boudinage and composite boudinage in superposed deformations and syntectonic migmatization abstract the banded gneisses of the jasidih deoghar area of east india behaved as a complex geological multilayer which evolved through the combined effects of deformation and leucosome emplacement the early foliation and banding were transposed and retransposed by two generations of isoclinal folds the intensity of foliation development the layer thickness ratios and the rheological contrasts within the gneisses changed both in space and in time under layer normal compression these complex multilayers gave rise to a variety of boudins and of their pegmatite filled separation zones the geometrical relations with successive generations of folds can distinguish the closely associated pre f 1 syn f 1 and syn f 2 boudins d 2 boudinage occurred at an advanced stage of f 2 folding so that boudinage induced subhorizontal extension was considerably less than the total subhorizontal extension during d 2 composite boudinage occurred during progressive syntectonic leucosome emplacement in the course of which a group of boudinaged layers with a profusion of coarse quartz feldspar leucosome became more competent than the adjoining rocks and underwent boudinage as a whole

identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

ore forming fluids and mineralization mechanism of laoshankou fe cu au deposit in northern margin of junggar the laoshankou ore district is located in the northern margin of junggar basin the fe cu au minerals mainly occur in the massive lumpy veinlike brecciaed and veinlet disseminaed forms in the diorite porphyrite and basaltic volcanic rocks garnets of the skarn period are characterized by the development of melt inclusions and fluid inclusions fluid inclusions in epidote of the retrogressive metamorphism stage are liquid inclusions fluid inclusions in calcite of the quartz sulfide carbonate period mostly contain liquid inclusions daughter mineral bearing inclusions and three phase co2 bearing inclusions homogenization temperatures of fluid inclusions at the early skarn stage vary from 212 to 550 and are even higher than 550 mostly in the range from 220 to 470 salinity w nacleq ranges from 7 02 to 17 96 ore fluid density ranges from 0 60 g cm3 to 1 00 g cm3 homogenization temperatures of fluid inclusions at the retrogressive metamorphism stage vary from 212 to 510 with the peak around 220 salinity w nacleq ranges from 6 16 to 21 04 ore fluid density ranges from 0 60 g cm3 to 0 95 g cm3 fluid inclusions in the quartz sulfide carbonate period have homogenization temperatures from 150 to 380 with the peaks around 160 and 220 salinity w nacleq ranges from 13 4 to 18 47 ore fluid density ranges from 0 75 g cm3 to 1 10 g cm3 the 18osmow values of garnet and calcite range from 5 2 to 17 8 with the corresponding 18oh2o values between 2 4 and 3 5 and dsmow values of fluid inclusions between 144 0 and 84 0 these isotopic data imply that the ore forming fluids were mainly derived from magmatic fluids and meteoric water the 13cpdb values of calcite define a narrow range of 6 8 to 3 5 and dsmow values of fluid inclusions vary between 11 6 and 17 8 indicating that the carbon in the ore fluids was mainly derived from the diorite magma closely related to the ore bodies with a minor part from carbonate rock the 34s values of pyrite mainly range from 0 to 3 indicating that the sulfur was derived from diorite magma closely related to the ore bodies in combination with the geological characteristics of the laoshankou deposit the authors hold that the ore forming process was related to the retrogressive metamorphism of the skarn

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

textures and geochemistry of magnetite indications for genesis of the late paleozoic laoshankou fe cu au deposit nw china abstract laser ablation inductively coupled plasma mass spectrometry la icp ms and electron probe x ray microanalysis epma have been employed to determine major and trace elemental concentrations in magnetite from different ores in the laoshankou deposit which is the most important fe cu au deposit in the northern margin of east junggar two magnetite associated paragenetic sequences have been defined in laoshankou including amphibole epidote magnetite alteration mineralization stage ii and pyrite chalcopyrite mineralization stage iii b on the basis of the magnetite textures and chemical compositions we have identified six generations of magnetite from three types of ores rocks including the high ti inclusion rich m 1 a and inclusion free m 1 b in massive magnetite epidote amphibole ores type h1 from stage ii the low ti high si inclusion rich m 1 c in massive magnetite sulfide ores type h2 from stage ii the ubiquitous low ti m 2 and pristine low ti low si m 3 in both h1 and h2 types and m 4 within massive chalcopyrite magnetite ores type h3 from stage iii b the discriminations of v versus ti ca mn al versus ti v and fe versus v ti as well as mineral assemblages and trace element concentrations of cr

ttgs in the making natural evidence from inyoni shear zone barberton south africa despite the consensus that ttgs the main constituents of the archaean continental crust worldwide originated by partial melting of garnet bearing amphibolites natural evidence is scarce a large variety of archaean amphibole rich rocks including migmatitic amphibolites and hornblende rich cumulates was exhumed as a tectonic melange in the inyoni shear zone isz near barberton south africa likely at the time of emplacement of the 3 2 ga nelshoogte badplaas plutons this unique collection provides the opportunity to investigate partial melting of garnet amphibolites as well as the differentiation processes occurring in the ttg magmas en route to the surface the isz migmatitic amphibolites are characterized by quartz plagioclase leucosomes in equilibrium with garnet amphibole titanite epidote garnet compositions are characterized by high almandine and grossular contents actually the leucosomes and neosomes likely lost part of their melt component and mesosomes may have been also modified towards restite rich compositions due to melt segregation restite bearing rocks are very iron rich according to their high contents in garnet besides the mg rich compositions of the hornblende cumulates and their ree distribution patterns resemble those of the nearby tt tonalite trondhjemite plutons thermobarometric estimates from the isz migmatitic rocks cluster in the range 720 800 c and 1 1 1 2 gpa for the melting reaction and the derived geothermal gradient is ca 17 22 c km these conditions are consistent with either water present melting or more likely water absent epidote dehydration melting such a geothermal gradient is therefore assigned to the genesis of large volumes of medium pressure ttg magmas that will likely form at greater depth unmelted garnet bearing amphibolites correspond to slightly lower conditions the magmatic cumulates crystallized at ca 0 6 gpa the cumulate rocks evidence that the ttg parental magmas en route to the surface experienced fractional crystallization of a large amount of amphibole before crystallizing as tonalite trondhjemite plutons at slightly shallower depths ca 0 5 gpa

disequilibrium melting of granite at the contact with a basic plug a geochemical and petrographic study mantle derived intrusions are potentially an important source of heat for melting in the crust yet there are few studies of anatectic melts occurring at the contacts of such intrusions to provide natural analogs this is a study of anatectic melts developed in a cretaceous granite at the contact with a 12 ma trachyan desite plug in the sierra nevada batholith california where a detailed textural and geochemical study was possible because the melt is now represented as a glass that has undergone limited devitrification a rb sr isochron age of 11 8 pm 0 6 ma for glasses and granite whole rocks is in agreement with the k ar age of 11 7 pm 0 7 ma for a similar trachyandesite plug nearby confirming that the melting was associated with the trachyandesite intrusion melting occurred at about 900 c or higher and at less than 1 kb the restite minerals consist dominantly of zoned plagioclase and sanidine both have rims of anorthoclase of similar composition quartz and magnetite the whole rock major

very high temperature moderate pressure metamorphism in the new russia gneiss complex northeastern adirondack highlands metamorphic aureole to the marcy anorthosite discussion alcock and muller 1999 assert four inferences regarding grenville gneisses near new russia n y named new russia gneiss complex by them and the adjacent ca 1130 ma marcy anorthosite massif these four inferences follow 1 metamorphism and anatexis of the new russia complex were due to contact effects in the thermal aureole of the ca 1130 ma marcy anorthosite 2 pressure estimates in the gneiss suggest anorthosite emplacement pressures of 750 mpa 3 heat from intrusion of the marcy anorthosite and coeval anorthosite mangerite charnockite granite amcg plutons caused regional granulite facies metamorphism of the adirondack highlands and 4 the marcy anorthosite massif which commonly is only mildly deformed in its core is a postkinematic intrusion thus implying that the adirondacks experienced no post marcy ottawan orogenesis at ca 1090 1030 ma we consider all four assertions to be seriously flawed and we address these and related issues beginning with inference 4 above which is critical to their entire argument alcock and muller ignore or misrepresent two critical pieces of widely reported data based upon field relations and u pb zircon geochronology in addition their own most recent geochronological results contradict the model that they propose these critical issues are discussed below under three separate headings 1 alcock and muller cite the existence of only younger undeformed or mildly deformed granites following the ca 1150 1130 ma amcg plutonism of the adirondack highlands this ignores the existence of the well established hawkeye granitic suite of the highlands that is closely related to buddington s 1939 younger hornblende granite and has been dated six samples from across the region by u pb zircon at 1095 13 ma chiarenzelli and mclelland 1991 mclelland et al 1996 in press the hawkeye suite commonly exhibits intense ductile strain fig d1 and therefore predates high grade granulite facies t 700 850 c metamorphism and penetrative deformation of the ottawan orogeny ca 1090 1030 ma the age of which has

