three s type volcanic suites from the lachlan fold belt southeast australia the concept that granitoids of the lachlan fold belt in southeast australia are derived from either igneous or sedimentary source rocks i or s type can be extended to volcanic rocks of the same age three suites of late silurian s type volcanics are described two of which can be matched quite closely with plutonic equivalents a large part of the paleozoic continental margin volcanic activity in southeast australia consisted of the magmatic recycling of old metasedimentary crust probably of late proterozoic age the three volcanic suites are moderately to strongly peraluminous with the corresponding presence of al rich minerals variation within the volcanic suites is ascribed chiefly to progressive removal of restite or source material residual from partial melting the most mafic suite the hawkins suite contains plagioclase cordierite orthopyroxene biotite and quartz as restite components with less abundant almandine these rocks are chemically equivalent to mafic biotite rich and cordierite bearing granitoids from parts of the berridale and murrumbidgee batholiths garnet is absent from the goobarragandra suite volcanics which are a little more felsic and close in compositon to granitoids of the young and maragle batholiths the s type character of the laidlaw suite is less pronounced although a sedimentary source seems to be established such a source would be less mature than those for the other two volcanic suites the laidlaw suite resembles but cannot be closely identified with felsic s type granitoids of the murrumbidgee and berridale batholiths low grade regional metamorphism in most of the volcanic rocks has resulted in much mineralogical alteration and mobility of alkali and alkaline earth elements despite this alteration unaltered rocks are present in all three suites compositional data for the phenocryst phases within the unaltered rocks has allowed estimation of some intensive parameters hawkins suite volcanics were extruded directly from their source region and preserve phenocryst equilibria established at 5 6 kbar at 800 c the laidlaw and goobarragandra suites reequilibrated at lower pressures than their source before extrusion the laidlaw suite reequilibrated at estimated temperatures of 725 730 c o2 of 10 15 5 to 10 14 bars and h2o of 2 to 2 5 kbar differing mineral compositions in the three suites are related to differing source rock compositons and oxygen fugacities relative biotite and orthopyroxene mg is possibly pressure dependent

active shoreline of ontario lacus titan a morphological study of the lake and its surroundings of more than 400 filled lakes now identified on titan the first and largest reported in the southern latitudes is ontario lacus which is dark in both infrared and microwave here we describe recent observations including synthetic aperture radar sar images by cassini s radar instrument 2 cm and show morphological evidence for active material transport and erosion ontario lacus lies in a shallow depression with greater relief on the southwestern shore and a gently sloping possibly wave generated beach to the northeast the lake has a closed internal drainage system fed by earth like rivers deltas and alluvial fans evidence for active shoreline processes including the wave modified lakefront and deltaic deposition indicates that ontario is a dynamic feature undergoing typical terrestrial forms of littoral modification

transient surface liquid in titan s polar regions from cassini cassini radar images of titan s south polar region acquired during southern summer contain lake features which disappear between observations these features show a tenfold increases in backscatter cross section between images acquired one year apart which is inconsistent with common scattering models without invoking temporal variability the morphologic boundaries are transient further supporting changes in lake level these observations are consistent with the exposure of diffusely scattering lakebeds that were previously hidden by an attenuating liquid medium we use a two layer model to explain backscatter variations and estimate a drop in liquid depth of approximately 1 m per year on larger scales we observe shoreline recession between iss and radar images of ontario lacus the largest lake in titan s south polar region the recession occurring between june 2005 and july 2009 is inversely proportional to slopes estimated from altimetric profiles and the exponential decay of near shore backscatter consistent with a uniform reduction of 4 1 3 m in lake depth of the potential explanations for observed surface changes we favor evaporation and infiltration the disappearance of dark features and the recession of ontario s shoreline represents volatile transport in an active methane based hydrologic cycle observed loss rates are compared and shown to be consistent with available global circulation models to date no unambiguous changes in lake level have been observed between repeat images in the north polar region although further investigation is warranted these observations constrain volatile flux rates in titan s hydrologic system and demonstrate that the surface plays an active role in its evolution constraining these seasonal changes represents the first step toward our understanding of longer climate cycles that may determine liquid distribution on titan over orbital time periods

titan s cloud seasonal activity from winter to spring with cassini vims abstract since saturn orbital insertion in july 2004 the cassini orbiter has been observing titan throughout most of the northern winter season october 2002 august 2009 and the beginning of spring allowing a detailed monitoring of titan s cloud coverage at high spatial resolution with close flybys on a monthly basis this study reports on the analysis of all the near infrared images of titan s clouds acquired by the visual and infrared mapping spectrometer vims during 67 targeted flybys of titan between july 2004 and april 2010 the vims observations show numerous sporadic clouds at southern high and mid latitudes rare clouds in the equatorial region and reveal a long lived cloud cap above the north pole ubiquitous poleward of 60 n these observations allow us to follow the evolution of the cloud coverage during almost a 6 year period including the equinox and greatly help to further constrain global circulation models gcms after 4 years of regular outbursts observed by cassini between 2004 and 2008 southern polar cloud activity started declining and completely ceased 1 year before spring equinox the extensive cloud system over the north pole stable between 2004 and 2008 progressively fractionated and vanished as titan entered into northern spring at southern mid latitudes clouds were continuously observed throughout the vims observing period even after equinox in a latitude band between 30 s and 60 s during the whole period of observation only a dozen clouds were observed closer to the equator though they were slightly more frequent as equinox approached we also investigated the distribution of clouds with longitude we found that southern polar clouds before disappearing in mid 2008 were systematically concentrated in the leading hemisphere of titan in particular above and to the east of ontario lacus the largest reservoir of hydrocarbons in the area clouds are also non homogeneously distributed with longitude at southern mid latitudes the n 2 mode wave pattern of the distribution observed since 2003 by earth based telescopes and confirmed by our cassini observations may be attributed to saturn s tides although the latitudinal distribution of clouds is now relatively well reproduced and understood by the gcms the non homogeneous longitudinal distributions and the evolution of the cloud coverage with seasons still need investigation if the observation of a few single clouds at the tropics and at northern mid latitudes late in winter and at the start of spring cannot be further interpreted for the moment the obvious shutdown of the cloud activity at titan s poles provides clear signs of the onset of the general circulation turnover that is expected to accompany the beginning of titan s northern spring according to our gcm the persistence of clouds at certain latitudes rather suggests a sudden shift in near future of the meteorology into the more illuminated hemisphere finally the observed seasonal change in cloud activity occurred with a significant time lag that is not predicted by our model this may be due to an overall methane humidity at titan s surface higher than previously expected

seasonal hydrological loading in southern alaska observed by gps and grace 1 we compare vertical seasonal loading deformation observed by continuous gps stations in southern alaska and modeled vertical displacements due to seasonal hydrological loading inferred from grace seasonal displacements are significant and gps observed and grace modeled seasonal displacements are highly correlated we define a measure called the wrms reduction ratio to measure the fraction of the position variations at seasonal periods removed by correcting the gps time series using a seasonal model based on grace the median wrms reduction ratio is 0 82 and the mean is 0 73 0 26 with a value of 1 0 indicating perfect agreement of gps and grace the effects of atmosphere and non tidal ocean loading are important we add the aod1b de aliasing model to the grace solutions because the displacements due to these loads are present in the gps data and this improves the correlations between these two geodetic measurements we find weak correlations for some stations located in areas where the magnitude of the load changes over a short distance due to grace s limited spatial resolution grace models can correct seasonal displacements for campaign gps measurements as well

possible two stage 87sr evolution in the stockdale rhyolite the rb sr total rock data for the stockdale rhyolite of significance for the palaeozoic time scale are more scattered about a single stage isochron than expected from experimental error two stage 87 sr evolution for several of the samples is explored to explain this as an alternative to variation in the initial 87 sr 86 sr which is customarily used in single stage dating models the deletion of certain samples having very high rb sr removes most of the excess scatter and leads to an estimate of 430 7 m y for the age of extrusion there is a younger alignment of rb sr data within each sampling site at 412 7 m y we suggest that the stockdale rhyolite is at least 430 m y old that its original range in rb sr was smaller than now observed and that it experienced a net loss in sr during later hydrothermal alteration at ca 412 m y

