Experimental investigation of magma rheology at 300 MPa: From pure hydrous melt to 76 vol.% of crystals

摘要: The rheological behaviour of synthetic crystal-bearing magmas containing up to 75 vol.% crystals (0≤ ΦS ≤ 0.75) has been investigated experimentally at a confining pressure 300 MPa and temperatures between 475 600°C shear rates 10-4 2x10-3 s-1. Starting hydrated glasses were synthesized from dry haplogranitic glass (Qz36Ab39Or29) 2.5 wt.% water mixed with 0 (pure hydrous melt), 16, 34, 54, 65 or Al2O3 sieved (45 < O 90 µm) crystals. Shear viscosity measurements performed in torsion Paterson gas-medium apparatus. For each composition, the data fitted power law form: (1) where is rate, stress , T temperature, R gas constant, A, n Q are empirical parameters defined as preexponential term, exponent activation energy, respectively. rheology found be newtonian (n=1) for pure melt 16 At higher crystal contents, behave pseudoplastic materials, exhibit thinning exponents 1.3, 1.9 2.8 54 crystals, energy seems nearly independent fraction mean value 231 kJ.mol-1. Einstein-Roscoe equation adequately estimates viscosities low contents (ΦS ~≤ 0.25), but progressively deviates measured increasing content becomes non-newtonian. A modified power-law formulation incorporating variable allows fit experimental set over whole range conditions.