syntectonic anatexis and magmatism in a mid crustal transpressional shear zone an example from the hercynian rocks of the eastern pyrenees abstract hercynian metamorphism and magmatism in the cap de creus peninsula eastern pyrenees occurred contemporaneously with non coaxial deformation in a transpressive regime an example of this has been taken from a migmatite complex in the northern coast the studied area is formed by partially melted sillimanite schists together with two different suites of igneous rocks a calc alkaline magmatic sequence consisting of small granitoid bodies and later peraluminous leucogranites and pegmatites all these rocks occur within a ne sw to e w trending sub vertical high strain zone where a first schistosity is tightly folded and transposed the relations between folds and crenulation cleavage in the metasediments and deformational fabrics in the granitoids and migmatites provide good evidence for the penecontemporaneity of deformational processes magmatism and migmatization furthermore the analysis of cross cutting relationships between different granitoids as well as the observation of their different degrees of deformation verifies that magmatism in this area took place as synkinematic consecutive intrusions from the more basic magmas to the peraluminous acid dykes

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

the rates and extent of textural equilibration in high temperature fluid bearing systems abstract the geometry of fluid filled pores in texturally equilibrated aggregates can in theory be uniquely determined given the porosity and the equilibrium dihedral angle for all possible orientations and combinations of the constituent solid phases while it is useful to be able to do this one should also ask whether and to what extent textural equilibrium is actually attained during fluid present intervals in high temperature rocks in fact textural equilibrium may be only rarely attained during melting of crustal rocks and equilibration under mid ocean ridges is possibly incomplete to depths as great as the garnet stability zone there is very little published information on the rates of attainment of textural equilibrium in fluid bearing geological environments the available experimental data for the rates of growth of equilibrated domains are consistent with a power law relationship between domain size and equilibration time with an exponent between 2 and 3 a simplified theoretical treatment of pore shape change governed by the gibbs thompson relationship demonstrates that an exponent of 3 is to be expected for equilibration by diffusion within the fluid phase with an effective diffusivity consistent with the available data

disequilibrium partial melting and rheomorphic layer formation in the contact aureole of the basistoppen sill east greenland the tholeiitic basistoppen sill was intruded into the upper part of the skaergaard complex shortly after the skaergaard magma had solidified heat from the cooling basistoppen magma caused disequilibrium partial melting in the adjacent skaergaard ferrogabbros olivine ferrobustamite and magnetite were selectively melted and removed from the rock as an iron rich melagabbro magma plagioclase acted as a refractory phase during partial melting and was left behind as an anorthositic gabbro restite modal and grain size layering formed rheomorphically in the previously solidified host rocks as a result of partial melting and recrystallization the rheomorphic layers are distinct from those found elsewhere in the intrusion

timescales and significance of high pressure high temperature metamorphism and mafic dike anatexis snowbird tectonic zone canada new geochronological isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1 9 ga high pressure high temperature metamorphism along the snowbird tectonic zone in northern saskatchewan high precision u pb zircon dates reveal anatexis of chipman mafic dikes at 1 896 2 0 3 ma during syntectonic and synmetamorphic intrusion at conditions of 1 0 1 2 gpa 750 c u pb zircon dates of 1 894 1 891 ma for cross cutting pegmatites place a lower bound on major metamorphism and deformation at the currently exposed crustal levels the persistence of elevated temperatures for 14 m y following peak conditions is implied by younger u pb titanite dates and by sm nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source limited melting of the host felsic gneiss at 1 9 ga despite high temperature is consistent with evidence for their previous dehydration by granulite facies metamorphism in the archean spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak temperature and compositional variability we correlate 1 896 ma chipman mafic dike emplacement and metamorphism with substantial 1 9 ga mafic magmatism over a minimum along strike extent of 1 200 km of the snowbird tectonic zone this suggests a significant continent wide period of asthenospheric upwelling that induced incipient continental rifting extension was subsequently terminated by hinterland contraction associated with trans hudson accretion and orogenesis little activity in the lower crust for ca 650 m y prior to proterozoic metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1 9 ga this episode of destabilization contrasts with the record of long term stability in most preserved cratons and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents

mineralization and ore genesis of the qiaoxiahala fe cu au deposit in the northern margin of east junggar terrane central asian orogenic belt constraints from fluid inclusions and stable isotopes abstract the qiaoxiahala fe cu au deposit 1 44 mt ore 43 53 fe 0 55 2 21 cu and 0 13 2 4 g t au is located in the northern margin of east junggar terrane nw china the deposit is hosted in the upper part of the middle devonian beitashan formation mafic and felsic volcanic rocks and sedimentary interbeds and is spatially closely related to local fractures six hypogene hydrothermal stages have been identified including stage i early skarn stage ii late skarn stage iii magnetite mineralization stage iv magnetite pyrite mineralization stage v chalcopyrite mineralization and stage vi late veins these six stages include three major mineralization events as represented by the stage iii magnetite epidote k feldspar quartz calcite stage iv magnetite pyrite garnet quartz calcite and stage v chalcopyrite chlorite assemblages the stage iii magnetite mineralization fluids were likely of high temperature 354 386 c low medium salinity 9 9 14 7 wt nacl equiv mg fe rich and organic rich with lithostatic pressure of 1 3 1 5 kbar and corresponding depth of 4 3 4 8 km oxygen and hydrogen isotopes showed that the 18o rich 9 7 11 2 and d rich 26 3 fluids were possibly modified from the early carboniferous seawater interacting with the beitashan formation organic rich limestone or tuff in comparison the stage iv magnetite pyrite mineralization fluids were likely of medium high temperature 272 453 c low medium salinity 2 9 19 5 wt nacl equiv mg fe rich with pressure of 0 8 1 2 kbar and corresponding depth of 2 6 4 0 km the stage v chalcopyrite mineralization fluids were likely of low medium temperature 186 270 c low medium salinity 1 4 21 8 wt nacl equiv ca or na rich with pressure of 0 4 0 6 kbar and corresponding depth of 1 2 km hydrogen and oxygen isotopic compositions stage iv dwater 141 to 92 18owater 8 9 11 1 stage v dwater 104 18owater 7 2 suggest that the ore fluids were of connate marine origin furthermore stage iv 13cwater values 0 6 to 0 also indicate interactions between seawater and sedimentary wall rocks the negative sulfur isotopic compositions of chalcopyrite and pyrite 4 2 to 0 2 may demonstrate a biogenic sulfur source compared with the arc related iocg deposits in the central andean orogen the qiaoxiahala fe cu au deposit shares many common features in geology mineralization alteration and various sources of fluids indicating a possible iocg like mineralization style and potential to discover other late paleozoic arc related iocg deposits in east junggar

towards a coupled physical and chemical model for tonalite trondhjemite granodiorite magma formation abstract tonalite trondhjemite granodiorite ttg magmatism provides a window into the composition of the earth s earliest crust and on rates of heat transfer during the archaean however the tectonic setting in which these magmas form and the physical mechanisms by which ttg melt segregates from its partially molten source rock are poorly understood here we present some simple models aimed at predicting the compositions of partial melts which segregate from thickened mafic amphibolitic or eclogitic lower crust our results suggest that buoyancy driven compaction with melt flow along grain edges can yield large volumes of segregated ttg melt over geologically realistic timescales 4000 years 10 my petrologic diversity is predicted even from a homogenous protolith the chemical composition of the segregated melt varies both spatially and temporally and is governed not only by the composition and mineralogy of the source rock the depth of melting and the melting reactions but also by the physical processes through which the melt migrates and segregates from its partially molten host this simple model represents the first step towards a properly coupled physical and chemical model of ttg formation which is closely constrained by geochemical field and laboratory data such models will compliment the existing geochemical work and help resolve some of the outstanding issues concerning ttg petrogenesis

