Pressure/temperature estimates based on different combinations of calibrated mineralogical thermometers and barometers and alternative assumptions concerning the Fe2+/(Fe2++Fe3+) ratios in the mineral phases are compared for a suite of fourteen nodules. Preferred P/T values have been obtained by simultaneous solution of eq. (12) of Wood (1974) for garnet-orthopyroxene equilibria and the Ellis and Green (1979) equation defining the P,T,X dependence of the Fe2+-Mg2+ partition coefficient for coexisting garnet and clinopyroxene. However, to obtain realistic results it is first necessary to calculate the Fe3+ contents in the minerals-conveniently done on a charge balance basis. The favoured mean P/T estimates of 654±36°C and 10.8±3.1 kbs are compatible with a lower crustal origin for this nodule suite.
|Number of pages||16|
|Journal||TMPM Tschermaks Mineralogische und Petrographische Mitteilungen|
|Publication status||Published - Sep 1981|