the geochemistry of mafic metavolcanics implications for the origin of the devonian massive sulfide deposits at zlate hory czechoslovakia mafic metavolcanic rocks in the area of the zlate hory massive sulfide deposits are interpreted as convergent plate margin basalts and basaltic andesites metamorphosed to the greenschist facies according to the major and trace element compositions the metabasites exhibit island arc tholeiitic to low k calc alkaline composition

the seismic cycle in the area of the 2011 mw9 0 tohoku oki earthquake we model seismic and aseismic slip on the japan megathrust in the area of the m w9 0 2011 tohoku oki earthquake based on daily time series from 400 gps stations of the geonet network and campaign measurements of six sea floor displacements the coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis based inversion method pcaim exploring a wide range of boundary conditions and regularization constraints we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench our model shows deep afterslip fringing the downdip edge of the coseismic rupture but also a dominant zone of shallow afterslip afterslip over the first 279 days following the main shock represents about 40 of the coseismic moment we compare the coseismic and postseismic models with an interseismic coupling model derived from inland and sea bottom measurements determined in a self consistent manner assuming that seismic and aseismic slip had to match the long term slip rate along the megathrust the recurrence time of m w9 0 earthquakes is estimated to 100 300 years while historical and paleotsunami records suggest a return period more of the order of 1000 years the discrepancy is smaller if the shallower portion of the megathrust is assumed to produce both aseismic slip as the afterslip model suggests and seismic slip during occasional large tsunamigenic earthquakes

anomalous low velocity zone and linear alignment of seismicity along it in the subducted pacific slab beneath kanto japan reactivation of subducted fracture zone 1 a detailed investigation of the hypocenter distribution beneath kanto japan reveals a nw se trending linear alignment of seismicity within the subducted pacific slab we estimate the 3d seismic velocity structure in the pacific slab to understand the factors controlling the genesis of such intraslab earthquakes a narrow low velocity zone is imaged within the subducted slab over a length of 150 km which partly penetrates into the mantle portion of the slab the low velocity zone correlates in space with the nw se trending earthquake cluster a reactivation of hydrated fracture zone formed prior to subduction is probably related to the low velocity anomaly dehydration reactions of the hydrated oceanic mantle as well as the oceanic crust might lower the seismic velocity along the fossil fracture zone accompanied by intraslab earthquakes these observations support the hypothesis of dehydration embrittlement as the most viable mechanism for generating intraslab earthquakes

sulfide remobilization during low temperature alteration of seafloor basalt abstract the behavior of sulfide minerals during the physical and chemical changes accompanying seafloor alteration was studied in three basalt flows from the bottom of d s d p hole 418a leg 53 the rocks are mildly altered and contain primary authigenic and vein sulfide minerals sulfide habit mineralogy and trace element content are inter related and are correlated with the extent and type of silicate and oxide alteration incipient alteration at 90 100 c was accompanied by low temperature reequilibration of pyrrhotite and locally by the oxidation of pyrrhotite to pyrite plus magnetite the dominant stage of alteration at 90 c is characterized by dissolution and local redistribution of pyrite and chalcopyrite whose precipitation appears to be controlled by the water rock ratio and the extent to which the water has been modified by reaction with the basalt chalcopyrite was concentrated relative to pyrite by slight changes in fluid composition caused by reaction with other minerals concurrent precipitation of smectite causes a net increase in rock volume tending to restrict seawater access calculations of rock cooling rate through time suggest that the most prolonged hydrothermal circulation occurs at low temperatures giving rise to pervasive low temperature alteration assemblages

geochemistry and origin of archaean quartz cordierite gneisses from the godthabsfjord region west greenland we report new data on the major minor and trace element compositions of metasedimentary quartzcordierite gneisses qcg an important member of the archaean malene supracrustal suite found throughout the godthabsfjord region of west greenland the analyzed qcg contain assemblages of quartz cordierite biotite garnet anthophyllite gedrite staurolite sillimanite plagioclase with abundant accessory zircon and minor rutile monazite and allanite and broadly resemble cordierite orthoamphibole rocks found in a great number of other metamorphic terrains chemically the qcg are characterized by 1 high but variable sio2 59 87 wt relative enrichments in mgo feo and al2o3 mg 0 35 0 85 and depletions in na2o k2o and especially cao 2 low concentrations of sc cr co ni and sr 3 high concentrations of y nb zr hf ta th u and ree rare earth elements with prominent negative eu anomalies in each case 5 high concentrations of ga 18 55 ppm with variable ga al ratios that are significantly higher than average crustal material low cr and ni together with enriched and fractionated ree displaying negative eu anomalies distinguish the malene qcg from published accounts of most other archaean sedimentary rocks furthermore all of the above mentioned trace element characteristics distinguish the qcg from ordinary malene clastic metasediments quartzites psammites and pelites suggesting a separate origin for the qcg these data point towards chemically evolved felsic igneous rocks being the source of the qcg consequently we propose that the malene qcg represent metamorphosed felsic volcaniclastic sediments that underwent hydrothermal alteration by heated seawater prior to metamorphism which resulted in gain of mg and fe loss of alkalis and lime and possibly eu and sr the overall trace element characteristics of the qcg elevated ga zr nb ree etc are features shared by a type granites and their volcanic equivalents such igneous rocks may represent the ultimate source material for the qcg protolith

resolving depth dependent subduction zone viscosity and afterslip from postseismic displacements following the 2011 tohoku oki japan earthquake abstract we developed a 3 d viscoelastic finite element model of the m9 2011 tohoku oki japan earthquake capable of predicting postseismic displacements due to viscoelastic relaxation and afterslip we consider seismically inferred slab geometries associated with the pacific and philippine sea plate and a wide range of candidate viscoelastic rheologies for each case we invert for afterslip based on residual surface displacements observed gps minus that predicted due to viscoelastic relaxation to develop combined viscoelastic relaxation and afterslip models we are able to find a mechanical model that fully explains all observed geodetic on land and seafloor horizontal and vertical postseismic displacements we find that postseismic displacements are in about equal parts due to viscoelastic relaxation and afterslip but their patterns are spatially distinct accurately predicting both horizontal and vertical on land postseismic displacements requires a mantle wedge viscosity structure that is depth dependent reflecting the manner in which temperature pressure and water content influence viscosity no lateral heterogeneities within the mantle wedge viscosity structure beneath northern honshu are required westward directed postseismic seafloor displacements may be due flow via low temperature plastic creep within the lower half of a pacific lithosphere weakened by plate bending the distribution of afterslip is controlled by the location of coseismic slip from the tohoku oki and other regional historic earthquakes the paradigm by which afterslip is thought of as the dominant postseismic mechanism immediately following earthquakes with viscoelastic relaxation to follow in later years is shown to no longer be valid

evidence of viscoelastic deformation following the 2011 tohoku oki earthquake revealed from seafloor geodetic observation the gps acoustic seafloor positioning has detected significant postseismic movements after the 2011 tohoku oki earthquake m9 0 just above the source region off the pacific coast of eastern japan in contrast to the coastal global navigation satellite systems sites where trenchward upward movements were reported the offshore sites above the main rupture zone in the northern part of the source region exhibit landward displacements of tens of centimeters with significant subsidence from almost 3 years of repeated observations at the sites above around the edge of the main rupture zone smaller amount of trench normal movements was found although the terrestrial movements were reasonably interpreted by afterslip beneath the coastal area these offshore results are rather consistent with effects predicted from viscoelastic relaxation in the upper mantle providing definitive evidence of its occurrence on the other hand the results in the southern part of the source region imply superposition of effects from viscoelastic relaxation and afterslip

