gold bearing mesothermal veins from the gubong mine cheongyang gold district republic of korea fluid inclusion and stable isotope studies the gubong deposit consists of five massive gold bearing mesothermal quartz veins that fill fractures oriented northeast and northwest along fault shear zones over an area of 14 km2 in precambrian metasedimentary rocks of the gyeonggi massif the veins are divided into three groups based on their orientation and location they have a ribbon texture that is interpreted to result from repeated hydraulic fracturing events mineral deposition was associated with hydrothermal fluid overpressuring within and below the active fault shear zones the vein mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes to be recognized separated by a major faulting event the ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes wall rock alteration minerals during stage i the main ore stage include sericite chlorite and minor pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena and argentite electrum also was deposited during stage ii mineralization in the one group of veins along with pyrite sphalerite chalcopyrite and galena but the second stage of deposition in other veins was barren petrographic examination of textural relationships among sulfides fluid inclusions microfracturing and quartz shows chronological and genetic relationships between gold deposition and fluid entrapment systematic studies of fluid inclusions in stage i vein indicate two contrasting events a relatively high temperature 203 432 c and pressure 943 2 098 bars event related to early sulfide deposition and associated with h2o co2 ch4 nacl n2 fluids less than about 13 4 wt nacl and a lower temperature 202 399 c and pressure 670 850 bars late sulfide depositional event involving h2o nacl fluids 3 9 17 3 wt nacl the h2o nacl fluid involved in ore related stage ii mineralization had a salinity of 0 4 to 4 2 wt percent nacl and a homogenization temperature of 201 to 378 c the calculated sulfur isotope compositions of hydrothermal fluids from the stage i veins 34sh2s 3 5 10 5 indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks the calculated and measured oxygen and hydrogen isotope compositions of the ore forming fluids stage i 18oh2o 1 1 9 0 d 92 to 21 stage ii 18oh2o 0 1 to 0 3 d 95 to 93 indicate that the fluids were derived from magmatic and or deep seated metasedimentary rocks stage i and evolved by mixing with local meteoric water stage ii by limited water rock exchange and by degassing during mineralization in uplift zones the h2o nacl fluids involved in the stage i development of these veins represent fluids that evolved either through unmixing of h2o co2 ch4 nacl n2 fluids following a decrease in fluid pressure or through mixing with deeply circulating meteoric waters possibly as a result of uplift and or unloading during mineralization the h2o nacl fluid involved in stage ii was derived from meteoric water early deposition of gold in stage i was caused by a decrease in sulfur fugacity h2s loss that accompanied the immiscible separation of carbonic vapor from h2o co2 ch4 nacl n2 fluids gold in late stage i and stage ii veins was precipitated from h2o nacl fluids by cooling and by dilution caused by mixing with meteoric water

40ar 39mineral ages from the scituate granite rhode island implications for late palaeozoic tectonothermal activity in new england j i gil ibarguchi abstract the alkalic scituate granite was emplaced into crystalline sequences within the new england esmond dedham terrane in the late devonian c 370 ma variably recrystallized amphibole iron rich hastingsite hastinpitic hornblende from four variably deformed samples of the pluton record south westerly younging ar ar plateau ages ranging between 276 and 263 ma these are interpreted to date diachronous cooling through temperatures appropriate for intracrystalline retention of argon following late palaeozoic orogenic activity iron rich biotite concentrates from the samples record only slightly younger ages and therefore suggest relatively rapid post metamorphic cooling the ar ar ages indicate that the late palaeozoic tectonothermal overprint was much more regionally pervasive than was previously considered the apparent timing of this activity is similar to previous estimates for the chronology of high grade metamorphism throughout the adjacent hope valley terrane and for phases of ductile movement on the intervening lake char honey hill fault system

a transitional alkalic dolerite dike suite of mesozoic age in southeastern new england dike rocks from the new england platform of rhode island and adjacent massachusetts consist of premetamorphic and post metamorphic suites the older group includes metamorphosed dolerite minette and schistose dioritic rocks post metamorphic dikes consist of dolerite and sparse monchiquite the post metamorphic dolerites are of comparable age to the eastern north american dolerite suite associated with the mesozoic basins along the eastern seaboard of north america however the southeastern new england dolerites exhibit mineralogy and chemistry more typical of a transitional alkalic suite compared to the more subalkalic tholeiitic dolerites of the eastern north american suite both suites are compatible with a rift tectonic setting but the more alkalic dolerites may represent a deeper source of small volume melts compared to the eastern north american dolerites these more alkaline melts may have concentrated at local centers or they may be typical of flank dolerites as opposed to the less alkalic varieties that occur within the central axial rift

40ar 39ar illite dating of late caledonian acadian metamorphism and cooling of k bentonites and slates from the welsh basin u k the vacuum encapsulation laser 40ar39ar technique allows extremely small 10 6 g samples of fine grained materials such as diagenetic clays to be dated here we show that the method can be extended to higher grade clay minerals the integration of transmission electron microscopic tem characterization with 40ar39ar dating of vacuum encapsulated samples permits the resolution of the timing of metamorphic growth cooling from the time of diagenesis we have applied this technique to well characterized lower paleozoic slates and k bentonites from the welsh basin which span the transition from anchizonal to epizonal grade which had been previously studied using rbsr and smnd dating tem observations of epizonal k bentonites and slate showed that illite in these samples is of 2m1 polytype of muscovite like composition and oriented parallel to cleavage suggesting that they are of metamorphic origin total gas ages equivalent to conventional kar ages for encapsulated epizonal k bentonites and slate 340 408 ma are considerably variable the ar retention ages calculated from 39ar and 40ar atoms retained in the sample after irradiation are more consistent 383 411 ma the 39ar recoil losses are minor for illites from whole rock samples of epizonal k bentonites but very significant for clay separates of epizonal slate plateaus in age spectra were observed in epizonal k bentonites and slate the plateau ages 414 421 ma and retention ages 383 411 ma can be correlated with the onset of acadian metamorphism and culmination of uplift and inversion of the welsh basin respectively these ages are significantly younger than the 450 ma ages previously reported for diagenetic clays using the same method suggesting that diagenetic history has been lost in these epizonal k bentonites and slate tem observations of anchizonal slates showed that there are two modes of illite the first mode is similar to that observed in epizonal samples suggesting a metamorphic origin the second mode consists of the 1md polytype has typical diagenetic illite composition and is oriented parallel to bedding suggesting a diagenetic origin total gas ages for encapsulated anchizonal slates vary considerably 361 422 ma the retention ages are more consistent 413 432 ma than the total gas ages the 39ar recoil losses are more significant than those for epizonal k bentonites and slate plateaus in age spectra are generally not observed however the consistent retention ages for the anchizonal slates correspond to the plateau ages for the epizonal samples and are inferred to represent the onset of acadian metamorphism these data when combined with our previously published results for diagenetic shales suggest that thermal conditions near the boundary of anchizonal and epizonal grades are necessary to completely reset ar systems in shales and slates

insar observations of post rifting deformation around the dabbahu rift segment afar ethiopia summary increased displacement rates have been observed following manylarge earthquakes and mag matic events although an order of magnitude smaller than the displacements associated with the main event the post seismic or post rifting deformation may continue for years to decades after the initial earthquake or dyke intrusion due to the rare occurrence of subaerial rifting events thereareveryfewobservationstoconstrainmodelsofpost riftingdeformation in2005 september a 60 km long dyke was intruded along the dabbahu segment of the nubia arabia plate boundary afar ethiopia marking the beginning of an ongoing rifting episode con tinued activity has been monitored using satellite radar interferometry and data from global positioning system instruments deployed around the rift in response to the initial intrusion using multiple satellite passes we are able to separate the rift perpendicular and vertical displacement fields around the dabbahu segment rift perpendicular and vertical rates of up to 180 and 240 mm yr 1 respectively here we show that models of viscoelastic relaxation alone are insufficient to reproduce the observed deformation field and that a large portion of the observed signal is related to the movement of magma within the rift segment our models suggest upper mantle viscosities of 10 18 19 pas overlain by an elastic crust of between 15 and 30km to fit the observations inflation and deflation of magma chambers in the centre of the rift and to the south east of the rift axis is required at rates of 0 13 and 0 08km 3 yr 1

the latest post variscan fluids in the spanish central system evidence from fluid inclusion and stable isotope data abstract the spanish central system has been subjected to repeated fluid incursions which were responsible for a variety of mineralizing episodes including w sn cu zn pb as ag f ba and barren quartz veins these hydrothermal fluids occurred over a 200 ma time period and the latest hydrothermal event is recorded in barren quartz veins this study is a multidisciplinary approach leading to the characterization of the hydrothermal fluids preserved in barren quartz veins which are spatially but not temporally related to hercynian upper crustal granites the veins were dated by the 39 ar 40 ar method and the fluids were examined using petrographic microthermometric chemical and isotopic methods fluid inclusions in barren quartz veins indicate that two fluids were related to this hydrothermal event the main part of the quartz veins were formed from an early low salinity 2 o nacl fluid this fluid was trapped at around 270 25 c and 0 1 1 kbar under sublithostatic to hydrostatic conditions 18 o 9 to 2 and d 70 to 34 5 values indicate a meteoric origin for water with significant water rock interactions the latest h 2 o nacl cacl 2 fluid is found in two types of fluid inclusions a primary liquid vapour type 16 24 wt nacl and 1 12 wt cacl 2 and secondary hypersaline type 7 15 wt nacl and 21 27 wt cacl 2 significant li concentrations in this fluid were confirmed this late ca bearing fluid formed quartz crystals in the central part of the veins and was trapped at 70 140 c at a maximum pressure of 0 5 kbar the low 18 o 20 to 6 and d 137 to 116 values suggest a meteoric origin for this fluid however its high salinity probably requires a source from triassic evaporite basins located in the ne tip of the spanish central system anomalously low isotopic values have been previously reported from kaolinites of lower cretaceous age anomalous climatic conditions during the cretaceous appear to be the main reason to explain this very negative meteoric water strong isotopic depletion in meteoric water has been observed in modern areas with monsoonal climates the hydrothermal evolution of barren quartz veins in the spanish central system is comparable to other hydrothermal post variscan events in central and south western europe related to the opening of the north atlantic during cretaceous time

