Source and pressure effects in the genesis of the Late Triassic high Sr/Y granites from the Songpan-Ganzi Fold Belt, eastern Tibetan Plateau

Late Jurassic Wenjiaping high Sr/Y granite: A product of partial melting of the Precambrian basement rocks trigged by lithospheric extension in the Songpan–Garzê fold belt, SW China

“…Numerous Mesozoic granitoids are widely exposed in the eastern SGFB, but rare in the western part (Figure 1b; Sigoyer et al, 2014;Zhan et al, 2020). Most of these granitoids occur as stocks with outcrop areas of <100 km 2 , and a few occur as batholiths (e.g., the Yanggon, Nianbaoyeche, and Riluku; Zhang, Zhang, Harris, Jin, & Yuan, 2006;Zhang et al, 2007;Zhan et al, 2020). Previous studies mainly focused on the Late Triassic-Early Jurassic granites, which primarily include the following four types: (1) high-K adakitic granitoids resulting from partial melting of (delaminated) thickened lower crust (Xiao et al, 2007;Yuan et al, 2010;Zhang et al, 2006Zhang et al, , 2007;…”

“…For instance, the modes of low-pressure partial melting (Kamei, Miyake, Owada, & Kimura, 2009) and low-pressure water-fluxed partial melting (Reichardt & Weinberg, 2012) of intermediate-acid rocks were advocated for the genetic interpretation of some adakites. However, partial melting of granitoids under low-pressure conditions will lead to low Sr contents in the melt (< 400 ppm; Zhan et al, 2020), and low-pressure waterfluxed partial melting of intermediate-acid intrusive rocks will result in low Rb contents and high Sr/Rb ratios (commonly >10) in the melt (Reichardt & Weinberg, 2012). Significantly, the Wenjiaping granite has much higher Rb (126-174) and Sr (407-643) contents (Table 3) with lower Sr/Rb ratios (<5), which is inconsistent with the above- (1.0-1.2 GPa), or low Sr/Y rocks under thickened lower crustal pressure condition (>1.5 GPa).…”

“…Significantly, the Wenjiaping granite has much higher Rb (126-174) and Sr (407-643) contents (Table 3) with lower Sr/Rb ratios (<5), which is inconsistent with the above- (1.0-1.2 GPa), or low Sr/Y rocks under thickened lower crustal pressure condition (>1.5 GPa). Therefore, the knowledge of the detailed source composition of the Wenjiaping high Sr/Y granite is vitally important to constrain its origin and tectonic setting (Zhan et al, 2020).…”

“…The Songpan–Garzê fold belt (SGFB), sandwiched between the Qiangtang, Kunlun–Qaidam, North China, and South China blocks (Figure 1a; Roger et al, 2003), is an important tectono‐magmatic belt and Li–Be–Sn–Cu–Au polymetallic metallogenic belt (e.g., Li, Li, Chou, Wang, & Xiong, 2019; Roger, Jolivet, & Malavieille, 2010; Xu et al, 2020; Xu, Hou, & Wang, 1992; Zhan et al, 2020; Zhao, Wang, Groves, & Deng, 2019; Zhou et al, 2017) in the eastern margin of the Tibetan Plateau. Due to its unique inverted triangle shape, orogenic polarity, sedimentation, and tectonic evolution, the SGFB is known as the “Chinese Geological Bermuda” (Xu et al, 1992).…”

“…Moreover, the Wenjiaping granite is characterized by enriched Sr-Nd isotope compositions (Figure8), similar to those of the LTHSG in the SGFB(Zhan et al, 2020 and references therein). Based on simple binary mixing calculations using Sr-Nd isotope data,Zhan et al (2020) proposed that to produce the LTHSG in the SGFB with relatively enriched Sr-Nd isotope characteristics, a…”