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Volatile contents of mafic magmas from cinder cones in the Central Oregon High Cascades: Implications for magma formation and mantle conditions in a hot arc

Citation

Ruscitto, DM and Wallace, PJ and Johnson, ER and Kent, AJR and Bindeman, IN, Volatile contents of mafic magmas from cinder cones in the Central Oregon High Cascades: Implications for magma formation and mantle conditions in a hot arc, Earth and Planetary Science Letters, 298, (1-2) pp. 153-161. ISSN 0012-821X (2010) [Refereed Article]

DOI: doi:10.1016/j.epsl.2010.07.037

Abstract

The Cascades arc is a warm-slab subduction zone characterized by the slow (3.5cm/a) subduction of young (<10Ma) oceanic crust. Elevated slab temperatures likely result in shallow dehydration beneath the forearc and reduced slab fluid addition to the mantle wedge beneath the volcanic front. Resulting calc-alkaline magmas should contain low volatile abundances relative to arcs with cooler subducting slabs. We test this hypothesis in Central Oregon, the region of the arc that has experienced the highest mafic output over the last 2Ma. Naturally quenched basalt and basaltic andesite melt inclusions from tephra erupted from monogenetic vents record pre-eruptive magmatic volatile contents. After accounting for the effects of degassing, our data show that initial volatile contents from seven calc-alkaline cinder cones range from 1.7 to 3.6wt.% H 2O, 1200-2100ppm S and 500-1200ppm Cl. Ratios reflecting volatiles recycled from the subducted slab (H 2O/Ce ~490-1700; S/Nb ~110-310; and Cl/Nb ~37-190) are elevated above MORB values but are low compared to those from the southern Cascades (Mount Shasta) and other arcs (Mexico, Central America, and Kamchatka). Positive correlations between H 2O, Pb/Ce and Ba/Zr suggest that small additions of a slab-derived component to the mantle wedge are responsible for observed volatile contents.Melt inclusion compositions are evolved (Fo 82-84 host olivines, 5.0-7.2wt.% MgO) and fractionated from primitive parental magmas by ~16% crystallization of predominantly olivine before being trapped as inclusions. Calc-alkaline basaltic and Sr-rich basaltic melts can be generated by 9-11% partial melting of spinel lherzolite. H 2O-rich basaltic andesite melts are highly depleted in incompatible elements and are probably generated from a more depleted mantle source by 12-16% melting. Subarc mantle temperatures inferred from H 2O and trace elements are similar to or slightly warmer than temperatures in other arcs. Additionally, compositional proxies for slab surface temperatures in Central Oregon are at the high end of the global arc spectrum, corresponding to temperatures of 850-950°C, and are consistent with a young, hot incoming plate. © 2010 Elsevier B.V.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Johnson, ER (Dr Emily Johnson)
ID Code:67886
Year Published:2010
Web of Science® Times Cited:39
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2011-03-08
Last Modified:2011-05-13
Downloads:0

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