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

u th pb ages of single zircons in archaean supracrustals from nain province labrador canada ion probe u pb dating of igneous zircons from an acid metavolcanite belonging to the nulliak supracrustal association of the saglek area northern labrador suggests an original age of 3776 8 ma 2 interpreted as the deposition age of the volcanite in accordance with the field model this is slightly but significantly older than the previously obtained ion probe u pb age of igneous zircons from the main phase of the uivak gneisses which carries inclusions of the supracrustal association a secondary event of zircon growth recorded in the metavolcanite has a maximum age of 3065 8 ma 2 a metapelite belonging to the weekes amphibolite supracrustal association of the hopedale area south of nain contains rounded low u zircons of 3258 24 ma 2 age occasional textural evidence suggests that some of these zircons are most likely detrital grains of igneous origin in which case 3258 24 ma is a minimum age of the source from which the sediment was derived and a maximum age for the deposition of

states of paleostress north and south of the periadriatic fault comparison of the drau range and the friuli southalpine wedge this study focuses on the analysis of structures and kinematics of a n s profile along the axis of maximum shortening of the european eastern alps the area includes the southern austroalpine unit in the north and the southalpine unit which is a part of the adriatic indenter the stratigraphically different units are separated by the periadriatic fault the major strike slip fault within the alps in order to assess the kinematics of these units mainly fault slip data from north and south of the periadriatic fault were analyzed we distinguish a succession of five main kinematic groups in both units 1 n s compression 2 nw se compression 3 ne sw compression 3 changes gradually from subvertical to subhorizontal 4 n s compression and 5 nw se compression our study reveals that the deformation sequence on either sides of the paf is similar the mean orientations of the principal stress axes however show small but consistent differences the subhorizontal axes north of the periadriatic fault plunge northward in the south southward a counterclockwise ccw rotation of the southern part in respect to the north is evident and in line with the well known counterclockwise rotation of the adriatic indenter as well as dextral displacement of the n fanning stress field along the periadriatic fault opposing plunge directions are interpreted as a primary feature of the internal stress field within an orogenic wedge further increased during ongoing compression

analogue modelling of reverse fault reactivation in strike slip and transpressive regimes application to the giudicarie fault system italian eastern alps abstract sandbox analogue models were used to study the reactivation of a reverse fault in strike slip and transpressive regimes for comparison with the evolution of the giudicarie fault system in the central eastern alps the giudicarie system is interpreted as resulting from late miocene sinistral transpressive reactivation of an older late oligocene reverse fault the old reverse fault was reproduced as a pre cut dilatant surface obtained by pulling a stiff metal wire through the model sand layer the position of the pre existing fault with respect to the base plate fault accommodating the strike slip and transpressive faulting phase controlled the extent and geometry of reactivation the clearest reactivation in a pure strike slip regime was achieved in experiments where the basal strike slip fault was immediately below the pre existing fault plane this strong reactivation involved lateral extrusion and lateral stepping of secondary faults from the basal fault to the pre existing reverse fault in the case of transpression the most spectacular reactivation was achieved for a convergence angle of 10 strongly asymmetric structures developed on either side of the pre cut dilatant zone the analogue experiments reproduced very closely the structural features of the giudicarie fault system supporting a model involving a twofold tectonic evolution for the giudicarie fault system with later reactivation in sinistral transpression of an older reverse fault

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

on the true antiquity of eoarchean chemofossils assessing the claim for earth s oldest biogenic graphite in the saglek block of labrador abstract a recent claim to have found traces of earth s earliest life 3 95 ga utilising isotopically light carbon in graphite bearing metapelites from the saglek block of northern labrador canada is re evaluated applying rigorous geological and geochronological criteria the establishment of these criteria in previous evaluations of early life claims from southern west greenland and northern canada is reviewed in order to provide a backdrop to discussion of the saglek claim in particular we emphasise the importance of the scale of lithological continuity in determining the veracity of such claims which are considerably easier to demonstrate from large relatively less tectonised supracrustal remnants like the isua greenstone belt than they are from smaller isolated enclaves of the kind found on akilia or the highly tectonised and imbricated unit that is found in the saglek block unambiguous field relationships between ca 3 9 ga tonalitic gneiss and the graphite bearing metasediments have not been demonstrated in the literature that the saglek claim relies upon and earlier u pb hf isotopic studies on zircon from metasediments at one of the localities used in the claim indicate a mesoarchean to neoarchean time of deposition we conclude that irrespective of the validity of the carbon isotopic evidence field relationships and geochronological evidence fail to demonstrate an age of 3 95 ga for the potential traces of life

replacement of primary monazite by apatite allanite epidote coronas in an amphibolite facies granite gneiss from the eastern alps accessory monazite crystals in granites are commonly unstable during amphibolite facies regional metamorphism and typically become mantled by newly formed apatite allanite epidote coronas this distinct textural feature of altered monazite and its growth mechanism were studied in detail using backscattered electron imaging in a sample of metagranite from the tauern window in the eastern alps it appears that the outer rims of the former monazites were replaced directly by an apatite ring with tiny thorite intergrowths in connection with ca supply through metamorphic fluid around the apatite zone a proximal allanite ring and a distal epidote ring developed this concentric corona structure with the monazite core regularly preserved in the center shows that the reaction kinetics were diffusion controlled and relatively slow quantitative electron microprobe analyses suggest that the elements released from monazite breakdown p ree y th u were diluted and redistributed in the newly formed apatite allanite and epidote overgrowth rings and were unable to leave the corona this supports the common hypothesis that these trace elements are highly immobile during metamorphism furthermore microprobe data suggest that the preserved monazite cores lost little possibly none of their radiogenic lead during metamorphism thus metastable monazite grains from orthogneisses appear to be very useful for constraining u th pb protolith ages on the basis of these findings and a review of literature data it seems that monazite stability in amphibolite facies metamorphic rocks depends strongly on lithologic composition while breaking down in granitoids monazite may grow during prograde metamorphism in other rocks such as metapelites

the schneeberg normal fault zone normal faulting associated with cretaceous se directed extrusion in the eastern alps italy austria abstract the cretaceous eo alpine collisional event in the european eastern alps is generally accepted to induce w nw directed thrusting both in basement and in sedimentary cover units this study presents the first evidence of eo alpine w nw directed normal kinematics along the schneeberg normal fault zone which separates eo alpine high pressure rocks in a footwall position from pre alpine basement rocks in a hanging wall position new garnet sm nd data indicate that exhumation of the high pressure rocks along the normal fault zone started around 95 ma ago and continued up to low greenschist brittle conditions at 76 ma as indicated by a rb sr age from a low temperature mylonite the occurrence of pre alpine basement rocks both in the hanging wall and the footwall of eo alpine high pressure rocks suggests exhumation by extrusion processes despite the displacement or removal of parts of the lower portion of the high pressure unit by tertiary strike slip faults eo alpine top to ese thrusting as expected for the structurally lower part of an extruding wedge was found at and below the base of the eo alpine high pressure rocks a rb sr age of 77 ma from a greenschist facies mylonite in this thrust shear zone shows the contemporaneity of deformation at the base and the top of the wedge the tectonic transport direction within the extruding wedge was e se opposite to the w nw direction so far reported for the eo alpine event in the eastern alps the contemporaneity of opposite tectonic transport directions during continental subduction may be explained by a double vergent wedge model with a narrow zone of ductile flow where the high pressure rocks were exhumed

the northern giudicarie and the meran mauls fault alps northern italy in the light of new paleomagnetic and geochronological data from boudinaged eo oligocene tonalites this study concentrates on small intrusions along two important faults of the giudicarie fault system the northern giudicarie and the meran mauls fault summarised under the term tonalitic lamellae magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the ne sw striking northern part of the giudicarie fault system the meran mauls fault overprinted by younger thrusting the regional stressfield was oriented approximately nnw sse during tertiary times the distinctive change in deformation along the meran mauls fault from dextral strike slip to top se thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation based on the assumption of a preliminary straight periadriatic lineament bent by the nnw wards advancement of the southalpine indenter the tonalitic lamellae may be interpreted as lenses sheared off from the adamello batholith during indentation new u pb data on zircon show that some of the lamellae are of oligocene rupelian others of late eocene priabonian age an amphibole gabbro lens occurring on the meran mauls fault provides a middle eocene bartonian age among the major periadriatic plutons only the southern units of the adamello batholith also intruded in the eocene that suggests a strong correlation between the tonalitic lamellae and the adamello batholith the analyses of the remanent magnetisation and the curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures this indicates slow cooling of the investigated intrusions along the giudicarie fault system down to approximately 300 c which is in contrast to the fast cooling determined for the adamello intrusion units currently at the surface the new zircon fission track data also show later cooling of the tonalites along the giudicarie fault system when compared with the adamello batholith in the south and the mauls lamellae in the north indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the adamello and the mauls region this may be due to important top se thrusting and transpressive faulting in the footwall of the northern giudicarie fault and the meran mauls fault

