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Granites of the southern Mongolia Carboniferous arc : new geochronological and geochemical constraints

By James H.S. Blight, Quentin G. Crowley, Michael G. Petterson and Dickson Cunningham

Abstract

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.\ud \u

Publisher: Elsevier
Year: 2010
DOI identifier: 10.1016/j.lithos.2010.01.001
OAI identifier: oai:nora.nerc.ac.uk:9545

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