Identification of Hercynian shoshonitic intrusive rocks in central Hainan Island and its geotectonic implications

Abstract

An identification has been made of some shoshonitic intrusive rocks in central Hainan Island recently. These rocks are K-rich (K 2 O=2.9%-5.1%, K 2 O/Na 2 O=0.95-2.12), distinctly enriched in LILE and LREE, strongly depleted in Nb, Ta, and moderately depleted in Sr and Ti, with ( 87 Sr/ 86 Sr)i = 0.70859-0.71425 and ε Nd (t) = (−2.77-−7.49). They were derived from an EMⅡ-type mantle source. The enrichment process is related to metasomatism of depleted mantle caused by a great amount of fluid-melt released from oceanic crust and terrigenous sediments at great depth (eclogite facies) during the subduction of the South China plate under the Indochina-South China Sea plate in the Carboniferous-Early Permian. A SHRIMP U-Pb zircon dating yields a crystallization age of 272±7 Ma for the shoshonitic intrusions, which is coeval with the strongly peraluminous granites found in central Hainan Island. These two kinds of rocks generally possess syn-intrusion ductile deformation structures. Thus they are considered to have been generated during the early stage (syn-thrust phase) of a post-collisional event. The primary magma of shoshonitic rocks was produced at a depth > 80 km by decompressiondehydration melting of previously enriched lithospheric mantle wedge, phlogopite-bearing garnet peridotite, which was in turn caused by the break-off of a descendent slab and upwelling of a hot asthenosphere. The rising of melts was accompanied by crustal contamination and crystallization fractionation (AFC). Combining with other related data, it is proposed that the southwards subduction and amalgamation of the South China plate with the IndoChina-South China Sea plate took place at ca. 287-278 Ma, which was a part of the convergence process of the Pangea supercontinent. The suture zone was probably located along the line of Song Ma-Beibu Gulf-north margin of the Yunkai Mountains-Wuyi Mountains.

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

“…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). Cretaceous granitoids and volcanic rocks with ages ranging from 160 to 80 Ma occur in the southern part of the island (Wang et al, 1991(Wang et al, , 2011(Wang et al, , 2015bJia et al, 2009) (Fig.…”

Detrital zircon U-Pb geochronology and Lu-Hf isotopic compositions of the Wuliangshan metasediment rocks in SW Yunnan (China) and its provenance implications

“…7). The igneous rocks with such an age-peak are usually observed along the Yuanjiang-Mojiang area of the Ailaoshan tectonic zone and Banpo area of the western Simao Block (Wen et al, 2013;Fan et al, 2010;Hennig et al, 2009;Jian et al, 2008;Li and Li, 2007;Li et al, 2006;Xie et al, 2006;He et al, 2003a, b). In addition, along the Ailaoshan-Song Ma tectonic zone, abundant Permian and Early Triassic granitic rocks are reported (Chen et al, 2013;Li et al, 2012;Liu et al, 2009).…”

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

“…9, area C). Representative igneous intrusions include the Jianfengling granite (249 Ma), Shilu granite (262 Ma), Panyangdong granite (234 Ma), Changtangling granite (264 Ma), Baolang granite (272 Ma), Tianzai granite (245 Ma) and Zhizhong granite (272 Ma) (Li et al, 2006;Xie et al, 2006aXie et al, , 2006bWen, 2013;Wen et al, 2013). The Yanshanian granitoids are mainly distributed in the southern and western parts of Hainan Island, and their UePb ages are mainly in the range of 170e80 Ma (Wang et al, 1991Jia et al, 2009).…”