The Ganj Complex reinterpreted as a Late Cretaceous volcanic arc: Implications for the geodynamic evolution of the North Makran domain (southeast Iran)

Abstract

The North Makran domain (southeast Iran) is part of the Makran accretionary wedge and consists of an imbricate stack of continental and oceanic tectonic units. Among these, the Ganj Complex was up to now regarded as an ophiolite unit. This Complex is represented by a >2000 m thick sequence consisting of a dyke-swarm showing transition to a volcano-sedimentary sequence with local interlayerings of turbidite beds. This sequence grades-up to a turbidite sequence whose calcareous nannofossil biostratigraphy indicates a Turonian-Coniacian age. Volcanic rocks and dykes are represented mainly by intermediate and acidic rocks and minor basalts. They show volcanic arc affinity, with calc-alkaline and island arc tholeiitic compositions, which locally show adakite signature. In the turbiditic arenites, volcanic-derived debris is predominant and it is associated with moderate amounts of coheval calcareous rock fragments and bioclasts; thus suggesting sediment provenance from intrabasinal volcanic arc and carbonatic platform source rocks.In contrast to previous interpretations, our new data indicate that the Ganj Complex represents remnants of a Turonian-Coniacian volcanic arc that was most likely forming in a relatively shallow marine environment in an extensional intra-arc setting. We therefore propose a new tectonic model in which the Ganj volcanic arc formed in the southern margin of the Lut block as a consequence of the north-dipping subduction of the North Makran oceanic basin. We suggest that this subduction was coeval with the subduction of the Southern Neo-Tethys, which was active to the south of the North Makran Ocean.