the laidlaw volcanics a late silurian point on the geological time scale mapping mineralogical and chemical studies of an area west and northwest of canberra southeastern australia have shownthat the laidlaw volcanics are unique in the region and that their age is tightly controlled stratigraphically as they lie both above and below early ludlow late silurian fossiliferous sediments k ar mineral analyses previously published rb sr mineral analyses and new rb sr wholerock and mineral analyses together give the laidlaw volcanics an age of 420 7 2 2 m y this result for the early ludlow is identical numerically with a recently published age of 421 3 m y for the ashgillian late ordovician stockdale rhyolite and suggests either that the time interval between the ashgill and ludlow does not exceed a few million yearsor that the age estimate for the stockdale rhyolite is too young

geochronology of late caledonian magmatism in northern britain rb sr k ar ar ar and sm nd isotopic data are presented for mineral separates and whole rock samples from old red sandstone ors lavas associated minor intrusions and 9newer granite9 intrusive complexes from the cheviot hills north to shetland these data yield 16 internally consistent rb sr mineral ages and one each of ar ar sm nd and k ar ages when considered with precise and reliable published data it is clear that there are systematic differences in the age of late caledonian magmatism through the geological regions of scotland in the grampian highlands and the scottish midland valley magmatism was concentrated during the period 423 to 410 ma ors volcanism in the highlands occurred around 420 ma with plutonism continuing to about 408 ma volcanism and plutonism in the midland valley took place between 415 and 410 ma in the southern uplands magmatism occurred earlier in the north with all magmatism close to the southern uplands fault dated around 408 ma and that close to the iapetus suture dated at around 394 ma as no evidence exists for ocean closure prior to c 400 ma the age of igneous activity north of the southern uplands fault is consistent with chemical evidence for a relationship to active nw directed subduction the younger magmatism of the s part of the southern uplands cannot be subduction related and the c 408 ma plutons nearer the southern uplands fault can only be subduction related if tectonic construction of the southern uplands was a two stage process

geochemical investigations of microgranitoid enclaves in the s type cowra granodiorite lachlan fold belt se australia the cowra granodiorite is a relatively mafic enclave rich s type pluton in the lachlan fold belt which has been cited as a type example of a restitic origin for all varieties of enclaves in lachlan fold belt s type granites microgranitoid enclaves from the pluton are subordinate to metasedimentary varieties and can be subdivided into two groups according to their mafic mineral assemblage pyroxene microtonalites and biotite microgranites no geochemical or isotopic distinction can be made between the two varieties petrographic evidence acicular apatites xenocrysts from the host granite suggests an origin as mingled more mafic magmas which have been variably contaminated by the more felsic host magma this is supported by the fact that the microgranitoid enclaves have isotopic compositions 87sr 86sr i 0 7095 to 0 7144 end i 9 2 to 6 9 that are generally more primitive than or similar to those of the host granite 87sr 86sr i 0 7142 end i 8 8 the spread in isotopic compositions like their trace element compositions is considered to be the consequence of variable degrees of diffusive exchange between the felsic and more mafic magmas during slow cooling several studied metasedimentary enclaves are not in isotopic equilibrium with their host granite and therefore cannot represent pristine samples of the bulk source region of the granite instead they represent portions of a lithologically and compositionally diverse source terrane or accidental xenoliths entrapped during emplacement

geomorphological significance of ontario lacus on titan integrated interpretation of cassini vims iss and radar data and comparison with the etosha pan namibia abstract ontario lacus is the largest lake of the whole southern hemisphere of titan saturn s major moon it has been imaged twice by each of the cassini imaging systems imaging science subsystem iss in 2004 and 2005 visual and infrared mapping spectrometer vims in 2007 and 2009 and radar in 2009 and 2010 we compile a geomorphological map and derive a hydrogeological interpretation of ontario lacus based on a joint analysis of iss vims and radar sar datasets along with the t49 altimetric profile acquired in december 2008 the morphologies observed on ontario lacus are compared to landforms of a semi arid terrestrial analog which resembles titan s lakes the etosha pan located in the owambo basin namibia the etosha pan is a flat floored depression formed by dissolution under semi arid conditions of a surface evaporitic layer calcretes controlled by groundwater vertical motions we infer that ontario lacus is an extremely flat and shallow depression lying in an alluvial plain surrounded by small mountain ranges under climatic conditions similar to those of terrestrial semi arid regions channels are seen in the southern part of ontario lacus in vims and radar data acquired at a 2 years time interval their constancy in location with time implies that the southern portion of the depression is probably not fully covered by a liquid layer at the time of the observations and that they most probably run on the floor of the depression a shallow layer of surface liquids corresponding to the darkest portions of the radar images would thus cover about 53 of the surface area of the depression of which almost 70 is located in its northern part these liquid covered parts of the depression where liquid ethane was previously identified are interpreted as topographic lows where the alkanofer raises above the depression floor the rest of the depression and mostly its southern part is interpreted as a flat and smooth exposed floor likely composed of a thick and liquid saturated coating of photon absorbing materials in the infrared this hypothesis could explain its dark appearance both in the infrared and radar data and the persistence of channels seen on the depression floor over the time shorelines are observed on the border of ontario lacus suggesting past high stand levels of the alkanofer table the analogy with the etosha pan suggests that ontario lacus depression developed at the expense of a soluble layer covering the region dissolution of this layer would be controlled by vertical motions of the alkanofer table over the time during flooding events liquid hydrocarbons covering the depression floor would dissolve the surface layer increasing progressively the diameter of the depression on geological timescales during drought episodes liquid hydrocarbons of the underground alkanofer would evaporate leading to crystallization of evaporites in the pores and at the surface of the substratum and to the formation of the regional soluble layer the presence of specific landforms lunette dunes or evaporites is compatible with such evaporitic regional settings alternatively but not exclusively the surface soluble layer might have formed by accumulation on the ground of soluble compounds formed in the atmosphere

the boambolo formation a silurian prograding fan delta sequence in southeastern new south wales australia abstract the silurian sandstones and gravels of the boambolo formation are subdivided into six descriptive lithofacies each of which is diagnostic of a particular set of hydrodynamic conditions of deposition analysis of the vertical sequence of hydrodynamic conditions together with limited lateral facies variability information has permitted interpretation of this formation in terms of a prograding fan delta model within this broad model it has been possible to recognise deposits of current dominated quiet shelf delta front shoreface back beach pond and braided river environments an overall coarsening upward trend from shale dominated facies at the base of the formation to mixed sandstone and gravel at the top reflects the upward transition from low to high energy environments superimposed on this trend in the submarine portion of the formation are six secondary coarsening upward cycles representing establishment progradation and abandonment of migrating delta front lobes in the coarse terrestrial portion of the formation debris flow deposits are either absent or volumetrically insignificant with even the coarsest gravels diameters up to 15 cm believed to be traction current deposits

the stratigraphy and deformation history of the tumut region implications for the development of the lachlan fold belt abstract the tumut region forms the southern part of the tumut synclinorial zone in the southeastern part of the lachlan fold belt lfb the area contains two major stratigraphie packages ordovician to early silurian quartz rich to quartz intermediate flysch and volcanics package a and overlying fossiliferous early late silurian volcanics and flysch package b rhyolite within the older package a yields a u pb zircon age of 428 6 ma both packages were meridionally folded during the siluro devonian bowning orogeny following intrusion of the gocup granite at 411 5 ma an earlier deformation characterised by thrust faulting e w recumbent folding and later local coaxial upright folding is present only in the older flysch and volcanics package a this earlier deformation is part of the benambran orogeny that affects the ordovician metamorphics of the wagga metamorphic belt and other parts of the lfb and is constrained to about 425 ma fold characteristics of this deformation are indicative of thin skinned intraplate transpressional deformation rather than classical collisional tectonics as envisaged by some workers for the benambran orogeny here and elsewhere in the lfb the composition and deformational history of the older flysch indicates that it is part of the ordovician to early silurian molong volcanic belt consequently the older concept of an early silurian tumut trough incorporating both packages of rocks is rejected instead it is proposed that up to 2500 m of early late silurian rocks formed in a pull apart basin the tumut basin thus the silurian depositional history of the tumut region previously considered unique in the lfb is little different from other basins of similar age throughout the lfb

a comparison of k ar and rb sr ages of rapidly cooled igneous rocks two points in the palaeozoic time scale re evaluated k ar and rb sr ages were measured on rapidly cooled igneous rocks from kinnekulle sweden ordovician bentonite the cerberean cauldron australia late devonian felsic volcanics mount dromedary australia cretaceous monzonite and cooma australia jurassic syenite no systematic bias was detected between the ages determined by the two techniques calculated using the constants recommended by the i u g s subcommission on geochronology the k ar and rb sr ages of the jurassic syenite also were indistinguishable from its zircon u pb age the kinnekulle a 1 bentonite gives a minimum age of 446 3 ma for the early caradocian diplograptus molestus zone the cerberean cauldron volcanics give a minimum age of 367 2 ma for the early frasnian these data are consistent with a small upwards revision of the ages in gale et al 9s 1979 time scale as proposed by gale et al 1980

polyphase tectonothermal evolution of exotic caledonian nappes in troms norway evidence from 40ar39ar mineral ages abstract 40 ar 39 ar incremental release ages have been determined for hornblende and muscovite from several high level exotic nappes in northern troms county norway within the nordmannvik nappe and upper tectonic levels of the lyngen nappe complex balsfjord group both minerals record plateau and isotope correlation ages between c 427 and 417 ma these indicate relatively rapid post metamorphic cooling which is interpreted to have occurred during scandian translation of exotic tectonic elements to higher crustal levels along the baltoscandian margin muscovite within various structural levels of the tromso nappe complex uppermost allochthon yeilds plateau ages of 427 410 ma which also record post scandian metamorphic cooling however hornblende within the tromso nappe complex records significantly older isotopic correlation ages which range between c 481 ma and 432 ma the 40 ar 39 ar spectra display no evidence of partial scandian rejuvenation and the isotope correlation ages are therefore interpreted to date cooling following pre scandian tectonothermal activity these results indicate that early paleozoic tectonothermal events affected outboard exotic tectonic elements at approximately the same time as the early caledonian orogenesis previously described for nappe units with initial baltic palinspastic affinities e g seve nappe complex

mapping and interpretation of sinlap crater on titan using cassini vims and radar data 1 only a few impact craters have been unambiguously detected on titan by the cassini huygens mission among these sinlap is the only one that has been observed both by the radar and vims instruments this paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition topography and surface roughness several units appear in vims false color composites of band ratios in the sinlap area suggesting compositional heterogeneities a bright pixel possibly related to a central peak does not show significant spectral variations indicating either that the impact site was vertically homogeneous or that this area has been recovered by homogeneous deposits both vims ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket since the ku band sar may see subsurface structures at the meter scale the difference between infrared and sar observations can be explained by the presence of a thin layer transparent to the radar an analogy with terrestrial craters in libya supports this interpretation finally a tentative model describes the geological history of this area prior during and after the impact it involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind subsequent evolution is then driven by erosional processes and aeolian deposition

major southward thrusting of the dalradian rocks of connemara western ireland the connemara schists are of dalradian late precambrian cambrian age and since the work of kilburn et al 1 it has been apparentthat they occupy an anomalous geographical position south southeast of the strike continuation of the dalradian rocks of scotland and ireland and south of the inferred position of the highland boundary fault fig 1 also the connemara schists are unusual in having reached a higher metamorphic grade and having had a different metamorphic history from most other parts of the dalradian the model which we propose here for the connemara dalradian that of an allochthonous thrust sheet offers an explanation for these anomalies and highlights hitherto unsuspected similarities between the tectonic histories of the south east margins of the metamorphic caledonides in the british isles and scandinavia

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

mineral age record of a polyorogenic evolution within the seve and koli nappes trondelag norway abstract in the central scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica hornblende within amphibolite at one locality within westernmost exposures of seve nappe units in trandelag norway displays an internally discordant 40 ar 39 ar age spectrum which suggests a polyphase thermal evolution including 1 1 initial post metamorphic cooling through argon retention temperatures at c 475 480 ma 2 2 partial rejuvenation during a silurian c 400 425 ma thermal overprint muscovite within the exposure was more extensively rejuvenated during the silurian overprint at twelve other trandelag sample locations hornblende muscovite and biotite within both the seve and koli nappe complexes record post metamorphic cooling ages between 420 and 435 ma and display no direct evidence of a pre silurian thermal record however the widespread occurrence of intracrystalline extraneous argon components and textural complexities clearly point toward a pre silurian tectonothermal history comparison with 40 ar 39 ar mineral ages reported elsewhere in the central scandinavian caledonides suggests a polyorogenic evolution consisting of 1 1 variable high pressure metamorphism of distal baltoscandian miogeoclinal sequences during entrainment in an accretionary wedge which developed in the late cambrian early ordovician over a west dipping subduction zone related arc volcanic activity occurred in more outboard western sectors 2 2 ductile imbrication of high and intermediate pressure sequences within the accretionary wedge diachronous cooling and or chronologically distinct tectonic episodes are indicated throughout the early and middle ordovician 3 3 ultimate accretion of a variety of eugeoclinal terranes along the baltica continental margin 4 4 imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the baltoscandian platform in the silurian crystalline baltica basement and overlying structural cover units were depressed to significant crustal depths during eastward nappe transport with resultant formation of high temperature eclogues previously reported crystallization ages of c 425 ma suggest that the eclogites formed at approximately the same time as minerals within the superencumbent nappe units cooled through argon closure temperatures following eastward nappe transport the basement experienced rapid uplift and resultant adiabatic decompression this was followed by rapid cooling through argon retention temperatures at 390 400 ma

aluminum in zircon as evidence for peraluminous and metaluminous melts from the hadean to present zircon structurally accommodates a range of trace impurities into its lattice a feature which is used extensively to investigate the evolution of silicate magmas one key compositional boundary of magmas is defined by whether the molar ratio of al2o3 cao na2o k2o is larger or smaller than unity here we report 800 al in zircon concentrations from 19 different rocks from the lachlan fold belt southeastern australia new england usa and arunachal leucogranites eastern himalaya with al2o3 cao na2o k2o whole rock values that range from 0 88 to 1 6 zircons from peraluminous rocks yield an average al concentration of 10 ppm which distinguishes them from crystals found in metaluminous rocks 1 3 ppm this difference is related to the materials involved in the melting assimilation and or magma differentiation processes for example magmas that assimilate al rich material such as metapelites are expected to produce melts with elevated alumina activities and thus zircons with high al concentrations these observations are applied to the archean and hadean jack hills detrital zircon record detrital archean zircons with ages from about 3 30 to 3 75 ga yield al in zircon concentrations consistent with origins in peraluminous rocks in 8 of the cases n 236 a single zircon from the pre 3 9 ga age group n 39 contains elevated al contents which suggests that metaluminous crustal rocks were more common than peraluminous rocks in the hadean weathered material assimilated into these hadean source melts was not dominated by al rich source material

the significance of isotopic dates from the english lake district for the ordovician saurian time scale the lower palaeozoic time scale is discussed in the light of a new date for the threlkeld microgranite and a reassessment of other published dates from the lake district which suggest ages of c 410 ma for the base of the devonian c 421 ma for the ashgill c 429 ma for the late caradoc c 439 ma for the early llandeilo and c 468 ma for the early llanvirn