fission track and fault kinematics analyses for new insight into the late cenozoic tectonic regime changes in west central sulawesi indonesia abstract the left lateral strike slip central sulawesi fault system csfs composed of the nnw palu koro pkf and the ese matano faults is located within the eastern indonesian triple junction between the pacific indo australian and eurasian plates fault kinematic and fission track analyses show that the late cenozoic central sulawesi deformation results from three successive tectonic regimes 1 a late miocene early pliocene 5 ma wnw trending shortening characterized by transpressional deformation along the pkf and compressional in the poso area this tectonics resulted from the collision between the banggai sula block with sulawesi it produced locally a transpressional regime as a consequence of the northward extrusion of the central sulawesi block limited by the pkf 2 a pliocene collapse tectonic regime associated with w trending extension coeval with these events regional cooling and exhumation took place 3 a quaternary transtensional regime resulting from the combined effects of the central sulawesi block northward motion and extension related to back arc spreading behind the north sulawesi subduction tomini gulf

experiments on the kinetics of partial melting of a leucogranite at 200 mpa h 2 o and 690 800 c compositional variability of melts during the onset of h 2 o saturated crustal anatexis we have experimentally investigated the kinetics of melting of an aplitic leucogranite quartz sodic plagioclase of ab90 k feldspar traces of biotite at 690 740 and 800 c all at 200 mpa h2o leucogranite cylinders 3 5 mm in diameter and 7 mm in length were run in the presence of excess h2o using cold seal pressure vessels for 11 2 925 h at 690 and 740 c and any experimental time and 800 c and short run times silicate glass melt at run conditions occurs as interconnected films along most of the mineral boundaries and in fractures with the predominant volume occurring along quartz feldspars boundaries and quartz plagioclase k feldspar triple junctions glass film thickness is roughly constant throughout a given experimental charge and increases with experimental temperature and run duration the results indicate that h2o saturated partial melting of a quartzo feldspathic protolith will produce an interconnected melt phase even at very low degrees 5 vol of partial melting crystal grain boundaries are therefore completely occluded with melt films even at the lowest degrees of partial melting resulting in a change in the mechanism of mass transport through the rock from advection of aqueous vapor to diffusion through silicate melt at 690 and 740 c the compositions of glasses are homogeneous and at both temperatures close to but not on the h2o saturated 200 mpa haplogranite eutectic glass compositions do not change with run duration at 800 c glasses are heterogeneous and plot away from the minimum although their molar ratios asi mol al2o3 cao na2o k2o and al na are constant throughout the entire charge at any experimental time glass compositions within individual 800 c experiments form linear trends in wt normative quartz albite orthoclase space the linear trends are oriented perpendicular to the 200 mpa h2o haplogranite cotectic line reflecting nearly constant albite orthoclase ratio versus variable quartz feldspar ratio and have endpoints between the 800 c isotherms on the quartz and feldspar liquidus surfaces with increasing experimental duration the trends migrate from the potassic side of the minimum toward the bulk rock composition located on the sodic side due to more rapid and complete dissolution of k feldspar relative to plagioclase the results indicate that partial melting at or slightly above the solidus 690 740 c is interface reaction controlled and produces disequilibrium melts of near minimum composition that persist metastably for up to at least 3 months relict feldspars show no change in composition or texture and equilibration between melt and feldspars might take from a few to tens of millions of years partial melting at temperatures well above the solidus 800 c produces heterogeneous disequilibrium liquids whose compositions are determined by the diffusive transport properties of the melt and local equilibrium with neighboring mineral phases feldspars recrystallize and change composition rapidly partial melting and equilibration between liquids and feldspars might take from a few to tens of years h2o saturated conditions at these temperatures well above the solidus

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

geochemistry of metamorphosed volcanic rocks in the neoarchean qingyuan greenstone belt north china craton implications for geodynamic evolution and vms mineralization abstract the qingyuan greenstone belt qgb situated in the northeastern section of the north china craton ncc is considered to be the unique metallogenic province in china that hosts both banded iron formations bifs and volcanogenic massive sulfide vms deposits traditionally the qgb is divided into the hunbei and hunnan terranes separated by the hunhe fault and grouped into the lower shipengzi middle hongtoushan and upper nantianmen formations which have undergone amphibolite to granulite facies metamorphism exposed supracrustal rocks are composed of plagioclase amphibolite and biotite plagioclase gneiss with minor amounts of bif marble and schist in this study detailed field and petrographic observations lithogeochemical u pb geochronological as well as whole rock sm nd isotope analyses were conducted on the metamorphosed mafic and felsic volcanic rocks i e plagioclase amphibolite and biotite plagioclase gneiss respectively in the qgb in order to discuss implications for tectonic evolution and comitant vms mineralization the supracrustal rocks of both hunbei and hunnan regions were formed synchronously from 2 57 to 2 53 ga and then had undergone 2 52 2 48 ga regional metamorphism specifically the lower section of the shipengzi formation is composed dominantly of transitional tholeiitic basalts with negative nb anomalies suggesting that they were likely generated by partial melting of a mantle source that was previously altered by variable amounts of slab derived fluids or melts in contrast the lithologic assemblages grade upward into interlayered bimodal volcanic rocks i e n morb type tholeiitic basalts and fi to fii type dacites of transitional to calc alkalic affinities representing a change in tectonic regime related to subduction from compression to extension among them all the basalts are characterized by consistently positive initial nd compositions end t 2 7 to 3 4 further indicate a depleted mantle source whereas those dacites possess negative to positive initial nd values end t 4 6 to 3 0 suggesting they were formed by partial melting of depleted mafic source likely lower mafic crust and accompanied with variable addition of old crustal material significantly vms deposits are genetically linked to this extensional event and closely associated with the fii type dacites that were generated by higher melting degree at high temperature conditions and shallow crustal level likely 10 15 km in all geochemical features e g negative nb anomalies and end value together with contamination from continental crusts for tholeiitic mafic rocks and inherited zircons from these volcanic rocks imply a continental arc setting where the qgb was evolved

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 wiley glacier complex antarctic peninsula pluton growth by pulsing of granitoid magmas early cretaceous gabbro quartz diorite granodiorite and tonalite granodiorite plutons of the wiley glacier complex in the antarctic peninsula magmatic arc were emplaced in a zone of syn magmatic extensional shearing the oldest component pluton is the creswick gap quartz diorite granodiorite pluton and this is cut by slightly younger hornblende gabbro of the moore point pluton these plutons form the wall rock to the burns bluff tonalite granodiorite pluton the youngest component of the complex the burns bluff pluton comprises tonalite granodiorite sheets which at the plutons margins are interleaved with screens of mylonite wall rock the moore point hornblende gabbro has nd141 of ca 4 and sr141 of ca 1 it is predominantly mantle in origin although its parent magma assimilated some continental crust during emplacement the creswick gap pluton has nd141 between ca 4 quartz diorite and ca 1 granodiorite and sr141 from ca 1 quartz diorite to ca 22 granodiorite this pluton contains both mantle and crustal components we suggest that the quartz diorite facies fractionated from a similar parent magma to that of the moore point gabbro whilst the granodiorite fractionated from a gabbro quartz diorite magma during continued crustal assimilation geochemical variations within the creswick gap pluton cannot be generated by afc models some of the granodiorite samples have chemical characteristics which typify partial melts of amphibole garnet bearing crust we conclude that the pluton comprises fractionates of basaltic magma and crustal partial melt the burns bluff tonalite granodiorite sheets have nd141 between ca 4 and ca 2 and sr141 from ca 5 to ca 31 their isotopic and chemical compositions suggest that some are fractionates of basalt gabbro magma others are predominantly partial melts of amphibole garnet bearing crust and some are mixtures of these two magma types the chemical and isotopic compositions of the burns bluff plutons constituent tonalite sheets and its dyke like internal structure suggest that it grew incrementally via the addition of melt batches from a variety of crustal and mantle sources the growth of this pluton via dyking may reflect magma pulsing associated with transtensional movement along the creswick gap shear zone moreover the burns bluff pluton may be a frozen conduit system for structurally higher plutons in the antarctic peninsula batholith

