a major late devonian early carboniferous hercynian thermotectonic event at the nw margin of the arabian nubian shield evidence from zircon fission track dating zircon fission track zft ages of 17 precambrian samples from deep boreholes and outcrops in southern israel and sinai fall within the range 328 373 ma late devonian early carboniferous single zircon grain age distributions are unimodal with a high chi square probability the age data indicate total resetting of the zft clocks but only partial resetting of coexisting sphenes constraining the temperatures attained to about 225 50 c followed by relatively rapid regional cooling at the times indicated in the study area the lower paleozoic section presently overlying precambrian rocks is limited to cambrian strata up to 300 m thick further stratigraphic evidence for sub carboniferous erosion is preserved only in sw sinai to the east in southern jordan a 2 2 5 km thick lower paleozoic succession is reported despite the lack of stratigraphic evidence in the study area the zft data 1 strongly suggest that an equivalent or thicker section also existed 2 constrain the timing of the erosion to late devonian early carboniferous hercynian and 3 indicate that thermal gradients may have reached 50 c km prior to the uplift erosion event regional stratigraphic evidence indicates that the late devonian early carboniferous event was confined to a relatively narrow belt extending from the gulf of suez area to the vicinity of ne syria and se turkey

sourcelands for the carboniferous pennine river system constraints from sedimentary evidence and u pb geochronology using zircon and monazite

application and limitation of fission track geochronology to quarternary tephras abstract zircon and glass are the principal materials used for fission track dating of quaternary tephras this is because zircon is a common accessory mineral in rhyolitic tephras and it usually contains sufficient uranium to produce detectable quantities of spontaneous fission tracks over the time span of the quaternary volcanic glass though uranium poor is typically the dominant component of rhyolitic tephras comprising up to 99 of some distal tephra fall deposits low uranium contents however result in low spontaneous track densities that make the age measurement difficult and laborious a condition exacerbated by very young glasses in addition fission tracks in glass shards are unstable and can partially anneal at ambient temperatures therefore unless the glass age is corrected by plateau or isothermal heating experiments partial annealing causes a reduction in the measured age compared to the true age of the sample fission track dating has a large subjective component that can contribute systematic errors to the analysis microlite inclusions and some structural defects resemble fission tracks and if misidentified and included in the count of spontaneous tracks the calculated age would be too old the most prevalent source of systematic error is contamination in the natural environment for many tephras in the stratigraphic record are reworked tuffaceous sediments these deposits may contain detrital components that could mask the primary age of the tephra however by using the external detector fission track method it is possible to calculate ages of single mineral grains and to distinguish contaminants from primary phases on the basis of their age distribution this grain discrete capability is the major advantage of the fission track method over bulk geochronological systems

constraints on provenance of the central european triassic using detrital zircon fission track data the type of provenance information obtained from dating detrital grains will depend upon the thermal sensitivity of the isotopic dating method for detrital zircon the two methods fission track and u pb in routine use have widely different thermal sensitivities and therefore may provide quite different provenance information zircon fission track data are sensitive to thermal overprinting in the temperature range 200 300 c and therefore have the unique ability to provide source thermal history data the purpose of this study is to evaluate the suitability of zircon fission track data for provenance studies of the triassic siliciclastic sediments of central europe with an emphasis on testing proposed sediment pathways zircon fission track data obtained during this study are consistent with a sediment pathway linking fennoscandia with the central german basin in addition during carnian times there must also have been a pathway linking the schilfsandstein formation of the german basin with the lunzersandstein of the tethyan realm pointing to a european wide fluvial transport system detrital zircon fission track data are therefore a useful means for discerning sediment source and reconstructing sediment pathways

fission track analysis reveals character of collisional tectonics in new zealand during the late cenozoic the pacific plate has been obliquely converging with the australia plate in south island new zealand this has resulted in westward obduction of continental crust of the pacific plate and consequently a major mountain range the southern alps has formed east of the alpine fault and within the leading edge of the pacific plate we have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the southern alps starting at the alpine fault to better understand the uplift age and structure of the continental collision the results show the following 1 uplift was underway at 7 ma in the south at haast pass and by 5 ma in the north at arthur s pass 2 profiles of the total amount of late cenozoic uplift show an exponential increase toward the alpine fault adjacent to the alpine fault there has been 14 5 to 21 5 km of uplift in the vicinity of haast pass 14 5 to 21 km near mt cook and 12 5 to 15 5 km in the arthur s pass transect adjacent to the alpine fault in the mount cook region the average uplift rate from 5 5 ma to 1 ma was 2 3 to 2 5 mm yr between 1 ma and the present it has averaged 6 2 mm yr the strongly asymmetric uplift pattern is responsible for the exposure of a 13 25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the alpine fault known as the alpine schists 3 late cenozoic uplift of torlesse greywackes and alpine schists was preceeded during the jurassic early cretaceous by 5 8 km of uplift the otago schist belt to the south was uplifted much more during this interval and in addition western parts of the otago schists were uplifted 5 6 km during the late cretaceous 4 the fission track data do not support the notion of significant late cenozoic shear heating about the alpine fault as previously suggested from spatial variations in k ar ages of the otago and alpine schists

cretaceous to cenozoic thermal evolution of the southwestern south carpathians evidence from fission track thermochronology abstract the southwestern south carpathian orogen is composed of various nappe complexes which were assembled during the cretaceous cenozoic orogeny these are from footwall to hangingwall 1 the danubian nappe complex including a cadomian variscan basement 2 the arjana and severin units with jurassic to early cretaceous rift and oceanic sequences and 3 the getic nappe complex with variscan continental basement fission track ft thermochronology on apatite zircon and sphene from samples collected from various units of the south carpathians in conjunction with field constraints and previous geochronology is used to characterise the alpine tectonic events and to restore the pattern and amount of exhumation since the cretaceous zircon from the flysch unit and the danubian liassic cover sequence yields ft ages around 200 ma suggesting cooling of the rift flanks prior to the opening of the severin rift zircon and sphene from the getic and danubian basement units yield ft ages averaging 110 ma and indicating cooling under 240 c of the basement contemporaneous with or postdating thrusting apatite ft ages display a decreasing age trend from the hangingwall 65 ma to the footwall units 30 ma the age data and corresponding horizontal confined track length distributions suggest that exhumation of the nappe pile occurred in two stages the first is related to the late cretaceous nappe stacking and the second one to the final thrusting of the south carpathians onto the top of the moesian platform apatite ft ages along major brittle wrench faults indicate reheating above ca 120 c during fluid flow associated with fault re activation during oligocene and neogene times thus shear zone rocks experienced a higher temperature overprint during cenozoic time than rocks of the unaffected nappe pile temperatures of hydrothermal flow along these zones decreased below 100 c progressively starting with the late oligocene early miocene when the area began to override the moesian platform

decrease in natural marine hydrocarbon seepage near coal oil point california associated with offshore oil production prolific natural hydrocarbon seepage occurs offshore of coal oil point in the santa barbara channel california within the water column above submarine vents plumes of hydrocarbon gas bubbles act as acoustic scattering targets using 3 5 khz sonar data seep distribution offshore of coal oil point was mapped for august 1996 july 1995 and july 1973 comparison of the seep distributions over time reveals more than 50 decrease in the areal extent of seepage accompanied by declines in seep emission volume in a 13 km 2 area above a producing oil reservoir declines in reservoir pressure and depletion of seep hydrocarbon sources associated with oil production are the mechanisms inferred to explain the declines in seep area and emission volume

