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 decantation, 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

The Sediment Green-Blue Color Ratio as a Proxy for Biogenic Silica Productivity Along the Chilean Margin

Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard-generated records of the green/blue (G/B) ratio. These changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate-related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high-resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox-sensitive sedimentary U/Th generally co-varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B-derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet-alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high-resolution paleoceanographic records that circumvent the traditionally laborious methodology.publishedVersio

Deep submarine infiltration of altered geothermal groundwater on the south Chilean Margin

Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here, using geochemical fingerprinting of pore water data from Site J1003 recovered from the Chilean Margin during D/V JOIDES Resolution Expedition 379 T, we show that substantial offshore freshening reflects deep and focused contributions of meteorically modified geothermal groundwater, which is likely sourced from a reservoir ~2.8 km deep in the Aysén region of Patagonia and infiltrated marine sediments during or shortly after the last glacial period. Emplacement of fossil groundwaters reflects an apparently ubiquitous phenomenon in margin sediments globally, but our results now identify an unappreciated locus of deep submarine groundwater discharge along active margins with potential implications for coastal biogeochemical processes and tectonic instability.publishedVersio

Magnetic fabríc analysis in analogue models ofclays

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 casoThis study shows the m agnetic fabric analysis applied to several analogue models developed with common commercial red clays. By dispersing the clays in water and after allowing their subsequent decantation, 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 registera coherent magnetic fabric in each cas

Late Paleozoic Iberian Orocline(s) and the Missing Shortening in the Core of Pangea. Paleomagnetism From the Iberian Range

Supercontinents are usually interpreted to be single and rigid continental plates. How and when Pangea became a rigid supercontinent is disputed, and age estimations vary from ~330 to ~240 Ma. The Gondwana‐Laurussia collision formed the Variscan‐Alleghanian belt, the most prominent witness of Pangea's amalgamation. In Iberia, this orogen draws an “S” shape featured by the Cantabrian Orocline and the Central Iberian curve. The curvature of Central Iberia is particularly evident in Galicia‐Trás‐os‐Montes and in a change of trend that it draws in the Aragonese Branch of the Iberian Range. Recent research showed that both curvatures are not coeval and that the Central Iberian curve had to form prior to ca. 318 Ma (i.e., not a secondary orocline). We report paleomagnetic and structural results from Paleozoic rocks in the Santa Cruz syncline (Aragonese Branch of the Iberian Range) that indicate two main vertical axis rotations events: (1) a Cenozoic (Alpine) clockwise rotation of >20° and (2) a late Carboniferous counterclockwise rotation of ~70°. Once the Cenozoic rotation is restored, the change in structural trend that allegedly evidences the outer arc of the Central Iberian curve disappears. Whereas the Cenozoic rotation is incompatible with a Central Iberian curve, the late Carboniferous rotation is fully compatible with the Cantabrian Orocline, enlarging the area affected by its counterclockwise rotations and the existence of a nonrigid Pangea until, at least, ~295 Ma

Late Paleozoic Iberian Orocline(s) and the Missing Shortening in the Core of Pangea. Paleomagnetism From the Iberian Range

Supercontinents are usually interpreted to be single and rigid continental plates. How and when Pangea became a rigid supercontinent is disputed, and age estimations vary from ~330 to ~240 Ma. The Gondwana‐Laurussia collision formed the Variscan‐Alleghanian belt, the most prominent witness of Pangea's amalgamation. In Iberia, this orogen draws an “S” shape featured by the Cantabrian Orocline and the Central Iberian curve. The curvature of Central Iberia is particularly evident in Galicia‐Trás‐os‐Montes and in a change of trend that it draws in the Aragonese Branch of the Iberian Range. Recent research showed that both curvatures are not coeval and that the Central Iberian curve had to form prior to ca. 318 Ma (i.e., not a secondary orocline). We report paleomagnetic and structural results from Paleozoic rocks in the Santa Cruz syncline (Aragonese Branch of the Iberian Range) that indicate two main vertical axis rotations events: (1) a Cenozoic (Alpine) clockwise rotation of >20° and (2) a late Carboniferous counterclockwise rotation of ~70°. Once the Cenozoic rotation is restored, the change in structural trend that allegedly evidences the outer arc of the Central Iberian curve disappears. Whereas the Cenozoic rotation is incompatible with a Central Iberian curve, the late Carboniferous rotation is fully compatible with the Cantabrian Orocline, enlarging the area affected by its counterclockwise rotations and the existence of a nonrigid Pangea until, at least, ~295 Ma

Tectonically controlled magnetic fabrics in the Triassic Iberian basin

Aplicamos las técnicas de ASM sobre facies rojas del Triásico de la Rama Castellana (Cordillera Ibérica, NE de España), una cuenca invertida tectónicamente durante el Terciario sin desarrollo de estructuras penetrativas asociadas a la compresión. El objetivo es diferenciar las fábricas magnéticas desarrolladas durante la etapa extensional de las modificadas durante la compresión, así como tratar de reconstruir la geometría de la cuenca y el régimen de esfuerzos actuante durante la extensión. En su mayoría, se observan fábricas oblatas, típicamente sedimentarias, en las que la lineación magnética presenta direcciones variadas, pero con un máximo ENE-OSO, lo que concuerda con un régimen de extensión transtensiva dextra. Las variadas direcciones de la lineación se deberían a las diversas orientaciones de las fallas que limitan los sectores de la cuenca. En menor medida se distinguen fábricas modificadas por la compresión terciaria, con desarrollo de “guirnaldas” de intercambio de ejes intermedio y mínimoWe apply AMS techniques in Triassic red beds from the Castilian Branch (Iberian Range, NE Spain), a tectonically inverted basin (during Tertiary) where no penetrative structures associated to compression were originated. Our goal is to differentiate magnetic fabrics developed during the extensional stage and the ones modified during compression. In addition we will try to describe the geometry of the basin and the stress pattern acting during extension. In most cases, we observe typical sedimentary oblate fabrics, with different lineation directions, but with an ENE-WSW oriented maximum, which fits with a transtensional dextral extension regime.Variations in the lineation orientation are probably related to the different orientations of the faults limiting the basin sectors. In a less proportion, we distinguish magnetic fabrics modified by Tertiary compression, with “girdles” developed between intermediate and minimum axe