Exhumation of high-pressure rocks: role of late faulting (Eastern Ossa–Morena Complex, Iberian Massif)

Abstract

[EN] Exhumation of high-pressure (P) rocks may require a long path and multiple deformation phases. During this journey, late faults and folds can introduce changes to the primary tectonic stacking and lead to misleading conclusions regarding subduction polarity and plate reconstructions. This hypothesis has been tested positively via mapping and structural analysis in the eastern section of the Central Unit (Eastern Ossa–Morena Complex, Iberian Massif), which comprises Devonian high-P rocks subducted during the Variscan Orogeny. Following subduction beneath Gondwana, exhumation was assisted by in-sequence underthrusting of the continental crust, along with thinning of the overlying and formerly accreted crust. Convergence persisted and was accommodated by Gondwana-directed, out-of-sequence thrusts. Subsequent extension favoured erosion and basin inception during the Early Carboniferous, whereas further convergence produced late folding and faulting during Late Carboniferous sinistral transpression. Late faults duplicated the Devonian suture zone several times, producing a series of closely-spaced exposures of a single suture. The manner in which late faults affected the Devonian suture produced an outcome that could be mistaken for a collection of individual suture zones. Late faults may distort the primary relationships between upper and lower plates; however, they provide a geometry-based approach for restoring the primary geometry of suture zones.