syn amphibolite facies archaean lode gold mineralisation in the mt york district pilbara block western australia the archaean lode gold deposits in the mt york district pilbara block western australia are hosted in banded iron formation main hill breccia hill prospect of the ca 3 33 ga gorge creek group and in amphibolites zakanaka prospect of the ca 3 46 ga warrawoona group gold mineralisation at the main hill breccia hill prospect is associated with breccias comprising quartz clasts in a quartz pyrrhotite matrix and quartz amphibole veins with lollingite being the major host for gold minimum temperatures for gold mineralisation at the prospect are constrained as 455 c to 550 c by arsenopyrite thermometry gold mineralisation at the zakanaka prospect is spatially associated with quartzclinopyroxene calcite microcline calcic amphibole veins and biotite altered wallrock adjacent to the veins temperatures for vein emplacement are estimated as 480 c to 570 c using both plagioclase amphibole thermometry and mineral equilibria with respect to t and xco2 the timing of gold mineralisation relative to the peak of metamorphism is constrained by mineral textures and the relative temperatures of hydrothermal alteration and metamorphism gold mineralisation at both deposits was broadly synchronous with the peak of regional amphibolite facies metamorphism which reached temperatures of 520 c to 640 c based on amphibole plagioclase and garnet biotite thermometry in this respect the deposits are similar to other well documented syn amphibolite facies lode gold deposits from the archaean southern cross greenstone belt in the yilgarn block and represent the deeper section of a crustal continuum of lode gold deposits that includes mesothermal deposits such as those at kalgoorlie at higher crustal levels

igneous and metamorphic petrology of the eclogitic seljeneset meta anorthosite and related jotunites western gneiss region norway abstract the seljeneset meta anorthosite consists of deformed and metamorphosed anorthosite and mafic rocks is situated in the high grade western gneiss region wgr of norway and is adjacent to the 1 52 ga flatraket quartz monzonite mangerite the wgr was metamorphosed to eclogite fades during caledonian tectonism 414 16 ma ago the meta anorthosite contains 46 57 wt sio 2 and displays chondrite normalized ree patterns typical of anorthosite indicating that metamorphism did not significantly affect ree abundances norms indicate that igneous anorthosite consisted of 90 modal plagioclase minor mafic silicates and 1 fe ti oxide mafic rocks 43 48 wt sio 2 are rich in total fe 2 o 3 13 20 tio 2 3 4 and p 2 o 5 1 3 poor in cr jotunites which are characteristic of proterozoic anorthosite mangerite complexes jotunite originally consisted of 50 modal andesine 25 mafic silicates 10 fe ti oxide and up to 7 apatite ree patterns of jotunite are highly variable which reflects variable igneous abundances and modification by metasomatism filter pressing of residual liquid trapped between cumulus plagioclase may have been important in the evolution of anorthosite and jotunite anorthosite contains ultramafic xenoliths high mgo cr and ni and depleted in lree which suggests that some mantle derived peridotite was present in the baltic crust by mid proterozoic time this may extend the crustal history of norwegian garnet peridotites by over one billion years seljeneset rocks display evidence of retrogression from eclogite through amphibolite facies meta anorthosite consists of ovoidal clots of margarite quartz plagioclase and relict kyanite set in a matrix of zoisite clinozoisite plagioclase quartz hornblende and biotite phase equilibria analysis of sequential assemblages shows that meta anorthosite records a retrograde p t path from 15 17 kbar to 4 3 8 2 kbar at 450 600 c mafic rocks vary from moderately well preserved eclogite through varieties containing symplectite to dynamically recrystallized amphibolite in one sample the rare na ca amphibole magnesio alumino taramite appears to be part of the eclogite assemblage calculations indicate eclogite formation at p 16 18 kbar at 750 c some mafic rocks contain veins and segregations of biotite muscovite pyrite allanite and zircon that considered together with geochemical data indicate metasomatic introduction of k rb ba ga s and rare earth and other high field strength elements by channelized fluids during retrogression the seljeneset meta anorthosite associated jotunites and adjacent flatraket quartz monzonite likely constitute a single complex here named the nordpollen plutonic complex this complex was emplaced 1 52 ga ago metamorphosed to eclogite facies during silurian continent continent collision largely retrograded to amphibolite facies during uplift of the orogen and locally metasomatised during retrogression

granitoid diapirism during protracted tectonism in an archaean granitoid greenstone belt yilgarn block western australia abstract the bullfinch parker dome area is an archaean granitoid greenstone terrain in the yilgarn block of western australia affected by a complex protracted tectonic event the majority of the deformation history was progressive rather than multiple discrete events finite strain patterns and structural and metamorphic zonation suggest that deformation in the greenstones was caused by regional ene wsw shortening and broadly simultaneous upward movement of granitoids by solid state diapirism and or ballooning plutonism rather than by core complex formation or multiple folding evidence for pluton related tectonism includes the foliation trends steeply plunging radial mineral lineations indications of upward movement of plutons increase of strain towards the batholith margins concordant structures in the pluton and the surrounding rocks such as lineation and foliation patterns constrictional tectonics near east west trending granitoid greenstone contacts syn to post kinematic peak metamorphism contact metamorphic zoning and pressure differences metamorphism largely of amphibolite facies was probably related to uprise of the granitoids at moderate crustal depths 10 12 km p 3 kbar causing both regional and contact metamorphism as a single thermal event relative and absolute timing defines an overlapping sequence of metamorphism progressive deformation and plutonism in this part of the yilgarn craton during the late archaean

nature of the elzevir mazinaw domain boundary grenville orogen ontario the mooroton shear zone msz of the metasedimentary belt of the grenville orogen in ontario separates the mazinaw domain to the east from the elzevir domain the shear zone is composed of mafic metavolcanic metaclastic and marble mylonites and is characterized by a subvertical foliation which crosscuts the regional foliation and a near vertical stretching lineation microstructures indicate deformation occurred under crystal plastic conditions and shear sense indicators give movement of east mazinaw side up the geometry of the msz which follows the eastern margin of the elzevir tonalite implies that lithologic anisotropy guided its location garnet biotite and garnet hornblende peak temperatures are juxtaposed across the msz with temperatures ranging from 460 to 530 c in the southeastern elzevir and 490 to 620 c in the southwestern mazinaw conditions in amphibolite facies limiting barometers applied to rocks in both domains show no significant offset petrologic data within the shear zone

