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Origin and emplacement of the andesite of Burroughs Mountain, a zoned, large-volume lava flow at Mount Rainier, Washington, USA

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Author(s): Karen R. Stockstill, Thomas A. Vogel, Thomas W. Sisson

Document Type:
Publisher: Journal of Volcanology and Geothermal Research
Published Year: 2003
Volume: 119
Number: 1-4
Pages: 275 to 296
DOI Identifier: 10.1016/S0377-0273(02)00358-X
ISBN Identifier:
Keywords: Mount Rainier Cascade Range andesites dacites magmatic differentiation lava flows

Burroughs Mountain, situated at the northeast foot of Mount Rainier, WA, exposes a large-volume (3.4 km3) andesitic lava flow, up to 350 m thick and extending 11 km in length. Two sampling traverses from flow base to eroded top, over vertical sections of 245 and 300 m, show that the flow consists of a felsic lower unit (100 m thick) overlain sharply by a more mafic upper unit. The mafic upper unit is chemically zoned, becoming slightly more evolved upward; the lower unit is heterogeneous and unzoned. The lower unit is also more phenocryst-rich and locally contains inclusions of quenched basaltic andesite magma that are absent from the upper unit. Widespread, vuggy, gabbronorite-to-diorite inclusions may be fragments of shallow cumulates, exhumed from the Mount Rainier magmatic system. Chemically heterogeneous block-and-ash-flow deposits that conformably underlie the lava flow were the earliest products of the eruptive episode. The felsic–mafic–felsic progression in lava composition resulted from partial evacuation of a vertically-zoned magma reservoir, in which either (1) average depth of withdrawal increased, then decreased, during eruption, perhaps due to variations in effusion rate, or (2) magmatic recharge stimulated ascent of a plume that brought less evolved magma to shallow levels at an intermediate stage of the eruption. Pre-eruptive zonation resulted from combined crystallization–differentiation and intrusion(s) of less evolved magma into the partly crystallized resident magma body. The zoned lava flow at Burroughs Mountain shows that, at times, Mount Rainier’s magmatic system has developed relatively large, shallow reservoirs that, despite complex recharge events, were capable of developing a felsic-upward compositional zonation similar to that inferred from large ash-flow sheets and other zoned lava flows.

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Suggested Citations:
In Text Citation:
Stockstill and others (2003) or (Stockstill et al., 2003)

References Citation:
Stockstill, K.R., T.A. Vogel, and T.W. Sisson, 2003, Origin and emplacement of the andesite of Burroughs Mountain, a zoned, large-volume lava flow at Mount Rainier, Washington, USA: Journal of Volcanology and Geothermal Research, Vol. 119, No. 1-4, pp. 275-296, doi: 10.1016/S0377-0273(02)00358-X.