Cathayasian Block may Have Been Part of Gondwana During Cambrian

The Gondwana connection of South China: Evidence from monazite and zircon geochronology in the Cathaysia Block

Authors:

Zhang et al

Abstract:

The tectonic evolution of the Cathaysia Block in South China has been debated, with limited information to constrain the early Paleozoic geodynamics and paleogeography in the context of the global Gondwana supercontinent. In this study, we report the petrology of mafic magmatic suites and metamorphic units, together with zircon and monazite U − Pb ages from several key areas in Cathaysia. Combined with a comprehensive synthesis of the data reported in previous studies, we argue that the Cathaysia was an early Paleozoic collisional orogen, and speculate the possible linkage of South China with the Gondwana supercontinent. The monazite and zircon U − Pb data presented in this study including the metamorphic ages of the rocks in the Gaozhou complex in Yunkai massif, the Wanquan Group in central Wuyi massif, the garnet-sillimanite gneiss from the Chencai Group, and the garnet amphibolite from the Longyou Group in the northeastern section of Wuyi massif show ages ranging from 447 Ma to 430 Ma. Gabbroic intrusions in the Longyou Group and pyroxenites in the Chencai Group in northeastern Wuyi massif were emplaced at ca. 425 Ma and 470 Ma, respectively. Furthermore, the ca. 470 Ma pyroxenite was overprinted by hydrothermal alteration at ca. 400 Ma. Whole-rock geochemistry and mineral compositions show that the Chencai pyroxenite possesses features similar to that of the Alaskan-type mafic intrusions, whereas the 420 Ma gabbroic intrusions in the Long Group exhibit post-collision signature, which are consistent with the broadly coeval voluminous post-collision granites in Cathaysia. Comprehensive synthesis of zircon and monazite U − Pb ages of the metamorphic rocks and granites in Cathaysia lead us to suggest that the transition from collision to post-collision occurred at ca. 430 Ma.

The early Paleozoic structures, metamorphism and magmatic activity suggest that the NE-extending Cathaysia was a typical collisional orogenic belt rather than an intraplate type. The predominance of late Neoproterozoic – Cambrian detrital zircons in the early Paleozoic granites and pre-Devonian metamorphic rocks in Cathaysia indicates that the at least some clastics of the lower Paleozoic rocks in Cathaysia were derived from the Gondwana continents, suggesting that South China was at the fringe of the Gondwana supercontinent. The Nanhai terrane (including the Hainan massif) could represent the missing link between South China and Gondwana, with the Zhenghe − Dapu fault marking the suture zone between South China and the Nanhai Terrane.