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Phase relations on the join CaTiSi [O.sub.5]-Ca[Si.sub.2][O.sub.5] were determined at 1350 [degrees] C over the pressure range 3.5-12 GPa by a combination of synthesis and reversal experiments in a piston cylinder and a multi-anvil press. Titanite-like phases were recovered from all experiments in this pressure range. At 3.5 GPa the maximum [Si.sup.VI] content of titanite is 3.0 [+ or -] 0.6 mol%, whereas bulk compositions with higher Si content yield a mixture of titanite solid solution plus coesite and walstromite-structured CaSi[O.sub.3]. The maximum SiTM content of the titanite increases with pressure to 21 [+ or -] 2 mol% at 7 GPa and 46 [+ or -] 2 mol% at 7.5 GPa. At pressures of 8.5 to 12 GPa all intermediate compositions yield a single titanite phase. X-ray and TEM analysis show that these have the A2/a symmetry of the titanite aristotype. The variations of the room-pressure unit-cell parameters of the A2/a phases with composition can be described by the equations a [[Angstrom]] = 7.040(9) - 0.492(15) X([Si.sup.VI]); b [[Angstrom]] = 8.713(7) - 0.316(11) X([Si.sup.VI]); c [[Angstrom]] = 6.564(4) - 0.220(7) X([Si.sup.VI]); [Beta] [[degrees]] = 113.721(6) - 0.537(12) [X.sup.2]([Si.sup.VI]); V (cell) [[[Angstrom].sup.3]] = 367.8(9) - 47.5(1.6) X([Si.sup.VI]). For the Ca[Si.sub.2][O.sub.5] composition the recovered material has II symmetry but is known to transform back to A2/a titanite structure at 0.2 GPa at room temperature. Similarly, with increasing pressure the P2/a CaTiSi[O.sub.5] transforms to A2/a symmetry at 3.6 GPa at room temperature. The conclusion is that at 1350 [degrees] C and pressures in excess of 8.5 GPa there is complete solid solution between CaTiSiO5 and CaSi2[O.sub.5] based upon the isovalent exchange of Si for Ti in the octahedral site of the A2/a structure. Rietveld structure analysis of intermediate compositions reveals no evidence for ordering or intermediate phases. Preliminary experiments at pressures between 13.5 GPa and 16 GPa yielded mixtures of titanite solid solution plus perovskite and stishovite. From these data and information on the phase relations for the CaSi[O.sub.3]-CaTi[O.sub.3] join the topology of the phase relations between [approximately]3 and [approximately]13 GPa in the central part of the CaO-Ti[O.sub.2]-Si[O.sub.2] ternary have been deduced.

Phase relations on the join CaTiSi [O.sub.5]-Ca[Si.sub.2][O.sub.5] were determined at 1350 [degrees] C over the pressure range 3.5-12 GPa by a combination of synthesis and reversal experiments in a piston cylinder and a multi-anvil press. Titanite-like phases were recovered from all experiments in this pressure range. At 3.5 GPa the maximum [Si.sup.VI] content of titanite is 3.0 [+ or -] 0.6 mol%, whereas bulk compositions with higher Si content yield a mixture of titanite solid solution plus coesite and walstromite-structured CaSi[O.sub.3]. The maximum SiTM content of the titanite increases with pressure to 21 [+ or -] 2 mol% at 7 GPa and 46 [+ or -] 2 mol% at 7.5 GPa. At pressures of 8.5 to 12 GPa all intermediate compositions yield a single titanite phase. X-ray and TEM analysis show that these have the A2/a symmetry of the titanite aristotype. The variations of the room-pressure unit-cell parameters of the A2/a phases with composition can be described by the equations a [[Angstrom]] = 7.040(9) - 0.492(15) X([Si.sup.VI]); b [[Angstrom]] = 8.713(7) - 0.316(11) X([Si.sup.VI]); c [[Angstrom]] = 6.564(4) - 0.220(7) X([Si.sup.VI]); [Beta] [[degrees]] = 113.721(6) - 0.537(12) [X.sup.2]([Si.sup.VI]); V (cell) [[[Angstrom].sup.3]] = 367.8(9) - 47.5(1.6) X([Si.sup.VI]). For the Ca[Si.sub.2][O.sub.5] composition the recovered material has II symmetry but is known to transform back to A2/a titanite structure at 0.2 GPa at room temperature. Similarly, with increasing pressure the P2/a CaTiSi[O.sub.5] transforms to A2/a symmetry at 3.6 GPa at room temperature. The conclusion is that at 1350 [degrees] C and pressures in excess of 8.5 GPa there is complete solid solution between CaTiSiO5 and CaSi2[O.sub.5] based upon the isovalent exchange of Si for Ti in the octahedral site of the A2/a structure. Rietveld structure analysis of intermediate compositions reveals no evidence for ordering or intermediate phases. Preliminary experiments at pressures between 13.5 GPa and 16 GPa yielded mixtures of titanite solid solution plus perovskite and stishovite. From these data and information on the phase relations for the CaSi[O.sub.3]-CaTi[O.sub.3] join the topology of the phase relations between [approximately]3 and [approximately]13 GPa in the central part of the CaO-Ti[O.sub.2]-Si[O.sub.2] ternary have been deduced.

A combination of scanning calorimetry and dilatometry analysis was used to study silicate expansivity-temperature relationships and to derive a density model for granite and pegmatite petrogenesis based from the characteristics of the haplogranitic melt. The addition of 4.55 wt% fluorine reduces the density of haplogranitic melts at 750 degrees C from 2.295 g/cm3 to 2.261 g/cm3. This, in turn, accelerates the gravity-driven crystal-melt fractionation processes.

Research describing the temperature-dependent thermal expansitivities of glasses and liquids in the ternary albite-anorthite-diopside is presented. Calorimetry, dilatometry, and Pt and Ir double bob Archimedean densitometry were applied to measure the given liquid's properties. Temperature-dependent thermal expansitivities or non-linear temperature dependence of molar volume were observed as glass transition and superliquids temperatures of liquid volumes were approached.

A study was conducted on the influence of B2O3 on the viscosity of haplogranatic liquids. A nonlinear decrease of viscosity was observed in haplogranite liquids with the introduction of B2O3. The liquids were subjected to a temperature interval of 600 to 1,600 degrees Celsius. The temperature dependence of the viscosity of the liquids tested was found to be Arrhenian. The results show that boron must be treated as a fluxing agent in boron-rich and pegmatitic systems.

Rates of cation diffusion (magnesium, iron, and nickel) have been determined in olivine and its high-pressure polymorph, wadsleyite, at 9 to 15 gigapascals and 1100° to 1400 ° C for compositions that are relevant to Earth's mantle. Diffusion in olivine becomes strongly dependent on composition at high pressure. In wadsleyite, diffusion is one to two orders of magnitude faster than in olivine, depending on temperature. Homogenization of mantle heterogeneities (chemical mixing) and mineral transformations involving a magnesium-iron exchange will therefore occur considerably faster in the transition zone than at depths of less than 410 kilometers., The diffusion of atoms in crystalline solids at high temperature is a process that is controlled by the concentration and mobility of point defects. In Earth's interior, solid state creep [...]