petrology and oxygen isotope geochemistry of a fossil seawater hydrothermal system within the solea graben northern troodos ophiolite cyprus hydrothermal mineral zonations and o isotope patterns of the northern troodos complex do not parallel the ophiolite pseudostratigraphy but reflect the convective geometry of an upper cretaceous seawater hydrothermal system large areas of the sheeted intrusive complex sic including the subaxial region of the solea graben are composed of 18o rich subgreenschist mineral assemblages and may represent regions of diffuse seawater recharge other areas of the sic are recrystallized to distinctive epidosite rocks granular high variance assemblages of epidote quartz chlorite that are depleted in 18o al2o3 na2o k2o zr cu and zn and are enriched in cao and sr compared with other mafic volcanic and dike rocks of the solea graben epidosite alteration occurred at temperatures of 310 370 c and involved fluids with 18o values and salinities similar to those of upper cretaceous seawater the epidosite zones are discordant with earlier mineral o isotope zonations and with the axis of spreading in the solea graben suggesting a postspreading off axis origin the seawater hydrothermal system responsible for solea graben massive sulfide deposits was probably driven by hypabyssal intrusions not exposed emplaced in a terminal failed spreading episode the geometries of o isotope surfaces within the solea graben imply that the epidosites formed in fossil upflow and deep recharge conduits depletions in base metals show that epidosite alteration liberated cu and zn to mineralizing fluids within the fossil upflow zone

an approach to geochemical characterization of productive versus barren granitoids in terms of iron in central turkey abstract the granitoids associated with and without skarn type mineralizations in central anatolia are termed as productive and barren granitoids respectively the study of the relationships between plutonic rocks in the central anatolian crystalline complex in central turkey suggests a direct genetic connection between the composition of plutons and their associated ore deposits in order to discriminate between productive and barren granitoids two fe skarn granitoids celebi and karamadazi and a series of barren plutons within central anatolia were examined the karamadazi and celebi granitoids are geochemically different from other barren plutons in central anatolia the parameters governing the productivity of these granitoids were determined by principal component analysis factor analysis method based on this method the factors controlling the geochemical characteristics of the celebi granitoids are al2o3 mgo fe2o3 p2o5 tio2 cao sio2 k2o rb na2o and rb sr ratios and for the karamadazi granitoid the fe2o3 mno mgo p2o5 y sio2 rb fmmy s and na2o k2o ratios these two granitoids are clearly distinguished from the barren central anatolian granitoids cag on harker diagrams based on these controlling factors parameters barren cag plutons are different from the productive celebi granitoids in their higher silica content and generally higher total alkali values this study suggests that iron producing granitoids are less differentiated and receive little contribution from continental crust compared to the barren granitoids higher apatite and zircon abundance in the celebi granitoids suggest that the celebi granitoids have more i type characteristics compared to barren plutons of cag the karamadazi granitoid is the most striking example for the granitoids in cag having a higher contribution from the continental crust as evidenced by higher rb ba th the highest mean sc v and mean zr y ni contents based on the factor analysis it is proposed that the karamadazi granitoid displays geochemical characteristics similar to the terlemez and agacoren granitoids of cag the factor analyses indicated that the first two factors are about the same for both the fe producing celebi and karamadazi granitoids therefore this similarity has let to a conclusion that the productivity or non productivity of the granitoids in central anatolia can be tested by examining and comparing the distribution of granitoids in diagrams designed according to the factors defined in this study

iron rich fragments in the yamansu iron deposit xinjiang nw china constraints on metallogenesis abstract volcanic rock hosted iron deposits are among the important iron ores in china however the nature of primary magma and petrogenesis associated with these iron ores remains controversial here we report iron rich fragments irf from the yamansu iron deposit in eastern tianshan mountains nw china which occurs in association with volcanic breccia submarine volcanic breccia and ignimbrite the irf is composed of five types including oligoclase iron oxide type oio oligoclase albite iron oxide type oaio albite iron oxide type aio albite k feldspar iron oxide type akio and k feldspar iron oxide type kio these fragments display typical volcanic fabric features such as porphyritic texture hyalopilitic texture of the groundmass and vesicles filled by minerals to form amygdales the feldspar phenocrysts of irf are dominantly albite the groundmass of irf consists of magnetite and feldspar the magnetite is distributed in between the feldspar laths and together display hyalopilitic texture which could be observed only in volcanic rocks the vesicles are filled with magnetite feldspar chlorite and calcite from the margin to the interior the irf has high si al fe ca ti na and k contents and low mg content the average total fe is 26 wt the magnetite is mostly titanium vanadium magnetite with the tio2 content ranging up to 4 86 wt and v2o3 content up to 3 20 wt the irf probably came from iron rich melts and represent the products of the fenner magma evolution the basaltic magma evolved into the fe na rich residual melts by crystallization under low oxygen fugacity condition in a closed magma chamber after intruding into the shallow crust the fe na rich residual melts were emplaced in hypabyssal environments or erupted generating the orebodies or providing the material source for the generation of the high grade iron ores which were subsequently enriched by the late stage hydrothermal fluids

seawater basalt reaction and the origin of greenstones and related ore deposits massive sulfide deposits of copper zinc and iron and associated stringer deposits multicomponent equilibrium calculations of the reaction of seawater with tholeiitic basalt at 300 degrees c followed by calculation of the effects of cooling the resultant solution to 25 degrees c and mixing it with seawater the calculated mineralogy and zoning patterns resemble many natural ore assemblages observed in deposits of the kuroko type east pacific rise west shasta district according to the calculations silica should be abundant in the massive sulfide deposits modified journal abstract

isotopic exchange in mineral fluid systems ii oxygen and hydrogen isotopic investigation of the experimental basalt seawater system abstract oxygen and hydrogen isotopic exchange reactions between basalt and seawater at t 300 to 500 c were investigated using oceanic tholeiitic basalt 18 o 5 7 d 70 natural seawater 18 o 1 2 d 5 and artificial seawater 18 o 5 3 as starting materials the starting basalts varied in the crystallinity from holocrystalline to glass but were ground to approximately the same grain size 100 mesh the water rock mass ratios ranged from 1 to 3 and the duration of the experiments ranged from 167 to 576 days in general depletion of 18o and enrichment of d in basalts occur at all temperatures with the magnitudes of change being greater as temperature time and to a lesser degree glass content increases the trends in isotopic shifts are directly related to changes in the style and intensity of mineralogic alterations in the basalt e g smectite at 300 c talc actinoiite at 400 500 c the changes in the 18 o values of basalts and seawater in the experimental systems were observed to follow closely with those expected from a first order rate law rate constants for the oxygen isotopic exchange between rock and water range from 10 9 5 to 10 8 0 moles oxygen m2 of solid surface sec for temperatures of 300 to 500 c the activation energy for the isotopic exchange reaction was calculated to be 11 5 kcal mol an application of our experimental rate data to natural systems suggests that the oxygen isotope equilibrium between basalt and seawater in the mid oceanic ridge may take place within approximately 1000 years at 350 c our experimental data also suggest the equilibrium oxygen isotopic fractionation factors between the altered basalt and seawater to be 3 5 0 5 at 300 c 2 0 0 4 at 400 c and 0 5 0 25 at 500 c the observed hydrogen isotopic fractionation factors between the altered basalts and seawater in our experimental systems were about 74 at 300 c about 62 at 400 c and about 48 at 500 c these fractionation factors are probably attributable to the equilibrium fractionation between fe rich secondary phases and seawater

an integrated chemical and stable isotope model of the origin of midocean ridge hot spring systems chemical and isotopic changes accompanying seawater basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs incorporating provision for addition and subtraction of a wide range of reactant and product minerals as well as cation and oxygen and hydrogen isotopic exchange equilibria the models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100 to 350 c with an overall water rock ratio of about 0 5 being constrained by an assumed 18 o h 2o at 350 c of 2 0 per mil h craig personal communication 1984 this is a realistic model because 1 the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust 2 the water rock ratio is high 50 at low temperatures and low 0 5 at high temperatures and 3 it allows for back reaction of earlier formed minerals during the course of reaction progress the results closely match the major element chemistry von damm et al 1985 and isotopic compositions craig et al 1980 of the hydrothermal solutions presently emanating from vents at 21 n on the east pacific rise the calculated solution chemistry for example correctly predicts complete loss of mg and so 4 and substantial increases in si and fe however discrepancies exist in the predicted ph 5 5 versus 3 5 measured and state of saturation of the solution with respect to greenschist facies minerals the calculated d h 2o is 2 6 per mil in excellent agreement with analytical determinations the calculated chemical mineralogic and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges humphris and thompson 1978 stakes and o neil 1982 as well as with data from ophiolites gregory and taylor 1981 predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite epidote chlorite tremolite greenschist assemblage at 350 c the models demand that the major portion of the water rock interaction occur at temperatures of 300 350 c interaction at temperatures below approximately 250 c results in negative 18 o h 2o shifts contrary to the observed positive 18 o values of the fluids exiting at midocean ridge vents hydrogen isotope fractionation curves by suzuoki and epstein 1976 lambert and epstein 1980 and liu and epstein 1984 among others are compatible with the model and require d h 2o to increase at all temperatures as a result of seawater basalt interaction

shale basins sulfur deficient ore brines and the formation of exhalative base metal deposits abstract the massive sulfide deposits of the iberian pyrite belt are interbedded with felsic volcanic rocks and shale and underlain by several thousand meters of siliciclastic sedimentary rocks known as the pq group isotope geochemistry and regional geology are both consistent with equilibration of the ore forming fluids with the pq group prior to ore deposition near the former seafloor the average cu zn pb ratio of the pq group rocks ca 26 55 19 is similar to the weighted average of all the massive sulfide orebodies combined ca 25 52 23 the genetic relationship between massive sulfide deposits and a siliciclastic sedimentary metal source is explained here by a thermodynamic model proposing that mildly reducing redox conditions imposed by equilibration with the sedimentary rocks are most critical for the formation of an effective ore forming fluid relatively metal rich but organic poor pyrite bearing shale undergoing dewatering of saline pore fluids is an effective source for the generation of sulfur deficient but relatively iron and base metal rich brines thus we propose that the giant deposits of the iberian pyrite belt owe their existence not to exceptionally metal enriched e g magmatic fluids but to the existence of a fairly ordinary but large metal source in reactive siliciclastic sediments combined with an underlying igneous heat source and a particularly efficient mechanism of sulfide precipitation by mixing with h 2 s rich fluids at or near the seafloor essentially similar mineral equilibria are imposed when saline fluids are buffered by typical continental basement rocks leaching of retrograde minerals and possibly residual salts from their magmatic or metamorphic prehistory is expected to generate similar variably metal rich but relatively sulfide deficient fluids thus the existence of mildly reducing rocks can be the dominant chemical control in the source of fluids generating many volcanogenic irish type or sedex deposits many of which are known to precipitate their metal load in response to biogenic sulfide addition at the ore deposition site

geochemical modeling of the zoned footwall alteration pipe hellyer volcanic hosted massive sulfide deposit western tasmania australia the mineralogy of hydrothermal alteration assemblages siliceous core chlorite zone sericite zone in the footwall pipe of the hellyer volcanic hosted massive sulfide vhms deposit is controlled mainly by the temperature ph and redox state of the hydrothermal fluids based on the results of our numerical modeling the zoned alteration system could have formed by a combination of water rock interaction and cooling with a siliceous core predicted to form at the center of the conduit passing outward to a chlorite dominated zone a sericite rich zone and finally grading out to unaltered andesite these mineralogical changes relate to a gradual evolution of fluid chemistry water rock ratio ph and temperature from the core to the margin of the system initial temperatures were probably close to 350 degrees c and the hydrothermal fluids were reduced h2s dominated at low temperatures 200 degrees c a peripheral alteration zone consisting mostly of k feldspar chlorite sericite and hematite is predicted to form this low temperature zone has not been recognized at hellyer but elevated k2o contents and local k feldspar development have been noted at other vhms deposits suggesting that this zone might form at low temperatures and low water rock ratios in the footwall of vhms deposits if the existence of barren outer k feldspar alteration zones is confirmed the findings could have important implications for exploration specifically with regards to distinguishing ore related alteration zones from barren alteration systems

use of intrusive and calc silicate compositional data to distinguish contrasting skarn types in the darwin polymetallic skarn district california usa the polymetallic pb zn ag w cu au skarn and vein ores of the darwin area california represent a metal association not common in skarn deposits detailed and regional geologic mapping combined with modal and chemical analyses of igneous rocks and electron microprobe and assay studies of calc silicate rocks shows that there are three separate mineralizing systems which have been superimposed by structural and intrusive events scheelite bearing skarns are associated with the alkaline darwin stock small cu au skarns are adjacent to sheared thrust emplaced granite granodiorite masses and pb zn ag vein skarns are zoned around small granite porphyry dikes and plugs calc silicate mineral compositions are also indicative of three different mineralization systems w skarns have high fe pyroxenes and moderate fe garnets cu skarns have low fe pyroxenes and high fe garnets and pb zn skarns have high mn pyroxenes and garnets patterns seen in other skarn deposits vein ores contain metals compatible with the subjacent skarns and apparently represent lower temperature remobilization of skarn ores

geochemistry and origin of cordierite orthoamphibole orthopyroxene phlogopite rocks from namaqualand south africa abstract a suite of cordierite orthoamphibole cordierite orthopyroxene and cordierite phlogopite gneisses are described from the amphibolite and granulite facies region of the western namaqualand metamorphic complex the gneisses are directly associated with underlying and overlying metapelitic rocks to which they show certain geochemical affinities using overall geochemical trends and comparisons between amphibolite and granulite facies samples particularly for na 2 o feo and tio 2 a residual origin by extraction of granite melt can be excluded and a premetamorphic origin proposed for the mg al rich bulk compositions the formation of these specific cordierite orthoamphibole orthopyroxene rocks by metamorphism of carbonate associated evaporite sequences is not supported by their field relationships or by their al fe rich character the bulk of the cordierite orthoamphibole orthopyroxene rocks have trace element contents that strongly resemble those of underlying mafic rocks an al rich group of cordierite phlogopite bearing rocks shows marked enrichment in zr ce and th suggesting residual concentration following weathering major element modelling of postulated premetamorphic constituents indicates that the majority of cordierite orthoamphibole orthopyroxene rocks comprise former mixtures of chlorite with lesser quartz and other minor clay components phlogopite rich rocks can be modelled as mixtures of chlorite illite and kaolinite the suite probably formed by weathering of mafic volcanic material and its local redeposition in an environment where relatively warm saline conditions favoured the development of chlorite rich assemblages

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

far reaching transient motions after mojave earthquakes require broad mantle flow beneath a strong crust 1 geodeticallyobservedpostseismicsurfacedisplacements in the 7 years following the 1999 hector mine earthquake demonstrate a previously unrecognized broad pattern of transient deformation throughout southern california and into nevada more than 200 km from the epicenter unlike previous postseismic observations in which trade offs between postseismic mechanisms and the depth of flow lead to non unique solutions this deformation pattern can only be explained by viscoelastic flow in a region of the mantle 100s of km wide and below a depth of 40 km this result enables two robust conclusions regarding the nature of lithospheric strength in this region the mantle is weaker than the lower crust and flow occurs over a wide region of mantle as opposed to within a narrow shear zone beneath

petrologic evolution of large failed rifts in the eastern pacific petrology of volcanic and plutonic rocks from the mathematician ridge area and the guadalupe trough

contrasting geochemical signatures between upper triassic mo hosting and barren granitoids in the central segment of the south qinling orogenic belt central china implications for mo exploration abstract as a world class molybdenum province the qinling orogenic belt is characterized by voluminous mesozoic granitoids which are attributed to the closure processes of the paleo tethys and the collision between the south china and north china blocks the middle segment of the south qinling orogenic belt is marked by widespread triassic granitoids several small intrusions occurring as porphyry stocks or apophyses are associated with mo mineralization that occurred at ca 200 ma as constrained by molybdenite re os dating to delineate the differences between ore hosting and barren granitic intrusions in this contribution we report new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages and element and sr nd hf isotope data the granitoids were emplaced episodically from 215 to 203 ma with the lithologies evolving from quartz diorites through granodiorites to monzogranites they are metaluminous to peraluminous high k calc alkaline rocks transitional to shoshonites showing arc affinity geochemical traits such as enrichment in liles and depletion in nb ta and ti the ore hosting intrusions are monzogranites with high sio2 contents 68 wt whereas the barren ones are quartz diorites and granodiorites with low sio2 contents 60 7 64 6 wt compared to the barren quartz diorites and granodiorites the ore hosting monzogranites show much lower mg lower contents of transition metals e g sc ti co and v and much stronger depletion of sr ba eu ti and p the isotopic ratios of the ore hosting monzogranites isr 0 7012 0 7060 end t 3 32 4 58 ehf t 0 81 2 30 and the barren granitoids isr 0 7058 0 7060 end t 1 24 5 80 ehf t 3 47 5 24 are similar but the former show slightly lower isr higher end t and higher ehf t this suggests that the ore hosting magmas originated from a slightly more juvenile source but were much more fractionated which is also supported by their younger ages compared to the barrens therefore the prolonged fractional crystallization is a feasible mechanism for the formation of the ore hosting monzogranites in addition the u th correlation and zr hf ratios indicate that the fluid process was responsible for the formation of quartz veins in both the barren and ore hosting intrusions consequently a combination of fractional crystallization and fluid action may have played a crucial role in the development of the mo mineralization

composition volume changes during hydrothermal alteration of andesite at buttercup hill noranda district quebec abstract hydrothermally altered andesites in the upper member of the amulet formation at buttercup hill noranda quebec represent part of the aquifer and cap of a self sealing geothermal system that focussed the discharge of hydrothermal fluids during the formation of massive cu zn sulfide deposits five alteration facies are recognized 1 pervasive greenschist facies regional metamorphism least altered andesite 2 epidotization silicification 3 albitization silicification 4 chloritization 5 sericitization silicification alteration is localized on permeable zones such as amygdules fractures flow tops discordant breccia dikes and conformable breccia horizons epidotized silicified andesite is enriched in ca sr eu and depleted in mg and first transition series metals ftsm relative to least altered andesite albitized silicified andesite is significantly enriched in na and depleted in most ftsm relative to least altered andesite the abundances and inter element ratios of the rare earth elements ree and most high field strength elements hfs y zr th u hf ta are similar in least altered epidotized silicified and albitized silicified andesites the most silicified andesites are strongly enriched in na si strongly depleted in mg and divalent ftsm and slightly but systematically depleted in ree and most hfs elements serialized andesites were previously silicified they are very strongly enriched in k rb cs ba very strongly depleted in na ca sr eu and slightly depleted in light ree relative to silicified andesite chloritized andesitic rocks exhibit heavy ree and hfs element ratios similar to those of leastaltered andesite but are relatively strongly enriched in mg and divalent ftsm strongly depleted in si and large ion lithophile lil elements and slightly depleted in light ree the coupled behavior of the heavy ree and most hfs elements during epidotization albitization silicification chloritization and serialization suggests that they were inert during hydrothermal modification of the andesite mass balance calculations suggest that volume was conserved during epidotization silicification and albitization silicification but that intense silicification was accompanied by volume increases up to 30 percent

age and tectonic setting of bocsa and ocna de fier dognecea granodiorites southwest romania and of associated skarn mineralisation the granodiorite intrusion at ocna de fier dognecea in the western south carpathians romania triggered the formation of a classic fe pb zn skarn deposit the intrusive is related to the larger composite bocsa laccolith five kilometres north that is part of the regional banatite suite previous work indicated a k ar age of 65 57 ma and postulated an andean type subduction related tectonic setting for the intrusions we report ion probe u pb zircon ages of 79 6 2 5 ma for the bocsa laccolith and 75 5 1 6 ma for the ocna de fier pluton which date their emplacement fission track dating on titanite gives slightly younger ages 78 4 ma for bocsa and 73 4 ma for ocna de fier together with zircon and apatite data from the same samples average cooling rates of 52 c ma and 83 c ma are calculated for the bocsa and ocna de fier intrusives respectively a post collision tectonic setting is proposed on the basis of field evidence the timing of intrusions in the context of regional tectonic evolution and trace element geochemistry

geochemical and isotopic evidence for seawater contamination of the hydrothermal system of taal volcano luzon the philippines the hydrologic structure of taal volcano has favored development of an extensive hydrothermal system whose prominent feature is the acidic main crater lake ph 3500 mg kg and low so4 cl ratios 0 3 the br cl ratio of most samples suggests incorporation of seawater into the hydrothermal system water and dissolved sulfate isotopic compositions reveal that the main crater lake and spring discharges are derived from a deep parent fluid t approximate to 300 degrees c which is a mixture of seawater volcanic water and lake taal water the volcanic end member is probably produced in the magmatic hydrothermal environment during absorption of high temperature gases into groundwater boiling and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the lakes and by the fact that lake taal was directly connected to the china sea until the sixteenth century the depth to the seawater meteoric water interface is calculated to be 80 and 160 m for the main crater lake and lake taal respectively additional data are required to infer the hydrologic structure of taal geochemical surveillance of the main crater lake using the so4 cl na k or mg cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system

a field chemical and stable isotope study of subseafloor metamorphism of the josephine ophiolite california oregon the josephine ophiolite is a large complete ophiolite generated in a late jurassic back arc basin along western north america the ophiolite underwent subseafloor metamorphism under a steep thermal gradient as indicated by downward changes in mineralogy and 18o values characteristic mineral zonation includes mica orthoclase and hematite in the lower extrusives greenschist facies assemblages in the upper sheeted dikes and amphibolite facies assemblages in the lower sheeted dikes and high level gabbro cumulate gabbros are only incipiently altered but are depleted in 18o indicating high temperature alteration with fluids that evolved at low water w rock r ratios a second off axis circulation system is recorded by metalliferous sediments that occur 8 21 m above the ophiolite alteration in the upper sheeted dike complex and especially the extrusive sequence is heterogeneous at outcrop scale as indicated by large variations in mineralogy chemistry and 18o values within individual pillows and dikes the heterogenity is due to 1 variations in w r ratio and starting material during alteration by downwelling seawater e g pillow cores versus glassy rims and 2 localized discharge mineralization mostly epidosites superimposed on the background recharge alteration epidosites occur largely as dike parallel stringers irregular replacement of pillow and massive lava and replacement of interpillow and pillow breccia matrices the chemistry of most extrusives and sheeted dikes is characterized by loss of ca and gain in na and mg consistent with alteration by downwelling fluids in addition the sheeted dikes are depleted in k2o and the lower sheeted dikes and high level gabbros are depleted in zn and cu the 18o and d values for most samples from the extrusive sequence indicate alteration by seawater at 50 rotation of the entire crustal sequence at the spreading axis suggests that the ophiolite formed at a slow spreading center where magma chambers were episodic

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

oxygen and sulfur isotope geochemistry revealing a significant crustal signature in the genesis of the post collisional granitoids in central anatolia turkey abstract late cretaceous granitoid rocks from central anatolia comprise s i a type plutons derived from the collisional stages of the neo tethyan convergence system in central turkey these granitoids intrude the tectonic imbrication zone consisting of blocks of supra subduction zone type ssz type central anatolian ophiolite and crustal metasediments which are present in the izmir ankara erzincan suture zone the plutons are overlain by late palaeocene early eocene or younger detrital sediments granitoid formation is thought to be related to magma generation processes occurring in a post collisional lithospheric detachment related geodynamic setting that resulted from slab break off or lithospheric delamination whole rock s and quartz feldspar o isotope data from these plutons yields a broad range of values and both parameters indicate a nearly exclusively supracrustal origin for the s type granites as well as a significant crustal contribution in the genesis of the hybrid i type and a type granitoids the more mafic i type and a type granitoid rocks of any given suite have lower s and o values indicative of their larger degree of mantle component the combined stable isotope geochemical compositions when coupled with major trace and ree geochemistry and regional geology provide evidence that the significant crustal contribution originated from a metasomatized mantle layer which was affected by earlier ssz derived fluids and then accreted into the subcontinental lithosphere as collision occurred the partial melting of such a metasomatized mantle layer in a post collisional extensional geodynamic setting supplied either by the slab break off or lithospheric delamination mechanisms provided the significant crustal signature in the hybrid magmas of the late cretaceous i type and a type granitoids in central anatolia turkey

coseismic slip distribution for the mw 9 2011 tohoku oki earthquake derived from 3 d fe modeling 1 the coseismic slip distribution of the mw 9 0 2011 tohoku oki earthquake has been estimated by inverting near field onshore and offshore geodetic data using green s function calculated with a 3 d finite element fe model the fe model simulates several geophysical features of the subduction zone that hosted the rupture surface of the event these features include a 3 d geometric configuration and distribution of material properties of the tectonic system a precise geometric configuration of the irregular rupture surface and an irregular free surface according to the topography and bathymetry a model that simulates rupture along the interface between the relatively weak overriding okhotsk plate and stiff subducting slab of the pacific plate requires less slip to produce the observed surface deformation compared to a model having uniform material properties across the rupture interface furthermore the estimated slip of the heterogeneous model is more widely distributed over the shallow portion of the plate boundary whereas the estimated slip of the homogeneous model is more focused updip of the epicenter this demonstrates the sensitivity of inverse analyses of geodetic data for the 2011 tohoku oki earthquake to the simulated domain geometry and configuration of material properties

geometry conditions and timing of off axis hydrothermal metamorphism and ore deposition in the solea graben the recent discovery of fossil spreading axes along the northern margin of the troodos ophiolite1 provides a unique opportunity to compare a fossil seawater hydrothermal system with systems of modern oceanic spreading centres2 6 whereas previous accounts of ophiolite hydrothermal systems7 13 including troodos14 16have elucidated many aspects of sea floor hydrothermal metamorphism earlier workers have not placed ophiolite hydrothermal features within any specific spreading centre structural framework most ophiolites exhibit complex histories of post accretion deformation that mask or obliterate early structures related to seafloor spreading the troodos ophiolite is apparently still in the process of being emplaced 17 and most structural elements at troodos appear to have originated beneath a cretaceous sea floor1 we have discovered an extensive area of intense seawater hydrothermal alteration within the sheeted dyke complex of the solea graben fig 1 the metamorphic petrology and oxygen isotope geochemistry of 100 dyke samples from this graben reveal the size and three dimensional geometry of the hydrothermal system and yield estimates of temperature salinity oxygen isotope composition and recharge discharge geometry for fluids that transported the constituents of massive sulfide orebodies geometric discordance between the trends of the hydrothermally altered area and of earlier seafloor spreading structures compels us to consider a post spreading off axis origin for the orebodies of the solea graben

water rock interaction in the active geothermal system of pantelleria italy abstract the geothermal fluid sampled in a deep 990 m b s l well drilled into the peralkaline volcano of pantelleria consists for the most part of seawater the fluid is depleted in ca and mg and enriched in k rb cs and f due to interaction with rocks of trachytic composition a forward geochemical model has been used to simulate the water rock interaction processes occurring within the geothermal system in the southern part of the island the simulation assumes different mixtures of seawater with groundwater and volcanic gas the system model that emerges from the simulation is the following the seawater flows through fractures and faults reaching temperatures of over 300 c in the southern part of the island where an upflow zone of volcanic gas is present volcanic gases increase the amount of c and s in the system lower the ph and enhance the dissolution of trachyte after reaction with trachyte the ph increases and the fluid reaches saturation conditions with respect to albite quartz saponite k feldspar and muscovite in agreement with the natural hydrothermal mineral assemblages the model confirms that the reservoir fluid is a mix between seawater and meteoric water more saline fluids possibly existing in deeper levels the fluid chemistry and the hydrothermal minerals are similar to those found in the icelandic geothermal systems of reykjanes and svartsengi

high temperature alteration of abyssal ultramafics from the islas orcadas fracture zone south atlantic ultramafic rocks dredged from the islas orcadas fracture zone along the sw indian ocean ridge 6 e and 54 s show evidence of progressive hydration beginning at temperatures greater than 600 c and perhaps as high as 900 c and continuing to less than 50 c there are two principal types of alteration present in the ultramafic rocks both of which are the result of hydration reactions the first type of alteration involves hydration of original clinopyroxene orthopyroxene and olivine to amphibole talc secondary olivine and serpentine the second is a vein type of alteration and results in the formation of veins of amphibole chlorite talc and serpentine the alteration appears to be episodic the sequence of events suggested by the petrography is 1 clinopyroxene altering to amphibole 2 orthopyroxene altering to talc or talc olivine 3 supersolvus hornblende veining 4 coexisting actinolite hornblende veining 5 chlorite chlorite actinolite or chlorite secondary clinopyroxene veining 6 talc veining 7 serpentine veining and 8 pervasive serpentinization the alteration fluid is most likely seawater it is suggested that the high temperature alterations may reflect seawater circulation into the upper mantle

zinc lead skarn mineralization at tin creek alaska fluid inclusions and skarn forming reactions the tin creek zn pb skarn in farewell district alaska is zoned from predominantly a garnet skarn with abundant chalcopyrite and stockwork quartz veining in the northern part mw zone to a pyroxene skarn dominated by sphalerite in the southern part tc1 zone microthermometric analysis of primary 2 phase liquid vapor nacl h2o fluid inclusions in quartz and calcite from the skarn indicates a corresponding variation in homogenization temperature th and fluid salinity higher th mostly 280 c and salinity 4 2 6 7 wt nacl equiv in the mw zone and lower th mostly 320 c and salinity 2 5 5 0 wt nacl equiv in the tc1 zone the mw zone is interpreted as proximal to the heat source probably a hidden igneous intrusive and the tc1 zone as a relatively distal facies of the same skarn forming event development of the skarn zonation likely resulted from thermal gradient progressive fluid rock reactions and continuous interaction and dilution of hydrothermal fluids along fluid flow path numerical modeling of skarn forming reactions by titrating an impure limestone 90 calcite and 5 each of quartz and kaolinite into an initial fluid composition constrained by fluid inclusion and mineralogie data produces a final mineral assemblage comparable to that at tin creek the calculation demonstrates that a complete sequence of skarn assemblages forms during progressive equilibration of a very small amount of limestone with the infiltrating fluid the model also predicts an extremely small concentration of co2 in the skarn forming fluid in agreement with the fluid inclusion data from tin creek and other skarn deposits this suggests that co2 escape is not a significant factor facilitating sulfide precipitation during skarn formation

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

alteration mineralogy of home plate and columbia hills formation conditions in context to impact volcanism and fluvial activity the mars exploration rover spirit investigated the igneous and alteration mineralogy and chemistry of home plate and its surrounding deposits here we focus on using thermochemical modeling to understand the secondary alteration mineralogy at the home plate outcrop and surrounding columbia hills region in gusev crater at high temperatures 300 c magnetite occurs at very high w r ratios but the alteration assemblage is dominated by chlorite and serpentine over most of the w r range quartz epidote and typical high t phases such as feldspar pyroxene and garnet occur at low w r at epithermal temperatures 150 c hematite occurs at very high w r a range of phyllosilicates including kaolinite nontronite chlorite and serpentine are precipitated at specific w r amphibole with garnet feldspar and pyroxene occur at low w r if the co2 content of the system is high the assemblage is dominated by carbonate with increasing amounts of an sio2 phase kaolinite carpholite and chlorite with lower w r at temperatures of hydrous weathering 13 c the oxide phase is goethite silicates are chlorite nontronite and talc plus an sio2 phase in the presence of co2 the mineral assemblage at high w r remains the same and only at low w r i e with increasing salinity carbonate precipitates the geochemical gradients observed at home plate are attributed to short lived initially high 300 c temperature but fast cooling events which are in agreement with our models and our interpretation of a multistage alteration scenario of home plate and gusev in general alteration at various temperatures and during different geological processes within gusev crater has two effects both of which increase the habitability of the local environment precipitation of hydrous sheet silicates and formation of a brine which might contain elements essential for life in diluted easily accessible form

