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Mantle-derived magmas at convergent plate boundaries provide unique insights into the nature of materials subducted to and recycled from depths. Here we present a study of OsSrMg isotopes on the Oligocene-Miocene ultrapotassic rocks aimed at better understanding sediment subduction and recycling beneath southern Tibet. New isotopic data confirm that ultrapotassic rocks in southern Tibet are of mantle origin, but underwent crustal contamination as evidenced by the variably high 187 Os/ 188 Os that obviously deviates from normal mantle reservoir. Still some samples with mantle-like 187 Os/ 188 Os exhibit δ 26 Mg significantly lower than mantle and crustal lithologies, suggesting that the isotopically light Mg may not result from crustal contamination but retain specific fingerprint of carbonate-related metasomatism in mantle sources. Mantle carbonatite metasomatism is manifested by the inverse δ 26 Mg 87 Sr/ 86 Sr correlations, as well as the depletion of high field strength elements relative to rare earth elements and the enrichment of CaO in ultrapotassic rocks. The positive co-variations between δ 26 Mg and Hf/Sm defined by those low-187 Os/ 188 Os ultrapotassic rocks provide evidence for the potential of recycled dolomites to modify mantle Mg isotopic composition. The correlated spatial variations of δ 26 Mg and Hf/Sm are interpreted to reflect carbonatitic metasomatism associated with the northward subduction of the Neo-Tethyan oceanic slab and its profound influence on postcollisional ultrapotassic magmatism.
Few studies have examined home exposure to secondhand smoke (SHS) in China. This study aimed to document: (1) the prevalence and correlates of exposure to SHS in homes (in adult non-smokers) in Shanghai, and (2) enforcement of rules, harm reduction behaviors, and self-efficacy for maintaining smoke-free homes in Shanghai. A total of 500 participants were recruited using a multistage proportional random sampling design in an urban and suburban district to complete a survey. Among the total 355 nonsmokers, 127 (35.8%) participants reported being exposed to SHS in the past 7 days. Participants living with smokers in the home, with no smoking restriction at home, and having children younger than 18 were more likely to be exposed to SHS at home. Higher self-efficacy in maintaining a smoke-free home was negatively associated with home SHS exposure. Having visitors who smoke was the greatest policy enforcement challenge. Ineffective measures such as opening windows were more commonly used in homes with partial bans. Educational initiatives to protect against SHS exposure in the home should promote smoke-free homes, address challenges to implementing such policies, and address misconceptions regarding the effectiveness of supposed harm reduction behaviors.
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