Melts of garnet lherzolite: experiments, models and comparison to melts of pyroxenite and carbonated lherzolite

Abstract

Phase equilibrium experiments on a compositionally modified olivine leucitite from the Tibetan plateau have been carried out from 2.2 to 2.8 GPa and 1380 to 1480 °C. The experiments produced liquids multiply saturated with spinel and garnet lherzolite phase assemblages (olivine, orthopyroxene, clinopyroxene and spinel +/-garnet) under nominally anhydrous conditions. These SiO 2-undersaturated liquids and published experimental data are utilized to develop a predictive model for garnet lherzolite melting of compositionally variable mantle under anhydrous conditions over the pressure range of 1.9 to 6 GPa. The model estimates the major element compositions of garnet-saturated melts for a range of mantle lherzolite compositions and predicts the conditions of the spinel to garnet lherzolite phase transition for natural peridotite compositions at abovesolidus temperatures and pressures. We compare our predicted garnet lherzolite melts to those of pyroxenite and carbonated lherzolite and develop criteria for distinguishing among melts of these different source types. We also use the model in conjunction with a published predictive model for plagioclase and spinel lherzolite to characterize the differences in major element composition for melts in the plagioclase, spinel and garnet facies and develop tests to distinguish between melts of these three lherzolite facies based on major elements. The model is applied to understand the source materials and conditions of melting for high-K lavas erupted in the Tibetan plateau, basanitenephelinite lavas erupted early in the evolution of Kilauea volcano, Hawaii as well as younger tholeiitic to alkali lavas from Kilauea lavas.

Origin of the Powai ankaramite, and the composition, P–T conditions of equilibration and evolution of the primary magmas of the Deccan tholeiites

“…In the Ol-Cpx-Qz diagram, they plot at normative Cpx values lower than the multiple saturation points and near the ~14 kb Ol + Opx saturation boundary (cf. Grove et al 2013) (Fig. 13b).…”

“…13b). Grove et al (2013) conclude that such characteristics may indicate melting of a non-lherzolitic mantle source such as olivine pyroxenite, and Melluso et al (1995) in fact inferred a clinopyroxene-rich source for the Saurashtra high-Ti picrites. Therefore, although the data show a large scatter in Fig.…”

“…13b). These magmas may have originated through melting of garnet lherzolite at ~25 kb (~80 km depth) and then equilibrated with harzburgite at shallower depths as proposed for the Hawaiian alkali basalts by Grove et al (2013). Some other estimated Saurashtra-Gujarat primary magmas (Melluso et al 1995) including the proposed primary magma of the Pavagadh (Fig.…”

Probing the Earth’s Deep Interior Through Geochemistry

“…The latter, they conceded, may well result from an admixture of recycled oceanic crust, but that after mixing the result was merely fertile peridotite. Comparing Hawaiian basalt compositions to a model derived from their phase equilibrium experiments, Grove et al (2013) found that "Magmas with major element compositional characteristics of pyroxenite melts are truly the rare exception in Hawaii, and only 3 emerge from this analysis of major element characteristics." They had, however, not considered nickel or other transition metals, which form some of the strongest evidence of a non-peridotite component, and concluded that, "From this major element evidence, it appears that we must identify processes that can reconcile both the major and trace element signatures of Hawaiian lavas."…”

Arc and Slab-Failure Magmatism in Cordilleran Batholiths II – The Cretaceous Peninsular Ranges Batholith of Southern and Baja California

“…As the xenoliths provide minimum pressure bounds (Chin et al 2012), they clearly were formed within the garnet peridotite field (Fig. 18), and as La Posta plutons have REE patterns of residual garnet (Gromet and Silver 1987), it is reasonable to assume that the slab failure basalt magma originated from rising asthenosphere at deeper levels, say in the garnet stability field (Grove et al 2013), than the precursors to typical arc magmas, which appear to be formed at shallower levels by melting in the plagioclase and spinel stability fields (Till et al 2012).…”