Large-scale flat-lying isoclinal folding in extending lithosphere: Santa María de la Alameda dome (Central Iberian Massif, Spain)

The exhumation mechanisms of deep-seated continental crust can be constrained by analyzing the structural and metamorphic imprints left in lithological ensembles. The Santa María de la Alameda dome formed during the collision of Gondwana and Laurussia in late Paleozoic time and is located in the Central Iberian Zone of the Iberian Massif (Spain). Rocks of the dome are part of the autochthonous Gondwanan sections of the Variscan belt, and they occur in the Variscan hinterland. The lithostratigraphy of the dome consists of metasedimentary rocks alternating with orthogneiss massifs showing irregular and sinuous structure. The metamorphic record indicates peak pressures indicative of lower-crust depths followed by isothermal decompression to middle-upper-crust levels. Exhumation resulted in the exposure of different crustal levels (represented by subsolidus vs. supersolidus mineral assemblages). The exhumation was accompanied by initial layer-parallel stretching and subsequent large-scale isoclinal folding developed in a heterogeneous, flat-lying shear zone with top-to-the-SE kinematics. SE-directed shearing and lateral extensional flow occurred in response to thermomechanical disequilibrium of previously thickened orogenic crust, probably assisted by coeval accretion of tectonic slices and lithospheric bending about a vertical axis. Positive feedback among partial melting, exhumation, and crustal attenuation resulted in the formation of a NE-SW–trending, migmatite-cored dome, and in refolding of early isoclinal folds and an associated axial surface regional foliation. The dome formed beneath a set of extensional detachments and was reshaped by WNW-ESE upright folds during later convergent deformation. The latter event brought in further instabilities throughout the belt, triggering in this region the development of a late extensional detachment under low-grade metamorphic conditions (top-to-the-S kinematics). The development of a regional train of flat-lying isoclinal folds is presented here as the macrostructural expression of the combination of vertical and lateral extensional flow, both of which are particularly common in orogens worldwide

Building and Collapse of the Cadomian Orogen: A Plate-Scale Model Based on Structural Data From the SW Iberian Massif

The Cadomian Orogeny produced a subduction-related orogen along the periphery of Gondwana and configured the pre-Variscan basement of the Iberian Massif. The architecture of the Cadomian Orogen requires detailed structural analysis for reconstruction because of severe tectonic reworking during the Paleozoic (Variscan cycle). Tectonometamorphic analysis and data compilation in SW Iberia (La Serena Massif, Spain) have allowed the identification of three Cadomian deformation phases and further constrained the global architecture and large-scale processes that contributed to the Ediacaran building and early Paleozoic dismantling of the Cadomian Orogen. The first phase (DC1, prior to 573 Ma) favored tabular morphology in plutons that intruded during the building of a continental arc. The second phase (DC2, 573–535 Ma) produced an upright folding and contributed to further crustal thickening. The third phase of deformation (DC3, ranging between ∼535 and ∼480 Ma) resulted in an orogen-parallel dome with oblique extensional flow. DC1 represents the crustal growth and thickening stage. DC2 is synchronous with a period of crustal thickening that affected most of the Gondwanan periphery, from the most external sections (Cadomian fore-arc) to the inner ones (Cadomian back-arc). We explain DC2 as a consequence of flat subduction, which was followed by a period dominated by crustal extension (DC3) upon roll-back of the lower plate. The Ediacaran construction of the Cadomian Orogen (DC1 and DC2) requires ongoing subduction beneath Gondwana s.l., whereas its dismantlement during the Early Paleozoic is compatible with oblique, sinistral convergence.Projects PID2020-112489GB-C21 and PID2020-112489GB-C22, funded by MCIN/AEI/10.13039/50110001103

Two-stage collision: Exploring the birth of Pangea in the Variscan terranes.

The Variscan suture exposed in NW Iberia contains a stack of terranes including two allochthonous units with continental affinity and Gondwanan provenance (Upper and Basal Units), separated by an ophiolite belt where the most common units show protolith ages at c. 395 Ma. Recent Lu–Hf zircon data obtained from these ophiolites indicate interaction between the gabbroic magmas and old continental crust. Hence, the ophiolites could not have originated in a deep ocean basin associated with a mature mid-ocean-ridge or intraoceanic subduction. The tectonothermal evolution of the continental terranes bounding the suture zone records two consecutive events of deep subduction. The Upper Units record an initial high-P/ultra-high-P metamorphic event that occurred before 400–390 Ma, while the Basal Units were affected by a second high-P/low-to-intermediate-T metamorphic event dated at c. 370 Ma. Continental subduction affected the most external margin of Gondwana and developed in a setting of dextral convergencewith Laurussia. Development of the two high-P events alternated with the opening of an ephemeral oceanic basin, probably of pull-apart type, in Early Devonian times. This ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the Variscan suture. Current ideas for the assembly of Pangea advocate a single collisional event between Gondwana and Laurussia in the Carboniferous. However, the new evidence from the allochthonous terranes of the Variscan belt suggests a more complex scenario for the assembly of the supercontinent, with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered. Based onmodern analogs of continental interaction, the development of complex collisions, as here suggested for Gondwana and Laurussia during the assembly of Pangea, could have been the norm rather than the exception throughout Earth history

