severe ionospheric disturbances caused by the sudden response of evening subequatorial ionospheres to geomagnetic storms by monitoring c band beacon signals from geostationary satellites in japan we have observed anomalously strong ionospheric scintillations several times during three years from 1978 to 1980 these severe scintillations occur associated with geomagnetic storms and accompany sudden and intense ionospheric perturbations in the low latitude region through the analysis of these phenomena we have identified a new type of ionospheric disturbances characterized by intensifications of equatorial anomalies and successive severe ionospheric scintillations that extend to the c band range the events occur only during a limited local time interval after the sunset when storm time decreases of midlatitude geomagnetic fields in the same meridian take place during the same time interval from the viewpoint of ionospheric storms these disturbances precede the occurrence of midlatitude negative phases and storm time depressions of equatorial anomalies to indicate that the cause of the events is different from disturbed thermospheric circulations the timing and magnitude of substorms at high latitudes not always correlate with the events we have concluded that the phenomena are closely related with penetrations toward low latitudes of electric fields owing to the partial closure of asymmetrical ring currents

discovering geochemical patterns using self organizing neural networks a new perspective for sedimentary provenance analysis abstract an unsupervised neural network technique growing cell structures gcs was used to visualize geochemical differences between sandstones of four different sedimentary provenance groups p1 mafic p2 intermediate p3 felsic and p4 recycled multidimensional data of four sandstone data sets comprising major elements log normalized major elements trace elements and high field strength elements hfse were projected into colored two dimensional maps that can be visually and quantitatively interpreted the cluster structure and variable distributions produced show that each sedimentary provenance group can be distinguished in the neural maps according to a unique combination of major or trace element concentrations in these terms the distinguishing features of each provenance group are p1 high fe2o3t tio2 mgo mno cao p2o5 sc v cr and cu p2 intermediate fe2o3t tio2 mgo mno cao sc v and cu p3 intermediate to high k2o intermediate sio2 and al2o3 low fe2o3t and tio2 and intermediate to low nb rb and th p4 high sio2 y nb rb th ba and zr coupled with low al2o3 cao na2o fe2o3t mgo mno and tio2 the elemental associations in p1 p2 and p3 reflect petrogenetic evolution of first cycle sources whereas the associations in p4 are compatible with the combined effects of recycling weathering and heavy mineral concentration

a mesozoic crustal suture on the gondwana margin in the new zealand region 1 marine crustal multichannel seismic data recorded offshore south island new zealand are used to provide constraints on the evolution of the gondwana margin in this region lower crustal and upper mantle seismic reflectivity off southeastern stewart island south of south island is interpreted in terms of a northeast dipping paleosubduction zone this inferred suture is considered to be related to the docking of the brook street oceanic island arc terrane to the gondwana margin in the triassic the junction of which is now largely covered by the median batholith a similar lower crustal upper mantle feature has been imaged off western south island both inferred sutures have similar strikes and are approximately collinear after restoration of the region for major cenozoic horizontal deformation it is proposed that they are parts of the same paleosuture that was oriented subparallel to the former gondwana margin and to the present paleozoic and mesozoic terranes forming south island

slab derived fluids and quartz vein formation in an accretionary prism otago schist new zealand regional quartz vein formation and the fluxes flow paths and sources of metamorphic fluids were investigated in the mesozoic accretionary prism of new zealand by using a new chemical mass balance analysis of outcrops samples were collected at meter or submeter intervals along outcrop length traverses and combined to obtain average chemical compositions of whole outcrops mass balance analysis used zr as an immobile reference frame and as a monitor of sedimentary sorting processes sio2 zr systematics produced by sedimentary processes differ greatly from those caused by metasomatic mass transfer of silica allowing evaluation of vein formation mechanisms relatively undeformed metasedimentary outcrops of low metamorphic grade mostly prehnite pumpellyite facies are nearly unveined and characterized by sedimentary compositional trends more deformed outcrops of higher metamorphic grade mostly greenschist facies contain 10 30 vol quartz veins these outcrops underwent mass addition of externally derived silica into quartz veins accompanied by addition of na and removal of k and w average silica additions suggest a time integrated fluid flux of 104 105 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document m 3 fluid end document batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document m 2 rock end document for fluids ascending through the prism dehydration of spilitized oceanic crust subducting beneath the prism is the most probable source for this large fluid flux and could also have caused the na k metasomatism the w removed from deep levels of the prism may have been deposited in focused retrograde au w quartz veins at shallow levels by ascending fluids transfer of sio2 from subducting slabs into accretionary prisms is a plausible mechanism for long term bulk silica enrichment of the continents beyond that possible by magmatic differentiation

permian evolution of sandstone composition in a complex back arc extensional to foreland basin the bowen basin eastern australia abstract the bowen basin is a permo triassic back arc extensional to foreland basin that developed landward of an intermittently active continental volcanic arc associated with the eastern australian convergent plate margin the basin has a complex polyphase tectonic history that began with limited back arc crustal extension daring the early permian this created a series of north trending grabens and half grabens which in the west accommodated quartz rich sediment derived locally from surrounding uplifted continental basement in the east coeval calc alkaline volcanolithic rich and volcaniclastic sediment was derived from the active volcanic arc this early extensional episode was followed by a phase of passive thermal subsidence accompanied by episodic compression during the late early permian to early late permian with little contemporaneous volcanism in the west quartzose sediment was shed from stable polymictic continental basement immediately to the west and south of the basin whereas volcanolithic rich sediment that entered the eastern side of the basin during this time was presumably derived from the inactive and possibly partly submerged volcanic arc during the late late permian flexural loading and increased compression occurred along the eastern margin of the bowen basin and renewed volcanism took place in the arc system to the east reactivation of this arc led to westward and southward spread of volcanolithic rich sediment over the entire basin accordingly areas in the west that were earlier receiving quartzose craton derived sediment from the west and south were overwhelmed by volcanolithic rich arc derived sediment from the east and north this transition from quartz rich craton derived sediments to volcanolithic rich arc derived sediments is consistent with the interpreted back arc extensional to foreland basin origin for the bowen basin

provenance of triassic cretaceous sandstones in the antarctic peninsula implications for terrane models during gondwana breakup abstract the antarctic peninsula is the largest of twelve micro continental fragments between southern south america east antarctica and new zealand their original positions and movement history following gondwana breakup are poorly constrained recent work on the antarctic peninsula fore arc arc back arc suggests it consists of two suspect terranes that originated elsewhere and collided with the pacific margin of gondwana in the cretaceous this study reviews provenance models for three laterally extensive kilometers thick sedimentary units in the antarctic peninsula using previous studies and new sandstone detrital modes and chemistry 1 the trinity peninsula group accretionary complex triassic was possibly derived from a glaciated continental margin and may consist of several accreted tracts the deformed quartzose view point and legoupil formations were eroded from a deeply eroded stable continental margin containing an old arc and mature quartzose sandstones with provenance ages suggesting sources in north patagonia and local antarctic peninsula basement the weakly deformed and more feldspathic hope bay formation was derived from an eroded arc possibly the early permian arc of the north patagonian massif 2 the lemay group accretionary complex middle triassic middle cretaceous is dominated by arkoses derived from an eroded continental margin of carboniferous and permian age possibly in the marie byrd land sector with several belts of volcanilithic sandstones representing episodes of arc magmatism the youngest part of the lemay group contains abundant metamorphic detritus derived from basement uplifted during mid cretaceous terrane docking 3 the latady formation in the southern antarctic peninsula has a completely different petrology comprising mature sublitharenites 190 ma of gondwanan provenance deposited in restricted rift basins younger volcanic litharenites 180 ma are dominated by ree enriched low eu eu rhyolitic material eroded from silicic calderas associated with gondwana breakup abundant dacitic to andesitic detritus in the youngest lf 160 145 ma was derived from a contemporaneous arc possibly on the thurston island block as the latady evolved into a back arc basin

