Granites of the Southern Mongolia Carboniferous Arc: New geochronological and geochemical constraints

The crust in southern Mongolia is part of the Central Asian Orogenic Belt. a vast accretionary orogen that records the opening and closure of the Palaeo-asian Ocean in the late Proterozoic to Palaeozoic The crustal evolution of the region is revealed in basement inliers that also contain intrusion-related porphyry ore bodies that are important mineral exploration targets The Saykhandulaan inlier in Southeast Mongolia is a Devonian-Carboniferous segment of island-arc crust, which is dominantly composed of extrusive and sedimentary lithologies. but which also contains the Oyut Ulaan I-type quartz-monzonite intrusion A U-Pb zircon age for the Oyut Ulaan monzonite indicates emplacement at 330 0 +/- 0 5 Ma To the east of the Saykhandulaan inlier. intrusive complexes dominate the neighbouring Mandakh inlier New ages are presented for four of these plutons, the Bronze Fox granodiorite (333.6 +/- 0 6 Ma), the Narin Hudag monzonite (333 2 +/- 0 6 Ma), the Shuteen quartz monzonite (325 5 1 0 Ma), and the North Mandakh granite (292 3 +/- 0 5) The intrusive bodies of the Saykhandulaan and Mandakh inliers have two distinct geochronological and geochemical associations: 1) mid-Carboniferous I-type monzonites that constitute the most easterly intrusive expression of the Southern Mongolia Carboniferous Arc and, 2) Early Permian A-type and peralkaline granites that represent a post-orogenic phase of voluminous granite emplacement Both groups are significantly younger than the nearby Oyu Tolgoi and Tsagaan Suvarga Cu-porphyry ore bodies. which have previously been dated as early- and late-Devonian respectively. The new data presented here provide constraints on the timing of the transition from island-arc magmatism to post-collisional extension-related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to Cu-Au mineralisation. (C) 2010 Elsevier B.V All rights reserved