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

identification and correlation of visible tephras in the lake suigetsu sg06 sedimentary archive japan chronostratigraphic markers for synchronising of east asian west pacific palaeoclimatic records across the last 150 ka abstract the lake suigetsu sg06 sedimentary archive from honshu island central japan provides a high resolution palaeoenvironmental record including a detailed record of explosive volcanism from japan and south korea thirty visible tephra are recorded within the 73 m long sg06 core which spans the last 150 ka here we describe and characterise these tephras based on major element glass composition which is useful for the identification and correlation of these tephras and the age models of the records in which they are found utilising the large number of radiocarbon measurements n 600 from terrestrial plant macrofossils in the lake suigetsu sg06 record we are able to provide precise and accurate ages for the tephras from eruptions within the last 50 ka glass compositional data of some of the largest eruptions from japan k ah at aso 4 aso a aso d and ata sampled at proximal outcrops are also presented these data show that the major element glass chemistry is distinctive for many of the visible sg06 tephra units and allows some of the layers to be correlated to known eruptions from volcanoes in japan and south korea namely k ah sg06 0967 u oki sg06 1288 at sg06 2650 aso 4 sg06 4963 sg06 4979 k tz sg06 5181 aso abcd sg06 5287 and ata sg06 5181 the following ages were obtained for the sg06 tephra units 3 966 4 064 cal ka bp 95 4 probability range for the sg06 0588 tephra 10 242 10 329 cal ka bp 95 4 probability range for sg06 1293 19 487 112 sg06 2012 ka bp 2 for sg06 1965 28 425 194 sg06 2012 ka bp 2 for sg06 2504 28 848 196 sg06 2012 ka bp 2 for sg06 2534 29 765 190 sg06 2012 ka bp 2 for sg06 2601 29 775 191 sg06 2012 ka bp 2 for sg06 2602 43 713 156 sg06 2012 ka bp 2 for sg06 3485 46 364 202 sg06 2012 ka bp 2 for sg06 3668 49 974 337 sg06 2012 ka bp 2 for sg06 3912 50 929 378 sg06 2012 ka bp 2 for sg06 3974 and improved ages for two of the most important tephra markers across japan the k ah 7 165 7 303 cal ka bp at 95 4 probability range sg06 0967 and at tephra 30 009 189 sg06 2012 ka bp at 2 sg06 2650

kinematic history of the narragansett basin massachusetts and rhode island constraints on late paleozoic plate reconstructions the formation of the narragansett basin of rhode island and massachusetts and the polyphase deformation geometry of the pennsylvanian age basin sediments can be explained by collision and strike slip interactions between an avalonian microcontinent the european north american plate and the african plate during the late paleozoic sinistral movement between an avalonian microcontinent and the european north american plate resulted in formation of pull apart basins subsequently africa moved toward north america along an east west trending dextral megashear zone and collided with the eastern margin of southern north america the narragansett basin is located on the avalonian microcontinent near the suture with the north american continent and in the transition zone between the megashear and the collision tectonic regimes the basin shape stratigraphy and sedimentary relationships can be explained by the coalescence of two composite grabens which formed at different times the thicker northern graben is only affected by one deformation whereas the southern graben shows evidence of four distinct phases of postrifting deformation the first two coaxial folding deformations of the basin sediments are attributed to the closure of the basin complex during collision of africa and north america the third and fourth deformations are interpreted as sinistral r riedal and dextral shears respectively associated with the east west trending megashear system a prograde barrovian metamorphic front started in the western portion of the southern graben slightly after the first deformation and migrated northward and eastward where it is synchronous with the second deformation

mineralogy of the tumanny au ag te hg epithermal veins western chukchi peninsula russia abstract the tumanny au ag te hg epithermal prospect chukchi peninsula russia is located in the near contact zone of the large vuknei pluton part of the early cretaceous egdykgych complex which is related to the peschanka porphyry copper deposit and the nakhodka porphyry epithermal ore district located 45 km north of tumanny mineralization at tumanny is characterized by an early carbonate base metal and a late gold silver sulfosalt mineral assemblage pyrite of the first assemblage is unzoned and as poor and tennantite tetrahedrite solid solutions ttrs are characterized by a weak oscillatory zoning caused by variable contents of sb and as low ag content and the widely variable sb sb as values pyrite of the second assemblage is zoned and as rich up to 5 2 wt and ttrs is weakly zoned and ag rich up to 10 35 apfu and has a comparatively narrow range of sb sb as value electrum au ag alloy kustelite au ag s phases hessite polybasite and imiterite recognized at the prospect belong to the second mineral assemblage the homogenization temperature of primary fluid inclusions in quartz ranges from 340 to 210 c and decreased during the mineralizing process fluid salinity varying from 0 8 to 5 2 wt nacl equiv is not evolved during the process cores of quartz crystals formed from a boiling fluid whereas crystal rims appear to have formed from a lower temperature non boiling liquid logfs2 decreased from 8 at the formation of carbonate base metal assemblage to 16 at the deposition of gold silver sulfosalt assemblage as temperature decreased from 340 to 200 c bulk icp oes analysis of mineralized samples indicated up to 38 ppm au 908 ppm ag 154 ppm mo 106 ppm te 53 ppm se 9246 ppm as 1284 ppm sb and 23 ppm bi cluster analysis of the data obtained identified three geochemical associations corresponding the carbonate base metal the gold silver sulfosalt and to the overlapped mineral assemblages the whole ore composition is controlled by mineralogy of these assemblages taking into account the geological setting mineralogy composition of minerals and fluid inclusion data the tumanny au ag te hg prospect is characterized as intermediate sulfidation epithermal style

tectonic stress controls on ascent and emplacement of magmas abstract the tectonic stresses can significantly affect the propagation of a magma filled crack it has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress however it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states we have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow the stress profiles were estimated by a simple model of lithospheric deformation we employed a three layer model of the lithosphere the upper crust the lower crust and the upper mantle have different rheological properties a constant horizontal force is applied to the lithosphere and the horizontal strain is assumed to be independent of depth when realistic tectonic forces 10 11 n m are applied the rheological boundaries mainly control the emplacement of magma the emplacement is expected at the moho the upper lower crust boundary and the brittle ductile boundary for lower tectonic forces 11 n m the tectonic stress no longer plays an important role in the emplacement of magmas when the tectonic stress controls the emplacement the roles of rheological boundaries strongly depend on the surface heat flow when the surface heat flow is relatively high 80 mw m 2 the stress in the mantle is quite low and the moho cannot trap ascending magmas for relatively low heat flow 2 on the other hand the moho acts as a magma trap and the upper lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high our results suggest that the emplacement depth can change responding to the change in the tectonic force and or that in the surface heat flow this may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and or thermal history

olivine dolerite intrusionsin the fastnet basin sills of olivine microgabbro and olivine dolerite 0 5 180 m thick intrude lower liassic hettangian sinemurian sediments in the fastnet basin a sw extension of the n celtic sea basin about lat 50 n long 10 w the evidence of 3 wells and 2300 km of seismic reflection profiles indicates 6 major sills and sill complexes and 3 possible igneous centres or plugs a high level sill may intrude lower cretaceous sediments and one plug apparently deforms cretaceous reflectors k ar ages on separated biotites from a thick sill intruding liassic sediments gave 170 4 ma bajocian this sill contains 30 olivine fo 70 73 20 clinopyroxene magnesian salite 45 plagioclase an 60 78 with accessory magnetite ilmenite edenitic hornblende ti phlogopite apatite zircon spinel in olivine and sulphides alteration to serpentine minerals chlorite sericitic mica and leucoxene is sporadic the magmatism in the fastnet province thus appears to have been active from the mid jurassic to the early tertiary related initially to the time of initial rifting between the european and american plates and subsequently to their final separation between greenland and rockall and associated thulean magmatism

models of single stage concomitant potassium argon exchange an interpretation of discordant whole rock k ar data from hydrothermally altered igneous rocks of the south pennine orefield u k abstract a model of single stage concomitant potassium and argon exchange is advanced to explain the existence of rectilinear isochrons in potassium argon correlation diagrams produced from suites of altered rocks negative isochron intercepts are shown to be a consequence of fractional argon loss which exceeds potassium loss and it is demonstrated that no information of immediate geological significance can be obtained from the gradient of such an isochron bounds to the primary formation age and age of exchange event may be established using extreme values of the observed potassium content and from estimates based on the inferred petrology and chemistry of the unaltered rock and or its alteration products ten carboniferous igneous units from the south pennine orefield involving thirty eight independent samples are investigated by means of the model and eight of the units are consistent with a model of potassium and argon exchange occurring in earliest mesozoic times ca 200 ma it is argued that this conclusion augments the already substantial body of evidence for an identifiable widespread igneous and hydrothermal province associated with early rifting processes in the north atlantic

a review of molybdenite and fluorite mineralisation in caledonian granite basement western ireland incorporating new field and fluid inclusion studies and re os and u pb geochronology abstract the recent discovery of late magmatic quartz vein hosted molybdenite and exceptional gem quality vein fluorite in the caledonian galway granite complex ggc has prompted a review of these contrasting styles of mineralisation in the late caledonian granite basement connemara western ireland existing published u pb and re os chronometry and fluid inclusion microthermometry are combined with new a geological field observations b u pb zircon and re os molybdenite geochronometry and c fluid inclusion microthermometry to generate a new pressure temperature time model p t t of mineralisation for the ggc re os chronometry molybdenite indicates that granite related molybdenite mineralisation extended from 423 to 380ma overlapping with the ggc emplacement history determined by u pb zircon chronometry the p t t model reflects initial granite emplacement and mo mineralisation at 423ma followed by lower p and t granite emplacement and related quartz vein hosted mo mineralisation at 410ma carna pluton 400ma kilkieran pluton and at 380ma costelloe murvey granite the gem quality fluorite veins in the ggc represent late triassic hydrothermal mineralisation these veins form part of a regional n atlantic european triassic jurassic hydrothermal mineralisation province vein emplacement was triggered by the rifting of the n atlantic facilitating crustal thinning and subsidence of continental crust and initiating hydrothermal activity at the margins of mesozoic basins

