Análisis de la fábrica magnética en modelos analógicos de arcillas

Este estudio presenta el análisis de la fábrica magnética en una serie de modelos analógicos realizados con arcillas rojas comerciales. A partir de la disgregación de la arcilla en agua y su posterior decantación conseguimos reproducir la adquisición de una fábrica magnética deposicional (geometría oblata del elipsoide magnético con el eje mínimo de susceptibilidad perpendicular al plano de depósito). En un modelo de deformación de desgarre (experimento de Riedel), la lineación magnética se dispone paralela a la dirección de estiramiento. En el modelo de acortamiento, la lineación magnética se orienta perpendicular a la dirección de acortamiento. Los resultados obtenidos ponen de manifiesto el gran potencial de la arcilla roja comercial para ser utilizada en este tipo de modelos analógicos, así como su capacidad de registrar una fábrica magnética coherente en cada caso. This study shows the magnetic fabric analysis applied to several analogue models developed with common commercial red clays. By dispersing the clays in water and after allowing their subsequent decan-tation, we were able to reproduce the acquisition of a depositional magnetic fabric (oblate geometry of the magnetic ellipsoid with the minimum susceptibility axis perpendicular to the deposit plane). In a strike-slip deformation model (Riedel experiment), magnetic lineation is parallel to the stretching direction. In the shortening model, magnetic lineation orients perpendicular to the shortening direction. The obtained results illustrate the great potential of these commercial red clays to be used in this type of analogue models, as well as their capacity to register a coherent magnetic fabric in each case

Influence of overlapping décollements, syn-tectonic sedimentation and structural inheritace in the evolution of contractional system: The central Kuqa fold-and-thrust bely (Tian Shan Mountains, NW China)

Contractional deformation in the Kuqa fold‐and‐thrust belt (southern foreland of the Tian Shan Mountains, NW China) is recorded by well‐preserved syntectonic continental sequences. In addition, its structural evolution was strongly controlled by synorogenic salt (Eocene in age) and presalt décollements with varying spatial distribution. We present a balanced and sequentially restored cross section across the central part of this fold‐and‐thrust belt that provides a new interpretation of the structure beneath the evaporites, in which Paleozoic and Mesozoic strata are deformed by a thrust stack involving (i) a thin‐skinned thrust system detached on Triassic‐Jurassic coal units and (ii) an ensemble of south‐directed basement thrusts. The latter formed from the inversion of Mesozoic extensional faults such as those preserved both in the Tarim foreland basin and beneath the frontal part of the Kuqa fold‐and‐thrust belt. The constructed section shows a total shortening of 35 km from the Late Cretaceous to the present. The restoration depicts a three‐stage evolution for the Kuqa fold‐and‐thrust belt: (i) minor Mesozoic extension, (ii) an early compressional stage (Late Cretaceous to early Miocene) with low shortening and syntectonic sedimentary rates, and (iii) a later compressional stage (late Pliocene‐Pleistocene) characterized by a greater and progressively increasing shortening rate and rapid deposition. Our results are discussed in light of previous analogue and numerical modeling studies and demonstrate the control exerted by the interplay between syntectonic sedimentation, the inversion of inherited basement structures, and the nature and extent of Triassic/Jurassic and Eocene décollements

Basement-Cover Relationships and Their Along-Strike Changes in the Linking Zone (Iberian Range, Spain): A Combined Structural and Gravimetric Study

Contractional deformation in the transition between the Iberian and Catalan Coastal Ranges (Linking Zone) generated both thin-skinned structures detached in low-strength Triassic units and basement-involved structures. To evaluate their extent and relative contribution to the overall structure, we carried out a study combining structural geology and gravimetry. New gravity data (938 stations) and density determinations (827 samples) were acquired and combined with previous existing databases to obtain Bouguer anomaly and residual Bouguer anomaly maps of the study area. Seven serial and balanced cross sections were built, their depth geometries being constrained through the 2.5-D gravity modeling and the 3-D gravity inversion that we accomplished. The residual Bouguer anomaly map shows a good correlation between basement antiforms and gravity highs whereas negative anomalies mostly correspond to (i) Meso-Cenozoic synclines and (ii) Neogene-Quaternary basins. Cross sections depict a southern, thick-skinned domain where extensional, basement faults inherited from Late Jurassic-Early Cretaceous times were inverted during the Cenozoic. To the north, we interpret the existence of both Triassic-detached and basement-involved deformation domains. The two deformation styles are vertically overlapped in the southernmost part of the Catalan Coastal Ranges but relay both across and along strike in the Eastern Iberian Range. These basement and cover relationships and their along-strike variations are analyzed in terms of the interplay between structural inheritance, its obliquity to the shortening direction, and the continuity and effectiveness of Triassic décollements in the study area

Petrophysical properties in the Iberian Range and surrounding areas (NE Spain): 1-density

We introduce the first map of density data in Northeastern Spain which can help in the interpretation of gravimetric surveying. The background map is a simplified version of the Geode continuous geological cartography (scale 1:200.000) of the Iberian Range and Ebro basin. These maps are synthetic and homogeneous maps based on previous 1:50, 000 scale geological maps (MAGNA). The map uses the ETRS89 datum and UTM coordinates (30T northern zone) and covers an area of 140, 000 sq km. The compiled data shown in the map come from previous papers of the region (˜ 700 points) as well as from more than 800 additional points developed in the course of an exploratory project focused on the underground characterization of a potential CO2 reservoir in the so-called ‘Linking Zone''. The new data accomplish some basic criteria; they are accurately georeferenced and lithology, stratigraphic age and other technical details about the measurements (e.g. means and error) and methods are fully displayed

Buscando a C19n: el potencial de la Formación Mendiorotz (cuenca de Jaca-Pamplona, Pirineos occidentales) para el GSSP del Bartoniense

El cron C19n es el principal marcador del límite Luteciense/Bartoniense, cuyo GSSP está todavía pendiente de ser determi- nado debido a la ausencia de secciones idóneas a nivel mundial. Aunque el Pirineo occidental alberga numerosas cuencas sedimentarias con formaciones marinas de edad Luteciense y Bartoniense, intentos anteriores de encontrar secciones poten- cialmente interesantes en dicha zona no han dado resultados satisfactorios (Payros et al., 2014). En este resumen se presenta el trabajo de campo que se ha realizado en la parte occidental de la cuenca de Jaca-Pamplona con el objetivo de identificar series estratigráficas susceptibles de ser datadas mediante magnetobioestratigráfía y posicionar el límite Luteciense/Bar- toniense. Fruto de este trabajo se ha explorado el sinclinal de Izaga, en cuya parte oriental afloran series de la Formación Mendiorotz, de edad Luteciense superior/Bartoniense inferior (Payros et al., 1999), caracterizadas por una sedimentación pelágica dominante y una exposición y continuidad estratigráfica idóneas para encontrar el marcador del límite, el cron C19n. Chron C19n is the main marker of the Lutetian/Bartonian boundary, whose GSSP is still to be defined due to the lack of suitable sections worldwide. Although the Western Pyrenees host a number of sedimentary basins with marine formations of Lutetian and Bartonian age, previous attempts of finding prospective sections in the area have resulted in an unsuccess- ful outcome (Payros et al., 2014). Here we present the results of a fieldwork study conducted in the western sector of the Jaca-Pamplona basin with the aim of identifying sedimentary successions where the Lutetian/Bartonian boundary can be found through magnetobiostratigraphic dating. As a result of this search, we have focused our attention on the eastern sector of the Izaga syncline, where dominantly pelagic sediments of the Mendiorotz Formation, upper Lutetian/lower Bartonian in age (Payros et al., 1999), crop out with enough exposure and stratigraphic continuity to allow identification of Chron C19n

Analizando la cinética de las remagnetizaciones por enterramiento. El caso de la Cuenca turbidítica de Jaca (Pirineos occidentales).

