Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc

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• 作者：Margaret Mangan ; Thomas Miller ; Christopher Waythomas ; Frank Trusdell ; Andrew Calvert ; Paul Layer
• 关键词：volcano ; geochemistry ; petrology ; geochronology ; Aleutian arc
• 刊名：Earth and Planetary Science Letters
• 出版年：2009
• 出版时间：15 October 2009
• 年：2009
• 卷：287
• 期：3-4
• 页码：363-372
• 全文大小：998 K

文摘

Emmons Lake Volcanic Center (ELVC) on the lower Alaskan Peninsula is one of the largest and most diverse volcanic centers in the Aleutian Arc. Since the Middle Pleistocene, eruption of ~ 350 km³ of basalt through rhyolite has produced a 30 km, arc front chain of nested calderas and overlapping stratovolcanoes. ELVC has experienced as many as five major caldera-forming eruptions, the most recent, at ~ 27 ka, produced ~ 50 km³ of rhyolitic ignimbrite and ash fall. These violent silicic events were interspersed with less energetic, but prodigious, outpourings of basalt through dacite. Holocene eruptions are mostly basaltic andesite to andesite and historically recorded activity includes over 40 eruptions within the last 200 yr, all from Pavlof volcano, the most active site in the Aleutian Arc.

Geochemical and geophysical observations suggest that although all ELVC eruptions derive from a common clinopyroxene + spinel + plagioclase fractionating high-aluminum basalt parent in the lower crust, magma follows one of two closely spaced, but distinct paths to the surface. Under the eastern end of the chain, magma moves rapidly and cleanly through a relatively young (~ 28 ka), hydraulically connected dike plexus. Steady supply, short magma residence times, and limited interaction with crustal rocks preserve the geochemistry of deep crustal processes. Below the western part of the chain, magma moves haltingly through a long-lived (~ 500 ka) and complex intrusive column in which many generations of basaltic to andesitic melts have mingled and fractionated. Buoyant, silicic melts periodically separate from the lower parts of the column to feed voluminous eruptions of dacite and rhyolite. Mafic lavas record a complicated passage through cumulate zones and hydrous silicic residues as manifested by disequilibrium phenocryst textures, incompatible element enrichments, and decoupling of REEs and HFSEs ratios. Such features are absent in mafic lavas from the younger part of the chain, highlighting the importance of plumbing architecture and longevity in creating petrologic diversity.

Supplemental Data include 156 major element (XRF) and 128 trace element (ICP-MS) whole-rock analyses, 23 new ⁴⁰Ar/³⁹Ar ages, a generalized geologic map with associated unit descriptions and field photographs, and photomicrographs of key petrographic features.