Melting phase relations were studied for a hawaiitic composition with 2.4 +/- 0.1 wt % water under a pressure of 600 bar and oxygen fugacity near the Ni-NiO buffer. These conditions correspond to the degassing and eruption of Etna Volcano, Sicily. The experimental liquidus temperatures of olivine (1120degreesC) and clinopyroxene (1105degreesC) are in agreement with the values calculated by the MELTS software package. The growth rates of olivine and clinopyroxene were estimated by the quench method using forsterite and diopside seeds. At an undercooling of DeltaT= 25 +/- 5 K, lathlike clinopyroxene grew at a rate of (2.0-2.5) x 10(-5) cm/s and contained 6.5-8.5 wt % Al-O-2(3). Under similar conditions, diopside seeds are evenly overgrown at an order of magnitude lower rate, (2-3) x 10(-6) cm/s. At DeltaT approximate to 5 K (T = 1100degreesC), diopside seeds are evenly overgrown with the formation of growth steps on the surface of crystals. The growth rate of olivine is low, 7 x 10(-7) cm/s at 1075degreesC (DeltaT = 45 +/- 5 K). This is consistent with the small amount of olivine forming during cooling of hydrous hawaiite melt calculated by the MELTS program.
Kinetics of clinopyroxene growth from a hydrous hawaiite melt
ARMIENTI, PIETRO
2003-01-01
Abstract
Melting phase relations were studied for a hawaiitic composition with 2.4 +/- 0.1 wt % water under a pressure of 600 bar and oxygen fugacity near the Ni-NiO buffer. These conditions correspond to the degassing and eruption of Etna Volcano, Sicily. The experimental liquidus temperatures of olivine (1120degreesC) and clinopyroxene (1105degreesC) are in agreement with the values calculated by the MELTS software package. The growth rates of olivine and clinopyroxene were estimated by the quench method using forsterite and diopside seeds. At an undercooling of DeltaT= 25 +/- 5 K, lathlike clinopyroxene grew at a rate of (2.0-2.5) x 10(-5) cm/s and contained 6.5-8.5 wt % Al-O-2(3). Under similar conditions, diopside seeds are evenly overgrown at an order of magnitude lower rate, (2-3) x 10(-6) cm/s. At DeltaT approximate to 5 K (T = 1100degreesC), diopside seeds are evenly overgrown with the formation of growth steps on the surface of crystals. The growth rate of olivine is low, 7 x 10(-7) cm/s at 1075degreesC (DeltaT = 45 +/- 5 K). This is consistent with the small amount of olivine forming during cooling of hydrous hawaiite melt calculated by the MELTS program.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