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

migration of seismicity and earthquake interactions monitored by gps in se asia triple junction sulawesi indonesia 1 global positioning system gps measurements made in sulawesi indonesia from 1992 to 1999 detected coseismic and transient postseismic deformation related to the 1 january 1996 mw 7 9 earthquake on the north sulawesi minahassa trench these motions are superimposed on the long term secular motion 40 mm yr of the left lateral palu fault in central sulawesi and continued for about 1 5 2 years following the earthquake a string of earthquakes of magnitude 6 migrated along the minahassa trench from west to east subsequently two earthquakes of magnitude 6 occurred on or near the palu fault migrating toward the south modeling the increase in coulomb stress generated by the successive earthquakes agrees with the hypothesis of interacting events an unclamping effect possibly due to fluid migration in the palu area is also suggested by the stress computations and the detected gps displacements

iron oxide copper gold mineralization of the devonian laoshankou deposit xinjiang nw china in the central asian orogenic belt abstract the laoshankou iron oxide cu au iocg deposit 41 km southwest of qinghe city xinjiang nw china is the most important magnetite deposit with economic cu and au metal reserve 3 26 mt fe 33 5 36 4 9 8 kt cu 0 2 0 4 and 0 14 t au 0 5 1 3 g t in the east junggar terrane of the central asian orogenic belt caob the deposit is hosted by volcanic rocks of the middle devonian beitashan formation in this study four hypogene hydrothermal alteration stages have been identified including the ca silicate alteration stage i amphibole epidote magnetite alteration mineralization stage ii pyrite chalcopyrite mineralization stage iii and late hydrothermal veining stage iv mineralogical fluid inclusion including laser raman spectroscopy and mineral sulfur oxygen hydrogen and carbon isotope analyses were carried out to elucidate the nature and origin of the hydrothermal fluids at laoshankou stage i hydrothermal fluids were likely derived from a 590 c magmatic fluid with 18 o water 9 2 9 7 subsequently the magnetite epidote amphibole assemblage may have precipitated from the fluids 530 c formed by the mixing of high temperature magmatic fluids with the seawater that reacted with 18 o rich wall rocks the fluid rock reactions are reflected from the 18 o water 9 6 10 7 and d water 25 5 23 8 values the sub economic stage iii a pyrite epidote quartz garnet mineralization likely occurred at 415 c and was formed by fluids with 34 s fluid 3 7 0 5 d water 110 94 and 18 o water 7 92 8 9 the lower temperature and presence of organic matter of the stage iii a fluids may have reflected the involvement of meteoric water and organic matter from the wall rocks the economic cu mineralization stage iii b was probably formed by the mixing of a meteoric water dominated fluid medium temperature low salinity and na dominated and a ca rich formation water in equilibrium with the volcanic wall rocks medium temperature medium salinity and ca fe mg dominated with 34 s fluid 2 6 18 o water 5 6 5 8 13 c water 3 3 3 1 and d water 92 95 towards the end of the fluid evolution meteoric water incursion may have continued and generated the ore barren low temperature low salinity and na dominated fluids although the laoshankou deposit contains distinct skarn alteration the ore mineral assemblage and ore fluid features indicate that it is not a typical skarn deposit but share many similarities with many central andean iocg deposits we conclude that the iocg ore forming setting in the devonian east junggar was analogous to the cretaceous central andes in that they both occurred during basin inversion in a volcanic arc setting

collision rotation and the initiation of subduction in the evolution of sulawesi indonesia the island of sulawesi indonesia has been shaped and deformed as a result of collision with the sula platform a sliver of continental material from the northern margin of australia new guinea the collision has resulted in rotation of the north volcanic arm of sulawesi and the development of the accretionary wedge of the north sulawesi trench the north sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west early stages of thrusting produce a steep frontal slope 8 16 indicative of relatively high basal shear stress whereas the more advanced western zone of thrusting produces a gentle 2 slope consistent with low basal shear stress reported paleomagnetic data suggest post late eocene counter clockwise rotation of the north arm and the offshore geophysics are explained by a pivot of the north arm with respect to the celebes basin about the eastern end of the arc convergence between the north banda basin and southeast sulawesi is documented by the presence of the tolo thrust its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30 40 km in the central part the northern end transforms to the leftlateral matano fault with a reported offset of 20 km the southern end of the thrust projects toward the deformed rocks of buton but the structural relations there are not clear the matano fault zone appears to connect westward with the palu fault which forms the western transform of the north sulawesi trench the palu matano fault system acts as a trench trench transform between the north sulawesi trench and the tolo thrust and this system is described by the same rotation pole as that for the sulawesi north arm

amphibolite dehydration melting sorting out the solidus amphibolite melts under vapour absent conditions by dehydration melting during which h 2o released from hornblende is transferred directly into h 2o undersaturated silicate liquid five independent 1991 studies on amphibolite dehydration melting differ from each other and from earlier conceptual treatments five solidi between 7 and 10 kb vary from 975 c to 740 c two solidi above 10 kb are near vertical near 975 c and 850 c some differences are due to different amphibolite compositions and mineralogy we use the results of earlier experiments involving garnet supported by our own new results to construct a closed system phase diagram for a simple fully hydra ted amphibolite hornblende plagioclase showing the solidus and the melting interval for hornblende garnet other minerals liquid the amphibolite vapour absent solidus is defined by the beginnings of two multivariant reactions 1 a near vertical curve large positive d p dt where the formation of augite dominates and 2 a near horizontal curve a t higher pressures where the formation of garnet dominates the solidus curve bends back estimated near 900 c 9 kb with slope changing to low positive dp dt the new phase diagram expands the field for liquid generation with garnet amphibolite residues to much lower temperatures and pressures than the other recent experimental results increasing the range from which small amounts of hydrous granitoid melts may be segregated by compaction the reversed near horizontal slope of the solidus near 10 kb has interesting petrological consequences

melting reactions and trace element relationships in selected specimens of migmatitic pelites from new hampshire and maine leucosomes and melanosomes in selected specimens of migmatitic sillimanite zone pelitic schists are modal and chemical complements formed by segregation within originally homogeneous paleosomes systematic bulk chemical and modal variations in melanosomes can be used to infer the reactions by which leucosomes were generated

gps compared to long term geologic motion of the north arm of sulawesi geodetic data acquired in the north arm of sulawesi are compared with geologic and palaeomagnetic data from north sulawesi and the celebes sea the objective of this study is to assess whether the long term motion deduced from palaeomagnetic and geological studies is coherent with the extrapolation of the current motions measured by gps palaeomagnetic data that have been collected in the north arm of sulawesi indicate that since 5 ma about 20 to 25o of semi rigid rotation occurred about a pole located north of manado this suggests 200 to 250 km of left lateral displacement along the palu koro fault with a displacement rate of 4 cm year a rather similar displacement on the palu fault is derived using the distribution of the asymmetric magnetic anomalies of the celebes seafloor the distribution implies that 200 to 250 km of oceanic crust was subducted at the north sulawesi trench another marker for the rotation is derived from the opening of the gulf of tomini and the nw migration of the calc alkaline subduction related volcanism the far field observation by gps of 4 cm year of left lateral strike slip motion over 17 months and the 5 year average of 3 4 0 3 cm year on a transect across the palu fault fit well with the geological observations that indicate a motion of 4 to 5 cm year of the north arm we therefore conclude that the current rates deduced from gps measurements approximate the long term rates and may hence be extrapolated over a few million years 1998 elsevier science b v all rights reserved

geochemistry and u pb dating of felsic volcanic rocks in the riotinto nerva unit iberian pyrite belt spain crustal thinning progressive crustal melting and massive sulphide genesis abstract we present new geochemical sm nd and u pb data on the felsic volcanic rocks containing the world class volcanic hosted massive sulphide deposits in the riotinto nerva unit iberian pyrite belt spain three new u pb ages from older plagioclase quartz phyric dacites and plagioclase phyric rhyolites to youngest plagioclase quartz phyric rhyolites indicate a time span for felsic volcanism ranging from 351 5 0 4 to 345 7 0 6 ma the youngest felsic rocks exhibit lower e nd as well as contrasting ti sr zr hf and eu eu values we interpret that in the riotinto nerva unit crustal melting successively affected shallower more evolved horizons in the crust progressive crustal melting is consistent with current interpretations of the iberian pyrite belt in terms of a late devonian early carboniferous transtensional setting coupled with underplating by basic magma we suggest that low e nd evolved crustal magmatism could be used as a proxy in studies of the genesis of these and possibly other phanerozoic massive sulphide deposits supplementary material details of the analytical methods and whole rock data for basalts are available at http www geolsoc org uk sup18452

