The You Yangs batholith in Southeastern Australia,the sources of its magmas and inferences for local crustal architecture |
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| Authors: | J D Clemens |
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| Institution: | Department of Earth Sciences, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa |
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| Abstract: | The 365-Ma You Yangs batholith is a mainly I-type monzogranitic body, containing rocks with both clinopyroxene and hornblende, but with a 2–2.5?km-wide rim of S-type rocks. In places, the margins of the intrusion wedge out laterally. A laccolithic shape may explain there being only low-grade contact metamorphism of the Ordovician metasedimentary wall rocks. The chemical and isotopic characteristics of the granitic rocks suggest that the magmas formed by partial melting of a source that contained some meta-igneous rocks but was dominated by chemically immature metasedimentary types, to impart an evolved Sr isotope signature (87Sr/86Srt?=?0.70877–0.71066 for the main monzogranitic rocks), combined with relatively non-radiogenic εNdt (–2.4 to –1.9). Crystal fractionation played little role in shaping the compositions of the granitic magmas, with the main variations interpreted to be source-inherited. Igneous-textured microgranular enclaves (IMEs) are prominent in the monzogranitic rocks. The IMEs probably had an ultimate enriched-mantle source, and their magmas did not mix significantly with the crustally derived granitic host magmas. The characteristics of the monzogranitic rocks hosting the enclaves suggest the possibility that an unrecognised metasediment-dominated terrane of ancient arc crust may be present beneath the Bendigo Zone. |
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| Keywords: | You Yangs batholith granite igneous microgranular enclaves petrogenesis basement geology |
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