Late Cretaceous age based on K/Ar dates of granitic rock from the Tambelan and Bunguran islands, Sunda Shelf, Indonesia

Abstract

K/Ar determination on two adamellites from the Tambelan and Bunguran Islands, on the Sunda Shelf between the Malay Peninsula and Borneo, indicate that these are pre-Tertiary, probably Late Cretaceous' Rb-Sr determinations on the rock from Bunguran Island' and a third granitic rock from Tambelan Island, are not definitive, but are consistent with a Late Cretaceous age for the intrusion of the granitic rocks. These determinations, the first age indications from the Tambelan and Bunguran Islands, throw doubt on the supposed "pre-Upper Triassic" age of the acid batholiths in the Anambas Zone of the Sunda Shelf and its extension into West Borneo.