unzipping long valley an explanation for vent migration patterns during an elliptical ring fracture eruption long valley caldera california formed during the cataclysmic pleistocene eruption of the bishop tuff previous stratigraphic and petrologic studies of this eruption deciphered an intriguing pattern of vent migration thought to mirror the lateral propagation unzipping of magma tapping ring fractures during caldera collapse from scaled analog models we show that this unzipping pattern was intrinsically related to the high plan view ellipticity of the precollapse magma chamber roof we also provide a first order kinematic explanation for the systematic location of initial elliptical roof failure and for the lateral propagation of highly elliptical ring fractures

neutral carbohydrate geochemistry of particulate material in the central equatorial pacific abstract neutral carbohydrate compositions were determined for particulate samples from plankton net tows shallow floating sediment traps mid depth and deep moored sediment traps and sediment cores collected along a north south transect in the central equatorial pacific ocean during the u s jgofs eqpac program total neutral carbohydrate depth profiles and patterns along the transect follow essentially the same trends as bulk and organic carbon oc fluxes attenuating with depth high near the equator and decreasing poleward oc normalized total aldose tch 2 o yields along the transect and with depth do not show any consitent patterns relative to a planktonic source neutral carbohydrate compositions in sediment trap and sediment core samples reflect preferential loss of ribose and storage carbohydrates rich in glucose and preferential preservation of structural carbohydrates rich in rhamnose xylose fucose and mannose there is also evidence for an intermediately labile component rich in galactose it appears that compositional signatures of neutral carbohydrates in sediments are more dependent upon their planktonic source than on any particular diagenetic pathway relative to other types of organic matter neutral carbohydrates are better preserved in calcareous oozes from 12 s to 5 n than in red clays at 9 n based on oc normalized tch 2 o yields due to either differing sources or sorption characteristics weight per cent glucose generally decreases with increased degradation of organic material in the central equatorial pacific region based on weight per cent glucose comparisons of samples between survey i el nion and survey ii non el nino indicate that during survey i organic material in the epipelagic zone in the northern hemisphere may have undergone more degradation than organic material in the southern hemisphere

poleward reach of the california undercurrent extension 1 the california undercurrent is known to transport relatively warm high salinity nutrient rich water from the equatorial pacific to vancouver island along the western continental slope of north america this transport helps maintain the high productivity of the eastern boundary california current system in this study we use several decades of water property survey data for the coasts of oregon washington british columbia and alaska to show that equatorial pacific water carried poleward by the undercurrent can eventually reach the aleutian islands roughly 11 000 km from the source region long term current meter records confirm the undercurrent as far north as vancouver island where the current is found to be weakest in spring but then to strengthen through the summer and fall before merging with the wind forced poleward flowing davidson current in winter the core depth of the equatorial water increases from 150 m 25 m off northwest washington near the northern end of the western north america coastal upwelling domain to 225 m 25 m off southeast alaska near the southern end of the gulf of alaska coastal downwelling domain

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

crustal scale ductile fault systems in the arunta inlier central australia detailed geologic observations along three 100 km long traverses across the early proterozoic arunta inlier central australia indicate that paleozoic ductile shear zones are organized into crustal scale structural systems which control the map pattern and distribution of metamorphic zones two provinces can be distinguished 1 1 a southern one where shear zones form a series of hinterland dipping and south verging imbricate reverse faults in the west redbank area grading eastward into a foreland dipping duplex in the arltunga nappe complex directly north of this complex flat lying paleozoic south directed ductile shear affects a large portion of the crust a point which has been underestimated so far 2 2 the northern province is characterized by both south and north dipping shear zones showing reverse motion to produce a crustal scale pop up structure presumably resulting from a more coaxial deformation history strike slip shear zones become predominant in the eastern part of this province stratigraphic and cross cutting relationships indicate that the southern systems developed first the northern systems probably developed in response to the lock up stages of overthrusting in the southern province one important result of this work is that the distribution of granulite facies rocks and major geophysical anomalies throughout the arunta inlier is best explained by their position relative to the paleozoic ductile fault systems described above there is no need to invoke extensive proterozoic uplift of these lower crustal materials

subaqueous eruption fed density currents and their deposits density currents fed directly from subaqueous eruptions can be divided conceptually into three groups based on modes of fragmentation and transport i explosive fragmentation with deposition from a gas supported current ii explosive fragmentation with deposition from a water supported current iii fragmentation of flowing lava with deposition from a water supported current fig 1 group i products include subaqueously emplaced welded ignimbrite and other high temperature emplaced subaqueous pyroclastic flow deposits group ii products are the most varied and include representatives of both high and low concentration turbidity currents grainflows and debris flows and are termed eruption fed aqueous density currents some clasts in such currents are transported and even deposited at high temperature but the transporting currents ranging from grain flows to dilute turbidity currents are water dominated even though steam may be developed along large clasts margins group iii products formed from lava flow fed density currents tend to be weakly dispersed down gradient along the seafloor and generally consist largely of fragments formed by dynamo thermal quenching and spalling bursting of bubbles formed by vapor expansion probably contributes to some group iii beds distinctive column margin fall deposits may form in water excluded zones that developed very locally around vents in association with group i and ii deposits and are distinguished by heat retention structures indicators of gas phase transport and absence of current formed depositional features 2000 elsevier science b v all rights reserved

role of increased marine silica input on paleo pco2 levels changing the supply of silica to the ocean may alter pco2 levels the increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake the increased silica levels shifted species composition diatom populations increased and coccolith populations decreased decreasing the population of coccoliths decreased the flux of calcite to the sediments which in turn lowered pco2 levels enough to explain the glacial interglacial pco2 transition furthermore the contemporary increase in dust delivered to the ocean s mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present to set the stage this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses

mafic replenishment of multiple felsic reservoirs at the mono domes and mono lake islands california the mono basin has been the site of frequent volcanic activity over the past 60 000 years including the emplacement of the mono domes and mono lake islands the mono basin lavas are the youngest and most poorly understood products of the long valley volcanic field we have undertaken a study of mono basin volcanism encompassing whole rock major and trace element sr nd pb and o isotopic and electron microprobe glass plagioclase and amphibole analyses variations in major and trace elements suggest that fractional crystallization of feldspar sr k2o apatite p2o5 titanomagnetite v zircon zr and allanite la ce has influenced the evolution of the mono basin lavas field observations petrography and chemistry together demonstrate that injection of more mafic magma is a common process throughout the mono basin mafic enclaves of the mono domes are stretched and rounded with chilled margins between enclave and host rhyolite thin sections reveal millimeter scale inclusions of rhyolite in the enclaves and vice versa along the host enclave border paoha island dacite has glass with 67 72 wt sio2 and contains microscopic clots of more mafic glasses with sio2 contents as low as 64 wt isotopically the june lake and black point basalts and the mono dome enclaves represent the least evolved material in the long valley volcanic field with 87sr 86sri 0 5126 the silicic mono lake lavas and mono dome rhyolites display a significant crustal component with 87sr 86sri 0 7058 and 143nd 144nd 19 and 18o 6 5 the mono lake lavas generally are younger and less evolved than the mono domes with enrichment in trace elements including ba and sr accompanied by lower 143nd 144nd and higher 206pb 204pb this implies that the mono domes and the mono lake lavas are derived from different magma batches if not from separate magma chambers there is no systematic relationship between the degree of chemical evolution and the lava ages indicating that several magma batches have been involved in the development of the mono domes complex pronounced differences in trace element composition nb y and isotopic values between the negit island and paoha island lavas indicate that they too are produced by the evolution of at least two different batches of intermediate composition magma

metamorphism and crustal considerations in the harts range and neighbouring regions arunta inlier central australia abstract the harts range region consists of several segments or terrains which have behaved essentially independently though some overlap of history permitting correlation is apparent some analogy with the terrane concept is envisaged the harts range terrains are 1 the strangways orogenic belt sob south of the muller thrust 2 the sob of the oonagalabi tongue 3 the sob of the entia dome together comprising a basement and 4 the harts range cover hrc all separated from each other by thrusts or faults the terrains consist of supracrustal sequences comprising metasediments and some metabasites thought to have been deposited in extensional rift depressions plus varying amounts of intrusive granitoids both granulite facies and amphibolite facies mineralogies characterise the basement terrain of the oonagalabi tongue and that south of the muller thrust the entia dome and cover terrains have only amphibolite facies mineralogy a combination of thermobarometry and petrogenetic data suggests equilibration of the sob south of the muller thrust at 700 800 c and 5 7 kbar and of the hrc in the ruby mine area at 680 780 c and 6 8 kbar some thickening of the supracrustal accumulations owing to compression is considered necessary for the development of these pressures comparison of the harts range terrains with the strangways terrain shows some similarities and some differences

middle eocene to early oligocene paleoceanography from agulhas ridge southern ocean ocean drilling program leg 177 site 1090 1 the agulhas ridge off the tip of africa between the atlantic and indian oceans is ideally located to capture the evolution of paleogene early neogene circulation patterns associated with global cooling multiproxy records of productivity biogenic barium baex opal caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox state of deep waters u enrichment from ocean drilling program odp site 1090 reflect hydrographic shifts in this region between the middle eocene and early oligocene 39 33 ma several peaks in increased export productivity and burial of organic matter occurred within the late eocene 36 5 34 and 33 7 ma which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pco2 to a threshold level that facilitated large ice sheet development on antarctica in the earliest oligocene our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle eocene to early oligocene by facilitating increases in the relative or absolute burial of organic carbon

anomalously warm july 2005 in the northern california current historical context and the significance of cumulative wind stress 1 in the northern california current the onset of the 2005 upwelling season was five weeks later than usual and well established upwelling with a cold surface signature did not occur until about seven weeks after this as part of the joint us canada pacific hake survey from 14 16 july 2005 we occupied the newport hydrographic line at 44 65 n from the oregon coast to 83 km offshore instead of the cold surface layer expected in july we observed anomalously warm water for example 10 m temperature at the shelf station nh 5 was the warmest ever recorded in july at this location 6 2 c above average with observations back to 1961 we explore the pivotal role played by cumulative time integrated wind forcing in the development of upwelling in both 2005 and previous years we find that 80 of july surface layer 0 30 m interannual temperature variance can be explained by cumulative upwelling index from the spring transition

rate of arunta inlier evolution at the eastern margin of the entia dome central australia abstract zircon dating in the entia dome of the arunta inlier helps to temporally define the multiphase successive strangways and harts range orogenies it appears that the entire activity of both orogenies took place between 1767 2 ma and 1731 1 ma with a major shearing and thrusting event associated with plutonic activity at 1747 2 3 ma these comparatively short time spans indicated are quite sufficient for the large horizontal movements required for the intra continental basin formation and deformation that has been postulated by james and ding the earlier of these events are later than those currently proposed for equivalent stages of other middle proterozoic inliers of the north australian orogenic province which raises difficulties with detailed correlations in grouping the inliers together monazite u pb muscovite rb sr and biotite rb sr isotopic systems had not closed until 360 ma 325 ma and 308 ma respectively indicating uplift and cover removal from 20 km to

timing relationships between pegmatite emplacement metamorphism and deformation during the intra plate alice springs orogeny central australia in the harts range central australia the upper amphibolite facies to lower granulite facies c 480 460 ma harts range metamorphic complex hrmc and the upper amphibolite facies c 340 320 ma entia gneiss complex are cut by numerous generally peraluminous pegmatites and their deformed equivalents the pegmatites have previously been interpreted as locally derived partial melts however shrimp u pb monazite and zircon dating of 29 pegmatites or their deformed equivalents predominantly from the hrmc reveal that they were emplaced episodically throughout almost the entire duration of the polyphase c 450 300 ma intra plate alice springs orogeny episodes of pegmatite intrusion correlate with the age of major alice springs age structures and with deposition of syn orogenic sedimentary rocks in the adjacent centralian superbasin similar alice springs ages have not been obtained from anatectic country rocks in the hrmc suggesting that the pegmatites were not locally derived instead they are interpreted as highly fractionated granites and imply that much larger parental alice springs age granites exist at depth the mechanism to allow repeated felsic magmatism in an intraplate setting where all exposed rock types had a previous high temperature history is enigmatic however we suggest that episodic underthrusting and dehydration of unmetamorphosed centralian superbasin sedimentary rocks allowed crustal fertility to maintained over a c 140 ma interval during the intra plate alice springs orogeny

metamorphic events in the eastern arunta inlier part 2 nd_sr_ar isotopic constraints in the harts ranges the central province of the eastern arunta inlier is characterised by upper amphibolite facies ortho and paragneisses previously published u pb dating of zircons as well as new sm nd and rb sr data indicate that the intrusive ages of both mafic and felsic orthogneisses are in the range 1780 1740 ma strangways orogeny these rocks had initial nd values of 0 to 3 and depleted mantle model ages of 2 5 2 1 ga and they intruded supracrustal rocks which are now preserved as paragneisses with initial nd of about 15 sm nd and rb sr whole rock isotope data indicate that the hornblende rich amphibolitic gneisses and mylonites in the harts range detachment zone ding and james 1989 were equilibrated at 1473 ma 133 when the rocks experienced hydration isotopic homogenisation and thrust faulting this is the anmatjira event described elsewhere in the arunta inlier and is a predominantly structural influence with thrust faults and hydrous fluid flux accordingly the record of this event by radiogenic geochronometers has been diffuse a problem also exacerbated by the probable influence on these rocks of least one more subsequent lower temperature amphibolite facies metamorphic event in spite of the indications of 1470 ma isotopic homogenisation of amphibolites in the harts ranges rb sr isotopic analyses of all minerals and 40ar 39ar from hornblendes yield ages in the range 450 300 ma using the sm nd system a few garnet hornblende pairs give 1400 1250 ma ages but several of these pairs also yield early palaeozoic ages these data suggest that the central province of the eastern arunta inlier also experienced an early palaeozoic thermal event having cooled from temperatures 550 c during and immediately before the carboniferous alice springs orogeny in the southern province south of the illogwa shear zone micas record mesoproterozoic ages 1500 1250 ma for the rb sr k ar and ar ar systems equivalent to the whole rock ages obtained from the central province to the north of the illogwa shear zone clearly the exposed southern basement cooled to 350 c presumably as a result of uplift and exhumation during the anmatjira event when basement now exposed in the central province remained at depth undergoing one or more additional amphibolite facies events the spectacular contrast in cooling histories across the illogwa shear zone emphasises that this is an important crustal scale tectonic structure

paleozoic deformation and isotopic disturbance in the southeastern arunta block central australia proterozoic metamorphic rocks of the arunta block central australia were thrusted southward over the northern margin of the neoproterozoic to mid paleozoic amadeus basin during the 400 300 ma alice springs orogeny the extent and nature of mid paleozoic ductile deformation in the southeastern arunta block is examined in light of available u pb 40ar39ar k ar rb sr and sm nd isotopic age data most of the proterozoic amphibolite and granulite facies rocks north of the zone of basement cover interaction were exhumed and cooled from above 500 to below 125 c as a result of mid paleozoic nappe formation this suggests that deformation early in the cooling history occurred at amphibolite facies conditions and progressed to greenschist facies conditions later in the cooling history in general shear zone rocks yield the youngest isotopic ages indicating that deformation induced recrystallization grain size reduction or localized thermal perturbations are responsible for the relatively young ages we conclude that shear zones of mid paleozoic age were active under greenschist and amphibolite facies conditions though further work is needed to differentiate whether amphibolite facies shear zones are paleozoic or proterozoic some proterozoic shear zones were uplifted passively in the mid paleozoic resulting in final closure and mixed ages in key minerals like hornblende

continuity of the poleward undercurrent along the eastern boundary of the mid latitude north pacific abstract several recent data sets improve our view of the poleward undercurrent of the california current system as part of a triennial national marine fisheries service nmfs survey of pacific whiting a series of 105 shipboard acoustic doppler current profiler adcp velocity sections across the shelf break from 33 to 51 n at about 18 km meridional spacing were collected from july to august 1995 significant 0 05 m s 1 subsurface poleward flow occurred in 91 of the sections a mean cross shelf section using the entire data set has statistical significance revealing an undercurrent core 0 1 m s 1 from 200 275 m depth 20 25 km off the shelf break the mean poleward volume transport in a 125 325 m layer is 0 8 0 2 10 6 m 3 s 1 we focus particular attention on the cape blanco to cape mendocino region and the nmfs results are compared with shipboard adcp three weeks later from a study of coastal upwelling processes near cape blanco adcp streamfunction maps are derived and strongly suggest that one portion of flow is continuous over the 440 km meridional extent of the analysis region other portions of the flow show evidence of offshore turning separation and the formation of anti cyclonic eddies we also note that isopycnic potential vorticity from alongslope ctd stations during the nmfs survey appears to be a tracer for the poleward flow

