Possible two-stage 87Sr evolution in the Stockdale Rhyolite

Abstract

The Rb-Sr total-rock data for the Stockdale Rhyolite, of significance for the Palaeozoic time scale, are more scattered about a single-stage isochron than expected from experimental error. Two-stage 87Sr evolution for several of the samples is explored to explain this, as an alternative to variation in the initial 87Sr/86Sr which is customarily used in single-stage dating models. The deletion of certain samples having very high Rb/Sr removes most of the excess scatter and leads to an estimate of 430 ± 7 m.y. for the age of extrusion. There is a younger alignment of Rb-Sr data within each sampling site at 412 ± 7 m.y. We suggest that the Stockdale Rhyolite is at least 430 m.y. old, that its original range in Rb/Sr was smaller than now observed, and that it experienced a net loss in Sr during later hydrothermal alteration at ca. 412 m.y. Show more