hydrodynamics and sediment dynamics of the wash embayment eastern england water and sediment movement in the wash embayment has been determined from an extensive set of data consisting of tidal current readings and suspended sediment concentration measurements instantaneous and residual currents in the embayment show a distinct lateral inhomogeneity whereas vertically the water column is almost homogenous the central deep water area 30 40 m of the embayment is dominated by a residual landward water movement whilst on the margins the residual movement is seaward sediment is supplied predominantly in suspension from the north through the northern extremity of boston deep suspended sediment pathways are coincident with the spring tide water movements and the subtidal channels act as the main conduits approximately 6 8 106 tonnes yr 1 of suspended sediments are supplied to the embayment from offshore areas bedload sediment supply is of lesser importance 1 4 104 tonnes yr 1 whereas suspended sediment movement appears to be the dominant mode of transport throughout the embayment bedload transport is important in reforming the sea bed into a variety of bedforms which are particularly well developed on the margins of channels and shoals

the western end of the eoalpine high pressure belt texel unit south tyrol italy eclogites in the texel unit eastern alps south tyrol italy represent the westernmost outcrops of the e w striking eoalpine high pressure belt ehb east of the tauern window the ehb forms part of a cretaceous intracontinental south dipping subduction collision zone however the same nappe stack displays a northwest dip at its western end this prominent change in dip direction gave rise to discussions on the general setting of the eoalpine collision based on our own observations and literature data we present a new tectonic model for the western end of the ehb due to the special situation of this area at the tip of the southalpine indenter originally south east dipping structures became overturned and former thrusts appear as normal faults e g schneeberg fault zone while former normal faults presently display thrust geometries e g jaufen fault thus we explain the current configuration with a coherent eoalpine subduction direction

an 40ar 39ar laser probe study of pseudotachylites in charnockite gneisses from the cauvery shear zone system south india the age of pseudotachylite formation in the crustal scale cauvery shear zone system of the precambrian southern granulite terrain south india has been analyzed by laser probe ar 40 ar 39 dating laser spot analyses from a pseudotachylite from the salem attur shear zone have yielded ages ranging from 1214 to 904 ma some evidence for the presence of excess ar is indicated by the scatter of ages from this locality the host gneiss preserves palaeoproterozoic rb sr whole rock biotite ages 2350 11 to 2241 11 ma a mylonite in the koorg shear ca 200 km to the north yielded an age of 895 17 ma the consistency of the age distribution from spot analyses precludes the presence of significant excess ar despite published evidence for the growth of high grade minerals within some components of the cauvery shear zone during the pan african event 700 550 ma the pseudotachylites in this study provide no evidence for pan african formation instead they document the first evidence for mesoproterozoic tectonism in the cauvery shear zone system thus prompting a review of the correlation between the cauvery shear zone system and the large scale shear zones located elsewhere in eastern gondwana c 2006 international association for gondwana research published by elsevier b v all rights reserved

thermochronological record of thrusting and strike slip faulting along the giudicarie fault system alps northern italy the giudicarie fault system represents the central approximately ne sw trending segment of the periadriatic fault system based on new fission track data the near surface evolution of the units bordering the giudicarie fault system gfs is analysed new and published zircon fission track zft data are compiled in an age contour map of the area and depict some first order features of cooling and exhumation pattern out of the three main permian plutons located in the footwall of the gfs the northern brixen pluton and southernmost kreuzberg pluton yielded zft ages of about 100 ma while the intermediate ifinger pluton cooled through the zircon partial annealing zone only in the miocene the ifinger granodiorite overthrusts the southalpine basement and the permian rocks of the athesian volcanic district along the nw dipping brittle naif fault across this thrust an important age jump from miocene to permian zft ages is observed suggesting that the deformation has jumped towards the southeast thus deactivating the related segment of the gfs the most eye catching feature of the age contour map is the corridor of young miocene zft ages from small tonalitic intrusions along the northern giudicarie fault this corridor connects early miocene 17 23 ma zft ages of the ne adamello with the middle late miocene 19 9 ma zft ages of the meran mauls basement and the western tauern window and provides evidence for a polyphase deformation along the gfs a three step evolution model is proposed for the gfs a shearing of the northern rim of the adamello batholith along the dextral strike slip periadriatic fault system b bending of the central part of the fault to a ne direction together with the adjacent intrusive rocks c dissection of the bend part meran mauls fault by the sinistral transpressive northern giudicarie fault and exhumation of small tonalitic bodies along this structure highlights different exhumation history for permian intrusions along the giudicarie fault system very consistent zft ages of 15 ma for the entire meran mauls basement corridor of miocene zircon fission track ages along the giudicarie fault system evidence for a polyphase deformation along the giudicarie fault system

titanium in quartz thermometry on synkinematic quartz veins in a retrograde crustal scale normal fault zone abstract previous studies have suggested that estimation of deformation temperatures in quartz mylonites by titanium in quartz geothermometry is only possible at temperatures 500 c above which efficient ti exchange is achieved via grain boundary migration recrystallization based on quartz mylonite samples collected across the simplon fault zone sfz we demonstrate that deformation temperatures of dynamic recrystallization can be obtained down to 350 c a prerequisite for such temperature estimates at the low temperature end of ductile deformation of quartz is the formation of synkinematic quartz veins and their immediate overprint either by subgrain rotation sgr or bulging recrystallization blg it is the slow growth of the synkinematically precipitating vein quartz that allows for equilibration of ti in the vein quartz this ti concentration may only slightly be modified during sgr hence ti in qtz thermometry provides a close approach to the vein formation temperature ti concentrations are partially reset during blg and resulting temperatures are thus maximum temperatures of quartz recrystallization importantly undeformed vein quartz always yield vein formation temperatures investigation of the dynamic recrystallization processes overprinting synkinematic quartz veins thus allows for a critical independent evaluation of the ti in quartz temperatures obtained for the sfz there is a decrease in recrystallized grain sizes towards the fault plane and a change in the dominant recrystallization process associated with a narrowing of the shear zone as indicated by the ti in quartz temperature estimates this strain localization correlates with cooling from 560 c in the oldest microstructures at the periphery of the shear zone down to 350 c in the youngest microstructures of the footwall near the hanging wall contact a great benefit of the approach presented here is that intermediate to low temperature plastic deformation in quartz can now also be assessed such novel temperature constraints on quartz crystallization are essential for better constraining deformation and rheology in the upper earth s crust

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

exploring the ar isotope record of an early miocene pseudotachylyte in an early oligocene intrusion rieserferner pluton eastern alps abstract we investigate the influence of unmelted clasts on the 40ar 39ar age record of a miocene pseudotachylyte within the early oligocene riesenferner pluton eastern alps this case study is ideal to investigate the effect of inherited ar retained in survivor clasts because although seismic faulting was only slightly younger 39ar laser analyses of low k microlitic domains free of discernable clasts yield slightly but significantly older ages than those from the high k matrix results suggest that older ages up to 4 on average from low k domains are due to contamination by plagioclase clasts and suggest an age of 17 12 0 22 ma for coseismic slip this age dates the last stage of activity of the giudicarie fault during tectonic indentation of the dolomites block of the southern alps against the nappe stack of the eastern alps

