| Summary: | Pebbles from Sperm Bluff Conglomerate (Taylor Group, Beacon Supergroup) include lithologies such as porphyritic rhyolites and tuffs that are not known in outcrop anywhere in southern Victoria Land. Zircon from the clasts yielded ages between 497 ± 17 Ma and 482 ± 9 Ma, with an older inherited component c. 540 Ma. The age and composition of the rhyolites and tuffs suggest that they are the shallow equivalents of Dry Valleys (DV) 2 suite granitoids from a local source, or a source with felsic magmatism of similar age to the DV2 suite. The best constrained ages show that rhyolitic volcanism occurred in the source region at c. 482 ± 9 to 484 ± 8 Ma, towards the end of Dry Valleys magmatism, while older zircon grains were formed at the same time as early phases of Dry Valleys magmatism. The ability of U-Pb ages of robust minerals such as zircon, to allow correlations of rocks that have been extensively altered, highlights the value of this technique (and particularly SHRIMP) in providing important geological constraints on altered rocks.
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