Petrology and emplacement dynamics of the intrusive and extrusive rhyolites of Obsidian Dome Inyo Craters volcanic chain, eastern California
Drilling at Obsidian Dome has provided continuous core samples of the distal and proximal portions of Obsidian Dome, its conduit, and an associated feeder dike. Both the dome and conduit are chemically and mineralogically zoned and consist of a finely porphyritic, high-Ba, low-silica rhyolite occurring in the basal portion of the dome and margins of the conduit and a finely porphyritic, low-Ba, higher silica rhyolite in the upper portion of the dome and center of the conduit. The high-Ba rhyolite contains two distinct phenocrysts assemblages with two distinct compositions, and represents mingled magmas. The low-Ba rhyolite in the dome and conduit contains significantly fewer disequilibrium phenocrysts and is only slightly mingled. The dike, sampled at 600 m depth, as well as a related tephra fall from Obsidian Dome vent, are entirely low-Ba rhyolite that contain no evidence of magma mingling. End members of the mingled magma, calculated using two different methods, are a 63 percent silica end member, and a silicic end member identical in composition to the dike and tephra fall from Obsidian Dome vent. This silicic end member was the first magma emplaced in the dike, and comprised much or all of the first magma vented to the surface during formation of the Obsidian Dome vent when eruption rates were high. Magma mingling of mafic and rhyolite magmas occurred during formation of the conduit. 59 refs., 16 figs., 10 tabs.
- Research Organization:
- Michigan State Univ., East Lansing, MI (USA). Dept. of Geological Sciences
- DOE Contract Number:
- FG02-87ER13721
- OSTI ID:
- 5727534
- Report Number(s):
- DOE/ER/13721-T1; ON: DE89016277
- Country of Publication:
- United States
- Language:
- English
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