Reconstructing the Yunkai terrane (West Cathaysia): Evidence for hot, thin end-Mesoproterozoic to early Tonian orogens at the edge of India, Antarctica, and Australia

Abstract

<p>Geological, zircon U-Pb-Hf-O isotopic, and elemental characteristics of sheared and metamorphosed basement sequence of the Yunkai terrane, South China, indicate an end-Mesoproterozoic to earliest Tonian time convergent continental margin setting. Finegrained paragneiss of the complex yielded dominant populations at 1300-970 Ma, with an upper age limit at ca. 970-900 Ma, juvenile zircon Hf-O isotopes, and very low chemical weathering index (CIA) values of 51-54 that indicate an immature felsic source. Overall, the geological evidence and data patterns suggest that the Yunkai basement units must have been deposited in a continental arc setting that extended from 1200 Ma to 970 Ma and possibly continued to ca. 900 Ma. This was followed by possible collision at ca. 900-860 Ma to form the proto-Cathaysia Block. A review of temporal and spatial distribution of orogens and data patterns across South China and major Rodinia fragments favors the Yunkai terrane as being linked to Western Australia, Antarctica, and India during early Rodinia assembly. Moreover, the Rodinia supercontinent cycle was largely anomalous, and characterized by a decoupling of Hf-O systems and juvenile addition, but no significant continen tal subduction. This, together with evidence for thin orogens and high-temperature metamorphism at this time, might have resulted from a tectonic regime of hot subduction that was partially related to incomplete breakup of the preceding Nuna (Columbia) supercontinent.<br></p>