constraints on temperature pressure conditions and fluid composition during metamorphism of the sullivan orebody kimberley british columbia from silicate carbonate equilibria the sullivan mine in southeastern british columbia is one of the world s largest sediment hosted massive sulphide deposits it has undergone at least one period of metamorphism since it was depo

brittle normal faulting in the highest grade sambagawa metamorphic rocks of central shikoku southwest japan indication of the exhumation into the upper crustal level abstract analysis of fault system in the high p t type sambagawa metamorphic rocks of central shikoku southwest japan shows that conjugate normal faults pervasively developed in the highest grade biotite zone upper structural level in three study areas asemi river oriu and niihama areas these conjugate normal faults consist of ne sw to e w striking and moderately north dipping set a and nnw sse striking and moderately east dipping set b faults the fault set a is dominant compared to the fault set b and hence most of deformation is accommodated by the fault set a leading to non coaxial deformation the sense of shear is inferred to be a top to the wnw to nnw based on the orientations of striation or quartz slickenfibre and dominant north side down normal displacement these transport direction by normal faulting is significantly different from that at d1 penetrative ductile flow i e top to the w to wnw it has also been found that these conjugate normal faults are openly folded during the d3 phase about the axes trending nw se to e w and plunging west at low angles or horizontally indicating that normal faulting occurred at the d2 phase d2 normal faults along which actinolite breccia derived from serpentinite by metasomatism sometimes occurs perhaps formed under subgreenschist conditions ca 250 c in relation to the final exhumation of sambagawa metamorphic rocks into the upper crustal level the pervasive development of d2 normal faults in the upper structural level suggests that the final exhumation of sambagawa metamorphic rocks could be caused by distributed extension and normal faulting removal of overburden in the upper crust

prograde and retrograde metamorphism of hematitebearing basic schists in the sanbagawa belt in central shikoku the mineral assemblages of hematite bearing basic schists in intermediate high pressure metamorphism are temperature dependent for assemblages with excess hematite albite muscovite and quartz the paragenetic relations can be dealt with in terms of a four component system without omitting or grouping major components in the sanbagawa belt in central shikoku the dominant amphibole in the hematite bearing basic schists changes from winchite via crossite and barroisite to hornblende the stability of amphibole is described chemographically within a pseudoternary system with another excess phase epidote many amphiboles are chemically heterogeneous owing to retrograde reactions which produced low t p amphibole around the prograde amphibole the examination of amphibole zoning makes it possible to draw a retrograde p t trajectory which passes on the lower pressure side of the prograde one

geochemical and sedimentological considerations of a permanently anoxic fjord framvaren south norway abstract framvaren a fjord in south norway is an example of extreme anoxia due to the geomorphological features sill depth 2 m basin depth 180 m the postglacial history of framvaren is outlined emphasizing the preservation of environmental changes in the properties of the water and the sediments high levels of hydrogen sulfide in the water 170 180 ml l 1 or 7 8 mm h 2 s dense populations of photosynthetic bacteria at the redox boundary total number 3 10 6 ml 1 metal sulfide formation in the anoxic water e g framboidal pyrite and zinc sulfide and organic rich bottom sediments with high metal content e g 1000 ppm zn are typical examples the rate of sedimentation is estimated in three independent ways suggesting an average annual flux of 100 g m 2 yr 1 in the central basin of framvaren fluxes of organic matter and zinc to the sediments are calculated and compared with potential sources

tectonic evolution of low grade metamorphosed rocks of the cretaceous shimanto accretionary complex central japan abstract we reconstructed the tectono metamorphic evolution of the low grade metamorphosed cretaceous shimanto accretionary complex in the kanto mountains central japan based on radiolarian fossils metamorphic temperatures derived from illite crystallinity analysis and timing of metamorphism based on illite k ar dating the accretionary age of the kobotoke group is turonian to maastrichtian 66 94 ma based on radiolarian fossils illite crystallinity data indicate metamorphic temperatures of approximately 300 c the illite k ar ages constrain the timing of metamorphism to the middle eocene around 40 ma combining our results and previous study we defined two types of low grade metamorphism within cretaceous shimanto accretionary complex of the kanto mountains the early metamorphism in excess of 300 c was related to the uplift of the sambagawa metamorphic rocks in turn associated with the subduction of the kula pacific ridge during the late cretaceous 65 75 ma this metamorphism is recorded in the otaki group within the northernmost part of the complex in the kanto mountains subsequent to the subduction of the kula pacific ridge a later period of metamorphism recorded in the kobotoke group is characterized by the thermal effects of the subduction of the young hot pacific plate during the middle eocene the effect of the early metamorphism occurred synchronously 500 km along the trench from southwest to central japan the later metamorphism occurred at 50 ma in kyushu and shikoku of southwest japan and at 40 ma in the kanto mountains of central japan this difference in the timing of metamorphism between southwest and central japan is explained by the northward migration of the young hot pacific plate

sulfur isotope and trace element data from ore sulfides in the noranda district abitibi canada implications for volcanogenic massive sulfide deposit genesis we examine models for volcanogenic massive sulfide vms mineralization in the 2 7 ga noranda camp abitibi subprovince superior province canada using a combination of multiple sulfur isotope and trace element data from ore sulfide minerals the noranda camp is a well preserved vms deposit rich area that is thought to represent a collapsed volcanic caldera due to its economic value the camp has been studied extensively providing a robust geological framework within which to assess the new data presented in this study we explore previously proposed controls on mineralization within the noranda camp and in particular the exceptional au rich horne and quemont deposits we present multiple sulfur isotope and trace element compositional data for sulfide separates representing 25 different vms deposits and showings within the noranda camp multiple sulfur isotope data for this study have 34sv cdt values of between 1 9 and 2 5 and 33sv cdt values of between 0 59 and 0 03 we interpret the negative 33s values to be due to a contribution of sulfur that originated as seawater sulfate to form the ore sulfides of the noranda camp vms deposits the contribution of seawater sulfate increased with the collapse and subsequent evolution of the noranda caldera an inference supported by select trace and major element analyses in particular higher concentrations of se occur in samples with 33s values closer to 0 as well as lower fe zn ratios in sphalerite suggesting lower pressures and temperatures of formation we also report a relationship between average au grade and 33s values within au rich vms deposits of the noranda camp whereby higher gold grades are associated with near zero 33s values from this we infer a dominance of igneous sulfur in the gold rich deposits either leached from the volcanic pile and or directly degassed from an associated intrusion

implications of mylonitic microstructures for the geotectonic evolution of the median tectonic line central japan the median tectonic line mtl the most prominent onshore fault in japan demarcates the cretaceous hiji quartz dioritic gneiss of the ryoke belt on the west from the high p t type sambagawa metamorphic rocks on the east in the takato area toward the mtl the hiji gneiss grades into strongly mylonitized rocks characterized by grain size reduction of quartz in the mylonitic rocks the development of fluxion banding sm is remarkably influenced by the existence of k feldspar forming a myrmekitic intergrowth brittle microstructures indicative of truly cataclastic deformation are observed only in mylonitic rocks close to the mtl early deep level ductile deformation apparently gave way to shallower brittle deformation at a later stage the attitude of stretching lineations lm and asymmetric microstructures observed in the mylonites suggest that sinistral strike slip shearing with a subordinate component of vertical slip took place during mylonitization in mid cretaceous time the mylonitic rocks and their protolith supposed to have constituted the eastern limb of the shear zone were probably eroded out and lost by upheaval of the sambagawa belt relative to the ryoke belt

erratum superimposed low grade metamorphism in the mount fisher area southeastern british columbia implications for the east kootenay orogeny middle proterozoic 1500 1350 ma belt purcell strata exposed in the purcell and southwestern rocky mountains were affected by at least three distinct episodes of deformation and regional metamorphism the oldest episode 1300 1350 ma apparently terminated belt purcell sedimentation and involved foiding regional metamorphism and granitic intrusion the second episode 800 900 ma occurred during deposition of the windermere supergroup and involved uplift block faulting and low grade regional metamorphism mesozoic cenozoic metamorphism deformation and plutonism overprinted the results of the earlier deformation and metamorphism illite crystallinity and muscovite polymorph ratios indicate that purcell strata in the mount fisher area are in the lower greenschist to prehnite pumpellyite facies of regional metamorphism in the steeples and fisher blocks this metamorphism is related to structures that formed during the late cretaceous paleocene deformation however in the sand creek block the regional metamorphism is related to the development of a spaced cleavage that is folded by a late cretaceous pdeocene nappe regional considerations suggest that this cleavage formed during the 1300 1350 ma episode of deformation and metamorphism the east kootenay orogeny as currently defined embraces the two older episodes of tectonism it is proposed that the term east kootenay orogeny be restricted to designate the 1300 1350 ma episode and that the term goat river orogeny designate the 800 900 ma episode of tectonism the east kootenay and goat rivet orogenies appearto be correlative with the racklan and hayhook orogenies recognized in the northern canadian cordillera

the origin of strain patterns resulting from contemporaneous deformation and metamorphism in the sambagawa metamorphic belt the magnitudes of plastic strains of 104 metacherts were determined from the deformed shape of initially spherical radiolarians in the sambagawa high p type metamorphic belt of western shikoku japan the strain magnitude increases with increasing metamorphic temperature from several per cent to 250 the a2 a3 ratio of strain ellipsoids in the higher metamorphic grades decreases with increasing metamorphic grade while the a1 a2 ratio increases rapidly the long axis of the strain ellipsoid for every grade is nearly parallel to the length of the metamorphic belt suggesting that the flow direction of the synmetamorphic deformation was uniform along the belt a map of strain zones within the sambagawa high p type metamorphic belt reveals that the metamorphic belt underwent a progressive bulk inhomogeneous shear deformation and that the high grade zones represent a deep seated boundary shear zone on the accretionary wedge between a subducting oceanic plate and the immobile rigid continental plate

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

double saloon door tectonics in the japan sea fossa magna and the japanese island arc abstract a number of criteria considered diagnostic of double saloon door rifting and seafloor spreading are matched by data from the japanese arc these include i a pair of terranes sw and ne honshu which rotated in opposite directions from 22 21 ma to 14 11 ma ii rotated terranes which comprise a retro arc fold thrust belt attached to an accretionary wedge intruded by a magmatic arc iii contemporaneous backarc extension from 24 to 21 ma which is brought to a halt by progressive collision of the izu bonin and japan arcs from 15 to 5 ma iv isolation of blocks of thicker continental crust by areas of thin continental or oceanic crust during backarc rifting v such isolation may be due to simultaneous rifting or to progressively seaward rifts associated with ridge jumps towards the subduction zone vi opposite rotations are accommodated by subduction rollback demonstrated by seaward migration of the volcanic front from 30 26 ma to 16 15 ma vii concurrent development of a major arc orthogonal rift the fossa magna from 23 18 ma to 14 ma which was thereafter inverted from 15 ma to the recent viii a northeast propagating rift in the northern japan basin demonstrated by the relationship of linear magnetic anomalies to the mapped continent ocean boundary driving mechanisms for double saloon door tectonics are discussed in relation to various reconstructions of the northwest pacific opposite rotational torques leading to opposite terrane rotations may be caused by rollback of a curved trench hingeline or by the divergent slab sinking forces of the pacific and philippine sea plates

pressure temperature trajectory of the sanbagawa metamorphism deduced from garnet zoning abstract most garnets in a small volume of the pelitic sanbagawa schists nucleated simultaneously grew and then ceased with their growth maintaining near equilibrium with coexisting minerals such as chlorite and biotite during the prograde metamorphism chemical trends of zoned garnets systematically shift from the pyrope poor to pyrope rich portions in a ternary mn fe mg system in order of ascending metamorphic grade a ternary mn fe mg model system suggests that the higher grade garnets started to grow at lower pressures and higher temperatures than the lower grade ones during prograde metamorphism it follows that high grade metamorphism took place at lower pressures in the garnet to oligoclase biotite zones of the sanbagawa metamorphic terrain in central shikoku

exhumation of the sanbagawa blueschist belt sw japan by lateral flow and extrusion evidence from structural kinematics and retrograde p t t paths

structural evolution of the sullivan fe pb zn ag orebody kimberley british columbia canada spectacular and complex fold structures three phases of folding late normal faults cut through all the earlier structures during tectonic deformation the sulfides are likely to have been extremely ductile modified journal abstract

why sedimentologists are interested in fjords abstract fjords offer a unique environmental setting to study geochemical and sedimentological processes and the interaction between these processes and biological systems they can be described generally as enclosed mini oceans where the rate of processes is fast and associated environmental gradients are large most fjords are easily accessible and the resources necessary to study them are relatively modest compared to those required for sedimentological work in the open ocean fjords differ significantly with respect to sediment input transport and depositional environment those situated in glaciated areas receive sediment laden meltwater that promotes high deposition rates that are often evident as deltaic deposits in these instances the bottom sediments are characteristically inorganic and show large variations in grain size in contrast fjords with low sediment input high organic production and insufficient deep water renewal may be anoxic either seasonally or permanently these highly organic environments tend to accumulate sedimentary facies that are especially applicable to geochemical process studies or to high resolution paleoclimatic investigations that are dependent on minimal post depositional sediment mixing e g bioturbation

the transfiguration continental red bed cu pb zn ag deposit quebec appalachians canada the transfiguration cu pb zn ag deposit enclosed within reduced grey sandstone is associated with continental red beds of the lower silurian robitaille formation in the quebec appalachians canada the robitaille formation rests unconformably on foliated cambro ordovician rocks the unconformity is locally cut by barite veins the basal unit of the robitaille formation comprises green wacke and pebble conglomerate which locally contain calcite nodules the latter have microstructures characteristic of alpha type calcretes such as floating fabrics calcite filled fractures crystallaria and circumgranular cracks massive grey sandstone overlies the basal green wacke and pebble conglomerate unit which is overlain in turn by red fine grained sandstone mineralisation occurred underneath the red sandstone unit chiefly in the grey sandstone unit as disseminated and veinlet sulphides chalcopyrite the most abundant cu sulphide replaced early pyrite calcrete disseminated carbonate and vein carbonate have stable isotope ratios varying from 7 5 to 1 1 13c and from 14 7 to 21 3 18o the negative 13c values indicate the oxidation of organic matter in a continental environment sulphur isotope ratios for pyrite chalcopyrite and galena vary from 19 to 25 34s as measured on mineral concentrates by a conventional so2 technique laser assisted microanalyses by fluorination of s isotopes in pyrite show an analogous range in 34s values from 21 to 25 negative and positive 34s values are compatible with bacterial sulphate reduction bsr in systems open and closed with respect to sulphate we interpret similarly high 34s values for sulphide concentrates 25 1 and for vein barite 26 2 to result from rapid and complete thermochemical reduction of pore water sulphate two early to late diagenetic stages of mineralisation best explain the origin of the transfiguration deposit the first stage was characterised by the ponding of groundwater over the taconian unconformity recorded by calcrete and early pyrite formation via bsr in grey sandstone early pyrite contains up to 2 wt pb which is consistent with pb fixation by sulphate reducing bacteria the second stage ii is defined by the replacement of early pyrite by chalcopyrite as well as by sulphide precipitation via either bsr or thermochemical sulphate reduction tsr in grey sandstone this event resulted from the synsedimentary fault controlled percolation and mixing of 1 an oxidising sulphate bearing cupriferous fluid migrating per descensum from the red bed sequence and 2 a hydrocarbon bearing fluid migrating per ascensum from the cambro ordovician basement mixing between the two fluids led to sulphate reduction causing cu sulphide precipitation the positive correlation between cu and fe3 fe2 bulk rock values suggests that fe acted as a redox agent during sulphate reduction stage ii diagenetic fluid migration is tentatively attributed to the late silurian salinic extensional event