plio pleistocene paleoclimate in the southwest pacific as reflected in clay mineralogy and particle size at odp site 1119 se new zealand clay mineralogical and particle size data from ocean drilling program odp site 1119 reflect processes associated with the deposition of the canterbury drifts and the evolution of the new zealand south eastern shelf and are strongly correlated with pliocene pleistocene climatic and oceanographic fluctuations elevated smectite contents at the base of site 1119 latest early pliocene 3 9 3 5 ma also occur regionally in the southern ocean and point towards an alternative sediment source other than nearby new zealand terranes the abrupt reduction in smectite content at 3 5 ma and replacement by dominant chlorite illite assemblages corresponds to the onset of late pliocene cooling climate conditions and more intense onland physical weathering high illite contents in late pliocene early pleistocene 3 0 1 7 ma sediments suggest a more southern terrane e g haast schist source influence and widened shelf conditions an upward increase in clay content reflects an increased supply of glacier derived detrital sediment concurrent with global climate deterioration during the late pliocene pleistocene grainsize fining of the background mean sortable silt mss signal indicates reduced southland current flow consistent with its forced seaward migration across site 1119 over time due to continual eastward shelf progradation clay mineralogy and particle size data at odp site 1119 exhibit a relationship with both global climatic conditions and with southwest pacific paleoceanographic and paleoclimatic regimes

geochemical characterization evolution and source of a mesozoic accretionary wedge the torlesse terrane new zealand whole rock major and trace element compositions of quartzofeldspathic permian cretaceous sandstones of the torlesse terrane new zealand display progressive changes which compare well with published petrographic data chemical indices in three permian early late triassic rakaia subterrane petrofacies show small contrasts as do the modes reflecting original source compositions a late triassic rakaia petrofacies displays sharp increases in sio 2 al 2 o 3 k 2 o na 2 o th sc la sc ce sc la n y n and decreases in ti zr and v la consistent with partial cannibalistic recycling and a small influx of lithic volcanic detritus in the post collisional late jurassic early cretaceous pahau subterrane sio 2 al 2 o 3 remains high but other indices decrease to levels seen in the permian due to recycling of the earlier rakaia petrofacies and influx of 10 30 mafic intermediate volcaniclastic detritus derived from inboard volcanogenic terranes the results are confirmed by additional suites including mudstones which cover a larger area but also show that some spatial variation occurs within the terrane as a whole whole rock data and chemical index of alteration indices indicate that the torlesse was derived from a relatively unweathered source with granodioritic bulk composition comparisons with data from a proposed rakaia source in the new england and hodgkinson orogens of eastern australia suggest that the observed chemical and modal compositions cannot be simply derived from that area as presently exposed

composition of modern deep sea sands from arc related basins summary petrographic and chemical examination of modern deep sea sands shows a clear distinction between active and passive plate tectonic settings among active settings sands from forearc basins of island arcs and basins from strike slip continental margins can be distinguished but those from other arc related settings overlap considerably in composition in particular sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable chemically arc related sands are very close in composition to ancient greywacke sandstones for instance sodium almost always exceeds potassium thus it is not necessary for sodium to be added to sands diagenetically to make greywackes as has been suggested the influence of tectonics on the composition of sandstones has long been a central feature of sandstone petrology the geosynclinal model of global tectonics stimulated much thought on this subject probably the best known ideas are those of krynine e g 1942 subsequently such research declined but the plate model for global tectonics has produced a new wave of interest e g crook 1974 schwab 1975 potter 1978 dickinson suczek 1979 much of this work has relied on data from ancient sediments where diagenetic changes and difficulty in de ciphering the tectonic setting limit the useful ness of the conclusions much more work is needed on recent sediments to establish a base line against which ancient sediments can be compared we have previously reported valloni maynard 1981 the results of our work on the petrography of a set of recent deep sea sands from piston cores in this paper we shall com pare this petrographic information with bulk chemistry and attempt to relate these to tecto nics in arc related settings

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

geochemical petrographic and grain size variations within single turbidite beds pronounced changes in chemical composition were detected upwards within single turbidite beds with sio2 contents deceasing by as much as 20 all other major elements and eighteen trace elements increase in abundance upwards enrichment factors from bed base to top range from 1 2 na2o to 5 7 cu these changes are related to textural and mineralogical grading that in turn were the result of turbidity current action before and during the deposition of the bed we found only slight changes in the modal petrographic composition of the sandstone fractions although this technique is operator dependent and only semi quantitative in nature chemical analysis appears to be a more sensitive more rapid and less subjective method of determining provenance and the compositional contrasts within beds chemical anomalies produced by dilution effects from quartz overgrowths and intrabasinal material however show the need for utilisation of a combination of techniques and for an appreciation of the interdependence of texture framework modes and bulk chemistry the chemical variations we detect in single beds also reflect the variation in a suite of representative samples collected from within a confined several km2 geographic area hence either sampling over a given area or specific sampling of individual beds provided that the bed is typical of the succession as a whole can be used to determine the compositional variations within a succession as a whole

deposition and deformation of an early cretaceous trench slope basin deposit torlesse terrane new zealand studies of modern convergent margins have highlighted the variety of depositional environments and deformational processes that occur in this tectonic setting and provide analogues by which ancient uplifted sequences can be interpreted the whatarangi formation is an early cretaceous trench slope basin deposit preserved within accretionary prism rocks of the pahau torlesse terrane of new zealand and is distinguished from the underlying accreted rocks by its younger age different depositional history structural style and metamorphic grade and lack of oceanic volcanic outcrops furthermore the whatarangi formation records the types of processes inferred to occur in modern slope basins sediments were derived from sources on the western side of the basin and were deposited mainly by gravity flows on channelized base of slope aprons the narrow elongate shape of the basin resulted in restricted longitudinal flow of the sandy turbidity currents and deposition of finer sediment farther down the inner trench slope or in the trench deformation of the turbidites produced open to tight asymmetric folds that are concentrated along the western margin and lower half of the formation the folds are best described by a model of simple shear and formed in response to active west over east thrusting in the underlying prism cleavage was initiated prior to folding in response to overall shortening of the basin with subsequent development of an axial planar cleavage in the tightest folds the compositional similarity between the slope basin strata and accreted sedimentary rocks of the aorangi range has important implications for the early cretaceous tectonic history of the torlesse terrane the sediments were eroded from an uplifted accretionary prism and an acid igneous source and the deposition of these sediments in upslope basins and the trench suggests that all the pahau sediments could have been transported from these transversely located sources

