Carbonatite and silicate melt metasomatism of the mantle surrounding the Hawaiian plume: Evidence from volatiles, trace elements, and radiogenic isotopes in rejuvenated‐stage lavas from Niihau, Hawaii

Abstract

[1] We present new volatile, trace element, and radiogenic isotopic compositions for rejuvenated-stage lavas erupted on Niihau and its submarine northwest flank. Niihau rejuvenated-stage Kiekie Basalt lavas are mildly alkalic and are isotopically similar to, though shifted to higher 87 Pb than, rejuvenated-stage lavas erupted on other islands and marginal seafloor settings. Kiekie lavas display trace element heterogeneity greater than that of other rejuvenated-stage lavas, with enrichments in Ba, Sr, and light-rare earth elements resulting in high and highly variable Ba/Th and Sr/Ce. The high Ba/Th lavas are among the least silica-undersaturated of the rejuvenated-stage suite, implying that the greatest enrichments are associated with the largest extents of melting. Kiekie lavas also have high and variable H 2 O/Ce and Cl/La, up to 620 and 39, respectively. We model the trace element concentrations of most rejuvenated-stage lavas by small degrees ($1% to 9%) of melting of depleted peridotite recently metasomatized by a few percent of an enriched incipient melt (0.5% melting) of the Hawaiian plume. Kiekie lavas are best explained by 4% to 13% partial melting of a peridotite source metasomatized by up to 0.2% carbonatite, similar in composition to oceanic carbonatites from the Canary and Cape Verde Islands, with lower proportion of incipient melt than that for other rejuvenated-stage lavas. Primary H 2 O and Cl of the carbonatite component must be high, but variability in the volatile data may be caused by heterogeneity in the carbonatite composition and/or interaction with seawater. Our model is consistent with predictions based on carbonated eclogite and peridotite melting experiments in which (1) carbonated eclogite and peridotite within the Hawaiian plume are the first to melt during plume ascent; (2) carbonatite melt metasomatizes plume and surrounding depleted peridotite; (3) as the plume rises, silica-undersaturated silicate melts are also produced and contribute to the metasomatic signature. The metasomatic component is best preserved at the margins of the plume, where low extents of melting of the metasomatized depleted mantle surrounding the plume are sampled during flexural uplift. Formation of carbonatite melts may provide a mechanism to transfer plume He to the margins of the plume.

Double layering of a thermochemical plume in the upper mantle beneath Hawaii

“…Ballmer et al, 2011). The predicted small flux of this melting and its widespread geographic distribution agrees well with observed occurrences of rejuvenated-stage (Dixon et al, 2008) and arch volcanism (Hanyu et al, 2005) (Figs. 1 versus 6).…”

“…1 versus 6). The predicted difference in origin for the rejuvenated-stage and arch volcanism (i.e., from the plume outskirts) versus shield-stage volcanism (i.e., from the plume core) is consistent with geochemical evidence that these two forms of volcanism have distinct source materials (Yang et al, 2003;Hanyu et al, 2005;Fekiacova et al, 2007;Dixon et al, 2008).…”

“…Bathymetry (colors) and contours of shear-wave velocity anomaly (Wolfe et al, 2009) at 200 km depth (1% contour interval for thick contours), two independent datasets, display consistent asymmetry about the island chain and indicate more buoyant asthenosphere southwest than northeast of the island of Hawaii. Triangles show sites of recent (<1 Ma) volcanic activity (Hanyu et al, 2005;Robinson and Eakins, 2006;Dixon et al, 2008). The pink dashed line denotes the location of the cross-section in Fig.…”

New determinations of 40Ar/39Ar isotopic ages and flow volumes for Cenozoic volcanism in the Terror Rift, Ross Sea, Antarctica

“…The experimentally determined solidus of peridotite +2.5 wt % carbonate [ Dasgupta et al , 2007, 2006] falls well below the McMurdo and NVL geotherms, but lower concentrations of carbonate would yield higher temperature solidii between the anhydrous peridotite solidus and the 2.5 wt % carbonated peridotite solidus. Similar carbonated or metasomatized sources have been suggested for the generation of alkaline volcanism from the Hawaiian Islands [ Dixon et al , 2008]. These compositions could also generate partial melting with limited decompression.…”

Evaluation of Recent Tectonomagmatic Discrimination Diagrams and their Application to the Origin of Basic Magmas in Southern Mexico and Central America

“…The island arc basic rocks (IAB) were compiled from the following areas and sources: Aleutian (FINNEY et al, 2008); Bicol and Bataan, Philippines (MCDERMOTT et al, 2005;DUFRANE et al, 2006); Indonesia (ELBURG and KAMENETSKY, 2007;SENDJAJA et al, 2009);Isu Bonin (TAMURA et al, 2007); Lesser Antilles (TURNER et al, 1996) The ocean-island basic rocks (OIB) were compiled from the following areas and sources: French Polynesia (TAKAMASA et al, 2009) andHawaiian Islands (XU et al, 2007;DIXON et al, 2008;MARSKE et al, 2008;IRELAND et al, 2009).…”