40ar 39ar ages from the narragansett basin and southern rhode island basement terrane their bearing on the extent and timing of alleghenian tectonothermal events in new england pennsylvanian sedimentary rocks record the effects of progressive barrovian metamorphism and polydeformation in the narragansett basin of rhode island whole rock phyllite samples from low grade portions of this terrane display internally concordant 40 ar 39 ar age spectra with plateau ages of 248 to 258 m y four samples biotite from higher grade rocks records plateau ages of 240 to 248 m y eight samples similar 40 ar 39 ar biotite ages are displayed westward across the southern rhode island basement terrane 239 to 250 m y nine samples although coexisting hornblende records slightly older plateau ages of 255 m y two samples the 40 ar 39 ar plateau ages are interpreted to date times of post metamorphic cooling through temperatures required for argon retention in the various mineral phases examined the ages suggest that a distinct late paleozoic alleghenian thermal event affected much of southern rhode island together with the depositional ages of the variably metamorphosed pennsylvanian rocks westphalian b stephanian a or b the 40 ar 39 ar data permit calibration of the sequence of alleghenian tectonothermal events recorded in the narragansett basin the controls suggest a permian event lasting about 40 to 50 m y between initial barrovian regional metamorphism and synchronous d 1 d 2 ductile deformation between 295 and 275 m y and post d 3 cooling below argon retention temperatures between 250 and 240 m y

deformation induced reconstitution and local resetting of mineral equilibria in polymetamorphic gneisses tectonic and metamorphic implications a sequence of at least three al2sio5 bearing mineral assemblages are preserved in successively overprinted ductile shear zones in the willimantic window connecticut the ductile deformation localized at and near the boundary between the putnam nashoba terrane and underlying avalon terrane is characterized by a network of anastomozing shear zones that outline metre scale tectonic blocks of migmatitic kfs sil gt bi pg qtz ilm ru gneiss these assemblages record acadian or older metamorphic conditions of 6 kbar 700d c mylonitic gneisses in shear zones that define block margins were formed by reconstitution and recrystallization of the migmatitic gneiss the reconstituted rocks exhibit relict ky st grt pl bt qtz rt ilm assemblages and require a minimum pressure for the ky str grade metamorphism of 8 5 kbar kyanite in block margins is widely replaced by sillimanite and locally by andalusite during a period of post alleghanian ductile deformation the interiors of blocks do not record this sequence of polymorphs the pattern of reconstitution is accounted for by localization of strain along block margins within a regionally extensive terrane bounding fault zone strain provided the activation energy for recrystallization and retrograde mineral reactions the p t conditions of post alleghanian ductile deformation evolved from 600d c and 6 kbar to 550d c and 3 kbar the occurrence of ky str bearing assemblages overprinting acadian kfs sil bearing assemblages and subsequently overprinted by alleghanian sillimanite and andalusite bearing assemblages along with reset hornblende 40ar 39 ar mineral ages from mississippian to permian requires a prograde alleghanian metamorphism of rocks previously metamorphosed during the acadian thus mineral assemblages from gneisses in the willimantic fault zone retain evidence of a protracted tectonothermal evolution that included high grade acadian orogenesis tectonic loading resulting from alleghanian collision of avalon with north america and tectonic exhumation in permo triassic time the c 3 kbar pressure decrease between prograde and retrograde alleghanian metamorphic conditions corresponds to 10 km of crust that must have been tectonically excised from the base of the putnam nashoba terrane cover sequence following alleghanian orogenesis in south eastern new england

magma discharge variations during the 2011 eruptions of shinmoe dake volcano japan revealed by geodetic and satellite observations we present precise geodetic and satellite observation based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of kirishima shinmoe dake volcano japan during these events the type and intensity of eruption drastically changed within a week with three major sub plinian eruptions on january 26 and 27 and a continuous lava extrusion from january 29 to 31 in response to each eruptive event borehole type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface these measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub plinian event these precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics and indicate that the shinmoe dake eruptions occurred in a critical state between explosive and effusive eruption

post rifting relaxation in the afar region ethiopia 1 crustal accretion at divergent plate boundaries typically occurs via the periodic intrusion of dikes but their emplacement and the associated deformation are rarely observed the few existing observations at subaerial rifts show that these diking events are followed by a decadal scale period with extension rates faster than the secular divergent plate motion this transient accelerated deformation has been explained by continued subsurface magma injection or by relaxation in the viscoelastic mantle of the stress changes imparted by dike opening for the first time gps measurements were collected within a few months of a rifting event at a major plate boundary the september 2005 60 km long dike intrusion in the dabbahu segment afar ethiopia extension rates for the first 3 years greatly exceed the plate motion nubia arabia secular divergence rate even at sites located more than 60 km from the rift axis here we show that these observations are consistent with stress relaxation in a viscoelastic upper mantle with a viscosity of about 5 1018 pa s overlain by a 12 14 km thick elastic crust the alternative model of continued diking requires continuous opening well below the moho and is therefore unlikely instead magma injection in afar since june 2006 has taken the form of smaller discrete diking events tapping into a mid crustal melt reservoir under the segment center

stable isotope and fluid inclusion studies of gold and silver bearing hydrothermal vein deposits cheonan cheongyang nonsan mining district republic of korea cheonan area the cheonan gold silver mineralized area is located approximately 80 km south southeast of seoul within the precambrian gyeonggi metamorphic belt of the korean peninsula the cheonbo ilbo seonggeo daeheung and chungnam mines which comprise the area are each located along gold bearing hydrothermal quartz veins that crosscut early proterozoic gneiss and jurassic and cretaceous granites mineralization can be separated into three distinct stages i ii and iii which fill preexisting fault breccia zones stages i and ii are terminated by the onset of fracturing and brecciation events fluid inclusion data suggest that quartz sulfide bearing stages i and ii each evolved from initial high temperatures near 400 degrees c to later lower temperatures near 200 degrees c each of these stages represents a separate mineralizing system which cooled and largely abated prior to the onset of the next stage fluid inclusion data from stage iii a postore carbonate stage of mineralization indicate a much cooler 240 degrees 115 degrees c more dilute 3 4 equiv wt nacl hydrothermal system which was the result of increasing influx of meteoric waters sulfur isotope and fluid inclusion evidence suggests electrum sphalerite galena ore mineralization was deposited during stage i at temperatures between 170 degrees and 255 degrees c from fluids with salinities between 3 and 9 equiv wt percent nacl fluid inclusion evidence of boiling suggests pressures of less than 100 to 300 bars this range of pressure is consistent with a depth of mineralization near 1 km under pressure conditions that alternated between hydrostatic and lithostatic sulfur isotope compositions of sulfide minerals are consistent with an igneous source of sulfur with a delta 34 s sub sigma s value near 5 0 per mil measured and calculated delta d and delta 18 o values of hydrothermal fluids in the cheonan area ore deposits are stage i 122 to 127 and 6 2 to 5 9 per mil stage ii 135 to 143 and 3 6 to 3 2 per mil stage iii 134 to 137 and 3 4 to 7 4 per mil respectively these values are consistent with progressive meteoric water involvement increasing water rock ratios with increasing paragenetic time comparison of these values with those of a deeper 2 3 km jurassic gold deposit delta d 78 102 delta 18 o 7 7 3 8ppm suggests a relationship between depth and water rock ratio in korean au ag bearing vein deposits the jurassic au system has ratios of 0 001 to 0 01 the cretaceous au ag system 0 02 to 0 5 the relationships among depth metal contents and water rock ratios in these korean au ag deposits suggest differences in the hydrodynamics and postmagmatic evolutions of granitic hydrothermal systems and may be indicative of the manner in which gold and silver are scavenged from cooling plutons

early rifting in the narragansett basin massachusetts rhode island evidence from late devonian bimodal volcanic rocks abstract the basal wamsutta formation of the narragansett basin massachusetts rhode island contains documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 373 pm 2 end document ma rhyolite that is unexpectedly 60 m yr older than sedimentary strata containing late pennsylvanian floras higher in the basin fill the transitional alkalic geochemistry of the rhyolite and associated basalt signifies late devonian rifting pre dating major basin subsidence surface rifting was accompanied by voluminous alkalic intrusions of the 380 370 m

permian bulk shortening in the narragansett basin of southeastern new england usa pennsylvanian age sediments within the narragansett basin allow the effects of alleghanian deformation to be distinguished from the taconic and acadian orogenies that affected the rocks to the west three dimensional microstructural analyses of both matrix foliations and structures preserved in porphyroblasts define two extended periods of deformation and metamorphism about two differently trending foliation intersection inflection axes in porphyroblasts fias ssw nne trending fias set 1 formed first followed by wsw ene trending fias set 2 the ssw nne fia trends from the south central zone lie parallel to regional folds in the entire southern graben the changes in fia trends reveal that the direction of maximum bulk shortening changed from wnw ese to nnw sse during amphibolite facies metamorphism within the central zone of the basin they reveal a more varied history than the simple kinematic framework of solely w e directed bulk shortening that was previously suggested

the influence of elastic thickness non uniformity on viscoelastic crustal response to magma emplacement application to the kutcharo caldera eastern hokkaido japan

mesothermal gold vein mineralization of the samdong mine youngdong mining district republic of korea mesothermal gold mineralization at the samdong mine 5 5 13 5 g ton au youngdong mining district is situated in massive quartz veins up to 1 2 m wide which fill fault fractures within upper amphibolite to epidote amphibolite facies precambrian banded biotite gneiss the veins are mineralogically simple consisting of iron and base metal sulfides and electrum and are associated with weak hydrothermal alteration zones 0 5 m wide characterized by silicification and sericitization fluid inclusion data and equilibrium thermodynamic interpretation of mineral assemblages indicate that the quartz veins were formed at temperatures between 425 and 190 c from relatively dilute aqueous fluids 4 5 13 8 wt equiv nacl containing variable amounts of co2 and ch4 evidence of fluid unmixing co2 effervescence during the early vein formation indicates approximate pressures of 1 3 1 9 kbars corresponding to minimum depths of 5 7 km under a purely lithostatic pressure regime gold deposition occurred mainly at temperatures between 345 and 240 c likely due to decreases in sulfur activity accompanying fluid unmixing the 34s values of sulfide minerals 3 0 to 5 3 and the measured and calculated o h isotope compositions of ore fluids 18o 5 7 to 7 6 74 to 80 indicate that mesothermal gold mineralization at the samdong mine may have formed from dominantly magmatic hydrothermal fluids possibly related to intrusion of the nearby ilmenite series kimcheon granite of late jurassic age

