sedimentology and c isotope geochemistry of the sturtian cap carbonate south australia abstract a combined sedimentary and isotopic analysis of the sturtian aged tindelpina cap carbonate in south australia has revealed a strong relationship between sedimentary facies and 13 c carb depositional water depths for the cap carbonate are difficult to constrain however a lack of diagnostic shallow water structures and the inferred magnitude of post glacial transgression several 100 m indicates a relatively deep water environment for each key facies the shallowest facies peloidal dolomite has 13 c values ranging between 3 6 and 0 3 in comparison to deeper water laminated limestones which have lighter values ranging between 5 5 and 3 5 equivalent calcareous shales deposited at basinal depths show even more 13 c depletion with values ranging between 6 7 and 3 7 the average difference in 13 c between the shallowest and deepest cap facies is up to 3 6 and may be an approximation of the seawater 13 c depth gradient at the time of deposition we interpret this high 13 c depth gradient as the result of prolonged physical ocean stratification both during and after deglaciation variations in the rates of upwelling mixing under this stratified regime may have significantly influenced the climate as well as controlling the precipitation and isotopic composition of the cap carbonate

a sedimentary prelude to marinoan glaciation cryogenian middle neoproterozoic keele formation mackenzie mountains northwestern canada abstract continental margin deposition between the sturtian and marinoan aged global glacial periods is represented in nw canada by a siliciclastic to carbonate grand cycle the keele formation a 300 600 m thick carbonate and siliciclastic deposit comprises the upper part of this interglacial cycle sedimentary facies in the lower carbonate dominated member of the keele span a broad spectrum of depositional environments from below storm wave base to peritidal to continental and are disposed across a relatively narrow paleogeographic belt lateral arrangement of facies and the gradual stratigraphic transitions between them suggest deposition in a ramp setting local slump structures and occasional debrites in deep water facies imply that the ramp was distally steepened fluvial facies are concentrated at a single locality indicating that terrigenous clastic sediment was derived from a point source or sources most strata of the carbonates are bahamian in character and similar to phanerozoic warm water carbonates in that they contain abundant calcite ooids of interpreted original aragonitic mineralogy and have well developed muddy peritidal facies nevertheless close juxtaposition of deep and shallow water facies in keele rocks indicates high amplitude sea level change during deposition on the order of 100 m suggesting accumulation in a climatic icehouse period this interpretation implies that although the globe possessed polar and high altitude glaciers at this time sea surface temperature at least at tropical latitudes warmed dramatically between neoproterozoic glacial episodes the onset of marinoan glaciation here is heralded by an abrupt shift to nearshore marine siliciclastic sedimentary rocks these deposits form the upper member of the keele formation informally called the keele clastic wedge and directly underlie ice brook formation diamictites carbonates are rare and are restricted to mudstones and flat pebble conglomerates that lack any indication of tropical conditions

qc qβ qi and qs attenuation parameters in the umbria marche italy region the attenuation of coda and s waves has been inferred for the umbria marche region central italy using seismic waveforms collected during the 1997 seismic crisis the selected dataset is composed of 343 small magnitude 1 4 ml 4 2 earthquakes recorded at a temporary array composed of 23 seismic stations the sato 1977 method based on the assumption of single isotropic scattering has been used to infer qc considering three different lapse times 20 30 and 40 s the coda normalization method aki 1980 has been used to infer q both qc and q show a clear frequency dependence with a different frequency dependent parameter the frequency dependence of qc is comparable with that previously found in the same area and around it using the method of wennerberg 1993 intrinsic and scattering attenuation have been separated intrinsic attenuation is found to be close to coda attenuation and dominates over scattering dissipation coda q increases with increasing lapse time but at a rate smaller than that observed in other areas of the earth coda and intrinsic attenuation in the umbria marche region are very high compared to other seismic active regions of the earth the retrieved high values of intrinsic attenuation may be explained in terms of the previously hypothesized fluid pressurized regime of the crust in the central apennines miller et al 2004

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

grenvillian granulite facies metamorphism in the arequipa massif peru a laurentia gondwana link abstract the arequipa massif is a major component of the central andean orogenic basement extensively exposed along the coast of southern peru in the vicinity of the arica bight and bolivian orocline the southern part of the massif is dominated by granulitic gneisses for which a ca 1900 ma age for metamorphism of a slightly older protolith has been accepted on the basis of rb sr whole rock isochrons and bulk u pb zircon dating new u pb single grain zircon geochronology however reveals two mesoproterozoic granulite facies domains 1200 ma to the ne of quilca 16 44 s 72 24 w and 970 ma in the vicinity of mollendo 16 58 s 72 03 w these ages correspond to the major metamorphic events represented in the grenville province of north america and lend credence to proposed reconstructions based on sparse isotopic data that grenvillian metamorphic belts underlie the western margins of south american cratons and constituted the conjugate rifted margin of eastern laurentia the protolith ages of the samples further substantiates the proposed neoproteozoic reconstruction in both domains of the massif the orthogneisses have zircon upper intercept ages of about 1950 ma and the paragneisses contain younger detrital zircons suggesting sedimentation in the early mesoproterozoic correlative zircon ages are found in the makkovik ketilidian belt and the adjacent trans labrador batholith of eastern laurentia the arequipa massif is therefore envisaged to represent an exotic terrane that originated as the tip of a pre grenville laurentian promontory comprising labrador greenland and scotland that was embedded into the proto andean margin during the grenville orogeny

u pb shrimp zircon dating of grenvillian metamorphism in western sierras pampeanas argentina correlation with the arequipa antofalla craton and constraints on the extent of the precordillera terrane abstract metamorphism of grenvillian age ca 1 2 ga u pb zircon dating is recognized for the first time in the western sierras pampeanas sierra de maz conditions reached granulite facies ca 780 c and ca 780 mpa comparing geochronological and petrological characteristics with other outcrops of mesoproterozoic basement particularly in the northern and central arequipa antofalla craton we suggest that these regions were part of a single continental crustal block from mesoproterozoic times and thus autochthonous or parautochthonous to gondwana

adria seismicity and seismotectonics review and critical discussion abstract we review the most recent advances in research on the seismicity and seismotectonics of adria a large number of earthquakes associated with this lithospheric block occur near the adria boundaries and seismicity has been perhaps the first dataset to allow its identification as a specific lithospheric block adria also hosts significant intraplate seismicity mostly concentrated in specific zones of intraplate brittle deformation the most important being a deformation belt located at the central adriatic latitude and including the gargano promontory and the tremiti islands after a brief excursus on adria seismicity we address some relevant research points and open questions answers to such questions and more in general advances in research on adria seismotectonics and seismicity will not only provide invaluable information for the seismic hazard assessment of this region but also a precious tool to understand the current geodynamics of the central mediterranean

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

continental flood basalt weathering as a trigger for neoproterozoic snowball earth abstract atmospheric co2 levels and global climate are regulated on geological timescales by the silicate weathering feedback however this thermostat has failed multiple times in earth s history most spectacularly during the cryogenian c 720 635 ma snowball earth episodes the unique middle neoproterozoic paleogeography of a rifting low latitude supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo under these primed conditions the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios 13 c of neoproterozoic seawater due to their elevated p contents in order to test these hypotheses we have compiled new and previously published neoproterozoic nd isotope data from mudstones in northern rodinia north america australia svalbard and south china and sr isotope data from carbonate rocks the nd isotope data are used to model the mafic detrital input into sedimentary basins in northern rodinia the results reveal a dominant contribution from continental flood basalt weathering during the ca 130 m y preceding the onset of cryogenian glaciation followed by a precipitous decline afterwards these data are mirrored by the sr isotope record which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early middle neoproterozoic ocean including a pulse of unradiogenic sr input into the oceans just prior to the onset of cyrogenian glaciation hence our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average 13 c of seawater in the neoproterozoic and to the initiation of the first sturtian snowball earth

the amazon laurentian connection as viewed from the middle proterozoic rocks in the central andes western bolivia and northern chile middle proterozoic rocks underlying the andes in western bolivia western argentina and northern chile and early proterozoic rocks of the arequipa massif in southern peru form the arequipa antofalla craton these rocks are discontinuously exposed beneath mesozoic and cenozoic rocks but abundant crystalline clasts in tertiary sedimentary rocks in the western altiplano allow indirect samples of the craton near berenguela western bolivia the oligocene and miocene mauri formation contains boulders of granodiorite augen gneiss 1171 20 ma and 1158 12 ma u pb zircon quartzose gneiss and granofels that are inferred to have arkosic protoliths 1100 ma source region u pb zircon quartzofeldspathic and mafic orthogneisses that have amphibolite and granulite facies metamorphic mineral assemblages 1080 ma metamorphism u pb zircon and undeformed granitic rocks of phanerozoic age the middle proterozoic crystalline rocks from berenguela and elsewhere in western bolivia and from the middle proterozoic belen schist in northern chile generally have present day low 206pb 204pb 15 57 and elevated 208pb 204pb 37 2 to 50 7 indicative of high time averaged th u values the middle proterozoic rocks in general have higher present day 206pb 204pb values than those of the early proterozoic rocks of the arequipa massif 206pb 204pb between 16 1 and 17 1 but lower than rocks of the southern arequipa antofalla craton 206pb 204pb 18 5 a difference inferred to reflect grenvillian granulite metamorphism the pb isotopic compositions for the various proterozoic rocks lie on common pb isotopic growth curves implying that pb incorporated in rocks composing the arequipa antofalla craton was extracted from a similar evolving pb isotopic reservoir evidently the craton has been a coherent terrane since the middle proterozoic moreover the pb isotopic compositions for the arequipa antofalla craton overlap those of the amazon craton thereby supporting a link between these cratons and seemingly precluding part of the arequipa antofalla craton from being a detached fragment of another craton such as eastern laurentia which has been characterized by a different u pb history pb isotopic compositions for the arequipa antofalla craton are furthermore distinct from those of the proterozoic basement in the precordillera terrane western argentina indicating a pb isotopic and presumably a tectonic boundary between them the pb isotopic compositions for the precordillera basement are similar to those of eastern laurentia and support other data indicating that these rocks are a detached fragment of north america finally the distinct pb isotopic evolution history of the arequipa antofalla craton and eastern laurentia require minor modification to tectonic models linking eastern north america scotland to the oroclinal bend in western south america

nanhuan manganese deposits within restricted basins of the southeastern yangtze platform china constraints from geological and geochemical evidence abstract the nanhuan manganese deposits in the southeastern yangtze platform occur in the black shale series in the lower part of the datangpo formation in order to constrain the genesis of the deposits a detailed study was undertaken that involved field observations major and trace element analyses organic carbon analyses and isotope analyses c o s the major findings are as follows 1 the ore bearing rock series morphology of the ore bodies and characteristics of ores in several deposits are similar the ore minerals are rhodochrosite and manganocalcite the gangue minerals are mainly quartz feldspar dolomite and illite minor apatite and bastnaesite occur in the manganese ores 2 the ores are enriched in ca and mg whereas they are depleted in si al k and ti compared to wall rocks the ores normalized to average post archean australian shale paas are enriched in co mo and sr the chondrite normalized rare earth element ree patterns for ores and wall rocks are between those of typical hydrogenous and hydrothermal type manganese deposits additionally the ores have positive ce anomalies with an average ce ce of 1 23 and positive eu anomalies with an average eu eu of 1 18 normalized to paas 3 the average content of organic carbon is 2 21 in the samples and the average organic carbon isotopic value 13cv pdb is 33 44 the average inorganic carbon isotopic value 13cv pdb of carbonates in gucheng is 3 07 while the values are similar in the other deposits with an average of 8 36 the oxygen isotopic compositions 18ov pdb are similar in different deposits with an average of 7 72 4 the sulfur isotopic values 34sv cdt of pyrite are very high and range from 37 9 to 62 6 average of 52 7 which suggests that the pyrite was formed in restricted basins where sulfate replenishment was limited the sulfate concentrations in the restricted basins were extremely low and enriched in 34s which resulted in the very high 34s values for the pyrite that formed in the manganese deposits therefore a terrigenous weathering origin for manganese can be excluded otherwise the sulfate would have been introduced into the basins together with terrigenous manganese which would have decreased the 34s values of pyrites the manganese which originated from hydrothermal processes was enriched in the restricted and anoxic basins and then it was oxidized to manganese oxyhydroxide in the overlying oxic waters whereby the products precipitated into the sediments the manganese oxyhydroxide in the sediment was then reduced to mn2 and released to the pore waters during the process of diagenesis some organic carbon was oxidized to co32 which made the depletion of 13c in manganese carbonates therefore we suggest that the nanhuan manganese deposits are hydrothermal sedimentary diagenetic type deposits

