reduced reused and recycled detrital zircons define a maximum age for the eoarchean ca 3750 3780 ma nuvvuagittuq supracrustal belt quebec canada abstract a key discovery from the hadean pre 3850 ma detrital zircon record has been that the dichotomy of granitic and basaltic crust was established within about 160 myr of earth s formation harrison 2009 understanding the origin and fate of this primordial crust would greatly add to what we know about the geodynamics of the hadean earth insights emerge from 147 146sm 143 142nd isotope data reported from different eoarchean terranes worldwide including the nuvvuagittuq supracrustal belt nsb in northern quebec some ca poor cummingtonite rich amphibolites and granitoid gneisses of the nsb preserve lower 142nd 144nd than bulk silicate earth bse these also show positive correlations against 147sm 144nd that were used by o neil et al 2008 o neil et al 2012 to assign a ca 4400 ma age alternatively the compositions were inherited during the formation of the nsb at around 3800 ma roth et al 2013 guitreau et al 2013 to resolve this discrepancy ion microprobe u pb ages are reported for detrital zircons from nsb meta sediments from within the same supracrustal successions that preserve low 142nd 144nd the youngest detrital zircon cores of igneous derivation define a maximum age for the nsb of ca 3780 ma this age is about 600 myr younger than that obtained from 142nd 144nd vs 147sm 143nd regressions thus just like the variable 142nd 144nd ratios reported for other eoarchean terranes non bse 142nd 144nd values of the nsb were inherited from an older component

formation age and metamorphic history of the nuvvuagittuq greenstone belt abstract the nuvvuagittuq greenstone belt ngb in northern quebec canada is dominated by mafic and ultramafic rocks metamorphosed to at least upper amphibolite facies rare felsic intrusive rocks provide zircon ages of up to 3 8 ga david et al 2009 cates and mojzsis 2007 establishing the minimum formation age of the ngb as eoarchean primary u rich minerals that may provide reliable formation ages for the dominant mafic lithology called the ujaraaluk unit have yet to be found metamorphic zircons rutiles and monazites are present in the unit and give variably discordant results with 207pb 206pb ages ranging from 2 8 ga to 2 5 ga the younger ages overlap 2686 4 ma zircon ages for intruding pegmatites david et al 2009 and sm nd ages for garnet formation in the ujaraaluk rocks suggesting this era as the time of peak metamorphism and metasomatism in the ngb coeval with regional metamorphism of the superior craton sm nd data for ujaraaluk whole rocks scatter about a sm nd vs 143nd 144nd correlation mswd 134 whose slope would correspond to 3 6 0 2 ga if interpreted as an isochron this isochron is seen to consist of a series of younger 3 2 2 5 ga slopes for the different geochemical groups within the ujaraaluk emanating from a baseline distribution older than 4 ga the 146sm 142nd chronometer is less affected by metamorphism at 2 7 ga because of 146sm extinction prior to 4 ga expansion of the 142nd dataset for the ujaraaluk and associated ultramafic rocks continues to show a good correlation between sm nd ratio and 142nd 144nd that corresponds to an age of 4388 15 17 ma the dataset now includes samples with superchondritic sm nd ratios that extend the correlation to 142nd excesses of up to 8 ppm compared to the terrestrial standard with a total range in 142nd 144nd of 26 ppm the upper sm nd ratio end of the ujaraaluk correlation is defined by rocks that are interpreted to be cumulates to compositionally related extrusive rocks indicating that this crystal fractionation had to occur while 146sm decay was active i e well before 4 ga intruding gabbros give 143nd and 142nd isochron ages of respectively 4115 100 ma and 4313 41 69 ma also supporting an hadean age for the gabbros and providing a minimum age for the intruded ujaraaluk unit 3 6 ga tonalites surrounding the ngb 3 8 ga trondhjemitic intrusive veins and a 2 7 ga pegmatite show a deficit in 142nd compared to the terrestrial standard these felsic rocks plot to the low sm nd ratio side of the ujaraaluk isochron and do not show a correlation between their sm nd and 142nd 144nd ratios which can be explained if they are melts of ancient lree enriched mafic rocks such as the ujaraaluk with the melting occurring after 146sm was extinct a subset of least disturbed ujaraaluk samples has coherent isotopic compositions for both short lived and long lived nd isotopic systems giving 143nd and 142nd isochron ages overlapping within error of 4321 160 ma mswd 6 3 and 4406 14 17 ma mswd 1 0 respectively this age represents our best age estimate for the ujaraaluk unit the ngb thus preserves over 1 6 billion years of early earth history including an expanse of mafic crust formed in the hadean

protocrustal evolution of the nuvvuagittuq supracrustal belt as determined by high precision zircon lu hf and u pb isotope data abstract the nuvvuagittuq supracrustal belt nsb in northern quebec canada represents one of the oldest known crustal fragments preserved in the earth s crust its age has however been disputed and different authors present crustal formation ages varying from ca 3 8 ga to 4 4 ga e g o neil et al 2012 guitreau et al 2013 here we report new high precision u pb geochronological and coupled lu hf isotope data from zircons that reveal the age of the nsb and provide new constraints on the source rocks to this piece of early crust two rocks have been analysed a felsic schist interpreted to represent a volcanite and a mylonitic tonalite that is intrusive into the nsb the felsic schist was emplaced at 3771 5 3 ma dating the formation of the nsb the lu hf model age indicates that the parental melt to the felsic schist was extracted from the mantle at this age or within a few tens of million years but no more than 300 m y before its extrusion this mantle extraction age provides an absolute maximum age for the nsb but the most probable age of its protocrust is ca 3 8 ga the mylonitic tonalite was emplaced at 3667 3 1 ma its lu hf isotopic composition reveals the presence of an older crustal component than that of the nsb requiring that its precursor melt formed from a hadean source that was older than the nsb based on recent models for archean ttg formation we propose that this source represents re melted hadean hydrated crust that must have been translated below the nsb at ca 3667 ma

aminostratigraphy of quaternary shorelines in the mediterranean basin the age and correlation of shorelines around the mediterranean basin have been addressed by analyzing the extent of isoleucine epimerization aile ile ratio in protein preserved in molluscan fossils collected from raised marine deposits the taxodont genera glycymeris and arca were selected as the primary taxa for this study because of their simple shell structure reproducible aile ile ratios and ubiquitous occurrence direct comparison of aile ile ratios in associated mollusks allows correlation of disjunct marine deposits and relative dating of sequential marine units in nearby areas that have similar thermal histories the thermal gradient across the mediterranean basin is however sufficiently high that shells from isochronous shorelines have significantly higher ratios at warmer than at cooler localities absolute dating primarily u series dates on corals directly associated with molluscan samples provides an independent calibration of the amino acid data and compensates for dissimilar thermal histories aile ile ratios in shells from 46 marine units cluster into 5 discrete groups c e f g and k that are related to positive sea level events interglacials interstadials associated with odd numbered deep sea isotopic stages the most complete sequences are in southern italy where group c ratios in glycymeris that average 0 30 are associated with the neotyrrhenian a post last interglacial late stage 5 high sea level event group e ratios 0 38 are associated with classical eutyrrhenian deposits from which four u series coral dates 126 7 ka substantiate the correlation to isotope substage 5e group f ratios 0 50 are associated with u series coral and mollusk dates between 200 and 300 ka the deposits are tentatively correlated with stage 7 deposits that have group g ratios 0 58 are correlated with stage 9 shells from lower pleistocene marine deposits that have ratios between 1 0 and 1 2 group k constrain the ages of the younger groups an exponential decrease in the epimerization rate inhibits resolution of the older events aile ile ratios in last interglacial deposits are similar in the northern and central region of the study area but increase sharply in southern sicily north africa and crete similar to the modern thermal gradient a lacuna between group g and group k is similar to gaps identified in california and alaska suggesting generally lower interglacial sea levels between stage 11 and sometime before the brunhes matuyama boundary

an ocean general circulation model view of the glacial mediterranean thermohaline circulation reconstructions of the sea surface temperature and salinity of the mediterranean sea during the last glacial maximum lgm suggest that extremely cold winters occurred in the western basin and the aegean with highly saline conditions in the eastern basin it is shown here that forcing the lgm mediterranean sea with a representative paleoclimate model results in significantly less extreme salinity conditions than are suggested by existing reconstructions modeled sea surface salinities are at most 0 1 0 2 higher than today at the lgm rather than the previously suggested 2 3 modeled sea surface temperatures over the western basin however show similar changes to these reconstructions being 3 4 c colder than present day another major difference between the lgm and control simulations is the location and spreading of subsurface water the western basin suffers complete loss of stability in the lgm winter leading to this basin becoming the source for the lgm deep water of the eastern basin the ocean general circulation model results are shown to be qualitatively consistent with cooler drier climate along the northern coast of the mediterranean but not with higher surface salinity thus refining existing paleoclimate reconstructions in the mediterranean region

optical dating using infrared diodes young samples abstract ages are reported for unburnt sediment samples from 9 archaeological sites in england spanning 1000 5000 years samples from two modern contexts have also been measured

crustal evolution of the western minto block northern superior province canada abstract geochemical and nd isotope data are presented for suites of meso to late archean 2 7 2 9 ga granitoid rocks from the western minto block of the northeast canadian superior province the samples provide coverage of the inukjuak and tikkerutuk domains and include biotite amphibole and or orthopyroxene bearing tonalites granodiorites and granites from tonalite trondhjemite granodiorite ttg and monzodiorite suites both suites are characterized by strong light rare earth element ree and large ion lithophile lil element enrichment variably negative to positive eu anomalies and moderate heavy ree depletion high la yb and sr y ratios with correspondingly low yb and y concentrations in both suites likely reflect parental melts that left residual garnet correlations between eu anomalies and fractionation indices suggest that compositional variations in both suites reflect plagioclase accumulation in tonalite samples and plagioclase and fe ti oxide fractionation among granitic samples the nd isotope compositions range from nd values of 2 to 10 the largest range found among granitoids of the minto block and indicate the presence of a crustal contaminant of ca 3 8 ga in age there is a decrease in nd values from east to west across the studied region and a measurable decrease across tikkerutuk and inukjuak domain boundary this suggests increasing addition of an older crustal component in the inukjuak domain possibly as a result of recycling of early archean crust from the nearby ca 3 8 ga nuvvuagittuq sequence

