Nova Terra 52

U-Pb geochronology and isotopic geochemistry of adakites and related magmas in the Ediacaran arc section of the SW Iberian Massif: The role of subduction erosion cycles in peri-Gondwanan arcs Esther Rojo-Pérez a, ⇑ , Ulf Linnemann b , Mandy Hofmann b , José M. Fuenlabrada c , Johannes Zieger b , Javier Fernández-Suárez a , Pilar Andonaegui a , Sonia Sánchez Martínez a , Rubén Díez Fernández d , Ricardo Arenas a a Departamento de Mineralogía y Petrología and Instituto de Geociencias (UCM, CSIC), Universidad Complutense, 28040 Madrid, Spain b Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Königsbrücker Landstr. 159, Dresden 01109, Germany c Unidad de Geocronología (CAI de Ciencias de la Tierra y Arqueometría), Universidad Complutense. 28040 Madrid, Spain d Instituto Geológico y Minero de España, 28760 Tres Cantos, Madrid, Spain a r t i c l e i n f o Article history: Received 25 August 2021 Revised 7 March 2022 Accepted 17 April 2022 Available online 22 April 2022 Handling Editor: Y.J. Liu Keywords: Peri-Gondwana arc Subduction erosion Adakite signature Cadomian basement a b s t r a c t In the peri -Gondwanan Ediacaran arc section outcropping in the SW of the Iberian Massif (Mérida region), changes in the subduction angle and subduction rate, variable participation of highly modified mantle sources together with the role of old crustal material and juvenile mafic rocks driven by the incoming slab, occur with a recognizable cyclicality and can be traced according to the geochronology, geochem- istry and isotopic sources of the magmatic bodies. Our results support the initial existence of a mantle wedge highly modified due to percolation of significant volumes of variably old crustal materials, whose isotopic sources are almost identical to those found in the oldest known metasedimentary sequence described in SW Iberian Massif, the Serie Negra Group. Old crustal sources, analogous to those of this ser- ies were introduced to high depths by common subduction an also probably by significant subduction erosion. During the oldest period recorded in the study arc section, between c. 602 and c. 550 Ma, sub- duction episodes that involve high rates of crustal material along with an eventual incorporation of mafic and ultramafic materials from the incoming oceanic plate, favoured by low subduction angles, lead to the generation of more silicic magmas with adakitic geochemical affinity and isotopic signature (Nd-Sr) with crustal tendency. However, an increase in the subduction angle and change to a roll-back stage dated at c. 540 Ma, caused significant decrease in the access of cortical material to the subduction channel, favouring generation of typical calc-alkaline magmas derived from the modified mantle wedge, which is also con- sistent with more juvenile Nd-Sr ratios. The correlation found between the magmatic events and the involved tectonic processes suggests that subduction erosion mechanisms have been very likely under- estimated as active dynamic processes along the peri -Gondwana margin during at least Neoproterozoic to Early Cambrian times. 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction Continental arcs have traditionally been considered as the main continental crust-forming setting, as well as destroying it in a roughly equivalent proportion (e.g. Taira et al., 1997; Rudnick and Gao, 2003; Stern and Scholl, 2010). In these areas, it is difficult to quantify and evaluate the role played by the mantle wedge and the slab components in the magma generation during the evolu- tion of the arc cycle, especially in ancient continental margins (e.g. Pearce and Parkinson, 1993; Plank and Langmuir, 1998; Schmidt and Jagoutz, 2017). Subduction zones are key conduits https://doi.org/10.1016/j.gr.2022.04.011 1342-937X/ 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Departamento de Mineralogía y Petrología e Instituto de Geociencias (UCM, CSIC), Facultad de Geología, Universidad Complutense de Madrid, C/ José Antonio Novais, No 12, 28040 Madrid, Spain. E-mail addresses: e.rojo@ucm.es (E. Rojo-Pérez), ulf.linnemann@senckenberg.de (U. Linnemann), mandy.hofmann@senckenberg.de (M. Hofmann), jmfuenla@ucm.es (J.M. Fuenlabrada), johannes.zieger@senckenberg.de (J. Zieger), jfsuarez@ucm.es (J. Fernández-Suárez), andonaeg@ucm.es (P. Andonaegui), s.sanchez@geo.ucm.es (S. Sánchez Martínez), r.diez@igme.es (R. Díez Fernández), rarenas@ucm.es (R. Arenas). Gondwana Research 109 (2022) 89–112 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr