Abstract
The Central Asian Orogenic Belt had been formed by amalgamation of voluminous subduction–accretionary complexes during the Late Neoproterozoic to the Mesozoic period. Mongolia is situated in the center of this belt. This study presents new zircon U–Pb geochronological, whole-rock major and trace element data for granitoids within central Mongolia and discusses the tectonic setting and evolution of these granitic magmas during their formation and emplacement. The zircon U–Pb ages indicate that the magmatism can be divided into three stages: the 564–532 Ma Baidrag granitoids, the 269–248 and 238–237 Ma Khangai granitoids. The 564–532 Ma Baidrag granitoids are adakitic, have an I-type affinity, and were emplaced into metamorphic rocks. In comparison, the 269–248 Ma granitoids have high-K, calc-alkaline, granodioritic compositions and are I-type granites, whereas the associated the 238–237 Ma granites have an A-type affinity. The 564–532 Ma Baidrag and 269–248 Ma Khangai granitoids also both have volcanic arc-type affinities, whereas the 238–237 Ma granites formed in a post-collisional tectonic setting. These geochronological and geochemical results suggest that arc magmatism occurred at the 564–532 Ma which might be the oldest magmatic activity in central Mongolia. Between the Baidrag and the Khangai, there might be paleo-ocean and the oceanic plate subducted beneath the Khangai and produced voluminous granite bodies during the 269–248 Ma. After the closure of the paleo-ocean, the post collisional granitoids were formed at the 238–237 Ma based on the result of later granitoids in the Khangai area.
Highlights
Mongolia is located within the central part of the Central Asian Orogenic Belt (CAOB), which is bounded to the north by the Precambrian Siberian craton and to the south by the Tarim and North China cratons (Badarch et al, 2002; Windley et al, 2007)
The new zircon U–Pb dates obtained during this study indicate that the Khangai region records three stages of magmatism at 564–532, 269– 248, and 238–237 Ma
Zircon U–Pb dating indicates that the magmatic activity in central Mongolia can be broadly divided into three stages that involved the formation of the 564–532 Ma Baidrag granitoids and the 269–248 and 238 –237 Ma Khangai granitoids
Summary
Mongolia is located within the central part of the Central Asian Orogenic Belt (CAOB), which is bounded to the north by the Precambrian Siberian craton and to the south by the Tarim and North China cratons (Badarch et al, 2002; Windley et al, 2007). Devonian and Carboniferous sedimentary rocks are widely distributed in the Khangai area (Fig. 1) and together constitute the Khangai–Khentii Basin (Tomurtogoo et al, 1998; Kelty et al, 2008; Purevjav and Roser, 2012) This basin is located within the central and northeastern parts of Mongolia and extends into Russia, where it forms the western end of the Khangai–Khentii– Daurian zone of the Mongol–Okhotsk Fold Belt (MOFB) (Zorin, 1999). These sedimentary rocks host voluminous early Permian and Triassic granitoids that are associated with large contact metamorphic aureoles (Orolmaa et al, 2008). The sampling undertaken during this study was undertaken along a longitudinal traverse, yielding a total of 105 granitic samples (Fig. 1)
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