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Crustal assimilation no match for slab fluids beneath Volcan de Santa Maria, Guatemala

Brian R. Jicha, Katy E. Smith, Brad S. Singer, Brian L. Beard, Clark M. Johnson and Nick W. Rogers
Crustal assimilation no match for slab fluids beneath Volcan de Santa Maria, Guatemala
Geology (Boulder) (September 2010) 38 (9): 859-862


New (super 238) U- (super 230) Th and Sr isotope data from (super 40) Ar/ (super 39) Ar-dated mafic lavas of the composite cone, A.D. 1902 dacitic tephra, and 1922-present dacitic dome lavas from the Santa Maria-Santiaguito volcanic complex in northwestern Guatemala indicate that genesis of magma beneath the western end of the Central American volcanic arc requires sources much different than previously envisioned. Although U-series data from historical lavas along the Central American volcanic arc, including Guatemala, show variable but small degrees of either (super 230) Th or (super 238) U excess, 72-35 ka basalts and basaltic andesites from the Santa Maria cone have 15%-26% (super 238) U excesses, among the largest measured in Central America. This implies that the mantle wedge beneath this sector of the arc was significantly modified by slab-derived fluids. A decrease in (super 87) Sr/ (super 86) Sr and ( (super 238) U/ (super 230) Th) ratios over the past 72 k.y. as basaltic andesite gave way to dacite is consistent with fractional crystallization coupled with progressive assimilation of crust that has relatively unradiogenic, mid-oceanic ridge basalt-like Sr isotope composition. Overall, our U-series data along with published (super 238) U/ (super 230) Th isotope results from Central America demonstrate that (1) slab-fluid flux can be high throughout Central America, including regions of relatively thick crust, and (2) the middle to lower crust beneath northwestern Guatemala may not be dominated by ancient metamorphic and granitic rocks.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 38
Serial Issue: 9
Title: Crustal assimilation no match for slab fluids beneath Volcan de Santa Maria, Guatemala
Affiliation: University of Wisconsin, Department of Geoscience, Madison, WI, United States
Pages: 859-862
Published: 201009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 33
Accession Number: 2010-077607
Categories: Quaternary geologyGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2010238
Illustration Description: illus.
N14°45'21" - N14°45'21", W91°34'00" - W91°32'60"
Secondary Affiliation: Open University, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201041
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