two diamictites two cap carbonates two δ13c excursions two rifts the neoproterozoic kingston peak formation death valley california stratigraphic mapping of the neoproterozoic glaciogenic kingston peak formation death valley california provides evidence for two temporally discrete extensional deformation episodes these episodes are bracketed by the sourdough limestone and noonday dolomite the facies characteristics and 13 c data ranging between 2 15 and 2 56 and 1 88 and 4 86 respectively of which make them equivalent to sturtian and varangian age cap carbonates respectively this constrains the two extensional episodes along the southwestern margin of laurentia to ca 700 ma and ca 600 ma these observations and data show that the field evidence for mid neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest neoproterozoic breakup are both correct thus neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m y or more confining rifting to within the kingston peak formation thereby places the younger proterozoic rocks of the southwestern great basin in the rift to drift tectonic phase

a critical revision of the seismicity of northern apulia adriatic microplate southern italy and implicationsfor the identification of seismogenic structures abstract northern apulia is an emerged portion of the adriatic microplate representing the foreland foredeep area of a stretch of the apennine chain in southern italy the interaction between the relatively rigid microplate and the contiguous more deformable domains is responsible for the intense seismicity affecting the chain area however strong sometimes even disastrous earthquakes have also hit northern apulia on several occasions the identification of the causative faults of such events is still unclear and different hypotheses have been reported in literature in order to provide guidelines and constraints in the search for these structures a comprehensive re examination and reprocessing of all the available seismic data has been carried out taking into consideration 1 the characteristics of historical events 2 the accurate relocation of events instrumentally recorded in the last 20 years 3 the determination of focal mechanisms and of the regional stress tensor the results obtained bring to light a distinction between the foreland and foredeep areas in the first region there is evidence of a regional stress combining nw compression and ne extension thus structures responsible for major earthquakes should be searched for among strike slip faults possibly with a slight transpressive character these structures could be either approximately n s oriented sinistral or e w dextral faults in the foredeep region there is a transition toward transtensive mechanisms with strikes similar to those of the previous zone or maybe also towards nw oriented normal faults more similar to those prevailing in the southern apennine chain in relation to a dominant ne extension this appears to be the effect of a reduction of the nw compression probably due to a decrease in efficiency of stress transmission along the more tectonised border of the adriatic microplate

origin of cap carbonates an experimental approach abstract an experimental study was carried out to assess the abiotic natural reactions associated with carbonate precipitation leading to the formation of neoproterozoic cap carbonate sequences for this purpose synthetic seawater solutions were prepared reflecting the presumed composition of neoproterozoic seawater these solutions were heated to 40 c undergoing degassing and or evaporation while monitoring their chemical composition sulphate concentration mg ca molar ratio and identifying the precipitated minerals the experimental results are in good agreement with previous studies allowing us to constrain the type of carbonate precipitates formed in the ocean during the snowball earth aftermath among the phases precipitated during heating of the solutions mg bearing carbonate minerals i e mg calcite magnesite and dolomite remain of minor importance compared to ca carbonates especially aragonite consequently the basal dolostone units of the cap carbonates i e cap carbonates s s were originally in the form of caco3 and evolved spontaneously toward dolomite cap carbonates s l i e cap limestones containing aragonitic cement could result from the degassing of the whole ocean and the concomitant precipitation of aragonite the calculated thicknesses of carbonates formed in this way are of the order of several metres in line with the field observations although this process of abiotic carbonate precipitation does not rule out biologically mediated carbonate formation it may represent an alternate route to produce carbonate particularly in environments which are not yet colonized by bacteria after the global ice melting

absorption and scattering 2 d volcano images from numerically calculated space weighting functions acknowledgments yosuke aoki and an anonymous reviewer greatly improved the quality of the paper all calculations were made with mathematica 10tm discussions with marie calvet danilo galluzzo mario la rocca salvatore de lorenzo jessie mayor and ludovic margerin are gratefully acknowledged the authors are supported by medsuv european project and by spanish project ephestos cgl2011 29499 c02 01 and nowaves tec2015 68752 the tides eu travel cost action provided travel money to support cooperation between luca de siena and the other authors

neoproterozoic a type magmatism in the western sierras pampeanas argentina evidence for rodinia break up along a proto iapetus rift a type orthogneisses of mid neoproterozoic age 774 6 ma u pb shrimp zircon age are reported for the first time from the grenvillian basement of the western sierras pampeanas in argentina these anorogenic meta igneous rocks represent the latest event of rodinia break up so far recognized in grenvillian basement exposures across andean south america moreover they compare well with a type granitoids and volcanic rocks along the appalachian margin of laurentia blue ridge thus adding to former evidence that the western sierras pampeanas grenvillian basement was left on the conjugate rifted margin of eastern laurentia during rodinia break up and the consequent opening of the iapetus ocean

correlation of sturtian diamictite successions in southern australia and northwestern tasmania by re os black shale geochronology and the ambiguity of sturtian type diamictite cap carbonate pairs as chronostratigraphic marker horizons recent geochronological studies have raised concerns regarding the accuracy of regional and global correlations of neoproterozoic sedimentary successions using relative dating methods such as carbon isotope chemostratigraphy and glaciogenic diamictite cap carbonate lithological and geochemical characteristics precise and accurate radio isotopic age constraints for neoproterozoic sedimentary rocks thus remain a high priority for establishing a reliable neoproterozoic chronostratigraphy here we present a new re os age of 640 7 4 7 ma from black shales of the upper black river dolomite togari group northwestern tasmania that represents a minimum age for deposition of the immediately underlying diamictite bearing julius river member the upper black river dolomite re os age is statistically identical to a re os age of 643 0 2 4 ma previously determined for the sturtian post glacial tindelpina shale member umberatana group adelaide rift complex southern australia consistent with previous lithostratigraphic and stromatolite biostratigraphic evidence the re os ages suggest broadly coeval deposition of the julius river member and sturtian diamictites and overlying organic rich marine shales consideration of the neoproterozoic geochronological database suggests that sturtian type diamictite cap carbonate pairs cannot be used as chronostratigraphic marker horizons for global correlation of the neoproterozoic rock record

early paleozoic accretionary orogenies in nw argentina growth of west gondwana abstract two early paleozoic orogenic cycles in the gondwana margin of nw argentina were driven by subduction and interrupted by collision of continental ribbons of laurentian affinity subduction started at the passive margin of gondwana possibly in response to the end of amalgamation of the supercontinent the passive margin was underlain by a hyper extended continent ocean transition and low angle subduction gave rise to a wide and hot fore arc region during the pampean orogenic cycle the arrival of the first continent ribbon ended the pampean cycle steepened the subduction further heating the fore arc and restarting arc magmatism after a magmatic lull 250 300 km trenchwards initiating the famatinian orogenic cycle this cycle started with a 30 ma long period of extension and marine sedimentation followed by the arrival of the second continent ribbon and inversion the back arc initiating a 20 ma long shortening event culminating with the shutting down of the arc this event gave rise to a 300 km wide low topography hot orogeny thus the many peculiarities of the two paleozoic orogens of nw argentina result from a subduction history that efficiently transferred heat to a 300 400 km wide belt of turbidite dominated sediments that was first part of the pampean fore arc and then part of the famatinian retroarc developed at the extended continental margin of gondwana the two orogenies with continued high heat flux lasted 110 ma giving rise to two calc alkaline arcs separated by a 300 km belt of high t low p migmatites and peraluminous granites formed by anatexis of sediments deposited on the passive margin as well as those deposited in the wide pampean fore arc these turbidite dominated sequences were metamorphosed and melted to form a continental crystalline basement and accreted to the cratonic margin adding 500 km of crystalline rocks to the margin of gondwana at the same time that a similar process was happening in eastern australia along the same continental margin interestingly this wide accretionary orogen has now become the region where the andean system developed a wide orogeny above flat slab subduction

cuyania an exotic block to gondwana review of a historical success and the present problems abstract a review of the early history of the cuyania terrane and the numerous pioneering works of the past century provides the present robust framework of evidence supporting a derivation from laurentia travel towards gondwana as an isolated microcontinent and final amalgamation to the protomargin of western gondwana in middle to late ordovician times the major remaining uncertainties and inconsistencies such as the time of deformation and collision with gondwana the lack of evidence of famatinian derived zircons the effects of strike slip displacements proposed along the suture as well as the potential sutures defined by ophiolite assemblages are discussed the precise boundary along the northern and southern limits is not yet well defined the most suitable hypothesis based on present data is that cuyania originated as a conjugate margin of the ouachita embayment south of the appalachian platform during early cambrian times the subsequent travel toward the gondwana protomargin is clearly depicted by the changing faunal assemblages in the carbonate platform new geochemical and age data on k bentonites presented by several authors reinforce the strong connection between cuyania ash fall tuffs and famatina volcanics by 468 470 ma indicating cuyania and gondwana were in close proximity at that time extension related to flexural subsidence preceded by the drowning of the carbonate platform in early llanvirnian times is recorded by abrupt facies changes in the sedimentary cover during late llanvirnian and early caradocian times this episode marked the beginning of contact between cuyania and gondwana the subsequent evolution of the foreland basin indicates that deformation lasted until latest silurian early devonian times the time of collision is tracked by the cessation of arc related magmatic activity in the upper plate gondwana protomargin at about 465 ma in western sierras pampeanas and ages around 454 ma corresponding to syncollisional and postcollisional magmatism the age of the collision is also preserved in the lower plate cuyania where both angular unconformities in the sedimentary cover and the ages of peak of regional metamorphism in the basement rocks point to 460 ma as the most probable age for the beginning of the collision evidence from the upper plate is essentially identical with an age of 463 ma thermal gradients along this suture vary from 13 c km in the lower plate to 18 c km in the fore arc upper plate reaching more than 30 c km along the famatinian arc based on these data a llandelian caradocian age for the collision can be postulated on firm grounds deformation continued through most of the early paleozoic until amalgamation of the chilenia terrane by the late devonian

intrinsic and scattering attenuation from observed seismic codas in the almeria basin southeastern iberian peninsula summary the anelastic attenuation in the almeria basin southeastern iberian peninsula is investigated by using seismic data collected during the summer of 1991 a multiple lapse time window analysis is applied to high frequency seismograms corresponding to 20 shallow seismic events with low magnitudes m 12 5 and distances less than 71 km recorded at six short period seismographic stations we have constructed corrected geometrical spreading and normalized energy distance curves for the region over the frequency bands 1 2 2 4 4 8 8 14 and 14 20 hz a theoretical model for body wave energy propagation in a randomly heterogeneous medium has been employed to interpret the observations two parameters describe the medium in this model the scattering attenuation coefficient qs kq3 and the intrinsic attenuation coefficient yi kq where k is the wavenumber and qr1 and q are the intrinsic and scattering attenuation respectively this model assumes that scattering is isotropic including all orders of multiple scattering and predicting the spatial and temporal energy distribution of seismic energy a least squares fitting procedure has been used to find the best estimates of the model parameters the analysis of the spectral amplitude decay of coda waves has provided coda q values at the same frequency bands the results obtained show that q q2 and q decrease with increasing frequency for frequencies lower than 3 hz scattering attenuation is stronger than intrinsic absorption and coda q takes values between intrinsic and total attenuation being very close to qy q is more frequency dependent than q for frequencies greater than 3 hz intrinsic absorption is the dominant attenuation effect and q and q3 have significant frequency dependence in order to correlate the results obtained with the major geological and tectonic features of the region a geotectonic framework for the area is provided and the predominant frequency decay in coda waves is analysed in order to obtain the coda q frequency dependence following a power law qc qo f fo where fo is a reference frequency in this way we have obtained regionalized values of coda q at 1 hz qo finally a first order approach has allowed us to obtain intrinsic and scattering quality factors from the obtained qo and v values leading us to obtain tentative distributions of q qs and qo at 1 hz for the area the derived intrinsic and scattering quality factor distributions are in good agreement with the tectonic history and the main geological features of the region large scattering and intrinsic attenuation qs n 80 qi 100 are found in the sedimentary neogene and quaternary basin while scattering is the dominant effect in the old palaeozoic rocks of the mountains qs 200 qi 1000 intrinsic q shows a higher sensitivity to the geological characteristics than scattering q

new insights into crustal structure cenozoic magmatism co2 degassing and seismogenesis in the southern apennines and irpinia region from local earthquake tomography we present high resolution vp and vp vs models of the southern apennines italy computed using local earthquakes recorded from 2006 to 2011 with a graded inversion scheme that progressively resolves the crustal structure from the large scale of the apennines belt to the local scale of the normal fault system high vp bodies defined in the upper crust and midcrust under the external apennines are interpreted as extensive mafic intrusions revealing anorogenic magmatism episodes that broadened on the adriatic domain during paleogene under the mountain belt a low vp region annular to the neapolitan volcanic district indicates the existence of a thermal fluid anomaly in the midcrust coinciding with a shallow moho and diffuse degassing of deeply derived co2 in the belt axial zone low vp vs gas pressurized rock volumes under the apulian carbonates correlate to high heat flow strong co2 dominated gas emissions of mantle origin and shallow carbonate reservoirs with pressurized co2 gas caps we hypothesize that the pressurized fluid volumes located at the base of the active fault system influence the rupture process of large normal faulting earthquakes like the 1980 mw6 9 irpinia event and that major asperities are confined within the high vp apulian carbonates this study confirms once more that preexisting structures of the pliocene apulian belt controlled the rupture propagation during the irpinia earthquake the main shock broke a 30 km long ne dipping seismogenic structure whereas delayed ruptures both the 20 s and the 40 s subevents developed on antithetic faults reactivating thrust faults located at the eastern edge of the apulian belt

separation of intrinsic and scattering seismic attenuation in the southern apennine zone italy summary scattered waves observed at the seismographs of the national italy s seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the southern apennines italy first we investigate the coda q properties then we apply the mltw analysis in the hypothesis of velocity and scattering coefficient constant with depth and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient results obtained in the hypothesis of a uniform model show that a low scattering q 1 and a relatively higher intrinsic q 1 characterize the lithosphere of the southern apennines numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle both with reasonable intrinsic dissipation coefficients in these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values this results lead to the consideration that scattering q 1 obtained using mltw analysis under the assumption of uniform medium are overestimated the values of the scattering q 1 estimated for apennines at low frequency 1 2 hz in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world the estimates obtained for frequencies ranging from 2 to 12 hz are very low if compared with those obtained in the same hypothesis for other areas around the world coda q 1 closely resembles intrinsic q 1

a major perturbation of the carbon cycle before the ghaub glaciation neoproterozoic in namibia prelude to snowball earth 1 a large 11 15 negative shift in 13c is observed in shallow water carbonates directly beneath neoproterozoic glacial deposits or correlative disconformity in northwest namibia ascribed to a snowball earth reproducibility and stratigraphic concordance of this anomaly in 16 sections across the ancient continental shelf support a primary origin and field relations show it predates the fall in sea level associated with the ghaub glaciation we crudely estimate the duration of the isotopic shift as 0 6 106 years from a simple thermal subsidence model similar or larger 13c anomalies are found directly beneath neoproterozoic glacial units in australia canada china scotland and svalbard after considering conventional interpretations for negative 13c anomalies we conclude that a prolonged methane release to the atmosphere is most consistent with the timescale magnitude and geological context of the anomaly in namibia counterintuitively an anomalous methane flux that is sustained for 100s kyr may be consistent with a snowball glaciation

filamentous fossil bacteria from the archean of western australia abstract four morphotypes of structurally preserved filamentous fossil bacteria have been discovered in petrographic thin sections of laminated carbonaceous cherts from the 3500 ma old warrawoona group of northwestern australia these tubular and septate microfossils are interpreted here as being syngenetic with warrawoona sedimentation as such they are apparently the oldest such fossils now known in the geological record the diversity of this assemblage and the evident complexity of its individual components suggest that the beginnings of life on earth may have appreciably pre dated the deposition of the warrawoona sediments

influence of global regional and local factors on the genesis of the jurassic manganese ore formation in the transdanubian range hungary abstract economically important black shale hosted manganese carbonate deposits occur in certain parts of the transdanubian range in hungary these ore deposits were formed in a short interval coinciding with the early toarcian global anoxic and mass extinction event that was associated with drastic perturbations of the oceanographic conditions during the early jurassic the transdanubian range unit was located between two ocean basins simultaneous opening of these two basins created an extensional regime resulting in a complex topography with tectonically controlled small scale basins above an attenuated continental lithosphere sluggish circulation led to the development of layered water masses in certain parts of these basins with oxygenated upper and oxygen depleted lower reservoirs this paleogeographic and paleoenvironmental setting favoured the microbially mediated accumulation of manganese and iron

manganese deposits in turkey distribution types and tectonic setting abstract manganese deposits in turkey are divided into four main groups on the basis of their age host rocks and processes of formation the first is hydrothermal hydrogenetic and rarely diagenetic type manganese deposits which are chiefly associated with radiolarian chert series these deposits occur as lenses and small ore beds within ophiolitic melanges zones of paleo tethyan karakaya and neo tethyan north anatolian and south anatolian suture belts the second is black shale hosted manganese deposits that is found in black shale calcareous shale and calciturbiditic limestone horizons of the passive margin sediments of late cretaceous age in the western taurides these deposits generally are metamorphosed to greenschist facies and include mn carbonate silicate and oxide minerals the third is volcanic arc hosted ores along the black sea margin which occur in different types of metasomatic hydrothermal and stratabound settings rock associations include upper cretaceous dacitic tuff reddish limestone marl and hemipelagic claystone the fourth is oligocene hosted ores in the thrace basin these deposits are similar to those of the paratethyan oligocene belt which occur on the eastern and northern margin of black sea and includes the chiatura georgia nikopol ukraine and varna bulgaria respectively the oligocene mn deposits of the thrace basin were formed by diagenetic replacement processes during a marine regression

a review of the famatinian ordovician magmatism in southern south america evidence of lithosphere reworking and continental subduction in the early proto andean margin of gondwana abstract along the proto pacific margin of gondwana from venezuela to northeastern patagonia the early middle ordovician famatinian orogeny was the first orogenic event following assembly of the supercontinent previous isotope studies of the igneous and meta sedimentary rocks of southwestern gondwana yield ambiguous implications for the role of juvenile mantle addition during the early crustal growth at the supercontinental margin to interpret the geological and tectonic evolution of the orogen and the magma sources in different episodes we look at evidence from a large area of southern south america including the 700 600 km type sector of the orogen in the sierras pampeanas 27 33 s the precordillera and northeastern patagonia previous geological geochemical and geochronological results are reviewed together with new u pb shrimp crystallization ages 177hf 176hf and 18o 16o data for dated zircon and whole rock sr and nd isotope compositions four geological domains are recognized in the sierras pampeanas western central eastern and foreland famatinian domains magmatism is mostly restricted to the interval 463 4 to 486 7 ma with the most intense period of emplacement between 468 and 472 ma constituting a magmatic flare up granitoid emplacement in both northeastern patagonia and the cordon de lila puna altiplano chile was effectively synchronous with that in the sierras pampeanas defining a continuous belt combined geochemical and isotopic data whole rock sr nd hf o in zircon indicate that the source of calcic metaluminous suites is the subcontinental lithosphere both mantle and mafic lower crust with variable contamination by the early paleozoic metasedimentary country rocks the lithospheric mantle involved is assumed to underlie the outcropping 1330 1030 ma age basement of the western domain which exhibits tectonic characteristics of active continental margin in the north and oceanic arc back arc in the south the latter sector is the potential source of some minor famatinian igneous rocks with less evolved isotopic compositions although a restricted asthenospheric addition cannot be discarded in this case minor peraluminous granites are spatially associated with the metaluminous sequence but major highly peraluminous batholiths occur on the eastern flank of the central domain field relations and geochemical isotopic evidence indicate that the most obvious source of these crustal melts was the very thick post early cambrian metasedimentary sequence comprising the host country rocks episodic tectono magmatic evolution of the famatinian magmatic belt in two overlapping stages is invoked to explain different characteristics in the four recognized domains in the type sector ca 474 486 ma roll back stage this is a mainly extensional interval involving asthenospheric upwelling and thinning of the subcontinental mantle full development of the marine ensialic basins and early emplacement of both metaluminous granites and highly peraluminous batholiths in the central and eastern famatinian domains trondhjemite plutons with an adakitic signature were emplaced in the foreland domain ca 468 472 ma slab break off stage steepening of the oceanic slab and arc migration to the southwest ended with slab break off due to subduction of continental crust during continental collision with the precordillera terrane this stage produced voluminous metaluminous magmatism at the western edge of the central domain the flare up episode k bentonites in the precordillera leucogranites in the western domain and scattered metaluminous and peraluminous plutons in all famatinian domains both slab roll back and break off stages developed during a high t regime typical of hot orogens although asthenospheric mantle was a necessary heat source for lithospheric melting its material contribution to the growth of early paleozoic crust was apparently very minor recycling of mesoproterozoic lithosphere including the subcontinental mantle coupled with crustal melting of early paleozoic metasedimentary sequences accounts for most famatinian magmatism comparable results from the central andes and east antarctica confirm that the early stages of the terra australis orogen in sw gondwana were dominated by lithospheric reworking processes

the survival of benthic macroscopic phototrophs on a neoproterozoic snowball earth the greatest ice ages in earth s history occurred during the 654 635 ma marinoan glaciation when glaciers reached tropical oceans and our planet approached a snowball earth condition paleontological and genomic data suggest that several eukaryotic groups must have survived the marinoan glaciation but their fossil record is scarce and limited to microbes whose ecological and physiological ranges are poorly constrained thus hampering a full understanding of how and where eukaryotic life particularly macroscopic phototrophs survived this snowball earth here we report carbonaceous compression fossils from the marinoan age nantuo formation in south china these fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid latitudinal yangtze block some of these fossils are interpreted as benthic macroalgae thus the marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid latitudinal continents such open waters may have been the refugia where macroscopic phototrophs survived the marinoan glaciation and subsequently diversified in the early ediacaran period

seismic wave attenuation in the greater cairo region egypt in the present study a digital waveform dataset of 216 local earthquakes recorded by the egyptian national seismic network ensn was used to estimate the attenuation of seismic wave energy in the greater cairo region the quality factor and the frequency dependence for coda waves and s waves were estimated and clarified the coda waves q c and s waves q d quality factor were estimated by applying the single scattering model and coda normalization method respectively to bandpass filtered seismograms of frequency bands centering at 1 5 3 6 12 18 and 24 hz lapse time dependence was also studied for the area with the coda waves analyzed through four lapse time windows 10 20 30 and 40 s the average quality factor as function of frequency is found to be q c 35 9f 0 9 0 02 and q d 10 2f 0 9 0 02 for coda and s waves respectively this behavior is usually correlated with the degree of tectonic complexity and the presence of heterogeneities at several scales the variation of q c with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth in fact by using the coda normalization method we obtained low q d values as expected for a heterogeneous and active zone the intrinsic quality factor q i 1 was separated from the scattering quality factor q s 1 by applying the multiple lapse time domain window analysis mltwa method under the assumption of multiple isotropic scattering with uniform distribution of scatters the obtained results suggest that the contribution of the intrinsic attenuation q i 1 prevails on the scattering attenuation q s 1 at frequencies higher than 3 hz

thick skinned tectonics in the external apennines italy new evidence from magnetic anomaly analysis 1 we discuss the tectonic implications of a new residual magnetic map of the apennine belt adriatic apulian foreland obtained by integrating ground and offshore data sets chiappini et al 2000a negative anomalies are documented over the adriatic apulian foreland areas whereas the external apennine belt is characterized by a ubiquitous low amplitude 30 nt long wavelength positive anomaly in the central northern apennines three 100 km wide more intense 100 200 nt round shaped anomalies are superimposed to the long wavelength feature finally in the tyrrhenian sea and margins high intensity short wavelength positive negative couplets coincide with magmatic outcrops or bodies at shallow depth the low amplitude anomaly pattern over italy suggests that the magnetic basement beneath the triassic evaporites is ubiquitously incorporated in the external belt compressive fronts implying a thick skinned tectonic style for the external apennines the new residual magnetic map resolves the inconsistency between previous aeromagnetic data agip spa italia 1981 which suggested a lack of basement involvement in the apennine belt and recent seismic data which imaged deep reflectors penetrating the basement two magnetic models along ne sw transects in the northern and southern apennines suggest consistent structural styles in the northern apennines positive anomalies roughly coincide with the external compressive fronts although there are local second order differences between the belt front and the edges of the anomaly here the magnetic data show that the basement rises southwestward along the thrust fronts from 6 7 km depth in the adriatic foreland to 2 3 km depth in the axial belt where some exploration wells have penetrated basement within the belt front basement exhumation is inferred to occur along high angle low displacement thrust faults inverting preexisting normal faults in the southern apennines a remarkable positive magnetic anomaly is parallel with and tens of kilometers southwest of the belt front seismic data and oil wells show that the basement surface cannot be shallower in the belt than in the foreland therefore the observed magnetic anomaly is produced by strongly magnetic basement beneath the belt likely an internal crustal wedge tectonically interposed between the apulian carbonate sequences and basement

excellent source rocks discovered in the cryogenian interglacial deposits in south china geology geochemistry and hydrocarbon potential abstract the cryogenian 720 635 ma is characterized by the well known sturtian and marinoan glaciations which plays a key role in understanding remarkable climate and sea level changes and oxygenation events that occurred during the neoproterozoic era however less attention has been paid to the interglacial deposits recently we paid great attentions to the excellent hydrocarbon source rocks toc 2 in the cryogenian interglacial datangpo formation 663 4 ma 654 3 8 ma in south china which mainly consists of black shales with thin manganese interbeds making the interglacial interval a new focus to elucidate their characteristics and depositional environments petrological and geochemical studies were conducted on fresh rock samples collected from six sections gucheng sanlian xiaoxi gaodongyuan xiaochayuan yanglizhang in manganese mining areas at southeastern south china sedimentary reconstructions suggest a transition from restricted to open ocean environment during the deposition of the datangpo formation and this formation records variations from warm and humid to dry and cold climate black shales were deposited in its lowest member during the warm period and showed greatest thicknesses more than 20 m at depocenters microscopic observations of the black shale samples exhibited abundant benthic algae with great diversities indicating a gradual recovery of the ecosystem biomarker analyses further reveal that these algae combined with bacterial microorganisms prosperous in low salinity reducing environments were the dominant organic contributors to the source rocks which were inferred by low pristane pr to phytane ph ratio pr ph low gammacerane high tricyclic terpene and high c27 sterane contents trace element records combined with isotopic data suggest that the deposition of source rocks in datangpo formation were related to a burst in surface water productivity due to warm climate and better preservations resulted from anoxic waters within a stratified water column these findings indicate the cryogenian source rocks may provide a new potential field for future explorations of shale gas and deep oil and gas

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

synthetic inversions for density using seismic and gravity data density variations drive mass transport in the earth from plate tectonics to convection in the mantle and core nevertheless density remains poorly known because most geophysical measurements used to probe the earth s interior either have little sensitivity to density suffer from trade offs or from non uniqueness with the ongoing expansion of computational power it has become possible to accurately model complete seismic wavefields in a 3 d heterogeneous earth and to develop waveform inversion techniques that account for complicated wavefield effects this may help to improve resolution of density here we present a pilot study where we explore the extent to which waveform inversion may be used to better recover density as a separate independent parameter we perform numerical simulations in 2 d to investigate under which conditions and to what extent density anomalies may be recovered in the earth s mantle we conclude that density can indeed be constrained by seismic waveforms mainly as a result of scattering effects at density contrasts as a consequence the low frequency part of the wavefield is the most important for constraining the actual extent of anomalies while the impact of density heterogeneities on the wavefield is small compared to the effects of velocity variations it is likely to be detectable in modern regional to global scale measurements we also conclude that the use of gravity data as additional information does not help to further improve the recovery of density anomalies unless strong a priori constraints on the geometry of density variations are applied this is a result of the inherent physical non uniqueness of potential field inverse problems finally in the limited numerical setup that we employ we find that the initially supplied anomalies in s and p velocity models are of minor importance

the early palaeozoic high grade metamorphism at the active continental margin of west gondwana in the andes nw argentina n chile the evolution of the early palaeozoic orogen of west gondwana in the cambrian to ordovician basement of the andes between 18 and 32 s is investigated for pressure and temperature conditions and age of metamorphism it is characterized by mid crust temperatures commonly above the wet granite solidus 650 c widespread felsic migmatite and rare granulite formed at pressures of ca 0 5 0 7 gpa locally 1 0 gpa these rocks represent the deepest exhumed sections of the early palaeozoic crust high pressure low temperature rocks are absent the crystallization ages compiled from the literature in combination with new data for near peak metamorphic conditions of these high grade metamorphic rocks in nw argentina and n chile are 530 500 ma and 470 420 ma both age groups are spatially overlapping radiogenic isotope signatures sr nd pb are used to characterize the early palaeozoic basement the pb and sr isotope compositions of the early palaeozoic basement indicate mixing arrays between pre palaeozoic unradiogenic and radiogenic crust crustal residence ages sm nd tdm indicate a prominent event of crust formation around 2 ga which is known continent wide this material was recycled during midproterozoic and early palaeozoic orogenies without prominent additions of new crust present in the isotope record i e accretion of compositional exotic material is absent

sr c and o isotope geochemistry and stratigraphy of precambrian and lower paleozoic carbonate sequences from the western sierras pampeanas of argentina tectonic implications abstract sr c and o isotope data are presented for carbonate rocks from the sierra de pie de palo and other crystalline outcrops of the western sierras pampeanas these are used to distinguish three groups of rocks of quite different ages within the nappe pile that constitutes the sierra de pie de palo carbonates from the grenville age ophiolitic unit at the bottom of the pile probably resulted from the interaction between hot seawater and contemporaneous oceanic crust these carbonates are tentatively classified as ophicalcites carbonates from the difunta correa sedimentary sequence are part of a cover sequence to a grenvillian basement together forming the upper nappes isotope stratigraphy suggests a middle to late neoproterozoic age 580 720 ma for these carbonates this cover might be correlated with cover sequences to the archean and early to middle proterozoic cratons that are well preserved over large areas of brazil this fact together with the apparently absence of an equivalent neoproterozoic carbonate bearing cover in the appalachian margin of laurentia suggests that the western sierras pampeanas which are considered part of the exotic argentine precordillera terrane of allegedly laurentian derivation could be autochthonous or para autochthonous to gondwana other geochemical and geological arguments reinforce this hypothesis the caucete group carbonates underlie the nappe pile and are separated from it by a first order thrust the pirquitas thrust these latter carbonates are cambrian in age and isotopically similar to the carbonate platform of the precordillera we thus conclude that the pirquitas thrust is the boundary between the exotic precordillera terrane and the autochthonous or para autochthonous western sierras pampeanas

reflectance of vitrinite like macerals as a thermal maturity index for cambrian ordovician alum shale southern scandinavia the middle cambrian to lower ordovician alum shale in southern scandinavia contains kerogen macerals resembling vitrinite the age of this rock unit excludes terrestrially derived vitrinite as an origin for these macerals nevertheless the vitrinite like macerals respond to heating in a way similar to that of suppressed vitrinite in younger shales this similarity is demonstrated both for the natural system where alum shale maturity ranges from immature to low grade metamorphic conditions and for hydrous pyrolysis experiments where an immature sample of alum shale was isothermally heated at temperatures ranging from 280 to 360 degrees c for 72 hr reflectance values from the naturally matured alum shale show an increase in standard deviations i e anisotropy with i creasing maturity and a negative relationship with atomic h c ratios of the total kerogen these relationships are similar to those observed in post ordovician vitrinites comparisons with other vitrinites subjected to hydrous pyrolysis indicate the vitrinite like macerals in the alum shale follow the suppressed vitrinite pathway rather than the coal vitrinite pathway the occurrence of vitrinite like macerals in the alum shale indicates that traditional vitrinite reflectance measurements are useful in evaluating thermal maturity of pre silurian rocks

cellular taphonomy of well preserved gaoyuzhuang microfossils a window into the preservation of ancient cyanobacteria abstract the 1500 ma gaoyuzhuang microfossils a representative mesoproterozoic cyanobacteria assemblage are crucial for understanding and searching for early precambrian life on earth the cellular taphonomy of fossils in this assemblage is poorly known however here we combined in situ microscopic and microanalytical techniques to study the detailed taphonomy of these microfossils light microscopy lm scanning electron microscopy sem and transmission electron microscopy tem observations show that gaoyuzhuang microfossils are mainly preserved in black chert layers and that silica particles can be found within fossilized cell walls and sheaths raman spectra show the characteristic first order bands at 1350 and 1605 cm 1 of carbonaceous material comprising microfossils indicating that they have experienced peak temperatures of 215 to 308 c raman maps show the spatial distribution of the carbonaceous matter as well as that of the silica matrix consistent with nano scale secondary ion mass spectrometry nanosims analyses variations in 13c versus 12c and 34s versus 32s within individual microfossils are likely the result of original differences in the isotopic compositions of cellular components confocal laser scanning microscopy clsm analyses provide fluorescence based 2 d and 3 d images of the cellular components of such microfossils at high spatial resolution the micro scale chemical isotopic and structural heterogeneities together with the subcellular morphological features support the preferential preservation of cyanobacterial cell walls and sheaths over cell contents in precambrian chert we proposed a potential taphonomic model perhaps responsible for the high fidelity of preservation for such microfossils permineralized in precambrian rocks the integrated approach has potential for deciphering the enigmatic nature of mesoproterozoic microorganisms preserved in stromatolitic cherts with significant implications for microbial preservation in the geological record

sedimentology and environmental significance of the cryogenian successions of the yangtze platform south china block abstract the neoproterozoic glaciations during sturtian c 720 ma and marinoan c 600 635 ma times are considered events of extreme climate change of global dimension sometimes interpreted according to the snowball earth hypothesis here we present for the first time a detailed sedimentological description and facies analysis of the deposits of both glacial events recorded on the yangtze platform of the south china block the yangtze platform was located at c 40 latitude during the older glaciation and close to the equator during the younger one the studied successions of nanhuan sinian age including both diamictite bearing units vary in thickness from 90 m to 1800 m and show some remarkable differences between the deposits of sturtian and marinoan age in general both diamictite bearing successions are composed of diamictites debris flow deposits turbidites structureless or laminated sand and siltstones and mudstones however diamictites of the lower unit were deposited from proglacial debris flows whereas those of the upper unit formed as lodgement deposits of the grounded zone laminated sand and siltstones containing dropstones are abundant in the lower unit and very rare in the upper one deposits of subaqueous mass flows are present in both units the lower diamictite unit is not overlain by cap carbonates the upper diamictite unit grades transgressively into 3 to 8 m thick successions of thin bedded and partly clast rich carbonate rocks representing the basal strata of the ediacaran doushantuo formation in view of a conformable contact between the upper diamictite unit and these carbonate layers and their similar lithostratigraphic position to those on other continents we consider them to represent cap carbonates our sedimentological data indicate different patterns of development of the two glaciations the sturtian event in south china is characterized by deposition of ice rafted debris distal to ice margins thus indicating ample open ocean space available for iceberg drift the marinoan record in south china registers depositional processes proximal to ice margins including lodgement deposits in consideration of the palaeogeographic position of the yangtze platform in intermediate sturtian and low marinoan latitudes during neoproterozoic time there were probably significant differences in intensity and extent between the glaciations the older one being less severe and characterized by regionally limited ice centres there is no evidence of a shutdown of the hydrological cycle during the deposition of the two diamictite units in conclusion our sedimentological data neither support a sturtian nor a marinoan hard snowball earth glaciation

2d kernel based imaging of coda q space variations in the gargano promontory southern italy abstract crustal seismic attenuation in the gargano promontory southern italy was inferred by analyzing coda waves of about one hundred small magnitude earthquakes recorded by the otrions local seismic network coda attenuation qc was computed using the sato 1977 model i e the assumption of single back scattering at different lapse times and at different frequencies average qc is comparable with the same quantity measured in the adjacent area of the umbria marche region central italy a recent kernel based imaging technique for qc was then applied and the results evidence a well confined zone located south west of the investigated area showing a sharp qc anomaly while qc cannot be directly related to the physical properties of the propagation medium its spatially dependent modeling allows an interpretation in the light of other geophysical and geological information our results were then interpreted following the two extreme hypotheses according to which qc could be representative of the effect of only intrinsic attenuation or of only scattering from the heterogeneities both the hypothesis correlate with the observation of anomalies in several geophysical parameters such as heat flow magnetic field gravity density seismic velocity in the southwestern gargano moreover the qc images support the results obtained in a recent study that shows clear variations in the rheological properties of the gargano the results obtained at local scale confirm and detail previous regional scale studies on attenuation and highlight for the first time the presence of a positive qc anomaly in the south western part of the gargano promontory

docking of the central metasedimentary belt to laurentia in geon 12 evidence from the 1 17 1 16 ga chevreuil intrusive suite and host gneisses quebec the chevreuil intrusive suite 1 17 1 16 ga represents a chronological field marker of regional extent that intruded the central metasedimentary belt in the western grenville province of quebec after peak metamorphism style and site of magma emplacement and extent of deformation of chevreuil plutons and dykes permit unravelling of the early grenvillian evolution of the belt with respect to cratonal north america the suite comprises a series of vertically layered gabbro stocks and monzonite diorite gabbro sheet intrusions and a swarm of microdiorite dykes that cut across gneisses the dykes display systematic variations in extent of deformation across the belt we targeted u pb geochronology on gneisses within the identified strain windows they preserve the record of a ca 1 20 ga high pressure temperature p t metamorphic event the sheet intrusions define magmatic corridors all along and concordant with the western northern and eastern tectonic boundaries of the belt the concordant and elonga

stratigraphic and tectonic implications of a newly discovered glacial diamictite cap carbonate couplet in southwestern mongolia we report here the discovery of a new end cryogenian glacial diamictite and an overlying basal ediacaran cap carbonate within the tsagaan oloom formation of southwestern mongolia the identifi cation of the cryogenian ediacaran boundary coupled with new 13 c chemostratigraphic profi les facilitates the integration of the neoproterozoic stratigraphy of mongolia with records elsewhere these correlations indicate that a previously unrecognized 16 cryogenian 13 c anomaly is present in the newly defi ned tayshir member informal of the tsagaan oloom formation furthermore chemostratigraphic and lithostratigraphic relationships suggest an 35 m y depositional hiatus below the phosphorite bearing zunne arts member informal of the upper tsagaan oloom formation and that subsidence renewed in the latest ediacaran early cambrian we propose that the lower 1500 m of the tsagaan oloom formation was deposited on a thermally subsiding passive margin after rodiniaage rifting whereas the zunne arts member and the overlying 1600 m of early cambrian strata were deposited in a foredeep basin that formed as the southern margin of the dzabkhan terrane was subducted beneath the khantayshir dariv arc

the gargano promontory a neogene contractional belt within the adriatic plate the gargano promontory lies on the adriatic plate between the dinaride and apennine fold and thrust belts and associated foredeeps neogene sediments and structures in the gargano promontory demonstrate the existence of significant contrac tional structures which have not been reported previously beginning in early miocene times the future gargano promontory experienced shortening along nw trending mainly sw vergent folds and thrusts deformation persisted until the tortonian and most likely until the messinian limited nw directed contraction affected the promontory probably during pliocene times morphological relief was minimal until the messinian but from the middle pliocene onwards it was substantially similar to the present day one partly as a consequence of extension along ne sw trending normal faults the along strike projection of kinematic relationships and quantities observed in the gargano might call for a re interpretation of previously underestimated structures nw and se of the promontory

0 3 byr of drainage stability along the palaeozoic palaeo pacific gondwana margin a detrital zircon study the palaeo pacific margin of gondwana in the present day south central andes is marked by tectonic activity related to subduction and terrane accretion we present detrital zircon u pb data encompassing the palaeozoic era in northern chile and northwestern argentina cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase the main age clusters for these zircon grains are ediacaran to palaeozoic with an additional peak at 1 3 0 9 ga and they can be correlated with grenvillian age and the brasiliano pampean and famatinian orogenies the zircon data reveal main transport from the nearby ordovician famatinian arc and related rocks the silurian sandstone units are more comparable with cambrian units with brasiliano and transamazonian ages 2 2 1 9 ga being more common because the silurian deposits were situated within or east of the extinct famatinian arc hence the arc acted as a transport barrier throughout palaeozoic time the complete suite of zircon ages does not record the accretions of exotic terranes or the palaeozoic glacial periods we conclude that the transport system along the palaeo pacific margin of gondwana remained stable for c 0 3 byr and that provenance data do not necessarily reflect the interior of a continent hence inherited geomorphological features must be taken into account when detrital mineral ages are interpreted supplementary material u pb data cl images and detailed geological maps are available at www geolsoc org uk sup18796

origin of the early sinian minle manganese deposit hunan province china abstract the minle mn ores occur at the base of the early sinian minle formation black shales on the southeast limb of the motianling anticline these rhodochrosite ores are rich in organic carbon and fossil algae and formed in a bay or lagoon on a paleo continental margin with adjacent island barriers the salinity of water in the depositional basin was probably brackish the partly restricted ocean basin was characterized by low oxygen bottom waters and pore water ph values ranging from 9 to 11 and neutral to negative eh values which produced alkaline and reducing conditions suitable for precipitation of mnco 3 growth of blue algae played a role in concentrating metals especially mn changing the sedimentary environment photosynthesis prior to deposition and degradation of organic matter during diagenesis and enhancing the deposition of mnco 3 during diagenesis the mn was mainly derived from the continent with some portion supplied from submarine volcanic activity and supracrustal deep seated hydrothermal fluids

retrowedge related carboniferous units and coeval magmatism in the northwestern neuquen province argentina the studied carboniferous units comprise metasedimentary guaraco norte formation pyroclastic arroyo del torreon formation and sedimentary huaraco formation rocks that crop out in the northwestern neuquen province argentina they form part of the basement of the neuquen basin and are mostly coeval with the late paleozoic accretionary prism complex of the coastal cordillera south central chile u pb shrimp dating of detrital zircon yielded a maximum depositional age of 374 ma upper devonian for the guaraco norte formation and 389 ma for the arroyo del torreon formation detrital magmatic zircon from the guaraco norte formation are grouped into two main populations of devonian and ordovician famatinian ages in the arroyo del torreon formation zircon populations are also of devonian and ordovician famatinian as well as of late neoproterozoic and mesoproterozoic ages in both units there is a conspicuous population of devonian magmatic zircon grains from 406 4 ma to 369 5 ma indicative of active magmatism at that time range the ehf values of this population range between 2 84 and 0 7 and the tdm hf are mostly mesoproterozoic suggesting that the primary sources of the devonian magmatism contained small amounts of mesoproterozoic recycled crustal components the chemical composition of the guaraco norte formation corresponds to recycled mature polycyclic sediment of mature continental provenance pointing to a passive margin with minor inputs from continental margin magmatic rocks the chemical signature of the huaraco formation indicates that a magmatic arc was the main provenance for sediments of this unit which is consistent with the occurrence of tuff mostly in the arroyo del torreon formation and very scarcely in the huaraco formation with a volcanic arc signature jointly indicating the occurrence of a carboniferous active arc magmatism during the deposition of the two units the guaraco norte formation is interpreted to represent passive margin deposits of mostly lower carboniferous age younger than 374 ma and older than 326 ma that precede the onset of the accretionary prism in chile and extend into the earliest stage of the accretion in a retrowedge position the arroyo del torreon and huaraco formations are considered to be retrowedge basin deposits to the early frontal accretionary prism eastern series of chile the presence of volcanism with arc signature in the units provides evidence of a mississippian magmatic arc that can be correlated with limited exposures of the same age in the frontal cordillera argentina the arc would have migrated to the west coastal batholith during pennsylvanian permian times coevally with the later basal accretionary prism western series the source of a conspicuous population of devonian detrital zircon interpreted to be of magmatic origin in the studied units is discussed in various possible geotectonic scenarios the preferred model being a magmatic arc developed in the chilenia block related to a west dipping subduction beneath chilenia before and shortly after its collision against cuyania gondwana at around 390 ma and not linked to the independent devonian mississippian arc developed to the south in patagonia

a critical look at iron paleoredox proxies new insights from modern euxinic marine basins enrichments in reactive iron occur under euxinic marine conditions that is where dissolved sulfide is present in the water column these enrichments result primarily from the export of remobilized iron from the oxic shelf which is scavenged from the euxinic water column during syngenetic pyrite formation and deposited in the underlying sediments strongly elevated ratios of highly reactive iron to total iron fehr fet and total iron to aluminum fet al and high degrees of pyritization dop are each products of this enrichment process these paleoredox proxies are among the most faithful recorders of ancient euxinia contrary to previous arguments iron enrichment is decoupled from biogenic sediment inputs but it does appear to be a uniquely euxinic phenomenon in other words we can rule out a major contribution from preferential physical transport of fehr rich detrital sediment to the deep basin which could also operate under oxic conditions furthermore enrichment via the shuttling of iron remobilized from oxic shelves appears to be limited by inefficient transport and trapping processes in deep oxic basins elevated fet al ratios in the euxinic sediments also cannot be a product of internal enhancement of the reactivity of the detrital iron pool without net fehr addition these conclusions are supported by observations in the modern black sea orca basin and effingham inlet fet al ratios are unambiguous recorders of paleoredox even in sediments that have experienced high degrees of metamorphic alteration however this study suggests that high siliciclastic accumulation rates can swamp the enrichment mechanism resulting in only intermediate dop values for euxinic sediments and fet al ratios that mimic the oxic shelf such dilution effects are well expressed in black sea basinal turbidites and rapidly accumulating muds on euxinic basin margins under conditions of persistent euxinia varying extents of fehr enrichment can illuminate spatial and temporal gradients in siliciclastic sedimentation the magnitude of enrichment is a function of the source shelf to sink ocean basin areal ratio suggesting that iron proxies can also record ocean scale paleoenvironmental properties through muted enrichments at times of very widespread euxinia for the first time manganese data are interpreted in light of the redox shuttle model as for the iron data the black sea orca basin and effingham inlet show enrichments in total manganese in the deep euxinic basin suggesting export from the suboxic porewaters of the oxic shelf and scavenging and burial in the basin the black sea data reveal iron and manganese enrichment across the broad deep euxinic basin suggesting efficient lateral transport and deep water mixing tied to the physical properties of the water column

