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Crystal chemistry and significance of cation ordering in Mg-Al rich spinels from high-grade hornfels (Predazzo-Monzoni, NE Italy)

Published online by Cambridge University Press:  05 July 2018

F. Princivalle
Affiliation:
Dipartimento di Scienze della Terra, Università di Trieste, Via E. Weiss 8, I-34127 Trieste, Italy
A. Della Giusta
Affiliation:
Dipartimento di Mineralogia e Petrologia, Università di Padova, C.so Garibaldi 37, I-35100 Padova, Italy
A De Min
Affiliation:
Dipartimento di Scienze della Terra, Università di Trieste, Via E. Weiss 8, I-34127 Trieste, Italy
E. M. Piccirillo
Affiliation:
Dipartimento di Scienze della Terra, Università di Trieste, Via E. Weiss 8, I-34127 Trieste, Italy

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. 400°C and indicates that the closure temperature of FAS1 and FAS2 is c. 500°C i.e. 150–200°C lower than the spinel crystallisation temperature.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999 

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