H. A. Seck

Solubility of Ca and Al in orthopyroxene from spinel peridotite: an improved version of an empirical geothermometer

AbstractGeothermometric equations for spinel peridotites by Fujii (1976), Gasparik and Newton (1984), and Chatterjee, and Terhart (1985) based on the reaction enstatite (en)+spinel (sp)→Mg−Tschermaks (mats)+forsterite (fo) were tested using a nearly isothermal suite of mantle xenoliths from the Eifel, West Germany. In spite of using activities of MgAl2O4, en, and mats to allow for the non-ideal solution behaviour of the constituent phases, temperatures calculated from these equations systematically change as a function of Cr/(Cr+AL+Fe3+) in spinel. We propose an improved version of the empirical geothermometer for spinel peridotites of Sachtleben and Seck (1981) derived from the evaluation of the solubilities of Ca and Al in orthopyroxene from more than 100 spinel peridotites from the Rhenish Volcanic Province. A least squares regression yielded a smooth correlation between

PARTITIONING OF HIGH FIELD-STRENGTH AND RARE-EARTH ELEMENTS BETWEEN AMPHIBOLE AND QUARTZ-DIORITIC TO TONALITIC MELTS : AN EXPERIMENTAL STUDY

{\text{(}}X_{{\text{Ca}}} {\text{)}}^{{\text{opx}}} {\text{ and 1n K}}_{\text{D}} = 1n\frac{{(x_{{\text{Fo}}}^{{\text{Ol}}} )^2 {\text{ * }}(x_{{\text{Al}}}^{{\text{Ml}}} )^{opx} }}{{(x_{{\text{Al}}}^{{\text{Sp}}} )^2 {\text{ * }}(x_{{\text{Mg}}}^{{\text{Sp}}} )^2 {\text{ * }}(x_{{\text{Mg}}}^{{\text{M1}}} )^{opx} }}

Granulite facies lower crustal xenoliths from the Eifel, West Germany: petrological and geochemical aspects

as measure of Al in orthopyroxene, if the mole fraction of (Mg,Fe)Cr2O4 [YSpCr] in spinel is allowed for. Fitting (XAl)opx and (XCr)opx or ln KD to temperatures derived from the new thermometer of Brey and Koehler (1990) based on (XCa)opx leads to the following equations:

Highly siderophile elements (PGE, Re and Au) in mantle xenoliths from the West Eifel volcanic field (Germany)

\begin{gathered} T{\text{(}}^\circ {\text{C)}} = 2248.25 + 991.58*1n{\text{ K}}_{\text{D}} + 153.32*(1n{\text{ K}}_{\text{D}} )^2 + 539.05*y_{Cr}^{Sp} \hfill \\ {\text{ }} - 2005.74*(y_{Cr}^{Sp} )^2 \hfill \\ T{\text{(}}^\circ {\text{C)}} = 636.54 + 2088.21*x_{{\text{Al}}}^{{\text{M1}}} + 14527.32*x_{{\text{Cr}}}^{{\text{M1}}} \hfill \\ \end{gathered}

A new sampling technique for fluid phases in hydrothermal experiments applied to the determination of the HF-fugacities of the WFQ-buffer

The last of these is more suitable for practical use but is applicable only over a limited range of (XAl)M1 and (XCr)M1 in orthopyroxene. The lack of steady-state equilibrium conditions due to young thermal perturbations or fast cooling may lead to discrepancies of temperatures calculated from (XCa)opx and (XAl)opx. Spinel peridotite xenoliths from Central Asia are shown to demonstrate this.

Partial fusion of basic granulites at 5 to 15 kbar: implications for the origin of TTG magmas

AbstractTwo suites of spinel peridotites of the Westeifel/West Germany were found to have equilibrated in a narrow temperature interval each. Temperatures calculated from the CaO-solubility in orthopyroxene using experimental data of Lindsley and Dixon (1976) are 945° C to 980° C for the amphibole bearing Ia-suite and 1,150° C to 1,165° C for the Ib-suite. From the study of phase equilibria in both series it appears that Al-solubility in orthopyroxene is controlled by the composition of the coexisting spinel. Temperatures calculated from Al-solubility in orthopyroxene using an equation of Fujii (1976) derived from the univariant reaction en+sp↔fo+Al-en in the MgO-Al2O3-SiO2 system show a clear dependence on the FeCr2O4 component in the spinel phase, although ideal solution correction allowing for additional components was made. Temperatures obtained for the most chromite rich spinel — orthopyroxene pairs are 1,370° C and 1,240° C, respectively. These temperatures are by 220° C higher than those from Cr-poor pairs and those obtained from Ca solution in orthopyroxene.For practical purposes of geothermometry in spinel peridotites, an empirical equation