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J. Lopez Ruiz

The zoning of garnets as an indicator of the P.T. history of their host-rocks

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Abstract

This paper deals with the different types of zoning shown by metamorphic and igneous garnets. A tentative relationship between zoning and physical conditions of the host-rock during and after crystallization of garnets is inferred.

On the basis of the data presented, it is suggested that rocks whose garnets show normal zoning (i.e. a progressive decrease in Mn-content from core to rim) were subjected to no further thermodynamic activity after the crystallization of this mineral. On the other hand, garnets with Mn-enriched rims and reverse zoning (i.e. a progressive enrichment in Mn from core to rim) indicate an important change in the P and/or T conditions after the initial crystallization of garnets.

It is suggested that garnets with Mn-enriched rims were subjected to the new thermodynamic activity for a relatively short space of time. Reverse zoning suggests activity over a longer period with temperatures high enough to allow significant internal diffusion.

To cite this article

J. Lopez Ruiz, «The zoning of garnets as an indicator of the P.T. history of their host-rocks», Annales de la Société géologique de Belgique [En ligne], Volume 99 (1976), Fascicule 2, 337 - 346 URL : https://popups.ulg.ac.be/0037-9395/index.php?id=5384.

About: J. Lopez Ruiz

Departamento de Petrología y Geoquímica. Instituto « Lucas Mallada » C.S.I.C. Madrid -3- (España).