Evolution of the Ediacaran-Cambrian arc section preserved in the SW Iberia (Ossa-Morena Complex, Variscan Belt)

The geochemistry of sedimentary sequences allows the recognition of patterns and shifts in geodynamic settings. On active margins, the contribution of these sequences to arc magmatism through processes such as subduction erosion is being actively investigated. Thick sequences were sedimented along the Gondwana margin between the Ediacaran and Cambrian times. These preserve the evolution of their sources, which are closely related to the activity of arc systems and nearby continental areas. In the Variscan Belt, the SW Iberian Massif (Ossa-Morena Complex) preserves a section of an arc whose evolution is followed through the characterisation of subduction-related magmatism and the coeval metasedimentary record, during a time interval spanning almost 100 Ma. This study reveals that arc magmatism was linked to synorogenic sedimentation in a complex and poorly explored way. In this sense, arc recycling is shown by the isotopic (Nd) equivalence between the sedimentary series and the mafic magmatism related with subduction onset (pre- to 602 Ma) preserved in this section. Early magmatic pulses of arc building (c. 602-550 Ma) are characterised by their adakitic signature related to the melting of a significant volume of slab-induced sediments, probably favoured by subduction erosion. Meanwhile, during late stages (c. 540-534 Ma), magmatism evolved towards greater mantle input associated with the progressive variation of the slab angle. This study provides a model for the petrogenetic and geodynamic evolution of the arc from the Ediacaran to the early Cambrian times, improving the accuracy of future paleogeographic reconstructions.