X Congreso Geológico de España, 5-7 Julio 2021, Vitoria - GasteizLas remagnetizaciones químicas regionales relacionadas con procesos de enterramiento y diagénesis son un proceso ampliamente extendido en cuñas orogénicas y cuencas sedimentarias. Este proceso conlleva la neoformación autigénica de minerales ferromagnéticos s.l. en relación con el aumento de temperatura asociado al enterramiento. Sin embargo, todavía no se conoce bien la cinética de estos procesos, debido en parte a que la mayoría de las remagnetizaciones de este tipo descritas en la literatura científica se produjeron durante supercrones magnéticos. Los materiales turbidíticos eocenos de la Cuenca de Jaca (Pirineos Occidentales) muestran una remagnetización química de doble polaridad, registrando varios crones a lo largo de la secuencia sedimentaria remagnetizada. Dentro del proyecto UKRIA4D (PID2019-104693GB-I00/CTA), se va a realizar un estudio multidisciplinar para relacionar temperatura de enterramiento, mineralogía magnética y edad de la remagnetización con la que evaluar de manera empírica las relaciones cinéticas entre los distintos factores

Palaeomagnetism and magnetic fabrics of the Late Palaeozoic volcanism in the Castejón-Laspaúles basin (Central Pyrenees). Implications for palaeoflow directions and basin configuration

The Castejón-Laspaúles basin is one of the South Pyrenean basins of Late Variscan age that were strongly inverted during the Alpine compression (Late Cretaceous-Tertiary). It is mainly composed by Stephanian pyroclastic and volcanic deposits that reach a maximum thickness of ~ 500 m, and are overlain by Permian and Triassic sedimentary units. A palaeomagnetic and magnetic fabrics (AMS) study was carried out in the Stephanian units, where the general absence of flow markers at the outcrop scale and the Alpine inversional structure prevent the straightforward reconstruction of the original volcanic and basinal configuration. Magnetic fabric data are not overprinted by Alpine internal deformation and can be interpreted in terms of primary volcanic and pyroclastic fabrics. The obtained directions coincide in the different sampled units, suggesting a constant source area during the development of the basin, and show the dominance of N-S-trending K1 axes that are interpreted to be parallel to flow directions. Palaeomagnetic data indicate the presence of a pre-folding palaeomagnetic component that is rotated clockwise by an average of +37° (±32°) with regards to the Stephanian reference. This rotation probably took place during Alpine thrusting since it is also registered by the overlying Triassic deposits. The whole dataset is interpreted in terms of basin development under sinistral transtension with two main fault sets: deep-rooted E-W-striking faults, probably responsible for magmatic emissions, and shallow-rooted, listric faults of N-S orientation. Copyright © Cambridge University Press 2013.The authors thank Cristina García and Teresa Román for her help during field and laboratory work and Manuel Tricas for the preparation of thin-sections. This work forms part of the research projects CGL2009-08969 and CGL2006-05817 (Spanish Ministry of Education) and is included in the objectives of the pre-doctoral grant AP-2009-0554 (Esther Izquierdo) (Programa de formación de profesorado universitario, Spanish Ministry of Education). Funding from the Instituto de Estudios Altoaragoneses is also acknowledged. BOU acknowledges the JAEDOC postdoctoral programme financed with ESF. The authors acknowledge the careful and constructive revisions by B. Henry and an anonymous reviewer.Peer Reviewe

Heterogeneous deformation recorded by magnetic fabrics in the Pyrenean Axial Zone

Magnetic fabrics studies (AMS) are a useful tool in order to describe the distribution of deformation in orogenic areas where conventional techniques are difficult to apply, especially due to the lack of proper strain markers. In the present study, AMS and structural analysis are used to define the distribution of deformation in the Central Axial and Nogueres Zones, an area of strong structural changes (i) in the geometry of the antiformal stack defining the Pyrenean Axial Zone and (ii) the distribution of Alpine cleavage. The studied rocks are Lower-Middle Triassic red beds that crop out in three different stacked thrust units (Bielsa, Nogueres and Orri). Primary sedimentary fabrics are preserved in the uppermost thrust units (Nogueres Zone), but a high percentage of the sampling sites shows an overprint of Alpine compression on magnetic fabrics, with the magnetic lineation mostly parallel to the tectonic grain defined by compressional structures and the magnetic foliation showing different orientations between the poles to cleavage and bedding. The development of compressional fabrics strongly depends on the structural position of the sites, and two deformation gradients can be inferred: the southern margin of the Axial Zone (Orri and Bielsa units) shows strong internal deformation, increasing towards the North; farther north (in the restored cross-section), deformation is in general terms lower, but increases towards the basal thrust of the Nogueres Zone. The heterogeneous distribution of Alpine internal deformation indicates a preferred development of cleavage in the Variscan basement and overlying units of the southern margin of the Axial Zone (mainly in the Orri unit), that could be partly controlled by the tectonic load resulting from the stacking of thrust sheets. © 2013 Elsevier Ltd.The authors thank Cristina Garcia and Teresa Román for their help during the field and laboratory work and Manuel Tricas (SAI Preparación de Rocas, Universidad de Zaragoza) for the preparation of thin sections. This work is part of the research projects CGL2009-08969 and CGL2006-05817 (Spanish Ministry of Education) and is included in the objectives of the pre-doctoral grant AP-2009 – 0554 (Esther Izquierdo, Programa de formacion de profesorado universitario, Spanish Ministry of Education). Funding from Instituto de Estudios Altoaragoneses are also acknowledged. The authors acknowledge the careful and constructive revisions from E. Saura and an anonymous reviewer.Peer Reviewe

On the origin of cleavage in the Central Pyrenees: Structural and paleo-thermal study

The present work provides a combined structural and paleothermal (fluid inclusions, illite content in mixed layers illite-smectite, Kübler index and vitrinite reflectance) investigation of the Alpine cleavage domain affecting the western South Pyrenean Zone (Central Pyrenees). Integration of structural and paleothermal data allows us (i) to determine the position of the cleavage front in the sedimentary sequence and (ii) to define mechanisms and temperature conditions for cleavage development. Cleavage in the eastern part of the study area is approximately limited to the forelimb of the Gavarnie hangingwall anticline, but to the West it extends progressively southwards, affecting younger turbiditic units. At regional scale, the cleavage front is oblique to the strike of bedding and the overall trend of macrostructures. Pressure-solution is the main mechanism for cleavage development, and a strong thermal control on the position of the cleavage front is inferred. The transition between sedimentary and tectonic, compressional fabric is marked by vitrinite reflectance values of 1.12-1.14%, Kübler index values between 0.71 and 0.74 °Δ2θ and the transition between R1 and R3 mixed layers illite-smectite. A lower thermal boundary of 140–160 °C is suggested for incipient cleavage development in the shaly beds of the turbiditic sequence, as well as an upper boundary constrained by a maximum measured value of about 215 °C

Magnetic fabric and structural study of the Eaux-Chaudes intrusion: Understanding the Variscan deformation in the Western Axial Zone (Pyrenees)

The present study provides new magnetic and microstructural data for the Eaux-Chaudes granodioritic massif (Western Axial Zone, Pyrenees) and contributes to the understanding of its geometry, internal structure and emplacement mechanism. Moreover, the geological crosssections and field data allow to reconstruct the evolution of the whole area from Variscan to Alpine times and to integrate the emplacement of the igneous body in the context of the Variscan orogeny. The Eaux-Chaudes pluton (301 ± 9 Ma) is mainly composed by granodiorite, describing a normal compositional zoning and an approximately concentric arrangement that is consistent with the zonation of the low-field magnetic susceptibility. Magnetic foliation is subhorizontal in the inner part of the intrusion and becomes parallel to the petrographical contacts along pluton margins, roughly describing the geometry of the intrusion. Magnetic lineations are dominantly subhorizontal, with E–W to ENE–WSW directional maximum. The general parallelism between Variscan structures of the host rock and the geometry and magmatic fabric of the intrusion reveals a late syn-Variscan emplacement. The tectonic regime registered during magma emplacement is in agreement with an N–S shortening and an E–W stretching direction, consistent with the transpressive regime deduced for other Pyrenean intrusions. Alpine overprint produced a slight tilting in the southern part of the intrusion, but it can be considered that the original Variscan structure is basically unchanged.The authors thank M. Tricas for the preparation of thin sections and Rocı´o Navarrete, Pablo Calvı´n and Gelu Lo´pez, for their help during the collecting and lab drilling of the samples. This work forms part of the research projects CGL2009-08969 and CGL2006-05817 (Spanish Ministry of Education) and is included in the objectives of the pre-doctoral grant AP-2009—0554 (Esther Izquierdo) (Programa de formacio´n de profesorado universitario, Spanish Ministry of Education). The authors acknowledge the careful and constructive revisions from Jose´ Marı´a Tubı´a and Karel Schulmann.Peer Reviewe