the new england batholith eastern australia geochemical variations in time and space the new england batholith australia is part of the upper paleozoic new england fold belt with most plutons intruded into the deformed trench complex metasedimetary rocks in the southeast part of the fold belt the batholith was emplaced in two major periods of plutonism the first during the upper carboniferous and the second during the upper permian and triassic with a major phase of metamorphism and deformation including westward overthrusting of the trench complex sedimentary rocks between the two periods on the basis of petrography geochemistry and isotopic characteristics the granitoids of the batholith are subdivided into five named intrusive suites and a group of leucoadamellites the differences between the six groups are considered to reflect differences in their source rock types the carboniferous granitoids are peraluminous s type and are divided into the bundarra plutonic suite a belt of very coarse grained adamellites with cordierite garnet and the hillgrove plutonic suite a belt of biotite rich garnet deformed adamellites and granodiorites both suites have 18o greater than 10 negative 34s 87sr 86sr initial ratios about 0 706 are ilmenite bearing and have low feo3 ratios the bundarra plutonic suite however is consistently sio2 rich greater than 70 contains cordierite and has higher 18o than the hillgrove plutonic suite the two s type suites are inferred to have formed by partial melting of the deepest parts of a wedge of trench complex sedimentary rocks oceanwards of an andean volcanic chain to the west analagous to the lower tertiary s type plutons of the sanak baranof plutonic belt of southern alaska of the remaining four groups of plutons emplaced during the upper permian and triassic two are metaluminous i type granitoids one the clarence river plutonic suite new name a group of k poor granodiorites and tonalites with low 87sr 86sr initial ratios average 0 7035 and the other the moonbi plutonic suite a group of k rich adamellites with low 87sr 86sr initial ratios average 0 7045 18o less than 10 and 34s positive the clarence river plutonic suite is inferred to have formed from the partial melting of a large ion lithophile element poor gabbro source region and the moonbi plutonic suite from a large ion lithophile element rich shoshonite source region a third group the uralla plutonic suite is less metaluminous has higher 87sr 86sr initial ratios average 0 706 18o only just less than 10 and negative 34s and is considered to have formed in a region containing a physical mixture of metaluminous and peraluminous source rocks gabbro and metasedimentary rocks plutons of the fourth group are leucoadamellites largely emplaced after the other suites with low 18o indicating an i type source it is argued that this group has resulted from low degrees of dry partial metling of an i type source region that had undergone an earlier melting event these four groups of plutons are largely confined to a narrow belt parallel to but 100 km west of the present rifted margin of australia their origin may be related to crustal thickening attendant on the overthrusting that occurred early in the permian and or a temperature increase in the lower crust due to the recovery of normal continental geotherms following the cessation of subduction

ionospheric disturbances during low latitude auroral events and their association with magnetospheric processes ionospheric disturbances associated with low latitude auroral events that occurred during geomagnetic storms on october 21 1989 and may 10 1992 are investigated from measurements of the total electron content tec by the u s navy navigation satellite system nnss and ionosonde data from the japanese meridian chain features of the ionospheric disturbances are then associated with the progression of geomagnetic disturbances during the storms after the onset of the main phase of each storm anomalous tec distributions characterized by depressed tec distributions on the high latitude side 35 geographic latitude and an enhanced equatorial ionization anomaly eia on the low latitude side 35 geographic latitude were observed over japan both by the nnss and by the meridian chain of ionosonde stations this enhancement of the eia suggests the penetration of magnetospheric electric fields during the storms corresponding to the anomalous tec decreases in the northern part of japan ionosonde stations in this region observed specific disturbances of ionospheric variation characterized by simultaneous decreases of 0f2 and increases of h f these features of ionospheric variations on the high latitude side can be attributed to the upward escape of ionospheric plasma caused by the heating and evacuation mechanisms which are induced by depletion of the plasmasphere and the resulting access of ring current particles to low latitudes after the appearance of the characteristic ionospheric variations mentioned above low latitude aurorae were observed at the maximum development stage of the dst associated with the recovery of midlatitude geomagnetic horizontal h components prior to the appearance of the low latitude aurorae magnetic disturbances in the auroral region increased with the decrease of midlatitude h components as a natural consequence of magnetic storms however they showed a recovery before the start of the low latitude aurorae while the magnitude of the low latitude magnetic field continued to decrease these observed features of the magnetic disturbances suggest that the position of the auroral oval shifted toward the equator before the appearance of the low latitude aurorae consequently these observations are consistent with the plasmapause and auroral zone moving toward the equator before the onset of low latitude aurorae we conclude that the convection electric field penetrating toward low latitudes causes the enhancement of the eia the shrinkage of the plasmasphere and the penetration of high energy particles toward the low latitude region

geochemical evolution of the tertiary succession of the nw shelf bengal basin bangladesh implications for provenance paleoweathering and himalayan erosion abstract whole rock major trace and rare earth element ree compositions of paleogene to neogene sedimentary rocks of the nw shelf succession province 1 of bangladesh contain a record of interaction of the india and asian plates himalayan tectonism and climatic development analyses of 66 sandstones and mudrocks from the tertiary succession of bangladesh were made to examine provenance source weathering and the influence of paleoclimate and tectonism the sediments display linear geochemical trends due to quartz dilution and varying quartz clay ratios produced by hydrodynamic sorting chondrite normalized ree patterns for both sandstones and mudrocks from different groups are similar to upper continental crust with moderate to high lree enrichment lithotypes within formations average lan ybn 5 31 11 41 and marked negative eu anomalies eu eu 0 51 0 69 based on geochemical criteria the succession can be divided into three parts jaintia barail surma and dupi tila very high silica contents in jaintia tura sandstones and high chemical index of alteration cia indices in kopili mudrocks fe shales suggest derivation from a deeply weathered and stable cratonic source india the tura sandstones are interpreted as first cycle quartz arenites produced while the indian plate drifted across equatorial regions during the paleocene eocene thermal maximum petm the barail surma and dupi tila sediments were derived from a felsic orogen the himalaya the barail surma sediments were mainly derived from the trans himalayan batholith and associated granitoids with significant contribution from the lesser himalaya mafic input is also evident probably from intraoceanic arc material within the himalaya barail mudrocks have uniformly high cia values 92 95 suggesting intense steady state weathering of their proto himalayan source and warm and humid climate in contrast cia values of surma mudrocks range from 66 to 93 average 84 suggesting non steady state weathering related to active uplift in the himalaya the dupi tila sediments were derived from a more felsic lesser himalaya source with significant contribution from the trans himalaya and very little or no ophiolitic or arc material dupi tila mudrocks have cia ratios of 62 99 average 72 also indicating non steady state weathering in the rising himalayan source geochemical compositions of the nw shelf sediments are comparable to coeval successions in the surma basin province 2 of bangladesh and the siwaliks india indicating similar source evolution of the indian monsoon and associated high precipitation caused intense chemical weathering of the surma and dupi tila source despite rapid uplift the surma group thus bears the signature of evolution of the asian monsoon in the bengal basin at 21 ma simultaneous with the development of the east asian monsoon this supports proposals that both monsoon systems developed at the same time