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

evolution of oceanographic conditions off baja california 1997 1999 abstract this paper examines the oceanic response off baja california mexico to the 1997 1998 el nino and the transition to la nina conditions the data presented were gathered during seven cruises over a grid based on the calcofi station plan from lines 100 130 out to station 80 t s diagrams with data obtained during the peak phase of el nino demonstrate that warmer and saltier spicier than normal conditions prevailed in the upper 600 m over this region temperature and salinity anomalies calculated for calcofi line 120 revealed waters near the coast at 50 m depth to be up to 8 7 c warmer and s 0 8 saltier than the climatology during october 1997 these large anomalies persisted through january 1998 with some slight diminution in the magnitudes near the surface this study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest identified as subtropical surface water stsw and that low salinity tropical surface waters tsw were blocked to the southeast in the vicinity of the tip of the peninsula subsurface waters associated with the california undercurrent cu fed from the eastern tropical pacific etp were also warmer and saltier than normal and indicate a significant expansion in volume of the cu presumably a result of intensification of poleward flow at depth we postulate that the well defined near surface and deep poleward flows in the study area reflect anomalous large scale cyclonic circulation affecting the flow in the southeastern region of the north pacific subtropical gyre east of 125 w following the el nino event warm and salty upper waters retreated to latitudes south of punta eugenia with the return to normal and cooler conditions equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity transition to la nina conditions would have been associated with re establishment of normal anticyclonic flow in the southeastern quadrant of the pacific subtropical gyre

secular trends in the thermal evolution of metamorphic terrains the thermal evolution of convergent orogens is sensitive to the deformation history of the mantle part of the lithosphere if the dense mantle lithosphere thickens as a consequence of convergent deformation and remains attached during subsequent denudation of the thickened crust then high pressure low to intermediate temperature glaucophane schist assemblages will form during both thickening and denudation the actual form of the p t paths for a given deformation depending primarily on the initial thermal state of the lithosphere and particularly the ratio of the thickness of the crust and mantle lithosphere however if mantle lithosphere is thinned during convergence by processes such as thermal boundary layer detachment then any early formed high pressure low to intermediate temperature glaucophane schist assemblages will be obliterated during subsequent high temperature overprints since the stability of the thermal boundary layer during convergent deformations is controlled by the rate of convergence and the convective vigour of the subjacent mantle any change in the convective vigour of the mantle through geologic time in response to for example changing global heat production may therefore be reflected in the thermal evolution of metamorphic terrains formed during convergent deformations models of the thermal evolution of deforming lithosphere appropriate to an earth in which the effect of declining global heat production and convective vigour is mediated by the process of thermal boundary layer detachment suggest that the preservation of high pressure low to intermediate temperature glaucophane schist assemblages in convergent orogens has become increasingly probable through geological time a suggestion in accord with the observed secular trend in the character of metamorphic terrains preserved in the geological record

strain and displacement in the harts range detachment zone a structural study of the bruna gneiss from the western margin of the entia dome central australia abstract a detailed structural and strain study has been carried out on the bruna granitic gneiss and its bounding thrusts from the western margin of the entia dome in the eastern harts ranges the zone containing the bruna gneiss has been described recently as comprising the harts range detachment zone hrdz a major low angle lithospheric detachment along which both major extensional and contractional movements have occurred the bruna gneiss contains a ductile fabric which varies from an augen streaky foliation through a ribbon gneiss to protomylonite and mylonite in what is predominantly a granitic gneiss conformably overlying the bruna gneiss is a distinctive dark coloured megacrystic gneiss layer which intruded independently from the bulk of the bruna gneiss and followed a different subsequent strain history principal stretch lineations are consistently north plunging or horizontal n s except where folded the bruna gneiss fabrics are complexly folded about axes in an asymmetric manner which suggests interruption of ductile slip and crumpling of the fabrics followed by continuing slip on other discrete surfaces and shear zones strain measurements of elongated feldspars and aggregates indicate moderate to high strains with predominantly plane strain symmetries strain is partitioned into planar parallel zones and suggests dominant heterogeneous simple shear as the main non coaxial flow mechanism flattening strains occur near the bases of two major zones and constrictional strains occur within some zones a strain integration profile across the detachment zone produces total displacements of only a few kilometres suggesting that much of the overall indicated displacement is partitioned into the discrete bounding thrusts asymmetric augen pressure shadows and shear bands provide kinematic indicators in the bruna gneiss most show reverse sense displacement of the overlying harts range cover in a southerly direction over the entia gneiss basement opposite extensional sense movements occur in some zones and especially at the margins of the detachment zone

detrital zircon provenance constraints on the evolution of the harts range metamorphic complex central australia links to the centralian superbasin until recently it has been widely accepted that protoliths to metasediments of the harts range metamorphic complex central australia were deposited prior to c 1 75 ga and form part of the palaeoproterozoic arunta inlier however new sensitive high resolution ion microprobe u pb analyses of detrital zircon together with recently published data suggest that they were deposited coeval with c 545 520 ma sediments from the adjacent little metamorphosed neoproterozoic to palaeozoic centralian superbasin protoliths of the harts range metamorphic complex were deposited in the irindina sub basin an early to mid cambrian rift located between the present day amadeus and georgina basin remnants of the centralian superbasin deposition occurred during a widespread and long lived interval of extension in parts of central australia associated with eruption of the voluminous kalkarinji continental flood basalts the harts range metamorphic complex was metamorphosed to upper amphibolite to granulite facies conditions within c 40 ma of deposition of its sedimentary protoliths

a volcanotectonic cascade activation of range front faulting and eruptions by dike intrusion mono basin long valley caldera california 1 stratigraphic data suggest that during the north mono inyo eruption sequence of 1350 a d a series of strong earthquakes occurred near the end of the north mono explosive phases and the beginning of the inyo explosive phases the temporal proximity of these events suggests the possibility of a causal relationship geological and geomorphic features of the hartley springs fault are consistent with rupture of the fault during the eruption sequence these features include steep central slope segments on several fault scarps and a fault scarp and stratigraphic offset since the deposition of 1200 year old tephra we hypothesize that the inyo dike found by drilling underneath the main inyo vents neared the hartley springs fault as it propagated southward from the mono basin circa 1350 a d we demonstrate that once the lateral distance between dike and fault was sufficiently small the mechanical interaction between them could have triggered the slip observed on the fault the slip in turn could have reduced the horizontal confining pressure in a region near the southern tip of the fault the presence of the main inyo vents in this region suggests that the reduction in confining stress was sufficient to allow magma to propagate to the surface the results suggest that a volcanotectonic cascade of eruptions and earthquakes is a possible mechanism by which a large section of a range front or rift system can be activated because of the positive feedback provided by each element to continued activity

upper ocean water mass characteristics of the california current summer 1993 abstract two large high resolution upper ocean surveys of the california current region were conducted in the summer of 1993 temperature and salinity were measured from a seasoar vehicle and velocity was measured by a ship borne acoustic doppler current profiler both surveys extended from the continental margin to 128 w and consisted of zonal sections 28 km apart the first survey 7 28 june extended from 39 5 n to 36 25 n and the second 16 august to 1 september extended from 39 0 n to 37 0 n the current field was fairly simple in june showing an equatorward surface jet with only one gentle meander a nearly continuous poleward california undercurrent near the continental margin and two anticyclonic subsurface eddies offshore of the jet by august meanders in the surface jet had strengthened and eddies dominated the flow field large scale trends in the water mass characteristics spiciness along three isopycnal surfaces 26 4 26 0 and 25 6 kg m 3 show that temperature and salinity tend to increase towards the equator and towards shore consistent with poleward advection along the continental margin local minima in spiciness tend to coincide with the equatorward surface jet local maxima in spiciness are associated with subsurface anticyclonic eddies which have a core depth of about 150 m and seem to originate in the california undercurrent over the continental slope at local latitudes we identified several different anticyclonic eddies each with different water mass characteristics all of the eddies we observed had diameters larger than the baroclinic radius of deformation water mass characteristics and migration rates are consistent with formation over the continental margin within the preceding 6 8 months

geochemical and nd isotopic systematics of granites from the arunta inlier central australia implications for proterozoic crustal evolution geochemical and sm nd isotopic results are reported for granites from the proterozoic arunta inlier of central australia these combined with new geochronological data for the granites zhao and bennett 1995 allow important constraints to be placed on proterozoic tectonic and crustal evolution in central australia granites from the arunta inlier can be divided into three major geochemical groups a calcalkaline trondhjemitic group cat a high heat production group hhp and a volumetrically significant main group the cat group which occurs only in the southern margin of the inlier is characterised by high na2o nak sr krb and sry and relatively low k2o rb rbsr th u ree nb and y analogous to calc alkaline suites occurring in modern convergent plate margins the hhp group which occurs mainly in the interior of the arunta inlier and is spatially associated with the main group is characterised by high k rb th u rbsr and rbzr and relatively low sr ba nak krb barb mgo cr and ni the main group which occurs throughout the arunta inlier is geochemically intermediate between the cat and hhp groups it is geochemically analogous to the 1880 1850 ma old barramundi igneous association recognised in other proterozoic terrains of central australia and can be further subdivided into four age subgroups 1820 1780 1750 1650 and 1615 1600 ma respectively all three groups show similar negative nb anomalies on the trace element normalized diagrams despite the geochemical diversity of the arunta granites no correlations between the nd isotopic and geochemical signatures are observed the ranges of initial nd values and nd depleted mantle model ages tnddm for the three groups of granites overlap with each other overall there are two groups of tnddm ages the most common ranging from 2 33 to 1 96 ga and the other from 1 83 to 1 72 ga although initial nd values of the granites show large variations there is a general trend for the nd values to increase i e become less negative with decreasing crystallization ages the large geochemical and isotopic variations of the arunta granites reflect considerable heterogeneity in the sources of the granites and do not support a uniform 2 3 2 1 ga old barramundi type underplate source for the origin of the granites the combined geochemical and nd isotopic data suggest the sources of the granites contain at least two main components an palaeoproterozoic mantle derived component and an older crustal component the older crustal component was incorporated into the source region of the granites either through magma assimilation of crustal materials at lower crustal levels or more probably via sediment subduction and mantle wedge metasomatism the increasing nd values with decreasing crystallization ages may be a result of progressively increasing proportions of newly accreted island arc materials being incorporated in the subducted sediments alternatively a juvenile mantle derived component may have been added to the source region of the younger granites it is apparent that the nd isotopic signatures in the granites has resulted from complex processes and neither simple mixing nor simple two stage protolith models can as yet satisfactorily explain the observations the petrogenesis of the three geochemical groups of granites can be interpreted in a plate tectonics scenario it is considered that the cat group was formed by fractionation of arc type magmas and or partial melting of arc related intrusions or underplates in a subduction related continental margin setting whilst the formation of the main group may involve partial melting of fractionated and or modified arc related underplates but not necessarily in a subduction environment the younger hhp group was probably generated by remelting of the coexisting main group during subsequent tectonothermal events

