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

contemporaneous extension and compression in the northern apennines from earthquake fault plane solutions summary the northern apenninic arc belongs to the deformation zones surrounding the adriatic plate which behaves as a rigid block it is a ne verging fold and thrust belt which developed since the miocene with the migration of an extensional compressional pair previous seismological data are roughly in agreement with this deformation picture although the outer compressional front was not clearly defined by the few available solutions in this work we confirm the existence of two adjacent zones of contemporaneous extension and compression in the northern apennines defining the extent of these two zones and their interim1 deformation better than was previously done this is accomplished through the analysis of 125 new focal mechanisms of earthquakes 2 6 md 4 8 recorded by the national network of the lstituto nazionale di geofisica in the period 1988 1995 the two deformation zones are clearly separated and lie very close to each other with a partial overlapping in the emilian tuscan apennines strikeslip events are scattered in most of the study area thrust faulting earthquakes are located in the internal part of the most recently active thrust front middle upper pleistocene there is a general trend of the compressional p axes of thrust fault and strike slip solutions to be perpendicular to the apenninic direction in the external zone while the tensional axes of the normal fault and strike slip solutions in the belt do not show a uniform orientation however clearly evident is the ene direction of extension in the peri tyrrhenian region consistent with the direction of shmln in the quaternary volcanoes of this region inferred from borehole breakouts and microearthquake fault plane solutions we determined the orientation of the stress tensor in the two main deformation zones by inversion of the 125 fault plane solutions determined in this study we found that the external belt is characterized by ne sw compression ol horizontal oriented n45 e while a normal faulting regime with o3 e w oriented is characteristic of the umbria tuscany back arc region

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

geochemistry geochronology and origin of the neoarchean planalto granite suite carajas amazonian craton a type or hydrated charnockitic granites abstract new whole rock geochemistry and la mc icpms and pb evaporation geochronological data were obtained on zircon from the neoarchean planalto suite granites and associated charnockitic rocks of the canaa area of the carajas province eastern amazonian craton brazil the pb evaporation ages of three samples from the planalto suite are around 2730 ma 2733 2 ma 2731 1 ma and 2736 4 ma whereas u pb la mc icpms concordia ages obtained for these samples are 2729 17 ma 2710 10 ma and 2706 5 ma respectively an orthopyroxene quartz gabbro associated with the pium complex and planalto suite yielded a u pb concordia age of 2735 5 ma interpreted as its crystallization age the planalto suite granites and the charnockitic rocks associated with the mesoarchean pium complex were probably crystallized at 2730 10 ma the planalto granites have ferroan character and are similar geochemically to reduced a type granites in previous studies they have been classified as such despite the fact that they are syntectonic the tectonic setting and the association between the planalto suite and charnockitic series led us to classify these biotite hornblende granites as hydrated granites of the charnockitic series the planalto suite and the neoarchean charnockitic magmas were more probably derived by partial melting of mafic to intermediate tholeiitic orthopyroxene bearing rocks similar to those of the pium complex at 2 76 ga upwelling of asthenospheric mantle in an extensional setting propitiated the formation of the carajas basin later on at ca 2 73 ga heat input associated with underplate of mafic magma induced partial melting of mafic to intermediate lower crustal rocks originating the planalto and charnockitic magmas the emplacement of these magmas occurred under active regional stress and resultant major shear zones found in the canaa dos carajas area the close association between the planalto suite and charnockitic rocks suggests that they are similar to the high temperature granite magmatism found near the borders of precambrian domains with different ages and tectonic evolution or in their zone of interaction

gold deposits of the carajas mineral province deposit types and metallogenesis the carajas mineral province is located in the south eastern part of the amazon craton and is divided into the southern and northern tectonic blocks which are referred to as the rio maria granitoid greenstone terrane and the itacaiunas shear belt respectively the geological evolution of this province occurred almost entirely in the archean with no tectonism from 2 4 to 1 9 ga and then an episode of very extensive intraplate granitic magmatism distinct types of gold deposits most associated with archean metavolcano sedimentary sequences including greenstone belts as old as 2 9 ga comprise 1 fe oxide poor cu au 2 fe oxide cu au u ree 3 shear zone related lode gold and 4 sedimentary rock hosted au pge the shear zone related deposits are more typical of the rio maria granitoid greenstone terrane whereas the other types are more abundant in the itacaiunas shear belt the first type represented by the serra verde deposit shows most characteristics of volcanogenic massive sulfide vms deposits except for the dominance of chalcopyrite over pyrite and or pyrrhotite some deposits of the second type igarape salobo and igarape bahia are also syngenetic but their ore mineralogy and paucity of pyrite and or pyrrhotite are inconsistent with or at least unusual for classic vms deposits other fe oxide cu au u ree deposits such as the cristalino and sossego occur as epigenetic stockwork mineralization related to archean granitoid stocks most shear zone related lode gold deposits are classified as orogenic gold deposits e g sapucaia babacu and tucuma that cut greenstone belt rocks the cumaru deposit is also hosted by a shear zone but may have a genetic association with a granitoid intrusion the aguas claras deposit although also hosted in a shear zone and perhaps intrusion related differs from the orogenic gold deposits by its extensional tectonic setting lack of co2 in the ore fluids and voluminous chalcopyrite the sedimentary rock hosted serra pelada au pge deposit is structurally controlled and occurs in an archean clastic chemical sedimentary rock sequence

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

the exhaust valve of the north atlantic during glacial periods climate records are marked by large amplitude oscillations believed to be a result of north atlantic na freshwater anomalies which weakened the thermohaline circulation thc and introduced instabilities such oscillations are absent from the present interglacial period with the aid of a semiglobal analytical model it is proposed that the bering strait bs acts like an exhaust valve for the above na freshwater anomalies specifically it is suggested that large instabilities in the thc are only possible during glacial periods because during these periods the bs is closed during interglacial periods when the bs the exhaust valve is open low salinity anomalies are quickly flushed out of the north atlantic by the strong southern ocean winds

isotopic dating of the migration of a low grade metamorphic front during orogenesis the southern margin of the pilbara craton in northwestern australia underwent regional heating folding and thrusting as well as extensive fluid flow during collision in the paleoproterozoic however the precise timing of this event is uncertain previous geochronologic studies of archean basement rocks have yielded a wide range of younger radiometric dates from ca 2 4 ga to ca 2 0 ga interpreted to record multiple hydrothermal alteration events in situ u pb geochronology of authigenic monazite and xenotime in very low grade archean metasedimentary rocks from across the craton suggests that the pilbara was affected by at least two cryptic thermotectonic events the first between ca 2430 ma and ca 2400 ma and the second between ca 2215 ma and ca 2145 ma the older event is restricted to three localities in the west and its cause is unknown the younger event affected most of the craton 100 000 km 2 spanning a 70 m y period from ca 2215 ma nearest the collisional margin in the south to ca 2145 ma toward the craton interior in the north the widespread geographic and stratigraphic distribution of ca 2 2 ga phosphates suggests that fluid flow was pervasive this event was probably driven by the northward advancing ophthalmian fold and thrust belt that developed during protracted collision the associated low grade metamorphic front migrated over 350 km at an average rate of 5 0 mm yr placing important constraints on the rate and duration of deformation and metamorphism in orogenic settings

low temperature replacement of monazite in the ireteba granite southern nevada geochronological implications the ireteba pluton is a relatively homogeneous 64 ma zircon ion probe age two mica granite that was intruded by two 16 ma miocene plutons at depths ranging from 5 to 13 km deeper levels of the ireteba and miocene plutons were ductilely deformed at 15 16 ma at shallow levels remote from the miocene plutons the ireteba granite appears to have experienced little miocene heating and deformation monazites from different portions of the pluton reflect the different histories experienced by the host rock irregularly shaped patchy zones with high huttonite component thsio4 are widespread in monazite at deep levels adjacent to miocene plutons but less common in shallow level rock monazite grains with extensive replacement generally have irregular embayed surfaces in undeformed rocks distant from the miocene plutons monazites are less modified and more nearly euhedral though fine networks of replacement veins are common and irregular rims are evident in some grains secondary monazite from these samples is poorer in huttonite ion probe th pb dating yields 60 65 ma ages for magmatic and some replacement zones in monazite from the shallow samples and veins yield apparent ages as young as mid tertiary monazites from deep samples yield a few 55 65 ma ages for remnant magmatic zones and abundant miocene ages for replacement zones 14 18 ma these data demonstrate extensive miocene replacement of magmatic monazite especially at deep levels near miocene plutons and they suggest an early replacement episode as well both events were probably related to influxes of fluid the first may have been associated with initial solidification of the ireteba pluton and the second with the miocene plutons and or extensional deformation ambient temperatures at the time of replacement indicate that secondary monazite growth occurred at t as low as 400 c or less

dating low grade metamorphic events by shrimp u pb analysis of monazite in shales although the u pb isotopic system is widely used to date magmatism and medium to high grade metamorphism dating low grade metamorphic events has been hampered by a scarcity of suitable minerals we show that monazite forms in shales during low grade metamorphism and can be dated by in situ u pb analysis providing precise ages for low temperature thermal events in proterozoic shales from the pine creek inlier of northern australia monazite and xenotime crystals that formed in a contact aureole yield ages synchronous with granite intrusion ca 1830 ma in the pilbara craton of northwestern australia monazite growth 2192 5 m y ago coincided with basaltic volcanism and rifting an event apparently responsible for hydrothermal iron oxide mineralization in a nearby giant iron ore deposit the mineralizing environment was highly oxic and bathed by meteoric fluids thus our results imply the existence of an oxygen rich atmosphere by 2200 ma given the abundance of shales in the stratigraphic record and the likely widespread distribution of monazite in such rocks in situ u pb dating of monazite may become an important chronometer for low grade metamorphic events

geochemistry and habitat of the oils in italy all varieties of liquid petroleum ranging from condensates 50 degrees api to immature sulfur rich heavy oils as low as 5 degrees api have been found in italy however nonbiodegraded heavy oils account for about 70 percent of the total original oil in place geochemical analyses indicate that 11 oil groups are present in the italian basins and two main types of source rocks have been identified triassic carbonates and tertiary shales about 95 percent of the oils were originated from middle and upper triassic carbonates containing type ii kerogen about 1 percent 4total organic carbon toc and 500 mg hydrocarbon g toc only a relatively minor amount of oil was generated by tertiary shales containing type iii kerogen with toc generally less than 1 percent timing of generation and migration and bulk properties of oils were controlled by geodynamic histories of the three main italian geologic settings 1 apennine and southern alp thrust belts 2 foredeep depression bordering the thrust belts and 3 foreland nondeformed african continental margin within the apennine thrust belts deep burial during the neogene resulted in the generation of substantially lighter oils not only from deeply buried triassic but sometimes also from tertiary source rocks in the late neogene foredeep depocenters located in the central adriatic and southern sicily high subsidence up to 1000 m m y a low geothermal gradient 22 degrees c km and compressional tectonics caused the generation of immature heavy oils generally at depths below 5000 m nd temperatures greater than 100 degrees c rapid burial and higher geothermal gradients 32 degrees c km which occurred since the jurassic resulted in the generation of light oils from the late cretaceous to the oligocene in the southern sector of adriatic foreland

anomalous fluid emission of a deep borehole in a seismically active area of northern apennines italy abstract the miano borehole 1047 m deep is located close to the river parma in the northern apennines italy a measuring station has been installed to observe the discharge of fluids continuously since november 2004 the upwelling fluid of this artesian well is a mixture of thermal water and ch4 as main components in non seismogenic areas a relatively constant fluid emission would be expected perhaps overlaid with long term variations from that kind of deep reservoir over time however the continuous record of the fluid emission in particular the water discharge the gas flow rate and the water temperature show periods of stable values interrupted by anomalous periods of fluctuations in the recorded parameters the anomalous variations of these parameters are of low amplitude in comparison to the total values but significant in their long term trend meteorological effects due to rain and barometric pressure were not detected in recorded data probably due to reservoir depth and relatively high reservoir overpressure influences due to the ambient temperature after the discharge were evaluated by statistical analysis our results suggest that recorded changes in fluid emission parameters can be interpreted as a mixing process of different fluid components at depth by variations in pore pressure as a result of seismogenic stress variation local seismicity was analyzed in comparison to the fluid physico chemical data the analysis supports the idea that an influence on fluid transport conditions due to geodynamic processes exists water temperature data show frequent anomalies probably connected with possible precursory phenomena of local seismic events

bering strait throughflow and the thermohaline circulation received 25 august 2005 revised 10 november 2005 accepted 14 november 2005 published 21 december 2005 1 in this study we employ a global coupled climate model to show that the bering strait is important to the variations of the thermohaline circulation three experiments are analyzed a present day control run and two freshwater hosing runs results show that as the thermohaline circulation weakens due to freshwater forcing in the northern north atlantic the bering strait throughflow weakens and even reverses its direction and the export of the arctic freshwater into the northern north atlantic is reduced or the arctic even takes freshwater from the latter thus helping the thermohaline circulation to recover relatively quickly after the end of the freshwater hosing citation hu a and g a meehl 2005 bering strait throughflow and the thermohaline circulation geophys res lett 32 l24610 doi 10 1029 2005gl024424

methane seeps and mud volcanoes in italy gas origin fractionation and emission to the atmosphere molecular composition ch 4 isotopes and gas flux of all main terrestrial mud volcanoes and other methane seeps in italy are being assessed for the first time whereas 74 of the italian gas reservoirs are biogenic about 80 of the seeps release thermogenic gas dry seep gas generally maintains the reservoir c 1 c 2 c 3 bernard ratio while mud volcanoes show molecular fractionation likely occurring during advective migration accordingly a simple and direct use of the bernard parameter might be misleading when applied to mud volcanoes as it could not always reflect the reservoir composition methane flux into the atmosphere from macro seep areas is in the order of 10 2 10 6 t km 2 y 1 microseepage is widespread throughout large areas and on a regional scale it provides the main methane output a first emission estimate for the total hydrocarbon prone area of italy suggests levels of 105 t y 1 comparable to national sources from fossil fuel industry

fractal approaches in investigating the time dynamics of self potential hourly variability fractal tools have been used to investigate the time dynamics of hourly self potential data recorded during the year 2001 by five geoelectrical stations located in one of the most seismic areas of southern italy scaling behaviour has been revealed by means of different statistics the lomb periodogram method the detrended fluctuation analysis the higuchi analysis and the mean distance spanned within the time l the values of the scaling exponents estimated by means of these methods indicate that the temporal fluctuations of the geoelectrical signals are not typical of purely random stochastic processes i e white noise but evidence the presence of long range correlations furthermore it is found that these correlations are linear

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

preseismic groundwater level changes induced by crustal deformations related to earthquake swarms off the east coast of izu peninsula japan 1 groundwater level changes since october 1994 of omuroyama kita omr well in izu peninsula japan were examined in relation to six earthquake swarms with which large crustal deformations were accompanied after removing not only tidal and barometric effects but rainfall effect on groundwater we detected four preseismic groundwater level changes accompanied with crustal deformations recorded at nearby stations those groundwater level changes are interpreted to have caused by crustal deformations or volumetric strain changes which seem to be caused by dike intrusions which are possible sources of the earthquake swarms off the east coast of izu peninsula

sources of mineralising fluids for the olympic dam deposit south australia smnd isotopic constraints abstract the olympic dam cu u au ag deposit south australia is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system the deposit is characterised by extreme enrichments of ree which are a product of the ore forming process therefore making the sm nd isotopic system an ideal tool for clarifying the complex relationships between the different ore and breccia types pyrite chalcopyrite and bornite chalcocite rich hematitic ores share an initial end signature of 2 5 which suggests that these ore types are cogenetic these ores together with sulphide poor hematitic breccias yield a 14 point sm nd isochron age of 1572 99 ma the host roxby downs granite has an initial nd of 5 and therefore cannot alone have been the source of the mineralising fluids for the hematitic ores in contrast to hematitic rocks volumetrically minor magnetite rich assemblages have the same initial nd signature as the host granite suggesting that they are cogenetic assuming that both hematite and magnetite were precipitated from solution their contrasting isotopic signatures require that ore deposition involved two distinct fluids the isotopic data do not allow the distinction between a model involving concurrent activity of such fluids in a mixing regime and a model involving temporally separate overprinting of magnetite by hematite cu sulphides the ore signature of nd 2 5 cannot have been derived solely from pre existing crustal rocks of the gawler craton it must have involved a contribution from a mantle derived source rock or magma the most likely source of this nd component are the mantle derived rocks produced during the gawler range volcanics event e g altered alkaline mafic ultramafic dykes within the deposit which have initial isotopic signatures as high as nd 4 assuming end member compositions equivalent to these dykes and the roxby downs granite the ore signature implies that 30 of the nd in the ores was derived from the mafic ultramafic source if nd was leached from source rocks rather than derived from magmatic volatiles the inferred rock fractions contributing ree to the deposit are 13 mafic ultramafic rocks and 87 roxby downs granite or its volcanic equivalent massbalance calculations indicate that 13 rock fraction of mafic ultramafics can account for 50 of the cu contained in the deposit the involvement of mafic ultramafic rocks is therefore inferred to have been crucial to the genesis of the cu enriched ores at olympic dam

correlation by genetic properties of the shallow gas seepages in the emilian apennine northern italy the knowledge of the deep geology in the northern apennine usually impervious to geophysical exploration can be partially improved by analysing the composition chiefly c2 content and isotopic composition 13c1 13c2 d of c1 of natural gases derived from surface seeps or shallow wells the gas is generally found in small volumes at low pressures in calcareous or arenaceous reservoirs that are randomly found in the clayey matrix of chaotic heterogeneous terrains such as the argille scagliose these shallow gas occurrences lack the typical charater of the conventional gas accumulations however with careful analysis these accumulations can be explained within a geologic context with two exceptions the analyses of more than 50 gas samples show thermogenic properties 40 13c1 29 25 c2 19 150 d 130 for almost all sampled gases the isotopic composition of these gases the areal distribution of seeps and the regional geologic context lead us to think that apenninic hydrocarbons underwent a vertical migration in fact the high isotopic values can be explained by deep burial caused by severe tectonic movements in the apennines which broke up the mesozoic substratum into small scattered reservoirs the location of deep still intact traps is therefore the goal of petroleum exploration and research the age and nature of the source rocks are poorly known riva et al 1985 but the available data lead us to a reliable following conclusion as we can compare gas compositions origin geological and depositional conditions of the gases found in the rest of the po basin particularly in the outer part of the apennine fold belts in fact the apennine gases due to their chemico physical and isotopic compositions seem to represent the end of the thermal degradation processes that affected the organic matter in the chain domain

earthquake m 5 1 induced hydrogeochemical and δ18o changes validation of aquifer breaching mixing model in koyna india summary hydrochemical parameters and oxygen 18 18o were measured in groundwater from wells and spring waters from the active seismic area around koyna warna reservoirs over a period of three years 2005 2007 to explore their relationship with seismicity in comparison to average values observed later hydrochemical data of one of the wells revealed increased concentrations of chloride 100 per cent sulphate 300 per cent and fluoride 700 per cent while the 18o value decreased contemporarily to the occurrence of an earthquake of magnitude 5 1 on 2005 march 14 based on the hydrochemical and isotopic characteristics of different well waters in this area we conceptualize a model of aquifer breaching and mixing of deep aquifer water with shallow aquifer water due to the earthquake we estimated the fractions of two components of different aquifer waters mixed using two conservative tracers chloride and 18o the necessary mixing proportions of 50 per cent are unprecedented and call for further work to understand the earthquake related processes causing the observed hydrogeochemical and isotopic anomalies in the koyna warna region

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

triassic mineralization with cretaceous overprint in the dahu au mo deposit xiaoqinling gold province constraints from shrimp monazite u th pb geochronology abstract the xiaoqinling terrane in central china is the second largest gold producing area in china previous application of age constraints has yielded ages for the gold mineralization ranging from paleoproterozoic through triassic indosinian to jurassic and cretaceous yanshanian shrimp u th pb dating of hydrothermal monazite in a mo mineralized quartz vein from the dahu au mo deposit in the northern xiaoqinling terrane identifies two mineralization episodes hydrothermal monazite intergrown with molybdenite yields an initial precipitation age of 216 5 ma which is identical to but more precise than the molybdenite re os isochron age of 218 41 ma a younger generation of monazite is distinguished by data falling on a mixing array it is inferred that the younger monazite was formed at the expense of the older ones during the yanshanian probably during a single event that occurred at 125 ma combining these results with available geochronological data and geological evidence we conclude that molybdenum mineralization accompanied by monazite deposition took place in the indosinian followed by a yanshanian tectono hydrothermal event that resulted in large scale gold mineralization in the xiaoqinling terrane our observation demonstrates that monazite is sensitive to hydrothermal overprint and thus is useful for dating fluid infiltration event

the collapse of the bering strait ice dam and the abrupt temperature rise in the beginning of the holocene this paper focuses on the abrupt increase in the oceanic and atmospheric temperature in the northern hemisphere at the beginning of the holocene approximately 11 000 yr before the present de boer and nof hypothesized that at that time the bering strait bs opened up abruptly because of the breakup of an ice dam by rising sea levels it is proposed further here that this sudden opening caused an abrupt increase in the mean temperature of the northern hemisphere an analytical coupled ocean atmosphere model is applied to the north atlantic in an attempt to quantify the temperature change resulting from the opening of the bs heat salt and mass are all conserved within a box in the north atlantic a convection condition allows water to enter the deep layer and the island rule relates the wind field to the mass fluxes the conventional approach that the meridional overturning cell moc was not operating during the younger dryas because of an overwhelming freshwater flux is adopted here opening the bs in the early holocene allowed these freshwater anomalies to be flushed out into the pacific reviving convection and the transport of heat northward restarting convection with an open bs increases mean oceanic and atmospheric temperature by 3 and 23 c respectively these values are comparable to those found in both the centre europeen de recherche et d enseignement des geosciences de l environnement cerege alkenone and greenland ice sheet project 2 gisp 2 ice core records of course restarting convection increases the temperature even with a closed bs but in the closed bs case the oceanic increase is slightly higher 4 c instead of 3 c whereas the atmospheric is much lower 17 5 c instead of 23 c this is because by requiring a continuous sea level around the americas an open bs allows the wind field to limit the amount of southern ocean water that enters the south atlantic this controlled volume flux 8 sv is considerably smaller than that allowed into the atlantic in the no wind control closed bs case 17 sv

subtropical countercurrent variations in cooling climates induced by freshwater forcing over the subarctic north atlantic the subtropical countercurrent stcc could affect ocean eddy activity and the atmosphere above how the stcc varied in a cooling scenario such as the stadials during the last deglaciation 19 11 ka ka 1000 years ago is still unclear by 1 sv 1 sv 106 m3 s 1 freshwater hosing over the subpolar north atlantic to suppress the atlantic meridional overturning circulation amoc the stcc variations under pre industrial pi and last glacial maximum lgm 21 ka conditions are analyzed in both hosing experiments the northern hemisphere cools the upper ocean becomes less stratified and the wintertime mixed layer deepens in the kuroshio oyashio extension koe region as a result more mode waters 20 are formed and they become more vertically uniform the enhanced mode waters induce a stronger vertical shear and accelerate the stcc based on thermal wind relationship the strengthened stcc further induces warm ocean temperature and upward air sea heat flux anomalies along it while the stcc strengthens in both hosing experiments the location variations are different in the pi hosing experiment the bering strait is open fresh water enters the north pacific through the bering strait and increases the stratification in the downstream of the koe region the mixed layer front shifts westward and induces a robust westward shift of mode waters and the stcc in the lgm hosing experiment on the contrast there is no obvious location shift because the bering strait is closed

u pb geochronology of archean magmatism and basement reactivation in the carajas area amazon shield brazil abstract the archean carajas subprovince is a metallogenic district bif bauxite cu ni mn au located in the easternmost amazonian craton in brazil the main conclusions from a u pb study of the itacaiunas supergroup and a locality in the xingu complex are the following the xingu basement complex the oldest unit underwent migmatization at 2859 2 ma and also grew new zircon at 2851 4 ma the luanga mafic intrusion is 2763 6 ma old and coeval with the 2759 2 ma felsic volcanics of the grao para group amphibolites from the salobo group contain 2851 ma zircons were metamorphosed 2761 3 ma and intruded by granitic veins ca 2758 ma at the time of grao para magmatism and also grew new zircon at 2732 2742 ma the data indicate that the salobo group is part of the xingu complex and not of the itacaiunas supergroup as heretofore believed the pojuca group possibly coeval with the salobo group was metamorphosed at 2732 3 ma a late archean reactivation event of regional extent is marked by titanite growth at 2581 5 ma in the mirim area intrusion of the old salobo granite at 2573 2 ma new zircon growth in salobo group amphibolites at 2555 4 3 ma and monazite growth in a metamorphosed iron formation at 2551 2 ma in addition k metasomatism associated with shear zones formed titanite in salobo group amphibolites at 2497 5 ma and new titanite at 2519 5 ma in the xingu complex events in the 2581 2497 ma interval are probably associated with the latest activity of a wnw ese sinistral shear system which could also be responsible for the establishment of a transtensional basin filled by the volcano sedimentary sequence of the grao para bahia and rio fresco groups finally undeformed proterozoic granitoid intrusions were dated at 1883 2 ma cigano 1883 5 2 ma musa 1880 2 ma carajas and 1874 2 ma pojuca

th u pb isotopic systems and internal structures of complex zircons from an enderbite from the pium complex carajas province brazil evidence for the ages of granulite facies metamorphism and the protolith of the enderbite abstract shrimp u pb micro analyses are reported for parts of complex zircons from a granulite facies enderbite from the pium complex in the carajas metallogenic province of the amazon craton of brazil zircons from the granulite consist of two types of grains a those with oscillatory zoned cores surrounded by rims composed of two or more curved overlapping nebulously zoned domains distinguished by differences in cathodoluminescence intensity and b grains which are composed entirely of such domains and have no obvious cores the shrimp u pb age of 3002 14 ma determined for oscillatory zoned zircon cores is interpreted as dating the parent rock of the enderbite this age is resolved from the u pb age of 2859 9 ma determined on zircon rims which is interpreted as a time point within the evolving granulite facies metamorphism shrimp u pb ages of cores and rim type zircon are generally concordant to slightly discordant where uranium contents are less than about 820 ppm but once this value is exceeded the zircon becomes strongly discordant suggesting that a threshold value of radiation damage exists above which zircon stability with respect to pb loss is sharply reduced the results provide the first substantial age determination of the granulite metamorphism in the carajas province the zircon u pb ages have not been influenced by the transamazonian metamorphism dated at ca 2 0 1 85 ga from ar ar and rb sr mineral ages

