Structural assemblage of high-pressure mantle and crustal rocks in a subduction channel (Cabo Ortegal, NW Spain)

Abstract

High-pressure metamorphic fold-nappes and ductile thrusts occur in the Cabo Ortegal upper allochthons. They involve arc-root lithospheric mantle peridotites, high-pressure volcanic-arc granulites, normal mid-oceanic ridge basalt eclogites and shallow crustal volcanosedimentary high-pressure gneiss units. Confluence of units from such disparate tectonic settings occured at an eo-Hercynian convergent plate margin. Their internal deformation, juxtaposition, and high-pressure synmetamorphic reworking resulted from kinematically simple but intense and polyphase ductile deformations. Fold nappes exhibit a remarkable sheath-like form and contain mineral and stretching lineations defined by high-pressure mineral assemblages subparallel to fold axes. We argue that these structures outline the internal organization of high-pressure sheets at deep tectonic realms of an oblique subduction/collision orogenic channel.