the emplacement of the wuluma granite melt generation and migration along steeply dipping extensional fractures at the close of the late strangways orogenic event arunta block central australia during the paleoproterozoic the strangways metamorphic complex in the arunta block central australia underwent two major deformation events under granulite facies conditions namely the early strangways event 1800 1780 ma and the late strangways event the early strangways event d1m1 produced a regional granulite facies gneissic foliation which outlines structural trends in the strangways metamorphic complex the late strangways event d2m2 is a compressional event which produced spectacular regional sheath folds and high temperature shear zones melt segregations bearing orthopyroxene garnet cordierite k feldspar quartz overprint these structures and mark the end of the second granulite facies event m2 in the wuluma hills sw strangways metamorphic complex pressures of 5 6 kbar and temperatures greater than 750 c were reached during this event the wuluma granite consists of steeply dipping sheets of granites which overprint the late strangways structures and are parallel to the regional gneissic foliation the rotation and steepening of the regional gneissic foliation occurred during the late strangways event the wuluma granite formed at the close of the late strangways event as extensional fractures opened parallel to the steeply dipping gneissic foliation fluids migrated into these extensional cracks causing in situ partial melting of the granulites the introduction of hydrous fluids and their subsequent release during the crystallization of the granitic melts generated a pervasive metasomatic event m3 which is characterized by the retrogression of cordierite to sillimanite biotite titanomagnetite a u pb ion probe zircon age of 1728 3 ma for the wuluma granite constrains the timing of m3 thus the wuluma granite is part of an orogenic cycle which began 1745 ma ago anamarra granite with regional folding under granulite facies conditions m2 and ended 1728 ma ago with the formation of the wuluma granite and pervasive regional retrogression m3

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

the atnarpa igneous complex southeast arunta inlier central australia implications for subduction at an early mid proterozoic continental margin abstract three distinctive igneous suites have been identified from the atnarpa igneous complex southeast margin of the arunta inlier central australia the 1879 11 10 ma gabbro diorite tonalite trondhjemite suite sio2 49 78 shows both calc alkaline and trondhjemitic affinities the overall depletion of nb ti y k and rb in this suite indicates that its parental magma must have been depleted in these elements it is the oldest zircon age so far obtained in the arunta inlier the 1873 11 10 ma low al tonalite trondhjemite granodiorite suite is also depleted in k and rb however unlike either the 1879 ma or the 1751 ma suites it has lower al2o3 and sr at comparable sio2 levels and display flat hrees and negative eu anomalies the 1751 12 ma younger tonalite suite is high in sr sr y and al2o3 and low in zr ti nb y th and u and displays a strongly fractionated ree pattern with hree depletion typical of archaean high al tonalite trondhjemite granodiorite suites such geochemical features contrast with the 1850 1880 ma old k rb ree th enriched na sr depleted barramundi igneous association widespread in proterozoic terrains of northern australia the parental magma of the 1879 11 ma suite is considered to be derived by subduction related partial melting of a metasomatised hybridised mantle wedge with phlogopite retained in the residue the parental magma of the 1873 11 ma low al suite by relatively low pressure partial melting of a mafic source with residual plagioclase left in the residue and the 1751 12 ma younger tonalite suite by partial melting of a subducted oceanic crust at mantle depth with residual garnet amphibole these processes contrast with models of restite unmixing of a geochemically uniform but fractionated preexisting mantle derived underplate previously proposed for the k rich barramundi igneous association combining geochemical features of the atnarpa igneous complex with reported data from the harts range and the alice springs areas we propose that the southeast margin of the arunta inlier represents a convergent continental margin during the early to middle proterozoic which has undergone at least two episodes of subduction related magmatism 1860 1880 ma and 1730 1770 ma such continental margin subduction could provide additional driving force for crust mantle delamination and ensialic a subduction within the preexisting continental crust further north both within plate vertical underplating and marginal lateral accretion could be important processes for proterozoic crustal evolution

particulate organic carbon fluxes compilation of results from the 1995 us jgofs arabian sea process study by the arabian sea carbon flux group abstract organic carbon fluxes in the arabian sea were measured as a function of depth season and distance from the coast of oman we present here a compilation of measurements of primary production water column export flux and sediment accumulation of organic carbon over a full annual monsoon cycle on a 1500 km transect from the coast of oman toward the central arabian sea this represents an integration of measurements spanning one day primary production to 1000 yr sediments and gives a broad overview of organic carbon removal and remineralization in the highly productive seasonally varying region of the northern indian ocean organic carbon fluxes decreased from the surface to the sediments by a factor of 500 10 000 with the largest rates of change in the upper ocean and at the sediment seawater interface organic carbon fluxes generally decreased with distance offshore with the largest gradient between surface and seafloor being at the offshore station sediment accumulation rates of organic carbon differed by a factor of 40 between nearshore and offshore while primary productivity varied only by a factor of 2 the decrease in carbon flux with depth that occurs between the deepest traps and the sediment becomes a greater proportion of the total loss with increasing distance from shore thus the influence of processes at the sediment water interface on the proportion of primary productivity preserved in the sediment increases offshore relative to upper water column processes carbon fluxes changed greatly with season with highest fluxes during the southwest monsoon export fluxes varied more with season than primary productivity or mid water fluxes

metamorphic events in the eastern arunta inlier part 1 metamorphic petrology abstract in the entia dome of the eastern arunta inlier kyanite facies metamorphism is recorded over a substantial area at least 160 km 2 and thus contrasts with the regionally extensive belts of high temperature low pressure andalusite sillimanite facies metamorphism documented elsewhere in the arunta inlier this amphibolite facies event appears to postdate regional granulite facies metamorphism evidence for which is almost totally obliterated in the entia dome prograde kyanite occurs in meta basites in comparatively rare associations involving hornblende staurolite and anorthite and in other rocks in association with gedrite and hornblende or garnet and biotite these kyanite bearing assemblages equilibrated at intermediate temperatures 570 710 c at peak pressures of 7 kbar and are overprinted by lower pressure assemblages including hornblende gedrite cordierite and sillimanite while this sequence of reactions may be simply interpreted in terms of a single clockwise orogenic cycle textural evidence and the available mineral isotopic data suggest a more complex history involving multiple heating and cooling episodes during the mesoproterozoic and possibly the palaeozoic the occurrence of regional retrogressive kyanite facies assemblages in the eastern arunta inlier provides evidence that the widely held perception that proterozoic crustal evolution in australia involved a distinct ensialic orogenic style characterised by high geothermal gradients etheridge et al 1987 loosveld and etheridge 1990 sandiford and powell 1991 is not universally true rather petrological evidence presented here with isotopic constraints described by foden et al 1995 suggests that the harts range region has experienced substantial crustal reworking at elevated temperatures during both the proterozoic and palaeozoic under thermal regimes more familiar to modern continental collision zones

shrimp u_pb zircon geochronology of granites in the arunta inlier central australia implications for proterozoic crustal evolution abstract new shrimp u pb zircon isotopic ages are reported for ten granitic suites in the eastern arunta inlier these data combined with previous u pb zircon studies in the region constrain the timing of major palaeoproterozoic igneous events within the arunta inlier and establish a geochronological framework for understanding lithostratigraphic relationships tectonic events and geochemical and isotopic evolution of the granites in the region most granites in the arunta inlier including both syn tectonic and post tectonic types yield zircon ages in the range of 1770 1710 ma which are significantly younger than the 1880 1850 ma orogenic barramundi igneous association recognised throughout many other proterozoic terrains in northern australia no rocks of the barramundi association have been identified in this study the previously proposed barramundi type suites including the jervois and dneiper granites yield ages of 1771 6 and 1771 15 ma respectively many of the granite suites contain inherited zircons with ages in the range of 1890 1830 ma similar to the age of the barramundi association this and the age of the atnarpa igneous complex zhao and cooper 1992 which is coeval with but geochemically distinct from the barramundi association suggest that the 1880 1850 ma orogenic event affected the arunta inlier but has been obscured by the younger tectonic events the youth of tectonic events in the arunta inlier as compared with other proterozoic terrains of northern australia may have resulted from the inlier being located on the southern margin of the northern australian orogenic province during the palaeoproterozoic with the generation of granites in the arunta inlier possibly being related to subduction the combined data indicate that major granitic activity occurred at 1880 1850 1820 1770 1750 1730 1710 1660 1650 and 1615 1590 ma this result is broadly consistent with earlier summaries of the other proterozoic terrains in northern australia although the intensity of each episode varies in different regions

an assessment based on u_pb zircon data of rb_sr dating in the arunta inlier central australia abstract the chronology of the arunta inlier was originally based mostly on rb sr dating although some of the ages derived from that technique are now shown to be erroneous those which were constrained by structural observations and which relied only on whole rock and not mineral analyses have proven to be remarkably realistic ion microprobe data show that even conventional multigrain u pb zircon analysis is not a particularly appropriate dating technique in a region of this complexity three new u pb zircon ages and others previously derived from the same isotopic system date three of the main tectonic events that were imposed on the arunta inlier the widespread strangways orogeny of the northern and central provinces occurred at 1760 1750 ma the argilke event is not older than 1680 ma demonstrating that the southern province is the youngest in the inlier the dominantly thermal ormiston event is dated at 1140 ma

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

the simpson strzelecki and tirari deserts development and sand provenance abstract sands of the simpson strzelecki and tirari deserts central australia can be divided into two main groups on the basis of their physical and chemical characteristics colour grainsize heavy minerals quartz oxygen isotope composition zircon u pb ages the first group encompasses the strzelecki tirari and southeastern simpson deserts while the second occupies the northern and the western simpson desert the boundary between the two groups corresponds approximately to the northern most extent of the kallakoopah lakes several lines of evidence suggest derivation of the sands mainly from local bedrock with very little subsequent aeolian transport ultimate protosources for the sands in order of importance are for the southeastern simpson tirari and strzelecki deserts the tasman orogenic system new england and lachlan fold belts georgetown inlier musgrave and arunta blocks gawler and curnamona cratons and for the north and western simpson desert arunta musgrave and mount isa blocks and tennant creek inlier sediment from the tasman orogenic system includes an additional exotic component from palaeozoic sediments probably derived mainly from antarctica sediment transport from these protosources across the several hundred kilometres to the surficial sedimentary basins was dominantly by fluvial not aeolian means quaternary aeolian transport or reworking has been minimal serving only to form the dunes by vertical corrasion of underlying sedimentary rocks or residual products of local basement weathering the deserts have received some recent localised sediment input from modern fluvial systems

pb and sr systematics of ultrapotassic and basaltic rocks from the central sierra nevada california this study presents sr and pb isotopic ratios and rb sr u th and pb concentrations of an ultrapotassic basaltic suite and related rocks from the central sierra nevada california the ultrapotassic suite yields a narrow range of sr and pb isotopic compositions 87sr 86sr 0 70597 0 70653 206pb 204pb 18 862 19 018 207pb 204pb 15 640 15 686 208pb 204pb 38 833 38 950 associated basalts containing ultramafic nodules have less radiogenic sr 87sr 86 0 70430 0 70521 and generally higher rb sr ratios than the ultrapotassic suite leucitites from deep springs valley california contain high 87sr 86sr 71141 0 71240 and low 206pb 204pb 17 169 17 234 ratios reflecting contamination by crustal granulite

u_pb zircon dating of tectonomagmatic events in the northern arunta inlier central australia abstract the mount doreen area of the northern arunta inlier has a proterozoic magmatic and tectonic history that extends over 300 ma the oldest unit the turbiditic lander rock beds lrb was folded and metamorphosed from greenschist to granulite grade during the yuendumu tectonic event a u pb zircon age of 1880 5 ma for the late tectonic ngadarunga granite provides a minimum age for this event and supports its correlation with the widespread barramundi orogeny of northern australia two subsequent major deformations the hardy and the wabudali tectonic phases considered to represent discrete phases of the strangways orogeny are tentatively placed at around 1770 ma the hardy tectonic phase locally retrogressed the lrb and produced strong foliations in some granites including one of the carrington suite dated at 1779 6 ma the wabudali tectonic phase formed high strain zones in places more than 2 km wide within which the sedimentary reynolds range group was tightly folded and the lrb were refolded and retrogressed felsic volcanics and arenites of the fault bound nicker beds and patmungala beds dated at 1772 5 ma and 1799 10 ma respectively were also tightly folded during the strangways orogeny juxtaposition of low grade and high grade lrb took place during faulting that occurred after the 1770 ma tectonism but prior to post tectonic granites which may be indirectly related to the 1600 ma chewings orogeny of the southern arunta inlier one post tectonic granite 1635 9 ma is associated with a mafic to intermediate intrusive complex and another 1567 11 ma is part of an extensive megacrystic suite that intrudes folded reynolds range group zircon inheritance was found in five of the six analysed samples with ages ranging from 1 85 to 3 45 ga

the palaeozoic history of an unusual intracratonic thrust belt in central australia based on 40ar 39ar k ar and fission track dating intraplate thrusting involving reactivation of a mid proterozoic province boundary within the basement metamorphic rocks of the arunta block occurs at the northern margin of the late proterozoic to mid palaeozoic amadeus basin in central australia earlier geological and geophysical studies show that the thrust system referred to as the alice springs orogen is 9thick skinned9 in the central part of the thrust belt and was dominated by the crust cutting redbank thrust zone several episodes of thrusting defined stratigraphically began about 400 ma ago analysis and modelling of 40 ar 39 ar age spectra on k feldspar from the basement rocks combined with regional geological constraints point to cooling rates of 3 10 c ma and moderate overall exhumation rates of 100 400 m ma during the alice springs orogeny without appreciably increased heat flow however final uplift along the thrust front at 300 320 ma was rapid as the time of final closure of small domains in k feldspar approximates apatite fission track ages by using 40 ar 39 ar age data as a constraint together with available geological and geophysical data crustal shortening across the thrust belt is thought to be approximately 20 to 30 overall convergence rates of 0 6 3 km ma are slow compared with rates of 5 km ma for continent continent collision zones

a barometric response to late compression in the strangways metamorphic complex arunta block central australia evidence for four major deformation events d1 d4 and two metamorphic events m1 m2 is shown by granulite and amphibolite facies rocks of the strangways metamorphic complex central australia which is divided into two domains the ongeva granulites to the east and the anamarra granite domain to the west d1 and d2 produced layer parallel foliations with many of the effects of d1 overprinted by intense non coaxial shear during d2 low pressure granulite facies metamorphism m1 accompanied d1 2 at conditions of p 5 3 1 2 kbar and t 750 c the effects of m1 are characterized by s1 spinel quartz bearing assemblages with overprinting s2b sillimanite biotite magnetite assemblages implying approximately isobaric cooling effects of m2 are characterized by s1 2 cordierite pseudomorphed by orthopyroxene sillimanite biotite magnetite symplectites at conditions of p 7 5 0 8 kbar and t 800 c this retrograde increase in pressure was probably the result of crustal thickening during d3 which produced ne plunging f3 and f4 folds in the ongeva granulites and a widespread shear foliation in the anamarra granite domain the increase in pressure with m2 may reflect the beginning of a clockwise p t t path typical of collisional style tectonics sillimanite and orthopyroxene bearing ultramylonites were produced during d4 an extension event parallel to the d3 transport axis and probably related to crustal collapse after thickening during d3 wide n dipping shear zones d5 containing sillimanite kyanite staurolite and overprinting greenschist facies assemblages bound the strangways metamorphic complex these zones indicate a s directed sense of shear and were probably responsible for bringing the strangways metamorphic complex to higher crustal levels during both a probable late proterozoic event and the mid carboniferous alice springs orogeny

the influence of variable slope water characteristics on dissolved oxygen levels in the northern california current system observations have suggested a trend of decreasing dissolved oxygen do and increasing spiciness in summertime mid depth slope waters and bottom shelf waters along the united states west coast over the past 50 years but they have also demonstrated a large amount of interannual and decadal variability shelf bottom water and slope water properties can be influenced by both local and remote effects including changes in circulation or changes in the characteristics of the source waters supplying the region a regional scale coupled physical biogeochemical model has been developed to simulate seasonal to decadal scale variability along the us west coast to discern the physical dynamics behind these spatial and temporal patterns a simulation run from 1981 through 2006 with forcing that incorporates the larger scale interannual trends reproduces the development of low do late in the upwelling season the considerable interannual variability and the reported tendency towards a shoaling more spicy and oxygen depleted northern california undercurrent cu whereas the trend in spiciness in the model results from increased influence of equatorial relative to subarctic source waters the decreases in do are found to additionally be a consequence of local biogeochemical processes in order to better understand the interannual variability years of the simulation were classified into four groups based on intensity of upwelling forcing and undercurrent strength slope water characteristics shelf slope exchange and slope basin exchange were compared across the four cases years with both strong upwelling and a strong undercurrent generated the most negative anomalies in slope water do late in the upwelling season

