paleoproterozoic arc and ophiolitic rocks on the northwest margin of the trans hudson orogen saskatchewan canada their contribution to a revised tectonic framework for the orogen abstract a new lithotectonic framework for the northwestern reindeer zone of the trans hudson orogen divides rocks into five northwest to north dipping volcano sedimentary assemblages 1 at the structural base the 1 92 1 87 ga largely sedimentary levesque bay assemblage partly equivalent to former maclean lake gneisses which lies within the confines of the kisseynew domain and is tectonically imbricated with metasedimentary rocks of the the lawrence point assemblage is interpreted as a dismembered supra subduction zone ophiolite high mgo refractory harzburgite group 1 ultramafic rocks at the structural base of the assemblage is geochemically identical to the upper mantle section of selected supra subduction zone ophiolites and mantle tectonites chromite and olivine compositions of the group 1 ultramafic rocks are also comparable to those of ophiolitic harzburgite and mantle tectonite mafic metavolcanic rocks of the assemblage are classified as subalkaline tholeiitic basalts their trace element patterns and hf ta th y nb and la element ratios resemble those of modern back arc basin basalts the reed lake assemblage represents a subduction generated arc complex that was built on top of the lawrence point assemblage its mafic metavolcanic rocks are subalkaline basalts with calc alkaline trends and elevated th and ce concentrations and negative nb anomalies feldspar porphyry dykes intruding the lawrence point and duck lake assemblages constrain timing of lawrence point ophiolite emplacement onto the duck lake assemblage to 1 86 1 84 ga the trace element geochemistry of the dykes suggests continued arc volcanism after ophiolite emplacement mafic metavolcanic rocks of the levesque bay assemblage are geochemically similar to those of the lawrence point assemblage other ultramafic rocks peridotite to pyroxenite are abundant in the lawrence point assemblage but have similar geochemistry to small ultramafic bodies intruding the reed lake duck lake and levesque bay assemblages they represent a separate later phase 1 86 ga of ultramafic plutonism which post dates ophiolite emplacement timing of lawrence point ophiolite emplacement between 1 86 and 1 84 ga and geochemistry of later felsic and mafic ultramafic volcanism suggest that the lawrence point ophiolite and overlying reed lake arc assemblage were not accreted to the hearne craton prior to 1 86 ga but were first accreted to the flin flon glennie complex after 1 86 ga

greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

petrology of the ispendere malatya ophiolite from the southeast anatolia implications for the late mesozoic evolution of the southern neotethyan ocean

petrology and petrogenesis of cumulate peridotites and gabbros from the marum ophiolite complex northern papua new guinea

late quaternary sediment yield from the high arctic svalbard area late quaternary sediment yields from the isfjorden drainage area 7327 km 2 a high arctic region on svalbard characterized by an alpine landscape have been reconstructed by using seismic stratigraphy supported by sediment core analysis the sediments that accumulated in the fjord during and since deglaciation can be divided into three stratigraphic units the volumes of these units were determined and converted into sediment yield rates averaged over the drainage basin during deglaciation 13 to 10 ka the sediment yield was sim 860 tons t cdot km 2 cdot yr 1 in the early holocene it decreased to 190 t cdot km 2 cdot yr 1 and then increased to 390 t cdot km 2 cdot yr 1 during the late holocene little ice age when normalized to the approximate glacierized area these rates correspond to a sediment yield of sim 800 t cdot km 2 cdot yr 1 sediment yield from non glacierized parts of the drainage is estimated to be 35 t cdot km 2 cdot yr

biological processes on glacier and ice sheet surfaces glacial ice covers around 10 of the earth s continents a review of the literature suggests that microbes living on glaciers and ice sheets are an integral part of both the glacial environment and the earth s ecosystem

terrane amalgamation in the philippine sea margin abstract the philippine sea plate includes plateaus of thickened crust interpreted as imbricated ophiolite and arc related terranes of late mesozoic early tertiary age separated by thinner oceanic crust the arrival of plateaus at the subducting southwest margin of the philippine sea plate has caused the philippine trench to propagate southward in increments and caused transfer of terranes to the philippine margin new data from the halmahera region indicate that the position nature and evolution of plate boundaries have been strongly influenced by the heterogeneous character of the philippine sea plate at present the philippine trench terminates at an oceanic plateau which is structurally continuous with an old forearc and ophiolite terrane on halmahera the position of this terrane has caused philippine sea plate eurasia convergence to be transferred from subduction at the philippine trench to the molucca sea collision zone through a broad ne sw dextral transpressional zone across halmahera this plate boundary configuration is unstable and requires the future development of a new subduction zone to the east of halmahera which will result in amalgamation of the halmahera ophiolite terrane to the philippine margin in the halmahera region amalgamation of terranes to the evolving philippine microcontinent is currently in process

petrogenesis and structure of the buck creek mafic ultramafic suite southern appalachians constraints on ophiolite evolution and emplacement in collisional orogens integration of detailed field petrological structural and geochemical observations of the buck creek mafic ultramafic suite which is among the larger southern appalachian ultramafic exposures points to an igneous origin as a mid ocean ridge cumulate massif with subsequent emplacement in a deep subduction zone setting these results help to clarify the unresolved role of alpine type ultramafic bodies in the southern appalachians a problem complicated by their generally small and fragmented nature and by significant tectonic overprinting as an ophiolite fragment the buck creek rocks are unusual in their preservation of relatively high pressure anhydrous conditions and thus they provide constraints on mechanisms of ophiolite emplacement field support for a cumulate origin for the buck creek suite includes centimeter to meter scale interlayering of dunite troctolite anorthosite and spinel rich layers and local gradation between buck creek troctolitic rocks and surrounding amphibolites relict anorthitic plagioclase forsteritic olivine and augitic clinopyroxene define a cumulate triangle on an mgo versus al 2 o 3 diagram meta troctolite and meta dunite compositions define a linear array between olivine and plagioclase compositions and many amphibolites fall within this triangle reflecting gabbroic protoliths the relatively abundant troctolite cumulates scarce pyroxene in the ultramafic rocks and the high al 2 o 3 tio 2 and low cr numbers in spinel best match lot or l type lherzolite ophiolites consistent with crystallization in a slow spreading mid ocean ridge setting sapphirine bearing spinel symplectites in the metatroctolites suggest that buck creek rocks remained anhydrous to 800 c and 0 9 1 1 gpa representing conditions atypical of ophiolite emplacement comparisons to the zermatt saas ophiolite and bergen eclogite suggest rapid subduction of buck creek rocks to depths of 30 km where partial hydration perhaps facilitated by pro grade dehydration reactions in surrounding rocks caused strain softening that permitted ductile disaggregation and aided in their emplacement into the overlying accretionary complex alternatively emplacement might have resulted from a switch in subduction polarity with hydration following emplacement uplift shortening and hydration within the accretionary sequences are responsible for the dominant structural features

behavior of a glacier derived suspended sediment plume in a small arctic inlet the changing configuration of a glacier derived turbid surface meltwater plume was observed over a 40 hr period in a small marine inlet in spitsbergen factors controlling plume position tides winds and melt stream discharge were also monitored tidal forcing was the dominant control on plume behavior over the study period when winds were calm or light the plume spread over much of the inlet on the flood and around high tide and was restricted to the north side on the ebb and at low water winds were generally 5 kts and only influenced plume position when reaching over 12 kts coriolis effects were unimportant sediments on the inlet floor fined progressively with distance from glacier fed stream effluxes short cores showed that deposition was mainly in the form of structureless sands and silts

paleoclimate analysis of h 2 h 1 ratios in peat sequences with variable plant composition abstract under equal climatic conditions the deuterium content of plants varies with species the deuterium content of peat cellulose therefore is related to the plant composition this dependence is calculated for each talon in specific peat sequences by means of multiple linear regression and subtracted from the deuterium content of the cellulose fraction of each sample the residual variation should contain a climatic effect such as the climatic temperature dependence of 2 h 1 h in precipitation which is to be correlated with other palaeotemperature records