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

provenance and paleo weathering of tertiary accretionary prism forearc sedimentary deposits of the andaman archipelago india abstract in order to understand the provenance and tectono sedimentary processes occurring in the andaman subduction zone asz the late cretaceous to oligocene sedimentary records from the andaman islands have been studied these sedimentary records are considered to have preserved the history of the india asia collision evolution of the himalayas climatic development and palaeo drainage reorganizations on the indian and asian plates about 47 sandstones and mudstones shales and siltstones samples were analyzed for whole rock major trace and rare earth element compositions the geochemical results suggest mixing of sediments derived from the mafic igneous sources comprising local ophiolites and volcanic arc of the asz and an older archean to proterozoic age felsic cratonic source with compositions similar to average granodiorite or upper continental crustal sources the compositions were dominated by sources of the mafic arc during deposition of the mithakhari group whereas they were controlled by continental sources during deposition of the andaman flysch group the hope town conglomerate unit of the mithakhari group was mainly derived from weathering and erosion of the subaerially exposed local ophiolite thrust sheets whereas its namunagarh unit contains significant detritus from volcanic arcs the andaman flysch turbidites were deposited with a greater supply of sediments from first cycle active continental margin sources probably located in the tibetan and eastern myanmar region and recycled quartzose sedimentary sources within the nascent himalayas the sediments supplied to both the mithakhari and the andaman flysch groups were characterized by varying values of cia pia and w these variable values were either due to non steady state weathering conditions in the sources or the changing climatic conditions owing to the motion of indian plate with reference to the equator the uniformly high cia and w values in the andaman flysch rocks can be related to high precipitation and strong chemical weathering associated with the initiation of the indian monsoon

sea level induced variations in clay mineral composition in the southwestern south china sea over the past 17 000 yr variations in clay mineral composition of sediment cores from the margin and continental slope of the sunda shelf southern south china sea se asia covering the past 17 000 yr reflect changing influences of sediment sources together with clay mineral partitioning processes in shallow waters we identify the deglacial sea level rise as the principal factor driving these changes during the late glacial high values of kaolinite are interpreted to reflect a higher contribution of clays from soils that have formed on the exposed sunda shelf and in the southern archipelagos of indonesia at this time core sites were located in close proximity to the mouths of the sunda shelf palaeo drainage systems on the emerged shelf sundaland the progressive landward displacement of the coastline and breakdown of these vast drainage systems during deglaciation led to a decrease in influence of the kaolinite rich southern sources when the coastline had retreated closely to its present day position in mid holocene times the former dominance of southern sources was replaced by a stronger influence of illite rich sources e g borneo the overriding control of sea level changes on the clay mineral distribution patterns precludes a definite climatic interpretation of clay mineral data in terms of climatic monsoonal changes in such highly dynamic sedimentary environment

provenance of the sedimentary rakaia sub terrane torlesse terrane south island new zealand the use of igneous clast compositions to define the source abstract the permian to late triassic rakaia sub terrane part of the torlesse superterrane of the new zealand eastern province is an accretionary complex that comprises an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single mineral grains fine sand and mud may be transported over thousands of kilometres with potential problems for provenance studies reinforcing the need for caution when interpreting provenance evidence from single heavy mineral grains this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources a detailed rock sampling programme and geochronological geochemical and sr nd isotope analysis of igneous clasts from four conglomerates boundary creek te moana mckenzie pass and lake hill have broadly characterised the igneous source for the rakaia sub terrane shrimp u pb zircon ages of rakaia sub terrane igneous clasts define three distinct periods of magmatic crystallisation the first period ranges in age from 292 to 243 ma permian to middle triassic with two clusters recognisable a minor early permian one ranging in age from 292 to 277 ma and a major late permian to middle triassic one from 258 to 243 ma all these clasts are confined to the kazanian permian te moana the dorashamian permian mckenzie pass and the carnian late triassic lake hill conglomerates the clasts which are subduction related calc alkaline to high k calc alkaline and metaluminous to peraluminous range in lithology from andesite to rhyolite and their plutonic equivalents many clasts at lake hill have chemical compositions characteristic of partial melts of a source of basaltic composition in equilibrium with amphibole pyroxene garnet adakites indicative of a thick crust in the clast source area the second period comprises carboniferous calc alkaline metaluminous to weakly peraluminous clasts of the permian boundary creek conglomerate ranging in age from 356 to 325 ma the third group consists of two cambrian clasts a monzogranite from te moana c 497 8 ma and a dacite from lake hill c 517 ma geochronology geochemistry and sr nd isotopes of rakaia igneous clasts correlate broadly with those of permian to triassic plutons and volcanics from the amundsen and ross provinces of marie byrd land thus the antarctic sector of the panthalassan margin of gondwana is the probable source for the rakaia sub terranes as opposed to the other postulated sources in eastern australia

evidence from zircon u pb age spectra for crustal structure and felsic magma genesis at taupo volcano new zealand u pb zircon age spectra from a metasedimentary xenolith and a young dacite provide evidence for rapid episodes of crustal melting and eruption at taupo volcano as well as unexpected crustal structure beneath the taupo volcanic zone ages from the xenolith in a 28 ka rhyolite dome match those from early cretaceous pahau terrane graywackes that crop out 75 km east of the volcano and were underthrust and partially melted during the penecontemporaneous accretion process boundaries between graywacke terranes in the north island are thus more complex than implied from map views in contrast ages from zircons in the 20 ka omega dacite match the nearby surficial graywacke of the jurassic kaweka terrane 55 of grains quaternary plutonic sources 39 and pahau terrane graywacke 6 five of 72 grains analyzed contain graywacke cores and pleistocene rims survival of euhedral xenocrystic zircons through the generation processes for omega dacite magma reflects wholesale melting of crustal protoliths including varieties not previously considered for petrogenetic modeling open system behavior and crustal melts being generated and erupted within 1 10 yr

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

the mid cretaceous transition from basement to cover within sedimentary rocks in eastern new zealand evidence from detrital zircon age patterns detrital zircon u pb ages for 30 late jurassic and cretaceous sandstones from the eastern province of eastern new zealand combined with previously published geochronological and palaeontological data constrain the time of deposition in the pahau and waioeka terranes of the cretaceous accretionary margin of zealandia and their adjacent cover strata the zircon age patterns also constrain possible sediment source areas and mid cretaceous geodynamic models of the transition from basement accretionary wedge to passive margin cover successions pahau terrane deposition was mainly barremian to aptian but continued locally through to late albian time with major source areas in the adjacent kaweka and waipapa terranes and minor inputs from the inboard median batholith waioeka terrane deposition was mainly albian with distinctive and exclusive sediment sources principally from the median batholith but with minor inputs from the western province alternative tectonic models to deliver such exclusive median batholith and western province derived sediment to the mid cretaceous zealandia continental margin are 1 the creation of a rift depression across zealandia or 2 sinistral displacement of south zealandia with respect to north zealandia to expose western province rocks directly at the zealandia margin detrital zircon age patterns of cretaceous cover successions of the eastern province of eastern new zealand demonstrate purely local sources in the adjacent kaweka and waipapa terranes cretaceous zircon components show a decline in successions of late early cretaceous age and disappear by late late cretaceous time suggesting the abandonment or loss of access to both the median batholith and western province as sediment sources

temporal and spatial patterns of sediment deposition in the northern south china sea over the last 50 000 years abstract sediment depositional patterns along the upper continental slope of the northern south china sea scs have been studied using two sediment cores geob16601 6 20 09 07 n 116 14 38 e 1012 m water depth and geob16602 4 18 57 12 n 113 42 64 e 951 m water depth recovered during rv sonne cruise so 221 invers sediment cores were analyzed for bulk sediment element composition by x ray fluorescence xrf core scanning and clay mineral assemblage by x ray diffraction xrd the bulk sediment element and the clay mineral compositions of the two cores suggest similar depositional patterns between 50 kyr bp and 29 kyr bp and 14 kyr bp to present but a clear difference in depositional patterns during the last glacial and deglacial 29 14 kyr bp when sea level was below 90 m between 29 14 kyr bp a higher kaolinite percentage in core geob16602 4 in comparison to core geob16601 6 is interpreted to reflect a higher contribution of clay supplied by the pearl river to core site geob16602 4 in contrast core geob16601 6 received less pearl river supplied clayey material during the same period when the sea level was below 90 m during the last glacial lowstand the detrital fine grained materials supplied by the pearl river were mostly transported by coastal currents to the southwest resulting in a higher contribution of pearl river discharged material at site geob16602 4 than at site geob16601 6 we suggest that sea level induced modifications of the land ocean distribution together with changes in the palaeo physiographic conditions such as the proximity of the palaeo rivers to the individual core sites might be responsible for the different sediment depositional patterns in the study area thus the overriding control of sea level induced changes on the sediment depositional environment might mask climate related changes in sediment depositional pattern in the northern scs

