proterozoic mafic ultramafic intrusions in the arunta region central australia part 2 event chronology and regional correlations abstract the arunta region in central australia records multiple proterozoic crustal processes over a 1500 million year period the timing of mafic ultramafic magmatism in this evolution is constrained by shrimp u pb dating of zircon which is a primary phase in mafic ultramafic intrusions across the region the earliest mafic magmatism was part of the 1810 1800 ma stafford event and a second episode is recognised during the 1790 1770 ma yambah event zircon overgrowths in some of these early intrusions record metamorphism during the strangways event a regionally pervasive metamorphic episode whose termination at ca 1690 ma coincided with intrusion of dolerite dykes gabbro intrusion during the ca 1640 ma liebig event is related to the geologically distinct warumpi province in the south of the region there is no record of mafic magmatism during the ca 1590 ma chewings event later systems include the ca 1130 ma alkaline ultramafic mordor complex and basaltic bodies are components of the irindina province which experienced high grade metamorphism during the palaeozoic the dating associates mafic ultramafic magmatism with each of these events which suggests that repeated extensional systems are an important aspect of the tectonic evolution the example of routinely obtaining zircon for dating from mafic and even ultramafic intrusions using an integrated approach of field and geochemical criteria to guide sampling opens the possiblility of dating mafic ultramafic intrusions elsewhere direct dating of mafic ultramafic magmatism permits its significance in proterozoic event systems to be evaluated directly free of assumed or conjectural timing correlations with the felsic plutons that are more often studied for age control

the mount hay block central australia another puzzle piece for paleo mesoproterozoic tectonic history abstract the 100 km 2 mount hay block arunta region central australia is a 15 km thick crustal cross section comprised of granulite facies tectonites containing a tectonothermal record from ca 1803 to ca 1552 ma as demonstrated by the combination of prior work and new monazite geochronology and thermobarometry igneous and sedimentary protoliths formed ca 1803 1798 ma during 1810 1790 ma stafford tanami time between ca 1790 and 1740 ma nearly continuous magmatism in the aileron province and possibly ages of recrystallized zircon and monazite in the mount hay block record subduction along the southern margin of the proterozoic australia mawson continent geologic mapping and zircon and monazite geochronology demonstrate that the mount hay block was penetratively deformed between ca 1720 ma and 1700 ma during 1735 1690 ma strangways time this includes the 8 km thick mount hay sheath fold which records ne sw subhorizontal shear once paleozoic tilting of the mount hay block is removed while still in the deeper crust 798 33 c 7 6 0 7 kbar fabrics along the northern edge of the mount hay block were transposed by the cross cutting 7 km thick capricorn ridge shear zone at ca 1551 7 5 5 ma during chewings time once restored the capricorn ridge shear zone records ne sw extension a jump in strain rate while at high temperatures 725 c initiated severe localization accommodated initially by pseudotachylite formation and cataclasis then mylonitization during fe rich fluid flux shearing may have continued to pressure temperature conditions as low as

low pressure granulite facies metamorphism in the larsemann hills area east antarctica petrology and tectonic implications for the evolution of the prydz bay area thermobarometric studies on various granulite facies areas along the prydz bay coast east antarctica 73 79 e 68 70 s show that at around 1100 ma during a late proterozoic orogeny the rocks of the larsemann hills suffered a lower pressure metamorphic peak than the surrounding areas along the prydz bay coast the rocks affected by this event include parts of the vestfold hills block plus all of the rauer group the larsemann hills and the munro kerr mountains the dykes in the south west corner of the vestfold hills were recrystallized during this event with little deformation at temperatures not quite as high as in the areas further south west 650 c 6 5 kbar collerson et al 1983 the rauer group was metamorphosed at 800 c and 7 5 kbar harley 1987a the larsemann hills at 750 c and 4 5 kbar and the munro kerr mountains probably at around 850 c and 5 kbar retrograde equilibration in the different areas occurred during decompression to about 10 km depth in all areas followed by isobaric cooling at this depth this paper shows that the peak metamorphism in the larsemann hills occurred at a pressure which is too low to have been the consequence of thermal relaxation of overthickened crust with normal mantle heat flow although other areas in prydz bay were metamorphosed at sufficiently high pressures so that their decompression paths are not inconsistent with a continental collision model the inferred pre metamorphic peak histories and the requirement of consistency with the larsemann hills make it unlikely that collision followed by erosion driven decompression is an appropriate model we suggest that the thermal regime of the crust in the larsemann hills region was controlled by a perturbation in the asthenosphere with magma invasion of the crust we suggest that the 500 ma event represented in prydz bay by granitic outcrops at landing bluff and by several k ar ages from the larsemann hills area was responsible for the final excavation of the terrane

tectonic feedback intraplate orogeny and the geochemical structure of the crust a central australian perspective the geological record of intraplate deformation in central australia implies that past tectonic activity basin formation deformation and erosion has modulated the response of the lithosphere during subsequent tectonic activity in particular there is a correspondence between the localization of deformation during intraplate orogeny and the presence of thick sedimentary successions in the preserved remnants of a formerly widespread intracratonic basin this behaviour can be understood as a kind of tectonic feedback effected by the longterm thermal and mechanical consequences of changes in the distribution of heat producing elements induced by earlier tectonism from a geochemical point of view one of the most dramatic effects of intraplate orogeny in central australia has been the exposure in the cores of the orogens of deep crustal rocks largely depleted in the heat producing elements the geochemical structuring of the crust associated with the erosion of the heat producing upper crust resulted in long term cooling of the deep crust and upper mantle with associated lithospheric strengthening this is illustrated here by mapping the consequences of deformation and associated tectonic responses onto the h qc plane where h is the characteristic length scale for heat production distribution and qc is the total crustal heat production because rates of intraplate deformation in central australia appear to be much slower than that typical of plate margin orogens it is possible that the ongoing geochemical structuring of the crust has played an important role in terminating intraplate orogeny in central australia by providing a thermal lock the diagnostic geophysical signature of this lock may be the extraordinary gravity anomalies of the central australian intraplate orogens central australia provides an intriguing record of intraplate deformation resulting in the development of a number of extraordinary orogens that expose deep crustal rocks in their cores forman 1971 teyssier 1985 goleby et al 1989 the spatial distribution of intraplate deformation during the alice springs and petermann orogenies suggests that the mechanical response of this region has varied through time consequently this response is important for our understanding of the processes controlling reactivation in intraplate settings in previous contributions it has been argued that the distribution of deformation in central australia has been strongly influenced by prior tectonic processes such as basin formation and erosion sandiford hand 1998a hand sandiford 1999 this paper focusses on the way in which intraplate deformation modifies the geochemical structure of the crust in this region in particular the distribution of heat sources recognizing that the distribution of heat sources provides a first order control on the thermal structure of the crust the consequences of intraplate deformation for the longterm thermal and mechanical evolution of the crust is then explored our aim is to demonstrate the relevance of a novel style of tectonic feedback which seems to have modulated the longterm tectonic behaviour of the central australian region and which may be relevant to continental interiors in general the notion of tectonic feedback is compatible with a highly temperature dependent lithospheric rheology as suggested by many experimental studies of natural rocks such feedback has profound implications for the longterm tectonic evolution of continental interiors particularly their potential for reactivation the record of intraplate deformation in

thermal modelling of very long lived 140 myr high thermal gradient metamorphism as a result of radiogenic heating in the reynolds range central australia abstract the reynolds range in the paleo mesoproterozoic aileron province of central australia exposes a differentially exhumed metamorphic rock system varying from greenschist to granulite facies calculated p t pseudosections indicate that peak metamorphic conditions in greenschist facies areas reached temperatures of 480 c and pressures of 3 2 5 kbar peak conditions at amphibolite facies are constrained to 500 620 c and 1 3 3 8 kbar p t modelling of two petrologically different granulite facies samples indicate that peak conditions in the exhumed granulite facies rocks reached 780 920 c and 3 5 5 4 kbar corresponding to high apparent thermal gradients of 152 218 c kbar in the amphibolite facies rocks in situ la icp ms u pb monazite geochronology records ages that range between 1680 and 1550 ma in contrast in the granulite facies rocks monazite records ages of ca 1560 ma the terrane contains significantly elevated rates of crustal heat production compared to global norms and when incorporated into lithospheric thermal models with reasonable boundary conditions and average thermal properties can plausibly account for the long lasting metamorphic conditions the thermal modelling shows that the long lasting 100 myr record of monazite u pb ages supported by previous studies reflects a continuous duration of elevated crustal temperatures an interpretation consistent with texturally simple mineral assemblages that lack any evidence for polymetamorphism in high crustal heat production terranes high thermal gradients and high temperatures will persist until exhumation removes the upper crust this physical reality provides a basis for the existence of arbitrarily long lived metamorphic systems even under high thermal gradients that are generally considered to be thermally anomalous however such thermal anomalism is not remarkable as there is abundant evidence for elevated rates of crustal heat production in the reynolds range and worldwide in terranes where accessory minerals record large continuous ranges of age robust volumetric measurements of crustal heat production rates are a necessary step in evaluating the potential thermal significance of such geochronological records failure to document rates of crustal heat generation invalidates many interpretations for drivers of metamorphism

successive overprinting granulite facies metamorphic events in the anmatjira range central australia the anmatjira range and adjacent reynolds range central australia comprise early proterozoic metasediments and othogneisses that were affected by three and possibly four temporally distinct metamorphic events m1 4 and deformation events d1 4 in the period 1820 1590 ma the north western portion of the range around mt stafford preserves the effects of 1820 ma m1 d1 and shows a spectacular lateral transition from muscovite quartz bearing schists to interlayered andalusite bearing migmatites and two pyroxene granofelses that reflect extremely low pressure granulite facies conditions over a distance of less than 10 km orthopyroxene cordierite garnet k feldspar quartz bearing gneisses occur at the highest grade implying peak conditions of 750 c and 2 5 0 6 kbar an anticlockwise p t path for m1 is inferred from syn to late d1 sillimanite overprinting andalusite petrogenetic grid considerations and quantitative estimates of metamorphic conditions for inferred overprinting assemblages the effects of m1 have been variably overprinted to the south east by a c 1760 ma m2 d2 event much of the central anmatjira range around ingellina gap comprises orthogneiss deformed during d2 and metapelites that have m1 andalusite and k feldspar overprinted by m2 sillimanite and muscovite the south eastern portion of the range around mt weldon comprises metasediments and orthogneisses that were completely recrystallized during m2 d2 with metapelitic gneisses characterized by spinel sillimanite k feldspar quartz bearing assemblages that suggest peak m2 conditions of 750 c and 5 5 1 kbar overprinting parageneses in metapelitic gneisses imply that d2 occurred during essentially isobaric cooling a third granulite facies event m3 affected rocks in the reynolds range immediately to the south of the anmatjira range at c 1730 ma a possible fourth event m4 with a minimum age of c 1590 my affected both ranges but resulted in only minor overprinting of m1 3 assemblages the superimposed effects of m1 4 mapped for the entire anmatjira reynolds range area indicate that only minor or no dislocation of the regional geology occurred during any of the metamorphic and accompanying folding events although the immediate cause of each of the metamorphic events involved advection the ultimate causes were external to the metasediments and most probably external to the crust

late paleoproterozoic magmatism in delhi fold belt nw india and its implication evidence from epma chemical ages of zircons abstract zircons from six granitoid plutons occurring in the northern part of the delhi fold belt nw india have been chemically dated using an electron microprobe most of the zircons occurring in the granites are chronologically unzoned and gave ages around 1 78 1 71 ga but younger ages of 1 1 0 9 ga have also been obtained from the rim of some grains monazite and zircons from the metasediments of delhi supergroup adjacent to the granitoids were also analyzed the older age of 1 9 1 7 ga obtained for monazites could possibly indicate their provenance age detrital zircon grains mostly rounded in the delhi metasediments which gave older ages of 1 9 ga could possibly have been derived from the archaean basement rocks exposed in this aravalli delhi fold belt the geochemical signatures of these granitoids are consistent with an extensional tectonic regime it is quite likely that contrary to the prevailing assumption of the granitoids being intrusive our geochronologic data suggests them to be the basement for sedimentation the new geochronologic information on these granitoids in the northern part of the delhi fold belt and their comparison with other correlative events establishes a widespread thermal event during late paleoproterozoic

physical sedimentation processes on a mid proterozoic 1800 ma shelf the reynolds range group arunta block central australia abstract shallow marine siliciclastic and carbonate deposits belonging to the 1800 ma old reynolds range group central australia represent a transgressive sequence deposited on a low gradient shelf that was affected by longshore currents tidal currents storm wave action and fair weather wave action the sediments comprise a 1100 m thick sequence in which three main depositional facies associations can be distinguished i a near shore and inner shelf quartz arenite facies association is overlain by ii a middle shelf mudstone facies association which contains lenses of iii a carbonate facies association the quartz arenite facies association mainly occurs along the northeast side of the range and grades into the mudstone facies association towards the southwest this suggests that the palaeo shelf extended towards the southwest which is in accordance with a concentration of southwest directed palaeo current directions within the quartz arenite facies a sudden increase in thickness of quartz arenite in the mount thomas area suggests this area was the locus for fluvial sediment input vertical and lateral stratigraphic transitions between the facies associations are generally gradational which may reflect coexistence of all facies on the shelf and small net relative sea level changes the quartz arenite facies association contains tide influenced bidirectional small scale trough cross bedded tabular cross bedded and parallel laminated sets that were deposited on the shoreface these are generally overlain by large scale trough and tabular cross bedded sets which were deposited on the inner shelf and record a southeast directed longshore current numerous truncation surfaces indicate that frequent storms eroded the shoreface and carried large volumes of sediment onto the shelf the mudstone facies association consists of alternating mudstone beds and generally thin sheetlike quartz sandstone beds that lack grading and traction structures they represent storm induced suspension deposits laid down on the middle shelf inferred water depths 100 m longshore and tidal currents appear to have had little influence in this environment stromatolite bioherms and rippled marls and grainstones constitute the carbonate facies association which formed on the middle shelf in shallow marine areas of low siliciclastic sediment input ripples in storm sands throughout the mudstone facies association and a lack of turbidites reflect the shallow depths and low gradient of the shelf slope a general lack of tidal deposits and the non barred nature of the palaeo coastline indicate a small tidal range 0 4 m the unidirectional southeast directed longshore current appears to have only influenced sedimentation on the inner shelf which suggests it resulted from prevailing westerly winds the described facies in the reynolds range group occur in strongly deformed and highly metamorphosed rocks and the paper serves as an example that even from such tectonised rocks valuable sedimentological information can be extracted

nd and sr isotopic systematics of central australian granulites chronology of crustal development and constraints on the evolution of lower continental crust nd and sr isotopic data are reported for a granulite terrain in the proterozoic arunta block of central australia sm nd data from a wide range of rock types define a crust formation age of 2 070 125 ma and provide further evidence for voluminous crustal growth in the proterozoic an nd value of 1 5 0 8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust field relationships geochemistry and rb sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism rb depletion at 1 800 ma rb sr data for strongly retrogressed granulites define an age of 1 700 ma which is interpreted as the time of retrograde biotite growth partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism sm nd and rb sr isotopic systematics of minerals indicate that the terrain cooled slowly did not experience significant uplift until 1 000 ma and remained at temperatures above 320 c until the late palaeozoic the mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain the granulite protoliths appear to have formed in a rift which closed within 280 ma of initial separation deformation and granulite facies metamorphism at 1 800 ma are interpreted to be a consequence of collision between the continental blocks which defined the rift regional retrogression and granitoid magmatism at 1 700 ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision subsequent events in the cooling and uplift history appear to have been controlled by the presence of long lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere the results of this study suggest that granulite terrains in general cannot be equated with lower continental crust but instead represent assemblages of mainly supracrustal rocks which in some instances have been involved in major collision events

the p t deformation path for a mid proterozoic low pressure terrane the reynolds range central australia the proterozoic low pressure high temperature lpht terrane of the reynolds range occurs in a 130 km long nw trending belt in the central part of the arunta block central australia the reynolds range has been affected by two mid proterozoic tectonic cycles di and dii associated with two metamorphic events mi and mii di mi effects are restricted to the older of two sedimentary successions the lander rock beds which are separated from the younger reynolds range group by an angular unconformity the dominant structural metamorphic features formed during dii mii affected both sedimentary successions and the various granites that intruded them and reworked most di mi effects the dii deformation history can be subdivided into one prograde two peak and one retrograde stage average p t calculations in the southeastern half of the range indicate a peak metamorphic pressure of 4 1 0 3 kbar because the calculated values are derived from the same stratigraphic level corresponding to the base of the reynolds range group which is exposed throughout the area it is likely that pressures were similar in the entire range in fact however the peak metamorphic temperature shows a dramatic increase from greenschist facies c 400 c in the northwest to granulite facies 740 60 c in the southeast indicating that mii was associated with anomalously high heat flows the p t path is anticlockwise with isobaric cooling from the metamorphic peak indicated by corona textures however the evidence of a prograde increase in pressure is indirect and based on the compressional nature of the structures peak metamorphic mineral assemblages and retrograde mineral assemblages in amphibolite facies shear zones show the same metamorphic zonation suggesting they formed in response to the same thermal event if this is true the implication is that a thermal perturbation external to the crust was maintained for a considerable period of time 110 ma based on zircon dating as it is not clear whether proterozoic asthenosphere active thermal perturbations operated for this long the alternative interpretation must be considered namely that the peak metamorphic events are separate from the shear zone event associated with reheating of the area

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

the proterozoic davenport province central australia regional geology and geochronology abstract the davenport province forms the southern part of the tennant creek inlier and lies to the north of the arunta inlier the oldest rocks exposed are turbidites and minor 1880 1870 ma old felsic volcanics of the warramunga group these were folded probably during the barramundi orogeny and intruded by granite before being overlain by the hatches creek group a sequence up to 10 000 m or more thick of fluvial to shallow marine sedimentary and bimodal volcanic rocks a rift sag model of basin development involving crustal extension in an intracratonic setting is suggested for this group interpretation of u pb zircon data for felsic volcanics in the lower part of the hatches creek group is hampered by problems of ancient pb inheritance but a preferred crystallization age of 1820 1810 ma is indicated two episodes of upright concentric folding about nw se and ne sw trending axes preceded emplacement of granite at 1660 ma or earlier rb sr whole rock data for felsic volcanics from the hatches creek group are tentatively interpreted to indicate a region wide hydrothermal alteration event at 1645 44 ma this alteration may have been associated locally with w cu bi and mo mineralization

the nolans bore rare earth element phosphorus uranium mineral system geology origin and post depositional modifications nolans bore is a rare earth element ree u p fluorapatite vein deposit hosted mostly by the 1805 ma boothby orthogneiss in the aileron province northern territory australia the fluorapatite veins are complex with two stages 1 massive to granular fluorapatite with inclusions of ree silicates phosphates and fluoro carbonates and 2 calcite allanite with accessory ree bearing phosphate and fluoro carbonate minerals that vein and brecciate the earlier stage the veins are locally accompanied by narrow skarn like garnet diopside amphibole wall rock alteration zones shrimp th pb analyses of allanite yielded an age of 1525 18 ma interpreted as the minimum age of mineralisation the maximum age is provided by a 1550 ma shrimp u pb age for a pegmatite that predates the fluorapatite veins other isotopic systems yielded ages from 1443 to 345 ma implying significant post depositional isotopic disturbance calculation of initial end and 87sr 86sr at 1525 ma and stable isotope data are consistent with an enriched mantle or lower crust source although post depositional disturbance is likely processes leading to formation of nolans bore began with north dipping subduction along the south margin of the aileron province at 1820 1750 ma producing a metasomatised volatile rich lithospheric mantle wedge about 200 million years later near the end of the chewings orogeny this reservoir and or the lower crust sourced alkaline low degree partial melts which passed into the mid and upper crust fluids derived from these melts which may have included phosphatic melts eventually deposited the nolans bore fluorapatite veins due to fluid rock interaction cooling depressurisation and or fluid mixing owing to its size and high concentration of th 2500 ppm in situ radiogenic heating caused significant recrystallisation and isotopic resetting the system finally cooled below 300 c at 370 ma possibly in response to unroofing during the alice springs orogeny surface exposure and weathering of fluorapatite produced acidic fluids and intense near surface kaolinitised zones that include high grade supergene enriched cheralite rich ores

decompressional coronas and symplectites in granulites of the musgrave complex central australia abstract in granulite facies metapelitic rocks in the musgrave complex central australia reaction between s1 garnet and sillimanite involves the development in s2 of both garnet cordierite hercynitic spinel biotite and hercynitic spinel cordierite sillimanite biotite the s2 assemblages occur either in coronas and symplectites mainly around garnet or in rocks in which s2 is more strongly developed as recrystallized assemblages ignoring the presence of biotite and ilmenite the mineral textures can be accounted for qualitatively by a consideration of the model system feo mgo al2o3 sio2 fmas the textural relationships accord with decompression accompanying the change from s1 to s2 however since biotite and ilmenite are involved in the assemblages the parageneses are better accounted for in terms of equilibria in the expanded model system k2o feo mgo al2o3 sio2 h2 tio2 fe2o3 kfmashto i e afm tio2 fe2o3 the coronas reflect the tectonic unroofing of at least part of the musgrave complex from peak s1 conditions of about 8 kbar to s2 conditions of about 4 kbar

a model for low pressure facies metamorphism during crustal thickening low pressure metamorphic facies i e high t p ratios are widespread in a wide range of tectonic settings explanations offered for the occurrence of these facies include extensional and or magmatic models however these fail to explain that the low p facies metamorphism is commonly coeval with a phase of pervasive crustal thickening with t p ratios increasing during or slightly lagging behind the thickening we propose an alternative explanation based on the approximate synchroneity of crustal thickening and erosion thinning of the mantle lithosphere

tchabal nganha volcano in adamawa cameroon petrology of a continental alkaline lava series abstract the mio pliocene tchabal nganha volcano in the adamawa plateau cameroon contains a broad range of rock types from ankaramites to phonolites and trachytes tchabal nganha is located on large n70 e strike slip faults that have been active since the cretaceous and delimit the adamawa plateau horst geological mapping revealed a succession of basaltic hawaiitic lava flow units mugearite benmoreite breccias phonolite and trachyte lava flows and plugs and finally tiny basaltic and intermediate outpourings olivine is fo 85 in basaltic lavas and has altered fayalitic compositions in trachytes clinopyroxene compositions range from ti rich salite in basaltic rocks to hedenbergite in phonolites and aegirine in trachytes kaersutite is present as megacrysts almost completely replaced by rhonite phlogopite salite olivine nepheline in ankaramites and as phenocrysts in phonolites the fe ti oxides indicate decreasing equilibration temperatures and oxygen fugacities from basalts to trachytes spinels occur as inclusions in ol and or cpx phenocrysts in ankaramitic basalts where al rich cr poor spinels are found exclusively in clinopyroxene phenocrysts feldspar occurs as phenocrysts of plagioclase in intermediate lavas and as sanidine and anorthoclase in phonolites and trachytes apatite is ubiquitous in intermediate and felsic lavas sphene is common in some phonolites and chevkinite in some trachytes differentiation indices vary from 17 to 93 with a gap in the range 60 75 ba may attain 4650 ppm in phonolites transition elements decrease strongly with differentiation in the basaltic lavas zr ta is constant along the series except in sphene bearing phonolites which are depleted in ta ree patterns are similar for basaltic and intermediate lavas some phonolites exhibit overall enriched ree patterns whereas peralkaline phonolites are strongly depleted in mree major and trace element variations confirm the dominance of crystal fractionation in the differentiation of the basaltic and phonolite series due to high ta contents along the series and to low sr isotope ratios

evidence for pre regional metamorphic fluid infiltration of the lower calcsilicate unit reynolds range group central australia grandite garnet rich calcsilicate rocks from the lower calcsilicate unit of the regionally metamorphosed reynolds range group central australia crop out along a strike parallel section in which a transition zone from m22 amphibolite to granulite facies rocks is exposed across this transition the grandite rich layers do not show systematic changes in mineral assemblages compositions and modes or stable isotope compositions these layers are deformed by f22 folds that are associated with the peak of regional low pressure high temperature metamorphism therefore the grandite rich layers appear to pre date regional metamorphism and to have acted as closed chemical systems during prograde m22 metamorphism mineral assemblages in the grandite rich layers are consistent with their formation through the infiltration of oxidized water rich fluids xco2 0 1 0 3 log fo2 16 to 14 the stable isotope values of calcite 13c 4 2 to 0 8 0 pdb 18o 10 5 14 0 0 v smow and bulk silicate fractions 18o 6 1 to 10 8 of the grandite rich layers are most consistent with the infiltrating fluid being from a magmatic source it is most likely that fluid infiltration occurred during the pre m22 contact metamorphism m21 that affected much of the reynolds range group the preservation of these assemblages is probably due to their high variance and little pervasive fluid rock interaction having occurred during m22 the clinopyroxene and feldspar rich calcsilicate rocks that host the grandite rich layers contain poikiloblastic grandite garnet that formed during prograde m22 metamorphism thin marbles that locally occur with the grandite rich layers contain a third garnet generation that is post or late m22 this grossular rich garnet occurs in coronas around calcite plagioclase clinopyroxene wollastonite and scapolite these coronas are consistent with cooling and or compression however because the marble assemblages are themselves overprinted by m21 grandite rich layers the development of coronal garnet does not reflect a continuous p t t path rather it more probably reflects the partial re equilibration of m21 contact metamorphic assemblages to post m22 conditions

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

the musgrave province stitching north west and south australia abstract the musgrave province in central australia is an east west trending 120 000 km2 region composed of lithologic units that range in age from earliest mesoproterozoic to neoproterozoic it is one of the few terrains in australia that records significant grenvillian aged tectonism and has a distinctly younger geological history than the surrounding fragments of proterozoic australia compared to other proterozoic terranes of australia the evolution of the musgrave province is poorly understood the region contains evidence for the development of earliest mesoproterozoic arc related magmatism with major juvenile crustal additions comprising intercalated felsic and mafic gneisses with protolith ages ranging from ca 1 60 to 1 54 ga this period of arc magmatism was followed by closure of the ocean separating the north australian craton nac from the south australian craton sac at ca 1 54 ga arc magmatism and collision was followed by a period of extension during which protoliths to the metasedimentary rocks of the eastern musgrave province were deposited at ca 1 4 ga the combined juvenile nd isotopic signature and detrital zircon ages from these metasediments suggests provenance from non australian sources with possible sources originating from laurentia granitic magmatic events occurred at ca 1 3 and 1 20 1 14 ga the latter comprising the voluminous a type granites of the pitjantjatjara supersuite the intrusion of these magmatic units provide key temporal constraints on deformational events and are coeval with the voluminous a type suites of laurentia which would invite correlation of australia with laurentia at ca 1 30 1 14 ga these magmatic episodes are accompanied by deformation at granulite facies at ca 1 30 ga unnamed event and 1 23 1 15 ga musgrave orogeny these deformation metamorphic events have completely recrystallised any primary layering within the pre 1 30 ga rocks forcing interpretations on their genesis to be inferred from geochemical and isotopic data the tectonic significance of these events is not clear however they may form part of a larger grenville aged deformational belt extending into the western australian albany fraser province and antarctica emplacement of the voluminous mafic ultramafic giles complex and associated granulite facies metamorphism of the giles event occurred at ca 1 078 ga the layered intrusions of the giles complex are generally fault bound and are considered to represent discrete bodies emplaced in an extensional regime associated with generation of the warakurna large igneous province the ca 1 08 ga alcurra dolerite unnamed ca 1 0 ga olivine dolerites and ca 0 8 ga amata dolerite dissect much of the musgrave province the alcurra dolerite and unnamed olivine dolerite dykes have been proposed as originating from a modified sub continental lithospheric mantle whereas the amata dolerite is proposed to be plume related coinciding with the initiation of rifting creating the centralian superbasin an earliest cambrian intraplate transpressional event is recorded in the ca 550 ma petermann orogeny this resulted in deep crustal exhumation of much of the northern musgrave province from beneath the centralian superbasin with mylonitic deformation recorded at pressures of 12 kbar and temperatures of 700 750 c

decomposition of k amphibole at high pressures and implications for subduction zone volcanism abstract the stability of k amphibole has been studied at pressures 12 6 16 5 gpa and at temperatures 940 1450 c k amphibole decomposes into an assemblage of clinoenstatite diopside an unknown phase x stishovite fluid at pressures above 16 gpa and temperatures below 1200 c the phase boundary has a negative clapeyron slope and the high temperature assemblage is clinoenstatite diopside x wadeite type k 2 si 4 o 9 fluid at pressures 14 16 gpa the x phase has a cation ratio of approximately k mg si 1 2 2 and contains 1 7 0 1 wt h 2 o as determined by sims measurements leading to a formula of k 4 mg 8 si 8 o 25 oh 2 the present results suggest that the decomposition of k amphibole in the dragged hydrous peridotite layer at the base of the mantle wedge may produce certain amounts of h 2 o rich fluid at 14 16 gpa 450 km depth while some of h 2 o is trapped in the new hydrous phase x and is further carried into deeper regions of the mantle the aqueous fluid released by the decomposition of k amphibole should react with phase to form hydrous phase in the mantle transition region thus the dehydration of k amphibole would not cause any volcanic activities in the back arc regions in contrast to the dehydrations of amphibole chlorite and phlogopite which are presumably responsible for the first and the second volcanic chains however some of the volcanic activities such as in muriah indonesia may be related to the dehydration of k amphibole in unusually hot regions above the subducting slab

low pressure and low temperature k bearing kosmochloric diopside from the osayama serpentinite melange sw japan kosmochloric diopside with high k content up to 0 56 wt 0 026 k atom per formula unit was discovered from the osayama serpentinite melange in the chugoku mountains sw japan k bearing clinopyroxene fills microcracks 5 150 m in wide together with uvarovite within albite vein of a tremolite rock compositions of analyzed clinopyroxene consist mainly ofkosmochlor augite 92 98 mol ko 1 9 3 8 aug 5 6 7 6 components and minor amounts of jadeite 0 6 mol aegirine 0 5 mol ca tschermak 0 3 mol and k kosmochlor 0 2 mol although the k content in clinopyroxene is also variable and heterogeneous even in a single vein clinopyroxene with higher k content occurs in ko rich part higher magnification secondary electron images confirmed that exsolution and inclusion are essentially absent in the analyzed clinopyroxenes the good negative correlation between cr na k and ca mg fe 2 indicates the cr incorporation into the octahedral site furthermore k correlates with na and cr indicating a simultaneous enrichment of k for na and cr during pyroxene growth textual relations and parageneses and compositions of minerals suggest that the k cpx precipitated together with uvarovite in brittle microcracks directly from a ca and cr rich hydrothermal fluid at approximately p 4 gpa environment permits to host relatively large k cation into the clinopyroxene structure our finding indicates that the incorporation of k into the kosmochlor diopside series solid solution with at least 0 2 cr cation p f u is possible even at low p conditions

grenvillian aged reworking of late paleoproterozoic crust of the southern north australian craton central australia implications for the assembly of mesoproterozoic australia abstract la icp ms u pb monazite and zircon geochronology from metapelites and migmatitic orthogneiss along the central southern margin of the north australia craton nac central australia reveal the presence of a regional scale grenvillian aged ca 1130 ma deformation system grenvillian aged deformation extends over a strike length of over 110 km from the southern aileron province in the vicinity of alice springs to the teapot granite complex within the warumpi province there is also evidence for grenvillian aged migmatisation and resetting of monazite further west in the mount liebig area which may extend the grenvillian aged footprint to a strike length of at least 250 km deformation associated with grenvillian aged reworking produced map scale east west trending folds and strongly foliated steeply dipping shear zones that define the structural architecture of the interface region between the aileron and warumpi provinces shallow westerly plunging folds associated with partial melting have evolved into shear zones and mylonites that record south side up movement phase equilibria modelling of age constrained garnet biotite sillimanite cordierite bearing metapelites from the southern aileron and warumpi provinces suggest grenvillian aged metamorphism reached temperatures in the range of 775 820 c and pressures of 5 5 5 kbar corresponding to thermal gradients of 130 165 c kbar 1 the extensive grenvillian aged system reworks and overprints late paleoproterozoic ca 1650 1630 ma high grade metamorphic rocks the grenvillian aged system occurs above a south dipping lithospheric scale interface that has been geophysically imaged to depths of at least 200 km this feature was interpreted to represent a fossil subduction zone of late paleoproterozoic age however the presence of regional scale grenvillian aged deformation in the crust above this feature suggests that it may instead be grenvillian aged if that is the case deformation along the southern margin of the nac may record suturing of the nac with the grenvillian aged musgrave province to the south this would effectively place the long lived late mesoproterozoic ultrahot orogen that is the musgrave province in southern central australia in an upper plate tectonic setting linked to the convergence of the nac with the south australian craton

lower crustal xenoliths from queensland australia evidence for deep crustal assimilation and fractionation of continental basalts abstract a suite of mafic granulite facies xenoliths from north queensland possesses petrographic and geochemical features of basaltic cumulates crystallized at lower crustal pressures negative correlations between incompatible trace elements and mg and positive correlations between compatible trace elements and mg suggest the xenoliths are genetically related and crystallized from a continuously evolving melt zr hf y hree ti and v do not correlate with mg but show excellent negative correlations with al2o3 content reflecting the proportion of cumulate plagioclase to clinopyroxene these chemical trends also suggest the trace element concentrations have not been affected by subsolidus recrystallization the xenoliths have a large range in sr and nd isotopic compositions 87 sr 86 sr 0 70239 to 0 71467 nd 9 5 to 6 1 which cannot be produced by crystal fractionation alone and excellent correlations between isotope ratios and mg suggest the variable isotope compositions are not due to mantle source heterogeneities these mafic xenoliths are proposed to be cumulate products from a melt undergoing simultaneous assimilation and fractional crystallization afc the data illustrate that only a few percent afc in lower crustal environments can dramatically change the sr and nd isotopic composition of a basaltic melt and suggest the use of caution when inferring mantle source isotopic compositions from continental basalts additionally the nd isotopic data plot on a positive trend on an sm nd isochron diagram with an age of 570 ma however if these xenoliths formed by afc the positive trend reflects mixing between two isotopic end members and has no age significance the correlations between sr and nd isotopic compositions with mg degrade as the isotopic ratios are back calculated to earlier times suggesting the xenoliths are relatively young the xenoliths may be related to the cenozoic igneous activity which occurs throughout eastern australia

geochronology of early to middle proterozoic fold belts in northern australia a review abstract this geochronological review integrates geologically relevant isotopic data from the several early to middle proterozoic fold belts of northern australia a number of firm chronological benchmarks largely established by means of u pb zircon studies now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes the apparent worldwide dearth of crustal events in the earliest proterozoic between 2500 and 2000 ma was broken in northern australia with the advent of a major crust forming episode between 1880 and 1850 ma ago these rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400 300 ma earlier that is evidenced from sm nd model ages the extent involvement and or degree of assimilation of any pre existing archaean crust is small but whether or not it is negligible or zero is not satisfactorily known the 1880 1850 ma event the barramundi orogeny is well represented in northern australia both lithologically and analytically and the rocks that pre and post date it have a similar tectonic setting over very wide areas of the continent two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals barramundi orogeny and crystallization of i type k rich felsic magmas closely following and in some cases overlapping with deformational processes in the halls creek inlier the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860 1850 ma this major yet short lived tectonism is mirrored in other fold belts such as pine creek tennant creek and mount isa in which u pb zircon ages give slightly older constraints of 1885 1870 ma 1920 1870 ma and 1885 10 ma respectively the ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years with the crystallization and emplacement of comagmatic volcanic plutonic pairs throughout in the interval 1870 1860 ma in the georgetown and arunta inliers direct evidence of this otherwise ubiquitous event if present is masked by younger high grade metamorphism in the latter however metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures the geochronological and geochemical coherency of the extensive early proterozoic 1870 ma magmatism contrasts with that of post 1800 ma magmatism which is less extensive generally anorogenic commonly bimodal in character and varies in age from one terrane to another several major sedimentary basins were being filled at this time major igneous events at 1790 1740 ma 1670 ma and 1500 ma are recognized elongate sublinear volcanic and plutonic belts 1790 1740 ma old are present at mount isa in high grade granitic gneisses of the arunta inlier a few u pb zircon ages and extrapolated rb sr protolith ages are coincident at about 1760 1750 ma indicating that this event may be important in the development of the division 2 sequences of that fold belt the platformal hart dolerite and oenpelli dolerite two of the largest mafic intrusions in the world were emplaced at 1762 25 ma and 1688 13 ma younger felsic plutonism and volcanism gave rise to rapakivi type granites in the mount isa tennant creek and the granites tanami inliers at 1670 ma a time close to that of the aileron deformational metamorphic event in central australia further at 1650 ma there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many rb sr ages gave rise to pegmatites and was possibly associated with mineralization in the davenport and eastern arunta inliers discrete middle proterozoic deformational events between 1610 and 1470 ma punctuate the tectonostratigraphic history in the arunta mount isa and georgetown fold belts where they are best documented

the retrograde p t t path for low pressure granulites from the reynolds range central australia petrological constraints and implications for low p high t metamorphism several aspects of the petrogenesis of low pressure granulite facies rocks from the reynolds range central australia are contentious including a the shape of the retrograde p t time path and whether it is an artefact of repeated thermal events at different p t conditions b the type of regional metamorphism and c the causes of metamorphism granulite facies rocks from the reynolds range group experienced three major periods of mineralogical equilibration metapelitic rocks underwent dehydration melting reactions to form migmatites under peak m2 p t conditions of c 5 0 5 3 kbar and c 750 800 c metapsammitic rocks that did not melt during m2 show spectacular garnet orthopyroxene intergrowths that developed at c 3 5 3 7 kbar and c 700 750 c after penetrative regional deformation but prior to amphibolite facies rehydration in discrete strike parallel zones rehydration occurred within the sillimanite stability field at p t conditions close to the granite solidus c 3 2 3 4 kbar and 650 700 c subsequently the terrane cooled into the andalusite stability field geochronological constraints suggest that a peak m2 conditions were reached at c 1594 ma b the garnet orthopyroxene intergrowths in unmelted metapsammites probably developed between c 1594 ma and c 1586 ma and c upper amphibolite facies rehydration occurred between c 1586 ma and 1568 ma the lack of petrological evidence for multiple dehydration and rehydration of the rocks suggests that the three episodes of mineralogical recrystallization can be linked to yield a single continuous retrograde p t t path of minor initial decompression c 1 5 kbar from the m2 peak followed by cooling c 100 c to the granite solidus over a period of c 26 ma late kyanite bearing shear zones that dissect the terrane are unrelated to this event and formed during the c 300 400 ma alice springs orogeny the shape of the p t t path and the duration of m2 metamorphism suggests that advective heating was not the major cause of high grade metamorphism and that some other longer lived heat source such as the burial of anomalously radiogenic pre tectonic granites is required

diapirism and gravity tectonics report of a tectonic studies group conference held at leeds university 25 26 march 1980 ir is now almost two decades since hans ramberg began his well known research of simulating diapiric structures in the laboratory and his application of this model work to the origin of major structures in orogenic belts ramberg 1963 1967 since then there has been a revolution of ideas in structural geology ideas ofhorizontal tectonics based on the movements of the earth s plates have largely taken preference to ideas based on vertical tectonics related to diapirism it was therefore considered timely to review the relative role of diapirism in regional deformation and hence the tectonic studies group affiliated to the geological society of london held a meeting on this theme on 25 26 march 1980 at the university of leeds this report includes the abstracts of all the contributions and it also summarises some of the conclusions most of which emerged during discussion following the contributions

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

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

the age and significance of the ngadarunga granite in proterozoic central australia abstract the emplacement of the ngadarunga granite in the arunta region of central australia directly constrains the timing of the first high grade metamorphic tectonic and magmatic event in the arunta region and the timing of the geographically extensive unconformity that separates the earliest regional basin phase from younger overlying sedimentary successions previous dating had correlated this event with the 1880 1840 ma barramundi orogeny interpreted in far north australia linking the arunta region to the barramundi model of widespread synchronous cratonisation in the period 1880 1840 ma new data revise this granite emplacement to 1803 6 ma placing it in the younger 1810 1800 ma stafford event of the arunta region the provenance of detrital zircons in early arunta region sedimentary rocks was dominated by crystalline rocks formed in the period 1840 1880 ma thus the earliest rocks in the arunta region were deposited after ca 1840 ma in a basin marginal to 1880 1840 ma continental crust and their subsequent tectonism began with the stafford event

proterozoic granulite facies metamorphism in the southeastern reynolds range central australia geological context p t path and overprinting relationships in the southeastern reynolds range central australia a low p granulite facies metamorphism affected two sedimentary sequences the lander rock beds and the reynolds range group in the context of the whole of the reynolds range and the adjacent anmatjira range this metamorphism is m3 in a sequence m1 4 that occurred over a period of 250 ma in particular m1 affected the lander rock beds prior to the deposition of the reynolds group m3 has an areally restricted high grade area in the southeastern reynolds range affecting both the reynolds range group and the underlying lander rock beds the effects of m3 are characterized by spinel quartz bearing peak metamorphic assemblages in metapelites which imply peak conditions of 750 c and 4 5 1 kbar and involved isobaric cooling or compression with cooling it is concluded that one of a series of thermal perturbations caused by thinning of mantle lithosphere contemporaneous with crustal thickening was responsible for m3 in the southeastern reynolds range evidence of both the unconformity between the two rock groups and previous metamorphism deformation has been completely erased by recrystallization during m3 d3

generation of pseudotachylite under granulite facies conditions and its preservation during cooling discontinuous ultramylonite zones cut proterozoic granulite facies gneisses in macrobertson land east antarctica and preserve evidence of ductile non coaxial flow and reverse sense of shear cross cutting relationships indicate that ultramylonite deformation involved overthrusting to the east but progressively rotated to involve overthrusting to the north rotation of the principal compressive stress axes is inferred extensive pseudotachylite developed during ultramylonitization the history of individual ultramylonite zones having involved a single episode of pseudotachylite generation neoblastic sillimanite indicates ultramylonitization occurred at 520 c on the basis of inferred recrystallized granulite facies mineral assemblages ultramylonitization occurred at 700 c and 7 3 0 5 kbar at ah2o 0 3 and low aco2 comparison of these values with those suggested by metamorphic assemblages in rocks unaffected by mylonitization indicates that the rayner complex experienced a late increase in pressure of 1 2 kbar during ultramylonitization the p t ah2o conditions of the ultramylonite zones are inferred to have been close to the solidus for minimum melting pseudotachylite generation having involved a limited pressure drop during brittle fracturing at high strain rates most of the pseudotachylite veins are undeformed the mechanism s of fracturing and melting must have caused strain hardening in rocks surrounding the ultramylonite further strain having been mostly accommodated by a new or subsidiary shear zone renewed stress at reduced strain rates or renewed stress in zones in which the proportion of pseudotachylite was significantly higher could have led to the rare occurrences of deformed pseudotachylite the preservation of fine grained pseudotachylite is dependent on it remaining dry

clockwise p t paths for crustal melting and h2o recycling in granite source regions and migmatite terrains abstract clockwise pressure temperature p t paths of metamorphism pass through two kinds of melting reactions with increasing temperature the first generates h 2 o saturated partial melts at the h 2 o saturated solidus only if excess h 2 o is present usually this accounts for less than 3 melt the second generates h 2 o undersaturated melts through dehydration melting reactions dmrs of micas or other hydrous minerals and occurs at temperatures higher than the h 2 o saturated solidus if h 2 o undersaturated melts remain in situ and the source regions are not exhumed then the crystallisation reactions encountered along the near reverse p t path may produce the same mineralogy as in the source rock in regions of exhumation along the decompression segments of clockwise p t paths two other types of crystallisation reactions occur the better known type occurs at the recrossing of the pelite h 2 o saturated solidus at shallower depth this can occur at mid crustal depths or much shallower at pressures lower than the appropriate invariant point which relates all of these reactions and will result in granitic pegmatites at the other type remaining mica can react with hydrous melt to generate anhydrous granulite with free h 2 o fluid such suprasolidus decompression dehydration reactions sddrs result in freezing of pelitic melts at mid crustal depth to k feldspar quartz assemblages and release of h 2 o which can induce h 2 o saturated melting in adjacent fertile lithologies lacking h 2 o e g psammite older granite distinct mineral proportions and textures will result from each reaction the actual reactions occurring are related through specific invariant points whose locations are known in the p t space the displacement of these invariant points due to additional components in the solid melt and fluid phases is reasonably well known the flat lying sddr very low d p d t will extend to much higher pressures if a low ah 2 o fluid is present sddr involving amphibole or epidote will occur in mafic to intermediate compositions over a large depth range depending on fe mg ca na etc of the rock compositions

theoretical phase relations involving cordierite and garnet revisited the influence of oxygen fugacity on the stability of sapphirine and spinel in the system mg fe al si o the theoreticalp t grid for stability relations of the phases cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and quartz qz of hensen 1971 has proved useful in the interpretation of metamorphic mineral assemblages formed at low oxygen fugacity both experimental data and evidence from natural rocks indicate that at high oxygen fugacity compatability relations change as a result of the enlargement of the stability field of spinel which causes a topological inversion and the stabilisation of the invariant points sa ga and cd this implies the stable existence of the univariant equilibria for f text o text 2 buffered conditions sp qz ga hy si o2 sa cd cd sp qz hy si o2 sa ga and sa sp qz hy si o2 ga cd and the divariant reaction sp qz hy si o2 sa ga cd these redox equilibria are restricted to conditions of high oxygen fugacity the proposed theoreticalp t grids for both low and high oxygen fugacity satisfactorily explain all experimental data and metamorphic mineral assemblages so far found in granulites

shrimp ionprobe dating of short lived proterozoic tectonic cycles in the northern arunta inlier central australia structural and metamorphic evidence from low p high t metamorphic terranes within the northern arunta inlier central australia indicates that two discrete tectonic cycles affected the region each cycle was associated with compressive deformation coincident with peak granulite facies metamorphism and granite intrusion shrimp u th pb analysis of zircons from early syn and late tectonic granitoids allows the age of the two tectonic cycles to be directly measured the age of the first cycle d1 is determined by emplacement of the mount stafford granite dated at or before 1818 15 ma after the first two foliations of the cycle had formed but before the axial plane cleavage associated with later upright folding the regional extent of this tectono magmatic event is confirmed by an emplacement age of 1818 8 ma measured on the large discordant harverson granite 40 km away the second cycle d2 consisted of four distinct deformation stages d2a 2d the ages of which are constrained by 1785 1775 ma old early syn and late tectonic granitoids the warimbi granite emplaced at or before 1785 22 ma and the granitic protolith to the napperby gneiss inferred to be 1780 10 ma pre date or formed during the earliest foliation s2a zircon considered to have grown at peak granulite facies metamorphic conditions during generation of the dominant s2b foliation gives an age of 1774 6 ma in the possum creek charnockite leucogranite in the napperby gneiss which post dates s2b and large scale upright nw se trending f2d folds yields an age of 1775 12 ma and confirms that the entire tectonic cycle d2a 2d formed in a rapid 10 ma period younger zircons which formed at 1659 6 ma in the napperby gneiss cannot be related to any local structural event but are similar in age to a major magmatic metamorphic episode in the southern arunta black and shaw 1992 150 km away they may be the peripheral manifestation of that event further zircon growth at 1600 ma in the napperby gneiss and possum creek charnockite was caused by hydrothermal fluid fluxing associated with post tectonic pegmatite emplacement these dykes were deformed by amphibolite facies retrograde shear zones ion probe dating of zircon stratigraphy from the granitoids has confirmed the discrete successive tectonic cycles identified by earlier structural and metamorphic studies for the northern arunta inlier at least those cycles or orogenies are associated with short lived 10 ma thermal pulses related to granite magmatism not prolonged thermal perturbations spanning 100 ma or more cf dirks and wilson 1990 dirks and hand 1991 such short lived pulses are intimately associated with granite intrusion and may be a general feature of low p high t metamorphism

phase relations of potassium bearing clinopyroxene in the system camgsi 2 o 6 kalsi 2 o 6 at 7 gpa the pseudo binary system camgsi2o6 kalsi2o6 modeling the potassium bearing clinopyroxene kcpx solid solution has been studied at 7 gpa and 1 100 1 650 c the kcpx is a liquidus phase of the system up to 60 mol of kalsi2o6 at higher content of kalsi2o6 in the system grossular rich garnet becomes a liquidus phase above 75 mol of kalsi2o6 in the system kcpx is unstable at the solidus as well and garnet coexists with kalsilite si wadeite and kyanite no coexistence of kcpx with kyanite was observed above the solidus kalsi2o6 content of the kcpx coexisting with melt increases with decreasing temperature near the solidus of the system about 1 250 c kcpx contains up to 5 6 wt of k2o i e about 22 26 mol of kalsi2o6 such high concentration of potassium in kcpx is presumably the maximal content of kalsi2o6 in the fe free clinopyroxene at 7 gpa in addition to the major substitution mgm1c 2 al 1k 2 the kcpx solid solution contains ca eskola and only minor ca tschermack components our experimental results indicate that the natural assemblage kcpx grossular rich garnet might be a product of crystallization of the ultra potassic sio2 rich alumino silicate mantle melts 200 km

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

geochemistry of pyroxene inclusions from the warrumbungle volcano new south wales australia pyroxenes provide an elegant key to understanding the tangled petrogenesis of the diverse midalkaline rocks of the warrumbungle volcano these rocks evolved from two primary magmas and the pyroxenes record the various stages in their origin and evolution trace element abundance patterns for chromian diopside crystals from a spinel lherzolite xenolith provide evidence of an early mantle depletion event depleted spinel lherzolite is an appropriate mantle source for the itep incompatible trace element poor series of rocks subcalcic augite megacrysts are common in the basic rocks of this series they crystallized in a high pressure intratelluric environment where they controlled the initial magmatic differentiation of the itep series aluminian augite occurs as megacrysts and also in gabbronorite xenoliths found in one of the more differentiated rocks of the itep series this pyroxene crystallized in a lower crustal magma chamber where its host magma was peraluminous and intermediate in composition a few clinopyroxene cpx megacrysts are fe rich and exceptionally enriched in rare earth elements ree they crystallized from a moderately differentiated magma locally contaminated by crustal material or were later subjected to a metasomatic event one of the nepheline normative basic rocks of the iter incompatible trace element rich series contains small inclusions of k rich omphacite this phase contains one of the highest k contents 0 6 2 3 wt ever reported in a cpx and crystallized from a k rich liquid at a greater depth than any of the other pyroxenes probably deep within the upper mantle orthopyroxene opx megacrysts are rare and belong to at least three geochemically distinct types in association with chromian diopside with subcalcic augite and with aluminian augite megacrysts each type of opx crystallized in a separate chemical and physical environment

age of the barramundi orogeny in northern australia by means of ion microprobe and conventional u pb zircon studies abstract u pb zircon geochronological studies are used to quantify the tectonostratigraphic history of a major crust forming event in early proterozoic terranes of northern australia magmatism and tectonic processes associated with this event the barramundi orogeny appear similar over very wide areas about one third of the australian continent the barramundi event marks the deformation metamorphism and cratonization of the earliest proterozoic 2 0 1 9 ga basinal successions and it was followed by and closely linked to extensive orogenic felsic magmatism the yaringa metamorphics are an inlier of paragneiss and schist that pre dates 1865 3 ma leichhardt felsic magmatism and younger basin formation in the mount isa inlier from an ion microprobe u pb zircon study of massive and migmatitic gneiss the time of yaringa metamorphism is established at 1890 8 ma recognized younger proterozoic deformations in the interval 1610 1550 ma are generally not evident in zircon u pb systems but have totally reset local rb sr whole rock values conventional u pb work on multi grain zircon samples of yaringa gneiss gives a geologically meaningless age 2090 40 ma that is an artifact of complex zircon growth part of which was initially inherited from a 2 55 to 2 2 ga provenance and the other major part of which was formed in situ during the 1890 ma high grade metamorphism predictably for simple zircon systems in low grade metavolcanic terranes conventional and ion microprobe zircon ages are in close agreement dating of volcaniclastic sequences above and below the barramundi tectonic break in the pine creek inlier brackets the orogeny in this terrane to a similar time frame 1885 1870 ma some zircons which crystallized at this time form selvedges around older cores whose age of 2100 2000 ma may be relics of an earlier deep crustal underplating the uniform chemistry of post barramundi felsic magmatism and the similar tectonic setting of the areally extensive barramundi event are mirrored by their temporal coherency cycles of geosynclinal deposition burial metamorphism and uplift took place during intervals of several million years or less implying comparable rates for early proterozoic orogenesis to those established for tertiary and quaternary settings

structural and metamorphic controls on the distribution of zircon in an evolving quartzofeldspathic migmatite an example from the reynolds range central australia three types of zircon occur in a complexly deformed and variably migmatized quartzofeldspathic gneiss from the reynolds range central australia the oldest type is inherited from the granitic precursor of the gneiss and is overgrown by a second group of zircon grains that formed during prograde granulite facies metamorphism partial melting of the gneiss resulted in solution of both the inherited and metamorphic zircon no new zircon growth accompanied crystallization of the partial melt suggesting loss of zirconium rich residual fluids hydrous amphibolite facies retrogression of the gneiss and its migmatized variants during late shearing produced new idiomorphic zircon in both the shear zone and its wall rocks important implications of this study are that i zircon has a tendency to dissolve if it comes into direct contact with a melt produced from anhydrous biotite breakdown in a quartzofeldspathic granulite ii melt crystallization is not necessarily accompanied by zircon growth and iii euhedral zircon can grow from a hydrous fluid phase under subsolidus amphibolite facies conditions e g within shear zones

crystal chemistry and evolution of the clinopyroxene in a suite of high pressure ultramafic nodules from the newer volcanics of victoria australia a clinopyroxene suite from lherzolite inclusions associated with the victorian australia newer volcanics has been investigated with the aim of understanding the clinopyroxene crystal chemical response to increasing temperature e g a melting model and or crystallization processes prevailing at high pressure

subduction of continental crust and terrigenous and pelagic sediments an experimental study abstract an important role for the recycling of terrigenous sediments in the mantle was proposed by armstrong 1 2 aspects of this hypothesis have been tested via an experimental study of phase equilibria in a composition similar to that of average upper continental crust over the pressure interval 6 24 gpa this composition is sufficiently close to those of the principal argillaceous and siliceous classes of pelagic sediments to use the results to interpret the behaviour of these latter sediments in addition to terrigenous sediments during subduction the subsolidus phase relationships displayed by lithologies derived from these materials are complex with major roles being played by k hollandite garnet na clinopyroxene and stishovite continentally derived lithologies achieve densities similar to or greater than surrounding mantle at depths greater than 200 km the geodynamical implications of these buoyancy relationships are discussed a reconnaissance study has also been made to assess the melting and element partitioning behaviours in the subducted continental crust lithologies during partial melting at relatively low pressures 5 10 gpa orthoclase wadeite and k hollandite are eliminated near the solidus whereas the stability field of na clinopyroxene extends to temperatures well above the solidus liquids formed by small to moderate degrees of partial melting of subducted continentally derived lithologies in this pressure interval have high k na ratios and high sio2 contents at higher pressures 16 24 gpa the stability fields of k hollandite and stishovite extend towards the liquidus whereas sodium bearing phases are eliminated much closer to the solidus resultant partial melts consequently possess relatively low k na ratios and sio2 contents lead possesses a high crystal liquid partition coefficient in k hollandite whereas uranium is excluded the broad stability field of k hollandite during partial melting of these lithologies at pressures above 15 gpa therefore has the capacity to cause fractionation of lead from uranium the petrological and geochemical implications of these results are discussed in the context of the partial melting of terrigenous materials during subduction and the interactions of the partial melts with the surrounding mantle

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

low pressure granulite facies metapelitic assemblages and corona textures from macrobertson land east antarctica the importance of fe2o3and tio2in accounting for spinel bearing assemblages low pressure granulite facies metasedimentary gneisses exposed in macrobertson land east antarctica include hercynitic spinel bearing metapelitic gneisses peak metamorphic mineral assemblages include spinel rutile ilmenite sillimanite garnet spinel ilmenite sillimanite garnet cordierite ortho pyroxene magnetite ilmenite garnet spinel cordierite biotite ilmenite and orthopyroxene cordierite biotite each with quartz k feldspar and melt the presence of garnet biotite and cordierite orthopyroxene bearing assemblages implies crossing tie lines in afm projection for the k2o feo mgo al2o3 sio2 h2o kfmash system this apparent contradiction and the presence of spinel rutile and ilmenite in the assemblages is acounted for by using the kfmash tio2 o2 system i e afm tio2 fe2o3 we derive a petrogenetic grid for this system applicable to low pressure granulite facies metamorphic conditions retrograde assemblages are interpreted from corona textures on hercynitic spinel and fe ti oxides the relative positions of the peak and retrograde metamorphic assemblages on the petrogenetic grid suggest that corona development occurred during essentially isobaric cooling

timing of proterozoic deformation and magmatism in a tectonically reworked orogen rayner complex colbeck archipelago east antarctica abstract the high grade metamorphic rocks of the colbeck archipelago comprise granulite facies metasedimentary gneisses and charnockitic gneisses of three ages a suite of rocks previously mapped as the colbeck gneiss is shown to be composite in age and origin consisting of metasedimentary and orthogneiss that are intruded by granitic gneiss and charnockitic gneiss an archaean granulite facies s1 gneissosity is preserved in the metasedimentary gneisses and early orthogneiss the development of s1 was followed by isobaric cooling from peak metamorphic conditions of t 750 c and p 5 1 0 8 kbar younger intrusions cut rocks containing s1 structures but were deformed by a 1200 ma granulite facies d2 event that resulted in reclined isoclinal f2 folds oriented parallel to a pervasive east trending l2 mineral and stretching lineation rocks bearing s2 structures are cut by the areally extensive 960 ma mawson charnockite which was affected by two upright folding events d3 and d4 at 920 ma events d2 4 comprise the proterozoic rayner structural episode which is characterized regionally by the retrogression of archaean assemblages the two pulses of extensive intermediate to felsic magmatism accompanied or immediately preceded the proterozoic orogenies evident as d2 4 and it is tempting to infer causal links however field relationships are consistent with intrusion having been contemporary with anomalously high conductive heat fluxes which could be due to advective heating from larger intrusions not exposed at the present structural level the formation of extensional granulite facies d5 ultramylonite pseudotachylite zones is the last deformation event in the area

some remarks on high temperature low pressure metamorphism in convergent orogens many high temperature low pressure high t low p metamorphic terranes show evidence for peak mineral growth during crustal thickening strain increments at pressures near the maximum attained during the heating cooling cycle such terranes are not readily explained as the conductive response to crustal thickening since the resulting moho temperatures would greatly exceed the crustal liquidus and because heating due to conductive equilibration on length scales appropriate to lithospheric scale strains must greatly outlast the deformation consequently high t low p metamorphism may be generated during crustal thickening only when significant heat is advected within the crust as for example may occur during the segregation of granitic melts we show that without the addition of asthenospheric melts and at strain rates appropriate to continental deformation the conditions required for significant lower crustal melting during deformation are only likely to be attained if heat flow into the lower crust during crustal thickening is increased substantially for example by removing the mantle part of the lithosphere a simple parameterization of lithospheric deformation involving the vertical strain on the scale of the crust c and the lithosphere 1 respectively allows the potential energy of the evolving orogen to be readily evaluated using this parameterization we show that an important isostatic consequence of the deformation geometries capable of generating such high t low p metamorphism during crustal thickening with c1 is an imposed upper limit to crustal thicknesses which is much lower than for homogeneous deformations fc f1 for the same initial lithospheric configuration

discrete proterozoic structural terranes associated with low p high t metamorphism anmatjira range arunta inlier central australia tectonic implications structural overprinting relationships indicate that two discrete terranes mt stafford and weldon occur in the anmatjira range northern arunta inlier central australia in the mt stafford terrane early recumbent structures associated with d1a 1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright km scale folds f1c which extend into areas of lower metamorphic grade structural relationships are simple in the low grade rocks but complex and variable in higher grade equivalents the three deformation events in the mt stafford terrane constitute the first tectonic cycle d1 d2 deformation in the weldon terrane comprises the second tectonic cycle the earliest foliation s2a was largely obliterated by the dominant reclined to recumbent mylonitic foliation s2b produced during progressive non coaxial deformation with local sheath folds and w to sw directed thrusts locally d2d tectonites have been rotated by n s trending upright f2c folds but the regional upright fold event f2d also evident in the adjacent reynolds range rotated earlier surfaces into shallow plunging nw se trending folds that dominate the regional outcrop pattern the terranes can be separated on structural metamorphic and isotopic criteria a high strain d2 mylonite zone produced during w to sw directed thrusting separates the weldon and mt stafford terranes 1820 ma megacrystic granites in the mt stafford terrane intruded high grade metamorphic rocks that had undergone d1a and d1b deformation but in turn were deformed by s1c which provides a minimum age limit for the first structural metamorphic event 1760 ma charnockites in the weldon terrane were emplaced post d2a and metamorphosed under granulite facies conditions during d2b constraining the second tectonic cycle to this period each terrane is associated with low p high t metamorphism characterized by anticlockwise p t t paths with the thermal peaks occurring before or very early in the tectonic cycle these relations are not compatible with continental style collision nor with extensional tectonics as the deformation was compressional the preferred model involves thickening of previously thinned lithosphere at a stage significantly after 50 ma the early extensional event compression was driven by external forces such as plate convergence but deformation was largely confined to and around composite granitoid sheets in the mid crust the sheets comprise up to 80 of the terranes and induced low p high t metamorphism including migmatization thereby markedly reducing the yield strength and accelerating deformation of the country rocks mid crustal ductile shearing and reclined to recumbent folding resulted followed by upright folding that extended beyond the thermal anomaly thus thermal softening induced by heat focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid crust localized around large granitoid intrusions

orogeny associated with anticlockwise p t t paths evidence from low p high t metamorphic terranes in the arunta inlier central australia low pressure high temperature metamorphic terranes from the proterozoic northern arunta inlier central australia are characterized by anticlockwise pressure temperature time paths the thermal peak was reached before or during the earliest folding and it was associated with abundant repeated intrusion of granite sheets we generalize our observations in the area to infer that low p high t metamorphism is induced principally by focusing of mid crustal heat from rapid repeated granite sheet intrusion which generates large metamorphic aureoles intrusion and associated metamorphism produce melting reactions which increase the fluid pressure and thermally soften the mid crust resulting in accelerated melt enhanced deformation shortening is accommodated generally by thrusting in the mid crust and by upright folding in the upper crust compression occurs during cooling of the terrane as indicated by near isobaric cooling paths and the preservation of upper crust sections the result is the production of discrete low p high t terranes that are localized around abundant granitoids show thin skinned deformation and have anticlockwise p t time paths continued granitoid intrusion produces posttectonic discordant plutons at high crustal levels within low p metamorphic belts

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

metamorphic evolution of the bunger hills east antarctica evidence for substantial post metamorphic peak compression with minimal cooling in a proterozoic orogenic event the bunger hills east antarctica experienced a low pressure granulite facies orogenic event during the proterozoic the stable coexistence of the s1 foliation parallel m1 assemblages garnet cordierite spinel ilmenite and garnet sillimanite spinel ilmenite rutile in quartz bearing pelitic gneisses is evidence for metamorphic peak pressures of around 4 kbar during m1 at temperatures of about 800 c the growth of massive reaction coronas of garnet and cordierite around hercynitic spinel and iron titanium oxides during m2 is evidence for the destabilization of the m1 assemblages during compression thermodynamic calculations on the m2 assemblages indicate formation pressures of 6 7 kbar at temperatures of about 750 c thus the gneisses from the bunger hills indicate about 2 kbar or more of compression during minimal cooling such a p t path is different from that of many other proterozoic terranes which are characterized by isobaric cooling or decompression a large charnockite body which is undeformed was intruded at 950 c towards the end of compression the low pressures during m1 can be best explained by metamorphism at mid crustal levels in thin continental crust in thin lithosphere above a thermal perturbation in the underlying asthenosphere we suggest that the compression during cooling was a result of gravitational backflow in which the action of body forces between adjacent normal thickness crust and the thin crust of the bunger hills is switched on by the thermal perturbation within such a model the timing of intrusion of the charnockite exposed in the bunger hills is consistent with its generation by partial melting during the metamorphic maximum of the lowermost crust

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

unconformity related rare earth element deposits a regional scale hydrothermal mineralization type of northern australia rare earth element ree orebodies are typically associated with alkaline igneous rocks or develop as placer or laterite deposits here we describe an economically important heavy h ree mineralization type that is entirely hydrothermal in origin with no demonstrable links to magmatism the mineralization occurs as numerous xenotime rich vein and breccia orebodies across a large area of northern australia but particularly close to a regional unconformity between archean metasedimentary rocks of the browns range metamorphics and overlying proterozoic sandstones of the birrindudu group the deposits formed at 1 65 to 1 61 ga along steeply dipping faults there is no known local igneous activity at this time depletion of hrees in the browns range metamorphics together with the similar nonradiogenic nd isotope composition of the orebodies and the browns range metamorphics indicates that ore metals were leached directly from the browns range metasedimentary rocks we propose an ore genesis model that involves fluid leaching hrees from the browns range metamorphics and subsequently mixing with p bearing acidic fluid from the overlying sandstones in fault zones near the unconformity the union of p and hrees via fluid mixing in a low ca environment triggered extensive xenotime precipitation this mineralization is unlike that of any other class of ree ore deposit but has a similar setting to unconformity related u deposits of australia and canada so we assign it the label unconformity related ree further discoveries of this ree mineralization type are expected near regional unconformities within proterozoic intracontinental sedimentary basins across the globe

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

comparing 1800 1600 ma accretionary and basin processes in australia and laurentia possible geographic connections in columbia abstract we focus on potential pinning points on the southern and eastern margins of australia and the southern and western margins of laurentia and interpret a convergent plate boundary along the southern margin of the proto australian continent during the palaeo to mesoproterozoic 1800 1600 ma specific geological events within the southern australian margin can be correlated with events preserved along the medicine bow yavapai mazatzal belt in southwestern laurentia these belts were characterised by southward continental growth with varying degrees of crustal reworking and accretion of juvenile material in australia crustal reworking appears to have been the dominant process from 1800 to 1670 ma with more juvenile material accreted at 1620 ma in contrast the southern laurentian terranes were dominated by accretion of juvenile material from 1800 to 1620 ma although reworked continental crust was also accreted to the margin in the interior of both continents basins developed with comparable histories from 1800 to 1670 ma thereafter the evolution of the interior basins diverged with sag phase processes dominant in northern australia and a protracted depositional hiatus in laurentia the geologic evolution is consistent with palaeomagnetic data and provides further evidence for geographic links between eastern australia and western laurentia from 1800 to 1600 ma

the age of the ormiston pound granite implications for mesoproterozoic evolution of the arunta inlier central australia the ormiston pound granite southern arunta inlier intruded during the terminal stages late to post d2 of a major n directed overthrust event called the chewings orogeny which deformed supracrustal rocks of the simpsons and chewings assemblages ion probe zircon u pb analysis of the granite indicates an emplacement age of 1603 10 ma more than 500 ma older than the rb sr isochron age timing of emplacement is confirmed by an age of 1575 20 ma for zircon mantles from a gneissic xenolith in the granite zircon cores from the xenolith yield an age of 1678 14 ma which is taken to represent the protolith age of the surrounding gneisses the shrimp age is similar to but more precise than the 1586 69 ma rb sr isochron age for the chewings orogeny determined by marjoribanks and black 1975 penecontemporaneous 1600 ma magmatism is evident as pegmatites and associated fluid flow zones in the anmatjira and reynolds ranges northern arunta inlier 1100 1030 ma rb sr mica ages from the 1600 ma ormiston pound granite coeval pegmatites and 1680 ma host rock gneisses are similar to a sm nd isochron age for the mafic stuart dyke swarm of the southern arunta inlier and the contemporaneous alcarra dyke swarm in the musgrave inlier some 500 km farther south the rb sr mica ages reflect isotopic resetting by a thermal perturbation either associated with regional crustal extension during 1080 ma dyke intrusion or with the 1150 ma magmatic event in the southern arunta cf black and shaw 1992 irrespective the 1050 900 ma ormiston event described by shaw et al 1984 as granite intrusion associated with high grade metamorphism migmatization and folding needs to be re defined or abandoned

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

characteristics of a kilometer scale high strain zone in the lower continental crust mt hay block central australia abstract a granulite facies high strain zone was studied on capricorn ridge part of the mt hay block granulites in the arunta inlier central australia deformation occurred in these primarily mafic composition granulites at lower crustal conditions 8 kb 800 c at 1740 1690 ma pervasive and consistently oriented foliation striking ssw and dipping steeply and lineations pitching steeply eastward occur within the shear zone the high strain zone is recognized by the presence of sl tectonites parallelism of grain shape fabrics and lithologic boundaries transposition of lithologic boundaries into parallelism with the foliation and the local occurrence of sheath like folds field based fabric mapping uses compositional foliation intensity as a proxy for finite strain to document strain variations within the capricorn ridge high strain zone there is no observed microstructural grain size reduction that corresponds to these strain variations fabric intensity increases from the centers of the major lithologic units towards the contacts 100 m scale strain localization within capricorn ridge occurs adjacent to major lithologic contacts indicating competency contrast during lower crustal deformation

mantle lower crust petrology from inclusions in basaltic rocks in eastern australia an outline abstract xenoliths megacrysts and xenocrysts of high pressure origin are abundant in post carboniferous alkali volcanics in eastern australia five xenolithic groups are recognized corresponding to episodes of metamorphism and partial melting metamorphic textured peridotites olivine fo 86 92 include ubiquitous spinel peridotites and rare garnet peridotites pyrope 72 75 of upper mantle origin metamorphic textured pyroxenites scattered in association with the metamorphic textured peridotites have patchy distribution and include intrusive and cumulate types hornblendites and diorites very localized include unique amphibole apatite rocks granulites and gabbros are widespread and include garnet scapolite granulites eclogites and charnockites and rarely associated corundum anorthoclasite and sanidinite this last group represents predominantly lower crustal material megacrysts and xenocrysts commonly accompany these xenoliths and include olivine orthopyroxene clinopyroxene spinels garnet amphibole ilmenite magnetites rutile apatite micas anorthoclase plagioclases sanidine corundum zircon and diamond the xenoliths demonstrate a complex series of exsolution recrystallization and mixing events in an inhomogeneous upper mantle which contains records of periodic activity over at least the last 2000 m y evidence from australian xenolith suites provides further insight into the structure rock relationships and events that have affected the upper mantle

the geological evolution of the reynolds range central australia evidence for three distinct structural metamorphic cycles the reynolds range is affected by three distinct structural metamorphic cycles di mi dii mii anddiii miii which represent the local expressions of a series of orogenic events that affected large sections of the arunta block central australia the tectonic cycles recognized in the reynolds range correlate extremely well with similar events in the nearby anmatjira range di mi took place around 1820 ma and only affected the nw reynolds range dii mii occurred between 1760 and 1650 ma and involved ne sw shortening with identical timing relationships between the deformations and metamorphism along the entire reynolds range dii commenced with the formation of a fabric sii1 preserved as inclusion trails in porphyroblasts sii1 formed early during a progressive event dii1 2 which involved the formation and tightening of upright nw se trending isoclinal folds a penetrative subvertical nw se trending fabric sii2 developed axial planar to these folds the general symmetry of dii2 microstructures suggests that fii2 folds were formed during progressive coaxial deformation under plane strain conditions dii3 structures are associated with conjugate sets of crenulation bands within the macroscopic crenulation bands large sections of earlier folds and fabrics are rotated to a near recumbent position the dominant set of crenulation bands is upright and trends ene wsw while the conjugate to this set trends nw se no penetrative fabric formed during dii3 dii4 is associated with a system of amphibolite grade ne dipping thrusts interconnected by numerous smaller shear zones the sense of movement is ne over sw during dii essentially penetrative coaxial deformation dii2 evolved into essentially localized non coaxial deformation dii3 dii4 dii deformation occurred concomitant with a low pressure granulite facies metamorphic event mii 1730 ma peak metamorphic sillimanite cordierite orthopyroxene ilmenite spinel garnet k feldspar quartz assemblages define sii2 oriented sillimanite biotite assemblages that formed early during dii3 and unoriented andalusite chlorite muscovite assemblages that formed late during dii3 indicate that cooling of mii was initially isobaric during dii4 thrusting staurolite garnet biotite quartz and biotite kyanite quartz assemblages defining the mylonitic fabric overprint the late dii3 andalusite assemblages dii4 shear movement is therefore accompanied by a slight rise in pressure dii4 shear zones gradually increase in grade eastward along the reynolds range this trend coincides with the variation in peak metamorphic grade attained during mii indicating that the rocks had not yet fully cooled when dii4 thrusting commenced diii miii is late devonian to carboniferous in age and caused minor differential movement 100 m and retrogression along dii4 shear zones

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

compositional variations major and trace elements of clinopyroxene and ti andradite from pyroxenite ijolite and nepheline syenite alno island sweden compositional variations major and trace elements of clinopyroxene and ti andradite from pyroxenite ijolite and nepheline syenite alno island sweden

thermal buffering effects at the solidus implications for the equilibration of partially melted metamorphic rocks abstract a simple thermal model is used to investigate to what extent buffering effects of latent heat of fusion may prolong the thermal evolution of a one dimensional statically cooling partially or completely melted heat source for a melting model appropriate for crustal rocks the time of cooling of rocks through the solidus may be about tripled by this process depending on the melting model cooling may halt completely near the solidus for time spans comparable to the thermal time constant of the heat source in order to test the influence of this buffering effect on the equilibration of partially melted metamorphic rocks these thermal model results are coupled with a simple diffusion model that relates the degree of equilibration of a simple assemblage to temperature and cooling rate it is shown that for a broad range of initial heat source temperatures freezing of selected mineral equilibria may occur in a comparably narrow temperature range at and around the solidus the calculations may have some relevance to low p high t metamorphic terranes in as much as they may provide an explanation for the widely observed equilibration and partial re equilibration of rocks near the crystallisation temperatures of partial melts

silicic magmas from the continental cameroon volcanic line oku bambouto and ngaoundere 40 ar 39 ar dates petrology sr nd o isotopes and their petrogenetic significance the intraplate cameroon volcanic line cvl straddles the african south atlantic continent ocean boundary and is composed mainly of alkaline basic volcanic rocks voluminous silicic volcanics characterize the continental sector of the cvl we present here new geochemical isotopic sr nd o and 40ar 39ar geochronological data on the main silicic volcanic centres of the western mt oku sabga and mt bambouto and eastern ngaoundere plateau cameroon highlands the silicic volcanism of mt oku sabga and mt bambouto occurred between 25 and 15 ma and is represented by voluminous quartz normative trachytes and minor rhyolitic ignimbrites at mt bambouto central volcano about 700 m of silicic volcanics erupted in less than 2 7 million years these silicic volcanics are associated with slightly to moderately alkaline basalts and minor basanites in general onset of the silicic volcanism migrated from ne oku 25 ma to sw sabga 23 ma bambouto 18 ma and mt manengouba 12 ma the silicic volcanism of the ngaoundere plateau eastern branch of the cvl is instead dominated by nepheline normative trachytes which are associated with strongly alkaline basalts and basanitic rocks these ne trachytes are younger 11 9 ma than the q trachytes of the western highlands the least differentiated silicic volcanics are isotopically similar 87sr 86sr 0 51278 to the associated alkaline basalts suggesting differentiation processes without appreciable interaction with crustal materials such interactions may however have played some role in the genesis of the most evolved silicic volcanics which have 87sr 86sr as high as 0 705 0 714 fractional crystallization is the preferred mechanism for genesis of the silicic melts of both western and eastern highlands as shown by modeling major and trace element variations the genesis of the least evolved q trachytes from the western highlands starting from slightly to moderately alkaline basalts is compatible with fractionation of dominantly plagioclase clinopyroxene and magnetite crystal fractionation may have occurred at low pressure and at qfm buffer f o2conditions parental magmas of the ngaoundere ne trachytes are likely instead to have been strongly alkaline basalts which evolved through crystal fractionation at higher p 6 2 kbar and f o2 qfm 2 the migration 25 to 12 ma of the silicic volcanism from ne to sw in the continental sector of the cvl is reminiscent of that 31 5 ma of the onset of the basic volcanism in the oceanic sector principe to pagalu islands of the cvl these ages and that 11 9 ma of the silicic volcanism of the ngaoundere plateau indicate that the cameroon volcanic line as a whole may not be easily interpreted as the surface expression of hot spot magmatism

nd isotope study of granites from the arunta inlier central australia constraints on geological models and limitation of the method abstract three chemically distinct types of granite high sr low y calc alkaline palaeoproterozoic normal and enriched are present in the palaeoproterozoic arunta inlier of central australia twenty one representative samples were selected for nd isotopic analysis to complement geological and geochemical data most samples analysed have depleted mantle nd isotope model ages tdm following mcculloch 1987 of 2 3 to 2 1 ga similar to most of palaeoproterozoic granites of northern australia mcculloch 1987 these ages do not show a younging trend from the northern to southern provinces although some post 1750 ma granites from the central and southern provinces with typical felsic crust 147 sm 144 nd ratios 0 09 0 11 have younger model ages less than 2 0 ga post 1700 ma normal type granites from the southern province have chemical compositions similar to older granites 1880 1760 ma of the same suite even though they have younger model ages 1960 1930 ma this implies an increase in a younger component within southern source regions through melting of new underplate and or additional mantle input the syn or post tectonic granites 1720 1140 ma of the enriched type high heat producing granites rich in th u and k have similar tdm model ages to older granites of the normal type from the same areas the enriched type granite from the teapot granite complex of the southern province are characterised by low cs sr and high rb cs 30 50 th u 7 20 ratios and high y contents these chemical characteristics are consistent with magma being formed through anatexis of normal type granite sources in contrast an 1820 ma s type granite from the harverson suite in the northern province has an older tdm model age 2 32 ga than the tdm 2 18 ga age of the nearby aileron metamorphics suggesting that the source rock of the granite may contain a significant archaean component the nd isotope data when integrated with geological and chemical information are compatible with the recycling of archaean crustal material such a process might have taken place very early in the history of the arunta inlier through subduction along a continental margin made up of a stretched dismembered thin archaean basement magmatic underplating may have taken place shortly before 1850 ma and continued episodically during subsequent tectono thermal events crustal melts of mixed source rocks formed during these events could contain different amounts of an archaean component

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

prediction of tropical cyclogenesis using scatterometer data in the present work a new technique based on the data mining approach has been discussed for the prediction of tropical cyclogenesis using the ocean wind vectors derived from the sea winds scatterometer on quikscat satellite the technique is based on similarity of given wind pattern with wind vector signatures of developing systems available from the past observations a database has been formed in this work using the quikscat observed vector wind patterns associated with the early stages of tropical cyclones that developed in the north indian basin during the years 2000 2008 the prediction of possibility of cyclogenesis in a given scene is determined by matching it with all the archived scenes in a database using vector block matching algorithm the system is predicted as developing if its matching index exceeds the predetermined threshold value 0 5 the prediction of cyclo genesis can be made 24 96 h prior to its classification as a tropical storm by the joint typhoon warning centre the probability of detection of the technique is determined using the equivalent of the jackknife approach in the database as 0 93 the algorithm is tested with a continuous wind data of years 2007 2009 for active cyclone months excluding the scenes archived in a database all the 14 tropical disturbances that developed into tropical storms during the test period were predicted using the discussed method and two false alarms were found

hercynite as the product of staurolite decomposition in the contact aureole of vedrette di ries eastern alps italy metapelitic hornfelses in the contact aureole of the vedrette di ries pluton exhibit the terminal decomposition of zn poor fe staurolite in a muscovite quartz free domain the reaction takes place only within coarsegrained sillimanite that has replaced andalusite porphyroblasts during prograde metamorphism the product is a gahnite poor hercynitic spinel which occurs as very small grains closely associated in space with resorbed staurolite microstructural observations indicate that bereynite growth postdates the pseudomorphs of sillimanite after andalusite the textural evidence for a genetic relationship between hercynite and staurolite is confirmed by the identical fe mg zn ratios of the two minerals which causes the collinearity of hercynite staurolite and al2sio5 in feo mgo zno al2o3 sio2 h2o composition space fmzash and indicates hercynite formed by the reaction fe staurolite 3 85hercynite 5 1sillimanite 2 55quartz 2h2o staurolite inclusions within andalusite did not break down to form hercynite indicating a kinetic control as well as little overstepping of the equilibrium conditions of the reaction forming hercynite assuming overstepping did not occur modelling of the reaction with existing thermodynamic data in the simplified fash system suggests that the terminal breakdown of staurolite to form hercynite occurred at 2 5 3 75kbar and 585 655 c

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

age geological setting and paragenesis of heavy rare earth element mineralization of the tanami region western australia metasedimentary rock hosted heavy rare earth element hree mineralization occurs as numerous orebodies distributed across a large district of the tanami region of central australia close to a regional unconformity between archean metasedimentary rocks of the browns range metamorphics brm and overlying proterozoic birrindudu group sandstones the orebodies consist predominantly of quartz xenotime and minor florencite and occur along steeply dipping structures within a stockwork of hydrothermal veins and breccias paragenetic stages of the mineralization include 1 a pre ore stage of a greenschist facies overprint of detrital minerals including quartz alkali feldspar plagioclase and muscovite aligned in the premineralization foliation 2 syn ore quartz and white mica alteration associated with a multistage mineralization of the ore minerals primarily in breccias and veins and 3 a post ore stage of veining and brecciation forming several generations of quartz plus hematite barite anhydrite and pyrite in situ u pb dating of xenotime from several deposits prospects yielded an age range for mineralization of 1 65 to 1 60 ga this timeframe lacks local magmatism or orogeny and is significantly younger than the ca 1 72 ga 40ar 39ar age of the pre ore muscovite far field stresses associated with the distal isan and liebig orogenies are invoked as drivers of large scale fluid flow and fault re activation in the region we propose that ore formation was achieved via fluid leaching of ree from the brm followed by fluid mixing in fault zones especially in the vicinity of the unconformity between the brm and overlying birrindudu group sandstones this mineralization style shares many features with unconformity related u deposits and there is significant potential for discovery of further ree orebodies of this style especially in the vicinity of regional unconformities in intercontinental sedimentary basins

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

isobaric cooling of proterozoic high temperature metamorphites in the northern arunta block central australia implications for tectonic evolution abstract protoliths of metamorphites in the proterozoic reynolds range region northern arunta block central australia included mafic and felsic igneous rocks pelites calcareous rocks and quartzites metamorphism began with an early high t low p facies stage followed by early rehydration in higher grade areas isobaric cooling and late high t low p facies hydration in and near shear zones metamorphic grade increases southeastwards shown by the change from andalusite in metapelites in the northwest to sillimanite in the southeast and by the incoming of cordierite cordierite biotite cordierite k feldspar sillimanite and cordierite garnet migmatites kornerupine quartz spinel and orthopyroxene k feldspar assemblages occur in the highest grade rocks downwarping at near peak temperatures is shown by garnet sillimanite replacing cordierite and by sillimanite pseudomorphing andalusite early in the near isobaric cooling that followed peak temperatures freezing of partial melts released water and biotite formed the hydrated retrograde assemblages formed after temperatures had fallen considerably are also zoned from northwest to southeast with andalusite sillimanite or kyanite bearing assemblages developed in appropriate bulk compositions the early high t metamorphism is best explained by tectonic models based on extension crustal delamination and underplating the hydration and deformation were caused by processes unrelated to the early history occurring at least 200 ma later possibly as late as the mid palaeozoic

satellite data analysis and numerical simulation of tropical cyclone formation 1 forecast of tropical cyclone tc formation has long been a great challenge owing to lack of reliable observations over vast open oceans recent satellite products provide a unique opportunity to reveal detailed atmospheric wave structures prior to tc formation using the quikscat surface wind and the tropical rainfall measurement mission microwave image data we document temporal and spatial structures of rossby wave trains induced by energy dispersion from a pre existing tc and easterly wave propagation characteristics prior to cyclogenesis in the western north pacific using a baroclinic model we further simulate cyclogenesis processes associated with the tc energy dispersion and easterly waves

monazite as a monitor for melt rock interaction during cooling and exhumation alexander m prent andreas beinlich laura j morrissey tom raimondo chris clark andrew putnis