petrogenesis of the greenhills complex southland new zealand magmatic differentiation and cumulate formation at the roots of a permian island arc volcano a permian 265 ma intrusive complex which formed as a magmatic feeder reservoir to an immature island arc volcano is fortuitously exposed in southern new zealand known as the greenhills complex this intrusion was emplaced at shallow crustal levels and consists of two layered bodies which were later intruded by a variety of dykes cumulates which include dunite olivine clinopyroxenite olivine gabbro and hornblende gabbro norite are related products of parent magma fractionation both primary magmatic and secondary platinum group minerals occur within dunite at one locality using the composition of cumulus minerals mafic dykes and melt inclusions we have determined that the parent magmas of the complex were hydrous low k island arc tholeiites of ankaramitic affinities progressive magmatic differentiation of this parent magma generated fractionated melt of high alumina basalt composition which is now preserved only as dykes which cut the complex field evidence and cumulus mineral profiles reveal that the magma chambers experienced turbulent magmatic conditions during cumulate rock formation recharge of the chambers by primitive magma is likely to have coincided with eruption of residual melt at the surface similar processes are inferred to account for volcanic rock compositions in other parts of this arc terrane and in modern island arc systems

petrology and geochemistry of lavas from the sumisu and torishima backarc rifts thirteen dredge hauls from the active sumisu and torishima rift grabens west of the izu bonin arc at about 30 31 n 140 e recovered a suite of tholeiitic basalts to sodic rhyolites volcanism occurs along tensional faults within and bounding the rift grabens and along the transfer zones between adjoining rift segments the sumisu and torishima rift lavas differ significantly from the lavas of the adjacent arc volcanic centers in having loweral2o3 na2o ba zr v ti andba ce and higher abundances of the rare earth elements the rift lavas also have characteristics of backarc basin basalts in that they are enriched in al2o3 and depleted in total iron and tio2 relative to mid ocean ridge basalt characteristics which are consistent with a higher water content in the source thus the model of a progressive change in backarc basin basalt composition from arc like to mid ocean ridge like as a function of evolution of the basin as has been suggested from many backarc regions is not generally applicable the comparison of the sumisu and torishima rift lavas with mariana backarc basin lavas indicates that backarc basin basalts differ in composition from one basin to another the comparison of these backarc basin suites with mid ocean ridge suites from similar axial depths indicates that the overall control over the spectrum of backarc basin basalt compositions may be different extents of melting of the mantle the sumisu and torishima rift lavas formed by a slightly higher extent of melting than the mariana backarc basin basalts a phenomenon which is related to the depth of the ridge segments furthermore the data suggest a systematically higher extent of melting in the arc lavas than in the backarc lavas for both of these arc backarc systems consistent with a greater flux of water beneath the arc than beneath the backarc region

changes in atmospheric co2 and its carbon isotopic ratio during the penultimate deglaciation abstract the largest natural increases in atmospheric co 2 concentration as recorded in ice cores occur when the earth climate abruptly shifts from a glacial to an interglacial state open questions remain regarding the processes at play the sequences of events and their similarities along different glacial interglacial transitions here we provide new combined data of atmospheric co 2 and its carbon isotopic ratio 13 co 2 for the penultimate glacial interglacial transition termination ii from the antarctic epica dome c ice core together with the strongest antarctic warming this transition bears the largest co 2 increase 104 ppmv of the last nine terminations ending with an overshoot of 21 ppmv occurring within 300 y and leading to higher levels than those of the late pre industrial holocene the full co 2 rise is accompanied by an overall decrease of the 13 co 2 minimum values on which three positive excursions are superimposed peak to peak 13 co 2 changes in our record can reach 1 the ice core atmospheric 13 co 2 appears more depleted by 0 2 during termination ii compared to termination i paralleling a similar carbon isotopic depletion recorded in marine data during both terminations most of co 2 and 13 co 2 variations are attributed to southern ocean stratification breakdown and decreased efficiency of the biological pump compared to termination i termination ii ice core data point to different timings of decrease in iron supply and sea ice extent suggesting that they could account for distinct patterns of the carbon cycle

bryozoans as carbonate sediment producers on the cool water lacepede shelf southern australia abstract modern sediments on the lacepede shelf and adjacent slope are typical mid latitude cool water palimpsest deposits dominated by bryozoan mollusc and quartz particles bryozoan bioclasts form autochthonous and to a lesser extent allochthonous accumulations across the grain size spectrum from mud to boulder size the bryozoan skeletons are grouped on the basis of architecture and style of disarticulation fragmentation into nine morphotypes erect rigid forms comprise 1 fenestrate 2 foliose 3 flat robust branching and 4 delicate branching morphotypes large adeona sp skeletons are recognised as a separate type of fenestrate form because of their distinctive shape mineralogy and restricted environment erect flexible forms are either 5 articulated branching or 6 articulated zooidal other important morphotypes are 7 encrusting 8 nodular arborescent and 9 vagrant differences in skeletal architecture result in distinct particle types encrusting morphotypes on soft organic substrates and the wide variety of erect rigid forms are broken into fragments erect flexible forms disintegrate upon death into definitive sand and silt size grains encrusting morphotypes on hard substrates nodular arborescent and vagrant forms remain whole and when large accumulate in place morphotypes are mineralogically distinct and so bryozoan sediment composition is environmentally controlled shallow water

paleoenvironmental reconstruction of the early to middle miocene central paratethys using stable isotopes from bryozoan skeletons stable carbon and oxygen isotope values from single bryozoan colonies were used to reconstruct the paleoenvironments of the early to middle miocene ottnangian to badenian sediments of the central paratethys this approach utilizes a locally abundant allochem while avoiding matrix and multiple allochem contamination from bulk rock samples bryozoan colonies and a few foraminifera and rock matrix samples from 14 localities yielded 399 carbon and oxygen isotope values data from six of the localities 15 of the total number of samples were interpreted as having been diagenetically altered and were rejected the remaining data indicate a primarily localized upwelling signal with lesser variation caused by global climatic and regional tectonic forcing of sea level salinity and temperature paleotemperatures were calculated to range from 12 to 21 c despite potential taxonomic and diagenetic problems bryozoan colonies are a powerful underutilized source of paleoenvironmental carbon and oxygen isotope data

collapse of the luzon volcanic arc during onset of arc continent collision evidence from a miocene pliocene unconformity eastern taiwan a regional miocene pliocene unconformity in the coastal range of eastern taiwan provides information about vertical motions that affected the colliding volcanic arc during initiation of arc continent collision the unconformity separates precollisional volcanic and volcaniclastic rocks of the miocene luzon arc and forearc basin from an overlying thick sequence of syncollisional pliocene pleistocene sedimentary rocks derived from the metasedimentary accretionary wedge of taiwan the duration of time represented by the unconformity averages 1 2 m y and locally ranges up to 4 m y the basal unit of the younger syncollisional sequence consists of bathyal mega slump folded mudstone pebbly mudstone and thin bedded turbidites sharp stratigraphic juxtaposition of these deep marine deposits directly above shallow marine limestone and epiclastic rocks upper part of the older arc sequence requires extremely rapid subsidence during initiation of the collisional basin the coastal range unconformity is interpreted to represent a period of latest miocene nondeposition and or erosion in the luzon arc that was related to initial subduction of the eurasian continental margin along the manila trench this period was followed in pliocene time by very rapid subsidence or collapse of the arc platform to 1 2 km water depth there are two dissimilar mechanisms of basin subsidence that may have controlled initiation of the collisional basin 1 extension rifting and crustal thinning in the luzon arc massif to form a series of small rift or pull apart subbasins or 2 flexural subsidence of oceanic lithosphere in a foreland style basin due to crustal loading in the expanding accretionary wedge of proto taiwan although data are insufficient to provide a unique solution the flexural subsidence model is supported by systematic younging of the initial subsidence event from west to east which may record eastward migration of an outer flexural bulge notable differences between the unconformity and paleogeography of the early collisional basin and analogous present day basins in the offshore region to the south suggest that arc continent collision and basin development in eastern taiwan have experienced secular change since late pliocene time

quantifying crustal thickness variations in evolving orogens correlation between arc basalt composition and moho depth a compilation of geochemical data from 50 active volcanoes where seismically defined moho depth measurements are available representing most volcanic arcs around the world indicates a relation exists between crustal thickness moho depth and the trace element composition of basalts the best correlation exists for maximum light heavy rare earth element ree ratios and we use maximum ce y r2 0 90 to show the exponential function with increasing depth to 50 km application to new zealand part of the eastern gondwanan margin through much of the phanerozoic shows that higher ce y ratios in arc basalts correspond to two periods of recognized crustal thickening plus an additional event at ca 240 ma which links new zealand to the gondwanide orogeny conversely low ce y ratios in basalts correlate with periods of recognized extension in eastern gondwana very high ce y ratios in ca 120 ma rocks imply an unusually thickened 50 km arc crust consistent with independent geological estimates of crustal thickness at that time the correlation shows that crustal thickness variations during orogenesis can be conservatively estimated to within 3 km

paleocene lower eocene carbonate platforms of westernmost tethys abstract the paleocene lower eocene succession is well exposed in sierra espuna mula basin betic cordillera s spain and carbonate platforms are well represented as part of this succession the study of the paleoenvironmental evolution of these platforms has allowed to cover an important gap in the knowledge in the westernmost tethys thirteen microfacies mf1 to mf13 were recognized based mainly on the fossil assemblage principally larger benthic foraminifera texture and fabric of the microfacies the fossiliferous assemblage of the entire succession shows a mixture of photozoan and heterotrophic biogenic elements typical of an inner to outer ramp environment of a warm temperate biogeographic province fragments of hermatypic corals have also been detected in the lower part of the succession paleocene allowing thinking in propitious conditions in this period the succession evolves upwards lower eocene to low energy shallow marine protected environments lagoon in inner ramp settings in addition abundant porcelaneous larger benthic foraminifera such as alveolinids and soritids are indicative of euphotic shallow marine conditions in moderately oligotrophic upper subtidal environments in the upper part of the succession hermatypic corals as displaced fragments and in situ isolated coral phaceloid colonies also appear together with other biogenic components indicating warm shallow and euphotic marine conditions coral maerl environment lenticular larger benthic foraminifera characterizing marine mesophotic and oligotrophic habitats can be found in the upper part of the middle ramp and flattened larger benthic foraminifera forms indicating lowermost mesophotic conditions in a distal middle ramp the obtained results have been compared with other similar tethyan sectors obtaining a broader view the biogenic marine association is characterized by the absence of the lockhartia community of the tethyan domain together with the dominance of alveolinids nummulitids and orthophragminids during most of the paleocene northern mediterranean tethys platforms were located in the middle paleolatitudes and characterized by coral reef and coralgal biofacies the studied platforms located at a latitude close to 25 n show in a ramp like context underdeveloped in situ coral constructions probably of patch reef type in the early eocene the expansion and abundance of the larger benthic foraminifera and the practical disappearance of coral took place in the sedimentary platforms through the entire tethys however in the study area small reef coral build ups have also been observed in the lower cuisian beds indicating that in westernmost tethys coral construction continued at these latitudes

modal composition and detrital clinopyroxene geochemistry of lithic sandstones from the new england fold belt east australia a paleozoic forearc terrane the new england fold belt of southeast australia is divided by the peel fault system into two time equivalent zones showing contrasting depositional structural and metamorphic histories these are inferred to represent a western magmatic arc frontal arc succession and an eastern subduction complex assemblage the composition of the early to middle paleozoic clastic rocks from both east and west of the peel fault system indicates derivation from an undissected volcanic arc detrital quartz is absent or present only in minor amounts and always as monocrystalline grains lithic fragments are almost exclusively volcanic and normally dominant over feldspar which is invariably plagioclase now largely albitized to the west of the fault the distribution of lathwork microlitic felsitic and vitric rock fragments as well as variation in the amount of detrital quartz indicates changes in provenance through time and two cycles of basaltic to silicic volcanic activity have been identified the composition of detrital calcic clinopyroxene grains particularly their low ti and al contents and their ti mn na ratios indicates that they crystallized mainly from subalkaline probably calc alkaline volcanic arc magmas the dominantly volcanogenic provenance of sandstone from east of the fault and the low ti content of most detrital clinopyroxene grains indicate that the volcanic chain that lay to the west of the peel fault was the most likely source for the major portion of the clastic debris in the eastern rocks however the presence of ti rich detrital clinopyroxenes identical in composition to those in the metabasalts of the subduction complex indicates that uplifted segments of the complex provided an additional sediment source

changes in bryozoan assemblages and bathymetric variations examples from the messinian of northwest algeria abstract studies of recent bryozoan faunas have shown that there is a correlation between colonial growth forms and various physical factors of the environment especially bathymetry each given assemblage of zoarial forms can thus be related to a certain depth interval in marine neogene deposits numerous extant bryozoan species occur and some of them have more or less restricted depth ranges they are used here to complement the indications given by the analysis of growth forms in the messinian uppermost miocene of northwestern algeria a general feature is the occurrence of well developed diatomaceous deposits interbedded with marl beds where benthic invertebrate remains are often abundant in the five sections under study bryozoans are represented by 87 species belonging to nine different colonial growth forms four different assemblages of these zoarial forms characterised by presence absence and number of fragments are distinguished corresponding to four depth intervals the first and deepest assemblage upper bathyal to lower circalittoral occurs in the bottom part of the sections where colonies of a conescharelliniform species strongly predominate the second assemblage lower circalittoral is represented by several species belonging to various zoarial forms conescharelliniform cellariiform vinculariiform adeoniform and reteporiform the third assemblage upper circalittoral is characterised by the absence of conescharelliniforms but membraniporiforms and celleporiforms are abundantly represented together with numerous erect colony fragments in the fourth assemblage infralittoral membraniporiforms and celleporiforms predominate although a number of erect zoarial forms are sometimes associated in various proportions the presence of several extant bryozoan species associated with each of these four assemblages is used as a confirmation for the suggested depth intervals a gradual shallowing is thus indicated by the study of the bryozoan assemblages through the five messinian sections the discussion shows that modern data on zoarial forms and species bathymetric distributions are clearly applicable to cenozoic faunas but that caution must be exercised when using results obtained from different oceanographic regions

petrology of mariana trough and lau basin basalts the crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid ocean ridge basalts n morb but some subtle but distinctive differences exist these are largely due to differences in volatiles fe oxidation ratio abundances of large ion lithophile elements lil and some high field strength hfs elements isotope data for sr pb nd he and o are variable but broadly are morb like we present data contrasting mariana trough mtb and lau basin basalts lbb showing how they differ in certain trace element and isotopic signatures and compare both to n morb relative to n morb and lbb the mtb are enriched in alkalis alkaline earths light rare earth elements ree h2o and fe fe even for primitive samples while having morb type he 3 4 7 8 to 8 4 ra sr 87 86 mean 0 70293 and nd e 10 2 the lau basin is zoned with a central area having n morb characteristics for h2o lil ree nd e 8 1 to 9 0 and o but a depletion in hfs elements sr is more radiogenic mean 87 86 0 70347 and 3he 4he 3 4 7 2 to 11 0 ra is high relative to n morb the lau basin has a zone bordering the adjacent island arcs which is like mtb in both back arc basins relatively primitive unfractionated basalts with mg 100 mg fe 62 are found which resemble postulated primitive n morb calculated parental magmas obtained by adding xenocrystic olivine plot near or on 3 and 4 phase boundaries at 1 1 5 gpa for the ol di si system low p fractional crystallization and magma mixing explain most of the observed rock types possible explanations for differences between mtb and lbb include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere the long and complex history of mariana trough mantle sources led to a metasomatized mantle which gives rise to the distinctive mtb in contrast the lau basin is dominated by basalts derived from a source depleted in volatiles lil and hfs elements a previous melting history is implied mixing with a mantle component enriched in 87sr and 3he may be due to mantle counterflow driven by the subduction process

pleistocene calabrian deep water corals and associated biodiversity in the eastern mediterranean karpathos island greece diversified deep water corals and associated communities occur in early pleistocene early calabrian 1 7 1 6 ma calcareous crusts discovered on the south western coast of karpathos island eastern greece apart from abundant and conspicuous solitary and colonial corals 12 species the accompanying fauna comprises mostly bivalves 10 species serpulid worms 4 species and bryozoans 40 species the growth and deposition of the studied organisms occurred in an upper bathyal environment at water depths around 400 600 m the calculated mean uplift rate after deposition of the crusts indicates that karpathos was drowned during the earliest calabrian and experienced severe uplifts by the late calabrian a comparison between these communities and those of the pleistocene to recent mediterranean and north east atlantic shows that a common stock of taxa exist ed among them two azooxanthellate colonial scleractinians lophelia pertusa and madrepora oculata are predominant

using melt inclusions to determine parent magma compositions of layered intrusions application to the greenhills complex new zealand a platinum group minerals bearing island arc intrusion the permian greenhills complex of southland new zealand is a small ultramafic to mafic layered intrusion that hosts primary magmatic platinum group minerals pgms as inclusions in cumulus chromian spinel grains we have determined the major and trace element chemistry of the parent magmas of the complex using the composition of rehomogenized melt inclusions trapped in cumulus spinel grains from dunite these melt inclusions have compositions similar to those of primitive ankaramite dikes that cut the complex verifying that our data are representative of the parent melt chemistry these magmas have high mgo and cao and are enriched in pb sr and large ion lithophile elements compared to high field strength and rare earth elements we suggest that the parent magmas to the complex were primitive low k island arc tholeiite basalts that formed by high degrees of melting of a spinel peridotite source the platinum group element contents of such magmas are expected to be very high therefore the primary pgms at greenhills are suggested to have precipitated directly from the melt following differentiation and cooling in a shallow magma chamber

an unusual messinian succession in the sinis peninsula western sardinia italy abstract recently completed sedimentological and palaeontological analyses of the messinian deposits of western sardinia yielded dating palaeoenvironmental and new sequence stratigraphic interpretations the basal marls and the capo san marco formation are referred to the messinian both formations were deposited in a ramp setting whereas the overlaying sinis limestone formation is interpreted as a carbonate platform of wide extent probably equivalent to part of the terminal carbonate complex all these deposits are considered to have formed under normal marine conditions the three formations developed during one and a half cycles of progradation retrogradation compared with other messinian mediterranean carbonate platforms the sinis peninsula exhibits several unusual features 1 the notable absence of scleractinian coral reefs is related to dominantly cool seawater in this area 2 the capo san marco formation contains widespread microbial bryozoan serpulid carbonate buildups partially associated with upwelling currents 3 the breccias at the top of the sinis limestone formation are regarded as resulting from a major seismic shock over the whole peninsula

late paleozoic radiolarian ages from the gwydir terrane new england orogen eastern australia discoveries of late devonian early mississippian radiolaria in the gwydir terrane eastern australia indicate that much of the terrane is younger than previously thought radiolaria provide valuable constraints on the timing of the development of the gwydir terrane moreover this new biostratigraphic data indicate that previously published models detailing the development of the new england orogen need to be reappraised

surficial cool water carbonate sediments on the otway continental margin southeastern australia abstract the otway continental margin of southern australia is a swell dominated open cool water carbonate platform it is partitioned into a series of depth related zones of biological sediment production and accumulation by three hydrodynamic interfaces 1 abrasion depth 70 m 2 swell wavebase 130 m and 3 storm wavebase 250 m the otway shelf profile drops steeply from the strandline the shallow shelf lies largely between 30 and 70 m and is a high energy zone of carbonate sediment production intensive destructive diagenesis and erosion the seafloor is characterized by widespread exhumed limestone substrates which host dense encrusting assemblages of molluscs sponges bryozoans and red algae loose sediment accumulation is patchy and consists of a thin quartz rich palimpsest gravel veneer the middle shelf 70 to 130 m is a zone of swell wave shoaling and production and accumulation of coarse mega rippled 2 d dunes bryozoan sands deep shelf areas 130 to 180 m accumulate finer bioclastic sands foraminiferal echinoid bryozoan that are intensely bioturbated and episodically reworked by storms grains are variably fragmented and marginally bored at the shelf edge and top of slope 180 to 350 m nutrient rich upwelling currents support laterally extensive aphotic biostromal hermal bryozoan sponge coral communities which generate and accumulate thick successions of muddy skeletal sand sediments of the upper slope 350 to 500 m are a bioturbated mixture of periplatform bioclastic debris and pelleted foraminiferal nannofossil mud turbidites and resedimentation features are common bioturbation and shelf derived skeletal content decrease progressively downslope and pelagic muds dominate below 500 m lower slope areas are cross cut by gullies and have low accumulation rates the base of slope is characterized by sediment apron deposits consisting of interbedded shelf derived coarse grained turbidites and pelagic ooze

the oligocene miocene stratigraphic evolution of the majella carbonate platform central apennines italy abstract the stratigraphic architecture of the bolognano formation documents the evolution of the majella carbonate platform in response to global and local changes that affected the mediterranean area during the oligocene miocene interval the bolognano formation consists of a homoclinal ramp that developed in a warm subtropical environment five different lithofacies associations have been identified lepidocyclina calcarenites cherty marly limestones bryozon calcarenites hemipelagic marls and marly limestones and lithothamnion limestones each association corresponds to a single lithostratigraphic unit except for the lepidocyclina calcarenites that form two distinct lithostratigraphic units lepidocyclina calcarenites 1 and 2 these six units reflect alternation of shallow water carbonate production and drowning specifically two of the three stages of shallow water carbonate production regard the development of wide dune fields within the middle ramp one stage dominated by red algae and a sea grass carbonate factory whereas the two drowning phases are represented by marly cherty limestones and calcareous marls a new biostratigraphic framework for bolognano formation is presented based on high resolution analysis of calcareous nannofossil assemblages which proved to be very useful for biostratigraphic constraints also in shallow water settings using this approach we have linked the first drowning phase late chattian aquitanian p p in age to western mediterranean volcanism and the mi 1 event and the second drowning phase late burdigalian serravallian in age to the closure of the indo pacific passage and the occurrence of the global monterey event these results permit a new deciphering in terms of sequence stratigraphy of the bolognano formation that is interpreted as a 2nd order super sequence that can be subdivided into 3 transgressive regressive sequences

geochemistry and chronology of tectonic blocks in serpentinite melange of the southern new england fold belt nsw australia abstract tectonic blocks are widely distributed throughout the serpentinite melange of the peel manning fault system southern new england fold belt australia two meta diorite blocks from the pigna barney area have distinctly differing chemical signatures one resembles boninite containing high ni and cr low rare earth element rees and high field strength element hfses contents further it exhibits an enriched chondrite normalized lree pattern and an atypical end536ma value of 4 well defined isochrons for this sample gave sm nd and rb sr ages of 536 177 38 ma and 426 177 38 ma respectively the former represents the emplacement age and the latter resetting of the rb sr system during a later metamorphic event the initial nd isotopic composition suggests an enriched source the other meta diorite block has a flat ree pattern a ti v ratio 10 and y la and nb values typical of tholeiitic magmas erupted in an island arc setting by contrast blueschists from this locality and from the glenrock station area show depleted ree patterns ti v 20 50 and end480ma 8 features characteristic of normal mid ocean ridge basalts n morb meta diorites from the glenrock station area have moderately depleted signatures end400ma 4 5 and ti v ratios and ree patterns typical of calc alkaline and tholeiitic island arc magmas these contrast with hornblende cumulate rocks from this location which have very high cr and ni low zr and y and show slight lree enriched chondrite normalized patterns chromites 100 cr cr al 85 and clinopyroxenes wo93en42 3fs7 7 wo48en43 7fs8 3 in these rocks reveal an island arc affinity the end420ma values vary from 2 to 4 and rb sr ages from 425 177 44 ma to 411 177 15 ma the core of a single grain of cumulus hornblende gave a poorly defined 40ar 39ar age of 394 ma in contrast to younger ages 235 263 ma obtained from other grains the younger ages are attributed to resetting of the k ar system during a metamorphic event this study has provided further evidence for an early paleozoic arc trench system along the eastern gondwana margin

new approaches to co2 analysis in polar ice cores gases trapped in polar ice sheets provide a means of obtaining samples of earth s atmosphere from times in the past we describe geochemical processes affecting gases trapped in ice and discuss how these mechanisms affect the composition of gas extracted from polar ice cores we review the methods for recovering samples of paleo atmospheres from ice cores and discuss the suitability of each method in different applications we conclude that extracting gas by mechanical disintegration e g crushing grinding shaving or milling is most easily performed on relatively young ice in which the content of the bubbles is still representative of the original atmosphere for ice recovered from greater depth where some or all of the gases have been driven into the ice matrix itself more care must be taken in interpreting the analysis of the extracted gases

the watonga formation and tacking point gabbro port macquarie australia insights into crustal growth mechanisms on the eastern margin of gondwana abstract a diverse assemblage of accretionary complex island arc ophiolitic and high pressure low temperature metamorphic rocks occurs within the serpentinite melange at port macquarie on the eastern extremity of the new england orogen of eastern australia new field observations u pb zircon dating petrography and geochemistry presented here establish a more robust chronology and interpretation of these rocks previously all basalt chert and volcaniclastic sandstones at port macquarie were grouped into the watonga formation ordovician to middle devonian radiolarians and conodonts from watonga chert basalt associations shows that they are older than and unrelated to watonga volcaniclastic rocks like those at green mound which contain volcanic detrital zircons as young as 335 ma that were derived from a carboniferous arc volcanic detritus with pillow lava forming a block within the serpentinite melange yielded 452 10 ma igneous zircons indicating an ordovician age the tacking point gabbro has an age of 390 7 ma devonian and geochemical affinities with intra oceanic arc igneous suites it was intruded into deformed cherts of the watonga formation giving a spatial link between an ordovician devonian accretionary complex and adjacent devonian island arc the morb like basalt chert association of the watonga formation and the devonian tacking point gabbro represents a mid paleozoic assemblage allochthonous to gondwana which possibly correlates with the djungati and gamilaroi terranes respectively located further west in the new england orogen zircon dating shows that post serpentinite mafic felsic dykes were emplaced into the port macquarie serpentinite at 247 20 ma and further disrupted therefore tectonism affecting the serpentinite continued into the early triassic with final movement during the hunter bowen orogeny our results from port macquarie are compatible with a tectonic model for the new england orogen that involves episodic island arc collisional events gamilaroi and gympie terranes interspersed with periods of continental margin andean type magmatism and accretion along eastern gondwana

implications of radiolarian research for analysis of subduction complex terranes in the new england orogen nsw australia radiolarians provide important age constraints on geologically complex strata in the new england orogen of eastern australia several terranes interpreted as subduction complexes were undated prior to radiolarian studies radiolarian faunas indicate that the djungati terrane is significantly younger than the previously inferred ordovician to sulurian age range basalt chert successions in the djungati terrane developed during the silurian to late devonian in an environment which was far from the influence of terrigenous sedimentation radiolarians from tuffs within overlying arc derived volcaniclastic sequences constrain the timing of tectonic assembly of the terrane at a convergent margin to the latest devonian early carboniferous the extensive but previously undated anaiwan terrane also contains radiolarians which indicate a latest devonian to early carboniferous age for siliceous oceanic sediments these sediments were accreted into a subduction complex volcaniclastic sediments within this subduction complex contain radiolarians which indicate that it developed during the early carboniferous radiolarians in the willowie creek beds provide the first age constraints late devonian for another lithotectonic entity the yugambal terrane which is located along the eastern edge of the southern new england orogen many of the recently determined radiolarian ages are at variance with age estimates used to develop models for the tectonic development of the orogen these new age data require major reappraisal of models detailed analysis of the geological evolution of individual terranes is required before an integrated model for the entire orogen can be developed

co2 measurements on 1 cm3 ice samples with an ir laserspectrometer irls combined with a new dry extraction device abstract a new dry gas extraction and analysis method for small 1 cm3 ice samples is presented the extraction device cooled to 20 c contains two movable steel needle matrices for crushing the ice during the crushing process the gas escaping from the ice sample is continuously analyzed for co2 with an infrared laserspectrometer this method enables a fast measurement few minutes of the co2 concentration in the air bubbles with high spatial resolution in the ice core and a minimum potential contamination an important co2 contamination source due to an interaction of water vapour with surfaces is shortly discussed the reproducibility of extraction and analysis is 2 we analyzed co2 concentrations in the trapped air from different ice cores originating from the greenland ice sheet and from antarctica

examination of the deep levels of an island arc evidence from the tonsina ultramafic mafic assemblage tonsina alaska the tonsina ultramafic and mafic assemblage located in the northern chugach mountains along the trans alaska crustal transect tact is interpreted to be the remains of a magma chamber that crystallized at the base of a mature interoceanic island arc it is one of a number of isolated masses of peridotite and gabbro that comprise the basal part of the peninsular terrane along the northern fringe of the chugach mountains in southern alaska these masses the roots of a mid jurassic island arc have been uplifted along the north dipping border ranges fault system and crop out sporadically for 700 km from kodiak island to eastern alaska the tonsina ultramafic mafic assemblage is a layered sequence whose basal rocks are dunite and harzburgite 1 km thick overlain by a narrow zone of websterite and clinopyroxenite above these ultramafic rocks is a 5 to 6 km thick layered gabbro that is garnet bearing at its base textural relationships and chemical trends throughout the series of dunite pyroxenite garnet bearing gabbro and spinel gabbronorite point to an origin by igneous accumulation from a hydrous tholeiitic parent magma at deep levels i e at the base of a mature island arc before being emplaced along the border ranges fault the rocks were crystallized from a melt at pressures between 9 5 and 11 kbar 28 to 33 km depth and equilibrated at temperatures of 800 to 90o c based on phase relationships in the cumulus assemblages pyroxene thermobarometry and olivine spinel thermometry transitional sequences from ultramafic to mafic rocks are characterized by increasingly al rich pyroxenes and spinels or garnet and the absence of olivine plagioclase assemblages deep level fractionation of al poor phases such as olivine and pyroxene at moderately high pressures and temperatures resulted in concentration of al in the evolving magma as crystallization continued the phases recorded this alumina concentration and the resultant gabbros are al rich this observed trend supports the theory of high alumina basalt generation by fractional crystallization of olivine and pyroxene comparison of the tonsina rocks with aleutian lower crustal xenoliths as well as other exposures of arc related lower crustal magma chambers in japan pakistan and western north america indicates that this process is a common mechanism for island arc magma evolution at depth

mosaic of environments recorded by bryozoan faunas from the middle miocene of hungary the marine sediments of the badenian middle miocene of hungary pannonian basin central paratethys are composed of abundant bryozoan skeletal grains seventy one bulk samples collected at 18 localities outcrops and boreholes yielded a total number of 238 bryozoan species in order to reconstruct the badenian palaeoenvironments the present study investigates the composition of this very diverse fauna using a combination of statistical and palaeoecological methods the statistical analyses make use of cluster analysis and non metric multi dimensional scaling the palaeoecological approaches are based on the known ecological requirements of the bryozoan colonial growth forms and of the numerous extant species five facies have first been differentiated on the basis of sedimentological and palaeontological features coral buildups coralline algal limestones biocalcarenites sands and marls each of them is characterized by the abundance the diversity and the types of growth forms of the bryozoans the palaeoecological statistical and facies analyses further permitted to identify four depositional settings carbonate platform distal and proximal terrigenous platform slope and basin these environments developed at depths between 0 to about 300 m in a mixed carbonate siliciclastic depositional system skeletal production and spatial distribution of carbonate factories were predominantly controlled by terrigenous input this resulted in a complex mosaic of facies habitats where rich bryozoan faunas could thrive many warm water organisms among them foraminifers zooxanthellate corals molluscs bryozoans and echinoids were recorded from the study sites the coexistence of coralgal and bryomol carbonate skeletal assemblages in this subtropical setting is explained mostly by variations in the productivity of surface waters periods of nutrient enrichment and increased benthic eutrophication affected coral diversity and abundance in favour of bryozoans

crystal capture sorting and retention in convecting magma the mystery of producing strong compositional diversity among suites of comagmatic igneous rocks is investigated by considering the dynamic evolution of basaltic magma in a sheet like chamber a central conclusion is that inward progressing crystallization produces strong viscosity and temperature gradients that promote convection only near the leading edge of the upper thermal boundary layer convection is apparently confined to an essentially isoviscous isothermal region that hugs the downward growing roof zone strong changes in viscosity with crystallization divide the upper and lower thermal boundary layers into regions of decreasing viscosity and crystallinity n called rigid crust n 0 5 mush 0 5 n 0 25 and suspension n 0 25 the strong increase in viscosity near the mush suspension interface acts as a capture front that overtakes and traps slowly settling crystals initial phenocrysts mostly escape capture but crystals nucleated and grown in the suspension zone can escape only if the capture front slows to a critical rate attainable only in bodies thicker than about 100 m escaping crystals are redistributed and sorted by convection driven by the advance of the capture front itself crystal laden plumes traverse the central hot core of the body and deposit partially resorbed and sorted crystals within the lower suspension zone convection is never vigorous but is part of an overall intimate balance between roofward heat loss rigid crust growth crystallization kinetics and transport and sorting of sinking escaped crystals there is a strong similarity between these processes and those producing both varves and saline pan deposits it is clear that lavas lava lakes and sills are indeed examples of true magma chambers strongly exhibiting certain aspects of this over all process these aspects commonly also characterize the large mafic magmatic bodies because strong compositional changes in the residual melt occur largely outward that is at lower temperatures and higher crystallinities of the capture front which is immobile and mostly within rigid crust the possible range in comagmatic compositions available for eruption anywhere within the active magma is very limited this is in broad agreement with the compositional range observed in basaltic lava lakes sills and plutons like skaergaard the tuning of convection crystallization kinetics and phase equilibria in chambers of this type can produce a variety of textures and layering but not a diversity of compositions

bryozoan beds in northern italy as a shallow water expression of environmental changes during the oligocene isotope event 1 abstract shifts in carbonate producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm the shallow marine calcare di nago formation exposed in the san valentino section northern italy covers the late eocene and earliest oligocene the succession is characterized by the occurrence of light dependent biota such as coralline algae and larger benthic foraminifera in the uppermost part of the section however the fossil association is dominated by bryozoans which are filter feeder organisms this ca 12 m thick interval locally contains up to 86 bryozoans while coralline algae as well as larger benthic foraminifera are absent coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds whereas orthophragminids do not recover the gradual disappearance of larger foraminifera and coralline algae within the bryozoan dominated deposits is coeval with a pronounced positive shift in 13c based on its biostratigraphic position this positive shift is interpreted to be linked to the positive shift in 13c recognized in deep sea records shortly above the eocene oligocene boundary which in turn is associated to the positive shift in 18o leading to the oi 1 oligocene isotope event 1 cooling phase total phosphorus content increases in the bryozoan beds suggesting enhanced nutrient supply to the neritic ecosystem this phosphorous peak is coeval with the globally recognized increment in ocean productivity around the oi 1 and 13c positive shift thus disappearance of light dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower sea surface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters resulting from enhanced primary productivity as bryozoan beds occur in several italian localities around the eocene oligocene boundary they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice house earth

application of bryozoan zoarial growth form studies in facies analysis of non tropical carbonate deposits in new zealand abstract the fragmental remains of bryozoan colonies are the dominant skeletal contributor in many modern and ancient occurrences of non tropical shelf carbonate deposits the taxonomic complexity of the bryozoa the difficulties of systematic classification except by specialists the wide range of particle sizes and of preservation state in the carbonate deposits and the often well cemented nature of host limestones all limit the sedimentological interpretation of the commonly diverse bryozoan component however following the pioneer work of stach in the 1930 s the potential exists for sedimentologists to obtain useful paleo environmental information about the deposits by recording simply the nature and relative abundances of the various growth shapes of the bryozoan material known as their zoarial colonial growth forms here we propose a simple descriptive terminology covering both cheilostome and cyclostome bryozoans that involves four main growth forms encrusting erect rigid erect flexible and free living and a selection of subcategories based on shape identification of these habitat related growth form types is aided by reference to line drawings specimen photographs and photomicrographs of thin section slices the scheme is illustrated by examining briefly some possible environmental controls on the spatial and or time variations in the nature and distribution of colonial growth forms in several examples of modern and tertiary bryozoan dominated carbonate deposits in new zealand we anticipate that the routine description and quantification of bryozoan colonial growth types in non tropical carbonates generally will facilitate the recognition and interpretation of contrasting sub facies within the global foramol bryomol group of carbonate deposits

stratigraphic sedimentology of tertiary cool water limestones se australia abstract mid tertiary limestones exposed as sea cliffs along the coast of victoria southeastern australia accumulated on the inner part of a cool water distally steepened ramp or open shelf all sediments are bioclastic dominated by particles of bryozoans echinoderms benthic foraminifers brachiopods and molluscs shallow grainy facies also contain coralline algae quartz and glauconite while deep muddy facies include ahermatypic corals ostracodes sponge spicules planktic foraminifers and terrigenous clays the fundamental depositional unit is a meter scale subtidal cycle or rhythm shallow shelf cycles are shallowing upward cross bedded or burrowed grainstone capped by a marine cemented hardground or quartz granule lag while mid shelf cycles are upward coarsening and thickening proximal to distal tempestites such cycles are interpreted to form by eustatically driven climatically controlled oscillations in abrasion wave base and swell wave base deep shelf rhythms are interbedded bryozoan marl and calcareous clay thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution lowstand systems tracts are depositional or erosional sequence boundaries are complex multigeneration mostly submarine surfaces condensed cycle boundaries that can be traced offshore into multiple omission surfaces and conformable contacts basinward facies shifts result in deposition of condensed lowstand wedges of stacked shallowing upward grainstone cycles transgressive systems tracts are thick bryozoan marl calcareous clay rhythms associated with facies backstepping and abrupt deepening such rhythmites typically grade stratigraphically upward into tempestite cycles highstand systems tracts are highly progradational wedge shaped rock bodies of shallowing upward grainy cycles these limestones provide the critical link of stratigraphy between modern cool water carbonate shelf deposits and the older mesozoic and paleozoic record of similar sediments

the western edge of the mediterranean pelagian platform a messinian mixed siliciclastic carbonate ramp in northern tunisia the marine messinian deposits of tunisia cover a narrow littoral strip some 300 km long between the northern bizerte and cap bon areas and the central eastern sahel region litho and biofacies analysis of six stratigraphic sections reveals the distinctive features of these deposits the lower messinian deposits are characterized by ubiquitous siliciclastics and abundant oolitic bioclastic limestones organized in an eastward facing ramp westward landward this ramp changes into coastal lagoons sometimes containing evaporites eastward the ramp passes to the reefal pelagian platform extending as far as lampedusa two main sedimentary cycles are distinguished 1 an early messinian siliciclastic retrogradational then oolitic bioclastic progradational cycle beni khiar formation and lower oued bel khedim formation 2 a late messinian brackish to continental cycle that probably accumulated in rapidly subsiding lagoons cued el bir formation and upper oued bel khedim formation the tunisian early messinian cycle is partly eustatically controlled but the late messinian cycle cannot be confidently correlated to other well known messinian series because of tectonic movements the lower messinian deposits of tunisia are also characterized by abundant suspension feeding organisms molluscs and bryozoans and rare corals calcareous algae echinoids and larger benthic foraminifers the proposed palaeoenvironmental model shows that the lower messinian ramp of tunisia was located on a current protected margin and subjected to continent derived sediment and nutrient supply eastward nutrient influx diminished and a shallow water isolated carbonate platform with coralgal facies developed between the western and the eastern mediterranean basins the main hydrological connection between these two basins occurred through a narrow seaway situated to the northeast of the pelagian platform south of sicily and malta

530 ma zircon age for ophiolite from the new england orogen oldest rocks known from eastern australia new ion microprobe data provide constraints on the timing of formation of ophiolitic rocks in the new england tectonic collage in eastern australia results for analyses of magmatic zircons from plagiogranite of the weraerai terrane ophiolite at upper bingara give a 206 pb 238 u age of 530 6 ma 2 this plagiogranite is the oldest rock from eastern australia yet identified existing tectonic models suggest that progressively younger crust was accreted to the eastern margin of gondwanan australia throughout the paleozoic this cannot be reconciled easily with the cambrian age for these ophiolitic rocks which are juxtaposed between devonian terranes and are at least 1000 km east of the nearest lithologically similar rocks of comparable age we speculate that younger thin skinned terranes may have been thrust westward over the continental freeboard of eastern australia during the late paleozoic

sedimentation and volcanism in a permian arc related basin southern new zealand an exceptionally well exposed ancient intra arc basin in the permian takitimu group of new zealand contains 14 km of interbedded primary volcanic and marine volcaniclastic rocks of basaltic to rhyodacitic composition these are the products of subaerial and submarine arc volcanism and closely associated turbidite sedimentation the takitimu oceanic arc basin setting formed a dynamic closed sedimentary system in which large volumes of volcaniclastic material generated at the arc was rapidly redeposited in marine basins flanking the eruptive centres volcanism probably included 1 moderate to deep water extrusion of lava and deposition of hyaloclastite 2 extrusive and explosive eruptions from shallow marine to marginally emergent volcanoes in or on the margin of the basin and 3 plinian and phreato plinian eruptions from more distant subaerial vents along the arc much of the newly erupted material was rapidly transported to the adjacent marine basin by debris flows slumping and sliding hemipelagic sedimentation predominated on the outer margin of the basin infrequently interrupted by deposition of ash from the most explosive arc volcanism and the arrival of extremely dilute turbidites turbidite sedimentation prevailed in the remainder of the basin producing a thick prograding volcaniclastic apron adjacent to the arc the volcaniclastic strata closely resemble classic turbidite deposits and show similar lateral facies variations to submarine fan deposits study of such sequences provides insight into poorly understood processes in modern arc related basins

middle ordovician high pt metamorphic rocks in eastern australia evidence from k ar ages phengite separated from a metagabbro three blueschist and one metabasite that occur as blocks in serpentinite melange in the new england fold belt eastern australia has yielded k ar ages of 465 480 ma significantly older than the age of most components of the belt the schists and metabasite contain either glaucophane and or crossite intergrown with the phengite providing the first conclusive evidence for early paleozoic subduction accretion associated with the east gondwana margin the tectonic affinity of the blocks is uncertain they and other small early paleozoic convergent margin elements in the new england fold belt may be allochthonous remnants of an arc system accreted in the devonian or carboniferous or they may be related to early paleozoic convergent margin components found farther inboard in the paleozoic fold belts of eastern australia

palaeoenvironmental changes across the danian selandian boundary in the north sea basin abstract the danian selandian boundary 60 ma marks the cessation of 40 million years of carbonate deposition in the north sea basin and a shift to siliciclastic deposition on the basis of variations in lithology benthic and planktonic foraminifera and calcareous nannofossils in three cores from storebaelt in the eastern part of the north sea basin we have reconstructed the palaeoenvironmental changes across the boundary the benthic foraminiferal faunas belong to the midway type fauna they are extremely rich and more than 260 taxa have been recognized q mode cluster analysis groups the benthic assemblages into four biofacies which correspond fairly closely to lithological units correlation of the storebaelt records with marine palaeorecords from the danish basin and the north sea basin indicate that the transformation of the north sea from a carbonate to a siliciclastic basin occurred in four steps separated by relatively long stable periods the most important external factors involved in the change are firstly a drop in the relative sea level during the late danian leading to the disappearance of bryozoans from the north sea basin and to non deposition and erosion in many areas secondly coinciding with the danian selandian boundary an uplift of the scotland shetland area resulting in a massive input of siliciclastic deposits to the north sea basin thirdly during the early selandian inversion of the sorgenfrei tornquist zone and mesozoic basins in the southern and eastern part of the north sea basin resulted in a huge influx of reworked cretaceous chalk and an almost complete stop of carbonate production finally later in the early selandian in connection to a general sea level rise and a reduction in the gateway between the north sea basin and the tethys sea the sea bottom conditions became colder and more acidic this resulted in partial dissolution of the carbonates and the deposition shifted from marl to clay comparison with records from the western pyrenees the nile basin and the eastern north america suggests that sea level changes across the danian selandian boundary are primarily of eustatic nature

chemical transects across intra oceanic arcs implications for the tectonic setting of ophiolites systematic spatial variations in ti y and zr are found in volcanic sequences sampled as transects from back arc through arc to trench within the western pacific intra oceanic arc systems these correlations occur regardless of eruption age reflecting the retention of relative positions between individual tectonic units concentrations of these incompatible elements are taken to reflect the nature of the underlying mantle at a particular trench volcano distance during the subduction process volcanics become more depleted trenchwards implying that progressively shallower levels melts were extracted from more refractory or harzburgitic mantle a model is proposed whereby a subduction system is superimposed on a compositionally stratified mantle which is a product of an earlier spreading event on the basis of this evidence the trench distance variation model is applied to the troodos ophiolite complex similar spatial changes in lava chemistry are found across the ophiolite providing evidence for the relative position of the troodos trench and direction of subduction beneath the troodos basin these findings have implications for studies in other orogenic terrains where structure and exposure permit their application

the border ranges ultramafic and mafic complex south central alaska cumulate fractionates of island arc volcanics a discontinuous elongate zone of mafic and ultramafic plutonic rock crops out in south central alaska for a distance of more than 1000 km intermediate and detailed scale geologic mapping petrographic study and compositional data suggest that the plutonic rocks are compositionally petrologically and mineralogically distinct from rocks in mid ocean ridge and back arc basin ophiolites the mafic and ultramafic rocks instead represent part of the plutonic core of an intraoceanic island arc the mafic ultramafic zone referred to as the border ranges ultramafic and mafic complex brumc is composed of ultramafic cumulates gabbronorite cumulates and massive gabbronorites a very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part of the brumc a thick sequence of andesitic volcanic rocks the talkeetna formation of early jurassic age lies to the north of and structurally above the mafic ultramafic zone voluminous calcalkaline plutons composed of quartz diorite

hornblende gabbro block in serpentinite melange peel manning fault system new south wales australia lu hf and u pb isotopic evidence for mantle derived late ordovician igneous activity abstract in the southern new england fold belt the peel manning fault system pmfs is a major structural element characterized by tectonic blocks in a serpentinite melange we document a large 1 km intensely deformed block of noncumulate and cumulate hornblende gabbro from the pmfs cumulate layering is preserved in some outcrops and relicts of magmatic plagioclase magnesio hornblende and minor clinopyroxene are recognizable microscopically despite the gabbro having undergone amphibolite facies and subsequently prehnite pumpellyite facies metamorphism the composition of the magmatic clinopyroxenes and amphiboles indicates low pressure crystallization suggesting formation in a shallow crustal reservoir zr tio2 ratios chondrite normalized rare earth elements documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath a

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

provenance determination of volcaniclastic rocks the nature and tectonic significance of a cambrian conglomerate from the new england fold belt eastern australia abstract the murrawong creek and pipeclay creek formations of the new england fold belt of eastern australia provide one of the few records of middle cambrian early ordovician sedimentation along the eastern gondwana margin they comprise conglomerate sandstone siltstone and laminated argillite that accumulated in an inner submarine fan environment sandstones are quartz poor volcanolithic varieties conglomerate clasts are mainly andesite but range from basalt to rhyolite all these rocks are porphyritic with phenocrysts of feldspar albite after calcic plagioclase augite and uncommonly titanomagnetite the augite is a low tio2 variety and titanomagnetite has only a modest tio2 content alteration has modified the magmatic composition of the clasts but the ess mobile elements indicate they were derived from a low k orogenic suite in consonance with petrographic and mineralogical data a western source and the presence of lower paleozoic subduction complex rocks to the east of the cambrian ordovician units indicates that the latter accumulated in a forearc setting the distributive province may have been the precursor of the macquarie volcanic belt of the eastern lachlan fold belt in n s w or one of the cambrian oceanic island arcs preserved in the fragmented gondwana margin sequences in southeastern australia northern victoria land antarctica and new zealand

age difference between polar ice and the air trapped in its bubbles air entrapped in bubbles formed in cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation the analysis of dated ice samples therefore enables the history of atmospheric composition to be investigated 1 3 the age of the entrapped air is however not the same as that of the surrounding ice because air bubbles only become isolated from the atmosphere during the transition from firn to ice typically the age of the ice at this transition is between 100 and 3 000 yr depending mainly on firn temperature and snow accumulation rate the mean age difference between ice and enclosed air as well as the age distribution width for a given sample are especially important for the investigation of the anthropogenic increase of co2 and trace gases in the atmosphere over the last centuries and for the comparison of climatic parameters recorded in the ice with parameters recorded in the bubbles for siple station antarctica this age difference and age distribution width were deduced from the bubble volume measured as a function of depth the values are 95 yr and 22 yr respectively

modern carbonate and terrigenous clastic sediments on a cool water high energy mid latitude shelf lacepede southern australia the wide lacepede shelf and narrow bonney shelf are contiguous parts of the south eastern passive continental margin of australia the shelves are open generally deeper than 40 m covered by waters cooler than 18 c and swept by oceanic swells that move sediments to depths of 140 m the lacepede shelf is proximal to the delta of the river murray and the coorong lagoon shelf and upper slope sediments are a variable mixture of holocene and late pleistocene quartzose terrigenous clastic and bryozoa dominated carbonate particles bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m they can be grouped into four depth related assemblages coralline algae the only calcareous phototrophs are important sediment producers to depths of 70 m active benthic carbonate sediment production occurs to depths of 350 m but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions the shelf is separated into five zones the strandline is typified by accretionary sequences of steep shoreface beach and dune carbonate siliciclastic sediments similar shoreline facies of relict bivalve limestone cobble ridges are stranded on the open shelf the shallow shelf c 40 70 m deep is a wide extremely flat plain with only subtle local relief it is a mosaic of grainy quartzose palimpsest facies which reflect the complex interaction of modern bioclastic sediment production dominated by bryozoa and molluscs numerous highstands of sea level over the last 80 000 years modern mixing of sediments from relatively recent highstands and local introduction of quartz rich sediments during lowstands the middle shelf c 70 140 m deep is a gentle incline with subtle relief where holocene carbonates veneer seaward dipping bedrock clinoforms and local lowstand beach complexes carbonates are mostly modern uniform clean coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes the deep shelf edge c 140 250 m deep is a site of diverse and active bryozoa growth resulting accumulations are characteristically muddy and distinguished by large numbers of delicate branching bryozoa the upper slope between 250 and 350 m depth contains the deepest platform related sediments which are very muddy and contain a low diversity suite of delicate branching cyclostome bryozoa this study provides fundamental environmental information critical for the interpretation of cenozoic cool water carbonates and the region is a good model for older mixed carbonate terrigenous clastic successions which were deposited on unrimmed shelves

crustal evolution of island arc ultramafic magma galmoenan pyroxenite dunite plutonic complex koryak highland far east russia alaskan type platinum bearing plutons and potassium enriched mafic to ultramafic volcanic rocks are temporally and spatially associated within the late cretaceous paleocene achalvayam valaginskii intra oceanic palaeo arc system allochthonousy present in the kogak highland and kamchatka peninsula far east russia the compositions of the parental magmas to the alaskan type complexes are estimated using the galmoenan platonic complex as an example this complex composed of dunites pyroxenites and minor gabbros is the largest 20 km3 in the system and the best studied owing to associated platinum placer deposits the compositions of the principal mineral phases in the galmoenan intrusive rocks olivine fo 79 92 clinopyroxene 1 3 5 wt al2o3 0 1 0 5 wt tio2 and cr spinel 5 15 wt al2o3 and 0 3 0 7 wt tio2 are typical of liquidus assemblages in primitive island arc magmas in intra oceanic settings and closely resemble the mineral compositions in the achaivayam valaginskii ultramafic volcanic rocks the temporal and spatial association of intrusive and extrusive units and the similarity of their mineral compositions suggest that both suites were formed from similar parental magmas ne composition of the parental magma for the galmoenan platonic rocks is estimated using previously reported data for the achaivayam valaginskii ultramafic volcanic rocks and phenocryst hosted melt inclusions quantitative simulation of crystallization of the parental magma in the galmoenan magma chamber shows that the compositions of the cumulate units are best modelled by fractional cryallization with periodic magma replenishment the model calculations reproduce well the observed mineral assemblages and the trace element abundances in clinopyroxene based upon the estimated composition of the parental magmas and their mantle source we consider that fluxing of a highly refractory mantle wedge similar to the source of boninites by chlorine rich aqueous fluids is primarily responsible for both high degrees of partial melting and the geochemical characteristics of the magmas including their enrichment in platinum group elements

trends in the development of paleozoic radiolaria abstract radiolaria may be the only planktonic or nektonic faunal group which has clear biostratigraphic potential and which is known from deposits of all phanerozoic systems in fact until recently it was assumed that they were even typical components of the precambrian biosphere an understanding of the kinds of evolutionary trends exhibited by paleozoic forms can provide a useful background against which subsequent radiolarian evolution can be better understood realizing that it is impossible to prepare an exhaustive survey we have tried to emphasize developmental trends which affect more than one paleozoic group so as to identify tendencies which may have more general significance it is suggested that such general tendencies include 1 recurrent trends toward lightening of the shell mass accompanied by increased complexity of shell construction 2 transformation of the structure of the internal framework which markedly affects the form of the external shell 3 the development of multiple internal shells through tangential rather than radial growth and 4 the occurrence of rapid radiations following the appearance of new shell forms e g albaillellaria stauraxon polycystines which are presumed to confer some selective advantage

the flaw in the crustal zircon archive mixed hf isotope signatures record progressive contamination of late stage liquid in mafic ultramafic layered intrusions

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

the fate of subducted oceanic slabs in the shallow mantle insights from boron isotopes and light element composition of metasomatized blueschists from the mariana forearc abstract serpentine muds from south chamorro seamount scs drilled during odp leg 195 at site 1200 contain metamafic clasts that experienced blueschist facies metamorphism including the critical mineral assemblage pumpellyite na amphibole epidote these schists represent fragments from the actual slab mantle interface at 27 km depth their heterogeneous lithology with a metasomatic character indicates significant mobility of major elements in the mariana forearc a region of melange formation as it can also be observed in onland exposures such as the catalina schist as the mariana forearc blueschists show no late stage alteration they permit the direct study of material transfer during the subduction processes at an active convergent margin this study presents the first data of detailed b isotope 11 b and light element variations in blueschist facies minerals from the mariana arc system the primary foci are b and li concentrations and 11 b values analyzed by sims and tof sims techniques minerals such as na rich amphibole phengite and chlorite are found to be strongly enriched in li up to 70 g g be up to 8 g g and b up to 35 g g and with 11 b values of 6 4 these new data are consistent with isotopically heavy b being released into the mariana forearc mantle wedge serpentinization of dry mantle peridotite after interaction with b rich slab released high ph fluids and confirm models of significant b loss and b isotope fractionation during forearc shallow slab dehydration the elevated li be and b concentrations in minerals that comprise the bulk of the rocks namely amphibole phengite and chlorite bear a strong potential to further transport li and b as well as the isotopically light component of b to greater depths in the mantle where ongoing metamorphism is responsible for further isotope and elemental fractionation and the formation of distinct mantle reservoirs e g volcanic arc and oceanic intra plate oib magmas

origin and emplacement of tertiary ultramafic complexes in northwest colombia evidence from geochemistry and kar smnd and rbsr isotopes abstract si undersaturated high mg basalts with early fractionated ultramafic cumulates viravira complex and a zoned ultramafic alaskan type intrusion condoto complex are located in the upper condoto river within the western cordillera of colombia these complexes are related in space and time and originated from a common parental magma the isotopic characteristics of the complexes are similar and plot close together near the mantle array in the nd vs sr diagram it is argued that the compositions of the viravira basalts and of geochemically comparable hornblende plagioclase dykes in the zoned complex are close to the parental melt from which both complexes derived this melt probably had a mafic tholeiitic composition and was supplied from two sources high grade partial melting 20 of moderately depleted mantle above a subduction zone major part and modification by a metasomatic lile and slightly lree enriched fluid which could have originated by dewatering of the subducting slab k ar dates of hornblende of the condoto complex indicate an emplacement age of about 20 ma this represents the youngest age on the earth of a zoned ultramafic intrusion textural features demonstrate that the zonal arrangement with a dunitic core was the result of a series of crystal mush intrusions of deeper seated unconsolidated cumulate fractionations the occurrence of these and further ultramafic complexes along a major n s strike slip fault substantiates an exceptional tectonic activity on the northwestern edge of the south american continent during the tertiary horizontal plate movements along the deeply penetrating fault system favoured a release of pressure and the formation of si undersaturated mg rich melts in the mantle high heat flow and the possibility of vertical migration allowed the intrusion of mantle derived melts into shallow levels of the upper crust in the condoto region these conditions were particularly provided by the intersection of the n s fault system with wnw ese trending transverse and oblique faults

granite gabbro and mafic microgranular enclaves in the gejiu area yunnan province china a case of two stage mixing of crust and mantle derived magmas geochronological geochemical whole rock sr nd and zircon hf isotopic analyses were carried out on the jiasha gabbro mafic microgranular enclaves mme and host longchahe granite samples from the gejiu area in the southeast yunnan province sw china with the aim of characterizing their petrogenesis compositional zoning is evident in the gabbro body as the cumulate textures and mineral proportions in the gabbro interior are distinct from the gabbro margin the longchahe granite largely comprises metaluminous quartz monzonite with distinctive k feldspar megacrysts but also contains a minor component of peraluminous leucogranite the mme have spheroidal to elongated lenticular shapes with sharp crenulated and occasionally diffuse contacts with the host granite which we attribute to the undercooling and disaggregation of mafic magma globules within the cooler host felsic magma field observations geochronology geochemistry sr nd and zircon hf isotopic compositions point to a complex petrogenesis for this granite mme gabbro association zircon 206pb 238u ages determined by la icp ms for a mafic enclave its host granite and the gabbro body are 83 1 0 9 ma 83 1 0 4 ma and 83 2 0 4 ma respectively indicating coeval crystallization of these igneous rock units crystal fractionation processes can explain much of the compositional diversity of the jiasha gabbro the geochemical features of the gabbro such as high mg up to 70 and cr up to 327 ppm enrichment in liles e g rb ba k2o and lrees and depletion in hfse e g nb ta ti together with initial 87sr 86sr ratios of 0 708 0 709 and negative end t values 5 23 to 6 45 indicate they were derived from a mantle source that had undergone previous enrichment possibly by subduction components the longchahe granite has a large range of sio2 59 87 74 94 wt is distinctly alkaline in composition and has sr nd hf isotopic compositions 87sr 86sr i 0 712 end t 6 93 to 7 62 and ehf t 5 8 to 9 9 that are indicative of derivation from a crustal source however the most primitive rocks of longchahe granite are compositionally distinct from any feasible crustal melt we interpret the spectrum of rock types of the longchahe granite to have formed via mixing between crustally derived peraluminous leucogranite magma and mantle derived magma of similar heritage to the jiasha gabbro we speculate that this mixing event occurred early in the magmatic history of these rocks at relatively high temperature and or deep in the crust to allow efficient physical mixing of magmas saturation and accumulation of k feldspar and zircon in the mixed magma is invoked to explain the megacrystic k feldspar and elevated k2o and zr content of some of the granitic rocks a later episode of magma mixing mingling is preserved as the mme that have geochemical and isotopic compositions that for the most part are intermediate between the granite and the gabbro the mme are interpreted to be fractionated melts of mafic magma related to gabbro that were subsequently injected into the cooler partly crystalline granitic magma mingling and mixing processes within the convectively dynamic upper crustal magma chamber resulting in a hybrid mme magma during this second mixing episode element interdiffusion rather than bulk physical mixing is interpreted to be the dominant mixing process

devonian intra oceanic arc rift sedimentation facies development in the gamilaroi terrane new england orogen eastern australia abstract silurian devonian rocks within the gamilaroi terrane part of the new england orogen of eastern australia provide a well preserved on land example of the development of an intra oceanic arc rift ten sedimentary facies represent different phases in the evolution of the gamilaroi rift and are typified by predominantly volcaniclastic conglomerates and mudstones with minor sandstones all of which were deposited by debris flows and turbidity currents subordinate facies include limestones crystal rich volcaniclastic sandstones volcanic breccias and olistostromes the facies are distributed throughout a succession of six lithostratigraphic units each of which represents a distinct phase in the history of the arc rift felsic volcanic and volcaniclastic rocks at the base of the section represent part of the original arc and are overlain by volcaniclastic sandstones and mudstones deposited within an arc basin lower devonian emsian limestones underwent rapid subsidence concurrent with an influx of volcaniclastic sediments indicating initiation of rift related faulting a thick conglomerate succession was deposited rapidly on a debris apron system adjacent to the steep sided rift walls overlying tuffaceous mudstones indicate a decrease in clastic input later in the history of the rift basin thick intervals of massive and pillowed basalts at the top of the succession indicate a major period of volcanism within the rift oceanic island arc rift sequences are characterised by highly variable sedimentary facies distribution facies distribution over the 400 km extent of the gamilaroi terrane is also highly variable modern arc rift zones are divided into a series of smaller separate elongate basins providing an explanation for the high facies variability observed in the field

volcanism in nascent back arc basins behind the shichito ridge and adjacent areas in the izu ogasawara arc northwest pacific evidence for mixing between e type morb and island arc magmas at the initiation of back arc rifting mineral chemistry major and trace elements and 87sr 86sr ratios are presented for 29 igneous rocks dredged from the northern portion of the izu ogasawara arc these rocks are compositionally bimodal basement gabbro and trondhjemite from the arc are extremely poor in k2o 0 05 0 19 and rb 0 48 0 62 ppm and their ree patterns and sr isotope ratios indicate that there are island arc tholeiites quaternary volcanic rocks from the present volcanic front shichito ridge active arc back arc seamounts east side inactive arc and torishima knoll between the two back arc depressions incipient back arc basins behind the active arc have the same geochemical characteristics as the above plutonic rocks though they are not as depleted in k and rb rhyolite pumice from the backarc depression is also the depleted island arc tholeiite whereas basalts from the depression have compositions that are transitional between morb and island arc tholeiites in trace element ti ni cr v y and zr and mineral chemistries the back arc depression basalts have relatively high ban cen 0 66 1 24 cen ybn 1 1 1 9 and k ba 45 105 and low 87sr 86sr 0 70302 0 70332 and ba sr 0 1 0 2 which are similar to other back arc basin basalts and e type morb but are quite unlike the depleted island arc tholeiites the diverse trace element and sr isotope compositions of basalt andesite from the back arc depressions imply the interplay between e type morb and island arc tholeiite these chemical characteristics and the relationships of ce yb n vs ba ce n and ce yb n vs 87sr 86sr suggest that the back arc depression magmas are generated by mixing of e type morb and depleted island arc tholeiite magmas geochemical characters of the associated rhyolite from the depression are compatible with partial melting of lower crust

the west pacific geodynamic model abstract between the asian and australian continents on the western side and the general subduction of the central pacific on the eastern side the west pacific presents two types of subduction towards the continents and towards the ocean as a consequence at the present day there are two main types of marginal seas the japan sea and the south china sea and in the geological past two types of orogenesis the japanese and the taiwanese types these are the models of the two main orogenic belts respectively the circum pacific and tethyan for a long period of the past the alps and the mediterranean sea were the tectonic model of reference however with the increase in geological studies oceanographic research geophysical surveying the west pacific gradually became an alternative model which grew more useful with each passing day the present day trench island arc marginal sea system appears to be a good model for the first stages of orogenic belts whereas the mountains of the east eurasian margins provide an example of the completion of formation of such belts the coexistence of different stages of mountain building is the main reason for the increasing interest shown by earth scientists in the west pacific

heishan mafic ultramafic rocks in the qimantag area of eastern kunlun nw china remnants of an early paleozoic incipient island arc abstract the heishan mafic ultramafic complex in the qimantag mountains of the eastern kunlun orogen consists of olivine pyroxenites pyroxenites gabbros and massive basalts zircons from the gabbros have magmatic sector zoning with th u ratios of 0 5 2 3 and yield a shrimp age of 486 6 ma mswd 0 31 which is taken as the time of magma crystallization spinel pyroxene and plagioclase mineral compositions indicate that the rocks formed in an island arc environment the cumulates have low la yb n ratios 0 6 0 8 and depleted lree patterns high abundances of cr 3031 1185 ppm co 119 50 ppm and ni 953 291 ppm and end t values of about 8 0 the massive basalts have somewhat higher contents of tio2 1 0 1 3 na2o 2 6 2 8 total ree and mg s 55 63 than those of the cumulates the la yb n ratios of the basalts range from 0 8 to 1 2 and the chondrite normalized ree patterns are flat end t values of the basalts range from 7 7 to 9 4 the compositions of the cumulates and volcanic rocks especially their similar nd isotopes suggest that the rocks were derived from similar depleted mantle sources the primary magmas were probably generated in an initial arc environment we conclude that the heishan mafic ultramafic complex in the qimantag area preserves a record of proto tethyan oceanic lithosphere formed in the early paleozoic it possibly marks a suture between the qaidam and north kunlun terranes in the western segment of the eastern kunlun orogen

sandstone compositions from the new england orogen eastern australia implications for tectonic setting abstract sandstones from the new england orogen are mainly quartz poor lithic to feldspathic types derived from a volcanic arc terrane the variation in detritus from lower devonian to permian in the tamworth belt records a change in the nature of volcanism the detritus becomes more felsic upwards from andesitic in the devonian to dacitic and rhyolitic in the upper carboniferous and lower permian detrital quartz content is always quartz poor but increases upwards from 1 to about 15 detrital pyroxene is common low in the sequence but in younger rocks hornblende is more common documentation of vertical changes in sandstone composition within the tamworth belt allows correlation with the virtually unfossiliferous sandstones in the tablelands complex to the east of the tamworth belt t e woolomin association is correlated with the early to middle devonian portion of the tamworth belt the sandon association with the late devonian portion and the coifs harbour association with the late carboniferous to early permian portion most sandstones from the new england orogen were thus derived from an undissected volcanic arc provenance which evolved from mafic to more felsic in composition through time the volcanic source existed for a period of more than 100 million years comparison with detrital sandstone compositions from known ancient and modern tectonic settings suggests that the sandstones were possibly deposited in a backarc basin but this has not been established unequivocally and a forearc setting is not precluded

andean analogue for late carboniferous volcanic arc and arc flank environments of the western new england orogen new south wales australia abstract late carboniferous continental conglomerates interbedded with silicic ignimbrite sheets outcrop along more than 400 km of the western margin of the southern portion of the new england orogen farther east the coeval sedimentary facies are volcanogenic shallow marine and turbidite deposits the volcanic source terrain no longer exposed was located to the west of the existing conglomerate ignimbrite sequences and was underlain by continental crust which is in part represented by the northern lachlan fold belt the regional late carboniferous palaeogeography was similar to that of the present day western continental margin of south america the geology of the oceanward flank of the andean arc in northern chile and a section of the late carboniferous continental sequence near currabubula are comparable in detail the andean stratovolcanoes and ignimbrite centres thus provide the means of reconstruction of the late carboniferous volcanic source terrain the geological record of both of these continental margin volcanic arcs preserved in deposits of the arc flanks is shaped by volcanism especially the eruption of voluminous ignimbrites and by uplift deformation and glaciation centered on the arc for the arc sections considered diversity in the flank sequences arises because these controls vary in importance spatially and during the life of the arc 20 30 ma for the entire andean arc arc parallel variations in the sites of active volcanism and its character appear to be related to differences in the continental crust thickness and the circumstances of subduction of oceanic crust particularly the dip of the benioff zone by analogy variation in the age duration and style of volcanic activity along the late palaeozoic magmatic arc of the western new england orogen perhaps reflects the former existence of significant differences in crust thickness and in the angle of subduction

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

crustal recycling processes in generating the early cretaceous fangcheng basalts north china craton new constraints from mineral chemistry oxygen isotopes of olivine and whole rock geochemistry the early cretaceous fangcheng basalts were erupted in the peak stage of lithospheric thinning of the north china craton ncc they have olivine phenocrysts with forsterite fo contents ranging from 74 to 92 clinopyroxene with high mg from 76 to 89 and contain pyroxenite xenoliths both the basalts and pyroxenite xenoliths have coexisting high ca and low al clinopyroxene and high mg and low ca olivine indicating that the parental magmas of the basalts have high water contents comparable with arc basalts they also show similar mineral chemistry and olivine o isotopic compositions 18o 5 5 7 2 trace element patterns with large ion lithophile elements liles and light rare earth elements lrees enrichments and high field strength elements hfses depletions as well as enriched sr nd hf isotopic features therefore the pyroxenite xenoliths are cognate with the basalts high 18o values average 6 5 of fresh olivine crystals from the basalts and xenoliths indicate the involvement of 18o rich crustal materials in the mantle source incorporation of 18o rich crustal materials to the mantle source is consistent with the highly evolved sr nd hf isotopic signatures of the basalts and the pyroxenite xenoliths modeling results based on the sr nd o isotopic compositions of the basalts indicate that both upper and lower crustal materials of the yangtze block may have been incorporated into the mantle source therefore the 18o rich crustal materials were likely derived from the subducted yangtze block in triassic time however neither the ncc subcontinental lithospheric mantle nor the deeply subducted yangtze crustal materials can provide sufficient water to produce hydrous basaltic magmas instead exotic fluids may have been derived from the subducted paleo pacific slab dehydration of the subducted paleo pacific slab may have released enough fluids to trigger extensive hydrous melting of the enriched mantle source beneath the fangcheng and its surrounding regions

palaeoenvironmental changes at the tortonian messinian boundary a deep sea sedimentary record of the eastern mediterranean sea abstract in the eastern mediterranean the island of crete offers excellent exposures of upper miocene marine deposits three detailed sections of the tortonian messinian sedimentary succession were measured and sampled in three different basins from west to east chania heraklion and sitia the biostratigraphic analysis based on planktonic foraminifera yielded ages ranging from about 7 58 to 6 72 ma nine bioevents were also recognised and provided good correlations between the studied sections rich benthic faunas commonly occurring together with fish otoliths have furthermore been recovered and analysed foraminifera mollusc mostly bivalves bryozoans and ostracods the autochthonous assemblages suggest deposition at middle upper bathyal depths at the base and outer inner shelf in the upper parts of the sections the shallowing upward trend observed in all three sections is accompanied by the occurrence in a few messinian levels of allochthonous fossils transported downslope and deposited in deep water environments dysoxic episodes were moreover recorded in some beds mostly in the messinian a comparison with other coeval basins and faunas indicates that similar palaeoenvironmental conditions predominated throughout the mediterranean sea during the late miocene this is consistent with the postulate of open connections through marine corridors between the mediterranean and the atlantic presumably until late in the messinian

provenance of the lower cretaceous hayang group gyeongsang basin southeastern korea implications for continental arc volcanism abstract provenance of the lower cretaceous hayang group in the gyeongsang basin korea was investigated using sandstone petrography and the composition of detrital plagioclase and clinopyroxene grains in sandstone and mudrock a magmatic arc tectonic setting is inferred for the source on the basis of sandstone composition detritus derived from granitic gneissic rock and incipient continental arc volcanic rock were mixed in a variable ratio in the hayang sedimentary rocks before deposition of the hayang group the source rock was composed mainly of granitic gneissic rocks this condition persisted in the north the euiseong subbasin during deposition of the lower part of the hayang group in the milyang subbasin the southern part of the gyeongsang basin source area volcanism occurred just before deposition of the hayang group compositions of detrital pyroxene and plagioclase revealed the source volcanic rock to be calc alkaline volcanic arc basaltic andesite to dacite later granitic gneissic rocks as well as volcanic rocks supplied detritus to both subbasins and the source volcanic rocks inferred from plagioclase composition might have been of silicic composition the hayang group was deposited in a transitional setting changing from strike slip movement with little volcanic activity to active subduction related volcanism in the eastern continental margin of asia during this transitional stage the source area was occupied by granitic gneissic rocks and within the source area intermediate to silicic volcanic rocks of dominantly calc alkaline affinity erupted sporadically

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

alteration of oceanic crust and geologic cycling of chlorine and water we report new estimates of transport rates for h2o and cl between the mantle and surface reservoirs our estimates take into consideration alteration of oceanic crust especially that of plutonic rocks and possible subduction of sediments the effect of hydrothermal alteration on the cl budget seems to be negligible but the effect on the h2o budget is significant altered oceanic crust excluding sediments contains about 10 times as much h2o as the unaltered crust and its subduction may result in a net transport of h2o to the upper mantle in subduction zones however the rate of expulsion of h2o from the mantle by subduction zone magmatism is comparable to the amount released by ridge magmatism and is only about 10 of the amount subducted therefore about 90 of the subducted h2o must be returned to the mantle or returned to the crust by other processes in addition subduction of oceanic sediments to mantle depths will result in 1 1 a further increase in the return rate of h2o to the mantle reservoir 2 2 possible net transfer of cl to the mantle depending on the rate of pore water expulsion

petrology and geochemistry of cambrian boninites and low ti andesites from heathcote victoria in the heathcote greenstone belt of central victoria a sequence of boninites and low ti andesites is overlain and intruded by tholeiitic basalts with affinities to backarc basin basalts two suites of boninites have been identified one type a with ti zr ratios of 63 4 la yb n of 2 3 and hree 5 times chondritic levels the other suite type b overlies type a boninites and has ti zr ratios of 23 3 and lower tio2 and hree contents 2 3 chondrite but shows significantly greater lree enrichment with la yb n greater than 5 fractionation within both suites was largely controlled by the low ca pyroxenes protoenstatite and enstatite plagioclase phyric low ti high mg andesites occur in fault contact with the boninites and have ti zr and la yb n ratios very close to those of type b boninites but at higher absolute abundances of tio2 and hree they are not related to either boninite suite by any realistic fractionation scheme but originated from the same source as type b boninites by approximately half the degree of partial melting that generated the boninites

a high precision method for measurement of paleoatmospheric co2 in small polar ice samples we describe a high precision method now in use in our laboratory for measuring the co 2 mixing ratio of ancient air trapped in polar ice cores occluded air in ice samples weighing 8 15 g is liberated by crushing with steel pins at 35 c and trapped at 263 c in a cryogenic cold trap co 2 in the extracted air is analyzed using gas chromatography replicate measurements for several samples of high quality ice from the siple dome and taylor dome antarctic ice cores have pooled standard deviations of 0 9 ppm this high precision technique is directly applicable to high temporal resolution studies for detection of small co 2 variations for example co 2 variations of a few parts per million on millennial to decadal scales

significance of devonian carboniferous radiolarians from accretionary terranes of the new england orogen eastern australia abstract radiolarians provide age constraints for many previously undated terranes in the new england orogen neo a tectonic collage developed along the eastern margin of australia djungati terrane the age range of which was previously unknown contains two distinctive siliceous sedimentary lithofacies the oldest is a thick sequence of red ribbon bedded cherts which probably accumulated in a deep ocean floor setting far from land middle silurian through late devonian radiolarians have been recovered from these cherts green tuffaceous cherts which contain a latest devonian famennian radiolarian fauna depositionally overlie the lower red ribbon bedded chert sequence these cherts are intercalated with volcaniclastic sediments and the fauna which they contain can be used to constrain the timing of accretion of older rocks into a subduction complex anaiwan terrane which was also previously undated contains thin ribbon bedded cherts which are depositionally overlain by tuffaceous chert siliceous siltstones and volcaniclastic sediments latest devonian late famennian and early carboniferous radiolarians have been recovered from these cherts and tuffaceous siltstones radiolarians also occur in fine grained siliceous sediments of the yarrimie formation part of the gamilaroi terrane these radiolarians are of late devonian frasnian affinity and their presence indicates that blocks of limestone which contain givetian conodonts and corals and were previously thought to indicate the age of the yarrimie formation are allochthonous

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

evolution of a miocene carbonate shelf northern apennines italy revealed through a quantitative compositional study abstract the evolution of the miocene san marino carbonate shelf torriana outcrop developed on the accretionary prism of the northern apennines has been interpreted through a stratigraphic and compositional study modal analysis allowed to quantify the framework components and to identify four microfacies through which the main steps of the carbonate ecosystem were traced the healthy phase of the carbonate shelf dominated by bryozoans and echinoids originated in a high energy transgressive setting and evolved during a warm period characterized by a progressive increase of nutrients the transitional stage is marked by a reduction of carbonate productivity and by terrigenous intermittent pulses associated with bioclast fragmentation the drowning succession corresponds to deepening upward facies formed by fine grained hybrid arenites to sandy marls with abundant planktonic foraminifera glauconitic grains and clay matrix the demise of the carbonate shelf might have resulted from a combination of regional and global factors that interplayed controlling the detrital input the nutrient budget and the deepening of the basin synsedimentary tectonics triggered subsidence of the basin and enhanced terrigenous discharge moreover the superposition of paleoclimatic and paleoceanographic events monterey and middle miocene climate optimum could have contributed with the intense weathering and remarkable detrital and nutrients supply

tectonic setting and paleoenvironment of terranes in the southern new england orogen eastern australia as constrained by radiolarian biostratigraphy abstract radiolarians are abundant in the gamilaroi djungati and anaiwan terranes of the new england orogen in eastern australia these microfossils present the first age constraints on the timing of development of hitherto undated lithologies within the various juxtaposed terranes of the orogen they give a biostratigraphic framework for interpreting the history of marine sedimentation in these terranes and have significant implications for published tectonic models radiolarians also show that the stratigraphically lowermost rocks of the gamilaroi terrane are most probably of devonian age better stratigraphic resolution permits interpretation of these rocks as part of an intra oceanic island arc succession which accreted to the eastern margin of australia gondwana around the end of the devonian this intra oceanic arc is distinct from a younger carboniferous superposed continental arc sequence which constitutes a successor basin that developed over the gamilaroi terrane subsequent to its accretion to the margin of australia radiolarians provide the basis for dating siliceous lithologies which dominate the djungati terrane and permit a more detailed analysis of the history of this terrane during the middle silurian through late devonian the djungati terrane was part of an oceanic basin which was isolated from any source of terrigenous sedimentation the djungati terrane was subsequently influenced by volcanic island arc activity and was tectonically disrupted during the latest devonian to early carboniferous radiolarian age data show that age correlations inferred on the basis of similarities in detrital sandstone petrography between lithostratigraphic units in the gamilaroi and djungati terranes are not always appropriate djungati terrane has been widely interpreted as a subduction complex related to the gamilaroi terrane radiolarian data now elucidate much of the structural complexity of this terrane significant differences between the djungati terrane and the style of well documented subduction complexes include the close spacing of zones of radiolarian chert the dominance of this lithology over others and the lateral extent of many of the chert horizons the anaiwan terrane has features which are characteristic of many well documented subduction complexes radiolarians are abundant in this terrane and can be used to show that it developed along the eastern margin of australia in response to early carboniferous subduction of late devonian to early carboniferous oceanic crust packages of chert accreted into the subduction complex are progressively younger towards the northeast indicating that subduction was directed to the southwest

early geochemical evolution of an oceanic island arc and backarc fiji and the south fiji basin the initial 25 to 35 ma of oceanic arc volcanism in fiji the early arc stage was dominated by eruption of lree depleted low k tholeiitic basalts and andesites the oldest volcanics include the highest hfse group morb like in composition plus high mg basalts and basic andesites with flat ree patterns as low as 4x chondritic concentrations these erupted either within the volcanic arc during its first 5 ma or in an adjacent backarc during its first ma of formation subsequent volcanics of the early arc stage apparently erupted onto early backarc basin crust most are intermediate between earlier extremes in hfse contents but at least one volcano produced strongly lree depleted island arc tholeiites in contrast medium k tholeiitic and calc alkaline andesites erupted during the mature arc stage parental basalts were enriched in lree but depleted in hree relative to earlier basalts due to a change in source composition counterflowing morb source asthenosphere within the mantle wedge dominated vol

ordovician continental margin terranes in the lachlan orogen australia implications for tectonics in an accretionary orogen along the east gondwana margin 1 four continental margin turbidite black shale terranes of the lachlan orogen in the southern tasmanides of eastern australia formed in two major systems along the east gondwana margin and constrain the ordovician assembly of this accretionary orogen key features are the dissimilar stratigraphies of the adjacent bendigo and melbourne terranes in the western system the dissimilar stratigraphies of the adjacent melbourne and albury bega terranes that reflect juxtaposition of the two systems during the middle devonian and the presence of the albury bega terrane both west and east of the macquarie arc in the eastern system that also includes the ocean floor narooma terrane and igneous ocean crust terrane s repetition of the albury bega terrane either side of the arc requires either rifting or orogen parallel strike slip duplication of a once contiguous package terrane interactions began in the earliest gisbornian with early docking uplift deformation and exchange of detritus amalgamation occurred in the earliest silurian benambran orogeny with accretion in the middle devonian over 40 myr discrete turbidite terranes aligned along the gondwana margin in two systems were converted into a very wide orogen characterized by the along strike juxtaposition of superficially similar terranes

cretaceous evolution of the central asian proto paratethys sea tectonic eustatic and climatic controls the timing and mechanisms of the cretaceous sea incursions into central asia are still poorly constrained we provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of cretaceous records of the proto paratethys sea fluctuations in the tajik and tarim basins the early cretaceous marine incursion in the western tajik basin was followed by major marine incursions during the cenomanian ca 100 ma and santonian ca 86 ma that reached far into the eastern tajik and tarim basins these marine incursions were separated by a turonian coniacian ca 92 86 ma regression basin wide tectonic subsidence analyses imply that the early cretaceous sea incursion into the tajik basin was related to increased pamir tectonism we find that thrusting along the northern edge of the pamir at ca 130 90 ma resulted in increased subsidence in a retro arc basin setting this tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the cenomanian ca 100 ma the following turonian coniacian ca 92 86 ma major regression driven by eustasy coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting the santonian ca 86 ma major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west siberian basin an early maastrichtian cooling ca 71 70 ma potentially connected to global late cretaceous trends is inferred from the replacement of mollusk rich limestones by bryozoan and echinoderm rich limestones

water saturated magmas in the panama canal region a precursor to adakite like magma generation amphibole while uncommon as a phenocryst in arc lavas is increasingly recognized as a key constituent in the petrogenesis of arc magmas fractional crystallization of water saturated arc magmas in the lower crust can yield substantial volumes of amphibole cumulates that depending on the pressure of crystallization may also contain garnet fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature this study examines newly dated late oligocene 25 37 0 13 ma hypabyssal amphibole rich andesites from cerro patacon in the panama canal region these andesites contain nodules of amphibole cumulates that are 4 6 cm in diameter and are almost entirely composed of 5 10 mm amphibole crystals dominantly ferri tschermakite geochemical variations optical and chemical zoning of the cerro patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite amphiboles hosted within the cumulate nodules differ from those hosted in the cerro patacon andesite and contain consistently higher values of ti we suggest these nodules represent the early stages of fractionation from a water saturated magma cerro patacon andesites have ree concentrations that plot at the most depleted end of central american arc magmas and exhibit a distinctive depletion in the middle ree these geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the cerro patacon andesite consistent with the petrographic evidence fractionation of water saturated magmas is a mechanism by which adakitic compositions may be produced and the cerro patacon andesites do exhibit adakite like geochemical characteristics e g elevated sr y 28 34 however the relatively elevated concentrations of y and hree indicate garnet was not stable in the fractionating assemblage during this early stage of arc development

unusual ruby sapphire transition in alluvial megacrysts cenozoic basaltic gem field new england new south wales australia abstract rare ruby crystals appear among prevailing sapphire crystals mined from placers within basaltic areas in the new england gem field new south wales australia new england ruby ner has distinctive trace element features compared to those from ruby elsewhere in australia and indeed most ruby from across the world the ner suite includes ruby up to 3370 ppm cr pink sapphire up to 1520 ppm cr white sapphire up to 910 ppm and violet mauve purple or bluish sapphire up to 1410 ppm cr some crystals show outward growth banding in this respective colour sequence all four colour zones are notably high in ga up to 310 ppm and si up to 1820 ppm high ga and ga mg values are unusual in ruby and its trace element plots laser ablation inductively coupled plasma mass spectrometry and suggests that magmatic metasomatic inputs were involved in the ner suite genesis in situ oxygen isotope analyses secondary ion mass spectrometry across the ner suite colour range showed little variation n 22 18 o 4 4 0 4 2 error and are values typical for corundum associated with ultramafic mafic rocks the isolated ner xenocryst suite corroded by basalt transport and with few internal inclusions presents a challenge in deciphering its exact origin detailed consideration of its high ga chemistry in relation to the known geology of the surrounding region was used to narrow down potential sources these include late palaeozoic triassic fractionated i type granitoid magmas or mesozoic cenozoic felsic fractionates from basaltic magmas that interacted with early palaeozoic cr bearing ophiolite bodies in the new england orogen other potential sources may lie deeper within lower crust mantle metamorphic assemblages but need to match the anomalous high ga geochemistry of the new england ruby suite

contrasting modes of eclogite and blueschist exhumation in a retreating subduction system the tasmanides australia abstract blueschists and eclogites located in the tasmanides of eastern australia preserve evidence of contrasting modes of exhumation a review of structural metamorphic geochronological and geochemical data indicates that these hp metamorphic rocks can be sub divided into three main groups i eclogite blueschists with calc alkaline and tholeiitic affinities contained within thick sedimentary sequences called continental hp rocks ii moderate pressure thermobarometric and geochronological data from eclogites and blueschists in the peel manning fault system new england orogen also provide evidence for discontinuous exhumation of subducted oceanic rocks these data indicate that eclogites were exhumed from depths of 70 km to 30 km during the ordovician 490 470 ma with terminal exhumation and exposure along the peel manning fault system probably occurring during the permian based on these timing constraints we suggest a model where hp rocks reside between depth dependant exhumation circuits for considerable lengths of time

volcanic arc reconstruction using discriminant function analysis of detrital clinopyroxene and amphibole from the new england fold belt eastern australia discriminant function analysis dfa of ca rich clinopyroxene and amphibole from modern arc volcanics allows identification of the parent magma type basalt andesite or dacite rhyolite with a view to understanding the provenance of arc derived sandstones the dfa approach has been applied to a suite of well studied cambrian to devonian volcaniclastic sandstones of the new england fold belt of eastern australia which contain significant arc derived detrital clinopyroxene and occasionally amphibole previous provenance studies of these rocks have been based on petrography identifying two cycles of volcanism but the results of this study show this to be oversimplified instead dfa analysis shows that some units comprise both intermediate and acidic volcanic components with significant along strike or vertical variations in terms of arc derived detritus the dfa approach avoids the pitfalls of a component mixing that limits the usefulness of whole rock chemical analysis and b the qualitative as

gamilaroi terrane a devonian rifted intra oceanic island arc assemblage nsw australia the gamilaroi terrane comprises part of the new england orogen of eastern australia and contains devonian strata preserving evidence of their development in a variety of arc related environments radiolarian studies provide new and more precise constraints on stratigraphy and together with geochemistry allow development of a new model for evolution of the terrane a diverse suite of volcaniclastic sedimentary rocks intercalated with regionally extensive extrusive and high level intrusive meta felsic igneous rocks of low k and calc alkaline volcanic affinity is present these rocks constitute the oldest in situ volcanic rocks in the gamilaroi terrane and are similar to those found in modern intra oceanic volcanic island arc settings basaltic intrusions and lavas occur at higher stratigraphic levels major and trace element compositions together with relatively flat chondrite normalized ree distributions resemble those from rocks formed in modern intra oceanic island arc rift zones the close spatial association of these rock types together with an absence of continent derived detritus is consistent with interpretation of development of the gamilaroi terrane in an intra oceanic island arc which experienced local rifting this interpretation is a departure from previous models for the new england orogen which interpret the gamilaroi terrane as a forearc basin that developed above a long lived cambrian to permian west dipping subduction zone fringing the continental margin of gondwana by analogy with modern arc continent collision zones in which crust between colliding continents and island arcs is preferentially subducted beneath the approaching arc we suggest that oceanic crust intervening between gamilaroi terrane and gondwana was subducted eastwards under the western margin of the gamilaroi terrane arc during a latest devonian collision event the gamilaroi terrane was obducted onto the gondwana margin this resulted in subduction flip and subsequent development of an east facing continental margin arc system on top of the gamilaroi terrane