Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)

摘要

The Iranian ophiolites are part of the vast orogenic suture zones that markthe Alpine-Himalayan convergence zone. Few petrological and geochronologicaldata are available from these ophiolitic domains, hampering a fullassessment of the timing and regimes of subduction zone metamorphism andorogenic construction in the region. This paper describes texture,geochemistry, and the pressure-temperature path of the Early Cretaceous maficgranulites that occur within the Tertiary Sabzevar ophiolitic suture zone ofNE Iran. Whole rock geochemistry indicates that the Sabzevar granulites arelikely derived from a MORB-type precursor. They are thus considered asremnants of a dismembered dynamo-thermal sole formed during subduction of aback-arc basin (proto-Sabzevar Ocean) formed in the upper-plate of theNeotethyan slab. The metamorphic history of the granulites suggests ananticlockwise pressure-temperature loop compatible with burial in a hotsubduction zone, followed by cooling during exhumation. Transition from anascent to a mature stage of oceanic subduction is the geodynamic scenarioproposed to accomplish for the reconstructed thermobaric evolution.When framed with the regional scenario, results of this study point todiachronous and independent tectonic evolutions of the different ophioliticdomains of central Iran, for which a growing disparity in the timing ofmetamorphic equilibration and of pressure-temperature paths can be expectedto emerge with further investigations.