Graduate Thesis Or Dissertation
 

Geochemistry of quaternary, rift-related volcanism in the Bransfield Strait, Antarctica

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  • The Bransfield Strait is the narrow, late Tertiary to Quaternary marginal basin separating the South Shetland Islands from the northern end of the Antarctic Peninsula magmatic arc. Quaternary volcanism in the strait is tholeiitic to mildly alkaline, and contrasts chemically with the pre-Quaternary calc-alkaline arc volcanism. Geochemical evidence presented here shows that the Quaternary volcanism is related to active rifting in the strait. All of the rift-related volcanoes are chemically related by different extents of partial melting of garnet peridotite variably enriched in alkali and alkali earth elements relative to rare earth elements. This enrichment is characteristic of subduction zones, where fluids from the dehydrating subducted slab concentrate alkalies and alkali earths that can then be mixed into, and partially melted with, the surrounding mantle. The lavas that erupted during the formation of the Bransfield Strait provide evidence that subduction zone processes influence the chemistry of marginal basin volcanism. The Bransfield Strait lavas are chemically similar to published analyses from other marginal basins, especially the Cretaceous marginal basin that is now preserved as the Sarmiento ophiolite of southern Chile. This confirms the interpretation that, prior to obduction, the Sarmiento was a narrow, immature marginal basin analogous to the present day Bransfield Strait.
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