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

time variable response characteristics of groundwater radon to earthquakes a clear coseismic anomaly of groundwater radon was observed for a magnitude 5 6 earthquake that occurred on may 11 1992 the coseismic radon anomaly was observed at a station which is located right on a major active fault in northeast japan and about 140 km away from the hypocenter this was the first time that an earthquake with m 6 had ever been accompanied by a clear radon anomaly at the station although we had observed 12 similar coseismic radon anomalies at the station during the observation period from 1984 to 1987 all of the earthquakes that were accompanied by radon anomalies in that period had been with magnitude 6 0 and over surprisingly the radon concentration has become more sensitive to show coseismic anomalies even for m 5 earthquakes since october 1992 this enhancement of sensitivity of the coseismic radon response may be attributed to the progress of micro crack formation in the fracture zone of the active fault which could be related to unusual stress accumulation in the region

about the potential of wells to reflect stress variations within inhomogeneous crust abstract kumpel h j 1992 about the potential of wells to reflect stress variations within inhomogeneous crust in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 317 336 numerous pre co and post seismic well level changes that are believed to reflect stress variations in the crust have been observed in various parts of the world so far analysis of these data has not favoured a distinct model of the processes that could be involved the benefit from the signals is in fact limited because understanding of the underlying physical mechanisms is poor the paper discusses the impact that inhomogeneities in the brittle crust can have on the observations in particular the following problems are considered 1 could the well level signals be induced by the invasion of pressurized pore fluid at some place 2 could the hydrological conditions close to the observation well modulate any remote pore pressure variation 3 which features of the crust are most likely to dominate the process of stress transfer in the crust 4 how should a stress sensitive well be designed the results can be summarized as follows 1 stress diffusion due to the invasion of pressurized pore fluid can lead to significant well level changes only when the source region is at closer distance than a few kilometres probably less than a few hundred metres from the well 2 local inhomogeneities in the vicinity of the observation well may strongly influence the well s response to remote pressure changes even sign reversal of the anomaly may be encountered 3 there is increasing evidence that the wide range of stiffness values of natural rocks from 100 mpa or less till 100 gpa manifested in a fractal distribution of fault like weak zones within relatively stiff formations dominates stress transfer in the brittle crust uncertainty about the effective rheology for time scales from 10 4 to 103 years limits the inversion of many geophysical observations at present 4 of various configurations a well tapping an extensive hydraulic fracture could act best as a sensitive stress sensor provided that the fracture volume is isolated from the pore space of the host rock however experimental evidence of the practicability of such configuration is still due the weakness of conventional wells as stress sensors results from the fact that the process of fluid flow often lacks a sufficient control on attenuation mechanisms for low frequency well level variations regardless of whether the wells end in stiff or weak formations to a large extent the presented findings are compiled from publications of investigators working in various fields

geostrophic control of fluctuating barotropic flow through straits abstract a simple model in which the cross strait sea surface slope is geostrophically balanced and the along strait slope is balanced by acceleration and friction is shown to be supported by the results of buchwald and miles for fluctuating flow through a gap between two semi infinite oceans for a narrow gap compared with the rossby radius and the scale of the motion in the far field the transport through it is exactly the same as that predicted by the model provided that the gap is regarded as having an elective length as determined in this paper the importance of the models is that they demonstrate that at low frequency the flow may be geostrophically controlled and the transport limited to a value much less than that which would arise in a nonrotating system the neglect of nonlinear advective terms in the models is justified by a comparison or the bernoulli set down in the strait with the driving head and the mean water depth the formula for the flux through a strait may be applied in stu

timing of multiple hydrothermal events in the iron oxide copper gold deposits of the southern copper belt carajas province brazil the southern copper belt carajas province brazil hosts several iron oxide copper gold iocg deposits including sossego cristalino alvo 118 bacuri bacaba castanha and visconde mapping and u pb sensitive high resolution ion microprobe shrimp iie zircon geochronology allowed the characterization of the host rocks situated within regional wnw ese shear zones they encompass mesoarchean 3 08 2 85 ga ttg orthogneiss granites and remains of greenstone belts neoarchean ca 2 74 ga granite shallow emplaced porphyries and granophyric granite coeval with gabbro and paleoproterozoic 1 88 ga porphyry dykes extensive hydrothermal zones include albite scapolite biotite scapolite tourmaline magnetite alteration and proximal potassium feldspar chlorite epidote and chalcopyrite formation u pb laser ablation multicollector inductively coupled mass spectrometry la mc icp ms analysis of ore related monazite and re os ntims analysis of molybdenite suggest multiple neoarchean 2 76 and 2 72 2 68 ga and paleoproterozoic 2 06 ga hydrothermal events at the bacaba and bacuri deposits these results combined with available geochronological data from the literature indicate recurrence of hydrothermal systems in the southern copper belt including 1 90 1 88 ga ore formation in the sossego curral ore bodies and the alvo 118 deposit although early hydrothermal evolution at 2 76 ga points to fluid migration coeval with the carajas basin formation the main episode of iocg genesis 2 72 2 68 ga is related to basin inversion coupled with neoarchean ca 2 7 ga felsic magmatism the data suggest that the iocg deposits in the southern copper belt and those in the northern copper belt 2 57 ga salobo and igarape bahia alemao deposits do not share a common metallogenic evolution therefore the association of all iocg deposits of the carajas province with a single extensive hydrothermal system is precluded

mineral chemistry of ore and hydrothermal alteration at the sossego iron oxide copper gold deposit carajas mineral province brazil abstract the sossego iron oxide copper gold deposit in the carajas mineral province comprises two major orebodies sequeirinho and sossego sodic alteration albite hematite and sodic calcic alteration zones represented by albite ferro edenite hastingsite up to 3 8 wt cl actinolite magnesiohornblende magnetite titanite epidote and calcite are predominant at sequeirinho magnetite bodies with envelopes of apatite rich actinolitite were formed with the sodic calcic event at high temperatures 500 c at 1 4 kbar in the sossego orebody potassic alteration with orthoclase and cl rich biotite up to 3 1 wt and chloritization are the main alteration types mineralized breccias in both orebodies have coarse grained zoned actinolite ferro actinolite cl apatite and magnetite within the matrix sulfides occur in equilibrium with a paragenetically late calcite quartz chlorite epidote allanite assemblage the al iv contents of the chlorite indicate crystallization at temperatures below 300 c chalcopyrite occurs associated with pyrite up to 2 3 wt co and 0 2 wt ni native gold up to 14 9 wt ag siegenite millerite vaesite pd melonite and hessite dilution and cooling of the hot metalliferous fluid 500 c by mixing with meteoric fluids may have been the main mechanisms responsible for the deposition of metals transported as metal chloride complexes in both orebodies of the sossego deposit

a review of the geochronology of the amazonian craton tectonic implications abstract the available geochronological data for the amazonian craton permit delineation of its main age provinces and their respective tectonic development demarcation of the boundaries of each age province is primarily based on rb sr whole rock isochrons supported by k ar determinations on minerals some u pb results on zircons pb pb whole rock isochrons and sm nd model ages complement these data in key areas at the center of the amazonian craton lies the archean age central amazonian province bounded in its northern part by the maroni itacaiunas mobile belt which developed during early proterozoic times the western and southern margins of the archean core are bordered by three tectonic provinces 1 the rio negro juruena magmatic arc 2 the rondonian mobile belt and 3 the sunsas mobile belt each belt borders the western margin of the preceding belt and each records a successively younger middle proterozoic orogeny within the central amazonian province 2 7 ga age determinations have been obtained from the serra dos carajas area although the maroni itacaiunas belt includes several reworked archean nuclei rock units formed during the 2 2 1 9 ga trans amazonian orogeny predominate the isotopic evidence suggests that a mantle derived component constituted a significant portion of the crust accreted at that time the rio negro juruena province is of mid proterozoic age 1 75 1 50 ga and includes almost entirely mantle derived material juxtaposed with the pre existent continental mass along a series of successive magmatic arcs the rondonian and sunsas provinces both exhibit older sialic basements 1 5 ga the former is characterized by important tectonomagmatic events in the 1 45 1 25 ga interval whereas the latter records tectonic reworking at 1 1 0 9 ga finally the amazonian craton is bordered to the east by the late proterozoic paraguai araguaia or araguaia tocantins fold belt