thermomechanics of shallow magma chamber pressurization implications for the assessment of ground deformation data at active volcanoes abstract in this study we utilize thermomechanical models to investigate how magma chambers overpressurize as the result of either magmatic recharge or volatile exsolution by implementing an adaptive reservoir boundary condition we are able to track how overpressure dissipates as the magma chamber expands to accommodate internal volume changes we find that the size of the reservoir greatly impacts the resultant magma chamber overpressure in particular overpressure estimates for small to moderate sized reservoirs 1 10 km 3 are up to 70 lower than previous analytical predictions we apply our models to santorini volcano in greece where recent seismic activity and ground deformation observations suggested the potential for eruption the incorporation of an adaptive boundary condition reproduces mogi flux estimates and suggests that the magma reservoir present at santorini may be quite large furthermore model results suggest that if the magma chamber is 100 km 3 overpressures generated due to the high magma flux may not exceed the strength of the host rock thus requiring an additional triggering mechanism for eruption although the adaptive boundary condition approach does not calculate the internal evolution of the magma reservoir it represents a fundamental step forward from elastic mogi models and fixed boundary solutions on which future investigations of the evolution of the magma can be built

differential response of zircon u pb isotopic systematics to metamorphism across a lithologic boundary an example from the hope valley shear zone southeastern massachusetts usa a detailed morphological chemical and isotopic study of zircons from a single outcrop of two mineralogically and chemically distinct units of the late precambrian ponaganset gneiss was undertaken to investigate the effects of mylonitization and metamorphism on u pb isotopic systematics late paleozoic amphibolite grade approx 600 c mylonitization of the ponaganset gneiss at this locality is associated with movement along the hope valley shear zone the response of zircon to metamorphism in each gneiss unit is distinct zircons in gray augen gneiss are uncorroded and not overgrown whereas zircons from fluorite bearing pink granitic gneiss are variably corroded and over 50 bear opaque overgrowths the zircon overgrowths are chemically distinct from the primary cores and contain high conentrations of hf u hree and th mylonite derived from the gray gneiss contains only a small population of hf u rich metamorphic zircon but zircons in the pink gneiss derived mylonite are dominated by the hf u rich metamorphic component in terms of their u pb isotopic systematics overgrowth free zircons from both units are markedly discordant gray 10 20 pink 35 but overgrown zircons from the pink gneiss are up to 70 discordant zircons from the mylonites yield younger pb pb and u pb ages than those of the protolith gneisses and isotopic data from each gneiss mylonite pair define a linear array on concordia plots upper intercept ages of the gray gneiss 621 27 ma and the pink gneiss 635 50 ma indicate that the crystallization of both units was coeval and the lower intercept ages gray 270 92 ma pink 285 26 ma fall within the range of other published age estimates for alleghanian metamorphism in southeastern new england e g zartman et al 1988 new growth of zircon suggests that zr was mobile during metamorphism the presence of fluorite in the pink gneiss and a discontinuity in log left f text h text 2 text o mathord left vphantom f text h text 2 text o f text hf right kern nulldelimiterspace f text hf right values obtained from biotite across the pink gneiss gray gneiss contact indicates that dissolution and reprecipitation of zircon may be related to local variations in hf fugacity zircon dissolution reprecipitation in the pink gneiss and the lack of similar features in the contiguous gray gneiss suggests that the degree of isotopic perturbation of zircon during metamorphism is related to bulk chemistry fluid chemistry and or the degree of fluid rock interaction

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

la icp ms trace element analysis of arsenopyrite from the samgwang gold deposit south korea and its genetic implications abstract the samgwang deposit previously classified as an orogenic gold deposit consists of several structurally controlled auriferous quartz veins hosted by metasedimentary rocks of the precambrian gyeonggi massif south korea the gold at samgwang occurs as electrum commonly associated with arsenopyrite laser ablation inductively coupled plasma mass spectrometry la icp ms coupled with ore microscopy was conducted on au and trace elements distributed in arsenopyrite grains contained in quartz vein and wall rock samples resulting profiles for au co ni and sb were relatively flat and showed little variability indicating that the elements were relatively homogeneously distributed and exchanged via substitution in arsenopyrite while variability and noisy depth profiles inferred that pb was present as tiny inclusions or discrete particles furthermore measured gold concentrations were typically higher in arsenopyrite grains from laminated quartz veins avg 2 07 ppm than in grains from massive quartz veins avg 0 26 ppm and wall rock samples avg 0 33 ppm in the case of wall rock and massive quartz vein samples arsenopyrite grains of euhedral shape illustrate an element distribution pattern whereby au concentrations tend to decrease towards the rims of the analyzed grains in contrast the rims of arsenopyrite grains in laminated quartz vein samples recorded much higher au concentrations of up to 20 1 ppm with increasing pb bi and ag particularly within domains of fractured or recrystallized arsenopyrite grains the newly acquired la icp ms data along with textural evidence may be interpreted in terms of the release and remobilization of invisible gold that was originally locked up in the arsenopyrite this release is linked to late deformation and hydrothermal event during which the remobilized invisible gold was redeposited as electrum in addition there is evidence for the introduction of additional gold and other precious and base metals by the late stage hydrothermal fluids based on the above and in contrast to previous genetic models we propose a more complex metallogenic concept for samgwang in which the economically important gold enrichment process was genetically related to intrusive activity during the waning stages of jurassic to early cretaceous daebo orogenesis

crustal thickening by tectonic wedging of the ganderian rocks southern new england usa evidence from cataclastic zircon microstructures and u pb ages abstract zircon grains in granites from avalonian and ganderian rocks in southern new england host brittle internal structures that are interpreted here to show the host rocks to be allochthonous significant among these structures are inherited cores that are commonly fractured and even dismembered this intense fracturing is interpreted as reflecting an important cataclastic event the maximum age of fracturing is constrained to be younger than the age of the youngest broken magmatic core 360 4 ma the minimum age must be older than the oldest zircon rim that heals these fractures that is early permian the occurrence of cataclastic zircon requires that these rocks were relatively cold i e in the upper crust during the carboniferous and therefore were not involved in the pervasive high grade acadian metamorphism the present map pattern of inter tonguing high grade and low grade slices of peri gondwanan rocks shows that they were assembled by crustal scale tectonic wedging the consequent thickening ultimately led to anatexis in the lower slices during the permian thus evidence for cataclasis of zircon grains from the avalon and gander terranes of southern new england suggests that these peri gondwanan terranes remained outboard of laurentia during the well documented early devonian acadian orogeny and were first fully accreted to north america during the alleghanian permian orogeny

40 ar 39 ar dating of cleavage formation in tuffs during anchizonal metamorphism 40ar 39ar incremental release analyses were carried out on whole rock and constituent white mica illite rich size fractions 0 63 1 to 6 3 20 m within two very low grade penetratively cleaved metatuffs of contrasting anchizonal metamorphic grade northeastern rheinisches schiefergebirge federal republic of germany one sample from the upper anchizone displays internally concordant 40ar 39ar spectra with plateau ages ranging between ca 316 and 325 ma these are similar to conventional k ar ages determined for the whole rock and size fractions together the isotopic results suggest that cleavage formed at ca 320 ma during a concomitant very low grade metamorphism this is consistent with biostratigraphic controls which suggest that metamorphism and cleavage formation occurred during the westphalian

hydrothermal fluid origins in a fluorite rich mississippi valley type district combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the south pennine ore field united kingdom the south pennine peak district ore field united kingdom is host to several fluorite rich mississippi valley type deposits and was chosen for study as an analogue to the illinois kentucky fluorspar district united states the study was undertaken to test the idea that the large scale carbonate dissolution and fluorite rich mineralogy characteristic of both districts may require a magmatic source of hf the data also provide constraints for water rock interactions and potential fluid sources relevant to the local geology of the south pennine ore field samples were studied from two of the largest and most economically important deposits within the south pennine ore field the hucklow edge and dirtlow rakes in vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ar ar kr and the halogens cl br i this was achieved simultaneously by noble gas mass spectrometry ar ar methodology and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations in addition he isotope analyses were obtained from unirradiated fluorite the he he ratio of the pennine ore fluids 0 1 ra where ra atmospheric he he ratio of 1 4 10 is significantly lower than the maximum value recorded in the illinois kentucky fluorspar district 0 35 ra kendrick et al 2002 this volume indicating a crustal fluid source and supporting existing basinal brine models the low ar ar ratios with most 50 to 60 percent halite dissolution water br cl mol ratio 0 57 0 92 10 the salinity of fluids included in the main stage of the hucklow edge mineralization avg of 22 wt nacl equiv places an upper limit on the extent of meteoric recharge at 15 vol percent a secondary vein present at hucklow edge has a lower salinity of 40 m y a time scale compatible with models in which fluids were derived from small local basins such as the widmerpool and edale gulfs

fluid inclusions in pre ore minerals from the carbonate hosted mercury deposits in the espadan ranges eastern spain abstract the fluids associated with pre ore minerals in the carbonate hosted mercury veins from the espadan ranges eastern spain have been studied using microthermometry cryo sem eds raman spectroscopy and crush leach analyses in order to determine their origin and the processes responsible for mineralization three primary fluid inclusion types have been found in quartz and dolomite 1 type s composed of liquid vapour mainly co 2 halite 2 type s v composed of liquid high density co 2 double bubble halite and 3 type v composed of high density co 2 n 2 mixtures type s fluid inclusions are preferentially trapped in betxi type veins characterized by the presence of hydrothermal dolomite whereas type v fluid inclusions are trapped almost exclusively in eslida type veins which were without dolomite from these data two different fluids can be inferred to occur during the period of formation of the veins 1 a complex polysaline brine of nacl kcl cacl 2 mgcl 2 so 4 2 h 2 o composition with a salinity of up to 33 eq wt nacl and a 2 co 2 n 2 rich fluid the brine halogen composition points to its secondary origin caused by the dissolution of underlying marine evaporites it is thought that these deposits were formed during jurassic or cretaceous rifting periods as a consequence of fluid mixing between a high salinity secondary brine and connate waters the generation of a co 2 n 2 rich phase caused the pressure increase of the fluids that favoured the hydraulic fracturing of the enclosing rock dolostone the origin of this volatile rich phase probably occurred due to the oxidation and thermochemical breakdown of the organic matter contained in the host rock this event is recorded by the coetaneous trapping of both aqueous and carbonic fluids in quartz crystals the formation conditions for the hypogene sulphide paragenesis are obscure but the coincidence between the preferential trapping of type v fluid inclusions the absence of hydrothermal dolomite and the major abundance of mercury in eslida type veins is thought to be linked to a mercury fractionation event to the vapour phase during the release of the volatiles

