期刊
EARTH AND PLANETARY SCIENCE LETTERS
卷 310, 期 3-4, 页码 518-525出版社
ELSEVIER
DOI: 10.1016/j.epsl.2011.08.032
关键词
crystal cumulate; silicic; zoned ignimbrite; assimilation; recharge; Ammonia Tanks
资金
- NSF-EAR [0809828]
- University of Washington
- Lawrence Livermore National laboratories
- Division Of Earth Sciences
- Directorate For Geosciences [0809828] Funding Source: National Science Foundation
Super-volcanic eruption deposits, such as the Ammonia Tanks Tuff (AT; similar to 900 km(3)), typically record the explosive evacuation of a chemically and thermally zoned shallow magma reservoir. Such zoning patterns require either 1) mixing between two magmas or 2) in-situ differentiation driven by crystal-liquid separation. Here we show, using a geochemical model firmly grounded on natural observations, that these processes are not mutually exclusive. Using an initial trachydacitic magma, the interstitial liquid evolves to a rhyolitic composition as the magma reaches high crystallinity (mush state: >=similar to 50% crystals). The low-density rhyolitic melt then migrates upwards and leaves behind a trachyandesite cumulate with distinctive trace element concentrations (e.g., high Ba, Sr, Zr) that can be modeled by crystal fractionation. During eruption, both liquid cap and underlying cumulate are evacuated from a shallow reservoir, leading to the observed chemical gradient. However, to account for the thermal gradient and low crystal fraction (similar to 25 vol.%) in the cumulate trachyandesite of the AT tuff, a mixing stage with hot mafic recharge must have occurred prior to eruption. The late recharge induced heating, partially melting a significant portion of the crystal cargo and ultimately triggering the eruption. (C) 2011 Elsevier B.V. All rights reserved.
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