Experimental Investigation of the Depth of Origin of the Alpe Arami Peridotite Massif, Switzerland

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9628342 Green Preliminary observations and analyses have been made on the fresh garnet lherzolite of the Alpe Arami peridotite massif in southern Switzerland. The new data suggest a history involving much higher pressure than the 4-5 GPa calculated from pyroxene thermobarometry. The older generation of olivine has large numbers of oriented oxide inclusions that are almost certainly products of exsolution. The difficulty is that the implied solubility of trivalent and tetravalent cations is very much greater than previously reported for olivine from any environment. Preliminary experiments at 6 and 14 GPa, 1700(K, confirm that the solubility of TiO2 in olivine increases greatly with pressure, and that it is significantly higher still in the high pressure polymorph of olivine. This project consists of a series of experiments at very high temperature and pressure to delineate under what conditions, if any, olivine can dissolve the observed amounts of Ti, Al and Cr, and under what conditions the observed structures, morphologies and topotaxies can be precipitated from solid solution. Three specific testable hypotheses will be examined. (1) The FeTiO3 rods originated by exsolution. (2) Their abundance probably represents more TiO2 than can dissolve in olivine under any circumstances, hence they may reflect some pre-existing phase. (3) If exsolution takes place in the ilmenite stability field, ilmenite would have precipitated directly as platelets and the (presumable) metastable oxide rods would not have formed at all.