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The Rutog granitic pluton lies in the Gangdese magmatic arc in the westernmost part of the Lhasa Terrane, NW Tibet, and has SHRIMP zircon U-Pb ages of c. 80 Ma. The pluton consists of granodiorite and monzogranite with SiO[sub2] ranging from 62 to 72 wt % and Al2 03 from 15 to 17 wt%. The rocks contain 2.33-4.93 wt% K[sub2]O and 3.42-5.52 wt% Na[sub2]O and have Na[sub2]O/K[sub2]O ratios of 0.74-2.00. Their chondrite-normalized rare earth element (REE) patterns are enriched in LREE ((La/Yb)n = 15 to 26) and do not show significant Eu anomalies (SEu = 0.68-1.15). On a primitive mantle-normalized trace element diagram, the rocks are rich in large ion lithophile elements (LILE) and poor in high field strength elements (HFSE), HREE and Y. Their Sr/Y ratios range from 15 to 78 with an average of 30. The rocks have constant initial [sup87]Sr/[sup86]Sr ratios (0.7045 to 0.7049) and slightly positive ϵ[subNd](t) values (+0.1 to +2.3), similar to I-type granites generated in an arc setting. The geochemistry of the Rutog pluton is best explained by partial melting of a thickened continental crust, triggered by underplating of basaltic magmas in a mantle wedge. The formation of the Rutog pluton suggests fiat subduction of the Neo-Tethyan oceanic lithosphere from the south. Crustal thickening may have occurred in the Late Cretaceous prior to the India-Asia collision. [ABSTRACT FROM AUTHOR]