seasonal variability of alongshore geostrophic velocity off central california seasonal variability of alongshore geostrophic velocity relative to 500 dbar is examined from 23 years of hydrographic data along two sections off central california one off point sur and the other off point conception the seasonal cycles are determined by least square fits of the gappy data records to harmonics with annual and semiannual periods attention is focused on variability over the outer continental slope geostrophic flow in the upper 100 m along both sections is coherent and predominantly annual with equatorward flow from february to september and poleward flow from october to january the flow deeper than 100 m is distinctly different along the two sections the nearshore deep flow is predominantly semiannual off point conception notably different from surface flow and poleward all year with maxima in december and june this semiannual variability at depth is a prevalent feature of the california current system the nearshore deep flow off point sur is unusual in that it is predominantly annual with maximum poleward flow in december and weak equatorward flow from march to may the seasonal variations over the continental slope compare favorably with existing models of eastern boundary current systems in two respects 1 the surface flow leads the predominantly annual wind forcing in this region by about one month and 2 the deep poleward counterflow is coherent with the local poleward barotropic pressure gradient at both locations with a phase lag of approximately 2 months however contrary to the results of existing dynamical models the semiannual poleward pressure gradient and undercurrent off point conception appear to be unrelated to the wind forcing which is predominantly annual in this region these semiannual variations are highly coupled to the semiannual flow throughout the water column inside the southern california bight suggesting that they may be topographically generated

the petrology and geochemistry of granitic gneisses from the east arunta inlier central australia implications for proterozoic crustal development the entia gneiss complex is an early to middle proterozoic inlier composed of upper amphibolite facies orthogneisses and paragneisses in the eastern end of the arunta block in central australia it is separated from overlying structurally distinct compositionally different and probably younger gneisses of the harts range complex by a subhorizontal detachment zone this paper discusses the petrology of four major granitic gneiss bodies one of these the bruna gneiss has intruded this detachment zone the other three are components of the structurally underlying entia gneiss complex the entia gneiss complex has a distinctive subhorizontally layered character with recumbent folds and flat lying schistosity the granitic gneisses that are components of this complex appear to have intruded an actively deforming terrain and are folded sheet like bodies the orthogneisses of the entia complex range from gabbro to true granite in composition and the granites are i type on both geochemical and petrographic criteria they are significantly different from the relatively alkali rich granites of equivalent age which occur in some of the other northern australian proterozoic blocks and are most like the granites of the modern cordilleran belts particularly in the association of diorite and gabbro with granodiorite it is suggested they are formed in narrow collisional belts formed as a result of closure of intracratonic rift basins the high surface area to volume ratio of these granites which is a consequence of the deformational environment into which they were intruded has resulted in considerable wall rock exchange in the more differentiated end members of the suites this has led to contamination by a net gain of k2o rb and ba and loss of relatively compatible elements including the ree y nb and tio2 compared with the syn tectonic entia granites the bruna granite gneiss is post tectonic and shows geochemical affinities with a type or anorogenic palaeozoic granites most of this granite is confined to the detachment zone but the very latest phases also intrude the harts range cover sequence an important conclusion of this study is that detachment zones of the type described from this area of the eastern arunta block exercise strong control on plutonism into the early to middle proterozoic crust as long as the very mobile style of early proterozoic tectonics continues the intracrustal dislocation zone confines syn tectonic granitic magmatism to deeper levels

structural evolution of the harts range area and its implication for the development of the arunta block central australia abstract a division of the high grade metamorphics of the arunta block in the harts range area into two main groups on the basis of lithology structure metamorphism and igneous activity is suggested as a result of detailed mapping the lower group is regarded as a basement terrain and comprises major layered felsic or granitic gneiss minor amphibolite and mafic granulite while the structurally overlying group is regarded as a cover sequence irindina supracrustal assemblage and comprises predominantly metasediments pelitic and semi pelitic gneiss calc silicate and quartzite and amphibolite anorthosite and ultramafic rock of the harts range meta igneous complex the cover sequence might have been deposited in an aulacogen or adjacent to a continental margin which developed by rifting of a pre existing basement the two groups both show early major ductile tectonothermal stages with four major fold generations and a later discrete shear event in the basement and two major fold generations and a later series of stacked nappes developing in the cover the basement s early orogenic evolution with associated granulite facies metamorphism is typical of intensely reworked early precambrian terrains and developed spatially and or temporally separated from the cover cover deformation closely resembles continental margin cordillera type overthrusting and thus thin skinned tectonics associated with large scale crustal shortening during the later harts range remobilization the basement and cover were juxtaposed by displacement on a fundamental crustal dislocation recumbent contraction fault mylonites repeatedly developed along the dislocation which was also isoclinally folded intruded by a major megacrystic granitoid bruna gneiss sheet and repeatedly rejuvenated the history of development of the dislocation is documented and described as a process of underthrusting of basement beneath cover which led to the final termination of the orogenic activity

sm nd and u pb zircon isotopic constraints on the provenance of sediments from the amadeus basin central australia evidence for ree fractionation abstract the amadeus basin of central australia is a late proterozoic to late palaeozoic ensialic depositional basin located between two proterozoic basement blocks of different nd crustal formation ages the older arunta block t dm nd 2 0 to 2 2 ga u pb zircon ages 1 5 1 9 ga to the north and the younger musgrave block t dm nd 1 7 to 1 9 ga u pb zircon ages 1 0 1 7 ga to the south initial nd isotopic compositions of the amadeus basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks indicating that the sediments are dominated by essentially two source components the older arunta block 147 sm 144 nd 0 114 and nd 0 20 4 and younger musgrave block 147 sm 144 nd 0 118 and nd 0 14 7 and or their equivalents stratigraphically higher sediments plot more closely to the evolutionary trajectory of the musgrave block this result together with the average provenance ages indicates the proportion of material from the musgrave block increases as the sediments become younger the sm nd isotopic data preclude a substantial involvement of archaean sources u pb zircon ion probe analyses of the late proterozoic heavitree quartzite and the late cambrian goyder formation are consistent with the sm nd isotopic constraints most of the zircons from the basal heavitree quartzite give concordant u pb zircon ages of 1500 to 1900 ma consistent with derivation from an arunta type source whilst zircons from the younger goyder sandstone give six discrete u pb zircon age groups of 511 20 615 15 960 109 1190 54 1633 24 and 1878 48 ma indicative of a dominantly musgrave type source with a minor contribution from the arunta block or reworked preexisting amadeus basin sediments the two youngest u pb zircon ages probably indicate some contribution from late proterozoic cambrian volcanics in central australia or a previously unrecognised younger local source in the basement blocks the 511 20 ma constrains the maximum depositional age of the sediment the amadeus basin sediments have a surprisingly wide range of 147sm 144nd ratios 0 077 0 136 irrespective of grain size and rock types in addition the calculated t dm nd values for samples from the same stratigraphic unit are well correlated with 147sm 144nd ratios with samples of different stratigraphic units forming sub parallel arrays these phenomena are interpreted in terms of ree fractionation and preferential sorting of preexisting ree rich phases during sedimentary recycling and deposition this process can lead to either an increase or a decrease in 147sm 144nd ratio of a sediment relative to its source and therefore an erroneous estimate of its t dm nd provenance age a theoretical model is developed which accounts for the observed correlation between t dm nd and 147sm 144nd ratios for suites of stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units assuming the average 147sm 144nd ratio of the source is known or can be estimated the provenance age for each stratigraphic unit of the amadeus basin has been calculated using this method the sm nd isotopic systematics in the amadeus basin sediments suggest that 1 1 ree fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered 2 2 the provenance of the amadeus basin sediments was controlled by local source regions and cannot be used to infer large scale continental averages hence some caution must be evoked in using sm nd isotopic constraints from restricted sampling for more generalised models of crustal evolution

particle fluxes to the interior of the southern ocean in the western pacific sector along 170 w abstract an array of five bottom tethered moorings with 19 parflux time series sediment trap at three depths 1 and 2 km below the surface and 0 7 km above the sea floor was deployed in the western pacific sector of the southern ocean along 170 w the five stations were selected to sample settling particles in the main hydrological zones of the southern ocean the sampling period spanned 425 days november 28 1996 january 23 1998 and was divided into 13 or 21 synchronized time intervals a total of 174 sequential samples were recovered and analyzed to estimate fluxes of total mass tmf organic carbon carbonate biogenic silica and lithogenic particles the fluxes of biogenic material were higher than anticipated challenging the notion that the southern ocean is a low productivity region organic carbon fluxes at 1 km depth within the polar frontal zone and the antarctic zone were relatively uniform 1 7 2 3 g m 2 yr 1 and about twice the estimated ocean wide average ca 1 g m 2 yr 1 carbonate fluxes were also high and uniform between the subantarctic front and ca 64 s 11 13 g m 2 yr 1 a large fraction of the carbonate flux in the antarctic zone was due to the presence of pteropod shells coccoliths were found only to the north of the polar front and calcium carbonate became the dominant phase in the subantarctic zone in contrast carbonate particles were nearly absent near 64 s latitudinal variations in biogenic silica fluxes were substantial the large opal flux 57 g m 2 yr 1 measured in the antarctic zone suggests that opal productivity in this region has been previously underestimated and helps to explain the high sedimentary opal accumulation often found south of the polar front unlike biogenic material fluxes of lithogenic particles were among the lowest measured in the open ocean 0 12 0 05 g m 2 yr 1 reflecting a very low dust input

