrustal assemblages and their metamorphosed equivalents in al2o3cao na2ok2o acnk space shales define a linear array which indicates that the unweathered source contained plagioclase and k feldspar in the ratio of 5 1 this particular array indicates that serpent fluvial systems tapped a variably weathered carapace developed on the superior province rather than purely fresh bedrock a modelled mixture of 80 tonalite and 20 granite group rocks reproduces ree and trace element characteristics of the serpent formation sandstones and shales average eu eu 0 87 lan smn 4 4 gdnybn 1 8 and th sc 1 65 mass balance considerations indicate that less than 5 supracrustal group rocks can be added at the expense of the granite group a unique source for serpent detritus is rejected because underlying and overlying units have approximately the same provenance composition plagioclase k feldspar ratios in serpent sandstones range from 2 1 to 1 2 which achieves mass balance among source mudstone and sandstone compositions when plotted in acnk space achievement of mass balance implies that sandstones and mudstones were derived from the same weathering profiles these findings indicate that plagioclase preservation in the serpent formation is related to less intense compared with other huronian arenites paleoweathering conditions probably a harbinger of the widespread continental glaciation recorded in the overlying gowganda formation

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

petrography and geochemistry of lower carboniferous greywacke and mudstones in northeast junggar china implications for provenance source weathering and tectonic setting abstract northeast junggar occupies an important position that links east junggar and chinese altai numerous magmatic and sedimentary rocks of the paleozoic in this area recorded the final amalgamation processes of east junggar and chinese altai this study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the early carboniferous nanmingshui formation in northeast junggar the provenance and tectonic setting of these clastic rocks are discussed petrography indicates that the composition and texture maturity of the sandstones are low the components of the sandstones are mainly volcanic fragments 61 87 feldspars 9 30 and monocrystalline quartz 2 18 with a few polycrystalline quartz and other minerals slice observation indicates that the majority of the volcanic fragments of sandstones are basic intermediate volcanic rocks with a few dacite and felsic plutonic fragments the detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs a low to moderate chemical index of alteration and the al2o3 cao na2o k2o diagram reflect a low to moderate weathering degree in the source area trace and rare earth element e g la th hf sc cr co and eu contents and their ratios suggest that the source rocks of the clastic rocks are intermediate basic rocks with some felsic rocks compared with sandstones the source rocks for mudstones are more felsic the petrography and geochemistry characteristics of the clastic rocks suggest that the proximal dulate arc should be the primary source area mixing calculations based on ree data suggest that approximately two thirds of the sandstone fragments are intermediate basic volcanic rocks the contents of the major and trace elements as well as the stratum features of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back arc basin the formation of this back arc basin is caused by the southward subduction of the zaysan erqis ocean

reversal of the middle upper songhua river in the late early pleistocene northeast china abstract the study of drainage evolution in the songnen plain northeast china is essential for understanding the interactions between tectonics topography climate drainage evolution in the region despite this it remains unclear whether the paleo songhua river upper middle reaches of the songhua river once flowed westward into the songnen plain and what forcings influenced the drainage development of the songnen plain in this contribution we provide insight into drainage development on the songnen plain using an integrated approach of magnetic susceptibility geochemical elemental and sr nd isotopic and heavy mineral composition recovered from a 102 m sediment core sediments extracted from the eastern edge of the songnen plain with sedimentological and topographic archives our results show that a dramatic provenance shift occurred at the depth of 62 2 m 0 94 ma in the core sediments it is proposed that the songhua river was separated by the jia yi jiamushi yilan divide into two segments before 0 94 ma the west flowing proto songhua river and the east flowing proto sanjiang river lower reach of the songhua river however the proto songhua river reversed direction at 0 94 ma when the jia yi divide was cut through by headward erosion of the proto sanjiang river marking the birth of the songhua river as a single eastward flowing river system tectonics is suggested as the first order control on the evolution of the songhua river before 1 20 ma whereas climate changes may be responsible after 1 20 ma

geochemistry of loess paleosol sediments of kashmir valley india provenance and weathering abstract middle to late pleistocene loess paleosol sediments of kashmir valley india were analyzed for major trace and ree elements in order to determine their chemical composition provenance and intensity of palaeo weathering of the source rocks these sediments are generally enriched with fe 2 o 3 mgo mno tio 2 y ni cu zn th u sc v and co while contents of sio 2 k 2 o na 2 o p 2 o 5 sr nb and hf are lower than the ucc chondrite normalized ree patterns are characterized by moderate enrichment of lrees relatively flat hree pattern gd cn yb cn 1 93 2 31 and lack of prominent negative eu anomaly eu eu 0 73 1 01 average 0 81 paas normalized ree are characterized by slightly higher lree depleted hree and positive eu anomaly various provenance discrimination diagrams reveal that the kashmir loess paleosol sediments are derived from the mixed source rocks suggesting large provenance with variable geological settings which apparently have undergone weak to moderate recycling processes weathering indices such as cia ciw and pia values 71 87 83 83 and 80 57 respectively and a cn k diagram imply weak to moderate weathering of the source material