low latitude ionospheric disturbances results for march 22 1979 and their general characteristics low latitude ionospheric disturbances which were characterized by severe scintillations in the c band range accompanied by complex dynamical behavior of the low latitude ionosphere were examined taking into consideration previous results from the analyses of fof2 and h f data these disturbance events are found to be characterized by a two stage process during the first stage which starts during the magnetospheric energy storage process before the onset of substorms h f begins to increase simultaneously at all observing stations due to eastward electric fields penetrating from the magnetosphere at subequatorial stations increases of fof2 follow as a signature of enhancements of the equatorial anomaly during the second stage values of h f increase again indicating a motion from north to south with no increase of fof2 in this stage dynamical effects including neutral winds become important as well as electric fields in addition it is shown from the analysis of one year s data for 1978 that the occurrence of disturbance events as presented in this paper is a general feature in the evening section under the condition of ring current developments

nd and sr isotopic signatures of metasedimentary rocks around the south pacific margin and implications for their provenance an nd sr isotope database including c 200 new analyses is presented for palaeozoic and mesozoic metasedimentary successions extending through southeastern australia new zealand west antarctica and the antarctic peninsula to southern south america combining with u pb detrital zircon age data this enables characterization of new zealand terranes especially within the eastern province where there is a progression from westernmost terranes of both volcanic volcaniclastic and accretionary origin with primitive sediment sources to easternmost terranes with mature continental sediment inputs in southern south america west antarctica and the antarctica peninsula similar accretionary complexes have nd model ages principally reflecting mixing of sedimentary material from multiple sources both mature and juvenile a mature gondwana continental provenance dominates in sedimentary basins inboard of the active margin especially in the palaeozoic western province new zealand interior west antarctica and nw argentina and contributes significantly to pre mesozoic sedimentary rocks of patagonia east of the andes along the gondwanaland margin nd systematics for younger late palaeozoic to early mesozoic accretionary complex metasediments reflect younger source inputs notably in the scotia metamorphic complex many of the accretionary complex deposits must involve significant crustal reworking there is no apparent south american equivalent of the primitive provenance of the westernmost accretionary terranes of new zealand

whole rock geochemical variations and evolution of the arc derived murihiku terrane new zealand arc flank volcaniclastic sedimentation in the murihiku terrane of new zealand lasted about 120 million years from late permian to early cretaceous time despite the effects of pervasive zeolite facies alteration whole rock geochemical parameters for sandstones siltstones and tuffs record changes in source rock composition both in time and along the length of the depositional basin sandstones are considered to give a more reliable indication of the state of evolution of the source volcanic arc than do the siltstones the siltstones commonly contain detrital white mica flakes that are generally lacking in the sandstones and are possibly of distal continental origin some also contain very fine felsic ash particles average abundances and normalized multi element diagrams are used to estimate proportions of three model end member source constituents average upper continen tal crust ucc high k rhyolite rhy and basaltic andesite and sandstone provenance for the southland syncline sector changed from a predominantly basaltic andesite source in late permian to early middle triassic time for example ucc rhy and 0 17 83 in the early to early middle triassic to highly felsic in the middle to late triassic reaching ucc rhy and 2 74 24 in the late triassic oretian stage a ucc component became increasing significant from latest triassic upward and the proportion of mafic to felsic volcanism increased again with ucc rhy and 15 30 35 in the middle jurassic temaikan stage mix modelling suggests that along arc source propor tions varied with greater mafic and upper continental crust contributions in the northern kawhia seg ment than in the southland segment these patterns may be explained by deposition at an oceanic aleutian type arc margin with transition to a continental oceanic arc character induced either by arc evolution and dissection forearc sliver translation or underplating of rafted microcontinental fragments

geodynamic evolution of the baguio mineral district unlocking the cenozoic record from clastic rocks abstract geochemical studies done on the baguio mineral district had dominantly looked at the igneous rocks a major gap is the scarcity of studies dealing with the sedimentary rock geochemistry for this district which this paper intends to address the petrographic data and major and trace element compositions of the siltstones sandstones from the lower member of the late oligocene to early miocene zigzag formation show that they are generally quartz rich and have high k2o th and la sc contents the chondrite normalized ree pattern exhibits a negative eu anomaly enrichment in lrees and flat hrees similar to typical post archean shales taken together the data indicate derivation of the lower member of the zigzag formation from intermediate to acid igneous rock sources generated in an active margin setting a likely candidate source is the cordon syenite complex palali formation in the northern sierra madre caraballo mountains derivation from mafic source rocks in an oceanic island arc setting is inferred for samples of the middle to late miocene klondyke late miocene to early pliocene amlang and late pliocene cataguintingan formations these samples are characterized by low k2o th and la sc but high cr th values unroofing of the pugo metavolcanics and the younger plutons in the central cordillera provided the materials which eventually produced the klondyke and amlang formations continuous uplift and shallowing of the basin resulted in the deposition of the cataguintingan formation the petrography geochemistry and geological features of the sedimentary rocks clearly define the change in sediment provenance from quartz rich during the oligocene to quartz deficit in the miocene this offers additional constraints in understanding the geological evolution of the mineral district

provenance of permian triassic and ordovician metagraywacke terranes in new zealand evidence from 40ar 39ar dating of detrital micas single crystal 40 ar 39 ar ages of detrital micas from greenland group ordovician low grade metagraywackes of the west coast south island new zealand indicate a source area having muscovite age patterns of 490 515 ma the detrital muscovite ages are characteristic of granitoid and gneiss terranes of the ross adelaide fold belt of antarctica therefore the source area for the greenland group sedimentary rocks was the immediately adjacent pacific margin of gondwana similar age determinations for rakaia terrane permian triassic torlesse supergroup metagraywackes of the wellington and canterbury regions of new zealand indicate that their source area included rocks having prominent muscovite cooling ages populations of 210 290 ma 80 and 410 460 ma 15 the torlesse detrital muscovite age data thus suggest that the source area of the metagraywackes was not within the lachlan fold belt of southeast australia and analogues in antarctica nor in the adjacent ross adelaide fold belt rather the rakaia terrane of the torlesse metagraywackes is a true suspect terrane derived from a source area within the hunter bowen fold belt of northeast australia and the immediately adjacent older orogens of eastern queensland

