Sm-Nd ages and Nd-Sr-Pb isotope signatures of the Xiugugabu ophiolite, southwestern Tibet

Abstract：The Xiugugabu ophiolite is situated in the western segment of the Yarlung-Zangbo ophiolite belt, southwestern Tibet, belonging to SSZ-type ophiolites. The crystallization age of gabbro-diabase in the ophiolite was determined using the Sm-Nd method. The internal isochron age of plagioclase, pyroxene and two whole-rock samples is 126.2±9.1 Ma, which represent the time range for the subduction of the Tethys Ocean. In addition, Nd-Sr-Pb analysis of gabbro-diabase indicates that the gabbro-diabase has high initial εNd(t) values (6.7-9.1), suggesting that the primitive magma was derived from a strongly depleted mantle and had not undergone contamination with continental crustal materials. The ophiolite has lower initial 206Pb/204Pb values of 17.412-17.523 but higher 208Pb/204Pb values of 37.352-37.706 and shows higher ISr values of 0.70278-0.70383, indicating that the Xiugugabu ophiolite originated from the Indian MORB mantle domain.