An experimental test of some geothermometer and geobaro-meter formulations for upper mantle peridotites with application to the ther-mobarometry of fertile lherzolite and garnet websterite
Taylor, W. R.
published: May 1, 1998
ArtNo. ESP154017202013, Price: 29.00 €
A series of high pressure (P), temperature (T) experiments (P = 1.0 to 3.5 GPa, T = 1050-1260 °C) were undertaken on Na20-, TiOz- and pyroxene-rich peridotite compositions under controlled f02 conditions. Compositions of olivine, pyroxene and garnet have been used to evaluate the suitability of existing geothermometer and geobarometer formulations in estimating the equilibration conditions of fertile peridotite. The quality of the mineral chemical data reported here represents an improvement over that in many earlier experimental studies due to: the absence of Fe-loss problems by use of graphite inner capsules; better approach to equilibrium because of increased run times and the presence of a fluid or melt phase; and control of f02 at low values so that silicate phases contain negligible Fe3 + contents. Of the geothermometers tested, only those of WELLS (1977) [two-pyroxene] and HARLEY (1984) [garnet-orthopyroxene] reproduce experimental temperatures with any accuracy. For the geobarometers, a version of the WOOD (1974) formulation [garnet-orthopyroxene] gave the most satisfactory results. However, somewhat better P estimates were obtained using a modified version of the NICKEL & GREEN (1985) barometer [NG85mod] in which a Ti correction was applied to the activity term for the Mg-tschermaks component: XMgTs = (AI - Cr + Ti + Na)/2.