The Geochemical Nature of an Archean Plutonic-Volcanic Suite as Exemplified by the Kakagi-Stephen Lakes Area, N.W. Ontario

Abstract

<p>The major and trace element geochemistry together with the Rb-Sr isotopic data indicate the Stephen Lake Pluton and Kakagi Lake volcanic suite to be possible differentiates of parent magmas of similar composition.</p> <p>A co-magmatic origin of plutonic and volcanic felsic rocks is weakly suggested by normative mineral differentiation trends, major element similarities, K/Rb, Rb/Sr and Rb/Sr/Ba ratios and by differences in K, Rb, Ba and Zr contents.</p> <p>Sr isotopic analysis reveals that the Stephen Lake Pluton possesses an initial ratio of 0.7015 ± 0.0007 and an isochron age of 2534 ± 96 Ma. The low initial ratio reflects a basaltic magma source and the introduction of new material into the crust at this time. The Kakagi Lake acid volcanic suite scatters about a reference isochron of 2600 Ma with a low initial ratio. The distinctive low initial ratios of both the pluton and the volcanics are strongly suggestive of a percentage of similar composition.</p> <p>Comparison with surrounding granitoid plutons of the same age suggest the source region was heterogeneous with Rb/Sr ratios ranging from 0.020 to 0.035.</p>