Conference proceeding
Post-glacial mantle evolution in Southern Chile and the development of the Carran-Los Venados volcanic field (40'20 degrees S)
American Geophysical Union Fall Meeting, Vol.2016
American Geophysical Union 2016 fall meeting
12/2016
Abstract
Deglaciation can locally enhance magmatism due to mantle decompression caused by glacial unloading. We investigate the geochemical effects of this process and on what timescale it occurred at the Carran-Los Venados (CLV) volcanic field (40'20 degrees S) in the Southern Volcanic Zone, Chile. The CLV has been volcanically active from approximately 5 ka to its last eruption in 1979 AD. It consists of approximately 70 basaltic scoria cones and maars, constructed over extensive inter- to postglacial basal basaltic lava flows. Mafic rocks erupted in this setting therefore provide an ongoing record of mantle evolution in pre-, inter- and post-glacial times. The longer lived, more evolved Puyehue-Cordon Caulle complex is located 20 km to the south and has been active from 500 ka until the present day. Whole rock major and trace element compositions combined with U-Th and Sr-Nd-Pb isotopic ratios and olivine compositions show a profound difference between the basal lavas underlying the volcanic field and the later monogenetic basalts. Differences in fluid mobile/immobile element ratios and incompatible trace element contents, in addition to changes in olivine Fo contents suggest that the former were produced by melting of a drier, more enriched source, whilst the monogenetic field was sourced by a significantly wetter, more depleted source. The most recent eruption within the field (Mirador) displays characteristics of both sources. We hypothesize that deglaciation drove the decompression and subsequent melting of relatively dry and enriched mantle at higher upwelling rates allowing the eruption of the extensive basal lava flows. As deglaciation slowed and upwelling rates decreased, this source became less dominant and smaller, more isolated fluid-fluxed melting events dominated magma genesis. This change occurred over a narrow window of time--a few thousands of years--suggesting that in such conditions shifts in source, melting dynamics and eruption style can occur relatively rapidly.
Details
- Title: Subtitle
- Post-glacial mantle evolution in Southern Chile and the development of the Carran-Los Venados volcanic field (40'20 degrees S)
- Creators
- Mark K Reagan - University of Iowa, Department of Geoscience Iowa City, IA USA United StatesLucy Emma McGeeGeoffrey M NowellMichael B TurnerLuis LaraHeather K Handley
- Resource Type
- Conference proceeding
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2016
- Conference
- American Geophysical Union 2016 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2016 fall meeting
- Language
- English
- Date published
- 12/2016
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240795202771
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