Orogenic Andesites and Crustal Growth
Orogenic andesites have long intrigued scientists because of their remarkable compositional similarities to the continental crust. The significance of orogenic andesites as proxies to continental crust formation has been recognized for over 30 years, but no consensus model of andesite genesis exists. Much of the controversy revolves around whether orogenic andesites are primary melts of slab and mantle materials, or instead evolve from basaltic mantle melts at shallower crustal levels. In three sections, this book provides an overview of andesite genesis at convergent margins that focuses on the slab–mantle interaction, crustal processing and andesite evolution through the life of volcanic arcs. Without favouring a particular view, the books aims to engender cross-fertilization and discussion that will smooth the pathway towards a holistic communal model of andesite petrogenesis and its role within the broader geochemical cycles of the Earth.
A genetic link between silicic slab components and calc-alkaline arc volcanism in central Mexico
Published:January 01, 2013
Susanne M. Straub, Georg F. Zellmer, Arturo Gómez-Tuena, Ramon Espinasa-Pereña, Ana Lillian Martin-del Pozzo, Finlay M. Stuart, Charles H. Langmuir, 2013. "A genetic link between silicic slab components and calc-alkaline arc volcanism in central Mexico", Orogenic Andesites and Crustal Growth, A. Gómez-Tuena, S. M. Straub, G. F. Zellmer
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A fundamental question in the formation of orogenic andesites is whether their high melt SiO2 reflects the recycling of silicic melts from the subducted slab or the processing of basaltic mantle melts in the overlying crust. The latter model is widely favoured, because most arc magmas lack the ‘garnet’ signature of partial slab melts. Here we present new trace element data from Holocene high-Mg# >64–72 calc-alkaline basalts to andesites (50–62 wt% SiO2) from the central Mexican Volcanic Belt that crystallize high-Ni olivines with the high 3He/4He=7–8 of the upper mantle. These magmas have been proposed to be partial melts from ‘reaction pyroxenites’, which formed by hybridization of mantle peridotite (c. 82–85%) and heavy rare earth element-depleted silicic slab melt (>15–18%). Forward and inverse models suggest that the absence of a garnet signature in these melts reflects the efficient buffering of the heavy rare earth elements (Ho to Lu) in the subarc mantle. In contrast, all elements more incompatible than Ho – excepting TiO2 – are more or less strongly controlled by the silicic slab flux that also directly contributes to the silicic arc magma formation. Our study emphasizes the strong link between slab recycling and the genesis of orogenic andesites.
Methods, additional data and modelling parameters are available at http://www.geolsoc.org.uk/SUP18686