application of thermochronology to hydrothermal ore deposits thermochronology finds many applications in economic geology utilizing temperature sensitive radiometric dating techniques to reveal low temperature upper crustal processes can elucidate many aspects of deposit genesis including timing and duration of mineralization processes rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential the tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information in addition when thermochronometers are combined with geochronometers e g zircon u pb over 800 c of thermal history is revealed from emplacement to erosion fig 1 with the advent of computational algorithms that provide more accurate and detailed models of thermochronology results the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect this chapter summarizes the various ways that low temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits these deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies in this section we review the fundamental application of u th he fission track and 40ar 39ar thermochronometry methods to mineralized systems we then present a synopsis of how these techniques can be used in thermal history analysis either alone or in combination with other chronometers in order to provide more information on deposit genesis the discussion is presented from low through to higher temperature thermochronometers corresponding to their presentation on figure 1 u th he thermochronology as documented earlier in the volume u th he thermochronology is based on measuring the accumulation of radiogenic 4he produced from u and th decay the daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change this closure temperature varies from

long term fluvial archives in the fen wei graben central china and their bearing on the tectonic history of the india asia collision system during the quaternary abstract staircases of large scale river terraces are striking features of the landscape in the fen wei graben adjacent to the qinling orogenic belts central china field investigations indicate that all five river terraces are composed of a basal channel gravel and an overlying thick loess palaeosol succession as chinese loess stratigraphy has been well studied it favours age determination of these terraces and their correlation with the marine oxygen isotope stages our research indicates that the ages of the five terraces are approximately 2 6 1 2 0 9 0 65 and 0 15 ma respectively the formation of these river terraces within the fen wei graben has been attributed to nw se crustal extension associated with left lateral displacement between the north and south china blocks in response to the northward movement of india towards asia since cenozoic time thus the stepped terraces in the fen wei graben reflects elements of the india asia collision systems in which terraces define episodes of accelerated northward movement of india towards asia during the quaternary

estimating relative ages from iron oxide total iron ratios of soils in the western po valley italy abstract nineteen samples were collected from deeper layers of as many terraces forming agesequences in five basins most samples were collected at depths of 1 m or more with some below 3 m soils at the sample sites were tentatively identified as alfisols entisols or inceptisols total amounts of iron and the amounts extractable by dithionite and by oxalate were determined for the 19 samples redness ratings were calculated from sample colors and related to amounts of extractable iron by regression mineralogies of the fine sand silt and clay fractions were also determined the percentage of the total iron fe t extracted by dithionite fe d minus the amount extracted by oxalate fe o increased gradually with ages of the terraces which range from early middle pleistocene to upper pleistocene holocene these percentages are independent of the total amounts of iron in the samples and of the general lithology of a basin such ratios thus promise to be useful in estimating relative ages especially where time sequences exist mineralogies of the samples were consistent with relative ages of terraces as estimated from the ratios of iron in different forms so were the redness ratings the regression of extracted iron on redness ratings suggests that colors can be used as preliminary field indicators of relative ages of terraces without time sequences

regional uplift and local tectonic deformation recorded by the quaternary marine terraces on the ionian coast of northern calabria southern italy abstract the setting of a flight of marine terraces along a 65 km long section of the ionian coast of northern calabria is the result of the interaction between interglacial sea levels regional uplift and local fault related elevation changes seven terraces with corresponding palaeoshoreline angles at elevations ranging from 12 m to 420 m were recognised by aerial photo interpretation and field surveying the terraces were correlated to the oxygen isotope stages 1 5a 5c 5e 7 9 15 which correspond to the 7 81 102 124 215 330 and 600 ka highstands of the palaeosea level curve the 600 ka long regional ascent of the terraces took place at an average uplift rate of 0 67 mm yr this value slightly but progressively increases southward along the coastline the elevation of the strandlines is related to the activity of tectonic structures three cases were analysed allowing us 1 to recognise the height anomalies of the terraces on the sibari plain as the result of cumulated coseismic deformation caused by the normal castrovillari fault and on this basis calculate a minimum slip rate and a mean recurrence time for a single event of deformation 2 to exclude the presence of significant vertical deformations and consequently activity on the easternmost section of the normal pollino fault and 3 to hypothesise the presence of an hitherto unknown active fault responsible for the strong vertical displacements of the flight of terraces near the river avena finally we find the ratio of the rate of regional uplift to the average rates of local tectonic deformation to be 2 to 3 1

a high resolution record of the last deglaciation in the southern tyrrhenian sea environmental and climatic evolution a multidisciplinary study was carried out on core c106 collected in the salerno gulf southern tyrrhenian sea two tephra layers recovered in the core n 18 o record of globigerinoides ruber and globigerina bulloides and seven 14 c calibrated ages provided the stratigraphic framework the core sediments cover the last 28 kyr bp seismostratigraphic analysis of a high resolution acoustic profile integrated by the dated core samples allowed us to reconstruct the architecture and age of sedimentary bodies on the continental shelf an integrated study based on different taxonomic groups nannofossils pteropods foraminifera and palynomorphs provided palaeoclimatic trends in agreement with changes in the isotopic composition of oxygen the upper part of the last glacial period the deglaciation phase and the holocene were identified correlation between marine and continental records of palaeoenvironmental changes confirms a similar reconstruction of the last deglaciation as in the central and southern mediterranean sea the late pleistocene holocene boundary was recognised at about 11 7 kyr bp between about 9 5 and 6 kyr bpand at 3 3 kyr bpsome warmer episodes were recorded the measured lower isotopic values together with some features of the fossil assemblages recorded from 9 5 to 6 kyr bp may be related to the oceanographic setting that led to the deposition of sapropel s1 in the mediterranean basin 2002 elsevier science b v all rights reserved

mechanisms of ar release from himalayan metamorphic hornblende changes in hornblende samples that occur during stepwise 39ar 40ar analysis were studied experimentally and mineralogically a complex succession of reactions was seen hornblende oxyhornblende clinopyroxene structured phase fine grained reaction products glasses in the temperature range 750 1300 c the release of ar from hornblende in the vacuum furnace appeared to occur by fundamentally different processes from those resulting in ar loss during metamorphism simple diffusional interpretations of the release patterns are therefore not capable of revealing the thermal history of samples in principle some useful information may be obtained if long standing fractures andother defects control both natural ar loss and mineral reactions within the laboratory

the timing of gold mineralization across the eastern yilgarn craton using u pb geochronology of hydrothermal phosphate minerals the highly mineralized eastern goldfields of the eastern yilgarn craton is an amalgamation of dominantly neoarchaean granitoid greenstone terranes and domains that record a history of early rifting followed by westward directed collision with initial arc formation collision and clastic basin formation and final accretion to the western yilgarn proto craton between 2 66 and 2 60 billion years ago the gold deposits that define this region as a world class gold province are the product of orogenic processes that operated during accretion late in the tectonic history after initial compressional deformation d1 d2 and the majority of granitoid magmatism minor gold was also deposited throughout the entire tectonic history in magmatic hydrothermal related systems however such mineralization mostly 0 3 g t gold is nowhere economic unless it overprints or is overprinted by much higher grade orogenic gold lodes robust shrimp u pb geochronology of gold related hydrothermal xenotime and monazite supports structural studies that gold mineralization occurred during late transpressional events d3 d4 shortly before cratonization however westward migration of collision and accretion produced a complementary diachroneity in the timing of gold mineralization of 5 to 20 m y between c 2 65 ma in the east including laverton district kurnalpi terrane to c 2 63 ma in the west including kalgoorlie terrane across the eastern part of the craton the robust geochronology refutes previous suggestions that significant gold mineralization events extended from de to d4 in the evolution of the orogen and that the kalgoorlie gold deposits formed over a period of 45 m y the crustal continuum model is applicable within terranes where orogenic gold depositional events were penecontemporaneous but must be modified to account for diachroneity of orogenic events and gold mineralization across the eastern goldfields

