Clinopyroxene geothermometry of spinel-iherzolites
- Univ. of Western Ontario, London
Experiments in the system CaO--MgO--Al/sub 2/O/sub 3/--SiO/sub 2/ showed that the calcium tschermak's molecule (CaAl/sub 2/SiO/sub 6/) content of clinopyroxene in the spinel--lherzolite assemblage (forsterite + clinopyroxene + orthopyroxene + spinel) varies sympathetically with the MgSiO/sub 3/ content with changes in temperatures and pressure. Such variations are predominantly temperature-dependent, although both pyroxene end-members decrease slightly in amount with increases in pressure at constant temperature. Using simple thermodynamic mixing models of the solid solution phases participating in the subsolidus exchange reactions, two temperature estimations can be made of natural spinel--lherzolites from the experimental data of the synthetic system. The first temperature estimation is based on the equilibrium exchange of Mg/sub 2/Si/sub 2/O/sub 6/ between clinopyroxene and orthopyroxene at 12 kbar (equilibrium constant K/sub 1/) and the second temperature estimation is based on the equilibrium exchange of CaAl/sub 2/SiO/sub 6/ between clinopyroxene, olivine, and spinel at 12 kbar (equilibrium constant K/sub 2/). Two temperature estimations were made from each of the analyses of the coexisting minerals of spinel--lherzolites from alpine-type intrusions and nodules in basalt (analyses obtained from the literature). The estimated temperatures for the spinel--lherzolite nodules in basalt range from the water-undersaturated peridotite solidus to the anhydrous solidus, indicating a close genetic relationship with the host basalts or those of the same fractionation suite. The temperatures estimated for most spinel--lherzolite intrusions indicate solidus temperatures followed by a cooling history of partial reequilibration to subsolidus temperatures. These temperatures probably bear little, if any, relationship to those of a normal geothermal gradient.
- OSTI ID:
- 6771600
- Journal Information:
- Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 61:7/8; ISSN AMMIA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
152004* -- Geothermal Data & Theory-- Isotope & Trace Element Studies
550400 -- Genetics
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ALUMINIUM SILICATES
CALCIUM COMPOUNDS
CALCIUM OXIDES
CALCIUM SILICATES
CHALCOGENIDES
COHERENT SCATTERING
COOLING
DIAGRAMS
DIFFRACTION
EQUILIBRIUM
FORECASTING
GEOTHERMOMETRY
IGNEOUS ROCKS
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MAGNESIUM SILICATES
MINERALS
MIXING
OXIDES
OXYGEN COMPOUNDS
PERIDOTITES
PHASE DIAGRAMS
PHASE STUDIES
PRESSURE DEPENDENCE
PRESSURE MEASUREMENT
PYROXENES
ROCKS
SCATTERING
SILICA
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SPINELS
TEMPERATURE DEPENDENCE
TEMPERATURE MEASUREMENT
X-RAY DIFFRACTION