3850 ma bif and mafic inclusions in the early archaean itsaq gneiss complex around akilia southern west greenland the difficulties of precise dating of zircon free protoliths in migmatites abstract the southern part of the early archaean itsaq gneiss complex southern west greenland on akilia and adjacent islands consists of polyphase dioritic tonalitic granitic injection components with inclusions of metavolcanic amphibolites chemical sediments such as banded iron formation bif gabbros and ultramafic rocks incipient in situ partial melting and strong deformation during several archaean tectonothermal events strongly modified these injection components so that they are now mostly banded schlieric migmatites with neosome produced during several events the margins of many inclusions have been loci for either segregation of neosome and or higher strain obliterating the relationship between the inclusions and the older components of the migmatites an added complication is that none of the inclusion lithologies in the southern part of the complex contain protolith zircon which would provide precise direct dates instead minimum ages of inclusions are obtained by dating invasive components of the granitic sensu lato migmatites previous age determinations of the inclusions were centred on a 200 m long body of amphibolites bif and ultramafic rocks on the southwestern corner of akilia geochronology of this locality has been controversial with our proposed age of 3850 ma making the inclusion the world s oldest dated sedimentary and mafic rocks we continue the debate on the age of the inclusion on southwest of akilia and we broaden it by presenting mapping and zircon dating studies of inclusions on islands with 20 km of akilia this 1 addresses the contentious ages of these rocks 2 examines the broader issue of how the complex field relationships in migmatites can lead to geochronological controversies and 3 addresses the problem of precise dating of rocks in gneiss complexes which do not carry zircon from their protoliths on qilanngaarsuit island a gneiss sheet cutting a metaperidotite inclusion has an age of 3850 ma on an islet 2 km west of akilia tonalite and quartz diorite which intrude and envelop two mafic amphibolite and hornblendite inclusions have dates of 3850 ma also with our proposed ages of 3850 ma these inclusions are older than similar rocks in the 3700 3800 ma isua supracrustal belt at other investigated localities 3850 ma zircon dates have not been obtained from the orthogneisses enveloping or intruding inclusions at two localities invasive leucogranite neosome and a discordant diorite sheet cutting inclusions have ages of 3600 3660 ma a period of known tectonothermal events including crustal melting and intrusion of gabbros and diorites at three localities banded schlieric orthogneisses adjacent to supracrustal gabbroic and ultramafic rocks contain 3800 3700 ma igneous components in these cases the inclusions could still be 3850 ma and be equivalent in age to similar rocks on akilia but this has been masked by the local tectonothermal history and greater amount of neosome development an alternative explanation is that some younger

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

kinematic analysis and analogue modelling of the passeier and jaufen faults implications for crustal indentation in the eastern alps crustal deformation in front of an indenter is often affected by the indenter s geometry rheology and motion path in this context the kinematics of the jaufen and passeier faults have been studied by carrying out paleostress analysis in combination with crustal scale analogue modelling to infer 1 their relationship during indentation of the adriatic plate and 2 their sensitivity in terms of fault kinematics to the geometry and motion path of adria the field study reveals mylonites along the jaufen fault which formed under lower greenschist facies conditions and is associated with top to the west northwest shear with a northern block down component in addition a brittle reactivation of the jaufen shear zone under nnw sse to nw se compressional and ene wsw tensional stress conditions was deduced from paleostress analysis the inferred shortening direction is consistent with fission track ages portraying neogene exhumation of the meran mauls basement south of the fault along the passeier fault deformation was only brittle to semi ductile and paleostress tensors record that the fault was subjected to e w extension along its northern segment varying into nw se compression and sinistral transpression along its southern segment in the performed analogue experiments a rigid triangular shaped indenter was pushed into a sand pile resulting in the formation of a passeier like fault sprouting from the indenter s tip these kinds of north trending tip faults formed in all experiments with shortening directions towards the nw n or ne consequently we argue that the formation of the passeier fault strongly corresponds to the outline of the adriatic indenter and was only little affected by the indenter s motion path due to induced strain partitioning in front of the different indenter segments the associated fault kinematics along the passeier fault including both e w extension and nnw to nw shortening however is most consistent with a northward advancing adriatic indenter

tidal sedimentation in the tees estuary during the 20th century radionuclide and magnetic evidence of pollution and sedimentary response abstract a series of short cores ca 0 5 m were collected from the intertidal zone and reclaimed lowlands of greatham creek in the tees estuary magnetic concentration data were combined with radionuclide chronologies based on down core profiles of unsupported 210 pb activity and 137 cs activity to establish the history of estuarine pollution the onset of metal pollution is dated to the latter part of the 19th century peak metal concentrations date from the early 1950s and the observed decline in metal pollution starts in the early 1980s radionuclide chronologies are considered unreliable in the outer part of the estuary where low 210 pb activities cannot be calibrated against 137 cs in the intertidal zone 137 cs inventories correlate well with sedimentation rate and can be linked to soil erosion in the catchment rather than the marine delivery of sellafield radionuclides in addition temporal offsets between reliable 210 pb and 137 cs chronologies in the intertidal zone can be attributed to erosion of the upper part of the sedimentary record both the intertidal and reclaimed regions exhibit enhanced sedimentation rates for the last 40 years this is likely to be a response to relative sea level rise although the impact of engineering works can also be observed in the tidal flats and saltmarshes during the last 25 years in the form of differential erosion and accelerated sedimentation

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

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

conceptualising and mapping coupled estuary coast and inner shelf sediment systems whilst understanding and predicting the effects of coastal change are primarily modelling problems it is essential that we have appropriate conceptual frameworks for 1 the formalisation of existing knowledge 2 the formulation of relevant scientific questions and management issues 3 the implementation and deployment of predictive models and 4 meaningful engagement involvement of stakeholders important progress continues to be made on the modelling front but our conceptual frameworks have not evolved at a similar pace accordingly this paper presents a new approach that re engages with formal systems analysis and provides a mesoscale geomorphological context within which the coastal management challenges of the 21st century can be more effectively addressed coastal and estuarine system mapping cesm is founded on an ontology of landforms and human interventions that is partly inspired by the coastal tract concept and its temporal hierarchy of sediment sharing systems but places greater emphasis on a hierarchy of spatial scales this extends from coastal regions through landform complexes to landforms the morphological adjustment of which is constrained by diverse forms of human intervention crucially cesm integrates open coastal environments with estuaries and relevant portions of the inner shelf that have previously been treated separately in contrast to the nesting of littoral cells that has hitherto framed shoreline management planning cesm charts a complex web of interactions of which a sub set of mass transfer pathways defines the sediment budget and a multitude of human interventions constrains natural landform behaviour conducted within a geospatial framework cesm constitutes a form of knowledge formalisation in which disparate sources of information published research imagery mapping raw data etc are generalised into usable knowledge the resulting system maps provide a framework for the development and application of predictive models and a repository for the outputs they generate not least flux estimates for the major sediment system pathways they also permit comparative analyses of the relative abundance of landforms and the multi scale interactions between them finally they articulate scientific understanding of the structure and function of complex geomorphological systems in a way that is transparent and accessible to diverse stakeholder audiences as our models of mesoscale landform evolution increase in sophistication cesm provides a platform for a more participatory approach to their application to coastal and estuarine management

k ar dating of synkinematic clay gouges from neoalpine faults of the central western and eastern alps abstract with ongoing alpine convergence and deformation during exhumation there is a general progression from ductile to brittle behaviour on the periadriatic fault and kinematically related faults farther north e g the simplon rhone fault and a diffuse discontinuous zone of generally dextral strike slip movement on the southern boundary of the aar massif k ar dating of fine grained illite from clay fault gouges provides a reliable method for establishing the maximum age of this transition to brittle faulting and for short lived faults the approximate time of faulting itself the new results establish that brittle faulting on the northeastern segment of the canavese fault i e the part of the periadriatic fault southwest of lago maggiore occurred around 20 ma with south side up kinematics a k ar age of ca 17 ma for the crosscutting giudicarie fault in the eastern alps is effectively identical with an already published pseudotachylyte age and places a lower limit on major and continuous strike slip movements of the periadriatic fault the age of brittle faulting farther north on the southern border of the aar massif is from 13 6 0 3 to 8 3 1 1 ma consistent with the younger cooling and exhumation in this area the dominantly dextral brittle faulting becoming younger to the north reflects the continued indentation and anticlockwise rotation of adria as alpine units become exhumed and progressively welded to the southern block in contrast to the eastern alps there is no field evidence for westward lateral extrusion of alpine units relative to adria and the european foreland

40ar 39ar dating of penninic front tectonic displacement w alps during the lower oligocene 31 34 ma direct absolute dating of the penninic frontal thrust tectonic motion is achieved using the 40 ar 39 ar technique in the pelvoux crystalline massif western alps the dated phengites were formed syn kinematically in shear zones they underline the brittle ductile stretching lineation pressure shadow fibres and slickensides consistent with underthrusting of the european continental slab below the propagating penninic thrust chlorite phengite thermobarometry yields 10 15 km and t 280 c while 40 ar 39 ar phengite ages mainly range between 34 and 30 ma with one younger age at 27 ma this early oligocene age range matches a major tectonic rearrangement of the alpine chain preservation of prograde 40 ar 39 ar ages is ascribed to passive exhumation of the pelvoux shear zone network sandwiched between more external thrusts and the penninic front reactivated as an e dipping detachment fault partial resetting in the low temperature part of argon spectra below 24 ma is ascribed to brittle deformation and alteration of phengites

biogenic indicators of suspended sediment transport in marginal marine environments quantitative examples from sw britain suspended sediment samples taken from the water column in the high energy western english channel and its western approaches contain size sorted benthic foraminiferal tests m in diameter derived from the continental shelf sediments similar associations of small tests are found in estuaries where the indigenous living assemblages are totally different net transport from the shelf to the estuaries is therefore inferred to have taken place tests m in size are probably equivalent to quartz spheres of silt size and they indicate the net transport path for this size grade an attempt has been made to quantify the transport budget and in spite of the paucity of data an order of magnitude estimate has proved to be possible

lateral extrusion in the eastern alps revisited refining the model by thermochronological sedimentary and seismic data 1 this study comprises a reassessment of the classical model of lateral extrusion in the eastern alps by using recently published geochronological data sedimentary ages from intramontane basins ages and distribution of magmatic rocks and information from seismic profiles extrusion related faulting continuously propagated from the western toward the central eastern part of the eastern alps during oligocene to middle miocene times this is confined by oblique convergence between the adriatic and european plates during middle miocene times extrusion became not only lateral in terms of parallel to the trend of the eastern alps but was characterized by a displacement vector at a high angle to the strike of the orogen this resulted in the exhumation of the schladming and pohorje blocks that were exhumed within extensional bridges at the northern and southern terminations of the pols lavanttal fault system respectively from middle miocene to recent times extrusion was controlled by overall extension between the dinaric and carpathian subduction zones the influence of north directed compression triggered by the northward moving adriatic plate diminished and the influence of the retreating carpathian subduction zone increased this gave rise to miocene volcanism that is exclusively found east of the dinaric subduction zone we therefore consider that lateral extrusion in the eastern alps can be subdivided into distinct tectonic phases with less pronounced eastward extension related displacement between late oligocene and middle miocene times as soon as the eastern alps passed the dinaric subduction zone the entire domain became highly extensive

sediment exchanges across the coastal margins of nw europe this contribution serves as an introduction to the coastal margins as sediment traps thematic set one of the most basic questions which faces those concerned with sediment transport in the marine environment is whether the coastal margin is a net source or sink for sediment the coastal margin is taken to mean the coast itself with its cliffs bays and estuaries and the immediate coastal zone stretching a few hundred metres to a few kilometres off shore it is not clear to what extent the coasts of nw europe have recovered from the last period of depressed sea level uncertainty exists as to whether sediment lost from the coastal margin is deposited in offshore sinks whether sediment originally laid down on the continental shelves is returning to depositional sites located principally in bays and estuaries or more particularly whether all coastal margins are subject to the same balance of processes the reason for this lack of knowledge is clear the calculation of the sediment budget of an estuary is difficult the calculation of the budget for a whole coastal sector including the continental shelf fronting it is even more problematical for entire seas our capacity for reliable quantification at the present time is negligible a perspective on this issue can be obtained by considering the situation in a parallel discipline oceanographers have been studying the circulation of our shallow seas for 70 80 years latterly with co operative experiments using tens of simultaneously deployed self recording current meters and the mathematical models

alteration and remelting of nascent oceanic crust during continental rupture evidence from zircon geochemistry of rhyolites and xenoliths from the salton trough california abstract rhyolite lavas and xenoliths from the salton sea geothermal field southern california provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust salton buttes rhyolite lavas contain xenoliths that include granophyres fine grained altered rhyolites felsite and amphibole bearing basalts zircon is present in lavas and xenoliths surprisingly even in the basaltic xenoliths where it occurs in plagioclase rich regions interpreted as pockets of crystallized partial melt zircons in the xenoliths are exclusively late pleistocene holocene in age and lack evidence for inheritance u th isochron ages are 20 5 1 2 1 2 ka granophyres 18 3 3 5 3 6 ka felsite 30 1 12 4 14 1 ka and 9 2 6 6 7 0 ka basalts all errors 1 the dominant zircon population in the rhyolite lavas yielded u th ages between 18 and 10 ka with few pre quaternary xenocrysts present 18ozircon values are lower than typical crustal basement values thus ruling out rhyolite genesis by melting of continental crust moreover 18ozircon values are 0 5 1 0 lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid ocean ridge basalt suggesting that basaltic crust and silicic plutons in the subsurface of the salton sea geothermal field isotopically exchanged with meteoric waters this is evidence for deep reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma

modes of orogen parallel stretching and extensional exhumation in response to microplate indentation and roll back subduction tauern window eastern alps the tauern window exposes a paleogene nappe stack consisting of highly metamorphosed oceanic alpine tethys and continental distal european margin thrust sheets in the eastern part of this window this nappe stack eastern tauern subdome etd is bounded by a neogene system of shear the katschberg shear zone system kszs that accommodated orogen parallel stretching orogen normal shortening and exhumation with respect to the structurally overlying austroalpine units adriatic margin the kszs comprises a 5 km thick belt of retrograde mylonite the central segment of which is a southeast dipping low angle extensional shear zone with a brittle overprint katschberg normal fault knf at the northern and southern ends of this central segment the kszs loses its brittle overprint and swings around both corners of the etd to become subvertical dextral and sinistral strike slip faults the latter represent stretching faults whose displacements decrease westward to near zero the kinematic continuity of top east to top southeast ductile shearing along the central low angle extensional part of the kszs with strike slip shearing along its steep ends combined with maximum tectonic omission of nappes of the etd in the footwall of the knf indicates that north south shortening orogen parallel stretching and normal faulting were coeval stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the kszs to have begun at 23 21 ma leading to rapid cooling between 21 and 16 ma this exhumation involved a combination of tectonic unroofing by extensional shearing upright folding and erosional denudation the contribution of tectonic unroofing is greatest along the central segment of the kszs and decreases westward to the central part of the tauern window the kszs formed in response to the indentation of wedge shaped blocks of semi rigid austroalpine basement located in front of the south alpine indenter that was part of the adriatic microplate northward motion of this indenter along the sinistral giudicarie belt offsets the periadriatic fault and triggered rapid exhumation of orogenic crust within the entire tauern window exhumation involved strike slip and normal faulting that accommodated about 100 km of orogen parallel extension and was contemporaneous with about 30 km of orogen perpendicular north south shortening of the etd extension of the pannonian basin related to roll back subduction in the carpathians began at 20 ma but did not affect the eastern alps before about 17 ma the effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the tauern window area therefore we propose that roll back subduction temporarily enhanced rather than triggered exhumation and orogen parallel motion in the eastern alps lateral extrusion and orogen parallel extension in the eastern alps have continued from 12 to 10 ma to the present and are driven by northward push of adria

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

zircon petrochronology and 40ar 39ar thermochronology of the adamello intrusive suite n italy monitoring the growth and decay of an incrementally assembled magmatic system the adamello intrusive suite is a composite batholith in northern italy with an estimated 2000 km3 volume assembled incrementally over a time span of 10 to 12 million years the history of crysta

nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions abstract in the neves area the pre alpine intrusive protolith of the zentralgneise unit tauern window eastern alps is well preserved in a kilometric scale low strain domain without pervasive alpine deformation it is compositionally heterogeneous consisting predominantly of granodiorites with lesser leucocratic granites and different generations of lamprophyres and aplites the intrusive rocks are crosscut by fractures that were locally infiltrated by fluids and surrounded by alteration haloes incipient alpine amphibolite facies ductile deformation is strongly localized on these precursor fractures and on lithological planar heterogeneities resulting in the development of several different types of shear zones fractures without alteration haloes initially accommodate slip entirely on the fracture itself with increasing deformation a foliation is progressively developed in the adjacent host rock eventually producing a single heterogeneous ductile shear zone with the typical sigmoidal foliation pattern strong layers aplite dykes and bleached alteration haloes developed to either side of precursor fractures localize shear on their boundaries to produce characteristic paired shear zones shearing is more evenly distributed within weak layers lamprophyres and quartz veins with a marked discontinuity in shear strain against the adjacent little deformed granodiorite shear zone development was accompanied by the formation of new fractures and quartz rich veins in the host rock which in turn also localized shear magmatic contacts fractures and quartz veins are mostly steeply dipping and effectively span the complete range of strike orientations the kinematics of the overprinting strike slip shear zones was determined by the orientation of the initial discontinuities relative to the local principal compressive stress axis 1 here oriented ca 345 discontinuities of almost all orientations show shear reactivation even in the case of very low resolved shear stress indicating an overall viscous response of the system without a specific yield stress the geometry and kinematics of the shear zone network suggest that the overall deformation in low strain domains was close to coaxial during deformation along the shear zone network compatibility was maintained by fracturing with the development of new quartz veins and by distributed ductile deformation of the host rock especially within contractional domains of the shear network and at shear zone intersections deformation never propagates into the undeformed homogeneous granodiorite as discrete ductile shear zones but is limited by the original extent of the precursor discontinuities shear zone development in intact rock is always preceded by fracturing which localizes subsequent shear reactivation

the oligocene alps domal unroofing and drainage development during early orogenic growth abstract the source of huge volumes of quartzofeldspathic detritus feeding oligo miocene foredeep turbidites of the apennines has long remained an unsolved geological enigma in this article we reinterpret the available sandstone petrography fission track stratigraphic and geomorphological evidence to demonstrate that the adriatic foredeep was dominantly sourced by a himalayan type tectonic aneurysm growing in the central alps since the late oligocene the lepontine dome the lepontine dome is the envelope of distinct subdomes that formed stepwise from east to west during northwestward indentation of adria beneath the axial alps focused erosion of domal culminations cut by antecedent drainage started suddenly in the late oligocene with unroofing of recently emplaced plutons and young amphibolite facies gneisses exhumation was tectonically driven and possibly accelerated by positive feedback between erosion and uplift of hot weak rocks from depth the huge volumes of resulting detritus gonfolite macigno clastic wedge were transported southward for hundreds of kilometers along the rapidly subsiding foredeep formed since middle eocene times in front of the alpine retrobelt and nascent apennine forebelt such massive sediment influx following 15 2 myr of starved foredeep sedimentation testifies to rapid formation of mountain relief in the central alps synchronous to dextral activity along the insubric fault the lepontine dome remains today as the only deeply dissected region in the alps where medium grade metamorphic rocks of the axial belt are extensively exposed the relationships between geological structures and drainage patterns still mirror those formed originally at oligocene times river headwaters have not been significantly displaced since then and their thalwegs constrain finite lateral displacement relative to the southalpine retrowedge to a maximum of 10 20 km our reconstruction has wide implications not only for a better understanding of the tertiary evolution of the alps apennines orogenic couple but also for general relationships among tectonic activity relief formation drainage development erosion distribution and long distance sediment transfer during continental collision and orogenic growth

interactions between serpentinite devolatilization metasomatism and strike slip strain localization during deep crustal shearing in the eastern alps the greiner shear zone in the tauern window eastern alps changes from a zone of distributed dominantly sinistral shear in supracrustal rocks to a series of narrow gully forming dextral splays where it enters basement gneisses within these splays granodiorite is transformed into quartz poor biotite and or chlorite schists reflecting hydration removal of si ca and na and concentration of fe mg and al stable isotope analyses show a prominent increase in d and a decrease in 18o from granodiorite into the shear zones these changes indicate significant channelized flow of an externally derived low 18o high d fluid through the shear zones the shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the greiner zone and the stable isotope data support alteration via serpentinite derived fluid monazite in schist from one shear zone yields spot dates of 29 20 ma indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the alpine orogeny c 30 ma we suggest that alpine metamorphism of serpentinites released large amounts of high d low 18o si undersaturated fe mg saturated fluids that became channelized along prior zones of weakness in the granodiorite infiltration of this fluid facilitated growth of chlorite and biotite which in turn localized later dextral strain in the narrow splays via cleavage parallel slip this dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the eastern alps this study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis

the pejo fault system an example of multiple tectonic activity in the italian eastern alps the pejo fault in the italian eastern alps is a major sinistral transtensional fault it marks the boundary between basement units displaying contrasting thermal histories with alpine i e mesozoic cenozoic cooling ages preserved in the footwall juxtaposed against variscan i e carboniferous permian age in the hanging wall structural investigations together with fission track analysis confirm a late cretaceous age for the pejo fault which excludes any direct kinematic contribution of the pejo fault to the late oligocene neogene evolution of the central eastern segment of the periadriatic fault however our results establish the importance of a major early oligocene north south to north northwest south southeast shortening phase in the central eastern alps which resulted in the development of new reverse shear zones in the reactivation of the pejo fault with a reverse motion and in regionally important folding the pejo mylonites are folded on a kilometer scale around an east northeast trending axis field observations and fission track analysis suggest a post oligocene age for the folding phase apatite fission track data in the pejo valley area reveal the base of a fossil apatite partial annealing zone exhumed to the surface this finding argues for 4 km of exhumation since the miocene which was related to a major pulse of exhumation that began at ca 15 ma this study suggests that the simple distinction between largely pre alpine fabrics of variscan age in the hanging wall of the pejo fault tonale nappe and alpine fabrics cretaceous in the footwall campo ortler nappe is not universally valid alpine overprinting is confined to the mylonitic shear zone itself deeper into the footwall pre alpine structures are still well preserved earlier maps and interpretations based on a clear distinction between tonale and campo should be viewed with caution

structure of the lithosphere beneath the eastern alps southern sector of the transalp transect abstract the interpretation of the seismic vibroseis and explosive transalp profiles has examined the upper crustal structures according to the near surface geological evidences and reconstructions which were extrapolated to depth only the southern sector of the transalp transect has been discussed in details but its relationship with the whole explored chain has been considered as well the seismic images indicate that pre collision and deep collision structures of the alps are not easily recognizable conversely good records of the neo alpine to present architecture were provided by the seismic sections two general interpretation models crocodile and extrusion have been sketched by the transalp working group 2002 both illustrate the continental collision producing strong mechanical interaction of the facing european and african margins as documented by giant lithosphere wedging processes arguments consistent with the extrusion model and with the indentation of adriatic southalpine lithosphere underneath the tauern window tw are according to the previous dss reconstructions the bouguer anomalies and the receiver functions seismological data the european moho descends regularly attaining a zone south of the periadriatic lineament pl the moho boundary and its geometry appear to be rather convincing from images of the seismic profile the tauern window intense uplift and exhumation is coherent with the strong compression regime which acted at depth thus originating the upward and lateral displacement of the mobile and ductile penninic masses according to the extrusion model the indentation of the penninic mobile masses within the colder and more rigid adriatic crust cannot be easily sustained wedging of the adriatic stiffened lower crust under high stresses and into the weaker penninic domain can be a more suitable hypothesis furthermore the intrusion of the european penninic crustal wedge underneath the dolomites upper crust is not supported by any significant uplifting of the dolomites the total average uplift of the dolomites during the neogene appears to be 6 7 times smaller than that recognized in the tw markedly the northward dip of the pl reaching a depth of approximately 20 km is proposed in our interpretation finally the adriatic upper crustal evolution points to the late post collision change in the tectonic grow up of the eastern alps orogenic chain the tectonic accretion of the northern frontal zone of the eastern and central alps was interrupted from the late miocene serravallian tortonian onward as documented by the molasse basin evolution on the contrary the structural nucleation along the s vergent tectonic belt of the eastern southern alps montello friuli thrust belt severely continued during the messinian and the plio pleistocene this structural evolution can be considered to be consistent with the deep under thrusting and wedge indentation of the adriatic lithosphere underneath the southern side of the eastern alps thrust and fold belt similarly the significance of the magmatic activity for the construction of the southern alps crust and for its mechanical and geological differentiation which qualified the evolution of the thrust and fold belt is highlighted starting with the permian triassic magmatism and progressing with the paleogene occurrences along the periadriatic lineament and in the venetian magmatic province lessini euganei hills

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

a seismotectonic picture of the inner southern western alps based on the analysis of anomalously deep earthquakes abstract the anomalously deep seismicity beneath the western po plain is here analyzed to shed light on the complex and still poorly understood tectonic configuration of the internal side of the western alps area the original dataset including 590 earthquakes deeper than 20 km recorded during the last 25 years has been accurately relocated with hypodd using both catalog and cross correlation differential times we found that the distribution of seismic events faithfully mirrors the presence of two distinct tectonic domains axial belt domains 1 and 2 originally belonging to the paleogene alpine wedge and now anomalously juxtaposed beneath the sedimentary infill of the western po plain shallow low magnitude earthquakes 8 km and accommodated in correspondence of the fault could be linked to its neogene activity coeval with the northward translation of the retreating adriatic slab

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

geochronological constraints on the evolution of the periadriatic fault system alps fault rocks from various segments of the periadriatic fault system paf alps have been directly dated using texturally controlled rb sr microsampling dating applied to mylonites and both stepwise heating and laser ablation 40ar 39ar dating applied to pseudotachylytes the new fault ages place better constraints on tectonic models proposed for the paf particularly in its central sector along the north giudicarie fault oligocene e se directed thrusting 29 32 ma is currently best explained as accommodation across a cogenetic restraining bend within the oligocene dextral tonale pustertal fault system in this case the limited jump in metamorphic grade observed across the north giudicarie fault restricts the dextral displacement along the kinematically linked tonale fault to 30 km dextral displacement between the tonale and pustertal faults cannot be transferred via the peio fault because of both late cretaceous fault ages 74 67 ma and sinistral transtensive fault kinematics in combination with other pseudotachylyte ages 62 58 ma widespread late cretaceous paleocene extension is established within the austroalpine unit coeval with sedimentation of gosau group sediments early miocene pseudotachylyte ages 22 16 ma from the tonale pustertal jaufen and passeier faults argue for a period of enhanced fault activity contemporaneous with lateral extrusion of the eastern alps this event coincides with exhumation of the penninic units and contemporaneous sedimentation within fault bound basins

a recipe for the use of rutile in sedimentary provenance analysis abstract rutile has received considerable attention in the last decade as a valuable petrogenetic indicator mineral based on both new and previously published data we carve out advantages and pitfalls regarding tio 2 minerals in sedimentary provenance analysis this results in a recipe for the use of rutile in provenance studies the main points are rutile geochemistry from different grain size fractions does not differ systematically and hence rutiles should be extracted from the fraction containing the most rutile grains usually 63 200 m similarly different magnetic susceptibility of rutile does not systematically imply different trace element composition before interpretation of tio 2 mineral data it is important to determine the polymorph type rutile anatase and brookite appear to differ systematically in trace element composition as an alternative to raman spectroscopy chemical classification according to nb cr sn fe v and zr concentrations can be applied for rutile a new host lithology discrimination scheme based on cr nb systematics is introduced x 5 nb ppm 500 cr ppm which leads to better classification results than previously published discrimination methods according to this equation metamafic rutiles have negative values of x while metapelitic rutiles have positive values evaluation of the growth temperature calculations of metamorphic rutile after different authors shows that the equations given by tomkins et al 2007 should be applied to both metamafic and metapelitic rutiles although there is a pressure effect on the zr incorporation in rutile the pressure range for most rutiles of 5 15 kbar introduces an uncertainty in calculated temperature of no more than 35 c the distribution of calculated temperatures from detrital rutiles is crucial only well defined temperature populations should be used for thermometry interpretation

organic facies of surface sediments in the north sea abstract surface sediments of the north sea were investigated by organic geochemical and sedimentological methods including organic carbon and nitrogen determination rock eval pyrolysis protokerogen microscopy gas chromatography of aliphatic hydrocarbons grain size fractionation and clay mineral analysis the total organic matter was found to be a mixture of mostly reworked or oxidized marine and terrestrial constituents with a generally strong influence of the latter throughout the platform locally improved hydrodynamic conditions yielded an incorporation of more freshly produced marine organic matter differences in water current velocities and turbulence also appeared to determine whether this supplement is incorporated into the fine or coarse fractions of the sediments a general constancy of the organic carbon contents within the individual size fractions was recognized independently of sediment type and age i e in recent and pre recent deposits this suggested that the latter have been effectively overprinted by the shelf processes operating at present or that these processes have been of comparable intensity since about the beginning of the holocene transgression the major factors controlling the spatial variations in the organic facies are the sediment grain size and the present day hydraulic regime

nature of sedimentary organic matter in the lower reaches of the godavari river basin india abstract the distribution and nature of sedimentary organic matter om have been examined in sediment cores collected from the lower reaches including estuary of the godavari river in order to understand sedimentation patterns sources and diagenesis of om the samples were analyzed for organic carbon corg total nitrogen amino acids and hexosamines the observed irregular trends in corg distribution with depth indicate the unstable nature of bed sediment in the lower reaches of the river yet in the lower estuarine region regular trends in corg distribution with depth reflect the deposition of sediment the atomic ratio of corg and total nitrogen c n 10 5 16 1 also supported this observation the distribution of amino acids and diagenetic indicators ala aba mol aa ha and glc nh2 gal nh2 in individual cores revealed the post depositional changes in the om in the core sediment from the lower reaches there was no clear cut trend in amino acid content with depth in the estuarine region however amino acid content was very low 50 5 and 186 5 g g 1 in the upper layers compared to that in the lower layers 558 5 and 1099 3 g g 1 reactivity index range 0 3 3 7 revealed that om in the upper few centimeters especially in the lower estuarine region was more reactive relative to that in the deeper layers

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

experimental determination of ree partition coefficients between zircon garnet and melt a key to understanding high t crustal processes the partitioning of rare earth elements ree between zircon garnet and silicate melt was determined using synthetic compositions designed to represent partial melts formed in the lower crust during anatexis the experiments performed using internally heated gas pressure vessels at 7 kbar and 900 1000 c represent equilibrium partitioning of the middle to heavy ree between zircon and garnet during high grade metamorphism in the mid to lower crust the dree zircon garnet values show a clear partitioning signature close to unity from gd to lu because the light ree have low concentrations in both minerals values are calculated from strain modelling of the middle to heavy ree experimental data these results show that zircon is favoured over garnet by up to two orders of magnitude the resulting general concave up shape to the partitioning pattern across the ree reflects the preferential incorporation of middle ree into garnet with dgd zircon garnet ranging from 0 7 to 1 1 dho zircon garnet from 0 4 to 0 7 and dlu zircon garnet from 0 6 to 1 3 there is no significant temperature dependence in the zircon garnet ree partitioning at 7 kbar and 900 1000 c suggesting that these values can be applied to the interpretation of zircon garnet equilibrium and timing relationships in the ultrahigh t metamorphism of low ca pelitic and aluminous granulites

dating fault generated pseudotachylytes comparison of 40ar 39ar stepwise heating laser ablation and rb sr microsampling analyses three different geochronological techniques stepwise heating laser ablation 40ar 39ar rb sr microsampling have been evaluated for dating fault generated pseudotachylytes sampled along the periadriatic fault system paf of the alps because pseudotachylytes are whole rock systems composed of melt clast and alteration phases chemical control from both ar isotopes cl k ca k ratios and empa analyses is crucial for their discrimination when applied to stepwise heating 40ar 39ar analyses this approach yields accurate melt related ages even for complex age spectra the spatial resolution of laser ablation 40ar 39ar analyses is capable of contrasting melt clast and alteration phases in situ provided the clasts are not too fine grained the latter of which results in integrated mixed ages without geological information elevated cl k and ca k ratios were found to be an invaluable indicator for the presence of clast admixture or inherited 40ar due to incomplete isotopic resetting during frictional melting rb sr microsampling dating did not furnish geologically meaningful ages on the basis of isotopic disequilibria among pseudotachylyte matrix phases and independent rb sr microsampling dating of cogenetic ultra mylonites the concordant 40ar 39ar pseudotachylyte ages are interpreted as formation ages the investigated pseudotachylytes altogether reveal a cretaceous to miocene history for the entire paf consistent with independent geological evidence individual faults however consistently reveal narrower intervals of enhanced activity lasting a few million years electronic supplementary material to this paper can be obtained by using the springer link server at http dx doi org 10 1008 s00410 002 0381 6