palaeopressures of south indian two pyroxene garnet granulites from thermochemically calibrated cmas barometers the enthalpy of reaction of plagioclase and pyroxene to produce garnet and quartz has been a major source of error in granulite geobarometry because of relatively uncertain enthalpy values available from high temperature solution calorimetry and compiled indirectly from experimental phase equilibria recent improved calorimetric measurements of hr are shown to yield palaeopressures which are internally consistent between orthopyroxene and clinopyroxene calibrations for many south indian granulites from the archaean high grade terranes of southern karnataka and northern tamil nadu this represents a considerable improvement over previous calibrations which gave disparate results for the two independent barometers involving orthopyroxene and clinopyroxene requiring a 2 kbar empirical adjustment to force agreement palaeopressures thus calculated for 30 well documented two pyroxene garnet granulites from south india give internally consistent pressures with a mean of 8 1 1 1 kbar at 750 c consistent with the presence of both kyanite and sillimanite in many areas those samples for which garnet pyroxene exchange thermometers give plausible granulite range temperatures and whose minerals are minimally zoned give the best agreement of the two barometers samples which yield low palaeotemperatures and different rim and core compositions of minerals yield pressures for the orthopyroxene assemblage as much as 2 kbar lower than for the assemblage with clinopyroxene this disparity probably represents post metamorphic peak re equilibration we conclude that considerable confidence may be placed in geobarometry of two pyroxene granulites where apparent palaeotemperatures are in the granulite facies range 700 c and where mineral zonation is minimal of the several possible sets of activity composition relations in use those constructed from analysis of phase equilibria give slightly higher palaeopressures and appear more consistent with analytical data from the nilgiri hills uplift where kyanite is the only aluminium silicate reported to be stable in peak metamorphic assemblages the present results support a palaeopressure gradient increasing generally from south to north across the nilgiri hills as inferred by previous geobarometry

a simple geometric model for the syn kinematic erosional denudation of thrust fronts abstract the syn kinematic denudation history of contractional orogenic systems is explored using a simple geometric construction the purpose is to gain a better appreciation of the relationship between thrust related shortening and erosion at the front of an orogen specifically in cases where rocks with marked differences in metamorphic grade are juxtaposed across faults although this analysis examines an obvious feature of orogenic fronts that erosion and thrusting occur synchronously the magnitude of the necessary erosional flux has not been appreciated the front of an orogen is modeled as a wedge comprising one component represented by the elevation above the level of the thrust toe and a second subsurface component between the dipping slab and the level of the toe of the thrust because pressure is a simple function of overburden it is possible to calculate the horizontal distance from the toe to the point along the slab at any given pressure thrusting by itself does not effect pressures in the hanging wall and hence the footwall would be expected to assume the pressure gradient of the hanging wall if a thrust juxtaposes rocks that record markedly different equilibrium pressures material must have been removed from the hanging wall syn kinematically if the thrust bounds the metamorphic front of an orogen and deposition occurs synchronously with thrusting in the foreland removal of material is required to occur syn kinematically otherwise the thrust will bury the foreland the amount of material that must be removed syn kinematically is dependent on the pressure differential across the thrust and the dip of the thrust for any given dip an increase in the differential pressure requires an increase in cross sectional area that must be removed both above and in the foreland direction of this point from these simple relationships it is possible to calculate that at least 1 10 7 km 3 of material was eroded from the main central thrust of the himalayas between about 20 and about 15 ma and that a comparable amount must have been removed from the southern front of the dabie shan sulu region of eastern china between the middle triassic and middle jurassic in both approximately equivalent sediment volumes are preserved in the sedimentary basins adjacent to the orogens in addition the rapid increase in the 87 sr 86 sr of the seawater during the interval from about 20 to 15 ma is compatible with erosion of this amount of material

precise determinations of the equilibria kyanite sillimanite and kyanite andalusite and a revised triple point for al 2 sio 5 polymorphs

metamorphic and structural setting of archaean amphibolitehosted gold deposits near southern cross southern cross province yilgarn block western australia abstract the southern cross archaean greenstone belt comprises dominantly low to mid amphibolite facies high strain domains which show evidence of a complex deformational and metamorphic history aeromagnetic field and petrographic data suggest that this complex structural metamorphic history was related to a single progressive deformation event which was broadly synchronous with granitoid emplacement between 2 68 and 2 62 ga lode gold deposits at corinthia hopes hill fraser s and polaris south occur in sequence from north to south along the fraser s corinthia shear zone in the southern cross greenstone belt corinthia and hopes hill are situated along a sheared granitoid greenstone contact whereas fraser s and polaris south occur within the greenstones about 200 m west of the contact gold mineralisation along the fraser s corinthia shear zone is associated predominantly with variably deformed quartz pyrrhotite pyrite plagioclase and or pyroxene calcite quartz plagioclase apatite veins with zoned alteration haloes of quartz plagioclase pyroxene calcite apatite and amphibole biotite chlorite there are accessory amounts of scheelite chalcopyrite arsenopyrite and galena with the fe sulphides bismuth and gold a variety of evidence including structural timing p t conditions deduced from critical metamorphic 550 c 2 5 3 7 kbars and metasomatic alteration assemblages 520 c 3 4 kbars the high thermodynamic variance of the metasomatic mineral assemblages and the zoning of individual alteration minerals indicates that gold related wallrock alteration occurred during or immediately after peak metamorphism there is some evidence for a sympathetic decline in metamorphic grade and the temperature of gold related alteration from south polaris south to north corinthia along the mineralised shear zone the shear zone acted as a major conduit for ore fluids at a depth of about 12 14 km 3 3 5 kbars lithostatic pressure in the crust gold mineralisation along the shear zone is related to large and small scale extensional crenulation cleavages the gold deposits might thus represent a relatively deep section of the crustal continuum of lode gold deposits proposed for the yilgarn block

