Heather Dalton

Bio: Heather Dalton is an academic researcher from Rice University. The author has contributed to research in topics: Plate tectonics & Terrestrial planet. The author has an hindex of 1, co-authored 1 publications receiving 491 citations.

Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes

Abstract: This work focuses on a rigorous analysis of the physical–chemical, compositional and textural relationships of amphibole stability and the development of new thermobarometric formulations for amphibole-bearing calc-alkaline products of subduction-related systems Literature experimental results (550–1,120°C, 021) and are inferred to represent xenocrysts of crustal or mantle materials Most experimental results on calc-alkaline suites have been found to be unsuitable for using in thermobarometric calibrations due to the high Al# (>021) of amphiboles and high Al2O3/SiO2 ratios of the coexisting melts The pre-eruptive crystallization of consistent amphiboles is confined to relatively narrow physical–chemical ranges, next to their dehydration curves The widespread occurrence of amphiboles with dehydration (breakdown) rims made of anhydrous phases and/or glass, related to sub-volcanic processes such as magma mixing and/or slow ascent during extrusion, confirms that crystal destabilization occurs with relatively low T–P shifts At the stability curves, the variance of the system decreases so that amphibole composition and physical–chemical conditions are strictly linked to each other This allowed us to retrieve some empirical thermobarometric formulations which work independently with different compositional components (ie Si*, AlT, Mg*, [6]Al*) of a single phase (amphibole), and are therefore easily applicable to all types of calc-alkaline volcanic products (including hybrid andesites) The Si*-sensitive thermometer and the fO2–Mg* equation account for accuracies of ±22°C (σest) and 04 log units (maximum error), respectively The uncertainties of the AlT-sensitive barometer increase with pressure and decrease with temperature Near the P–T stability curve, the error is 35%) and lower-T magmas, the uncertainty increases up to 24%, consistent with depth uncertainties of 04 km, at 90 MPa (~34 km), and 79 km, at 800 MPa (~30 km), respectively For magnesiohornblendes, the [6]Al*-sensitive hygrometer has an accuracy of 04 wt% (σest) whereas for magnesiohastingsite and tschermakitic pargasite species, H2Omelt uncertainties can be as high as 15% relative The thermobarometric results obtained with the application of these equations to calc-alkaline amphibole-bearing products were finally, and successfully, crosschecked on several subduction-related volcanoes, through complementary methodologies such as pre-eruptive seismicity (volcano-tectonic earthquake locations and frequency), seismic tomography, Fe–Ti oxides, amphibole–plagioclase, plagioclase–liquid equilibria thermobarometry and melt inclusion studies A user-friendly spreadsheet (ie AMP-TBxls) to calculate the physical–chemical conditions of amphibole crystallization is also provided

Identification of Source Lithology in the Hawaiian and Canary Islands: Implications for Origins

Abstract: Results are reported of an exploration of mantle source lithology for intraplate magmas using whole-rock and olivine phenocryst compositions.This analysis includes modern mid-ocean ridge basalts and Archean komatiites as low- and high-temperature reference frames. It is shown that the Ni, Ca, Mn, and Fe/Mn contents of olivine phenocrysts in modern mid-ocean ridge basalts and Archean komatiites are consistent with a normal peridotite source. In contrast, olivine phenocrysts in shield-building lavas on Hawaii are higher in Ni and Fe/ Mn, and lower in Mn and Ca than those expected to crystallize from meltsofa normal peridotite source, and point tothe importance ofpyroxenite as proposed by Sobolev and co-workers. Hawaiian shield stage lavas and their olivine phenocrysts are similar to those expected from partial melts of a 100% stage 2 pyroxenite source. Such a source might form from a variety of melt^rock, melt^melt, and rock^rock reactions. Primary pyroxenite-derived magmas have a range of SiO2 contents that are positively correlated with 187 Os/ 188 Os and negatively correlated with 3 He/ 4 He.These results are consistent with a Hawaiian plume containing recycled crust within a peridotite matrix.Variable amounts of free silica are inferred in Hawaiian pyroxenite sources, which contribute to the production of SiO2-rich magmas. In contrast, peridotite and olivine pyroxenite melting are inferred to produce SiO2-poor pre-shield magmas at Loihi.The interaction of SiO2-rich and -poor magmas in the Hawaiian plume will trigger crystallization, not mixing. Mixing is permitted at low pressures in melt conduits and magma chambers, and work on olivine-hosted melt inclusions will be useful to evaluate its importance. In contrast to Hawaii, many ocean island basalts in localities such as the Canary Islands are deficient in SiO2, and may have been generated by partial melting of olivine pyroxenites that formed by solid-state reaction between recycled crust þ peridotite in the lower mantle. There is likely to be a wide range of whole-rock pyroxenite compositions in the mantle, as well assignificant variability in Mn and Fe/Mn in both peridotite partial melts and their olivine phenocrysts. In general, there are not likely to be welldefined end-member peridotite and pyroxenite sources in the mantle. Nevertheless, taxonomical difficulties encountered in source lithology identification may yield rich rewards, such as a better understanding of the relationship between lithological diversity in the lower mantle and its petrological expression in intraplate magmatism.