Basaltic magmas found in intraplate suites appear to follow more than one differentiation trend. Many ocean island suites follow the ocean island tholeiitic trend, with the basalts differentiating from olivine tholeiite through basaltic andesite, andesite, and dacite to sodic rhyolite. Many continental intraplate magmatic regimes, such as those of the Snake River Plain and the plutonic sequences associated with massif anorthosites, follow the potassic silica-saturated alkalic trend, in which basalt differentiates from olivine tholeiite through ferrobasalt (jotunite or ferrodiorite), Fe-rich intermediate rocks (trachybasalt or monzonite), and trachyte (syenite) to potassic rhyolites and granites. Crystallization experiments on an olivine tholeiite from the Snake River Plain show that the basaltic portions of the ocean island tholeiitic trend and the potassic silica-saturated alkalic trend (which leads to strong alkali, P, Ti, and Fe enrichment and silica depletion) can arise from the same ‘dry’ tholeiitic parental magma. These compositional differences are induced by changes in phase equilibria as a function of pressure, with the ocean island tholeiitic series arising from crystal–liquid differentiation at low pressure and the potassic silica-saturated alkalic series arising via differentiation at elevated pressures.

Elastic wave velocities of synthetic polycrystalline Mg₃Al₂(SiO₄)₃ garnet have been successfully measured to 20 GPa and temperatures up to 1700 K by ultrasonic interferometry combined with energy-dispersive synchrotron x-ray diffraction in a Kawai-type multi-anvil apparatus. Compressional (Vp) and shear (Vs) wave velocities as well as the adiabatic bulk (Ks) and shear (G) moduli exhibit monotonic increase with increasing pressure and decrease with increasing temperature, respectively. Two-dimensional (P-T) linear fittings of the present data yield the following parameters: K_S0 = 170.0(2) GPa, əKs/əP = 4.51(2), əKs/əT = −0.0170(1) GPa/K, G₀ = 93.2(1) GPa, əG/əP = 1.51(2), and əG/əT = −0.0107(1) GPa/K, which is in good agreement with the earlier results by Brillouin scattering and/or ultrasonic measurements at relatively low P-T conditions. The observed linear pressure and temperature dependence in both Vp and Vs is in contrast to the non-linear behavior of Vp and Vs for majorite garnet with the pyrolite composition, in particular for Vs.

A new multi-anvil deformation apparatus, based on the widely used 6-8 split-cylinder, geometry, has been developed which is capable of deformation experiments at pressures in excess of 18 GPa at room temperature. In 6-8 (Kawai-type) devices eight cubic anvils are used to compress the sample assembly. In our new apparatus two of the eight cubes which sit along the split-cylinder axis have been replaced by hexagonal cross section anvils. Combining these anvils hexagonal-anvils with secondary differential actuators incorporated into the load frame, for the first time, enables the 6-8 multi-anvil apparatus to be used for controlled strain-rate deformation experiments to high strains. Testing of the design, both with and without synchrotron-X-rays, has demonstrated the Deformation T-Cup (DT-Cup) is capable of deforming 1–2 mm long samples to over 55% strain at high temperatures and pressures. To date the apparatus has been calibrated to, and deformed at, 18.8 GPa and deformation experiments performed in conjunction with synchrotron X-rays at confining pressures up to 10 GPa at 800 °C .