40ar 39ar mineral ages within metamorphic clasts from the kuma group eocene central shikoku japan implications for tectonic development of the sambagawa accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku records a high p t metamorphism it is comprised by the oboke nappe and the structurally overlying internally imbricated besshi nappe complex the besshi nappe complex locally is unconformably overlain by the kuma group eocene which consists of conglomerates and subordinate sandstones and mudstones clasts within kuma conglomerates exposed in the kamegamori district include low grade schists derived from the unconformably underlying sambagawa complex and high grade metamorphic rocks of uncertain provenance including garnet amphibolite and oligoclase bearing pelitic schist 36 ar 40 ar vs 39 ar 40 ar isotope correlation ages recorded by hornblende from two amphibolite clasts are 131 1 4 9 ma and 156 8 4 3 ma these are interpreted to date post metamorphic cooling through temperatures required for intracrystalline retention of argon and are older than cooling ages previously reported from any presently exposed segments of the sambagawa terrane plateau ages of 108 8 0 7 ma and 115 7 0 6 ma are recorded by muscovite from two clasts of schist muscovite within a proximal basement exposure of unconformably underlying sambagawa pelitic schist records a plateau age of 78 7 0 5 ma combined with isotopic ages previously reported for the sambagawa terrane 40 ar 39 ar data from clasts in the kuma group suggest that metamorphic culmination within a high grade source terrane occured at c 185 145 ma sectors of this complex cooled through c 500 c at c 150 ma other portions cooled through c 500 c at c 130 ma contrasts in the cooling ages likely reflect internal imbrication within the source terrane the besshi nappe complex reached peak metamorphic conditions at c 100 90 ma and experienced relatively rapid uplift and cooling at c 85 75 ma the besshi nappe complex was structurally emplaced onto the oboke nappe which attained peak metamorphic conditions at c 75 ma subsequently the entire sambagawa section was exhumed and most high grade metamorphic rocks were removed the eocene kuma group was unconformably deposited over the sambagawa terrane at c 50 ma

genesis of the paleoproterozoic nico iron oxide cobalt gold bismuth deposit northwest territories canada evidence from isotope geochemistry and fluid inclusions abstract the nico deposit is located in the southern portion of the paleoproterozoic great bear magmatic zone northwest territories canada the majority of the mineralization lies within the bowl zone hosted by the treasure lake group tlg where heavily altered precursor rocks are interpreted to be carbonate rich wackes and siltstones these rocks are crosscut by a set of pre ore quartz calcite amphibole k feldspar veins s1 the co au bi w cu mo mineralization at nico is contained in stratabound ore lenses within the bowl zone and comprises a prograde assemblage of co rich arsenopyrite arsenopyrite i and loellingite cobaltite pyrite actinolite ferrohornblende biotite and rare scheelite molybdenite along with minor magnetite and amphibole retrograde assemblages resulted from re crystallization of the co bearing phases to form arsenopyrite ii and iii along with precipitation of marcasite pyrite hastingsite native bi au te and minor bismuthinite and magnetite the latest stage of retrograde mineralization comprises chalcopyrite hastingsite chlorite and hematite emplectite two sets of barren quartz dolomite amphibole k feldspar chalcopyrite veins s2 and s3 post date the mineralization the southern breccia zone hosts minor u cu mo mineralization and is interpreted to be the deepest portion of the nico system two molybdenite samples from the bowl zone and the southern breccia yielded re os ages of 1865 9 and 1877 8 ma respectively consistent with the interpreted ca 1870 ma age of the nico deposit this age is also synchronous with the onset of magmatism in the great bear magmatic arc ca 1875 1850 ma ore mineral 34s values 3 3 6 7 sulfides indicate that crustal sulfur was assimilated by upwelling felsic magmatic melts the 18o values of the fluids precipitating magnetite and co rich arsenopyrite 6 and 8 and from pre and syn mineralization magnetite 0 8 to 1 5 support a magmatic hydrothermal origin of the fluids two out of three calcite samples from pre s1 and post ore s3 veins have also 13c values consistent with a magmatic origin 5 5 to 3 6 however one calcite sample from the s3 veins has a value that indicates a reduced sulfur source 15 6 this value is similar to those of the much younger secondary trails of native bi in s1 vein quartz are associated with liquid vapor lv and liquid vapor halite lvs inclusions which indicates that bi and possibly au were transported in saline to hyper saline brines lv bi 2 16 wt nacl equiv 8 22 wt cacl2 equiv lvs bi 37 wt nacl equiv with homogenization temperatures of 137 216 c and 192 to 350 c for lv bi thl v l and lvs bi thl s l respectively the presence of calcium rich fluids might indicate extensive equilibration of those solutions with the host tlg rocks if a pressure correction is applied to the lv inclusions using a minimum entrapment temperature of 271 4 c the bi melting point a minimum crystallization depth of between approximately 5 and 8 km is indicated trace element analyses carried out in this study and compiled from acosta gongora et al 2014 show that the least altered metasedimentary tlg rocks contain up to six times more as carbonate unit 30 5 ppm than the average upper continental crust conversely concentrations of au

nappe structure of the sambagawa belt the thermal structure of the sambagawa belt which is reflected by minerals produced during the highest temperature of metamorphism generally is characterized by the occurrence of the highest grade schists in the middle of the structural pile the origin of this structure has been analysed in the upper horizon of the sambagawa schist sequence in central shikoku as an example for the structure of the whole belt the upper horizon of the sambagawa schist sequence in central shikoku consists of three nappes the saruta nappe ii the saruta nappe i and the fuyunose nappe in descending order of structural level the saruta nappe ii shows a downward increase of metamorphic grade from the garnet zone through the albite biotite zone to the oligoclase biotite zone the saruta nappe i consists mainly of rocks in the albite biotite zone and partly in the oligoclase biotite zone but the direction of the increase of metamorphic grade is not clear the fuyunose nappe shows an upward increase in metamorphic grade which changes from the glaucophane zone to the barroisite zone it is concluded that the saruta nappe ii and saruta nappe i were overturned and then mechanically coupled with the fuyunose nappe the sambagawa metamorphic field which is of the highest temperature phase of metamorphism appears to have had an inverted thermal gradient and a thermal structure comparable with that expected in the deeper parts of a subduction complex

sulfur isotope variability in sediment hosted massive sulfide deposits as determined using the ion microprobe shrimp i an example from the rammelsberg orebody discussion

reactivation of an old plate interface as a strike slip fault in a slip partitioned system median tectonic line sw japan abstract in models for strain partitioning at obliquely convergent plate boundaries trench parallel slip occurs on a vertical fault trench parallel slip at the nankai subduction zone sw japan is mapped along the median tectonic line mtl which dips approximately 40 n to understand its structural context and how the mtl functions in this slip partitioned system we collected a set of three seismic profiles in the kii peninsula south of osaka using a multi scale acquisition strategy that provides increasingly fine resolution to understand its fault kinematics we analyzed microseismic activity in two locations on the fault using source data from japan s hi net monitoring network structural details suggest that the mtl functioned as a megathrust during subduction of the cretaceous sanbagawa hp metamorphic belt its current pattern of microseismicity shows that it behaves as a strike slip fault with no indication of a vertical fault at or around its surface trace thus trench parallel slip at the nankai is now accommodated on an inclined fault plane in an unusual form of partitioning this system appears to have developed out of a two phase tectonic history in which a thrust structure that formed under initial phase compressive stresses has been reactivated as a strike slip fault under subsequent phase shear stresses its unusual kinematics show that shear failure can occur on an existing non vertical fault plane at a regional scale in preference to the rupture of a new ideal vertical fault plane