palaeomagnetic data from a mesozoic philippine sea plate ophiolite on obi island eastern indonesia abstract palaeomagnetic data are presented from part of the halmahera ophiolite exposed on obi island eastern indonesia until the late neogene obi formed part of the southern philippine sea plate it is now isolated from that plate and is located between fault strands in the left lateral sorong fault zone two areas were sampled the first area comprised two sites from a microgabbro and a third site in a thin intruding dyke and the second area yielded one site from a sheeted dyke suite the mean in situ direction for the two areas is d 216 1 i 23 3 where the angular separation is 34 7 rotating the mean directions back to the palaeo vertical clusters the vectors so that d 219 4 i 12 1 where the angular separation is 20 1 this clustering together with other lines of palaeomagnetic evidence suggests that the magnetisation is primary the ophiolite is mesozoic and most likely formed in the jurassic this information together with recently published palaeomagnetic data from nearby upper cretaceous philippine sea plate formations suggest that the oldest parts of the philippine sea plate were situated close to the equator in the western pacific in the middle mesozoic

plate kinematics origin and tectonic emplacement of supra subduction ophiolites in se asia abstract a unique feature of the circum pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust in se asia a majority of the ophiolites appear to have originated at convergent margins and specifically in backarc or island arc settings which evolved either along the edge of the sunda eurasia and australian cratons or within the philippine sea plate these ophiolites were later accreted to continental margins during the tertiary because of fast relative plate velocities tectonic regimes at the active margins of these three plates also changed rapidly strain partitioning associated with oblique convergence caused arc trench systems to move further away from the locus of their accretion we distinguish relatively autochthonous ophiolites resulting from the shortening of marginal basins such as the present day south china sea or the coral sea and highly displaced ophiolites developed in oblique convergent margins where they were dismantled transported and locally severely sheared during final docking in peri cratonic mobile belts i e the philippine mobile belt we find a series of oceanic basins which have been slightly deformed and uplifted varying lithologies and geochemical compositions of tectonic units in these basins as well as their age discrepancies suggest important displacements along major wrench faults we have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro geochemical data to their original location and their former tectonic settings some of the ophiolites occurring in front of the sunda plate represent supra subduction zone basins formed along the australian craton margin during the mesozoic the philippine sea basin the huatung basin south of taiwan and composite ophiolitic basements of the philippines and halmahera may represent remnants of such marginal basins the portion of the philippine sea plate carrying the taiwan philippine arc and its composite ophiolitic continental crustal basement might have actually originated in a different setting closer to that of the papua new guinea ophiolite and then have been displaced rapidly as a result of shearing associated with fast oblique convergence

input composition and potential impact of terrigenous material from free drifting icebergs in the weddell sea abstract the hypothesis that fe fertilization of the southern ocean could account for at least part of the glacial interglacial difference in atmospheric co2 has lead to a search for the fe source iron fertilization in the open ocean can occur naturally through increased dust input cross shelf export upwelling of fe replete deep water and release of terrigenous fe from icebergs however the relative importance of these mechanisms in terms of the flux and bioavailability of the fe is the source of much interest and debate an unambiguous tracer of terrigenous material excess 224ra was used to show that free drifting icebergs are a significant fe source to surface waters in the southern ocean activity of 224ra half life 3 7 days was measured in the weddell sea in surface waters surrounding three free drifting icebergs and in iceberg alley inventories of excess 224ra indicate a local terrigenous input 1 3 orders of magnitude greater than estimates of aeolian dust fluxes to the southern ocean burdens of fine terrigenous material associated with current rates of iceberg ejection are estimated to be on the order of 90 106 tons per year for antarctica yielding a total fe input of 3 106 tons per year chemical and mineralogical composition of the terrigenous material confirms that 0 04 0 4 exists as labile fe in ferrihydrite that is potentially bioavailable on the order of 4 40 104 tons of per year these results suggest that free drifting icebergs can contribute significantly to atmospheric co2 drawdown though fe fertilization in the southern ocean

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

fluvial suspended sediment transport from cold and warm based glaciers in svalbard an analysis of temporal variability in proglacial suspended sediment concentration is undertaken using time series data collected from three svalbard basins which include one largely cold based glacier austre broggerbreen one largely warm based glacier finsterwalderbreen and one intermediate polythermal glacier erdmannbreen the temporal variability in proglacial suspended sediment concentration is analysed using multiple regression techniques in which discharge is supplemented by other predictors acting as surrogates for variability in sediment supply at diurnal medium term and seasonal timescales these multiple regression models improve upon the statistical explanation of suspended sediment concentration produced by simple sediment rating curves but need to account for additional stochastic elements within the time series before they may be considered successful an interpretation of the physical processes which are responsible for the regression model characteristics is offered as a basis for comparing the different arctic glaciofluvial suspended sediment transport systems with that of their better known temperate glaciofluvial counterparts it is inferred that the largely warm based glacier is dominated by sediment supply from subglacial reservoirs which evolve in a similar manner to temperate glaciers and which cause a pronounced seasonal exhaustion of suspended sediment supply the largely cold based glacier however is dominated by sediment supply from marginal sources which generate a responsive system at short time scales but no significant seasonal pattern the intermediate polythermal glacier basin which was anticipated to be similar to the warm based glacier instead shows a highly significant seasonal increase in suspended sediment supply from an unusual subglacial reservoir emerging under pressure in the glacier foreland the temperate model of glaciofluvial suspended sediment transport is therefore found to be of limited use in an arctic context copyright 1999 john wiley sons ltd

glacier hydrology in svalbard norwegian high arctic abstract progress in glacier hydrology has focused on temperate glaciers although partly or wholly non temperate glaciers are found in many parts of the world and significant areas of former ice sheets were probably non temperate it has usually been assumed that drainage from non temperate glaciers consists of relatively dilute and invariable supraglacial runoff in this paper the hydrology of glaciers in the high arctic archipelago of svalbard is examined variations in the thermal regimes of glaciers and their implications for drainage are first addressed results from svalbard concerning meltwater discharge and storage and solute and suspended sediment dynamics are then reviewed in general meltwater penetration of non temperate ice is limited and drainage from non temperate glaciers in svalbard has many of the characteristics of sub aerial drainage however it would be erroneous to view this drainage simply as dilute supraglacial runoff as significant material transport occurs in suspension and solution furthermore twentieth century climate change has probably led to changes in the thermal regimes of some svalbard glaciers such that relict drainage structures are sometimes observed while meltwater yields are augmented by runoff which can be attributed to the loss of mass from glaciers at large spatial scales turbid plumes observed at the marine margins of polythermal ice caps indicate that meltwater can be routed subglacially through non temperate ice

igneous petrogenesis of the yakuno ophiolite japan in the context of the diversity of ophiolites an ophiolite complex includes three major members basaltic volcanics mafic ultramafic cumulates and residual peridotite from the aspect of igneous petrology three distinct types are recognized among the associations of the three members liguria type alkalic basalt plagioclase type cumulates and lherzolite yakuno type high alumina tholeiite clinopyroxene type cumulates and clinopyroxene bearing harzburgite papua type low alumina tholeiite orthopyroxene type cumulates and clinopyroxene free harzburgite in the light of recent experimental studies the three types represent cogenetic complementary products of low 30 degrees of partial melting in the lherzolitic source mantle respectively the cumulates of the yakuno ophiolite show structural and chemical continuity to the underlying residual peridotite and were recrystallized at high pressures 5 10 kb they originated in a deep soft floored magma chamber directly overlying the partially melted residual harzburgite from which the magma was extracted the three members of the yakuno ophiolite were cogenetically formed through a magmatic event induced by a moderate degree of partial melting in the mantle