co seismic thrusting rupture and slip distribution produced by the 2008 mw 7 9 wenchuan earthquake china field investigations reveal that the mw 7 9 wenchuan china earthquake of 12 may 2008 produced a 285 km long surface rupture zone with dominantly thrusting slip accompanied by a right lateral component along the central northern segments of the zone and left lateral component along the southern segment along the longmen shan thrust belt eastern margin of the tibetan plateau the co seismic ruptures mainly occurred along the pre existing yingxiu beichuan guanxian anxian and qingchuan faults which are the main faults of the longmen shan thrust belt the displacements measured in the field are approximately 0 5 6 5 m in the vertical typically 1 3 m accompanied by an average left lateral component of 2 m along the 50 km long southernmost segment of the rupture zone and an average right lateral component of 1 m along the 150 km long central northern segments the maximum thrust slip amount is estimated to be 10 m accompanied by 9 m of shortening across the rupture zone this finding is consistent with estimates based on seismic data the rupture length and maximum vertical displacement are the largest among all intracontinental thrust type earthquakes reported to date our findings demonstrate that i the wenchuan earthquake occurred upon pre existing active faults of the longmen shan thrust belt thereby controlling the spatial distribution of co seismic surface rupture and displacement and the rupture processes of the earthquake ii the long rupture length and large thrusting slip resulted from compressive stress associated with eastward extrusion of the tibet plateau as it accommodates the ongoing penetration of the indian plate into the eurasian plate and iii present day shortening strain upon the eastern margin of the tibetan plateau is mostly released by seismic slip along thrust faults within the longmen shan thrust belt

the potential for supershear earthquakes in damaged fault zones theory and observations the potential for strong ground shaking in large earthquakes partly depends on how fast the earthquake rupture propagates it is observed that strike slip earthquakes usually propagate at speeds slower than the rayleigh wave speed v r but occasionally jump to speeds faster than the s wave speed v s or supershear speeds supershear earthquakes can be more catastrophic and cause unusually large ground motions at long distances here we use both fully dynamic rupture simulations and high resolution seismic observations to show that supershear earthquakes can be induced by damaged fault zones the low velocity layers of damaged rocks that typically exist around major faults and serve as waveguides for high frequency energy in contrast to supershear ruptures in homogeneous media supershear ruptures in damaged fault zones can occur under relatively low fault stress and propagate stably at speeds within the range usually considered as unstable

accessory phase controls on the geochemistry of crustal melts and restites produced during water undersaturated partial melting the profound geochemical conseqences of accessory phase behaviour during partial melting of highgrade metapelites are demonstrated with reference to two geochemically distinct crustal melts produced by biotite dehydration melting reactions under granulite facies kbar 860 cc conditions these two leucogneiss suites from the brattstrand bluffs coastline eastern antarctica have similar field relations transport distances 10 100 s of metres and major element chemistry type 1 leucogneisses have low zr th and lree positive eu anomalies and zr zr and lreet lreet values less than 1 0 i e less than required to saturate the melt mass balance constraints suggest that these melts have been extracted before equilibration with host melanosomes the dry peraluminous nature of vapour undersaturated melts inhibits monazite and zircon solubility and results in concentration of these phases in the residue melts are consequently depleted in lree and hree melanosomes show complementary enrichment in lree while hree patterns are dominated by residual garnet type 2 leucogneisses in contrast have strongly enriched zr th and lree abundances negative eu anomalies and zr zr and lreet lreet 1 resulting from accessory phase entrainment vapour absent partial melting under moderate 6 8 kbar pressure granulite facies conditions of a pelitic source containing monazite is likely to give disequilibrium melts depleted in lree and hree as monazite and garnet are concentrated in the residue if temperatures are high enough 850 870 c to permit relatively large degrees of partial melting then the feldspar component of the source will be removed almost completely giving melts with large positive eu anomalies melts formed under vapour present conditions are unlikely to show such extreme lree and hree depletion or positive eu anomalies even at high degrees of partial melting disequilibrium melting coupled with source entrainment could fortuitously produce ree and trace element signatures similar to those typical of s type granites and usually ascribed to equilibrium melting conditions

apatite dissolution into peraluminous haplogranitic melts an experimental study of solubilities and mechanisms apatite ap dissolution and solubility in the peraluminous haplogranite system were investigated in three sets of experiments at 750 c and 200 mpa ph2o as functions of ap grain size abundance melt ap ratio and melt asi alumina saturation index mol al2o3 na2o k2o cao between an asi of 1 1 1 metaluminous to mildly peraluminous the solubility of ap as measured by p2o5 in the melt is low 0 1 wt p2o5 which agrees with previous work in equilibrium runs with more strongly peraluminous compositions however ap solubility increases linearly with asi to p2o5 0 63 wt in melt at asi 1 3 and can be denned by a simple equation p2o5 3 4 3 1 asi r 0 833 which agrees within error with previous calculations reported in the literature in experiments where ap grains are sparce and widely separated i e simulating ap distribution in an ap bearing peraluminous protolith undergoing anatexis the dissolution of ap involves transient disequilibrium that promotes higher solubility of p2o5 up to nearly six times the equilibrium values adjacent to ap at a given bulk asi of melt and this increases the al si of melt in the ap dissolution aureole the approach to equilibrium between ap and melt is hastened by increasing the ap melt ratio within the local melt pool e g the capsule or by decreasing ap grain size for a similar melt ap ratio diffusivity calculations using inverse error function methods for the normal diffusion of p and ca yield dp 10 11 cm2 s and dca 10 10 cm2 s confirming prior results that diffusion of p away from ap surfaces is the rate limiting factor in ap dissolution these results combined with previous work at higher temperatures but on similar hydrous melts yield an activation energy e for p diffusion of 16 5 kcal mol and a frequency factor d0 of 1 4 10 3 cm2 s phosphorus diffusion through the melt is accompanied by uphill diffusion of al resulting in an increase of up to 2 wt al2o3 in melt near the ap within the ap dissolution aureole melt contains one additional al cation for every p cation i e al p 1 1 which is suggestive of an associated alpo4 complex the exchange reaction in melt is represented by alpsi 1 in which 2 to4 clusters are created in the place of 1 this exchange should be accompanied by discernable changes in melt properties e g density molar volume viscosity the results have applications to equilibrium and local disequilibrium effects during anatexis of apbearing metapelites and to the saturation limits of ap during crystallization of peraluminous magmas the dissolution of flux bearing minerals such as ap e g those containing p b or f may influence the stability and solubility of other trace element bearing minerals during anatexis of metapelites texture e g grain size and distribution and spacial relationship to other minerals plays an important role in reaction kinetics and at least temporarily in mineral solubilities the disequilibrium behavior of accessory minerals has critical consequences for ree modelling of granites

a two stage thermal evolution model of magmas in continental crust when a basaltic magma is emplaced in a continental crust a introduction silicic magma is generated by melting of the crust the light silicic when magma is emplaced into continental crust it is magma forms a separate magma layer with little chemical interaction believed to be stored in a magma chamber for a certain with the underlying dense basaltic magma layer extensive melting period extensive studies have revealed how petrological occurs at the boundary between the silicic magma and the crust and geochemical features of magmas are controlled by while the basalt acts a heat source the mass and heat transfer at processes in magma chambers such as crystallization of the boundary between the silicic magma and the crust controls the magma melting of crustal materials and mixing of thermal evolution of the silicic magma the thermal evolution of magmas e g mcbirney 1980 huppert turner 1981 the silicic magma after the basalt emplacement is divided into two sparks et al 1984 koyaguchi blake 1991 this paper stages in the first stage the temperature in the silicic magma rises discusses how petrologic processes such as assimilation above and then decays back to the melting temperature of the crust and fractional crystallization affect the thermal evolution on a short timescale 10 years the results of fluid dynamics and the residence times of magmas in magma chambers experiments suggest that the silicic magma generally has a lower in continental crust melting temperature than the crust because of fractional crystallization some exploratory models for the residence time of a and mixing of partial melts during the first stage and that it can magma chamber in continental crust have been proposed be effectively liquid at the end of the first stage in the second stage on the basis of the physics of heat and mass transfer the silicic magma cools slowly by heat conduction on a much longer spera 1979 huppert sparks 1988a marsh 1989 timescale 10 years petrological features of the magma in the to formulate the present problem it is helpful to introduce second stage are strongly constrained by petrological features of the the model by huppert sparks 1988a in which the surrounding crust as well as those of the supplied magma itself its physics of crystallization and melting at the chamber roof temperature remains at or just below the melting temperature of the as well as the effects of thermal convection in the magma crust for a long time because of the slow cooling rate its phenocryst are taken into account according to their model a content reflects the difference in the melt fraction vs temperature basalt emplaced into continental crust results in extensive relationships between the magma and the crust judging from the melting of the crustal materials at the chamber roof to distinct cooling rate between the two stages erupted magmas are form a silicic magma the temperature in the silicic statistically more likely to reflect the characteristics of magmas in magma rises above and then decays back to the fusion the second stage temperature of the crust in general the effective fusion

