Two Mg-Al spinels (FAS1 and FAS2) in high-grade hornfels from the Toal de Mason skarn (Predazzo Monzoni, NE Italy) were investigated by means of single crystal X-ray diffraction and electron microprobe analysis in order to evaluate the last intra-crystalline closure temperature. The evidence provided by crystal chemical data from the investigated spinels, compared with that for two other spinels from a websterite dyke and a chlorite schist (TS2 and SP78a, respectively) with similar chemical characteristics, yielded a new empirical geothermometer. This allowed estimation of intra-crystalline temperatures as low as c. 4008C and indicates that the closure temperature of FAS1 and FAS2 is c. 5008C, i.e. 150ÿ2008C lower than the spinel crystallisation temperature.
Crystal chemistry and significance of cation ordering in Mg-Al rich spinels from high-grade hornfels (Predazzo-Monzoni, NE Italy)
PRINCIVALLE, FRANCESCO;DE MIN, ANGELO;PICCIRILLO, ENZO MICHELE
1999-01-01
Abstract
Two Mg-Al spinels (FAS1 and FAS2) in high-grade hornfels from the Toal de Mason skarn (Predazzo Monzoni, NE Italy) were investigated by means of single crystal X-ray diffraction and electron microprobe analysis in order to evaluate the last intra-crystalline closure temperature. The evidence provided by crystal chemical data from the investigated spinels, compared with that for two other spinels from a websterite dyke and a chlorite schist (TS2 and SP78a, respectively) with similar chemical characteristics, yielded a new empirical geothermometer. This allowed estimation of intra-crystalline temperatures as low as c. 4008C and indicates that the closure temperature of FAS1 and FAS2 is c. 5008C, i.e. 150ÿ2008C lower than the spinel crystallisation temperature.Pubblicazioni consigliate
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