Os, Pb, and Nd isotope geochemistry of the Permian Emeishan continental flood basalts: Insights into the source of a large igneous province

Os–Nd–Sr isotopes in Miocene ultrapotassic rocks of southern Tibet: Partial melting of a pyroxenite-bearing lithospheric mantle?

“…Repeat analyses of the ultrapotassic rocks in the two laboratories show consistent results. The details of the analytical procedures are described by Li et al (2010Li et al ( , 2014 and Xu et al (2007).…”

“…5), and there are two main potential scenarios that could explain this: (1) their parental magmas were contaminated by crustal components during magma evolution (Esser and Turekian, 1993;Hattori et al, 2003), or (2) these ultrapotassic rocks inherited high 187 Os/ 188 Os ratios from their mantle source (Schaefer et al, 2000;Carlson and Nowell, 2001 Table 3), suggesting that crustal materials were involved in the formation of the ultrapotassic magmas with low Os contents. The samples with low Os contents (e.g., CM10-04-17, CM10-04-20, CM10-04-24, and CM10-04-29) also have low MgO contents and high 187 Os/ 188 Os ratios, and they were possibly contaminated by crustal materials, and therefore cannot represent the initial magmas and sources (Xu et al, 2007). The Os isotopic data of these low-Os rocks will not be considered further in the following discussion on the mantle source of the ultrapotassic rocks in southern Tibet.…”

“…4), which render their Os-Nd-Sr isotopic systems relatively immune to contamination (Turner et al, 1996;Miller et al, 1999;Williams et al, 2004), and (3) the presence of mantle xenoliths and xenocrysts in the ultrapotassic rocks (Miller et al, 1999;Zhao et al, 2008;Liu et al, 2011Liu et al, , 2014a testify to their rapid transport through the crust, further hinting that they were little contaminated by the crust, at least with regard to samples with high Os contents. (2000); SCLM (sub-continental lithospheric mantle) data from Ellam et al (1992), Meisel et al (2001), Shirey and Walker (1998), Walker et al (1989Walker et al ( , 2002 and Widom and Shirey (1996); OIB data from Shirey and Walker (1998) and Xu et al (2007).…”

“…Plot of c Os (t) vs e Nd (t) for the ultrapotassic rocks of southern Tibet. The mantle reservoirs and base figure are from Shirey and Walker (1998) and Xu et al (2007). The Sailipu and Xungba ultrapotassic rocks are shown for comparison.…”

“…radioactive mother-daughter isotopes during both partial melting and fluid activity. The Re-Os isotope system provides a way of overcoming this problem because Re is a moderately incompatible element whereas Os is a compatible element during partial melting of mantle peridotite, thereby making it possible to distinguish the Os isotopic characteristics of crust, lithospheric mantle, and asthenospheric mantle (Shirey and Walker, 1998;Xu et al, 2007;Callegaro et al, 2013). In this paper we provide high-precision Re-Os isotope data, and in combination with previous research, our comprehensive Os-Nd-Sr isotopic investigations of the ultrapotassic rocks of southern Tibet allow us to evaluate the source of the ultrapotassic volcanic rocks as well as constrain the dynamic mechanisms involved in the formation of the Tibetan Plateau.…”