100 ma timing paradox of archean gold abitibi greenstone belt canada new evidence from u pb and pb pb evaporation ages of hydrothermal zircons abundant hydrothermal zircon occurs within quartz tourma line veins at four gold deposits in the val d or district of the archean abitibi greenstone belt canada host rocks to the gold bearing veins are characterized by pronounced metasomatic enrichment of zr hf y and rare earth elements hydrothermal zircons contain inclusions of quartz tourmaline scheelite pyrite and gold in hydrothermal zircons and quartz primary low salinity h2 co2 fluid inclusions coexist with co2 rich inclusions indicating co2 unmixing and gold precipitation at 260 to 380 c and 2 kbar the zircons have 207pb 206pb evaporation ages of 2683 20 to 2703 4 ma close to a concordant u pb age of 2693 2 ma both commensurate with previous shrimp ages for the zircons the same vein systems have u pb ages on rutile and titanite sm nd dates on scheelite and 40ar 39ar ages on muscovite that scatter between 2630 to 2579 ma these ages gave rise to a late gold model in the archean superior province vein gold deposits are related in space and time to terrane boundary structures which mark the diachronous accretion of allochthonous tectonostratigraphic terranes from south to north from 2720 to 2680 ma consequently the vein zircon ages of 2690 to 2680 ma at val d or represent the primary mineralizing event consistent with its late kinematic timing throughout the superior province and with late archean supercontinent assembly globally whereas the young scattered ages record the time of secondary fluid events associated with reactivation of the structures resetting some isotopic systems below their conventional blocking temperature

the iron content of some red mediterranean soils from northeast spain and its pedogenic significance abstract alfisols cover 18 of the surface of the ne edge of the garraf massif se of barcelona catalonia most of these are mediterranean red soils some representative pedons especially over mesozoic limestones are discussed in this paper climate of the zone is littoral mediterranean mean temperature 16 c precipitation 650 mm pedoclimatic regimes are xeric and thermic vegetation is quercetum ilicis galloprovinciale horizon b is 5yr and 2 5yr in munsell hue with a phw of 7 2 to 8 6 all of them are base saturated and the majority recarbonated organic matter content is 2 5 some have an isohumic character the illuviation clay index ranges from 0 37 to 0 87 and the mean value of the illuviation fe index is 0 76 the nearly constant fed clay ratio indicates co illuviation values for fed are between 0 40 and 2 81 the mean feo is 0 057 and it ranges between 0 to 0 14 generally redness rating rr increases with fed values of fed fe1 vary from 0 22 to 0 82 and the mean is 0 54 rubefaction according to redness rating is moderate taxonomically calcic haploxeralfs predominate and are located at 50 70 m above sea level calcic palexeralfs at 70 80 m and again at 150 m and petrocalcic palexeralfs at 80 130 m are also found typic haploxeralfs are frequent over limestones at higher altitudes 260 m or overlying silicic rocks found at 35 65 m according to the 1967 french classification system they are red fersialitic and brown fersialitic soils and some are integrades with cinnamotnic soils marron encroute

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

an integrated micropalaeontological approach applied to late pleistocene holocene palaeoclimatic and palaeoenvironmental changes gaeta bay tyrrhenian sea

39ar recoil artifacts in chloritized biotite biotite separates from the metamorphosed granitic rocks of eastern taiwan yield disturbed 40ar39ar age spectra their disturbed profiles become more pronounced with increasing degree of chloritization and are attributed to mixed release of argon from sub micron scale biotite and chlorite intercalations 39ar internal recoil best explains the discordance of the age spectra chlorite is randomly intercalated with biotite at scales ranging from 10 a to several tens of microns both 40ar and k were evidently lost during the chloritization reaction during the neutron irradiation 39ar atoms recoil into the chlorite from the adjacent biotite intercalations the recoil and chloritization combine to produce a variable 40ar39ar spatial distribution in the intercalated biotite chlorite during 40ar39ar step heating analyses argon in biotite is released in two pulses centered at 650 c and 950 1050 c which represent two stages of dehydroxylation of the biotite chlorite out gasses in two pulses centered at 550 c and 700 900 c during dehydroxylation and then decomposes this differential thermal release of argon from each mineral phase with variable 40ar39ar ratios yields discordant incremental heating age spectra

dating of archean auriferous quartz vein deposits in the abitibi greenstone belt canada 40 ar 39 ar evidence for a 70 to 100 ma time gap in between plutonism metamorphism and mineralization discussion

archean gold mineralization synchronous with the final stages of cratonization yilgarn craton western australia sm nd ages of pegmatite dikes that crosscut gold bearing structures in the southern yilgarn craton western australia provide minimum age constraints of 2640 6 11 ma 2628 6 10 ma and 2620 6 36 ma for gold mineralization at the westonia and nevoria yellowdine terrane and scotia norseman terrane gold deposits respectively similarly a post gold mineralization dike at westonia has a u pb zircon age of 2637 68 ma theseconstraintsareconsistentwith andprovidefurthersupportfor suggestionsthatthe majority of gold deposits in the yilgarn craton formed during a regionally extensive gold mineralization event at ca 2630 ma i e 2630 6 10 ma in combination with recent geochronological results these data also provide further evidence that although mineralization appears to significantly postdate the majority of magmatic and metamorphic activity at higher crustal levels widespread thermal reworking of the lower middle crust involvingpartialmelting amphibolitetogranulitefaciesmetamorphism andlowercrustal granitoid intrusion occurred concurrently with gold mineralization at ca 2630 ma it is probable that the large scale hydrothermalfluidflow that produced widespread gold deposition was also part of this tectonothermal event models developed for other archean terranes whereby gold mineralization postdates formation and cratonization of host granite greenstone terranes and is therefore unrelated to these processes are not required to explain the timing of the majority of gold deposits in the yilgarn craton

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

fluvial response to late quaternary climate changes western india we review here the fluvial response to late quaternary climatic changes in the semi arid regions of western india i e the thar desert and its margins and maharashtra the rivers in the thar desert show a spectrum of environments from gravel bedload braided to ephemeral sand bed streams to sheet flows and sheet floods while those in the thar margin and maharashtra show dominantly two modes i e braided and meandering rivers the streams became defunct and aeolian sands were deposited during periods of relatively greater aridity in the thar desert and its margins incisions occurred during the wet phases in ois 1 it is inferred that changes in the monsoon precipitation led to relative changes in the discharge and sediment supply which were routed through those in the vegetation cover and played a key role in determining the fluvial style an inter comparison of the late quaternary alluvial deposits in the semi arid regions of western india suggests a continuum of fluvial environments interrelated through a precipitation gradient further a global comparison indicates that the response of semi arid western indian rivers was synchronous with the rivers in other climatic settings

40ar 39ar geochronological evidence for multiple postmetamorphic hydrothermal events focused along faults in the southern abitibi greenstone belt thermal histories in the abitibi and pontiac subprovinces vary for three general domains 1 zones of impermeable rock with cooling rates of 8 c ma 2 zones of impermeable rock that are spatially associated with monzogranite plutons with apparent cooling rates of 1 2 cima and 3 permeable high strain zones with apparent cooling rates of 2594 ma from the volcanogenic massive sulphide related sericite alteration with the coarser mica yielding the younger date based on radiometric dating impermeable rocks were affected weakly by postmetamorphic hydrothermal events minerals in zones of higher permeability were reset during the intrusion of monzogranite plutons highly permeable zones such as the larder lake cadillac and porcupine destor faults were overprinted repeatedly this produces a drawn out series of dates from minerals with varying closure temperatures radiometric ages from fault zones or ore deposits cannot be used to interpret the cooling history and evolution of the abitibi belt as a whole

alluvial terraces on the ionian coast of northern calabria southern italy implications for tectonic and sea level controls abstract in this paper we present the results of an integrated geomorphological pedological and stratigraphical study carried out along the ionian coast of northern calabria southern italy this area is characterised by the occurrence of five orders of alluvial terraces that are striking features of the landscape where large and steep catchments debouch from the mountain front to the hilly coastal belt field investigations indicate that the deposits of all five terraces are suggestive of shallow gravel bed braided streams on the basis of the age of the pleistocene substratum and morphostratigraphic correlation with marine terraces cropping out in the nearby areas each order has been associated to specific marine oxygen isotope stages consequently we focused on the interplay of allocyclic factors influencing stream aggradation degradation soil features and other climatic proxies suggest that climate didn t play an important role with respect to tectonic and base level changes in controlling fluvial dynamics in particular we recognised that during the middle pleistocene the study area experienced a period of subaerial landscape modelling as suggested by the thick and complex alluvial sequence of the highest terrace t1 the onset of regional uplift marks a change in the geomorphic scenario with tectonic and eustatically driven changes in base level working together in causing switches in fluvial aggradational erosional phases t2 t5 terraces because of the uplift river dissection occurred during phases of sea level fall whereas aggradation phases occurred during periods of climate amelioration sea level rise just before highstands were attained as a consequence the stepped terraces in the study area reflect the interplay between tectonics uplift and sea level changes in which terraces define episodes of relative sea level fall during the late quaternary

the nature and dimensions of regional and local gold related hydrothermal alteration in tholeiitic metabasalts in the norseman goldfields the missing link in a crustal continuum of gold deposits the archaean lode gold deposits at norseman western australia consist of auriferous quartz veins in dextral reverse ductile brittle shear zones within tholeiitic metabasalts of upper greenschist to amphibolite facies metamorphic grade three types of deposits northern central southern are delineated on the basis of their spatial distribution veining style alteration mineraloty and metamorphic grade of host rocks northern deposits hosted in upper greenschist to lower amphibolite facies rocks comprise massive to laminated quartz veins with selvedges of quartz chlorite calcite biotite plagioclase assemblages central deposits hosted in lower amphibolite facies rocks consist of laminated to massive quartz veins with selvedges of quartz actinolite biotite plagioclasecalcite assemblages southern deposits hosted in middleamphibolite facies metabasalts consist of banded quartz diopside calcite microcline zoisite veins all deposits exhibit variable ductile deformation of veins and contiguous alteration haloes consistent with a syn deformational genesis at high temperatures from northern to southern deposits the alteration assemblages are indicative of higher temperatures of formation and there are progressively greater degrees of dynamically recovered textures in alteration and gangue minerals these observations imply that a thermal variation of gold related hydrothermal alteration exists within the norseman terrane over a distance of 40 km with tnorthern tcentral tsouthern this thermal zonation is corroborated by t xco 2 phase relations between vein selvedge assemblages which signify formation temperatures of approximately 420 475 c 470 495 c and 500 c for northern central and southern deposits respectively the sum of structural petrographic and mineral chemistry data indicates that the alteration assemblages formed in high temperature open hydrothermal systems and have not been subsequently metamorphosed the thermal differences between the deposit groups may reflect 1 a temperature gradient at relatively constant p corresponding to the proximity of the deposits to regional granitoid complexes or 2 formation of the deposits at progressively deeper crustal levels from north to south in either case the deposits represent a continuum of gold deposition from upper greenschist to amphibolite facies now exposed in an oblique section through the archaean crust at norseman

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

the crustal continuum model for late archaean lode gold deposits of the yilgarn block western australia most archaean gold ores belong to a coherent genetic group of structurally controlled lode deposits that are characteristically enriched in au with variable enrichments in ag as w sb bi te b and pb but rarely cu or zn and are surrounded by wallrock alteration haloes enriched in k lile and co2 with variable na and or ca addition evidence from the yilgarn block of western australia combined with similar evidence from canada and elsewhere indicates that such deposits represent a crustal continuum that formed under a variety of crustal regimes over at least a 15 km crustal profile at pt conditions ranging from 180 c at 1 kb to 700 c at 5 kb individual deposits separated by tens to hundreds of kilometres collectively show transitional variations in structural style of mineralisation vein textures and mineralogy of wallrock alteration that relate to the pt conditions of their formation at varying crustal depths specific transitions within the total spectrum may be shown also by deposits within gold camps although nowhere is the entire continuum of deposits recorded from a single gold camp or even greenstone belt

disturbed 40ar39ar spectra from hornblendes thermal loss or contamination abstract accurately weighed aliquots of the 500 ma old interlaboratory standard hornblende mmhb 1 were mixed with known quantities of a 100 ma old himalayan biotite and subjected to normal 40 ar 39 ar incremental heating analysis the addition of the biotite created monotonically increasing apparent ages similar to profiles interpreted as showing ar diffusive loss in the literature the release of ar from biotite dominates the low temperature portion of the spectra and lowers the observed age lower ca k ratios in the first increments are consistent with contamination but do not distinguish the composition of the contaminant phase a large number of published amphibole diffusive loss profiles may in fact be due to contamination by biotite or other phases which release ar at low extraction temperatures

archean polyphase deformation in the lake johnston greenstone belt area implications for the understanding of ore systems of the yilgarn craton abstract a structural and geochronology study on the 2900 ma lake johnston greenstone belt ljgb has defined multiple deformation events quantitative u pb age constraints have been obtained on the ductile deformation and peak metamorphic assemblages the d 1lj event is associated with the development of fold nappes during interpreted nne ssw shortening u pb shrimp dating on monazite from a dyke folded by the d 1lj event gives an age of 2634 1 ma providing an upper age limit on d 1lj this age could have been reset by the d 2lj metamorphic event a major metamorphic thermal event post dates the d 1lj event and is inferred to be the result of elevated temperatures coeval with the emplacement of granitoid intrusions the d 2lj event is associated with peak metamorphic temperatures and reflects nne ssw to ne sw shortening associated with dextral shearing a dyke that intrudes and crosscuts d 2lj fabrics yield a u pb shrimp age on monazite at 2629 1 ma and provides a lower age limit on the d 2lj event d 3lj is defined by crenulation cleavages developed during e w shortening the d 4lj episode is defined by brittle deformation and a series of n to ne trending steep dipping dextral faults formed during craton scale shortening under a ne sw directed far field stress the brittle d 5lj event is characterized by e w shortening with dip slip reverse n s faults the new d 2lj deformation age is younger than previously constrained ages for major deformation in the 2900 ma greenstone belts deformation within the ljgb was broadly coeval with the waning stage of formation of gold deposits in adjacent greenstone belts most peak magmatic and metamorphic events preserved in the greenstone belts have been constrained to ca 2640 2650 ma the presence of such a high temperature deformation event recorded at ca 2630 ma in the ljgb belt has implications for the thermal history fluid formation and geodynamic context of the development of these gold systems the 2630 ma age correlates with late stage and post gold emplacement of pegmatite dykes in surrounding terranes the ljgb is interpreted to have been a mobile belt associated with high grade metamorphism that was inboard west of and active during the formation of major world class gold systems in the eastern goldfields terranes the d 1lj to d 2lj changes in the kinematics of the system i e d 1lj to d 2lj may correlate with a stress switch linked to the influxes of gold bearing fluids in adjacent greenstone belts

broad synchroneity of three gold mineralization styles in the kalgoorlie gold field shrimp u pb and 40ar 39ar geochronological evidence there has been a long standing controversy regarding the timing and number of gold mineralization events at kalgoorlie uranium pb dating of zircons and hydrothermal monazite and xenotime as well as ar 40 ar 39 analysis of metasomatic fuchsite and white mica are used to date pre to synore dikes alteration and orebodies in order to resolve this issue the majority of gold mineralization at kalgoorlie including ductile brittle fimiston brittle ductile oroya and brittle mount charlotte style gold are different expressions of a complex mineralizing system that was active at broadly the same time at ca 2 64 ga gold mineralization was thus deposited in both ductile and brittle structures at approximately the same crustal level at broadly the same time limier similar pt conditions this giant ore system formed after ea 2 69 ga basic magmatism intrusion of the golden mile dolerite sill at 2680 9 ma and intrusion or calc alkaline feldspar quartz porphyry dikes at 2670 5 ma gold mineralization was broadly coeval with lamprophyre dike intrusion at 2642 6 ma and overlapped the waning stages of hornblende and albite bearing porphyry dike emplacement at 2650 6 ma and regional metamorphism subsequent brittle deformation in the kalgoorlie gold held way accompanied by hydrothermal activity that may have led to some late gold mineralization or remobilization in extensional quartz vein arrays in the golden mile between about 2 61 and 2 60 ca this late hydrothermal activity and associated brittle deformation marks the last event to significantly affect the rocks it kalgoorlie and may be related to uplift lift and final cooling of the terrane despite this late event the geometry of the kalgoorlie gold field and its contained lode systems has remained essentially the same since the time of gold mineralization