equatorial density depletions observed at 840 km during the great magnetic storm of march 1989 early on march 14 1989 a thermal plasma probe on the defense meteorological satellite program dmsp f9 spacecraft detected extensive and dramatic decreases in the ion density at 840 km near 2130 lt during two consecutive transequatorial passes over south america the order of magnitude decreases in the ion density extended more than 4000 km along the satellite track the depletions were accompanied by upward and westward plasma drifts both in excess of 100 m s their onsets and terminations were marked by extremely sharp density gradients dmsp f9 observed no similar depletions over the atlantic during preceding orbits a partial depletion was detected over the eastern pacific during the following orbit the dmsp f9 ground track passed slightly west of a brazilian total electron content tec station and two brazilian ionosondes during the first depletion encounter the tec fell far below normal during the night of march 13 14 the ionosonde measurements indicate that in the hour after sunset before dmsp passed through the depletions the f2 layer rose rapidly and disappeared but at the time of the first depletion encounter hmf2 was decreasing over one of the stations the dmsp f8 satellite which orbits in the dawn dusk meridian made related measurements on march 13 and 14 crossing the equator at dust on march 13 at the same longitude where dmsp f9 encountered the first depletion dmsp f8 detected upward and westward drifts but it measured extremely large rather then depleted ion densities during two dawn passes over the eastern pacific on march 14 dmsp f8 observed depletions somewhat similar to those detected by dmsp f9 large westward drifts accompanied the depletions detected by dmsp f8 it is quite probable that the morningside depletions detected on march 14 are remnants of those detected earlier by dmsp f9 in the evening sector we develop a phenomenological model reconciling dmsp f8 f9 and ground based measurements our calculations show that rapid upward drifts sustained for several hours can produce depletions in the equatorial ion density with sharp gradients at their high latitude boundaries consistent with the data we discuss possible contributing mechanisms for generating these upward drifts these include direct penetration of the magnetospheric electric field to low latitudes the electric fields generated by the disturbance dynamo and the effects of conductivity gradients near the dusk terminator and the south atlantic anomaly

reconstruction of holocene monsoon history from the pearl river estuary southern china using diatoms and carbon isotope ratios this study employs a multiproxy approach in the reconstruction of holocene monsoon history from sedimentary sequences obtained from the pearl river estuary southern china a set of modern surface sediment samples were collected within and outside the estuary and a sediment core was obtained from the mouth of the estuary a range of modern environmental variables were recorded including water salinity summer winter and annual average and water depth the diatom results show a good relationship with water salinity with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux this pattern is matched by the bulk organic carbon isotopes the isotope values vary between 21 1 0 3 0 for samples from the fully marine environment between 23 2 0 8 and 23 7 0 8 for samples from the mid to outer estuary brackish water environment and less than 24 7 1 3 for samples from the inner estuary close to the freshwater sources similarly the c n ratios vary from below 7 0 6 in the marine end members to over 14 8 3 0 in the freshwater end members both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal yr bp resulting from the enhanced summer monsoon regime in early holocene the strength of freshwater flux reached its highest between 7500 and 6000 cal yr bp in the last 6000 years freshwater flux decreased towards present reflecting a gradual weakening of the summer monsoon

limestone and chert in tectonic blocks from the esk head subterrane south island new zealand the esk head subterrane is a continuous belt generally 10 20 km wide of tectonic melange and broken formation on the south island of new zealand this subterrane separates older and younger parts of the torlesse terrane which is an extensive accretionary prism composed mostly of quartzo feldspathic submarine fan deposits ranging from permian to early cretaceous in age the torlesse is the most pacific ward of several permian and mesozoic accreted terranes in new zealand that record tectonic amalgamation and ultimate accretion against the pacific facing gondwana margin the esk head subterrane of the torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt associated seamount and sea floor limestones and cherty rocks thought to be representative of the subducted plate limestones in tectonic blocks are of late triassic and probably jurassic ages and include 1 submarine cemented pelagic bivalve geopetal packstone grainstone 2 brachiopod bryozoan encrinite and 3 radiolarian pelagic lime mudstone most of the triassic blocks have been dated using conodonts which have remarkably low color alteration index cai values paleogeographic inferences drawn from megafossils bioclasts and radiolarians as well as from carbonate cements indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the new zealand part of the gondwana margin but higher than paleoequatorial latitudes these oceanic sediments and their basaltic substrates were evidently emplaced in the torlesse accretionary prism following off scraping from an extensive subducting oceanic plate probably the phoenix plate which was obliquely convergent with the northwest trending gondwana margin during late jurassic and or early cretaceous time

petrography and whole rock geochemistry of the tertiary sylhet succession northeastern bengal basin bangladesh provenance and source area weathering abstract detrital modes and the geochemical compositions of sandstones and mudrocks from the paleocene to plio pleistocene jaintia barail surma tipam and dupitila groups of the sylhet basin in bangladesh have been examined to identify their provenance and source area weathering conditions barail and surma group sandstones are quartz rich feldspar poor and are rich in sedimentary and metamorphic lithic fragments indicating a recycled orogen source geochemically the succession is divisible into three parts paleocene late eocene jaintia group mudrocks form separate trends and have very high chemical index of alteration cia values suggesting derivation from a stable cratonic source the second part the late eocene to miocene barail and surma groups forms single trends on variation diagrams maximum cia ratios decrease from the barail to the surma group suggesting rapid influx of detritus from a common felsic source undergoing active uplift compatible with weathering and erosion proxies from the bengal and indus fans average bulk geochemical and ree characteristics of these two groups are identical as are a cn k trends these features and comparison with potential himalayan sources support derivation of both the barail and surma groups from that orogen and hence supply of himalayan detritus to the sylhet basin as early as the late eocene rather than from the neogene the third part the non marine tipam late miocene pliocene and dupitila pliocene pleistocene groups forms slightly differing geochemical trends and has higher maximum cia values ree fractionation between sandstones and mudrocks is more marked but ree patterns and parameters remain unchanged suggesting that the overall source remained unchanged higher cia and greater ree fractionation in the tipam and dupitila groups may be a product of their fluvial deposition and more intense weathering on the floodplain during intensification of the south asian monsoon from 4 ma onwards

provenance analysis using conglomerate clast lithologies a case study from the pahau terrane of new zealand abstract the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single minerals this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources the torlesse terranes part of the new zealand eastern province are accretionary complexes that comprise an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages two terranes are recognised in the south island the permian to late triassic rakaia terrane and the late jurassic to early cretaceous pahau terrane geochronology geochemistry and sr nd isotopes of igneous clasts from pahau terrane conglomerates identify the median tectonic zone s l as a major contributor of detritus to the pahau depositional basin shrimp u pb zircon ages of igneous clasts range from 128 to 123 ma and from 147 to 135 ma calc alkaline clasts of the latter range are indistinguishable in age chemical composition and petrogenesis from the calc alkaline granitoids of the darran suite whereas alkaline clasts correlate with the electric granite both parts of the median tectonic zone an early jurassic calc alkaline rhyolite clast from kekerengu 188 3 ma correlates with the bounty island granite campbell plateau the petrography and geochemistry of pahau terrane sandstone clasts indicate the recycling of permian to early late triassic older rakaia terrane rocks this is further supported by the detrital zircon age data igneous conglomerate clasts are capable of placing exceptionally tight constraints on pahau provenance and on its mesozoic tectonic setting within the southwest pacific margin of gondwana they provide the best evidence yet that the pahau terrane is locally derived