introduction to special section mechanisms and consequences of melt segregation from crustal protoliths much of petrological effort has been concentrated on attempts to discern define and interpret regularly recurring patterns of igneous and metamorphic petrogenesis i do not wish to deny the existence of discernable order in petrological phenomena but every geological event is unique if we concentrate too heavily on discernment of order and pattern may we perhaps overlook or underrate the unique quality of each igneous or metamorphic episode possibly uniqueness may have as great significance as conformity to pattern when we attempt to fit the phenomena of petrology into the broad framework of geology francis j turner presidential address to the mineralogical society of america november 11 1969

garnet growth during amphibolite anatexis implications of a garnetiferous restite formation of a garnet clinopyroxenite restite may have important physicochemical consequences for deep crustal and mantle processes we have experimentally simulated the dehydration melting of amphibolite and report the modal and compositional evoltuion of the mafic granulitic mineral assemblage the restite with an emphasis on garnet a natural low k calcic amphibolite was powdered and run in sealed gold capsules in a piston cylinder apparatus at 10 kbar 750 1000 c 1 to 9 day runs and fo 2 ni nio garnet first appears in 8 day runs at 825 25 c above 850 c clinopyroxene and poikilitic garnet comprise most of the restite garnet peaks at 950 c at 32 vol of the material within the capsule or 41 vol of the restite assemblage and disappears between 975 1000 c there is no cross over of fe mg partitioning between coexisting liquids and garnets liquids remain mg poorer than garnets throughout the melting interval but do increase in mg with increasing temperature thus the hotter liquids may be less likely to react with mantle wedge peridotite the modes are consistent with ree patterns of archean tonalitic trondhjemitic rocks generated by the partial melting of garnet bearing mafic crust a garnet clinopyroxenite with 41 vol garnet has a density of 3 5g cm 3 which may induce lower crustal delamination in hot nonthickened amphibolitic crust this crust is seismically indistinguishable from lithosphere or mantle because garnet growth traps water bearing hornblende inclusions the restite may contain up to 0 3 wt water thus delivery of poikilitic garnet to the mantle possibly by delamination or by subduction may be an important mechanism for adding water to the mantle

melting and diffusion processes in closed system migmatization estimated variations in mineral concentrations across leucosomes suggest that leucosomes are generated during anatexis by a diffusive exchange between the leucosome and the mesosome and not by the migration of melt from the mesosome however the presence of melt is a precondition for the diffusive exchange to take place initially a crack is formed due to shear stress the formation of a crack allows a diffusive exchange to take place through the melt which causes melting of minerals situated near the crack the diffusive exchange of material is less efficient in the mesosome where the melt is isolated at grain corners and edges the microcline enrichment of some granitic leucosomes is thought to be due to the diffusive depletion of the mesosome caused by growth of alkali feldspar during the consolidation of the migmatite in general it seems unnecessary to invoke concentrations of water in the leucosome or the intrusion of external fluids or magmas for migmatite formation

quantitative modeling of granitic melt generation and segregation in the continental crust 1 we present a new quantitative model of granitic in a broad sense melt generation and segregation within the continental crust we assume that melt generation is caused by the intrusion of hot mantle derived basalt and that segregation occurs by buoyancy driven flow along grain edges coupled with compaction of the partially molten source rock we solve numerically the coupled equations governing heating melting and melt migration in the source rock and cooling and crystallization in the underlying heat source our results demonstrate that the spatial distribution and composition of the melt depends upon the relative upward transport rates of heat and melt if melt transport occurs more quickly than heat transport then melt accumulates near the top of the source region until the rock matrix disaggregates and a mobile magma forms as the melt migrates upward its composition changes to resemble a smaller degree of melting of the source rock because it thermodynamically equilibrates with rock at progressively lower temperatures we demonstrate that this process of buoyancy driven compaction coupled with local thermodynamic equilibration can yield large volumes of mobile granitic magma from basaltic and meta basaltic amphibolitic protoliths over timescales ranging from 4000 years to 10 myr the thickness of basaltic magma required as a heat source ranges from 40 m to 3 km which requires that the magma is emplaced over time as a series of sills concurrent with melt segregation these findings differ from those of previous studies which have suggested that compaction operates too slowly to yield large volumes of segregated granitic melt

rupture segmentation and process of the 2001 mw 7 8 central kunlun china earthquake field investigations allow us to constrain the coseismic surface rupture zone of 400 km with a strike slip up to 16 3 m associated with the 2001 m w 7 8 central kunlun earthquake that occurred along one of the western segments of the kunlun fault northern tibet the rupture zone may be divided into four segments based on the geological structures tectonic landform features spatial displacement distributions obtained from field observations and analysis of teleseismic waveforms the deformational characteristics of the surface ruptures and focal mechanism solutions reveal that the earthquake had a nearly pure strike slip mechanism the inversion results from seismic data show that the rupture started from the west near the epicentral area bilaterally and rapidly extended to the east in an unilateral manner for 380 km and that the largest slip region was limited in the subsegment 150 280 km east of the epicenter consistent with field observations the average stress drop is estimated to be 7 mpa in the area where the largest displacements occurred a value typical of intraplate earthquakes the geologic evidence and the inversion results from seismic data clearly show that temporal and spatial displacement distributions and the rupture process are restricted by the pre existing geological structures of the kunlun fault

very high temperature moderate pressure metamorphism in the new russia gneiss complex northeastern adirondack highlands metamorphic aureole to the marcy anorthosite the new russia gneiss complex in the northeastern adirondack highlands of new york includes meta anorthosite gneiss and anatectic gneiss derived from metagabbro mangerite and charnockite metamor

chemical exchange in migmatites during cooling abstract the chemistry of the leucosome components in limited size migmatitic associations is generally believed to reflect the composition of the partial melt that could have been extracted to yield an anatectic magma several well documented studies of migmatites indicate that the distributions of some trace elements in leucosome melanosome pairs are inconsistent with equilibrium partial melting but are rather in agreement with chemical reequilibration during cooling in migmatites the liquid fraction does not leave the system this may induce an alteration of the chemical composition of the whole migmatite system by extensive chemical exchange between the liquid and the solid residue during cooling if this is the case the leucosome and melanosome components are not representative of the chemical composition of the liquid and solid residue respectively at the time of partial melting a rough evaluation of the residences time of the melt fractions in cooling in situ migmatitic bodies yields minimum estimates of 1 to 10 ma for such time spans the characteristics distances of diffusion distances of diffusion induced chemical transfer exceed the sizes of individual mineral grains which is consistent with a re equilibration process the release of latent heat of crystallization in cooling migmatitic systems and the presence of an interstitial liquid phase are critical in determining the extent and scale of chemical exchange the mechanism involves 1 reducing the cooling rate and 2 promoting the efficiency of chemical diffusion through the liquid phase thus some doubt is cast on the ability of small scale migmatitic systems to provide relevant information about chemical mass balance during partial crustal melting

accessory minerals and the geochemical evolution of crustal magmatic systems a summary and prospectus of experimental approaches it has recently been recognized that accessory minerals in continental rocks may contain a substantial fraction of the whole rock complement of trace elements and geochemically important isotopes this observation is in itself interesting but its importance is magnified many fold when one considers the possible consequences to the geochemical rearrangement that accompanies crustal melting if for example an accessory phase is insoluble in early formed partial melts it may effectively retain in the residue many incompatible elements e g ree and daughter isotopes e g radiogenic pb that would otherwise be partitioned into the melt in addition should an unmelted accessory mineral e g zircon be entrained in a departing melt fraction it may carry with it radiogenic components pb nd143 hf176 characteristic of the source region the effectiveness of phases such as zircon apatite sphene allanite epidote and monazite in the roles noted above can only be gauged from knowledge of the three fundamental accessory phase parameters i e 1 the solubilities of the accessory minerals in crustal melts 2 the equilibrium mineral liquid partition coefficients for the trace element and isotopes of interest and 3 the diffusivities that govern the rates at which equilibrium will be approached in general these parameters can only be measured in laboratory experiments and relatively few data have been accumulated to date it does seem clear however that apatite generally is residual insoluble during crustal melting and zircon can be depending on melting conditions and abundance of zircon in the source petrographic and geochemical studies indicate that monazite allanite and epidote may also be highly insoluble in some cases but the specific circumstances that promote insolubility remain unknown the few experimentally determined partition coefficients now available for apatite and zircon agree qualitatively with natural rock data on mineral separates however preliminary diffusion measurements and inferences from natural systems suggest that trace element and isotopic equilibrium between undissolved accessories and crustal melts is in fact rarely approached ironically it is this very disequilibrium in the form of preserved diffusion profiles that may afford the most information on time temperature histories of melting events continued experimental interest in the fundamental accessory phase parameters will eventually provide the tools that will enable rigorous assessment not only of the timing and duration of crustal melting episodes but also of the extent of melting and re distribution of trace elements and radiogenic isotopes