pedogenic correlation of lateritic river terraces in central taiwan abstract the pakua chushan and touliu terraces are three groups of lateritic river terraces resulting from different fluvial systems in central taiwan their geomorphic features do not enable regional correlations to be made in this study an alternative scheme based on the quantification of a pedogenic development is proposed for this correlation four soil pedons from the chushan and touliu terraces are classified as ultisols cs 1 cs 2 and tl 1 and an inceptsol tl 4 following the soil taxonomy an additional six soil pedons including an oxisol pk 1 ultisols pk 2 3 4 and 5 and an inceptsol pk 6 from the pakua terraces were included from a previous study tsai h huang w s hseu z y chen z s 2006 a river terrace soil chronosequence of the pakua tableland in taiwan soil science 171 167 179 the weighted mean profile development indices wpdi for the pedons suggest a chronological order of i pk 1 ii pk 2 iii pk 3 iv pk 4 cs 1 and tl 1 v pk 5 and cs 2 vi pk 6 and vii tl 4 the correlation suggests the chushan and touliu terraces correspond to the same surface of an anticline separated by the chinshui river surface deformation reflects the growth of the underlying structure in which uplift folding occurred in the hinge zone and tilted to the east along the fold limb as a result of the southern extension of the pakua anticline however the different geometries on both the surface and subsurface from southern pakua anticline indicate a mechanism of fault bend folding for touliu hill

mafic dike swarms in the south shetland islands volcanic arc unravelling multiepisodic magmatism related to subduction and continental rifting eight groups of mafic dikes and related high level stocks cut triassic accretionary complex and mesozoic magmatic arc formations on livingston island some are affected by silicic sericitic alteration related to cretaceous hydrothermal activity and propylitic epidosite alteration analogous to that in ocean floor sheeted dikes alteration was accompanied by major and trace element metasomatism ar ar analysis of the freshest rocks indicates five intrusive events some of which are unexpectedly young groups 1 3 were intruded in the mid to late cretaceous 108 74 ma and were coeval with the calc alkaline arc between 70 and 50 ma relatively rapid and oblique plate convergence led to strike slip tectonism and a pause in magmatism at 52 ma orthogonal slow convergence resulted in extensional faulting and emplacement of calc alkaline group 2 and primitive tholeiitic dikes groups 4 6 between 51 and 45 ma extension of antarctic peninsula southern south american crust culminated in emplacement of mafic to intermediate medium grained plutons and group c porphyries between 44 and 36 ma localized hydrothermal flow along fault zones resulted in partial to complete argon loss from nearby cretaceous lavas and ar ar reset ages of 40 ma in mid cretaceous hydrothermal k feldspar primitive olivine basalts group d and epithermal carbonate veins 31 29 ma were emplaced during along arc extension accompanying the opening of drake passage and powell basin excess argon occurs in two forms strongly held in melt inclusions in the primitive tholeiites and weakly held in some secondary alteration there is no radiometric evidence in the area studied for magmatism related to late cenozoic subduction nor to the pleistocene recent opening of the back arc bransfield rift

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

thermochronology of the camflo gold deposit malartic quebec implications for magmatic underplating and the formation of gold bearing quartz veins the dominant ore host at camflo is a small monzonite pluton cut by main stage gold bearing quartz veins containing hydrothermal titanite and k feldspar main stage veins are spatially and temporally related to brittle ductile faults emplaced into most faults are younger transitional stage quartz pyrite lodes with sericite rutile alteration halos titanite in main stage gold quartz veins is replaced by rutile calcite quartz where overprinted by transitional stage sericitic alteration a u pb zircon age from the camflo monzonite indicates that the stock was emplaced at 2685 or 10 ma a u pb age of 2621 or 4 ma for hydrothermal titanite and a pb pb isochron age of 2621 or 7 ma defined by seven titanite and two k feldspar samples indicate that the gold quartz veins formed approximately 60 m y later which precludes a direct genetic link between these two events rutile analyses plot below the titanite feldspar pb pb isochron and so support field and petrographic evidence suggesting rutile did not precipitate from the same fluid that formed the titanite and k feldspar incremental heating and total fusion 40 ar 39 ar ages of hydrothermal micas related to gold quartz veins and quartz pyrite lodes are 70 to 170 m y younger than the hydrothermal u pb ages in addition 40 ar 39 ar ages of micas on the 1650 level are approximately 10 to 15 m y older than like micas on the 3475 level the younger 40 ar 39 ar ages are interpreted as cooling and not recrystallization or reset ages 40 ar 39 ar ages indicate cooling rates of approximately 1 degrees c m y for 2600 to 2550 ma rutile vein muscovite approximately 0 6 degrees c m y for 2550 to 2511 ma vein muscovite wall rock muscovite and approximately 0 3 degrees c m y for 2507 to 2452 ma large biotite small biotite an apparent uplift rate of approximately 0 04 km m y for 2520 to 2478 ma is calculated by comparing biotite and white mica ages from the 1650 and 3475 levels the u pb and 40 ar 39 ar thermochronology is consistent with an accretionary tectonic setting for camflo during the terminal stages of tectonic construction of the superior province a critical feature of this setting is large volumes of mantle derived basalt underplating the lower crust during peak granulite formation at approximately 2648 to 2640 ma co 2 rich fluids liberated by solidification of ponded mafic magma after peak granulite formation interacted with other fluids magmas and rock either at their source or during migration in shear zones to upper crustal levels where they deposited significant quantities of gold at camflo at approximately 2621 ma slow cooling and slow apparent uplift at camflo ensued for 150 m y after magmatic under plating resulting in the young 40 ar 39 ar cooling ages recorded by hydrothermal minerals this model is consistent with ages for granulite facies metamorphism in the kapuskasing structural zone postpeak metamorphic ages for co 2 h 2 o fluid inclusions in regional granulite terranes and geochronological data from other gold deposits and may have widespread implications for the formation of gold deposits in the southern superior province

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

dating of archean auriferous quartz vein deposits in the abitibi greenstone belt canada 40 ar 39 ar evidence for a 70 to 100 m y time gap between plutonism metamorphism and mineralization the sigma mine at val d9or quebec in the abitibi belt is typical of vein type gold deposits in archcan greenstone belts although the relative timing of gold mineralization with respect to magmatism metamorphism deformation and hydrothermal events in the mine is well documented precise isotopic age constraints have until recently been lacking this paper presents the results of a 40 ar 39 ar dating study of the sigma mine and of the davidson tisdale deposit in the abitibi belt in the sigma mine dates on metamorphic amphibole indicate that the regional metamorphism which predates the vein formation occurred at ca 2 68 ga muscovite from the gold bearing quartz veins yields a plateau date of 2579 or 9 ma 2sigma whereas biotite from the veins shows disturbed saddle shaped age spectra the mild disturbance of the biotite is attributed to later diabase dike emplacement and a 40 ar 39 ar date on a dike indicates that this event is younger than 2 3 ga thermal effects of the grenville orogeny 1 2 1 0 ga may also be present a muscovite separate from a gold bearing quartz vein at the davidson tisdale deposit yields a 2607 or 10 ma 2sigma plateau date although the amphibole and muscovite dates at the sigma mine bracket the gold mineralization event at between ca 2 68 and 2 58 ga a number of tectonothermal histories are possible for this time interval it is concluded based on all evidence that the muscovite plateau dates are the time of vein and gold formation which thus occurred in the sigma mine ca 100 m y and in the davidson tisdale deposit ca 70 m y after syn to post tectonic magmatism and regional metamorphism