age of mineralization of the candelaria fe oxide cu au deposit and the origin of the chilean iron belt based on re os isotopes re os isotopes are used to determine the age of iron oxide cu au mineralization at candelaria chile and to explore possible genetic links with the batholithic intrusions in the area re os ages calculated from molybdenite are 114 2 0 6 ma and 115 2 0 6 ma and they are interpreted to represent the age of mineralization these ages are consistent with previously reported ages for biotite alteration that range from 114 to 116 ma an isochron calculated by re os ratios from hydrothermal magnetite and sulfides constrains an initial 187 os 188 os ratio of 0 36 0 10 the initial 187 os 188 os ratio for sulfide from bronce mine a small satellite of the candelaria orebody is 0 33 0 01 these values are broadly similar to the calculated initial 187 os 188 os ratio for magmatic magnetite in nearby batholithic rocks that range from 0 20 to 0 41 the relatively radiogenic initial 187 os 188 os ratio represents a mixture of mantle and crustal components in the ores and batholitic rocks the similarity in initial 187 os 188 os ratio of the ore and magmatic oxides suggest that the granitic plutons could be the source of metals in the candelaria district these data are consistent with the existence of a significant magmatic fluid component in the hydrothermal system as suggested by previously published work in order to establish a regional perspective we analyzed ore minerals from other chilean deposits of the iron oxide cu u au rare earth elements ree class magnetite from the manto verde iron oxide cu au deposit has os and re concentrations of 11 to 17 parts per trillion ppt and 4 to 6 parts per billion ppb respectively the initial 187 os 188 os ratio is approximately 0 20 and is similar to that of ore minerals from candelaria and of the early cretaceous batholithic intrusions these data indicate a similar metal source for the mineralization at manto verde and candelaria magnetite from three magnetite apatite deposits of the chilean iron belt have re concentrations between 0 8 and 3 ppb and os concentrations between 11 and 76 ppt calculated initial 187 os 188 os ratios of these magnetites range from 1 2 to 8 4 and are distinctly different from those of the iron oxide cu au deposits the cause of the comparatively high radiogenic signatures in the magnetite apatite ores is probably related to fluid interactions with i e leaching the surrounding sedimentary rocks during their genesis in contrast to the iron oxide cu au systems the os in magnetite apatite ores could be derived from sedimentary rocks this evidence suggests that predominantly basin derived nonmagmatic brines formed these magnetite apatite deposits

gravity tectonics driven by quaternary uplift in the northern apennines insights from the la spezia reggio emilia geo transect abstract the neotectonics of the northern apennines is illustrated using a crustal scale geoseismic cross section based on seismic profiles and field mapping the geological profile crosses a variety of tectonic settings from the val di vara and val magra vv vm grabens in the inner side of the apennines to the pede apennine thrust fronts ptf and finally to the external fronts of the apennines both the vv vm extensional system and the ptf show evidence of early pleistocene tectonic activity whereas thrusting in the external apennine ended by late pliocene the sole decollement of the external thrusts cuts down westwards into the basement to a depth of about 15 km whereas the ptf joins a shallower detachment surface that follows the top of the basement this basal surface also represents the basal detachment of the vv vm extensional system with the vv vm and ptf defining a large scale gravitational spreading system we hypothesise that the regional quaternary uplift that affected the internal sector of the apennines promoted a gravitational spreading in the upper part of the orogenic wedge accounting for the coeval extension in the vv vm and shortening at the ptf and applicable to a 100 km long sector of the northern apennines

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

new geologic fluid inclusion and stable isotope studies on the controversial igarape bahia cu au deposit carajas province brazil the igarape bahia cu au deposit in the carajas province brazil is hosted by steeply dipping metavolcano sedimentary rocks of the igarape bahia group this group consists of a low greenschist grade unit of the archean 2 750 ma itacaiunas supergroup in which other important cu au and iron ore deposits of the carajas region are also hosted the orebody at igarape bahia is a fragmental rock unit situated between chloritized basalt with associated hyaloclastite banded iron formation bif and chert in the footwall and mainly coarse to fine grained turbidites in the hanging wall the fragmental rock unit is a nearly concordant 2 km long and 30 250 m thick orebody made up of heterolithic usually matrix supported rocks composed mainly of coarse basalt bif and chert clasts derived from the footwall unit mineralization is confined to the fine grained matrix and comprises disseminated to massive chalcopyrite accompanied by magnetite gold u and light rare earth element lree minerals and minor other sulfides like bornite molybdenite cobaltite digenite and pyrite gangue minerals include siderite chlorite amphibole tourmaline quartz stilpnomelane epidote and apatite a less important mineralization style at igarape bahia is represented by late quartz chalcopyrite calcite veins that crosscut all rocks in the deposit area fluid inclusions trapped in a quartz cavity in the ore unit indicate that saline aqueous fluids 5 to 45 wt nacl cacl2 equiv together with carbonic co2 ch4 and low salinity aqueous carbonic 6 wt nacl equiv fluids were involved in the mineralization process carbonates from the fragmental layer have 13c values from 6 7 to 13 4 per mil that indicate their origin from organic and possibly also from magmatic carbon the 34s values for chalcopyrite range from 1 1 to 5 6 per mil with an outlier at 10 8 per mil implying that most sulfur is magmatic or leached from magmatic rocks whereas a limited contribution of reduced and oxydized sulfur is also evident oxygen isotopic ratios in magnetite quartz and siderite yield calculated temperatures of 400 c and 18o enriched compositions 5 to 16 5 per mil for the ore forming fluids that suggest a magmatic input and or an interaction with 18o rich probably sedimentary rocks the late veins of the igarape bahia deposit area were formed from saline aqueous fluids 2 to 60 wt nacl cacl2 equiv with 18ofluid compositions around 0 per mil that indicate contribution from meteoric fluids with respect to geological features igarape bahia bears similarity with syngenetic volcanic hosted massive sulfide vhms type deposits as indicated by the volcano sedimentary geological context stratabound character and association with submarine volcanic flows hyaloclastite and exhalative beds such as bif and chert on the other hand the highly saline ore fluids and the mineral assemblage dominated by magnetite and chalcopyrite with associated gold u and lree minerals and scarce pyrite indicate that igarape bahia belongs to the fe oxide cu au iocg group of deposits the available geochronologic data used to attest syngenetic or epigenetic origins for the mineralization are either imprecise or may not represent the main mineralization episode but a later superimposed event the c s and o isotopic results obtained in this study do not clearly discriminate between fluid sources however recent b isotope data obtained on tourmaline from the matrix of the fragmental rock ore unit xavier wiedenbeck dreher rhede monteiro araujo chemical and boron isotopic composition of tourmaline from archean and paleoproterozoic cu au deposits in the carajas mineral province 1 simposio brasileiro de metalogenia gramado brazil extended abstracts cd rom 2005 provide strong evidence of the involvement of a marine evaporitic source in the hydrothermal system of igarape bahia evaporite derived fluids may explain the high salinities and the low reduced sulfur mineral paragenesis observed in the deposit evaporite derived fluids also exclude a significant participation of magmatic or mantle derived fluids reinforcing the role of nonmagmatic brines in the genesis of igarape bahia considering this aspect and the geological features the possibility that the deposit was generated by a hydrothermal submarine system whose elevated salinity was acquired by leaching of ancient evaporite beds should be evaluated

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

hydrothermal fluid evolution and metal transport in the kiruna district sweden contrasting metal behaviour in aqueous and aqueous carbonic brines abstract iron oxide copper gold iocg deposits and fe oxide apatite deposits from norrbotten sweden formed in similar settings and in some cases iocg mineralisation overprinted fe oxide apatite mineralisation fluid inclusions in quartz veins cutting fe oxide apatite deposits range in salinity from 33 to 37 wt nacl eq and those in iocg type deposits from 41 to 54 wt nacl eq minimum trapping conditions for these inclusions are 200 300 mpa and 200 300 c in the fe oxide apatite bodies and 250 to 300 mpa and 300 500 c in the iocg deposits deformed cu au deposits have similar early fluid characteristics but contain complex secondary fluid inclusion assemblages including halite saturated 20 30 wt nacl eq aqueous carbonic 3 13 wt nacl eq x co 2 0 17 0 29 and co 2 rich fluids the aqueous carbonic and carbonic inclusions are consistent with aqueous carbonic fluid immiscibility at 150 mpa a secondary population with a high ca content occurs in all deposit types the chemical composition of these inclusions has been determined by crush leach analysis and la icpms halogen contents indicate a range of salinity sources with possible inputs from both magmatic and halite dissolution brines element ratios suggest the alkali content of the fluid exceeded the buffer capacity of the host rocks iron and other transition metal contents correlate strongly with cl concentrations with secondary controls on solubility from ph redox and temperature copper and ag contents are higher in lower salinity aqueous carbonic brines up to 5000 ppm cu 900 ppm ag than in the most saline brines up to 2297 ppm cu 837 ppm ag this may reflect differences in metal source between deposit types but is also consistent with the complexation of cu by bisulphide in the lower salinity fluids late stage aqueous carbonic fluid flux through the deformed deposits either introduced additional copper to the deposits remobilised pre existing copper or both

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

spatial and temporal zoning of hydrothermal alteration and mineralization in the sossego iron oxide copper gold deposit carajas mineral province brazil paragenesis and stable isotope constraints the sossego iron oxide copper gold deposit 245 mt 1 1 cu 0 28 g t au in the carajas mineral province of brazil consists of two major groups of orebodies pista sequeirinho baiano and sossego curral with distinct alteration assemblages that are separated from each other by a major high angle fault the deposit is located along a regional wnw ese striking shear zone that defines the contact between metavolcano sedimentary units of the 2 76 ga itacaiunas supergroup and tonalitic to trondhjemitic gneisses and migmatites of the 2 8 ga xingu complex the deposit is hosted by granite granophyric granite gabbro and felsic metavolcanic rocks the pista sequeirinho baiano orebodies have undergone regional sodic albite hematite alteration and later sodic calcic actinolite rich alteration associated with the formation of massive magnetite apatite bodies both these alteration assemblages display ductile to ductile brittle fabrics they are cut by spatially restricted zones of potassic biotite and potassium feldspar alteration that grades outward to chlorite rich assemblages the sossego curral orebodies contain weakly developed early albitic alteration and very poorly developed subsequent calcic sodic alteration these orebodies contain well developed potassic alteration assemblages that were formed during brittle deformation that resulted in the formation of breccia bodies breccia matrix commonly displays coarse mineral infill suggestive of growth into open space sulfides in both groups of deposits were precipitated first with potassic alteration and more importantly with a later assemblage of calcite quartz epidote chlorite in the sequeirinho orebodies sulfides range from undeformed to deformed sulfides in the sossego curral orebodies are undeformed very late weakly mineralized hydrolytic alteration is present in the sossego currral orebodies the sulfide assemblage is dominated by chalcopyrite with subsidiary siegenite and millerite pyrrhotite and pyrite are minor constituents of ore in the sequerinho orebodies while pyrite is relatively abundant in the sossego curral bodies oxygen isotope partitioning between mineral pairs constrains temperatures in the deposit spatially and through time in the sequeirinho orebody the early sodic calcic alteration stage was characterized by temperatures exceeding 500 c and delta text 18 text o text h text 2 text o values for the alteration fluid of 6 9 0 9 temperature declines outward and upward from the zone of most intense alteration paragenetically later copper gold mineralization displays markedly lower temperatures 300 c and was characterized by the introduction of 18o depleted hydrothermal fluids 1 8 3 4 the calculated dh2o and delta text 18 text o text h text 2 text o values suggest that the fluids that formed the early calcic sodic alteration assemblage were of formational metamorphic or magmatic origin the decrease of delta text 18 text o text h text 2 text o values through time may reflect influx of surficially derived waters during later alteration and mineralization events influx of such fluids could be related to episodic fluid overpressure resulting in dilution and cooling of the metalliferous fluid causing deposition of metals transported as metal chloride complexes

3 geochronology and geodynamics of late cretaceous magmatism and cu au mineralization in the panagyurishte region of the apuseni banat timok srednogorie belt bulgaria abstract the apuseni banat timok srednogorie abts belt europe s most extensive belt of calc alkaline magmatism and cu au mineralization is related to the subduction of the tethys ocean beneath the european continental margin during the late cretaceous phase of the alpine himalayan orogeny economic deposits are restricted to certain segments along the belt and all major porphyry style and high sulphidation ore deposits in bulgaria are aligned on the panagyurishte corridor a narrow zone obliquely crossing the abts belt this paper reviews the geology geochemistry and geochronology of igneous and hydrothermal events along this corridor in a profile extending from the european continental basement in the north to the accretionary complex of the rhodopes in the south extensive u pb dating of zircons from subvolcanic intrusions and major plutons supplemented by published age data for magmatic rocks and hydrothermal ore deposits obtained by other methods reveals a general younging of magmatism from ca 92 ma in the north elatsite to ca 78 ma in the south capitan dimitrievo cu au deposits are restricted to the northern and central parts of the profile ranging in age from 92 to 86 ma while the southernmost part exposes more deeply eroded mid crustal plutons devoid of economic mineralization the age progression correlates with a north to south geochemical trend of decreasing crustal input into mantle derived magmas magmatism and ore formation in individual magmatic hydrothermal complexes along the profile is much shorter lived for example subvolcanic intrusions and porphyry cu au mineralization at the elatsite deposit and andesitic volcanism and high sulphidation au as cu mineralization at chelopech all occurred within a time span of about 1 million years the age progression of calc alkaline magmatism within the panagyurishte region bulgaria from north to south is explained as a consequence of slab retreat during oblique subduction this led to transtensional block faulting and subsidence and thus to the preservation of near surface magmatic hydrothermal products including economic cu au deposits accretion of continental fragments in the rhodopes south of the abts belt led to greater uplift of the youngest late cretaceous intrusions this removed any ore deposits that might have been formed in this area

