Protolith natures and U‐Pb sensitive high mass‐resolution ion microprobe (SHRIMP) zircon ages of the metabasites in Hainan Island, South China: Implications for geodynamic evolution since the late Precambrian

Abstract

Metabasites within the Paleozoic volcanic-clastic sedimentary sequences in Hainan Island, South China, show large differences not only in the nature of protoliths, but also in zircon U-Pb sensitive high mass-resolution ion microprobe (SHRIMP) ages. The protoliths for the Tunchang area metabasites have intraoceanic arc geochemical affinities. In the east-central island gabbroic to diabasic rocks and pillow lavas are also present, while the Bangxi area metabasites with back-arc geochemical affinities in the northwest island consist of basaltic, gabbroic and/or picritic rocks. Three types of zircon domains/crystals in the Tunchang area metabasites are defined. Type 1 is comagmatic and yields concordant to approximately concordant 206 Pb/238 U ages ranging from 442.1 Ϯ 13.7 Ma to 514.3 Ϯ 30.2 Ma with a weighted U-Pb mean age of 445 Ϯ 10 Ma. Type 2 is inherited and yields a weighted 207 Pb/206 Pb mean age of 2488.1 Ϯ 8.3 Ma. Type 3 is magmatic with a 207 Pb/206 Pb age of ca 1450 Ma. Magmatic zircons in the Bangxi area metabasites yield a weighted U-Pb mean age of 269 Ϯ 4 Ma. We suggest 450 Ma is the minimum age for crystallization of protoliths of the Tunchang area metabasites, because the age range of ca 440-514 Ma probably corresponds to both the time of igneous crystallization and the high-temperature overprint. The presence of abundant inherited zircons strongly favors derivation of these rocks from a NMORB-like mantle proximal to continental crust. A protolith age of ca 270 Ma for the Bangxi area metabasites probably records expansion of an epircontinental back-arc basin and subsequent generation of a small oceanic basin. The presence of ophiolitic rocks with an age of ca 450 Ma, not only in Hainan Island, but also in the Yangtze block, highlights the fact that the South China Caledonian Orogeny was not intracontinental in nature, but characterized by an ocean-related event.

Zircon U-Pb geochronology and heavy mineral composition constraints on the provenance of the middle Miocene deep-water reservoir sedimentary rocks in the Yinggehai-Song Hong Basin, South China Sea

“…There are also some Mesoproterozoic zircons (1187 Ma and 1196 Ma), which may correspond to the "Jinning Movement" in South China (Wang et al, 1991). The Mesoproterozoic felsic volcanic rocks have been discovered in western Hainan Island, which would be considered relating to Grenvillian in Asia (Xu et al, 2007b;Li et al, 2008). Ages older than 450 Ma are scarce in this sample, whereas such grains are abundant in the source of Yangtze and Indochina blocks.…”

“…1430 Ma Precambrian volcaniclastic rocks have been discovered in western Hainan (Fig. 9), which may associated to the Grenvillian Orogenic event in this region (Xu et al, 2007b;Li et al, 2008). Representatives of the Indosinian intrusions in Hainan ranging from 280 to 220 Ma (Li et al, 2006;Xie et al, 2006aXie et al, , 2006bWen, 2013;Wen et al, 2013).…”

Late Miocene provenance change on the eastern margin of the Yinggehai-Song Hong Basin, South China Sea: Evidence from U–Pb dating and Hf isotope analyses of detrital zircons

“…The two grains have older Hf mode ages than their UePb ages, suggesting some degree of reworking of existing crust in the magmatic episode (He et al, 2013). The Mesoproterozoic felsic volcanic rocks in the western Hainan Island were dated at 1460e1430 Ma, which was considered to be related to the Grenvillian orogeny in Asia (Xu et al, 2007;Li et al, 2008).…”

Late Early Cretaceous adakitic granitoids and associated magnesian and potassium‐rich mafic enclaves and dikes in the Tunchang–Fengmu area, Hainan Province (South China): Partial melting of lower crust and mantle, and magma hybridization

“…Jurassic: Th~107 Ma Tunchang-Fengmu intrusive rocks contain 168-160 Ma magmatic zircons, which are consistent with the widespread occurrence of 165-155 Ma I-and A-type granites and syenites following the initiation of intraplate basaltic and/or bimodal igneous magmatism at 190-170 Ma in central South China (e.g., Zhao et al, 1998Zhao et al, , 2001Chen et al, 2002;Li et al, 2003Li et al, , 2004aLi et al, , b, 2007Wang et al, , 2008cHe et al, 2010;Zhu et al, 2010) and Jurassic gabbros in the Hainan area (e.g., Liu, 1991). These Jurassic igneous rocks are considered to represent a major anorogenic magmatic event linked to foundering of an early Mesozoic subducted flat-slab beneath the SE China continent or lithospheric or back-arc extension induced by Jurassic subduction of the Paleo-Pacific Plate (e.g., Zhou et al, 2006a;He et al, 2010;Zhao et al, 2012).…”

“…1b) (e.g., Li et al, 2008). Phanerozoic (Cambrian-Silurian and Carboniferous-Cretaceous) strata (e.g., Wang et al, 1991;Li et al, 2002a, b;Xu et al, 2007Xu et al, , 2008Zhang et al, 2011), and Cenozoic basalts (e.g., Wang et al, 1991), also crop out on the island.…”