Max W. Schmidt

Amphibole composition in tonalite as a function of pressure: an experimental calibration of the Al-in-hornblende barometer

AbstractThe Al-in-hornblende barometer, which correlates Altot content of magmatic hornblende linearly with crystallization pressure of intrusion (Hammarstrom and Zen 1986), has been calibrated experimentally under water-saturated conditions at pressures of 2.5–13 kbar and temperatures of 700–655°C. Equilibration of the assemblage hornlende-biotite-plagioclase-orthoclasequartz-sphene-Fe-Ti-oxide-melt-vapor from a natural tonalite 15–20° above its wet solidus results in hornblende compositions which can be fit by the equation: P(±0.6 kbar) = −3.01 + 4.76 Alhbltotr2=0.99, where Altot is the total Al content of hornblende in atoms per formula unit (apfu). Altot increase with pressure can be ascribed mainly to a tschermak-exchange (

H2O transport and release in subduction zones: Experimental constraints on basaltic and andesitic systems

t\vec k,{\text{ Mg}}_{{\text{ - 1 }}} {\text{Al}}^{{\text{VI}}} {\text{Si}}_{{\text{ - 1}}} {\text{ Al}}^{{\text{IV}}}

Experimental Constraints on Recycling of Potassium from Subducted Oceanic Crust

) accompanied by minor plagioclase-substitution (

Epidote in calcalkaline magmas; an experimental study of stability, phase relationships, and the role of epidote in magmatic evolution

\vec pl,{\text{ Ca}}_{{\text{ - 1 }}} {\text{Na}}^{{\text{M(4)}}} {\text{ Al}}_{{\text{ - 1}}}^{{\text{IV}}} {\text{ Si}}

Element partitioning: the role of melt structure and composition.

). This experimental calibration agrees well with empirical field calibrations, wherein pressures are estimated by contact-aureole barometry, confirming that contact-aureole pressures and pressures calculated by the Al-in-hornblende barometer are essentially identical. This calibration is also consistent with the previous experimental calibration by Johnson and Rutherford (1989b) which was accomplished at higher temperatures, stabilizing the required buffer assemblage by use of mixed H2O-CO2 fluids. The latter calibration yields higher Altot content in hornblendes at corresponding pressures, this can be ascribed to increased edenite-exchange (