multipoint observations of a small substorm in this paper the authors present multipoint observations of a small substorm which occurred just after 0110 ut on april 25 1985 the observations were made by spacecraft ampte cce ampte irm dmsp f6 and dmsp f7 ground auroral stations eiscat magnetometer cross syowa narssarssuaq great whale river and fort churchill and mid latitude stations furstenfeldbruck toledo and argentine island these data provide them with a broad range of observations including the latitudinal extent of the polar cap visual identification of substorm aurorae and the magnetic perturbations produced directly beneath them in situ magnetic field and energetic particle observations of the disruption of the cross tail current sheet and observations concerning the spatial expansion of the current disruption region from two radially aligned spacecraft the dmsp data indicate that the event took place during a period when the polar cap was relatively contracted yet the disruption of the current sheet was observed by cce at 8 56 r sub e they have been able to infer a considerable amount of detail concerning the structure and westward expansion of the auroral features associated with the event and they show that those auroral surges were located more than 10 degree equatorward of the boundary between open andmore closed field lines moreover they present evidence that the current sheet disruption observed by cce in the neutral sheet was located on field lines which mapped to the westward traveling surge observed directly overhead of the ground station at syowa furthermore the observations strongly imply that disruption of the cross tail current began in the near earth region and that it had a component of expansion which was radially antisunward less

past present and future of thermochronology in one form or another geochronologists have been practicing thermochronology 1 the use of radioisotopic dating to constrain thermal histories of rocks and minerals for over 40 years building from lessons learned over these four decades thermochronology continues to evolve due to technical developments increasingly sophisticated theoretical models and an expanding range of applications in geologic and planetary science most recently interest in earth surface processes and interactions between tectonics erosion and climate has drawn attention to techniques that can address the timing and rates of processes operating at temperatures below about 300 c the purpose of this rimg volume is to assess the current state of thermochronology as of circa 2005 which is coincidentally the 100th anniversary of the first radioisotopic date rutherford 1905 1906 excellent review papers and books on specific topics within this field have been published but no single volume has yet provided a comprehensive review of current practices basic theory and illustrative examples the motivation for this volume stems from these considerations knowing that in a fast developing field a book like this can quickly become dated we tried to include sufficient review of fundamentals and the literature to offer students and new users a useful introduction to thermochronology that may have some staying power in this chapter we first review the salient points of thermochronology s history before assessing our current capabilities and challenges and then taking the risk of suggesting where the field is headed we do not provide a comprehensive history of the method that does full justice to the work of the large and growing cohort of thermochronologists in this short space we instead opted to give our perspectives on where the intellectual and technological roots of the discipline lie which run deeper and go back farther than is sometimes appreciated

simultaneous observation of the poleward expansion of substorm electrojet activity and the tailward expansion of current sheet disruption in the near earth magnetotail in this paper we present observations of a substorm that occurred on june 7 1985 the data consist of energetic ion and magnetic field data from ampte cce magnetometer data from the ground stations of the eiscat magnetometer cross stare radar data and pi 1 data from sodankyla cce was in the finnish local time sector and the model field line threading cce came down near the center of the eiscat magnetometer cross furthermore cce was located near the neutral sheet and observed the disruption of the cross tail current in situ at 2209 ut sodankyla registered a pi 1 burst and the eiscat stations recorded the onset of a negative bay simultaneously cce observed the onset of current sheet disruption and ion energization the energetic ions observed during this initial burst had gyrocenters earthward of cce an intensification of activity occurred at 2212 ut and it was observed essentially simultaneously on the ground and in space it consisted of an intensification of pi 1 activity an intensification of the westward electrojet poleward of the initial breakup latitude as determined from magnetometer and radar data and magnetic turbulence and a burst of energetic ions at cce in the magnetotail significantly this second burst was composed only of ions with gyrocenters tailward of the satellite and the magnetic turbulence was considerably weaker than that observed during the initial current disruption this strongly suggests that the current disruption region had moved tailward of cce the event provides a direct observational link between the tailward expansion of active regions in the near earth magnetotail and the poleward expansion of ionospheric electrojet activity during substorms

implications of quartz grain microtextures for onset eocene oligocene glaciation in prydz bay odp site 1166 antarctica abstract this paper presents the results of the scanning electron microscopic sem analysis of quartz grains from a selection of samples at site 1166 ocean drilling program leg 188 drilled site 1166 on the prydz bay continental shelf antarctica to document onset and fluctuations of east antarctic glaciation this site recovered upper pliocene holocene glacial sediments directly above cretaceous through lower oligocene sediments recording the transition from preglacial to early glacial conditions sem analysis of quartz grains at site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures angular edges edge abrasion as well as arcuate to straight steps are the most frequent features in glacial deposits the highest frequency of grains with round edges is present in middle late eocene fluvio deltaic sands however angular outlines fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces the results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution such as the transition from the east antarctic preglacial to glacial conditions on the continental shelf from middle late eocene to late eocene early oligocene time

