Preserved Sm-Nd Isotopic Composition as Useful Provenance Indicators in Neoproterozoic Sandstones in the Voltaian Basin, Ghana

Chris Anani,Johnson Manu,Patrick Asamoah Sakyi,Prosper Nude,Daniel Asiedu,Jacob Kutu

doi:10.4236/ijg.2012.33049

Abstract

The provenance of sandstones derived from theLower Voltaian Kwahu-Morago Group and the Middle Voltaian Oti-Pendjari Group of the Neoproterozoic Voltaian basin are discriminated by their Sm-Nd Isotopic compositions. Plots from the Sm-Nd data suggested provenance of the Kwahu-Morago Group to be from the Birimian metasediments and associated “basin type”granitoids. The Sm-Nd studies have further revealed an average TDM model age of whole rock samples in the Kwahu-Morago Group to be 2.2 Ga which shows that this portion of the Voltaian Supergroup represents eroded remnants of “basin type” granitoids. Sm-Nd data from the Oti-Pendjari Group suggested provenance from the Birimian volcanic rocks and probably with contribution from the Pan African rocks. Its average TDM model age of whole rock samples was 2.0 Ga, which generally falls in the range of the model ages for the basement Birimian volcanic rocks as well as the model ages for the granitoid rocks and thus suggests the major source rock of the Oti-Pendjari Group as coming from the volcanic belts. The model ages for both groups seem to indicate clastic supply from an early Proterozoic crustal provenance. This study shows that whole rock isotopic analyses can also be complementary in providing an insight into the origin and development of sedimentary successions.

Highlights

Sm-Nd model ages provide a good basis for determining the average crustal residence age of clastic sediments [1]
The provenance of sandstones derived from the Lower Voltaian Kwahu-Morago Group and the Middle Voltaian OtiPendjari Group of the Neoproterozoic Voltaian Basin are discriminated by their Sm-Nd Isotopic compositions
The Sm-Nd studies have further revealed an average TDM model age of whole rock samples in the Kwahu-Morago Group to be 2.2 Ga which shows that this portion of the Voltaian Supergroup represents eroded remnants of “basin type” granitoids

Summary

Introduction

Sm-Nd model ages provide a good basis for determining the average crustal residence age of clastic sediments [1]. One of the strengths of the Sm-Nd model age method, as applied to whole-rock systems, is that it provides the opportunity to see back through erosion, sedimentation, high-grade metamorphism and even crustal melting events which may reset other dating tools [2]. The sediments of the Voltaian Basin in Ghana is partly postulated to have probably been derived from the surrounding crystalline Birimian rocks [3,4]. To test this hypothesis and deal with the relatively complex situation posed by the high compositional maturity [4,5] of the Voltaian sandstones, we conducted Sm-Nd isotope analyses on selected samples and used the data to evaluate the possible provenance of the sandstones

Geological Setting and Study Area

Sample Preparations and Analytical Procedures

Results and Discussion

Conclusion