late archean mantle composition and crustal growth in the western superior province of canada neodymium and lead isotopic evidence from the wawa quetico and wabigoon subprovinces abstract neodymium and lead isotopes are presented for late archean rocks from the wawa quetico and wabigoon subprovinces sp in the western superior province ontario canada the isotopic compositions were determined on greenstone volcanic sequences pre tectonic 2 73 2 69 ga trondhjemite tonalite granodiorite ttg suites metasedimentary rocks and post tectonic 2 69 2 67 ga dioritic to granitic plutons in order to characterize the mantle and crustal reservoirs involved in the evolution of the southern part of the western superior province although derived from a depleted mantle almost all the greenstone volcanism and pre tectonic ttg suites record contamination by crustal material as old as 3 2 ga neodymium and lead isotopic compositions of the pre tectonic ttg can be modeled as products of the melting of amphibolitic crust e g subducted basalts contaminated by 1 10 of subducted sediments moreover lead isotopes of ttg suites provide evidence that the isotopic compositions of these subducted sediments varied as a result of the addition of new ca 2 7 ga juvenile material in agreement with neodymium isotopic differences recorded by sedimentary units of the quetico sp 50 50 mix of young old crusts and wawa sp 75 25 young old neodymium and lead isotopes of the post tectonic ree enriched archean sanukitoid suites define an isotopic trend which is distinct from that of the ttg suites and which is interpreted to reflect the importance of crustal assimilation in the evolution of these suites furthemore such plutons found in the wawa sp have more juvenile neodymium and lead isotopic compositions and higher nd contents than those intruded into the quetico and wabigoon sp which have more crustal isotopic signatures and lower nd concentrations this geographical difference could be due either to differences in nd contents of initial archean sanukitoid magmas lesser assimilation in the wawa sp or more probably because the wawa crust is on average more juvenile than the quetico and wabigoon crusts in agreement with the fact that the geographical difference mirrors that recorded by metasedimentary rocks deposited in quetico and wawa sp

late archaean terrane accretion in the godthab region southern west greenland tectono stratigraphic terranes fault bounded blocks of the earth s crust characterized by a geological history distinct from that of adjacent terranes1 are now widely recognized in phanerozoic and proterozoic orogenic belts and their present configurations are thought to result from plate tectonic processes similar to those in operation today2 4 there has been much debate about whether such processes operated in archaean times5 6 here we present new data from the archaean high grade gneiss complex of the godthab now nuuk region of southern west greenland which show that discrete tectonic units recognized in the south of the region7 can be more widely identified at least four terranes are recognized each of which evolved separately until their juxtaposition in the late archaean this suggests that at least some archaean high grade gneiss complexes may resemble more recent orogenic belts formed by plate tectonic processes

stratigraphic and geochemical evidence for the depositional environment of the early archaean isua supracrustal belt southern west greenland the highly deformed c 3800 ma isua supracrustal belt is a fragment of a more extensive early archaean sedimentary and volcanic succession intruded by and tectonically intercalated with tonalitic and granitic amftsoq gneisses in the period 3800 3600 ma the supracrustal rocks recrystallised under amphibolite facies conditions between 3800 and 3600 ma in the late archaean and locally at c 1800 ma layered sequences of rock of sedimentary and probable volcanic origin form over 50 of the belt bodies of high mg al basic rocks and ultramafic rocks were intruded into the layered sequences prior to isoclinal folding and intrusion of amitsoq gneisses the layered rocks which are 1 km thick are divided into two sequences that are in faulted contact with each other the way up of these sequences has been determined from facing directions of locally preserved graded layering in felsic metasediments at several localities the overall upwards change in sedimentary succession is interpreted as showing change from dominantly basic to dominantly felsic volcanism which provided the major clastic component of the sediments clastic sedimentation took place against a background of chemical sedimentation shown by interlayers of banded iron formation metachert and calc silicate rocks throughout the sequences the felsic rocks locally preserve graded bedding and possible conglomerate structures indicating deposition from turbidite flows and possibly as debris flows nodules in the felsic rocks contain structures interpreted as fiamme there is an irregular enrichment in k2o na2o in many of the felsic rocks at constant sio2 and al2o3 content interpreted as owing to alteration of original andesitic to dacitic volcanic rocks banded iron formations locally contain conglomeratic structures suggesting sedimentary reworking possibly under shallow water conditions lithological and geochemical characters of the clastic components of the supracrustal sequences are consistent with derivation from felsic and basic volcanic rocks and do not require a continental source

building archean cratons from hadean mafic crust geologic processing of earth s surface has removed most of the evidence concerning the nature of earth s first crust one region of ancient crust is the hudson bay terrane of northeastern canada which is mainly composed of neoarchean felsic crust and forms the nucleus of the northeastern superior province new data show these 2 7 billion year old rocks to be the youngest to yield variability in neodymium 142 142nd the decay product of short lived samarium 146 146sm combined 146 147sm 142 143nd data reveal that this large block of archean crust formed by reworking of much older 4 2 billion year old mafic crust over a 1 5 billion year interval of early earth history thus unlike on modern earth mafic crust apparently could survive for more than 1 billion years to form an important source rock for archean crustal genesis

setting and origin for problematic rocks from the 3 7 ga isua greenstone belt southern west greenland earth s oldest coarse clastic sediments abstract whether or not coarse detrital sedimentary rocks occur within the 3 7 ga isua greenstone belt igb southern west greenland has been debated for some time repeated regional metamorphic deformational and metasomatic events have obscured most protolith lithologies leading to misunderstandings about the stratigraphy and environments of deposition rocks here interpreted as meta conglomerate crop out in a fault bounded structural domain that is lower in strain relative to adjacent domains the meta conglomerate has a strike length of 1 km and is 10 m thick bed thickness ranges from 10 cm to more than 1 m and beds may be either framework or matrix supported a poorly sorted and variably rounded polymict assemblage of framework clasts consisting of meta chert bif and a variety of mafic volcanic rock fragments are set into a matrix of biotite quartz garnet schist clast compositions indicate reworking of adjacent stratigraphic units a lack of structural similarity in framework clasts range of grain sizes range of rounding and polymict composition demand a primary sedimentary origin for the deposit inferred depositional processes include traction and debris flow which would be consistent with subaerial or shallow subaqueous environments although the limited extent of the meta conglomerate warrants interpretational caution

a comparison of bulk versus laser ablation trace element analyses in banded iron formations insights into the mechanisms leading to compositional variability abstract banded iron formations bif represent one of the few chemical sedimentary archives available for exploring the redox state of the precambrian atmosphere ocean system and the marine availability of biologically critical trace nutrients through time temporal records compiled for a number of trace elements show a relatively wide spread in concentrations spanning several orders of magnitude within a single deposit it has been suggested that this spread is present in both bulk rock digestion and laser ablation data however the comparability of data from the two methods has not been thoroughly evaluated here we provide a statistical assessment of how comparable laser ablation data of individual bif hematite and magnetite grains are to one another as well as how closely averages of laser ablation data approximate bulk rock values to do so we use laser ablation high resolution inductively coupled plasma mass spectrometry la hr icp ms data from 14 bif slabs and corresponding powders that span four different formations we focus in particular on bif from the 3 75 ga nuvvuagittuq supracrustal belt quebec canada and multiple bif deposits of the 2 6 2 45 ga hamersley group north western australia representing deposits separated by over a billion years and of differing metamorphic grade the scaling between selected transition metals is also evaluated in light of expectations for possible delivery mechanisms of trace elements from seawater to bif precursor sediments the adsorption to hydrous ferric oxides biological vectors and detrital influence our findings show that average trace element concentrations between bulk versus laser ablation data typically vary within an order of magnitude furthermore reproducibility between the two methods appears to be independent of formation age metamorphic grade or depositional setting these findings underscore the overall fidelity of the bif record at capturing seawater compositional signatures at various scales we demonstrate that evaluations of ancient seawater chemistry using the bif record are best served by a combined approach utilizing both bulk rock and laser ablation data as bulk methods offer the most conservative proxy data for ancient seawater composition but may mask significant enrichments or depletions that are detectable at the grain scale by laser ablation

early crustal evolution of the superior craton a u pb hf and o isotope study of zircon from the assean lake complex and a comparison to early crust in other cratons abstract we report u pb hf o isotopic measurements of zircon extracted from meta igneous rocks exposed in the assean lake crustal complex northwestern superior craton canada with crystallization ages of ca 3 22 ga zircon from the assean lake crustal complex are among the oldest reported in the superior craton the hf and o isotope compositions of zircon indicate that these meta igneous rocks derive from a mantle component with a relatively primitive hf isotope composition similar to chondrites that was uncontaminated by elevated 18o material ehf initial 0 and 18ovsmow 5 5 these features are shared by the large majority of the zircon extracted from the oldest meta igneous rocks exposed in archean terranes positive ehf deviations in archean zircons are typically observed in magmas that post date the oldest magmatic activity in a given terrain this temporal variability in magma source regions may reflect a sequence of events comprising i felsic magmatism derived from undepleted mantle components followed by ii re melting of the same mantle component producing the depleted hf signatures in zircon and then iii accretion of the proto craton and reworking of the whole system enabling stabilization

young poorly crystalline graphite in the 3 8 gyr old nuvvuagittuq banded iron formation carbonaceous minerals in 3 8 billion year old rocks from west greenland have been used as evidence for early life on earth geochemical analyses of similar carbon minerals in 3 75 to 4 2 billion year old rocks from canada show that they can be derived from subsequent alteration more than a billion years after the initial formation

geochemical and textural investigations of the eoarchean ukaliq supracrustals northern quebec canada abstract structural geochronological and geochemical studies of pre 3 75 ga rocks of volcano sedimentary protoliths in the inukjuak domain in the superior province in quebec have been mostly focused on the nuvvuagittuq supracrustal belt nsb the porpoise cove outcrops at the southwestern limit of the nsb are the de facto type locality for the supracrustals of the inukjuak complex yet it remains unclear whether the nsb rocks are geochemically distinct from or are in fact common to a host of other supracrustal enclaves locked in the dominantly gneissic inukjuak domain here we report detailed textural and geochemical studies for a suite of rocks from the ukaliq supracrustal belt usb located approximately 3 km northeast of the nsb we find that the usb and nsb have a similar protracted metamorphic history both experienced amphibolite grade metamorphism and contain granitoid gneiss sheets quartz magnetite rocks banded iron formation s l and quartz biotite schists within amphibolitized rocks of basaltic affinity with local retrogressions if the various inukjuak supracrustal belts were once a part of a larger coherent now dismembered terrane they should show similar emplacement ages and source chemistry new zircon u pb geochronology from five gneissic units and two quartz biotite metasedimentary schists reveal the oldest emplacement ages across all units of each individual rock type to be 3 68 0 07 ga granitoid gneisses and 3 65 0 06 ga quartz biotite schists these new ages are similar to those documented as likely minimum emplacement ages of the nsb determined by u pb geochronology zircons from the quartz biotite schist were also analyzed by ion microprobe for their u pb geochronology and were found to yield statistically identical albeit more precise ages than those obtained by la icp ms possible detrital zircons from the usb quartz biotite schists were analyzed by ion microprobe for their coupled 30sinbs28 and 18ovsmow values with respective values between 0 75 and 0 07 30sinbs28 and 5 61 and 6 59 18ovsmow the 18ovsmow values which are on average above mantle derived zircon indicate contribution of altered non mantle derived material into the source of the rocks that weathered to form the quartz biotite schists zircon mineral inclusions quartz feldspar apatite biotite muscovite and other unrecognized fe al si rich phases along with the major and trace element contents for the rocks were analyzed to substantiate this interpretation together with 30sinbs28 18ovsmow our results suggest that lithologies like authigenic silica and serpentinized rocks re melted to form the parent melts that gave rise to zircons found in the usb quartz biotite schists additional lu hf studies reported here on the same zircons also show similarities with nsb zircons the ehf values showed a positive correlation with the measured u pb age from 22 7 0 8 to 1 9 1 1 the lu hf system also reveals that the usb extracted at ca 3 8 ga carries isotopic signatures of an older hadean reservoir having been formed from an eoarchean mafic melt that incorporated them taken together this supports a co genetic origin for the nsb and the usb

