U-Pb detrital zircon geochronology for Tabbowa beds in Sri Lanka

Abstract

Detrital zircon geochronology has proven to be a useful tool for correlating sedimentary sequences with their source rocks. The objective of this study was to get provenance details of Tabbowa Beds utilizing U-Pb detrital zircon geochronology. Two rock samples were collected from Tabbowa Beds. The analysis to get U-Pb isotopic ratios has been performed using LA-ICP-MS system for 200 zircon grains separated from the samples.

Zircon populations showed complex internal texture variations. Three main regions were identified from the histograms and concordia diagrams plotted for the isotopic data which showed a clear relationship to the crust formation age and the post geological events happened in the Wanni Complex of Sri Lanka. Most of the detrital cores showed comparatively older U-Pb ages which indicated the crust formation age of the Wanni Complex. Magmatic zircons identified from the samples showed 850 – 700 Ma and 1000 - 880 Ma age ranges giving evidences for the Pre Pan African magmatic events happened in the Wanni Complex. Overgrowth of detrital cores and newly grown metamorphic zircons identified from the samples had 650 – 430 Ma age range which signified the metamorphic age of the Wanni complex. U-Pb detrital zircon ages and their morphology gave evidences for three different source rocks that supplied sediments to the Tabbowa Basin. Therefore, it was concluded that the identified source rocks of Tabbowa Beds existed in the Wanni Complex and the age data represented the post magmatic events and metamorphism happened in the Wanni Complex.