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

the role of fission track dating in discrimination of provenance determination of single crystal ages by fission track dating analysis of zircons and subordinately apatites within a detrital heavy mineral assemblage together with frequency distribution and radial plot analysis of the measured ages permits identification of different age modes synopses are presented of published fission track provenance studies in north central victoria northeastern tasmania barbados the rockall trough the english wealden mexico utah and the central alps from authors

a method for evaluating basement exhumation histories from closure age distributions of detrital minerals we have developed a two dimensional thermokinetic model that predicts the closure age distributions of detrital minerals from pervasively intruded and differentially exhumed basement using this model we outline a method to determine the denudation history of orogenic regions on the basis of closure age distributions in synorogenic to postorogenic forearc strata at relatively high mean denudation rates of 0 5 km m y 1 sustained over millions of years magmatic heating events have minimal influence upon the age distributions of detrital minerals such as k feldspar that are moderately retentive of radiogenic ar at lower rates however the effects of batholith emplacement may be substantial we have applied the approach to detrital k feldspars from forearc strata derived from the deeply denuded peninsular ranges batholith prb agreement of the denudation history deduced from the detrital k feldspar data with thermochronologic constraints from exposed prb basement lead us to conclude that exhumation histories of magmatic arcs should be decipherable solely from closure age distributions of detrital minerals whose depositional age is known c 1999 american geophysical union

erosional and depositional history of the atlantic passive margin as recorded in detrital zircon fission track ages and lithic detritus in atlantic coastal plain sediments comparison of fission track ft ages of detrital zircons recovered from atlantic coastal plain sediments to ft ages of zircons from bedrock in source terranes in the appalachians provides a key to understanding the provenance of the sediments and in turn the erosional and depositional history of the atlantic passive margin in appalachian source terranes the oldest zircon fission track zft ages from bedrock in the western appalachians defined for this paper as the appalachian plateau valley and ridge and far western blue ridge are notably older than the oldest ages from bedrock in the eastern appalachians piedmont and main part of the blue ridge the age difference is seen both in zft sample ages and in individual zircon grain ages and reflects differences in the thermotectonic history of the rocks in the east zft data indicate that the rocks cooled from temperatures high enough to partially or totally reset zft ages during the paleozoic and or mesozoic the majority of the rocks are interpreted to have cooled through the zft closure temperature 235 c at various times during the late paleozoic alleghanian orogeny in contrast most of the rocks sampled in the western appalachians have never been heated to temperatures high enough to totally reset their zft ages reflecting their contrasting thermotectonic histories nearly 80 percent of the sampled western rocks yield one or more zircon grains with very old ft ages in excess of 800 ma zircon grains yielding ft ages this old have not been found in rocks in the piedmont and main part of the blue ridge the zft data suggest that the asymmetry of zircon ages of exposed bedrock in the eastern and western appalachians was in evidence by no later than the early cretaceous and probably by the late triassic detrital zircon suites from sands collected in the atlantic coastal plain provide a record of detritus eroded from source terranes in the appalachians during the mesozoic and cenozoic in virginia and maryland sands of early cretaceous through late early oligocene age do not yield any old zircons comparable in age to the old zircons found in bedrock in the western appalachians very old zircons yielding ft ages 800 ma are only encountered in coastal plain sands of middle early miocene and younger age miocene and younger fluvial deltaic deposits associated with the major mid atlantic coastal plain rivers that now head in the western appalachians the hudson delaware susquehanna potomac james and roanoke contain abundant clasts of fossiliferous chert and quartzite and other distinctive rock types derived from paleozoic rocks of the western appalachians these distinctive clasts have not been reported in older coastal plain sediments the zft and lithic detritus data indicate that the drainage divide for one or more east flowing mid atlantic rivers migrated west into the western appalachians and the river s began transporting western appalachian detritus to the atlantic coastal plain sometime between the late early oligocene and middle early miocene by no later than late middle miocene most if not all of the major rivers that now head west of the blue ridge were transporting western appalachian detritus to the coastal plain prior to the drainage divide migrating into the western appalachians the zft data are consistent with the dominant source of atlantic coastal plain sediments being detritus from the piedmont and main part of the blue ridge with possible input from distant volcanic sources the zft data suggest that the rapid increase in the rate of siliciclastic sediment accumulation in middle atlantic margin offshore basins that peaked in the middle miocene and produced almost 30 percent of the total volume of post rift siliciclastic sediments in the offshore basins began in the early miocene when atlantic river s gained access to the relatively easily eroded paleozoic sedimentary rocks of the western appalachians

dive site geology dsv alvin 2006 and rov jason ii 2007 dives to the middle lower continental slope northern gulf of mexico abstract use of dsv alvin 2006 and rov jason ii 2007 provided access to never observed or sampled sites of fluid gas expulsion from the little studied middle and lower continental slope of the northern gulf of mexico below water depths of 1000 m dives were focused on 15 locations selected by 3 d seismic surface attributes and shallow subsurface geologic analyses the linkage between highly positive seafloor reflectivity and hard bottoms proved to be an efficient indicator of potential sites of interest through observation and sampling of reflective sites starting in the mid 1980s it has become apparent that most hard bottoms on the northern gulf s continental slope are created by the precipitation of authigenic carbonates at hydrocarbon seep sites access to the bureau of ocean energy management regulation and enforcement s extraordinary archive of slope wide 3 d seismic data made efficient site selection possible from thousands of sites that display the characteristics of fluid gas expulsion 15 were observed and sampled during the 2006 and 2007 cruises water depths in which these 15 sites were located ranged from 2750 to 970 m all sites exhibited evidence of hydrocarbon seepage or more rapid venting chemosynthetic organisms authigenic carbonates barite gas hydrates highly anoxic surface sediments brine pools and hydrocarbon laced brine flows were identified and sampled high resolution acoustic autonomous underwater vehicle auv data including multibeam bathymetry side scan sonar swaths and chirp sonar subbottom profiles were collected at four locations ac601 wr269 gc852 and at340 data sets from the 2006 and 2007 dives resulted in a greatly improved understanding of both cross slope and along slope variability in the characteristics of fluid gas expulsion sites and associated habitats our studies confirmed the importance of fluid gas expulsion processes for sustaining chemosynthetic communities and impacting seabed geology on the middle and lower continental slope of the northern gulf of mexico

apatite fission track analysis of oligocene strata in south texas u s a testing annealing models analysis of apatite fission track data from forty seven surface and subsurface samples of fine grained sandstone to pebbly conglomerate from the oligocene catahoula gueydan frio and vicksburg formations documents the response of fission track ages and track length distributions to simple post depositional thermal histories characterized by monotonic heating data from outcrop samples document that the apatite component was derived from source areas characterized by rapid cooling through the temperature range from 120 to 50 c during the early tertiary the apatite population is characterized by a log normal chlorine distribution mean 0 3 wt 0 3 wt consisting predominantly of low cl apatites 80 is 0 5 wt mean track lengths from core samples decrease systematically with increasing depth and temperature the decrease in apatite fission track ages with increasing depth and temperature is less systematic due to the scatter in inherited ages at the time of deposition no tracks were observed in apatite from samples at temperatures above 130 c mean track lengths for the south texas data agree well with those for a similar data set from the otway basin southeastern australia for present day temperatures of 70 c at higher temperatures mean lengths are 1 to 9 m longer than those observed from the otway basin this discrepancy is interpreted to reflect up to 40 ma longer residence times at maximum burial temperatures for the otway basin samples standard deviations about mean lengths are also lower than observed in the otway basin study consistent with the wider variation of cl contents mean 0 8 wt 0 7 wt that characterize apatite from the otway basin recently published apatite fission track annealing models predict significantly different mean track length vs present day temperature profiles for thermal histories believed to be representative of those experienced by sampled south texas strata because of the large uncertainties attributed to present day temperatures 10 c the predicted mean length vs temperature trends for these models essentially fall within or on the uncertainty envelope for the observed trend residuals of predicted minus observed mean lengths suggest that the previously published carlson composite parameter model using an initial mean length of 15 8 m instead of 16 5 m or the crowley et al model for track length reduction down to 11 m provide the best estimates of mean track length reduction over geologic time scales for near end member f apatite populations

provenance and thermal history of the franciscan accretionary complex constraints from zircon fission track thermochronology the franciscan accretionary complex of california contains large belts of sediments that were subducted to depths of 10 to 30 km metamorphosed under high pressure and low temperature conditions and later returned to the surface reconnaissance zircon fission track ft data 21 samples place constraints on the sedimentary provenance thermal history and or exhumation history of various franciscan units in a transect across the northern coast ranges through mendocino pass metagraywacke samples from the valantine springs formation of the franciscan eastern belt experienced maximum temperatures tmax ranging from 250 to 310 c zircon ft and previously reported apatite ft data indicate that parts of the western eastern and eastern central belts cooled at about 100 70 ma from 300 c to 100 c considering the low paleogeothermal gradient of roughly 9 c km during franciscan subduction these rocks were apparently uplifted and exhumed from 30 to 10 km depth at this time one sample from the eyler mountain sequence in the northwestern diablo range similarly shows tmax 310 c and major cooling at 100 70 ma this uplift and exhumation may have reflected accelerated accretion at the base as well as the front of the franciscan wedge accompanied by extensional thinning at shallower levels as a result of massive sediment influx into the franciscan trench from the sierra nevada magmatic arc in the northern coast ranges the western part of the central belt and the coastal belt experienced lower tmax probably 200 c and retain source area detrital zircon ft ages burnt hills terrane samples in the diablo range also experienced tmax 230 c and retain detrital ages the detrital single grain age patterns from these areas are compatible with those expected from the sierra nevada magmatic arc and its country rocks this is consistent with derivation of franciscan sediments from arc terranes in california and provides no particular suggestion that these parts of the franciscan are highly allochthonous paleogene coastal belt sandstones also yield detrital ages compatible with derivation from the sierra nevada but also include early tertiary zircon populations compatible with reconstructions suggesting these sandstones were sourced partly from the idaho batholith