genesis of the wolverine volcanic sediment hosted massive sulfide deposit finlayson lake district yukon canada mineralogical mineral chemical fluid inclusion and sulfur isotope evidence the wolverine deposit is a high grade 6 2 mt at 12 7 zn 1 3 cu 1 6 pb 370 9 g t ag and 1 8 g t au volcanic and sedimentary rock hosted massive sulfide deposit in the finlayson lake area yukon territory the area has the potential to become an important mining camp and currently contains more than 30 million tons mt of massive sulfide ore in five deposits a succession of metamorphosed early mississippian felsic volcanic and sedimentary rocks that are interpreted to have formed on the margin of an ensialic back arc ocean basin between the yukon tanana terrane and the ancestral north american craton hosts the wolverine deposit the massive sulfide ore occurs at a single horizon that marks a significant change in the character of the volcanism from quartz and feldspar phyric rhyolite of the footwall to aphyric rhyolite and chemical sedimentary exhalative rock of the hanging wall the deposit consists of two discrete zn pb ag massive sulfide lenses situated at the same stratigraphic level connected by strata bound semimassive replacement style zn pb ag mineralization copper rich massive sulfide commonly replaces the zn pb ag massive sulfide at the base of the lenses and in the footwall replacement zones beneath the massive mineralization several zones of sulfide stringer veins and chlorite sericite carbonate alteration occur within permeable footwall volcaniclastic rocks alteration minerals preferentially associated with massive sulfide mineralization include ba rich phengitic mica biotite mg rich chlorite and siderite microthermometric measurements of fluid inclusions in the massive sulfide bodies and accompanying stringer zones indicate formation at temperatures of 235 to 353 c primary aqueous liquid rich fluid inclusions in hydrothermal quartz from quartz sulfide stringer veins contain low salinity fluids 2 1 8 5 wt nacl equiv mean 6 0 there is no evidence of fluid boiling in the inclusions and based on the average fluid salinity and temperature of homogenization mineralization took place under a minimum water depth of 1 000 m in situ analyses of 34sv cdt in sulfide minerals from massive sulfide lenses means 0 8 and sulfide stringer veins mean 12 0 display a bimodal distribution lower 34s values characterize sulfides near the top of the lenses versus higher more positive values in underlying veins may reflect different processes of reduction of seawater sulfate sulfur in sulfides from the tops of the lenses was likely derived mainly from bacterial reduction of seawater sulfate whereas sulfur in the stringer veins and at the base of the lenses was mainly from inorganic reduction of seawater sulfate sulfide minerals precipitated both on the sea floor and in the subsea floor from hydrothermal fluids that vented from multiple mounds the presence of black shales and the strongly positive sulfur isotope compositions of the sulfides provide evidence that the ambient bottom water in the basin in which the wolverine deposit formed was likely anoxic this environment may have contributed to the preservation of the sulfide mounds based on its tectonic setting host rock types local geologic setting metal grades age and source s of sulfur the wolverine deposit best exemplifies the volcanic sediment hosted massive sulfide vshms class of syngenetic massive sulfide deposits in the district

origin of tin mineralization in the sullivan pb zn ag deposit british columbia constraints from textures geochemistry and la icp ms u pb geochronology of cassiterite

shock temperature in calcite caco3 at 95 160 gpa the temperatures induced in crystalline calcite caco 3 upon planar shock compression 95 160 gpa are reported from two stage light gas gun experiments temperatures of 3300 5400 k are obtained by fitting six channel optical pyrometer radiances in the 450 900 nm range to the planck gray body radiation law thermodynamic calculations demonstrate that these temperatures are some 400 1350 k lower than expected for vibronic excitations of the lattice with a 3r mole atom specific heat r is gas constant the temperature deficit along the hugoniot is larger than that expected from only melting in addition to melting it appears likely that shock induced decomposition of calcite occurs behind the shock front we modeled disproportionation of calcite into cao solid plus co 2 gas for temperature calculations specific heat at constant volume for 1 mole of co 2 is taken to be 6 7r as compared to 9r in the solid state whereas a mole of calcite and a mole of cao have their solid state values 15r and 6r respectively calculations suggest that the calcite decomposes to cao and co 2 at 110 10 gpa along the hugoniot recent reanalysis of earlier visar measurements of particle velocity profiles 1 indicates that calcite shocked to 18 gpa undergoes disproportionation at much lower pressures upon isentropic expansion

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

southward extrusion of eclogite bearing mafic ultramafic bodies in the sanbagawa belt central shikoku japan abstract several mafic rock masses which have experienced eclogite facies metamorphism are distributed in flat lying non eclogitic schists in an intermediate structural level thermal core of the sanbagawa belt the largest iratsu mass and an associated peridotite the higashi akaishi mass extend e w for about 8 km and n s for about 3 km and are surrounded by pelitic basic and quartz schists the iratsu mass consists of metabasites of gabbroic and basaltic origin with intercalations of ultramafic rocks felsic gneiss quartz schist and metacarbonate the iratsu mass can be divided into two layers along a wnw trending metacarbonate layer the higashi akaishi mass consists of peridotite with intercalations of garnet clinopyroxenite it is situated beneath the western half of the iratsu mass and their mutual boundary dips gently or steeply to the n or ne these masses underwent eclogite and subsequent epidote amphibolite facies metamorphism as has been reported elsewhere the iratsu higashi akaishi masses and the surrounding rocks underwent ductile deformation under epidote amphibolite facies or lower p t metamorphic conditions their foliation generally trends wnw and dips moderately to the nne and the mineral lineation mostly plunges to the n and ne in non eclogitic schists surrounding the iratsu higashi akaishi masses the foliation generally trends wnw and dips gently or steeply to the n or s and the mineral lineation mostly plunges to the nw n and ne kinematic analysis of deformation structures in outcrops and oriented samples has been performed to determine shear senses consistent top to the north normal fault displacements are observed in peridotite layers of the higashi akaishi mass and eclogite bearing epidote amphibolite layers of the iratsu mass top to the northeast or top to the northwest displacements also occur in non eclogitic pelitic quartz schists on the northern side of the iratsu mass in the structural bottom of the iratsu higashi akaishi masses and to the south reverse fault top to the south movements are recognized in serpentinized peridotite and non eclogitic schists these observations provide the following constraints on the kinematics of the rock masses 1 northward normal displacement of iratsu relative to higashi akaishi 2 northward normal displacement of non eclogitic schists on the north of the iratsu mass and 3 southward thrusting of the iratsu higashi akaishi masses upon non eclogitic schists in the south the exhumation process of the iratsu higashi akaishi masses can be explained by their southward extrusion

structural and microstructural constraints on the mechanism of eclogite formation in the sambagawa belt sw japan abstract eclogites in the seba basic schist of the sambagawa belt show contrasting textures in one type of eclogite coarse grained omphacite is randomly oriented and cross cuts the schistosity suggesting post tectonic growth in contrast in the second type fine grained omphacite is preferentially aligned parallel to the schistosity suggesting pre to syn tectonic growth the former type of eclogite has been regarded as a product of solid state contact metamorphism after the formation of the schistosity while the latter type has been related to the sambagawa regional metamorphism the idea that eclogite can form by contact metamorphism is unconventional and if true could have major implications for the interpretation of eclogitic rocks in general in the seba basic schist it has generally been assumed that the dominant schistosity formed during a single phase of deformation however field and microstructural studies show i there are two different schistosities one formed before and the other during eclogite formation and ii the differences in eclogite texture reflect the strength of deformation during the second stage therefore the various textural types of eclogite in the seba basic schist all formed during a single phase of regional metamorphism and there is no need to invoke contact metamorphism

