Late Triassic adakitic rocks in the Selenge igneous rock complex, northern Mongolia: petrogenesis and tectonic implications

Abstract

In northern Mongolia, in the region along the southern margin of the former Siberian continent, Permian–Triassic adakitic rock complexes formed by the melting of the oceanic slab are widely exposed (Selenge Igneous Rock Complex: SIC). However, the petrogenesis of the SIC remain incompletely constrained. This study presents new whole-rock geochemical data of volcanic rocks from the Bugat area and of intermediate dikes intruding into the SIC. Besides, we report U Pb zircon ages for the volcanic rock and a dike. The volcanic rock succession in the Bugat area consists of intermediate to felsic lava and pyroclastic rocks. The intermediate lava is characterized by high La/Yb, Sr/Y, and Sr/La ratios and low K 2 O/Na 2 O ratio, consistent with adakitic characteristics. The samples from the lava yield zircon U Pb ages of 219.3 ± 4.5 Ma and 223.0 ± 1.4 Ma. The intermediate dike also exhibits adakitic geochemical characteristics and yields a zircon U Pb age of 211.2 ± 4.9 Ma. Previous studies have documented Permian–Triassic adakitic magmatism at ca. 257–236 Ma and ca. 226 Ma within the SIC and its northeastern extension, while this study identifies the Late Triassic magmatic events at ca. 220 Ma and ca. 211 Ma. Together with previous studies and our results, it is suggested that episodic or long-lived slab-melt-related adakitic magmatism had occurred along the Siberian continental margin spanning approximately 50 Myr.