the tectonothermal evolution of the kirwanveggen h u sverdrupfjella areas dronning maud land antarctica abstract three episodes of deformation spanning a period of 900 ma are recognised the first deformation at 1000 ma involved progressive yet distinct stages within a protracted composite event involving recumbent folding low angle thrust faulting and locally highly oblique transpressive strike slip shearing these structures suggest tectonic transport from the south and southeast during d 1 d 2 at 500 ma is variable in the different areas and involved thrust faults and folding with locally developed axial planar foliations the orientations of the fault planes and axial planar structures suggest transport from the west and northwest in western sverdrupfjella and from the southeast in kirwanveggen d 3 involved normal faulting and jointing adjacent and parallel to the jutulstraumen glacier in the west the joints affect the alkaline complexes some of which are jurassic in age and consequently d 3 is related to the breakup of gondwana four phases of metamorphism related to the deformation are recognised the dominant mineral assemblages m 1 3 are typical of medium to high grade metamorphism discordant mafic intrusions provide evidence of a long history of metamorphism mafic nodules from the eastern part of the area contain high pressure assemblages representing m 1 assemblages and textures indicate that m 2 was related to isothermal decompression related to the uplift caused by thrust faulting during d 1 the period between m 2 and m 3 appears to have involved annealing at mid crustal levels m 3 mineral development is dominated by biotite which is oriented axial planar to d 2 folds m 4 assemblages are typically low grade and involve hydrothermal alteration resulting in chloritisation and sausseritisation related to d 3

comparison of garnet biotite calcite graphite and calcite dolomite thermometry in the grenville orogen ontario canada the elzevir terrane of the grenville orogen in southern ontario contains metapelites and abundant graphitic marbles that were regionally metamorphosed from the upper greenschist to upper amphibolite facies comparative thermometry was undertaken with widely used calibrations for the systems garnet biotite calcite dolomite and calcite graphite temperatures that are obtained from matrix biotites paired with prograde garnet near rim analyses are usually consistent with those determined using calcite graphite thermometry however calcite graphite thermometry occasionally yields low temperatures due to lack of equilibration of anomalously light graphite application of calcite graphite and garnet biotite systems may yield temperatures up to 70 c higher than calcite dolomite in amphibolite facies rocks calcite dolomite temperatures most closely approach those from calcite graphite and garnet biotite when the samples contain a single generation of dolomite and calcite grains contain no visible dolomite exsolution lamellae however some of these samples yield temperatures considerably lower than temperatures calculated from calcite graphite and garnet biotite thermometry indicating that the calcite dolomite thermometer may have been partially reset during retrogression estimated peak metamorphic temperatures of regional metamorphism between madoc upper greenschist facies and bancroft upper amphibolite facies range from 500 to 650 c these results place the chlorite staurolite isograd at 540 c the kyanite sillimanite isograd at 590 c and the sillimanite k feldspar isograd at 650 c although each thermometer may have an absolute uncertainty of as much as 50 c the 50 to 60 c temperature differences between the isograds are probably accurate to 10 to 20 c an incomplete picture of the thermal gradients can result from the application of only one thermometer in a given area simultaneous application of several systems allows one to recognize and overcome the inherent limitations of each thermometer

multiple generations of extensional detachments in the rhodope mountains northern greece evidence of episodic exhumation of high pressure rocks abstract an integrated structural and petrological study shows that exhumation of high rocks of the rhodope occurred in several pulses the structurally uppermost kimi complex recording an early cretaceous high p metamorphism was exhumed between about 65 and 42 ma the sidironero kardamos and kechros complexes that record early tertiary high metamorphism at least 19 kbar at 700 c were exhumed at 42 30 ma exhumation occurred with isothermal decompression strain episodes depict thrusting of medium high grade above lower grade high p rocks syn thrusting extension and post thrusting extension polyphase extension created several generations of detachment zones which in sum excise about 20 km of material within the crustal profile this reduction in crustal thickness is consistent with a reduction of the present crustal thickness from more than 40 km to less than 30 km in the eastern rhodope we mapped the post thrusting xanthi low angle detachment system over 100km from its break up zone above the sidironero complex central rhodope into the eastern rhodope this detachment shows an overall ese dip with a ramp and flat geometry cutting across the earlier thrust structures the kimi complex is the hanging wall of all synand post thrusting extensional systems on top of the kimi complex marine basins were formed from the lutetian c 48 43 ma through the oligocene during extension successively at c 26 to 8 ma the thasos pangeon metamorphic core complexes were exhumed in these times representing the early stages of aegean back arc extension the strymon and thasos detachment systems caused crustal thinning in the western rhodope renewed heating of the lithosphere associated with magmatism and exhumation of hot middle crust from beneath the sidironero complex occurred we focusoxn the geometry timing and kinematics of extension and contraction structures related to the 42 30 ma interval and how these exhumed high p rocks we interpret high rocks exhumed in this interval as a window of the apulian plate beneath the earlier in the cretaceous accreted kimi complex

magmatic evolution of the penon rosado granite petrogenesis of garnet bearing granitoids garnet is an uncommon accessory mineral in igneous rocks but is petrologically significant the penon rosado granite 469 4ma at cerro asperecito is an s type granite that contains an unusual amount of magmatic garnet combined petrology chemistry mineralogy and whole rock geochemistry indicates that the magma was produced by partial melting of the surrounding metasedimentary rocks and subsequent differentiation by fractional crystallization during emplacement with garnet occurring throughout the crystallization sequence three facies are recognised prg1 sio2 65 70 represents cumulates prg2 sio2 70 88 represents a differentiated melt and prg3 sio2 74 59 a residual melt the fractionation of mn in garnet and the proportion of garnet crystallizing are roughly controlled by the evolving composition of the different granitic facies geothermobaric calculations reveal an initial crystallization temperature of 764 792 cand a pressure of 5 9 6 0 kb indicating that the parental magma was emplaced atmiddle crustal depths 1920 km in moderate low magmatic temperature conditions major cao na2o k2o and trace element rb sr ba contents in the penon rosado granite strongly suggest anatexis was the outcome of h2o fluxed melting of metagreywacke with heat input from a major metaluminous suite our studies reveal that garnet formed by direct crystallization from peraluminous magma in equilibrium with solid phases such as biotite and white mica we confirm previous suggestions that zoning in garnet is strongly temperature dependent thus magmatic garnets in granitic rocks crystallized above 700 c have spessartine inverse bell shaped profile or are unzoned whereas garnet exhibiting spessartine bell shaped profile must be considered of metamorphic origin i e xenocrystic or formed in very felsic magmas sio2 73 76 crystallizing below 700 c 2006 elsevier b v all rights reserved

provenance information recorded by mineral inclusions in detrital garnet abstract garnet single grain analysis is an often used and well established tool in sedimentary provenance studies especially when metamorphic source rocks are involved so far however solely the geochemical composition of detrital garnets is considered to draw conclusions concerning probable source rocks the gained information is often limited by i geochemical overlap of garnets derived from different lithology and metamorphic grade ii similar probabilities of belonging to more than one source rock type and iii the limitations of discriminating different protolith compositions here we present the first attempt of using mineral inclusions in detrital garnet as a provenance tool we analyzed the inclusions of 300 fine to medium sand sized detrital garnets from two proximal modern sand samples taken in the hp uhp western gneiss region of sw norway all mineral inclusions 2 m were identified by raman spectroscopy showing that i most garnets from hp uhp metamorphic source rocks contain mineral inclusions 2 m ii raman spectroscopy is a very powerful tool to characterize the inclusion types and iii less stable mineral phases like kyanite omphacite diopside enstatite coesite amphibole group and epidote group minerals occur as inclusions in garnet these minerals which are important for provenance studies can thus be preserved in the sedimentary record as long as garnet is stable the combination of inclusion types in garnet and geochemical garnet classification shows that i inclusions well reflect the geological characteristics of the sampled catchments implying that they are useful indicators for hp uhp provenance and ii inclusions in garnet can be used to support and enhance the provenance information obtained by garnet geochemistry

sphysicochemical conditions of fluid wall rock interaction at amphibolite facies conditions in two archean hydrothermal gold deposits in the mt york district pilbara craton western australia synamphibolite facies archean gold mineralization in the mt york district pilbara craton western australia is hosted in metamorphosed banded iron formation main hill breccia hill prospect amphibolites and ultramafic schists zakanaka prospect mineralization at main hill occurs in quartz breccias with sulfide matrices and in altered wall rock adjacent to quartz biotite amphibole clinopyroxene veins alteration associated with quartz veins is zoned with biotite pyrrhotite vein selvedges and a distal calcic amphibole arsenopyrite lollingite zone hydrothermal biotite and actinolite have highest mg mg fe ratios where associated with abundant sulfarsenides in the distal alteratin zone whole rock geochemical analyses and calculated metasomatic reactions indicate the addition of k al s as au ag and ni during hydrothermal alteration mineralization at zakanaka is characterized by a broad wall rock alteration halo of biotite amphibole and zoned quartz calc silicate veins proximal to ore

compositional zoning patterns of garnet during prograde metamorphism from the yanai district ryoke metamorphic belt southwest japan abstract in the yanai district southwest japan garnet crystals in pelitic and siliceous rocks are normally zoned reversely zoned or homogeneous normally zoned crystals show a continuous decrease in mn content from the core towards the margin whereas reversely zoned crystals show enrichment of mn at the margin normally zoned garnet grew by one of two distinct coarsening mechanisms either nucleation and growth or impingement and overgrowth in pelitic rocks there is a systematic change from normal zoning to homogeneous and reverse zoning with increasing metamorphic grade this can be ascribed to the enhancement of internal diffusion with increasing metamorphic temperature in the cordierite i zone with an estimated metamorphic temperature of 560 30 garnet in pelitic rocks with a grain size larger than 0 2 mm preserves its zoning pattern whereas garnet in siliceous rocks with a similar grain size is homogeneous this suggests that both rock type and grain size are factors that influence the degree to whole growth zoning of garnet is homogenized the relative paucity of biotite in siliceous rock can explain the development of fine grained garnet in this rock type which is therefore easily homogenized coarse homogeneous garnet in the siliceous rocks was formed by impingement of small grains during prograde metamorphism such aggregates are easily homogenized by both internal and grain boundary diffusion

tectonics of the scandian orogeny and the western gneiss region in southern norway two crust forming events dominate the precambrian history of the western gneiss region wgr at about 1800 1600 ma and 1550 1400 ma the influence of the sveconorwegian orogeny 1200 900 ma is restricted to the region south of moldefjord romsdalen a series of anorthosites and related intrusives are present possibly derived from the now lost western margin of the baltic craton that may have been emplaced in the wgr as an allochthonous unit before the ordovician

shock induced formation of kyanite al2sio5 from sillimanite within a dense metamorphic rock from the ries crater germany a dense 3 34 g cm 3 garnet sillimanite rich metamorphic rock from the suevite breccia of the ries impact crater was studied by scanning electron microscopy and raman microprobe spectroscopy in the strongly shocked rock clast kyanite was formed from sillimanite under momentary high pressures of natural shock waves kyanite aggregates were found as thin 0 3 2 0 m seams along grain boundaries between and fractures within sillimanite grains within these seams kyanite c axes are oriented perpendicular to original grain boundaries and fractures in addition larger up to 10 m isolated kyanite grains were rarely found within host sillimanite filamentary kyanite aggregates and isolated crystals typically show shrinkage cracks due to volume decrease 10 locally broad interstices between sillimanite crystals are filled with aluminosilicate glass containing a high volume fraction of sub micrometer sized euhedral crystals the silica rich glass suggests incongruent melting of sillimanite at local post shock temperatures significantly higher than 1 300 c the edges of adjacent sillimanite grains are thermally and chemically altered the local generation of temperature spikes is attributed to strong shock wave interactions due to very high shock impedance contrasts