the sis palaeovalley a record of proximal fluvial sedimentation and drainage basin development in response to pyrenean mountain building the sis conglomerate body represents the middle eocene to oligocene transfer zone trunk palaeovalley fill of the sis fluvial system a drainage system established within the pyrenees during late palaeocene times the spatial stability of the fluvial transfer zone active for at least 38 my and hence the longevity of its aggradational palaeovalley component 19 5 my was controlled by its location between long lived pre existing structures coarse grained fluvial facies dominate the palaeovalley fill with alluvial fan facies shed from its defining marginal structures the detailed sedimentology of very proximal fluvial facies deposited within the dominantly erosional realm of an active mountain belt has rarely been documented before because of their poor preservation potential the sis conglomerate body contains a robust internal stratigraphy with stratigraphic units defined by distinct bounding surfaces across which there are pronounced changes in facies and provenance these mark the reorganization of the headward portions of the sis fluvial system during the evolution of the pyrenean axial zone antiformal stack major changes in discharge resulted demonstrating the highly variable nature of even mountain belt scale fluvial systems when viewed on timescales of several to tens of millions of years provenance details indicate that initial unroofing of hercynian granitoids situated within the pyrenean axial zone occurred around 54 5 ma early ypresian immediately before the first significant exhumation event within the drainage basin of the sis fluvial system this is earlier than previously constrained by apatite fission track studies rock uplift accelerated in the lutetian and bartonian with the initial aggradation of the palaeovalley fill the cajigar and cornudella formations and sis one and two members this became marked in the priabonian sis three and four members with significant activity on local structures including the morreres backthrust an increase in basement derived clasts and a headwater decapitation event also indicate pronounced axial zone antiformal stack development at this time axial zone development intensified further in the oligocene with the deposition of the collegats formation and the switch in the main depositional loci of the system from the tremp graus thrust sheet top basin to the ebro basin to the south

relative and absolute timing of gold mineralization along the meliadine trend nunavut canada evidence for paleoproterozoic gold hosted in an archean greenstone belt the meliadine area of the neoarchean rankin inlet greenstone belt is located on the western shore of hudson bay canada and is host to several important orogenic or mesothermal gold deposits supracrustal rocks comprise alternating southeast striking panels of mafic volcanic and clastic sedimentary rocks both of which are host to banded iron formation the dominant structural element is the pyke break a several kilometer wide high strain zone characterized by multiple foliations and regionally important shear zones gold mineralization is spatially associated with these shear zones the maximum age of mineralization is constrained by the observation that auriferous veins crosscut ca 2450 ma mafic dikes and a minimum age is constrained by undeformed postore lamprophyre dikes emplaced at ca 1830 ma highly concordant shrimp determined ages on hydrothermal monazite indicate auriferous veining occurred at ca 1850 ma these relative and absolute timing constraints suggest gold was concentrated in neoarchean supracrustal rocks during paleoproterozoic tectonothermal activity that was widespread in the western churchill province at ca 1850 ma these observations do not preclude the presence of archean gold occurrences in the rankin inlet greenstone belt but no early deformed ores can be linked to auriferous veins introduced at ca 1850 ma suggesting remobilization from earlier formed deposits was not a factor in concentrating gold at meliadine

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

using the analysis of iron and iron oxides in paleosols tem geochemistry and iron forms for the assessment of present and past pedogenesis abstract this study investigates the iron oxide chemistry and mineralogy of two relict paleosols a ferri endostagnic lixisol bathiplinthic and a profondi endostagnic luvisol chromic the estimated inception of their pedogenesis is early pleistocene the two paleosols belong to the same geomorphic body but are found at different elevations and have experienced different hydrology expressed as either dark red or mottled dominant colors throughout their profile we hypothesized that the difference in color reflected a recent transformation of iron oxides that were mainly formed in the past the aim of the research was to discriminate recent from relict soil forming processes by evaluating iron oxide composition soluble forms and geochemistry in the studied profiles hematite and goethite feooh are the main iron oxides their fate depends on the present pedogenic conditions both hematite and goethite are a source of iron for recently synthesized iron oxides feroxyhyte feooh and fe protophases but hematite is preferentially dissolved in reducing conditions in the red soil profile hematite content still masks the presence of the other iron oxides while the mottled color of the topographically lower profile with poorer internal drainage is a consequence of a more advanced hematite dissolution the iron oxides hematite goethite and recently synthesized iron oxides are the result of different pedoclimatic conditions in former and present time hematite is inherited from past pedogenesis while feroxyhyte and fe protophases have been recently formed goethite can be of either current transformed from feroxyhyte or inherited origin these results indicate that the soils studied are polygenetic the red color and hematite content are the results of past soil forming processes acting in different climatic and drainage conditions

testing the apatite magnetite geochronometer u pb and 40ar 39ar geochronology of plutonic rocks massive magnetite apatite tabular bodies and iocg mineralization in northern chile abstract detailed zircon and apatite u pb dating and 40 ar 39 ar dating of actinolite have been carried out on the carmen sierra aspera kiruna type magnetite apatite and iron oxide cu au iocg district in the coastal cordillera of northern chile 26 s they define a precise succession of magmatic and hydrothermal events associated with early cretaceous andean magmatism apatite and magnetite from a magnetite apatite tabular body with intergrowth texture in the carmen deposit yield a total pb u isochron age of 131 0 1 0 ma this result is the first direct dating of magnetite apatite mineralization in an early andean deposit and the age coincides with zircon ages of a quartz diorite stock that partially hosts mineralization 130 6 0 3 ma magnetite from the studied tabular body contains only small amounts of radiogenic pb and serves to constrain the initial common pb isotopic composition the high degree of correlation suggests that both minerals closed for pb diffusion at essentially the same time and at a relatively high temperature close to that of zircon making the apatite magnetite pair a reliable geochronometer for igneous or hydrothermal crystallization zircon from the sierra aspera composite pluton yields ages between 131 3 0 3 ma and 127 4 0 1 ma clearly resolving the timing of intrusion of discrete intrusive phases actinolite 40 ar 39 ar ages partially overlap the ages of plutonic phases of the sierra aspera pluton but are younger than the magnetite apatite tabular body the initial pb isotopic composition of the melts and or fluids from which the magnetite apatite tabular bodies crystallized is very similar to the primitive pb isotopic composition of granitic magmas associated with early cretaceous plutons measured in k feldspar the pb isotopic correspondence combined with the temporal and spatial association between magnetite apatite mineralization and the dioritic quartz dioritic magmatism strongly suggests a genetic relationship between early cretaceous continental arc magmatism massive magnetite apatite deposits and iocg mineralization

exsolution in hornblende and its consequences for 40ar39ar age spectra and closure temperature abstract step heating studies of hornblende and biotite which coexist in an amphibolite near north walpole vermont reveal dramatically different 40 ar 39 ar age spectra the biotite mg 59 is characterized by a plateau over 98 percent 39ar release at 343 5 ma in strong contrast to the amphibole which exhibits both a complex age spectrum and a k ar age significantly younger than the biotite the amphibole release pattern contains three complete age cycles which range between extremes of 199 ma and 408 ma interestingly the k ca ratio calculated from reactor produced isotopes also varies with ar release but follows a trend which is antipathetic to the 40 ar 39 ar age pattern detailed microstructural examination including transmission electron microscopy tem reveals a complex exsolution structure that is consistent with both the complexity of the release pattern as well as the low degree of radiogenic 40ar 40ar retentivity in the amphibole this result underscores the variability of closure temperature tc for 40ar in metamorphic amphiboles and should warn against accepting a single universal value of tc

compositional controls on 40 ar 39 ar ages of zoned mica from a rare element pegmatite a high spatial resolution ar ar dating study of compositionally zoned micas using uv laser extraction has been used to investigate the effect of composition and compositional boundaries upon argon diffusion in mica the crystals are characterised by muscovite cores and li f rb cs rich lepidolite rims produced by the interaction of a residual melt vapour phase with the original muscovite during the late stages of pegmatite crystallisation single crystals exhibit dramatic intra grain age variations with a maximum range of 2 880 2 117 ma backscattered electron images combined with uv laser analyses reveal that apparent ages younger than 2 600 ma are directly associated with the compositionally distinct rims suggesting that ar diffusion was faster in the lepidolite than in muscovite although it is not possible to be fully quantitative using the present data it seems that argon diffusion rates in lepidolite are similar to those in biotite major rearrangements of the crystal structure needed to accommodate high concentrations of lithium fluorine and large interlayer cations rb cs in muscovite account for lower argon retentivity of the crystal rims in most cases the age profiles show no disturbance at the compositional boundary despite the transition from a di octahedral to tri octahedral mica indicating that in general the boundaries do not act as fast diffusion pathways however in some cases there is a clear drop in ages at the compositional boundary which acts as an effective sub grain boundary the difference between the two types may be related to the internal structure of the compositional boundaries or their degree of contact with the grain boundary network of the rock

