From the simplest chemical system to the natural one: garnet peridotite barometry

The Orthopyroxene-Garnet Geobarometer for Peridotites

“…The compositions of the orthopyroxenes and garnets from these samples (the raw data for the present calculations of crystallochemical coefficients) are given in the table. Figure 5 shows the results of calculations for three recently developed versions [24,33,45] of the garnet-orthopyroxene geobarometer and for the version proposed in this paper. The temperatures were calculated from the olivine-garnet paragenesis [47].…”

“…The main difficulty in calculating the ideal activity lies in determining the intracrystal equilibrium distribution of cations at high temperatures and its dependence on the com position of the orthopyroxene solid solution. In published versions of the orthopyroxene-garnet geobarometer [1,15,24,33,45], Eqs. (4) are variously replaced by simplified expressions of the ideal activity.…”

“…Gr + Opx + Ol paragenesis from Phanerozoic kimberlites (AB-75 [21], F 5-75 [35], 23 [53]). 1) Pressure calculated from proposed geobarometer (double dash shows maximum permissible error of geobarometer); temperatures calculated from geothermometer of [47]; 2) error in esti mating pressure, depending on equilibrium temperature (pressure calculated from proposed geobarometer for arbitrary temperature values); 3, 4) analogous calculations using geobarometer in [33]; 5, 6) ditto, using geobarometer in [45]; 7) pres sure calculated from geobarometer in [24] for arbitrary temperature values; 8) conductive geotherm for surface heat flow of 40 mW/m 2 [51]; 9) pressure calculated from proposed geobarometer, temperature from [58]. The Gr + Opx + Cpx paragenesis from Proterozoic kimberlite of the Premier pipe (P 7/75) [42].…”

Recent Developments in Igneous Petrology

“…Debate continued on the shape of the geotherm in the Cretaceous mantle of northern Lesotho, with estimates ranging from a lower thermal gradient inflection at high pressure [ Bertrand et al ., 1986], no inflection [ Carswell and Gibb , 1987; Adams and Bishop , 1986], and a higher thermal gradient inflection [ Finnerty and Boyd , 1987; Finnerty , 1989]. The disagreement centers on techniques for estimating pressures of equilibration for garnet lherzolite xenoliths.…”

MK-1 Orthopyroxene—A New Potential Reference Material for In-Situ Microanalysis

“…In addition, crystal zoning patterns always occurred in orthopyroxene (e.g., Cr zoning [8] and Ti zoning [9]), which have been recognized as archives of magmatic processes such as fractional crystallization [10,11], magma replenishment [12,13], magma convection [14], and subsolidus equilibration [15,16]. Furthermore, the calculation of temperature and pressure also require knowledge of the contents of trace elements (e.g., Al, Ti, Cr, Ca, and Na) in orthopyroxene, such as Opx-Cpx thermometer [17] or Grt-Opx barometer [18,19]. Consequently, trace elements in orthopyroxene have become powerful tools in unraveling the mantle nature and magma processes.…”