biogenic and thermogenic sulfate reduction in the sullivan pb zn ag deposit british columbia canada evidence from micro isotopic analysis of carbonate and sulfide in bedded ores abstract the layered clastic hosted sedex type proterozoic ca 1475 ma sullivan pb zn ag deposit was metamorphosed by several episodes of metamorphic recrystallization that have extensively modified or erased primary grain to grain textural relationships yet genetically significant variations of sulfur and carbon isotope ratios have been preserved at the millimeter and greater scale whereas sulfur isotope fractionations on a grain to grain scale cannot distinguish between likely formation temperatures and post peak metamorphic cooling the preserved fine scale and deposit scale stratigraphic variations of 34 s and 13 c bear on the origin and formational history of this deposit high spatial resolution documentation of accurate grain to grain and stratigraphic sulfur isotope variations in selected portions of bedded ore from the sullivan deposit was made possible by use of a cold stage during in situ laser assisted isotopic analysis pyrrhotite formed from biogenic sulfate reduction in the water column can be distinguished from sulfides e g sphalerite with higher 34 s values that formed in response to hydrothermal fluids in a brine pool isotopic analysis of carbonates in the presence of abundant sulfides was facilitated by development of a gas chromatographic carbonate extraction system with a high efficiency cryogenic trap calcite present in interlayered massive sulfide and siliciclastic layers in the bedded ore zone in trace amounts to a few weight percent records a carbon isotopic stratigraphy that suggests variable thermogenic sulfate reduction stratigraphic curves illustrating the variation in carbon and sulfur isotopes from the base of the main band to above the hu bands mine stratigraphic names in the bedded ore zone are similar in shape values of 13 c decrease abruptly at the base of the main band decrease slightly to the c band then increase to pre ore values the values of 34 s decrease from the base of the main band to the c band and then increase to pre ore values this similarity suggests some linkage between carbon and sulfur isotopic systematics and a sulfur budget dominated in the early stages of massive sulfide precipitation by hydrothermal processes involving thermogenic sulfate reduction giving way to bacteriogenic sulfate reduction in a closed then finally open marine basin

a re evaluation of eclogite facies metamorphism in sw japan proposal for an eclogite nappe known eclogite occurrences in the sanbagawa metamorphic belt of sw japan are dominantly in metagabbro bodies which have complex polyphase metamorphic histories these bodies are generally described as tectonic blocks and their relationship to the sanbagawa metamorphism is unclear new findings of foliated eclogite in the seba and kotsu areas show that eclogite facies metamorphism is much more widespread than generally thought evidence that the foliated eclogite units originated as lavas or sediments implies that these units can be treated as a high grade part of the subduction related sanbagawa metamorphism although separated by an along strike distance of 80 km the seba and kotsu eclogites have very similar garnet and omphacite compositions suggesting that they were formed under similar metamorphic conditions however differences in the associated retrograde assemblages epidote amphibolite in the seba unit and epidote blueschist in the kotsu unit suggest contrasting p t paths in both units the eclogite rocks occupy the highest structural level of the sanbagawa belt and overlie rocks metamorphosed at lower pressure the lower boundary to the eclogite units is therefore a major tectonic discontinuity locally decorated with lenses of exotic material these features can help trace the boundary into other areas the previously known outcrops of eclogite show enough similarities with the newly found areas to suggest that all the eclogite facies rocks in the sanbagawa belt constitute a single nappe that lies at the highest structural levels of the orogen

p t d path of eclogite from the sambagawa belt deduced from combination of petrological and microstructural analyses both structural and petrological data can be used to constrain the introduction p t path of an eclogitic schist unit the seba basic schist in the metamorphism of the sambagawa belt of sw japan was sambagawa belt of sw japan the relationships between these classified by miyashiro 1973 as an intermediate hightwo sets of data are well defined by porphyroblastic and other pressure facies series petrological chronological and microstructures the derived p t path for the seba basic schist structural data suggest that the evolution of the sambahas an overall clockwise trajectory with the decompression or gawa belt is in general compatible with the predictions exhumation related path taking place under a lower p t gradient made for metamorphism in the deeper parts of an acthan the burial or subduction related path the clockwise nature cretionary wedge e g banno sakai 1989 enami et of the p t path is qualitatively supported by chemical zoning of al 1994 takasu et al 1994 wallis 1998 the belt is amphibole coexisting with eclogitic minerals the significant feature composed mainly of metamorphosed sediments that have of the p t path is the presence of two temperature maxima the pelitic basic or siliceous compositions the mineral asfirst in the eclogite facies and the second in the epidote amphibolite semblages of most rocks are characteristic of metafacies the existence of two temperature maxima gives a simple morphism under greenschist blueschist or epidoteexplanation for the observation that metamorphic zonal boundaries amphibolite facies conditions however eclogite facies postdating the eclogite facies metamorphism cross cut the distribution mineral assemblages have also been reported e g takasu of the main eclogite bodies in the sambagawa belt estimates of 1989 which occur dominantly within metagabbro bodmetamorphic pressure using the jadeite content of clinopyroxene in ies most of these eclogite bearing bodies are located in the seba area demonstrate the existence of a tectonic discontinuity the besshi district fig 1 the estimated p t paths between the eclogitic schist and surrounding non eclogitic schist for the eclogite bearing bodies are distinct from those structural studies show that although these two units have experienced estimated for the surrounding epidote amphibolite grade very different peak metamorphic conditions they became juxtaposed rocks and show considerable variation amongst them

coupled micro faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the sambagawa metamorphic rocks southwest japan abstract in the sambagawa schist southwest japan while ductile deformation pervasively occurred at d 1 phase during exhumation low angle normal faulting was locally intensive at d 2 phase under the conditions of frictional viscous transition of quartz c 300 c during further exhumation into the upper crustal level accordingly the formation of d 2 shear bands was overprinted on type i crossed girdle quartz c axis fabrics and microstructures formed by intracrystalline plasticity at d 1 phase in some quartz schists the quartz c axis fabrics became weak and finally random with increasing shear accompanied by the decreasing degree of undulation of recrystallized quartz grain boundaries which resulted from the increasing portion of straight grain boundaries coinciding with the interfaces between newly precipitated quartz and mica we interpreted these facts as caused by increasing activity of pressure solution the quartz grains were dissolved mostly at platy quartz mica interface and precipitated with random orientation and pinned by mica thus having led to the obliteration of existing quartz c axis fabrics in the sheared quartz schist the strength became reduced by the enhanced pressure solution creep not only due to the reduction of diffusion path length caused by increasing number of shear bands but also to enhanced dissolution at the interphase boundaries

microboudin structures of piemontite along the sambagawa metamorphic belt japan implications for lateral variation of differential stress during regional metamorphism evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains p in a quartz matrix in metacherts it is proposed that p is a practical indicator of relative differential stress analysis of 123 metacherts from the 800 km long sambagawa metamorphic belt japan reveals that p values range from 0 01 to 0 7 in this region most samples from wakayama in the mid belt area have p values of 0 4 0 6 whereas those from western shikoku have p values of 0 1 this difference cannot be explained by variations in metamorphic temperature and is instead attributed to a regional lateral variation in differential stress during metamorphism

shrimp u pb zircon dating of quartz bearing eclogite from the sanbagawa belt south west japan implications for metamorphic evolution of subducted protolith in order to decipher the origin of eclogite in the high p t sanbagawa metamorphic belt shrimp u pb ages of zircons from quartz bearing eclogite and associated quartz rich rock metasandstone were determined one zircon core of the quartz rich rock yields an extremely old provenance age of 1899 79 ma suggesting that the core is of detrital origin eight other core ages are in the 148 134 ma range and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139 135 ma from the sanbagawa schists ages of metamorphic zircon rims 132 112 ma from the quartz rich rock are consistent with metamorphic zircon ages from the quartz bearing eclogite indicating that eclogite facies metamorphism peaked at 120 110 ma these new data are consistent with both the iratsu eclogite body and surrounding highest grade sanbagawa schists undergoing coeval subduction zone metamorphism and subsequent re equilibration under epidote amphibolite facies conditions during exhumation

the higher grade metamorphic zonation of the sambagawa metamorphic belt in central shikoku japan the higher grade metamorphic zonation of the sambagawa sanbagawa belt is established for the first time for the whole area of central shikoku as discontinuous reactions to define the isograd are absent the metamorphic grade is primarily determined by the mg fe partitioning between garnet and chlorite along representative traverses however for regional mapping mineralogical features of the pelitic schists such as using mineral assemblages of more than divariant equilibrium the modal garnet to chlorite ratio and the optical properties of chlorite are employed as auxiliary criteria the presence of the highest grade mineral zone in the middle of the structural level is confirmed but its spatial distribution is far more complex than hitherto accepted thermal axes are now confirmed at three different structural levels a model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re equilibrated local anomalies of metamorphic grade represented by mixing of schists of different metamorphic grade exist but they are due to a later stage event