the timing of strike slip shear along the ranong and khlong marui faults thailand 1 the timing of shear along many important strike slip faults in southeast asia such as the ailao shan red river mae ping and three pagodas faults is poorly understood we present 40ar 39ar u pb shrimp and microstructural data from the ranong and khlong marui faults of thailand to show that they experienced a major period of ductile dextral shear during the middle eocene 48 40 ma centered on 44 ma which followed two phases of dextral shear along the ranong fault before the late cretaceous 81 ma and between the late paleocene and early eocene 59 49 ma many of the sheared rocks were part of a pre kinematic crystalline basement complex which partially melted and was intruded by late cretaceous 81 71 ma and early eocene 48 ma tin bearing granites middle eocene dextral shear at temperatures of 300 500 c formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement dextral shear along the ranong and khlong marui faults occurred at the same time as sinistral shear along the mae ping and three pagodas faults of northern thailand a result of india burma coupling in advance of india asia collision in the late eocene 37 ma the ranong and khlong marui faults were reactivated as curved sinistral branches of the mae ping and three pagodas faults which were accommodating lateral extrusion during india asia collision and himalayan orogenesis

incremental heating of hornblende in vacuo implications for 40ar 39ar geochronology and the interpretation of thermal histories increasing evidence of the incompatibility between the geologic thermal histories deduced from the sup 40 ar sup 39 ar incremental heating technique and those derived form other methods have necessitated a careful evaluation of the assumptions inherent in the former approach sup 40 ar sup 39 ar age spectra are frequently used to infer the spatial distribution of ar in hydrous minerals and as such require that the mineral remains stable while heated in vacuo aliquots of mmhb 1 and inter laboratory hornblende standard used for k ar and sup 40 ar sup 39 ar dating were heated in vacuo at temperatures of 500 700 930 and 1 050c for 30 min up to 700c no physical changes in the hornblende were observed with the scanning electron microscope although x ray diffraction data indicate that it had dehydroxylated to oxyhornblende at this temperature the onset of the structural decomposition of the oxyhornblende as revealed by backscattered and secondary electron images occurs at approximately 930c and is directly correlated with the initial release of 6 of its radiogenic ar sup 40 ar the breakdown of the oxyhornblende by the internal nucleation of incongruent melt is almost 93 complete by 1 050c the reaction products being titano magnetite melt a pyribole phase and internal voids because ar is released simultaneously frommore these products and is subsequently homogenized in vacuo this breakdown can yield plateau age spectra regardless of any original ar spatial gradients in the mineral consequently independent evidence may be required to establish whether a plateau date from hornblende is truly a geologically significant age less

raised pleistocene marine terraces of the crotone peninsula calabria southern italy facies analysis and organization of their deposits abstract wide marine terraces well known in the italian literature are present in the crotone peninsula ionian calabria they are related to the interplay between pleistocene sea level changes and the progressive uplift of the calabrian arc from the middle pleistocene onwards we present a description of facies organization and stratigraphical characteristics of the terrace deposits along with a new geological map of the area all the marine terraces unconformably overlie a plio pleistocene slope succession known as cutro clay the oldest and highest terrace named cutro terrace is placed between 90 and 200 m of elevation and is gently inclined south eastwards four younger terraces placed at progressively lower elevations and dipping seawards at low angles have been recognized the sedimentary deposits of the terraces are represented by mixed carbonate and siliciclastic bodies up to 10 m thick algal reefs and grainstone to rudstone deposits are common in the south eastern part of the study area whereas mostly siliciclastic sandstone units of shoreface environments are more abundant northwards and westwards the deposits of some terraces are made up of minor cycles bounded by subaerial transgressive and flooding surfaces referred to minor sea level fluctuations nne ene e and wnw trending normal fault systems are present within the study area and dissect the marine terraces specifically the activation of ene trending faults took place after the formation of the oldest terrace but prior to the formation of the younger terraces

neotectonically controlled fluvial features walbrzych upland middle sudeten mts southwestern poland abstract the landscape of the walbrzych upland sudeten mts southwestern poland has developed over a long time involving three main stages i the oligocene early pliocene ii the late pliocene early pleistocene and iii the middle late pleistocene stage iii is neotectonically controlled and is discussed in detail the entire walbrzych upland was covered by a continuous ice cover during the early saalian and at least in its marginal part during the elsterian the pre early saalian fluvial landscape shows no evidence of tectonic activity in contrast with that of post early saalian time the post early saalian valleys have been formed during the intensive and short term uplift of the mountain upland with simultaneous re activation of fault zones the main geomorphological effects of this uplift are abandonment of valleys formation of deep river valleys cut within bedrock varying shapes of newly incised valleys highly irregular longitudinal profiles of channels varying numbers of terraces and their heights along the valleys tilting of terraces and formation of fault scarps at some fault lines the main geological effects are variable thicknesses of alluvial deposits caused by rotation of bedrock blocks synsedimentary increases of thickness of alluvial deposits at some fault lines and breaking of the continuity of some alluvial surfaces at the major fault lines the uplift of the walbrzych upland was controlled by glacio isostatic rebound after the early saalian glaciation supplemented by localised extensional tectonics total tectonic uplift was about 40 50 m

part ii evaluation of 40ar 39ar quartz ages implications for fluid inclusion retentivity and determination of initial 40ar 36ar values in proterozoic samples the argon isotope systematics of vein quartz samples with two different k reservoirs have been evaluated in detail potassium is hosted by ultra high salinity fluid inclusions in quartz samples from the eloise and osborne iron oxide copper gold iocg deposits of the mt isa inlier australia in contrast k is hosted by accidentally trapped mica within lower salinity fluid inclusions of a sample selected from the railway fault 13 km south of the mt isa copper mine australia imprecise apparent ages have been obtained for all of the samples studied and conclusively demonstrate that quartz fluid inclusions are retentive to ar and have not leaked over billions of years iocg samples that host k in fluid inclusions only have k cl values of 1 and the ages obtained represent the maximum ages for mineralization in contrast the railway fault samples that include accidentally trapped mica have k cl values of 1 excess 40 are plus cl hosted by fluid inclusions and radiogenic 40 arr plus k are strongly correlated in these samples and define a plane in 3d 40 ar 36 ar k cl space in this case the plane yields an excess 40 are corrected age of 1030 ma that is 100 s of ma younger than nearby cu mineralization at mt isa the age is interpreted to reflect 40 ar loss from the accidentally trapped mica into the surrounding fluid inclusions and is not related to the samples age of formation the initial 40 ar 36 ar value of fluid inclusions is widely used to provide information on fluid origin for the iocg samples that host k in fluid inclusions only the initial 40 ar 36 ar values are close to the measured values at every temperature of stepped heating experiments for samples that include accidentally trapped mica the correction for post entrapment radiogenic 40 arr production is significant furthermore because 39 ark present in accidentally trapped mica crystals is released at different temperatures to radiogenic 40 arr lost to the surrounding fluid inclusions intra sample 40 ar 36 ar variation cannot be reliably documented the results demonstrate that noble gas analysis is readily applicable to proterozoic or older samples but that if k mineral impurities are present within quartz the abundance of k must be determined before calculation of mean 40 ar 36 ar values that are

the devonian goniatite genera pinacites and foordites from alaska the devonian goniatite genera pinacites and foordites are described from west central alaska this is the first time that pinacites has been found in north america the faunas are compared with tho

mineralogy of iron oxides in two soil chronosequences of central spain abstract the iron oxide mineralogy of soils of two river terrace sequences of the rivers jarama and henares central spain which are in close proximity was studied the degree of weathering increases with age as shown by several mineralogical and geochemical indicators such as the increase in the ratio dithionite extractable free fe total fe low values for oxalate extractable fe indicate that the fe oxides are essentially crystalline in the jarama sequence goethite is the dominant pedogenic fe oxide in the henares sequence both goethite and hematite are present in significant amounts the difference is attributed to pedoenvironmental differences such as the lower ph and the moister pedoclimate of the jarama sequence soils the sensitivity of the goethite hematite system to pedoenvironmental factors shows the limited value of iron oxides for the estimation of paleoclimatic conditions or relative age in chronosequences even in relatively small geographical areas

midcrustal shearing and doming in a cenozoic compressive setting along the ailao shan red river shear zone the cenozoic xuelong shan antiformal dome is located along the northern segment of the ailao shan red river shear zone in yunnan china subhorizontal foliation in the gneiss core is recognized representing a broad top to ne shear initiated under amphibolite facies conditions and propagating into greenschist facies in the mantling schist and strike slip shear zone microfabrics of crystallographic preferred orientations cpos in quartz suggest that the deformation temperatures increased with increasing structural depth from the upper crust 300 500 c in the mantling schist to the midcrust 15 km or more 650 c in the gneissic core this trend is mirrored by variations in the metamorphic grade of the syn kinematic mineral assemblages and microstructures which range from garnet amphibole biotite sillimanite rutile feldspar in the core to garnet staurolite biotite epidote muscovite within the limb units the dome experienced the following deformation history 1 a broad top to ne shear in the subhorizontal foliation of the gneiss core during the first stage of deformation d1 2 opposing reverse sense shear along the two schist limbs of the dome during contraction related doming d2 d3 3 sinistral strike slip shearing within the eastern limb d4 and 4 extensional deformation d5 the structural thermal patterns suggest the antiformal dome formation was roughly coeval with top to ne ductile shearing in the midcrust of tibet at 32 ma or earlier a major implication is that there was a phase of contractional ductile deformation in the region prior to the initiation of strike slip deformation

disturbed 40ar39ar systematics in hydrothermal biotite and hornblende at the scotia gold mine western australia evidence for argon loss associated with post mineralisation fluid movement hornblende and biotite that formed during gold mineralisation at the scotia mine western australia have erratic 4oar 3gar release spectra and total gas ages that are 200 900 million year younger than the ca 2600 2620 ma minimum age of gold mineralisation as given by 4oar 3gar plateau muscovite ages of crosscutting pegmatite dykes analysed homblendes are dominated by magnesio hornblende but also contain small domains of ferro actinolitic hornblende actinolitic hornblende and actinolite biotite also appears to be substantially altered to chlorite along cleavage planes relatively young apparent ages and high k ca ratios of argon released from homblendes at tempera tures less than 1000 c are interpreted to be the result of degassing of contaminant biotite however this cannot totally explain the young ages of homblendes gas fractions released at furnace temperatures above looo c where the effect of biotite degassing is demonstrably negligible still have apparent ages that are 200 900 million years younger than the age of muscovite from post gold pegmatite dykes the close proximity of disturbed hydrothermal hornblende samples to apparently undisturbed pegmatite muscovite samples less than a few metres in some cases is difficult to reconcile with argon loss in hydrothermal hornblende being the product of thermally driven volume diffusion given a suitable thermal history argon loss could occur preferentially in homblendes if 1 the closure for slow cooling and blocking for reheating temperatures of hydrothermal homblendes were lower than published estimates as has been observed in structurally complex metamorphic homblendes and or 2 the closure and blocking temperature of pegmatite muscovite were higher than commonly estimated however neither of these interpretations can easily explain the large variation in hornblende ages it is instead suggested that argon loss occurred during mineral fluid interaction during movement of a retrograde fluid along the mineralised lode structures and that this occurred at ambient temperatures below the blocking temperature of pegmatite muscovite there is abundant geological evidence for the passage of such a fluid at the scotia mine including the presence of numerous late brittle fractures containing retrogressive low temperature mineral assemblages late fluid movement is probably related to proterozoic erogenic activity along the nearby southeastern margin of the yilgarn craton the difference in argon systematics between hydrothermal minerals and pegmatite muscovite is largely ascribed to the relatively low permeability of the more massive pegmatite dykes with respect to ore zones preventing fluid egress to muscovite samples the variations in ages of hydrothermal minerals are probably related to the extent of fluid mineral interaction as this is a function of parameters such as fluid rock ratio fluid p t x conditions permeability and mineral microstructures that may vary on short time and length scales recognition of possible argon loss in hornblende via fluid interaction is important for the interpretation of 4oar 3gar systematics in environments such as many hydrothermal ore deposits where minerals may be exposed to fluids after crystallisation copyright 0 1997 elsevier science ltd

the somme valley terrace system northern france a model of river response to quaternary climatic variations since 800 000 bp recent research on the somme valley terrace deposits that began in 1987 has resulted in an integrated sequence of geological and geomorphological evidence for this area that is of particular significance for prehistoric investigations this has been achieved using previous evidence and new results from archaeological and geological excavations these include longitudinal profiles cartography and detailed synthesis of sections of alluvial deposits stratigraphy of river deposits and overlying loess sequences the work based on a study of the geometry of the terrace system has resulted in the identification of ninestepped alluvial formations that occur along 70 km of the valley detailed study permits the integration of the various alluvial sequences this suggests that each alluvial sequence results from sedimentation through a single glacial interglacial climatic cycle this hypothesis is confirmed by investigation of soil and loess sequences of the deposits overlying the fluvial sediments the synthesis presented provides a basis for understanding the deposition of the terrace system and an initial chronostratigraphic interpretation for the deposits

apparent argon diffusive loss 40ar 39ar age spectra in amphiboles detailed investigations have been made of two amphibole samples where 40ar 39ar age spectra have been interpreted to show argon diffusive loss both samples display complex compositional zoning that reflects partial major and minor element chemical re equilibration during later thermal events that is associated with the loss of radiogenic 40ar the apparent diffusive loss age spectra in these samples are an artefact of this chemical re equilibration process one sample additionally shows the effect of potassium gain and contamination with a potassium rich phase biotite the resulting ages in this sample are geologically meaningless and the apparent fit to a theoretical diffusive loss curve is coincidental this study shows that volume diffusive loss of argon appears to operate at slower rates than argon loss by chemical re equilibration in amphiboles

the age of the paludi formation a major constraint to the beginning of the apulia verging orogenic transport in the northern sector of the calabria peloritani arc a stratigraphic revision of the paludi formation cropping out in northern calabria on the north eastern side of sila massif has confirmed that it has been deposited between two main tectonic phases actually the formation is involved only by top to the north east thrusts different from those separating the crystalline and ophiolitic nappes of northern calabria and rests unconformably on the sila unit the uppermost nappe of the tectonic stack in the frame of the interpretation of northern calabria as a fragment of the alps the paludi formation play the role of a deposit post dating the eo alpine tectonic phases and pre dating the apenninic orogenic transport therefore the aquitanian age of the formation obtained by nannofloras analyses can be considered the minimum age to the apulia verging orogenic transport witnessed by top to north east thrusts it fairly corresponds to the age referred to the lucanian ocean closure

late quaternary climatic changes in northern cilento southern italy an integrated geomorphological and paleopedological study abstract this paper reports a contribution to the knowledge of the local morphodynamic and pedogenetic response to late quaternary climatic changes in northern cilento southern italy three representative geomorphological units and associated paleosols have been characterised in detail by field work chemical and mineralogical analyses and micromorphological observations of thin sections the data confirm an intense degree of weathering and a complex history of soil formation often representing different environments in contrast with the present pedoclimatic regime two of the three profiles reveal a polygenetic character recording typical interglacial conditions characterised by high temperatures and humidity with important soil development followed by the occurrence of periglacial conditions possibly occurring during cold glacial stages namely the last glacial at mid latitude coastal regions of southern italy the third paleosol appears essentially monogenetic and developed under interglacial like conditions

clay illuviation in red mediterranean soils abstract theories regarding pedogenesis in red mediterranean soils have undergone several stages of development the concept of clay illuviation in these soils was not a part of early theories and it is not yet unanimously accepted as a leading soil forming process a methodology is presented for studying the illuviation of clay in these soils emphasizing typology of textural features and fabrics the problem of age determination is also addressed through the use of radiometric dates and correlation with archaeological artifacts clay illuviation in red mediterranean soils under present day environmental conditions suggests that it occurs presently only on humid and sub humid margins of the mediterranean basin elsewhere illuvila clay accumulations are inherited from interglacial periods red mediterranean soils during glacial periods were eroded coluviated aggraded with aeolian dust calcitic fraction of which was redistributed in form of calcitic features and eventually were affected by water logging an example of water logging of red mediterranean soils mamora morocco which took place during the last glacial cycle consists of yellow illuvial clays accompanied by a yellowing of the ground mass during earlier cycles water logging resulted in whitish grey stains in which hydromorphic textural features were deposited

eustatic and tectonic control on late quaternary alluvial fans along the tyrrhenian sea coast of calabria south italy abstract the late quaternary evolution of the western coastal range northern calabria has been reconstructed by means of a multidisciplinary approach we have focused on the role of allocyclic mechanisms tectonics and base level change considered as factors influencing alluvial fan development in particular we identify no clear evidence for a major influence of climate age constraints were provided by a tephra layer and a paleosol coupled with geomorphological correlations middle pleistocene perched terraces and fan relicts hanging above fault scarps indicate that tectonics caused switches in fan dynamics between aggradational and erosional phases as tectonic activity declined during late middle pleistocene eustatically driven changes in base level possibly plus low rates of tectonic subsidence represent the main factor which controlled late pleistocene fan development the two major fan aggradation phases occurred during periods of climate amelioration prior to highstands whereas high sea levels ois 5 and 1 promoted channel incision into the fan surfaces this continued during periods of climate deterioration with a seaward progradation of alluvial deposition sea level rise is seen as creating accommodation space producing very open fans locally within mountain embayments the fans are characterised by a mushroom shape in plan view and by a retrograde stacking pattern of alluvial fan facies

modelling the effect of arbitrary p t t histories on argon diffusion in minerals using the macargon program for the apple macintosh argon diffusion in mineral grains has been numerically modelled using p t t histories that may be relevant to multiply metamorphosed orogenic terranes and for rocks that have resided at high ambient temperatures in the earth s crust for long durations the macargon program1 generates argon concentration profiles in minerals assuming argon loss occurs via volume diffusion it can be run on an apple macintosh computer with arbitrary p t t histories used as input finite difference equations are used in the calculation of 40ar concentration profiles across individual diffusion domains the associated macspectrometer generates model spectra after a p t t history has been specified the form of model 40ar39ar apparent age spectra suggests that considerable caution needs to be exercised in the use of the closure temperature concept and in the interpretation of the significance of plateaux observed in many 40ar39ar apparent age spectra particularly in cases involving metamorphic rocks where complex p t t histories might apply although modelled spectra cannot be directly compared to experimentally determined 40ar39ar age spectra especially when hydrous phases are involved or in cases where loss of argon has not occurred via volume diffusion they do provide insight into theoretically expected age spectra for samples that have experienced complex p t t histories

40 ar 39 ar and u pb age constraints on the timing of gold mineralization in the kalgoorlie gold field western australia the 40 ar 39 ar ages of three hydrothermal muscovite samples associated with auriferous gold stockwork systems at the mount charlotte deposit in the kalgoorlie gold field have a weighted mean of 2602 or 8 ma 40 ar 39 ar age errors are 2sigma at the nearby golden mile deposit 40 ar 39 ar ages from two muscovite samples associated with shear hosted lode gold mineralization have a weighted mean of 2629 or 9 ma on the balance of available evidence these ages are interpreted to represent the timing of gold mineralization in the two deposits these data indicate that formation of auriferous gold stockwork systems at mount charlotte occurred at least 10 million years after formation of the gigantic golden mile lode system this is consistent with geologic relations between the two different styles of mineralization and suggests that separate hydrothermal episodes were responsible for stockwork and shear hosted gold mineralization a weighted mean 207 pb 206 pb zircon age for a postregional metamorphism biotite porphyry intrusion of 2674 or 6 ma 95 confidence limits provides a minimum estimate for the timing of regional metamorphism of the surrounding greenstone sequence and associated compressive deformation hypotheses for the formation of archcan gold deposits which invoke fluids that are derived from regional metamorphic devolatilization of upper middle crustal greenstone sequences or from intrusion of spatially related porphyries cannot account for the gold mineralization in the kalgoorlie gold field these data indicate that the events occurred 30 to 40 and 60 to 70 million years prior to mineralization at the golden mile and mount charlotte respectively formation of the golden mile appears to have been part of a widespread gold mineralizing event at ca 2630 to 2640 ma supporting models in which crustal scale hydrothermal circulation at this time is used to explain archcan gold mineralization within the yilgarn block however such models must now contain the caveat that discrete younger episodes of mineralization such as that responsible for mount charlotte may also produce significant gold deposits with features similar to typical archcan gold deposits

soil chronosequences on quaternary marine terraces along the northwestern coast of calabria southern italy abstract two soil chronosequences representative of four orders of marine terraces from early to late pleistocene have been studied along the tyrrhenian coast of northern calabria in southern italy all soil profiles show a high degree of weathering although the degree of soil evolution varies according to the age of each terrace the soils are characterized by reddish to reddish brown colors clayey textures abundant clay coatings slickensides fe mn features or calcium carbonate concretions the dominance of kaolinite and illite among phyllosilicate clay minerals in all soil horizons the intense depletion in caco 3 na and k and the severe etching of quartz crystals in the older soils all record a highly leached pedogenic environment that is progressively more intense from younger to older soils despite the carbonate bedrock quartz feldspar and mica minerals also occur suggesting a partly allochthonous eolian origin of the parent material the major pedogenic features and their formative processes occurred polycyclically on the different orders of marine terraces and we interpret the soils to have mainly developed during repeated quaternary interglacials some surface a and bw horizons show quite different features suggesting a clear change in pedogenetic processes and possibly in climate and duration of soil formation these horizons have the typical field appearance of volcanic soils with andic properties brown colors loamy textures high porosity low bulk density high water retention thixotropy the occurrence of very small volcanic glass fragments and the possible presence of short range order aluminosilicate minerals confirmed some pyroclastic supply during soil formation

fluvial architecture and sequence stratigraphy of the eocene to oligocene iwaki formation northeast japan channel fills related to the sea level change abstract the iwaki formation the lowermost part of the eocene to oligocene shiramizu group northeast japan consists of conglomeratic braided drainage sediments the formation displays fining upward succession that reflects an overall transgressive sequence with two other overlying formations of the group although the clast supported conglomerates are by far the major components of the formation they also intercalate with many concave up channel sediments filled up with sandy deposits the lower part of the formation mainly consists of multistorey large scale channel sandstones with minor amount of small scale single storey channel sandstones which are related to low rates of base level rise in contrast the middle to upper part of the formation comprises single storey strata with relatively small scale channels which were probably associated with more rapid rates of base level rise the field evidence shows that the change of scale and internal structures of channel sandstones within the conglomerates most likely reflect the rate of changes of sea level rise

timing of late archaean granulite facies metamorphism in the southwestern yilgarn craton of western australia evidence from upb ages of zircons fro mafic granulites abstract conventional single and multigrain zircon u pb ages were determined from six samples of mafic granulites from locations widely distributed throughout the southwestern yilgarn craton zircons interpreted to have formed during the granulite facies event record ages within the narrow time range of 2649 2640 ma interpretation of this as the age of the granulite facies metamorphism is supported by an identical age on metamorphic titanite from one of the granulite samples zircons in two of the samples contained remnant euhedral zoning interpreted to have been inherited from the igneous protolith however u pb ages of these zircons were not significantly different from the metamorphic age suggesting that emplacement of the parent rocks was coeval with metamorphism or that the zircons were completely reset during the metamorphic event a third sample of mafic granulite contains rounded zircons with complex forms which record an age of 2798 ma indicating that these are inherited from an older protolith at present there is no geochronological evidence for rocks of this age in greenstone belts in the yilgarn craton placing in doubt suggestions that all the mafic granulites are high grade metamorphic equivalents of greenstone belts found elsewhere in the craton the granulite facies metamorphism is significantly younger than the age of 2670 ma for lower grade greenstones to the west supporting the hypothesis that the western limit of granulite facies rocks marks the boundary between two terranes that accreted after the peak of metamorphism