a multistage origin for neoarchean layered hematite magnetite iron formation from the weld range yilgarn craton western australia abstract the origins of iron formations remain somewhat enigmatic despite much progress over the past decades this is due in part to continuing research demonstrating that these deposits do not have a single origin but rather can be formed under various and variable conditions this study describes a formation pathway for an algoma type banded iron formation bif from the 2 75 billion year old weld range of western australia based on petrographic and fe isotope analyses of drill core samples the bif is composed of alternating layers of jaspilitic and fe poor chert magnetite layers of varying thickness and abundance and rare pyrite petrographic analysis indicates the minerals formed in the order hematite magnetite and then pyrite with the latter two clearly replacive of primary bedded hematite hematite 56fe values from all portions of the drill core are positive and essentially identical 56fe 0 61 0 05 magnetite 56fe values are positive as well 56fe 0 51 0 07 but vary systematically with total magnetite content of the core samples pyrite 56fe values are positive and higher than both hematite and magnetite 56fe 1 03 0 05 combined these analyses reveal a multistage formational model for the weld range bif initial deposition occurred by the partial oxidation of hydrothermally sourced aqueous fe ii to form a fe iii si co precipitate probably by anoxygenic photosynthetic iron oxidizers this material would have been converted to hematite under equilibrium conditions with excess aqueous fe ii magnetite formed by a later intrusion of reducing fluids mostly along bedding planes but also as cross cutting veins this produced large quantities of magnetite layers parallel and sub parallel to the original bedding but that do not represent a primary depositional feature pyrite was produced in some portions of the unit likely under equilibrium conditions by later infiltration of reducing fluids containing sulfide the entirely positive 56fe values for all fe phases in the weld range bif stands in stark contrast to the more massive superior type bifs of the paleoproterozoic hamersley and transvaal basins of western australia and south africa respectively which have 56fe values that average close to 0 but vary over nearly the entire range of 56fe values measured in nature 56fe 2 5 to 2 6 the weld range bif 56fe values are similar to those of older algoma type bifs such as the paleoarchean isua bif of greenland but are less positive on average this overall trend of decreasing average 56fe values through time likely records an overall increasing trend of oxygenation of the archean surface ocean from 3 8 to 2 45 billion years ago

early archaean zircon ages from orthogneisses and anorthosites at mount narryer western australia abstract u th pb isotopic analyses have been made with an ion microprobe of 20 30 m areas within zircons from gneisses adjacent to the mount narryer quartzite western australia in which detrital zircons up to 4200 ma old have been found the cores of the zircons yield protolith crystallization ages of 3678 6 ma 95 confidence limits for the meeberrie banded monzogranite gneiss and 3381 22 ma for the dugel syenogranite leucogneiss in agreement with observed intrusive relationships zircons from inclusions of deformed leucogabbro and meta anorthosite within the dugel gneiss formerly part of the manfred layered igneous complex are 3730 6 ma old the remnants of the manfred complex are therefore the oldest rocks currently known on the australian continent analyses of discrete post magmatic grains and of overgrowths on older grains indicate an episode of subsolidus zircon growth in the region at 3296 4 ma which is interpreted as a time of local metamorphism of the gneisses subsequently the zircons have been rounded and embayed and have lost radiogenic pb in both ancient and recent times all the zircon ages determined in this study are within the age range for detrital zircons in the mount narryer quartzite it is therefore possible that these felsic gneisses and anorthositic rocks were a local source for some of the sedimentary material however the lateral extent of this early archaean terrain and the source rocks for the rare 4100 4200 ma old zircons in the metasediments are yet to be determined

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

radiocarbon dating of irish sea sediments abstract radiocarbon dating has been carried out on three cores from areas of muddy sediments in the n irish sea to estimate rates of sediment accumulation 14c age profiles of the two eastern basin cores revealed a near constant age from the sediment surface to the base of the core 12 500 1000 years bp the 14c age profile of the western basin core revealed a zone of apparent mixing to a depth of 55 cm underlain by a zone of constant sedimentation rate 0 018 cm y 1 to 160 cm these data are discussed in relation both to previously reported sedimentological studies of the area and to the authorised discharges of low level radioactive waste from the sellafield nuclear fuel reprocessing plant

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

microfossil like objects from the archaean of greenland a cautionary note recent reports1 4 have described yeast like microfossils isuasphaera isua pflug2 in 3 800 myr old5 metaquartzites from the isua supracrustal belt of south west greenland a biogenic interpretation of these objects is inconsistent with the tectonic history of the isua region6 8 with the petrology of the metaquartzites and with the morphology of the microstructures themselves the putative microfossils are indistinguishable from limonite stained fluid inclusions microstructures which are demonstrably inorganic and post depositional in origin as such we contend here that these objects should not be regarded as evidence of early archaean life forms

the control of precursor brittle fracture and fluid rock interaction on the development of single and paired ductile shear zones abstract ductile shear zones can occur as relatively isolated single structures as arrays or as characteristic paired zones in continuous glaciated exposures of metagranodiorites from the tauern window eastern alps the control of initial dilatant brittle fracture and associated fluid rock interaction on the geometry of subsequent ductile shear zones can be unequivocally established shearing occurred under amphibolite facies conditions fractures in weakly deformed metagranodiorites are often less than 1 mm thick but extend for tens of metres many are healed joints without shear offset others show minor mm cm discrete dextral offset such brittle faults commonly display a low angle en echelon arrangement with displacement transferred between discrete fracture segments by ductile compressive bridges the geometry of more strongly reactivated zones depends on the degree and heterogeneity of fluid rock interaction which is related to fluid infiltration and veining along the primary fractures with little fluid rock interaction reactivation produces single heterogeneous ductile shear zones centred on and immediately flanking the pre existing fracture with increased fluid rock interaction a bleached halo is developed symmetrically to either side of a central epidote quartz garnet calcite vein ductile shear zones commonly flank this bleached zone to develop a characteristic paired pattern strain is partitioned localizing in the central fracture vein and the flanking shear zones paired zones may anastomose in accordance with changes in the width of the central bleached zone but are always symmetrically spaced with regard to the central fracture vein with increasing deformation the ductile shear zones broaden into the adjacent metagranodiorite but not into the bleached zone which remains preserved as a low strain region paired shear zones can also develop to either side of aplite dykes examples of characteristic paired shear zones usually with a clear central vein are found in many areas ranging from greenschist to eclogite facies suggesting that the mechanism of their formation is quite general

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

transition from orogen perpendicular to orogen parallel exhumation and cooling during crustal indentation key constraints from 147sm 144nd and 87rb 87sr geochronology tauern window alps abstract the core of the alpine orogen in the eastern alps tauern window experienced a change from orogen normal shortening and post nappe doming to predominantly orogen parallel extension and tectonic unroofing during late oligocene to miocene northward indentation of the adriatic microplate a new 147 sm 144 nd isochron age of 25 7 0 9 ma on a garnet bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the tauern window indicates that high temperatures related to post nappe barrovian type metamorphism overlapped in time with the onset of doming new 87 rb 87 sr biotite ages from this same complex combined with previously published 87 rb 87 sr white mica ages suggest that doming and exhumation began no later than 28 ma immediately in front of indenting austroalpine crustal blocks then migrated laterally to the ese during rapid exhumation and orogen parallel stretching beginning at about 23 ma rapid cooling ended at approximately 17 ma in the footwall of the katschberg normal fault which delimits the eastern margin of the tauern window a similar pattern of migrating doming orogen parallel extension and cooling is recognized in the western part of the tauern window where rapid exhumation began at about 20 ma some 2 3 ma later than in the eastern part this difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the tauern window are attributed to fragmentation of the aforementioned austroalpine blocks along the leading edge of the main adriatic indenter southern alps as this indenter advanced to the north

in situ sr isotope analysis of mantle carbonates constraints on the evolution and sources of metasomatic carbon bearing fluids in a paleo collisional setting abstract carbonate bearing wedge peridotites attest the mobilization of carbon c by slab fluids melts circulating in a subduction setting in general coh fluids are thought to derive from the dehydration partial melting of the crustal portions of slabs especially during the exhumation of crust mantle melanges along continental subduction channels in this study we combined textural observations with in situ sr isotope analyses of mantle carbonates occurring in different microstructural sites to test whether the fluids responsible for the carbonation of a mantle wedge are derived from the subducted continental crust or not we focus on the ulten zone peridotites eastern italian alps associated with high grade felsic rocks where carbonates occur mainly as dolomite and minor magnesite and calcite in situ laser mc icp ms analysis of peridotites representing different episodes of a complex metasomatic history indicates that sr isotopic variations can be linked to the different microstructural positions of carbonates the c metasomatism of the uz peridotites is proposed to have occurred in two stages the first stage is the hp carbonation at peak eclogite facies conditions with formation of interstitial matrix dolomite in textural equilibrium with hornblende to pargasite amphibole and cl apatite this dolomite exhibits relatively unradiogenic 87sr 86sr present day values of 0 70487 0 00010 requiring different sources with respect to the associated migmatites and the overhanging mantle wedge carbonation continued during exhumation with local injection of c rich fluids forming a dolomite vein in association with tremolite and chlorite the dolomite vein shows a wide range of 87sr 86sr 0 7036 0 7083 reflecting both the primary composition of carbonates and the consequent interaction with crustal fluids as expected in a crust mantle melange the second stage is c remobilization by dolomite dissolution and precipitation of brucite intergrowths with calcite during the final exhumation this remobilization event has resulted in a similar sr composition to the precursor dolomite the mantle wedge is therefore capable of storing carbonates which have been shown to represent a complex metasomatic evolution from eclogite facies conditions to very shallow structural levels therefore fluids released from subducting slabs of continental lithosphere might be responsible for the crystallization of metasomatic minerals such as amphibole phlogopite and zircon in the overlying ultramafic rocks conversely the role of these metasomatic fluids on the carbonation of mantle wedge is likely overestimated the combination of geochemical isotopic and textural evidence suggests that dolomite inclusions and interstitial dolomite are derived in large part from a distinct source of c bearing fluids that could be related to depleted mantle wedge sources and or trondhjemitic igneous activity in contrast at the end of exhumation residual coh fluids released by the associated stromatic gneisses and orthogneisses resulted in late stage dolomite veins having the highest sr isotope values in the ulten zone peridotites

highly siderophile element abundances in eoarchean komatiite and basalt protoliths plume derived mg rich volcanic rocks komatiites high mg basalts and their metamorphic equivalents can record secular changes in the highly siderophile element hse abundances of mantle sources an apparent secular time dependent enrichment trend in hse abundances from paleoarchean to paleoproterozoic mantle derived rocks could represent the protracted homogenization of a late veneer chondritic contaminant into the pre late veneer komatiite source to search for a possible time dependence of a late accretion signature in the eoarchean mantle we report new data from rare 3700 myr old mafic and ultramafic schists locked in supracrustal belts from the inukjuak domain quebec canada and the akilia association west greenland our analysis shows that some of these experienced hse mobility and or include a cumulate component touboul et al in chem geol 383 63 75 2014 whereas several of the oldest samples show some of the most depleted hse abundances measured for rocks of this composition we consider these new data for the oldest documented rocks of komatiite protolith in light of the late veneer hypothesis

jura alps and the boundary of the adria subplate abstract the thin skinned jura fold thrust belt is the frontal part of a thick skinned late miocene alpine nappe important late miocene structures in the alps that help define this nappe are the external massifs in the north the orobic thrusts and the piemontese southern alps in the south the giudicarie brenner line in the east and more vaguely the south end of the belledonne massif in the west a bottom boundary compatible with the data is the brittle ductile transition bdt this jura nappe is separated from the latest oligocene early miocene helvetic nappe system most obviously by the late miocene orobic giudicarie brenner fault complex in contrast the distinctive boundary of the early miocene thick skinned helvetic nappe was the iorio tonale line it in the south merging into the piemontese southern alps at what may be termed the locarno singularity the point of minimum width of the thick skinned alps the northern boundary passed through the gotthard and montblanc massifs motion along the southern boundary was dextrally transpressive associated with complex strain partitioning patterns one part of these patterns is the confusing entity comprising the piemontese southern alps and the lepontine dome the slivers composing the piemontese southern alps are dragged dextrally by the iorio tonale strike slip at the locarno singularity and thereby exhibit an important characteristic trait of exotic terranes crustal slivers dragged along strike slip faults the lepontine dome around the locarno singularity on the north side of the iorio tonale line displays the characteristics of a backstop in thrust systems as modeled in sandbox experiments the special boundary functioning as a backstop compatible with the transpressive kinematics was the ivrea body a strong mafic ultramafic granulitic complex which in the early miocene migrated dextrally along the iorio tonale line forcing detachment to descend into the hot middle crust and producing an upsurge of the hot masses in the late miocene jura phase this particular impediment had moved to the west enabling decollement at the brittle ductile transition to propagate across the insubric line into the lombardic domain large scale strain partitioning manifestations resemble those of the equally dextrally transpressive southern boundary of the caribbean plate in spite of a difference in scales the foremost of these manifestations are regional right slip faults slicing through a broad band of contraction accompanied by collapse basins

sediment exchanges between the seine estuary and its adjacent shelf the study of sediment dynamics within the seine estuary and its adjacent shelf permits some conclusions regarding sediment exchanges in this coastal zone on the shelf sediment transport is directed toward the seine estuary and contributes to the infilling of the estuary by marine sands and muds these were originally derived from land carried to the shelf at times of lower sea level and subsequently transported shoreward by dominant tidal and wave induced currents in the estuarine section tidal processes form a turbidity maximum both by inducing strong bed resuspension and by trapping fluvial and marine sediments due to flood current predominance occasionally this turbid zone extends seaward during periods of river floods and sediment is redispersed onto the shelf this phenomenon has been amplified by man made modifications of the estuarine morphology however currents patterns tend to retard the natural seaward escape of fluvial material mainly due to dredging operations at the present time thus man has changed the natural role of the estuary from a sink to a source of fluvial sediments for the shelf a tentative sedimentary budget is proposed taking into account the various sources of material and the complexity of sediment dynamics

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

k ar and ar ar dating the aim of this chapter is to present the k ar and ar ar dating techniques in the context of noble gas studies since there are already several recent texts on k ar and ar ar dating dickin 1995 mcdougall and harrison 1999 the focus of this section will be aspects of argon transport and storage in the crust which affect k ar and ar ar dating including ar loss from minerals by diffusion and ar gain by minerals or excess argon the k ar dating technique was one of the earliest isotope dating techniques developed soon after the discovery of radioactive potassium and provided an important adjunct to u pb and u he dating techniques the ease of measurement and ideal half life 1250 million years see table 2 below for dating geological events has made this the most popular of isotopic dating techniques aldrich and nier 1948 first demonstrated that 40ar was the product of the decay of 40k and soon after k ar ages were being measured in several laboratories most often using an absolute method such as a mcleod gauge to measure argon concentrations the first published k ar results by such a technique were those of smits and gentner 1950 who analyzed sylvite from the buggingen oligocene evaporite deposits obtaining an age of 20 million years mass spectrometers which simultaneously measured very small amounts of gas and the isotope ratios necessary to make corrections for atmospheric contamination quickly replaced manometric techniques crucially the use of static vacuum techniques pioneered by john reynolds at the university of california berkeley meant that mass spectrometers were sufficiently sensitive to analyse the small amounts of gas released from common rocks and minerals although the earliest mass spectrometers were built in house the introduction of the commercially available ms10 farrar et al 1964 a small 180 metal mass spectrometer built for

crustal structure of the eastern alps along the transalp profile from wide angle seismic tomography abstract the objective of the transalp project is an investigation of the eastern alps with regard to their deep structure and dynamic evolution the core of the project is a 340 km long seismic profile at 12 e between munich and venice this paper deals with the p wave velocity distribution as derived from active source travel time tomography our database consists of vibroseis and explosion seismic travel times recorded at up to 100 seismological stations distributed in a 30 km wide corridor along the profile in order to derive a velocity and reflector model we simultaneously inverted refractions and reflections using a derivative of a damped least squares approach for local earthquake tomography 8000 travel time picks from dense vibroseis recordings provide the basis for high resolution in the upper crust explosion seismic wide angle reflection travel times constrain both deeper crustal velocities and structure of the crust mantle boundary with low resolution in the resulting model the adriatic crust shows significantly higher p wave velocities than the european crust the european moho is dipping south at an angle of 7 the adriatic moho dips north with a gentle inclination at shallower depths this geometry suggests s directed subduction azimuthal variations of the first break velocities as well as observations of shear wave splitting reveal strong anisotropy in the tauern window we explain this finding by foliations and laminations generated by lateral extrusion based on the p wave model we also localized almost 100 local earthquakes recorded during the 2 month acquisition campaign in 1999 seismicity patterns in the north seem related to the inn valley shear zone and to thrusting of austroalpine units over european basement the alignment of deep seismicity in the trento vicenza region with the top of the adriatic lower crust corroborates the suggestion of a deep thrust fault in the southern alps