Paleozoic subduction of the Mongol-Okhotsk oceanic plate: insight from the petrogenesis of Ordovician to Devonian granitic plutons in the Hangay Range, central Mongolia

Abstract

<p>Email: pengfeili@gig.ac.cn; pengfeili2013@gmail.com</p><p> </p><p>The pre-Mesozoic subduction history of the Mongol-Okhotsk oceanic plate has been poorly understood. Here we conducted geochronological and geochemical studies on four granitic plutons in the westernmost Mongol-Okhotsk Orogen (Hangay Range), with an aim to understand their petrogenesis and role in the Paleozoic tectonic evolution of the Mongol-Okhotsk Orogen. Our geochronological results constrain four granitic plutons to be emplaced from middle Ordovician to early Devonian. Geochemically, the Ordovician pluton belongs to A2-type granites, and three Silurian to Devonian plutons show the characteristics of I-type granites. These granitic plutons were probably generated by partial melting of basaltic rocks in the lower crust given the high contents of Na<sub>2</sub>O and K<sub>2</sub>O. The negative ε<sub>Nd</sub>(t) values (-4.7 to -0.9) and variable ε<sub>Hf</sub>(t) values (-2.6 to +6.1) for the four granitic plutons suggest that ancient basement materials were possibly involved in the magma source. We further investigate the geodynamic origin of these plutons in the context of the Paleozoic tectonics of the Mongol-Okhotsk Orogen, and we conclude that they were probably formed in response to the Ordovician to Devonian subduction of the Mongol-Okhotsk oceanic plate.</p>