timing of low temperature metamorphism and cooling of the paleozoic and mesozoic formations of the bukkium innermost western carpathians hungary k ar ages of illite muscovite and fission track ages of zircon and apatite were determined from various lithotypes of the bukkium which forms the innermost segment of the western carpathians the stratigraphic ages of these dinaric type formations cover a wide range from the late ordovician up to the late jurassic the grade of the orogenic dynamo thermal metamorphism varies from the late diagenetic zone through the anchizone up to the epizone chlorite maximally biotite isograd of the greenschist facies the k ar system of the illite muscovite in the 2 m grain size fraction approached equilibrium only in epizonal and high temperature anchizonal conditions the orogenic metamorphism culminated between the eo hellenic 160 120 ma phase connected to the beginning of the subduction in the dinarides and the austrian 100 95 ma phase characterized by compressional crustal thickening no isotope geochronological evidence was found for proving any hercynian recrystallization the stability field of fission tracks in zircon was approached using the thermal histories of the different tectonic units a temperature less than 250 c and effective heating time of 20 30 ma had only negligible effects on the tracks whereas total annealing was reached between 250 and 300 c apatite fission track ages from the paleozoic and mesozoic formations show that the uplift of the bukk mountains occurred only in the tertiary not earlier than ca 40 ma ago thermal modeling based on apatite fission track length spectra and preserved paleogene sediment thickness data proved that the late neogene burial of the recently exhumed plateau of the bukk mountains exceeded 1 km

the effect of allochthonous salt on the petroleum systems of northern green canyon and ewing bank offshore louisiana northern gulf of mexico the northern green canyon ewing bank region northern gulf of mexico basin contains the oxfordian neogene tithonian neogene albian neogene turonian neogene and eocene neogene petroleum systems the systems encompass 42 fields or discoveries in the study area and include four subsalt discoveries essential elements of the systems include source shales of oxfordian tithonian albian turonian and eocene age neogene siliciclastic turbidite reservoirs allochthonous salt and overburden strata ranging in age from jurassic to quaternary the petroleum systems of the area are significantly affected by the evolution of allochthonous salt the high thermal conductivity of salt retards the thermal maturation of subsalt petroleum source rocks and causes late generation and migration from them most traps were formed during the pliocene pleistocene and the generation migration accumulation of petroleum ranges from early miocene to the holocene the critical moment of peak oil generation for each source varies spatially and temporally as a function of the overlying sediments and allochthonous salt evolution the impermeability of salt prevents vertical petroleum migration and causes migration pathways to be deflected laterally up the dip of base salt where salt welds form petroleum migration is unimpeded and continues vertically by integrating predictions of potential source rocks structural restorations thermal maturation modeling regional salt maps and petroleum systems logic we can determine petroleum migration pathways and zones of concentration all 42 fields or discoveries within the study area are associated with predicted zones of paleosubsalt petroleum concentration present day salt geometries do not delineate many of these zones because of salt weld formation during the pleistocene this generation migration and accumulation technique enables geoscientists to focus their exploration efforts toward areas with a greater probability of success

natural oil slicks in the gulf of mexico visible from space natural oil seepage in the gulf of mexico causes persistent surface slicks that are visible from space in predictable locations a photograph of the sun glint pattern offshore from louisiana taken from the space shuttle atlantis on may 5 1989 shows at least 124 slicks in an area of about 15 000 km2 a thematic mapper tm image collected by the landsat orbiter on july 31 1991 shows at least 66 slicks in a cloud free area of 8200 km2 that overlaps the area of the photograph samples and descriptions made from a surface ship from aircraft and from a submarine confirmed the presence of crude oil in floating slicks the imagery data show surface slicks near eight locations where chemosynthetic communities dependent upon seeping hydrocarbons are known to occur on the seafloor additionally a large surface slick above the location of an active mud volcano was evident in the tm image in one location the combined set of observations confirmed the presence of a flourishing chemosynthetic community active seafloor oil and gas seepage crude oil on the sea surface and slick features that were visible in both images we derived an analytical expression for the formation of floating slicks based on a parameterization of seafloor flow rate downstream movement on the surface half life of floating oil and threshold thickness for detection applying this equation to the lengths of observed slicks suggested that the slicks in the atlantis photograph and in the tm image represent seepage rates of 2 2 30 m3 1000 km 2 d 1 and 1 4 18 m3 1000 km 2 d 1 respectively generalizing to an annual rate suggests that total natural seepage in this region is of the order of at least 20 000 m3 yr 1 120 000 barrels yr 1

fission track dating of granitic rocks from the eastern cordillera of peru evidence for late jurassic and cenozoic cooling apatite and zircon fission track ages of three samples of the huachon granite and one sample of the quiparacra granite from the eastern cordillera of the andes of central peru have been determined zircons from the huachon granite yielded two groups of ages an older group made up of zircons with the lowest uranium content gave an age of c 270 ma the zircons with high uranium content from this granite gave ages of c 160 ma the zircon ages from the huachon granite show no correlation with elevation the age of 270 ma is interpreted as the age of probable emplacement the 160 ma age is evidence of a mild cooling 200 c event that ended in late mid jurassic time this cooling correlates in central peru with thick conglomerates in the sub andes and strong exhumation in the eastern cordillera during bathonian to malm times zircons from the quiparaca granite which is a component of a composite batholith of possible precambrian to tertiary age show ages of c 30 ma which are interpreted as the emplacement age these zircons were totally annealed prior to the cooling in the oligocene this required temperatures 200 c apatite fission track dating of the huachon granite yielded only neogene ages which reflect the total annealing of the tracks present in the apatite before exhumation began c 22 ma apatite ages show a correlation with elevation and indicate two periods of cooling during the neogene at c 21 ma and between 12 ma and the present these young ages suggest approximately 4 to 6 km of erosion in the eastern cordillera of central peru in the past 30 ma these amounts are consistent with known geological data and fission track ages obtained from other parts of the eastern andes

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

wind driven freshwater buildup and release in the beaufort gyre constrained by mesoscale eddies recently the beaufort gyre has accumulated over 20 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades here we explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy resolving model of the beaufort gyre we demonstrate that a realistic halocline can be achieved when its deepening tendency due to ekman pumping is counteracted by the cumulative action of mesoscale eddies based on this balance we derive analytical scalings for the depth of the halocline and its spin up time scale and emphasize their explicit dependence on eddy dynamics our study further suggests that the beaufort gyre is currently in a state of high sensitivity to atmospheric winds however an intensification of surface stress would inevitably lead to a saturation of the freshwater content a constraint inherently set by the intricacies of the mesoscale eddy dynamics

from source terrains of the eastern alps to the molasse basin detrital record of non steady state exhumation fission track cooling ages of detrital apatite aft in the east alpine molasse basin display age groups corresponding to geodynamic events in the orogen since jurassic times these age groups are typical of certain thermotectonic units which formed a patchwork in the swiss and eastern alps by a combination of petrographic and thermochronologic data progressive erosion of source terrains is monitored in different catchments since the oligocene the aft cooling ages show a decrease in lag time until when rapidly cooled debris derived from tectonically exhumed core complexes became exposed after termination of tectonic exhumation lag times of debris derived from the core complexes increased neither on the scale of the entire eastern alps or on the scale of individual catchments steady state exhumation is observed due to the highly dynamic changes of exhumation rates since late eocene collision d 2005 elsevier b v all rights reserved

zircon fission track age for middle pleistocene rangitawa tephra new zealand stratigraphic and paleoclimatic significance rangitawa tephra is an important stratigraphic marker in mid pleistocene marine and terrestrial sequences in new zealand and adjacent ocean basins zircon fission track ages zfta on rangitawa tephra from five sites in the southern north island yield mean site ages in the range 0 34 to 0 40 ma with a weighted mean of 0 35 0 04 ma 1 on the basis of glass shard major element chemistry ferromagnesian mineralogy zfta and similarity of paleomagnetic dates of proposed tephra correlatives in deep sea cores it is concluded that rangitawa tephra represents a major eruptive event in the taupo volcanic zone most probably associated with eruption of the whakamaru group ignimbrites 0 35 0 39 ma or less likely the paeroa range group ignimbrites 0 36 0 38 ma pollen analyses from two onshore sites together with regional loess stratigraphy show that rangitawa tephra was erupted during a glacial period the zfta and previously reported oxygen isotope data from dsdp site 594 indicate that rangitawa tephra was erupted near the end of oxygen isotope stage 10

thermochronologic constraints on ore formation at the gays river pb zn deposit nova scotia canada from apatite fission track analysis fission tracks in detrital apatites from the cambro ordovician metasedimentary basement in the vicinity of the carboniferous hosted gays river pb zn deposit nova scotia provide a record of final

anomalous mesozoic thermal regime central appalachian piedmont evidence from sphene and zircon fission track dating a total of 17 sphene and 45 zircon fission track ages fta are reported from the piedmont province of pennsylvania delaware and maryland the reading prong of new jersey and the newark basin of pennsylvania with the exception of one sphene sample fta fall within a relatively restricted age range sphene 190 217 ma average 199 ma and zircon 143 218 ma average 184 ma near concordance of fta over a large tract of crystalline basement sim20 000 km 2 and within upper triassic sediments in the newark basin indicates late triassic early jurassic total resetting of the fission track clocks followed by regional cooling between sphene sim275 pm 25 circ c to zircon sim 220 pm 40 circ c closure temperatures at rates of 4 8 c ma fourteen rb sr whole rock mica ages together with previously reported 40 ar 39 ar biotite and hornblende ages generally indicate no regional mesozoic resetting thus the maximum temperature experienced by the samples was 300 c sphene fta clo

thermal effects of exhumation of a metamorphic core complex on hanging wall syn rift sediments an example from the rechnitz window eastern alps the removal of overburden by tectonic processes displaces the rock masses and their temperature with respect to the surface consequently high cooling rates and increased heat flow have been reported from rapidly exhuming terrains previous studies were mainly focused on the greenschist and amphibolite facies tectono thermal evolution of the footwall a two dimensional numerical thermal model presented in this study concentrates on the thermal history of the hanging wall and the footwall blocks and evaluates the variation of the near surface heat flow above an evolving metamorphic core complex based on structural thermobarometric and geochronological constraints from the rechnitz core complex of the eastern alps the modelling suggests that rapid movement along the extensional fault took place between 22 and 17 ma during this period the heat flow reached values of 140 150 mw m 2 in the hanging wall in a 10 15 km wide zone parallel to the fault trace the increased heat flow caused the high coal rank in the miocene syn rift sediments deposited on the hanging wall apatite fission track geochronology of the thermally overprinted sedimentary deposits gives the time at which the bottom of the syn rift sediment pile passed through 110oc 13 6 0 9 ma the vitrinite reflectance data rr 0 67 1 04 suggest significant burial of the margin of the hanging wall at the time of core complex formation considering the coal rank data and the thermal conductivity of the sedimentary deposits by modelling of the organic maturation we calculate syn rift early middle miocene burial of the hanging wall margin of the rechnitz core complex to be 1100 1600 m this value shows the importance of the post middle miocene erosion of the region which was related to the inversion of the pannonian basin 1998 elsevier science b v all rights reserved

post grenvillean transpression in the chilka lake area eastern ghats belt implications for the geological evolution of peninsular india abstract results of a combined structural and geochronological study of the area around the 0 79 ga chilka lake anorthosite complex in the eastern ghats belt of india place important constraints on the geological history of peninsular india th u pb epma dating of monazites from the outer margin of the anorthosite complex and from country rocks reveals that the emplacement of the anorthosite occurred at the beginning of a protracted middle neoproterozoic tectono magmatic event encompassing leucogranite emplacement and or cooling in the aureole of the anorthosite between 762 and 743 ma and a fabric defining transpressional deformation at 690 662 ma the progressive deformation was accompanied by granulite facies metamorphism a thermal event at 520 505 ma led to local resetting of the th u pb systematics in some monazites ages of 964 921 ma obtained from metapelitic granulites constituting the oldest lithological component imply that the chilka lake area was involved in the global grenvillean orogenesis which was the fabric defining tectonothermal event in most parts of the eastern ghats belt in combination with additional data from these authors and published data from other domains of the eastern ghats belt these results indicate that the post grenvillean evolution of the eastern ghats belt is characterized by a sequence of neoproterozoic tectonothermal events between 792 and 662 ma and a pan african thermal event at 520 505 ma it further implies slow cooling of the entire granulite terrain in view of appreciably different metamorphic conditions between the low grade proterozoic supracrustal cover of the archean cratons east dharwar and bastar and the neighbouring proterozoic granulites of the eastern ghats belt it is suggested that final thrusting of the eastern ghats belt over the archean forelands took place in early phanerozoic time

fission track analysis and provenance studies in calabrian are sedimentary rocks southern italy fission track analysis has been applied to the stilo capo d9orlando formation of southern italy this is a terrigenous syn orogenic sedimentary deposit of oligo miocene age that accumulated during a phase of accelerated denudation that affected the nearby crystalline basement rocks of the calabrian arc between c 30 and 15 ma seven conglomerate clasts and two sandstone samples from the base of the formation have produced eight apatite fission track ages nine zircon fission track ages and six apatite confined track length analyses the zircon fission track data confirm that detritus was derived from local hercynian igneous and metamorphic rocks in addition apatite fission track results from the two sandstone samples reveal that the basal part of the stilo capo d9orlando formation was exposed to maximum palaeotemperatures in excess of 70 c after deposition despite this apatite fission track ages much older than those obtained from the in situ crystalline basement source rocks of the calabrian are have been acquired these ages are interpreted as being derived from lost cover that is rocks originating from the structurally highest levels of the basement complex that have now been completely removed by erosion fission track analysis demonstrates that erosion in addition to previously identified extensional tectonism was a major factor during accelerated denudation of the calabrian are basement rocks during the late oligocene and early miocene

thermal history of rocks in southern san joaquin valley california evidence from fission track analysis the theory of the fission track method and its application to sedimentary basin analysis is illustrated by a case study in the southern san joaquin valley california fission tracks provide a powerful tool for studying the thermal history of sedimentary basins because the two minerals most commonly used in fission track studies apatite and zircon occur as detrital constituents in many sedimentary rocks and their annealing temperatures span the main temperature range for oil generation fission tracks also provide information on the sedimentation record and provenance of rocks in a basin we have used fission track analysis to study the thermal and depositional history of the subsurface tertiary sedimentary rocks on both sides of the active white wolf reverse fault in the southern san joaquin valley the distinctly different thermal histories of the rocks in the two structural blocks are clearly reflected in the apatite fission track data which suggest that rocks in the rapidly subsiding basin northwest of the fault have been near their present temperature for only about 1 m y compared with about 10 m y for rocks southeast of the fault these estimates of heating time agree with previous estimates for these rocks zircon fission track data indicate that the tertiary sediments were derived from parent rocks of more than one age however from at least the eocene to late miocene or pliocene the major sediment source was rocks related to the youngest sierra nevada mesozoic intrusive complexes which are presently exposed east and south of the southern san joaquin valley

