Trace Element Composition of Quartz as a Tool for Sedimentary Provenance: A Case Study from the Bega River Catchment

Abstract:

Understanding the formation and history of sediments is a fundamental aspect of geologic research. The abundance of quartz makes the mineral an important component of continentally-derived sediments, yet most sedimentary provenance studies rely on minerals that generally exist in low abundance in both clastic sediments and source rocks. Quartz crystallizes over a wide range of geologic conditions— from low temperature α-quartz (e.g., veins) to the high temperature and pressure α- and β-quartz stability limits in igneous and metamorphic regimes. The diversity of quartz-forming environments is reflected in similarly unique trace-element signatures (notably Ti and Al) in quartz. The Ti and Al content of quartz can therefore be used to determine the original quartz-forming environments and provenance of grains that have been weathered from their parent rocks. Here we demonstrate the efficacy of quartz-based provenance research with a case study from the Bega River Catchment in New South Wales, Australia.

Bedrock in the Bega River catchment is composed primarily of pera- to metaluminous granitoids, while bedrock outside of the basin is mainly peraluminous and peralkaline granitoids. Quartz from these different granitoids display unique trace-element signatures that can be used to fingerprint sediments derived from them. Trace-element composition of quartz grains from sand in the Bega River catchment indicate that ~69.5 % (n=193) of the quartz population is derived from weathering of pera-metaluminous granitoids. This observation is consistent with the bedrock geology of the catchment and suggests that most of the quartz grains in the sediment load of the Bega River are derived from weathering of granitoids within the basin. The remaining quartz population is composed of 24.5 % (n=68) peralkaline granitoid and 6 % (n=17) low-Ti quartz, suggesting granitoids from within the basin are not the sole contributor to the basin’s sedimentary load.