hydrothermal alteration fluid inclusions and stable isotope systematics of the alvo 118 iron oxide copper gold deposit carajas mineral province brazil implications for ore genesis the alvo 118 iron oxide copper gold iocg deposit 170 mt at 1 0 wt cu 0 3 g t au lies in the southern sector of the itacaunas shear belt carajas mineral province along a wnw ese striking 60 km long shear zone close to the contact of the 2 76 ga metavolcano sedimentary itacaiunas supergroup and the basement 3 0 ga xingu complex the alvo 118 deposit is hosted by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following hydrothermal alteration sequence towards the ore zones 1 poorly developed sodic alteration albite and scapolite 2 potassic alteration biotite or k feldspar accompanied by magnetite formation and silicification 3 widespread pervasive chlorite alteration spatially associated with quartz carbonate sulphide infill ore breccia and vein stockworks and 4 local post ore quartz sericite alteration the ore assemblage is dominated by chalcopyrite 60 bornite 10 hematite 20 magnetite 10 and subordinate chalcocite native gold au ag tellurides galena cassiterite f rich apatite xenotime monazite britholite y and a gadolinite group mineral fluid inclusion studies in quartz point to a fluid regime composed of two distinct fluid types that may have probably coexisted within the timeframe of the cu au mineralizing episode a hot 200 c saline 32 8 to 40 6 wt nacl eq solution represented by salt bearing aqueous inclusions and a lower temperature 200 c low to intermediate salinity 15 wt nacl eq aqueous fluid defined by two phase lh2o vh2o fluid inclusions this trend is very similar to those defined for other iocg systems of the carajas mineral province 18oh2o values in equilibrium with calcite 1 0 to 7 5 at 277 c to 344 c overlap the lower range for primary magmatic waters but the more 18o depleted values also point to the involvement of externally derived fluids possibly of meteoric origin furthermore sulphide 34s values 5 1 to 6 3 together with available boron isotope and cl br na cl data provide evidence for a significant component of residual evaporative fluids e g bittern fluids generated by seawater evaporation in this scenario that together with magma derived brines would be the main sources of the highly saline fluids involved in the formation alvo 118 iocg deposit the restricted high temperature sodic alteration the pervasive overprinting of the potassic alteration minerals by chlorite proximal to the ore zones ore breccias with open space filling textures in brittle structures microthermometric and stable isotope data indicate collectively that the alvo 118 iocg system developed at structurally high levels and may be considered the shallower representative of the iocg systems of the cmp

re os and pb pb geochronology of the archean salobo iron oxide copper gold deposit carajas mineral province northern brazil rhenium osmium ages were determined for two molybdenite samples and a pb pb age was derived from bornite chalcopyrite magnetite at the salobo iron oxide copper gold deposit to determine the timing of mineralization and its relation to the nearby old salobo granite rhenium osmium dating of molybdenite spatially associated with copper sulfide minerals yields ages with weighted means of 2576 8 and 2562 8 ma removing the error multiplier introduced by the decay constant uncertainty appropriate for comparing ages from the same isotopic system these data convincingly argue for two temporally separated pulses of molybdenite deposition at 2576 1 1 4 ma n 2 and 2561 7 3 1 ma n 3 the 2576 8 ma age coincides with a previously published u pb age of 2573 2 ma for the old salobo granite suggesting that main stage ore formation may have been contemporaneous with granite magmatism the slightly younger 2562 ma age most likely represents new molybdenite precipitation associated with the development or reactivation of local shear zones lead lead stepwise leaching of copper sulfide minerals yields a less precise isochron age of 2579 71 ma and supports an archean age for the salobo ores this is the first documentation of an archean iron oxide copper gold deposit and the re os and pb pb geochronology herein support 2580 2550 ma estimates for basement reactivation and regional granite magmatism associated with the development of brittle ductile shear zones

zircon geochronology geochemistry and origin of the ttg suites of the rio maria granite greenstone terrane implications for the growth of the archean crust of the carajas province brazil abstract ttg suites are the most voluminous granitoid rocks exposed in the mesoarchean rio maria granite greenstone terrane rmggt southeastern amazonian craton extensive field work in key areas of the rmggt integrated with petrographic geochemical and geochronological studies the latter employing the pb pb evaporation and u pb la mc icpms on zircon techniques indicates that the ttg magmatism in the rmggt can be divided into three episodes 1 at 2 96 0 02 ga the older rocks of the arco verde tonalite and the mogno trondhjemite 2 at 2 93 0 02 ga caracol tonalitic complex mariazinha tonalite and the younger rocks of the arco verde tonalite and 3 at 2 86 0 01 ga agua fria trondhjemite the new data demonstrate that the mogno trondhjemite is significantly older than thus far assumed reveal the existence of a new ttg suite mariazinha tonalite and indicate that the volume of ttg suites formed during the 2 86 event was relatively small the arco verde tonalite yielded significant age variations 2 98 2 93 ga but domains with different ages could not be discerned the tonalitic trondhjemitic suites of the rmggt derived from sources geochemically similar to the metabasalts of the andorinhas supergroup that were extracted from the mantle during the mesoarchean 3 0 2 9 ga three groups of ttg granitoids were distinguished in rio maria 1 high la yb group with high sr y and nb ta ratios derived from magmas generated at relatively high pressure 1 5 gpa from sources with residual garnet and amphibole 2 medium la yb group with magmas formed at intermediate pressure 1 0 1 5 gpa but still in the garnet stability field and 3 low la yb group with low sr y and nb ta ratios crystallized from magmas generated at lower pressures 1 0 gpa from an amphibolitic source with residual plagioclase these three geochemical groups do not have a direct correspondence with the three episodes of ttg generation and a single ttg unit can be composed of rocks of different groups a model involving hot subduction underneath a thick oceanic plateau was envisaged to explain the tectonic evolution of the rmggt in this context the low la yb group was formed from magmas originated by the melting of the base of a thickened basaltic oceanic crust at comparatively lower pressures ca 1 0 gpa whereas the medium and high la yb groups were derived from slab melting at differing pressures 1 0 1 5 and 1 5 gpa respectively part of the ttg magmas formed between 2 98 and 2 92 ga reacted during their ascent with the mantle wedge and were consumed in the process leaving behind a metasomatized mantle 50 m y later at ca 2870 ma thermal events possibly related to slab break off and resultant asthenosphere mantle upwelling or to a mantle plume induced melting of the metassomatized mantle to form sanukitoid magmas these magmas may have heated the base of the archean continental crust and could have led to local melting of basaltic crust forming the agua fria trondhjemite magma