Magmatism and early-Variscan continental subduction in the northern Gondwana margin recorded in zircons from the basal units of Galicia, NW Spain

In situ uranium-lead dating (LA-SF-ICPMS and SIMS) and Lu-Hf isotope analyses (LA-MC-ICP-MS) of zircon from eclogite facies rocks from the basal units of the Variscan Belt in Galicia constrain their magmatic and metamorphic evolution and give some clues about the nature and origin of the involved basement. The samples studied are two felsic gneisses, two eclogites, and one eclogitic gneiss of intermediate composition (metatonalite). Oscillatory-zoned zircon cores from the felsic samples gave a main clustering of U-Pb ages at 493 ± 2 and 494 ± 2 Ma, and some older ages that represent inherited cores. Zircon grains from the intermediate and one of the mafi c rocks show no inherited cores and yielded ages of 494 ± 3 and 498 ± 6 Ma, respectively, interpreted as time of protolith crystallization. Variably developed homogeneous zircon rims in one felsic gneiss yielded an age of 372 ± 3 Ma, and very tiny zircons of one eclogite gave 350 ± 2 Ma, both of which we interpret as metamorphic ages. The new age data demonstrate that the calc-alkaline magmatic suite described in the basal unit is ca. 20 Ma older than the alkaline to peralkaline plutonic suite of the same unit (dated at 472 ± 2 Ma; Rodríguez et al., 2007), and thus probably represents a distinct geologic event. Overgrowth rims are interpreted as metamorphic on the basis of their Lu/Hf and Th/U ratios. The 372 ± 3 age is considered as dating the high-pressure (high-P) metamorphism, and is essentially in agreement with previous Ar-Ar and Rb-Sr data. This high-P metamorphism marks the initial early-Variscan subduction of the Gondwana margin. The inherited zircon ages and Hf isotopic composition of zircons point to a considerable input of crustal material with West African Craton provenance to the felsic magma

A novel role for the tumor suppressor gene itf2 in tumorigenesis and chemotherapy response

Despite often leading to platinum resistance, platinum-based chemotherapy continues to be the standard treatment for many epithelial tumors. In this study we analyzed and validated the cytogenetic alterations that arise after treatment in four lung and ovarian paired cisplatin-sensitive/resistant cell lines by 1-million microarray-based comparative genomic hybridization (array-CGH) and qRT-PCR methodologies. RNA-sequencing, functional transfection assays, and gene-pathway activity analysis were used to identify genes with a potential role in the development of this malignancy. The results were further explored in 55 lung and ovarian primary tumors and control samples, and in two extensive in silico databases. Long-term cell exposure to platinum induces the frequent deletion of ITF2 gene. Its expression re-sensitized tumor cells to platinum and recovered the levels of Wnt/β-catenin transcriptional activity. ITF2 expression was also frequently downregulated in epithelial tumors, predicting a worse overall survival. We also identified an inverse correlation between ITF2 and HOXD9 expression, revealing that Non-small cell lung cancer (NSCLC) patients with lower expression of HOXD9 had a better overall survival rate. We defined the implication of ITF2 as a molecular mechanism behind the development of cisplatin resistance probably through the activation of the Wnt-signaling pathway. This data highlights the possible role of ITF2 and HOXD9 as novel therapeutic targets for platinum resistant tumors.This research was funded by the Fondo de Investigación Sanitaria-Instituto de Salud Carlos III, PI15/00186 and PI18/00050, CP19/00063, and CM19/00100 for HR and by MINECO, RTC-2016-5314-1 to I.I.C; by the MINECO, SAF2016-75531-R, by the CAM B2017/BMD-3724 and by the AECC GCB14142311CRES to P.S; and the European Regional Development Fund/European Social Fund FIS (FEDER/FSE, Una Manera de Hacer Europa)

Cadomian and Variscan sutures of Iberia: a comparison

p.11-12. -A meeting held as a tribute to Teodoro Palacios on his retirement as Professor of Palaeontology at the University of Extremadura, Badajoz, Spain, 26th & 27th January, 2022, University of Extremadura, Badajoz. Edited by Sören Jensen[EN] The Iberian Massif holds evidence of two pre-Mesozoic orogenies, namely the Cadomian and Variscan. The Cadomian Orogeny resulted from long-lived subduction under the periphery of Gondwana during the Neoproterozoic and early Paleozoic. The Variscan Orogen resulted from the progressive collision of Gondwana, Laurussia and their pericontinental terranes during the Devonian and Carboniferous, after the closure of the Rheic Ocean and other marginal basins located along their mainlands. Despite these two orogens differ from one another in the global context from which they emerged, in Iberia they share some characteristics that make them intriguingly alike. The Variscan Orogen contains two major sutures zones. One that separates mainland Gondwana from peri-Gondwanan terranes (intra-Gondwana suture), and another one separating Laurussia from the latter terranes (Rheic suture). The Variscan intra-Gondwana suture is Tectonically dismembered and separates a collection of terranes with continental crust affinity that were transported inland from the periphery of Gondwana during the closure of a (Devonian) marginal basin opened during ongoing convergence between Gondwana and Laurussia (e.g., Careón Ophiolite), ⁓15 million years after the onset of the Variscan Orogen. This process was the result of subduction polarity towards Laurussia, i.e. away from mainland Gondwana. The exhumation of the ophiolites and high-P rocks in this suture was largely controlled by syn-convergence extensional tectonics. The current structure of the Rheic suture, on the other hand, is the result of reworking after the opening of an ephemeral oceanic basin (Beja-Acebuches Ophiolite). Subduction polarity during both the closure of the primary suture zone and the closure of the ephemeral basin were beneath mainland Gondwana. However, the closure of the ephemeral basin developed flake tectonics and obduction of pieces of the ocean basin onto the upper plate. Suture zones in the Cadomian Orogen went unnoticed until few years ago. Despite being intensely reworked by Variscan deformation, the ongoing structural, tectonometamorphic, geochemical and geochronological studies provide first-order constrains on their primary (Cadomian) geometry as well as insight on the paleogeographic location of subduction zones that led to their formation. A collective, yet preliminary analysis of these sutures, pictures a major architecture of the Cadomian Orogen that contain, at least, two sutures zones. One Cadomian suture is identified in the Mérida Ophiolite, which separates an upper and lower plate, both with continental crust affinity and likely Gondwanan derivation (intra-Gondwana suture). This intra-Gondwana suture was formed after the closure by subduction away from mainland Gondwana of a marginal basin that opened during ongoing convergence between Gondwana and an oceanic plate, millions of years after the onset of the Cadomian Orogen. The exhumation of the ophiolite and mid-P rocks that make this suture was largely controlled by syn-convergence extensional tectonics. Another Cadomian suture is represented by the Calzadilla Ophiolite, whose protoliths formed in a fore-arc basin to the most external part of Gondwana. The location of this suture zone is explained by flake tectonics, which contributed to the obduction of the ophiolite onto the upper plate while ongoing subduction was beneath mainland Gondwana. Cadomian and Variscan sutures share fundamental characteristics regarding the paleolocation of the ocean basins they derive from and the overall resulting geometry and tectonic processes involved in their formation. The suture zones that represent the closure of basins located at the outermost section of peri-Gondwana, and closely facing subduction underneath Gondwana (Calzadilla and Beja-Acebuches ophiolites), were obducted inwards onto mainland Gondwana (upper plate). The intra-Gondwana suture zones (Careón and Mérida ophiolites) formed after subduction of a marginal basin beneath the periphery of Gondwana, and the exhumation of rock units of the subduction system was largely assisted by syn-convergence extensional tectonics following subduction-accretion. The Variscan and Cadomian orogens, despite being formed in different contexts (oceanic subduction vs. continental collision), share two major features. Both are (i) mostly built by Gondwanan lithosphere, and (ii) occupy the upper plate of a subduction zone that consumed a large ocean. These two orogens alternate phases of contraction and extension (mostly concentrated in the upper plate). In both cases, extension was intense enough as to create marginal ocean basins and to favor exhumation of deep-seated rocks (quite common in upper plates). Perhaps, these major features they share may explain the resemblance of the final global architecture of these two orogens, and provide additional arguments to consider Gondwana as resistant to subduction and recycling in the mantle and prone to crustal growth, being the upper plate to the orogenic systems it was involved in during at least 300 m.y.Peer reviewe