Micro-continental blocks in Gondwana assembly: Geological and geochemical evidence of the Indochina block, SE Tibetan Plateau

Tectonic processes from the breakup of Rodinia to Gondwana assembly have been studied on large continents. However, the role of micro-continental blocks in Neoproterozoic supercontinental cycle is barely known. Geochronological and geochemical studies on a combination of 57 (meta-) sedimentary and (meta-) igneous rocks (one igneous rock and four meta-sedimentary samples are from this study) in the Indochina block (including its north part, i.e. the Simao terrane) reveal the paleoposition and tectonic processes during Precambrian supercontinental cycle. A mylonitized monzogranite from the NW part of the Indochina block (the Chongshan area) shows zircon UPb ages of 867 ± 19 Ma. Precambrian and Early Paleozoic strata share similar zircon UPb age peaks at ca. 2.5 Ga and ca. 0.95 Ga. The ca. 1.75 Ga age peak in the Precambrian strata is absent in those Early Paleozoic strata. The newly discovered 867 ± 19 Ma felsic intrusion in the Chongshan Metamorphic Belt and the shift of detrital zircon age patterns from the Neoproterozoic to Early Paleozoic confirm the presence of Precambrian magmatic activities in the Indochina block. Paleoposition and magmatic records show the Indochina block should be part of an Andean-type orogeny along the NW margin of the Rodinia during the Neoproterozoic. During the Neoproterozoic to Early Paleozoic, the role of Indochina as a continental block coherent with the Indian Craton at least during the breakup of Rodinia and Gondwana assembly. After Gondwana assembly, the Indochina block, as a section of an Andean-type continental arc along the eastern margin, blocked the exotic inputs and changed the age distribution patterns dramatically.