a fluid inclusion and stable isotope study of 200 ma of fluid evolution in the galway granite connemara ireland fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the caledonian galway granite these fluids were examined by petrography microthermometry chlorite thermometry fluid chemistry and stable isotope studies the earliest fluid was a h2o co2 nacl fluid of moderate salinity 4 10 wt nacl eq that deposited late magmatic molybdenite mineralised quartz veins v1 and formed the earliest secondary inclusions in granite quartz this fluid is more abundant in the west of the batholith corresponding to a decrease in emplacement depth within veins and to the east this fluid was trapped homogeneously but in granite quartz in the west it unmixed at 305 390 c and 0 7 1 8 kbar homogeneous quartz 18o across the batholith 9 5 0 4 n 12 suggests v1 precipitation at high temperatures perhaps 600 c and pressures 1 3 kbar from magmatic fluids microthermometric data for v1 indicate lower temperatures suggesting inclusion volumes re equilibrated during cooling the second fluid was a h2o nacl kcl low moderate salinity 0 10 wt nacl eq moderate temperature 270 340 c high d 18 2 low 18o 0 5 2 0 fluid of meteoric origin this fluid penetrated the batholith via quartz veins v2 which infill faults active during post consolidation uplift of the batholith it forms the most common inclusion type in granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of biotite and hornblende sericitization and saussuritization of plagioclase and reddening of k feldspar the salinity was generated by fluid rock interactions within the granite within granite quartz this fluid was trapped at 0 5 2 3 kbar having become overpressured this fluid probably infiltrated the granite in a meteoric convection system during cooling after intrusion but a later age cannot be ruled out the final fluid to enter the granite and its host rocks was a h2o nacl cacl2 kcl fluid with variable salinity 8 28 wt nacl eq temperature 125 205 c d 17 to 45 18o 3 to 1 2 13cco2 19 to 0 and 34ssulphate 13 23 that deposited veins containing quartz fluorite calcite barite galena chalcopyrite sphalerite and pyrite v3 correlations of salinity temperature d and 18o are interpreted as the result of mixing of two fluid end members one a high d 17 to 8 moderate 18o 1 2 2 5 high 13cco2 4 low 34ssulphate 13 high temperature 205 230 c moderate salinity 8 12 wt nacl eq fluid the other a low d 61 to 45 low 18o 5 4 to 3 low 13c 10 high 34ssulphate 20 23 low temperature 80 125 c high salinity 21 28 wt nacl eq fluid geochronological evidence suggests v3 veins are late triassic the high d end member is interpreted as a contemporaneous surface fluid probably mixed meteoric water and evaporated seawater and or dissolved evaporites whereas the low d end member is interpreted as a basinal brine derived from the adjacent carboniferous sequence this study demonstrates that the galway granite was a locus for repeated fluid events for a variety of reasons from expulsion of magmatic fluids during the final stages of crystallisation through a meteoric convection system probably driven by waning magmatic heat to much later mineralisation concentrated in its vicinity due to thermal tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic heat has abated

the signature of depth dependent viscosity structure in post seismic deformation summary geodetic observations of post seismic ground motion reflect the integrated effects of several relaxation mechanisms to evaluate the viscous relaxation component accurately the crustal viscosity structure beneath a region must be estimated in this study using a 3 d finite element model we describe the viscoelastic relaxation that follows an instantaneous strike slip faulting event in a crustal layer whose viscosity decreases exponentially with depth at any surface observation point the depth dependent viscosity ddv model displacement history closely fits the history predicted for a uniform viscosity unv model the difference can be minimized to obtain the unv viscosity u that best fits the ddv model displacement at that location the differences in displacement histories between ddv and best fit unv models are minor but depend on distance from fault the viscosity gradient and the fault configuration in the near field the ddv model prediction can be well approximated by the unv model regardless of the viscosity gradient and fault configuration on the other hand in the far field small differences between ddv model and best fit unv model become apparent the displacements are controlled by greater viscosities in later phases and the differences are greater for ddv models with greater viscosity gradient the more important result we obtain is that apparent viscosity u decreases with distance from the fault and its rate of decrease is directly diagnostic of the vertical viscosity gradient this result points to a practical method of analysing post seismic ground displacement data for the variation of viscosity in the ductile crust the apparent crustal viscosity should be determined at a series of points at increasing distance from the fault the variation of apparent viscosity with distance can then be used to directly infer the vertical gradient of viscosity in the crust

the distribution style and intensity of alleghanian metamorphism in south central new england petrologic evidence from the pelham and willimantic domes abstract alleghanian metamorphism in south central new england is characterized by late pennsylvanian documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm kyanite mathrm muscovite mathrm staurolite end document grade heterogeneous reconstitution of migmatitic documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepack

mechanics of active magmatic intraplating in the rio grande rift near socorro new mexico 1 we investigate long term deformation due to the socorro magma body smb one of the largest active intrusions in the earth s continental crust using interferometric synthetic aperture radar insar observations and finite element simulations insar data spanning 15 years 1992 2007 indicate that the magma body is associated with a steady crustal uplift at a rate of about 2 mm yr 1 previous work showed that while the pattern of surface uplift is consistent with an elastic inflation of a large sill like magma body the smb could not have formed via steady elastic inflation because the latter would be outpaced by magma solidification we resolve this problem using coupled thermo visco elastic models and place constraints on the intrusion history as well as the rheology of the ambient crustal rocks we demonstrate that observations rule out the linear maxwell response of the ductile crust but are consistent with laboratory derived power law rheologies our preferred model suggests that the age of the smb is of the order of 103 years and that the apparent constancy of the present day uplift may be due to slow heat transfer and ductile deformation in a metamorphic aureole of a giant sill like magma intrusion rather than due to a steady increase in the magma overpressure the smb is a contemporaneous example of magmatic intraplating a process by which large volumes of mafic melt stall and spread at midcrustal depths due to density or rheology contrasts

genetic environment of germanium bearing gold silver vein ores from the wolyu mine republic of korea the wolyu mine is one of the largest vein type gold silver bearing epithermal systems in the youngdong district and is the first gold silver deposit in korea found to contain significant germanium in the form of argyrodite ag8ges6 mineralized veins 78 9 1 2 ma crosscutting late cretaceous hostrock tuff and quartz porphyry 81 5 1 8 ma consist of three stages of quartz and carbonates the first of which contains pyrite basemetal sulfides and au ag minerals stage i au ag ge mineralized veins show a systematic variation of mineral assemblage with time 1 quartz pyrite 2 quartz pyrite sphalerite electrum argentite 3 carbonate quartz sphalerite electrum argentite 4 carbonate native silver argentite ag sulfosalts argyrodite sphalerite calculated values of temperature and sulfur activity are assemblage 1 360 280 c and 10 7 10 10 2 280 210 c and 10 10 10 14 3 210 180 c and 10 14 10 16 4 180 155 c and 10 17 10 18 these data the frequent association of gold with sulfides and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time within the main ag au ge mineralization d and 18o values decrease with the transition from quartz to carbonate deposition from 78 and 2 8 to 90 and 8 7 respectively indicating increasing involvement mixing of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow 370 600 m wolyu epithermal system

permian clockwise rotations of the ebro and corso sardinian blocks during iberian armorican oroclinal bending preliminary paleomagnetic data from the catalan coastal range ne spain abstract paleomagnetic investigations of early permian and triassic magmatic rocks from catalan coastal ranges provide three magnetic directions which are interpreted as primary magnetizations and partly as overprints the succession of magnetic directions is interpreted in terms of a succession of large scale clockwise rotations which bring the whole assembly of pyrenees catalonia corsica sardinia and maures esterel massifs from the southeast of the massif central to the west during permian this major movement is associated with clockwise rotation of northern limb of the iberian orocline during latest carboniferous and early permian 305 290 ma subsequently permian large scale dextral transtensional extensional shearing operated along aquitanian shear belt between the massif central in the northeast and the iberian variscan massifs in the southwest the latest phase of the rotation in the late permian early triassic is associated with alkaline magmatism probably linked to neo tethys opening activity in western europe

deformation of upper carboniferous coal measures in the sydney basin evidence for late alleghanian tectonism in atlantic canada upper carboniferous stephanian coal measures of the sydney basin are deformed by reverse faults and folds with dips of up to 50 on the limbs these structures represent compressional or transpressional events donkin episode of unknown sequence and timing offshore swath bathymetry data indicate that northwest striking reverse faults are folded by prominent northeast trending folds vitrinite reflectance patterns of oriented coal samples from the fold limbs are uniaxial negative with minimum reflectance axes rmin near normal to bedding and fanning across fold axes this pattern implies that the bulk of coalification took place through burial compaction without directed horizontal stress prior to the deformation that produced the folds slight divergence between rmin axes and poles to bedding may reflect slight tilting associated with differential subsidence or early reverse faulting before or during coalification or may lie within analytical error one moderately biaxial sample suggests that some deformation accompanied coalification locally available apatite fission track data for the sydney basin indicate that cooling of the coal measures to below 100 20 c was underway by the middle to late triassic or earlier because cooling implies that coalification was largely complete the fission track results are compatible with latest paleozoic or early mesozoic deformation we infer that the donkin episode represents late alleghanian permian compression within the appalachian orogen if so the sydney structures are manifestations of a little known tectonic episode in atlantic canada however mesozoic cenozoic deformation cannot be ruled out resume les series houilleres du bassin de sydney carbonifere superieur stephanien sont deformees par des failles inverses et des plis deverses dont les flancs atteignent des pendages de 50o ces structures representent des evenements de compression ou de transpression episode donkin dont la sequence et la synchronisation sont inconnues les donnees de bathymetrie par secteurs au large indiquent que les failles inverses a direction nord ouest sont pliees par des plis proeminents a tendance nord est les patrons du facteur de reflexion de la vitrinite provenant d echantillons de charbon orientes preleves sur les flancs des plis sont uniaxes negatifs avec des axes de reflectance minimum rmin presque perpendiculaires au litage et se dispersant en travers des axes de plis ce patron implique que la plus grande part de la carbonisation a eu lieu par compaction d enfouissement sans contrainte horizontale directe avant la deformation qui a produit les plis la legere divergence entre les axes rmin et les poles du litage pourrait refleter un leger basculement associe a une subsidence differentielle ou a des failles inverses precoces avant ou durant la carbonisation ou encore cette divergence pourrait etre a l interieur de la fourchette de l erreur analytique notre echantillon moderement biaxe suggere qu une certaine deformation ait localement accompagne la carbonisation pour le bassin de sydney les donnees disponibles de datation par traces de fission sur l apatite indiquent que le refroidissement des series houilleres a des temperatures inferieures a 100 20 oc etait deja en cours au trias moyen a tardif ou plus tot puisque le refroidissement implique que la carbonisation etait presque terminee les resultats de datation par traces de fission concordent avec la deformation au paleozoique terminal ou au mesozoique precoce nous concluons que l episode donkin represente une compression a l alleghanien tardif permien a l interieur de l orogene des appalaches si tel est le cas les structures de sydney sont des evidences d un episode tectonique peu connu au canada atlantique cependant une deformation au mesozoique cenozoique ne peut etre rejetee d emblee

