Origin of Late Oligocene adakitic intrusives in the southeastern Lhasa terrane: Evidence from in situ zircon U–Pb dating, Hf–O isotopes, and whole-rock geochemistry

• Published in: Lithos 2012-09, Vol.148, p.296-311
• Main Authors: Zheng, Yuan-Chuan, Hou, Zeng-Qian, Li, Qiu-Yun, Sun, Qing-Zhong, Liang, Wei, Fu, Qiang, Li, Wei, Huang, Ke-Xian
• Format: Article
• Language: English
• Subjects: Adakitic rocks; Geochemistry; In situ zircon Hf–O isotopes; Lhasa terrane; U–Pb zircon age
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/j.lithos.2012.05.026

We describe the whole-rock geochemistry, biotite Ar–Ar and zircon U–Pb geochronology, and in situ Hf–O isotopic compositions of the Linzhi two-mica granitoid in the southeastern Lhasa terrane. The granitoids are calc-alkaline to high-K calc-alkaline in composition, and they have geochemical affinities with adakites. The whole-rock geochemistry, with high SiO2 and Al2O3 contents, low MgO, Cr, and Ni contents, low Mg# values, negative εNd(t) (−6.2 to −2.9), and low 87Sr/86Sr(i) (0.7059–0.7074), together with the in situ zircon Hf–O isotopic data (εHf(t)=−2.7 to 2.7; δ18O=7.2‰–8.8‰), indicates that the granitoid was derived mainly from the partial melting of a rejuvenated lower crust underneath the Lhasa terrane. This lower crust was dominated by ancient crustal material with the minor involvement of juvenile mantle inputs (