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

the cretaceous southeast bohol ophiolite complex central philippines a highly disaggregated supra subduction zone ophiolite abstract the southeast bohol ophiolite complex seboc represents a complete ophiolite sequence with a pelagic chert cap yielding an early cretaceous age the residual peridotite suite of this ophiolite complex is dominated by harzburgite with rare occurrences of lherzolite and dunite pods layered ultramafic cumulate rocks made up of clinopyroxenite wehrlite dunite and massive to layered mafic cumulate rocks consisting of gabbro and norite are present although disaggregated the ophiolite complex includes a sheeted dike complex and a preponderance of sheet flows over pillow lavas in the volcanic section geologic observations such as gabbro pods included within residual harzburgite and deep water sedimentary and volcanic rocks directly overlying the harzburgite have often been reported from the mid atlantic ridge and other slow spreading centers however such situations are never encountered in the seboc geochemical data on seboc show that this ophiolite complex exhibits transitional mid ocean ridge basalt island arc tholeiite geochemical affinities this suggests formation in a subduction related marginal basin the field geological characteristics of seboc show that aside from being a harzburgite ophiolite type this crust mantle sequence was formed in a fast spreading center later tectonic events resulted in its emplacement as a forearc ophiolite

manganese rich brown layers in arctic ocean sediments composition formation mechanisms and diagenetic overprint we present inorganic geochemical analyses of pore waters and sediments of two late quaternary sediment cores from the western arctic ocean southern mendeleev ridge rv polarstern expedition ark xxiii 3 focussing on the composition and origin of distinct brown colored mn rich sediment layers carbonate enrichments occur in association with these layers as peaks in ca al mg al sr al and sr mg suggesting enhanced input of both ice rafted and biogenic carbonate for the first time we show that the mn rich layers layers are also consistently enriched in the scavenged trace metals co cu mo and ni distinct bioturbation patterns specifically well defined brown burrows into the underlying sediments suggest these metal enrichments formed close to the sediment water interface the geochemical signature of these metal and carbonate rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover both rivers and sea ice delivered trace metals to the arctic ocean while enhanced seasonal productivity exported reactive organic matter to the sea floor the coeval deposition of organic matter mn oxyhydr oxides and trace metals triggered intense diagenetic mn cycling at the sediment water interface these processes resulted in the formation of mn and trace metal enrichments and the degradation of labile organic matter with the onset of cooler conditions reduced riverine runoff and or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter resulting in deposition of grayish yellowish metal poor sediments oxygen depletion of arctic bottom waters under these cooler conditions is not supported by our data and did not cause the sedimentary mn distribution while the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes pore water data show that diagenetic mn redistribution is still affecting the organic poor deeper sediments given persistent steady state conditions purely authigenic mn rich brown layers may form while others may be partly or completely dissolved the degree of diagenetic mn redistribution largely depends on the depositional environment the mn and organic matter availability and apparently affected the co mo ratios of mn rich layers thus brown arctic layers are not necessarily synchronous features and should not be correlated across the arctic ocean without additional age control

evaluation of olivine spinel geothermometry as an indicator of thermal history for peridotites olivine and spinel in peridotites from the miyamori ultramafic complex and the ichinogemata crater of northeast japan show a systematic variation in the mg mg fe ratio which is correlated mainly with the grain size of spinel this correlation can be explained by a diffusion model assuming a semi infinite composite sphere under cooling or heating conditions in order to obtain absolute temperatures of thermal events the olivine spinel geothermometer is applied to pairs of spinel core and olivine core average composition the calculated temperatures range over two hundred degrees and have a systematic relationship with the grain size of spinel in the miyamori complex the calculated temperatures decrease monotonically with decrease in grain size of spinel whereas in the ichinomegata lherzolite nodule those of spinel smaller than 0 2 mm increase as the grain size decreases and those of spinel larger than 0 2 mm remain constant regardless of further increase in grain size these observations in the light of the diffusion model suggest that the miyamori complex may have cooled from higher than 800 c to lower than 600 c and that the lherzolite nodule from the ichinomegata crater may have been in equilibrium at 900 c before it was heated above 1 100 c for less than a few days these two examples indicate that olivine spinel pairs of peridotites do not always indicate an appropriate equilibration temperature we cannot interpret the supposed equilibration temperatures until the existence of isothermal stages in the thermal history of peridotites is established by carefully checking the chemical heterogeneity

porewater ph and authigenic phases formed in the uppermost sediments of the santa barbara basin abstract in this paper porewater and solid phase analyses are used in combination with in situ o 2 and ph microelectrode measurements to characterize early diagenetic processes in the uppermost sediments of the santa barbara basin california rapid reduction of dissolved oxygen nitrate solid phase manganese and iron and dissolved sulfate is observed between sediment depths of 0 and 2 cm reductive solubilization of ferric iron phases releases fe 2 adsorbed phosphate and fluoride to the porewaters and contributes to a sharp increase in porewater ph between 2 and 4 cm sulfate reduction rates peak ph levels off and acid volatile sulfides and pyrite become the dominant forms of solid phase iron saturation state calculations which depend largely on ph indicate that the porewaters of the santa barbara basin become saturated with respect to carbonate fluorapatite and calcite within the first 0 25 mm of the sediment and are highly supersaturated by and below 2 cm in spite of this result porewater evidence of phosphate and fluoride removal into a solid phase is observed only in the first 5 cm of some cores whereas dissolved ca profiles suggest dispersed calcite precipitation throughout the sediment column this finding is interpreted as an indication of the nonsteady state nature of the surface reactions that may given sufficient nucleation sites and time lead to carbonate fluorapatite genesis in anoxic sediments finally microelectrode ph profiles from two other basins in the california borderlands are presented these demonstrate that the porewaters of the santa barbara basin are more alkaline than those of other basins this outcome is attributed to the lack of particle mixing and a unique interplay between fe liberation and fes precipitation reactions in the santa barbara basin

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

characteristic mineralogy of arc related cumulate gabbros implications for the tectonic setting of gabbroic plutons and for andesite genesis several mineralogically distinct suites of gabbroic cumulates occur as xenoliths in basalt and andesite from active arc volcanos and in plutons exposed in deeply eroded arcs calcic an85 100 plagioclase and moderately fe rich fo60 80 olivine commonly occur together in arc cumulate gabbros but not in cumulate gabbros from mid ocean ridges ocean islands or tholeiitic layered intrusions compositions of coexisting olivine and plagioclase in gabbro cumulates can establish the tectonic setting of ancient volcano plutonic complexes in deeply eroded arcs gabbroic cumulates typically occur in zoned plutons that also contain gabbros diorites and quartz diorites of basaltic to andesitic composition in many cases it is clear that the cumulate gabbros are chemically and physically related to the gabbro diorite basalt andesite fractionation trends seen in the zoned plutons zoned plutons in deeply eroded arcs provide physical evidence that crystal fractionation plays an important role in andesite petrogenesis

basement rocks of halmahera eastern indonesia implications for the early history of the philippine sea the oldest rocks known on halmahera eastern indonesia are petrologically and chemically similar to supra subduction ophiolites and include boninitic volcanics resembling those dredged from the marianas forearc the age of the ophiolitic rocks is unknown in east halmahera they are overlain by late cretaceous and eocene volcanics and associated sediments similar volcanics form the basement of western halmahera plutonic rocks intruding the ophiolite and associated metamorphic rocks also yield late cretaceous to eocene radiometric ages the petrology and chemistry of the igneous rocks indicate an island arc origin these rocks are locally overlain by shallow water eocene limestones and all are overlain unconformably by neogene sediments the halmahera basement rocks have many structural petrological and stratigraphic similarities to submarine plateaus of the southern and northern philippine sea and basement terranes of the eastern philippines the authors suggest that these similarities indicate the existence of an extensive region of late cretaceous and eocene volcanism built upon probable mesozoic ophiolitic basement the resultant thickened crust was later fragmented by spreading in the west philippine sea central basin and backarc spreading in the eastern philippine sea it is difficult to reconcile the present distribution of these crustal fragments with a linear arc but equally more difficult to propose a simple alternative a proto philippine archipelago with short lived arcs separated by small oceanic basins may be the closest modern analog the development of younger subduction zones has been influenced by the distribution of thickened crustal fragments as they have re amalgamated since the miocene less