chronology of magmatism and mineralization in the kassandra mining area greece the potentials and limitations of dating hydrothermal illites abstract various geochronological methods u pb rb sr and k ar have been applied to constrain the timing of magmatism and polymetallic mineralization in the kassandra mining district northern greece these data provide the first geochronological evidence that porphyry copper mineralization proximal copper skarns and distal high temperature carbonate hosted pb zn ag au replacement ores formed contemporaneously and probably within less than 2 million years polymetallic mineralization is temporally related to the emplacement of granodioritic to quartz dioritic porphyries 24 25 ma that postdate the largest post tectonic intrusion of the area the stratoni granodiorite 27 9 1 2 ma andesite porphyry dikes which crosscut the pb zn ag au ores and associated alterations represent the last magmatic phase in the area 19 1 0 6 ma and did not contribute to metal concentration the combination of k ar rb sr and oxygen isotope studies of hydrothermal illite rich clays and careful granulometric analysis constrains the reliability of these geochronological methods and emphasizes the importance of characterizing the post formational history of the sample we identify various processes which partly disturbed the k ar and rb sr system of some clays such as retrograde alteration by heated meteoric waters superimposed supergene illitization and resetting of both isotopic systems due to a hydrothermal overprint related to the intrusion of the andesite porphyry our data however suggest that diffusive ar loss from the finest clay fractions k ar system conventional k ar ages of 200 c therefore do not give reliable formation ages the loss of ar may be used to model the cooling history of the hydrothermal system applying the concept of closure temperatures dodson 1973 40k 40arrad isochrons of natural coarser grained 0 6 m size fractions of illites from single samples even when slightly contaminated with feldspars may yield meaningful ages either of the formation or of a reheating event the rb sr dating of hydrothermal clays is sensitive to contamination by adsorbed strontium which may not be cogenetic with the clay as well as feldspars which may not have been homogenized isotopically by the illitization process

regional variations in the lead isotopic composition of galena from southern korea with implications for the discrimination of lead provenance abstract this study presents a comprehensive database n 215 of lead isotopes in galena from the southern korean peninsula using new and published data of the 69 metal mines examined predominantly skarn and hydrothermal type pb zn au ag cu deposits were observed and were associated with mesozoic magmatic activities galena samples from each geotectonic unit showed discrete lead isotopic signatures the gyeongsang basin samples were characteristically unradiogenic and had restricted variations in lead isotopic composition 206pb 204pb 18 16 18 59 207pb 204pb 15 48 15 64 208pb 204pb 37 87 38 77 their 208pb 204pb range indicated an involvement of source materials less thorogenic than the associated granites the galena samples from cambro ordovician carbonate rocks of the northeastern yeongnam massif and eastern taebaeksan basin had the most radiogenic 206pb 204pb 19 28 0 14 and 207pb 204pb 15 833 0 027 ratios their lead isotopic trend indicated a combined contribution of ore lead from granitic magmas precambrian basements and overlain host rocks less radiogenic galena samples from the middle to southwestern parts of the yeongnam massif and okcheon belt showed limited lead isotopic variations 206pb 204pb 18 332 0 065 207pb 204pb 15 693 0 012 208pb 204pb 38 93 0 07 on average probably resulted from mixing with a common crustal basement the differences in lead isotopes between the radiogenic and unradiogenic groups from the yeongnam massif and okcheon belt may reflect the spatial dissimilarity of involved crustal rocks the old crust appears to have significantly contributed ore lead to galenas from the western gyeonggi massif but the geochronological meaning of their steep 207pb 204pb 206pb 204pb trend is not clear the comprehensive database constructed by the present study suggests that lead province in the southern korean peninsula may be subdivided into four discrete zones linear discriminant analysis showed that more than 90 of the compiled data were correctly reclassified within their a priori zones such discrimination may be useful for a wide range of applications including mineral exploration archaeological correlation and environmental characterization

fluid inclusion evidence for basement decompression during permo triassic extension se new england usa co2 bearing fluid inclusions in strongly lineated but weakly foliated late precambrian gneisses within the hope valley shear zone of connecticut and rhode island are of mixed composition xco2 0 1 7 wt nacl equivalent and variable density 0 59 0 86 g ml and occur mainly as isolated inclusions also present are dilute 3 wt nacl equivalent aqueous inclusions which occur on healed fractures related to greenschist facies retrograde metamorphism isochores for dense isolated co2 bearing inclusions indicate pressures of 7 5 9 kbar at 500 600 c the estimated temperature conditions of peak metamorphism published 40ar 39ar hornblende plateau age spectra indicate cooling through about 500 c at 265 5 ma isochores for low density co2 bearing inclusions and aqueous inclusions intersect at the conditions of retrograde metamorphism 325 400 c and indicate pressures of 3 4 kbar published 40ar 39ar biotite plateau ages indicate cooling through about 300 c at 250 5 ma these data define a p t uplift curve for the region which is convex towards the temperature axis and indicate uplift rates between 0 4 and 3 3 mm year in permian time exhumation of basement gneisses was coeval with normal west down motion along the regional basement cover contact honey hill lake char willimantic fault system and is interpreted as due to post orogenic extensional collapse of the alleghanian orogeny

alleghanian polyphase deformation of the hope valley shear zone southeastern new england structural petrographical and rb sr isotopic studies in the highly deformed basement rocks of southern rhode island have allowed the identification of the southern continuation of the hope valley shear zone hvsz previous work recognized the hvsz as an alleghanian tectonic boundary separating the distinct late precambrian esmond dedham and hope valley terranes in southeastern new england two important components of the esmond dedham terrane the late precambrian ponaganset gneiss and the devonian scituate granite gneiss now have been traced with structural continuity into southern rhode island the distribution of these gneissic units and their structures shows that the southern segment of the hvsz has been strongly deformed abruptly deflecting it from a nw se orientation to a n s trend the deflection of the hvsz marks an abrupt structural boundary between two distinct regionally developed mineral lineation domains a northwestern domain with north to nnw trends characteristic of most of the hvsz and a southeastern domain with ne trends structural relations suggest that all mineral lineations were originally parallel along the hvsz with a north to nnw trend the deflection formed during a subsequent phase of ductile right lateral shear producing a clockwise rotation of both lineations and the hvsz in southern rhode island thus basement gneisses in southeastern new england have suffered polyphase alleghanian deformation at high metamorphic grades it has been argued that during the late paleozoic southern new england was located in a structural transition zone between convergent tectonics in the central and southern appalachians and wrench tectonics in the northern appalachians the structural link between these two distinct tectonic regimes is an e w right lateral transcurrent fault the late dextral shear deformation described in southern rhode island basement rocks appears to have resulted from right lateral movement at depth within this transcurrent fault zone

discussion on gold deposits of the tapajos and alta floresta domains tapajos parima orogenic belt amazon craton brazil by santos jos groves di hartmann la moura ma mcnaughton nj mineralium deposita 36 278 299 2001

a shear zone origin for alleghanian permian multiple deformation in eastern massachusetts the area around worcester massachusetts has been used to determine which deformational and metamorphic features are due to the alleghanian permian orogeny and which are pre alleghanian isolated fault bounded inliers of carboniferous rocks display evidence of a single metamorphism and the formation of two prominent cleavages the first cleavage formed synchronously with metamorphism pre carboniferous metasedimentary rocks have been affected by two metamorphisms and contain three prominent cleavages the initial cleavage formed during the first metamorphism and the second cleavage formed during the second retrogressive metamorphism thus the second two cleavages and the second metamorphism in pre carboniferous rocks are interpreted as alleghanian normal displacements on two distinct faults are bracketed by the formation of the first and second alleghanian cleavages the initial faulting along the newly defined wachusett mylonite zone wmz formed a wide zone of ductile mylonites which dips moderately to the northwest and contains elongation lineations which trend northwest the second faulting along the clinton newbury fault cnf occurred along a steeply inclined plane which cuts the wmz mylonites and contains a thin zone of phyllonites and mylonites which have elongation lineations which trend west alleghanian cleavages and metamorphism are confined to a mappable zone which is approximately 15 km wide where well defined this zone is interpreted as a ductile shear zone which moved twice forming the first and second alleghanian cleavages early formed pre alleghanian metamorphic minerals are retrograded to hydrous phyllosilicates and new hydrous minerals formed in the shear zone indicating that it was a pathway for fluid flow the initial motion was left lateral with a thrust component the second cleavage formed during top to the northwest normal displacements thus the history of alleghanian tectonism in this area began with sinistral faulting and then included three displacements along normal faults or shear zones this suggests that the strain history included two distinct episodes with the second experiencing slightly different strain orientations at different times resulting in first wmz normal motion then cnf normal motion and finally normal displacements related to the second alleghanian cleavages this history agrees well with other work on the nature of the alleghanian orogeny in the northeast united states

cretaceous epithermal gold silver mineralization and geodynamic environment korea abstract epithermal precious metal mineralization in the korean peninsula mainly occurred along nne trending major strike slip fault systems that are associated commonly with formation of pull apart basins and major volcanic activity during the cretaceous sedimentation in the basins was initiated in the hauterivian and continued into the albian whereas much of the volcanism occurred sporadically from ca 110 to 50 ma with a major episode between ca 90 and 70 ma epithermal au ag mineralization in korea took place between approximately 100 and 70 ma overlapping with the shallow magmatic activity styles of epithermal au ag deposits in korea include those of the mugeug type found in sediment dominant basins in the central portion and the haenam type in volcanic dominant basins in the southwest epithermal au ag deposits associated with the volcanic dominant basins in the southern korea generally formed at very shallow crustal levels