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

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

large scale silicate liquid immiscibility during differentiation of tholeiitic basalt to granite and the origin of the daly gap the dearth of intermediate magmatic compositions at the earth s surface referred to as the daly gap remains a major issue in igneous petrology the initially favored explanation invoking silicate liquid immiscibility during evolution of basalt to rhyolite has lost support because of the absence of any firm geological evidence for separation of fe and si rich liquids in igneous rocks this work presents a record of large scale magmatic differentiation due to immiscibility in the tholeiitic sept iles intrusion canada one of the largest layered plutonic bodies on earth gabbroic cumulate rocks from the critical zone of this intrusion show a bimodal distribution in density and p2o5 content despite identical major element chemistry of the principal magmatic phases immiscibility is supported by the presence of contrasting fe rich and si rich melt inclusions trapped in cumulus apatite phase diagrams and well documented occurrences of small scale immiscibility confirm that liquid liquid unmixing and the separation of fe rich and si rich liquids may contribute significantly to the daly gap along the tholeiitic liquid line of descent

seismic q for the lithosphere of the montenegro region yugoslavia frequency depth and time windowing effects abstract the availability of accelerometric data for the montenegro earthquake of 15th april 1979 makes it possible to investigate seismic q of the lithosphere in that region in particular its dependence on frequency on the depth reached by seismic waves and on the length of time windows in which signals are processed two different spectral methods s phase energy ratio and coda envelope decay are applied respectively to direct and scattered shear waves similar results are obtained using different portions of the recordings i e coda waves for the envelope decay fit and the s wave train with a significant duration of 10 s for the energy ratios the same apparent q q 40 f where f is the frequency expressed in hz that is found for other neighbouring central mediterranean regions e g ancona on the central italian adriatic coast valnerina in the central apennines irpinia in the southern apennines is also found for the southern yugoslavian coast in the band 1 25 hz up to a maximum range of 120 km from the focus this strong frequency dependence is probably connected with the type of small scale heterogeneity and the same geological age and level of tectonic activity peculiar to all these seismotectonic areas in order to compare the apparent q of the whole s wave train 10 s long with the intrinsic apparent q of the single direct s wave usually 1 s or less the maximum entropy method is applied in the energy spectrum computation for shorter wave trains the use of shorter time windows does not reveal any significant variation in the tendency of q to increase linearly with frequency as the length of the time window containing the sample of the s waves decreases this seems to indicate that scattering dependent q is generally inseparable from intrinsic q in the lithosphere when estimates based on variations with distance of the seismic signal spectrum are used while the type of linear growth with frequency does not seem to undergo any variations it remains of the q qf type the data show there are a considerable decrease in the coefficient of proportionality q with decreasing duration of the window of s waves analysed probably as a result of variations in seismic attenuation with depth

nd sr isotopic mapping of the chinese altai and implications for continental growth in the central asian orogenic belt article i nfo the chinese altai orogen is a typical domain of the central asian orogenic belt and in previous syntheses was divided into six tectonic units or terranes in this paper 41 new and 36 published whole rock nd and sr isotopic data for granitoid intrusions and mafic dykes within units 2 and 3 of the central altai and units 4 to 6 of the southern altai were used for isotopic mapping the age of the samples used is known from u pb zircon dating end t values range from 4 to 2 in the central altai units 2 and 3 and from 1 4 to 6 in the southern altai units 4 and 5 and up to 8 4 in unit 6 correspondingly nd model ages tdm decrease from 1 6 1 1 ga in the central altai to 1 0 0 5 ga in the southern altai except for a continental fragment in unit 4 isr is elevated in the central units decreasing to b0 705 in the southern units 5 and 6 these results demonstrate that the central altai contains widespread old crustal components in its basement whereas the southern altai comprises a higher proportion of juvenile crust when integrated with published u pb zircon ages our data show that new crust grew southwards in the chinese altai in addition our data suggest that units 2 and 3 are a single tectonic unit whereas the southern altai unit 4 which previously was regarded as a single young accretionary terrane should be subdivided into two units a younger arc and an older continental fragment the granitoids in the chinese altai can be divided into syn and post non orogenic groups the syn orogenic granitoids have ca 50 80 mantle derived component whereas the post non orogenic granitoids contain ca 70 90 the generation of syn and post non orogenic granitoids represents horizontal lateral and vertical crustal growth which contributed ca 18 28 and 7 8 respectively to the area of the chinese altai this work shows that isotopic mapping is an effective approach to elucidate terrane composition in the central asian orogenic belt and thereby better constrain palaeozoic crustal growth

c o sr and pb isotope systematics of carbonate sequences of the vindhyan supergroup india age diagenesis correlations and implications for global events abstract the vindhyan supergroup of central india records a substantial portion of proterozoic time and contains some of the most disputed precambrian cambrian fossil discoveries despite the significance of these fossil finds many issues including reliable geochronology remained unresolved similarly the geochemical aspects of the sedimentary sequences and their implications to the evolution of proterozoic oceans have been studied only at a reconnaissance level here we report the results of the pb pb dating for the rohtasgarh limestone from the lower vindhyan supergroup giving an age of 1601 130 ma an estimate that is in accord with the recent u pb zircon dating of the lower vindhyan supergroup by rasmussen et al geology 30 2002 103 and ray et al geology 30 2002 131 sr isotope stratigraphy of carbonates from the upper vindhyan supergroup suggests a mid neoproterozoic 750 650 ma age for these formations this in turn argues for a long hiatus between the deposition of the lower and upper vindhyan supergroups our results conflict with the reports of cambrian age small shelly fossils and ediacaran fossils from the upper vindhyan rocks at the same time they suggest that the alleged trace fossils in the lower vindhyan rocks must be of paleoproterozoic age the most common 18 o values for calcitic components from limestone formations of the supergroup range from 10 to 7 similar to paleo neoproterozoic carbonates worldwide the modes of 13 c in the lower and upper vindhyan supergroups are 0 2 and 3 2 respectively again consistent with the worldwide dataset the secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the vindhyan basin c and sr isotope data provide new calibration points for the seawater evolutionary curves particularly for the paleoproterozoic for strontium isotopes the data from the lower vindhyan supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed

paleoclimatology and provenance of the glaciogenic gowganda formation paleoproterozoic ontario canada a chemostratigraphic approach the gowganda formation dated as about 2 3 ga is widely but not universally interpreted as glaciogenic and our chemostratigraphic study supports such an interpretation the bulk compositions of diamictite matrix materials and associated argillites are considered to have resulted from the mixture of two detrital components one is glacial flour similar in composition to the unweathered archean upper crust whereas the other is chemically weathered detritus resembling average proterozoic shale in composition the first component has a chemical index of alteration cia value of 50 reflecting the abundance of feldspar and dearth of aluminous clay minerals the second component has a cia value of 70 and was produced primarily in weathering profiles by chemical weathering typical of temperate climatic regimes diamictite matrix materials 92 samples have an average cia value of 57 the argillites have higher values the average is 62 97 samples the lower cia values of the diamictites reflect a higher proportion of glacial flour suggesting a stronger influence of frigid climatic conditions than that which prevailed during deposition of the argillites systematic trends in cia values are developed across diamictite argillite boundaries and within a thick argillite between two major diamictite units these values reflect climatic variations with maximum amelioration during deposition of the middle section of the argillite rare earth element data and th sc and ti al ratios from the diamictite matrix materials all suggest a provenance that included a large supracrustal component 45 together with lesser amounts of tonalite trondhjemite granite and granite the proportion of supracrustal materials such as volcanic rocks and shales may have been exaggerated by selective comminution during glacial transport the matrix materials of the gowganda diamictites are severely depleted in ca and proportionally enriched in na relative to the source the anorthitic component of plagioclase has been selectively replaced by an albitic component during diagenesis and metamorphism a chemostratigraphic approach provides high resolution data for reconstruction of paleoclimatic conditions and valuable information concerning provenance and metasomatic processes

slope controlled seismic deformation and tectonic framework of deposition koldaha shale india abstract penecontemporaneous deformations with remarkable lateral continuity at selected stratigraphic levels record frequent seismicity in the meso proterozoic koldaha shale vindhyan supergroup central india their consistent bipolar orientation reflects the master control of basinal tectonics boudinage small scale conjugate faults and bidirectional joint planes indicate east northeast west southwest basinal extension detailed study of a 27 km strike parallel stretch between chorhat and shikarganj against a broader perspective reveals existence of multiple nw se elongated subbasins stratigraphic and sedimentologic criteria point to inheritance and subsequent sustenance of steep western and gentler eastern flanks of the sub basins it is also indicated that the perennial supply of sediment took place from the east while the western slope contributed only during tectonic seiches the relatively large scale faults are correlatable with the steeper and the smaller deformation structures to the gentler flank the nnw oriented half graben structures that were reactivated time and again is elicited previous geophysical studies inferred roughly e w elongated rift valley in the granitic basement and the present observations indicate that the rifting continued at least up to the time of koldaha shale deposition the half graben could then be guided by cross faults resulted from dextral shear it is imperative then the basin interior sedimentation and deformation patterns were more closely controlled by the cross faults rather than by the basin margin faults only a set of slump folds in a 10 m thick interval indicates that the northern margin of the main basin was relatively steeper this is further corroborated by concentration of large fans in mineralogically immature sediments and southerly paleocurrent at the northern fringe of the basin in contrast the vindhyan sediments commonly belong to orthoquartzite carbonate association a regional northerly slope of the vindhyan basin floor towards the relatively steeper flank provides an explanation for the general northwesterly paleocurrent even though the eastern flank of the sub basins sloped wsw this integrated study of the physical aspects of the sedimentary pile against the background information of basement tectonics recognize rifting with a dextral shear component as the overriding factor controlling the early part of evolution of the vindhyan basin

oceanic environment changes caused the late ordovician extinction evidence from geochemical and nd isotopic composition in the yangtze area south china the ordovician silurian o s transition was a critical interval in geological history multiple geochemical methods are used to explore the changes in oceanic environment the nd isotopic compositions in the yangtze sea are controlled by two sources the continental erosion and the panthalassa ocean high end t values during the katian late hirnantian and rhuddanian intervals are associated with the high sea level which resulted in less terrestrial input based on the low ti al and zr al ratios in contrast low end t values during the early hirnantian interval are related to the sea level fall in this case the exposure of submarine highs and the growth of yangtze oldlands could lead to more continental materials being transported into the yangtze sea based on high ti al and zr al ratios in addition the negative end t excursion can also be attributed to the weak circulation between the yangtze sea and panthalassa ocean when sea level was low furthermore the sea level eustacy plays a significant role in the changes in redox water conditions the redox indices mainly uef ce ce and corg pt across the o s transition show a predominance of anoxic ocean over the yangtze sea during the katian late hirnantian and rhuddanian intervals and an oxygenated episode was briefly introduced during the early hirnantian period because of the fall in sea level the late ordovician biotic crisis was marked by two phase extinction events and the change in sea level and redox chemistry may be the important kill mechanisms

