New geodynamical model for the regional Tertiary extension during the Zagros orogeny: A transtensional arc?

The Zagros orogeny in Iran is associated with two successive geodynamic events during the Tertiary period, a Paleogene NE-directed regional crustal extension followed by a Miocene NW-directed regional crustal extension and a magmatic flare-up. The current study was undertaken to reanalyze previous structural work developed on the extensional Chapedony metamorphic core complex in Central Iran exhumed during Paleogene times. A new strain framework based on progressive dextral transtensional tectonics is proposed to explain the recorded structures. Its regional significance with other extensional areas in Iran is examined and an improved tectonic model is proposed to explain the southwestward drift of extension. This study emphasizes the key role of strain partitioning on the overriding plate as it relates to the increase in convergence obliquity during the Tertiary period. It is proposed that the regional extension is related to development of transtensional tectonics.