Paleozoic tectonothermal event in Mt. Dongbatu, Dunhuang terrane, southernmost Central Asian Orogenic Belt (CAOB): Implications for petrogenesis and geological evolution.

Abstract In this contribution, systematic petrographical, whole-rock geochemical, geochronological and zircon Lu-Hf isotopic investigations were conducted on Paleozoic (ca. 410–400 Ma) metamorphic-magmatic rocks from Mt. Dongbatu in the central Dunhuang terrane. The metamorphic rocks in the Shangkouzi area are of meta-calcsilicate rocks, and granitoid rocks occurring within these rocks are geochemically of trondhjemite. Whereas, metamorphic rocks in the Gangou area are metabasaltic rocks. LA-ICP MS zircon U-Pb dating results reveal that these metamorphic-magmatic rocks recorded ca. 1.6 Ga magmatic event and metamorphic events of ca. 410–400 Ma and ca. 370 Ma. Field occurrence, whole-rock geochemistry, mineral composition and zircon Hf isotopes suggest that the 1.6 Ga mantle-derived basaltic magma, together with iron-rich and Ca-rich components and mica-quartz schist of Paleoproterozoic supracrustal rocks probably contributed to protolith of meta-calcsilicate rocks in the Shangkouzi area, and granitoid rocks within meta-calcsilicate rocks were possibly generated by partial melting of calcsilicate rocks. Combined with previously published data, it is suggested that the protoliths of Paleozoic high-grade metamafic rocks in the Dunhuang terrane are predominantly composed at least of basaltic rocks produced by magmatic events of 2.5–1.8 Ga, ca. 1.8 Ga and ca. 1.6 Ga. The Paleozoic granitoid rocks in the Dunhuang terrane might have been derived from different magma sources as partial melting of subducted plate, or thickened lower continental crust, or pre-existing basaltic rocks produced by 1.6 Ga and 1.8 Ga magmatic activities, and calcsilicate rocks genetically associated basaltic magmatism at ca. 1.6 Ga. Considering regional tectonic evolution, it can be concluded that the Dunhuang terrane was probably in a post-collisional extension setting at ca. 1.6 Ga, producing certain amount of basaltic and calcsilicate rocks. From the beginning of Silurian (ca. 440 Ma), the Dunhuang terrane was involved in the orogenic processes related to the closure of the southern Paleo-Asian Ocean, becoming the active continental margin of the southernmost CAOB. Graphical abstract Unlabelled Image Highlights • Calcsilicate rock was regionally formed during 1.6 Ga magmatic process. • Paleozoic metamorphism-magmatism widely took place in the Dunhuang terrane. • Protolith of Paleozoic metamafic rocks is mainly of Paleoproterozoic basic rocks. • Paleozoic granitoids derived from various magmatic sources. • Dunhuang terrane witnessed Paleozoic geological evolution of southernmost CAOB. [ABSTRACT FROM AUTHOR]