BSGF - Earth Sciences Bulletin最新文献

{"title":"Cambro–Ordovician ferrosilicic magmatism along the northern Gondwana margin: constraints from the Cézarenque–Joyeuse gneiss complex (French Massif Central)","authors":"S. Couzinié, P. Bouilhol, O. Laurent, T. Grocolas, J. Montel","doi":"10.1051/bsgf/2022010","DOIUrl":"https://doi.org/10.1051/bsgf/2022010","url":null,"abstract":"It is well-acknowledged that the northern margin of the Gondwana supercontinent was affected by a major magmatic event at late Cambrian (Furongian) to early Ordovician (Tremadocian) times. However, an accurate assessment of its extent, origin, and significance is partly hampered by the incomplete characterization of the numerous gneiss massifs exposed in the inner part of the Variscan belt, as some of them possibly represent dismembered and deformed Furongian–Tremadocian igneous bodies. In this study, we document the case of the “Cézarenque–Joyeuse” gneisses in the Cévennes parautochton domain of the French Massif Central. The gneisses form decametre- to kilometre-thick concordant massifs interlayered within a pluri-kilometric sequence of mica- and quartz schists. They encompass two main petrological types: augen gneisses and albite gneisses, both typified by their blue and engulfed quartz grains with the augen facies differing by the presence of centimetre-sized pseudomorphs after K-feldspar and the local preservation of igneous textures. Whole-rock geochemistry highlights that many gneisses have magmatic ferrosilicic (acidic with anomalously high FeOt and low CaO) compositions while others are akin to grauwackes. Collectively, it is inferred that the bulk of the Cézarenque–Joyeuse gneisses represent former rhyodacite lava flows or ignimbrites and associated epiclastic tuffs. Volumetrically subordinate, finer-grained, and strongly silicic leucogneisses are interpreted as microgranite dykes originally intrusive within the volcanic edifices. LA–ICP–MS U–Pb dating of magmatic zircon grains extracted from an augen gneiss and a leucogneiss brackets the crystallization age of the silicic magmas between 486.1±5.5 Ma and 483.0±5.5 Ma which unambiguously ties the Cézarenque–Joyeuse gneisses to the Furongian–Tremadocian volcanic belt of SW Europe. Inherited zircon date distributions, Ti-in-zircon and zircon saturation thermometry demonstrate that they formed by melting at 750–820 °C of Ediacaran sediments. Zircon Eu/Eu* and Ce/Ce* systematics indicate that the melts were strongly reduced (fO2 probably close to the values expected for the iron–wustite buffer), possibly because they interacted during ascent with Lower Cambrian black shales. This would have enhanced Fe solubility in the melt phase and may explain the peculiar ferrosilicic signature displayed by many Furongian–Tremadocian igneous rocks in the northern Gondwana realm. We infer that crustal melting resulted from a combination of mantle-derived magma underplating in an extensional environment and anomalously elevated radiogenic heat production within the Ediacaran sedimentary sequences.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127046142","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transgressive-regressive cycles in saline lake margin oolites: paleogeographic implications (Priabonian, Vistrenque basin, SE France)","authors":"N. Semmani, F. Fournier, P. Léonide, M. Feist, S. Boularand, J. Borgomano","doi":"10.1051/bsgf/2022012","DOIUrl":"https://doi.org/10.1051/bsgf/2022012","url":null,"abstract":"The integrative analysis of a lacustrine carbonate succession from Butte Iouton hill (Vistrenque basin, SE France) brings new insights into depositional models of oolitic saline lake margins and provides new details regarding the late Eocene paleogeography of southeast France. Depositional facies analysis and paleoenvironmental reconstructions allow reconstructing an oolitic lacustrine ramp model, displaying from the proximal to the distal areas: 1) shallow marginal saline lake domain with deposition of planar microbial laminites, and molluscan-ostracodal wackestone, 2) a more distal and open lacustrine environments with low to moderate energy characterized by the deposition of peloidal grainstones and 3) a domain of higher energy with accumulation of ooids mixed with peloids in the vicinity of the area of ooid production. Lake margin carbonate sedimentation dominantly occurred during stages of lake transgression while subaerial exposure surfaces developed during periods of negative inflow-evaporation balance. Carbon and oxygen isotopes together with vertical trends in salinity inferred from molluscan associations show that lake transgression does not result from increasingly positive freshwater-evaporation balance volume but from the combination of subsidence and outflow from neighbouring salt waterbodies. The Butte Iouton carbonate margin is part of a set of interconnected saline lakes, occupying continental basins from Languedoc and Rhodanian region during the Priabonian, with a siliciclastic-dominated sedimentation in the southern margin, sourced by collapsing Pyrenean reliefs, and a carbonate-dominated northern margin with significant oolitic sedimentation in high-energy nearshore area.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127454567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The age of North America’s youngest Paleozoic continental vertebrates: a review of data from the Middle Permian Pease River (Texas) and El Reno (Oklahoma) Groups","authors":"M. Laurin, R. W. Hook","doi":"10.1051/bsgf/2022007","DOIUrl":"https://doi.org/10.1051/bsgf/2022007","url":null,"abstract":"The youngest Paleozoic vertebrate-bearing continental deposits of North America are Middle Permian (Guadalupian) in age and occur in the Chickasha Formation (El Reno Group) of central Oklahoma and the lithostratigraphically lower San Angelo Formation (Pease River Group) of North-Central Texas. Although regarded originally as Guadalupian, these deposits have been assigned recently to the Early Permian on the basis of marine fossils and questionable lithostratigraphic extrapolations from marine to continental strata. A review of ammonoid genera recovered from the Blaine Formation, which overlies both the Chickasha and San Angelo in Oklahoma and Texas, shows that they range globally in age from the Early to Late Permian but most occur in the Guadalupian or Middle Permian. A modest but intensively studied paleobotanical record of compression fossils from the San Angelo, as well as palynomorphs in rocks associated with the Chickasha, presents an unquestionably Middle to Late Permian flora dominated by voltzian conifers. The Chickasha and San Angelo vertebrate assemblages are overwhelmingly dominated by large caseid synapsids and indicate a biostratigraphic signal of early Guadalupian. The occurrence of the tupilakosaurid temnospondyl Slaugenhopia, the parareptile Macroleter, and the eureptile Rothianiscus suggest a Roadian age (lowermost Guadalupian) given the global records of closely related forms. These plant and vertebrate assemblages contrast sharply with those of underlying Cisuralian rocks of the Hennessey Formation of Oklahoma and the Clear Fork Formation of Texas, both of which are much more fossiliferous than those of the Guadalupian in the region. A barren interval of up to 300 m in thickness separates these fossil-bearing intervals. This true void, first reported a half century ago by E.C. Olson, has not been recognized in recent biochronology studies. These findings, as well as those of other vertebrate paleontologists who have evaluated the San Angelo and Chickasha data by other means, strongly refute the notion of “Olson’s Gap” as currently entertained.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"128 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132793511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Carboniferous tectono-metamorphic evolution of the Variscan crust in the Belledonne-Pelvoux area.","authors":"Kevin Freville, P. Trap, J. Vanardois, J. Melleton, M. Faure, O. Bruguier, M. Poujol, Phillipe Lach","doi":"10.1051/bsgf/2022008","DOIUrl":"https://doi.org/10.1051/bsgf/2022008","url":null,"abstract":"Based on new structural, petrological and U-Th-Pb data, a reappraisal of the Variscan tectono-metamorphic history of the SW Belledonne-Pelvoux (Eastern Cristalline Massifs, French Alps) mid-lower crust is proposed. These results are keys to better understand the flow pattern of the variscan partially molten crust and the geodynamic evolution of the sub-meridional branch of the variscan belt. The SW Belledonne area exposes the suprastructure where the medium grade metamorphic rocks record a middle Carboniferous evolution, with a westward gently dipping S1 foliation refolded by east-verging inclined folds (F2) with a subvertical to west-dipping axial plane cleavage S2. Further east, in the Pelvoux area, the high-grade metamorphic rocks of the infrastructure, mostly migmatites, record a prominent D2 deformation with a penetrative NE-SW steeply dipping S2 foliation and a network of NS and NW-SE trending shear zones the kinematics of which indicate a bulk sinistral transpression. D1 and D2 features are interpreted as reflecting a NW–SE contraction, first marked by dominant nappe stacking and subsequently overprinted by transpressional shearing. The supra/infrastructure boundary is typified by a D3 deformation zone that consists of a flat laying S3 foliation with a NW-SE stretching lineation along which top to NW sense of shear is observed. The D1 event corresponds to mid-carboniferous crustal thickening. Exhumation of deep-seated rocks during the transpressional D2 event followed a near isothermal (ca. 700 °C) evolution down to pressure of ca. 5kbar in the period 325-306 Ma. From ca. 306 Ma, D2 and D3 acted synchronously while the mid-lower crust recorded a near isobaric temperature increase up to 850 °C before final cooling and retrogression. The P-T-t history of the Pelvoux area is very similar to the nearby Velay dome and suggest that the Belledonne-Pelvoux area may belong to the Western Moldanubian zone of the Variscan Belt. In that vision, we suggest that coupling between D2 and D3 deformation enable the south-eastward migration, i.e. from the orogenic plateau to the foreland, of the hot and low-viscosity partially-molten crust.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128223635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A 20 year-long GNSS solution across South-America with focus in Chile","authors":"E. Klein, C. Vigny, J. Nocquet, H. Boulze","doi":"10.1051/bsgf/2022005","DOIUrl":"https://doi.org/10.1051/bsgf/2022005","url":null,"abstract":"Over the last 3 decades, GPS measurements have been instrumental in quantifying tectonic plates current motion and deformation. Complex patterns of deformation along the plate boundaries revealed heterogeneous coupling on the plates interface and imaged seismic segments at different stages of their seismic cycle. Along the South-American trench in Chile, where large earthquakes occur frequently, continuous GPS observations (cGPS) captured both the long-term plate motion and the transient deformations associated to the seismic cycle. Over the years, a network of hundreds of cGPS stations has been deployed all across the South-American continent by many different institutions for m{many ?}all sorts of purposes ranging from geographic reference to Tsunami early warning. We report here on the processing of 20 years (2000-2020) worth of data over a selection of cGPS stations, devoted to the quantification and analysis of the deformation along the Chilean subduction zone between 18°S and 40°S. We use all available data near the trench in Chile and a less dense network inside the continent where the gradient of deformation is lesser. Our database, named SOAM_GNSS_solENS, provides time series of precise daily station position, obtained from double difference (DD) processing and expressed in the International Terrestrial Reference Frame 2014 (ITRF14). These time series allow to quantify, with m{sub-?}sub-millimetric precision, any kind of ongoing deformation process, either from tectonic origin such as interseismic deformation, co- and post-seismic displacements associated with earthquakes, transient deformation associated to seismic swarms and/or a-seismic slow-slip events, or of other origin such as hydrological loading (for ex, the Amazonian basin load) or any other type of loading affecting the surface of the earth (tides, atmosphere, etc...). We also provide a database of coseismic displacements associated with close to 60 earthquakes of Mw larger than 6.5 that occurred over the last 20 years within the observation area. All time series are directly accessible through a deposit and we also plan make them available through a web interface that will allow any user to perform elementary operations like estimating offsets, detecting outliers, detrending, filtering and stacking. That database will evolve with time, aggregating more data. In the future, we also plan to complement that database with a rapid solution in quasi real time processed in Precise Point Positioning (PPP), and with hourly atmospheric delays associated to water vapor contains of the lower layer of the atmosphere.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134106029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rising sea level and increasing tropical cyclone frequency are threatening the population of San Andrés Island, Colombia, western Caribbean","authors":"M. Bernet, Liliana Torres Acosta","doi":"10.1051/bsgf/2022003","DOIUrl":"https://doi.org/10.1051/bsgf/2022003","url":null,"abstract":"The Colombian island of San Andrés is a popular tourist destination located about 195 km offshore of the east coast of Nicaragua in the southwestern Caribbean Sea. Together with Providencia and Santa Catalina, San Andrés is part of the UNESCO Seaflower Biosphere Reserve. With a 26 km2 surface area and 78,000 inhabitants, San Andrés is one of the most densely populated islands in the Caribbean with on average ~3000 inhabitants/km2. The majority of the population and the mass tourism are concentrated in the low-elevation (0.5 - 6 m) areas, particularly in the north and along the east coast of the island. These areas are prone to flooding during storm events such as hurricane Eta and Iota in 2020. A review of the geological, environmental and the socio-economic situation of the island, and the record of tropical cyclones since 1911, shows why the local population has become increasingly vulnerable to storm events and rising sea level. Tropical cyclones may form locally in the southwestern Caribbean or originate in the eastern Caribbean/Atlantic Ocean. The latter tend to be stronger and cause more damage when they reach San Andrés. The HURDAT2 dataset shows that the frequency of storm events affecting San Andrés has increased in recent decades, with six storms over the past 20 years, including three category 4-5 hurricanes since 2007. Increasing storm frequency and intensity may be linked to increasing sea surface temperatures caused by global warming. The growing population density since the 1950s, has augmented the potential for disaster.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"135 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116598198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrological disparity of the Lutetian Paris and Hampshire basins revealed by stable isotopes of conid gastropods","authors":"Alexander J. Clark, J. Vellekoop, R. Speijer","doi":"10.1051/bsgf/2022002","DOIUrl":"https://doi.org/10.1051/bsgf/2022002","url":null,"abstract":"During the Eocene greenhouse (56.0–33.9 Ma), northwest Europe was dominated by a semi-arid para-tropical climate but the paleohydrological conditions are poorly known. To gain more insight into seasonal hydrological conditions in the region, we compare Lutetian (middle Eocene, ~44-45 Ma) mollusk δ18O records from two shallow marine basins on either side of the English Channel, i.e. the Paris and Hampshire Basins. The semi-circular Paris Basin was open to the Atlantic Ocean, while the Hampshire Basin was more enclosed and influenced by the draining of several rivers. The proximity of the basins suggests that they experienced roughly similar seawater temperatures but the seasonal hydrology is expected to have been different between these basins. Among the numerous mollusks present in both basins are several members of Conidae, a gastropod family that is particularly well-suited for paleoseasonality reconstructions. To assess the paleohydrological differences between these basins we analyzed the stable oxygen isotopic composition of three specimens of Eoconus deperditus from the Banc a Verrains in the middle part of the Calcaire Grossier Formation of the Paris Basin (France), and three specimens of Eoconus edwardsi from the Shepherd’s Gutter Bed in the upper part of the Selsey Formation of the Hampshire Basin (United Kingdom). While the seasonal variability appears to have been similar between these basins, the δ18O values of the Hampshire Basin specimens are consistently lower than those in the Paris Basin, suggesting a regional difference in δ18Osw of 1-2‰ between the basins. This difference in δ18Osw was likely related to a hydrological disparity between the Paris and Hampshire basins.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"121 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114332007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessing controls on organic matter enrichments in hemipelagic homogenous marls of the Cretaceous Vocontian Basin (France): an unexpected variability observed from multiple organic-rich levels","authors":"A. Caillaud, M. Quijada, Stephan R. Hlohowskyj, A. Chappaz, V. Bout‐Roumazeilles, J. Reynaud, A. Riboulleau, F. Baudin, T. Adatte, J. Ferry, N. Tribovillard","doi":"10.1051/bsgf/2022001","DOIUrl":"https://doi.org/10.1051/bsgf/2022001","url":null,"abstract":"The Marnes Bleues Formation from the Vocontian Basin (Southeastern France) shows many organic rich levels, some concomitant to oceanic anoxic events OAE1a and OAE1b. These organic-rich levels are scattered through a thick homogeneous succession of marls, poor in organic matter (OM). Through a multi-parameter approach, the organic-rich levels from the Aptian-Albian were characterized. Our results show that all OM-rich levels exhibit variable characteristics, such as OM nature (marine vs. continental), sedimentation and accumulation rates, redox conditions, surface-water productivity and relative sea level, but they all show low to modest enrichments in OM. Furthermore, all the levels share in common the fact that they formed under conditions of normal to low productivity and oxic to suboxic conditions. Thus, our results strongly suggest that, in the absence of high productivity and anoxic bottom conditions, the other factors reputed to favor OM accumulation only led to sporadic and low enrichments in organic contents. It is as if such factors could only enhance OM accumulation but could not induce it alone. What was true for the Vocontian Basin may be extended to other settings, regardless of their time of deposition or location.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121301956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Re-assessing copper and nickel enrichments as paleo-productivity proxies","authors":"N. Tribovillard","doi":"10.1051/bsgf/2021047","DOIUrl":"https://doi.org/10.1051/bsgf/2021047","url":null,"abstract":"Copper (Cu) and nickel (Ni) are elements frequently enriched in sedimentary deposits rich in organic \u0000matter (OM). In the marine environment, they are mainly supplied to the sediments in association \u0000with sedimentary OM. In current environments, a good correlation between the intensity of \u0000phytoplankton productivity and the quantities of Cu & Ni transferred to sediments made it possible \u0000to establish paleo-productivity calculations based on the contents of ancient sediments in \u0000these two metals. The present study is a re-evaluation of the value that can be attributed to these \u0000two metals as paleo-productivity proxies. The approach adopted here is based on the examination \u0000of a large database already available in the scientific literature. The choice was made to favor \u0000the examination of a large amount of data by simple means: comparisons of total organic carbon \u0000(TOC) content, enrichment in Cu & Ni (or even other trace metals), and value of the Fe:Al ratio that \u0000makes it possible to assess the availability of reactive iron. The basic idea is that the examination \u0000of a large number of geological formations thanks to the large database makes it possible to encompass \u0000all kinds of paleo-environmental settings, thus comprising an extreme variety of the factors \u0000conventionally involved in the mechanisms of accumulation of OM. The aim is to identify \u0000strong trends, valid in a large number of paleo-situations, which will have to be carefully taken into \u0000account in future detailed paleo-environmental reconstructions. It emerges from this study that, in \u0000many cases, Cu and Ni cannot be considered as faithfully reflecting the quantity of OM initially \u0000deposited. Several factors acting on the loss of Cu and Ni can be retained, and among them, (1) a \u0000rapid loss linked to the decomposition of the OM before the conditions conducive to sulfate-reduction \u0000set in; (2) a low abundance of reactive iron which limits the quantity of pyrite liable to \u0000form, which significantly hampers Cu & Ni fixation in sediments. If Cu & Ni are not reliably retained \u0000in the sediments, that is, proportional to the quantity of OM supplied to the sediment, the paleoenvironmental \u0000reconstitutions involving the concentrations of these metals may provide underestimated \u0000values of paleoproductivity. An interesting clue is the Fe:Al ratio that makes it possible to \u0000quickly know whether the values of the Cu & Ni enrichments are likely to be \"abnormally\" low.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"283 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134369658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of extensional detachment systems in thinning the crust and exhuming granulites: analogies between the offshore Le Danois High and the onshore Labourd Massif in the Biscay/Pyrenean rifts","authors":"Patricia Cadenas, R. Lescoutre, G. Manatschal, G. Fernández‐Viejo","doi":"10.1051/bsgf/2021045","DOIUrl":"https://doi.org/10.1051/bsgf/2021045","url":null,"abstract":"Large uncertainties remain about the architecture, timing and role of the structures responsible for high degrees of crustal thinning and the exhumation of mid-crustal granulites in the Pyrenean and Biscay rift systems. Both, Le Danois High in the North Iberian margin and the Labourd Massif in the Western Pyrenees preserve evidence of extensional detachment faults and include exhumed granulites, which are locally reworked in syn-rift sediments. In this study, we compare the crustal structure and their link to the overlying sediments at the two sites based on the interpretation of high quality 2D seismic reflection profiles offshore and field observations and published geological cross-sections onshore. New reported seismic and field observations support the interpretation that the Le Danois High and the Labourd Massif are capped by extensional detachment systems, advocating for a similar tectonic evolution of the two sites. We propose that the two detachment systems were responsible for high degrees of crustal thinning and the exhumation of the pre-rift brittle-ductile transition and associated mid-crustal granulites during Aptian to Cenomanian extension, leading to the formation of the Le Danois and Labourd crustal tapers. Tilted and uplifted during the Alpine convergence, the two basement blocks lay at present in the hanging-wall of major Alpine thrusts. Their position at overlapping, en-echelon hyperextended rift segments at the end of rifting, and the occurrence of shortcutting structures linking neighbouring rift segments, can explain the preservation of the rift-related detachment systems. This study not only proposes for the first time analogies between the offshore Le Danois High and the onshore Labourd Massif, but it also demonstrates the importance of extensional detachment systems in thinning the crust and exhuming mid-crustal granulites at the seafloor in the Biscay and Pyrenean domains during Aptian to Cenomanian extension.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130864157","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}