Javier Fernández‐Suárez

Universidad Complutense de Madrid

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Gabriel Gutiérrez‐Alonso

Universidad de Salamanca

Ricardo Arenas

Universidad Complutense de Madrid

J. Brendan Murphy

St. Francis Xavier University

Teresa E. Jeffries

Natural History Museum

Sonia Sánchez Martı́nez

Universidad Complutense de Madrid

Jacobo Abati

Universidad Complutense de Madrid

Alicia López-Carmona

Instituto de Geociencias

Rubén Díez Fernández

Instituto Geológico y Minero de España

J. Duncan Keppie

Universidad Nacional Autónoma de México

Axel Gerdes

Goethe University Frankfurt

Cooperative Institutions

Universidad de Salamanca

Universidad Complutense de Madrid

Universidad de Oviedo

Consejo Superior de Investigaciones Científicas

Instituto Geológico y Minero de España

Instituto de Geociencias

Centre National de la Recherche Scientifique

Planetary Science Institute

St. Francis Xavier University

Université de Rennes

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Orocline triggered lithospheric delamination

Geological Society of America eBooks (2004)

Gabriel Gutiérrez‐Alonso Javier Fernández‐Suárez Arlo Brandon Weil

Late- to post-orogenic oroclinal bending in conjunction with thinning of the lithospheric mantle is potentially an important component of the waning stages of plate convergence in collisional orogenies. This paper addresses possible and hitherto unexplored cause-effect relationships between oroclinal bending of an originally linear orogenic belt and lithospheric thinning and delamination based on an example from the Western European Variscan Belt. We suggest that late- to post-orogenic bending of the lithosphere around a vertical axis may cause thickening and eventual detachment of the lithospheric root of orogenic belts such as the Western European Variscan Belt. The proposed hypothesis is consistent...

Delamination

Thinning

10.1130/0-8137-2383-3(2004)383[121:otld]2.0.co;2

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Citations (119)

100 myr cycles of oceanic lithosphere generation in peri-Gondwana: Neoproterozoic–Devonian ophiolites from the NW African–Iberian margin of Gondwana and the Variscan Orogen

Geological Society London Special Publications (2020)

Ricardo Arenas Sonia Sánchez Martı́nez Richard Albert Faouziya Haissen Javier Fernández‐Suárez

Abstract The Variscan Orogen in Iberia and the Anti-Atlas Mountains in Morocco contains a set of ophiolites formed between Neoproterozoic and Devonian times, during the complex evolution of the NW African–Iberian margin of Gondwana. During this time interval, the margin evolved from an active margin ( c. 750–500 Ma: the Reguibat–Avalonian–Cadomian arc) to the final collision with Laurussia in Devonian times to form Pangaea. In this context, one of the oldest recognized ophiolites is the Bou Azzer Ophiolite from the Anti-Atlas Mountains, dated at c. 697 Ma and containing two types of mafic rocks, the youngest of which has a boninitic composition. To the north, in the SW Iberian Massif, the Calzadilla Ophiolite contains mafic rocks also of boninitic composition dated at c. 598 Ma. Farther north, in the NW Iberian Massif, the Vila de Cruces Ophiolite is formed by a thick sequence of mafic rocks with an arc tholeiitic composition and minor alternations of tonalitic orthogneisses dated at c. 497 Ma. In the same region, the Bazar Ophiolite has a similar age of c. 495 Ma. Also in NW Iberia, there is a group of ophiolites with varied lithologies and dominant mafic rocks with arc tholeiitic composition (Careón, Purrido and Moeche ophiolites) dated at c. 395 Ma. The composition of all these peri-Gondwanan ophiolites is of supra-subduction zone type, showing no evidence of preserved mid-ocean ridge basalt type oceanic lithosphere. Consequently, these ophiolites were generated in the peri-Gondwanan realm during the opening of forearc or back-arc basins. Forearc oceanic lithosphere was promptly obducted or accreted to the volcanic arc, but the oceanic or transitional lithosphere generated in back-arc settings was preserved until the assembly of Pangaea. Based on the ages of the described ophiolites, the peri-Gondwanan realm has been a domain where the generation of oceanic or transitional lithosphere seems to have occurred at intervals of c. 100 myr. These regularly spaced time intervals may indicate cyclic events of mantle upwelling in the peri-Gondwanan mid-ocean ridges, with associated higher subduction rates at the peri-Gondwanan trenches and concomitant higher rates of partial melting in the mantle wedges involved. The origin of the apparent cyclicity for mantle upwelling in the peri-Gondwanan ocean ridges is unclear, but it could have possibly been related to episodic deep mantle convection. Cycles of more active deep mantle convection can explain episodic mantle upwelling, the transition from low- to fast-spreading type mid-ocean ridges and, finally, the dynamic context for the episodic generation of new supra-subduction zone type oceanic peri-Gondwanan lithosphere.

Devonian

myr

Peri

Margin (machine learning)

Passive margin

10.1144/sp503-2020-3

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Citations (25)

High-pressure rocks in the Variscan belt of Western Europe: the Malpica-Tui Complex (NW Iberian Massif)

Alicia López-Carmona Jacobo Abati Pavel Pitra James Lee Gabriel Gutiérrez‐Alonso

Pods and relicts of high-pressure (HP) rocks are the best record of the subduction of the north Gondwana margin at the onset of the Variscan collision. Across Western Europe, blueschist-facies terranes are restricted to scarce and relatively small areas, whereas eclogite-facies terranes are more abundant. The Malpica-Tui complex (MTC) is the westernmost exposure of HP rocks in the NW Iberian Massif, and in the Variscan belt of Western Europe. It comprises two tectonically juxtaposed units separated by an extensional detachment: (i) an upper unit consisting of rocks in the blueschist-facies, and (ii) a lower unit in the medium temperature eclogite-facies conditions. Assuming a northwest-directed component of subduction, in present day coordinates, the characteristics of each sequence suggest that the upper unit would occupy an oceanward position compared to the lower unit before the Variscan collision. Thus, the lower unit is interpreted as a slice of continental crust, whereas the upper unit may represent a transitional to oceanic crust of the same continental margin. The MTC preserves evidence of late Devonian HP metamorphism varying from eclogite (P~26 kbar and T~650 °C) to blueschist-facies conditions (19-22 kbar and 460-560 °C). Petrological analysis involving P-T-X pseudosections in the (Mn)NCKFMASHTO chemical system on the HP rocks reveals a P-T evolution characterised by a subisothermal decompression to ~10 kbar, 480 °C in the blueschist-facies rocks and 650 °C in the eclogites, followed by cooling to ~5 kbar at 380 °C and 500 °C, respectively. New 40Ar/39Ar data indicate a minimum age of ~370 Ma for the subduction-related HP metamorphism. Subsequent decompression to pressures of about 10 kbar started at ~360 Ma and was contemporaneous with thrust-and-fold nappe tectonics and intrusion of early Variscan granodiorites dated at ~350- 340 Ma. Final, “post-nappe”, exhumation is interpreted to have taken place from ~345-335 Ma to 320 ± 5 Ma, which is the age of the syntectonic igneous rocks emplaced in the autochthon of the MTC. These ages support the equivalence of the HP rocks from NW Iberia and their counterparts in the southern Armorican Massif. From a methodological point of view, modelling calculations of H2O and Fe2O3 on the metamorphic evolution of blueschist-facies rocks reveals trends that may have general applications in the investigation of rocks with similar composition: (i) subduction-zone metamorphism may occur in H2O-undersaturated conditions induced by the crystallization of a significant modal amount of lawsonite, although the transition from lawsonite blueschist facies to amphibolite-greenschist facies may involve significant hydration, principally as a result of lawsonite breakdown. (ii) The analysed values of Fe2O3 may not reflect the oxidation state during the main metamorphic evolutionary stage and are probably easily modified by superficial alteration, even in apparently fresh samples

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Massif

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Citations (1)

Geoquímica de las micas blancas detríticas de las rocas ediacarenses y cámbricas del Antiforme del Narcea (NO España)

Geogaceta (2006)

Isabel Abad Gabriel Gutiérrez‐Alonso Frank García Javier Fernández‐Suárez

Detrital minerals provenance studies have become a common tool to decipher paleogeographic scenarios in many orogenic belts. Together with the geochronological single mineral dating, the geochemistry of detrital minerals can provide insights on the source rocks of the studied detrital minerals. In this paper we study the chemistry of the detrital micas from two samples of Ediacaran and Cambrian age. The obtained results provide an almost identical chemical signature for the studied detrital white micas in both samples. The fengitic vector conditions the Fe+Mg proportion with some influence of the ferrimuscovitic vector mainly in the cambrian sample. The results point towards an origin of the sediments from LP igneous or metamorphic source rocks.

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The Calzadilla Ophiolite (SW Iberia) and the Ediacaran fore-arc evolution of the African margin of Gondwana

Gondwana Research (2018)

Ricardo Arenas Javier Fernández‐Suárez P. Montero Rubén Díez Fernández Pilar Andonaegui

Ultramafic rock

10.1016/j.gr.2018.01.015

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Citations (42)

Genesis and rank distribution of Upper Carboniferous coal basins in the Cantabrian Mountains, Northern Spain

International Journal of Coal Geology (2008)