onset of cenozoic antarctic glaciation abstract this paper considers the wide range of evidence both direct and indirect for the onset of cenozoic antarctic glaciation it distinguishes two useful phases of antarctic glacial onset an initial phase of mountain glaciation from which ice streams occasionally and in isolated locations reached sea level and a subsequent phase of full glaciation with an ice sheet as large as today s extending everywhere to sea level according to direct evidence generally proximal from the continent itself or surrounding southern ocean the first of these occurred probably during the late eocene while the second developed at the eocene oligocene boundary indirect evidence mainly involving proxy measurements from dsdp and odp sites remote from the southern ocean suggests that middle and late eocene glaciations may have been full also ice sheets possibly even larger than today s but short lived and that the e o boundary onset differed from these mainly in producing a stable ice sheet in pursuing the notion of glacial onset we examined the direct record separately for east antarctica west antarctica and the antarctic peninsula the different sub ice topography and geographic positions of which suggest that their glacial histories could have been different the direct record for an initial middle or late eocene phase is very sparse only the rare occurrence of ird at southern ocean dsdp and odp sites suggests the possibility of early ice and all three regions include mountains that could have hosted such ice although the indirect record and climate modelling in combination suggest that full glaciation of each region was probably synchronous we find differences in the available direct evidence there is abundant evidence that east antarctica became fully glaciated in the earliest oligocene but certain evidence of glaciation of a similar age extending to sea level is sparse for the antarctic peninsula and is not found until the late oligocene for west antarctica high resolution direct evidence is required to resolve uncertainties in glacial history

the source of ore fluids and solutes in archaean lode gold deposits of western australia abstract the ore fluids which produced archaean lode gold deposits in sub amphibolite facies rocks of the yilgarn block western australia are characteristically low to moderate salinity h 2 o co 2 ch 4 fluids wall rock alteration and ore deposition were from a generally reducing near neutral fluid at 200 350 c and 1 3 kbar although more oxidising fluids produced some assemblages in the giant golden mile deposit gold was transported as reduced sulphur complexes the ore fluid composition and stable and radiogenic isotope data indicate multiple sources for the fluid and solute deep plumbing systems are invoked with the fluids being either metamorphic fluids that derived solutes from the lower and upper crusts or fluids exsolved from deep seated granitoids formed by anatexis of such crust

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

age constraints on recycled crustal and supracrustal sources of archaean metasedimentary sequences eastern goldfields province western australia evidence from shrimp zircon dating abstract shrimp u pb zircon dating of sedimentary volcanic and subvolcanic intrusive rocks from unconformity bounded sequences in the eastern goldfields province defines maximum depositional ages for those sequences the kambalda sequence which records a backarc basin was deposited prior to 2700 ma and from at least 2715 ma the spargoville sequence which records an arc adjacent volcano bound basin was deposited between 2700 and 2683 ma the kalgoorlie sequence which records an intra arc rift basin comprises two tectonic stages with depositional ages of 2681 2670 and 2661 2655 ma deposition of the spargoville and kalgoorlie sequences overlapped with the intrusion of granitoids and subvolcanic porphyries thereby indicating that those granitoids were emplaced during crustal extension younger submarine fan kurrawang sequence and braided fluvial merougil and jones creek sequences deposits of a remnant ocean basin were deposited at when coupled to palaeocurrent data provenance dating of detrital zircon suites fingerprints southeast oriented amalgamation of felsic detritus from multiple sources within longitudinal depositional systems and longitudinal reworking of felsic detritus from single sourced transverse systems most felsic detritus was recycled from coeval volcanoplutonic arcs and the orogen to the remnant ocean basin sequences with zircon ages ranging from 2730 to 2660 ma older felsic sources with age ranges of 3570 3130 3030 2900 2870 2770 and 2760 ma could have been structural enclaves within the volcanoplutonic arcs or orogen but were more likely within a distant cratonic basement when coupled with stratigraphic data it is concluded that detrital zircon age distributions preserve evidence for the sedimentary recycling of coeval volcanoplutonic arc or orogenic sources uplifted basin floor and dissected arc successions and cratonic basement virtually all source terrains have apparently vanished presumably through the combination of tectonic and sedimentary recycling and tectonic severance increased use of detrital zircon suites from archaean sedimentary sequences is advocated in order to quantify the balance between sedimentary recycling of felsic rocks from contemporaneous volcanoplutonic sources which themselves document crustal growth in arc environments and from relict volcanoplutonic and crustal basement sources which document the degree of crustal recycling

