Burd Gol Granite Massif as a product of the Late Cambrian post-orogenic magmatism in the SE part of the Lake Zone, Gobi Altay, SW Mongolia

Abstract

*Corresponding author Intrusion of the Cambrian Burd Gol Granite Massif into the Proterozoic metamorphic rocks of the Zamtyn Nuruu and molasse-like sediments of the Boomyn Khudag Fm. culminated the collisional events of the Caledonian evolution in the SE part of the Lake Zone, Gobi Altay, SW Mongolia. The monotonous leucogranites of the Burd Gol Massif have a high-K calc-alkaline, subaluminous to slightly peraluminous geochemical signature with an intermediate initial Sr ratio ( 87 Sr/ 86 Sr 510 = 0.7064) and rather unradiogenic Nd (e 5 Nd 10 = –1.5 and –0.2). The laser ablation ICP-MS U–Th–Pb radiometric dating of monazites and zircons from these rocks yields intrusive ages between 506.4 ± 5.4 and 513.4 ± 4.3 Ma (2σ). The final stage of magmatic activity is documented by the Ar–Ar dating of muscovite from a pegmatite dyke at 485.1 ± 3.2 Ma. The granites intruded and thermally influenced the terrestrial clastic sediments of the Boomyn Khudag Formation, whereby the thermal metamorphism of sediments was characterized by a muscovite growth. These new data argue against the previously assumed Permian age of the Burd Gol Massif and the Lower–Middle Devonian age of the Boomyn Khudag sedimentary formation and illustrates the terrestrial evolution in this part of the Lake Zone during the Cambrian.