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

mineralogical and geochemical characteristics of hydrothermal alteration of basalt in the kuroko mine area japan implications for the evolution of a back arc basin hydrothermal system abstract basalt in the furutobe district of the kuroko mine area in japan is characterized by abundant chlorite and epidote fluid inclusion studies indicate that chlorite is formed at lower temperatures 230 250 c than epidote 250 280 c the seawater basalt mass ratio for the early chlorite rich alteration was high max 40 but that for the later alteration was low 0 1 1 8 the cao na2o and sio2 of the bulk rock correlate negatively with mgo while feo and fe correlate positively with mgo these changes in the characteristic features of hydrothermal alteration from early to late are generally similar to those for a mid ocean ridge geothermal system accompanying basalt alteration the mgo feo ratios of chlorite and actinolite and the fe2o3 concentration of epidote from the basalt are greater than those of mid ocean ridge basalt probably owing to the differences in the fe2o3 feo and mgo feo ratios of the parent rocks the lower cao concentration and the higher na2o concentration of the bulk rock compared with altered mid ocean ridge basalt can be interpreted in terms of the difference in original bulk rock compositions the furutobe basalt as well as other submarine back arc basalts contains more vesicles filled with hydrothermal minerals epidote calcite quartz chlorite pyrite than do the mid ocean ridge basalts the abundance of vesicles plays an important role in controlling the secondary mineralogy and geochemistry of hydrothermally altered submarine back arc basin basalts

high temperature hydrothermal alteration of ultrmafic cumulates from the base of the sheeted dikes in the josephine ophiolite nw california ultramafic cumulate pods occur locally just below the base of the sheeted dike complex in the josephine ophiolite in north western california these ultramafic rocks occur with metagabbros and both are extensively intruded by mafic dikes the ultramafic cumulates contain evidence of high temperature hydrothermal alteration early alteration possibly above 900 c which continued to progressively lower temperatures 350 c this hydrothermal alteration has been partially obscured by later low grade regional metamorphism petrographic evidence for the hydrothermal alteration includes 1 hydration of primary clinopyroxene to hornblende 2 supersolvus secondary hornblende 3 subsolvus coexisting hornblende actinolite and actinolite chlorite 4 alteration of hornblende to chlorite 5 alteration of orthopyroxene and olivine to serpentine and 6 serpentine veining the composition of the altering fluid appears to change with temperature

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

geology fluid inclusion and sulphur isotope characteristics of the el cobre vhms deposit southern cuba the el cobre deposit is located in eastern cuba within the volcanosedimentary sequence of the sierra maestra paleogene arc the deposit is hosted by tholeiitic basalts andesites and tuffs and comprises thick stratiform barite and anhydrite bodies three stratabound disseminated up to massive sulphide bodies produced by silicification and sulphidation of limestones or sulphates an anhydrite stockwork and a siliceous stockwork grading downwards to quartz veins sulphides are mainly pyrite chalcopyrite and sphalerite gold occurs in the stratabound ores fluid inclusions measured in sphalerite quartz anhydrite and calcite show salinities between 2 3 and 5 7 wt nacl eq and homogenisation temperatures between 177 and 300 c sulphides from the stratabound mineralisation display 34s values of 0 to 6 0 whilst those from the feeder zone lie between 1 4 and 7 3 sulphides show an intra grain sulphur isotope zonation of about 2 usually 34s values increase towards the rims sulphate sulphur has 34s in the range of 17 to 21 except two samples with values of 5 9 and 7 7 sulphur isotope data indicate that the thermochemical reduction of sulphate from a hydrothermal fluid of seawater origin was the main source of sulphide sulphur and that most of the sulphates precipitated by heating of seawater the structure of the deposit mineralogy fluid inclusion and isotope data suggest that the deposit formed from seawater derived fluids with probably minor supply of magmatic fluids

metamorphism of deep seated rocks from the garrett ultrafast transform east pacific rise near 13 25 s in spite of 10 years of extensive exploration of the east pacific rise the petrology of the fast slipping transforms remains poorly documented in 1980 metagabbros and serpentinites were dredged from the deepest trough 4616 4820 m in depth of the garrett ultrafast transform which intersects the east pacific rise near 13 25 s 16 cm yr total spreading rate previous works on their protolith concluded that the samples consist of serpentinized refractory upper mantle and lower crust gabbroic cumulates in addition several ultramafic rocks showing evidences of magmatic impregnation were believed to represent mantle crust transition zone as observed in ophiolite complexes the present work focuses on the postigneous evolution of the rocks affected by hydrothermal circulation an early stage of amphibolitization occurred at about 700 400 c and probably down to 300 c in the most evolved gabbros ti fe gabbros the amphibole compositional variations suggest evolution of the metasomatic solution and temperature through time from the amphibolite facies down to the lower greenshist facies high chlorine ferruginous hornblendes 3 5 wt cl found in veins of the ferrogabbros suggests that pore fluids in this type of material evolved in situ to a ferruginous brine the decreasing temperature 300 200 c and further fracturing favored more or less pervasive serpentinization of the olivine rich samples ultramafics and olivine gabbros the release of ca in the solution contributed to the alteration of the plagioclase bearing rocks troctolites and gabbros which were invaded by calc silicates hydrogrossular prehnite pumpellyite and epidote a process which is referred to as rodingitization the occurrence of monomineralic veins of al pumpellyite in some metagabbros suggests very low o2 conditions in the lower ocean crust ph2o 2 kbar low o2 also inferred from the composition of the other calc silicates and indicates low permeability and limited fluid circulation during retrograde metamorphism further uplift and emplacement of the rocks on the seafloor of the transform domain were accompanied by low temperature crystallization of zeolite and aragonite high mg and co2 in monomineralic veins and clay minerals in veins and in external alteration rims the garrett s samples are by many respects comparable to typical ocean floor metabasites from various settings the rocks recorded igneous and metamorphic transformations similar to those expected beneath spreading ridges unaffected by transform tectonics the metamorphism is a consequence of the dynamics of spreading propagation of the cracks and penetration of seawater deeper in the cooling crust however the extent of fissuring and the subsequent hydration probably increase drastically with proximity to the garrett transform most of the observed metasomatic reactions have a limited extent and occurred at depth without significant deformation of the rocks rapid uplift of the rocks initiated by vertical components of the transform tectonics was probably induced by serpentinization of the ultramafics buoyancy of serpentinite and intense mass wasting at the surface of seafloor however emplacement by diapirism is not completely ruled out if the dredged samples are relatively undeformed poorly altered rocks carried up by protusions of ductile serpentine which is now too fragile to be sampled by dredging

using apatite to discriminate synchronous ore associated and barren granitoid rocks a case study from the edong metallogenic district south china abstract in order to find criteria to discriminate the synchronous ore associated and barren granitoid rocks we have determined apatite chemistry associated with ore associated cu au and barren granitoid rocks in the edong district of the middle and lower yangtze river metallogenic belt south china both rock types give zircon u pb ages between 135 0 and 138 7 ma apatite has a higher volatile and li content cl 0 19 0 57 wt average 0 35 wt so3 0 08 0 71 wt average 0 32 wt li 0 49 7 99 ppm average 3 23 ppm in ore associated rocks than those in barren rocks cl 0 09 0 31 wt average 0 16 wt so3 0 06 0 28 wt average 0 16 wt li 0 15 0 89 ppm average 0 36 ppm apatite la yb n ratios and eu eu values are relatively high and show wider variation in ore associated rocks than those in barren rocks apatite la sm n and yb sm n show positive correlation in ore associated rocks but negative in barren rocks the higher volatile content occurs in ore associated magma favoring cu au transportation and deposition furthermore amphibole fractional crystallization in ore associated magma further enriched the ore elements in the residual melt barren rocks may have undergone fluid exsolution before emplacement which makes it barren in cl s and ore elements cu s these signatures emphases the significance of volatile and magma evolution in mineralization and indicate that analyses of magmatic apatite can serve to distinguish ore associated from barren intrusions