distribution and origin of igneous rocks from the landward slopes of the mariana trench implications for its structure and evolution the landward slope of the mariana trench is composed largely of igneous rocks serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m seamountlike features on the trench slope break are the surface expression of serpentinite diapirs cumulate and massive gabbros are found several varieties of volcanic rocks are common including boninites altered and metamorphosed basalts andesites and dacites the chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism together with the gabbros these volcanic rocks represent what is probably a late eocene arc complex these rocks were probably the first volcanic products to result from the subduction of the pacific plate beneath the phillippine sea plate their exposure on the trench slope today implies a significant amount of tectonic erosion of the landward slope since eocene time most of this removal of material appears to have occurred during the early stages of subduction there are isolated occurrences on the landward slope of rock assemblages including alkalic basalts chert hyaloclastites upper cretaceous siliceous sediments and shallow water limestones these assemblages are very similar to rocks dredged from seamounts on the offshore flankmore of the trench and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion there has been episodic accretion of seamount fragments to the landward slope less

magmas and magma chamber evolution troodos ophiolite cyprus the troodos ophiolite traditionally has been considered to have formed by constructive processes at an oceanic spreading center new information on the phase layering and cryptic variation in gabbros and ultramafic cumulates overlying tectonized harzburgites however does not support the existence of a large steady state frequently replenished axial magma chamber compositional evidence suggests that the troodos ophiolite was formed by two distinct and chemically unrelated magmatic systems a stratigraphically lower websteritic and gabbroic cumulate sequence exhibits only one major magma chamber replenishment suggesting a nonspreading environment an upper gabbroic cumulate sequence suggests frequent magma chamber replenishments pointing to a relatively fast spreading environment this suggests that the alleged troodos axial magma chamber formed in an off axis nonspreading tectonic environment probably by magmatic underplating of a thin oceanic crust spreading related magmatic activity in the troodos ophiolite was confined to the upper gabbros and dike complex

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

origin and emplacement of ophiolites ever since their recognition ophiolites have been a source of controversy although all workers have agreed upon their importance a number of conflicting schools of thought have become unified in the interpretation of ophiolite complexes as fragments of oceanic crust and mantle formed at spreading centers an expanded version of the penrose ophiolite definition is proposed herein called the ophiolite association taking into account rocks which bear upon the origin and significance of ophiolite complexes an ideal ophiolite association includes the following units from bottom to top 1 a crystalline basement and shallow water sedimentary sequence 2 a tectonic unit of thrust slices of continental margin and rise and abyssal sediments and or melange 3 a metamorphic unit as much as a few hundred meters thick generally with higher grade rocks over lower grade ones 4 ultramafic tectonite unit composed dominantly of multiply deformed peridotite dunite and minor chromitite 5 a cumulate complex ultramafic at the base grading to mafic or intermediate at the top 6 a noncumulus unit of varitextured gabbro and minor trondhjemite 7 a sheeted dike complex 8 an extrusive section of massive and pillowed flows and intercalated sediments 9 an abyssal or bathyal sediment sequence which may include radiolarian chert red pelagic limestone metalliferous sediments breccias and or pyroclastic deposits and 10 postemplacement deposits of laterite reef limestone or shallow marine or subaerial sediments this expanded ophiolite association allows greater precision in inferring original origin and emplacement some ophiolite complexes particularly in the tethys herein designated tethyan type exhibit units 1 2 3 and 4 whereas others particularly in the cordilleran belt herein termed cordilleran type lack units 1 2 3 and in places 4 the emplacement of the former probably occurred during collision of a passive margin with a subduction zone or incipient subduction zone emplacement of the cordilleran type generally is not clear cut the nature of the spreading center which produced a given ophiolite is indicated more clearly by the presence or absence of units 5 9 than by chemistry or mineralogy some ophiolite complexes lack complete sections and may have formed along transform faults others contain volcanic pyroclastic deposits instead of pelagic sedimentary sequence and probably formed within or near an arc several ophiolite complexes may have originated by conversion of a transform fault into a subduction zone such conversion may result from normal plate evolution or from major plate reorganization major times of ophiolite emplacements appear to correspond with global plate reorganizations

petrology and geochemistry of the plutonic rocks of the halmahera ophiolite eastern indonesia an analogue of modern oceanic forearcs

geochemistry of cumulus peridotites and gabbros from the marum ophiolite complex northern papua new guinea the layered cumulus rocks of the marum ophiolite complex in northern papua new guinea range from highly magnesian dunite wehrlite and lherzolite through pyroxenite to norite gabbro with minor anorthosite and ferronorite gabbro near the top of the sequence most of the cumulates particularly the gabbroic rocks are characterised by recrystallised adcumulus textures and all intercumulus melt mesostasis has been expelled trends in the cumulate sequence from mg rich to more fe ca and al rich compositions are consistent with the formation of the layered sequence by magmatic accumulation from mafic tholeiitic magmas with varying degrees of differentiation the cumulates are characterised by extremely low levels of incompatible elements k ba rb p zr nb hf y and ree at all levels of differentiation ree patterns are strongly depleted in lree hree abundances range from 0 3 chondrites in peridotite to 3 x chondrites in the norite gabbros

climate controlled variability of iron deposition in the central arctic ocean southern mendeleev ridge over the last 130 000 years abstract distinct brown coloured mn rich layers are common features in quaternary sediments of the central arctic ocean but their paleoenvironmental significance is disputed glacial interglacial changes in bottom water ventilation variable riverine input and diagenetic processes have all been suggested to cause the cyclicity in optical and geochemical parameters in these deposits to better assess the nature and origin of these sediment intervals and their implications for nutrient cycles we applied bulk geochemical analyses and a sequential fe extraction scheme to a sediment record covering the last 130 ka on the southern mendeleev ridge all brown layers in this core are enriched in mn but also in fe oxyhydr oxides e g ferrihydrite lepidocrocite goethite that contribute to the characteristic sediment colour phosphorus and several trace metals as co cu mo ni are also enriched indicating that both mn and fe oxyhydr oxides adsorbed p and trace metals from the water column the metal enrichments are most probably caused by a combination of enhanced mn and fe input from arctic rivers and or the erosion of shelf deposits coupled with early diagenetic processes leading to precipitation of authigenic mn and fe oxyhydr oxides close to the sediment water interface both primary supply and diagenetic recycling of metals should have been enhanced by a more intense hydrological cycle under warmer climate conditions combined with seasonal increases in productivity and reactive organic matter export during ice free conditions in the central arctic ocean consequently the studied metal oxyhydr oxide rich layers were formed under interglacial interstadial climatic conditions in contrast sheet silicate bound fe e g chlorite a second major fe pool in these sediments 15 35 of total fe is enriched between the oxide rich layers thus the delivery of fe rich sheet silicates from the east siberian hinterland or the bering sea and subsequent deposition on the mendeleev ridge was enhanced by more intense physical weathering during glacial stadial periods these contrasts in fe speciation between the brown layers and the adjacent sediments document the direct response of biogeochemical element cycles to glacial interglacial variations in river input weathering regime and sea level in the arctic ocean

