U-series disequilibrium in young Tengchong volcanics: Recycling of mature clay sediments or mudstones into the SE Tibetan mantle

作者：Zou, Haibo^*; Shen, Chuan-Chou; Fan, Qicheng; Lin, Ke

来源：Lithos, 2014, 192: 132-141.

DOI：10.1016/j.lithos.2014.01.017

• U-series disequilibrium
• Clay-rich sediments
• Tengchong
• Tibetan plateau
• Volcanism

We report U-series disequilibrium data in the youngest volcanic rocks from Maanshan, Dayingshan and Heikongshan volcanoes in the Tengchong volcanic field, representing the only 3 volcanoes from the Indo-Asian suture zone (southwestern Tibet to western Yunnan) that are young enough to preserve U-238-Th-238 disequilibrium. The most striking feature of these young Tengchong lavas is their extremely low (Th-230/Th-232) (0.303 to 0.376) and (U-238/Th-232) (0.289 to 0.360) activity ratios (or ultra-high Th/U concentration ratio). These young lavas also show small to moderate (4% to 10%) Th-230 excesses. Such Th-238 excesses, together with tomographic results, suggest that partial melting initiated at depths greater than 75 km in the garnet stability field. U-series isotope data, together with major and trace element and Nd-Sr-Pb isotope data, indicate that Tengchong lavas are derived from partial melting of an enriched subcontinental lithospheric mantle. The ultra-high melt Th/U concentration ratios of 9.5 +/- 0.7 further indicate recycling of continentally derived clay-rich mature sediments or mudstones into the SE Tibetan mantle. The materials with ultra-high Th/U ratios may come from the clay-rich mature sediments from Indian Ocean or Neo-Tethyan Ocean or the mudstones/shales from the subducted Indian continental plate.

• 出版日期2014-4
• 单位中国地震局