tracking crustal processes by ft thermochronology in a forearc high hikurangi margin new zealand involving cretaceous subduction termination and mid cenozoic subduction initiation abstract raukumara peninsula is a forearc high on the pacific margin of new zealand its basement comprises two sedimentary terranes that formed in subduction prisms during the late jurassic mid cretaceous marking the end of subduction along the pacific margin of eastern gondwanaland the cover includes allochthonous late cretaceous oligocene passive margin slope to basin facies emplaced into the forearc during the early miocene initiation of the current subduction regime as well as autochthonous neogene sediments apatite and zircon fission track ft data are reported and interpreted for the basement and cover sediments the detrital zircon ft ages constrain the maximum depositional ages of the low grade zeolite and pumpellyite facies basement pahau terrane is no older than 152 13 ma this zircon ft mode and older ones 198 8 ma 232 58 ma recording cooling denudation in the source areas probably including rakaia terrane waioeka terrane located oceanward of pahau terrane is no older than 125 2 ma being the age of volcanic derived zircons and supports early cretaceous dinoflagellate ages reported previously omaio petrofacies comprises the youngest part of the waioeka terrane and has a zircon ft age of 108 6 3 ma this indicates that basement sequences accumulated in the northeast contemporaneously with cover sequences koranga fm in the southwestern part of the peninsula these zircon ft ages together with the results of thermal history modelling of certain waioeka terrane samples are consistent with migration of a thrust system in a subduction prism environment during the late jurassic cretaceous until about 85 ma as proposed earlier when mesozoic subduction terminated apatite ft data indicate for all basement samples a phase of neogene heating and cooling associated with basin formation sediment accumulation and subsequent uplift and erosion resulting in almost complete removal of the neogene stratigraphic record over western parts of the peninsula forward modelling of the data imply rapid earliest miocene downwarping of the crust in bay of plenty coinciding with initiation of subduction of pacific plate followed by emplacement of a 1 5 2 0 km thick wedge of east coast allochthon from the northeast early miocene sediments accumulated in a foredeep along the front sw margin of the allochthon probably sourced from a block of pahau basement west of whakatane fault which was exhumed and denuded by 4 km contemporaneously during the late early to middle miocene the basin depocentre migrated further to the southwest while areas previously downwarped northeast were uplifted and eroded the depocentre migration and subsequent inversion is a pattern that affected most of north island and is related to mechanical or dynamical interaction of the two plates as the slab of pacific oceanic lithosphere was emplaced beneath north island this may be a general feature of young subduction zones

exhumation of an accretionary prism results from fission track thermochronology of the shimanto belt southwest japan abstract the along arc variation of the thermal history of the shimanto accretionary prism was studied with fission track thermochronology to investigate tectonic factors that control the exhumation of an accretionary prism twelve apatite and 35 zircon ages were analyzed on sandstone and granite samples from the kii and kyushu regions southwest japan and the samples are interpreted in combination with the previously reported data from the shikoku region zircon samples show various degrees of age resetting after deposition that are dependent on their position within the prism some of the zircon samples constrain the time of maximum heating within or cooling through the zircon partial annealing zone two lines of observation i e simultaneous exhumation revealed along across arc transect with relatively high maximum burial at the rear part of the prism and along arc coeval rebound from burial to exhumation indicate that the exhumation of the entire wedge was probably caused by a progressive accretionary process such as underplating at depth because the driving force for this type of exhumation is the growth of the wedge this exhumation process is probably a general exhumation process that occurs in all accretionary complexes apatite samples record cooling at 10 ma except for samples from sites in the north of the kii region whose ages are 35 ma suggesting the effect of the southwest japan block obduction onto the subducting young philippine sea plate this implies along with the distribution of locally reset zircon ages that the exhumation of the prism was also forced by local episodic events for example collision of blocks during differential rotational movement change of the subduction parameters and possible accelerated underplating beneath a narrow region probably caused by the increased material influx from the igneous activities

downstream changes of alpine zircon fission track ages in the rhone and rhine rivers zircons from 13 sediment samples from the rhone and rhine drainages were dated by the fission track method to study downstream changes in detrital fissiontrack grain age distributions in large river systems draining the european alps the orogen parallel rhone river shows a zircon fission track grain age distribution similar to that in its alpine source areas this signal is well preserved because there are alpine sources along its full length and input from non alpine sources is small in contrast only the headwaters of the north flowing rhine river are located in the alps as a consequence alpine derived zircons which are distinguished by young fission track ages become progressively diluted downstream by older ages from zircon sources external to the alps nevertheless the alpine component is persistent and can easily be detected in sediments more than 1000 km downstream at the rhine delta these results demonstrate that fission track dating of detrital zircons can provide useful information about orogenic processes even where sediments have been transported hundreds of kilometers from the orogenic source crossing ephemeral lakes and subsiding basins deposits along the lower reaches of the river appear to have a short residence time 1 myr and thus many of these deposits serve to smooth out variations in the supply of sediment from fast eroding heterogeneous sources in the alpine headwaters of these drainages for the rhone and the rhine rivers we show that fast erosion in the alps accounts for most of the sediment load this finding supports a widespread observation that the sediment in most large continental drainages is usually derived from a small part of the drainage where uplift relief and erosion rates are greatest

insights on the thermal history of the valles caldera new mexico evidence from zircon fission track analysis abstract the zircon fission track dating method was applied to the vc 2b core obtained from the active hydrothermal system at sulphur springs valles caldera new mexico four samples were analyzed to obtain both zircon ages and track length data from permian strata to precambrian quartz monzonite the present temperatures of which are from 222 to 294 c zircon ages obtained from the deeper three samples indicate partially annealed ages of about 450 600 ma thus zircons from permian strata probably originated from precambrian rocks contrary to the normal relationship between ft ages and temperatures of the sampling points non correlation between them is probably due to hot fluid flow and or hot vein emplacement associated with recent volcanic activity zircon ages of the shallowest sample were much younger than the permian the reason for which is unknown the closure temperature of the zircon fission track dating method seems to be higher than that previously determined from geological data

natural long term annealing of the zircon fission track system around a granitic pluton we measured 24 ages and 14 length distributions of fission tracks in zircons separated from basement sandstones around a granitic pluton to investigate natural long term annealing behaviors of the zircon fission track zft system samples were collected from three cretaceous coherent units of the shimanto accretionary complex shikoku japan along an eastward traverse at distances of between 1 6 and 10 6 km from the intrusion contact of 15 ma takatsukiyama granite exposing about 5 km in diameter sampling was carried out around the expected position of the transition zone of track retention i e the fossil partial annealing zone fpaz based on previous regional zft age distributions approaching the contact original zft ages of 100 ma show a continuous reduction to 15 ma at 3 km distance their single grain age distributions accordingly change from widespread multimodal patterns reflecting provenance ages to unimodal ones characterizing the secondary heating by the granite intrusion mean and distributions of zft lengths also show notable variations within the fpaz as a result of mixing both preexistent tracks that were shortened by the miocene heating and unannealed ones having original long lengths that have been formed and accumulated after the cooling of the pluton these facts along with observed track segmentation and annealing anisotropy suggest that the shortening patterns of tracks in nature a heating duration of 105 106 years estimated from thermal modeling are indistinguishable from those previously demonstrated at laboratory timescales this basically validates the conventional approach of extrapolating laboratory based kinetic parameters to geologic timescales the observed fpaz and thermal modeling results in conjunction with laboratory heating data previously reported and recent constraints from an ultradeep borehole favor a relatively narrow temperature range for the partial annealing zone i e 230 to 330 c for a heating duration of 106 years

cretaceous tertiary rhenodanubian flysch wedge eastern alps clues to sediment supply and basin configuration from zircon fission track data the provenance of cenomanian to eocene flysch deposits accreted along the northern margin of the eastern alps has been investigated by means of zircon fission track ft geochronology and zircon morphology the rhenodanubian flysch and ybbsitz klippen zone comprise several nappes representing the main flysch and laab basins the laab basin received sediments of stable european provenance indicated by pre variscan variscan and permian triassic zircon ft ages and was thus located in the immediate south of the european margin the main flysch basin was supplied mainly from the evolving eastern alps and was therefore situated south of the laab basin zircon populations with permian to jurassic cooling ages in the main flysch basin are related to increased heat fluxes during the break up of pangaea and are probably derived from the northwestern part of the eastern alps the dominant cretaceous zircon ft cooling ages reflect eoalpine metamorphism in the austroalpine realm

thermochronology of the torlesse accretionary complex wellington region new zealand the torlesse complex comprises several mesozoic accretionary prism complexes together forming continental basement over large parts of new zealand this study focuses on the thermal history of relatively low grade graywacke rocks exposed in a transect in southern north island that crosses the structural grain of the torlesse complex including its older and younger parts zircon fission track ft ages for the late triassic rakaia terrane which is the most inboard of the accretionary complexes are partially annealed some possibly reset and may indicate early cretaceous 134 10 ma cooling from maximum temperatures tmax probably related to imbrication of younger complexes of the pahau terrane numerical modeling of the zircon ft ages and published 40ara 39ar muscovite and biotite ages for the rakaia terrane suggest tmax values of 265 310 c and exhumation from depths of 10 12 km the rocks underlying the aorangi range and involving the youngest accretionary complex have experienced much lower tmax values of 210 and 110 c bracketed by reset apatite ft ages and detrital zircon ft ages the occurrence of a circa 100 ma component of zircon ft ages in both the weakly and highly indurated rocks beneath the aorangi range as well as in remnants of an overlying albian accretionary slope basin whatarangi formation imply multistorey accretion and incorporation of sediment into the youngest prism this circa 100 ma zircon ft age component also places a maximum age on the termination of mesozoic subduction beneath the new zealand region the occurrence of reset apatite ft ages across the whole of the wellington transect indicates that at least 4 km of exhumation occurred during the late miocene

formation of low magnesium calcite at cold seeps in an aragonite sea this study investigates the conditions of occurrence and petrographic characteristics of low mg calcite lmc from cold seeps of the gulf of mexico at a water depth of 2340m such lmc mineral phases should precipitate in calcite seas rather than today s aragonite sea the c 13 depleted carbonates formed as a consequence of anaerobic oxidation of hydrocarbons in shallow subsurface cold seep environments the occurrence of lmc may result from brine fluid flows brines are relatively ca2 enriched and mg2 depleted mg ca mole ratio 0 7 relative to seawater where the mg ca mole ratio is 5 which drives high mg calcite and aragonite precipitation the dissolution of aragonitic mollusk shells grains and cements was observed aerobic oxidation of hydrocarbons and h2s is the most likely mechanism to explain carbonate dissolution these findings have important implications for understanding the occurrence of lmc in deep water marine settings and consequently their counterparts in the geological record

activation of optimally and unfavourably oriented faults in a uniform local stress field during the 2011 prague oklahoma sequence the orientations of faults activated relative to the local principal stress directions can provide insights into the role of pore pressure changes in induced earthquake sequences here we examine the 2011 m 5 7 prague earthquake sequence that was induced by nearby wastewater disposal we estimate the local principal compressive stress direction near the rupture as inferred from shear wave splitting measurements at spatial resolutions as small as 750 m we find that the dominant azimuth observed is parallel to previous estimates of the regional compressive stress with some secondary azimuths oriented subparallel to the strike of the major fault structures from an extended catalogue we map ten distinct fault segments activated during the sequence that exhibit a wide array of orientations we assess whether the five near vertical fault planes are optimally oriented to fail in the determined stress field we find that only two of the fault planes including the m 5 7 main shock fault are optimally oriented both the m 4 8 foreshock and m 4 8 aftershock occur on fault planes that deviate 20 29 from the optimal orientation for slip our results confirm that induced event sequences can occur on faults not optimally oriented for failure in the local stress field the results suggest elevated pore fluid pressures likely induced failure along several of the faults activated in the 2011 prague sequence

thermal and exhumation history of the eocene chumstick basin washington state usa this study investigates the cenozoic evolution of the cascades mountains usa by means of reconstructing the thermal history of the chumstick basin deposits that are located on the eastern flank of the orogen we present new detrital apatite u th sm he and detrital apatite fission track ages from the middle eocene 48 37 ma chumstick formation and modern river detritus these data are integrated with the published thermochronometric ages of the adjoining cascade mountains basement the new thermochronometer results are combined with existing vitrinite reflectance data for modeling of the basin s thermal history results suggest constant temperatures throughout the late oligocene to early miocene followed by rapid cooling since 17 10 ma results indicate that the middle to late miocene uplift of the cascades resulted in reactivation of the fault zones bounding the chumstick basin the structural reactivation and the weaker lithology of the basin strata in comparison to the harder and more resistant basement rocks of the cascades resulted in significant basin exhumation this interpretation is determined from younger apatite u th sm he cooling ages observed in the reset detrital bedrock of the chumstick formation than in the adjoining basement rocks these observations suggest a structural and lithological control on exhumation magnitudes in this region

lipid biomarker patterns reflect different formation environments of mussel and tubeworm dominated seep carbonates from the gulf of mexico atwater valley and green canyon abstract mussels and tubeworms thriving at many methane seeps typically live in symbiosis with chemosynthetic chiefly methanotrophic or thiotrophic bacteria it has been shown that the activities of chemosymbiotic animals can result in large differences in the sedimentary environments of their habitats here we put forward the concept that such environmental variability can be archived in the lipid biomarker inventories of authigenic carbonates forming in different locally confined environments at seeps mussel beds and tubeworm bushes in this case to test this hypothesis lipid biomarker patterns of carbonates from mussel and tubeworm environments from two seep sites atwater valley 340 and green canyon 852 of the gulf of mexico were analyzed previous work revealed stronger carbon isotope fractionation between the methane source and biomarkers of anaerobic methane oxidizing archaea 2 anme 2 sulfate reducing desulfosarcina desulfococcus dss consortia than for anme 1 dss consortia both performing anaerobic oxidation of methane aom similar 13cmethane values were found at the mussel and tubeworm sites from the same seeps and the local microbial consortia also appear to be largely similar based on the observed aom biomarker inventories yet a large average offset of 32 between the 13c values of molecular fossils of sulfate reducing bacteria srb involved in aom was observed with lower values typifying tubeworm carbonates than mussel carbonates this pattern is interpreted to reflect local effects on isotope fractionation caused by the chemosymbiotic metazoans at mussel and tubeworm dominated sites at tubeworm dominated sites the excess sulfate produced by thiotrophic symbionts of tubeworms and pumped down into the sediment results in persistent production of aom derived bicarbonate and the enrichment of 12c in sub surface sediments interestingly tubeworm carbonates also contain high amounts of non isoprenoidal dialkyl glycerol diethers dages with extreme 13c depletions representing compounds that derived from non dss cluster srb most likely 13c depleted aom derived organic intermediates were used as carbon sources by the dage producing non dss cluster srb possibly performing organoclastic sulfate reduction our study identifies significant variation in biomarker patterns between mussel and tubeworm carbonates at two seep sites in the gulf of mexico such variation allows to characterize different habitats at seeps which are shaped by the interaction of chemosymbiotic seep metazoans and their symbionts with the local environment metazoan community composition apparently controls geobiological interaction in seep ecosystems to a large degree which may allow tracing of the effects of chemosymbiosis into the rock record

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

denudational history along a transect across the drakensberg escarpment of southern africa derived from apatite fission track thermochronology 1 the denudational history of a 500 km long transect across the drakensberg escarpment on the high elevation passive margin of se africa is quantified on the basis of thermal history modeling of apatite fission track data for 15 deep borehole samples supplemented by an additional 10 outcrop samples a minimum of 4 5 km of denudation since formation of the margin 130 myr ago is estimated for the coastal zone with a marked early cretaceous episode of accelerated denudation broadly coincident with continental breakup samples from the swartberg borehole sw 1 67 located 30 km seaward of the present position of the drakensberg escarpment indicate a total depth of denudation of 3 1 1 2 km since 91 myr with a phase of accelerated denudation of 2 1 0 9 km at a mean rate of 95 43 m myr between 91 and 69 myr samples from the ladybrand borehole la 1 68 west of the lesotho highlands indicate 1 7 0 5 km of denudation since 78 myr with a phase of accelerated denudation at 82 43 m myr from 78 to 64 myr average denudation rates declined to about 10 m myr during much of the tertiary although the apatite fission track data do not provide any direct constraints on the denudational history of the lesotho highlands interpolation between the two boreholes constrained by geological evidence and extrapolated in situ produced cosmogenic 36cl derived denudation rate estimates suggests a pattern of denudation compatible with numerical modeling studies of escarpment evolution involving rapid river incision seaward of a preexisting inland drainage divide these patterns of denudation are incompatible with constant retreat of the drakensberg escarpment from an initial position near the present coast we suggest that the drakensberg escarpment formed by rapid post breakup river incision seaward of a preexisting drainage divide located just east of the present escarpment location and became pinned at this divide with subsequent retreat rates of only 100 200 m myr

subnormal geothermal gradients in the great valley forearc basin california during franciscan subduction a fission track study outboard parts of forearcs commonly have subnormal geothermal gradients because relatively cold lithosphere subducts beneath them the strata of the 10 to 15 km thick late jurassic tertiary great valley forearc basin accumulated in the forearc of the franciscan subduction zone of coastal california in this study paleogeothermal gradients in this basin were reconstructed to constrain the tectonic history of the convergent plate margin backstripping was used to reconstruct the burial histories of outcropping basin strata and apatite fission track analysis was used to determine the maximum burial temperatures experienced by 64 rock samples plots of maximum burial temperatures versus maximum burial depths indicate earliest tertiary time of deepest burial forearc basin geothermal gradients of about 9 c km backstripping shows that strata from the lower parts of two sections were deeply buried 6 5 km for the period 90 65 ma without experiencing high temperatures 105 c indicating that gradients were at least moderately subnormal throughout that period the data permit gradients no greater than about 15 c km at 90 ma decreasing to no greater than about 9 c km at 65 ma lower strata in another section were probably deeply buried without experiencing high temperatures from 130 or 120 ma until the latest cretaceous or early tertiary indicating that subnormal gradients probably existed throughout that period k ar ages of franciscan complex blueschists indicate subnormal gradients in the california forearc in the late jurassic and early cretaceous fission track data from the sierra nevada indicate subnormal gradients in the early and middle cenozoic and modern heat flow patterns indicate subnormal gradients in the late cenozoic together these indicators suggest that thermal gradients in the forearc were continuously subnormal from the initiation of franciscan subduction in the late jurassic until the termination of subduction in the late cenozoic gradients in the range that would permit blueschist facies metamorphism in the franciscan complex were thus long lived the broad range of k ar ages noted for franciscan blueschists need not reflect multiple discrete metamorphic events but are also consistent with a continuous extended period of high p t conditions blueschists need not have been uplifted soon after metamorphism to avoid overprinting by normal p t conditions but rather may have remained at depth for extended periods preliminary modeling indicates that an interruption in subduction of longer than 5 20 m y should cause detectable heating of forearc basin strata while a much shorter interruption should heat accretionary wedge rocks since there is no evidence of such heating it appears that convergence at the franciscan trench was essentially continuous if allochthonous terranes traveled northward parallel to the california margin during the late jurassic to late cenozoic period of franciscan subduction they apparently did so during oblique subduction not during extended interludes of pure transform motion

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

thermal history of the eastern gulf of suez ii reconstruction from apatite fission track and k feldspar measurements abstract apatite fission track aft measurements from miocene graben fill sediments of the eastern gulf of suez in three deep boreholes belayim 113 m 2 6 ras garra m 1 and alma 2 yield a wide range of ages from 125 to 320 ma and mean track lengths 10 1 12 7 m this range is similar to that recorded from precambrian crystalline basement flanking the graben which is the major source for the rift fill since the aft ages exceed the age of the host strata which are presently at their highest post depositional temperatures the rift related thermal regime is one of only moderate heating downhole aft data in the belayim 113 m 2 6 borehole attest to a higher rift temperature than in the ras garra m 1 borehole some 85 km to the south where little or no thermal overprinting is evident these findings are consistent with previously reported bottom hole temperatures and vitrinite reflectance data in the study area despite the higher syn rift thermal regime indicated for belayim 113 m 2 6 apatite provenance ages in ras garra m 1 are considerably younger thus the aft data in the ras garra m 1 area do not record significant rift related thermal effects but rather they mainly retain a pre rift provenance signature which reflects the order and depth of erosion at the uplifted flanks the younger aft ages in ras garra m 1 despite the weaker rift related thermal effect suggest a deeper level proportional to an additional 5 10 c of exhumation of the uplifted crystalline basement southwards along the eastern rift flank by mid miocene time this result is consistent with earlier findings which indicate both increased extension and heat flow southwards in the gulf of suez and earlier exhumation of the rift flank immediately preceding extension and opening of the gulf of suez the most deeply exhumed basement rocks presently exposed on the rift flanks were heated to temperatures 110 c total annealing of apatite but 40 ar 39 ar data and non resetting of zircon ft clocks in sinai 40 ar 39 ar data from granite penetrated in graben drilling at 3 89 km further corroborates pre rift palaeotemperatures

the record of middle jurassic volcanism in the carmel and temple cap formations of southwestern utah altered volcanic ash beds in the middle jurassic temple cap and carmel formations in southwestern utah record a pulse of active arc related volcanism between 166 and 171 ma a second pulse between 148 and 155 ma has previously been documented in the upper jurassic morrison formation volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in california in the inyo mountains the cowhole mountains the palen mountains and the central mojave desert the upper part of the volcaniclastic mount wrightson formation and the strata of cobre ridge in southern arizona are ca 170 ma in age and appear to be time correlative with the middle jurassic formations in southwestern utah the altered ash beds found in the temple cap and carmel formations typically contain phenocrysts of sanidine quartz biotite apatite zircon and titanite plagioclase was likely present originally in all of the ashes but was removed by alteration and is now found only in the temple cap red beds quartz and sanidine are absent in two crystal poor ash beds that contain two pyroxenes hornblende and biotite although major and trace element concentrations in the ash beds have been substantially modified compositions of relict phenocrysts reveal that the magmas were calc alkaline rhyolites to andesites two pyroxene two feldspar biotite and biotite apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 8c hornblende geobarometry yields pressures of 1 2 kilobars for the two ash beds that contain the appropriate buffer assemblage the mafic silicates all have moderately high mg fe ratios this fact combined with the presence of hornblende biotite and titanite suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of california the ash probably erupted from a low lying arc cut by strikeslip faults in what is now southern california and western nevada major jurassic unconformities occur near or within the ash bearing formations in southwestern utah laser fusion singlecrystal 40 ar 39 ar measurements have defined the ages of the unconformities and the associated volcanism the age of the j 1 unconformity found at the base of the temple cap formation in southwestern utah is older than ca 170 5 ma the j 2 unconformity which lies between the temple cap and carmel formations formed between ca 169 and 168 ma the origin of these unconformities is still unclear but may be related to the middle jurassic pulse of magmatism and the oblique plate convergence along the western margin of north america the age range of ash beds in the carmel formation between 166 3 and 168 0 6 0 5 ma is consistent with a bajocian bathonian boundary of ca 166 ma

melange forming processes in the development of an accretionary prism evidence from fission track thermochronology to give thermotectonic constraints on melange forming processes and to understand the significance of melange in the evolution of accretionary complexes fission track analysis was carried out on samples collected from sandstone blocks in melange matrix and coherent sandstone sequences adjacent to melange units in the cretaceous to miocene shimanto accretionary complex southwest japan which is one of the typical accretionary complexes with an accumulation of geological information nineteen zircon ages and 15 track length distributions from melanges indicate with some local variation that materials with higher maximum paleotemperatures are exposed at the rear part of the prism as is the case of the coherent units two apatite ages are contemporaneous with previously reported apatite ages of 10 ma obtained from coherent units in the region emphasizing the regional cooling through the apatite closure temperature of 100 c at that time there is no evidence for substantial relative motion of the melanges with respect to the surrounding coherent units melange formation is explained by processes that exclude large vertical transport i e 5 km of melange forming materials these thermotectonic characteristics observed in the shimanto accretionary complex are maintained during subsequent local internal deformation caused by the successive growth of the wedge

exhumation and relief history of the southern carpathians romania as evaluated from apatite fission track chronology in crystalline basement and intramontane sedimentary rocks the combination of apatite fission track ft thermochronology from basement units and the ft age distributions of apatites in the miocene intramontane sedimentary rocks allows describing the exhumation history of the central segment of the southern carpathians romania exhumation and cooling from the total track annealing temperature 120 c of the cozia and cibin massifs occurred in the palaeocene early eocene between the eocene and middle miocene there was a stagnation period concerning vertical displacement the presently exposed part of the basement was buried in shallow depth the present crests of the cozia and cibin mountains were at temperatures around 80 c and 50 c respectively the second exhumation period occurred in middle miocene times the magnitude of the miocene vertical displacement is on the order of the present day relief the vertical apatite ft age distribution in the basement and the age clusters in the sedimentary rocks prove that the levels of the crests were already close to the surface in palaeogene times therefore the post palaeocene erosional removal from the crest zones is very limited

the palaeogene forearc basin of the eastern alps and western carpathians subduction erosion and basin evolution scarce palaeogene sediment remnants in the eastern alps and western carpathians are interpreted as remains of a continuous forearc basin new apatite fission track geochronological data corroborate mild paleocene eocene exhumation and relief formation in the eastern alps palinspastic restoration and nine palaeogeographical maps of the eastern alps and western carpathians ranging from the paleocene to the late oligocene epoch illustrate west to east migration of subsidence in the forearc basin subsidence isochrons indicate that oblique subduction of the european plate below the adriatic plate was responsible for forearc basin migration at a rate of 8 mm a 1 the periadriatic lineament was formed as a result of shearing by oblique subduction the neogene to recent sumatra forearc basin is an analogue for the evolution of the east alpine west carpathian forearc basin

