The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

Abstract

The tectonothermal evolution of the eclogite facies gneisses of the Cabo Ortegal Complex has been investigated using new field and petrologic studies. This gneissic unit is included in the high-pressure and high-temperature (HP-HT) upper units of the allochthonous complexes of NW Iberia, a Cambrian arc-derived peri-Gondwanan terrane emplaced above ophiolitic units considered to represent the Rheic Ocean suture. Two detailed cross-sections performed in excellent exposures on the Cantabrian coast allows a clear understanding of the lithological constitution and deformations affecting the unit. The eclogitic gneiss unit is constituted by metasedimentary gneisses with abundant mafic inclusions, felsic rocks and rare ultramafic inclusions. The felsic rocks range from centimetric leucosomes to metric bodies and most of them were generated during extensive partial melting affecting the unit. The first tectonic fabric detected in the unit is a rarely preserved S1 foliation developed during subduction (ca. 400-390 Ma; 22 kbar). A drastic and fast exhumation (ca. 390 Ma; 12-10 kbar) generated a regional mylonitic foliation which represents the most prominent structural feature in the HP-HT upper units. The consecutive generation of extensional detachments, recumbent folds and a basal thrust occurred during the change from continental-type subduction to the underthrusting of ophiolitic units. These consecutive structures are probably related and the consequence of a long and pronounced exhumation of the subducted complex. The tectonothermal evolution of the eclogite facies gneisses of the Cabo Ortegal Complex represents an illustrative example of the intricate history of these deeply subducted units, which are relatively frequent in the suture zone of the Variscan Belt. It is important to remark that the structural, metamorphic and geochronological patterns in the evolution of this gneissic unit follows almost perfectly the ISSN (print): 1698-6180. ISSN (online): 1886-7995

The metahyaloclastitic matrix of a unique metavolcanic block reveals subduction in the Somozas Mélange (Cabo Ortegal Complex, NW Iberia): tectonic implications for the assembly of Pangea

“…The lower section of this terrane is affected by a high-P and high-T metamorphic event that has been correlated with other ultra-high-P events recorded in other regions of the Variscan orogen (Vogel, 1967;Gil Ibarguchi et al, 1990;Lardeaux et al, 2001;Arenas & Mart ınez Catal an, 2002;Abalos et al, 2003). This high-P metamorphic event has been dated at c. 410-390 Ma, both in eclogites and in mafic granulites (Ord oñez Casado et al, 2001;Fern andez-Su arez et al, 2007;Albert, 2015). The U-Pb geochronology and Hf isotopic content of detrital zircon confirm the same provenance and maximum depositional ages for all sections of the upper units, including the lower part affected by high-P metamorphism (Albert et al, 2015b).…”

“…This high‐ P metamorphic event has been dated at c . 410–390 Ma, both in eclogites and in mafic granulites (Ordóñez Casado et al ., ; Fernández‐Suárez et al ., ; Albert, ). The U–Pb geochronology and Hf isotopic content of detrital zircon confirm the same provenance and maximum depositional ages for all sections of the upper units, including the lower part affected by high‐ P metamorphism (Albert et al ., ).…”

Provenance of the HP–HT subducted margin in the Variscan belt (Cabo Ortegal Complex, NW Iberian Massif)

“…112989) is from the Area da Vaca beach (43°43′31.2″N, 7°51′44.6″W), at the 270 m point of the Area da Vaca geological section presented by Albert et al . (). Sample GCH–21 (ref.…”

Serpentinite from Moeche (Galicia, North Western Spain). A Stone Used for Centuries in the Construction of the Architectural Heritage of the Region

“…The study area is located in the NW of Spain and belongs to the Cabo Ortegal Complex, one of the five allochthonous complexes outcropping in the NW of the Iberian Massif and framed within a context of collision between Gondwana and Laurasia [22][23][24][25] (Figure 1).…”

“…Our samples were collected in quarries located in Moeche, in one of the massifs from the uppermost unit of this complex. [25]. The solid black arrow shows the Moeche study area.…”