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

muscovite k ar ages of the sanbagawa schists japan and argon depletion during cooling and deformation seventy muscovites from schists in the sanbagawa terrain in central shikoku were dated by the k ar method the muscovite ages are consistently older with increasing metamorphic grade within the same zone the ages are significantly younger in schists which have been more severely deformed these k ar age variations could be due to systematic argon depletion during deformation i e to the dynamic recrystallization of muscovites during ductile deformation that formed a large scale recumbent fold during the uplift and cooling argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low temperature deformation than the higher grade zone the relationships between age and grain size in a pelitic schist suggest that coarse grained muscovites lost more argon than the finegrained ones there was no significant resetting of ages in the vicinity of major strike slip faults such as the median tecotonic line or near thrust faults the combination of geochronological and geological data constrains the cooling rate of the sanbagawa schists to 9 12 c ma in the oligoclase biotite zone in central shikoku japan

evolution of the sambagawa metamorphic belt japan abstract the high pressure sambagawa metamorphic belt evolved within a mesozoic accretionary prism that developed in the convergent margin along the east of the eurasian continent although extensively researched recent studies in this region have revealed a number of important features that allow more complete reconstruction of the tectonic history i the grouping of radiometric ages suggests the existence of three major structural units with distinct metamorphic histories one of these has since been completely eroded away ii the difference of ages recorded by different minerals is in many cases small suggesting rapid exhumation after reaching peak metamorphic conditions iii the dominant ductile deformation of the sanbagawa belt representing major orogen parallel flow is commonly related to retrograde metamorphic reactions this shows that the associated fabric developed during exhumation not subduction iv kinematic studies suggest that the main ductile deformation caused major ductile thinning of the region which was probably a significant factor in causing exhumation of the region

sulfur isotope evidence for thermochemical reduction of dissolved sulfate in mississippi valley type zinc lead mineralization bongara area northern peru the bongara area northern peru contains mississippi valley type mvt zn pb mineralization hosted in late triassic jurassic carbonate rocks of the pucara group mineralization is interpreted to have formed during the late cretaceous peruvian orogenic event florida canyon and florcita located within 30 km of each other in the bongara area were studied to determine the origin and possible sources of sulfur in the mineralization one hundred and two in situ sulfur isotope analyses were determined on sphalerite galena and pyrite the narrow and symmetric distributions of the sphalerite 1 34s values are consistent with sulfate reduction in an open system with regard to sulfate the 34s values of sphalerite 1 from florida canyon 13 7 to 14 2 v cdt median 1 9 v cdt are lower and more variable than those for florcita 6 2 to 19 3 v cdt median 15 9 v cdt sphalerite 2 34s 0 3 to 17 6 v cdt median 2 4 v cdt postdating sphalerite 1 probably formed in a closed system with regard to sulfate the geologic setting fluid inclusion microthermometry and 34s values indicate that thermochemical reduction of dissolved sulfate tsr was the principal h2s production mechanism for metal precipitation possible sources of sulfate include late cretaceous seawater 34s 18 to 21 and evaporitic sulfate minerals in the middle late triassic chambara condorsinga formations 34s 12 to 15 and or in the late jurassic sarayaquillo formation 13 to 18 reduced sulfur from thermal cracking of organosulfur compounds and probably also remnants of h2s formed by bacterial sulfate reduction bsr might have been present during metal precipitation in florida canyon sample scale 34s variations observed in some samples from both areas reflect variable proportions of sulfate from different sources temperature effects on isotopic fractionation from sulfate to sulfide and the addition of reduced sulfur from organic compounds sample scale 34s variations can be interpreted as evidence for in situ sulfate reduction during mineralization this study places constraints on the mineralization mechanism the nature of sulfate reduction and the source of sulfur in mvt mineralization in northern peru the observed sample scale 34s variations lend support to the conclusion that in situ thermochemical sulfate reduction can occur during mineralization in these environments

early mesozoic subduction in the eastern mediterranean evidence from triassic eclogite in northwest turkey an eclogite forms a 40 m long tectonic lens enveloped in serpentinite within a metabasite phyllite marble unit of permian triassic age in northwest turkey the eclogite consists mainly of garnet omphacite glaucophane and epidote it is associated with other lenses of serpentinite and metagabbro single grain laser probe 40ar 39ar dating of phengites from the eclogite gives ages of 203 to 208 ma corresponding to the triassic jurassic boundary regional geologic considerations also suggest a latest triassic to earliest jurassic metamorphic age for the eclogite and the enclosing metabasite marble phyllite unit the eclogite along with serpentinite and gabbro lenses were probably emplaced as diapirs into the metabasite phyllite marble unit during late triassic subduction the eclogite provides evidence for the often elusive triassic subduction history of the paleo tethys in the eastern mediterranean area

origin of sulfur and crustal recycling of copper in polymetallic cu au co bi u ag iron oxide dominated systems of the great bear magmatic zone nwt canada the great bear magmatic zone in northwest canada contains numerous polymetallic mineral occurrences prospects and deposits of the iron oxide copper gold deposit iocg family the mineralization is hosted by the treasure lake group and igneous rocks of the great bear arc and was deposited concomitantly with the arc magmatism ca 1 88 to 1 87 ga in situ 34s n 48 and 65cu n 79 analyses were carried out on ore related sulfides from a number of these systems the 34s values mainly vary between 0 and 5 consistent with derivation of sulfur from the mantle lower 34s values 7 7 to 1 4 from the sue dianne breccia may indicate so2 disproportionation of a magmatic hydrothermal fluid the 65cu values vary between 1 2 and 0 3 and are lower than the igneous 65cu range of values 0 0 0 27 the s and cu isotopic data are decoupled which suggests that cu and possibly some s was dissolved and remobilized from supracrustal rocks during early stages of alteration e g sodic alteration and then precipitated by lower temperature more oxidizing fluids e g ca fe k alteration a limited fluid inclusion dataset and 13c and 18o values are also presented the 18ofluid values are consistent with a magmatic origin or a host rock equilibrated meteoric water source whereas the 13cfluid values support a marine carbonate source combined the s and cu isotopic data indicate that while the emplacement of the great bear magmatic bodies may have driven fluid convection and may be the source of fluids and sulfur metals such as cu could have been recycled from crustal sources

clasts of high grade sanbagawa schist in middle eocene conglomerates from the kuma group central shikoku south west japan middle eocene conglomerates which overlie the sanbagawa metamorphic rocks contain clasts of metamorphic rock with isotope ages of 120 85 ma which fall within the age range reported from the sanbagawa metamorphic rocks they were derived from the chlorite to oligoclase zones of the sanbagawa metamorphic belt clasts of garnet amphibolite and oligoclase biotite schist show a mineral assemblage similar to the highest grade sanbagawa schists however the metamorphic temperatures estimated by various mineralogical thermometers show that some of the clasts were formed at higher temperatures than the in situ sanbagawa metamorphic rocks such higher grade rocks were at the surface by the middle eocene and for the most part they have been eroded away cretaceous and post cretaceous sediments overlie or are in fault contact with the sanbagawa metamorphic rocks which suggests that rocks in the belt were uplifted and eroded from the latest cretaceous to middle eocene time after strike slip movement along the median tectonic line since the middle eocene the belt has experienced relatively slow uplift which was locally around 2 km in central shikoku