the erosion history of the central alps evidence from zircon fission track data of the foreland basin sediments fission track dating on detrital zircons of alpine debris in the swiss molasse basin provides information about the erosion history of the central alps and the thermal evolution of source terrains during oligocene times only sedimentary cover nappes and austroalpine basement units were eroded incision into austroalpine basement units is indicated by increasing importance of cretaceous cooling ages in granite pebbles upsection erosion of penninic basement units started between 25 and 20 ma early oligocene zircon ft ages show that penninic basement units were exposed at 20 ma deeper penninic units of the lepontine dome became exposed first at 14 ma contemporaneously with the opening of the tauern window in the eastern alps a middle miocene cooling rate of 40 c myr 1 is deduced for the lower penninic units of the lepontine dome

seafloor reflectivity an important seismic property for interpreting fluid gas expulsion geology and the presence of gas hydrate a bottom simulating reflection bsr is a seismic reflectivity phenomenon that is widely accepted as indicating the base of the gas hydrate stability zone the acoustic impedance difference between sediments invaded with gas hydrate above the bsr and sediments without gas hydrate but commonly with free gas below are accepted as the conditions that create this reflection the relationship between bsrs and marine gas hydrate has become so well known since the 1970s that investigators when asked to define the most important seismic attribute of marine gas hydrate systems usually reply a bsr event research conducted over the last decade has focused on calibrating seafloor seismic reflectivity across the geology of the northern gulf of mexico gom continental slope surface to the seafloor this research indicates that the presence and character of seafloor bright spots sbs can be indicators of gas hydrates in surface and near surface sediments figure 1 it has become apparent that sbss on the cont

thermal and tectonic history of the east midlands shelf onshore uk and surrounding regions assessed by apatite fission track analysis apatite fission track analysis has been used to study the thermal and tectonic history of the east midlands shelf and surrounding areas of onshore uk apatites from outcrops of palaeozoic crystalline basement give fission track ages between 300 29 and 420 31 ma which are the oldest yet reported in the uk region and reflect the relative stability of this cratonic region mean track lengths in these samples are between 12 and 13 m namurian and triassic sandstones from outcrop give apatite fission track ages between c 100 and c 390 ma with mean track lengths generally between 10 and 12 5 m distributions of single grain ages and track lengths suggest that all samples have been annealed implying exposure to higher temperatures since deposition with maximum palaeotemperatures reached some time in the 50 80 ma range prior to the onset of cooling samples from five exploration wells show consistent patterns in which apatite fission track ages decrease sharply from around or just less than the stratigraphic age at near surface to values in the 50 80 ma range at depths of c 1 2 km present temperatures of c 40 70 c showing that the samples studied have all been exposed to higher temperatures single grain ages and track length data suggest that maximum palaeotemperatures were attained at or before c 60 ma subsequent cooling was protracted and the data are compatible with two phases in the early and mid tertiary palaeotemperature analysis suggests that palaeo geothermal gradients were similar to present values and that elevated palaeotemperatures were due to greater depth of burial with cooling due to subsequent uplift and erosion estimates of uplift and erosion vary from c 1 1 5 km on the east coast around the humber estuary to c 2 2 km in the east midlands and southern pennines compilation of palaeotemperature estimates from all samples analysed from the uk onshore region shows that mesozoic burial and tertiary uplift has affected a wide area and that uplift was due to broad scale regional warping with recognized inversion axes being areas where uplift and erosion were particularly pronounced or where younger sediments and or inverted basinal structures allow the identification of uplift and erosion the recognition of late cretaceous early tertiary unconformities across wide areas of northwest europe both onshore and offshore suggests that the regional uplift and erosion may have been far more widespread than previously recognized this has important implications for hydrocarbon exploration in northwest europe

lateglacial and early holocene dynamics of adjacent valley glaciers in the western swiss alps the alps play a pivotal role for glacier and climate reconstructions within europe detailed glacial chronologies provide important insights into mechanisms of glaciation and climate change we present 26 10be exposure dates of glacially transported boulders situated on moraines and ice moulded bedrock samples at the belalp cirque and the great aletsch valley switzerland weighted mean ages of 10 9 11 1 11 0 and 9 6 ka for the belalp on up to six individual moraine ridges constrain these moraines to the egesen kartell and schams stadials during lateglacial to early holocene times the weighted mean age of 12 5 ka for the right lateral moraine of the great aletsch correlates with the egesen stadial related to the younger dryas cooling these data indicate that during the early holocene between 11 7 and 9 2 ka glaciers in the swiss alps seem to have been significantly affected by cold climatic conditions initiated during the younger dryas and the preboreal oscillation these conditions resulted in glacier margin oscillations relating to climatic fluctuations during the second phase of the younger dryas and continuing into boreal times as supported by correlation of the innermost moraine of the belalp cirque to the schams early holocene stage copyright 2011 john wiley sons ltd

paleogeography and catchment evolution in a mobile orogenic belt the central alps in oligo miocene times abstract in this study we reconstruct the surface evolution of the oligo miocene central alps using geochronological geochemical and petrographical methods on the foreland basin sediments of both flanks of the mountain range our model is illustrated in four sketch maps of different time slices between mid oligocene to middle miocene times for each time slice we try to 1 give a palinspastic reconstruction of the central alps based on the post collisional lateral extrusion model 2 show which tectonic units had become exposed to the surface due to exhumation processes in the central alps 3 describe the thermochronologic evolution of lithological units formerly exposed but completely eroded today 4 differentiate the catchment areas of the paleo river systems which delivered debris to the foreland basins and 5 describe the position of the main drainage divide relative to the exposed tectonic units

evaluating the petroleum systems of the northern deep gulf of mexico through integrated basin analysis an overview exploration and development activity has increased significantly during the past 5 years in the northern deep gulf of mexico this activity has been caused by several factors including significant discoveries in deep water 1500 ft water depth outstanding reservoir performance in some of these discoveries expiration of 10 year leases originally purchased in the mid 1980s innovative production techniques and new federal royalty relief exploration and production has occurred in three general exploration subprovinces present shelf deep water and the subsalt that extends from shelf into upper slope each subprovince consists of slightly different geology and subsequently different economic scenarios this paper introduces the geologic setting for a portion of the outer shelf and upper to middle slope region in the northern gulf of mexico the following eight papers demonstrate how the petroleum systems of the deep gulf of mexico can be analyzed by using an integrated approach this issue of the bulletin includes papers that describe the petroleum geology of the northern green canyon and ewing bank region petroleum fields and discoveries sequence stratigraphy biostratigraphy three dimensional seismic stratigraphic interpretation structural geology using restorations interaction of salt tectonics and sedimentation and geothermal modeling and path migration prediction

resolving poly metamorphic paleoarchean ages by chemical dating of monazites using multi spectrometer u th and pb analyses and sub counting methodology abstract chemical u th total pb dating method is a low cost and reliable technique to estimate the age of monazites of detrital and diagenetic origin or those found in low to high t metamorphic or magmatic rocks using electron microprobe emp analyses the method has been commonly applied for age estimation in phanerozoic and proterozoic rocks and less commonly in neoarchean rocks monazite dates from the paleoarchean era are rare and the associated error of spot age 2 error absolute age 100 is high i e between 2 and 26 the errors associated with chemical dating of monazite are significantly larger compared to isotope methods which impede precise age estimation and age resolution in polygenetic monazites of neoarchean and older rocks in this study simultaneous element analyses in multiple spectrometers and the sub counting method of analyses are employed to obtain precise estimates of u th and pb concentrations in monazite using vanadinite pb 5 vo 4 3 cl as the pb standard instead of pbs the method yields an age of 3118 28 ma with mount narryer mesoarchean monazite thermal ionization mass spectrometry tims age 3132 1 ma and 516 12 ma with moacyr monazite tims age 509 1 ma emp monazite age 497 10 ma as the reference samples the modifications led to 40 reduction in spot age errors in the mount narryer sample relative to those obtained by conventional monazite dating method the reduced errors in spot ages helped in resolving statistically un mixed age populations 3152 16 ma 3322 15 ma and 3420 140 ma in polygenetic monazites within muscovite quartz schists from the singhbhum craton eastern india the significance of these dates is briefly discussed