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Deciphering the presence of axial-planar veins in tectonites

Geoscience Frontiers 2019年第6期10卷 2101-2115页

作者： elena druguet Departament de Geologia Universitat Autonoma de Barcelona

Veins and dikes are often oriented subparallel to the axial surfaces of folds in the adjacent layered or foliated *** implies an awkward situation,since veins would lay in planes close-to-parallel to the maximum stretching axis.A series of geometric models have been conceived in order to gain insight into the possible mechanisms for their *** models are based on the analysis of a varied selection of field structures and on the review of similar structures in the existing literature.A first categorization consists on distinguishing between axial-planar veins achieved by either progressive or polyphase *** models of axial-planar veins resulting from progressive deformation are described and discussed:(1) fold-related veins associated with the standard folding mechanisms,(2) fracture arrays localized along the short limbs of folds(asymmetric fold-related veins),(3) folds associated with rotation of extension veins(vein-related folds),(4) high strain and transposition of early veins,and(5) high strain and late veins parallel to axial planar foliations(axial planar foliation-related veins).The axial planar geometry is achieved through variable amounts of progressive rotational strain,except in model 5,in which the co-planarity is acquired at the time of vein *** possibility for axial-planar veins to have developed in two distinct phases in the context of polyphase or polyorogenic tectonics has also been explored and *** study contributes to a better understanding of the intriguing interplays between deformation,metamorphic and magmatic processes in orogenic belts.

关键词： Dike Fold Fracture Metamorphic rock Migmatite Shear

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Early Paleozoic accretionary orogens along the Western Gondwana margin

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Geoscience Frontiers 2021年第1期12卷 109-130页

作者： Sebastián Oriolo Bernhard Schulz Silvana Geuna Pablo DGonzález Juan E.Otamendi JiíSláma elena druguet Siegfried Siegesmund CONICET-Universidad de Buenos Aires Instituto de Geociencias BasicasAplicadas y Ambientales de Buenos Aires(IGEBA)Intendente Güiraldes 2160C1428EHABuenos AiresArgentina Institute of Mineralogy Division of Economic Geology and PetrologyTU Bergakademie FreibergBrennhausgasse 14D-09596FreibergSaxonyGermany Instituto de Investigacion en Paleobiología y Geología(UNRN-CONICET) Avenida Julio A.Roca 1242R8332EXZGeneral RocaArgentina CONICET Departamento de GeologíaUniversidad Nacional de Río CuartoCampus UniversitarioX5804BYARío CuartoArgentina Institute of Geology The Czech Academy of SciencesRozvojova 269CZ-16500Prague 6Czech Republic Departament de Geologia Universitat Autonoma de Barcelona08193BellaterraBarcelonaSpain Geoscience Centre Georg-August-Universit€at G€ottingenGoldschmidtstraße 337077GottingenGermany

Early Paleozoic accretionary orogens dominated the Western Gondwana margin and were characterized by nearly continuous subduction associated with crustal extension and back-arc basin *** southwestern margin is represented by Famatinian and Pampean basement realms exposed in South America,both related to the protracted Paleozoic evolution of the Terra Australis Orogen,whereas the northwestern margin is mainly recorded in Cadomian domains of Europe and adjacent ***,no clear relationships between these regions were so far *** on a compilation and reevaluation of geological,paleomagnetic,petrological,geochronological and isotopic evidence,this contribution focuses on crustal-scale tectonic and geodynamic processes occurring in Western Gondwana accretionary orogens,aiming at disentangling their common Early Paleozoic *** show that accretionary orogens were dominated by high-temperature/lowpressure metamorphism and relatively high geothermal gradients,resulting from the development of extended/hyperextended margins and bulk transtensional *** this sense,retreating-mode accretionary orogens characterized the Early Paleozoic Gondwana margin,though short-lived pulses of compression/transpression also *** existence of retreating subduction zones favoured mantle-derived magmatism and mixing with relatively young(meta)sedimentary sources in a thin continental *** reworking of previous forearc sequences due to trenchward arc migration thus took place through assimilation and anatexis in the arc/back-arc ***,retreating-mode accretionary orogens were the locus of Early Paleozoic crustal growth in Western Gondwana,intimately associated with major flare-up events,such as those related to the Cadomian and Famatian *** roll back,probably resulting from decreasing convergence rates and plate velocities after Gondwana assembly,was a key factor for orogen-scale geodynamic ***

关键词： Retreating accretionary orogen Lower Paleozoic Crustal growth Hf isotopic array Famatinian Cadomian

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