Among the Devonian igneous complexes of central and northeastern Victoria, the S-type Tolmie Igneous Complex (TIC) occupies a unique spatial position, astride the Governor Fault and the Mount Wellington Greenstone Belt, a probable terrane boundary, and also bridges the boundary between
the Strathbogie and Tabberabbera granite provinces. This stitching position makes it important to determine the nature of the crustal source involved in its genesis. Here we present a new U–Pb zircon age for a sample of the Toombullup Ignimbrite, which forms a large part of the TIC.
This age (377 ± 2 Ma) allows us to comment far more reliably on the initial Sr and Nd isotope ratios of the TIC magmas. The corrected data (initial 87Sr/86Sr = 0.70804 to 0.71085, εNdt = –0.08 to 0.44) confirm a heterogeneous sediment-dominated
protolith, but unlike those of other S-type granitic and felsic volcanic rocks of the region, one composed of materials that had not long previously been extracted from the mantle. This finding has importance in the context of future models for the geological and tectonic development of this
part of southeastern Australia.
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