freshwater fluxes through the western fram strait two hydrographic and d18o transects across fram strait aug sept 1997 1998 are used to examine freshwater contributions to the east greenland current egc the egc featured up to 16 meteoric water in both years but was made comparatively more saline through the formation of up to 11 m of sea ice we derive meteoric water fluxes of 3680 km3yr 1 in aug sept 1997 and 2000 km3yr 1 in aug sept 1998 the 1997 and 1998 data show a long term me m sea ice flux through fram strait around half the long term mean meteoric water flux a 1991 d18o section bauch et al 1995 yielded a very similar ratio our 1998 section reveals fresh 1ow 6180 water on the east greenland shelf whose comparatively large volume constitutes a potentially significant contribution to the total freshwater flux through fram strait such fluxes are important to the regional and global thermohaline circulation we suggest that efforts towards monitoring both the egc and east greenland shelf waters are thus required

petrology and geochemistry of boninite series volcanic rocks from the mariana trench boninite series volcanic rocks have been recovered from three dredge hauls on the inner slope of the mariana trench these hauls included olivine boninites boninites boninitic andesites and boninitic dacites as well as island arc tholeiitic basalts and andesites the boninite series volcanics range from 52 to 68 sio2 and are characterized by very low abundances of high field strength cations and heavy rare earth elements boninites and olivine boninites have phenocrysts of olivine and orthopyroxene the andesites phenocrysts of orthopyroxene and clinopyroxene and the dacites orthopyroxene clinopyroxene and plagioclase most of the major and trace element variation in the series from boninite to boninitic dacite can be modelled by fractionation of olivine orthopyroxene clinopyroxene and plagioclase in the proportions 2 5 4 1 2 leaving 47 residual liquid the fractionation must be in part open system reverse zoned phenocrysts resorbed olivine and plagioclase xenocrysts and bulk rock compositions which cannot be fit by simple closed system crystallization indicate some magma mixing and phenocryst accumulation two boninitic magma stems can be identified with similar high field strength element abundances but different amounts of ca na al and light rare earth elements there is also evidence for a magma stem transitional in chemistry from the boninites to arc tholeiites the compositions of these boninites are consistent with hypotheses for boninite formation by partial melting of a depleted mantle mixed with an incompatible element enriched fluid the mariana forearc boninite series lacks a strong iron enrichment but produces andesites with lower ti al and y zr and higher mg ni and cr than typical calcalkaline arc andesites and dacites boninites in the mariana system were erupted only in the earliest phases of subduction zone activity

source and tectono metamorphic evolution of mafic and pelitic metasedimentary rocks from the central quetico metasedimentary belt archean superior province of canada abstract a study of the sedimentary rocks in the jean lake area of the quetico metasedimentary belt superior province canada was conducted in order to evaluate the origin source and evolution of rocks including mafic rocks previously mapped as ultramafics rocks bulk compositions of these sedimentary rocks show a mixing between two end members quartzo feldspathic sedimentary rock and komatiitic basalt high cao and mgo contents of the rocks suggest a proximal source of the komatiitic basalt the rocks in the study area record a pressure temperature p t path with three tectono metamorphic stages the first stage formed staurolite 500 700 c under medium p t mp mt metamorphic conditions shortly after the sedimentation the second stage yielded the biotite sillimanite garnet assemblage under the peak conditions of 0 6 0 1 gpa and 700 70 c during transpressional deformation the third stage low p medium t lp mt 0 25 0 11 gpa 540 80 c metamorphism was associated with regional south southeast compression and its timing is constrained by a new u th pb monazite age of 2667 20 ma combining the regional deformation events we suggest the burial metamorphism of sediments up to mp mt conditions during the d1 deformation at 2698 2689 ma they attained the peak metamorphic conditions during the regional transpressive d2 d3 deformation 2689 2671 ma and retrograded to lp mt condition during the south southeast compression regional d4 at 2671 2667 ma a short time span between the sedimentation and mp mt metamorphism accompanied by d1 deformation suggest that the quetico sedimentary rocks formed in an acretionary prism the studied rocks in the jean lake area deposited close to the wabigoon subprovince transported towards the south and buried up to 20 km by rapid underthrusting to amphibolite facies conditions subsequent dextral transpressive deformation d2 d3 during the oblique docking of the quetico belt to the wabigoon subprovince to the north and wawa greenstone belt from the south resulted in the displacement of the sedimentary rocks to the west from the original depositional site the p t time path of the quetico sedimentary rocks is similar to that in modern arc accretion prisms except for a high geothermal gradient of 30 c km recorded in the former compared to 10 c km in modern counterparts the high temperature gradient in the archean accretionary prism explains the lack of high pressure metamorphic rocks such as blueschist that are common in modern accretionary prisms

the west philippine basin an eocene to early oligocene back arc basin opened between two opposed subduction zones 1 based on geological and geophysical data collected from the west philippine basin and its boundaries we propose a comprehensive cenozoic history of the basin our model shows that it is a back arc basin that developed between two opposed subduction zones rifting started around 55 ma and spreading ended at 33 30 ma the initial spreading axis was parallel to the paleo philippine arc but became inactive when a new spreading ridge propagated from the eastern part of the basin reaching the former one at an r r r triple junction spreading occurred mainly from this second axis with a quasi continuous counter clockwise rotation of the spreading direction the gagua and palau kyushu ridges acted as transform margins accommodating the opening arc volcanism occurred along the palau kyushu ridge eastern margin during the whole opening of the basin whereas the paleo philippine arc decreased its activity between 43 and 36 ma the western margin underwent a compressive event in late eocene early oligocene time leading to the rising of the gagua ridge and to a short subduction episode along eastern luzon in the western part of the basin the spreading system was highly disorganized due to the presence of a mantle plume overlapping spreading centers and ridge jumps occurred toward the hot region and a microplate developed shortly after the end of the spreading a late stage of amagmatic extension occurred between 30 and 26 ma in the central part of the basin being responsible for the deep rift valley that cut across the older spreading fabric

inputs of glacially derived dissolved and colloidal iron to the coastal ocean and implications for primary productivity 1 glacial meltwaters draining shield bedrock under the greenland ice sheet gis contain 0 4 m total dissolved fe tdfe with an average flow weighted concentration of 53 nm the concentrations of 0 03 and 0 03 0 4 m fe vary over the ablation period with weighted means for each of these fractions being respectively 22 4 nm and 30 8 nm these concentrations are lower estimates as an adjacent larger glacier a more representative source of glacial meltwater had higher dissolved fe concentrations and reactions of meltwaters with proglacial sediments could also enhance dissolved fe concentrations this source of tdfe is additional to the reactive oxyhydr oxide phases identified by raiswell et al 2006 that are also introduced to adjacent polar seas from glaciers the fe concentrations in the shield bedrock underlying the gis are lower than those of other crustal rocks 4 0 cf 6 2 but we argue that these fe concentrations are not limiting on the total dissolved fe concentrations we measure the biogeochemical weathering processes operating on the subglacial debris and suspended sediment in our catchment are likely to be similar to those in other glaciated catchments therefore the meltwater fe concentrations reported here can be used to give a first estimate of global fluxes of meltwater dissolved fe to coastal polar waters a lower estimate of the global flux of tdfe from glacial meltwaters is 75 106 moles fe a this glacial meltwater input of fe to adjacent polar waters will be greatest around greenland where there are highest annual meltwater discharges however the greatest impact of this source of glacial meltwater fe is anticipated to be in antarctic high nutrient low chlorophyll hnlc waters where phytoplankton productivity is typically limited by availability of fe for antarctic waters the estimated meltwater fe tdfe input is about 10 of that suggested to come from sea ice melting but glacial inputs continue throughout the austral summer ablation period after sea ice melt is complete

