Allochthonous terranes involved in the Variscan suture of NW Iberia: A review of their origin and tectonothermal evolution

Arenas, Ricardo; Martı́nez, Sonia Sánchez; Fernández, Rubén Díez; Gerdes, Axel; Abati, Jacobo; Fernández‐Suárez, Javier; Moreno, Pilar Andonaegui; Cuadra, P. González; López-Carmona, Alicia; Albert, Richard; Fuenlabrada, José Manuel; Pascual, Francisco J. Rubio

doi:10.1016/j.earscirev.2016.08.010

Cited by 77 publications

(39 citation statements)

References 111 publications

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“…The three allochthons where assembled in an accretionary prism during early Variscan plate convergence (Middle and Upper Devonian), related with oceanic closure and subduction (Arenas et al, ; Martínez Catalán et al, ). At the beginning of the Carboniferous, a collisional regime was installed, and several contractional episodes have been distinguished (Alcock et al, ; Martínez Catalán et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

Magnetic Anomalies in Extensional Detachments: The Xistral Tectonic Window of the Lugo Dome (NW Spain)

et al. 2018

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The Eastern Galicia Magnetic Anomaly (EGMA) is a conspicuous feature of the aeromagnetic map of Iberia, which structurally overlaps the Lugo and Sanabria domes, two spatially linked late Variscan extensional structures that delineate a segment of the Ibero‐Armorican Arc. In the northern part of the Lugo Dome, the Xistral Tectonic Window exposes a deep section of the continental crust, which includes several extensional detachments and associated shear zones. The aim is to check whether or not there is a correlation between the extensional process and the EGMA. A map of the magnetic anomaly of the Xistral Tectonic Window acquired on land improves the resolution of the aeromagnetic data and shows that the EGMA is actually composed by several shorter wavelength anomalies reaching amplitudes up to 1,214 nT. Their location in relation to outcropping rocks and structures, together with 2‐D modeling, shows a conspicuous link between the anomalies and the extensional detachments. On a larger scale, the EGMA forms the northern part of a largeanomaly occupying the core of the Central Iberian Arc. This anomaly can be related to extension caused by gravitational collapse of the thickened Variscan crust, implying that like the EGMA, local anomalies might reflect extensional structures, many of which may remain buried. Our study may shed light on the origin of magnetic anomalies in other gneiss domes as it shows that they can be related with the doming process instead of being inherited from older rocks presently outcropping at the core of the domes.

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Section: Geological Settingmentioning

confidence: 99%

Magnetic Anomalies in Extensional Detachments: The Xistral Tectonic Window of the Lugo Dome (NW Spain)

et al. 2018

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“…There is, however, some controversy regarding (1) whether there was a significant magmatic event in the early Carboniferous, for which there was previously scarce evidence (see following), and (2) whether the Variscan magmatic activity was continuous or occurred through discrete and relatively short-lived pulses. Unravelling these issues is one of the key elements to better constrain and interpret the different processes involved in the collisional scenarios that led to the Variscan orogeny in Iberia during late Paleozoic time (e.g., Matte, 2001;Martínez Catalán et al, 2007;Ballèvre et al, 2009;Arenas et al, 2016; and the subsequent development of the IberoArmorican arc (e.g., Weil et al, 2013, and references therein; Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?

et al. 2018

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In this study we report laser ablation-inductively coupled plasma-mass spectrometer U-Pb ages of granitoids from the so-called early granodiorites of the northwest Iberian Variscan belt. The U-Pb results attest to significant magmatic activity in Visean time (ca. 347-337 Ma) that generated a hitherto poorly constrained granitoid suite in the northwest Iberian tract of the western European Variscan belt realm. This early Carboniferous suite (ECS) is mainly composed of peraluminous cold and hot crustal granodiorites and monzogranites with minor associated mafic rocks that attest to minor involvement of mantle melting. Based on the geochronological and geochemical data, we compare the Visean granitoids with younger Variscan granitoids in northwest Iberia and, in view of the tectonothermal scenarios of the Variscan collision in northwest Iberia, propose a model for the genesis of the ECS in northwest Iberia that involves rapid melting upon fast exhumation of the thickened Gondwanan crust in the course of the protracted Variscan collision.

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“…The Allochthonous Complexes comprise three main sets of tectono-metamorphic units (Arenas et al, 1986(Arenas et al, , 2016b. The top is occupied by an Upper Allochthon of Upper Proterozoic-Lower Paleozoic metasediments and Cambrian intrusives with 70 HP-HT and MP metamorphic recrystallizations, Early Devonian in age.…”

Section: The Allochthonous Complexesmentioning

confidence: 99%

“…The parautochthonous domains of the European Variscan Orogen represent paleogeographic and geodynamic intermediate pieces that separate a mainland autochthon, resting below, from an upper set of allochthonous terranes with ophiolites and High-Pressure (HP) rocks representing a suture zone or zones (Matte and Burg, 1981;Arenas et al, 1986;Farias et al, 1987;Martínez Catalán, 1990;Ribeiro et al, 1990;Franke, 2000;Ballèvre et al, 2009;Díez Fernández et al, 2012a;Farias et al, 2014). In contrast to the Early Variscan subduction-related HP-LT metamorphism that affected the overlying Basal Units of 40 the Lower Allochthon in NW Iberia (Munhá et al, 1984;Gil Ibarguchi and Dallmeyer, 1991;Arenas et al, 1995Arenas et al, , 1997Gil Ibarguchi, 1995;Martínez Catalán et al, 1996;Rodríguez et al, 2003;Balcázar et al, 2005;López Carmona et al, 2013) and other correlatable Variscan suture outcrops of the Iberian Massif (Díez Fernández and Arenas, 2015;Arenas et al, 2016a;2016b;Abati et al, 2018), the parautochthonous units are commonly thought not to have been involved in the continental subduction process. Their noticeable imprints of intermediate to low-pressure 45 metamorphism correspond to the subsequent collisional tectonics that also affected the autochthonous domains (e.g.…”

Section: Introduction 35mentioning

confidence: 99%

From subduction to collision in the Parautochthon and autochthon of the NW Variscan Iberian Massif

Pascual

Parra

Valverde-Vaquero

et al. 2020

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A stacking of nappes forms the Parautochthonous Domain located beneath the Allochthonous Complexes of the NW Iberian Massif. Lower Paleozoic metasedimentary and felsic metavolcanic rocks, including some riebeckite gneiss, form the uppermost nappe of the Parautochthon. Micaschists of this nappe may contain albite porphyroblasts with aligned mineral microinclusions defining a relic internal schistosity. Thermobarometric estimates on the relic mineral assemblage 15 suggest an early M1 stage of High-Pressure, Low-Temperature (HP-LT) metamorphism (11-14 kbar; 450-500 ºC), probably related to the same continental subduction process that affected the overlying Lower Allochthon nappes or Basal Units. This uppermost nappe was emplaced onto its relative autochthon by a broad, ductile shear zone that shows top-to-the-E/ENE shear-sense and whose exposure has lateral continuity through to the basal thrust of the Lower Allochthons in the Bragança Complex. The HP-LT metamorphism and its hanging wall position relative to the basal thrust of the Allochthonous 20Complexes, suggest a re-interpretation of this uppermost parautochthonous nappe as another nappe of the Lower Allochthon.In turn, the other parautochthonous nappes comprise both, Lower Paleozoic pre-orogenic rocks, with no M1 relics, and Upper Paleozoic syn-orogenic rocks. Shear-sense criteria related to the current juxtaposition of the Parautochthon Domain onto the Central Iberian autochthon show contrasting top-to-the-S/SE kinematics. The whole orogenic section was affected by an M2 episode of recrystallization under intermediate P/T conditions during the first stages of collision. P-T estimates on 25 kyanite-bearing schists from the upper sections of the autochthon (9.0 kbar; 425-450 ºC) are consistent with a geothermal gradient somewhat lower than the classical Barrovian one at the beginning of collision. Thermobarometric calculations on schists from the lower parautochthonous nappes yield peak metamorphic conditions around 7.5 Kbar and 600-700 ºC, constraining the original thickness of the allochthonous/parautochthonous pile to about 22.5-27.0 km. Schists sampled from deeper sections of the autochthon yield M2 conditions around 11-12 kbar and 700-725 ºC, matching those registered by 30 correlative regions from Central Iberia. Subsequent M3 syn-collisional recrystallization under High-Temperature and Low-Pressure conditions is associated with top-to-the-N/NW and top-to-the-S/SE extensional flow. The early metamorphic 2 Geological setting The NW of the Variscan Iberian Massif is formed by an allochthonous/parautochthonous tectonic pile (Ries and Shackleton, 1971), the so-called Galicia -Trás-os-Montes Zone (GTMZ, Farias et al., 1987; Fig. 1), emplaced onto the autochthonous Central Iberian Zone (CIZ) in Early Carboniferous times (Dallmeyer et al., 1997). The Galicia -Trás-os-Montes Zone in overview 65The GTMZ is divided into the Domain of the Allochthonous Complexes, structurally above, and the parautochthonous Schistose Domain, below. The Allochthonous ComplexesThe All...

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Allochthonous terranes involved in the Variscan suture of NW Iberia: A review of their origin and tectonothermal evolution

Cited by 77 publications

References 111 publications

Magnetic Anomalies in Extensional Detachments: The Xistral Tectonic Window of the Lugo Dome (NW Spain)

Magnetic Anomalies in Extensional Detachments: The Xistral Tectonic Window of the Lugo Dome (NW Spain)

Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?

From subduction to collision in the Parautochthon and autochthon of the NW Variscan Iberian Massif

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