seismic rheological model and reflection coefficients of the brittle ductile transition it is well established that the upper cooler part of the crust is brittle while deeper zones present ductile behaviour in some cases this brittle ductile transition is a single seismic reflector with an associated reflection coefficient we first develop a stress strain relation including the effects of crust anisotropy seismic attenuation and ductility in which deformation takes place by shear plastic flow viscoelastic anisotropy is based on the eigenstrain model and the zener and burgers mechanical models are used to model the effects of seismic attenuation velocity dispersion and steady state creep flow respectively the stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity which is obtained by the arrhenius equation and the octahedral stress criterion the p and s wave velocities decrease as depth and temperature increase due to the geothermal gradient an effect which is more pronounced for shear waves we then obtain the reflection and transmission coefficients of a single brittle ductile interface and of a ductile thin layer the pp scattering coefficient has a brewster angle a sign change in both cases and there is substantial ps conversion at intermediate angles the pp coefficient is sensitive to the layer thickness unlike the ss coefficient thick layers have a well defined brewster angle and show higher reflection amplitudes finally we compute synthetic seismograms in a homogeneous medium as a function of temperature

crustal structure of the alps as seen by attenuation tomography abstract we develop a simple tomographic approach exploiting the decay rate of coda waves to map the absorption properties of the crust in a region delimited approximately by the rhine graben to the north the apennines to the south the massif central to the west and the dinarides to the east our dataset comprises 40 000 coda records of about 2000 weak to moderate crustal earthquakes with magnitude ranging from 2 8 to 6 and recorded by broad band accelerometric and short period stations after proper choice of a coda window minimizing the effects of variable epicentral distances we measure the coda quality factor q c in five non overlapping frequency windows covering the 1 32 hz band for all available source station pairs these measurements are subsequently converted into maps of absorption quality factor q i using a linearized approximate relation between q c and q i in practice the following procedure is applied in each frequency band 1 we divide the target region into 40 40 km cells 2 for each source station pair we assign the measured q c value to each pixel intercepted by the direct ray path 3 the results are averaged over all paths and subsequently smoothed with a 3 3 pixels moving window our approach is consistent with the high sensitivity of q c to the value of q i between source and station our tomographic approach reveals strong lateral variations of absorption with length scales ranging from 100 km to 1000 km at low frequency 1 hz the correlation with the surface geology is clear cenozoic and mesozoic sedimentary basins resp crystalline massifs being recognized as high resp low absorption regions furthermore the q i map delineates finer geological features such as the ivrea body the rhone valley or felsic intrusions in the central alps at high frequency 16 hz only the thickest cenozoic sedimentary deposits show up as high attenuation regions and a north south dichotomy is apparent in the absorption structure the limit between low attenuation regions to the north and high attenuation region to the south correlates geographically with the location of the periadriatic lineament pl a major late alpine crustal to lithospheric scale structure furthermore the attenuation structure seems to prolong the pl to the west along a line marked by large historical earthquakes the apennines orogenic belts exhibit a distinct frequency behavior with high attenuation at low frequency and low attenuation at high frequency low frequency absorption may likely be explained by the relatively thick cover of cenozoic sedimentary materials as well as by shallow geothermal activity we hypothesize that the frequency dependence of the attenuation structure in particular in the apennines is caused by a change of the wavefield composition which accentuates the sensitivity of the coda to the deeper parts of the medium as the frequency increases

the pacific gondwana margin in the late neoproterozoic early paleozoic detrital zircon u pb ages from metasediments in northwest argentina reveal their maximum age provenance and tectonic setting abstract u pb detrital zircon ages are reported from puncoviscana formation late neoproterozoic early cambrian and meson group late cambrian greywackes of northwest argentina to constrain provenance and depositional environment the new data are combined with previously published detrital zircon ages to show that puncoviscana formation age patterns contain two broad groups late mesoproterozoic early neoproterozoic 1150 850 ma and late neoproterozoic early cambrian 650 520 ma with their relative proportions varying inversely with youngest component age the 1150 850 ma age components are dominant in greywackes with oldest late neoproterozoic components 600 ma the former diminish considerably when late neoproteozoic components become dominant and younger to 520 ma a northernmost greywacke sample from purmamarca jujuy is distinctive whilst its zircon age pattern partly resembles other puncoviscana formation samples it contains no cambrian late neoproterozoic ages the youngest ages being early neoproterozoic this may reflect an early neoproterozoic passive margin depocentre for the formation or an older early neoproterozoic succession within it which may predate the brasiliano orogeny in brazil the youngest age components c 520 ma in a greywacke from rancagua cachi salta province dominate an almost unimodal pattern suggestive of contemporary volcanic sources at a late early cambrian depocentre detrital zircon age patterns of the meson group lizoite formation have major cambrian latest neoproterozoic components resembling those of the puncoviscana formation but its mesoproterozoic component is diminished and there are no significant age components of this age small youngest components at c 500 ma suggest a maximum late cambrian stratigraphic age the puncoviscana formation detrital zircon patterns suggest a provenance in a continental hinterland having a stabilised extensive late mesoproterozoic orogen with minor paleoproterozoic and archean precursors and a more variable late neoproterozoic orogen containing an evolving sequence of less extensive subcomponents a direct relationship with the brazilian shield is suggested with sediment supplies originating within active margin orogens of the interior and collisional orogens at the suture between african and south american cratons but ultimate deposition in passive margin environments of western gondwanaland

age constraints on the tectonic evolution and provenance of the pie de palo complex cuyania composite terrane and the famatinian orogeny in the sierra de pie de palo san juan argentina abstract new u pb age determinations confirm earlier interpretations that the strongly deformed and metamorphosed mafic and intermediate igneous rocks of the pie de palo complex represent a mesoproterozoic fragment of suprasubduction zone oceanic crust a gabbroic pegmatite interpreted to have formed during arc rifting or subsequent back arc spreading yielded a u pb age of 1204 5 3 4 7 ma highly tectonized ultramafic mafic cumulates occurring at the structural base of the pie de palo complex and previously interpreted to represent remnants of a primitive arc phase prior to rifting and back arc spreading could not be dated but should be older than 1204 ma if these inferences are correct tabular sill like bodies of leucogabbro diorite and calc alkaline tonalite granodiorite sills yielded ages of 1174 43 and 1169 8 7 ma respectively they may represent a younger more evolved arc phase established after arc rifting or a younger tectonically unrelated mesoproterozoic arc shrimp analysis of metamorphic zircon rims with low th u ratios in vvl 110 gave a 206pb 238u age of 455 10 ma similar to lower intercept dates determined by discordia lines combined these data indicate that the bulk of the amphibolite facies metamorphism present in the pie de palo complex was generated during the famatinian orogeny analysis of six single detrital zircon grains in a metasedimentary quartzofeldspathic garnet mica schist tectonically interleaved with the igneous rocks of the pie de palo complex and tentatively correlated with the difunta correa metasedimentary sequence of other workers yielded three age populations 1150 1160 ma 1050 1080 ma and 665 ma indicating that these sedimentary rocks were deposited during the late neoproterozoic or early paleozoic in addition they confirm structural evidence that intercalation of rocks of the pie de palo complex with isolated slivers of these sedimentary rocks is due to tectonic imbrications these ages are also consistent with a laurentian provenance and earlier interpretations that these rocks once represented a sedimentary cover to the pie de palo complex the zircon population of 1050 1080 ma could be derived from grenville age felsic plutons identified elsewhere in the pie de palo complex by other workers however no evidence has been found in our samples for a grenville age orogenic event invoked previously to explain accretion of the oceanic pie de palo complex to laurentia prior to the late neoproterozoic early cambrian rifting and drift of cuyania

grenvillian massif type anorthosites in the sierras pampeanas we report the discovery of massif type anorthosites in the andean basement of the western sierras pampeanas of argentina u pb zircon dating by sensitive high resolution ion microprobe of a cogenetic gabbronorite dyke yields ages of 1070 41 ma for igneous emplacement and 431 40 ma for metamorphism these anorthosites are petrologically and geochemically comparable with those of the grenville province of laurentia palaeogeographical reconstructions of rodinia at 1 0 1 1 ga suggest that the sierras pampeanas anorthosites were part of a large anorthosite province in the late mesoproterozoic

a cryogenian chronology two long lasting synchronous neoproterozoic glaciations the snowball earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons here we present four new re os geochronology age constraints on sturtian 717 660 ma and marinoan 635 ma termination glacial deposits from three different paleocontinents a 752 7 5 5 ma age from the base of the callison lake formation in yukon canada confirms nonglacial sedimentation on the western margin of laurentia between ca 753 and 717 ma coupled with a new 727 3 4 9 ma age directly below the glacigenic deposits of the grand conglomerate on the congo craton africa these data refute the notion of a global ca 740 ma kaigas glaciation a 659 0 4 5 ma age directly above the maikhan uul diamictite in mongolia confirms previous constraints on a long duration for the 717 660 ma sturtian glacial epoch and a relatively short nonglacial interlude in addition we provide the first direct radiometric age constraint for the termination of the marinoan glaciation in laurentia with an age of 632 3 5 9 ma from the basal sheepbed formation of northwest canada which is identical within uncertainty to u pb zircon ages from china australia and namibia together these data unite re os and u pb geochronological constraints and provide a refined temporal framework for cryogenian earth history

two cryogenian glacial successions compared aspects of the sturt and elatina sediment records of south australia abstract two cryogenian glacial sequences the sturt and elatina occur within the adelaide rift complex s australia and are part of an 8 km thick succession recording rodinia fragmentation and subsequent passive margin development we compare and contrast these glacial successions presenting new data including detailed logged sections for both glacial sequences facies analysis reveals a total of six facies associations recording a range of glacial and glacially related processes these are a diamictite facies association ice proximal debris flows a sheet sandstone facies association fluvial deposits a flaser and rhythmically bedded facies association tidal flat a hummocky cross stratified sandstone facies association shoreface to offshore transition zone deposits and an underflow facies association recording offshore deposition a sixth facies association a ferruginous lonestone bearing siltstone is restricted to the top of the elatina formation and records rapid environmental amelioration and emergence from glaciation in the central flinders ranges the sturt succession commences with a glacial erosion surface ges which in agreement with previous workers was probably enhanced by rifting this ges is overlain in ascending order by the pualco tillite holowilena ironstone and wilyerpa formation with the warcowie dolomite member at the base of this latter formation a second ges is preserved within this latter unit and is overlain by a stratigraphic motif that records an alternation of offshore transition zone and offshore deposits significant base level falls within the wilyerpa formation are identified by fluvial deposits sitting disconformably upon offshore deposits in contrast within the elatina formation a single ges is proposed which defines the base of the formation the elatina formation is split into two informal members on the basis of analysis of sediment stacking patterns and the recognition of a sharp stratigraphic surface that divides the formation apart from a locally preserved basal diamictite the lower member consists of fluvial deposits whereas the upper member is dominated by a mixture of tidal flat sediments and debris flow deposits the boundary between these units is therefore interpreted as a hybrid surface recording tidal ravinement in some areas and a glacial advance in others deglaciation left contrasting deposits the sturt deglaciation culminated in deposition of black shale of the tindelpina shale member of the tapley hill formation seemingly as a sheet like deposit over the adelaide rift complex and beyond into the amadeus basin of central australia the elatina deglaciation meanwhile began first with deposition of the sixth facies association ferruginous dropstone bearing siltstone then proceeded with deposition of cap dolostone of the nuccaleena formation

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

separation of depth dependent intrinsic and scattering seismic attenuation in the northeastern sector of the italian peninsula summary we investigated the intrinsic dissipation and scattering properties of the lithosphere under the friuli region northeastern italy using two hypotheses i a uniform earth model and ii two reasonable non uniform layered crustal models for case i we measured the coda q and used the multiple lapse time window analysis mltwa technique to obtain separate estimates of intrinsic absorption and scattering attenuation results for the uniform earth model show that the lithosphere in northeastern italy is characterized by a low scattering attenuation small scattering q inverse q 1 and by a relatively high intrinsic attenuation high intrinsic q inverse q 1 a comparison between the investigated region and other areas around the world shows that both q 1 and q 1 for the friuli region are among the lowest values ever measured with the exception of the southern apennines which has the lowest measured q 1 for case ii numerical simulation of the energy envelopes was performed using two layered earth models where the values of the intrinsic and scattering attenuation coefficients are both within reasonable ranges when compared with the geological information the theoretical envelopes calculated for the homogeneous model give a good fit to the synthetic envelopes calculated for the layered models the best fit is obtained for scattering attenuation coefficients of the uniform model always greater than those of the layered model the main result is consequently that scattering q 1 obtained using the mltwa under the assumption of a uniform medium is overestimated on average by a factor 2 finally coda q 1 appears to be closer to the total q 1 than to the intrinsic q 1 a spredicted

the age of the nantuo formation and nantuo glaciation in south china a u pb sensitive high resolution ion microprobe shrimp age of 654 5 3 8 ma from an ash bed immediately below the nantuo formation in south china provides the lowest age constraint for the nantuo glaciation which has been correlated with the global marinoan glaciation a u pb shrimp age of 636 3 4 9 ma from a fallout tuff within the basal layer of the nantuo formation along with the existing age of 635 2 0 6 ma from its overlying doushantuo cap carbonate suggests that the traditionally defined nantuo formation may have been deposited in a short time period at the end of the nantuo glaciation in combination with available ages globally the data support a relatively short duration and rapid termination of marinoan glaciations

site response of strong motion stations in the umbria central italy region we used near field and regional records from 16 earthquakes m l 4 6 5 9 located in the epicentral area of the 1997 umbria marche sequence to estimate the site response of 40 strong motion stations the distribution of hypocenters covers a distance range from 5 to 100 km we estimated site amplification factors using two techniques namely a generalized spectral inversion method and horizontal to vertical component spectral ratios hvsrs of ground acceleration for the first approach we inverted observed spectral amplitudes for site q and source using a reference site since the site response estimated using hvsrs assumes that the vertical component of motion is amplification free we also separated source and site effects by inverting the vertical component of the acceleration spectra we found that although most of the stations do not show important amplifications on the vertical component a few of them have a significant vertical amplification at low frequencies f q representative of the s wave train shows a frequency dependence that can be approximated by the relation q s 31 2 f 1 2 between 0 3 and 9 5 hz however at high frequencies f 10 hz this dependence weakens and q s takes an approximately constant value of 438

spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands i model and the case of tenerife island this work has been partially supported by the spanish project ephestos cgl2011 29499 c02 01 by the eu project ec fp7 mediterranean supersite volcanoes med suv by the basque government researcher training program bfi09 277 and by the regional project grupo de investigaci on en geof isica y sismolog ia de la junta de andaluc ia rnm104 edp has been partly supported by dpc ingv projects unrest speed and v2 precursori

isotopic studies on detrital zircons of silurian devonian siliciclastic sequences from argentinean north patagonia and sierra de la ventana regions comparative provenance the silurian devonian siliciclastic sedimentary units known as sierra grande formation and the upper part of the ventana group crop out in the eastern area of the north patagonian massif and in the ventania system toward the atlantic border of argentina both sequences show similar stratigraphical characteristics and were deposited in a shallow marine platform paleoenvironment previous contributions have provided evidence of an allochthonous patagonia terrane that amalgamate to gondwana during the permian triassic however other lines of research support a crustal continuity southward where the pampean and famatinian events extend into the northern patagonia in either case the detrital input to the eo mesopaleozoic basins generated along the passive margin tectonic setting should reflect the sedimentary sources in this contribution new age data on the sedimentary provenance of these units is provided by u pb and lu hf isotopic studies on detrital zircons using la icp ms and shrimp methodologies the main sedimentary sources of detrital zircons for both regions are of cambrian ordovician and neoproterozoic age while a secondary mode is mesoproterozoic zircons from older cratonic sources mesoarchean paleoproterozoic ages are scarcely recorded the sample from the upper section of the devonian lolen formation ventana group shows an important change in the sedimentary provenance with a main mode of mesoproterozoic detrital zircons detrital source areas considering the orogenic cycles known for southwest south america famatinian pampean brasiliano mesoproterozoic grenvillian and paleoproterozoic transamazonian are proposed

tectonics of the mattinata fault offshore south gargano southern adriatic sea italy implications for active deformation and seismotectonics in the foreland of the southern apennines the mattinata fault is an e w trending feature 50 km long that cuts across the gargano promontory in the foreland of the southern apennines most researchers agree that it is a strike slip fault although the timing of activity is not well known mainly because of the scarce occurrence of cenozoic sediments this contribution aims to describe the eastward extent of the mattinata fault in the adriatic sea using a grid of multichannel seismic profiles specifically acquired for this study and taking advantage of the occurrence of offshore oligocene to quaternary sediments to help date the deformation results indicate that from the late miocene to the quaternary compression dominated and only a limited component of strike slip occurred along the fault a strike slip tectonic regime on the other hand was likely dominant during the late cretaceous to paleogene seismicity affects gargano at basement depth and extends northward into the central adriatic suggesting that the offshore extent of the mattinata fault may not currently represent the main site of foreland deformation within the adriatic region although the mattinata fault probably originated as a crustal scale strike slip fault it has been subsequently reactivated in different tectonic regimes the strike slip ml 5 4 2002 san giuliano molise earthquake located 70 km west of the mattinata fault outcrop seems to have been related to the reactivation of a set of preexisting foreland faults and it does not characterize the seismotectonics of the entire mattinata fault our reconstruction has wide implications not only for a better understanding of the tertiary evolution and active tectonics of the adriatic foreland but also for general relationships among preexisting structures foreland tectonics and seismotectonics

the mesoproterozoic maz terrane in the western sierras pampeanas argentina equivalent to the arequipa antofalla block of southern peru implications for west gondwana margin evolution the rocks of sierra de maz and sierra del espinal western sierras pampeanas represent pre famatinian ordovician basement isotope compositions nd and pb of metasedimentary rocks and shrimp u pb dating of detrital zircons combined with other geological evidence show that three parallel n s domains can be recognized the central maz domain contains pre grenvillian metasedimentary rocks deposited between 1 2 and 1 6 ga that underwent grenvillian granulite facies metamorphism and were intruded by mafic igneous rocks and massif type anorthosites metasedimentary rocks have high nd tdm ages 1 7 2 7 ga and very radiogenic pb 9 8 10 2 suggesting provenance from reworked early proterozoic or archean continental crust the domains to the east and west of the maz domain consist of three metasedimentary sequences with nd tdm ages between 1 2 and 1 6 ga and variably radiogenic pb 9 6 10 0 u pb shrimp dating of detrital zircons nd tdm model ages and comparison with other data suggest that these sequences are post grenvillian i e neoproterozoic and or early paleozoic the maz domain is interpreted as a suspect terrane similar to the northern arequipa antofalla craton that forms the basement of the central andes both underwent grenville age orogeny and were probably once continuous along the western margin of amazonia west gondwana

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

geochemistry of the sinian cambrian gas system in the sichuan basin china abstract based on the outcrops core samples drilling cuttings seismic and geochemical data natural gases of the sinian cambrian gas system were derived from four sets of over mature high quality source rocks the cambrian qiongzhusi source rock is sapropelic with toc of 1 94 ro eq of 1 83 3 90 and a thickness of 140 m on average the sinian 620 541 ma doushantuo source rock is sapropelic with toc of 1 69 ro eq of 2 08 3 83 and a thickness of 11 m on average the 3rd member of the dengying fm is also sapropelic with toc of 1 43 ro eq of 3 16 3 21 and a thickness of 13 m on average the 2nd and 4th members of the dengying fm are dominated by algal dolomite with toc of exhibiting 0 39 ro eq of 1 97 3 46 and a thickness of 246 m on average most of the 13c2 values are lower than 28 and gas dryness is 99 indicating that the natural gas is oil derived with high maturity the high contents of isoparaffins and cycloparaffin suggest that natural gas in the sinian cambrian reservoir was originated from secondary oil cracking the cambrian longwangmiao gas was mainly derived from the cambrian qiongzhusi source rock and the gas within the sinian dengying formation mainly originated from the three sinian source rock layers the area with gas generation intensity superimposed the four sets of source rocks exceeding 6 109 m3 km2 covered 80 of the sichuan basin the proved reserves exceed 1 0 1012 m3 in the sinian cambrian gas system and the accumulated gas resource in the sinian cambrian gas system might exceed 5 1012 m3

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

late diagenetic changes in manganese ores of the upper proterozoic penganga group india sedimentary manganese oxide ores occur interstratified with chert and minor calcareous shale and enclosed in limestone in the transgressive upper proterozoic marine sequence of the penganga group andhra pradesh india this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed the manganeseoxide ores show unusual coexistence of the primary sedimentary minerals todorokite and birnessite with their diagenetic conversion products manganite braunite and bixbyite the mineralogical characters and chemical compositions of the important phases as well as their texture are discussed braunite occurs in two generations one earlier or contemporaneous with bixbyite and the other later than bixbyite the different stages of conversion of todorokite and birnessite to braunite and todorokite to manganite are preserved the general observations suggest that bixbyite was also produced by conversion of todorokite birnessite pyrolusite and cryptomelane conventionally considered as diagenetic products of mn oxide hydroxide precursors deposited as primary sediments are here rarely present and then only as supergene derivatives this documentation of diagenetic transformation of primary todorokite and birnessite directly to braunite and bixbyite should be considered while extrapolating the progenitor mineralogy of the metamorphosed manganese oxide ores that abound in the precambrian

sources of iron for pyrite formation in marine sediments more than two hundred aerobic continental margin aerobic deep sea dysaerobic and anaerobic euxinic sediments have been examined for their variations in different operationally defined iron fractions each of which represents a different reactivity towards dissolved sulfide aerobic continental margin deep sea and dysaerobic sediments contain similar contents of highly reactive iron dithionite soluble iron plus pyrite iron poorly reactive iron iron soluble in hcl less that soluble in dithionite and unreactive iron total iron less that soluble in hcl by contrast non turbidite euxinic samples from the black sea as well as euxinic samples from the cariaco basin and framvaren are enriched in highly reactive iron these sediments contain a small lithogenous fraction and a large biogenous organic c rich fraction which decays by sulphate reduction in an iron rich water column to form pyrite rich sediment other anaerobic euxinic samples from the black sea orca basin and kau bay contain lower concentrations of biogenous sediment and are not therefore enriched in highly reactive iron degrees of pyritization dop for all the aerobic dysaerobic and anaerobic euxinix samples except those low in biogenous material are consistent with analogous ancient sediments and indicate that most pyrite formation occurs form the highly reactive iron fraction

early evolution of the proto andean margin of south america from a detailed study of a 500 km transect in the sierras pampeanas central west argentina two pre silurian tectono magmatic episodes are recognized and defined each culminating in micro continental collisions against the proto andean margin of gondwana the pampean orogeny started in early cambrian time with short lived subduction indicated by ca 535 ma calc alkaline granitoids following pampean terrane collision burial to granulite facies conditions ca 9 kbar generated widespread migmatites and ca 520 ma highly peraluminous granites in the eastern sierras pampeanas after brief quiescence a second major episode the famatinian orogeny started with subduction ca 490 ma forming a wide continental arc and ensialic backarc basin this heralded the approach of laurentia to gondwana during which the precordillera terrane separated from the southern appalachian region finally colliding with gondwana in silurian devonian time

scattering and anelastic attenuation of seismic energy in the vicinity of north anatolian fault zone eastern turkey abstract erzincan basin eastern turkey is seismically very active pull apart basin and developed in between the eastern segments of the north anatolian fault zone a study of the regional and site attenuation of seismic waves of earthquakes in this area will contribute in predicting earthquake generated ground motion and becomes vital in making decisions for earthquake regulations and building codes especially for the cities on the north anatolian fault zone in this paper anelastic and scattering attenuation in erzincan region is investigated by using of multiple lapse time window mltw method based on the hypothesis of multiple isotropic scattering with uniform distribution of scatters it is found that the scattering and intrinsic q 1 are almost equal for 3 hz and lower frequencies and intrinsic attenuation is dominant over scattering attenuation for 6 hz and higher frequencies model fitting was quite good for almost all frequencies at long distances more scattered data and observed poor model fitting at low frequencies 1 5 hz and short distances 5 15 km may indicate the complexities in the shallower part of crust in erzincan the seismic albedo is 0 52 for 1 5 hz and 0 32 for 12 hz l e 1 value increases slightly with frequency as 0 058 for 1 5 hz and 0 032 for 12 hz the coda q c 1 determined from the decay rate of coda waves is similar to q s 1 for 1 5 and 3 hz and it is close to q t 1 for frequencies higher than 3 hz we found that the scattering attenuation is strongly frequency dependent decreasing proportional to f 1 48 whereas intrinsic q i 1 is considerably less frequency dependent f 1 1 a decrease of q s 1 faster than f 1 0 with increasing frequency implies that the medium may be characterized by a gaussian rather than exponential auto correlation function

depth dependent seismic attenuation in the granada zone southern spain abstract coda q estimates for the granada basin southern spain are obtained by analyzing earthquakes occurring within or close to the borders of this area the data set is composed of 54 earthquakes with local magnitudes ranging between 2 2 and 4 0 and with epicentral distances to the nearest station smaller than 10 km a single scattering process is assumed coda q values obtained show a clear dependence on frequency according to the relationship q q o f n where n ranges from 0 81 to 0 89 after removing the main site effects and discussing the possible multiple scattering influence the lapse time dependence is interpreted as due to attenuation variations with depth this result agrees with the variation of coda q obtained by using different sets of events with increasing hypocentral depth ranges

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

the origin and petrologic evolution of the ordovician famatinian puna arc elemental chemistry radiogenic isotopic data and zircon u pb inheritance patterns for the famatinian puna arc suggest that the primary petrogenetic process operating in the arc was mixing between subarc mantle derived gabbroic magmas and metasedimentary materials without a substantial component of lower crustal continental basement rocks this mixing is observable in the fi eld and evident in variations of chemical elemental parameters and isotopic ratios revealing that hybridization coupled with fractionation of magmas took place in the upper 25 km of the crust intermediate and silicic plutonic rocks of the famatinia puna arc formed in a subduction setting where the thermal and material input of mantle derived magmas promoted fusion of fertile metasedimentary rocks and favored mixing of gabbroic and dioritic magmas with crustal granitic melts whole rock geochemical and isotopic data for the famatinian puna magmatic belt as a whole demonstrate that the petrologic model studied in detail in the sierra valle fertil la huerta section has the potential to explain generation of plutonic and volcanic rocks across the early ordovician western gondwanan proto pacifi c margin this example further underscores the signifi cance of passive margin sedimentary accumulations in generating continental arcs ducea email arizona edu ducea m n otamendi j e bergantz g w jianu d and petrescu l 2015 the origin and petrologic evolution of the ordovician famatinian puna arc in decelles p g ducea m n carrapa b and kapp p a eds geodynamics of a cordilleran orogenic system the central andes of argentina and northern chile geological society of america memoir 212 p 125 138 doi 10 1130 2015 1212 07 for permission to copy contact editing geosociety org 2014 the geological society of america all rights reserved on september 24 2014 memoirs gsapubs org downloaded from

spatial and temporal correlation between coda q and seismicity in china a map of coda q at 1 hz q was constructed for china by analyzing more than 1000 seismograms from 80 seismic stations distributed throughout china the resultant contour map of q shows a strong correlation with the epicenters of historic great earthquakes in china the high q regions are devoid of the epicenters and the low q regions are full of them a remarkably linear relation was found between the logarithm of coda q and the maximum earthquake within the area sampled by coda waves radius of about 150 km from each station when we consider earthquakes which occurred from 1700 to present roughly speaking if q is 1000 m max is about 4 and if q is 100 m max is about 8 this relation will be very useful for siting critical facilities such as nuclear power plants and waste disposal sites we also found evidence in support of the migration of low q region coincident with the well known migration of high seismicity region over the distance of several hundred kilometers during the period of several hundred years if the migration is due to a diffusion process the diffusion constant is of the order of 100 km2 yr which agrees very well with those associated with the aftershock migration fluid injection and vp vs anomaly comparison of coda q with q1 estimated from the intensity data shows that they agree very well for q1 150 supporting the validity of the s to s single backscattering model for coda waves for q1 150 however coda q becomes constant independent of q1 this behavior is qualitatively consistent with numerical experiments of frankel and clayton and suggests that coda q may be measuring the intrinsic q of about 150 for these regions where q1 150 this limiting coda q value may depend on regions because coda q lower than 100 has been observed in some active regions in this study and also coda q as low as 30 to 40 has been reported in california mexico and italy

pre and post marinoan carbonate facies of the democratic republic of the congo glacially or tectonically influenced deep water sediments abstract the upper carbonate rich parts of the west congo supergroup 1000 560 ma from the democratic republic of the congo have hitherto been considered as a record of abrupt eustatic and climatic events accompanying glaciation and deglaciation of a snowball earth type marinoan ice age that was of global extent these strata have however never been investigated in detail results of new sedimentological work at key outcrops over a 1300 km outcrop belt show that pre and post marinoan carbonates are respectively storm influenced sediments deposited principally in a mid outer ramp setting and deep water slope carbonates calicturbidites representing a lobe fringe or levee overbank setting the upper diamictite formation held previously by some to be a subglacial tillite comprises gravity flows debrites deposited in deep water below wave base along the unstable margins of a carbonate ramp a direct glacial influence on sedimentation for diamictites or any accompanying facies cannot be readily identified sedimentary facies reported here primarily record the presence of deep water submarine to alluvial fan systems related to extensional tectonic processes of the central southern macaubas basin now located in brazil between 700 ma and 660 ma followed by the 630 ma onset of the pre collisional magmatic arc in the aracuai west congo orogen no extreme short lived climatic or eustatic events of a snowball earth type ice age are recorded in the studied succession which primarily reflects long term overriding regional tectonic controls resulting in diachronous sedimentation along the western margin of the congo craton

seismic constraints on the present day kinematics of the gargano foreland italy at the transition zone between the southern and northern apennine belts 1 the 1995 2004 seismicity in the gargano promontory hereafter gp foreland at the transition zone between southern and northern apennine belts italy is analyzed with the aim to put constraints on the present day kinematics of this key area of the foreland the spatial distribution of earthquakes and 54 calculated focal mechanisms show that that the main gp ruptures develop along e w striking right lateral strike slip faults and nw se normal to left lateral second order faults that move in response to a prevailing nw se compression i e ne sw extension tacking into account the depth of the relocated seismicity and the available geological information we propose that the gp shear zone represents an e w striking major crustal discontinuity separating sectors of the foreland that move in response to the higher northeastward propagation velocity of the thrust front of the northern apennines with respect to that of the southern apennines

relationship between depth of seismicity and heat flow the case of the gargano area italy we consider a thermo rheological model made of a viscoelastic half space with maxwell rheology and temperature dependent viscosity the half space is made of layers with different values of density thermal conductivity activation energy and heat productivity the model relates the surface heat flow to the depth of the brittle ductile transition and the thickness of the seismogenic layer the model is applied to the gargano area italy which is subject to a frequent low magnitude seismic activity although it lies out of the apennine axis which is the main italian seismogenic area the seismic activity in the gargano area and surroundings occurs at depths that are systematically different in the north eastern zone with respect to the south western zone in correspondence with the change in depth of earthquake foci we observe a change in the value of surface heat flow starting from these observations and from the knowledge of the lithospheric structure we propose two different geotherms for the two zones assuming a constant strain rate the shear stress is computed as a function of depth and the thickness of the seismogenic layer in the two zones is inferred the comparison of the results of the thermo rheological model with the seismological observation is good

the neoproterozoic early paleozoic metamorphic and magmatic evolution of the eastern sierras pampeanas an overview the eastern sierras pampeanas were structured by three main events the ediacaran to early cambrian 580 510 ma pampean the late cambrian ordovician 500 440 ma famatinian and the devonian carboniferous 400 350 ma achalian orogenies geochronological and sm nd isotopic evidence combined with petrological and structural features allow to speculate for a major rift event ediacaran dividing into two mesoproterozoic major crustal blocks source of the grenvillian age peaks in the metaclastic rocks this event would be coeval with the development of arc magmatism along the eastern margin of the eastern block closure of this eastern margin led to a cambrian active margin sierra norte arc along the western margin of the eastern block in which magmatism reworked the same crustal block consumption of a ridge segment input of oib signature mafic magmas which controlled granulite facies metamorphism led to a final collision pampean orogeny with the western mesoprotrozoic block sm nd results for the metamorphic basement suggest that the tdm age interval of 1 8 1 7 ga which is associated with the less radiogenic values of end 540 6 to 8 can be considered as the mean average crustal composition for the eastern sierras pampeanas increasing metamorphic grade in rocks with similar detrital sources and metamorphic ages like in the sierras de cordoba is associated with a younger tdm age and a more positive end 540 value pampean pre 540 ma granitoids form two clusters one with tdm ages between 2 0 and 1 75 ga and another between 1 6 and 1 5 ga pampean post 540 ma granitoids exhibit more homogenous tdm ages ranging from 2 0 to 1 75 ga ordovician re activation of active margin along the western part of the block that collided in the cambrian led to arc magmatism famatinian orogeny and related ensialic back arc basin in which high grade metamorphism is related to mid crustal felsic plutonism and mafic magmatism with significant contamination of continental crust tdm values for the ordovician famatinian granitoids define a main interval of 1 8 1 6 except for the ordovician ttg suites of the sierras de cordoba which show younger tdm ages ranging from 1 3 to 1 0 ga in devonian times achalian orogeny a new subduction regime installed west of the eastern sierras pampeanas devonian magmatism in the sierras exhibit process of mixing assimilation of depleted mantle signature melts and continental crust achalian magmatism exhibits more radiogenic end 540 values that range between 0 5 and 4 and tdm ages younger than 1 3 ga in pre devonian times crustal reworking is dominant whereas processes during devonian times involved different geochemical and isotopic signatures that reflect a major input of juvenile magmatism