hydrogen isotope values in lacustrine kerogen abstract kerogen derived from plankton and sedge cattail that accumulated in sediment during two distinct phases of swan lake s development was extracted from segments of radiocarbon dated cores carbon c hydrogen h and nitrogen n amounts and the d values of kerogen extracts were determined kerogen extracts younger than 3900 ybp contained higher average h c and n c atom ratios than older kerogen 5000 to 3900 ybp the more recent kerogen extracts were derived primarily from plankton in open water sediment and are characterized by significantly higher lipid and protein fractions than those from the sedge cattail that formed the marsh layer plankton derived kerogen was more depleted in d averaging 20 per mil lighter than that from older extracts 5000 to 3900 ybp which according to pollen analysis were dominated by sedge cattail derived kerogen in the sediment profiles differences in the d values appear more related to kerogen source than to postdepositional hydrogen loss or temperature

cenozoic motion of the philippine sea plate palaeomagnetic evidence from eastern indonesia the history of motion of the philippine sea plate is poorly known because it is isolated from the oceanic ridge system interpretation of palaeomagnetic results from the plate has been controversial because declination data have been obtained only from the eastern margin where subduction related tectonic processes may have caused local rather than plate wide rotations new palaeomagnetic data relevant to the problem have been obtained from 34 sites north of the sorong fault and 29 sites within the sorong fault system these sites record south ward movement during the eocene and northward movement during the neogene sites within the sorong fault system record both counterclockwise and clockwise rotations interpreted as the result of neogene block movements at the southern boundary of the philippine sea plate north of the sorong fault all sites record clockwise declinations neogene rocks have small deflections consistent with rotation about the present day eurasia philippine sea plate pole oligocene middle eocene rocks show consistent clockwise declination deflections of 40 o declinations of lower eocene rocks indicate 90 o of clockwise rotation we propose that the entire area north of the sorong fault in east indonesia has always been part of the philippine sea plate and that the whole plate has rotated clockwise in a discontinuous manner by approximately 90 o since the early eocene the new data from north of the sorong fault provide a basis for determining rotation poles which satisfy all the palaeomagnetic data from the philippine sea plate and permit its reconstruction

free drifting icebergs as sources of iron to the weddell sea abstract in recent years glaciers on the antarctic peninsula have retreated resulting in loss of mass from ice shelves and increased supply of icebergs to the southern ocean free drifting icebergs may serve as an important source of fe to surrounding waters we measured concentrations of dissolved fe and fe content of suspended particulate material via flow injection chemiluminescence and icp ms respectively in the waters surrounding several icebergs during cruises to the scotia and weddell seas in june 2008 and march 2009 surface dissolved fe dfe concentrations varied from 0 58 to 2 92 nm and were elevated up to 60 at some stations 10 km from the icebergs indicating general fe enrichment in the lower salinity surface layer however surface dfe within 1 km of the iceberg was similar to that measured at depths below the draft of the iceberg a feature that may result from upwelling of circumpolar deep water caused by basal melting at the face of the iceberg iron concentrations in ice collected following calving events were highly variable 4 600 nm but were elevated above concentrations in seawater particulate fe normalized to particulate p in suspended particulate material was up to 20 fold higher within 0 6 km of two large tabular icebergs but no enrichment was observed at two smaller icebergs iron phosphorus ratios of suspended particulate material were also higher in deeper 40 m waters compared to shallow ca 15 m waters at the iceberg face iron release appeared to be episodic producing a spatially heterogeneous environment around icebergs this source term may increase in coming years as antarctic ice shelves degrade further potentially impacting the ecology and biogeochemistry of low fe waters of the southern ocean

reconstruction of the variability of the southwest monsoon during the past 3 ka from the continental margin of the southeastern arabian sea from temporal variation in 18o in globigerinoidesruber and g sacculifer and geochemical indices of weathering erosion chemical index of alteration al and ti we infer rapid southwest monsoon swm deterioration with dwindling fluvial and detrital fluxes at ca 450 650 1000 and 1800 2200 cal a bp during the late holocene we have evaluated the role of solar influx reconstructed and high latitude climate variability archived in grip and gisp 2 cores on swm precipitation broadly our 18o climate reconstruction is concordant with grip and gisp 2 and supports a teleconnection through atmospheric connection between the swm and the north atlantic climate albeit temporal extents of the little ice age and medieval warm period from high latitude are not entirely coeval moreover there is a humid climate and enhanced precipitation during the terminal stages of the little ice age the medieval warming ca ad 800 1300 is not synchronous either and is punctuated by an arid event centred at 1000 a bp although the delineation of the specific influence of solar influx on swm precipitation is elusive we surmise that swm precipitation is a complex phenomenon and local orography along southwestern india may have a role on the entrapment of moisture from the southwest trade winds when these hit land copyright 2009 john wiley sons ltd

plate boundary evolution in the halmahera region indonesia abstract halmahera is situated in eastern indonesia at the southwest corner of the philippine sea plate active arc arc collision is in process in the molucca sea to the west of halmahera new stratigraphic observations from halmahera link this island and the east philippines and record the history of subduction of the molucca sea lithosphere the halmahera basement complex and the basement of east mindanao were part of an arc and forearc of late cretaceous early tertiary age and have formed part of a single plate since the late eocene early oligocene there is no evidence that halmahera formed part of an oligo miocene arc but arc volcanism associated with eastwards subduction of the molucca sea beneath halmahera began in the pliocene and the pliocene arc is built on a basement of the early tertiary arc arc volcanism ceased briefly during the pleistocene and the arc shifted westwards after an episode of deformation the present active arc is built upon deformed rocks of the pliocene arc the combination of new stratigraphic information from the halmahera islands and models of the present day tectonic structure of the region deduced from seismic and other geophysical studies is used to constrain the tectonic evolution of the region since the miocene diachronous collision at the western edge of the philippine sea plate which began in mindanao in the late miocene impeded the movement of the philippine sea plate and further motion has been achieved by a combination of strike slip motion along the philippine fault subduction at the philippine trench and subduction of the molucca sea lithosphere beneath halmahera

a paleoproterozoic ultramafic mafic assemblage and associated volcanic rocks of the boromo greenstone belt fractionates originating from island arc volcanic activity in the west african craton abstract the loraboue birimian ultramafic mafic assemblage located in the boromo greenstone belt burkina faso is interpreted as the remains of a magma chamber that crystallized at the base of an island arc the ultramafic rocks exhibit an heteradcumulate texture being generally made up of wehrlites and more rarely dunites the crystallization sequence inferred from the cumulates is olivine chromite followed by clinopyroxene amphibole orthopyroxene biotite the gabbroic rocks are mainly layered and grade into more differentiated facies with sub pegmatitic texture containing up to 70 modal plagioclase including zircon and more commonly apatite crystals textural relationships and mineral phase chemistry are indicative of crystallization at elevated pressures 8 kbar the parental magma being generated by a moderate to high degree of partial melting of a mantle source affected by previous metasomatic events above a subducted oceanic slab the loraboue volcanic formations exhibit a range of geochemical features they consist dominantly of calc alkaline basalts pyroclastites and rhyolite and more rarely of basalt dolerite and gabbro of tholeiitic affinity these different types of basalt as well as the dolerite and the isolated massive gabbro show the classic features of arc magmatic suites namely lile and pb enrichment depleted hfse patterns and high ce nb and th nb ratios thus the calc alkaline plutonic and volcanic assemblages of loraboue could represent the roots of an island arc and the associated coeval volcanic rocks the paleoproterozoic crust of the west african craton was heterogeneous and was not the consequence of a single process of genesis as some modern igneous province the birimian crust was generated by both volcanic arc accretion and oceanic plateau accretion

