VISCOSITY OF HYDROUS KIMBERLITE AND BASALTIC MELTS AT HIGH PRESSURES
E.S. Persikov1, P.G. Bukhtiyarov1, A.G. Sokol2
1Institute of Experimental Mineralogy, Russian Academy of Sciences, ul. Akademika Osip'yana 4, Chernogolovka, 142432, Moscow Region, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Viscosity, kimberlite, basalt, water, temperature, pressure, melt, model, mantle, Earth’s crust
Abstract
New experimental data on the temperature and pressure dependences of the viscosity of synthetic hydrous kimberlite melts (82 wt.% silicate + 18 wt.% carbonate; degree of depolymerization: 100·NBO/ T = 313 for anhydrous melts and 100·NBO/ T = 247 for melts with 3 wt.% H2O) were obtained at a water pressure of 100 MPa and at lithostatic pressures of 5.5 and 7.5 GPa in the temperature range 1300-1950 °C. The temperature dependence of the viscosity of these melts follows the exponential Arrhenius-Frenkel-Eyring equation in the investigated range of temperatures and pressures. The activation energies of viscous flow for hydrous kimberlite melts were first shown to increase linearly with increasing pressure. Under isothermal conditions ( T = 1800 ºC), the viscosity of hydrous kimberlite melts increases exponentially by about an order of magnitude as the pressure increases from 100 MPa to 7.5 GPa. The new experimental data on the viscosity of hydrous kimberlite melts (error ±30 rel.%) are compared with similar viscosity data for anhydrous kimberlite and basaltic melts (100·NBO/ T = 51.5) and for hydrous basaltic melts (100·NBO/T = 80). It is shown that at comparable temperatures, the viscosity of hydrous kimberlite melts at a moderate pressure (100 MPa) is about an order of magnitude lower than the viscosity of hydrous basaltic melts, whereas at a high pressure (7.5 GPa), it is more than twice higher. It is first established that water dissolution in kimberlite melts does not affect seriously their viscosity (within the measurement error) at both moderate (100 MPa) and high (7.5 GPa) pressures, whereas the viscosity of basaltic melts considerably decreases with water dissolution at moderate pressures (100 MPa) and remains unchanged at high pressures ( P > 3.5 GPa).
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