a long lived hydrothermal system in bushveld granites at the zaaiplaats tin mine lead isotope evidence tin mineralization at zaaiplaats is hosted in alkali feldspar granites of the lebowa granite suite which intrude the rashoop granophyre suite from the upper contact downward the alkali feldspar granites include the marginal pegmatite fine grained lease granite and the coarse grained bobbejaankop granite the major mineralization styles consist of subhorizontal tabular low grade orebodies in the lease granite a lower zone of disseminated cassiterite mineralization in the bobbejaankop granite and shallowly plunging and branching pipe orebodies in both granites fluid inclusion data show a continuous evolution of the magmatic hydrothermal system from 600 degrees to 200 degrees c with cassiterite and scheelite precipitation above 400 degrees c mineral compositions and oxygen isotope fractionations indicate reequilibration of minerals within the granites during pervasive alteration at temperatures generally between 200 degrees and 300 degrees c the emplacement age of these and other bushveld granites is ca 2050 ma yet pb pb whole rock isochron ages for the different variably mineralized granite bodies at zaaiplaats show a relatively restricted range from 961 or 129 ma for the rashoop granophyre to 1187 or 51 ma for the lease granite thus the analyzed sample suites consistently record an event approximately 1 b y after the emplacement of the granites modeling their pb isotope evolution indicates that each suite evolved independently between 2050 and ca 1100 ma suggesting that hydrothermal fluid circulation was essentially confined within each granite body and or fluid rock ratios were low and that the overall 238 u 204 pb within each suite from 2050 to ca 1100 ma was not unusually high or low for fractionated granites suggesting largely closed system behavior of u and pb within each suite during this interval the ca 1100 ma event which caused closure of the u pb systems at zaaiplaats is interpreted to reflect a blocking temperature age related to uplift and cooling of a long lived hydrothermal system and precipitation of the latest stage minerals e g galena at 200 degrees to 300 degrees c the high steady state temperature required to maintain the hydrothermal system at zaaiplaats at temperatures above 200 degrees c for ca 1 b y was provided by radioactive decay current heat production characteristics calculated from present day u th and k 2 o concentrations range from 4 2 mu w m 3 for the rashoop granophyre to 11 5 mu w m 3 for the lease granite preweathering heat production of 30 3 mu w m 3 is inferred for the mineralized bobbejaankop granite after accounting for dramatic recent losses of u and th the low level of hydrothermal fracturing combined with stable and pb isotope evidence effectively rules out convective cooling by external fluids as a significant heat loss mechanism at zaaiplaats fluid pathways within the granites were controlled dominantly by grain boundaries microfractures and vugs which allowed internal circulation and elevated subsolidus temperatures to be maintained indefinitely under a thermal blanket of an estimated 4 km of postemplacement cover uplift and erosion of the terrain caused cooling through the pb exchange blocking temperatures at ca 1100 ma

reconstructions of antarctic topography since the eocene oligocene boundary abstract accurate models of past antarctic ice sheet behaviour require more realistic reconstructions of the evolution of bedrock topography however other than a preliminary attempt to reconstruct antarctic topography at the eocene oligocene boundary the long term evolution of antarctica s subglacial topography throughout its glacial history has not previously been quantified here we derive new reconstructions of antarctic topography for four key time slices in antarctica s climate and glacial history the eocene oligocene boundary ca 34 ma the oligocene miocene boundary ca 23 ma the mid miocene climate transition ca 14 ma and the mid pliocene warm period ca 3 5 ma to reconstruct past topography we consider a series of processes including ice sheet loading volcanism thermal subsidence horizontal plate motion erosion sedimentation and flexural isostatic adjustment and validate our models where possible using onshore and offshore geological constraints our reconstructions show that the land area of antarctica situated above sea level was 25 larger at the eocene oligocene boundary than at the present day offshore sediment records and terrestrial constraints indicate that the incision of deep subglacial topographic troughs around the margin of east antarctica occurred predominantly in the oligocene and early miocene whereas in west antarctica erosion and sedimentation rates accelerated after the mid miocene changes to the topography after the mid pliocene were comparatively minor our new palaeotopography reconstructions provide a critical boundary condition for models seeking to understand past behaviour of the antarctic ice sheet and have implications for estimating changes in global ice volume temperature and sea level across major cenozoic climate transitions

early east antarctic ice sheet growth recorded in the landscape of the gamburtsev subglacial mountains the gamburtsev subglacial mountains are regarded as a key nucleation site for the antarctic ice sheet and they retain a unique long term record of pre glacial and early glacial landscape evolution here we use a range of morphometric analyses to constrain the nature of early glaciation and subsequent ice sheet evolution in the interior of east antarctica using a new digital elevation model of the gamburtsev subglacial mountains derived from an extensive airborne radar survey we find that an inherited fluvial landscape confirms the existence of the gamburtsev subglacial mountains prior to the onset of glaciation at the eocene oligocene climate boundary ca 34 ma features characteristic of glaciation at a range of scales are evident across the mountains high elevation alpine valley heads akin to cirques identified throughout the mountains are interpreted as evidence for early phases of glaciation in east antarctica the equilibrium line altitudes associated with these features combined with information from fossil plant assemblages suggest that they formed at or prior to 34 ma it cannot be ruled out that they may have been eroded by ephemeral ice between the late cretaceous and the eocene 100 34 ma hanging valleys overdeepenings truncated spurs and steep sided linear valley networks are indicative of a more widespread alpine glaciation in this region these features represent ice growth at or before 33 7 ma and provide a minimum estimate for the scale of the east antarctic ice sheet between ca 34 and 14 ma when dynamic fluctuations in ice extent are recorded at the coast of antarctica the implications are that the early east antarctic ice sheet grew rapidly and developed a cold based core that preserved the alpine landscape the patterns of landscape evolution identified provide the earliest evidence for the development of the east antarctic ice sheet and can be used to test coupled ice climate evolution models

the development of the substorm expansive phase the eye of the substorm the explosive onset and development of a clearly defined auroral substorm has been analysed using data from the ultraviolet imager aboard the viking satellite these data permit the evolution of the substorm to be traced with a time resolution as high as 40 seconds the envelope of the disturbed region the eye expands both poleward and azimuthally to the east and west reaching an azimuthal extent of almost six hours of magnetic local time after about 15 minutes the poleward expansion involves irregular poleward motion accompanying intensifications within the eye with the maximum poleward displacement being at the meridian of the center of the eye within the eye discrete regions of enhanced luminosity develop with a tendency for each newly disturbed region to be to the west of the previous ones it is however observed that a newly excited region can be to the east of the pre existing activated region each new intensification is accompanied by a brief further poleward expansion of the high latitude edge of the eye each region of enhanced luminosity within the eye remains relatively stationary and fluctuates in intensity over its lifetime we identify these regions of enhanced luminosity with westward traveling surges as defined from ground observations in the earlier literature our uv imager data demonstrate that these surges do not necessarily propagate although the overall envelope of the substorm disturbed region expands both eastward and westward during the lifetime of the event

ice cover landscape setting and geological framework of lake vostok east antarctica abstract lake vostok located beneath more than 4 km of ice in the middle of east antarctica is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment melting and freezing at the base of the ice sheet which slowly flows across the lake controls the flux of water biota and sediment particles through the lake the influx of thermal energy however is limited to contributions from below thus the geological origin of lake vostok is a critical boundary condition for the subglacial ecosystem we present the first comprehensive maps of ice surface ice thickness and subglacial topography around lake vostok the ice flow across the lake and the landscape setting are closely linked to the geological origin of lake vostok our data show that lake vostok is located along a major geological boundary magnetic and gravity data are distinct east and west of the lake as is the roughness of the subglacial topography the physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake s circulation lake vostok is a tectonically controlled subglacial lake the tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small but significant amounts of thermal energy into the lake

timing of deformation in the norseman wiluna belt yilgarn craton western australia establishing relative and absolute time frameworks for the sedimentary magmatic tectonic and gold mineralisation events in the norseman wiluna belt of the archean yilgarn craton of western australia has long been the main aim of research efforts recently published constraints on the timing of sedimentation and absolute granite ages have emphasized the shortcomings of the established rationale used for interpreting the timing of deformation events in this paper the assumptions underlying this rationale are scrutinized and it is shown that they are the source of significant misinterpretations a revised time chart for the deformation events of the belt is established the first shortening phase to affect the belt d1 was preceded by an extensional event d1e and accompanied by a change from volcanic dominated to plutonic dominated magmatism at approximately 2685 2675 ma later extension d2e controlled deposition of the ca 2655 ma kurrawang sequence and was followed by d2 a major shortening event which folded this sequence d2 must therefore have started after 2655 ma at least 20 ma later than previously thought and after the voluminous 2670 2655 ma high ca granite intrusion younger transcurrent deformation d3 d4 waned at around 2630 ma suggesting that the crustal shortening deformation cycle d2 d4 lasted approximately 20 30 ma contemporaneous with low volume 2650 2630 ma low ca granites and alkaline intrusions time constraints on gold deposits suggest a late mineralisation event between 2640 2630 ma thus d2 d4 deformation cycle and late felsic magmatism define a 20 30 ma long tectonothermal event which culminated with gold mineralisation the finding that d2 folding took place after voluminous high ca granite intrusion led to research into the role of competent bodies during folding by means of numerical models results suggest that buoyancy driven doming of pre tectonic competent bodies trigger growth of antiforms whereas non buoyant competent granite bodies trigger growth of synforms the conspicuous presence of pre folding granites in the cores of anticlines may be a result from active buoyancy doming during folding 2002 elsevier science b v all rights reserved

evidence for iceberg armadas from east antarctica in the southern ocean during the late miocene and early pliocene abstract sediments from ocean drilling program site 1165 in the indian ocean sector of the southern ocean off prydz bay contain a series of layers that are rich in ice rafted debris ird here we present evidence that ird rich layers at site 1165 at 7 4 8 and 3 5 ma record short lived massive discharges of icebergs from wilkes land and adelie land more than 1500 kilometers to the east of the depositional site this distant source of icebergs is clearly defined by the presence of ird hornblende grains with 40ar 39ar ages of 1200 1100 ma and 1550 1500 ma ages that are not found on the east antarctic continent in locations closer to site 1165 this observation requires enormous amounts of detritus carrying drifting icebergs most likely in the form of large icebergs these events probably reflect destabilization surge and break up of ice streams on the wilkes land and adelie land margins of the east antarctic ice sheet in the vicinity of the low lying aurora and wilkes basins they occurred under warming conditions but each coast seems to have produced ice rafting events independently at different times the data presented here constitute the first evidence of far traveled icebergs from specific source areas around the east antarctic perimeter launch of these icebergs may have happened during quite dramatic events perhaps analogous to heinrich events in the north atlantic

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

the structure and origin of prydz bay and macrobertson shelf east antarctica abstract a marine geophysical survey in early 1982 conducted by the australian bureau of mineral resources indicated that much of prydz bay is underlain by a sedimentary basin severe seismic multiples preclude an accurate estimate of total sediment thickness but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km the trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall nne trend roughly orthogonal to the continental margin in the south of prydz bay two series of seismic sequences are evident separated by a mildly erosional unconformity the lower series ranges from poorly to well stratified has minor folding and faulting and probably derives from continental and perhaps shallow marine pre breakup sediments the upper series is generally well stratified and prograded near the shelf edge it probably represents shallow marine post breakup sediments the seabed is distinctly unconformable with the underlying sediments implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the amery ice shelf and that present sedimentation rates are very low possible thin moraines or tillites in the northeast part of the prydz bay are also attributed to these glacial advances the continental slope and rise sedimentary section ranges from at least 3 km thick off prydz bay to thin off the macrobertson shelf to the west reflecting the more prolific sediment source in prydz bay the deep water section includes several seismic sequences the most distinctive being interpreted as sheet volcanics and turbidite fans the deepest visible unconformity is locally strongly faulted and may separate the pre breakup and post breakup sediments indo antarctic breakup has been tentatively dated as early neocomian 130 ma and the e w orientation of the resultant antarctic coast invites interpretation of the lambert glacier prydz bay structure as a possible failed rift arm of a triple junction direct information on the age and nature of the sediments under prydz bay is lacking but permian continental sediments cropping out at beaver lake to the south may correspond to the lower pre breakup series this interpretation gains some support from analogies with fault bounded intracratonic basins in india which contain permian to triassic continental strata and which may have been juxtaposed prior to breakup the upper series probably consists of upper cretaceous and cainozoic sands and shales with moraines or tillites at the top of the section

