Geochemistry of the Paleoproterozoic Espanola Formation, Bruce Mines—Elliot Lake area, Ontario, Canada: implications for provenance, paleo-weathering, and tectonic setting

Abstract

The Espanola Formation of the Paleoproterozoic Huronian Supergroup is a mixed carbonate-siliciclastic succession that is well exposed in the Bruce Mines-Elliot Lake Area, Ontario, Canada. The siliciclastic portion of the formation is mainly dominated by shale with subordinate content of wake and arkose. Elemental geochemical analysis of the rocks was conducted in order to decipher their provenance, paleo-weathering conditions, and plate tectonic setting. The analyzed Espanola Formation samples display steep REE distribution patterns with high LaN/YbN ratios ranging from 3.68 to 20.83 (average LaN/YbN = 16.4), and are characterized by consistently negative Eu anomalies (average Eu/Eu* = 0.69). Furthermore, on the La-Th-Sc ternary model, the samples cluster around the average granodiorite and tonalite-trondhjemite-granodiorite (TTG) compositions with a clear linear trend toward felsic sources. A similar distribution and trend are also displayed on the Co/Th and La/Sc ratio plot. Such geochemical characteristics indicate derivation from an exposed upper continental crust of granodioritic and TTG compositions, namely the Archean Superior Province to the north, with minor contributions from mafic volcanic and/or sedimentary rocks, as further demonstrated by provenance discriminant models (La-Th-Sc and Co/Th-La/Sc). The source rocks were subjected to relatively low to moderate chemical weathering as reflected by their generally low chemical index of alteration values (average CIA = 62.90). Tectonic discriminant models (K2O/ Na2O-SiO2 and SiO2/Al2O3-K2O/Na2O) indicate significant contributions of siliciclastic sediments from sources within a stable passive continental margin, with minor contributions from an active continental margin and continental island arcs. The Zr/Sc-Th/Sc model further confirms that the composition of the analyzed Espanola Formation siliciclastic samples was mainly controlled by tectonic setting and provenance with minimal influence of sediment recycling.