Differentiation and magma mixing on Kilauea's east rift zone: a further look at the eruptions of 1955 and 1960. Part II. The 1960 lavas |
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Authors: | T L Wright R T Helz |
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Institution: | (1) Smithsonian Institution, National Museum of Natural History, NHB-119, Washington, DC 20560, USA, US;(2) U.S. Geological Survey, 107 National Center, Reston, Virginia 22092, USA, US |
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Abstract: | New and detailed petrographic observations, mineral compositional data, and whole-rock vs glass compositional trends document
magma mixing in lavas erupted from Kilauea's lower east rift zone in 1960. Evidence includes the occurrence of heterogeneous
phenocryst assemblages, including resorbed and reversely zoned minerals in the lavas inferred to be hybrids. Calculations
suggest that this mixing, which is shown to have taken place within magma reservoirs recharged at the end of the 1955 eruption,
involved introduction of four different magmas. These magmas originated beneath Kilauea's summit and moved into the rift reservoirs
beginning 10 days after the eruption began. We used microprobe analyses of glass to calculate temperatures of liquids erupted
in 1955 and 1960. We then used the calculated proportions of stored and recharge components to estimate the temperature of
the recharge components, and found those temperatures to be consistent with the temperature of the same magmas as they appeared
at Kilauea's summit. Our studies reinforce conclusions reached in previous studies of Kilauea's magmatic plumbing. We infer
that magma enters shallow storage beneath Kilauea's summit and also moves laterally into the fluid core of the East rift zone.
During this process, if magmas of distinctive chemistry are present, they retain their chemical identity and the amount of
cooling is comparable for magma transported either upward or laterally to eruption sites. Intrusions within a few kilometers
of the surface cool and crystallize to produce fractionated magma. Magma mixing occurs both within bodies of previously fractionated
magma and when new magma intersects a preexisting reservoir. Magma is otherwise prevented from mixing, either by wall-rock
septa or by differing thermal and density characteristics of the successive magma batches.
Received: July 10, 1995 / Accepted: October 10, 1995 |
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Keywords: | Kilauea Magma mixing Magmatic temperatures Glass composition Basalt composition Magmatic plumbing/storage/transport |
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