40ar 39ar mineral age constraints for the tectonothermal evolution of the sambagawa metamorphic belt central shikoku japan a cretaceous accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku japan is tectonostratigraphically represented by the oboke and structurally overlying besshi nappe complexes oboke units consist of metamorphic rocks largely derived from clastic protoliths sandstone and conglomerate whereas besshi units are dominated by rocks with oceanic protolith affinities shale chert and greenstone whole rock schist samples from low grade oboke units record intermediate temperature 40 ar 39 ar plateau ages of 70 77 ma which are interpreted to closely date attainment of maximum metamorphic conditions whole rock schist samples from besshi units chlorite zone record plateau ages of 85 94 ma suggesting an earlier metamorphic climax within this structural level amphibole within the albite biotite zone in besshi records 36 ar 40 ar vs 39 ar 40 ar plateau isotope correlation ages of 84 87 ma which are interpreted as dating the post metamorphic cooling through temperatures required for intracrystalline retention of argon a slightly older isotope correlation age 94 ma is recorded by amphibole from the higher grade oligioclase biotite zone contrasts in amphibole cooling ages are interpreted as reflecting thrust related metamorphic inversion and resultant earlier cooling of higher grade structural units muscovite from all structural levels of the besshi nappe complex records 40 ar 39 ar plateau ages of 76 89 ma these are interpreted to date post metamorphic cooling through appropriate closure temperatures following structural assembly of the besshi nappe complex protoliths of the besshi units originated at approx 130 ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx 90 100 ma higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex during subsequent structural uplift to shallower crustal levels the besshi nappe complex was tectonically emplaced over oboke units

exhuming the sanbagawa metamorphic belt the importance of tectonic discontinuities tectonic processes that have been proposed to explain the transport to the surface of regional metamorphic belts can be broadly divided into two types i corner flow within a convergent margin bounded by two essentially rigid plates associated with extension at shallow levels this type of model assumes deformation is distributed throughout the margin and that any discontinuities are of secondary importance ii expulsion or extrusion of coherent metamorphic nappes in this second idea tectonic discontinuities are fundamental in the transport to the surface of metamorphic rocks the wealth of geological data available from a variety of studies in the sanbagawa metamorphic belt southwest japan makes it well suited for studying the relative importance of continuous vs discontinuous deformation in the process of exhumation in the sanbagawa belt a sudden decrease in metamorphic pressure going down section of several kilobars suggests the presence of a major tectonic contact separating two major regional nappes an overlying higher pressure besshi nappe and an underlying lower pressure oboke nappe major tectonic discontinuities have also been proposed within the besshi nappe however indicators of metamorphic temperature the results of radiometric age dating and microstructural studies all suggest that post metamorphic discontinuities are minor and that this nappe formed and remained as an essentially coherent unit lithological associations and petrological studies suggest the following positions for the two nappes the besshi nappe formed deep within the former accretionary wedge adjacent to the overlying mantle wedge and with a dip of roughly 30 c in contrast the oboke nappe formed at moderate depths within the accretionary wedge was distant from the mantle wedge and was roughly horizontal penetrative deformation that post dates the peak of metamorphism has affected nearly all of the sanbagawa belt and has played an important role in its exhumation however the presence of a broad coherent besshi nappe overlying the lower pressure oboke nappe suggests that some process such as buoyancy driven extrusion was also important in the exhumation process and in forming the structure of the sanbagawa metamorphic belt

stable isotope δ13c δ18o analysis of sulfide bearing carbonate samples using laser absorption spectrometry hydrothermally altered country rocks surrounding hydrothermal ore deposits are commonly characterized by altered 18 o and 13 c values relative to distal unaltered rocks stable isotopes have been recognized as a powerful tool to complement traditional geochemical and geophysical approaches during mineral exploration particularly in carbonate replacement and carlin type deposits however wall rock alteration and carbonate veining during ore formation is often accompanied by the precipitation of sulfide minerals complicating stable isotope analysis the classic phosphoric acid extraction technique for carbonate minerals results in the release of additional h 2 s gas interfering with isotope ratio mass spectrometry irms and laser absorption spectrometry las analysis of co 2 here we present the first results from a novel off axis integrated cavity output spectrometer oa icos instrument capable of determining the stable isotope composition 13 c 18 o of mixed co 2 h 2 s gas evolved from carbonate sulfide mixtures instrument calibration was performed by analyzing in house and commercially available caco 3 stable isotope reference materials analyses of mixed co 2 h 2 s tank gas and sulfide spiked stable isotope reference materials containing up to 40 wt chalcopyrite and sphalerite demonstrate that the method outlined here is capable of effectively analyzing previously problematic high sulfide samples the analytical capabilities together with the robust nature of the oa icos instrument may be of direct practical use for mineral exploration in carbonate hosted hydrothermal systems including ore deposits

geochemistry and origin of piemontite quartz schists in the sanbagawa metamorphic belt central shikoku japan abstract in the sanbagawa metamorphic belt of central shikoku geochemical characteristics are used to demonstrate that piemontite quartz schists had a manganiferous sedimentary protolith the sanbagawa metamorphic belt was formed during a cretaceous regional intermediate high pressure type of metamorphism which is present throughout southwest japan based on a detailed mineralogical study of the asemi gawa and besshi areas in central shikoku the sanbagawa piemontite quartz schists can be divided into talc bearing and talc free types phlogopite occurs only in talc bearing assemblages and the modal percentage of piemontite in talc bearing types is higher than in talc free types plotting analyses of piemontites and garnets from talc bearing and talc free types in the al2o3 fe2o3 mn2o3 mno al fe3 mn3 mn2 diagram for the asemi gawa and besshi areas separately shows that the piemontite which accompanies talc is richer in mn3 and poorer in fe3 also garnets from talc bearing assemblage contain a slightly higher amount of mn2 and a lower amount of al than talc free types the al2o3 sio2 fe2o3 feo plot shows that sanbagawa piemontite quartz schists have a composition between deep sea pelagic clay and pure silica by the use of pearson s product moment correlation coefficient method and plotting elements against each other after removing silica and volatiles it is possible to distinguish four components which are able to explain the variance of the samples these components are first component al2o3 tio2 mgo na2o k2o zr rb y nb and to lesser degree fe2o3 feo ni th ba second component sio2 third component mno and fourth component cao al2o3 tio2 zr and other elements with positive coefficient relations with them have a detrital origin biogenic origins are considered for cao and sio2 and it was concluded that mno was derived from an hydrothermal source because the sanbagawa metamorphic belt has been subjected to much detailed research and also contains talc bearing and talc free piemontite quartz schists it provides the best opportunity to find an explanation for the occurrence of talc in some types of piemontite schist and its absence from others mineralogical and geochemical evidences show that the oxygen fugacity for talc bearing and talc free types is similar oxygen fugacity is so high that almost all of the iron is present as fe3 in hematite pressure and temperature is considered to have been constant for talc bearing and talc free types in each locality because the samples were collected from a known metamorphic context the talc absent present problem is discussed using phase relations of the samples with the greatest number of phases in each locality consideration of talc clinochlore piemontite and garnet in the system al2o3 mn2o3 mno mgo cao acmmn with excess phases albite quartz hematite phengite and water shows that talc coexists with piemontite and garnet which are richer in the piemontite and spessartine end members respectively

proterozoic pb isotope evolution in the belt purcell basin constraints from syngenetic and epigenetic sulfide deposits sediment hosted massive sulfide and ag pb zn veins are two major deposit types which contain large concentrations of lead in the middle proterozoic belt purcell basin new pb isotope data on the sullivan sediment hosted massive sulfide deposit and the st eugene ag pb zn vein deposit are combined with existing data to provide a comprehensive overview of proterozoic pb isotope evolution in the belt purcell basin the pb isotope ratios for sulfides in the sullivan deposit form a linear array the sullivan array bedded sulfides plot within this array and no systematic change in pb isotope ratios with stratigraphic position time is observed the sullivan array results from the mixing of leads from the upper crustal and or orogen pb reservoirs represented by metasedimentary rocks of the lower aldridge formation in the footwall of the sullivan deposit with perhaps leads derived from the precambrian basement of the belt purcell basin a zone within the massive sulfides of the sullivan deposit has been altered to chlorite pyrite calcite the center of the alteration zone is comprised of massive pyrite calcite which has more radiogenic pb isotope compositions the sullivan alteration the sullivan alteration apparently formed from the same pb reservoirs as the sullivan array perhaps as a product of the east kootenay orogeny 1370 ma after a period of up to 108 m y which allowed radiogenic pb growth ag pb zn occurrences in the belt purcell basin form an array in pb isotope space the coeur d alene array which is not collinear with the sullivan array it is characterized by pb isotope compositions less radiogenic than those of the sullivan array the coeur d alene array is a mixture of leads derived from the upper crustal and mantle pb reservoirs it is proposed that mantle lead was introduced into the belt purcell basin at 1468 ma by the mafic moyie sills leads in sediment hosted massive sulfide deposits in middle aldridge rocks and leads of the coeur d alene array in epigenetic veins formed after intrusion of the moyie sills but before east kootenay orogeny metamorphism

