dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

fluid inclusion petrography of sw england granites and its potential in mineral exploration fluid inclusions in granite quartz from sw england provide a record of the complex and protracted hydrothermal history of this important metallogenic province regional variations in terms of the different types of inclusions can be correlated on an inter pluton scale with both the texture of the host granite and the extent to which it is mineralized on an intra granite scale those areas where mineralization is particularly pronounced show a higher overall inclusion abundance than areas where little or no mineralization is known to occur the types of fluid inclusion most commonly related to sn w cu mineralization are halite free moderate temperature inclusions inclusions containing visible co2 at room temperature are restricted to two localities in sw england both of these contain stockwork vein swarm tungsten mineralization these regional fluid inclusion anomalies show that fluid inclusion petrography using a simple petrographic microscope has potential application in the field of mineral exploration

late pleistocene glaciation of the kosciuszko massif snowy mountains australia abstract late pleistocene glaciation of the australian mainland was restricted to a small area of the southeastern highlands geomorphic mapping of the area and exposure dating using the in situ produced cosmogenic isotope 10be provides evidence for at least two distinct glaciations the early kosciuszko glaciation consisted of a single glacier advance before 59 300 5400 years ago snowy river advance the late kosciuszko glaciation comprised three glacier advances 32 000 2500 headley tarn advance 19 100 1600 blue lake advance and 16 800 1400 years ago mt twynam advance the early kosciuszko glaciation was the most extensive and the late kosciuszko advances were progressively less extensive these periods of glaciation in the highlands correspond to episodes of periglacial activity and peaks in lake levels and river discharge at lower elevations in southeastern australia glacier advances on the kosciuszko massif correlate with advances in tasmania south america and new zealand and are broadly representative of hemispheric climate changes during the last glacial cycle

loess and floods high resolution multi proxy data of last glacial maximum lgm slackwater deposition in the flinders ranges semi arid south australia abstract terrace remnants of late pleistocene fine grained valley fill deposits silts deeply entrenched by ephemeral traction load streams in arid areas remain a puzzle they have been attributed to a variety of origins ranging from lacustrine to alluvial floodplains we here report a centimetre scale multi proxy study of a 7 m section of silts in the semi arid flinders ranges of south australia which span the lead up to and peak of the last glacial maximum lgm the results of detailed lithostratigraphic mapping high resolution parametric particle size analysis automated mineralogy induced magnetic susceptibility carbon stable isotope geochemistry and a chronostratigraphy based on 27 ams radiocarbon and 6 luminescence ages are discussed in terms of sediment provenance depositional environment and weathering history with the aim of reconstructing the regional palaeo environment the data are consistent with a fluctuating aeolian fluvial interplay dominating the extended lgm environment with a greater impact on the landscape than all combined geomorphic processes since then accordingly weathered slope mantles and loess accessions were eroded and entrained by numerous small and at least a dozen large scale flood events and trapped in an intra montane floodplain extending into brachina gorge upstream of this narrow constriction recurrent backflooding is discussed resulting in a thick sequence of layered to laminated slackwater couplets aggradation and degradation of valley fills appear to be largely controlled by fine sediment supply from the valley slopes replenished by wind blown dust from upwind playa lakes and source bordering dunefields in conclusion this study demonstrates how dust storms and flooding rains can account for pluvial features previously explained by the opposing effects of reduced precipitation and evaporation in the colder more arid glacial landscape of southern australia

origin of mesozoic and tertiary granite in the western united states and implications for pre mesozoic crustal structure 2 nd and sr isotopic studies of unmineralized and cu and mo mineralized granite in the precambrian craton in the cordilleran region of the western united states mesozoic and tertiary peraluminous granitic rocks display regional variations in initial 143nd 144nd end end 10 to 12 in southern arizona 17 to 19 in the northern great basin ngb and 30 in the northern rocky mountains initial 87sr 86sr values are between 0 710 and 0 721 and show no regional pattern metaluminous granitic rocks have a wider range of end values extending from values similar to those of the peraluminous granites to much higher values the 87sr 86sr values are mostly fairly low between 0 705 and 0 710 except in the ngb where values as high as 0 7157 are observed no systematic differences between the end or 87sr 86sr values of cu or mo mineralized and unmineralized granite were discerned except for cu mineralized granite in eastern nevada and mo mineralized granite in colorado which have end values higher 0 and lower 10 0 respectively than unmineralized granite in the same region comparison to end values of exposed precambrian rock suggests that the peraluminous granite and the mo granite in colorado were derived exclusively from felsic precambrian basement rocks and that the regional variations in the end values reflect the regional variation in the average crustal age the nd data confirm that the precambrian basement underlying the ngb and eastern california is isotopically distinct from precambrian crust in the remainder of the western united states the similarity between the end values of peraluminous granite and precambrian crust also suggests that the high 147sm 144nd 0 13 and the low total light rare earth element lree abundances characteristic of peraluminous granite in southern arizona were imposed during the chemical evolution of the magmas metaluminous granite are interpreted to have formed via mixing of mantle derived magma and large proportions of low 87sr 86sr granulite facies lower crust except in the eastern ngb where the mantle magmas mixed with a lower crustal source with a significantly higher 87sr 86sr ratio ree abundance patterns for metaluminous granite in the ngb are characterized by extreme lree enrichment which supports the proposed origin for these rocks by mantle crust mixing or by remelting of the lower crust alone no systematic difference exists between the sources of cu or mo mineralized and unmineralized metaluminous granite but the data suggest that the cu sources are in the mantle and the mo sources are in preexisting crust overall the nd data indicate that continental interior granite in the western united states was primarily derived from preexisting crust and although changes in the thermal structure of the continental mantle may have triggered magma formation the resulting granites do not represent significant juvenile additions to the continental crust

fluid inclusion evidence for immiscibility in magmatic differentiation abstract after a brief review of recent work on melt inclusions in diamond and in normal magmatic environments the nature of the fluid inclusion evidence for various stages of magmatic immiscibility is summarized during magmatic differentiation by crystal fractionation from originally low volatile content silicate melts yielding normal plutonic rocks through hydrous silicate melts yielding pegmatites to late stage water rich fluids yielding quartz veins and ore deposits the composition of the residual liquid changes drastically in some geologic environments this change in composition of the residual liquid may be continuous with no phase change in the fluid part of the system under most natural conditions however it is far more likely to have one or more stages in the evolution during which globules of a separate new immiscible fluid phase exsolve the term immiscibility is used here in its more general sense to refer to the existence at equilibrium of two or more non crystalline polycomponent solutions fluids differing in properties and generally in composition i believe that the great bulk of the magmatic inclusions that are being studied today have come about through the intervention of one or more such stages of immiscible fluid separation i e magmatic differentiation by fluid immiscibility examples include silicate melt dense co2 fluid silicate melt sulfide melt silicate melt silicate melt silicate melt low density vapor i e vesiculation and as presented in more detail in this paper various stages of silicate melt hydrous saline melt aqueous fluid co2 fluid immiscibility generally only parts of these stages are recorded by the trapping of fluid inclusions and the interpretation of the inclusion record is commonly ambiguous and difficult particularly that stage between hydrous silicate melts and the hydrous saline melts and aqueous solutions responsible for many ore deposits the ambiguity results mainly from problems of inclusion origin and nonrepresentative trapping within any given individual inclusion thus the probability of trapping of only one vs various amounts of two immiscible fluids or of trapping solid phases along with the fluid present severe difficulties in addition there is the almost universal superposition of various stages of trapping of fluids within any given sample these problems can only be approached by very careful petrography and analysis of optimum material combined with field data and experimental p v t x studies of pertinent systems completely unequivocal statements of the course of evolution of the fluids in such natural systems may never be possible

late pleistocene landscape response to climate change eolian and alluvial fan deposition cape liptrap southeastern australia abstract sea cliffs along the western coast of cape liptrap at arch rock provide nearly continuous exposure of calcareous eolianites dated at 68 112 ka five optically stimulated luminescence osl ages calcareous eolian deposition began immediately after the last interglacial marine highstand oxygen isotope stage ois 5e and continued during sea level fall until the beginning of ois 4 west southwesterly winds transported calcareous sand across 12 km of exposed continental shelf by the beginning of ois 4 a brief period of cold arid windy continental climate with ephemeral but intense surface runoff immediately preceded the last glacial maximum lgm this resulted in fluvial reworking of the calcarenites into an alluvial fan dated at 23 25 ka four osl ages the fan overlies peat dated at 25 279 yr cal bp and is capped by a paleosol dated at 6010 yr cal bp concurrent eolian reworking by northwesterly winds of siliceous sediments on marine terraces along the eastern and central portion of cape liptrap formed siliceous longitudinal dunes with ages ranging from 19 to 24 ka five osl ages the phase of maximum landscape instability at cape liptrap coincides with solar insolation and air temperature minima and preceded the lgm by several thousand years

long lived interaction between hydrothermal and magmatic fluids in the soultz sous forets granitic system rhine graben france the 5 km deep drilling at soultz sous forets samples a granitic intrusion under its sedimentary cover core samples at different depths allow study of the evolving conditions of fluid rock interaction from the syn tectonic emplacement of hercynian granites at depth until post cooling history and alteration close to the surface hydrogen carbon and oxygen isotope compositions of co2 and h2o have been measured in fluid inclusions trapped in magmatic quartz within samples collected along the drill core early fluid inclusions assemblage fia contains aqueous carbonic fluids whereas the latest fia are h2o rich in the early fia the amount of co2 and the 13c value both decrease with depth revealing two distinct sources of carbon one likely derived from sedimentary carbonates 13c 2 v pdb and another from the continental crust 13c 9 v pdb the carbon isotope composition of bulk granites indicates a third carbon source of organic derivation 13c 20 v pdb using a d 18o plot we argue that the water trapped in quartz grains is mainly of meteoric origin somewhat mixed with magmatic water the emplacement of the soultz sous forets granite pluton occurred in a north 030 040 wrench zone after consolidation of the granite mush at 600 c sinistral shear 1 concentrated the final leucocratic melt in vertical planes oriented along 1 2 crystallization of this residual leucocratic melt occurred while shearing was still active at a temperature of 550 c crystallization ended with the formation of vertical quartz veins spaced about 5 mm and exhibiting a width of several cm the quartz veins form a connected network of a few kilometers in height generated during hydrothermal contraction of the intrusion quartz crystallization led to the exsolution of 30 by volume of the aqueous fluid as quartz grains were the latest solid phase still plastic shearing localized inside the connected quartz network aqueous fluid was thus concentrated in these vertical channels eventually when the channels intersected the top of the crack network water boiling caused the formation of primary inclusions at the same temperature the saline magmatic waters which were denser than the meteoric waters initiated thermohaline convection with the buoyant cold hydrothermal water layer this mechanism can explain the mixing of surface and deep seated fluids in the same primary inclusions trapped during the crystallization of magmatic minerals this study which separately considers fluid rock interactions at the level of successive mineral facies brings new insights into how fluids may be different their origin and composition and depending on tectono thermal conditions bears implications for eventual ore forming processes

late quaternary climates of the australian arid zone a review abstract aridity in australia has generally been associated with glacial intervals of the last few glacial cycles the causes and nature of aridity varied from north to south over the continent in northern and central australia reduced monsoon rain in global cold stages caused lakes and rivers to dry vegetation to become more sparse sand dunes to become active and dust advection to increase while the monsoon is correlated with warmer global temperatures and high sea levels overall the exact timing of the greatest development of the monsoon in stage 5 remains uncertain in southeastern australia the proxy records give a less clear picture while vegetation seems to have been more sparse in cold stages and sand dune activity and dust flux consequently greater records of runoff in rivers and lakes have mixed or opposite behaviour to northern or central australia the nature of aridity in southeastern australia is not analogous to conditions anywhere on the continent today greatly reduced temperatures over the central and southern interior greater influence of snow and periglaciation on runoff high groundwater tables lower rainfall and reduced atmospheric carbon dioxide levels may all have contributed to and interacted to produce the reconstructed picture of a cold sparsely vegetated arid landscape with large rivers and perennial lakes the largest changes in circulation patterns over the glacial cycle probably occurred in the location and or intensity of summer tropical convergence in northern australia over southern australia changes to the temperature and humidity of the westerly circulation have been more significant than the small fluctuations in latitude of the sub tropical high pressure ridge

abrupt return of the summer monsoon 15 000 years ago new supporting evidence from the lower white nile valley and lake albert abstract the last glacial period ended with an abrupt return to warmer and wetter conditions at a number of sites in intertropical africa asia australia and south america 15 000 years 15 ka ago similar abrupt warming is also evident at this time in high latitudes and in air trapped in greenland ice we here report new supporting evidence of this event from a climatically sensitive region in africa the white nile valley of the central sudan and lake albert in the uganda headwaters during the last glacial maximum the white nile valley was even more arid than it is today with desert dunes active as far south as latitude 12 s the sudden overflow of lake victoria in the ugandan headwaters of the white nile 14 5 ka confirmed here by sr isotope statigraphy caused extensive flooding in the lower white nile valley and severe flooding in egypt the volume of fresh water flowing into the eastern mediterranean at this time ultimately resulted in accumulation of highly organic sediments sapropel 1 on the floor of the mediterranean sea flooding in the central sudan attained an elevation of 382 m along a north south distance of 400 km the recessional shoreline of the 382 m white nile is indicated by concentrations of now buried freshwater gastropod shells and beach sands dated respectively by calibrated ams radiocarbon and osl to 15 16 ka this mega flood event marks the abrupt return of the summer monsoon and may reflect a globally synchronous event

continental tectonics and continental kinetics abstract we present a model of continental growth which combines the results of geochemical studies and tectonic ideas about the evolution of continents through geological time the process of continental growth is mainly controlled by surface phenomena continental material is extracted from the mantle along subduction zones at the periphery of oceans and is destroyed in collision zones where it is remobilized and made available for subduction we derive an equation for s the portion of the earth s surface occupied by continents which reads as follows ds dt a 1 s b s coefficients a and b depend on the geometry of plates on their number and on their velocities we assume that they decrease exponentially with time with the same time scale this model satisfies both geochemical and tectonic constraints and allows the integration of several current observations in a single framework

the enigma of a late pleistocene wetland in the flinders ranges south australia abstract lying in a semi arid region the flinders ranges have rocky weathering limited hillslopes and streams within the ranges are active only during rare downpours when they transport boulders gravel and coarse sand however silt and clay rich valley fill deposits incised by present streams occur as terraces and terrace remnants such deposits are not accumulating today in and upstream of brachina gorge in the central ranges these remnant valley fills are exposed in bank sections up to 18 m high at some localities exposures show horizontal centimetre scale beds of fine sand and clayey silt that can be traced for several hundred metres and contain gastropods diatoms and phytoliths consistent with sluggish shallow water flow under fresh to brackish conditions ams 14 c and osl dating shows that these valley fill deposits accumulated between 33 and 17 ka an interval that embraces the last glacial maximum lgm formerly thought to be lake beds aust j earth sci 46 1999 61 the valley fills are shown here to have accumulated in a fluvial wetland that extended westward from the middle reaches of brachina creek through brachina gorge and joined with aggraded fan deposits beyond the ranges aggradation of this wetland requires a substantial reduction of both rainfall variability and evaporation which would be favoured by the low temperatures and reduced incursions of summer rainfall this is consistent with climatic reconstructions by miller et al nature 385 1997 241 and johnson et al science 284 1999 1150 for lake eyre north of the flinders ranges at the lgm demise of the wetland was heralded by a major influx of coarse alluvium followed by channelling and dissection erosion was interrupted by an episode of aggradation and floodplain widening represented by remnants of a wide terrace inset below the primary wetland surface this episode which is interpreted as a return to lower climatic variability ceased with establishment of the present climatic regime which has resulted in stripping of the late pleistocene deposits from much of the brachina valley

facies analysis of an ancient dismembered large caldera complex and implications for intra arc subsidence middle jurassic strata of cobre ridge southern arizona usa abstract the middle jurassic 170 ma cobre ridge caldera is an elongate caldera complex that formed during the eruption of the tuff of pajarito a crystal rich rhyodacite ignimbrite with an estimated volume 1000 km 3 the caldera subsided in two subequal blocks to the southeast caldera forming ignimbrite is as much as 3000 m thick whereas the northwest half of the caldera subsided to lesser depths during the initial eruption but was the locus of subsidence during subsequent eruptions providing a depocenter for a 1 5 km thick section of secondary and post collapse volcanic and sedimentary strata these strata record moat formation and filling and waning volcanism including 1 areally restricted ignimbrites up to several tens of meters thick that may have been ponded between caldera margins and or fault scarps 2 a 600 m thick ignimbrite whose eruption probably caused further collapse of the caldera or enlargement of the caldera margins 3 a localized debris apron deposit up to 500 m thick that represents material reworked from intra caldera pyroclastic deposits and possibly caldera walls and 4 eolian and fluvial sandstones and water lain tuffs megabreccia blocks as large as 0 5 km along strike probably demarcate approximate caldera margins suggesting that the composite caldera was approximately 50 km long by 25 km wide the preserved thickness of the strata of cobre ridge 4500 m is greater than many ancient continental volcanic sequences suggesting external i e tectonic controls on subsidence but preservation of this great thickness of strata is apparently due entirely to volcanic subsidence

late mesozoic intrusive complexes in the coastal area of fujian se china the significance of the gabbro diorite granite association abstract the pingtan and daiqianshan igneous complexes southeastern china are typical of calc alkaline series developed at active continental margins these two complexes are dominated by granites or gabbros with minor diorites and granodiorites and these rock types closely coexisted both temporally and spatially the major and trace element signatures of gabbros indicate they were crystallised from high aluminium basaltic magmas which were generated from metasomatised upper mantle the typical metaluminous calc alkaline composition trace element patterns and sr nd isotopes indicate the granites in the complexes are i type granites which may have been generated from the deeper crust by a thermal contribution from the mantle field relationships petrography and geochemistry favour a mechanical mingling together with a limited chemical mixing between high aluminium basaltic magma and granitic magma resulting in the formation of diorites or granodiorites the essentially bimodal character of these complexes reflects the general character of back arc extensional magmatism which was induced by the subduction of the pacific plate beneath the eurasian continent in late mesozoic time

k feldspar muscovite andalusite quartz brine phase equilibria an experimental study at 25 to 60 mpa and 400 to 550 c abstract felsic magmas may evolve one or more water or chlorine rich fluid phases which can transport heat and solutes into associated hydrothermal systems and can contribute to alteration and ore deposition to understand the role of a high salinity aqueous phase in the magmatic hydrothermal environment the composition of a subcritical vapor undersaturated high salinity liquid phase brine in equilibrium with k feldspar muscovite quartz and muscovite andalusite quartz was determined for pressures and temperatures ranging from 25 mpa and 400 c to 60 mpa and 550 c with total cl nacl kcl hcl concentrations ranging from 3 42 to 8 56 moles of solute kg solution values of log 10 kcl hcl have been obtained for the equilibria 1 5 k feldspar hcl 0 5 muscovite 3 quartz kcland muscovite hcl 1 5 andalusite 1 5 quartz 1 5 h 2 o kcl for the k feldspar muscovite quartz brine equilibrium log 10 kcl hcl 1 6 0 1 0 81 0 06 0 54 0 04 and 0 42 0 08 at 25 mpa and 400 c 40 mpa and 450 c 50 mpa and 500 c and 60 mpa and 550 c pressures and temperatures of the experiments respectively for the muscovite andalusite quartz brine equilibrium log 10 kcl hcl 0 63 0 1 0 063 0 06 0 17 0 05 and 0 25 0 08 at the pressures and temperatures of the experiments respectively comparison of our results with previous studies conducted at higher pressures and with lower salinity aqueous phases show that the mineral stability fields in the k feldspar muscovite andalusite quartz system shift to lower kcl hcl values with increasing salinity and decreasing pressure

considerations for u series dating of sediments insights from the flinders ranges south australia abstract uranium isotope ratios have been determined for the fine grained detrital fraction of pleistocene wilkawillina valley fill sediments four local proterozoic bedrock samples and fine grained aeolian material from a sand dune deposit of the flinders ranges south australia the aim was to quantify the comminution age i e the time elapsed since physical weathering of the bedrock and residence time of the valley fill sediments and to place tighter constraints on input parameters for the comminution age calculation despite using two independent approaches for determination of the recoil lost fraction of 234 u from the sediment weighted geometric and surface area estimates samples fail to produce realistic comminution ages and hence residence times the issues involved in the ability to determine sediment comminution ages are discussed the 234 u 238 u activity ratio of the local bedrock is not in secular equilibrium despite the bedrock being much older than 1 ma i e the timeframe for 234 u and 238 u to reach secular equilibrium in a closed system using the average flinders ranges bedrock 234 u 238 u ratio instead of an assumed 234 u 238 u activity ratio of unity for the source would significantly reduce calculated residence times this result warrants concern for future studies using the comminution approach for which a secular equilibrium source 234 u 238 u activity ratio is assumed significant input of aeolian material may modify the measured 234 u 238 u activity ratios such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data future comminution studies would benefit from further consideration of the importance of 1 leaching lost 234 u from source rock and bulk sediment samples 2 wind deposition of fine grained material and 3 the appropriateness and robustness of sample pre treatment procedures

optical dating preliminary results on the anomalous fading of luminescence from feldspars abstract luminescence emitted from various beta dosed alkali feldspars and plagioclase feldspars has been measured under optical stimulation the luminescence sensitivities were compared as the initial stage of an on going study of short term anomalous fading of the optically stimulated luminescence osl signal anomalous fading was observed in the luminescence stimulated by both green light 514 5 nm and ir 880 80 nm from samples representing each of the major compositional regimes of the feldspar series means of alleviating the influence of this fading in luminescence dating applications are under investigation particularly the effect of isothermal storage at 100 c initial findings show that anomalous fading in these samples does not lead to a stable remanent level within the storage times used a practical consequence is that use of a fading monitoring procedure is strongly recommended in optical dating

last glacial to holocene evolution of semi arid rangelands in southeastern australia pollen sequences from playa lakes in the darling anabranch dunefields of southwestern new south wales record vegetation changes over the last glacial period and into the holocene this interval was one of marked taxonomic and structural reorganization with the plant communities that became established after the last glacial maximum lgm 24 18 ka distinct from those that had prevailed over the build up to full glacial conditions 70 24 ka the glacial period was characterized by a gradual reduction of woodland and tall shrubland cover recolonization of the dunefields involved a similar gradual succession from herbfields and low shrublands to tall shrublands and finally woodlands these changes are likely to have been driven by climatic change particularly fluctuations in temperature precipitation and atmospheric co2 as global climate systems entered and emerged from the last glaciation

zircon u th pb and whole rock rb sr age patterns of lower mesozoic igneous rocks in the santa rita mountains southeast arizona implications for mesozoic magmatism and tectonics in the southern cordillera volcanic and plutonic rocks and associated sediments in the santa rita mountains southeast arizona represent one of the most complete mesozoic sections in the cordillera zircon from the lower member of the mt wrightson formation the oldest of the dated units has lost radiogenic lead and contains a component of older zircon accordingly only an imprecise maximum age of 220 ma could be obtained for an andesite from near the middle of this unit the lower member is intruded by the piper gulch granodiorite which gave a concordant zircon u th pb age of 188 2 2 ma complex isotopic systematics of zircon from dacite in the middle member of the mt wrightson formation allow its age to lie between 172 and 190 ma because the piper gulch is interpreted to also cut the base of the middle member a hiatus of no longer than 30 m y is likely to separate the lower and middle members this stratigraphic break marks the change from early predominantly basaltic and andesitic volcanism to later dacitic to rhyolitic lavas and tuffs the silty to conglomeratic red beds and minor volcanic rocks of the gardner canyon formation for which we obtained a nearly concordant u th pb age of 200 5 ma on an abraded fraction of zircon may identify a rift dominated tectonic regime and mark the transition to felsic volcanism a second cycle of andesite and rhyolitic volcanism and sedimentation represented by the temporal and bathtub formations was dated at 151 5 2 ma by the whole rock rb sr isotopic method compared to previous age estimates our results suggest an earlier initiation of arc magmatism in this part of the cordillera apparently by the late triassic this area was already an uplifted continental arc margin analogous to the present day andes shedding volcanic material to what is now the colorado plateau the volcanic rocks we dated fall within the range of ages measured for cobbles of similar lithology from the upper triassic chinle formation in the colorado plateau therefore it is not necessary to invoke the tectonic removal of an early mesozoic arc terrane along the proposed mojave sonora megashear

magmatic immiscibility and fluid phase evolution in the mount genis granite southeastern sardinia italy the mount genis granite is one of the post tectonic intrusives emplaced late in the magmatic history of the hercynian batholith in sardinia devitrified silicate melt inclusions are present in some magmatic rock forming and miarolitic quartz these magmatic remnants show initial melting at 680 720 c high temperature observations 700 800 c revealed the presence in some of the inclusions of mixed hydrosaline melt l1 and silicate melt l2 with extremely variable l1l2 ratios electron microprobe analyses indicate l1 to be k na dominated chlorides inclusions of mixed silicate and hydrosaline melts are interpreted to have been formed by heterogeneous trapping of two immiscible fluid phases silicate hydrosaline after second boiling most likely during the final crystallization stage magma derived brines 63 eq wt nacl circulated at subsolidus conditions from 600 c and were retained in the miarolitic cavities down to about 400 c fluid unmixing occurred locally in the miarolitic cavities from 550 to 412 c at temperatures of 400 to 100 c the microgranite was invaded by diluted waters 4 5 eq wt nacl a possible model for fluid evolution begins with a hydrosaline melt exsolving from the magma at the late magmatic stage the absence of boiling within the volatile hydrosaline system shows that brines can occur by direct magmatic immiscibility the comprehensive hydrothermal evolution suggests a nearly isobaric cooling path with local boiling episodes in the miaroles probably in coincidence with invasion of external waters

the composition of a primary granite derived ore fluid from s w england determined by fluid inclusion analysis abstract electrolyte concentrations in aqueous fluid inclusions in quartz from a high temperature hydrothermal rock have been measured for 15 elements by an improved crush leach procedure the primary hydrothermal fluid was dominated by nacl and has been shown by previous studies to have been about 3 m with respect to cl on this basis the molar concentrations include fe 0 21 mn 0 06 and zn 0 02 and the fluid is interpreted as parental to some of the s w england ore bodies

tectono magmatic evolution of the west philippine mariana region and the origin of boninites re examination of published data on the tectomagmatic evolution of the west philippine mariana region indicate that arc magmatism and back arc extensional pulses are not synchronous but are largely asynchronous arc volcanism ceases within a few million years of the development of a back arc basin and recommences oceanward on a new arc during the final stages in the development of the back arc basin following karig s model we believe that ascent beneath the arc axial chain of a line of diapirs of morb source mantle interferes with processes of arc magma generation and arc magmatism wanes partial melting of the diapirs produces voluminous morb type tholeiites which split the arc and form the crust of a widening back arc basin we show for both the west philippine mariana region and occurrences of boninite like lavas in ophiolites that boninites appear to be erupted after arc magmatism and immediately before eruption of morb type lavas passage of a diapir of hot morb source mantle through refractory sub arc peridotite which has been enriched in lile and h2o will result in limited partial melting of the hydrous peridotite and the restricted production of boninitic magmas these are more likely to erupt modified or only slightly modified by crystal fractionation through the thin forearc crust continued ascent of the morb source mantle diapir will result in it partially melting to yield morb tholeiites which erupt shortly after and in considerably more voluminous amounts than the boninites finally we suggest that forearcs regions are likely to be incorporated into foldbelts and that boninite or low ti lava bearing ophiolites may characterize such regions

structure and kinematics along a segment of the mojave sonora megashear a strike slip fault that truncates the jurassic continental magmatic arc of southwestern north america 1 similarities between crystalline crust and overlying pre jurassic cover in northwestern sonora mexico and in the inyo mountains death valley region california are attributed to left lateral displacement along the mojave sonora megashear a late jurassic transform fault related to the opening of the gulf of mexico three exposures of mylonitic rocks extending 25 km along the postulated fault occur within sierra de los tanques sonora mexico the exposures 13 km southwest of sonoita reveal a tripartite assemblage of 1 jurassic volcanic and volcaniclastic strata to the northeast 2 an axial zone of mylonitic rocks and 3 masses of granitic rocks and compositionally banded quartzo feldspathic gneiss of proterozoic and late triassic age to the southwest mylonitic foliation in rocks within the axial zone strikes northwesterly and lineations plunge shallowly microstructues record left lateral shear shallow thrusts folded mylonite and steeply dipping mylonitic foliation with downdip mineral lineation record transpression triassic and precambrian crystalline rocks are emplaced above shallow thrusts onto ductilly deformed jurassic rocks northeast of the principal fault in the central and northwestern exposures pervasively foliated and lineated rocks are cut by weakly foliated cretaceous granite that also may contain inclusions of mylonite the northwesterly strike of steep foliation left lateral kinematics and relationships with cretaceous intrusive rocks preclude correlation with episodes of cretaceous contraction and tertiary extension that are recognized in the southwestern united states the fault is interpreted to have formed in the late jurassic and records a change in tectonic setting from arc magmatism to rifting and basin development

eroding australia rates and processes from bega valley to arnhem land we report erosion rates determined from in situ produced cosmogenic 10 be across a spectrum of australian climatic zones from the soil mantled se australian escarpment through semi arid bedrock ranges of southern and central australia to soil mantled ridges at a monsoonal tropical site near the arnhem escarpment climate has a major effect on the balance between erosion and transport and also on erosion rate the highest rates averaging 35 m ma 21 were from soil mantled transport limited spurs in the humid temperate region around the base of the se escarpment the lowest averaging about 1 5 m ma 21 were from the steep weathering limited rocky slopes of kings canyon and mt sonder in semi arid central australia between these extremes other factors come into play including rock type slope and recruitment of vegetation we measured intermediate average erosion rates from rocky slopes in the semi arid flinders and macdonnell ranges and from soil mantled sites at both semi arid tyler pass in central australia and the tropical monsoonal site at soil mantled sites in both the se and tropical north soil production generally declines exponentially with increasing soil thickness although at the tropical site this relationship does not persist under thin soil thicknesses and the relationship here is humped results from tyler pass show uniform soil thicknesses and soil production rates of about 6 5 m ma 21 supporting a longstanding hypothesis that equilibrium soil mantled hillslopes erode in concert with stream incision and form convex up spurs of constant curvature moreover weathering limited slopes and spurs also occur in the same region the average erosion rate for rocky sandstone spurs at glen helen is 7 m ma 21 similar to the tyler pass soil mantled slopes whereas the average rate for high quartzite spurs at mount sonder is 1 8 m ma 21 the extremely low rates measured across bedrock dominated landscapes suggest that the ridge valley topography observed today is likely to have been shaped as long ago as the late miocene these rates and processes quantified across different undisturbed landscapes provide critical data for landscape evolution models

holocene climate change in arid australia from speleothem and alluvial records new high resolution mc icpms u th ages and c and o isotopic analyses from a holocene speleothem in arid south central australia provide evidence for increased effective precipitation ep relative to present at c 11 5 ka and c 8 5 ka peak moisture at 7 6 ka and onset of an arid climate similar to present by c 5 ka 18o and 13c time series data exhibit marked 1 contemporaneous excursions over base line values of 5 3 and 11 0 respectively suggesting pronounced moisture variability during the early middle holocene climatic optimum optically stimulated luminescence and 14c ages from nearby terraced aggradational alluvial deposits indicate a paucity of large floods in the late pleistocene and at least five large flood events in the last c 6 kyr interpreted to mark an increased frequency of extreme rainfall events in the middle holocene despite overall reduced ep increased ep in south central australia during the early to middle holocene resulted from 1 decreased el nino southern oscil

the pre atlantic hf isotope evolution of the east laurentian continental margin insights from zircon in basement rocks and glacial tillites from northern new jersey and southeastern new york abstract this paper presents laser ablation u pb age and hf isotope data for zircons from basement rocks and glacial deposits in northern new jersey and southeastern new york the purpose is to understand the eastern laurentian continental margin s hf isotope record in relation to its geologic evolution prior to the opening of the atlantic ocean the basement samples encompass a meso to neoproterozoic continental margin arc an anatectic magmatic suite as well as a late ordovician alkaline igneous suite emplaced during post orogenic melting of the lithospheric mantle additional samples were collected from terminal moraines of two quaternary continental ice sheets across the entire dataset zircons with ages corresponding to the timing of continental margin arc magmatism 1 4 ga to 1 2 ga have positive e hf initial values that define the more radiogenic end of a crustal evolution array this array progresses towards more unradiogenic e hf initial values along a series of low 176 lu 177 hf 0 022 to 0 005 trajectories during subsequent anatectic magmatism 1 2 ga to 1 0 ga and later metamorphic and metasomatic re working 1 0 ga to 0 8 ga of the continental margin arc crust in contrast nearly chondritic e hf initial values from the late ordovician alkaline magmas indicate that the laurentian margin was underlain by a re fertilized mantle source such a source may have developed by subduction enrichment of the mantle wedge beneath the continental margin during the mesoproterozoic additionally preliminary data from a metasedimentary unit of unknown provenance hints at the possibility that some of the sediments occupying this portion of the laurentian margin prior to the ordovician were sourced from crust older than 1 9 ga

bedrock erosion and relief production in the northern flinders ranges australia cosmogenic 10be concentrations in exposed bedrock surfaces and alluvial sediment in the northern flinders ranges reveal surprisingly high erosion rates for a supposedly ancient and stable landscape bedrock erosion rates increase with decreasing elevation in the yudnamutana catchment from summit surfaces 13 96 1 29 and 14 38 1 40 m myr 1 to hillslopes 17 61 2 21 to 29 24 4 38 m myr 1 to valley bottoms 53 19 7 26 to 227 95 21 39 m myr 1 indicating late quaternary increases to topographic relief minimum cliff retreat rates 9 30 3 60 to 24 54 8 53 m myr 1 indicate that even the most resistant parts of cliff faces have undergone significant late quaternary erosion however erosion rates from visibly weathered and varnished tors protruding from steep bedrock hillslopes 4 17 0 42 to 14 00 1 97 m myr 1 indicate that bedrock may locally weather at rates equivalent to or even slower than summit surfaces 10be concentrations in contemporary alluvial sediment indicate catchment averaged erosion at a rate dominated by more rapid erosion 22 79 2 78 m myr 1 consistent with an average rate from individual hillslope point measurements late cenozoic relief production in the yudnamutana catchment resulted from 1 tectonic uplift at rates of 30 160 m myr 1 due to range front reverse faulting which maintained steep river gradients and uplifted summit surfaces and 2 climate change which episodically increased both in situ bedrock weathering rates and frequency magnitude distributions of large magnitude floods leading to increased incision rates these results provide quantitative evidence that the australian landscape is in places considerably more dynamic than commonly perceived copyright 2006 john wiley sons ltd

geologic setting depths of emplacement and regional distribution of fluid inclusions in intrusions of the central wasatch mountains utah nine mid tertiary calc alkaline stocks a subvolcanic porphyry system and coeval volcanic rocks are exposed in a 45 km long east trending belt across the central wasatch mountains utah the intrusions vary systematically from west to east in texture style of emplacement extent of contact metamorphism hydrothermal alteration and mineralization pressure depth estimates based on metamorphic mineral assemblages stratigraphic reconstructions and fluid inclusion data indicate a regular variation in paleodepths ranging from about 11 km on the west to less than 1 km on the east these data indicate that the central wasatch mountains have been tilted down to the east about 20 degrees during the late cenozoic fluid inclusion populations in igneous quartz also vary systematically with paleodepth high salinity halite saturated fluid inclusions are present in the eastern porphyry stocks and in the upper parts of the alta and clayton peak stocks in the center of the belt but are absent in the deeper parts of the alta and clayton peak stocks and in the little cottonwood stock on the west side of the belt in the alta and clayton peak stocks nearly planar high paleosalinity horizons presently dipping 15 degrees to 20 degrees east separate rocks containing high salinity fluid inclusions above the high paleosalinity horizon from those lacking such fluid inclusions comparison of fluid inclusion populations in igneous and vein quartz in the alta and clayton peak stocks indicates that high salinity fluids predated most of the vein forming hydrothermal activity and provide the earliest record of fluids to circulate in these stocks high salinity fluids probably formed either by boiling of fluids released during the late stages of crystallization in the parts of the intrusions where pressure was less than about 1 300 bars or by exsolution of immiscible high salinity brines from the crystallizing magmas most hydrothermal mineralization associated with the intrusions including ag pb zn ores in the park city district are associated spatially with parts of the intrusions where high salinity fluids were present the major exception is the porphyry molybdenum system in the eastern part of the little cottonwood stock which probably was at too great a depth approximately 7 km to form high salinity brines and is dominated by low salinity co 2 rich fluids

holocene valley aggradation and gully erosion in headwater catchments south eastern highlands of australia late quaternary stratigraphy of a 50 km2 catchment on the south eastern highlands of australia reveals processes and history of denudation and helps resolve a long standing debate about factors controlling episodic valley aggradation and degradation during holocene times valley sedimentation occurred when swampy vegetation fully colonized valley floors and obliterated all channels promoting aggradation for periods of several thousand years with most incoming sediment being trapped in swampy meadows much of the sediment was reworked from late pleistocene alluvial fan and valley fill deposits and primary hillslope erosion was minor during the holocene differing sedimentation patterns between the late pleistocene holocene and post european settlement periods reflect regional changes in sediment supply and transport capacity as a result of major environmental change within the holocene however valley fill stratigraphy is controlled by massive episodic gully erosion terminating aggradation gully initiation appears to be controlled more by thresholds of incision into vegetated valley floors than by changes to sediment supply whether the thresholds are exceeded because of climatic change autonomous change or extreme events cannot yet be determined overall the holocene history represents continuing complex response to events of the late pleistocene and does not support the k cycle concept which has strongly influenced late quaternary geomorphology in australia

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

crust mantle interaction in continental arcs inferences from the mesozoic arc in the southwestern united states arc magmas ranging in composition from basaltic andesites to rhyolites and intrusive equivalents were emplaced into the western margin of the north american craton starting in late triassic time giving way to rift0related sedimentation in the late jurassic the region of this study cuts across proterozoic basements of contrasting nd model ages 1 7 1 8 ga average nd 11 in eastern arizona and 2 0 to 2 3 ga average nd 18 in western arizona and eastern california bennett and depaolo 1987 the mesozoic rocks have initial nd of 3 4 to 6 4 in the eastern part of the study area and 7 1 to 9 2 in the western part all of the rocks have elevated 87sr 87sr initial ratios 0 706 trends in initial nd values of mesozoic arc rocks are directly correlated with the nd model ages of the basement through which they passed simple two component mixing calculations indicate that recycled continental crust in the arc magmas represents on average about 65 a minimum of 35 mantle input into continental arc magmas as recent as the mesozoic represents a significant contribution to the growth of the continental crust in the absence of a return flow of continental material into the mantle of similar magnitude in a detailed study in the santa rita mountains arizona there is a pattern of increase of nd with time early basaltic andesites have more negative nd than later felsic rocks a correlated pattern of depletion with time is also observed with trace element and major element data we attribute this either to progressive hybridization of the lower crust by repeated injection of mantle magmas or the progressive thinning of the continental crust during prolonged arc magmatism the present data do not allow distinction between the two models progressive decrease in crustal contribution to arc magmas with time may be an important feature of continental arc evolution hybridization of the lower crust due to repeated injection of mantle melts during arc magmatism may help contribute to small scale heterogeneities in lower crust inferred from seismic and xenolith data similarly whether there is a well defined moho or sharp crust mantle boundary in any given segment of the continental crust may in part depend on the extent of crust modification as a result of continental arc magmatism

evolution of high temperature hydrothermal fluids associated with greisenization and feldspathic alteration of a tin mineralized granite northeast queensland greisenization albitization and k feldspathization occur as pervasive background alteration and fracture controlled selvage style alteration in the go sam granite in the herberton mount garnet tin fields of northeast queensland optical sem and microthermometric investigations of fluid inclusions principally from vug filling minerals in selvage style alteration permit interpretation of the nature and evolution of hydrothermal fluids responsible for alteration of the granite saline hydrothermal fluids are dominated by na k ca fe chloride solutions with mg mn zn si al th ce and la relatively minor but important components salinities of up to 70 wt percent total dissolved salts have been calculated using the phase volume method indicated trapping temperatures of 600 degrees to 650 degrees c for many saline inclusions in vug filling minerals from feldspathic rocks record minimum temperatures for feldspathic alteration inferred temperatures for greisenization are similar and slightly lower 450 degrees 525 degrees c trapping temperatures and the composition of fluids in saline inclusions suggest late magmatic to early postmagmatic alteration of the granite by predominantly magmatic fluids inclusions containing relatively dilute fluids of possible meteoric origin homogenize between 100 degrees and 400 degrees c salinities as low as 2 equiv wt percent nacl are indicated and significant co super 2 3 hco super 3 or so super 2 4 may be present associated vapor rich inclusions indicate that the dilute fluids were probably boiling between 300 degrees and 400 degrees c a continuous range of salinities from dilute fluids to saline fluids has been found in the inclusions investigated dilution of very saline high temperature fluids could have occurred by separation of dissolved components as the fluid cooled and by mixing with dilute fluids below 400 degrees c data from fluid inclusions in magmatic quartz from the go sam granite are similar to those obtained from vug filling minerals in fracture controlled metasomatic rocks they suggest that pervasive alteration and fracture controlled alteration occurred contemporaneously and as a result of interaction with the same fluids consistently high temperatures inferred for the formation of all feldspathic rocks and associated greisens do not fit an established soviet model which emphasizes falling temperatures for the origin of comparable rocks a tentative model which emphasizes high temperature evolution of hydrothermal fluids due to changes in chemical parameters ph salinity na k f sub f 2 and confining pressures is discussed

solid inclusions of halite in quartz evidence for the halite trend abstract compositions of fluid inclusions containing halite and sylvite daughter minerals can define a linear trend of decreasing salinity when plotted in the nacl kcl h 2 o ternary system this is termed the halite trend and is attributed to halite precipitation from the fluid before trapping salt crystals observed in vein quartz crystals from mineralized zones in the capitan mountains nm usa using an electron microprobe are evidence of halite precipitation causing the halite trend the crystals observed on both polished and broken sample surfaces are often euhedral and enclosed in quartz with little suggestion of associated fluid cavities based on the textural evidence these salt crystals are interpreted as solid inclusions that were trapped during the growth of quartz given halite saturated fluids trapping of heterogeneous liquid halite fluid inclusions is possible leading to the potential to overestimate the fluid inclusion salinities

quantifying particle aggregation in sediments sediments often occur as non normal size distributions composed of discrete partially aggregated particle populations these populations reflect provenance dispersal pathways and their depositional environments recent experimental laboratory studies describing mud flocculation in turbulent marine systems prompted this investigation of the potential of aggregates to record size sensitive transport dynamics in a terrestrial fluvial system here sediment size distributions in their natural condition of particle aggregate mixtures are analysed by parametric statistics a practical and freely available decompositional approach is outlined and field tested which allows sediment to be viewed in both its conventional particulate form and as its naturally occurring mixture of transport stable aggregates and elementary particles from a sequence of upward fining slack water couplets in the flinders ranges south australia it is demonstrated that the characteristics provenance and depositional history of fine grained sediments consisting of particle aggregate mixtures can best be understood fully by quantifying aggregation

climatic evolution in the australian region over the last 94 ka spanning human occupancy and unveiling the last glacial maximum abstract the quaternary is well known for being a period of the geological record that saw significant and alternating climatic fluctuations here we concentrate on the last 94 millennia that saw australia and its surrounding seas undergo significant environmental changes importantly also it is during that this period of time includes the arrival and settlement of humans in australia following on from marine isotopic stage 4 mis4 that saw over the period of 71 59 ka bp a significant eustatic sea level drop 100 m low sea surface temperatures as well as glacial conditions on land australia experienced wet conditions again but eventually progressively entered into a glacial phase by then humans had arrived on this large continent and later the megafauna progressively became extinct this paper describes in detail the climate over this period based principally on the high resolution record of two marine sediment cores located offshore of the southern australian margin and that are then compared with known events on land as well as other deep sea cores particular emphasis is placed on the period that spans the last glacial maximum lgm the extent of which thus far had been poorly defined in the australian region emphasis is placed on the period from 34 to 14 ka to demonstrate that 1 the lgm defined here as the period 24 to 18 ka was not always extremely dry and cold and 2 that people were able to live in inland australia as water existed in places despite generally cold conditions we also show using a series of ten maps at 2 ka intervals over the 34 14 ka period the waxing and waning of oceanic fronts such as the subtropical and subantarctic fronts link sea surface temperatures sst with periods of glacial expansion in the australian alps and tasmania as well as the south island of new zealand and the extent of the leeuwin current down to south of australia aeolian dust was transported at sea over the main core site from 26 to 18 ka period pointing to arid conditions in australia but this period was punctuated by two significant reductions in dust transport to both core sites coinciding with a retreat of the subantarctic front away from the australian southern coastline and slight sst shifts for a few centuries at 24 and 22 21 ka bp at the peak of the cold phase from 23 to 18 4 ka summer sst were of the order of 9 c below that experienced during the middle of the holocene at about 6 ka bp a similar temperature drop was also experienced offshore the northwestern corner of western australia periglacial activity dates for the australian mainland and tasmania pool around 22 ka on either side of the 24 ka event the chain of lakes in the willandra lakes retained water and human activity was registered in the area elsewhere in australia water was present to sustain human populations during the cold and dry times it is postulated here that northern australia was at times quite wet especially during mis4 the cessation of the lgm is set on 18 4 ka from offshore southern australia as confirmed for the deep sea cores by several proxies and more likely at 18 ka inland finally we document that it took two millennia for glacial conditions to end in the australian region as registered in our deep sea core records well after the lowest global sea level 20 6 and 20 ka respectively started to rise there is also evidence of another very cold period determined on the australian mainland tasmania and the south island of new zealand centred around 27 ka after which time warmer conditions occurred before the start of the lgm this is matched with our deep sea records with very cold conditions and changes in oceanographic conditions

quantitative estimates of the effect of climate change on dust storm activity in australia during the last glacial maximum quantitative estimates are made of the effect of climate change upon dust activity during the last glacial maximum lgm which peaked 18 000 years ago using present day measurements of the occurrence of dust storms recalculated in the light of information on lgm climatic change dust activity was increased by 57 in northeast australia and by 52 in the southeast in relation to present day dust storm seasons were lengthened and dust paths were modified estimates based upon climate alone without considering the increased supplies of sediment to dust source areas during the lgm however probably underestimate lgm dust activity

ecogeomorphology in the australian drylands and the role of biota in mediating the effects of climate change on landscape processes and evolution

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

distribution of fluid inclusions in igneous quartz of the capitan pluton new mexico usa abstract fluid inclusions in granites have been used extensively in studies of magmatic hydrothermal processes but few studies have documented the distribution of secondary fluid inclusions within the nonmineralized main body of an intrusion previous work on fluid inclusions in th u ree quartz fluorite vein deposits in the capitan pluton suggests that these veins resulted from high temperature high salinity magmatic fluids in fractured and brecciated zones in the cooled outer carapace of the pluton petrographic examination of phenocryst quartz in forty four thin sections of granite from the capitan pluton reveals that these same fluids are found in secondary fluid inclusions fluid inclusions with daughter minerals commonly occur in the outer granophyre and aplite zones but are usually absent in the porphyritic core microthermometric data and calculated salinities from fifty eight fluid inclusions in phenocryst quartz and thirty one fluid inclusions in miarolitic quartz both samples taken from the granophyre zone also correlate fairly well with the data from the th u ree quartz fluorite vein deposits and similar types of fluid inclusions are found in all three occurrences of quartz a major difference however is that vapor rich inclusions abundant as secondary inclusions in igneous phenocryst quartz are extremely scarce in the vein quartz liquid vapor homogenization temperatures of high salinity inclusions in phenocryst quartz range from 204 509 c with an average of 384 c halite dissolution temperatures of high salinity inclusions range from 442 583 c with an average of 525 c total homogenization temperatures are not as well documented due to decrepitation of many of the high salinity inclusions before total homogenization samples of miarolitic quartz appear to contain more low salinity fluid inclusions than the phenocryst quartz but high salinity inclusions are present as well these observations suggest that the magmatic hydrothermal fluids responsible for vein mineralization were not only concentrated in the vein systems but were also widely dispersed within the outer portions of the pluton furthermore the greater abundance of fluid inclusions in the outer textural zones of the pluton suggests that the interior of the pluton had not yet fully crystallized when these fluids exsolved from the magma

australian dust deposits modern processes and the quaternary record abstract dust raising and transport are common and important processes in australia today the aridity of the australian continent and high climatic variability result in widespread dust raising in the arid and semi arid areas and transport to the humid margins and surrounding oceans the supply of erodible particles appears to be the greatest limitation on total flux of transported dust dust raising is greatest in the lake eyre basin including the simpson desert and murray darling basin where internal drainage renews supplies of fine particles to the arid zone in the west and northwest dust entrainment is low despite considerable aridity the marine record of dust flux shows at least a threefold increase in dust flux compared with the holocene in the last glacial maximum in both tropical and temperate australia driven by weakened australian monsoon rains and drier westerly circulation respectively despite the widespread confirmation of aeolian dust deposits in southeastern and southwestern australia dated or quantified records are extremely rare the dominant model of australian dust deposits the clay rich parna is shown to be poorly substantiated while modern and ancient dust deposits examined in detail are shown to bear a strong similarity to conventional definitions of loess

river response to quaternary climatic fluctuations evidence from the son and belan valleys north central india abstract the last glacial period was cold and dry in peninsular india in north central india the interval from 39 9 to 16 3 ka was associated with widespread and prolonged aggradation in the son and belan valleys the aggradation ended with sustained vertical incision after 16 3 ka and reflects a return to warmer wetter conditions in this region it would appear that terminal pleistocene to holocene river incision was broadly synchronous with a strong summer monsoon regime and higher levels of river discharge and the preceding river aggradation with lower discharge and a weaker or more variable summer monsoon regime two older phases of prolonged aggradation followed by vertical incision are evident in the son and belan valleys before 39 ka one of these phases is centred towards 73 4 ka when ash from the toba mega eruption in sumatra was deposited across peninsular india the following phase of aggradation has yielded infrared stimulated luminescence ages of 58 6 and 45 12 ka the youngest phase of aggradation began towards 5 5 ka and seems to mark a return to a weaker summer monsoon regime

protactinium 231 dating of carbonates by thermal ionization mass spectrometry implications for quaternary climate change measurement of protactinium 231 231pa in carbonates by thermal ionization mass spectroscopy yields 231pa ages that are more than 10 times more precise than those determined by decay counting carbonates between 10 and 250 000 years old can now be dated with 231pa methods barbados corals that have identical 231pa and thorium 230 230th ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the astronomical theory two devils hole calcite subsamples record identical 231pa and 230th ages suggesting that the chronology of this climate record is accurate

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

interactions between fluvial and eolian geomorphic systems and processes examples from the sahara and australia abstract the remains of once integrated drainage systems are still discernible in many of the hot deserts of the world some of these date back to the mesozoic as in arid western australia where they now form chains of salt lakes others were active in miocene times such as the sahabi rivers that once flowed from chad to the mediterranean a few remained active during quaternary interglacials as in the sahara all contributed sediments that were reworked by wind during drier phases to form desert dunes the desert dunes of australia and of the 9500 km long chain of deserts extending from the sahara through arabia to the thar desert of india originated from sediments eroded from the uplands and deposited in closed interior basins formed during the course of late mesozoic and cenozoic faulting rifting and epeirogenic movements it was the unconsolidated neogene sediments laid down in large subsiding sedimentary basins such as the kufra sirte basin in libya and the chad basin which provided the source material for the late pliocene and quaternary desert dunes of the sahara one effect of the progressive build up of high latitude ice sheets during the neogene was to steepen the temperature and pressure gradients between the equator and the poles resulting in increased trade wind velocities stronger winds were better able to mobilize the alluvial sands of the increasingly dry sahara and adjacent deserts and to fashion them into desert dunes a more subtle form of interaction between eolian and fluvial processes concerns the interplay between desert dust loess accumulation on hill slopes in arid regions and the onset of fine grained valley fill accumulation by sluggish low energy streams in mountain valleys some of these late pleistocene wetlands served as refuge areas for plants reptiles and invertebrates at a time when the surrounding desert plains were very cold and dry as in the flinders ranges of south australia in the arid flinders ranges such valley fills were built up between 35 kyr and 15 kyr ago after which the return of the summer monsoon led to stream channel incision and the formation of a network of gullies often erroneously attributed to human activities understanding the causes of such accelerated erosion can prevent unnecessary and expensive attempts at restoration since the latter are based on the incorrect assumption that overgrazing and present day land use are responsible

aggradation incision transition in arid environments at the end of the pleistocene an example from the negev highlands southern israel abstract one of the most significant environmental processes that occurred at the transition from the last glacial phase into the present inter glacial phase in arid regions was the shift from aggradation to incision in the drainage systems this is evident by the sharp transition from a fluvial regime depositing fine grained sediment within the wadis to intensive incision which formed gullies and narrow channels that dissected the late pleistocene sediments in order to investigate this transition we studied three small scale basins in the arid region of the negev highlands southern israel although the selected basins drain toward different base levels their geomorphological parameters particle size distribution of alluvial units and their osl ages are similar sediments from the penultimate glacial cycle are found in patches in the bigger catchments fluvial loess was widely deposited since at least 67 ka until after 28 ka covering valleys and slopes between 28 and 24 ka loess was washed from the slopes into the channels exposing the underlying colluvium at 24 ka erosion began with the transport of slope colluvium as gravels into the valleys that eroded the underlying loess sediments incision became dominant at 12 ka and is still ongoing and intensifying dust and reworked loess continued to be deposited during the main incision stages it is proposed that the transition from aggradation to incision was controlled by rates of loess supply and removal until 24 ka dust choked the drainage system and only after reduction in dust supply was erosion and incision possible it began first on the slopes and then in the channels our results show that an increase in precipitation is not a prerequisite for initiation of incision as is often assumed similar processes are described in other arid zones around the world

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

tectonic models for early cretaceous rifting in southeastern arizona the early cretaceous tectonic setting of southeastern arizona was one of northeast southwest extensiomal deformation characterized by differential vertical movements along northwest trending normal faults local fault block uplifts created a basin and range type paleogeography that included local clastic filled basins and mountain ranges rimmed by alluvial fans the glance conglomerate the basal formation of the lower cretaceous bisbee group represents the proximal parts of these syntectonic alluvial fans this extensional back arc tectonic setting is strikingly different from the compressional setting found behind the continental margin magmatic arc farther to the north sevier orogeny possible explanations for this profound difference in back arc tectonic style include propagation of an aulacogen from the gulf of mexico to southeastern arizona variable dip subduction along the continental margin magmatic arc and an apparent anticlockwise rotation of the north american plate relative to the continental margin arc

remagnetization of jurassic volcanic rocks in the santa rita and patagonia mountains arizona implications for north american apparent polar wander paleomagnetic poles for the jurassic corral canyon sequence and glance conglomerate in southern arizona have been used to construct apparent polar wander apw paths for the north american plate but they are controversial and conflict with higher latitude poles from new england lower jurassic dacites and ash flow tuffs of the mount wrightson formation in the santa rita mountains were initially sampled to provide an additional paleopole for southern arizona these rocks however have a predominantly reversed polarity characteristic magnetization in situ i 47 d 154 95 9 which is statistically indistinguishable from that for the nearby latest cretaceous elephant head pluton i 48 d 165 95 8 although magnetizations of both polarities are observed in the ash flow tuffs they are mostly carried by hematite and dual polarity components are observed within some specimens moreover widespread mineralization and a k ar age of 67 ma for altered rocks of the mount wrightson formation imply that these rocks were subjected to a prolonged episode greater than one polarity interval of low temperature alteration and remagnetization middle jurassic ash flow tuffs of the corral canyon sequence in the patagonia mountains to the south have a similar geologic setting they are exposed along strike amid mineralized rocks on the eastern flank of a mountain range cored by paleocene intrusions hematite is also the dominant remanence carrier in most of the corral canyon sequence and its predominantly normal polarity direction in situ i 51 d 326 95 9 is indistinguishable from that for the nearby patagonia granodiorite i 49 d 342 95 8 rocks of the corral canyon sequence therefore are likely remagnetized as well problems also exist with the glance conglomerate pole these rocks are situated within a caldera structure and have been potassium metasomatized this potassic alteration could have occurred shortly after emplacement or at a later time postdeformation the low latitude jurassic apw path for north america and j 2 cusp therefore are not well supported and may need revision

of droughts and flooding rains an alluvial loess record from central south australia spanning the last glacial cycle david haberlah peter glasby martin a j williams steven m hill frances williams edward j rhodes victor gostin anthony o flaherty and geraldine e jacobsen

crustal melting by ponding of mafic magmas a numerical model abstract we examine the possibility that an abating period of mantle related volcanic activity at continental margins triggers the production of crustal derived melts a vertical zone permeated by rising mafic melts is established below the volcanic arc if long lasting mantle derived magmatism occurs this situation can be assumed to exist at continental arcs we propose that mafic magmas release heat and water into the crustal environment if subsequent magma ascent is stopped due to establishment of a density barrier this process enhances intracrustal partial melting using a finite element program we simulate in a 2d model area the time dependent change of the crustal thermal structure the spatial distribution of potential melting zones and their degree of partial melting within the crust is computed the amount of generated melt able to segregate is calculated and compared with volume estimates given by field investigation and geochemical constraints in a natural test case we chose the altiplano puna volcanic complex apvc which is part of the central andes as an example where the process may have happened and show from simple approximations that the model can explain the volumes of crustal melts represented by the felsic volcanics in this region although the model parameters and assumptions used are specific to this geologic context the proposed model is generally applicable to any arc setting

late quaternary palaeoenvironmental change in the australian drylands in this paper we synthesise existing palaeoenvironmental data from the arid and semi arid interior of the australian continent for the period 40 0 ka moisture is the predominant variable controlli

low latitude glacial cooling in the southern hemisphere from amino acid racemization in emu eggshells the record of natural climate variability over glacial interglacial timescales provides a framework from which a better mechanistic understanding of the climate system may be derived but this approach is limited by the number and distribution of well dated and reliable palaeoenvironmental archives particularly vexing is the conflicting evidence for low latitude cooling during the last glacial maximum and the apparent synchrony in glacial activity between the hemispheres despite out of phase insolation forcing1 4 here we utilize the temperature dependent amino acid racemization reaction in radiocarbon dated emu eggshell fragments from the continental interior of australia to reconstruct low altitude subtropical temperatures for the past 45 kyr racemization rate changes indicate that millennial scale average air temperatures were at least 9 c lower between 45 and 16 kyr bp than since 16 kyr bp a temperature change of this magnitude coupled with other low latitude palaeotemperature records that indicate substantial cooling3 4 must reflect global processes which we speculate involved glacial age reduction in atmospheric water vapour content

the ridgeway gold copper deposit a high grade alkalic porphyry deposit in the lachlan fold belt new south wales australia ridgeway is a high grade gold copper porphyry deposit 54 mt at 2 5 g t au and 0 77 cu related to an alkalic intrusive complex of monzonitic composition the deposit occurs within the cadia district of new south wales australia which consists of a cluster of four late ordovician gold copper porphyry deposits and two iron copper gold skarn deposits with a combined gold resource in excess of 574 metric tonnes t the deposits lie on a 7 km long northwest oriented corridor of alteration and mineralization transverse to the axis of the postulated volcanic arc alteration and mineralization at ridgeway are zoned around a vertically attenuated intrusive complex of monzodioritic to quartz monzonitic composition distinct styles of veining and alteration are related to different intrusive phases of the monzonite complex with the intensity of alteration and grade of mineralization decreasing from early to late mineral intrusions early mineral intrusions are associated with intense actinolite magnetite biotite calc potassic alteration and up to four stages of high grade quartz magnetite sulfide veining bornite is the most abundant sulfide formed during early stage alteration and correlates well with gold moderate to weak intensity orthoclase biotite plus or minus magnetite potassic alteration accompanies the inter and late mineral intrusions this alteration being associated with chalcopyrite and pyrite rich quartz orthoclase veins propylitic and sodic albite pyrite alteration assemblages are peripheral to and locally overprint the potassic alteration phyllic alteration is restricted to the margins of late stage faults the fluid inclusion assemblage comprises one and two salt bearing brine inclusions in addition to aqueous liquid vapor inclusions of low to moderate salinity no low density vapor rich inclusions are present indicating that the fluids from which the quartz veins precipitated did not enter the liquid vapor field of the h2o nacl system the brine inclusions undergo final homogenization to liquid via halite dissolution this phenomenon in addition to the absence of low density vapor inclusions suggests that the mineralizing fluids at ridgeway were nonboiling hypersaline brines that exsolved directly from the crystallizing magma the presence of mineralized aplitic vein dikes and comb quartz layering are interpreted to indicate that the early and transitional stages of mineralization at ridgeway formed at the transition between magmatic and hydrothermal conditions

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

rapid uplift and crustal growth in extensional environments an isotopic study from the death valley region california the willow spring diorite in the black mountains of the central death valley extended terrain yields a u pb zircon age of 11 6 plus minus 0 2 ma sup 40 ar sup 39 ar analyses of hornblende and u pb analyses of sphene from this sample give ages of about 10 ma indicating that the batholith remained above about 500 c for about 1 5 m y after crystallization geologic relations indicate that the diorite was exposed to erosion by about 5 ma bracketing the evolution of the diorite within the time between onset of extension and uplift of the black mountain crustal block initial sup 87 sr sup 86 sr ratios range from 0 7060 mafic diorite to 0 7083 felsic diorite in samples collected from an area 200 x 100 m these data combined with structural and petrologic evidence suggest that the batholith represents a rare view of a mid crustal zone of mixing between mantle derived magma and crustal material often suggested to exist on the basis of observations of intermediate volcanic rocks the black mountains may therefore expose a cross section through a continental rift magmatic system from partially contaminated mafic to intermediate intrusive rocks in the deep crust up to their volcanic equivalents the relatively low initial sup 87 sr sup 86 srmore and high epsilon sub nd minus 1 4 of the diorite which is within proterozoic basement with epsilon sub nd approximately minus 18 is consistent with significant amounts of mantle input in continental rifts inferred from geophysical data and measurement of he isotopic ratios such additions to the crust in continental rights may represent a significant process of crustal growth furthermore the emplacement of igneous bodies with a large mantle component may help reconcile the large crustal pull apart in the basin and range in excess of 140 km with the fact that the crust still has as normal thickness of about 30 35 km less

a chemical and isotopic study of the laramide granitic belt of northwestern mexico identification of the southern edge of the north american precambrian basement along the laramide belt of northwestern mexico granitic rocks of similar bulk composition show isotopic and trace element signatures that help to delineate the position of the southern edge of the north american precambrian basement in the northern part the laramide plutons the northern granites intruded proterozoic crystalline rocks and a thick late proterozoic through paleozoic miogeoclinal cover of north american affinity in the central part the granitic bodies the central granites were emplaced into a sequence of paleozoic eugeoclinal rocks overlain by late triassic clastic units the southern part of the belt the southern granites intruded a less known crust characterized by middle to late mesozoic island arc related volcanic and sedimentary rocks of the guerrero terrane data from a suite of metaluminous to slightly peraluminous calc alkalic granitic rocks along the belt display north to south geochemical and isotopic variations which could correlate with the type of intruded basement the northern and central granites are characterized by strongly fractionated light rare earth element ree enriched patterns which display generally pronounced negative europium anomalies whereas the southern granites have lower total ree enrichments and much flatter chondrite normalized slopes displaying almost no europium anomalies isotopic results also suggest regional variations as shown by the following initial sr and end ranges 0 7070 to 0 7089 and24 2 to25 4 respectively for the northern granites 0 7060 to 0 7079 and23 4 to25 1 for the central granites and 0 7026 to 0 7062 and20 9 to 14 2 for the southern granites on the basis of their isotopic similarities the proterozoic mafic to intermediate lower crust revealed by xenoliths from young volcanic flows in southern arizona and northern mexico is interpreted as a reasonable parental source for the northern and central granites however mantle derived melts are not excluded the more primitive southern granites are interpreted to come from a source that lacked proterozoic basement instead they were probably derived by mixing of juvenile mantle melts with partial melts of the lower parts of the guerrero terrane in general the north to south compositional variations of the laramide granitic rocks of northwestern mexico reflect the crustal structure underneath the batholiths the sr and nd data indicate that the edge of the north american precambrian basement extends approximately southeastward from the coastal batholith of central sonora then about 200 km south of hermosillo in southern sonora the edge bends eastward and continues to the east beneath the sierra madre occidental volcanic province

glacial and deglacial climatic patterns in australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract this study forms part of a wider investigation of late quaternary environments in the southern hemisphere we here review the terrestrial and near shore proxy data from australia indonesia papua new guinea png new zealand and surrounding oceans during 35 10 ka an interval spanning the lead up to the last glacial maximum lgm the lgm proper 21 2 ka and the ensuing deglaciation sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval a stratigraphically consistent chronology and one or more sources of proxy climatic data tropical australia indonesia and png had lgm mean annual temperatures 3 7 c below present values and summer precipitation reduced by at least 30 consistent with a weaker summer monsoon and a northward displacement of the intertropical convergence zone the summer monsoon was re established in northwest australia by 14 ka precipitation in northeast australia was reduced to less than 50 of present values until warmer and wetter conditions resumed at 17 16 ka followed by a second warmer wetter phase at 15 14 ka lgm temperatures were up to 8 c lower than today in mainland southeast australia and up to 4 c cooler in tasmania winter rainfall was much reduced throughout much of southern australia although periodic extreme flood events are evident in the fluvial record glacial advances in southeast australia are dated to 32 2 5 19 1 1 6 and 16 8 1 4 ka with periglacial activity concentrated towards 23 16 ka deglaciation was rapid in the snowy mountains which were ice free by 15 8 ka minimum effective precipitation in southern australia was from 14 to 12 ka in new zealand the glacial advances date to 28 21 5 and 19 ka with the onset of major cooling at 28 ka or well before the lgm there is no convincing evidence for a younger dryas cooling event in or around new zealand but there are signs of the antarctic cold reversal in and around new zealand and off southern australia there remain unresolved discrepancies between the climates inferred from pollen and those inferred from the beetle and chironomid fauna at a number of new zealand sites one explanation may be that pollen provides a generalised regional climatic signal in contrast to the finer local resolution offered by beetles and chironomids sea surface temperatures ssts were up to 5 c cooler during the lgm with rapid warming after 20 ka to attain present values by 15 ka the increase in summer monsoonal precipitation at or before 15 ka reflects higher insolation warmer ssts and steeper thermal gradients between land and sea the postglacial increase in winter rainfall in southern australia is probably related to the southward displacement of the westerlies as ssts around antarctica became warmer and the winter pack ice and antarctic convergence zone retreated to the south

the geology of the mccoy mountains formation southeastern california and southwestern arizona the mccoy mountains formation is a 7 3 km thick metasedimentary sequence exposed in at least 6 mountain ranges in southeastern california and southwestern arizona the siliciclastic mccoy mountains formation is deposited on and interbedded at its base with a jurassic volcanic terrane and is intruded by undeformed upper cretaceous plutons it has been assigned a cretaceous paleocene age on the basis of fossil angiosperm wood found within the upper third of the sequence presently known exposures of mccoy mountains formation define a west northwest trending basin 140 km long by 25 km wide which was filled from the north by predominantly alluvial processes the mccoy mountains formation is divided into six members each containing distinctive stratigraphy and sedimentary petrology sandstone consists of quartz feldspar and lithics and each member has a different composition the source evolved from volcanic sedimentary to plutonic sedimentary composition with time much thinner laterally equivalent clastic sequences are now known on the craton adjacent to the basin s northern margin the mccoy mountains formation is homoclinal and south dipping and its uppermost strata are deformed into a north verging overturned syncline with sympathetic south dipping cleavage northern exposures of mccoy mountains formation and underlying jurassic volcanic terrane contain a north dipping cleavage and south verging overturned folds sympathetic to the cleavages and folding are north and south bounding faults which limit mccoy mountains formation exposures and place the north american craton north side and the mojave sonora complex or tujunga terrane south side onto mccoy basin rocks structural analysis and paleomagnetic data strongly suggest that the thrusting over and folding of the mccoy basin rocks took place in late jurassic time as a single event the fault along the southwestern margin of the mccoy basin is thus apparently a jurassic terrane boundary and may be a northern extension of the jurassic mojave sonora megashear if true proposed early tertiary accretion of the tujunga terrane must have occurred farther to the southwest

environmental dose rates and radioactive disequilibrium from some australian luminescence dating sites abstract determination of geological archaeological ages by luminescence dating requires the measurement of the rate of delivery of radiation dose from the sample and its environment for all age determinations it is necessary to assess whether the dose rate has been constant during the time that the dose has been accumulating and to make allowance for it if it was not we report here results from a number of australian sites to illustrate the information that can be found about element concentrations about their distribution and about dose rates tests for radioactive disequilibrium form part of these measurements such tests take the form of comparison of independent measurements of dose rates and or individual elements in general there is little or no evidence for disequilibrium in aeolian dune systems even when the age of the system exceeds 500 ka however disequilibrium has been found in several sites subject to wet conditions

geochemistry of late cretaceous granitoids from northeastern washington implication for genesis of two mica cordilleran granites mesozoic two mica granites and i type granodiorites from northeastern washington have initial sup 87 sr sup 86 sr ratios around 0 7100 similar to many other cordilleran granitoids metapelite and calcsilicate country rocks equivalent to the belt supergroup have measured sup 87 sr sup 86 sr ratios in the range of 0 91 to 0 98 unlike many of their cordilleran counterparts the northeastern washington two mica granites are enriched in u rb and other incompatible elements and therefore cannot have been derived from depleted lower crust sedimentary sources both the two mica granites and the i type granodiorites have similar rare earth element and trace element enrichment patterns trace elements modeling shows that it is feasible to derive the two mica granites by 60 partial melting of a granodiorite like source the close association of cordilleran metamorphic core complexes and older i type granodiorites with two mica granites supports this model

cretaceous age of the upper part of the mccoy mountains formation southeastern california and southwestern arizona and its tectonic significance reconciliation of paleobotanical and paleomagnetic evidence the upper part of the 7 km thick mccoy mountains formation in southeastern california contains fossil angiosperm wood that closely resembles the genus paraphyllanthoxylon which is known only from strata of late early cretaceous and younger age this wood in conjunction with geologic field relations supports previous interpretations that the upper part of the mccoy mountains formation is of late early cretaceous and or late cretaceous age in contrast to a more recent interpretation that the entire formation is of jurassic age alternatives are therefore needed to the recent hypothesis that deposition deformation and metamorphism of the mccoy mountains formation were related to movement on the jurassic mojave sonora megashear

geochemistry δ13c δ15n 13c nmr and residence times 14c and osl of soil organic matter from red brown earths of south australia implications for soil genesis abstract soil forming processes important to the development of red brown earths duplex soils in southeastern australia have been investigated by a combination of techniques including isotopic 13c 15n 14c spectroscopic 13c nmr mir optically stimulated luminescence dating osl and phytolith analyses a distinct increase in clay content corresponding changes in the abundance of major elements as well as changes in organic chemistry 13c nmr stable isotope trends 13c 15n and phytolith abundance are apparent in the transition from the very sandy a horizon to the clayey b horizon in three soil profiles from the coonawarra padthaway region of south australia these structural and chemical changes between the a and the b horizons are associated with an abrupt increase in both 14c bulk soil organic matter and osl burial ages of individual quartz grains while previous interpretations have promoted the formation of duplex red brown earths as due to clay illuviation we propose a two stage soil formation which may be related to paleoclimatic changes during and after the last glacial maximum our data suggest that a major part of the a horizon was aeolian derived and was deposited over the last 10 000 years whereas much of the b horizon although originally aeolian has been extensively modified over much longer periods of time tens of thousands of years these results indicate the influence of different substrates sandy versus clayey process and time for formation as well as paleoclimatic history on the physical properties of the soil and the chemical characteristics of the organic matter within the soil profile

a geospatial visualisation and chronological study of a late pleistocene fluvial wetland surface in the semi arid flinders ranges south australia abstract the semi arid flinders ranges of south australia contain abundant remnants of fine grained late pleistocene valley fills we have mapped these deposits using real time kinematic rtk gnss and topographic surveying techniques for data acquisition and integrate the surveyed data in a geographical information system gis to interpolate a 3 dimensional palaeo surface representing the uppermost remnant sediments of the late pleistocene floodplain our analysis of sedimentary and landscape profiles indicates a continuous surface and consistent westward slope suggesting that the remnants present today are still largely consistent with the original alluvial surface in addition secondary levels are identified and interpreted integration of the geospatial landscape characterisation with chronologies from selected sites microfossil and stable isotope data provides new evidence for the timing rates of aggradation and mode of deposition of the late pleistocene fine grained valley fill formation the use of gis for 2 d and 3 d data management analysis and visualisation provides a visual and quantitative model of landscape changes and helps to clarify how the valley fill deposits accumulated

diagnosing open system magmatic processes using the magma chamber simulator mcs part i major elements and phase equilibria the magma chamber simulator mcs is a thermodynamic tool for modeling the evolution of magmatic systems that are open with respect to assimilation of partial melts or stoped blocks magma recharge mixing and fractional crystallization mcs is available for both pc and mac in the mcs the thermal mass and compositional evolution of a multicomponent multiphase composite system of resident magma wallrock and recharge reservoirs is tracked by rigorous self consistent thermodynamic modeling a recharge assimilation assimilated partial melt or stoped blocks fractional crystallization rnasnfc ntot 30 scenario is computed by minimization or maximization of appropriate thermodynamic potentials using the family of rhyolite and pmelts engines coupled to an excel visual basic interface in mcs during isobaric cooling and crystallization resident magma thermally interacts with wallrock that is in internal thermodynamic equilibrium wallrock partial melt above a user defined percolation threshold is homogenized i e brought in to chemical potential equilibrium with resident magma crystals that form become part of a cumulate reservoir that remains thermally connected but chemically isolated from resident melt up to 30 instances n 30 of magma mixing by recharge and or bulk assimilation of stoped wallrock blocks can occur in a single simulation each recharge magma or stoped block has a unique user defined composition and thermal state recharge magmas and stoped blocks hybridize equilibrate with resident melt yielding a single new melt composition and temperature mcs output includes major and trace element concentrations and isotopic ratios sr nd hf pb os and o as defaults of wallrock recharge magma stoped blocks resident magma melt and cumulates the chemical formulae of equilibrium crystalline phases in the cumulate reservoir wallrock and recharge magmas stoped blocks are also output depending on the selected rhyolite melts engine the composition and properties of a possible supercritical fluid phase h2o and or co2 are also tracked forward modeling of theoretical magma systems and suites of igneous rocks provides quantitative insight into key questions in igneous petrology such as mantle versus crustal contributions to terrestrial magmas the record of magmatism preserved in cumulates and exsolved fluids and the chronology of rasfc processes that may be recorded by crystal populations melt inclusions and whole rocks here we describe the design of the mcs software that focuses on major element compositions and phase equilibria mcs phaseeq case studies that involve fractional crystallization magma recharge mixing and crustal contamination of a depleted basalt that resides in average upper crust illustrate the major element and phase equilibria consequences of these processes and highlight the rich array of data produced by mcs the cases presented here which represent an infinitesimal fraction of possible rasfc processes and bulk compositions show that the records of recharge and or crustal contamination may be subtle and are not necessarily those that would be predicted using conventional intuition and simple mass balance arguments mass and energy constrained thermodynamic tools like the mcs quantify the open system evolution of magmas and provide a systematic understanding of the petrology and geochemistry of open system magmatic processes the trace element and isotope mcs computational tool mcs traces is described in a separate contribution part ii

probing the structure of the deep continental crust old buried deformed crystalline rocks apparently make up most of the 40 kilometer thick continental crust this part of the earth is poorly explored and constitutes a major frontier of modern earth science two techniques seismic reflection profiling and drilling which were developed by industry for other purposes offer special potential for such exploration seismic profiling of the deep crust by cocorp the consortium for continental reflection profiling has already produced important information including evidence for extensive thin skinned thrusting of older rocks over a continental margin as the corresponding ocean basin closed deep drilling of crystalline rocks of the continents for scientific purposes is so far relatively unexploited in the united states but is already being carried on elsewhere in general big science is likely to become more important in basic geology as this frontier is explored

chronology of murrumbidgee river palaeochannels on the riverine plain southeastern australia four major periods of palaeochannel activity have been identified on the murrumbidgee sector of the riverine plain of southeastern australia on the basis of stratigraphic information the channels reveal a picture of changing flow conditions during the last full glacial cycle the ages of the periods were determined from nearly 40 thermoluminescence dates on surficial fluvial and aeolian sediments these are named the coleambally phase which occurred from 105 to 80 ka the mid to latter part of oxygen isotope stage 5 the kerarbury phase from 55 to 35 ka stage 3 the gum creek phase from 35 to 25 ka late stage 3 to early stage 2 and the yanco phase from 20 to 13 ka late stage 2 the present flow regime was established by about 12 ka stage 1 the first two phases correlate with episodes of enhanced fluvial activity in northern and central australia and with reduced dust activity globally the phases in stage 2 appear to be associated with seasonal snow melt and increased peak flows in periods flanking the last glacial maximum source bordering aeolian dunes associated with the coleambally kerarbury and yanco phases were found however the tl dates show that some have undergone aeolian reworking thermoluminescence dating and fluvial stratigraphy have revealed a detailed picture of late quaternary climate and flow regime changes that has the potential to extend to identified deposits stratigraphically older than those described here

changes in vegetation and seasonal climate since the last full glacial at lake frome south australia abstract results are presented from stratigraphy radiocarbon and pollen analysis from lake frome south australia close to the summer winter rainfall boundary at 30 south latitude the pollen sequence shows that tree vegetation was minor around 18 000 yr b p the landscape was dominated by chenopod low shrublands and ephemeral tubuliflorae vegetation by 17 000 yr b p callitris moved in and rose to 25 of the pollen sum values of casuarina myrtaceous shrubs acacia dodonaea and cyperaceae also rose at about the same time between 17 000 and 14 500 yr b p callitris and eucalyptus dominated the tree vegetation with callitris reaching its maximum values eucalpt woodlands were associated with undershrubs belonging to myrtaceae acacia dodonaea and gyrostemonaceae whereas callitris woodlands had probably supported only a sparse understorey chenopodiaceae today distributed mainly in the winter rainfall zone continued to show high values 25 gramineae today associated with high summer rainfall generally remained below 20 the sporadic presence of a number of taxa which now grow in temperate areas further south suggest that average annual temperatures were a little lower than at present from 14 500 to 13 000 yr b p there was a sudden decline in the values of callitris and a more gradual decline in chenopodiaceae and dodonaea the rise of ephemeral vegetation together with a fall in chenopodiaceae would indicate that winter precipitation had started to decline between 13 000 and 4500 yr b p chenopodiaceae and tubuliflorae ephemerals declined and gramineae rose to its highest values tribulus pollen a subtropical tropical taxon first appeared 13 000 yr b p overall plants from the summer rainfall zone became more prominent and taxa from the temperate south declined summer monsoon incursions apparently strengthened and temperature increased during this phase since 4500 yr b p both chenopodiaceae and tubuliflorae returned to high values whereas gramineae declined values of acacia and myrtaceous shrubs rose but those of casuarina declined and callitris remained extremely low these changes were accompanied by the onset of playa environments which have since persisted vegetation during this phase suggests that summer precipitation declined and summer monsoon incursions became rare during the late holocene