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

Abstract

The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west. KEY WORDS: detrital zircon U-Pb dating, Lu-Hf isotopic composition, Wuliangshan sandstone sequence, Middle Triassic, Simao-Indochina. INTRODUCTIONThe SE Asia has been assembled by a series of collision and accretion processes involving numerous continental blocks or fragments separated from the East Gondwana since the Paleozoic (Faure et al., 2014;Metcalfe, 2006). The catchment areas of the Lancang, Jinsha and Nujiang rivers (also named Sanjiang in Chinese literature) in SW Yunnan (SW China) have preserved abundant paleotethyan heritages (e.g., the Lincang giant igneous zone) at which kilometer-thick Triassic volcanic rocks and Upper Triassic/Lower Jurassic molasse sediments are considered to have resulted from closure of the Paleotethys main ocean and subsequent continental collision (Peng et al., 2008(Peng et al., , 2006 Jian et al., 2003a, b;Mo et al., 1998;Zhong, 1998; Cong et al., 1993;Mahawat et al., 1990;Liu et al., 1989;Zhang et al., 1985).It has been commonly accepted that the Paleotethys main ocean was closed by an eastward subduction beneath the Indochina-Simao Block in the Permian-Triassic (Zaw et al., 2014;Wang et al., 2010). However, the precise timing of the initial collision of the Baoshan and Simao-Indochina blocks remains to be disputed. Previous studies focused on the origin of the Triassic igneous rocks along the Lancangjiang tectonic zone. Little attention has been paid to the coeval sedimentary rocks which preserved abundant geological records on the Paleotethyan tectonic evolution. The sedimentary rocks can provide key information to the time of closure of the Paleotethyan Ocean and subsequent collision of the Baoshan and Simao-Indochina blocks. The Wuliangshan Group occurs to the east of the Lancang giant igneous zone. It is mainly composed of low-grade metamorphosed sedimentary rocks. This group is likely syn-orogenic product of the Paleotethyan orog...

Prototethyan Accretionary Orogenesis Along the East Gondwana Periphery: New Insights From the Early Paleozoic Igneous and Sedimentary Rocks in the Sibumasu

“…As a result, our age-data, along with the reported results in SW Yunnan and SE Asia portions of the Sibumasu (e.g., Chen et al, 2007;Dong et al, 2013aDong et al, , 2013bKawakami et al, 2014;S. Liu et al, 2009;Lin et al, 2013;Quek et al, 2018;Song et al, 2007;Wang et al, 2011Wang et al, , 2012X. Xing et al, 2016;Zhao et al, 2016), reveal the presence of a zone of latest Cambrian to early Silurian igneous rocks, which extends from SW Yunnan (China) to South Thailand, then to western Peninsular Malaysia, and on to East Sumatra.…”

“…Our dating results show the orthogneiss and migmatite (11ML-68C 1 and -77A) from the Pake Complex (traditionally mapped as part of the Pake Formation) formed at 474-462 Ma (Figures 5a and 5b). Such data, along with published age data (e.g., Xing et al, 2016), suggest that the previously defined Precambrian Ximeng Group is most likely a metamorphic complex involving orthogneiss, migmitite, granite, and volcano-sedimentary rocks formed in the latest Cambrian-Ordovician in age (Figure 10b).…”

“…As shown Figure 2a, accompanying the felsic igneous rocks in the SW Yunnan portion of the Sibumasu, there are a series of lensoid bodies of dunite and harzburgite, cumulate gabbro, pyroxenite, and plagiogranite, which have been observed along the Yunxian‐Menghai area in SW Yunnan (e.g., Liu et al., 2017, 2020; Wang et al., 2013, 2018). These mafic‐ultramafic rocks are coeval with the marble, shale, pelite, and greywacke of the Lancang Group and its equivalents (e.g., Nie et al., 2015; Xing et al., 2015, 2016). The meta‐basalt and high‐Mg andesite exhibit an arc‐like geochemical affinity in the Ordovician (454–467 Ma) Huimin Formation of the Lancang Group (e.g., Nie et al., 2015; Xing et al., 2015).…”

“…In western Peninsular Malaysia of the southern Sibumasu, the Gerik-Dinding metamorphosed felsic to intermediate volcanic rocks to the west of the Bentong-Raub suture zone have been mapped as the products of the Cambrian-Ordovician Machinchang Formation (Figure 1b; e.g., Quek et al, 2018;Sone & Metcalfe, 2008;Ueno & Hisada, 2001). Wang et al (2011Wang et al ( , 2012; Dong et al (2013aDong et al ( , 2013b; Lin et al (2013); Kawakami et al (2014); Xing et al (2016); Zhao et al (2016); Hieu et al (2016); Gardiner et al (2017); Liu et al (2018Liu et al ( , 2021; Shi et al (2019); Minh et al (2020) and Wang et al (2020aWang et al ( , 2020bWang et al ( , 2020c.…”

Zircon U–Pb ages and Hf–O isotopes of Xiaomasa Miocene granite in the Ximeng area, western Yunnan, southwest China: Constraints on petrogenesis and tectonic setting

“…Previous studies have suggested that outcrops in the Ximeng area are composed of Precambrian metamorphic basement, which consists of the Proterozoic Laojiezi Formation granulite (Pt 3 l ), Pake Formation schist (Pt 3 p ) and Early Paleozoic Wangya Formation schist (Pz 1 w ) (Yunnan Geology and Mineral Resources Development Bureau, 1982). In recent years, zircon U–Pb dating has provided new chronological information about magmatic events in the Ximeng area, showing that the Early Paleozoic gneissic granites are present in the Laojiezi and Pake formations with emplacement ages ranging from 430.37 to 465.50 Ma (Chen et al, 2017; Wang et al, 2013; Xing et al, 2015). These ages correspond with commonly observed Early Paleozoic granite magmatism in the Tengchong and Baoshan blocks, which are considered to be related to the Proto‐Tethyan Andean orogenesis (Chen et al, 2017; Dong et al, 2010; Li et al, 2010, 2012; Liu et al, 2009; Wang et al, 2013; Xing et al, 2015); however, Early Paleozoic granite magmatism‐related mineralization has not yet been reported in the Ximeng area.…”