occurrence and geochronology of the eoarchean 3 9 ga iqaluk gneiss in the saglek block northern labrador canada evidence for the oldest supracrustal rocks in the world abstract understanding earth s early evolution requires decoding the cryptic geological record that is preserved in a few extremely rare terrains on earth the saglek hebron block in the north atlantic craton is one of the oldest terrains in the world to better understand the eoarchean history of the saglek hebron block we undertook a comprehensive geological and geochronological investigation of this terrain the saglek hebron locality contains orthogneisses and supracrustal rocks which are classified into two groups of the eoarchean and mesoarchean suites based on field associations defined by intrusion of the mesoarchean mafic saglek dykes the eoarchean suites contain the nulliak supracrustal rocks and uivak gneisses in this paper we report cathodoluminescence cl observations and u pb ages of zircons from the eoarchean orthogneisses to constrain the evolution of the saglek hebron block we made detailed sketch maps 1 20 of critical outcrops to establish relative chronological relationships between lithologies at least seven generations of mafic and felsic units were recognized in an outcrop of the st john s harbour south area the first and second generations are mafic supracrustal rocks whereas the third to seventh generations are tonalitic gneisses which are intruded into the supracrustal units we study cl observation geochemistry and u pb dating of zircons from the oldest and youngest tonalitic gneisses the cl observation of internal structures of the zircons showed they typically comprise three domains of core mantle and rim the cores have clear oscillatory zoning whereas the mantles lack oscillatory zoning and exhibit dark cl emission and structureless cl images the obvious correlation between the ages and chemical compositions of u contents and th u ratios indicates that the cores with low u contents and high th u ratios preserve the protolith age the cores with clear oscillatory zoning low u contents and high th u ratios of zircons from the oldest suite plot on a concordia line with ages ranging from 3953 to 3797 ma the oldest and average ages of the six oldest spots on the concordia line are 3953 54 and 3920 49 ma respectively on the other hand the average age of the four old spots of zircons from a younger generation of orthogneiss is 3869 63 ma the geological and geochronological relationships between the third and seventh generation orthogneisses are consistent with each other confirming an eoarchean age of ca 3 9 ga for the oldest suite of the uivak gneisses we name this oldest suite the iqaluk gneiss as the protolith of the iqaluk gneiss was clearly intruded into the nulliak supracrustal rocks the nulliak supracrustals must have a minimum age of ca 3 9 ga indicating that they are the oldest supracrustal rocks on earth but further studies should be necessary to obtain more precise age of the iqaluk gneiss and nulliak supracrustal rocks

u pb ages 3 8 2 7 ga and nd isotope data from the newly identified eoarchean nuvvuagittuq supracrustal belt superior craton canada we report new u pb ages and sm nd isotope data for an eoarchean volcano sedimentary sequence in the northeast superior province of northern quebec canada the nuvvuagittuq supracrustal sequence is characterized by mafi c amphibolite rocks with rare felsic schists accompanied by ultramafi c sills oxide rich and quartz rich iron formations and possible conglomeratic units with peak metamorphism having reached upper amphibolite facies the sequence crops out as an open shallow south plunging synform with tonalites in the center and around the exterior margins of the fold structure a 3817 16 ma age from a felsic schist is interpreted to represent a maximum age for the sequence whereas a 3661 4 ma age from the enclosing tonalites suggests a minimum age detrital zircons from a conglomeratic unit yielded similar old ages of ca 3 78 ga younger ages of ca 3 66 and 3 3 ga from a conglomeratic unit and a felsic schist and 2 7 ga ages from an amphibolite gabbro and a pegmatite dike underline the polymetamorphic history of the sequence initial nd isotope compositions end 3 8 0 5 to 2 3 for mafi c amphibolites and felsic schists are indicative of a moderately depleted mantle sm nd analyses of a 2 7 ga pegmatite dike and the ca 3 66 ga tonalites both yield nd depleted mantle model ages tdm of ca 3 9 ga indicating that they were derived from a crust of juvenile eoarchean origin we propose that fragments of paleoarchean to eoarchean terranes that rim the superior province represent remnants of a larger terrane s that was rifted and dismembered prior to the formation of the 3 0 2 7 ga superior craton

nd isotopic evidence for early to late archean 3 4 2 7 ga crustal growth in the western superior province ontario canada abstract new sm nd analyses of archean metavolcanic plutonic gneissic and metasedimentary rocks from sachigo and berens river subprovinces north caribou terrane and winnipeg river and wabigoon subprovinces in conjunction with previously published data are used to trace the crustal evolution of the western superior province wsp from ca 3 4 to 2 7 ga the extensive wsp geochronological database which contains 3 17 2 55 ga plutonic rocks allows the calculation of precise e t nd values and the identification of the main periods of new crustal addition at 3 4 0 1 3 02 2 92 and 2 76 2 69 ga mass balance calculations indicate that the western superior province represents a collage of archean crusts comprising 7 44 and 48 wt of crust created at 3 4 3 0 and 2 7 ga respectively although these calculations depend on the isotopic signatures of the mantle and those of the average crust at different times several important observations can be made 1 the importance of pre 2 7 ga terranes recycled in the 2 7 ga orogen 2 the existence of time intervals of 150 300 ma dominated by intra crustal processes resulting in a large range of crystallization ages u pb zircon ages that do not reflect new additions from the mantle 3 much of the new crustal additions at 2 7 ga were contaminated by crustal material subducted into the source region ttg suites or were contaminated during intrusion into the crust sanukitoids

glacial holocene salinity changes in the mediterranean sea hydrographic and depositional effects oxygen isotope changes as recorded by pleistocene foraminifera from open ocean sediments are primarily a function of changes in the isotopic composition of the global seawater reservoir caused by ice volume changes with a secondary temperature component1 oxygen isotope records from marginal basins such as the gulf of mexico2 the mediterranean sea3 5 and the red sea6 also exhibit the global signal but are far more complicated owing to the strong overprint of local climate conditions in particular glacial interglacial changes in continental aridity and river runoff produce significant salinity changes in these semi enclosed basins using available oxygen isotope records we estimate that glacial 18 000 yr bp salinities in the eastern and western mediterranean sea were 2 7 and 1 2 higher respectively than at present these elevated glacial salinities played an important part in preconditioning the eastern mediterranean for the eventual accumulation of organic carbon rich sediments sapropels at the end of deglaciation

nature of assean lake ancient crust manitoba a combined shrimp id tims u pb geochronology and sm nd isotope study abstract the assean lake crustal complex alcc located at the northwest periphery of the superior province in northern manitoba canada hosts an ancient assembly of rocks that record a complex and prolonged crustal history spanning more than two billion years from 3 9 to 1 8 ga a supracrustal assemblage consisting of amphibolite grade greywacke quartz arenite arkose mafic to intermediate volcanics and to a lesser extent iron formation dominates the alcc and likely formed in a shallow marine arc back arc setting the supracrustal rocks are intruded by amphibolite grade calc alkaline tonalite to granite orthogneiss nd model ages for felsic para and orthogneisses range from 3 5 to 4 2 ga and suggest that paleoarchean basement may be preserved at assean lake shrimp u pb zircon ages and id tims conventional u pb zircon and monazite ages show that felsic magmatism occurred at 3 1 3 2 ga whereas a record extending back to at least 3 9 ga is preserved in detritus in paragneiss that may have a depositional age of 3 2 ga orthogneiss was metamorphosed at 2 68 ga whereas local migmatisation of paragneiss occurred at 2 61 ga monazite growth events at 2 6 2 45 and 1 8 ga might represent episodes of accretion of archean crustal segments including the alcc and possibly the sask craton trans hudson basement along the northwest superior province margin at present matching segments of the exotic alcc are unknown but remnants may exist in parts of the sask craton

new pieces to the archaean terrane jigsaw puzzle in the nuuk region southern west greenland steps in transforming a simple insight into a complex regional tectonothermal model in the south of the nuuk region of west greenland our 1980s mapping recognized four archaean gneiss terranes f ringehavn tre brodre tasiusarsuaq and akia terranes with different protolith ages and separate early tectonothermal histories later in the archaean these were juxtaposed and then experienced the same 2700 2500 ma tectonothermal events here we abandon extrapolation of only these four terranes across the whole region and distinguish two new terranes in the ne the northernmost isukasia terrane previously regarded as the northernmost exposure of the f ringehavn terrane consists of palaeoarchaean rocks 3600 ma tectonically bounded on its south by the 3075 2960 ma kapisilik terrane these were juxtaposed and metamorphosed together by 2950 ma the previously recognized f ringehavn terrane to the sw is another separate entity of palaeoarchaean rocks that was juxtaposed with adjacent terranes only after c 2800 ma hence in an increasingly complex regional model there were several mid to neoarchaean terrane assembly events with superimposed orogenies from c 2950 ma until after 2700 ma although the f ringehavn and isukasia terranes were incorporated into the later archaean terrane collage at different times they might be fragments from a larger palaeoarchaean complex rifted apart from c 3500 ma onwards

brittle deformations in the upper pleistocene deposits of the crotone peninsula calabria southern italy abstract the structural setting of the crotone peninsula calabria southern italy is discussed in this paper structural analyses were carried out both on a regional and an outcrop scale to detect the main structural systems and the stress field which affected the area during the late pleistocene the tectonic features observed in the area are represented by normal faults and extensional joints the regional scale faults are arranged in five main systems striking ene wsw nne ssw e w nw se and nnw sse they are responsible for the dislocation of four marine depositional units cutro terrace correlatable with the isotopic stage 7 s leonardo campolongo isola di capo rizzuto terrace correlatable with the isotopic substage 5e le castella capo rizzuto terrace correlatable with the isotopic substage 5c and capo colonne terrace correlatable with the isotopic substage 5a in several distinct terraces from the studies carried out on a mesostructural scale it is possible to conclude that for the last 200 000 yrs the crotone peninsula was affected by an extensional stress field the comparison between the average uplift rates calculated for the crotone peninsula terraces and those computed for several upper pleistocene deposits located in sicily calabria and campania suggests that the intense tectonics which affected the crotone peninsula can be related to the geodynamic activity of the calabrian arc

metamorphic zircon trace elements and neoarchean metamorphism in the ca 3 75 ga nuvvuagittuq supracrustal belt quebec canada abstract the nuvvuagittuq supracrustal belt nsb in northwestern quebec ranks as one of the oldest granitoid gneiss complexes thus far discovered emplacement ages for intrusive trondhjemitic dikes that transect amphibolites and quartz magnetite schists at the porpoise cove outcrops of the nsb cluster at 3 75 ga as with all other pre 3 7 ga terranes thus far documented the nsb has been metamorphosed and multiply deformed in a combined approach to explore the thermal history of the nsb conventional garnet biotite and plagioclase hornblende geothermometry was coupled with zircon u th pb depth profiles ree partitioning and ti in zircon thermometry to show that neoarchean metamorphism in the belt reached upper amphibolite facies conditions 640 c this metamorphism resulted in some cases in thick zircon overgrowths on older cores and likely corresponds to the amalgamation of terranes in the northeast superior province and the initiation of widespread igneous activity in the vicinity of the nsb an earlier resolvable metamorphic episode from a zircon depth profile recorded at 3 62 ga probably corresponds to the intrusion of the granitoids which envelope the nsb

giant granulite terranes of northeastern superior province the ashuanipi complex and minto block the ashuanipi complex and minto block of the superior province are large regions that have been classified as high grade gneiss terranes on the basis of the presence of orthopyroxene bearing units like the granite greenstone and metasedimentary subprovinces of the southern superior province the two terranes consist predominantly of intrusive rocks but are distinguished by their primary magmatic orthopyroxene both high grade and gneiss are misnomers because granulite facies gneisses are only sparingly present and the regions consist dominantly of massive unmetamorphosed plutonic rock the ashuanipi complex consists of a deformed metamorphosed package of metasedimentary rocks and primitive early tonalite cut by widespread orthopyroxene garnet granodiorite diatexite as well as plutons of tonalite granite and syenite based on its lithological and chronological similarity and on strike position the complex appears to be the continuation of metasedimentary subprovinces such as the quetico its evolution involved deposition of immature greywacke in an accretionary prism early arc tonalitic magmatism and deformation followed by widespread intracrustal magmatism in the period 2700 2670 ma both metamorphic and igneous rocks record equilibration under granulite facies conditions 700 835 c 0 35 0 65 gpa a 0 3 and indicate exposure levels of 20 km the minto block at the latitude of leaf river consists of several north northwest trending domains of similar scale and diversity to the east trending subprovinces of the southern superior province the central goudalie domain is dominantly amphibolite facies tonalitic rocks including some with ages 3 ga with small belts of volcanic and sedimentary origin lake minto domain contains poorly preserved supracrustal remnants in a plutonic complex comprising hornblende granodiorite clinopyroxene orthopyroxene granodiorite orthopyroxene biotite diatexite and granite the hornblende granodiorite suite constitutes most of the utsalik and tikkerutuk domains and is thought to represent continental arc magmatism on the basis of their distinct aeromagnetic and lithological character two additional domains are evident north of the leaf river area the inukjuak domain in the west and the douglas harbour domain in the east the northerly grain of the minto block appears to have been established in situ with respect to the easterly belts of the southern superior province i e no large scale block rotation during the same interval of time 3 0 2 7 ga modification of the tectonic framework for the superior province is required to explain minto arc magmatism in the interval 2730 2690 ma ago a continental magmatic arc built the berens river and bienville subprovinces and minto block on the southern and eastern edges respectively of a northern protocratonic foundation in the same period primitive volcanic arcs and accretionary prisms developed outboard on oceanic crust and were accreted to form a southern tectonic regime

u pb geochronology of the southern brasilia belt se brazil sedimentary provenance neoproterozoic orogeny and assembly of west gondwana abstract the brasilia belt borders the western margin of the sao francisco craton and records the history of ocean opening and closing related to the formation of west gondwana this study reports new u pb data from the southern sector of the belt in order to provide temporal limits for the deposition and ages of provenance of sediments accumulated in passive margin successions around the south and southwestern margins of the sao francisco craton and date the orogenic events leading to the amalgamation of west gondwana ages of detrital zircons by id tims and la mc icpms were obtained from metasedimentary units of the passive margin of the sao francisco craton from the main tectonic domains of the belt the internal allochthons araxa group in the araxa and passos nappes the external allochthons canastra group serra da boa esperanca metasedimentary sequence and andrel ndia group and the autochthonous or cratonic domain andrel ndia group the patterns of provenance ages for these units are uniform and are characterised as follows archean paleoproterozoic ages 3 4 3 3 3 1 2 7 and 2 5 2 4 ga paleoproterozoic ages attributed to the transamazonian event 2 3 1 9 ga with a peak at ca 2 15 ga and to the ca 1 75 ga espinhaco rifting of the sao francisco craton ages between 1 6 and 1 2 ga with a peak at 1 3 ga revealing an unexpected variety of mesoproterozoic sources still undetected in the sao francisco craton and ages between 0 9 and 1 0 ga related to the rifting event that led to the individualisation of the sao francisco paleo continent and formation of its passive margins an amphibolite intercalation in the araxa group yields a rutile age of ca 0 9 ga and documents the occurrence of mafic magmatism coeval with sedimentation in the marginal basin detrital zircons from the autochthonous and parautochthonous andrel ndia group deposited on the southern margin of the sao francisco craton yielded a provenance pattern similar to that of the allochthonous units this result implies that 1 6 1 2 ga source rocks must be present in the sao francisco craton they could be located either in the cratonic area which is mostly covered by the neoproterozoic epicontinental deposits of the bambui group or in the outer paleo continental margin buried under the allochthonous units of the brasilia belt crustal melting and generation of syntectonic crustal granites and migmatisation at ca 630 ma mark the orogenic event that started with westward subduction of the sao francisco plate and ended with continental collision against the parana block and goias terrane continuing collision led to the exhumation and cooling of the araxa and passos metamorphic nappes as indicated by monazite ages of ca 605 ma and mark the final stages of tectonometamorphic activity in the southern brasilia belt whilst continent continent collision was proceeding on the western margin of the sao francisco craton along the southern brasilia belt eastward subduction in the east was generating the 634 599 ma rio negro magmatic arc which collided with the eastern sao francisco margin at 595 560 ma much later than in the brasilia belt thus the tectonic effects of the ribeira belt reached the southernmost sector of the brasilia belt creating a zone of superposition the thermal front of this event affected the proximal andrel ndia group at ca 588 ma as indicated by monazite age the participation of the amazonian craton in the assembly of western gondwana occurred at 545 500 ma in the paraguay belt and ca 500 ma in the araguaia belt this together with the results presented in this work lead to the conclusion that the collision between the parana block and goias terrane with the sao francisco craton along the brasilia belt preceded the accretion of the amazonian craton by 50 100 million years

earliest part of earth s stratigraphic record a reappraisal of the 3 7 ga isua greenland supracrustal sequence investigations of the isua supracrustal rocks in west greenland allow us to identify the protoliths and alteration history for most isua rocks the protoliths consisted of alternating basalt and banded iron formation this sequence was invaded by dunitic sills metamorphosed and later intruded by felsic gneisses pervasive carbonation and k metasomatism produced a sequence of lithologies mimicking those found in modern platform deposits however the protoliths could have originated in a purely oceanic environment with no sialic detrital components the isua sequence probably consists of several tectonic panels some of which are cut by 3810 ma felsic intrusive rocks

oxygen isotope record of sea level and climate variations in the sulu sea over the past 150 000 years the sulu sea is located in the warm pool of the western pacific ocean where mean annual temperatures are the highest of anywhere on earth because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change changes in the oxygen isotope composition of planktonic foraminifera from sulu sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial interglacial and millenial timeseales and such records have been obtained for the late pleistocene epoch and the last deglaciation1 3 here i present results that extend the millenial time resolution record back to 150 000 years before present on timescales of around 10 000 years the sulu sea oxygen isotope record matches changes in sea level deduced from coral terraces on the huon peninsula4 this is particularly the case during isotope stage 3 an interglacial period 23 000 to 58 000 years ago where the sulu sea oxygen isotope record deviates from the specmap deep ocean oxygen isotope record5 thus these results support the idea4 6 that there were higher sea levels and less continental ice during stage 3 than the specmap record implies and that sea level during this interglacial was just 40 50 metres below present levels the subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought

sims analyses of silicon and oxygen isotope ratios for quartz from archean and paleoproterozoic banded iron formations banded iron formations bifs are chemical marine sediments dominantly composed of alternating iron rich oxide carbonate sulfide and silicon rich chert jasper layers isotope ratios of iron carbon and sulfur in bif iron bearing minerals are biosignatures that reflect microbial cycling for these elements in bifs while much attention has focused on iron banded iron formations are equally banded silica formations thus silicon isotope ratios for quartz can provide insight on the sources and cycling of silicon in bifs bifs are banded by definition and microlaminae or sub mm banding are characteristic of many bifs in situ microanalysis including secondary ion mass spectrometry is well suited for analyzing such small features in this study we used a cameca ims 1280 ion microprobe to obtain highly accurate 0 3 and spatially resolved 10 lm spot size analyses of silicon and oxygen isotope ratios for quartz from several well known bifs isua southwest greenland 3 8 ga hamersley group western australia 2 5 ga transvaal group south africa 2 5 ga and biwabik iron formation minnesota usa 1 9 ga values of d 18 o range from 7 9 to 27 5 and include the highest reported d 18 o values for bif quartz values of d 30 si have a range of 5 from 3 7 to 1 2 and extend to the lowest d 30 si values for precambrian cherts isua bif samples are homogeneous in d 18 o to 0 3 at mm to cm scale but are heterogeneous in d 30 si up to 3 similar to the range in d 30 si found in bifs that have not experienced high temperature metamorphism up to 300 c values of d 30 si for quartz are homogeneous to 0 3 in individual sub mm laminae but vary by up to 3 between multiple laminae over mm to cm of vertical banding the scale of exchange for si in quartz in bifs is thus limited to the size of microlaminae or less than 1 mm we interpret differences in d 30 si between microlaminae as preserved from primary deposition silicon in bif quartz is mostly of marine hydrothermal origin d 30 si 0 5 but silicon from continental weathering d 30 si 1 was an important source as early as 3 8 ga

minto block superior province missing link in deciphering assembly of the craton at 2 7 ga plate tectonic models of the superior province are rooted in the granite greenstone and metasedimentary belts of the southern part of the craton north striking domains of the minto block in the northeastern part of the province evolved at similar times in 3 1 2 8 2 725 and 2 69 ga events requiring expansion of models of late archean assembly to accommodate minto geology western and eastern protocratons 3 1 2 8 ga rifted at 2 79 ga to produce an ocean basin that was mostly consumed by subduction at 2 725 ga the leaf river plutonic suite of cale alkalic hornblende biotite orthopyroxene clinopyroxene granodiorite represents magmatic arcs built on the protocratons whereas the intervening goudalie domain containing fault bounded fragments of rifted continental crust rift volcanics primitive oceanic crust 2724 ma island arc rocks and a 2718 ma back arc assemblage marks the suture terminal collision at 2 7 ga led to thickening and crustally derived granitoid magmatism the southern superior province also experienced vigorous activity between 2 725 and 2 69 ga as island arcs oceanic plateaus continental fragments and accretionary prisms were amalgamated progressively from north to south in a regime of dextral transpression then stitched by granites a northern proto superior craton had continental magmatic arcs built on its eastern and southern flanks in response to west northwest directed subduction orthogonal convergence in the east produced wide plutonic arcs in contrast to terrane accretion tectonics in the more oblique regime along the southern margin

atlantic mediterranean water exchange during the late neocene the nature of water exchange between the mediterranean and the atlantic is examined for three time periods during the late neogene in order to assess the impact of flow patterns between these basins on bottom water conditions in the oceans the large volume of carbonates and evaporites deposited in the mediterranean during the messinian salinity crisis appears to have caused the open ocean to become more undersaturated in calcium carbonate resulting in increased dissolution of deep sea carbonates during the latest miocene during the earliest pliocene an estuarine type of flow existed between the atlantic and mediterranean waters entered the mediterranean at depth and flowed out at the surface benthic foraminiferal stable isotopic evidence from the north atlantic indicates that north atlantic deep water nadw was produced throughout the early pliocene and that the absence of saline mediterranean outflow did not have a significant effect on bottom water production eustatic lowering of sea level during the last glacial maximum 18 000 years b p reduced water exchange between the atlantic and the mediterranean as a result salinities in the mediterranean increased substantially but it seems unlikely that diminished nadw production during the last glacial episode can be attributed to a reduction in mediterranean outflow

study on mode i ii hybrid fracture criteria for the stability analysis of sliding overhanging rock abstract overhanging rock is widely distributed in mountainous regions of the world and therefore poses a potential geohazard to life and property because of fracturing and ultimately failure the maximum circumferential stress criterion is widely used in fracture mechanics however it is inadequate with respect to predicting the failure of sliding overhanging rock that is subject to extension and shear fracturing in this paper the maximum shear stress at a crack tip and a fracture method in combination with the mohr coulomb criterion are used to examine rock with mixed mode i ii fractures the methods are ultimately used to analyze the stability of sliding unstable rocks the two fracture criteria have been compared according to the most unfavorable conditions and the stability of the sliding rock masses are calculated using these new fracture criteria in two case studies the calculations show that the rock stability calculated by the comprehensive fracture criterion is very close to that calculated by the limit equilibrium method but in addition the two methods can also determine the fracture angle overall the maximum shear stress approach and a fracture mechanics criterion based on the mohr coulomb model are more suitable than the limit equilibrium method for evaluating the stability of sliding overhanging rock

pre 3750 ma supracrustal rocks from the nuvvuagittuq supracrustal belt northern quebec geochemistry and u pb ion microprobe zircon geochronology guided by high resolution mapping 1 50 scale was used to define a minimum age of ca 3750 ma for supracrustal rocks from the nuvvuagittuq supracrustal belt nsb in the northern superior province quebec canada mineralogy and geochemistry of critical field relationships preserved at the porpoise cove locality describe a supracrustal succession of mafic amphibolites and ultramafic rocks finely banded quartz magnetite units with intermixed coarse grained ferruginous quartz pyroxene rocks and quartz biotite schists that superficially resemble polymict metaconglomerates with large up to 10 cm deformed polycrystalline quartz and mafic clasts all units in the mapped outcrop have sharp lithological contacts narrow dominantly trondhjemitic orthogneiss sheets locally preserve intrusive contact relationships to the supracrustals the total extent of the supracrustal enclave is 8k m 2 it is strongly deformed and the full deformation history appears to be shared by all units with later modifications from leucogranitoid intrusions the quartz biotite schists record complex zircon growth at 3500 and 2800 ma interpreted to reflect metamorphic events zircons separated from orthogneisses in the enclave including one sheet that transects a banded quartz pyroxene magnetite unit yield magmatic 207 pb 206 pb ages of ca 3750 ma these ages are slightly younger than earlier provisional reports for an nsb orthogneiss from porpoise cove the nuvvuagittuq supracrustals are the oldest rocks thus far reported for the minto block they overlap in age with the ca 3 70 3 83 ga isua supracrustal belt and akilia association rocks in west greenland and they represent an important new area for exploration of the early earth

thermoluminescence dating tests of pleistocene sediments from uplifted marine shorelines along the southwest coastline of the calabrian peninsula southern italy abstract this paper presents tl age estimates of pleistocene raised marine terraces from southern calabria southern italy it focuses on the dating of last interglacial shallow marine sand deposits including several tyrrhenian key reference deposits whose stratigraphic assignment is based on biostratigraphic evidence presence of a strombus bubonius fauna and geochronometric data amino acid data calibrated with u th dates on coral the tl age estimates are obtained on alkali feldspar coarse grains using their blue tl emission they are in good agreement with the ir osl age estimates obtained on the same feldspar samples our feldspar tl method is tested on two tyrrhenian key reference sites ravagnese and bovetto in the reggio di calabria area their measured tl age estimates 97 11 ka and 100 10 ka are lower than their estimated geological age i e oxygen isotope substage 5e the correction for long term fading suggested by mejdahl 1988 is tested on these two samples using a lifetime of 446 ka as estimated from both calabrian and miocene sand collected within the same area this correction would yield preliminary tl ages 116 13 ka and 116 12 ka that are in better agreement with the expected geological age the application of our tl method to paleoshorelines lying below the tyrrhenian reference shoreline of ravagnese bovetto yields stratigraphically consistent tl age estimates the tl method is also applied to two supposedly pre last interglacial paleoshorelines which are geomorphologically older than the tyrrhenian reference shorelines they remain however chronologically undifferentiated both by the tl and the amino acid methods finally the preliminary feldspar tl results obtained on the miocene and the calabrian sand deposits 1 ma suggest that our feldspar tl method is limited in the sw calabrian area to about 200 ka

luminescence dating of sediments using single aliquots new procedures abstract the application of luminescence dating to quaternary sediments has been hampered by the labour intensive procedures involved determination of equivalent doses using single aliquots measured using an automated luminescence reader offers a significant reduction in labour equivalent dose determinations using two single aliquot additive dose methods are compared with equivalent doses measured using standard multiple aliquot methods for a suite of 12 dune sand samples from southwest north island new zealand the single aliquot correction method based upon adjusting the magnitude of the measured luminescence signal is found to give underestimates for those samples whose equivalent dose is greater than 80 gy and whose luminescence response to dose is non linear a second correction method based upon adjusting the value of the total added dose that the sample has received is described this second method gives equivalent dose results similar to those measured using standard multiple aliquot methods over the range from 0 1 to 400 gy

chemical sedimentary protoliths in the 3 75 ga nuvvuagittuq supracrustal belt quebec canada abstract analyses of chemical sedimentary precipitates such as banded iron formation bif provide a direct means to explore the nature and composition of the early hydrosphere the recently discovered 3750 myr old nuvvuagittuq supracrustal belt nsb in the northeast superior province quebec canada hosts a suite of iron oxide rich pyroxene and amphibole units that are interpreted to be the metamorphosed equivalents of fe oxide facies bif and a collection of bif like ca fe mg silicate rocks the nsb rocks provide a rare glimpse of trace metal availability in eoarchean ca 3800 ma seawater as they may be contemporaneous with the relatively well studied isua supracrustal belt of southern west greenland their comparison provides an opportunity to enhance our basic understanding of the eoarchean oceans at a global scale work since the initial discovery of the nsb in 2001 has established the basic lithological geochemical and petrographic characteristics of these bif and bif like rocks here we review the current state of knowledge of nsb rocks of probable chemical sedimentary origin including aspects of their geology likely origin and age we conclude by examining the implications of results thus far for our understanding of early seawater compositions and for the emergence of life in the context of early metallo enzyme evolution

geology of the eoarchean 3 95 ga nulliak supracrustal rocks in the saglek block northern labrador canada the oldest geological evidence for plate tectonics the earth is a unique planet which has been highly evolved diversified and complicated through geologic time and underwent many key events including giant impact magma ocean core formation large scale mantle differentiation and late heavy bombardment especially in its dawn but our knowledge of early earth is limited due to the lack of the hadean supracrustal rocks the supracrustal rocks with the eoarchean ages provide key evidence for the earth s early evolution but few supracrustal rocks have been comprehensively investigated therefore we mapped in seven areas of the saglek block northern labrador where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses early studies suggested that some of them have the mesoarchean ages because of the lack of the mesoarchean saglek dyke but we found the saglek dykes in the areas to recognize the eoarchean nulliak supracrustal rocks and uivak gneiss in all the areas recent reassessment of u pb dating and cathodoluminescence observation of zircons from the oldest suites of the uivak gneiss showed that the uivak gneiss has the eoarchean age 3 95 ga and forms the iqaluk uivak gneiss series because our geological survey clearly showed that the iqaluk uivak gneisses were intruded into the nulliak supracrustal belts the nulliak supracrustal rocks are the oldest supracrustal rock in the world the supracrustal belts consist of piles of fault bounded blocks which are composed of the ultramafic rocks mafic rocks and sedimentary rocks in ascending order similar to modern ocean plate stratigraphy ops in addition small scale duplex structures are found over the areas the presence of duplex structure and ops indicates that the 3 95 ga nulliak supracrustal belts originate from an accretionary complex the presence of the accretionary complex ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early earth

constraints on the geodynamic evolution of the southern superior province u pb la icp ms analysis of detrital zircon in successor basins of the archean abitibi and pontiac subprovinces of ontario and quebec canada abstract to investigate the tectonic development of the southern superior province new u pb laser ablation inductively coupled mass spectrometry analysis of detrital zircon was conducted on graywacke samples from successor basins of the abitibi and pontiac subprovinces the three successor basin successions investigated are the 2690 2685 ma porcupine assemblage and the 2679 2669 ma timiskaming assemblage of the abitibi subprovince and the 2682 ma sedimentary rocks of the pontiac subprovince predominately neoarchean zircon grains 80 95 of the total zircon population reflect local sources in the abitibi and pontiac subprovinces the successor basins were deposited within 100 ma of the majority of the detrital zircon grains primary crystallization ages which is consistent with patterns observed at modern convergent margin settings porcupine assemblage samples contain 5 mesoarchean zircon while pontiac subprovince and timiskaming assemblage samples contain 18 and 13 respectively no local mesoarchean sources exist in the abitibi or pontiac subprovinces suggesting input from an adjacent hinterland the higher proportion of mesoarchean zircon in the timiskaming assemblage relative to the porcupine assemblage suggests that detritus from the hinterland was more prevalent during the later stages of collision probably as a result of progressive uplift and denudation of the hinterland the high proportion of mesoarchean zircon in the pontiac subprovince sedimentary rocks may reflect an additional mesoarchean source comparison to previously published geochronology data for the superior province indicates that the hinterland was to the northwest and is in part composed of the winnipeg river marmion and opatica subprovinces patterns of contractional deformation successor basin formation and felsic plutonism progressively young to the south in the southern superior province and are interpreted in terms of accretionary processes detrital transport across subprovince or terrane boundaries progressive hinterland emergence and foreland directed propagation of the deformational front recorded by successor basins is similar to that observed in modern style collisional or accretionary orogens

the southeastern churchill province synthesis of a paleoproterozoic transpressional orogen the paleoproterozoic southeastern churchill province secp is located in the northeastern canadian shield of labrador and quebec the secp formed through the oblique collisions of the archean nain and superior cratons with a third intervening archean block the core zone the belt has a tripartite structure comprising the torngat orogen to formed by nain craton core zone collision in the east the core zone in the centre and the new quebec orogen nqo formed by superior craton core zone collision in the west the secp thus records transpressional development on the flanks of the superior and nain cratons as they indented northwards to form the larger trans hudson nagssugtoqidian orogenic belt to the north principal stages of tectonic development were 1 2 2 2 1 ga crustal rifting of nain and superior cratons 2 ca 1 9 ga subduction under eastern nain craton 3 ca 1 87 1 85 ga collision of nain craton and core zone to form the to 4 1 845 1 820 ga sinistral transpression in the to and subduction under the western core zone and 5 1 82 1 77 ga collision of superior craton and core zone to form the nqo in association with dextral transpression crustal scale cross sections of the secp have been developed from reflection and refraction seismic data the western part of the nqo is dominantly west vergent and associated with an imbricate thick skinned thrust stack that ramps from the base of the crust the core zone is characterized by a 35 40 km thick crust and pervasive east dipping fabrics related to westerly thrusting the to is a narrow doubly vergent belt associated with a 48 km thick crust that forms a crustal root with a moho relief of 12 km the root is interpreted to result from attempted subduction of the core zone under the nain craton possibly as a result of mid crustal wedging by the nain craton the to was the site of intense convergence that resulted in excision of juvenile crust possibly including tectonic removal of the axial magmatic arc as a result the middle to lower levels of the secp consist largely of refractory archean lithosphere this may account for the lack of widespread post collisional plutonism in the secp and the preservation of the to root

widespread poly metamorphosed archean granitoid gneisses and supracrustal enclaves of the southern inukjuak domain quebec canada abstract the 12 000 km2 inukjuak domain in northern quebec is part of the archean minto block in the northwestern superior province of canada eoarchean ca 3800 3780 ma rocks of the nuvvuagittuq supracrustal belt nsb are the best known occurrence of otherwise abundant pb zircon geochronology from rocks within and surrounding the nsb these include the little studied but volumetrically significant voizel suite gneisses results show that intra nsb fold belt rocks of the central tonalitic gneiss ctg preserve mainly ca 3650 ma zircons beyond the nsb the voizel gneisses previously considered contemporaneous with the ctg are instead about 100 myr younger 3550 ma tonalitic ortho gneisses at the margin of the nsb were previously assigned a ca 3650 ma age and the surrounding boizard suite gneisses may be about 2700 ma we find the boizard rocks contain inherited zircon cores up to ca 3700 ma with younger overgrowths dated at ca 2700 ma a tonalitic gneiss that transects another highly deformed supracrustal enclave north of the nsb dubbed the ukaliq supracrustal belt yields maximum concordant zircon ages of 3653 16 ma 2 detrital zircons from ukaliq and nuvvuagittuq quartzites and quartz biotite schists define a maximum age of ca 3780 ma no indication of u pb zircon ages older than about 3800 ma exist in this terrane from our geochronological surveys new reconnaissance sampling of gneisses to the west of the nsb fold belt yielded more zircon bearing rocks with ages of ca 3760 ma this discovery of more pre 3700 ma rocks beyond the nsb outcrops calls attention to the existence of hitherto unidentified but widespread scattered occurrences of eoarchean and paleoarchean rocks throughout the region

early life recorded in archean pillow lavas pillow lava rims from the mesoarchean barberton greenstone belt in south africa contain micrometer scale mineralized tubes that provide evidence of submarine microbial activity during the early history of earth the tubes formed during microbial etching of glass along fractures as seen in pillow lavas from recent oceanic crust the margins of the tubes contain organic carbon and many of the pillow rims exhibit isotopically light bulk rock carbonate 13 c values supporting their biogenic origin overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3 5 billion years ago

middle to upper pleistocene morphostructural evolution of the nw coast of sicily thermoluminescence dating and palaeontological stratigraphical evaluations of littoral deposits abstract infralittoral and terrigenous middle to upper pleistocene deposits outcropping at the nw coast of sicily gulf of castellammare and peninsula of capo san vito were investigated in order to recognise glacio eustatically caused sea level highstands and the interference between tectonics eustasy and local conditions of the coast the results originating from a stratigraphically important area were obtained by palaeontological stratigraphical analyses physical age determination with the thermoluminescence method and by detailed morphostructural studies the marine deposits situated at 3 40 m a s l mainly provide an oligotypic molluscan fauna referable to modern sgcf sfhn and sfbc biocoenoses of the infralittoral zone which live on various substrates in water of moderate to strong energy the senegalese molluscan forms providing the palaeocommunity of tyrrhenian age oxygen isotope substage 5e is comparable with the modern ap biocoenose which live on hard substrates in water of moderate energy the age determinations and estimates of the terraces indicate at most four glacio eustatic sea level highstands one perhaps two highstands between 800 ka and 250 ka isotope stages 24 8 a further event between 250 ka and 190 ka stage 7 and the youngest highstand event between 140 ka and 75 ka stage 5 the last glaciation stage 4 2 is represented by a terrigenous sequence which suggests rapid alternation of morphodynamically stable and unstable intervals as well as changes in moisture and seasonality of climate the terraces are affected by ne sw orientated faults causing brittle deformation and uplifting in rates of approximately 0 14 0 25 m ka with increasing intensity towards the east the oxygen isotope stratigraphy indicates 7 warming events during the past 800 ka the morphostructural pattern of the nw coast of sicily gives evidence for the sensible interference between local coastal conditions like sediment drift sea water currents and sediment supply on the one hand the absolute rise of eustatic sea level and the absolute uplift rate on the other hand it is obvious that eustatic oscillations deduced from deep sea sediment values does not automatically coincide with those recorded in the inner shelf area

autochthonous development of superior province greenstone belts abstract models for superior province greenstone belt development have changed over the last 30 years from ensimatic generally autochthonous models to suspect allochthonous terrane models based on the plate tectonic paradigm models intermediate between these end members such as autochthonous terrane models have not been prominent within the superior province there is a secular variation from early ca 3 ga platformal assemblages with overlying rift related komatiite tholeiite units representing breakup of ca 3 ga continental fragments to late ca 2 7 ga pull apart basins autochthonous terranes should demonstrate some sort of logical order such as that described above whereas allochthonous terranes will be largely oceanic in character and should be essentially random in their occurrence rather than exhibiting secular order in the face of this situation this paper reviews evidence from throughout the superior province that suggests many but not all greenstone assemblages developed autochthonously or parautochthonously the earliest greenstone assemblages in the superior province are generally quartzite and carbonate bearing platform sequences in the north caribou terrane and the marmion terrane deposited unconformably upon granitoid or greenstone basement the evidence for autochthonous parautochthonous development includes the presence of unconformities between keewatin type greenstone units such as 1 basal unconformities between ca 3 ga granitoid or volcanic basement and slightly younger platformal assemblages 2 between ca 2 9 ga platformal assemblages and younger platformal and andean arc assemblages stratigraphic patterns such as adjacent greenstone belt assemblages representing sharply differing geodynamic settings with some indication of palinspastic order or progression in the northern central and southern superior province are considered suggestive of orderly autochthonous progression from platforms through rifting of continental fragments and late assembly during the kenoran orogeny petrogenetic data indicating involvement of older granitoid crust in genesis of greenstone assemblages of a variety of ages throughout the superior province suggests the presence of older basement implying autochthonous or parautochthonous development of many assemblages younger greenstone assemblages in the abitibi wawa subprovince and the north caribou terrane contain xenocrystic zircons similar in age to stratigraphically underlying greenstone assemblages this pattern has been interpreted to represent autochthonous greenstone development the current above enumerated evidence for autochthonous development of greenstone assemblages is generally indirect few actual unconformities between keewatin type greenstone assemblages have been recognized in the superior province to aid in future recognition of unconformities in keewatin type greenstone assemblages examples of unconformities of varying degrees of subtlety in archean sequences are reviewed archean unconformities ranging from sharp angular discordances in the northern superior province to subtle stratigraphic patterns to weathering related geochemical mobilization along inter formational contacts are described these styles of unconformity in archean sequences suggest previously unrecognized major disconformities and unconformities may well exist between keewatin type assemblages in the superior province generally and the abitibi wawa subprovince specifically the most important disconformity suggested in the abitibi wawa subprovince is between the ca 2726 ma deloro and the ca 2708 ma tisdale assemblages the presence of unconformities and disconformities coupled with the indirect lines of evidence cited above suggest an autochthonous origin for many superior province greenstone belts this autochthonous origin involves either autochthonous or parautochthonous evolution of assemblages at least in part in place that is development of ca 3 ga platform sequences in selected locales followed by in place evolution of a succession of plume oceanic and arc assemblages culminating in late pull apart basin sequences implications of the autochthonous model for greenstone belts of the superior province particularly the abitibi wawa subprovince include the future ability to recognize unconformity bounded sequences potentially improving regional scale correlation

the plateau method for dating partially bleached sediments by thermoluminescence abstract the plateau method for dating sediments that have been incompletely bleached prior to deposition is described by exposing aliquots of a sample to sunlight for different periods of time a range of residual values is obtained and combined with the additive dose or the regeneration technique to yield a series of paleodoses the correct paleodose is taken as that for which the longest plateau in a plot of paleodose vs temperature is obtained

an update on the fracture toughness testing methods related to the cracked chevron notched brazilian disk ccnbd specimen this paper reviews the use of the cracked chevron notched brazilian disc ccnbd for fracture toughness testing theoretical and experimental backgrounds of the method are described some issues regarding the current development i e recalibration of the specimen geometry are presented and discussed a number of geometries related to the ccnbd proposed recently for fracture toughness testing of rock are then introduced and commented on

chronological separation of interglacial raised beaches from northwestern europe using thermoluminescence thermoluminescence tl age estimates have been obtained on coarse grained detrital feldspar from eemian beach sand substage 5e early weichselian dune sands substages 5d and 5b and pre eemian beach sand the past radiation dose is obtained using the additive dose method even for the oldest samples which date to 300 000 yr b p by other methods the tl signal is not in saturation and can be doubled by the addition of laboratory radiation doses without saturation being achieved this is contrasted with the behavior of polymineral silt sized grains from loess in the adjacent area the tl age estimates are systematically underestimated by about 40 when compared with the expected geological ages however they are in correct stratigraphic order and demonstrate that stage 5 beach deposits can be distinguished from those resulting from earlier high sea levels using tl signals from potassium feldspars

recognizable primary volcanic and sedimentary features in a low strain domain of the highly deformed oldest known 3 7 3 8 gyr greenstone belt isua west greenland a low strain domain has been identified in the metamorphosed mostly highly deformed volcanic and sedimentary rocks of the early archaean isua supracrustal belt this domain contains well preserved volcanic and sedimentary features including basaltic pillow lavas pillow breccia heterogeneous volcanic breccia amygdules in metabasalt and polymict conglomerate dominated by recrystallized chert and volcanic clasts the low strain domain is bounded by highly deformed rocks mostly derived from basalt chert and banded iron formation these discoveries demonstrate that some primary features have escaped the pervasive metasomatism dominant in other parts of the belt and furthermore strengthen the characterization of the isua supracrustals as a typical greenstone belt

eoarchean to neoarchean evolution of the nuvvuagittuq supracrustal belt new insights from u pb zircon geochronology the nuvvuagittuq supracrustal belt in northern quebec is a rare 9 km2 fragment of the earth9s early crust the belt contains a metamorphosed volcano sedimentary sequence that is at least eoarchean in age including amphibolites of the ujaraaluk unit that may have protoliths as ancient as 4400 million years old ma o9neil and others 2012 upper amphibolite facies metamorphism and high strain deformation have obscured many primary field relationships and disturbed whole rock isotope systematics leading to debate over the interpretation of previous geochronological data we report new shrimp u pb isotopic analyses of zircons from key meta igneous and newly identified metasedimentary units of the belt the analyzed samples fall into four categories a felsic gneisses including sheets interlayered with the supracrustal assemblage and a tonalitic orthogneiss at the margin of the belt b a newly identified metasedimentary unit c fuchsite bearing quartz rich layers d mafic gneisses including a garnet biotite amphibolite from the ujaraaluk unit and a meta gabbro the felsic lithologies place constraints on the minimum age of the supracrustal assemblage oscillatory zoned zircons separated from a felsic orthogneiss sheet form a discordant array with an upper intercept age of 3774 32 ma and the tonalitic orthogneiss yielded oscillatory zoned zircons with an upper intercept age of 3781 11 ma a metasedimentary unit dominated by quartz albite and clinozoisite has been identified within a lower strain domain interfolded with amphibolites of the ujaraaluk unit a sample of this unit yielded zircons with highly variable cl structures and near concordant ages of between 3390 and 3780 ma zircons from a fuchsite bearing quartz layer have oscillatory zonation similar to the orthogneiss grains and define an upper intercept age of 3794 16 ma petrologic observations and geochemical data suggest that this lithology is a metasomatically altered felsic orthogneiss band rather than a meta sedimentary rock belonging to the supracrustal package electron microscopy of polished thin sections was used to locate zircons within 6 samples of the ujaraaluk unit amphibolites and two samples of meta gabbro large 500 m zircons separated from a garnet biotite amphibolite together with grains from a meta gabbro are sector zoned and yield ages of 2700 to 2640 ma recording the timing of pervasive high temperature metamorphism in the region the new zircon u pb data add important new detail to the geological history of the nuvvuagittuq belt the volcano sedimentary sequence and mafic ultramafic intrusive rocks were formed prior to 3800 million years ago subsequent geological evolution included extensive and protracted early archean ttg magmatism and crustal re melting paleo to mesoarchean uplift and sedimentation and neoarchean high grade metamorphism and regional magmatism during consolidation of the superior craton