imaging a low viscosity zone beneath the kutcharo caldera eastern hokkaido japan using geodetic data abstract geodetically observed volcano deformation has been analysed in terms of either elastic or viscoelastic crustal rheology for which the presence of magma has usually been considered as a deformation source from a rheological viewpoint however a magma and the peripheral rocks it influences are presumably low viscosity materials which allows detection of the presence of magma as a zone that has rheologically less strength in this study using a 3 dimensional finite element model that introduces a rectangular low viscosity zone lvz into relatively high viscosity crust the response of the linear maxwell viscoelastic crust to the emplacement of a spheroidal sill is adopted for interferometric synthetic aperture radar insar data of the kutcharo caldera eastern hokkaido japan to image a spatial crustal viscosity variation the observed temporal displacement at the surface point where the line of sight los displacement is largest in the deformation field requires the lvz to have a spatially uniform viscosity of 4 5 10 17 pa s the lvz is also required to be present immediately below a 5 km elastic layer down to mid crustal depths or deeper with a horizontal extent of at least 10 km models with acceptable minimum sizes of lvz are found to satisfy the overall temporal displacement field with root mean square misfits of less than 2 cm the geodetic data reasonably accept the presence of an lvz beneath the kutcharo caldera that is consistent with the magnetotelluric image of the accumulated magma providing the mechanical aspect of the low resistivity domain the lvz model behaviour suggests an important implication that the accumulation of magma in the middle to lower crust is detectable using geodetic data after magma emplacement into the upper crust where the deformation rate represents the degree of magmatic influence on the crustal viscosity

p t t paths and differential alleghanian loading and uplift of the bronson hill terrane south central new england late paleozoic u pb ages of sphene and 4 0 ar 3 9 ar cooling ages of amphibole and muscovite from rocks of the bronson hill terrane in connecticut and central massachusetts reflect a late paleozoic alleghanian overprinton acadian metamorphic rocks prograde alleghanian sphenes crystallized during the late pennsylvanian and eliminate the possibility that amphibole ages reflect delayed permian cooling from devonian acadian metamorphism fourteen new amphibole ages from connecticut form a north to south trend of decreasing age from 294 to 245 ma while in massachusetts four new amphibole ages together with three others from the literature produce a random carboniferous pattern seven new muscovite ages support existing data indicating uniform cooling throughout the bronson hill terrane through 350 c in the early triassic the rate of permian cooling defined by amphibole muscovite pairs increases from 4 c my in northern connecticut to 50 c my near long island sound hinged loading and hinged but delayed exhumation in the southern part of the bronson hill terrane with the hinge in central connecticut explain these ages and cooling rates as well as a southerly increasing metamorphic field gradient one dimensional thermal modeling indicates that loading of bronson hill rocks must have begun by the late mississippian the time of peak alleghanian metamorphic temperature decreases southward from early permian in northern connecticut to late permian to the south these results demonstrate that the metamorphic effects of the alleghanian orogeny are not restricted to the avalon terrane of southeastern new england on the contrary the alleghanian orogeny reset 4 0 ar 3 9 ar mineral ages recrystallized minerals partially melted felsic rocks and transposed fabrics at least as far west as the bronson hill terrane in south central new england

40ar 39ar ages of detrital muscovite and whole rock slate phyllite narragansett basin ri ma usa implications for rejuvenation during very low grade metamorphism late pennsylvanian sedimentary rocks in the narragansett basin were metamorphosed lower anchizone to sillimanite grade during late paleozoic regional metamorphism at ca 275 280 ma twenty five variably sized concentrates of detrital muscovite were prepared from samples collected within contrasting low grade areas diagenesis lower greenschist facies microprobe analyses suggest that the constituent detrital grains are not chemically internally zoned however some grains within several concentrates display very narrow 25 m compositionally distinct low grade epitaxial peripheral overgrowths detrital muscovite concentrates from the lower anchizone are characterized by internally concordant 40ar 39ar age spectra which define plateau ages of ca 350 360 ma these are interpreted to date post devonian acadian cooling within proximal source areas concentrates from lower grade sectors of the middle anchizone display slightly discordant spectra in which apparent ages systematically increase from ca 250 275 ma to define intermediate and high temperature plateaus of ca 360 400 ma detrital muscovite within samples from higher grade sectors of the middle anchizone and the upper anchizone are characterized by systematic low age discordance throughout both low and intermediate temperature increments high temperature ages only range up to ca 330 ma six size fractions of detrital muscovite from a sample collected within the lower greenschist facies have similarly discordant spectra in which apparent ages increase slightly throughout the analyses from ca 250 ma to 275 ma the detrital muscovite results are interpreted to reflect variable affects of late paleozoic regional metamorphism however it is uncertain to what extent the systematic low age spectra discordance reflects intracrystalline gradients in the concentration of 40ar and or experimental evolution of gas from relatively non retentive epitaxial overgrowths however low age discordance occurs regardless of the extent of epitaxial overgrowth intermediate temperature increments evolved during 40ar 39ar whole rock analyses of five slate phyllite samples are characterized by internally consistent apparent k ca ratios these are attributed to gas evolved from constituent very fine grained white mica samples from lower grade portions of the middle anchizone are characterized by intermediate temperature apparent ages which systematically increase from ca 275 300 ma to ca 360 375 ma before evolution of a high temperature contribution from detrital plagioclase feldspar this age variation may reflect partial late paleozoic rejuvenation of very fine grained detrital material with a source age similar to that for the detrital muscovites slate phyllite samples from upper sectors of the middle anchizone and from the upper anchizone were completely rejuvenated during late paleozoic metamorphism and record intermediate and high temperature plateau ages of ca 270 290 ma these data document that metamorphic conditions of the lower to middle biotite zone ca 325 350 c are required to completely rejuvenate intracrystalline argon systems of detrital muscovite therefore the 40ar 39ar dating method may be useful in determination of detrital muscovite provenance and in resolution of the metamorphic evolution of low grade terranes

contrasting p t t paths thermochronologic evidence for a late paleozoic final assembly of the avalon composite terrane in the new england appalachians strongly contrasting pressure temperature time paths for the avalon composite terrane and the structurally overlying putnam nashoba zone in eastern new england obtained from thermochronologic and thermobarometric data are best explained by a late paleozoic underthrusting of cover rocks by the avalon composite terrane we present new ar and u pb thermochronologic data that show that in the southern hope valley zone permian 280 ma anatectic metamorphic conditions of 700 c and 6 kbar were quenched by relatively rapid cooling 12 c m y and exhumation 0 5 km m y for 40 m y in contrast peak metamorphic conditions in the putnam nashoba zone predate silurian intrusions and slower cooling 3 5 c m y began at about 400 ma one dimensional thermal modeling suggests that these two belts were not in thermal equilibrium during the permian metamorphism of the avalon composite terrane because of the absence of high grade alleghanian metamorphism in rocks overlying the avalon terrane we conclude that high grade alleghanian metamorphism in the avalon terrane occurred east of rocks now overlying it and that significant motion between avalon and this cover occurred after peak alleghanian metamorphism similarly contrasting metamorphic histories between avalon inliers willimantic window massabesic complex gneiss pelham dome and their cover rocks reveals the regional significance of this boundary the core rocks all show permian cooling but the cover rocks show post acadian cooling ages decreasing from east to west to the pelham area where hornblende ages in avalon and cover differ by only 35 rather than 80 m y model calculations show that thermal equilibrium between instantaneously thrusted blocks of rocks is generally obtained in tens of millions of years consequently underthrusting of avalon is constrained to be middle mississippian or younger because the leading edge of the underthrusting block would have been heated the longest and would have most closely approached thermal equilibrium with its cover core rocks of the pelham dome must have been relatively close to this leading edge thus carboniferous to permian underplating from a generally eastward direction best explains these thermochronologic relationships

viscoelastic crustal response to magma supply and discharge in the upper crust implications for the uplift of the aira caldera before and after the 1914 eruption of the sakurajima volcano abstract crustal viscoelasticity is expected to influence volcano deformation as the crustal viscosity at volcanoes is lowered from regional values by higher crustal temperatures and the eventual presence of magma in this study we examine viscoelastic crustal response to continuous magma supply into and sudden discharge from a sill emplaced in the upper crust using a three dimensional 3 d finite element model composed of an elastic layer underlain by a linear maxwell viscoelastic layer with spatially uniform viscosity we find that viscoelastic response to sill deflation due to magma discharge is an important driving force for post eruption surface displacement influenced both by how much viscoelastic relaxation occurs in response to sill inflation due to magma supply in the pre eruption period and by the amount of co eruptive sill deflation following an eruption the surface elevation is always recovered later than the sill volume because the viscoelastic response to the sill inflation detracts from the uplift we apply this viscoelastic model to geodetic observations in the aira caldera southern kyushu japan over a time span of more than 100 yr it is found that a sill emplacement with constant inflation rate can well explain the observed first order exponential like surface recovery after the 1914 eruption until 1975 if the effective crustal viscosity is 5 10 18 pa s the sill emplacement with an equatorial radius of 2 km occurs at a depth of 11 km and the sill is deflated by 0 4 km3 during the 1914 eruption 4 times less than the eruptive volume the sill emplacement is also required to have begun 50 yr before the 1914 eruption with a constant inflation rate of 0 009 km3 yr in the post eruption period the accumulation of magma in the sill during the first 50 yr is lower than that estimated by an elastic model but larger thereafter it is necessary to introduce temporal variation of the inflation rate for higher order improved fitting to the geodetic data after 1975 our results suggest that geodetic signals observed before and after magma discharge due to an eruption need to be revisited considering the effects of crustal viscoelasticity

paleomagnetism and potassium argon age of the messejana dike portugal and spain angular limitation to the rotation of the iberian peninsula since the middle jurassic abstract a paleomagnetic and potassium argon dating investigation has been carried out on a 530 km long dike system which transects the western iberian peninsula in a northeasterly direction the k ar age determinations were made on mineral separates exclusively they range between 160 and 200 ma and the authors suppose that this reflects the actual time interval of the intrusion in accord with previous results the paleomagnetic pole derived from 12 sites regularly distributed along the dike 71 n 236 e coincides well with other mesozoic paleomagnetic poles from the western africa a contemporaneous pole from stable europe is tentatively deduced from african and north american late triassic early jurassic poles using different reconstruction models around the north atlantic ocean the divergence between this pole and the iberian pole corresponds to the result obtained for permian poles

geochemistry of syntectonic crustal fluid regimes along the lithoprobe southern canadian cordillera transect in conjunction with the lithoprobe southern canadian cordillera program an extensive examination of geochemical indicators of origins movement chemical evolution and economic significance of paleocrustal fluids was conducted the study area covers approximately 360 000 km2from the canadian rockies to vancouver island research incorporated petrological mineralogical fluid inclusion 18o d 13c and rb sr studies of samples of quartz carbonate veins and other rock types the results of the study document a variety of pre syn and postorogenic crustal fluid events in the rockies a major pre laramide hydrothermal event was identified which was comprised of a west to east migration of warm saline brines this was followed by a major circulation of meteoric water in the rockies during laramide uplift in the southern omineca extensional zone convecting surface fluids penetrated to the brittle ductile transition at 350 450 c and locally into the underlying more ductile rocks a principal c

