Review on Age of Magmatism and Crust Formation in Sri Lanka: U–Pb and Lu–Hf Isotopic Perspectives

Abstract

Recent studies on zircons at high resolution separated from metamorphosed rocks of igneous origin of the four tectonic domains of Sri Lanka by Lu–Hf and U–Pb isotope systematics have shed light upon its tectono-magmatic history. While providing better insights, the new dataset is not contradictory with Nd-model ages and U–Pb zircon dates discovered from Sri Lanka in early 90s. These new data suggest that both Wanni (WC) and Vijayan (VC) Complexes were magmatic arcs with the former being relatively older than the latter, and the Kadugannawa Complex (KC) is a marginal arc magmatic suite in the vicinity of WC. The oldest Highland Complex (HC) has been derived of Mesoproterozoic to Archean crustal and subducted sedimentary components. The Lu–Hf systematics of rocks from the HC record the oldest Hf-crustal model age of ~ 3.5 Ga and highly negative eHf(t)(t) values (up to − 30) inferring contribution of older subducted sediments and/or crustal components. In the WC and KC tectonic units, variable eHf(t) of zircon from negative to positive values from gneisses indicate the involvement of both juvenile mantle components and older continental materials in the generation of the arc-related magma with Hf-model ages from ~ 700 to 2800 Ma. On the other hand, the meta igneous rocks of the VC have distinct positive eHf(t) data with Hf-modal ages in the range of ~ 700–1600 Ma supporting entirely a juvenile origin. During the Neoproterozoic to Cambrian (ca. 700–500 Ma), the HC has predominantly served as a suture zone for the collision of the WC and VC arcs. This suggests that the Sri Lankan terrains were juxtaposed at an active continental margin setting associated with two-staged subduction during the Gondwana amalgamation. The metamorphism took place during the Neoproterozoic in the entire basement up to the granulite facies conditions reaching intermittently ultrahigh temperature (UHT) conditions.