coastal trapped waves alongshore pressure gradients and the california undercurrent abstractthe california undercurrent cuc a poleward flowing feature over the continental slope is a key transport pathway along the west coast of north america and an important component of regional upwelling dynamics this study examines the poleward undercurrent and alongshore pressure gradients in the northern california current system ccs where local wind stress forcing is relatively weak the dynamics of the undercurrent are compared in the primitive equation navy coastal ocean model and a linear coastal trapped wave model both models are validated using hydrographic data and current meter observations in the core of the undercurrent in the northern ccs in the linear model variability in the predominantly equatorward wind stress along the u s west coast produces episodic reversals to poleward flow over the northern ccs slope during summer however reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south

geochronological constraints on orogenic events in the arunta inlier a review early workers subdivided the arunta inlier central australia into three major tectonic provinces classified the principal tectonostratigraphic units into three divisions and separated the tectonomagmatic history into five discrete events ranging in age from 1800 ma to 300 ma a review of the evidence for tectonic boundaries within the arunta inlier suggests that no major structural discontinuity exists between the northern and central tectonic provinces but that the redbank thrust zone is at least in part a province boundary the tectonostratigraphic division concept also requires revision as division 3 rocks of the northern and southern arunta cannot be time equivalents division 1 rocks grade into division 2 in the northern region and division 3 of the northern region may be equivalent to division 1 in the central region rocks originally assigned to divisions are better grouped into a larger number of lithological assemblages until better stratigraphic and isotopic correlations can be made compilation of rb sr and 40ar39ar age determinations obtained before 1984 indicate an almost complete age spectrum from 1800 ma to 1000 ma but age clusters exist at 1400 ma 1100 ma and 400 300 ma which have geological significance subdivision of older ages into discrete tectonic events was not justified from this data alone but more recent u pb isotopic analysis of zircons in rocks designated to particular structural metamorphic events has revealed a complex tectonic history in the 1880 1600 ma interval the northern and central provinces underwent major tectonism between 1780 1730 ma but much of the southern province was not deformed until 1600 ma the revised tectonic history nomenclature is proposed for the arunta inlier following deposition of a widespread turbiditic unit at or before 1880 ma possibly on thinned archaean crust the northern and central provinces underwent localized tectonism magmatism at 1880 ma yuendumu tectonic event and 1820 ma stafford tectonic event prior to the widespread strangways orogeny which is subdivided into an early phase at 1780 1770 ma and late phase at 1745 1730 ma it is not clear whether the strangways orogeny is a single arunta wide event or a series of separate short lived smaller scale events although the major deformation in all areas appears to have involved w to sw directed thrusting in the southern province the major events occurred at 1680 ma argilke tectonic event and 1600 ma chewings orogeny the latter involving n directed thrusting that was penecontemporaneous with post tectonic pegmatite intrusion in the northern province suggesting linkage of both regions at this stage the younger history of the inlier is characterised by several stages of uplift and isolated thermal magmatic events major mesoproterozoic crustal exhumation anmatjira uplift phase has been interpreted from widespread 1500 1400 ma ages including regional scale closure of 40ar 39ar systems in hornblende from mafic granulite outcrop scale rb sr total rock isotopic systems in mylonitized granitoids and sm nd garnet hornblende pairs in mylonitized amphibolites a 1150 ma thermal event in the southern part of the inlier teapot magmatic event is recorded by intrusion of granite pegmatites and the alkaline mordor igneous complex and by isotopic resetting of rb sr mineral systems dolerite dyke injection at 1050 ma reflects limited extensional tectonism that may have related to formation of the amadeus basin the second major uplift event was the alice springs orogeny at 400 300 ma an unusual intracratonic thick and thin skinned thrust event that involved limited retrograde amphibolite facies but extensive greenschist facies metamorphism and restricted pegmatite intrusion

granulite facies metamorphism in the mallee bore area northern harts range implications for the thermal evolution of the eastern arunta inlier central australia abstract the mallee bore area in the northern harts range of central australia underwent high temperature medium to high pressure granulite facies metamorphism individual geothermometers and geobarometers and average p t calculations using the program thermocalc suggest that peak metamorphic conditions were 705 810c and 8 12 kbar partial melting of both metasedimentary and meta igneous rocks forming garnet bearing restites occurred under peak metamorphic conditions comparison with partial melting experiments suggests that vapour absent melting in metabasic and metapelitic rocks with compositions close to those of rocks in the mallee bore area occurs at 800 875c and 9 10 kbar the lower temperatures obtained from geothermometry imply that mineral compositions were reset during cooling following the metamorphic peak the rocks underwent local mylonitization at 680 730c and 5 8 7 7 kbar after mylonitization ceased garnet retrogressed locally to biotite which was probably caused by fluids exsolving from crystallizing melts these three events are interpreted as different stages of a single continuous clockwise p t path the metamorphism at mallee bore probably occurred during the 1745 1730 ma late strangways orogeny and the area escaped significant crustal reworking during the anmatjira and alice springs events that locally reached amphibolite facies conditions elsewhere in the harts ranges

caterpillar tectonics in the harts range area a kinship between two sequential proterozoic extension collision orogenic belts within the eastern arunta inlier of central australia abstract we propose that in the harts range area of the arunta inlier of central australia a basement and cover relationship previously described by us represents a thick complexly deformed contact zone between an early middle proterozoic fold belt the strangways orogenic belt sob and a younger middle proterozoic orogenic belt the harts range orogenic belt both of which contain their own supracrustal sequences rocks of the sob were deposited and possibly metamorphosed to a maximum grade of granulite facies at 1800 ma during an early phase of crustal extension they were subsequently intruded by a significant proportion of acidic magmas at 1767 ma and compressed to form a distinctively nne ssw trending orogenic belt a wnw ese trending shallowly north dipping zone of intense and repeated deformation termed the harts range detachment zone hrdz formed initially during a period of nne ssw crustal extension as a major low angle normal shear detachment zone within and crosses at a high angle to the trend of the basement rocks of the sob the hrdz has been intermittently active as a zone of crustal weakness since its initiation the first extensional movement on this zone began the formation of the harts range mobile belt hrmb which displays many of the characteristics of modern tectonic zones activated by plate movement a supracrustal cover sequence the harts range cover hrc formed in the major geosynclinal basin which developed on the subsiding upper plate of the hrdz continued crustal extension juxtaposed the cover sequence which was then metamorphosed to a maximum grade of amphibolite facies and granulite facies basement of the hrdz before a fundamental change in movement sense led to crustal contraction and a collision related thrusting phase the hrmb which includes the hrdz and the hrc was then internally deformed over a relatively very short time span 15 20 ma before voluminous granitic magma intruded mainly along the hrdz during the harts range orogeny hro the intrusion of this major granitoid at 1747 ma precisely fixes the time scale of evolution for the earlier phases of the hro the hro is documented in detail as a peculiar orogenic style of crustal contraction which was largely taken up by reverse sense discrete thrusting and shearing on faults and shear zones associated with the hrdz displacement on the hrdz was a stick slip process with repeated punctuation of thrust slip movement by pinning at points located progressively to the south each period of cessation of thrust slip movement was followed by folding of discrete thrusts of captured basement lobes within the hrdz and of the overlying supracrustal sequence the individual discrete movement phases and folding episodes are each named and described as is a model of this unusual type of proterozoic tectonic activity

timing of volcanism in the sierra nevada of california evidence for pliocene delamination of the batholithic root recent seismic experiments across the southern sierra nevada california show that the range lacks a thick crustal root xenolith studies indicate that delamination and loss of much of the lower crust may have occurred between 10 and 3 ma we estimate that delamination occurred ca 3 5 ma on the basis of a sudden pulse of mafic potassic magmatism within and just east of the sierra nevada from 4 to 3 ma this pulse interrupted the low level of volcanism that had prevailed regionally since 13 ma delamination could have promoted magmatism via decompression melting heating of the shallow lithosphere by upwelling asthenosphere and foundering of crustal rocks into the mantle and could have provided dynamic support to the range foundering of the lower crust may have occurred spontaneously owing to negative buoyancy or may have been triggered by extension between the sierra nevada and death valley