the eastern palmer land shear zone a new terrane accretion model for the mesozoic development of the antarctic peninsula a major ductile fault zone the eastern palmer land shear zone has been identified east of the spine of the southern antarctic peninsula this shear zone separates newly identified geological domains and indicates that during late jurassic terrane accretion and collision two and possibly three separate terranes collided resulting in the palmer land orogeny the orogeny is best developed in eastern palmer land and eastern ellsworth land there shallow marine sedimentary rocks of the latady formation and a metamorphic and igneous basement complex of possible lower palaeozoic to pre early jurassic age are thrust and folded this forms an arcuate east directed foreland fold and thrust belt up to 100 km wide and 750 km long parallel to the axis of the antarctic peninsula the newly identified antarctic peninsula domains include 1 a parautochthonous eastern domain that represents part of the margin of the gondwana continent comparable to the western province of new zealand the ross province superterrane of marie byrd land the eastern series of south central chile the pampa de agnia and tepuel rocks of north patagonia and the cordillera darwin rocks of tierra del fuego 2 a suspect central domain that represents an allochthonous microcontinental magmatic arc terrane comparable to the median tectonic zone of new zealand the amundsen province superterrane of marie byrd land and coastal cordillera of north chile and 3 a suspect western domain with strong similarities to the eastern province of new zealand western series of south central chile and chonos metamorphic complex of north patagonia that represents either a subduction accretion complex to the central domain or another separate crustal fragment although an allochthonous terrane hypothesis for the antarctic peninsula remains to be fully tested this has much in common with models for the new zealand and south american parts of the pacific margin of gondwana the identification of a potential allochthonous terrane continent collision zone allows us to define the edge of the gondwana continent in the antarctic peninsula sector of the supercontinent margin which has implications for mesozoic reconstructions of gondwana

prompt midlatitude electric field effects during severe geomagnetic storms meridian plane elevation scans with the millstone hill incoherent scatter radar provide evidence of a strong perturbation of the coupled mid latitude magnetosphere ionosphere system during the early phases of the november 4 1993 magnetic storm a narrow ionospheric trough formed at l 3 5 in the pre midnight sector immediately poleward of the millstone hill site the most pronounced radar signature of the developing activity was a brief 20 min uplifting of the f region plasma equatorward of the trough such that the peak altitude increased with distance away from the trough a similar signature had been observed during storm onset on march 20 1990 and in that event a pronounced topside ionospheric depletion developed in the region far equatorward of the mid latitude trough and was observed by the radar and the dmsp f9 satellite during the november 4 1993 event the dmsp f10 satellite observed narrow magnetically conjugate regions of plasma density depletion and strong horizontal and upward plasma velocity 1500 m s at l 1 5 at the time of the uplifting of the mid latitude f region observed by the radar these observations were confined to longitudes near the south atlantic magnetic anomaly and in the nov 1993 case the perturbation was coincident with the peak of the precipitating particle fluxes associated with innerbelt losses at the anomaly both the uplifting of the ionospheric f layer and the triggering of topside density perturbations can be explained in terms of an eastward electric field imposed on the mid and low latitude ionosphere during the initial stages of the geomagnetic storm the low latitude ionospheric perturbations in these events were similar to supersonic equatorial bubbles triggered by the destabilizing effects of the upward e b drift associated with the eastward electric field

observation of a large density dropout across the magnetic field at 600 km altitude during the 6 7 april 2000 magnetic storm 1 the first republic of china satellite rocsat 1 at 600 km altitude observed two groups of equatorial spread f esf plasma depletion structures located in either side of the midnight meridian during the 6 7 april 2000 magnetic storm recovery phase in the group of postmidnight esf irregularities a large density dropout was observed in two consecutive rocsat orbits this large density dropout structure is similar to the density depletion event observed by defense meteorological satellite program dmsp f9 spacecraft during the 13 14 march 1989 magnetic storm greenspan et al 1991 except that the rocsat orbit traverses the magnetic field in the east west direction the postmidnight group of depletions together with the large density dropout was observed to drift westward with the background plasma at 170 m s 1 we examine the properties of the large density dropout through the plasma data taken from the drift meter dm and retarding potential analyzer rpa sensors in three consecutive orbits the apparent widening of the density depletion is explained by the different locations of the satellite within the depletion region the extreme low density level inside the upwelling depletion indicates that of the nighttime f peak passed over the rocsat orbit at 600 km the existence of no ions inside the dropout is consistent with such an elevation of the f peak

investigating the history of east asian monsoon and climate during the last glacial interglacial period 0 140 000 years mineralogy and geochemistry of odp sites 1143 and 1144 south china sea abstract monsoon climate is an important component of the global climatic system a comprehensive understanding of its variability over glacial interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate continental weathering and productivity a detailed multiproxy study including bulk and clay mineralogy grain size analysis phosphorus geochemistry sedex extraction organic matter characterization and nitrogen stable isotopes was carried out on samples from odp sites 1143 and 1144 leg 184 south china sea covering the past 140 000 years we tentatively reconstruct the complex sedimentation and climatic history of the region during the last glacial interglacial cycle when sea level variations linked to the growth and melting of ice caps interact with monsoon variability during interglacial periods of high sea level summer monsoon was strong and humid and warm climate characterized the adjacent continent and islands clay minerals bear signals of chemical weathering during these intervals high calcite and reactive phosphorus mass accumulation rates mars indicate high productivity especially in the southern region of the basin during glacial intervals strong winter monsoon provided enhanced detrital input from the continent as indicated by high detrital mar glacial low sea level resulted in erosion of sediments from the exposed sunda shelf to the south and clay mineral variations indicate that warm and humid conditions still prevailed in the southern tropical areas enhanced supply of nutrients from the continent both by river and eolian input maintained high primary productivity reduced circulation during these periods possibly induced active remobilization of nutrients such as phosphorus from the sediments intense and short cold periods recorded during glacial and interglacial stages correlate with loess records in china and marine climatic records in the north atlantic confirming a teleconnection between low and high latitude climate variability

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

onset conditions of equatorial range spread f at fortaleza brazil during the june solstice case studies are made of the ionospheric thermospheric and geomagnetic conditions associated with the occasional onset of range spread f at fortaleza 4 s 38 w dip latitude 1 8 and magnetic declination 21 w brazil in the june solstice a season in which frequency spread f is typically seen in the postsunset hours after 2000 lt it is found that the f layer experiences quite consistently a large vertical drift early in the evening hours 1815 1915 lt on days of range spread f in comparison to days of only frequency spread f the anomalously large dusk time vertical plasma drift occurs under both geomagnetically disturbed and quiet conditions there is no significant change in the pattern of meridional neutral winds at and prior to the time of onset of range spread f estimated from the data of f layer peak height hmax at the low latitude station cachoeira paulista 23 s 45 w and dip 26 5 s using a modified form of the servo model the results strongly suggest that though the meridional poleward wind is very effective in inhibiting the growth of rayleigh taylor r t instability and hence range spread f at fortaleza during the june solstice as shown by maruyama 1996 its variability does not play an important role in creating favorable conditions for r t instability on a day to day basis the prerequisite for the occasional occurrence of range spread f at fortaleza in the june solstice seems to be the presence of an impulsive and large f layer vertical plasma drift a condition favorable for destabilizing the bottomside f region through r t instability mechanism because of the high altitude of the layer

provenance history of a carboniferous gondwana margin forearc basin new england fold belt eastern australia modal and geochemical constraints abstract the visean stephanian myall trough eastern australia formed part of a forearc basin to the east of a magmatic arc situated along the palaeo pacific margin of gondwana petrographic modal whole rock geochemistry and mineral phase chemistry of sandstones siltstones conglomerates and associated igneous rocks provide a consistent and coherent data set which indicate sediment derivation from a magmatic arc of predominantly silicic volcanic composition the low quartz modes of the sandstones the largely volcanic origin of lithic fragments and the overall high sio 2 content of the siliciclastic sediments and igneous rocks require the arc source to be largely dacitic to rhyolitic in composition the predominance of vitric type highly siliceous volcanic rocks lithic fragments suggests a source composed largely of silicic pyroclastics the presence of potassium feldspar as well as the presence of biotite as the principal detrital ferromagnesian phase in the sandstones suggest a source of medium to high k tholeiite composition the high trace element abundances of relatively immobile elements such as zr la ce v nb y and th and corresponding high th u zr y la y la sm ratios and low zr th zr nb la th and ti zr ratios for both the igneous rocks and derived siliciclastic sediments in the myall trough also require a high k and or strongly medium k arc source a lack of temporal or spatial trends in the data indicate that the magmatic arc remained of uniform composition throughout the 25 ma interval of strata preserved within the trough the provenance history of the myall trough requires accumulation along an andean type continental margin rather than an intra oceanic arc outboard of the gondwana margin

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

the role of earthquakes and climate in the formation of diamictic sediments in a new zealand mountain lake we used itrax xrf magnetic susceptibility grain size and micro ct scanning to provide a facies classification for a late holocene sediment sequence from lake chappa ai in the southern alps new zealand the record contained multiple diamictic layers and our objective was to determine the environmental significance of these deposits clast fabric analysis indicated that the diamicts comprise dropstones transported to the centre of the lake by ice rafting diamicts belonging to facies 1 represent rock falls onto lake ice triggered by earthquakes that produced mmi modified mercalli intensity 8 shaking in the catchment mmi 8 earthquakes may need to occur when the lake has ice cover to produce facies 1 diamicts mmi 8 earthquakes in the ice free season or mmi 7 8 earthquakes may also result in an increased flux of large 1 mm clasts to the centre of the lake but may not produce a facies 1 diamict more work is required to establish the role of climate related processes on the formation of non facies 1 diamicts in lake chappa ai climate change may directly lead to diamict formation by changing lake ice cover and facilitating transport of large clasts by anchor ice or increasing the likelihood of rain on snow events in the spring changing ice cover conditions will also affect how mountain lakes record past earthquake events lakes that are ice free will not produce earthquake diamicts and lakes that have perennial ice cover may produce a single diamict representing multiple earthquakes if the lake becomes ice free a reduction in the duration of winter ice cover will also decrease the probability of capturing primary rockfall deposits from earthquakes additional data such as a diatom or chironomid record from lake chappa ai may help to resolve the contribution of climate processes to diamict formation we should consider the lake chappa ai record as an indicator of minimum earthquake activity until we can disentangle the effects of climate change on non facies 1 diamict formation this study highlights the multiple mechanisms that can lead to diamict formation in mountain lake sediments these processes should always be considered before attributing the presence of diamict deposits to ice rafted debris in a pro glacial lake this is particularly true in seismically active settings where earthquake triggered rockfalls may lead to diamict formation

using geochemical fingerprinting to determine transpressive fault movement history application to the new zealand alpine fault 1 geochemical fingerprinting of conglomerate clasts from depocenters adjacent to a strike slip fault and of source areas on the opposite side of the fault provides a method of determining fault movement history in instances where potential piercing points have been removed by erosion or buried in pull apart or down warp basins our example demonstrating this method is the neogene maruia basin adjacent to the new zealand alpine fault the on land australian pacific plate boundary which shows permian pelorus caples terrane offset by 480 km twenty six sandstone and schist conglomerate clasts from the maruia basin rappahannock group were analyzed for major elements and 18 trace elements by x ray fluorescence and compared to similar analyses from potential regional source areas significant source terranes the caples group and the torlesse terrane were identified both located southeast of the fault dextral movement on the fault provided a conveyor belt of material to the maruia basin first supplying at 11 5 ma caples sandstone then caples schist followed by torlesse schist from 9 5 ma which translates to an average neogene movement rate of 36 37 mm yr 1 the increase in metamorphic grade reflects accelerated exhumation of source rocks as they passed through a restraining bend adjacent to the maruia basin and from later regional uplift from a change in the australian pacific plate motion vector and more transpressive movement from 5 ma this robust method of geochemical fingerprinting could be readily applied to determining movement history of transpressive faults of other regions

petrography and geochemistry of the carboniferous triassic trinity peninsula group west antarctica implications for provenance and tectonic setting the carboniferous triassic trinity peninsula group is a metasedimentary sequence that crops out widely in the northern antarctic peninsula these are some of the most extensive outcrops in the area and hold the key to evaluating the connections of the antarctic peninsula in gondwana however they are still poorly understood here we present our provenance study of the trinity peninsula group using petrographic and geochemical approaches in combination with cathodoluminescence of detrital quartz in order to constrain its source characteristics and tectonic setting using differences in modal composition and quartz cathodoluminescence characteristics we define three petrofacies derived from the progressive uplift and erosion of a volcano plutonic continental arc which exposed the plutonic metamorphic roots as indicated by major and trace elements the source is felsic with a composition ranging from tonalitic to granodioritic the relatively unweathered condition of the source area points to a dry and cold climate at the time of deposition but this does not necessarily mean that it was glaciated deposition of the sediments occurred within an active continental margin relatively close to the source area probably along the south patagonia antarctic peninsula sector of gondwana strong chronological petrological and chemical similarities with the sediments of the duque the york complex in patagonia suggest that they were derived from the same source

geochemistry and detrital zircon u pb dating of pliocene pleistocene sandstones of the chittagong tripura fold belt bangladesh implications for provenance abstract the bengal basin originated during the collision of india with eurasia and burma the provenance analysis of the chittagong tripura fold belt ctfb which is the folded eastern flank of the bengal basin as well as the neogene belt of the indo burman ranges ibr is key to better understand the possible sources of sediment input from the complex interplay of the indian eurasian and burma plates we report new whole rock geochemical and detrital zircon u pb data from the upper neogene sandstones of tipam dupi tila formations pliocene to plio plestocene succession from the ctfb detrital zircon u pb age spectra show three predominant peaks at

schmidt hammer exposure age dating shd of late quaternary fluvial terraces in new zealand schmidt hammer sh r values are reported for surface clasts from numerically dated holocene and pleistocene fluvial terraces in the south island of new zealand the r values are combined with previously obtained weathering rind radiocarbon terrestrial cosmogenic nuclide and luminescence terrace ages to derive sh r value chronofunctions for greywacke clasts from four distinct locations our results show that different weathering rates affect the form of the sh r value versus age curve however a fundamental dependency between the two remains constant over timescales ranging from 102 to 105 years power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic precipitation and temperature and sedimentologic variables source terrane petrology age uncertainties of 22 of the surface age suggest that schmidt hammer exposure age dating shd is a reliable calibrated age dating technique for fluvial terraces copyright 2013 john wiley sons ltd

environmental change of the fluvial estuary system in relation to arase dam removal of the yatsushiro tidal flat sw kyushu japan chemical composition of 24 elements for sediments and suspended solids water parameters and the diatoms from yatsushiro bay tidal flat kuma river and arase dam have been determined to examine changes from 2002 to 2013 in 2002 sediment delivered to the bay by the kuma river was restricted by the arase dam however in april 2010 two gates were opened and also repeated seasonal flushing allowing resumption of natural sediment transport bulk chemical composition of the tidal flat sediments has changed since 2002 with marked decreases in concentrations of as zn pb and total sulfur decreased heavy metal contents in 2012 and 2013 for bay sediments after opening the dam and repeated flushing is attributed to dilution by previously impounded quartz and feldspar restoration of natural sediment transport by opening the dam and repeated flushing has thus brought about a recovery in the yatsushiro marine environment