Origin of Primitive Silica-Undersaturated Arc Magmas: Evidence from Olivine-Hosted Melt Inclusions from Aoba Volcano (Vanuatu Arc)
Abstract
To what extents the parental magmas of arc lavas are Si-undersaturated is a key question. Heterogeneous and metasomatized sources are commonly invoked to account for ne-normative, high-CaO compositions [1-6], which strongly contrast with those of experimental melts derived from lherzolite. We focus here on a series of olivine-hosted melt inclusions from Aoba volcanic island, in Vanuatu arc, which were analyzed for both major, volatile and trace elements. They delineate a differentiation trend of calc-alkaline silica-undersaturated basalts, with typical pattern of arc magmas. The most primitive melt inclusions (entrapped in high magnesian olivines; Fo ≥ 89) are ne-normative. They also differ in their trace element, Cl and K2O contents, and their extent of LILE enrichment. Only one population with intermediate LILE concentrations (La/Yb ~ 7.6) is representative of the parent magma of the lava-series and the most evolved inclusions. Two other populations depart from this crystal fractionation trend in being either significantly enriched or extremely depleted in LILE. Medium LILE melts require multi-stage mixing process involving melts generated by the high pressure partial melting of peridotite, and that of clinopyroxene-rich lithologies, whereas high- and low-LILE melts would involve the melting of amphibole-bearing and amphibole-free clinopyroxenites, respectively. Preliminary major and volatile element data on Si-undersaturated primitive melt inclusions from other island arcs strongly suggest the existence of a continuum between high-pressure peridotite melts and amphibole-bearing clinopyroxenite melts. This continuum, formed by the whole group of primitive island arc melt inclusions, is particularly well illustrated in the CMAS projections. As expected, amphibole also plays a significant role in the silica-undersaturation degree of derived melts. Mixing between melts derived from clinopyroxenitic lithology either as amphibolite veins in the mantle or as cumulate at the lower arc crust, and peridotite is the dominant and suitable process to account for Si-undersaturated island arc parental magmas recorded as primitive melt inclusions. References: [1] Schiano P. et al. (2000) G3: 1, paper number 1999GC000032; [2] Schmidt M. W. et al. (2004) Journal of Petrology, 45: 531-554; [3] Médard E. et al. (2006) Journal of Petrology, 47: 481-504; [4] Elburg M. A. et al. (2007) Chemical Geology, 240: 260-279; [5] Georgiev S. et al. (2009) Journal of Petrology, 50: 1899-1933; [6] Marchev P. et al. (2009) Lithos, 113: 228-245.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V33B2374S
- Keywords:
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- 1037 GEOCHEMISTRY / Magma genesis and partial melting;
- 1043 GEOCHEMISTRY / Fluid and melt inclusion geochemistry;
- 8413 VOLCANOLOGY / Subduction zone processes