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

gravity fields in eastern halmahera and the bonin arc implications for ophiolite origin and emplacement classic ophiolites as exemplified by the troodos massif in cyprus and the papuan ultramafic belt in eastern new guinea are large overthrust masses which are generally associated with large positive gravity anomalies however similar rocks occurring in extensive fragmented terranes which have also been described as ophiolitic do not produce large gravity effects the eastern part of the island of halmahera in northeastern indonesia is an ophiolite of this latter type on the two eastern arms of the island a mesozoic ophiolitic basement is overlain by and imbricated with upper cretaceous and paleogene arc volcanic and sedimentary rocks bouguer gravity values are generally in the range 50 to 150 mgal and are characterised by steep local gradients indicative of shallow sources the bouguer gravity average suggests that the crust is at least 20 km thick and it must be even thicker if a significant part of the anomalous gravity field is due to the presence of a cold and therefore dense lithospheric slab within the asthenosphere associated with the present day subduction beneath halmahera the absence of any exposures of continental basement rocks or of quartzose sediments in eastern halmahera suggests that these ophiolites have not been overthrust onto continental crust and that the thickening occurred in an intraoceanic island arc the paleogene arc was evidently characterised by volcanism occurring over an unusually wide area in this it resembles the izu bonin volcanic arc which like halmahera has been situated at the margin of the philippine sea plate throughout its history the gravity field of the halmahera ophiolite is comparable with that of the bonin volcanic arc but there is no halmahera parallel to the very high gravity fields recorded over the bonin islands forearc ridge the equivalents of this part of the paleogene arc may be represented by the ophiolitic complexes now distributed along the northern margin of the orogenic belt in new guinea

benthic iron and phosphorus fluxes across the peruvian oxygen minimum zone benthic fluxes of dissolved ferrous iron fe2 and phosphate tpo4 were quantified by in situ benthic chamber incubations and pore water profiles along a depth transect 11 s 80 1000 m across the peruvian oxygen minimum zone omz bottom water o2 levels were 2 mol l 1 down to 500 m water depth and increased to 40 mol l 1 at 1000 m fe2 fluxes were highest on the shallow shelf maximum 316 mmol m 2 yr 1 moderate 15 4 mmol m 2 yr 1 between 250 m and 600 m and negligible at deeper stations in the persistent omz core continuous reduction of fe oxyhydroxides results in depletion of sedimentary fe al ratios tpo4 fluxes were high maximum 292 mmol m 2 yr 1 throughout the shelf and the omz core in association with high organic carbon degradation rates ratios between organic carbon degradation and tpo4 flux indicate excess release of p over c when compared to redfield stoichiometry most likely this is caused by preferential p release from organic matter dissolution of fish debris and or p release from microbial mat communities while fe oxyhydroxides can only be inferred as a major p source on the shallow shelf the benthic fluxes presented here are among the highest reported from similar oxygen depleted environments and highlight the importance of sediments underlying anoxic water bodies as nutrient sources to the ocean the shelf is particularly important as the periodic passage of coastal trapped waves and associated bottom water oxygenation events can be expected to induce a transient biogeochemical environment with highly variable release of fe2 and tpo4

advection of atlantic water to the western and northern svalbard shelf since 17 500 cal yr bp abstract the changes in flow and character of the warm atlantic water through the last 17 500 cal yr are reconstructed from the distribution of benthic foraminifera species planktonic and benthic foraminifera abundances stable oxygen isotopes and lithology in two cores from the western and northern shelf of svalbard the results show almost continuous presence of atlantic water at the shelf areas since 14 500 cal yr bp the bolling and allerod intervals stand out as periods of highest bottom waters temperatures the strong inflow of saline but chilled atlantic water during the early holocene was followed by cooling and freshening of the bottom waters during the mid and late holocene the two records reveal synchronous oceanographic changes that are closely tied to changes in the flow of atlantic water recorded further south in the nordic seas the early holocene warming was not just an effect of higher solar insolation but was also due to increased heat flux from the stronger atlantic water inflow driven by wind force and or thermohaline circulation

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

recent distribution and accumulation of organic carbon on the continental margin west off spitsbergen the study compiles the controlling factors for organic matter sedimentation patterns from a suite of organogeochemical parameters in surface sediments off spitsbergen and direct seabed observations using a remotely operated vehicle rov in addition we assess its storage rates as well as the potential of carbon sinks on the northwestern margin of the barents sea with short sediment cores from a selected fjord environment storfjord while sedimentation in the fjords is mainly controlled by river meltwater discharge and coastal erosion by sea ice glaciers resulting in high supply of terrigenous organic matter atlantic water inflow and thus enhanced marine organic matter supply characterizes the environment on the outer shelf and slope local deviations from this pattern particularly on the shelf are due to erosion and out washing of fine grained material by bottom currents spots dominated by marine productivity close to the island have been found at the outer isfjord and west off prins karls forland as well as off the kongsfjord krossfjord area and probably reflect local upwelling of nutrient rich atlantic water derived water masses accumulation rates of marine organic carbon as well as reconstructed primary productivities decreased since the middle of the last century negative correlation of the isfjord temperature record with reconstructed productivities in the storfjord could be explained by a reduced annual duration of the marginal ice zone in the area due to global warming extremely high accumulation rates of marine organic carbon between 5 4 and 17 2 g m 2 yr 1 mark the storfjord area and probably high latitude fjord environments in general as a sink for carbon dioxide

basement rocks of the halmahera region eastern indonesia a late cretaceous early tertiary arc and fore arc halmahera is a k shaped island located at the junction of several major arc trench systems of the western pacific eastern indonesia region western halmahera is an active volcanic arc above a zone of intense seismicity which characterizes the north molucca sea eastern halmahera has a basement of dismembered ophiolitic rocks with slices of mesozoic and eocene sediments overlain unconformably by middle oligocene and younger sedimentary and volcanic rocks the mesozoic and eocene sediments reveal notable stratigraphical and petrological similarities to the marianas fore arc and the eastern halmahera basement complex is interpreted as a pre oligocene fore arc lacking an accretionary complex there is some evidence that the pre oligocene volcanic arc behind this fore arc now forms part of the basement of western halmahera the mesozoic and tertiary sediments were imbricated together with igneous and metamorphic rocks representing the deeper parts of the fore arc during the late eocene plate reorganization event recognized throughout the western pacific margins the eastern halmahera basement complex can be traced into eastern mindanao probably further northwards in the eastern philippines and may be related to similar terranes within and around the present philippine sea plate in contrast the southern part of the island of bacan at the southwestern end of the halmahera group has a basement of continental metamorphic rocks associated with a deformed ophiolitic complex quite different to the basement of eastern halmahera the metamorphic rocks are interpreted to be part of the north australian continental margin basement which is separated from the halmahera basement complex by a splay of the sorong fault system and the deformed ophiolite complex of bacan is suggested to represent magmatism in the fault zone

iron and manganese speciation and cycling in glacially influenced high latitude fjord sediments west spitsbergen svalbard evidence for a benthic recycling transport mechanism abstract glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese phases to the coastal ocean in high latitude regions little is known about the fate and biogeochemical cycling of glacially derived iron and manganese in the coastal marine realm sediment and porewater samples were collected along transects from the fjord mouths to the tidewater glaciers at the fjord heads in smeerenburgfjorden kongsfjorden and van keulenfjorden along western svalbard solid phase iron and manganese speciation determined by sequential chemical extraction could be linked to the compositions of the local bedrock and hydrological weathering conditions below the local glaciers the concentration and sulfur isotope composition of chromium reducible sulfur crs in kongs and van keulenfjorden sediments largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers the varying input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the pathways of organic carbon mineralization in the sediments of the three fjords high reducible iron and manganese oxide concentrations and elevated metal accumulation rates coupled to low input of fresh organic matter lead to a strong expression of dissimilatory metal oxide reduction evidenced in very high porewater iron up to 800 m and manganese up to 210 m concentrations in kongsfjorden and van keulenfjorden sediment reworking by the benthic macrofauna and physical sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese cycling in these fjords on going benthic recycling of glacially derived dissolved iron into overlying seawater where partial re oxidation and deposition occurs facilitates the transport of iron across the fjords and potentially into adjacent continental shelf waters such iron dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond by contrast low delivery of reducible iron oxyhydr oxide phases and elevated organic carbon mineralization rates driven by elevated input of fresh marine organic matter allow organoclastic sulfate reduction to dominate carbon remineralization at the outer smeerenburgfjorden sites which may limit iron fluxes to the water column

origin and motion history of the philippine sea plate abstract the philippine sea plate is the one major plate whose tertiary motion is poorly constrained and whose origin is problematical its southern boundary is the sorong fault system which is part of a major left lateral fault system at the northern margin of the australian plate the southern part of the plate in eastern indonesia has been neglected in most syntheses but includes some of the oldest rocks within the plate which are separated from remnant arcs of the daito ridge province of the northern philippine sea by the west philippine central basin the east indonesian islands of the halmahera waigeo region contain a good mesozoic and tertiary stratigraphic record indicating a long arc history for the southern part of the plate new palaeomagnetic data from these islands define two sub areas an area forming part of the philippine sea plate north of the sorong fault and an area within the sorong fault system the area north of the fault records a long term clockwise rotation history whereas that within the fault zone records local rotations interpreted as due to deformation at the plate edge rocks of philippine sea plate origin within both areas record similar latitudinal shifts the rotation of the area north of the sorong fault is considered to represent the motion of the southern part of the philippine sea plate the new data indicate large tertiary clockwise rotations similar to earlier suggestions for other parts of the plate but record a discontinuous and more complex motion history than previously suggested for the southern part of the plate there was 40 rotation with northward translation between 0 and 25 ma no significant rotation between 25 and 40 ma and there was 50 rotation with southward translation between 40 and 50 ma we show that the new palaeomagnetic data form part of a single set with earlier palaeomagnetic data from elsewhere in the plate the translation history of the southern part of the plate in eastern indonesia can be reconciled with northward motions recorded elsewhere and can be used to determine rotation poles for the plate 15 n 160 e for the interval 5 25 ma and 10 n 150 e for the interval 40 50 ma reconstructions based on these poles predict that at 45 ma the palau kyushu ridge had a wnw ese orientation which is very different from that postulated by many models used to explain the widespread boninite volcanism in the izu bonin marians forearc at this time the long arc history of the southern part of the plate and the reconstructions based on the rotation poles calculated from the palaeomagnetic data favour an origin for the west philippine basin by spreading in a backarc basin

holocene climate variability revealed by oxygen isotope analysis of sphagnum cellulose from walton moss northern england abstract stable isotope analyses of sphagnum alpha cellulose precipitation and bog water from three sites across northwestern europe raheenmore ireland walton moss northern england and dosenmoor northern germany over a total period of 26 months were used to investigate the nature of the climatic signal recorded by sphagnum moss the 18o values of modern alpha cellulose tracked precipitation more closely than bog water with a mean isotopic fractionation factor cellulose precipitation of 1 0274 0 001 1 27 sub samples of isolated sphagnum alpha cellulose were subsequently analysed from core wlm22 walton moss northern england yielding a sphagnum specific isotope record spanning the last 4300 years the palaeo record calibrated using the modern data provides evidence for large amplitude variations in the estimated oxygen isotope composition of precipitation during the mid to late holocene estimates of palaeotemperature change derived from statistical relationships between modern surface air temperatures and 18oprecipitation values for the british isles give unrealistically large variation in comparison to proxies from other archives we conclude that use of such relationships to calibrate mid latitude palaeo data must be undertaken with caution the 18o record from sphagnum cellulose was highly correlated with a palaeoecologically derived index of bog surface wetness bsw suggesting a common climatic driver

molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction a 40 cm deep sphagnum dominated peat monolith from bolton fell moss in northern england was systematically investigated by lipid molecular stratigraphy and compound specific 13c and d analysis using gas chromatography gc gc mass spectrometry gc ms gc combustion isotope ratio ms gc c irms and gc thermal conversion irms gc tc irms techniques 210pb dating showed the monolith accumulated during the last ca 220 yr a period encompassing the second part of little ice age while the distributions of lipids including n alkan 1 ols n alkan 2 ones wax esters sterols n alkanoic acids alkandioic acids and hydroxy acids display relatively minor changes with depth the cooler climate event was recorded in the concentrations of n alkanes and organic carbon cpi values of n alkanes and n alkanoic acids and the ratio of 5 n alkylresorcinols sterols superimposed on the fossil fuel effect the relatively cooler climate event was also recorded by 13c values of individual hydrocarbons especially the c23n alkane a major compound in certain sphagnum spp the d values of the c29 and c33n alkanes correlated mainly with plant composition and were relatively insensitive to climatic change in contrast the c23n alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in scotland germany and the usa with more negative values occurring during the second part of little ice age these biomarker characteristics including the compound specific 13c and d records provide a new set of proxies of climatic change potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced

acceleration in thinning rate on western svalbard glaciers 1 geodetic measurements indicate that a number of glaciers in western svalbard ranging in size from 5 1000 km2 are losing mass at an accelerating rate the average thinning rate for midtre lovenbreen the glacier with the best data coverage has increased steadily since 1936 thinning rates for 2003 2005 are more than 4 times the average for the first measurement period 1936 1962 and are significantly greater than presented previously on slakbreen thinning rates for the latest measurement period 1990 2003 are more than 4 times that of the period 1961 1977 thinning of several glaciers along a previously measured airborne lidar profile in wedel jarls land has also increased doubling between the period 1990 1996 and 1996 2002 our results imply an increased sea level contribution from svalbard in addition the mass loss is an important influence on measured rates of rebound on western svalbard and should be factored into analysis of grace results

mid ocean ridge and supra subduction affinities in the pindos ophiolites greece implications for magma genesis in a forearc setting abstract the pindos ophiolitic massif is considered an important key area within the albanide hellenide ophiolitic belt and is represented by two tectonically distinct ophiolitic units 1 a lower unit including an intrusive and a volcanic section and 2 an upper ophiolitic unit mainly including mantle harzburgites both units share similar metamorphic soles and tectono sedimentary melanges at their bases the intrusive section of the lower unit is composed by an alternation of troctolites with various ultramafic rock types including dunites lherzolites olivine websterites olivine gabbros anorthositic gabbros gabbros and rare gabbronorites the volcanic and subvolcanic sequence of the lower unit can geochemically be subdivided into three groups of rocks 1 basalts and basaltic andesites of the lower pillow section showing a clear high ti affinity 2 basaltic andesites of the upper pillow section with high ti affinity but showing many geochemical differences with respect to the first group 3 very low ti boninitic basaltic and basaltic andesitic lava flows separating the lower and upper pillow sections and dykes widespread throughout the pindos ophiolites these different magmatic groups originated from fractional crystallization from different primary magmas which were generated in turn from partial melting of mantle sources progressively depleted by previous melt extractions group 1 volcanics may have derived from partial melting ca 20 of an undepleted lherzolitic source while group 2 basaltic rocks may have derived from partial melting ca 10 of a mantle that had previously experienced mid ocean ridge basalt morb extraction finally the group 3 boninites may have derived from partial melting ca 12 17 of a mantle peridotite previously depleted by primary melt extraction of groups 1 and 2 primary melts in order to explain the coexistence of these geochemically different magma groups two petrogenetic models formerly proposed for the albanian ophiolites are discussed

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications

palaeoclimate records in compound specific δd values of a lipid biomarker in ombrotrophic peat compound specific d values recorded by means of gas chromatography thermal conversion isotope ratio mass spectrometry gc tc irms of the biomarker n alkane n tricosane n c23 representative of the dominant sphagnum species in a 40 cm peat profile from bolton fell moss cumbria uk correlate with vegetation changes in the past 200 years age depth model based on 210pb dating the bog vegetation is sensitive to climate change correlating with the global scale cooler period of the later 19th and early 20th centuries the correlation with meteorological records suggests compound specific d values of lipid biomarkers have potential for use as a new climate proxy

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd