rare earth elements systematics of west shasta metavolcanic rocks petrogenesis and hydrothermal alteration west shasta district bimodal volcanics copley greenstone and balaklala rhyolite are members of a low k calc alkaline suite they have rare earth element distributions characterized by pronounced light rare earth element depletion and unfractionated heavy rare earth elements the striking similarities of the rare earth element patterns between the two compositions suggest derivation by partial melting of the same previously depleted source region in the devonian upper mantle or lower crust these sources are even more depleted in incompatible elements than the sources for similar low k suites in the southwest pacific and caribbean the basic volcanics appear to be similar to low ti normal or i type midocean ridge basalts clinopyroxene wo 42 en 51 fs 7 now partially altered to chlorite mg mg fe 0 73 0 95 was the apparent high pressure liquidus phase in the basalts the absence of an eu anomaly indicates that the source had no intrinsic anomaly and that no significant low pressure fractionation of plagioclase took place prior to or during the emplacement of the andesitic lavas the balaklala extrusions have a pronounced negative eu anomaly whereas the intrusive coeval mule mountain trondhjemite does not consequently the anomaly in the balaklala could not be inherited from the source region but must instead reflect the fractionation of plagioclase in shallow magma chambers prior to eruption hydrothermal fluids associated with the formation of volcanogenic massive sulfide deposits have modified the rare earth patterns of the acid extrusions in the immediate vicinity of apparent feeder systems indicated by the presence of stockworks europium has been selectively mobilized probably as a consequence of reduction to the divalent state and deposited around the vents the light rare earth elements have as a group been selectively extracted by the hydrothermal fluids resulting in their severe depletion relative to the heavy rare earth elements oxygen isotope signatures are dominated by regional low to moderate temperature exchanges with seawater copley greenstone delta 18 o values reflect the opposing effects of chloritization decreasing delta 18 o and albitization increasing delta 18 o the balaklala rhyolite tends to be enriched in 18 o relative to the copley greenstone due to a higher content of quartz hydrogen isotopes show the regional effects of chloritization light hydrogen except in the immediate area of hydrothermal vents where a pronounced increase in delta d is observed the increase in delta d is a consequence of the formation of coarse muscovite in the altered vent rocks

a new indicator of movement direction during orogenesis measurement technique and application to the alps the orientation of axes of sigmoidal staircase or spiral inclusion trails within porphyroblasts provides an indicator of the direction of movement during deformation that is synchronous with metamorphism a simple technique is presented in detail to find this axis in 3d by radially sectioning a horizontal slab cut from an oriented sample when viewed from one direction the switch in asymmetry of the porphyroblast inclusion trails in these sections defines the trend of the axis further radial sectioning of a vertical slab cut parallel to this trend determines the plunge of this axis this technique is independent of the model adopted for the formation of sigmoidal or spiral shaped inclusion trails and can be used to evaluate the mechanism by which they form it can also be used to evaluate theories of folding and orogenesis measurements of spiral and sigmoid axes in garnet porphyroblasts from the european alps show that they reflect the movement of the african plate relative to europe better than linear indicators preserved within the same rocks

3 μm spectrophotometric survey of m and e class asteroids many asteroids show absorption features diagnostic of hydrated minerals in the 3 m region of the spectrum reflectance studies in this region can determine the hydration state of surface minerals and by inference the thermal histories of bodies we have made spectrophotometric observations of eight e class m class x class and p class asteroids in december 1991 and eight e class and m class asteroids in august 1993 using the infrared telescope facility on mauna kea hawaii in 1991 we discovered a 3 m absorption band on the e class asteroid 44 nysa and the p class asteroid 50 virginia and found a possible absorption on the e class asteroid 64 angelina we confirmed the presence of a 3 m absorption band on 44 nysa and on the m class asteroid 92 undina t d jones et al 1990 icarus 88 172 192 and detected this feature on the m class asteroid 201 penelope in 1993 these data demonstrate that high albedo and medium albedo objects such as e and m class asteroids can be hydrated and need not be interpreted as primarily of igneous origin we revise the interpreted mineralogy of some e and m class asteroids as a result

nd isotopic and geochemical constraints on provenance of sedimentary rocks in the eastern officer basin australia implications for the duration of the intracratonic petermann orogeny sm nd isotopic and geochemical data from neoproterozoic to cambrian sedimentary rocks in the intracratonic eastern officer basin in central australia highlight the evolving provenance roles of the basement complexes that underlie and bound the basin initial e nd values of around 12 for the basal units indicate that both were largely derived from the late archaean to mesoproterozoic gawler craton which bounds the basin to the south at c 720 ma an influx of juvenile glacially derived sediment indicates partial uplift of the mesoproterozoic musgrave block along the basin9s northern margin in a regime interpreted to be broadly extensional at around 600 ma synchronous with the development of a foreland architecture there was a large influx of musgrave block derived sediments this is interpreted to mark the onset of the intracratonic petermann orogeny which was a long lived event or series of events spanning more than 70 ma subsequent to c 600 ma the nd isotopic composition of sequences within the officer basin indicates an increasing contribution from the gawler craton despite up to 45 km of denudation of part of the musgrave block this suggests that the majority of sediment derived from the petermann orogen bypassed the eastern officer basin for much of the history of the petermann orogeny

radar observations of asteroid 216 kleopatra radar observations of the main belt m class asteroid 216 kleopatra reveal a dumbbell shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers 25 the asteroid9s surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of lunar soil kleopatra9s shape is probably the outcome of an exotic sequence of collisional events and much of its interior may have an unconsolidated rubble pile structure

the deep layers of a paleozoic arc geochemistry of the copley balaklala series northern california abstract ree zr nb concentrations and sr nd isotope compositions have been measured in copley basalts and andesites balaklala rhyolites and mule mountain trondhjemites northern california which represent the deep layers of a well preserved intra oceanic island arc of siluro devonian age 87sr 86sr is shifted towards high values up to 0 707 whereas ce is preferentially removed from rhyolites a large proportion of the analyzed samples including some acidic rocks shows a pronounced depletion in light ree the end t values of most copley balaklala and mule mountain rocks fall in the range 6 to 8 which suggests that they originated from a normal morb type source end t 9 contaminated with either sediments or an oib type component in modern island arcs only the shallow levels are accessible comparison with the copley balaklala mule mountain series suggests that at depth an immature island arc is likely to comprise thick layers of lile depleted tholeiites and rhyolites intensely altered by pervasive circulation of seawater least square solutions of trace element models suggest that rhyolites and trondhjemites represent remelting of mafic volcanics from the arc basement rather than residual melts of basalt andesite differentiation

rare earth element mobility at constant inter ree ratios in the alteration zone at the phelps dodge massive sulphide deposit matagami quebec rare earth elements ree from la to ho were mobile and enriched in hydrothermally altered rocks below the archean phelps dodge cu zn volcanogenic massive sulphide deposit in northwestern quebec largest net enrichment was in the moderately altered quartz chlorite zone where la concentration increased six fold and lanybn steepened from 1 9 to 13 0 the intensely altered chloritite zone had both minor net ree enrichment and depletion yb and lu were immobile throughout both zones the mobile ree were added and subtracted in constant chondrite normalized inter ree proportions 1 0 la 0 79 ce 0 57 nd 0 49 sm 0 01 eu 0 10 tb and 0 02 hb small additions of eu relative to generally larger additions of lree and tb produced enhanced negative eu anomalies the ree were mobilized at the hot 300 c core of the alteration system and deposited at the cooler periphery other sites of intense alteration and water rock interaction display similar ree changes indicating that selective ree enrichment at constant inter ree ratios is a widespread phenomenon

trace and rare earth element geochemistry in tourmaline and cassiterite from the yunlong tin deposit yunnan china implication for migmatitic hydrothermal fluid evolution and ore genesis abstract yunlong tin deposit is a medial sized hydrothermal deposit in western yunnan province of china this deposit is unusual because the tin mineralization occurs exclusively within the migmatite bodies the genesis of the ore deposit has been hotly debated and various models have been proposed including granite related magmatic hydrothermal and migmatitic hydrothermal origins this paper reports a systematic trace and rare earth elements ree geochemical study in tourmaline and cassiterite from the orebodies and associated migmatites from the yunlong tin deposit tourmaline and cassiterite from this deposit show light ree lree enriched patterns with variable eu and ce anomalies consistent with hydrothermal fluids being derived from local high grade metamorphism and migmatization the data suggest that tourmaline and cassiterite were likely precipitated from migmatitic hydrothermal fluids and indicate that the yunlong tin deposit was probably formed during migmatitic hydrothermal process the high concentrations of transition metals e g sc ti v cr mn and zn in tourmalines are also consistent with this model the high concentrations of sn sr and especially sc v and cr in tourmalines can be used to discriminate tourmaline from barren deposits relative to those associated with economic tin mineralization

development of the australian proterozoic crust as inferred from gravity and magnetic anomalies abstract gravity anomalies in australia have been used to map trends within basement blocks to map the margins of the blocks and to determine the relative ages of the blocks the inferred pattern of continental growth is consistent with that found by isotopic dating and from exposed geology the ages of cratonization of the total area of land basement are 18 archaean 53 proterozoic and 29 phanerozoic exposed basement generally has higher gravity variability than basement overlain by cover sediments the higher gravity variability is due to alternating bands of granite volcanics and the relative uplift and exposure is attributed to associated crustal underplating proterozoic crustal reworking takes several forms parts of archaean blocks were remobilized by extensive proterozoic metamorphism young blocks cratonized against older blocks caused reworking at least 50 km into the older blocks crustal rifts over 700 km long and 70 300 km wide were formed simple rifting resulted in crustal attenuation and sedimentation while more complex rifting resulted in the introduction of new igneous material and reworking of the older crustal material

sources of metals in the porgera gold deposit papua new guinea evidence from alteration isotope and noble metal geochemistry the porgera gold deposit is spatially and temporally associated with the late miocene mafic alkalic epizonal porgera intrusive complex pic located in the highlands of papua new guinea png the highlands region marks the site of a tertiary age continent island arc collision zone located on the northeastern edge of the australasian craton the pic was emplaced within continental crust near the lagaip fault zone which represents an oligocene suture between the craton and volcano sedimentary rocks of the sepik terrane magmatism at porgera probably occurred in response to the late miocene elimination of an oceanic microplate and subsequent early pliocene collision between the craton margin and an arc system located on the bismarck sea plate gold mineralization occurred within 1 ma of the time of magmatism metasomatism accompanying early disseminated au mineralization in igneous host rocks resulted in additions of k rb mn s and co2 and depletions of fe mg ca na ba and sr rare earth and high field strength elements remained largely immobile pervasive development of illite k feldspar quartz carbonate alteration assemblages suggests alteration by mildly acidic 200 to 350 c fluids at high water rock ratios strontium and lead isotopic compositions of minerals from early base metal sulphide veins associated with k metasomatism and later quartz roscoelite veins carrying abundant free gold and tellurides are remarkably uniform e g 87sr86sr 0 70745 0 00044 n 10 207pb204pb 15 603 0 004 n 15 these compositions fall between those of unaltered igneous and sedimentary host rocks and specifically sedimentary rocks from the jurassic om formation which underlies the deposit igneous rocks 87sr86sr 0 7035 207pb204pb 15 560 om formation 87sr86sr t 0 7153 207pb204pb 15 636 it is therefore suggested that the hydrothermal fluids acquired their sr and pb isotopic signatures by interaction with or direct derivation from a plutonic root of the pic and host sedimentary rocks of the om formation it is likely that au was also derived from one or both of these two sources concentrations of au in unaltered igneous and sedimentary rocks from porgera 10 ppb au do not indicate that either lithology represents a significantly enriched protore although au and platinum group element pge abundances in the igneous rocks suggest a mild primary magmatic enrichment of au relative to the pge average au pt pd mantlenormalized 14 0 6 5 n 8 evidence that the porgera magmas were rich in volatiles permits speculation that au may have been concentrated in a magmatic fluid phase but alternative possibilities such as derivation of au by hydrothermal leaching of solidified igneous materials or sedimentary rocks cannot be excluded at this time

distinguishing and correlating multiple phases of metamorphism across a multiply deformed region using the axes of spiral staircase and sigmoidal inclusion trails in garnet schists from the appalachian orogen in south east vermont have undergone multiple phases of garnet growth these phases can be distinguished by the trend and relative timing of foliation inflexion or intersection axes fias of foliations preserved as inclusion trails in garnet porphyroblasts the relative timing of different generations of fias is determined from samples containing porphyroblasts with two or three differently trending fias developed outwards from core to rim multi fia porphyroblasts schists from south east vermont show a consistent pattern of relative clockwise rotation of fia trends from oldest to youngest four populations or sets of fias can be distinguished on the basis of their relative timings and trends from oldest to youngest the four sets have modal peaks trending sw ne w e nnw sse and ssw nne these peaks show that each of the four fia sets has a statistically consistent trend at all scales across a 35 125 km area containing numerous mesoscopic and macroscopic folds the fias of set 4 are defined by inclusion trails that are continuous with matrix foliations have trends subparallel to most folds and are inferred to have developed contemporaneously with these structures conversely sets 1 to 3 are oblique to and pre date most matrix foliations and folds all four fia sets occur in siluro devonian rocks and must have formed in the acadian orogeny the lack of statistically significant differences in the distribution of fia trends across the study area and their consistent relative timings in multi fia porphyroblasts despite a complex regional deformation history involving numerous phases of folding at all scales suggest the porphyroblasts have not rotated relative to one another the change in fia trend with time resulted from rotation of the kinematic reference frame of bulk flow possibly as a consequence of the reorganization of lithospheric plates responsible for acadian orogenesis recognition of distinct generations of fias provides a means of distinguishing different phases of porphyroblast growth four periods of garnet porphyroblast growth occurred in the schists of south east vermont this growth was heterogeneously distributed on the cm2 m2 scale no single porphyroblast records all stages of growth and adjacent samples from the same or dissimilar rock types commonly contain porphyroblasts that preserve different sequences of growth factors that may have been responsible for switching porphyroblast growth on and off at this scale include i subtle differences in bulk chemical composition ii oscillating levels of heat owing to the buffering effect of endothermic garnet forming reactions iii channelized infiltration of fluids with localized fluid buffering of bulk composition and iv cyclic controls on the rates of diffusion and material transport of reactants either by channelized fluid flow or by a changing pattern of microfracturing during foliation development consistency in fia trend and relative timing provide a new method for potentially distinguishing and correlating successive metamorphic events or even phases of metamorphism within a progressive tectonothermal event along and across orogens using a consistent pattern of core to rim changes in fia trend multiple phases of growth of a single porphyroblastic mineral can be quantitatively distinguished allowing correlation of different phases of growth around and across macroscopic folds the relative timing of growth of different porphyroblastic minerals can also be quantitatively determined using fia data and correlated around and across macroscopic folds conceptually the paragenetic history preserved in each generation of porphyroblast growth in the form of chemical zoning and the minerals in inclusion trails could be combined to produce a more detailed p t t deformation path than previously determined

the significance of e w structural trends for the alice springs orogeny in the charters towers province north queensland e w structural and igneous trends in the charters towers province are highly anomalous within the overall n s trending tasman orogen of eastern australia and resulted from a sequence of n s shortening events a succession of e w trending fias foliation intersection inflexion axis preserved within porphyroblasts dated at 474 7 7 2 413 13 and 381 1 8 1 ma correspond with adjacent granite crystallization ages and e w trending fia ages in the greenvale province to the nw the magnetic anomaly map of australia reveals that this e w trending portion of the tasman orogen links with and truncates several earlier formed orogens the e w trend of the charters towers province resulted from overprinting of early palaeozoic n s trending structures in the tasman orogen by younger e w ones during the alice springs orogeny 450 300 ma resolving the e w pluton shape and distribution of cambrian to devonian magmatic activity plus the truncational nature of aeromagnetic data from central australia to the east coast

u pb single zircon pb evaporation and sm nd isotopic study of a granulite domain in se madagascar madagascar is a poorly known precambrian domain at the eastern border of the mozambique belt strongly affected by the pan african orogeny this large island represents a key part of gondwanaland and the accurate dating of the major metamorphic event is critical for the reconstruction of that supercontinent in the southeastern zone of the island metamorphism has reached high temperature and low pressure conditions 850 c and 5 kbar with moderate retrogression a u pb conventional multigrain single zircon stepwise pb evaporation and sm nd geochronological study on meta felsic rocks has shown that basement of at least lower proterozoic age was strongly metamorphosed around 570 580 ma this tectometamorphic event nearly obliterated any pre pan african zircon isotopic memory the granulite facies metamorphism is associated with the syn metamorphic emplacement of the anosyan charnock ites and granites a strong channelized fluid contribution at 545 ma has produced the re crystallization of biotite apatite

the m x asteroid menagerie results of an nir spectral survey of 45 main belt asteroids abstract diagnostic mineral absorption features for pyroxene s olivine phyllosilicates and hydroxides have been detected in the near infrared nir approximately 0 75 2 50 m spectra for 60 of the tholen classified tholen 1984 1989 m x asteroids observed in this study nineteen asteroids 42 exhibit weak band i approximately 0 9 m band ii approximately 1 9 m absorptions three asteroids 7 exhibit a weak band i approximately 1 05 1 08 m olivine absorption four asteroids 9 display multiple absorptions suggesting phyllosilicate oxide hydroxide minerals one 1 asteroid exhibits an s asteroid type nir spectrum and 18 asteroids 40 are spectrally featureless in the nir but have widely varying slopes tholen m asteroids are defined as asteroids exhibiting featureless visible wavelength spectra with moderate albedos tholen 1989 tholen x asteroids are also defined using the same spectral criterion but without albedo information previous work has suggested spectral and mineralogical diversity in the m asteroid population rivkin et al 1995 2000 busarev 2002 clark et al 2004 hardersen et al 2005 birlan et al 2007 ockert bell et al 2008 2010 shepard et al 2008 2010 fornasier et al 2010 the pyroxene bearing asteroids are dominated by orthopyroxene with several likely to include higher ca clinopyroxene components potential meteorite analogs include mesosiderites cb ch chondrites and silicate bearing nife meteorites the eos family olivine bearing asteroids are most consistent with a co chondrite analog the aqueously altered asteroids display multiple weak absorptions 0 85 0 92 0 97 1 10 1 40 and 2 30 2 50 m indicative of phyllosilicate hydroxide minerals the spectrally featureless asteroids range from metal rich to metal poor with meteorite analogs including nife meteorites enstatite chondrites and stony iron meteorites

ore controls in the charters towers goldfield ne australia constraints from geological geophysical and numerical analyses the approach taken in this paper namely synthesising a wealth of previous information with new data and a genetic model in combination with integrated numerical analyses led to new insights into the geological controls on the localisation of auriferous veins and residual prospectivity of the charters towers goldfield ne australia the method also has implications for the assessment of other mature goldfields worldwide despite a number of different ore controls having operated within the charters towers goldfield the controlling factors can be linked to a single genetic model for orogenic granitoid hosted lode gold mineralisation in a brittle deformation regime d4 of ne sw to nne ssw shortening under conditions of supralithostatic fluid pressure and low stress difference spatial autocorrelation results suggest district scale alignment of the auriferous veins parallel to and overlapping with the ese wnw to e w striking charters towers ravenswood lineament a major crustal boundary in the basement to the ravenswood batholith at the camp scale auriferous veins have abundance and proximity relationships with nw se nnw sse ne sw and ene wsw oriented lineaments suggesting that structures that controlled gold deposition in one camp did not necessarily control mineralisation in other camps fractal dimensions obtained with the box counting method range from 1 02 to 1 10 whereas veins in the charters towers city camp are characterised by a significantly higher fractal dimension of 1 28 this discrepancy may be taken to imply that most or all outcropping and near surface deposits within the charters towers city camp have been found and that new discoveries are more likely to occur at greater levels of depth or outside the boundaries of this camp the new understanding has implications for the assessment of the residual prospectivity of the charters towers goldfield where large areas of prospective rock types and structures e g approximately 40 of the charters towers ravenswood lineament are hidden under cover this parameter space was inaccessible to the historic prospectors and has received relatively little attention from recent explorers the following steps are suggested for the development of a targeting strategy for lode gold exploration in areas of the goldfield under cover 1 identify from geological and geophysical data the ene wsw 15 and nnw sse 15 striking structures and geological boundaries within a 20 km wide corridor parallel to and centred upon the charters towers ravenswood lineament the potential control on gold deposit distribution at the regional to district scale 2 interpret from geological and geophysical data the distribution of pre middle devonian granitoids within these areas that are the preferred host rocks of the payable gold deposits 3 deduce from geophysical data the ene wsw 15 and nnw sse 15 striking structures that cut or bound the intrusions identified in step 2 4 locate segments along the structures identified in step 3 that deviate most from the geometry of a straight line e g potential bends or splays and or intersect other structures or geological contacts or both and 5 define and rank potential targets within the prospective areas identified in step 4 and systematically test the best ones

rare earth element mobility around the volcanogenic polymentallic massive sulfide deposit at que river tasmania australia abstract the que river volcanogenic base and precious metal deposit is located in the cambrian mt read volcanics of western tasmania the host andesites and dacites adjacent to mineralization have been hydrothermally altered during mineralization and the entire sequence has undergone devonian regional prehnite pumpellyite facies metamorphism rocks petrographically recognizable as andesites exhibit chondrite normalized ree patterns similar to modern orogenic high k andesitic rocks with ce yb n ratios ranging from 6 4 to 8 6 dacites are more fractionated with ce yb n ranging from 10 6 to 16 0 like the andesites the dacites are characterized by negative eu anomalies eu eu 0 73 0 85 except for a more extreme eu anomaly in one sample eu eu 0 57 polymict volcaniclastic rocks have patterns very similar to those of the andesites the chondrite normalized ree patterns for the hydrothermally altered volcanics fall into three groups that can also be distinguished petrographically a single chloriterich sample has a substantial eu anomaly and shows less relative depletion in the middle ree than do either the andesites or the dacites highly silicified samples are all characterized by large negative eu anomalies eu eu 0 37 0 46 and many are relatively unfractionated with ce yb n ratios ranging from 3 5 to 7 7 a third group of samples characterized by the development of phengitic mica and carbonate show ree patterns similar to the andesites although their eu anomalies are generally smaller a sample of massive zn 1bpb ore has very low ree abundances showing light ree enrichment and a small negative eu anomaly eu eu 0 82 massive pyrite has a similar pattern except for higher overall abundances and a small positive eu anomaly eu eu 1 10 except for the eu anomalies the andesites and dacites show no evidence for ree mobility eu anomalies in the andesites are probably due to alteration of phenocrystic plagioclase and subsequent removal of divalent eu substantial ree mobility has occurred in the hydrothermally altered volcanic rocks the degree of mobility correlating with alteration style and intensity eu has been leached from both former plagioclase phenocrysts and the groundmass some of the eu leached from zones of the most intense alteration may have been redeposited in lower temperature more distal alteration zones

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

the aqueous geochemistry of the rare earth elements and yttrium 4 monazite solubility and ree mobility in exhalative massive sulfide depositing environments abstract although there is considerable evidence that rare earth elements ree and particularly the light ree lree have been mobile in the alteration zones below many massive sulfide deposits there is some disagreement over the cause of this mobility most researchers have argued or implied that the ree were mobilized by analogues of modern seafloor hydrothermal vent fluids however the few measurements that have been made of the ree concentrations of these modern fluids suggest that their ability to mobilize ree is negligible in order to shed further light on this problem we have carried out calculations of monazite solubility monazite is thought to be the principal host for the lree in a model vent fluid at temperatures from 200 to 300 c these calculations show that at 300 c the model fluid will contain 0 08 ppb ce 0 07 ppb la and 0 03 ppb nd at 200 c the concentrations increase to 0 54 ppb 0 37 ppb and 0 15 ppb respectively a decrease in ph of one unit at 300 c also increases ree solubility significantly 7 4 ppb ce 5 7 ppb la and 1 1 ppb nd these solubilities are similar to the concentrations of ree measured in seafloor hydrothermal vent fluids however they are considerably lower than required to account for the scale of ree mobility in alteration zones associated with massive sulfide deposits if the mass ratio of typical hydrothermal vent fluid to rock reached 1000 concentrations of ree in the altered rock the predicted to be in the range

how to resolve the controls on mesothermal vein systems in a goldfield characterized by sparse kinematic information and fault reactivation a structural and graphical approach current mine exposures of auriferous veins in the charters towers goldfield ctgf are characterized by a scarcity of kinematic indicators furthermore the dip direction of exposed and historically mined orebodies largely coincides with the orientation of pre existing discontinuities consequently the reactivation of earlier structures during gold deposition is strongly indicated both factors complicate the structural analysis of the auriferous vein systems as slip on earlier faults likely occurred before new rock failure and evolution of fault networks reflecting the stress field present at the time of gold deposition despite access to drillcore open pits and underground workings extracted data were limited to ten occurrences of wear groove striations and three reverse separations of dykes and a pegmatite cut by sulphide bearing quartz veins because of the scarcity of kinematic information the structural analysis focused on the geometry of veins and ore shoots also applying basic graphical and kinematic methods

mobilization of ree during crustal aging in the troodos ophiolite cyprus ree data for secondary minerals from low and high temperature alteration environments in the troodos ophiolite have been determined using a combined mass spectrometry neutron activation technique smectite and analcime ree mimic fresh rock profiles and have concentrations ranging from 1 5 times chondritic values celadonite is depleted in lree and total ree relative to the rocks groundmass replacing chlorite and epidote are similar to or enriched in ree relative to fresh rocks in contrast fault related chlorite and void filling epidote are lree enriched with large positive eu anomalies and yield comparable ree profiles to those of hydrothermal fluids venting at mid ocean ridges the zeolites clinoptilolite and laumontite are also lree enriched with ree contents significantly lower than rock values carbonate is enriched in hree relative to lree and concentrations vary from 0 2 to 18 times chondritic values ree data for these minerals indicate that seawater ree contents are modified by seawater rock interaction in volcanic sequences and sheeted dykes in oceanic crust during axial hydrothermal alternation and subsequent crustal aging the absolute and relative abundances of ree in seawater derived solutions evolve in response to the precipitation of secondary minerals and the prevailing water rock ratios rocks altered at low temperatures will show no change or a decrease in ree content the lree hree ratio will reflect the proportion of smectite celadonite and carbonate in the groundmass assemblage in contrast rocks altered at high temperatures will show no change or an increase in ree the lree hree ratio will reflect the proportion of void filling and groundmass replacing chlorite and epidote in the rock

a radar survey of m and x class asteroids abstract we observed ten m and x class main belt asteroids with the arecibo observatory s s band 12 6 cm radar the x class asteroids were targeted based on their albedos or other properties which suggested they might be m class this work brings the total number of main belt m class asteroids observed with radar to 14 we find that three of these asteroids have rotation rates significantly different from what was previously reported based on their high radar albedo we find that only four of the fourteen 16 psyche 216 kleopatra 758 mancunia and 785 zwetana are almost certainly metallic 129 antigone has a moderately high radar albedo and we suggest it may be a ch cb bencubbinite parent body three other asteroids 97 klotho 224 oceana and 796 sarita have radar albedos significantly higher than the average main belt asteroid and we cannot rule out a significant metal content for them five of our target asteroids 16 psyche 129 antigone 135 hertha 758 mancunia and 785 zwetana show variations in their radar albedo with rotation we can rule out shape and composition in most cases leaving variations in thickness porosity or surface roughness of the regolith to be the most likely causes with the exception of 129 antigone we find no hydrated m class asteroids w class rivkin a s howell e s lebofsky l a clark b e britt d t 2000 icarus 145 351 368 to have high radar albedos

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

the setting style and role of magmatism in the formation of volcanogenic massive sulfide deposits throughout earth s history all volcanogenic massive sulfide vms hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry petrochemical assemblages indicative of formation at anomalously high temperatures within extensional geodynamic environments in mafic dominated juvenile ophiolitic vms environments there is a preferential association with mafic rocks with boninite and low ti tholeiite mid ocean ridge basalt morb and or back arc basin basalt affinities representing forearc rifting or back arc initiation mid ocean ridges or back arc basin spreading or back arc basins respectively felsic rocks in juvenile oceanic arc environments in archean terrains are high field strength element hfse and rare earth element ree enriched in post archean juvenile oceanic arc terrains felsic rocks are commonly hfse and ree depleted and have boninite like to tholeiitic signatures in vms environments that are associated with continental crust i e continental arc and back arc and dominated by felsic volcanic and or sedimentary rocks evolved environments felsic rocks are the dominant hosts to mineralization and are generally hfse and ree enriched with calc alkalic a type and or peralkalic affinities representing continental arc rifts continental back arcs and continental back arcs to continental rifts respectively coeval mafic rocks in evolved environments have alkalic within plate ocean island basalt like and morb signatures that represent arc to back arc rift versus back arc spreading respectively the high temperature magmatic activity in vms environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments e g mid ocean ridges back arc basins and intra arc rifts underplated basaltic magma provides the heat required to drive hydrothermal circulation extensional geodynamic activity also provides accommodation space at the base of the lithosphere that allows for the underplated basalt to drive hydrothermal circulation and induce crustal melting the latter leading to the formation of vms associated rhyolites in felsic dominated and bimodal vms environments rifts also provide extensional faults and the permeability and porosity required for recharge and discharge of vms related hydrothermal fluids rifts are also critical in creating environments conducive to preservation of vms mineralization either through shielding massive sulfides from seafloor weathering and mass wasting or by creating environments conducive to the precipitation of subseafloor replacement style mineralization in sedimented rifts subvolcanic intrusions are also products of the elevated heat flow regime common to vms forming environments shallow level intrusive complexes i e within 1 3 km of the seafloor may not be the main drivers of vms related hydrothermal circulation but are likely the manifestation of deeper seated mantle derived heat i e 3 10 km depth that drives hydrothermal circulation these shallower intrusive complexes are commonly long lived i e millions of years and reflect a sustained thermally anomalous geodynamic environment such a thermally anomalous environment has the potential to drive significant hydrothermal circulation and therefore multi phase long lived subvolcanic intrusive complexes are excellent indicators of a potentially fertile vms environment the absence of intrusive complexes however does not indicate an area of low potential as they may have been moved or removed due to post vms tectonic activity in some cases shallow level intrusive systems contribute metals to the vms hydrothermal system

paleozoic terranes of eastern australia and the drift history of gondwana abstract critical assessment of paleozoic paleomagnetic results from australia shows that paleopoles from locations on the main craton and in the various terranes of the tasman fold belt of eastern australia follow the same path since 400 ma for the lachlan and thomson superterranes but not until 250 ma or younger for the new england superterrane most of the paleopoles from the tasman fold belt are derived from the lolworth ravenswood terrane of the thomson superterrane and the molong monaro terrane of the lachlan superterrane consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic australia by the late early devonian the lolworth ravenswood terrane is interpreted to have undergone a 90 clockwise rotation between 425 and 380 ma although the tamworth terrane of the western new england superterrane is thought to have amalgamated with the lachlan superterrane by the late carboniferous geological syntheses suggest that movements between these regions may have persisted until the middle triassic this view is supported by the available paleomagnetic data with these constraints an apparent polar wander path for gondwana during the paleozoic has been constructed after review of the gondwana paleomagnetic data the drift history of gondwana with respect to laurentia and baltica during the paleozoic is shown in a series of paleogeographic maps

trace and rare earth elements in cassiterite sources of components for the tin deposits of the mole granite australia trace and rare earth elements have been determined for cassiterite from deposits associated with the mole granite and hosted by granite metasediments and metavolcanics the ree of cassiterite is controlled by the ree of the the ore fluid and the rocks through which this fluid circulated the ree distribution factor and lree hree value of cassiterite is strongly influenced by the associated mineral assemblage the fluid chemistry and the crystal chemical characteristics of the host mineral cassiterite from deposits hosted by granite have trace and rare earth element characteristics similar to those determined for the mole granite cassiterite from deposits hosted by metasediments or acid volcanics have most trace and rare earth element characteristics similar to those of the enclosing rocks and some characteristics similar to the mole granite the ore fluid had chemical components derived from the parental granite and components acquired by passage through the metamorphosed aureole

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

asteroid 21 lutetia at 3 μm observations with irtf spex abstract we present observations of asteroid 21 lutetia collected 2003 2008 using the spex instrument on the nasa infrared telescope facility irtf covering 2 4 m we also reevaluate nsfcam observations obtained in 1996 rivkin a s lebofsky l a clark b e howell e s britt d t 2000 icarus 145 351 368 taken together these show deeper 3 m band depths of order 3 5 in the southern hemisphere of lutetia and shallower band depths of order 2 or less in the north such variation is consistent with observations at shorter wavelength by previous workers nedelcu d a et al 2007 astron astrophys 470 1157 1164 lazzarin m et al 2010 mon not r astron soc 408 1433 1437 who observed hemispheric level variations from c like spectra to x like spectra while the shallowness of absorption bands on lutetia hinders identification of its surface composition goethite appears plausible as a constituent in its southern hemisphere beck p quirico e sevestre d montes hernandez g pommerol a schmitt b 2011 astron astrophys 526 a85 a89 mathematical models of space weathered goethite are most consistent with lutetia s southern hemisphere spectrum but more work and further observations are necessary to confirm this suggestion

a new investigation of hydration in the m type asteroids abstract we obtained 2 4 m spectra of six m type asteroids using the spex spectrograph at nasa s infrared telescope facility we find evidence for hydrated minerals on all six asteroids including two that were previously thought to be dry one of our targets 216 kleopatra shows rotational variability in the depth of its 3 m feature we also studied three of these asteroids in the 0 8 2 4 m range using the nics instrument at the telescopio nazionale galileo tng in la palma spain the discovery of spectral signatures of hydrated minerals on so many m types is difficult to reconcile with a highly thermally evolved composition it has been suggested that the hydrated minerals could have been delivered to m types via impacts with primitive objects or that the m types may actually have primitive compositions that are not represented in meteorite collections understanding the origin and type of hydration on these asteroids will help determine which of these interpretations is correct

hydrothermal alteration in oceanic ridge volcanics a detailed study at the galapagos fossil hydrothermal field abstract the galapagos fossil hydrothermal field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern galapagos rift between 85 49 w and 85 55 w the discharge zone of the hydrothermal system is revealed along scarps thus providing an opportunity to examine the uppermost mineralized and highly altered interior parts of the crust altered rocks collected in situ by the submersible alvin show complex concentric alteration zones microsamples of individual zones have been analysed for major minor trace elements and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration interlayered chlorite smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene phenocrysts and matrix grains of plagioclase are unaffected during alteration using a modification of the gresens equation we demonstrate that the trivalent rare earth elements rees are relatively immobile and calculate degrees of enrichment and depletion in other elements strontium isotopic ratios increase as sr concentrations decrease from least altered cores to most altered rims and cross cutting veins in individual samples and can be modeled by open system behaviour under low fluid rock ratio

concordant paleolatitudes for neoproterozoic ophiolitic rocks of the trinity complex klamath mountains california 1 new paleomagnetic results from the eastern klamath mountains of northern california show that neoproterozoic rocks of the trinity ophiolitic complex and overlying middle devonian volcanic rocks are latitudinally concordant with cratonal north america combining paleomagnetic data with regional geologic and faunal evidence suggests that the trinity complex and related terranes of the eastern klamath plate were linked in some fashion to the north american craton throughout that time but that distance between them may have varied considerably a possible model that is consistent with our paleomagnetic results and the geologic evidence is that the trinity complex formed and migrated parallel to paleolatitude in the basin between laurasia and australia east antarctica as the rodinian supercontinent began to break up it then continued to move parallel to paleolatitude at least through middle devonian time although the eastern klamath plate served as a nucleus against which more western components of the klamath mountains province amalgamated the klamath superterrane was not accreted to north america until early cretaceous time index terms 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 5475 planetology solid surface planets tectonics 8149 8157 tectonophysics evolution of the earth plate motions past 3040 9350 information related to geographic region north america 9619 information related to geologic time precambrian

spiral and staircase inclusion trail axes within garnet and staurolite porphyroblasts from schists of the bolton syncline connecticut timing of porphyroblast growth and the effects of fold development in the littleton formation garnet porphyroblasts preserve three generations of growth that occurred before formation of the bolton syncline inclusion trails of foliations overgrown by these porphyroblasts are always truncated by the matrix foliation suggesting that garnet growth predated the matrix foliation in contrast many staurolite porphyroblasts grew synchronously with formation of the bolton syncline however local rim overgrowths of the matrix foliation suggest that some staurolite porphyroblasts continued to grow after development of the fold during younger crenulation producing deformations the axes of curvature or intersection of foliations defined by inclusion trails inside the garnet porphyroblasts lie oblique to the axial plane of the bolton syncline but do not change orientation across it this suggests the garnets were not rotated during the subsequent deformation associated with fold development or during even younger crenulation events three samples also contain a different set of axes defined by curvature of inclusion trails in the cores of garnet porphyroblasts suggesting a protracted history of garnet growth foliation intersection axes in staurolite porphyroblasts are consistently orientated close to the trend of the axial plane of the bolton syncline on both limbs of the fold in contrast axes defined by curvature or intersection of foliations in the rims of staurolite porphyroblasts in two samples exhibit a different trend this phase of staurolite growth is associated with a crenulation producing deformation that postdated formation of the bolton syncline measurement of foliation intersection axes defined by inclusion trails in both garnet and staurolite porphyroblasts has enabled the timing of growth relative to one another and to the development of the bolton syncline to be distinguished in rocks where other approaches have not been successful consistent orientation of foliation intersection axes across a range of younger structures suggests that the porphyroblasts did not rotate relative to geographical coordinates during subsequent ductile deformation foliation intersection axes in porphyroblasts are thus useful for correlating phases of porphyroblastic growth in this region

deformation partitioning foliation successions and their significance for orogenesis hiding lengthy deformation histories in mylonites although orogenesis commonly lasts 100 million years a maximum of three foliations are usually preserved within any outcrop they record little of the total history due to the effects of preferential partitioning of progressive shearing along s0 such reactivation eventually destroys or rotates multiple successive foliations into parallelism with any layering that is present plate motion subjects a collisional orogen to spatially partitioned episodic but non stop deformation the bulk forces operating are horizontal and intermittently vertical associated with gravitational load due to crustal thickening forming sub vertical and sub horizontal foliations these orientations are preserved in the strain shadows of anything competent that hinders reactivation of the compositional layering deformation partitioning results in portions of rock remaining unaffected for many events gravitational collapse of over thickened orogen cores leads to significant extrusion in orogen rims and a dominance of sub horizontal foliations in the latter and episodically continues throughout orogenesis reactivation causes decrenulation and or rotation of foliations into parallelism with s0 destroying evidence that multiple sub vertical and sub horizontal foliations have developed except where preserved as inclusion trails in porphyroblasts and multiply truncated foliations in mylonites however the same processes operate in both the cores of orogens and ductile portions of their margins

multi stage growth of the trachytic lava dome of the puy de dome chaine des puys france field geomorphological and petro geochemical evidence abstract understanding lava dome eruptions is a major concern in volcanology regarding the assessment of associated hazards this question is usually addressed through the study of active calc alkaline domes however alkaline domes remaining poorly known the puy de dome is the most prominent volcano of the chaine des puys quaternary intraplate volcanic field in the french massif central it is a complex trachytic lava dome ca 11 ka old field investigations geomorphological and petro geochemical studies were performed to understand the magmatic system of this dome and reconstruct its volcanic evolution the different lava facies were fully characterised and their relationships with the volcano building stages have been established a new four step evolution is proposed for the growth of this edifice mineralogical and geochemical variations document magmatic differentiation with self mixing and minor crustal contamination in a zoned reservoir within the upper crust magma mixing and crustal contamination through fluids interactions during magma ascent and the involvement of fumarolic activity throughout the edifice building are also documented further this work highlights the specific features of the puy de dome compared to calc alkaline domes lack of lava flows and almost complete magma degassing during ascent resulting in the lack of significant explosive activity until the last eruption step

geological sulfur isotopic and mineral trace element constraints on the genesis of the xiyi pb zn deposit baoshan block sw china abstract the recently discovered xiyi pb zn deposit in yunnan province sw china contains 1 2 mt of pb and zn metal it is located within the baoshan block in the sanjiang tethys orogenic belt and is hosted along fractures within carbonates of the lower carboniferous xiangshan formation the deposit is hosted by veins within ne sw trending strike slip and steeply dipping nw se trending normal fault zones the formation of the deposit involved sedimentary hydrothermal and supergene oxidation stages the hydrothermal stage associated with mineralization include three sub stages i a steeply dipping quartz calcite rich sphalerite sub stage ii a polymetallic sulfide sub stage and iii a vein host calcite pyrite sub stage the deposit is enriched in pb zn sb cd ag and u and depleted in ni se ti and co the ores have total rare earth element ree concentrations of 17 4 186 ppm and are enriched in the light ree lree with la yb n ratios of 3 75 9 23 and strongly positive eu eu eu 1 42 4 60 and slightly negative ce ce ce 0 70 0 88 anomalies the positive eu anomalies and lree enrichment suggest that the ore forming fluids were exsolved from a concealed intrusion during magmatic degassing the s isotopic compositions of sulfides and sulfates indicate that s within the deposit was derived from both magmatic sources and barite within the hosting carbonates via thermochemical sulfate reduction in situ la icp ms analysis indicates that sphalerite within the deposit is texturally and chemically variable with elevated fe mn cd cu ag sb sn pb and tl contents in comparison galena within the deposit is enriched in sb ag cd sn and tl and pyrite has elevated ag as sb and pb contents the trace element compositions of sphalerite and galena indicate that the xiyi deposit may be the product of a distal hydrothermal event although the direct genetic relationship is not clear the fracture hosted nature mineral assemblages geochemistry and mineral s isotopic and trace element compositions of the xiyi pb zn deposit indicate that it is an epigenetic carbonate hosted pb zn deposit this study also indicates that sphalerite is a more useful mineral than galena in terms of using mineral trace element geochemistry to discriminate different deposit types

multi scale kinking in northeast tasmania crustal shortening at shallow crustal levels abstract analysis of s 1 cleavage trends in the ordovician devonian mathinna group of northeast tasmania has identified mega scale up to 9 km axial surface spacing kink bands and kink folds these formed after the regional steep slaty cleavage and are contemporaneous with but post date small scale cm scale vertical kink bands small scale sinistral kink bands strike approximately 032 and predominate in number over the approximately e w striking dextral kink bands the geometry of the small scale kink bands indicates a 166 10 trending principal shortening during kinking kink bands overprint minerals in the contact aureole of the middle to upper devonian granite granodiorite scottsdale batholith and pre date deposition of the parmeener supergroup of upper carboniferous age megakinking in ne tasmania is correlated with megakinking in the lachlan fold belt new south wales which occurred under the same bulk shortening direction and also during the middle carboniferous prior to kinking the regional slaty cleavage in the mathinna group was near vertical and trended 157 which is subparallel to the principal shortening direction during kinking 166 10 because of this close alignment and the presence of a pre existing planar anisostropy throughout the region megakinks developed despite only 4 5 bulk shortening kinking in ne tasmania occurred at 120 45 mpa approximately 4 2 km depth the brittle and instantaneous nature of kinking is consistent with deformation at such shallow crustal levels megakinking may be a typical expression of crustal tectonics of minor bulk shortening at shallow crustal levels only in the case of regions with a pre existing steep planar structural grain subparallel to the principal shortening direction

geology geochemistry fluid inclusion and genesis of the guijeh qaleh ioa type iron ore deposit north of takab district northwestern iran abstract the guijeh qaleh iron deposit located in the takab district of northwestern iran contains ca 0 3 million metric tons mt of ore at 48 wt fe the host rocks are eocene to oligocene volcano sedimentary sequences consisting of andesite trachy andesite to basaltic andesite flows intruded by granites to granodiorite intrusions the hydrothermal alterations include argillic sericitic silicified carbonate and hematitic zones silicified and hematitic alteration zones are spatially associated with the mineralization and occur proximal to ore bodies whereas sericite carbonate and argillic alteration zones are distal to main ore bodies iron mineralization occurred as several quartz hematite specularite veins 0 5 to 5 m wide and 10 to 20 m long which were formed within and along normal and strike slip fault zones the mineralogy of ore bodies consists of hematite specularite pyrite subordinate magnetite and apatite together with minor malachite after chalcopyrite with open space filling disseminated massive and breccia textures geochemical analyses of high grade ore bodies show that fe concentration is strongly correlated with mo zn mn pb sio2 mgo tio2 and p2o5 the chondrite normalized ree patterns of the altered and mineralized ore bodies displays with lree hree ratio with a negative eu anomaly and low eu eu values characteristic of the kiruna type ioa deposits fluid inclusion studies from quartz occurring with the mineralization characterized mineralizing fluids with homogenization temperatures ranging from 133 to 464 c and apparent salinities between 0 2 to 23 2 wt nacl equ interpretation of fluid inclusion data suggest that mixing of magmatic and meteoric fluids and cooling caused ore precipitation geology mineralogy ore textures geochemistry and fluid inclusion data suggest that iron mineralization in the guijeh qaleh deposit is similar to kiruna type ioa deposits the presented data show that the takab district has the potential for hosting kiruna type ioa mineralization in the northwest of iran

sm nd evidence for high grade ordovician metamorphism in the arunta block central australia sm nd ages from the harts range in the south eastern arunta inlier in central australia indicate that regional metamorphism up to granulite facies occurred in the early ordovician c 475 ma this represents a radical departure from previous tectonic models for the region and identifies a previously unrecognized intraplate event in central australia peak metamorphic assemblages 800 c and 10 5 kbar formed at around 476 14 ma and underwent approximately 4 kbar of near isothermal decompression at 475 4 ma a coarse grained unfoliated garnet clinopyroxene bearing marble inferred to have recrystallized late in the decompressional evolution gives an age of 469 7 ma two lines of evidence suggest the early ordovician tectonism occurred in an extensional setting first the timing of the high grade lower crustal deformation coincides with a period of marine sedimentation in the amadeus and georgina basins that was associated with a seaway that developed across central australia second isothermal decompression of lower crustal rocks was associated with the formation of a regional sub horizontal mid crustal foliation in the entia gneiss complex which forms the structurally lowest part of the harts range upper amphibolite facies metamorphism c 700 c 8 9 kbar occurred at 479 15 ma there is no evidence that p t conditions in the entia gneiss complex were as high as in the overlying units this implies that the extensional system was reworked during a later compressional event sm nd data from the mid amphibolite facies c 650 c and 6 kbar detachment zone that separates the irindina supracrustal assemblage and entia gneiss complex give an age of 449 10 ma this age corresponds to the timing of a change in the pattern and style of sedimentation in the amadeus and georgina basins and indicates that the change in basin dynamics was associated with mid crustal deformation it also suggests that compressional deformation culminating in the devonian to carboniferous 400 300 ma alice springs orogeny may have begun as early as c 450 ma at present the extent of early ordovician tectonism in central australia is unknown however granulite facies metamorphism and associated intense deformation imply an event of regional extent an implication of this work is that high grade lower crustal metamorphism and intense deformation occurred during the development of a broad shallow slowly subsiding intraplate basin

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

mineralogy of carbonaceous chondrite clasts in hed achondrites and the moon the majority of the carbonaceous chondrite clasts found in howardites eucrites and diogenites are cm2 material a lesser proportion is cr2 material and other rare types are present a single clast that was found on the moon and called the bench crater meteorite is apparently shocked cm1 material the cm2 clasts are matrix supported mixtures of olivine pyroxene phyllosilicate sulfide bearing aggregates loose olivines and pyroxenes sulfides carbonates and sinuous spinel phyllosilicate diopside calcium aluminum rich inclusions cais magnetite and metal are rare some aggregates have fine grained rims of material resembling matrix the opaque fine grained matrix consists predominantly of serpentine of extremely variable composition and sulfides tochilinite is occasionally present the trace element data for one jodzie clast from this study and the average of similar clasts from kapoeta support a cm classification volatiles are depleted relative to ci and enriched relative to cr material the cr2 clasts are found in small numbers in only four howardites bholghati jodzie kapoeta and y793497 petrographically they are matrix supported mixtures of olivine aggregates sometimes containing sulfides loose olivines pyrrhotite pentlandite low ca pyroxene minor hedenbergite rare kamacite rare and only found within olivine ca carbonates and abundant magnetite framboids and plaquets phyllosilicates are fine grained and largely confined to matrix they are mixtures of serpentine and saponite the matrix of cr2 clasts also contains pyrrhotite pentlandite chromite and a significant fraction of poorly crystalline material with the same bulk composition as matrix phyllosilicate there is evidence of heating in a substantial number of clasts both cm2 and cr2 including 1 corrugated serpentine flakes 2 pseudomorphs of anhydrous ferromagnesian material after flaky phyllosilicates and 3 hedenbergite rims on calcite while the timing of the hedenbergite rims is debatable the destruction of phyllosilicates clearly occurred at a late stage plausibly during impact onto the hed asteroid s and moon and required peak heating temperatures on the order of 400 c we note that in general cm2 material was the most common carbonaceous chondrite lithology impacting the hed asteroids with howardites and eucrites taken together as it is for the earth today a total of 61 out of 75 carbonaceous chondrite clasts from hed meteorites belong to the cm clan petrologic grade 2 this is also supported by published siderophile and volatile element data on howardites eucrites and diogenites that are taken to indicate that cm like materials were the most common impactors on the hed asteroid s the ratio of cr cm clasts in hed asteroids is essentially the same as for modern falls at earth this may indicate that the ratio of disaggregated cm2 to cr2 asteroidal material has been approximately constant through the history of the solar system finally our results are also compatible with type 2 carbonaceous chondrites being equivalent to or from the same source as the material that originally accreted to form the hed asteroid

megakinking in the lachlan fold belt australia abstract the regional n s tectonic grain of the easternmost lachlan fold belt is produced by upright tight folds with well developed quasi vertical axial surface foliation and comprises domains in which the early folds and foliation have consistent orientation the domains are up to a few tens of kilometres along trend and are separated by narrow zones across which the tectonic grain swings commonly by 20 to 30 to produce a regional tectonic kink pattern these megakinks have both sinistral 070 10 and dextral 110 10 trends the dextral zones being more common in the megakink bands which may be up to 10 km wide there are commonly second order kink zones a few hundred metres wide in which the pre existing fold trends are rotated 90 or more from their regional n s trend small scale kink bands of metre to millimetre width are much more common in the megakink bands than in the planar domains between outcrop scale kink folds were formed by a subhorizontal principal compression acting parallel to the tectonic grain even where that grain is more than 90 oblique to the regional trend outcrop scale kinks are thus interpreted to have formed first under regional n s compression with the megakink domains rotating later the megakinking event is mid carboniferous c 330 ma being younger than the regional early carboniferous folding and older than the latest carboniferous basal sediment of the sydney basin the megakinks appear to have nucleated along strike of pre existing ese and ene trending lineaments in the lachlan fold belt possibly under continent wide n s compression

an extension of the bus asteroid taxonomy into the near infrared the availability of asteroid spectral measurements extending to the near infrared resulting from the development of new telescopic instruments such as spex rayner 2003 provides a new basis for classifying asteroid reflectance spectra we present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0 45 to 2 45 microns this system of 24 classes is constructed using principal component analysis following most closely the visible wavelength taxonomy of bus 1999 which itself builds upon the system of tholen 1984 nearly all of the bus taxonomy classes are preserved with one new class sv defined for each class we present boundary definitions spectral descriptions and prototype examples a flow chart method is presented for classifying newly acquired data spanning this wavelength range when data are available only in the near infrared range 0 85 to 2 45 microns classification is also possible in many cases through an alternate flow chart process within our sample several classes remain relatively rare only 6 objects fall into the a class 349 dembowska and 3628 boznemcova reside as the only objects in their respective r and o classes eight q class objects are all near earth asteroids we note 1904 massevitch as an outer main belt v type while 15 other v type objects have inner main belt orbits consistent with an association with vesta

texture mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of cheshire seamount western woodlark basin the western woodlark basin lies within a gold rich metallogenic province this area is characterized by detachment faults that record ongoing extension and act as major pathways for the circulation of hydrothermal fluids dredging from the flanks of a submarine ridge southeast of cheshire seamount western woodlark basin retrieved hydrothermally altered monomictic to polymictic crackle mosaic and chaotic breccias with at least 30 clasts n2 mmin diameter the precursor rocks are andesitic to rhyolitic in composition but have been intensely hydrothermally altered with about 90 of the volcanic glass replaced by secondaryminerals the breccias show five generations of quartz growth with the first being related to magmatic processes and the remaining four to alteration stages including silicification chloritization illitization sericitization albitization and sulfidation needle like crystals ofmordenite zeolite withmultiple growth centers growon the fourth generation of quartz notable textural variants in the breccias are vesicles perlitic cracks and zoned alteration halos that mantle the rims of clasts electron microprobe analyses on chlorite from breccia samples have identified clinochlore as the main chlorite type and indicate a formation temperature in the range of 210 304 c this and the elevated au as ag hg zn pb sb contents of a mineralized sample indicate hydrothermal alteration temperatures n200 c suggesting that these breccias may represent the upflow zone of a hydrothermal system and highlight the potential for seafloor massive sulfides in the area the breccias show elevated contents of immobile trace elements and lree as well as a depletion in ta and nb suggesting that the precursor rocks were formed in a rift related suprasubduction environment

spectroscopic survey of m type asteroids abstract m type asteroids as defined in the tholen taxonomy tholen d j 1984 asteroid taxonomy from cluster analysis of photometry ph d dissertation university of arizona tucson are medium albedo bodies supposed to have a metallic composition and to be the progenitors both of differentiated iron nickel meteorites and enstatite chondrites we carried out a spectroscopic survey in the visible and near infrared wavelength range 0 4 2 5 m of 30 asteroids chosen from the population of asteroids initially classified as tholen m types aiming to investigate their surface composition the data were obtained during several observing runs during the years 2004 2007 at the tng ntt and irtf telescopes we computed the spectral slopes in several wavelength ranges for each observed asteroid and we searched for diagnostic spectral features we confirm a large variety of spectral behaviors for these objects as their spectra are extended into the near infrared including the identification of weak absorption bands mainly of the 0 9 m band tentatively attributed to orthopyroxene and of the 0 43 m band that may be associated to chlorites and mg rich serpentines or pyroxene minerals such us pigeonite or augite a comparison with previously published data indicates that the surfaces of several asteroids belonging to the m class may vary significantly we attempt to constrain the asteroid surface compositions of our sample by looking for meteorite spectral analogs in the relab database and by modeling with geographical mixtures of selected meteorites minerals we confirm that iron meteorites pallasites and enstatite chondrites are the best matches to most objects in our sample as suggested for m type asteroids for 22 kalliope we demonstrate that a synthetic mixture obtained enriching a pallasite meteorite with small amounts 1 2 of silicates well reproduce the spectral behavior including the observed 0 9 m feature the presence of subtle absorption features on several asteroids confirms that not all objects defined by the tholen m class have a pure metallic composition a statistical analysis of spectral slope distribution vs orbital parameters shows that our sample originally defined as tholen m types tend to be dark in albedo and red in slope for increasing value of the semi major axis however we note that our sample is statistically limited by our number of objects 30 and slightly varying results are found for different subsets if confirmed the albedo and slope trends could be due to a difference in composition of objects belonging to the outer main belt or alternatively to a combination of surface composition grain size and space weathering effects

mineralogy and geochemistry of the masa valverde blind massive sulphide deposit iberian pyrite belt spain abstract masa valverde is a blind volcanic hosted massive sulphide deposit recently discovered in the spanish sector of the iberian pyrite belt ipb the deposit is more than 1 km long and is located at depths between 400 and 850 m in direct spatial association with a residual gravimetric anomaly the ore body is concealed beneath culm sedimentary rocks which cover the western extension of a hercynian age anticline a few kilometers west of an area where older massive sulphide workings existed the masa valverde deposit consists of two main ore bodies composed dominantly of massive and banded pyrite which are hosted by a volcano sedimentary sequence made up of felsic tuffs interlayered with shale siliceous exhalite and radiolarian chert the abundance of sedimentary host rocks to the deposit is a feature shared by other large massive sulphide deposits in the eastern sector of the ipb and is interpreted as significant with respect to the origin of the deposit a break in volcanic activity the thickness of the upper massive sulphide orebody varies between a few meters and 70 m and it consists of lenses and blankets of massive sulphides with interbedded tuff and shale and occasionally stockwork zones the lower orebody is smaller and thinner than the upper one but this may be due to incomplete drilling two types of stockwork occur beneath the massive sulphide bodies the more common type consists of irregular and anastomosing sulphide veinlets and irregular blebs formed by replacement stockwork with cross cutting generally straight sided sulphide veins is by contrast suggestive of formation by hydraulic fracturing the mineralogy and alteration processes of the ore and host rocks at masa valverde are analogous to those of other ipb massive sulphides the average temperature of formation of the components of the ore zones estimated on the basis of chlorite thermometry are as follows siliceous exhalites 290 c massive sulphides 325 c and stockworks 305 c rare earth element measurements indicate that the lowest metal concentrations occur in chloritites which occasionally host cu rich stockwork and are characterised by a strongly negative eu anomaly by contrast rocks hosting the sulphide lenses where silicification sericitization and carbonatization are more intense are enriched in lree two main stages of hydrothermal activity are suggested for the masa valverde deposit during an early stage ore fluids would have discharged onto the sea floor resulting in the deposition of pyrite with sphalerite and galena later on with continued input of high temperature fluids 290 to 315 c chalcopirite precipitated especially in the stockworks and at the base of the sulphide lenses at masa valverde this late cu rich hydrothermal event would have produced an ascending cu front which overpassed the stockwork zone and reached a higher temperature 325 c at the base of the massive sulphide lenses the combination of geological mineralogical and geochemical features of the masa valverde deposit provide guidelines for exploration for new blind orebodies in this part of the ipb where tuffs and sedimentary rocks are the dominant host lithologies the masa valverde deposit can be considered as a vhms subtype transitional to shms

terminal fold belt deformation relationship of mid carboniferous megakinks in the tasman fold belt to coeval thrusts in cratonic australia megakinks in the meridional tectonic grain of the tasman fold belt were formed by north south compression in the mid carboniferous and appear to be related to the same stress system that formed intracratonic thrusts in central australia during the alice springs orogeny

tasman orogenic system a model for its subdivision and growth history based on gravity and magnetic anomalies the basement of the tasman orogenic system can be subdivided using gravity and magnetic anomalies into 11 geophysical domains the unity of each domain is given by subparallel trends which show the direction of the dominant tectonic structure in the nonsedimentary part of the upper crust basement crosscutting trends at domain boundaries indicate the relative ages of the domain cratonization these relative ages are consistent with the dated ages of first deformation and they show that cratonization occurred in numerous episodes and resulted in an apparent growth of the tasman orogenic system from west to east between the cambrian and the carboniferous each domain can be subdivided into bands of different character in the main area of basement outcrop the southern part of the lachlan orogen the position of the boundaries of these domains and bands agree with boundaries based on the composition of granites structure and strontium isotope ratios over the larger part of the tasman orogenic system where basement is under cover these geophysically defined domains and bands are our best estimate of basement subdivision and history near domain boundaries there are characteristic associations of gravity and magnetic anomalies due to reworking of the margin of the older crust by deformation intrusion and metamorphism differences between domains in mean upper crustal density and magnetization and the common occurrence of volcanic bands ophiolite serpentinite and deep elongate sedimentary troughs caused by crustal extension the domains can be divided into a sedimentary basement type formed by crustal extension and sedimentation or by the addition of an accretionary wedge and a volcanic arc basement type added by the accretion

stratigraphy structure and volcanic hosted mineralization of the mount windsor subprovince north queensland australia the mount windsor subprovince contains a major belt of mineralized cambro ordovician subaqueous volcanogenic rocks at the northern end of the tasman orogenic belt the base of the stratigraphic sequence is a thick continent derived siliciclastic package intruded by alkali andesites typical of intraplate settings this is overlain by massive subaqueous rhyolitic units and then by a mixed association of basaltic andesitic dacitic and rhyolitic volcanics and volcaniclastics containing numerous small elongate pods of quartz hematite or magnetite exhalite the cessation in active volcanism is marked by a change to a sandstone siltstone unit dominated by volcanic sources the majority of volcanics form a coherent group of low to medium k calc alkaline lavas similar to those in modern island arc settings extensional growth faults produced local variation in the stratigraphic thickness the largest growth fault in the area is close to the reward highway and handcuff deposits the sequence has been multiply folded and faulted in the paleozoic but the large scale structure remains relatively simple volcanic hosted massive sulfide vhms deposits occur at the top of the massive rhyolite and in the mixed volcanic package above it with the exception of the reward pyrite pipe the mineralization occurs as blanketlike deposits with low thickness lateral extent ratios the thalanga reward and waterloo deposits are copper rich whereas agincourt magpie liontown handcuff and warrawee are zinc rich and copper poor with a significant barite component

near ir spectral evidence for the presence of iron poor orthopyroxenes on the surfaces of six m type asteroids abstract the first verifiable near infrared absorption features in the 0 9 m spectral region are reported for asteroids 16 psyche 69 hesperia 110 lydia 125 liberatrix 201 penelope and 216 kleopatra these weak features 1 3 are attributed to orthopyroxenes present on the surfaces of these asteroids 16 psyche and 125 liberatrix have full rotational coverage while 69 hesperia 110 lydia 201 penelope and 216 kleopatra have 75 rotational coverage qualitative 2 m absorption features are present but are very weak 1 absorption band positions suggest relatively low abundances of calcium and iron in the pyroxenes this indicates relatively reducing redox conditions for these asteroids their parent bodies and the nebular regions in which they formed four potential interpretations for these asteroids include 1 they are exposed metallic cores or core fragments of differentiated parent bodies with residual orthopyroxene mantle material 2 they are the result of a smelting like reaction that converts olivine to pyroxene and metallic iron in the presence of carbon at high temperatures 3 they are analogs to the primitive metal rich bencubbinite meteorites or 4 they represent metallic surfaces which have accumulated silicate debris from external sources of the two original interpretations for the m asteroids the enstatite chondrite interpretation chapman and salisbury 1973 icarus 19 507 522 gaffey and mccord 1979 mineralogical and petrological characterizations of asteroids in gehrels t ed asteroids univ of arizona press tucson pp 688 723 can be eliminated for these asteroids because the pyroxene in enstatite chondrites is iron free and does not exhibit such absorption features the iron meteorite interpretation remains valid but with modification for m asteroids 16 psyche and 216 kleopatra these spectral results combined with previous determinations of high radar albedos indicate that these bodies are most probably exposed core fragments of differentiated bodies m asteroids 69 hesperia 110 lydia 125 liberatrix and 201 penelope exhibit similar spectral features consistent with exposed core fragments but radar observations would be needed to confirm a high metal abundance observations of m asteroids 136 austria and 325 heidelberga suggest the absence of absorption features in the 0 4 to 2 5 m region within the scatter of the data verification of the presence or absence of features across the surfaces of these two asteroids requires full rotational coverage the interpretations for these featureless m asteroids are not well constrained but remain consistent with the iron meteorite and enstatite chondrite interpretations