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doi:10.2204/iodp.proc.320321.211.2013

Conclusions

We report morphology and major element compositions of volcanic glasses separated from a from the Eocene–Oligocene transition interval at Site U1333. Among 23 sediment samples, we found five samples containing volcanic glass shards: one from uppermost Eocene radiolarian ooze and the others from lower Oligocene white calcareous oozes. Volcanic glasses from these samples are dominated by clear silicic glass shards 80–300 μm in size, and they are classified into plate-type, tube-type, and balloon-type based on their morphology. Vesicle walls are smooth, and no clear evidence of argillation was found. Electron microprobe analyses of 181 glass shards from Sample 320-U1333C-14H-6W, 92–94 cm, revealed that the glass shards have uniform rhyolitic compositions relatively rich in alkaline elements (Na and K) but depleted in Fe, Mg, and Ca. These results suggest that the origin of these glass shards was explosive silicic volcanos with either a single source or a mixture of multiple sources with similar compositions. The samples that contain volcanic glasses suggest episodic explosive volcanic eruptions at this time. Given the rhyolitic compositions and proximity of Site U1333 to Central America, we regard Central American arc volcanism as the most likely source of the glass shards found at Site U1333.

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