Opening and closure of Cadomian peri-Gondwanan oceans: age and evolution of the Mérida Ophiolite (SW Iberia)



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Arenas Martín, Ricardo and Rojo-Pérez, Esther and Díez Fernández, Rubén and Albert, R. and Novo Fernández, Irene and Sánchez Martínez, Sonia and Andonaegui Moreno, Pilar and Moreno Martín, Diana and Gerdes, Axel and Garcia Casco, Antonio (2022) Opening and closure of Cadomian peri-Gondwanan oceans: age and evolution of the Mérida Ophiolite (SW Iberia). International geology review . ISSN 0020-6814

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In the SW Iberian Massif, the Ossa-Morena Complex contains a stack of units of different origin and tectonothermal evolution. Individual terranes of the complex record a Cadomian history, traditionally interpreted in relation to the dynamics of a peri-Gondwanan volcanic arc. The interpretation of the Cadomian terranes is a key issue in the reconstruction of the Ediacaran margin of Gondwana in NW Africa. In the Mérida Massif, a mafic – ultramafic unit stacked between two units of continental or arc affinity is interpreted as a Cadomian ophiolite, the Mérida Ophiolite. Within it, mafic lithologies dated at c. 596 Ma (U-Pb in zircon) have calc-alkaline or tholeiitic affinity, indicating generation in a supra-subduction zone setting. The ophiolite shows a main event of Cadomian metamorphism (c. 590 Ma, U-Pb garnet dating) with a prograde P-T path and peak conditions at c. 700°C and 8 kbar. The mafic rocks show Nd isotopic compositions clearly different from those characteristics of the mafic rocks formed in the axial zone of the volcanic arc. Hence, the Mérida Ophiolite probably represents oceanic lithosphere of a back-arc basin, opened between the volcanic arc and the outer margin of Gondwana. Closure of the back-arc occurred during collision of the volcanic arc with the margin of Gondwana (starting at c. 590 Ma), which caused rapid accretion of the back-arc oceanic lithosphere beneath the arc and prograde metamorphism typical of subduction inception. The Mérida Ophiolite was finally obducted above the continental margin of Gondwana, presently preserved in gneissic unit piled beneath the ophiolite. Cadomian evolution of this peri-Gondwanan arc section continued with new tectonothermal events dated in the range 560–540 Ma that alternated with episodes of intense magmatic activity and preceded the collapse of the magmatic arc and its erosive levelling, followed by the generation of a new episode of intense magmatic activity in the arc and the unconformable deposition of the Ediacaran-Cambrian Malcocinado Formation.

Item Type:Article
Uncontrolled Keywords:Ophiolites; Ediacaran oceans; peri-Gondwana; Cadomian Orogeny; subductioninception; Iberian massif
Subjects:Sciences > Geology > Geodynamics
Sciences > Geology > Petrology
ID Code:75774
Deposited On:25 Nov 2022 17:52
Last Modified:28 Nov 2022 08:04

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