quaternary tectonics and large scale gravitational deformations with evidence of rock slide displacements in the central apennines central italy eight cases of large scale gravitational movements with evidence of rock slide type displacements evolving close to quaternary faults have been analysed in the central apennines geomorphological and structural surveys have defined the relationship between the gravitational displacements and the tectonically controlled modifications of the landscape the evolution of all the investigated cases has been conditioned by the presence of fault planes located along the mountain slopes in most cases mt cefalone cima della fossa villavallelonga casali d aschi gioia dei marsi the faults played or are playing a primary role in increasing the local relief and their activity represents the main geomorphic factor conditioning the gravitational movements this kind of relationship has been observed along mountain slopes bordering depressions which have not been drained for most of their geomorphic history or have been characterised by an evolution of the hydrographic network that has been conditioned only by the local tectonic subsidence in such cases the gravitational movements develop in the footwalls of the faults in other cases fiamignano pescasseroli the faults have played a passive role since they only bound the sliding masses and coincide with the surficial expressions of the sliding planes therefore the gravitational displacements develop in the hangingwall of the faults the evolution is conditioned by the incision of the hydrographic network in response to regional quaternary uplift the illustrated case studies provide a wide range of examples of the gravitational response of slopes to the modifications of the landscape due to linear and areal tectonics the identification of the geomorphic traces of the large scale gravitational movements along fault controlled mountain fronts has implications for hazard particularly for the evolution of the displacement the quantitative analysis of the vertical displacements and data on the characteristics of the surface breaking during historical earthquakes demonstrate that along fault offsets strongly increases where the unstable large scale rock masses are located therefore the large coseismic vertical offset may represent a major problem for the displacement of utilities and may represent a potential cause for the sudden and catastrophic evolution of the gravitational movement

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

u pb ages constraining batholith emplacement contact metamorphism and the formation of gold and w mo skarns in the southern cross area yilgarn craton western australia gold mines in the archean southern cross greenstone belt central yilgarn craton have produced more than 220 metric tons t of gold the deposits are characterized by a pyroxene rich gangue and have been interpreted as synmetamorphic amphibolite facies replacement deposits and as postmetamorphic intrusion related skarns we present ion microprobe u pb zircon data constraining the age of amphibolite facies contact metamorphism in the aureole of the ghooli dome the largest granitoid batholith intruding the southern cross belt drill cores from the copperhead gold mine provided zircons from an altered quartz porphyry sill located 300 m southwest of the ghooli dome and zircons from the monzogranite gneiss at the border of the batholith the porphyry sill contains embayed igneous zircons dated by a concordant u pb age of 2912 5 ma and euhedral zircons of metamorphic crystal habitus dated by a second concordant age of 2772 5 ma the igneous zircons are slightly younger than those recovered from another sill of quartz porphyry sampled at the southern star mine which define a single concordant u pb age of 2934 7 ma the metamorphic zircons in the porphyry at copperhead record the same age as the igneous zircons 2775 10 ma in the monzogranite gneiss of the ghooli dome this pluton extends more than 40 km to the southeast of copperhead and also forms the batholith border at the corinthian and fraser s mines these gold deposits too are hosted by amphibolite facies greenstones contact metamorphosed at 2772 5 ma the corinthian skarn 2620 6 ma formed 150 m y after high grade metamorphism and consequently cannot be classified as synmetamorphic or metamorphogenic a review of field relationships and of published geochronometric data suggests that the gold skarns in the southern cross area are related in space and time to a suite of magnetite series granite pegmatite complexes these granites dated regionally at 2 66 to 2 60 ga are also associated with gold bearing w mo skarn greisen or skarn systems of up to 6 km strike length the numerous skarns exposed in the deeply eroded 14 km paleodepth central yilgarn craton are members of a recently recognized group of intrusion related gold deposits which are part of continental margin tungsten tin provinces

tectonic evolution of proterozoic rocks in the cimarron mountains northern new mexico usa abstract portions of three proterozoic tectonostratigraphic sequences are exposed in the cimarron mountains of new mexico the cimarron river tectonic unit has affinities to a convergent margin plutonic volcanic complex igneous hornblende from a quartz diorite stock records an emplacement pressure of 2 2 6 kbar rocks within this unit were subsequently deformed during a greenschist facies regional metamorphism at 4 5 kbar and 330 50 c the tolby meadow tectonic unit consists of quartzite and schist mineral assemblages are indicative of regional metamorphism at pressures near 4 kbar and temperatures of 520 20 c a low angle ductile shear zone separates this succession from gneisses of the structurally underlying eagle nest tectonic unit gneissic granite yields hornblende pressures of 6 8 kbar pelitic gneiss records regional metamorphic conditions of 6 7 kbar and 705 15 c overprinted by retrogression at 4 kbar and 530 10 c comparison of metamorphic and retrograde conditions indicates a p t path dominated by decompression and cooling the low angle ductile shear zone represents an extensional structure which was active during metamorphism this extension juxtaposed the tolby meadow and eagle nest units at 4 kbar and 520 c both units were later overprinted by folding and low grade metamorphism and then were emplaced against the cimarron river tectonic unit by right slip movement along the steeply dipping fowler pass shear zone an argon isotope correlation age obtained from igneous hornblende dates plutonism in the cimarron river unit at 1678 ma muscovite associated with the greenschist facies metamorphic overprint yields a 40 ar 39 ar plateau age of 1350 ma by contrast rocks within the tolby meadow and eagle nest units yield significantly younger argon cooling ages hornblende isotope correlation ages of 1394 1398 ma are interpreted to date cooling during middle proterozoic extension muscovite plateau ages of 1267 1257 ma appear to date cooling from the low grade metamorphic overprint the latest ductile movement along the fowler pass shear zone post dated these cooling ages argon released from muscovites of the eagle nest tolby meadow composite unit at low experimental temperatures yields apparent ages of c 1100 ma similar ages are not obtained north east of the fowler pass shear zone suggesting movement more recently than 1100 ma

an experimental determination of the effect of bulk composition on phase relationships in metasediments at near solidus conditions sediments of terrigenous origin represent a conspicuouspart of the cover of the oceanic and continental crust taylor mclennan 1985 wedepohl 1991 pelitesand greywackes are involved in a variety of processes from deep mass transfer in subduction environments e g chopin 1984 smith 1984 sobolev shatsky 1990 reinecke 1991 responsible for dehydration and fluidrelease during dehydration schmidt etal 2004 to partialmelting in continental collision zones which is at theorigin of intracrustal differentiation clemens vielzeuf 1987 the evolution of metapelites and metagreywackescan be reconstructed if the dependence of phase relation ships on pressure temperature and bulk composition iswell known and under h

pressure dependence and anisotropy of p wave velocities in ultrahigh pressure metamorphic rocks from the dabie sulu orogenic belt china implications for seismic properties of subducted slabs and origin of mantle reflections the compressional wave velocities vp pressure derivatives vpv and anisotropy a of three types of eclogites and country rocks from the dabie sulu ultrahigh pressure uhp metamorphic belt china have been measured under confining pressures up to 800 mpa type 1 eclogites which are coarse grained and subjected to almost no retrograde metamorphism experienced recovery accommodated dislocation creep at peak metamorphic conditions in the diamond stability field type 2 eclogites are fine grained reworked type 1 materials that experienced recrystallizationaccommodated dislocation creep under quartz coesite boundary conditions during the early stage of exhumation type 3 eclogites are retrogressed samples that were overprinted by significant amphibolite facies metamorphism during a late stage of exhumation within the crust type 1 eclogites are richer in al2o3 and mgo but poorer in sio2 and na2o than type 2 and type 3 eclogites anisotropy of type 1 and type 2 eclogites is generally low b4 because volumetrically important garnet is elastically quasi isotropic while type 3 eclogites can exhibit high anisotropy n10 due to the presence of strongly anisotropic retrograde minerals such as amphibole plagioclase and mica the transition of the pressure dependence of velocity from the poroelastic to elastic regimes occurs at a critical pressure pc which depends mainly on the density and distribution of microcracks and in turn on the exhumation history of rocks the vp pressure relationship can be expressed by vp a lnp 2 blnp c pvpc and vp v0 dp pzpc where p is the confining

comparison of calcite dolomite thermometry and carbonate silicate equilibria constraints on the conditions of metamorphism of the llano uplift central texas u s a temperatures based on the composition of calcite coexisting with dolomite calcite dolomite thermometry range from 475 to 600 c for 63 marbles from the llano uplift of central texas the highest temperatures 600 c were obtained by carefullyreintegrating calcite containing exsolved lamellae of dolomite in some cases these high temperatures were determined for marbles that contain an isobarically invariant assemblage consisting of calcite dolomite tremolite diopside forsterite at a pressure of 3 kbar these five minerals are stable at 630 ocand xco 0 62 in contrast relatively low calcite dolomite temperatures of 475 480 cwere obtained for marbles containing the assemblage calcite dolomite tremolite talc this talc bearing assemblage is stable at 475 oc depending on fluid composition at a pressure of 3 kbar additional isobarically univariant equilibria are stable at intermediate temperatures generallybetween 535 and 630 0q and these are also generallyconsistent with results obtained from calcite dolomite thermometry agreement between the calcite dolomite temperatures and those inferred from silicate carbonate equilibria in the marbles indicates that the temperatures generally reflect peak conditions of metamorphism although some resetting has occurred the marbles having the highest calcite dolomite temperatures as well as those containing the hightemperature isobarically invariant assemblage are generally found close to post tectonic pluton contacts indicating that some of the amphibolite facies assemblagesare related to the emplacement ofthe granitic intrusions relatively low temperatures are recorded within approximately 2 km of pluton contacts suggestinga possible thermal aureole however relatively high temperatures of 550 600 c are recorded in marbles that are not spatially related to post tectonic granites 2 km from pluton contacts these temperatures may be relicts of an earlier metamorphic event although they could be related to granites that were emplaced above or below the current erosional level

thermobarometric constraints on the depth of exposure and conditions of plutonism and metamorphism at deep levels of the sierra nevada batholith tehachapi mountains california we present thermodynamic estimates of pressures temperatures and volatile activities in variably deformed gabbroic to granitic cretaceous 115 100 ma batholithic and framework rocks of the tehachapi mountains southernmost sierra nevada california al contents of hornblende in granitoids imply igneous emplacement at 8 kbar in the southernmost tehachapi mountains with lower pressures 3 7 kbar to the north metamorphic pressures and temperatures for garnet bearing paragneisses and metaigneous rocks were estimated on the basis of garnet hornblende plagioclase quartz and garnet biotite plagioclase quartz thermobarometers disparate results for the metaigneous rocks from the latter system point to the difficulty of applying pelite based thermobarometers to rocks of contrasting composition and mineralogy preferred pressures cluster at 7 1 9 4 and 3 6 4 3 kbar incomplete knowledge of reaction histories however limits our interpretation of the lower pressures because they are minimum estimates the 4 kbar samples are all from a small area and if our interpretation is correct they imply a local more shallow event superimposed on crust once residing at deeper structural levels garnet hornblende and garnet biotite temperatures are less coherent likely owing to retrograde fe mg exchange and range from 570 to 790 c the majority of the rocks are igneous and affected by recrystallization and metamorphism during subsolidus cooling they are not granulites country rock paragneisses are typically migmatized at peak metamorphic conditions near that of the wet granite solidus 690 c veinlike paragenesis of garnet in the metaigneous rocks suggests formation related to the presence of a fluid phase thermodynamic estimates of volatile activities in these garnet bearing assemblages suggest variable mostly co 2 rich fluid compositions in the absence of any pervasive fluid flux the igneous rocks of the tehachapi mountains were thus intruded at depths of 30 km making them the deepest known exposed components of the cretaceous sierra nevada batholith metamorphism occurred at these great depths and perhaps locally after 15 km of uplift before 87 ma implying an uplift rate of 1 2 mm yr a minimum uplift rate is 0 6 mm yr this original uplift and possible subsequent uplift events may have been related to underthrusting of a block of rand schist from what is now the southeast with concomitant widespread ductile deformation the deduced pressure temperature and uplift history is similar to those of high pressure high temperature cretaceous batholithic rocks in salinia and the san gabriel mountains but direct correlation is not wan anted when compared with higher level intrusive rocks from analogous portions of the sierra nevada batholith to the north the tehachapi rocks reveal a deep batholith that is more heterogeneous and somewhat more mafic on average but displaying a similar level of isotopic hybridization involving mantle and crustal sources the batholith is quartz rich at these levels suggestive of a weak ductile middle crust susceptible to prolonged deformation and possible delamination