plate movements ductile deformation and geochronology of the sanbagawa belt sw japan tectonic significance of 89 88 ma lu hf eclogite ages prograde p t paths and thermal modelling suggest metamorphism in the sanbagawa belt represents unusually warm conditions for subduction type metamorphic belts and these likely reflect conditions of a convergent margin a few million years before the arrival of an active spreading ridge radiometric age data and kinematic indicators of ductile deformation suggest the sanbagawa belt formed in a cretaceous convergent margin associated with a plate movement vector that had a large sinistral oblique component with respect to the belt the east asian margin plate reconstructions for the cretaceous to tertiary for this region show that the only plausible plate compatible with such motion at this time is the izanagi plate these reconstructions also show that progressively younger sections of the izanagi plate were subducted beneath eastern asia i e a spreading ridge approached until 85 83 ma when the izanagi plate ceased to exist as an independent plate the major reorganization of plates and associated movements around this time is likely to be the age of major interaction between the ridge and convergent margin the ridge approach model for the sanbagawa metamorphism therefore predicts that peak metamorphism is a few million years older than this age range new lu hf dating of eclogite in the sanbagawa belt gives ages of 89 88 ma in excellent agreement with the prediction combining this estimate for the peak age of metamorphism with published p t t results implies vertical exhumation rates of greater than 2 5 cm yr 1 this high rate of exhumation can explain the lack of a significant thermal overprint in the sanbagawa belt during subduction of the ridge

pressure temperature path of sanbagawa prograde metamorphism deduced from grossular zoning of garnet the zonal structure of prograde garnet in pelitic schists from the medium grade garnet zone and the higher grade albite biotite zone was examined to investigate the evolution of prograde p t paths of the sanbagawa metamorphism the garnet studied shows a bell shaped chemical zoning of the spessartine component which decreases in abundance from the core towards the rim almandine and pyrope contents and xmg mg mg fe2 increase monotonously outwards the general scheme of the zonal structure for grossular content xgrs ca fe2 mn mg ca can be summarized as 1 xgrs increases outwards inner segment and reaches a maximum at an intermediate position between the crystal core and the rim then decreases towards the outermost rim outer segment 2 the inner segment of garnet in the garnet zone samples tends to have a higher xgrs xsps values for a given xsps than those in the albite biotite zone samples 3 average xsps at the maximum xgrs position in the albite biotite zone samples ranges from 0 02 to 0 12 and is lower than that in the garnet zone samples 0 13 0 32 4 the maximum xgrs in the albite biotite zone samples 0 34 0 39 on average tends to be higher than that in the garnet zone samples 0 26 0 36 and 5 differences of xgrs between the maximum and rim in the albite biotite zone samples are between 0 10 and 0 14 and higher than those in the garnet zone samples 0 11 these facts imply that albite biotite zone materials a were recrystallized under lower dp dt conditions at an early stage of the prograde metamorphism b began their exhumation under higher p t conditions and c have been continuously heated during exhumation for a longer duration than the garnet zone materials the systematic changes of prograde p t paths can be interpreted as documenting the evolution of the sanbagawa subduction zone

precision analysis of multisulfur isotopes in sulfides by femtosecond laser ablation gc irms at high spatial resolution abstract a new laser ablation method has been developed for measurements of multiple sulfur isotopes in sulfides using a femtosecond laser ablation system in combination with a reactor for sulfide aerosol conversion into sf6 gas a cryogenic and chromatographic purification system and an isotope ratio mass spectrometer fsla gc irms in this method femtosecond laser generated aerosol sulfide particles were transferred by the helium carrier gas from the sample chamber into the reactor to convert them to sf6 via reaction with brf5 cryogenically and chromatographically purified sf6 was transferred by helium carrier gas to the interface that was developed for introducing sf6 into the ion source of a mass spectrometer running in high vacuum operation mode for the routine analysis of sulfide a precision of 0 1 0 2 1 for 34s and higher than 0 03 1 for 33s values has been obtained with an ablation crater size of 80 m diameter and 40 m depth the method was tested using reference materials iaea s 1 iaea s 2 iaea s 3 and nbs 123 as well as some natural pyrite sphalerite and galena samples the 34s values obtained by our method are in good agreement within analytical precision with the results obtained by the conventional dual inlet method the fsla cg irms method was applied to study sulfur isotope ratios in archean rocks of the cheremshanskaya formation sharyzhalgai uplift in the southeastern siberian craton we found that 33s values in sulfides from these rocks ranged 2 30 to 2 68 the reliability of the results obtained here was confirmed by comparative analyses of isotope ratios in sulfides from rocks younger than 2 4 ga in which the anomaly of the 33s isotope could be unlikely to occur the calculated 34s ln 34s 1000 1 1000 and 33s ln 33s 1000 1 1000 values of this set of samples yielded a straight line passing through the origin with a slope of 0 5152 0 002 on a conventional sulfur three isotope plot that is in good agreement with a slope of 0 515 which was theoretically calculated for the mass dependent fractionation of sulfur isotopes

iron and sulphur isotopes from the carajas mining province para brazil implications for the oxidation of the ocean and the atmosphere across the archaean proterozoic transition abstract mineralogical analyses and major and trace element geochemistry combined with iron and sulfur isotopes were applied to banded iron formations bifs and pyrite bearing sandstones from the carajas mineral province brazil the bifs belong to the 2 7 ga old grao para group and show a rather simple mineralogy hematite and quartz or cryptocrystalline silica their ree y patterns suggest deposition under marine sub oxic conditions fe isotopes show highly positive values 57 fe irmm 14 2 06 0 34 in average which can be explained by the partial oxidation of fe 2 aq in the surface ocean subsequent to the upwelling of deep anoxic seawater the resulting iron oxy hydroxides likely formed in the shallow photic zone as a seasonal process and acquired highly positive iron isotope signature values consistent with a rayleigh distillation model the pyrite bearing sandstones belong to the aguas claras formation of palaeoproterozoic younger age and were cored at the base of the giant azul manganese deposit diagenetic pyrite is characterized by positive 57 fe irmm 14 1 02 0 2 and 34 s vctd 11 97 0 12 average values that are different from values of modern marine biogenic pyrite results likely indicate that dissolved sulfate was the limiting factor controlling biogenic pyrite formation at that time near zero 33 s values 0 013 0 003 indicate minimal mass independent sulfur isotope fractionation mif s consistent with the 2 1 ga age previously obtained from the aguas claras pyrites this result suggests deposition at a time when the oxygen partial pressure in the atmosphere was already high enough 10 5 to 10 2 pal or present atmospheric level to hinder mif s by photochemical reactions incidentally this also confirms that the giant mn deposit of carajas is in the same age range 2 1 0 2 ga as other mn ores in gabon and south africa pointing to the importance of mn precipitation in paleoproterozoic times

microtectonic evidence for eastward ductile shear in the jurassic orogen of sw japan abstract two jurassic deformation phases are responsible for the thrust and nappe structures in the infrastructure of the outer belt of the mesozoic chain of sw japan the first phase was synmetamorphic and took place under hp lt conditions microtectonic analysis shows that the penetrative deformation corresponded to a ductile shear directed from w to e parallel to the stretching and mineral lineation at the regional scale the first phase corresponded to the obduction of the greenschist nappes upon the kurosegawa continent during the second phase the greenschist nappes were sliced leading to an apparent reverse metamorphic zoning the first phase structures were then locally reworked by folds giving rise to an apparent westwards sense of shear