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natural and experimental systems due to their high spatial reso- lution and their ability to avoid inclusions that can compromise the trace-element compositions of mineral separates (Foley et al. 1996). For this study, we used laser ablation ICPMS to measure D-values for an extensive suite of trace elements in augite, low- Ca pyroxene, plagioclase, and olivine phenocrysts in fraction- ated tholeiitic lavas from the 1955 eruption of Kilauea volcano, Hawaiʼi. This phenocryst assemblage is unusual among Hawaiian tholeiites (e.g., Garcia et al. 2003). It provides the

producing this trend. Whitaker et al. (2007) showed that equilibrium crystalliza- tion of a single “dry” (0.05 wt% H2O) olivine tholeiite melt (10.62 wt% MgO) at 9.3 kbar (~30 km depth) gave rise to residual liquids that followed the same compositional trend as the ferrobasalts of the Craters of the Moon lava Þ eld in the SRP and the ferrodiorites found in the LAC. However, because the experiments reported in Whitaker et al. (2007) were conducted in graphite capsules, there were no means of distinguishing the effect of pressure on the liquid evolution paths from

mantle-derived gas fluxes in the Yellowstone area (e.g., Hurwitz and Lowenstern 2014 ) require there to be a deep-seated thermal anomaly distinct from that extending westward into the Snake River Plain. Volcanism along the YSRP locus has typically been considered as bimodal. Olivine tholeiites dominate the mafic compositions and are inferred to provide heat to partially melt solidified, underplated tholeiitic intrusive forerunners that, in turn, become parental magmas to the voluminous ferroan rhyolites ( Christiansen and McCurry 2008 ; McCurry and Rodgers 2009

alkalic magmas to be reached at lower pressures than in CO2- bearing tholeiitic magmas having identical volatile contents. However, if variations in ma- jor element and volatile concentrations were linked by variations in the extent of melting, then volatile-rich, strongly alkalic magmas would begin to exsolve a vapor at slightly higher pressures than volatile-poor alkali olivine basalts or tholeiites. Partitioning of H2O and CO2 into the vapor during volatile exsolution is controlled by the difference between H2O and CO2 solubilities. As melts become more alkalic, the

(Nb/Ta: 14.2±1.8 and Zr/Hf: 35, [ 16 ]). Th/Ta ratios increase from Group 1 (1.3-2.0) to Group 2 (2.7-8.0). Th/Nb ratios are nearly constant (≈0.1) in Group 1 and vary from 0.2 to 0.4 in Group 2 dolerites. In the Th-Tb-Ta diagram ( Figure 6A , after [ 17 ]), Mongo dolerites display an array of continuous variation from Group 1 to Group 2, especially within the field of continental tholeiite or contaminated magmas. High Ba/Nb (31-74), Ba/La (20-30), Rb/Nb (1.1-4.2), K/Nb (562-1572), La/Nb (1.5-3.0) ratios vary in the same range with systematic increase from Group 1

accuracy with which magma storage pressures can be estimated, we assessed the performance of various published clinopyroxene-liquid barometers. To anticipate our results, we find that some barometers overestimate reported experimental pressures at <7 kbar. We thus develop a new jadeite-inclinopyroxene barometer optimized for use at crustal pressures on hydrous and anhydrous compositions. We then recalculate storage pressures for a series of Icelandic rift tholeiites from which diverse clinopyroxene-liquid pressures have been reported in recent years. The number of

different petrogenetic and cool- ing histories, were analyzed for a and their stoichiometry was assessed. Diamond-indi- cator spinel from the Aries kimberlite and Argyle lamproite is stoichiometric. Spinel in- clusions in olivine phenocrysts from Ti-poor tholeiite from the Hunter Fraction Zone and Ca-rich boninite from the Tonga Trench show a range of nonstoichiometry. High FeH / FeH values calculated assuming stoichiometry for such spinel are invalid. Spinel samples from metamorphosed volcanics from the Peak Hill-Glengarry Basin and the Heazlewood River Ultramafic

. 2013 (3) Trondhjemite (magnesian-calcic) Partial melting and/or differentiation of basaltic rocks Wainivalau pluton, Fiji Stork 1984 Udu volcanics, Fiji 5 (4) Ferroan alkali-calcic Partial melting and/or differentiation of tholeiite Nebo Granite Kleeman and Twist 1989 Hill et al. 1996 Yellowstone Hildreth et al. 1991 (5) Magnesian calc-alkalic or calcic Differentiation of high-Al basalt or andesite Half Dome leucogranite, Tuolumnei Coleman et al. 2012 South Sister Fierstein et al. 2011 Brophy and Dreher 2000 (6) Peralkaline ferroan Differentiation of transitional or

spectroscopy (FTIR) and range from 0.45–1.26 wt%. Despite large differences in FeO* and MgO contents, the CO2 solubilities in Y 980459 are similar to that in a less primitive synthetic martian basalt based on the Humphrey rock and to a Hawaiian tholeiite. The lack of enhanced solubility in Fe2+- and Mg2+-rich melts is likely owing to the complex structural role of these cations in silicate melts, acting partly as network formers, rather than network modifiers. The small sensitivity of CO2 solubility to compositional variations among martian and tholeiitic basalts means