metamorphism denudation and sea level in the archean and cooling of the earth abstract over long enough time scales an antagonistic balance acting between tectonics uplift and rifting and the sedimentary cycle erosion and deposition probably keeps continental surfaces close to sea level we argue that this balance constitutes the primary mechanism for keeping long term continental freeboard constant by regulating the continental thickness an important implication is that the long term uplift or down warp history of ancient continental segments provides direct information on secular changes in the isostasy of the adjacent ocean basins through time the amount of uplift can be estimated from the regional metamorphic grade the burial pressures at present exposure of ten undisturbed archean granite greenstone segments are estimated to be 1 5 0 5 kb from this we infer a maximum long term uplift and erosion of 5 2 km for stable continent since 3 0 ga implying a mean continental thickness of 46 km at the time of crustal stabilization for a constant mean ocean depth isostasy requires a palaeo oceanic crust 14 2 km thick in the middle archean alternatively if little continent existed then the oceans would have been shallower and the palaeo oceanic crust 21 2 km thick assuming plate spreading did occur in the archean potential temperatures in the shallow mantle at 3 ga were 90 30 c or 170 20 c for no continent hotter than those prevailing today these temperatures translate into time averaged cooling rates for the shallow mantle of 57 c ga 1 and are comparable to estimates of the present day cooling rate for the whole earth the low burial pressures are a strong argument against the existence of catastrophic mantle flush events in the geological past which have been predicted by some mantle convection models taken together these constraints suggest a plume related geological setting i e oceanic plateau like flood basalt for the initial stage of greenstone belt evolution

empirical evaluation of solution models for pelitic minerals and their application to thermobarometry one of the major sources of uncertainty for thermobarometry in pelitic rocks is the inability of solution models to represent accurately the non ideal behavior of important pelitic minerals in particular garnet biotite and plagioclase in recent years a large number of different solution models have been proposed for these phases the purpose here is to test the effects on the overall uncertainty of the most commonly used solution models using the garnet muscovite annite plagioclase gmap barometer and the empirical calibration technique the gmap reaction has been empirically calibrated several times with varying results due in large part to the choice of solution models the method s dependence on the choice of solution model makes it an excellent was in which to address the quality of specific models by repeating the calibration exercise for different combinations of solution models it is possible to determine which set of solution models results in the lowest uncertainties using a sample set of 72 published electron microprobe analyses of pelitic rocks containing the assemblage garnet muscovite biotite plagioclase aluminum silicate quartz as an independent test of the suitability of solution models we compare the fit of the sample set to the kyanite sillimanite equilibrium curve obtaining thermobarometric estimates by simultaneous solution of the garnet biotite exchange thermometer and gmap calibrated from thermochemical data

carbon isotopic thermometry and geobarometry of sillimanite isograd in thermal aureoles the depth of emplacement of upper crustal granitic bodies carbon isotope fractionation between coexisting calcite and graphite c has been studied in metamorphosed limestones from three thermal aureoles around cretaceous granitic bodies i e tanohata tono and senmaya aureoles in the kitakami mountains northeast japan c in each aureole decreases toward the granitic bodies and becomes virtually uniform near the sillimanite isograd for metapelites although calcite has variable isotopic ratios reflecting the original sedimentary compositions the relationships indicate that isotopic equilibrium has been attained in metamorphosed limestone of sillimanite grade estimated c at the sillimanite isograd is similar in the tanohata and tono aureoles but different in the senmaya aureole with smaller carbon isotopic fractionations from the temperature dependence of c and the negative dp dt of andalusite sillimanite equilibrium we conclude that the sillimanite isograd in the senmaya aureole was under higher temperature and lower pressure than in the other two localities temperatures at the sillimanite isograd are estimated by using existing calibrations of carbon isotopic exchange between calcite and graphite whereas pressures are estimated from carbon isotopic temperatures and the andalusite sillimanite equilibrium holdaway and mukhopadhyay 1993a consistency of the p t estimates is examined in the light of phase equilibria in the pelitic system the estimated pressures at the sillimanite isograd are at about 2 1 2 7 0 2 kbar for the tanohata and tono aureoles and less than 1 kbar for the senmaya aureole respectively geobarometry of sillimanite isograd in thermal aureoles indicates a marked difference in the depth of solidification of upper crustal granitoids the senmaya pluton has intruded and solidified at a very shallow level of less than 4 km whereas the tanohata and tono plutons are more deep seated ca 8 10 km the method can also be an effective tool in studying low pressure type metamorphism in which geothermobarometry using garnet is not always applicable

essential ingredients to the dynamics of westerly wind bursts abstractwesterly wind bursts wwbs are brief anomalously westerly winds in the tropical pacific that play a role in the dynamics of enso through their forcing of ocean kelvin waves they have bee

the urumieh plutonic complex nw iran a record of the geodynamic evolution of the sanandaj sirjan zone during cretaceous times part i petrogenesis and k ar dating the urumieh plutonic complex is located in the northwestern part of the sanandaj sirjan zone iran the urumieh plutonic complex comprises three components i e a dioritic suite a granitic suite consisting of biotite bearing granites and younger stocks i e an alkaline suite alkali syenite and alkali granite and a muscovite bearing granite based on k ar chronology of separated minerals amphibole biotite muscovite and feldspar and field observations the urumieh complex was built during two distinct episodes the diorite and granite suites were emplaced between 100 and 92 ma whereas the younger suites were emplaced between 82 and 80 ma the dioritic suite has sio2 contents in between 56 59 wt and major and trace elements characteristic of mafic i type granitoids a ckn molar ratio 0 81 0 88 this suite is characterized by relatively high mg 49 low na2o content 3 5 wt and a relatively high abundance of lile incompatible elements their chondrite normalized ree patterns are relatively flat la yb n 7 in average and show small or no negative eu anomalies eu eu 0 9 in average some diorites show mingling and mixing textures that may support local crustal contamination of the dioritic melt geochemical features suggest that diorites formed in a subduction setting by partial melting of metasomatized mantle the coeval granites are peraluminous 1 04 molar a ckn 1 37 with sio2 contents between 66 69 wt their chondrite normalized ree patterns are slightly enriched in lree relative to hree la yb n 11 in average with negative eu anomalies eu eu 0 4 in average these granites have biotite as the main mafic mineral and locally contain restitic xenoliths they originated by partial melting of metasediments the younger alkaline syenite and granite are only slightly peraluminous molar a cnk 1 04 in average they show enrichment in hfse high contents of ree and relatively high feo mgo and ga al ratios typical of a type magmas the other younger granite pluton dourbeh granite has peculiar mineralogical and geochemical features none of these late syenite and granites were intruded by mafic dikes and they do not contain any comagmatic mafic enclaves they seem to have been derived only from crustal melting changing of magmatic sources during the 100 80 ma time interval is discussed with respect to the geodynamic context the first magmatic episode 100 92 ma is regarded as subduction related whereas the second one at ca 80 ma likely ocurred during the collision between the arabian margin and the sanandaj sirjan zone