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

linking the acadian orogeny with organic rich black shale deposition evidence from the marcellus shale abstract the trace and rare earth elements ree analyses were conducted on samples collected from a 30 m core of the marcellus shale obtained from greene county southwestern pennsylvania our results suggest that organic matter enrichment trends in the marcellus shale can be directly linked with the acadian orogeny the acadian orogeny has been recognized as a main sediment source for the marcellus shale synthesis of tectonic history and recent ash bed geochronology reveals that deposition of the organic carbon rich or zone characterized by toc 4 located between 2393 m and 2406 5 m core depth in the studied marcellus shale core was coincident with tectonically active and magmatic quiescent period of the acadian orogeny ca 395 380 ma this time period also corresponds to the highest rate of mountain building in the acadian orogeny the light rare earth lree and selected trace elemental e g ta cs composition of the or zone sediments is similar to that of the bulk continental crust supporting the lack of magmatic activity in the source area i e acadian orogeny in contrast subsequent deposition of the organic carbon poor op sediments characterized by toc

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

a combined petrographical geochemical provenance study of the newland formation mid proterozoic of montana a provenance study was conducted on the mid proterozoic newland formation in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation sandstones of the newland formation are typically arkosic sands and arkoses with very well rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments the predominant feldspar types are k spar and microcline feldspar grains are smaller than quartz grains and feldspars show little alteration due to weathering detrital modes of newland sandstones qfl diagrams indicate that they were derived from a stable cratonic source these petrographical features imply a source area dominated by granites and granitoid gneisses semi arid to arid climate tectonic quiescence and overall peneplain conditions shales of the newland formation are dominated by illite quartz silt and fine crystalline dolomite they have small la th rations relatively large hf contents and small contents of cr co and ni all indicative of derivation from crust of granitic composition small tio 2 al 2 o 3 ratios also suggest source rocks of granitic composition the average chemical index of alteration cia for newland shales is 71 8 which in light of the probable granitoid source indicates modest amounts of chemical weathering relatively large sio 2 contents and large k 2 o na 2 o ratios reflect derivation from stable cratonic areas and tectonic quiescence thus in general the petrography of sandstones and geochemistry of shales provides the same provenance clues for the newland formation one notable discrepancy between the two approaches is that the sandstones indicate an arid to semi arid climate with very minor chemical weathering whereas the cia of the shales indicates at least modest amounts of chemical weathering this indicates on one hand the need to better calibrate the cia with a large variety of muds from modern climatic settings and on the other hand the possibility that this discrepancy is due to transport segregation

provenance and paleoweathering reconstruction of the mesoproterozoic hongshuizhuang formation 1 4 ga northern north china this is the first study presenting major and trace elemental data from the mesoproterozoic hongshuizhuang formation shales in yanshan basin north china in order to reconstruct its provenance and chemical weathering history the shales are strongly depleted in na2o and sr and enriched in y and transition metal elements relative to upper continental crust low zr concentrations and various discriminant plots e g th sc zr sc and al2o3 tio2 zr indicate insignificant mineral sorting or recycling of these shales the rocks show light rare earth element ree enrichment la ybcn 3 99 6 92 flat heavy ree and significantly negative eu anomalies euan 0 57 0 68 in chondrite normalized ree patterns similar to post archean australian average shales the fairly uniform ree patterns and trace element ratios indicate that the hongshuizhuang formation shales were derived from a felsic source area with granodiorite as the dominant contributor mixing calculations suggest a mixture of 30 granite porphyry 5 basalt and 65 granodiorite as the possible source of the shales also supporting that granodiorite was the predominant source intense chemical weathering of the source terrain is indicated by high values of the premetasomatized chemical index of alteration plagioclase index of alteration rb sr a strong positive correlation between tio2 and al2o3 depletion of cao na2o and sr and mineral compositions such strong chemical weathering suggests a warm and wet paleoclimate perhaps due to high atmospheric co2 and ch4 concentrations and a near equatorial location of the north china craton in the columbia supercontinent at 1 4 ga

sediment chemistry and detrital zircon record in the bosque and paseo del mar coastal areas from the southwestern gulf of mexico abstract in this study we analyzed the mineralogy and bulk chemical composition of 20 sediment samples as well as trace rare earth element ree concentrations and u pb ages of 400 detrital zircons retrieved from the bosque pb and paseo del mar pm coastal sediments southwestern gulf of mexico to investigate the provenance the xrd study revealed that the pb sediments are associated with quartz muscovite cordierite albite and anorthite the pm sediments are associated with calcite aragonite and biogenic materials which derived probably within the coastal environment the weathering indices like chemical index of alteration cia chemical index of weathering ciw and plagioclase index of alteration pia revealed a moderate intensity of weathering for the pb sediments the chondrite normalized ree patterns of the pb and pm sediments are with negative and positive europium anomalies eu eu suggesting that the sediments were derived by the combination of felsic and mafic source rocks the th u ratios 0 3 of the pb and pm zircons indicated an igneous origin the chondrite normalized ree patterns of the pb and pm zircons are depleted in low ree lree and enriched in heavy ree hree with positive cerium and negative europium anomalies a wide variation in chondrite normalized ree patterns of zircons with respect to ages was observed the pb is dominated by proterozoic 551 2500 ma and paleozoic zircons 445 480 ma ordovician whereas pm is dominated by cenozoic zircons 5 21 ma miocene indicating that the zircons were derived from different source terranes the chiapas massif cmc and chuacus complexes are identified as the potential source areas which contributed proterozoic zircons to pb on the other hand cuicateco terrane cui and tuxtla volcanic field tvf are considered as the potential source areas which supplied significant number of cenozoic zircons to the pm coastal area the zircon u pb ages and the bulk sediment geochemistry together indicate that the source terranes which supplied sediments to the pb and pm coastal areas consist of mafic and felsic rocks the results of this study further illustrated the importance of littoral currents in distributing sediments although rivers are considered as a carrier and agent of distributing sediments along the coastal areas

anomalously low al2o3 tio2 values for archean cherts from the pilbara block western australia possible evidence for extensive chemical weathering on the early earth geochemical sedimentological and mineralogical features of 3 0 ga archean cherts and intercalated bifs from the pilbara block western australia were studied chert layers that are well exposed at point samson 20 km north northeast of roebourne consist of various types of chert white light gray chert brownish yellow chert gray chert dark gray chert massive black chert and light gray chert the cherts other than brownish yellow chert consist mostly of microcrystalline quartz with a minor amount of fine silicate minerals and carbonates the brownish yellow chert is characterized by a high concentration of goethite most cherts contain thin layers characterized by high concentrations of ti bearing minerals such as rutile anatase fe ti aggregates and fine tio2 grains accordingly al2o3 tio2 values in some samples are very low 1 0 indicating that these samples contain more tio2 than al2o3 this geochemical feature is attributed mainly to the supply of detrital materials with high ti bearing minerals to the site of deposition because the ti bearing minerals are generally associated with detrital quartz and zircon ti enriched detrital materials are possibly formed by al ti fractionation during 1 extensive chemical weathering or 2 hydrothermal alteration of the source rocks in the first hypothesis which we prefer it is suggested that low ph values 4 of meteoric waters accelerated the decomposition of rock forming minerals and prevented precipitation of dissolved al3 such low ph values of meteoric waters could have been attributed to more violent volcanic activities issuing acid materials e g h2s and hcl and or a higher concentration of atmospheric co2 in the archean than today

geochemistry of quaternary sediments of the jeongokri archaeological site korea implications for provenance and palaeoenvironments during the late pleistocene the geochemical characteristics of an approximately 6 m long sediment core collected from the jeongokri archaeological site hantan river korea were examined to determine the provenance of the sediments and to reconstruct the palaeoenvironment of the study area during the late pleistocene 200 127 ka the core sediments were subdivided into two parts based on grain size an upper 0 380 cm depth and lower part 380 cm depth the lower part was deposited primarily by fluvial processes during an interglacial period marine isotope stage mis 7 with warm and humid conditions conversely the upper part was mainly deposited by aeolian processes during a cold and dry glacial period mis 6 geochemical characteristics represented by major trace and rare earth element ree compositions and textures of the jeongokri core sediments show distinct differences between the upper and lower parts the mineralogy and major trace and ree compositions indicate that the influence of felsic source rocks e g granite was dominant in the lower sediments which were derived from the hantan river in contrast increased quartz content and the very fine and homogeneous grain size in the upper sediments indicate an aeolian origin ree ratios and distribution patterns and geochemical signatures indicate that these sediments were derived predominantly from chinese loess deposits and partially from local sediments from the korean peninsula the possible source area of the upper sediments is the northern part of the yellow sea basin the yellow sea basin having mixed geochemical signatures between chinese loess and korean derived sediments was exposed because of low sea levels during mis 6 the exposed yellow sea basin was located in the path of winter monsoon winds which may have carried a great deal of airborne sediments from the basin to the jeongokri area copyright 2011 john wiley sons ltd

depositional environments provenance and paleoclimatic implications of ordovician siliciclastic rocks of the thango formation spiti valley tethys himalaya northern india abstract recently published findings indicate that the ordovician period has been much more dynamic than previously anticipated thus making this period significant in geological time the ordovician of india can best be studied in the spiti region because the spiti basin records the complete uninterrupted history of excellent marine sedimentary rocks starting from cambrian to paleogene which were deposited along the northern margin of india due to these reasons the geochemical data on the ordovician rocks from the spiti region is uncommon the present geochemical study on the ordovician thango formation sanugba group is mainly aimed to understand the provenance and the paleoclimatic conditions the sandstones are the dominant lithology of the thango formation with intercalations of minor amount of shales detailed petrographic and sedimentological analysis of these rocks suggest that three major depositional environments viz fluvial transitional and marine prevailed in the basin representing transgressive and regressive phases the major and trace element ratios such as sio2 al2o3 k2o na2o and la th sc discrimination diagram suggest that these rocks were deposited in passive margin tectonic settings various geochemical discriminants and elemental ratios such as k2o na2o al2o3 tio2 la sc th sc cr th zr sc gd yb n and pronounced negative eu anomalies indicate the rocks to be the product of weathering of post archean granites the striking similarities of the multi elemental spider diagrams of the studied sediments and the himalayan granitoids indicate that sediments are sourced from the proterozoic orogenic belts of the himalayan region chemical index of alteration cia values of the studied sediments 55 72 suggest that the source rocks underwent low to moderate degree of chemical weathering the span of the cia values 55 72 recorded in the sediments from the spiti region may have resulted from varying degrees of weathering conditions in the source area this in turn reflects variable climatic conditions prevailing during the ordovician period which is consistent with the global studies the high cia values observed by numerous studies on siliciclastic sediments may imply warm paleoclimate attributed to an increase in atmospheric carbon dioxide and or methane levels inducing an acidic weathering environment and enhanced silicate weathering while the low cia values indicates prevalence of arid glacial conditions where negligible chemical alteration is possible this study documents the noteworthy events like fluctuating rise and fall atmospheric co2 and sea levels during the ordovician period a conclusion which is consistent with the other such studies on the phanerozoic glaciation or mass extinction events on gondwana supercontinent

