Low-Ti Silurian-Early Devonian continental rift tholeiites and plagiogranites in the Tumut area, NSW

Abstract

A suite of low-Ti Silurian to Early Devonian basaltic rock and plagiogranite in the Tumut area have previously been interpreted as back-arc tholeiitic basalt and ophiolitic rocks formed in an oceanic environment. Re-examination of these rocks and their geological contacts show that they closely resemble low-Ti continental rift tholeiites and their felsic shallow intrusive differentiation products. The mafic rocks have strong similarities to the low-Ti Jurrassic break up dolerites in Tasmania. The basalts and intrusive rocks were probably derived from the sub-continental mantle during Silurian- Devonian rifting well after the initial emplacement of the ophiolitic rocks in the Tumut area.