Topic
Hedenbergite
About: Hedenbergite is a research topic. Over the lifetime, 295 publications have been published within this topic receiving 10016 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this article, the authors proposed a new model based on jadeite crystallization and diopside + hedenbergite exchange equilibria to calculate the depths and temperatures at which magmas partially crystallize.
Abstract: Our ability to calculate the depths and temperatures at which magmas partially crystallize can prove crucial as petrologists test hypotheses of magma transport and evolution. Yet whereas numerous magma transport arguments involve hydrous and SiO2-rich volcanic products, current clinopyroxene-liquid thermobarometers have been calibrated only from basaltic liquid compositions. To remedy this deficiency, new thermobarometers have been calibrated using new experiments that include hydrated (water-undersaturated) and SiO2-rich liquids ranging to 71.3 wt% SiO2. As with prior models, the new calibrations are based on jadeite crystallization and jadeite-diopside + hedenbergite exchange equilibria:
![Formula][1]
![Formula][2]
Here, T is in Kelvins and P is in kbar. Jdcpx is the mole fraction of jadeite in clinopyroxene, where pyroxene cations are calculated on the basis of 6 O atoms, and Jd is the lesser of Na or VIAl; remaining Al is used to form CaTs. DiHdcpx is the mole fraction of diopside + hedenbergite in clinopyroxene, calculated as the fraction of Ca remaining after forming CaTs (= VIAl – Jd), CaTiAl2O6 [= (IVAl – CaTs)/2], and CaCr2SiO6 (=Cr/2). Terms such as Alliq refer to the cation fraction of AlO1.5 in the liquid, Fmliq is the sum FeOliq + MgOliq, and Mg′liq is the cation fraction ratio MgOliq/(MgOliq + FeOliq). Errors are similar to earlier models that utilize basalt compositions only. For the barometer, R 2 = 0.97 and the standard error of estimate (SEE) is 1.7 kbar for the regression data; for the thermometer R 2 = 0.96 and the SEE is 33 K. The models are applied to Neogene lavas from the Tibetan Plateau, and Neogene-Quternary lavas from the eastern Snake River Plain (SRP), Idaho. Crystallization depths for Tibet cluster at the middle/lower crust boundary. Magma-crust density relationships suggest that the middle crust may act as a level of neutral buoyancy. In the SRP, however, magmas appear to bypass several possible density traps. We suggest that fracture properties, such as dike size and aspect ratio, control magma transport in the SRP.
[1]: /embed/tex-math-1.gif
[2]: /embed/tex-math-2.gif
557 citations
TL;DR: In this article, a new thermodynamic model for sodic pyroxenes involving jadeite-diopsidehedenbergite-acmite is presented, which allows for ordering of Mg, Al, Fe2+, and Fe3+ on the M 1 sites, with coupled Na and Ca ordering on the 2 sites.
Abstract: A new thermodynamic model for sodic pyroxenes involving jadeite-diopside-hedenbergite-acmite is presented. This model allows for ordering of Mg, Al, Fe2+, and Fe3+ on the M1 sites, with coupled Na and Ca ordering on the M2 sites. It is calibrated on the basis of experiments in three chemical subsystems together with available information on ordering in different pyroxenes and on the limited calorimetric data. Central to the determination of the parameters of the model is the use of relationships among the end-member Gibbs energies and the interaction energies in the various possible non-independent sets of end-members. An important aspect of this model, which uses the symmetric formalism, is that Fe-Mg (FM) and Al-Fe3+ (AF’) mixing is not assumed to be ideal. The model accounts successfully for the experiments at both 600 °C and at higher temperatures involving ordered and disordered pyroxenes coexisting with albite and quartz in NCMAS, NCFAS, NF’AS systems as well as the available calorimetry. It is also able to predict the positions and slopes of tielines in coexisting jadeite + omphacite and omphacite + augite found in nature at lower temperatures. Although the model requires a large number of energy parameters, some of these are not critical to the behavior of the model, while for others the constraints from experiment, calorimetry, ordering state and solvi lead to very limited allowable combinations. The model places some restrictive constraints on the shape of the phase relations in the jadeite–augite–acmite system. Petrological applications of the model are illustrated via a phase diagram example for a MORB bulk composition eclogite.
533 citations
TL;DR: In this article, a geothermometer for estimating the pressure and tem- perature of igneous rocks from coexisting clino- pyroxene and liquid compositions is presented.
Abstract: Models for estimating the pressure and tem- perature of igneous rocks from co-existing clino- pyroxene and liquid compositions are calibrated from existing data and from new data obtained from experi- ments performed on several mafic bulk compositions (from 8—30 kbar and 1100—1475i C). The resulting geothermobarometers involve thermodynamic expres- sions that relate temperature and pressure to equili- brium constants. Specifically, the jadeite (Jd; NaAlSi 2 O 6 )—diopside/hedenbergite (DiHd; Ca(Mg, Fe) Si 2 O 6 ) exchange equilibrium between clinopyroxene and liquid is temperature sensitive. When composi- tional corrections are made to the calibrated equili- brium constant the resulting geothermometer is (i) 104 " "6.73!0.26* ln C Jd19*Ca-*2*Fm-*2 DiHd19*Na-*2*Al-*2D
518 citations
TL;DR: In this article, the authors investigated the relationship between alteration processes in carbonaceous carbonaceous chondrites and their origins in the nebular and asteroidal models for their origins and found that they were closely related in time and space.
Abstract: — Calcium- and aluminum-rich inclusions (CAIs), chondrules, dark inclusions and matrices in certain CV3 carbonaceous chondrites appear to have been modified by different degrees of late-stage alteration processes that caused significant variations in mineralogy and chemistry. Some chondrules and CAIs are rimmed with fayalitic olivine. Metal in all components may be oxidized and sulphidized to magnetite, Ni-rich metal and sulfides. Silicates in all components are aqueously altered to different degrees to phyllosilicates. Primary minerals in some CAIs experienced Fe-alkali-halogen metasomatism forming nepheline, sodalite, wollastonite, hedenbergite and other secondary minerals. In CV3 chondrites with metasomatized CAIs, nepheline, sodalite, etc. are also present in chondrule mesostases and in matrices. McSween's (1977b) reduced subgroup of CV3 chondrites generally shows minimal alteration of all components and may represent the unaltered precursors for the oxidized CV3 chondrites, which generally show major alteration. Most studies have been focused on specific components in CV3 chondrites and have not considered possible relationships between alteration processes. We infer from the correlated occurrences of the alteration features that they were closely related in time and space and review nebular and asteroidal models for their origins. We prefer an asteroidal model.
384 citations
Journal Article•
372 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2022 | 1 |
| 2021 | 1 |
| 2019 | 7 |
| 2018 | 4 |
| 2017 | 12 |
| 2016 | 2 |