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

mineral compositional and textural evidence for magma mingling in the saraykent volcanics abstract upper cretaceous paleocene calc alkaline dacitic and rhyodacitic lava flows and domes are exposed in the saraykent yozgat region within central anatolian crystalline complex cacc saraykent volcanics are generally plagioclase hornblende biotite titanomagnetite quartz augite phyric subrounded vesicular magmatic enclaves ranging from a few millimeters to a few centimeters in size are present in the saraykent dacites the enclaves are mainly holocrystalline and have similar mineral assemblage to the host dacites almost all phases in saraykent volcanics exhibit varying degrees of disequilibrium features indicative of magma mingling plagioclase phenocrysts display sieved and normal type populations a wide range in rim compositions and oscillatory zoning maximum core to rim compositional change in sieved rhyodacite plagioclases is up to 24 mol increase in an some plagioclase core compositions are unusually ca rich they range from an27 to an75 for the saraykent dacites and from an30 to an66 for the saraykent rhyodacites hornblende and biotite phenocrysts have reaction rims indicating disequilibrium crystallization with magma both hornblende and biotite crystals show reverse zoning in terms of decreasing mg mg fe quartz phenocrysts are corroded and embayed presence of normally and reversely zoned augites in the same sample and high ti high al augites more comparable with basaltic compositions are other lines of evidence for disequilibrium the enclave hornblendes are both edenitic and pargasitic the latter being more typical of mafic compositions the enclave biotite crystals have higher mg mg fe2 ratios than the host dacite biotite crystals and display normal reverse and oscillatory zoning plagioclase core compositions vary between an44 and an55 in the enclaves although the development of sieve texture in plagioclase and reaction rims on mafic minerals may be attributed to decompression this cannot explain the observed compositional change and normal type of plagioclase in the same sample similarly a cognate i e fractionation origin for the enclaves can be suggested due to their mineralogical similarity to the host dacite however other criteria such as oscillatory zoning and unusually calcic cores of plagioclases heterogeneity of plagioclase rims resorbed and embayed phenocrysts and augite compositions indicating a more mafic magma are enough to support the suggestion that magma mingling was a viable process in the generation of the saraykent volcanics

a model for the ni cu pge ores of the noril sk region and its application to other areas of flood basalt five principal magma types characterize the 3 8 km vertical thickness of flood basalt of the noril9sk region from base to top these are 1 a high tio 2 type with alkalic affiliations ivakinsky and syverminsky suites 2 a tio 2 rich picrite bearing magma gudchichinsky suite 3 a picrite bearing tio 2 poor magma tuklonsky suite 4 a crustally contaminated tio 2 poor magma lower nadezhdinsky suite and 5 a picrite free magma mokulaevsky kharayelakhsky kumginsky and samoyedsky suites similar but not identical in its chemistry to the tuklonsky and separated from the lower nadezhdinsky by transitional suites upper nadezhdinsky and morongovsky the ni cu ores are associated with olivine rich intrusions that are geochemically similar to the mokulaevsky magma they are associated with about 1 15 to 1 10 of their mass in pge rich sulfides this requires that these sulfides equilibrated with 15 to 200 times more magma than is represented by the intrusions themselves following the model of naldrett et al 1992 it is proposed that crustal contamination of the original tuklonsky type magma occurred at the top of a vertically extensive fault controlled magma chamber and caused segregation of immiscible sulfides with a low r factor these depleted this magma in chalcophile elements and settled deeper in the chamber as they settled they reacted with less contaminated magma scavenging additional chalcophile elements they finally came to rest near the base of the chamber to form a zone of sulfide and thus chalcophile element enriched magma eruption and in some instances intrusion of progressively stratigraphically lower less contaminated and thus less depleted layers in the chamber gave rise to the observed sequence of basalts and intrusions the answer to the strong enrichment in ni cu and pge associated with the ore bearing intrusions is that these metals came from the magma that is now represented by the basalt magma with which the sulfides have come into contact and which shows chalcophile element depletion key metallogenic characteristics of the noril9sk region are 1 a hot region in the mantle giving rise to vast amounts of basalt 2 continental scale rifting 3 major faults serving as controls for extrusive and intrusive magmatism 4 crustal contamination of magma 5 chalcophile element depletion of contaminated magma 6 intrusion of magma that has inherited sulfide removed from the depleted magma and 7 the presence of evaporites in the sedimentary sequence underlying the basalts the simplest way to recognize chalcophile element depletion is to plot ni mgo vs mg number at mg mg 0 9fe total a strong indication that basalts have undergone crustal contamination is the correlation of high la sm ratios with high sio 2 contents the lake superior region shows many of the key metallogenetic characteristics of the noril9sk region including continental rifting a triple junction huge thicknesses of basalt and cu ni sulfide bearing intrusions duluth complex crystal lake gabbro some of the keweenawan basalts of the region show ni depletion correlated with chalcophile element depletion the region is an example of the potential application of the noril9sk model to exploration

transport and deposition of ree in h2s rich fluids evidence from accessory mineral assemblages abstract it is shown in four examples from geologically different environments that accessory or minor minerals rich in rare earth elements ree are often texturally associated with base metal sulfides the examples demonstrate that ree can migrate in hydrothermal fluids containing large amounts of reduced sulfur s ii species i e h 2 s hs and s 2 in certain fluids complexes of ree with s ii species may be important for the ree transport but most probably only in the absence of other strong ligands such as fluoride carbonate or possibly phosphate textural relationships and geochemical data suggest that the formation of ree bearing minerals in s ii rich environments is genetically related to the precipitation of basemetal sulfides

the pb rich sulfide veins in the boccassuolo ophiolite implications for the geochemical evolution of hydrothermal activity across the ocean continent transition in the ligurian tethys northern apennine italy abstract galena bearing sulfide veins have been discovered coexisting with fe cu zn dominated veins in the hydrothermal stockwork of the boccassuolo ophiolite external ligurides northern apennine italy the galena rich veins cut across a volcanic pile composed of pillow lava flows pillow breccia and ophiolitic sandstone bulk ore analyses indicate significant enrichment in pb giving raise to mantle normalized pb ag au zn cu patterns with unusual negative slope in contrast with the average flat pattern of most sulfide deposits in the internal liguride ophiolites which reflect the fe cu zn assemblage of ophiolite hosted volcanic associated massive sulfide vms deposits all over the world a wide literature shows that in contrast with the internal ligurides plutonic and volcanic rocks of the external ligurides display less depleted and even enriched geochemical characters not consistent with common oceanic crust at mid oceanic ridges mor but probably originated in the ocean continent transition of the adria continental margin in this geodynamic context pillow basalts become locally enriched in pb with high pb cu ratios and other crustal compatible elements such as mo and u the pb enrichment observed in the veins boccassuolo is interpreted to be a result of leaching of such anomalous volcanics forming the ophiolitic substrate the case of boccassuolo supports the conclusion that the geochemical character of hydrothermal activity evolved from cu zn rich in mor type assemblages of the internal ligurides towards composition enriched in pb in the external liguride domain representing the transition from the ligurian ocean to the adria continental margin

afterslip and viscoelastic relaxation following the 2011 tohoku oki earthquake mw9 0 inferred from inland gps and seafloor gps acoustic data we simultaneously estimate 2 5 years of afterslip and viscoelastic relaxation as well as coseismic slip for the 2011 tohoku oki earthquake displacements at inland gps and seafloor gps acoustic stations are inverted using viscoelastic green s functions for a model with an upper elastic layer and lower viscoelastic substrate the result shows that afterslip is isolated from the rupture area and possibly asperities of historical earthquakes and has almost decayed by 10 september 2013 2 5 years after the main shock the inversion result also suggests that observed landward postseismic displacements at the seafloor gps acoustic stations are caused by the viscoelastic relaxation whereas trenchward displacements at inland stations are mainly an elastic response to afterslip