kar ages of clay size concentrates from the mineralisation of the pedroches batholith spain and evidence for mesozoic hydrothermal activity associated with the break up of pangaea abstract the k ar ages of 32 clay concentrates extracted from samples of ore gangue and wallrock associated with mineralisation in the pedroches batholith lie in the range 119 285 ma although some of the mineralisation is of permian age more than half of the ages lie between 210 and 230 ma and indicate a hydrothermal event at this triassic time a comparison with age data for mineralisation and certain anorogenic magmatism in other areas of the north atlantic reveals a consistent pattern of a major event at ca 210 230 ma and a minor event at ca 160 ma with little cretaceous or tertiary activity it is proposed that the ca 210 230 ma event was related to an initial rapid fracturing of the crust associated with the break up of pangaea which was related with an increase in the geothermal gradient and penetration of the deep crust by surface waters which returned via both new and rejuvenated fissure systems

semi brittle deformation within the alpine fault zone new zealand abstract this paper reports the results of an attempt to identify the deformation micromechanisms in the brittle ductile transition zone of the alpine fault new zealand characterization of sequentially developed microstructures was carried out using optical microscopy hvem and stem analysis it was found that the transition zone corresponds to a broad zone of retrogression produced initially by microcracking and fluid infiltration the non catastropic nature of the fracturing indicates that fluid enhanced sub critical cracking is a significant crustal deformation mechanism after the initial phase of retrogression both ductile and brittle processes coexist and cyclically alternate in response to stress cycling the relative importance of macroscopic brittle processes may decrease with time as more ductile minerals especially phyllosilicates develop during continued retrogression

repressurization following eruption from a magma chamber with a viscoelastic aureole i analyze an approximate solution for spherical magma chambers radius r1 surrounded by maxwell viscoelastic shells radius r2 in elastic half spaces following a sudden decrease in pressure mass flux into the chamber is proportional to the pressure difference between a deep source and chamber p p t solutions depend on r2 r1 c m c where m c are magma and chamber compressibilities the relaxation time tr and the recharge time for the elastic system without recharge the system exhibits either post eruptive deflation or for incompressible magmas partial reinflation more generally immediate post eruptive inflation is favored by large tr and small r2 r1 with short tr and large the time for magma chamber pressure to recover increases significantly post eruptive creep increases the chamber pressure decreasing the pressure gradient driving recharge delaying pressure recovery following eruption the hoop stresses which are initially compressive relax toward the radial stress causing them to go through a local relative tension maximum the magma pressure in excess of the dike normal compression at the chamber wall can recover to pre eruptive values well before the chamber pressure or erupted mass recovers this suggests that dikes could nucleate at the chamber margin well before sufficient pressure has recovered to drive them far from the chamber for some parameters co eruptive deflation has not fully recovered when the magma overpressure relative to hoop stress in the elastic region is restored to pre eruptive values a condition assumed to be sufficient for eruption

mineralogical fluid inclusion and stable isotope constraints on mechanisms of ore deposition at the samgwang mine republic of korea a mesothermal vein hosted gold silver deposit the samgwang mine is located in the cheongyang gold district cheonan metallogenic province of the republic of korea it consists of eight massive gold bearing quartz veins that filled ne and nw striking fractures along fault zones in precambrian granitic gneiss of the gyeonggi massif their mineralogy and paragenesis allow two separate vein forming episodes to be recognized temporally separated by a major faulting event the ore minerals occur in quartz and calcite of stage i associated with fracturing and healing of veins hydrothermal wall rock alteration minerals of stage i include fe rich chlorite fe fe mg ratios 0 74 0 81 muscovite illite k feldspar and minor arsenopyrite pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena argentite pyrargyrite and argentian tetrahedrite only calcite was deposited during stage ii fluid inclusions in quartz contain three main types of c o h fluids co2 rich co2 h2o and aqueous inclusions quartz veins related to early sulfides in stage i were deposited from h2o nacl co2 fluids 1 500 5 000 bar average 3 200 with thtotal values of 200 c to 383 c and salinities less than about 7 wt nacl equiv late sulfide deposition was related to h2o nacl fluids 140 1 300 bar average 700 with thtotal values of 110 c to 385 c and salinities less than about 11 wt nacl equiv these fluids either evolved through immiscibility of h2o nacl co2 fluids as a result of a decrease in fluid pressure or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization or both measured and calculated sulfur isotope compositions 34sh2s 1 5 to 4 8 of hydrothermal fluids from the stage i quartz veins indicate that ore sulfur was derived mainly from a magmatic source the calculated and measured oxygen and hydrogen isotope compositions 18oh2o 5 9 to 10 9 d 102 to 87 of the ore forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water rock exchange and by partly degassing in uplift zones during mineralization while most features of the samgwang mine are consistent with classification as an orogenic gold deposit isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the jurassic to cretaceous daebo orogeny

a tectonic model for the late paleozoic of southeastern new england hornblende and biotite sup 40 ar sup 39 ar age spectra from rocks in south central connecticut help define a permian triassic cooling curve for the area together with petrologic and structural information a time temperature pressure strain path is established similar data for the narragansett basin in rhode island and massachusetts allow correlation of the late paleozoic histories of the two areas together these data suggest that in the late paleozoic south central new england was part of a fold thrust belt and the narragansett basin was a retroarc foreland basin nw se compression during the final assembly of pangaea resulted in se directed thrusting causing the development of clastic wedges in adjacent rhode island and massachusetts in the late carboniferous early permian a clockwise rotation of this deformation from nw to nne led to northward underthrusting and concomitant uplift of both eastern connecticut and rhode island in the permian and triassic

magma compressibility and the missing source for some dike intrusions 1 dike intrusions are often accompanied by localized deflation interpreted as depressurizing magma chambers feeding the dike in some cases the inferred volume decrease is a factor of 4 or 5 less than the volume increase of the dike here we explore whether this discrepancy can be explained by compressibility of the magma combined with the fact that cracks are much more compliant than equidimensional magma chambers if pressure changes are small the magma compressibility m is constant and the dike ends up in hydrostatic equilibrium with an ellipsoidal magma chamber at the same depth the ratio rv of the volume of the crack to the volume lost by the chamber is rv 1 4 m 3 1 where is the host rock rigidity for gas poor magmas m 0 6 2 10 10 pa 1 and 3 25 gpa we find 1 2 rv 7 7 large changes in magma compressibility due to gas exsolution increase rv

palaeomagnetic evidence for the age of the cumbrian and manx hematite ore deposits implications for the origin of hematite mineralization at the margins of the east irish sea basin uk examples of epigenetic hematite mineralization located at the margins of the east irish sea basin have been sampled for palaeomagnetic investigation to establish the timing of ore formation samples collected from 10 sites in cumbria are dominated by hematite of near pure composition and characterized by dual polarity and in part dual component magnetizations that yield palaeopoles nine sites between 50 n 130 e and 50 n 150 e in contrast samples recovered from seven sites on the isle of man have more varied mineralogical compositions that include ferromagnets with lower unblocking temperatures manx hematite mineralization also exhibits dual polarity but magnetizations yield steeper inclinations with palaeopoles lying between 55 n 130 e and 70 n 150 e steeper directions probably reflect minor tilting of the manx block following hematite emplacement correlation of poles with the european apparent polar wander path indicates that these ore deposits formed during the middle triassic results show that hematite mineralization sited at the margins of the east irish sea basin is essentially contemporaneous and establishes for the first time an underlying temporal relationship between these geographically dispersed ore bodies dating places the mineralization within a broader extensional geotectonic regime associated with the early rifting of pangaea in the north atlantic the context implies a causal link between crustal extension development of ore forming fluids within the evolving east irish sea basin and subsequent migration of fluids to basin margins where iron was precipitated as hematite supplementary materials locations and details of palaeomagnetic sample sites and a tabulation of selected reference palaeomagnetic poles defining the triassic and early jurassic segment of the apparent polar wander path for the european sector of the eurasian plate are available at www geolsoc org uk sup18691

alleghanian paleostress reconstruction in the northern appalachians intraplate deformation between laurentia and gondwana a numerical paleostress tensor analysis using striated fault planes has been conducted in the quebec reentrant of the northern appalachians to characterize the stress field of late paleozoic deformations three directions of maximum compressional stress axes s1 have been found and correlated to 1 an early north northwest south southeast compression 2 a north northeast south southwest compression and 3 a late west northwest east southeast compression fault populations associated with these stress regimes are present in all tectonic zones of the quebec and northern new brunswick appalachians directions of 1 axes determined in the northern appalachians resemble in orientation and in relative chronology layer parallel shortening fabrics and joint patterns found in the appalachian foreland of the central appalachians the paleostress regimes are interpreted as the record of intraplate deformation related to the indentation of gondwana into laurentia during the late paleozoic alleghanian orogeny

potassium and argon loss patterns in weathered micas implications for detrital mineral studies with particular reference to the triassic palaeogeography of the british isles abstract potassium argon ages are reported for 16 muscovite and 14 biotite samples separated from triassic sandstones of the manx furness carlisle solway firth and lough neagh arran basins disturbance of the k ar isotopic system in these minerals during weathering erosion transport and lithification is discussed and loss of potassium shown to be as important a parameter as argon loss published data from tropical weathering profiles are used to establish the pattern of loss for these two elements during the formation of clay minerals from biotite the data being displayed in a potassium argon loss diagram the loss curve so produced is then used to interpret our new biotite data and previously published age data for detrital biotite from the cheshire basin the limit of interdigitation of northerly and southerly derived materials in the irish sea basins is shown to lie north of the fylde district of lancashire age data from detrital muscovite are used to establish a potassum argon loss curve for muscovite the features of the two curves are markedly similar little effect on the apparent k ar age is observed until about 20 loss of potassium occurs at this point massive argon loss takes place with little loss of potassium due to either potassium stabilisation or structural expansion the suitability of micas as k ar chronometers may be a consequence of the correlated potassium argon loss rather than intrinsic high argon retentivity if both mica curves are applied to detrial micas of the namurian millstone grit series a source area of age of ca 900 ma is indicated for both muscovite and biotite indicating a probable pre cambrian age source area probably in scandinavia