Proterozoic tectonics of Hainan Island in supercontinent cycles: New insights from geochronological and isotopic results

Abstract

Hainan Island in southwestern south China has 1.43Ga crystalline rocks as part of the Proterozoic basement rocks for the Cathaysia Block. Understanding Proterozoic tectonics of the island is thus essential for constraining the paleogeographic positions of the Cathaysia Block in Precambrian supercontinents. We report here new geochronological and Hf–O isotopic results for Mesoproterozoic gneisses, metavolcanic and metasedimentary rocks, and quartz sandstones from Hainan Island. Together with published data from the region, we divide Hainan Mesoproterozoic rocks into three major tectonostratigraphic units: (1) the amphibolite-facies Baoban Complex, consisting mainly of 1.43Ga volcanic/plutonic rocks and sedimentary rocks formed in a continental rift setting but subsequently experienced high-grade metamorphism during 1.3–1.0Ga; (2) the greenschist-facies Shilu Group, consisting of 1.43Ga rift sediments with 1.44Ga tuff in the “fifth layer” that are coeval with the protolith of the Baoban Complex, and ca. 1.0Ga foreland basin sediments in the “sixth layer”, all underwent upper greenschist-facies metamorphism soon after the deposition of the “sixth layer”; (3) the Shihuiding Formation that unconformably overlies the Shilu Group, consisting of <1.1Ga (most likely ⩽1.0Ga) coastal marine to lagoon sediments deposited in a post-orogenic setting. Inter-continental provenance and magmatic comparisons suggest a united Tasmania-Cathaysia-Laurentia landmass during the Mesoproterozoic, likely all received similar-sourced rifting sediments from Cathaysia-like basements during the Nuna breakup at ∼1.43Ga. The 1.3(?)–0.9Ga Grenville-aged Sibao orogeny welded the Yangtze Block with the Cathaysia-Laurentia landmass, bringing Tasmania, Yangtze and the Cathaysia-Laurentia landmass together. Sedimentary detritus were shed from the orogen to basins covering Hainan Island, western Yangtze, Tasmania and western Laurentia during the assembling of Rodinia.