extremely low long term erosion rates around the gamburtsev mountains in interior east antarctica the high elevation and rugged relief 3 km of the gamburtsev subglacial mountains gsm have long been considered enigmatic orogenesis normally occurs near plate boundaries not cratonic interiors and large scale tectonic activity last occurred in east antarctica during the pan african 480 600 ma we sampled detrital apatite from eocene sands in prydz bay at the terminus of the lambert graben which drained a large pre glacial basin including the northern gamburtsev mountains apatite fission track and u th he cooling ages constrain bedrock erosion rates throughout the catchment we double dated apatites to resolve individual cooling histories erosion was very slow averaging 0 01 0 02 km myr for 250 myr supporting the preservation of high elevation in interior east antarctica since at least the cessation of permian rifting long term topographic preservation lends credence to postulated high elevation mountain ice caps in east antarctica since at least the cretaceous and to the idea that cold based glaciation can preserve tectonically inactive topography

an antarctic stratigraphic record of stepwise ice growth through the eocene oligocene transition earth s current icehouse phase began 34 m y ago with the onset of major antarctic glaciation at the eocene oligocene transition changes in ocean circulation and a decline in atmospheric greenhouse gas levels were associated with stepwise cooling and ice growth at southern high latitudes the antarctic cryosphere plays a critical role in the ocean atmosphere system but its early evolution is still poorly known with a near field record from prydz bay antarctica we demonstrate that antarctic ice growth was stepwise and had an earlier onset than previously suggested prydz bay lies downstream of a major east antarctic ice sheet drainage system and its sedimentary records uniquely constrain the timing of ice sheet advance onto the continental shelf we investigated a detrital record extracted from three ocean drilling program drill holes within a new depositional and chronological framework spanning the late eocene to early oligocene ca 36 33 ma the chemical index of alteration cia and the s index calculated from the major element geochemistry of bulk samples yielded estimates of chemical weathering intensities and mean annual temperature on the east antarctic continent we document evidence for late eocene mountain glaciation along with transient warm events at 35 8 34 8 ma from 34 4 ma associated with the eocene oligocene transition precursor 18o excursion glaciers advanced into prydz bay coincident with a decline in chemical weathering and temperature we conclude that antarctic continental ice growth commenced with the eocene oligocene transition precursor glaciation during a time of subantarctic surface ocean cooling and a decline in atmospheric pco2 these results call for dynamic high latitude feedbacks that are currently poorly represented in earth system models and emphasize the need for additional near field glacio sedimentological high latitude sea surface temperature and pco2 records across the eocene oligocene transition

two stepping into the icehouse east antarctic weathering during progressive ice sheet expansion at the eocene oligocene transition in conjunction with increasing benthic foraminiferal 18 o values at the eocene oligocene transition eot ca 34 ma coarse grained ice rafted debris ird 425 m appears abruptly alongside fossil fish teeth with continentally derived neodymium nd isotope ratios e nd in kerguelen plateau southern ocean sediments increased antarctic weathering flux as inferred from two steps to less radiogenic e nd values coincides with two steps in benthic foraminiferal 18 o values these results indicate that two distinct surges of weathering were generated by east antarctic ice growth during the eot weathering by ice sheets during a precursor glaciation at 33 9 ma did not produce significant ird accumulation during the first e nd shift glacial weathering was sustained during a terrace interval between the two steps probably by small high elevation ice sheets a large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca 33 7 ma rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions parallel changes in antarctic weathering flux and deep sea carbonate accumulation suggest that ice sheet expansion during the eot had a direct impact on the global carbon cycle possible mechanisms include associated changes in silicate weathering on the east antarctic craton and enhanced fertilization of southern ocean waters both of which warrant further investigation

the archean chalice gold deposit a record of complex multistage high temperature hydrothermal activity and gold mineralisation associated with granitic rocks in the yilgarn craton western australia abstract the chalice gold deposit 20 t au produced in the southwestern portion of the late archean norseman wiluna greenstone belt of the yilgarn craton western australia is hosted both in a sequence of intercalated mafic and ultramafic amphibolites and a post peak metamorphism monzogranite dike the deposit is flanked on the western side by calc alkaline plutonic rocks and to the east by a predominantly monzogranitic pluton with at least four generations of monzogranitic dikes that intrude the local mine stratigraphy locally four deformation events d 1 d 4 have affected this sequence of amphibolites and two stages of gold mineralisation are recognised controlled by the progressive d 2 event main stage gold mineralisation 95 of the resource which is demonstrably later than all granitic bodies except second generation and subsequent monzogranite dikes is controlled by localised d 2 asymmetric folds developed in the mafic amphibolite it is expressed as veins and wall rock replacement characterised by a prograde assemblage of quartz diopside plagioclase k feldspar titanite pyrrhotite pyrite magnetite garnet hornblende scheelite and biotite second stage gold mineralisation 5 of the resource is associated with the intrusion of a monzogranite dike and is expressed as disseminated gold in the dike as well as foliation discordant veins of quartz gold quartz diopside gold actinolite gold and molybdenite tellurobismuthite gold detailed field mapping and petrography suggest that main stage gold mineralisation at chalice is equivalent to hypozonal orogenic lode gold mineralisation in other archean greenstone belts of the yilgarn craton whereas monzogranite associated second stage gold mineralisation is atypical of such deposits the main stage mineralisation cannot be correlated to any particular granitoid in the local environment although temporally it is bracketed by granitic magmatism a deep magmatic or metamorphic source cannot be resolved from the field data it is also uncertain as to whether second stage mineralisation represents a true magmatic gold event or is a product of the assimilation and remobilisation of main stage gold during the intrusion of the monzogranite dike however its distinctive metal association of au bi mo te w suggests the former irrespective of this uncertainty chalice remains as a deposit which is more intimately related both spatially and temporally to granitic magmatism than other yilgarn deposits

mapping using the tsyganenko long magnetospheric model and its relationship to viking auroral images the tsyganenko long magnetospheric model 1987 has been used in conjunction with ultra violet images taken by the viking spacecraft to investigate the relationship of the auroral distribution to different magnetospheric regions the model describes the large scale structure of the magnetosphere reasonably well for dipole tilt angles near zero but it appears to break down at higher tilt angles even so a wide variety of auroral configurations can be accurately described by the model it appears that the open closed field line boundary is a poor indicator of auroral arc systems with the possible exception of high latitude polar arcs the auroral distribution typically called the oval maps to a region in the equatorial plane quite close to the earth and can be approximately located by mapping the model current density maximum from the equatorial plane into the ionosphere although the model may break down along the flanks of the magnetotail the large scale auroral distribution generally reflects variations in the near earth region and can be modeled quite effectively

timing and duration of high temperature gold mineralization and spatially associated granitoid magmatism at chalice yilgarn craton western australia the chalice gold deposit in the eastern goldfields province yilgarn craton western australia is located in a middle to upper amphibolite facies metamorphic domain and is hosted by a mafic ultramafic rock sequence that has been locally intruded by four generations of monzogranite dikes two stages of gold mineralization identified on the basis of crosscutting relationships formed under broadly synpeak to postpeak metamorphic conditions main stage gold mineralization 95 of the resource comprises foliation parallel quartz albite diopside titanite garnet gold veins and wall rock replacement both within locally developed asymmetric folds in mafic amphibolite second stage gold mineralization 5 of the resource is temporally associated with a second generation monzogranite dike that crosscuts the folds and hence is younger than the main event it is represented by disseminated gold in the dike as well as by foliation discordant quartz gold quartz diopside gold actinolite gold and molybdenite tellurobismuthite gold veins gold is in textural equilibrium with the hydrothermal alteration assemblages in both mineralization stages and also with primary igneous phases quartz and feldspar in the monzogranite dike in the second stage ore magmatic zircons and titanite from second and fourth generation monzogranite dikes and a monzogranite stock as well as hydrothermal titanite and molybdenite in equilibrium with gold from hydrothermal alteration assemblages allow dating of the important magmatic and hydrothermal events using the u pb and re os isotope systems two gold events are identified main stage mineralization is coincident with asymmetric fold development at 2644 8 ma shrimp u pb on titanite and second stage mineralization 2621 10 ma re os on molybdenite is coeval within the error of the isotopic ages with the intrusion of the gold mineralized second generation monzogranite dike 2626 9 ma shrimp u pb on zircon ages of hydrothermal titanite in monzogranite dikes 2631 10 ma 2624 7 ma 2623 5 ma and 2619 6 ma shrimp u pb ages indicate contemporaneous hydrothermal alteration gold mineralization and evolving magmatism during the second stage event a fourth generation flat lying pegmatite which truncates all mine rock units constrains the minimum age of mine scale gold bearing alteration and magmatism to 2622 13 ma the geologically constrained geochronologic data suggest that the chalice gold deposit is a product of two independent gold events separated by up to 20 m y within an extended period of granitoid magmatism also extending over 20 m y it demonstrates for the first time in the extensively gold mineralized yilgarn craton a clear interdependence and interplay between ongoing granitoid magmatism deformation hydrothermal alteration and gold mineralization in amphibolite hosted deposits however although integrated field and geochemical research establish a clear chronology of events the controversy of contribution from magmatic and or metamorphic fluids for the ore remains unresolved because these events are broadly coeval within the resolution of the isotopic techniques

