Spatial and temporal variation in source component of the Linzizong volcanic succession in southern Tibet: Implications for the India-Asia collision

Compositional variations in continental arc magmatism in time and space are often linked with tectonic events associated with subduction- and collision-related processes. This paper reports the mineral, zircon U-Pb age and Hf isotopic, whole-rock elemental and Sr-Nd-Pb-Hf-Mg isotopic data for the Linzizong volcanic succession (LVS) from four locations with discernible distance to the Indus-Yarlung suture. The LVS rocks in this study can be divided into two groups: a calc-alkaline Group 1 (69-55 Ma), mainly including basaltic-andesitic varieties, and a shoshonitic Group 2 (55-50 Ma), consisting predominantly of silicic rocks with minor mafic compositions. Group 1 samples likely derived from the fractional crystallization of primitive basaltic melts due to the partial melting of a metasomatized mantle wedge. The composition of such a mantle source was strongly influenced by slab-derived fluids and ancient lithospheric mantle-derived melts as a function of the distance to the suture. For example, samples located near the suture display depleted Sr-Nd-Pb-Hf isotopic compositions, have heave δ²⁶Mg value, and high Ba/Th and Sr/Th ratios, which are mainly affected by the dehydration of the subducted Neo-Tethyan slab, whereas samples located further from to the suture have enriched Sr-Nd-Pb-Hf isotopic compositions, as well as high Th/La and La/Sm ratios, which can be attributed to the involvement of the ancient central Lhasa lithospheric mantle-derived melts. A different spatial trend characterizes in the Group 2 silicic samples. These samples are isotopically enriched both near and far from the suture, which is due to the input of crustal materials from the Indian continent and ancient basement-derived material in the central Lhasa subterrane, respectively. Group 2 mafic samples have depleted isotopic compositions and are characterized by elevated (La/Yb)_N and Dy/Yb ratios as well as low Zr/Nb ratios, indicating an enriched garnet-bearing lithospheric mantle origin with contributions from asthenosphere-derived materials. Our results demonstrate that the tectonic implications of the variations in the whole-rock Nd and zircon Hf isotopic compositions towards negative values at ~51 Ma should be interpreted with caution, depending on the distance between the samples and the suture.