the rare earth element compositions of sediments from the loess tableland in the liyang plain southern china implications for provenance and weathering intensity to identify the weathering intensity and to deduce the provenance of sediments black brown soil and loess from the loess tableland in the liyang plain is of great importance for understanding the development and origin of civilization of this critical region in china the geochemical results show similar ree distribution patterns among sediments sampled from the yc profile in the liyang plain reticulated red soils from the dongting lake area xiashu loess in zhenjiang and loess from the loess plateau in china these similarities imply a single provenance from dust storms rees especially the lree hree ratio and eu anomaly can trace weathering intensity higher lree hree ratios and remarkably eu anomalies are present in the top loess l0 lower lree hree ratios and insignificant eu anomalies are present in black brown soil s0 from the liyang plain these demonstrate that the black brown soils have undergone a lower intensity of weathering than the loess of yc profile moreover cia values for sediments from the yc profile provide powerful evidence to support the above result comparisons of analyses of the ree contents of sediments from the yc profile of reticulated red soils from the dongting lake area xiashu loess from the yangtze river and loess from the loess plateau clearly show the weathering intensity decreases according to the following sequence reticulated red soil from the dongting lake area sediments of yc profile from the liyang plain which formed from dust storms xiashu loess from lower reach of the yangtze river loess from the loess plateau

structure and composition of the aleutian island arc and implications for continental crustal growth we present results of a seismic reflection and refraction investigation of the aleutian island arc designed to test the hypothesis that volcanic arcs constitute the building blocks of continental crust the aleutian arc has the requisite thickness 30 km to build continental crust but it differs strongly from continental crust in its composition and reflectivity structure seismic velocities and the compositions of erupted lavas suggest that the aleutian crust has a mafic bulk composition in contrast to the andesitic bulk composition of continents the silicic upper crust and reflective lower crust that are characteristic of continental crust are conspicuously lacking in the aleutian intraoceanic arc therefore if island arcs form a significant source of continental crust the bulk properties of arc crust must be substantially modified during or after accretion to a continental margin the pervasive deformation intracrustal melting and delamination of mafic to ultramafic residuum necessary to transform arc crust into mature continental crust probably occur during arc continent collision or through subsequent establishment of a continental arc the volume of crust created along the arc exceeds that estimated by previous workers by about a factor of two

a vendian cambrian island arc system of the siberian continent in gorny altai russia central asia an extended vendian cambrian island arc system similar to the izu bonin mariana type is described in the gorny altai terrane at the margin of the siberian continent three different tectonic stages in the terrane are recognized 1 a set of ensimatic active margins including subducted oceanic crust of the paleo asian ocean the uimen lebed primitive island arc oceanic islands and seamounts the set of rocks is assumed to be formed in the vendian 2 a more evolved island arc comprising calc alkaline volcanics and granites a fore arc trough in middle late cambrian time was filled with disrupted products of pre middle cambrian accretionary wedges and island arcs 3 collision of the more evolved island arc with the siberian continent folding metamorphism and intrusion of granites occurred in late cambrian early ordovician time in the late paleozoic the above mentioned caledonian accretion collision structure of the siberian continent was broken by large scale strike slip faults into several segments this resulted in the formation of a typical mosaic block structure

late paleozoic early mesozoic geodynamics of central asia abstract correlation and synthesis of published and new structural paleomagnetic and geochronological data from central asia show the important role of strike slip faulting in their evolution the pattern of major strike slip faults outlines a terrane collage produced by a late devonian early carboniferous collision of the gondwana derived altai mongolia tuva composite microcontinent with siberia and a late carboniferous permian collision of east europe and kazakhstan with siberia the accreted continental margins were cut by strike slip faults and conjugate thrusts into numerous terranes which mixed with one another and disturbed the previous structural and facies framework those complex and multi stage deformations resulted from the late devonian early carboniferous collision of gondwana derived terranes the deformations reached their peak in the late carboniferous permian due to the collision of the kazakhstan east european baltica and siberian continents a system of sinistral strike slip faults formed a mosaic block structure of central asia along the margin of the siberian continent as a result of the late carboniferous permian collision this resulted in the formation of the northern eurasia continent early mesozoic strike slip faulting and conjugate thrusting resulted from the rotation of the siberian and east european cratons

geochemistry of shales from the paleoproterozoic to neoproterozoic vindhyan supergroup implications on provenance tectonics and paleoweathering abstract major trace and rare earth element ree concentrations were measured for 88 shale samples from the paleoproterozoic to neoproterozoic vindhyan supergroup in central india the major and trace element data of the vindhyan shales are compared with north american shale composite upper crust mid oceanic ridge basalts and many other shale standards of archean proterozoic and phanerozoic age ree concentrations of the vindhyan shales are comparable to the upper continental crust various discriminant diagrams were used to reveal the inferred provenance tectonics and paleoweathering conditions a predominantly granitic source rock is inferred for the lower vindhyan shales whereas partial contribution from basaltic source is evident during deposition of the upper vindhyan shales existing paleocurrent data and the present geochemical investigations together suggest archean paleoproterozoic basement rocks exposed beyond the southern basin margin of the vindhyan outcrops as the possible source rocks the deposition of the vindhyan shales took place in an intracratonic basin where sediments were primarily derived from stable continental areas moderate climatic conditions are inferred during the deposition of the shales the upper vindhyan shales however reflect more intense weathering compared to the lower vindhyan shales which may be attributed to relative tectonic stability and more humid conditions during deposition of upper vindhyan shales

neoproterozoic middle paleozoic tectono magmatic evolution of the gorny altai terrane northwest of the central asian orogenic belt constraints from detrital zircon u pb and hf isotope studies abstract the gorny altai terrane ga is a key area in understanding the crustal evolution of the central asian orogenic belt caob this paper reports u pb and hf isotope data for detrital zircons from cambrian to early devonian sedimentary sequences to constrain their provenance as well as the tectono magmatic events and crustal growth in this region nearly all the detrital zircons are characterized by euhedral to subhedral morphology high th u ratios ca 0 1 1 6 and typical oscillatory zoning indicating a magmatic origin the three samples from the gorny altai group middle cambrian to early ordovician yield detrital zircon populations that are composed predominantly of 530 464 ma grains followed by a subordinate group of 641 549 ma old the silurian and devonian samples exhibit similar major zircon populations 555 456 ma and 525 463 ma respectively but a significant amount of additional 2431 772 ma zircons occur in the early devonian sample our results suggest that detritus from the nearby kuznetsk altai intra oceanic island arc served as a unitary source for the cambrian silurian sedimentary sequences but older detritus from other sources added to the early devonian sequence the low abundance of ca 640 540 ma detrital zircons may testify that this island arc was under a primitive stage in this period when mafic volcanic rocks probably dominated in contrast the dominant population of ca 530 470 ma zircons may indicate an increased amount of granitic rocks in the source area suggesting that the kuznetsk altai island arc possibly evolved into a mature one in the cambrian to early ordovician the ca 530 470 ma detrital zircons are almost exclusively featured by positive e hf t values and have two stage hf model ages of ca 1 40 0 45 ga indicating that the precursor magmas were sourced predominantly from heterogeneous juvenile materials we conclude that the late neoproterozoic to early paleozoic magmatism in the kuznetsk altai arc made a significant contribution to the crustal growth in the caob the absence of middle ordovician to early devonian detrital zircons possibly implies that the area changed to a passive margin in the middle ordovician of special significance are the 2431 772 ma zircons in the early devonian sample which are quite comparable to the precambrian detrital zircons from the altai mongolian terrane am but distinct from those from the siberian continent this indicates that the am is a plausible source for the 2431 772 ma zircons our data therefore imply that the ga possibly amalgamated with the am before the early devonian rather than in the late devonian to early carboniferous as previously suggested

geochemical evidence for the paleoproterozoic arc back arc basin association and its importance in understanding the evolution of the central indian tectonic zone abstract the central indian tectonic zone citz is considered to be one sector in a series of paleoproterozoic orogens that stitched together the supercontinent columbia the paleoproterozoic mahakoshal belt forms the foundation of the citz metabasalts and metaclastic rocks of the mahakoshal belt have been studied for major elements and trace elements including the rare earth elements ree metabasalts of the lower saleemanabad formation are grouped into two types however both types of metabasalt depict a back arc basalt character by showing enrichments in large ion lithophile elements liles like k rb cs and ba and light rare earth elements lrees but show depletions in high field strength elements hfses like nb ta y and ti and hree heavy rare earth elements in comparison to the n morb this is further supported by some key elemental ratios like ba nb nb ta la nb eu eu nb nb and ree patterns the geochemistry of the metaclastic rocks of the lower saleemanabad middle parsoi and upper dudhmaniya formations of the mahakoshal belt show an arc signature rather than the cratonic signature in the bundlekhand ttg and n morb normalised diagrams the arc signature calc alkaline series of metaclastic rocks is further supported by various tectonic discrimination diagrams the overall study indicates that the mahakoshal belt was formed as a back arc rift basin very close to continental arcs on the hinterland of the bundelkhand craton at the initial stage of subduction as a result of trench rollback followed by thermal relaxation and basin inversion the sediment supply started from the continental arcs lying south of the mahakoshal basin furthermore the present study strengthens the mechanism of subduction related outgrowth of columbia along its continental margins and implies that the citz is a major precambrian crustal boundary that began as a mahakoshal back arc rift by northward subduction

geochemistry of mesoproterozoic sedimentary rocks of upper vindhyan group southeastern rajasthan and implications for weathering history composition and tectonic setting of continental crust in the northern part of indian shield abstract the upper vindhyan succession of southeastern rajasthan is divisible into kaimur rewa and bhander groups the major and trace element including rare earth elements data of the upper vindhyan shales and sandstones are investigated to determine the weathering history composition and tectonic setting of mesoproterozoic continental crust cia chemical index of alteration values a cn k plot a al2o3 cn cao na2o k k2o and depletion in u na2o cao sr and ba suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions provenance modeling indicates that the kaimur sandstones are best modeled with a mixture having 40 granitic gneiss 20 tonalite trondhjemite granodiorite ttg 20 mafic enclaves and 20 berach granite of the banded gneissic complex bgc a mixture of 60 granitic gneiss 20 mafic enclaves and 20 berach granite of the bgc can model the rewa and bhander groups it is suggested that the upper vindhyan sedimentation commenced at the time of delhi sausar orogeny at about 1100 1000 ma the orogenic movements uplifted the parts of old continental crust in the bgc terrain creating positive areas which exposed older crustal blocks containing ttg as important component the debris of kaimur sandstone probably derived from these uplifted blocks as indicated by palaeocurrent data the rewa and bhander formations were derived from bundelkhand granitic gneiss complex bggc occurring to the north of the basin and or the chotanagpur granitic gneiss complex cggc of eastern indian shield the derivation of lower and upper groups of vindhyan succession from different source terrains of identical composition suggests that at the time of vindhyan sedimentation the bgc of rajasthan the bggc of central india and the cggc of eastern india had similar lithological composition this implies that well before the origin of the vindhyan basin these discrete terrains evolved as a single unit that existed as a mesoarchaean nucleus in the northern part of the indian shield

