The presence of ophicalcites in serpentinized peridotites together with fragments of these rocks in Cretaceous breccias along several North-Pyrenean basins led to the interpretation of complete mantle exhumation to the seafloor. The westernmost outcrop of peridotites in the Pyrenean-Cantabrian belt is located in Ziga (eastern Basque-Cantabrian Basin), associated to a band of HT metamorphism related to the Leiza fault (Marble Unit). We present a petrological and geochemical study of the marbles and Ziga peridotite-hosted calcite, including standard stable isotope composition and clumped isotope geothermometry. These isotopic techniques allow the determination of different types of formational fluids and crystallization temperatures, and are a useful tool for studying carbonation processes in hyperextended basins. Fieldwork and analytical studies lead us to conclude that during the opening of the Bay of Biscay, mantle rocks were unroofed at the base of the sedimentary pile of the eastern Basque-Cantabrian Basin. However, the ophicalcite veins were recrystallized from meteoric fluids at low temperatures (498C). The primary carbonate phase may have been formed either during the mid-Cretaceous unroofing of the mantle or in a post-exhumation stage. The process of mantle exhumation was accompanied with HT-LP metamorphism and fluid circulation along major faults that reset the marine isotopic signature in the nearest marbles. For comparison, ophicalcites from Urdach and Lherz (North-Pyrenean Zone) were included in the clumped isotope study. Results show that they were recrystallized from hot (200-2308C), saline fluids, and from meteoric fluids at near ambient temperatures (32-428C), respectively.

Low‐temperature thermochronology studies have increased our knowledge of the orogenic processes along the Pyrenean‐Cantabrian mountain belt by placing time constraints on the exhumation history of its rocks. However, a significant gap in the data existed between the western Pyrenees and the central Cantabrian Mountains, hampering a comprehensive view of the tectonothermal evolution along the belt. We present a new apatite fission track and zircon (U‐Th)/He (ZHe) data set for the eastern Basque‐Cantabrian zone–western Pyrenees. Apatite fission track central ages cluster in the Eocene‐Oligocene. ZHe samples can be separated into two groups: Group 1 depicts clustered ZHe ages‐eU concentration (Cinco Villas massif) and Group 2 depicts dispersed ZHe ages‐eU concentration (Alduides massif and a Paleozoic rock pinned along the Leiza thrust). A sample from the Oroz‐Betelu massif shows intermediate behavior. Inverse modeling suggests that samples from Group 1 reached 240–280 °C in the Late Cretaceous, implying deep sedimentary burial of the Cinco Villas massif before its major exhumation phase, most probably in the early to middle Eocene, postdating the phase of rapid exhumation of the western part of the Leiza thrust. The sample from the Oroz‐Betelu massif, far from the Mesozoic exhumed mantle domain, experienced maximum temperatures close to 200 °C by burial beneath the Jaca‐Pamplona basin. It was later exhumed in the hanging wall of the Gavarnie thrust in the Bartonian‐Priabonian. This work provides new insights into the tectonothermal evolution of the Basque massifs and the inversion of a hyperextended margin.

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Abstract. Normal incidence seismic data provide the best images of the crust and lithosphere. When properly designed and continuous, these sections greatly contribute to understanding the geometry of orogens and, together with surface geology, to unravel their evolution. In this paper we present an almost complete transect of the Iberian Massif, the westernmost exposure of the European Variscides. Despite the heterogeneity of the dataset, acquired during the last 30 years, the images resulting from reprocessing with a homogeneous workflow allow us to clearly define the crustal thickness and its internal architecture. The Iberian Massif crust, formed by the amalgamation of continental pieces belonging to Gondwana and Laurussia (Avalonian margin) is well structured in upper and lower crust. A conspicuous mid-crustal discontinuity is clearly defined by the top of the reflective lower crust and by the asymptotic geometry of reflections that merge into it, suggesting that it has often acted as a detachment. The geometry and position of this discontinuity can give us insights on the evolution of the orogen, i.e. of the effects and extent of the late Variscan gravitational collapse. Also, its position and the limited thickness of the lower crust in central and NW Iberia constraints the response of the Iberian microplate to Alpine shortening. This discontinuity is here observed as an orogeny-scale feature with characteristics compatible with those of the worldwide, Conrad discontinuity.

Abstract. Normal incidence seismic data provide the best images of the crust and lithosphere. When properly designed and continuous, these sections greatly contribute to understanding the geometry of orogens and, along with surface geology, unraveling their evolution. In this paper we present the most complete transect, to date, of the Iberian Massif, the westernmost exposure of the European Variscides. Despite the heterogeneity of the dataset, acquired during the last 30 years, the images resulting from reprocessing the data with a homogeneous workflow allow us to clearly define the crustal thickness and its internal architecture. The Iberian Massif crust, formed by the amalgamation of continental pieces belonging to Gondwana and Laurussia (Avalonian margin), is well structured in the upper and lower crust. A conspicuous mid-crustal discontinuity is clearly defined by the top of the reflective lower crust and by the asymptotic geometry of reflections that merge into it, suggesting that it has often acted as a detachment. The geometry and position of this discontinuity can give us insights into the evolution of the orogen (i.e., of the magnitude of compression and the effects and extent of later-Variscan gravitational collapse). Moreover, the limited thickness of the lower crust below, in central and northwestern Iberia, might have constrained the response of the Iberian microplate to Alpine shortening. Here, this discontinuity, featuring a Vp (P-wave velocity) increase, is observed as an orogen-scale boundary with characteristics compatible with those of the globally debated Conrad discontinuity.

Abstract. Seismic reflection data (normal incidence and wide angle) are unique assets for solid Earth sciences as they provide critical information about the physical properties and structure of the lithosphere as well as about the shallow subsurface for exploration purposes. The resolution of these seismic data is highly appreciated; however they are logistically complex and expensive to acquire, and their geographical coverage is limited. Therefore, it is essential to make the most of the data that have already been acquired. The collation and dissemination of seismic open-access data are then key to promote accurate and innovative research and to enhance new interpretations of legacy data. This work presents the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open-access online databases that stores seismic data registered with a permanent identifier (DOI). The datasets included here are openly accessible online and guarantee the FAIR (findable, accessible, interoperable, reusable) principles of data management, granting the inclusion of each dataset in a statistics referencing database so its impact can be measured. SeisDARE includes seismic data acquired in the last 4 decades in the Iberian Peninsula and Morocco. These areas have attracted the attention of international researchers in the fields of geology and geophysics due to the exceptional outcrops of the Variscan and Alpine orogens and wide foreland basins, the crustal structure of the offshore margins that resulted from a complex plate kinematic evolution, and the vast quantities of natural resources contained within. This database has been built thanks to a network of national and international institutions, promoting a multidisciplinary research and is open for international data exchange and collaborations. As part of this international collaboration, and as a model for inclusion of other global seismic datasets, SeisDARE also hosts seismic data acquired in Hardeman County, Texas (USA), within the COCORP project (Consortium for Continental Reflection Profiling). SeisDARE aims to make easily accessible old and recently acquired seismic data and to establish a framework for future seismic data management plans. SeisDARE is freely available at https://digital.csic.es/handle/10261/101879 (a detailed list of the datasets can be found in Table 1), bringing endless research and teaching opportunities to the scientific, industrial, and educational communities.

Abstract. Seismic reflection data (normal incidence and wide-angle) are unique assets for Solid Earth Science as they provide critical information about the physical properties and structure of the lithosphere, as well as about the shallow subsurface for exploration purposes. The resolution of these seismic data is highly appreciated, however they are logistically complex and expensive to acquire and their geographical coverage is limited. Therefore, it is essential to make the most of the data that has already been acquired. The collation and dissemination of seismic open access data is then key to promote accurate and innovative research and to enhance new interpretations of legacy data. This work presents the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open access online databases that stores seismic data registered with a permanent identifier (DOI). The datasets included here are openly accessible online and guarantee the FAIR (Findable, Accessible, Interoperable, Reusable) principles of data management, granting the inclusion of each dataset into a statistics referencing database so its impact can be measured. SeisDARE includes seismic data acquired in the last four decades in the Iberian Peninsula and Morocco. These areas have attracted the attention of international researchers in the fields of geology and geophysics due to the exceptional outcrops of the Variscan and Alpine orogens and wide foreland basins; the crustal structure of the offshore margins that resulted from a complex plate kinematic evolution; and the vast quantities of natural resources contained within. This database has been built thanks to a network of national and international institutions, promoting a multidisciplinary research, and is open for international data exchange and collaborations. As part of this international collaboration, and as a model for inclusion of other global seismic datasets, SeisDARE also hosts seismic data acquired in Hardeman County, Texas (USA), within the COCORP project (Consortium for Continental Reflection Profiling). SeisDARE aims to make easily accessible old and recently acquired seismic data and to establish a framework for future seismic data management plans. The SeisDARE is freely available at https://digital.csic.es/handle/10261/101879, bringing endless research and teaching opportunities to the scientific, industrial and educational communities.

The critical zone (CZ) represents the most-shallow subsurface, where the bio-, hydro-, and geospheres interact with anthropogenic activity. To characterize the thickness and lateral variations of the CZ, here we focus on the Eastern Betic Shear Zone (EBSZ), one of the most tectonically active regions in the Iberian Peninsula. Within the EBSZ, the Guadalentín Depression is a highly populated area with intensive agricultural activity, where the characterization of the CZ would provide valuable assets for land use management and seismic hazard assessments. To achieve this, we have conducted an interdisciplinary geophysical study along the eastern border of the Guadalentín Depression to characterize the CZ and the architecture of the shallow subsurface. The datasets used include Electrical Resistivity Tomography (ERT), first-arrival travel time seismic tomography, and multichannel analysis of surface waves (MASW). The geophysical datasets combined help to constrain the high-resolution structure of the subsurface and image active fault systems along four transects. The resulting geophysical models have allowed us to interpret the first ~150 m of the subsurface and has revealed: (i) the variable thickness of the CZ; (ii) the CZ relationship between the fault zone and topographic slope; and (iii) the differences in CZ thickness associated with the geological units. Our results provide a method for studying the shallow subsurface of active faults, complementing previous geological models based on paleo-seismological trenches, and can be used to improve the CZ assessment of tectonically active regions.