Mathematics – Logic
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008e%26psl.267..571c&link_type=abstract
Earth and Planetary Science Letters, Volume 267, Issue 3-4, p. 571-583.
Mathematics
Logic
16
Scientific paper
The rheological behaviour of synthetic crystal-bearing magmas containing up to 76 vol.% of crystals (0 ≤ ϕS ≤ 0.76) has been investigated experimentally at a confining pressure of 300 MPa and temperatures between 475 and 1000 °C at shear rates between 10- 4 and 2 × 10- 3s- 1. Starting hydrated crystal-bearing glasses were synthesized from a dry haplogranitic glass (Qz36Ab39Or29) and 2.5 wt.% water mixed with 0 (pure hydrous melt), 16, 34, 54, 65 or 76 vol.% of Al2O3 sieved (45 < Ø < 90 µm) crystals. Shear viscosity measurements were performed in torsion (simple shear) in a Paterson gas-medium apparatus. For pure hydrated melt and for 16 vol.% of crystals, the rheology is found to be Newtonian. At higher crystal contents, the magmas exhibit shear thinning behaviour (pseudoplastic). The Einstein Roscoe equation adequately estimates viscosities of the crystal-bearing magmas at low crystal contents (ϕS ≤ ~ 0.25), but progressively deviates from the measured viscosities with increasing crystal content as the rheological behaviour becomes non-Newtonian. On the basis of a power law formulation, we propose the following expression to calculate the viscosity as a function of temperature, crystal content and applied stress (or shear rate):γ.=A(τ)exp(-QRT), where γ. is shear rate (s- 1), τ is shear stress (MPa), Φ is the crystal volume fraction, T is temperature (K), Φm is the relative maximum packing density, R is the gas constant, Q = 231 kJ mol- 1 is the activation energy of the viscous flow and A0, K, K1 and K2 are empirical parameters.
Arbaret Laurent
Bystricky Misha
Champallier Rémi
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