effects of volatiles on mixing in calc alkaline magma systems the intimate mixing between different magmas of disparate densities characteristic of some calc alkaline magma systems is explained by a new mechanism involving the emplacement of a layer of wet undersaturated mafic magma at the base of a magma chamber containing more differentiated magma turbulent transfer of heat between the mafic magma and the overlying magma leads to crystallization and exsolution of volatiles in the lower layer for an initial water content of a few per cent the bulk density of the mafic magma can become equal to that of the overlying magma causing overturning and intimate mixing of the magmas the mechanism is most probable in the low pressure environment of a high level magma chamber

mo ni and organic carbon isotope signatures of the mid late mesoproterozoic oxygenation abstract this study performed a redox sensitive trace element rste and organic carbon isotope investigation on the shallow section of 1 2 ga bijaigarh shale kaimur group vindhyan supergroup the results demonstrate that unlike the coeval deeper section in which mo and ni concentrations are several folds higher compared to the upper continental crust ucc the shallow section contains mo and ni equivalent to the upper continental crust ucc this spatially heterogeneous burial of mo and ni is very similar to the modern stratified basins i e black sea and cariaco basin where ni and mo composition of the sediments underlying a shallow oxic water column is comparable to the ucc however the deeper sediments underlying the anoxic euxinic contains several folds higher mo and ni compared to the ucc bulk precipitation of mo in a hydrosphere is mainly controlled by sulphide present in the anoxic euxinic layers of the water column on the other hand ni precipitation is generally controlled by oxygenic primary productivity though the shallow section of the bijaigarh shale is depleted in ni a significant correlation between ni and toc is still relevant and indicates an oxygen rich surface water layer for the respective palaeohydrosphere furthermore 13c org values between 32 0 and 30 4 from the shallow section suggests that the organic carbon exported into the sediments during the bijaigarh shale deposition was primarily derived from oxygenic photosynthesis in the concurrent surface water layers

early middle paleozoic granitoids in gorny altai russia implications for continental crust history and magma sources abstract major element and trace element compositions as well as nd isotope ratios and protolith model ages of early to middle paleozoic granitoids from the russian gorny altai are summarized and discussed in terms of the compositions and tectonic settings the observed geographic variations of compositions in the granitoid assemblages correlate with three groups of late neoproterozoic to middle paleozoic terranes corresponding to oceanic island arc and turbidite basin settings plutonic rocks in the oceanic and island arc terranes are commonly low alkali metaluminous tonalite and trondhjemite that formed by melting of oceanic crust the island arc terranes also contain tonalite trondjemite granodioritic and tonalite granodiorite granitic rocks with higher alkali and potassium contents which result from anatectic melting of volcanics and sediments granitoids in the turbidite basins are potassic peraluminous monzogranite produced by anatectic melting of upper crustal turbidites as well as subalkaline tonalite granodiorite and granite derived from upper crustal metasediments and metamorphosed mafic oceanic crust underlying the turbidite basins alkaline granitoids emplaced during two major tectonomogamatic events early and late devonian and are present in terranes of all three settings their source is of crustal origin like in other groups of granitoids but it was a mixture of crustal and mantle material thus the compositional trends of early and middle paleozoic granitoids in the gorny altai record the history of continental crust

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

re os depositional age for black shales from the kaimur group upper vindhyan india abstract proterozoic sedimentary deposits from the vindhyan supergroup central india are excellent archives of paleo environmental conditions meaningful interpretation of these geological signatures and their global correlation requires depositional age information for the sediments data on which are limited for the upper vindhyan sediments in this work re os isotopic study of the bijaigarh shale kaimur group from the upper vindhyan has been carried out to infer their depositional age and paleo hydrological conditions the re os isochron for the bijaigarh shale a lagoonal deposit with an open ocean connection provides a depositional age of 1210 52 ma model 3 mswd 69 n 15 2 this age for the kaimur group is younger by 400 ma than the underlying semri group age 1600 ma confirming existence of a long sedimentary hiatus between the two groups the isochron derived initial 187os 188os osi ratio for these shales 0 6 is higher than those reported for mesoproterozoic marine shales 0 3 from other global margins osi ratios of shales could be regulated by regional paleo hydrological conditions osmium mass balance calculations for the restricted basin of the bijaigarh shale show that a minor increase in freshwater influx as low as 2 4 i e salinity change by 0 8 psu to the euxinic deep water of the basin is sufficient to elevate osi ratio from 0 3 marine value to 0 6 osi ratio of the lagoonal shale in contrast to lagoonal shales the osi ratios of marine shales seem to mimic the seawater 187os 188os during their deposition period compilation of marine osi ratios shows coarse synchrony between temporal changes in osi during the proterozoic eon and the atmospheric oxygen level pointing to the dominant role of oxidative continental weathering on paleo seawater 187os 188os ratio