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

distribution of partial melt in a felsic system the importance of surface energy the texture distribution and infiltration tendency of a quartz albite melt in equilibrium with a synthetic texturally equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1 250 c and 8 kbar hydrostatic pressure wetting angle measurements from melt distribution experiments show a dihedral angle of 60 degrees implying a quartz quartz interfacial energy approximately 1 7 times the quartz melt value because of this specific relationship between interfacial energies the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections possibly forming some interconnected channels stability of melt in pockets and along grain edge intersections was observed in a fourteen day dispersed melt experiment yet melt pools failed to disperse into the quartzite during infiltration experiments comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically

the role of water mixing processes and metamorphic fabric in the genesis of the baume migmatites ardeche france the baume migmatites arose from melting of a high grade metamorphic sequence comprising quartzofeld spathic and biotite plagioclase gneisses geochemical data and ree modelling suggest that melting occurred under open system conditions and was caused mainly either by the infiltration along shears of an alkali rich k rb aqueous fluid phase or by the injection along foliation planes of granitic magma some leucosomes result from mixing between in situ partial melts and externally derived granitic materials melting appears to be almost independent of the paleosome composition but rather is dependent on the amount of introduced material itself controlled by the metamorphic fabrics of parent gneisses and or tectonic structures

generation of plagiogranite by amphibolite anatexis in oceanic shear zones field geochronological and rare earth element ree evidence obtained from the fournier oceanic fragment of the canadian appalachians indicates that its plagiogranite component was generated by the anatexis of amphibolite and not by the fractionation of basic magma we propose that the process occurred in two stages first gabbro was plastically deformed at high temperature to form dry low angle shear zones that subsequently evolved to amphibolite via the addition of light ree enriched hydrothermal solutions second the amphibolite underwent partial melting during shear to yield a migmatite comprising bands of plagiogranite alternating with amphibolite restite the plagiogranite locally coalesced to form pods dikes and lenses that injected the surrounding undeformed gabbro we attribute the development of the fournier plagiogranite to dynamothermal processes occurring in proximity to a spreading center due to asthenosphere induced shear within ocean layer 3 this serves as an important illustration of the dynamic nature of metamorphism and melting that can occur in the ocean crust

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

recurrent liquefaction in christchurch new zealand during the canterbury earthquake sequence continuous observational monitoring of a study site in eastern christchurch new zealand following the 2010 m w 7 1 darfi eld earthquake has recorded ten distinct liquefaction episodes in the mainshock aftershock sequence three nearby accelerometers allow calibration between the geological expressions of liquefaction and the intensity of earthquake induced surface ground motion at the site sand blow formation was generated by m w 5 2 7 1 earthquakes with m w 7 5 normalized peak ground accelerations pga 7 5 of 0 057 g acceleration due to gravity silt drapes between successive sand blow deposits provide markers for delineating distinct liquefaction inducing earthquakes in the geologic record however erosion quickly modifi es the surface of sand blows into alluvial and aeolian forms that complicate geologic diagnosis the two feeder dike generations identifi ed in subsurface investigations signifi cantly underrepresent the number of liquefaction inducing earthquakes due to extensive dike reactivation new constitutive equations enable pga 7 5 variations to be estimated from the thickness and areal extent of sand blows

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

monitoring of the palu koro fault sulawesi by gps years of gps measurements across the palu koro fault sulawesi indonesia state left lateral strike slip 3 4 cm yr with a small normal component 0 4 cm yr the measurements on intermediate points of the transect show that the fault is locked at a depth estimated around 8 16 km by a very simple model the best measured baseline linking the two most separate sites watatu and toboli shows very interestingly a constant rate of 2 6 cm yr from 1992 to 1995 and an increased rate of 6 3 cm yr since then this increase is due to an earthquake on january 1 1996 in the minahasa trench presumably affecting station toboli s position by 2 cm of co seismic and 2 cm of post seismic displacement which is added to its long term velocity we interpret this phenomenon as additional stress loading on the palu fault driven by the slip during the earthquake 100 km to the north east

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

co seismic displacements folding and shortening structures along the chelungpu surface rupture zone occurred during the 1999 chi chi taiwan earthquake abstract a nearly 100 km long surface rupture zone called chelungpu surface rupture zone occurred mostly along the pre existing chelungpu fault on the northwestern side of taiwan accompanying the 1999 chi chi ms 7 6 earthquake the chelungpu surface rupture zone can be divided into four segments based on the characteristics of co seismic displacements geometry of the surface ruptures and geological structures these segments generally show a right step en echelon form and strike ne sw to n s and dip to the east with angles ranging from 50 to 85 the co seismic flexural slip folding structures commonly occurred in or near the surface rupture zone from a few meters to a few hundreds of meters in width which have an orientation in fold axes parallel or oblique to the surface rupture zone the displacements measured in the southern three segments are approximately 1 0 3 0 m horizontally and 2 0 4 0 m vertically the largest displacements were measured in the northern segment 11 1 m horizontally and 7 5 m vertically respectively the amount of co seismic horizontal shortening caused by flexural slip folding and reverse faulting in the surface rupture zone is generally less than 3 m it is evident that the co seismic displacements of the surface rupture zone are a quantitative surface indicator of the faulting process in the earthquake source fault the relations between the geometry and geomorphology of the surface rupture zone dips of the co seismic faulting planes and the striations on the main fault planes generated during the co seismic displacement show that the chelungpu surface rupture zone is a reverse fault zone with a large left lateral component

liquid segregation parameters from amphibolite dehydration melting experiments we have experimentally obtained some of the parameters necessary for understanding the segregation of silicate liquid from amphibolite undergoing dehydration melting at 1 gpa and 750 1000 c the solidus for this calcic amphibolite 68 mg hb 32 pl an 90 is 750 c amphibolites begin to melt at relatively high temperatures in the garnet absent field but the solidus appears to backbend at 1 gpa coincident with the garnet in boundary hornblende breakdown due to garnet formation releases h 2o and causes melting thus in the garnet present field 1 gpa the amphibolite dehydration melting solidus may be coincident with the h 2o saturated solidus liquid interconnectivity may be achieved at 900 c and 5 vol liquid based on both physical and chemical data from solid rock runs mass balance calculations from powdered rock runs suggest that small amounts 5 15 vol of hydrous 4 wt h 2o low viscosity 10 3 10 4 pa s heavy rare earth element depleted felsic liquid may be segregated during amphibolite dehydration melting at 875 c the rapid breakdown of coarse grained hb cores may lead to the formation of transient h 2o saturated liquids with even lower viscosities 10 2 pa s although comprising only a small portion of the melting cycle these h 2o rich conditions may enhance the segregation of liquid by reduction of liquid viscosities and by mechanical effects on the restite e g increased deformation and liquid fracturing during anatexis of coarse grained natural rocks transient conditions may control the initial stages of liquid segregation

partial melting and the formation of granulite facies assemblages in namaqualand south africa abstract dehydration melting reactions in which water from a hydrous phase enters the melt leaving an anhydrous solid assemblage are the dominant mechanism of partial melting of high grade rocks in the absence of externally derived vapour equilibria involving melt and solid phases are effective buffers of ah2 o the element partitioning observed in natural rocks suggests that dehydration melting occurs over a temperature interval during which for most cases ah2o is driven to lower values the mass balance of dehydration melting in typical biotite gneiss and metapelite shows that the proportion of melt in the product assemblage at t 850 c is relatively small 10 20 and probably insufficient to mobilize a partially melted rock body granulite facies metapelite biotite gneiss and metabasic gneiss in namaqualand contain coarse grained discordant unfoliated anhydrous segregations surrounded by a finer grained foliated matrix that commonly includes hydrous minerals the segregations have modes consistent with the hypothesis that they are the solid and liquid products of the dehydration melting reactions bt sil qtz pi grt crd kfs l metapelite bt qtz pl opx kfs l biotite gneiss and hbl qtz opx cpx pl l metabasic gneiss the size shape distribution and modes of segregations suggest only limited migration and extraction of melt growth of anhydrous poikiloblasts in matrix regions development of anhydrous haloes around segregations and formation of dehydrated margins on metabasic layers enclosed in migmatitic metapelites all imply local gradients in water activity also they suggest that individual segregations and bodies of partially melted rock acted as sinks for soluble volatiles the preservation of anhydrous assemblages and the restricted distribution of late hydrous minerals suggest that retrograde reaction between hydrous melt and solids did not occur and that h2o in the melt was released as vapour on crystallization this model combined with the natural observations suggests that it is possible to form granulite facies assemblages without participation of external fluid and without major extraction of silicate melt

ion microprobe determinations of trace element concentrations in garnets from anatectic assemblages abstract trace element data for garnet cordierite plagioclase alkali feldspar and tourmaline have been obtained by ion microprobe analysis of assemblages from a pelite derived leucogranite a sillimanite grade anatectic gneiss and a kyanite grade sub solidus schist from the high himalaya results confirm that for equilibrium melting residual plagioclase will cause depletion in sr and eu in the melt and residual garnet will result in strong depletion of y and hree consistent with their published partition coefficients all trace elements of interest are strongly incompatible in cordierite implying that for equilibrium fractional melting of pelites at shallow depths hree concentrations in garnets from metasediments are independent of metamorphic grade but the metamorphic garnets are significantly less enriched in hree than is the leucogranite garnet this suggests either that the leucogranite is derived from a source with lower modal abundances of garnet than the analysed metasediments or that garnet from the anatectic gneiss has not reached chemical equilibrium with a granitic melt the latter possibility is consistent with sluggish self diffusion rates in garnets for ree at temperatures of 5 kbar

relationship between observed liquefaction at kaiapoi following the 2010 darfield earthquake and former channels of the waimakariri river abstract the darfield earthquake caused widespread damage in the canterbury region of new zealand with the majority of damage resulting from liquefaction and lateral spreading one of the worst hit locations was the small town of kaiapoi north of christchurch an area that has experienced liquefaction during past events and has been identified as highly susceptible to liquefaction the low lying town sits on the banks of the kaiapoi river once a branch of the waimakariri a large braided river transporting gravelly sediment the waimakariri has been extensively modified both by natural and human processes consequently many areas in and around the town were once former river channels using historical accounts and maps of the region areas of land reclamation and old channels that had been cut off from the river since the beginning of european settlement in the 1850s were identified these areas correlated well with many of the areas having significant liquefaction damage following the darfield event substantial lateral spreads and sand boils developed in areas of reclamation along the current river path causing significant damage to stopbanks and structures along the river with fissures up to 2 m deep and 1 m wide much of the residential housing was damaged by lateral spreading with cumulative displacement offsets up to 3 m parallel to old channel beds that had aggraded over time due to river shifts in former channel areas that were free of lateral spreading large volumes of ejecta were present over wide areas with depths of up to 400 mm in places houses in these regions were damaged as a result of settlement and tilting in all these areas underground services and roadways were severely impacted as a result of ground deformation the severity of this damage indicates the importance of knowing the location of old channels when defining liquefaction prone regions

compressional wave velocity of granite and amphibolite up to melting temperatures at 1 gpa abstract compressional wave velocities vp at above solidus temperatures and at 1 gpa were obtained for a granite and amphibolite which are considered to be major constituents of the continental crust the temperature variation of velocities showed that the vp values of granite decreased with rising temperature but substantially increased beyond the melting temperature 850 900 c such an increase may be caused by the transition of quartz the velocities of amphibolite decreased linearly with increasing temperature and dropped sharply at temperatures above the solidus 700 c indicating that partial melting of amphibolite acts to significantly lower the seismic velocities

rock pulverization at high strain rate near the san andreas fault rocks near the san andreas fault are pervasively crushed at distances of up to 400 m from its core laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates 150 s 1 associated with a supershear rupture a rupture propagating at a velocity equal to greater than that of seismic shear waves

rapid rotations about a vertical axis in a collisional setting revealed by the palu fault sulawesi indonesia global positioning system gps measurements from 1992 to 1995 indicate that the left lateral palu fault in central sulawesi slips at a rate of 38 8 mm a with a locking depth between 2 and 8 km from the measured slip rate and the historic seismicity of the fault we estimate that the palu fault currently has stored enough strain to produce a mw 7 earthquake the palu and other nearby faults accommodate rapid clockwise rotation of nearly 4 ma of e sulawesi relative to eastern sunda the rotation of east sulawesi transfers e w shortening between the pacific and eurasian plates to n s subduction of the celebes basin beneath sulawesi

generation and evolution of subduction related batholiths from the central urals constraints on the p t history of the uralian orogen abstract batholiths from the accreted terranes in the urals were generated by repeated episodes of melting and intrusion verkhisetsk the largest and one of the most complex subduction related batholiths from the urals comprises an outer envelope of older tonalites trondhjemites and granodiorites dated at 315 320 ma and equilibrated at 6 kbar intruded by an inner core of younger granodiorites adamellites and granites dated at 275 290 ma and equilibrated at 4 kbar older rocks have a high a1 ttd adakite chemistry 320machur nd 2 5 and initial 87 sr 86 sr 0 7043 with pronounced lateral zoning marked by the increase of lree hree cr ni and mg eastwards they were originated by melting of metabasalts in a subducted slab of young hot oceanic lithosphere with a temperature depth trajectory that intersected the garnet in univariant at 1050 c and 13 kbar thus causing the lateral zoning we believe that such a warm trajectory can be attributed to the oblique subduction of a young lithosphere younger rocks range from na rich metaluminous granodiorites to k rich peraluminous two mica granites with relict epidote crystals and have almost the same isotopic signature as older rocks from which they were generated by anatexis as a consequence of a melting event that occurred throughout the urals at 275 290 ma and produced most of the huge continental type batholiths on the eastern side this melting event is tentatively supposed to be the result of underplating by mafic magmas which also caused the growth of the urals crust from the moho downwards until it reached the increased thickness revealed by seismological studies

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic

evolution of major and trace element composition during melt migration through crystalline mush implications for chemical differentiation in the crust we present the first quantitative model of heat mass and both major and trace element transport in a mush undergoing compaction that accounts for component transport and chemical reaction during melt migration and which is applicable to crustal systems the model describes the phase behavior of binary systems both eutectic and solid solution with melt and solid compositions deter mined from phase diagrams using the local temperature and bulk composition trace element concentration is also determined the results demonstrate that component transport and chemical reaction generate compositional variation in both major and trace elements that is not captured by existing geochemical models in particular we find that even for the simplest case of a homogenous insulated column that is instantaneously melted then allowed to compact component transport and reaction leads to spatial variations in major element composition that in this case produces melt that is more enriched in incompatible elements than predicted by batch melting in deep crustal hot zones dchz created by the repeated intrusion of hot mantle derived magmas buoyant melt migrating upwards accumulates in high porosity layers but has a composition corresponding to only a small fraction of batch melting because it has locally equilibrated with mush at low temperature moreover melt migration and chemical reaction in a layered protolith may lead to the rapid formation of high porosity melt layers at the interface between different rock compositions in both of these cases the melt in the high porosity layer s is less enriched in incompatible trace elements than predicted if it is assumed that melt with the same major element composition was produced by batch melting this distinctive decoupling of major and trace element fractionation may be characteristic of magmas that originate in dchz application of the model to a number of crustal systems including the ivrea verbano zone the rum layered intrusion and the holyoke flood basalt suggests that composi tional heterogeneity can be explained by buoyancy driven melt migration and compo nent transport through a reactive crystalline mush