regional scale hydrothermal alteration in the central blake river group western abitibi subprovince canada implications for vms prospectivity the late archean blake river group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the abitibi greenstone belt it contains a number of silicic volcanic centers of different size including the large noranda volcanic complex which is host to 17 past producing volcanogenic massive sulfide deposits the noranda complex consists of a 7 to 9 km thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism massive sulfide formation coincided with a period of intense magmatic activity cycle iii and the formation of the noranda cauldron hydrothermal alteration in these rocks is interpreted to reflect large scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex the alteration includes abundant albite chlorite epidote and quartz silicification which exhibit broad stratigraphic and structural control and correlate with previously mapped whole rock oxygen isotope zonation the mine sequence volcanic rocks are characterized by abundant iron rich chlorite fe fe mg 0 5 hydrothermal amphibole ferroactinolite and coarse grained epidote of clinozoisite composition 10 wt fe2o3 lacking the clinozoisite solid solution alteration in the mine sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits as far as several tens of kilometers and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale the lack of similar alteration in the pre cauldron sequences is consistent with limited 18o depletion and suggests that the early history of the volcanic complex did not support large scale high temperature fluid flow in these rocks comparisons with a much smaller barren volcanic complex in nearby ben nevis township reveal important differences in the alteration mineralogy between volcanoes of different size with implications for area selection during regional scale mineral exploration the ben nevis complex consists of a 3 to 4 km thick succession of mafic intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion alteration of the volcanic rocks comprises mainly low temperature assemblages of prehnite pumpellyite magnesium rich chlorite fe fe mg 10 wt fe2o3 and calcite actinolite magnetite alteration occurs proximal to the intrusive core of the complex but the limited extent of this alteration indicates only local high temperature fluid circulation adjacent to the intrusion a distal zone of carbonate alteration is located 4 6 km from the center of the volcano although iron bearing carbonates are present locally within this zone the absence of siderite argues against a high temperature origin for this alteration these observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit

geochemistry mineralogy and chemical modeling of the acid crater lake of kawah ijen volcano indonesia the kawah ijen volcano with a record of phreatic eruptions has its 1000 m wide crater filled with a lake that has existed for at least one century at present the lake waters are hot t 37 c strongly mineralized tds 105 g l and extremely acidic ph 0 4 by its volume the javanese lake is probably the largest accumulation in the world of such acidic waters mineralogy of the suspended solids within the lake waters suggests that concentrations of si ca ti and ba are controlled by precipitation of silica gypsum anatase and barite lake sediment is composed of chemical precipitates with composition similar to the suspended solids thermodynamic calculations predict that the lake waters have reached equilibrium with respect to cristobalite barite gypsum anglesite celestite and amorphous silica in agreement with the analytical observations significant concentrations of ferric iron suggest that the current lake waters are fairly oxidized sulfides are absent in the water column but are always present in the native s spherules that form porous aggregates which float on the lake the presence of native s provides direct evidence of more reduced conditions at the lake floor where h 2 s is probably being injected into the lake with progressive addition of h 2 s to the acid waters native s pyrite and enargite are theoretically predicted to be saturated reactions between upward streaming h 2 s bearing gases discharged by subaqueous fumaroles and metals dissolved in the acidic waters could initiate precipitation of these sulfides a model of direct absorption of hot magmatic gases into cool water accounts for the extreme acidity of the crater lake results show that strongly acidic sulfate rich solutions are formed under oxidizing conditions at high gas water ratios reactions between the acidic fluids and the ijen andesite were modeled to account for elevated cation concentrations in lake water current concentrations of conservative rockforming elements are produced by dissolution of approximately 60 g of andesite per kg of acid solution complete neutralization of the acid lake waters by reaction with the wallrock produces a theoretical alteration assemblage equivalent to that observed in volcano hosted acid sulfate epithermal ore deposits

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

comment on the papers by large salt accumulations as a consequence of hydrothermal processes associated with wilson cycles a review part 1 and 2 abstract the geological model of large hydrothermal salt accumulations linked to wilson cycles as reviewed by hovland and coworkers un adequately addressed 1 the lack of well exposed submarine volcanogenic hydrothermal feeder zone 2 the sequential precipitation of different hydrothermal evaporite minerals and 3 the absence of hydrothermal alteration mineralogy around the major evaporites these aforementioned points are the main classical features to be linked to the hydrothermal model of evaporites experimentally heating seawater during submarine volcanism firstly results in precipitation of anhydrite followed by halite other evaporite minerals serpentine brucite talc metallic sulfides oxides and related hydrothermal alterations in this regard mg ca cl mg ca so4 mg ca na cl and mg ca tds biplots show that hydrothermal brines of riftogenic and subduction zone settings plot in a separate field than the subduction related andean salars as well as seawater this indicates that the hydrothermal serpentinization of basaltic oceanic crust and mantle peridotites removes magnesium from seawater and incorporates the mg into serpentine brucite and other hydrous mg silicates rather than the hydrothermal brines finally our comment arose from a recent global classification of the most distinguished marine non marine and exhalative hydrothermal evaporites

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

chemistry of seafloor hydrothermal systems the past four years saw advances in a number of aspects of hydrothermal chemistry high temperature venting was documented at a number of sites in association with the spectrum of seafloor volcanic activity slow to fast spreading normal ridges seamounts back arc settings sediment hosted and sediment starved sites significant progress was made in the description both theoretical and observational of the geometry of circulation and the nature of water rock reaction hydrothermal plumes received extensive study expanding the range of documented anomalies and demonstrating more clearly the links to hydrothermal sedimentation biological chemical interactions began to be explored in a quantitative way pore fluid advection on sedimented ridge flanks was characterized at a number of sites though the general question of the importance of off axis basalt seawater interaction remains unresolved

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

fluid interaction and geochemical mobility in metabasalts an example from the central appalachians deformation of metabasalts in the central appalachians has produced contrasting zones of fabric development within individual flows more schistose zones reflect metamorphic textures and mineralogies while more massive zones still retain igneous textures and locally relict igneous clinopyroxene samples from a single flow show chemical variations that appear to be a function of fabric development composition volume relationships indicate that more massive zones were least affected by greenschist facies metamorphism and their geochemical signatures are therefore closest to that of the original magmas more schistose zones may have acted as conduits for metamorphic fluids most likely nacl rich brines which transported components into and out of the system these more schistose zones therefore may have lost or gained material during metamorphism cation exchange reactions and silica solubility are used to measure reaction progress and to estimate fluid rock ratios in different zones within a flow the

fluids during diagenesis and sulfate vein formation in sediments at gale crater mars we model the fluids involved in the alteration processes recorded in the sheepbed member mudstones of yellowknife bay ykb gale crater mars as revealed by the mars science laboratory curiosity rover investigations we compare the gale crater waters with fluids modeled for shergottites nakhlites and the ancient meteorite alh 84001 as well as rocks analyzed by the mars exploration rovers and with terrestrial ground and surface waters the aqueous solution present during sediment alteration associated with phyllosilicate formation at gale was high in na k and si had low mg fe and al concentrations relative to terrestrial groundwaters such as the deccan traps and other modeled mars fluids and had near neutral to alkaline ph ca and s species were present in the 10 3 to 10 2 concentration range a fluid local to gale crater strata produced the alteration products observed by curiosity and subsequent evaporation of this groundwater type fluid formed impure sulfate and silica rich deposits veins or horizons in a second separate stage of alteration partial dissolution of this sulfate rich layer in yellowknife bay or beyond led to the pure sulfate veins observed in ykb this scenario is analogous to similar processes identified at a terrestrial site in triassic sediments with gypsum veins of the mercia mudstone group in watchet bay uk

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting

bending stress and dissipation in subducted lithosphere 1 oceanic lithosphere undergoes permanent deformation during subduction once the stresses exceed the elastic limit departures from elastic behavior occur by brittle failure in the shallow lithosphere and by a combination of low and high temperature creep at greater depths we combine laboratory based rheological models with estimates of slab shape from earthquake hypocenters to quantify the bending stress and dissipation in subduction zones the peak stress occurs at the depth of the brittle ductile transition which is controlled mainly by lithospheric age integrals of the stress over the thickness of the plate are used to evaluate the resistive bending force and the bending moment a representative value for the resistive force on old oceanic lithosphere is 3 1012 n m 1 which is comparable in magnitude to ridge push but opposite in direction both the bending force and moment are remarkably insensitive to the rate of subduction in fact the bending moment can be approximated using a simple power law rheology and a stress exponent of n 14 such a large exponent implies that the lithosphere behaves like a perfectly plastic solid for most subduction zones the bending moment saturates along the entire plate as a consequence the bending stress does not influence the development of curvature during subduction this behavior may explain why the curvature of subducted lithosphere is nearly independent of age