关键词: 花岗质岩体, Hf同位素组成, 岩石成因, 印度-欧亚大陆碰撞, 日喀则桑桑

Abstract:

To better understand the petrogenesis and tectonic implications of the Sangsang granitic pluton located in the western part of
the middle segment of the Gangdese belt, we have conducted an integrated study of the geochronology, elemental geochemistry, and
zircon Hf isotopic compositions of the granitic pluton. Zircon LA-ICP-MS U-Pb dating for the Sangsang granitic rocks yields ages of
49~54 Ma, indicating that they were emplaced during Eocene. Chemically, all the rocks are subalkaline, metaluminous and poor in
phosphorus (A/NKC<1.10，P2O5<0.20%), thus can be grouped into calc-alkaline I-type granites. They are enriched in Cs, Rb, Ba, Th, U,
K, Pb and LREE, and depleted in Nb, Ta, P, Ti, showing the geochemical characteristics of arc magmatic rocks. The granitic rocks have
variable zircon εHf(t) values which are scattered from positive to negative values (=-4.24~ + 5.49), implying that different source
components have contributed to magma genesis. The integrated petrologic, elemental and isotopic compositions suggest that the
Sangsang granitic rocks were mainly originated by partial melting of juvenile crust, with some ancient crustal materials involved in their

petrogenesis. In combination with the regional tectonic setting, the authors suggest that the ancient crustal components were likely derived
fromthesubductedIndiacrust,andherebyinferredthattheinitialtimeoftheIndia-Eurasiacollisionshouldbeearlierthan54Ma

Key words: granitic pluton, Hf isotopic compositions, petrogenesis, India-Eurasia collision, Sangsang, Xi’gaze