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

luminescence chronology of late pleistocene raised beaches in southern italy new data of relative sea level changes abstract littoral sediments forming terraces along the crotone peninsula coast southern italian have been investigated using sedimentological analysis and luminescence dating techniques and adopting assessments from previous work on fossil assemblages all sediment layers analysed were deposited in the nearshore environment between 20 m below and few metres above sea level during the falling sea level of a temperate warm climate interval the restoration of almost identical environmental conditions occurred in oxygen isotope substages 5e and 5a and in oxygen isotope stage 3 limits given by luminescence physics prevented accurate dating of the uppermost lying terrace former crotonian stage terrace and the presence of a substage 5c terrace is masked by the lack of suitable material for dating constraints on the positions of relative sea level from the reliable data set show that the sea level fell from 2 m during substage 5e to 29 m during substage 5a and then rose to 15 m during stage 3 observations for oxygen isotope stage 3 sea level at the crotone peninsula coast are inconsistent with those at the huon peninsula new guinea and in the western pacific the disagreement highlights the lack of knowledge concerning mediterranean thermohaline circulations and sea water exchanges between the atlantic and mediterranean seas during glacial cycles

fracture toughness anisotropy in shale the use of hydraulic fracturing to recover shale gas has focused attention on the fundamental fracture properties of gas bearing shales but there remains a paucity of available experimental data on their mechanical and physical properties such shales are strongly anisotropic so that their fracture propagation trajectories depend on the interaction between their anisotropic mechanical properties and the anisotropic in situ stress field in the shallow crust here we report fracture toughness measurements on mancos shale determined in all three principal fracture orientations divider short transverse and arrester using a modified short rod methodology experimental results for a range of other sedimentary and carbonate rocks are also reported for comparison purposes significant anisotropy is observed in shale fracture toughness measurements at ambient conditions with values as high as 0 72mpam1 2 where the crack plane is normal to the bedding and values as low as 0 21mpam1 2 where the crack plane is parallel to the bedding for cracks propagating non parallel to bedding we observe a tendency for deviation towards the bedding parallel orientation applying a maximum energy release rate criterion we determined the conditions under which such deviations are more or less likely to occur under more generalized mixed mode loading conditions we find for mancos shale that the fracture should deviate towards the plane with lowest toughness regardless of the loading conditions

sulfur and oxygen isotope constraints on the sedimentary history of apparent conglomerates from the nuvvuagittuq greenstone belt nunavik quebec abstract mafic igneous rocks of the nuvvuagittuq greenstone belt ngb crystallized before 3 8 ga and possibly as early as 4 3 ga potentially making the belt the oldest known supracrustal sequence on earth however detrital zircons from a rare quartz biotite schist in the ngb yield significantly younger ages of 3 77 ga or less these appear to be inconsistent with the ages of the mafic igneous rocks as the quartz biotite schist has been interpreted as a metaconglomerate formed by the dismantling of preexisting lithologies in order to assess this genetic interpretation we performed a sulfur and oxygen isotope study of the quartz biotite schist sulfide grains found in quartz clasts and the matrix show significant mass independent fractionation of sulfur isotopes 0 2 33s 1 0 mean 33s 0 5 0 1 secondary sulfides from crosscutting veins do not show mass independent fractionation of sulfur isotopes 0 1 33s 0 3 mean 33s 0 1 0 1 oxygen isotope compositions of quartz from clasts matrix and a fine grained lens are highly enriched in 18o 16 9 18o 26 7 non zero 33s values indicate a surficial origin for sulfur probably the eoarchean atmosphere while high 18o values suggest a low temperature 65 18 c origin for the quartz likely as chemical precipitation of a chert precursor from si saturated seawater therefore the coupled s and o isotope measurements show that primary isotopic signatures characteristic of surficial environments survived the protracted metamorphic history of the ngb and suggest that the quartz biotite schist contains material that originated as chemical metasediments the near mono mineralic compositions of the clasts quartz and their shared 18o enrichment suggest that they had a common protolith which was deposited prior to the formation of the schist and subsequently reworked whether the quartz biotite schist represents a metaconglomerate or a structural melange it preserves remnants of some of the oldest chemical sediments on earth

in situ k ar dating on mars based on uv laser ablation coupled with a libs qms system development calibration and application of the karmars instrument abstract absolute dating is needed to check and calibrate the relative martian chronology presently available from meteoritic crater counting for such purpose a new analytical system karmars has been developed to experiment the feasibility of in situ k ar for future landing planetary missions it consists in a laser ablation based system built to vaporize a reproducible volume of rock potassium content is measured by laser induced breakdown spectroscopy libs and argon by quadrupole mass spectrometry qms instrument calibration and checking of the reliability of the measurements for martian analyses requires terrestrial analogues for such purpose total chemistry electron microprobe analyses flame absorption spectrometry and mass spectrometry have been performed in order to qualify the stoichiometry the mineralogy the k concentration and the ar isotopic composition from a collection of old terrestrial rocks these new analyses coupled with published data allowed us to select mineral phases e g feldspars phlogopite muscovite amphibole showing a large range of k content 0 3 8 5 wt all these mineral phases display a k ar age older than 300 ma hence the content of radiogenic ar atoms per gram is within the range of martian samples on the order of 1 ga for 0 4 wt of k we have shown that the ablated mass can be precisely estimated by measurement of ar extracted from a similar mineral of known amount of radiogenic ar content per gram then it has been possible to derive a well defined relationship between the ablation time and the sample mass extracted from uv laser ablations for different minerals using an isochron approach from multiple ablations of several samples analyzed as unknowns we have shown that karmars can be successfully used for dating samples with different compositions and with ages varying by an order of magnitude from 0 3 to 3 ga in situ k ar ages obtained here for plagioclase and amphibole crystals display uncertainties as low as about 10 and with accuracy i e difference with the reference age of only 10 such results further support in situ k ar dating based on qms and libs instruments as a reliable approach to be implemented onboard martian rovers in case a return mission is made possible karmars can also be a valuable tool to select the most relevant samples for return and ensure onsite which samples are representative of most of the surface at a given landing site

inherited 142nd anomalies in eoarchean protoliths abstract geological records of the earliest history of the earth are rare rocks older than 3700 ma comprise only a few percent of continental surfaces evidence is mounting however that vestiges of primordial planetary differentiation continued to influence the compositions of the oldest rocks during the hadean and into the archean here we report new whole rock 147 146sm 143 142nd data for the ancient nuvvuagittuq supracrustal belt nsb in quebec canada and confirm the 142nd deficits reported by o neil et al 2008 we show that the assigned o neil et al 2008 and recently revised kinoshita et al 2012 142nd age of 4362 54 35 ma claimed for nsb amphibolites is at odds with the younger 147sm 143nd record this discrepancy can be reconciled by partial nd isotope equilibration of rocks with hadean model ages of up to 4500 ma during magmatic and metamorphic perturbations associated with the emplacement of the nsb at ca 3750 ma cates and mojzsis 2009 our model further predicts a whole rock 147sm 143nd age of 3800 ma for other nsb lithologies in agreement with u pb zircon chronology cates and mojzsis 2007 hence 146sm 142nd systematics for the eoarchean nsb rocks represent inheritance of a hadean signature that was stored either in pre existing crust or in early enriched mantle sources the decoupled 147 146sm 143 142nd systematics of the nsb is similar but complementary to the hadean mantle isochron preserved in eoarchean rocks from west greenland bennett et al 2007 rizo et al 2011

the blue emission of k feldspar coarse grains and its potential for overcoming tl age underestimation abstract this paper presents preliminary tl ages on k feldspar coarse grains from raised shallow marine sediments of nw europe and southern italy comparisons between tl ages using different optical filters suggest the use of the blue transmitting corning 7 59 filter allows measurement of an apparently stable tl component in k feldspar which could overcome the problem of age underestimation in the 75 300 ka range

late pleistocene records of littoral processes at the tyrrhenian coast central italy depositional environments and luminescence chronology two cliff sites on the tyrrhenian coast of central italy have been investigated in order to investigate late pleistocene depositional environments by microfacies analysis and chronostratigraphy by luminescence age estimations both sections cover the period from the last interglacial to the end of the last glaciation in the buca dei corvi site an increasing rate of uplift is recognised which is responsible for significant environmental change and formation of the modern coastal fault scarp at around 9 ka in the golfo di baratti site the vertical succession of three marine horizons previously recognised by cortemiglia et al 1983 is attributed to the ois stages 5c 5a and 3 respectively this cliff section is affected by nne ssw orientated normal faults confirming that extentional structural processes are still active the coastal deposit of stage 3 today located at 7 m a s l suggests abnormal high uplift rate if the position of the palaeo shoreline was assumed at 40 to 50 m both central mediterranean coastal records strongly suggest that the eustatic sea level has dropped to a smaller amount than that of the open oceans

protoliths of the 3 8 3 7 ga isua greenstone belt west greenland abstract the isua greenstone belt fig 1 contains the oldest known relatively well preserved metavolcanic and metasedimentary rocks on earth the rocks are all deformed and many were substantially altered by metasomatism but both the deformation and metasomatism were heterogeneous transitional stages can be seen from relatively well preserved primary volcanic and sedimentary structures to schists in which all primary features have been obliterated likewise different kinds and different episodes of metasomatic alteration can be seen that produced a diversity of different compositions and metamorphic mineral assemblages from similar protoliths new geological mapping has traced out gradations between the best preserved protoliths and their diverse deformed and metasomatised equivalents by this means the primary nature of the schists that make up most of the isua greenstone belt was reinterpreted and a new map that better portrays the primary nature of the rocks has been produced the previously mapped stratigraphy was found to be of little value in understanding the geology stratigraphic units were defined by different and diverse criteria such as current composition structure metamorphic texture and inferred protoliths much of this stratigraphy represents a misinterpretation of the primary nature of the rocks the new work indicates that most of the isua greenstone belt consists of fault bounded rock packages mainly derived from basaltic and high mg basaltic pillow lava and pillow lava breccia chert bif and a minor component of clastic sedimentary rocks derived from chert and basaltic volcanic rocks a previously mapped extensive unit of felsic volcanic rocks was found to be derived from metasomatised basaltic pillow lava and pillow breccia intruded by numerous sheets of tonalite

maximum sea levels for the last glacial period from u series ages of submerged speleothems pleistocene sea levels reflect changes in the surface distribution of land sea and ice which in turn significantly influence the earth s climate1 the most complete record of sea levels for the last glacial cycle has come from raised coral reef terraces of the huon peninsula papua new guinea2 4 but interpretation of this record is hampered by relatively large age uncertainties and the possibility of variation in the rate of tectonic uplift subaerial speleothems stalagmites stalactites and flowstones from submerged caves in tetonically stable areas provide an alternative source of data5 8 as their growth stops when rising sea levels flood the caves previous studies of speleothems have been limited by dating precision5 6 and sample availability5 7 here we present high precision thermal ionization mass spectrometric 230th ages9 11 for a comprehensive suite of speleothem samples from the bahamas our results provide a record of maximum elevation of sea levels for the period from 80 to 10 kyr before the present for much of which sea levels are poorly known we also find that regional palaeoclimatic change can be an important factor in the termination of speleothem growth

preservation of 3 4 3 5 ga microbial biomarkers in pillow lavas and hyaloclastites from the barberton greenstone belt south africa exceptionally well preserved pillow lavas and inter pillow hyaloclastites from the barberton greenstone belt in south africa contain textural geochemical and isotopic biomarkers indicative of microbially mediated alteration of basaltic glass in the archean the textures are micrometer scale tubular structures interpreted to have originally formed during microbial etching of glass along fractures textures of similar size morphology and distribution have been attributed to microbial activity and are commonly observed in the glassy margins of pillow lavas from in situ oceanic crust and young ophiolites the tubes from the barberton greenstone belt were preserved by precipitation of fine grained titanite during greenschist facies metamorphism associated with seafloor hydrothermal alteration the presence of organic carbon along the margins of the tubes and low d 13 c values of bulk rock carbonate in formerly glassy samples support a biogenic origin for the tubes overprinting relationships of secondary minerals observed in thin section indicate the tubular structures are pre metamorphic overlapping metamorphic and igneous crystallization ages thus imply the microbes colonized these rocks 3 4 3 5 ga although the search for traces of early life on earth has recently intensified research has largely been confined to sedimentary rocks subaqueous volcanic rocks represent a new geological setting in the search for early life that may preserve a largely unexplored archean biomass d 2005 elsevier b v all rights reserved

recent and active tectonics in the calabrian arc southern italy normal faulting which has developed since the middle pleistocene with an overall ese wnw extension is the dominant mode of deformation which has characterized the calabrian arc up to the present quaternary normal faults extend for a total length of about 180 km along the inner side of the arc the different normal fault segments which during the pleistocene controlled the evolution of the main marine sedimentary basins are varying in length from 10 to 20 km and have fault escarpments showing a very young morphology which define the fronts of the major mountain ranges of the arc the morphological features of the fault escarpments suggest slip rates of 0 8 1 1 mm yr for the last 700 k y and values of 0 6 0 9 mm yr for the last 120 k y indicating a uniform rate of faulting since the middle pleistocene crustal seismicity and the mesoseismic areas of historical large events 6 5 m 7 1 which occurred in the calabrian arc are located within a narrow belt along the hanging walls of the quaternary normal fault segments this suggests that the normal faults which dissect the inner side of the calabrian arc may be seismically active

the composition of earth s oldest iron formations the nuvvuagittuq supracrustal belt quebec canada abstract the composition of iron formations in the 3 75 ga yr old nuvvuagittuq supracrustal belt in northern quebec provides a proxy for seawater composition of the eoarchean and perhaps hadean oceans as well as constraints on the types of nutrients available to earth s earliest life forms integrated petrologic and geochemical relationships mapped between mineral phases in thin section and whole rock chemistry provide a framework for interpreting bulk and micro scale variations in these chemical sedimentary precipitates results show that there are two distinct chemical sedimentary units in the nuvvuagittuq belt i a banded iron formation bif consisting of alternating micro bands of magnetite ca mg fe silicates and quartz and ii a more silicate rich fe poor unit the banded silicate formation bsf of alternating micro bands of quartz and ca mg fe silicates precursor bif and bsf deposits were likely layered amorphous silica and ferric oxyhydroxides fine grained carbonate oozes and or ca mg fe rich silicate gels deposited in a marine setting low al2o3 tio2 and hfse concentrations show that they are relatively detritus free with distinctively seawater like ree y profiles and consistently positive eu anomalies these features suggest that the rocks preserved their seawater like compositions despite metamorphic overprinting the most significant trace elements in the sediments are ni and zn experimentally derived partitioning coefficients show that ni was enriched in eoarchean seawater as compared to today up to 300 nm while zn was fairly similar up to 20 nm compositional resemblances between the nuvvuagittuq sediments and those documented in the ca 3 8 ga isua supracrustals west greenland provide a plausible case that global ocean processes in terms of trace metal abundances had reached steady state by the eoarchean

carbon isotopes as biogeochemical recorders of life over 3 8 ga of earth history evolution of a concept ever since pioneering studies in the late 1930s had shown that the conversion of inorganic carbon into biogenic substances entails sizeable redistributions of the stable carbon isotopes biologically mediated 13c 12c fractionations have come to be recognized as a common corollary of biochemical reactions meanwhile it is firmly established that the universal bias in favour of 12c characterizing biological materials primarily derives from a kinetic isotope effect that is imposed on the first carbon fixing enzymatic carboxylation reaction in the primary metabolism of co2 fixing autotrophic organisms this preference for 12c has turned out to be one of the most enduring relics of the ordered state of the biological precursor substances that may be preserved in fossil organics over billions of years with the currently known sedimentary record at hand it can be stated with confidence that biological carbon isotope fractionations have persisted throughout 3 8 ga of recorded earth history indicating that microbial prokaryotic and archaeoprokaryotic ecosystems had been prolific already on the archean earth while for the time span 3 5 ga the isotopic evidence is unequivocal the information encoded in the preceding record is commonly blurred by a metamorphic overprint this holds particularly for the metasediments of the 3 8 ga old isua supracrustal belt of west greenland which apart from widespread metasomatism have suffered amphibolite grade metamorphism it is known that 13c 12c exchange occurs in organic kerogenous rock constituents during both amphibolite and granulite facies metamorphism if a second carbon partner is available as either fluids or carbonate with isotopic re equilibration often only partially achieved due to the sluggish kinetics of the exchange reaction thermodynamic equilibria predict however that 13c 12c ratios in kerogen and graphite increase during this process hence high t exchange equilibria are always bound to drive 13c values in positive direction the lowermost values encountered being consequently the least exchanged and most pristine with the lowest values of reduced graphitic carbon obtained in early isua studies falling into the range 22 to 28 pdb we had straightforward evidence since the late 1970s that carbon constituents with the isotopic composition of biogenic matter were indeed present in the pre metamorphic isua suite it was therefore by no means surprising that the results of recent isotope work performed on apatite hosted carbonaceous microdomains in isua banded iron formation utilizing advanced techniques of instrumental microanalysis had prompted similar conclusions hence the mainstream of the sedimentary carbon isotope record can be best interpreted as the geochemical manifestation of the isotope discriminating properties of the principal co2 fixing reactions s in biological carbon assimilation suggesting an extreme degree of evolutionary conservatism in the biochemistry of autotrophic carbon fixation as a consequence biological modulation of the geochemical carbon cycle had been established at least 3 8 ga ago having been fully operative by the time of formation of the earth s oldest sediments

geochemical evolution of the minto block a 2 7 ga continental magmatic arc built on the superior proto craton abstract a 400 km long by 100 km wide geological transect across the minto block of northeastern superior province reveals five plutonic suites and minor amphibolite to granulite grade supracrustal remnants the oldest regionally significant plutonic rocks include 3 0 0 1 ga foliated to gneissic tonalite characterized by high na k ratios high al contents light ree enrichment and initial gend 1 8 the leaf river plutonic suite is the most widespread with crystallization ages of about 2725 5 ma across the transect the suite comprises massive to foliated pyroxene and hornblende bearing granodiorite tonalite granite diorite and minor gabbro pyroxenite and syn plutonic mafic dykes the rocks are i type calc alkaline have variable na k ratios moderate to high ba and sr contents and ree patterns with variable light ree enrichment depletion of heavy rees with increasing silica and neutral negative or positive eu anomalies initial nd values for the suite range from 0 5 to 1 3 mean 0 4 and initial 87 sr 86 sr ratios isr are 0 7020 the diatexite plutonic suite 2713 ma occurs within a 150 km wide zone and consists of orthopyroxene garnet granodiorite containing 25 50 inclusions of granulite grade mafic supracrustal and tonalitic inclusions the variable major and trace element chemistry of the suite with generally high ni and cr contents reflects heterogeneous source materials and the presence of non liquid components initial nd values are from 0 1 to 1 7 monzogranite and orthopyroxene granite dykes plugs and plutonic masses both 2690 ma comprise the last important plutonic suites both biotite monzogranite and orthopyroxene granite are light ree enriched but the former have negative eu anomalies and the latter positive initial nd values range from 0 7 to 3 2 for monzogranite isr 0 7016 to 0 7067 and 0 7 to 0 2 for orthopyroxene granite isr 0 701 to 0 702 the initial nd and isr values of the 2 7 ga plutonic suites are lower and higher respectively than estimatesf of the contemporaneous depleted mantle suggesting significant and wide scale reworking of older tight ree enriched high rb sr lithosphere early tonalite orthogneiss from goudalie domain may be derived by partial melting of mafic crust at high pressures the lithological and geochemical diversity of the 2725 ma leaf river plutonic suite indicate a range of parental magma compositions and petrogenetic processes but fractional crystallization of mantle derived basaltic melts which had assimilated small amounts of significantly older lower crust may have been the dominant mechanism crustal inclusion charged granodioritic diatexite 2713 ma was probably derived by partial melting of heterogeneous lower crustal materials under relatively dry conditions late biotite monzogranite was generated by partial melting of older sialic crust and orthopyroxene granite by deeper melting or fractional crystallization of more juvenile source materials with garnet as a residual mineral we infer from the presence of coeval mafic dykes in all plutonic suites that heat for melting was ultimately derived from intrusion of basaltic magmas at depth the 2 7 ga magmatism in the minto block occurred during a period of active production and accretion of juvenile oceanic terranes in the southern superior province the northwest directed subduction regime inferred from the southern superior province arc terranes may also have been responsible for the magmatism that acted on 3 ga lithosphere in the northern superior province melting within the mantle wedge beneath the proto cratonic lithosphere and in the lower crust occurred within a tectonic setting similar to that of modem continental magmatic arcs