Late Cambrian Syn‐Intrusive Thickening of the Ikh Mongol Arc Domains in the Mongolian Collage

Abstract Structural analysis, U–Pb monazite and xenotime dating, Ar–Ar dating of biotite and amphibole and thermodynamic modeling of peak metamorphic assemblages allow constraining the tectono‐thermal evolution of the migmatite‐magmatite domain on the southern periphery of Precambrian Zavkhan Block. The main subvertical metamorphic fabric resulted from upright folding and almost complete transposition of early sub‐horizontal foliation of uncertain age. P–T conditions of 760–790°C at 0.7–0.8 GPa and in situ U–Pb metamorphic monazite 505–495 Ma ages characterize this tectono‐metamorphic event. It was associated with syn‐deformational partial melting and intrusion of axial planar syntectonic leucogranite veins. Monazite and xenotime from these veins give U–Pb age of c. 500 Ma, confirming that the migmatization and formation of subvertical fabric were coeval. Such time constraints are contemporaneous with ages of gneissified Ikh‐Mongol Arc granite sheets intruding horizontally shortened partially molten crust thereby confirming syn‐compressional nature of arc emplacement. Thermal modeling of cooling history of the whole migmatite‐magmatite domain constrained by Ar–Ar ages is compatible with the shortening of the hot system followed by moderate erosion. The P–T and geochronological data of the Zavkhan block margin are almost identical to those of short lived late Cambrian magmatism and metamorphism described in the Khondalite belt in Far East China and in other places of Mongolian Collage suggesting that these two domains may have formed a continuous belt.