mineral equilibria and zircon garnet and titanite u pb ages constraining the ptt path of granite related hydrothermal systems at the big bell gold deposit western australia the big bell deposit 75 t gold is located in a narrow spur of the meekatharra greenstone belt yilgarn craton western australia two ore bodies are located in a calcic potassic contact alteration zone overprinting lineated granodiorite dykes and amphibolite almandine cummingtonite hornblende skarn 1 3 g t au 1700 g t as 330 g t w and the muscovite microcline gneiss 3 5 g t au 580 g t sb 620 g t w of the main lode genetic models vary from pre to post metamorphic replacement hornblende plagioclase pairs in amphibolite constrain peak metamorphic temperature to 670 50 c in contrast garnet biotite thermometry provides estimates of 578 50 and 608 50 c for garnet cordierite biotite schist bordering the skarn and enveloping the main lode garnet cordierite and garnet hornblende pairs extend the range of fluid temperature to 540 65 c well below peak metamorphic temperature at 540 600 c the alteration assemblage andalusite sillimanite constrains pressure to 300 400 mpa corresponding to 11 14 km crustal depth published u pb ages indicate that metamorphism took place in the aureole of the southeast granodiorite tonalite batholith 2740 2700 ma followed by gold mineralization at 2662 5 ma and by the emplacement of biotite granite and sn ta nb granite pegmatite dykes at 2625 2610 ma amphibolite xenoliths in granite northwest of the deposit record the lowest temperature 628 50 c suggesting it lacks a metamorphic aureole the rare metal dykes are spatially associated with epidote albite and andradite diopside skarns 1 5 g t au mined where enriched in the weathered zone we analysed hydrothermal zircon intergrown with andradite concordant u pb ages of 2612 7 and 2609 10 ma confirm the presence of a second granite related system the zircons display oscillatory zoning and have low th u ratios 0 05 0 08 low th titanite from an albite granite dyke has a concordant but reset u pb age of 2577 7 ma

rapid quench hydrothermal experiments at mantle pressures and temperatures new experimental methods for the encapsulation extraction and analysis of large volumes of aqueous fluids enable studies of mineral solubilities and dissolution kinetics with the piston cylinder apparatus quench rates and volumes of experimental fluids with these methods are comparable with those used in modern hydrothermal experiments employing cold seal vessels analyses of fluid compositions are reproducible and consistent with independent results the techniques permit experimental investigations that will better characterize fluid rock interaction in such environments as subducting slabs the mantle wedge barrovian metamorphic belts and middle to lower crustal granulites

alternating contraction and extension in the hinterlands of orogenic belts an example from the raft river mountains utah combined macroscopic to microscopic structural analyses detailed geologic mapping and thermochronology were used to study the structural evolution of midcrustal rocks of the sevier orogenic belt hinterland in northwestern utah these results when combined with previous studies provide new insight into the structural history of this region and suggest alternating tectonic contraction and extension during mesozoic to early cenozoic time two allochthons form the upper plate of the miocene raft river detachment fault in the eastern raft river mountains the lower allochthon comprises neoproterozoic ordovician and pennsylvanian strata and is bounded below by the raft river detachment fault and above by the middle detachment fault strata within the lower allochthon were dramatically attenuated by two episodes of ductile deformation the first deformation d1 took place at metamorphic temperatures of 500 c and resulted in penetrative fabrics throughout these rocks that record combined flattening and top to northeast shearing strains the second deformation d2 resulted in significant stratigraphic attenuation along discrete top to the west shear zones that are generally parallel to lithologic contacts separates of synkinematic muscovite from the penetrative fabric yield 40ar 39ar cooling ages that indicate that d1 deformation occurred prior to cooling ca 90 ma both fabrics were subsequently folded about d3 kilometer scale recumbent folds the areally extensive middle allochthon composed chiefly of pennsylvanian and permian rocks metamorphosed in the greenschist facies was emplaced d4 along the low angle middle detachment fault this fault cuts across various structural levels of the recumbently folded lower allochthon in its footwall and juxtaposes greenschist facies over amphibolite facies metamorphic rocks the lower and middle allochthon were subsequently deformed d5 into open folds with north trending axes neogene extension d6 produced an 200 m thick top to east ductile shear zone in precambrian rocks and formed the younger raft river detachment fault which forms the present upper contact of the ductile shear zone northeast vergent d1 fabrics probably record shortening deformation on the basis of fabric correlations with the grouse creek and albion mountains deformation kinematics and synkinematic prograde metamorphism d2 attenuation faults have been interpreted to record crustal extension of late cretaceous age if d3 recumbent folds developed during extension then the deformation sequence records early shortening followed by protracted extensional unroofing with variable structural styles the favored alternative is that d3 recumbent folds developed during shortening in this case d1 through d4 record episodic alternations of contraction and extension such alternations are consistent with observations from analog and theoretical models of contractional mountain belts and suggest that the hinterland of the sevier orogenic belt underwent dynamic adjustments in crustal thickness and deformation kinematics in response to changes in the boundary conditions of the orogenic belt