particle settling rates increase with depth in the ocean abstract time and depth scales of particulate organic carbon degradation and caco3 and biogenic opal dissolution are critical to understanding the depth distribution of co2 and dissolved nutrients in the ocean the speed at which particles sink and the factors that control sinking speed are of primary importance to the distribution of oceanic nutrient concentrations and to the preservation of biogenic material in the sediment record sequencing sediment trap collectors deployed at us jgofs sites in the equatorial pacific and arabian sea provided a time series of particle fluxes from which particle settling rates were estimated a comparison of settling velocities obtained from 100 500 m pilskaln et al deep sea research 45 1998 1803 to settling velocities obtained for depths between 1000 and 3500 m indicate an increase of a factor of 2 10 between 100 and 2000 m and an increase of 15 60 between 2000 and 3500 m the increase in settling velocity in the deep ocean is generally correlated with the loss of corg with depth lithogenic content does not appear to impact particle settling rate variability in particle settling rate is systematically related to physical forcing of the surface ocean in the equatorial pacific but not in the arabian sea the increase in particle settling rate with depth likely influences the delivery of caco3 to the sea floor

upb and rbsr geochronology and geological evolution of the harts range ruby mine area of the arunta inlier central australia abstract supracrustal and meta igneous rock units from the ruby mine area of the harts range eastern arunta inlier central australia have been dated by the zircon u pb and rb sr total rock tr and mica methods a well defined zircon discordia for a weakly deformed specimen of the bruna granite gneiss yields an age of emplacement of 1748 4 5 ma thereby constraining the minimum age of the irindina supracrustal assemblage metapelitic gneiss within the supracrustals and a meta igneous ultramafic boudin from the associated harts range meta igneous complex yield highly discordant zircon data revealing a strong early palaeozoic overprint rb sr tr data from anorthositic gneisses associated with the ultramafic boudin are highly disturbed also apparently during the lower palaeozoic however rb sr model age calculations and the zircon u pb data suggest a maximum age of about 2000 ma for the supracrustal and meta igneous rocks and argue for new proterozoic crust formation zircon u pb data from a deformed pegmatite emplaced in the meta igneous complex yield an emplacement age of 520 4 5 ma further pointing to lower palaeozoic magmatism and deformation correlations of u content and calculated 206 pb 238 u age for the ultramafic boudin zircons suggest that new growth of low u zircons occurred during retrogression associated with this event the sr isotope systematics of the anorthositic gneisses can also be interpreted in terms of introduction of palaeozoic sr our data suggest lower palaeozoic possibly delamerian tectonothermal activity to be more important in the evolution of the harts range area than previously recognised on the other hand rb sr mica ages for deformed and undeformed pegmatites and tr isochrons for the latter show that pervasive tectonothernal activity had ceased by about 315 ma and that regional cooling occurred between about 345 and 325 ma local shear zone biotite resetting may have persisted to about 300 ma consistent with the previously recognised alice springs orogeny possible dilational pb loss in the bruna zircons occurred at about 103 ma

evidence for 600 year old basalt and magma mixing at inyo craters volcanic chain long valley caldera california andesite inclusions are found within the vent areas of two 600 year old rhyolite domes in the inyo craters volcanic chain eastern california both domes lie within the present northwestern sector of 0 73 ma long valley caldera inclusion morphology indicates that they were partially molten and ductile during incorporation within coarsely porphyritic rhyolite the xenocryst assemblage within the inclusions plagioclase hornblende biotite quartz sanidine is identical to the phenocryst assemblage within the host rhyolite microprobe analyses of xenocrysts within the andesite inclusions show that they have compositions similar to phenocrysts in the host rhyolite these data suggest that the andesite inclusions are the result of mixing of the coarsely porphyritic rhyolite with a more mafic end member whole rock geochemistry of the inclusions generally supports a simple mixing model between the coarsely porphyritic rhyolite of the inyo domes and typical postcaldera mafic lavas found throughout the western caldera moat the inclusions provide the first evidence for involvement of basaltic magma in the 600 year old rhyolite eruptions of the inyo craters volcanic chain and suggest the possibility that the rhyolitic eruptions were initiated by injection of basalt into the lower part of the silicic magma system periodic thermal replenishment of the magmatic system through basaltic injection may explain the relatively high temperatures encountered in drill holes within the western caldera moat the inclusions further suggest that although rhyolite eruptions are statistically more likely from the inyo craters volcanic chain future basaltic eruptions cannot be ruled out

metamorphic and tectonic evolution of granulites arunta block central australia petrographical and chemical evidence presented here indicate a prolonged metamorphic evolution of the granulite terrain in the northern strangways range arunta block central australia nsr in fig 1 beginning with migmatization followed by dry granulite metamorphism at high temperatures t and moderate pressures p estimated at 850 920 c 8 1 kbar1 this occurred at 1 800 myr refs 2 3 very shortly after deposition of the protolith4 a bimodal volcanic suite5 and associated sediments granulite metamorphism was followed by isobaric cooling during which there was an episode of pervasive but partial hydration later retrogression and hydration localized along shear zones occurred at the normal geothermal gradient in the kyanite stability field a tensional rift like regime best describes the geological environment in which the protolith formed was deeply buried metamorphosed with high heat flow and then remained in isostatic equilibrium metamorphic parageneses recording uplift may be matched with mid palaeozoic tectonic events in central australia if this correlation is correct the rocks of the northern strangways range may have remained deeply buried for 1 400 myr during which the shear zones were reactivated several times fig 2

widespread influence of resuspended sediments on oceanic particulate organic carbon insights from radiocarbon and aluminum contents in sinking particles globally widespread also a strong correlation is found to exist between d 14 c values of organic carbon and aluminum content in sinking particles that is consistent over a range of oceanic settings together these findings imply that aged organic carbon associated with lithogenic material from sediment resuspension is responsible for the observed low d 14 c values as opposed to other processes such as incorporation of dissolved inorganic carbon or dissolvedorganiccarbonintopocatdepth anestimatebasedonpocflux weightedd 14 c values shows that about 35 of sinking poc at the locations studied is derived from resuspended sediment our results suggest that resuspension of sediment and its subsequent lateral transport is an important component of the oceanic carbon cycle and should be considered in models of oceanic carbon export and burial

ordovician high grade metamorphism of a newly recognised late neoproterozoic terrane in the northern harts range central australia granulite facies rocks from the northernmost harts range complex arunta inlier central australia have previously been interpreted as recording a single clockwise cycle of presumed palaeoproterozoic metamorphism 800 875 c and 9 10 kbar and subsequent decompression in a kilometre scale e w striking zone of noncoaxial high grade c 700 735 c and 5 8 6 4 kbar deformation however new shrimp u pb age determinations of zircon monazite and titanite from partially melted metabasites and metapelites indicate that granulite facies metamorphism occurred not in the proterozoic but in the ordovician c 470 ma the youngest metamorphic zircon overgrowths from two metabasites probably meta volcaniclastics yield 206pb 238u ages of 478 4 ma and 471 7 ma whereas those from two metapelites yield ages of 463 5 ma and 461 4 ma monazite from the two metapelites gave ages equal within error to those from metamorphic zircon rims in the same rock 457 5 ma and 462 5 ma respectively zircon and possibly monazite ages are interpreted as dating precipitation of these minerals from crystallizing melt within leucosomes in contrast titanite from the two metabasites yield 206pb 238u ages that are much younger 411 5 ma 417 7 ma respectively than those of coexisting zircon which might indicate that the terrane cooled slowly following final melt crystallization one metabasite has a second titanite population with an age of 384 7 ma which reflects titanite growth and or recrystallization during the 400 300 ma alice springs orogeny the c 380 ma titanite age is indistinguishable from the age of magmatic zircon from a small late and weakly deformed plug of biotite granite that intruded the granulites at 387 4 ma these data suggest that the northern harts range has been subject to at least two periods of reworking 475 460 ma 400 300 ma during the palaeozoic detrital zircon from the metapelites and metabasites and inherited zircon from the granite yield similar ranges of proterozoic ages with distinct age clusters at c 1300 1000 and c 650 ma these data imply that the deposition ages of the protoliths to the harts range complex are late neoproterozoic or early palaeozoic not palaeoproterozoic as previously assumed

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial pacific ocean abstract a systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the u s jgofs egpac transect from l2 n to l5 s at 140 w fluxes of lipids out of the euphotic zone varied spatially and temporally ranging from 0 20 0 6 mmol lipid c m 2 day 1 lipid fluxes were greatly attenuated with increasing water column depth dropping to 0 002 0 06 mmol lipid c m 2 day 1 in deep water sediment traps sediment accumulation rates for lipids were 0 0002 0 00003 mmol lipid c m 2 day 1 lipids comprised 11 23 of corg in net plankton 10 30 in particles exiting the euphotic zone 2 4 particles in the deep egpac and 0 1 1 in sediments lipids were in general selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids fatty acids were the most labile compounds with polyunsaturated fatty acids pufas being quickly lost from particles branchedchain c15 and c17 fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment indicating inputs of organic matter from bacteria long chain c39 alkenones of marine origin and long chain c20 c30 fatty acids alcohols and hydrocarbons derived from land plants were selectively preserved in sediments compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds and hence of organic matter as a whole a thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is thus essential for using the sediment record for reconstructing past oceanic environments