proterozoic crustal evolution of central east antarctica age and isotopic evidence from glacial igneous clasts and links with australia and laurentia abstract rock clasts entrained in glacial deposits sourced from the continental interior of antarctica provide an innovative means to determine the age and composition of ice covered crust zircon u pb ages from a suite of granitoid clasts collected in glacial catchments draining central east antarctica through the transantarctic mountains show that crust in this region was formed by a series of magmatic events at 2 01 1 88 1 85 1 79 1 57 1 50 1 41 and 1 20 1 06 ga the dominant granitoid populations are ca 1 85 1 45 and 1 20 1 06 ga none of these igneous ages are known from limited outcrop in the region in addition to defining a previously unrecognized geologic history zircon o and hf isotopic compositions from this suite have 1 mantle like 18o signatures 4 0 4 5 and near chondritic hf isotope compositions ehf 1 5 for granitoids of 2 0 ga age 2 mostly crustal 18o 6 0 8 5 and variable hf isotope compositions ehf 6 to 5 in rocks with ages of 1 88 1 85 1 79 and 1 57 ga in which the 1 88 1 79 ga granitoids require involvement of older crust 3 mostly juvenile isotopic signatures with low mantle like 18o 4 5 and radiogenic hf isotope signatures ehf 6 to 10 in rocks of 1 50 1 41 ga age with some showing crustal sources or evidence of alteration and 4 mixed crustal and mantle 18o signatures 6 0 7 5 and radiogenic hf isotopes ehf 3 to 4 in rocks of 1 2 ga age together these age and isotopic data indicate the presence in cratonic east antarctica of a large composite igneous province that formed through a punctuated sequence of relatively juvenile proterozoic magmatic events further they provide direct support for geological correlation of crust in east antarctica with both the gawler craton of present day australia and proterozoic provinces in western laurentia prominent clast ages of 2 0 1 85 1 57 and 1 45 ga together with sediment source linkages provide evidence for the temporal and spatial association of these cratonic elements in the columbia supercontinent abundant 1 2 1 1 ga igneous and metamorphic clasts may sample crust underlying the gamburtsev subglacial mountains indicating the presence of a mesoproterozoic orogenic belt in the interior of east antarctica that formed during final assembly of rodinia

synmetamorphic lode gold deposits in high grade archean settings lode gold deposits that formed under conditions of the middle to upper amphibolite and granulite facies have been identified in the yilgarn block of western australia these deposits which form a continuum with lower metamorphic grade mesothermal gold depos its show that at least some of the fluids responsible for mesothermal gold deposits originated in or below the middle crust studies of 18 o suggest that fluid compositions were controlled by the wall rocks at least for some elements these more proximal gold deposits provide more information about deep fluid sources than do investigations of higher level mineralization deposited from fluids strongly modified by wall rock interaction during the early part of their ascent

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

late eocene glaciofluvial to glaciomarine transition in the lambert graben constraints from lithofacies and mineralogy of odp site 1166 sediments prydz bay antarctica

joint two dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents 32 auroral zone currents during the passage of a westward travelling surge

precambrian tectonic history of the west australian craton and adjacent orogens this review is a synthesis of the precambrian geology of the west aus tralian craton and its fringing orogens it describes the evidence that has recently been reinvestigated and reinterpreted to reveal a long dynamic history of repeated aggregation and dispersal of crustal fragments cratons are large composite geological units of continental crust that have survived intact for significant periods of geological time they are generally tabular bodies with great areal extent millions of square kilo meters and lithospheric thickness 200 400 km orogens are narrow steep zones of tectonic and metamorphic activity associated with the deposition of sediments and the intrusion of plutonic rocks they occur within or along the margins of continents and are generally a few hundred kilometers wide thousands of kilometers long and extend to the base of the litho sphere most orogens are initially associated with compressive tectonics crustal thickening and the transient formation of mountain belts cratons and orogens may survive for very long periods of time but as part of a thin crust on a dynamic mantle they are inherently mobile and travel as rafts for great distances around the surface of the earth they may be torn apart dispersed and reassembled with other continental fragments the boundaries of these crustal fragments once established remain zones of crustal weakness that may be reactivated as intra continental mobile belts or lines along which cratons are assembled and dismembered cf hoffman 1 988

on the timing relationship between fluid production and metamorphism in metamorphic piles some implications for the origin of post metamorphic gold mineralisation abstract the relative timing of metamorphism at different crustal levels is quantified for a range of metamorphic environments associated with convergent deformation we characterise different metamorphic environments by making simple assumptions about the nature of heat input and the nature of heat withdrawal from the terrane if internal heat production is the major heating agent during crustal thickening then deep crustal levels reach their metamorphic temperature peak later than shallow levels in terranes heated from below such relationships apply only if erosion commenced early in the thermal history or if erosion rates are fast quantitative knowledge of these relations can be used together with simple assumptions about prograde fluid release to predict the likely timing of fluid passage through rocks higher in the column in terranes with deep later characteristics the evidence for fluid penetration may be preserved in the form of mineralised quartz veins or late stage alteration within our simple parameterisation of crustal heat sources we can use the grade of a metamorphic rock together with field evidence on the timing of metamorphism igneous intrusion and deformation in order to constrain the time scale of the underlying thermal perturbation and erosion process for a given terrane we demonstrate that time intervals up to several tens of million years may separate metamorphism and fluid emplacement in model evolutions that are scaled to describe greenschist facies metamorphic terranes that formed at low pressure such timing relationships are in fact recorded in many greenschist facies metamorphic terranes that host late stage mesothermal gold deposits we suggest therefore that there is no conflict between the observation that the emplacement of many gold deposits occurred demonstrably after peak metamorphism of their host rocks and the interpretation that metamorphic fluids are responsible for the mineralisation

evidence against a young volcanic origin of the gamburtsev subglacial mountains antarctica 1 the gamburtsev subglacial mountains of east antarctica are among earth s most enigmatic mountain ranges they are situated in the middle of antarctica buried under hundreds of meters of ice and reach an elevation of more than 3000 m these characteristics have given rise to speculation about their origin and composition in particular whether they are a hotspot or remnants of ancient orogenic events we studied fluvio deltaic sands from odp site 1166 in prydz bay which were deposited prior to the onset of east antarctic glaciation to address the question of their origin results for u pb dating of detrital zircons reveal an important age population of 530 ma which is accompanied by a dominant 40ar 39ar age population of 519 ma for detrital hornblendes the data show no sign of young volcanic contributions suggesting an old continental origin of the mountains leaving as enigmatic the cause of their great height and size

analysis of antarctic glacigenic sediment provenance through geochemical and petrologic applications abstract the number of provenance studies of glacigenic sediments in antarctica has increased dramatically over the past decade providing an enhanced understanding of ice sheet history and dynamics along with the broader geologic history such data have been used to assess glacial erosion patterns at the catchment scale flow path reconstructions over a wide range of scales and ice sheet fluctuations indicated by iceberg rafted debris in circumantarctic glacial marine sediments it is notable that even though most of the bedrock of the continent is ice covered and inaccessible provenance data can provide such valuable information about antarctic ice and can even be used to infer buried rock types along with their geo and thermochronologic history glacigenic sediments provide a broader array of provenance analysis opportunities than any other sediment type because of their wide range of grain sizes and in this paper we review methods and examples from all size fractions that have been applied to the antarctic glacigenic sedimentary record interpretations of these records must take careful consideration of the choice of analytical methods uneven patterns of erosion and spatial variability in sediment transport and rock types which all may lead to a preferential identification of different elements of sources in the provenance analyses because of this we advocate a multi proxy approach and highlight studies that demonstrate the value of selecting complementary provenance methods

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

case for the gamburtsev subglacial mountains of east antarctica originating by mid carboniferous shortening of an intracratonic basin the present drainage of east antarctica with ice radiating from a central dome draped over the thick crust of the gamburtsev subglacial mountains recapitulates the early permian scene including the south polar paleolatitude the permian radial drainage was on the same scale as the present drainage around the thick crust of the tibetan plateau another high region in carboniferous permian time was the upland of europe on crust thickened during the variscan collision to form pangea the ancestral gamburtsev subglacial mountains and a central australian upland may have formed because of long distance stress from the variscan collision acting on zones of weak crust attenuated during prolonged subsidence of intracratonic basins the mid carboniferous inception of widespread glaciation was possibly linked with vast uplands in northern and southern pangea through the effects of variscan topography and the removal of atmospheric co 2 during accelerated erosion and weathering

a multiproxy provenance approach to uncovering the assembly of east gondwana in antarctica east gondwana is generally thought to have assembled through the amalgamation of indo antarctica and australo antarctica along the ediacaran cambrian kuunga orogen the location of a boundary between indo antarctica and australo antarctica within this key gondwana forming orogen remains controversial because extensive ice cover in east antarctica precludes traditional characterization of terranes here we integrated pb isotope analysis of detrital feldspar grains with u pb dating of detrital monazite and zircon grains from offshore sediments to infer the location of the onshore boundary between indo antarctica and australo antarctica new and compiled data from onshore basement exposures highlight the different age and pb isotope signatures of indo antarctica and australo antarctica holocene sediments offshore from mirny station queen mary land east antarctica have detrital feldspar pb isotope signatures and detrital monazite and zircon u pb ages that reflect contributions from both indo antarctica and australo antarctica the presence of both indo antarctic and australo antarctic crust beneath ice cover near mirny station implies proximity to a fundamental terrane boundary within the kuunga orogen which could coincide with a geophysical lineament at 94 e mirny fault the geophysical expression of this boundary extends into the subglacial interior of east antarctica where prior to more recent rifting it may have connected with one or more previously inferred gondwana forming sutures the revised geometry of the kuunga orogen suggests that the assembly of east gondwana involved dominantly strike slip motion in the mirny region coupled with high angle convergence between indo antarctica and australo antarctica to the west

isotopic interrogation of a suspected late eocene glaciation ephemeral polar glaciations during the middle to late eocene 48 34 ma have been proposed based on far field ice volume proxy records and near field glacigenic sediments although the scale timing and duration of these events are poorly constrained here we confirm the existence of a transient cool event within a new high resolution benthic foraminiferal 18o record at ocean drilling program odp site 738 kerguelen plateau southern ocean this event named the priabonian oxygen isotope maximum prom event lasted 140 kyr and is tentatively placed within magnetochron c17n 1n 37 3 ma based on the correlation to odp site 689 maud rise southern ocean a contemporaneous change in the provenance of sediments delivered to the kerguelen plateau occurs at the study site determined from the 63 m fraction of decarbonated and reductively leached sediment samples changes in the mixture of bottom waters based on fossil fish tooth nd were less pronounced and slower relative to the benthic 18o and terrigenous nd changes terrigenous sediment nd values rapidly shifted to less radiogenic signatures at the onset of the prom event indicating an abrupt change in provenance favoring ancient sources such as the paleoproterozoic east antarctic craton bottom water nd reached a minimum value during the prom event although the shift begins much earlier than the terrigenous nd excursion the origin of the abrupt change in terrigenous sediment provenance is compatible with a change in antarctic terrigenous sediment flux and or source as opposed to a reorganization of ocean currents a change in terrigenous flux and or source of antarctic sediments during the oxygen isotope maximum suggests a combination of cooling and ice growth in east antarctica during the early late eocene

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz