Plutonic rocks classification: a child's play

Gaetano Ortolano (1), Alberto D'Agostino (1), Roberto Visalli (1) & Rosolino Cirrincione (1)
(1) Università di Catania - Dpt. Sc. Biol. Geol. Amb. - Corso Italia 57 - 95129 - Catania (Italy). Corresponding author e-mail: rvisalli@unict.it


DOI: https://doi.org/10.3301/ROL.2019.51         Pages: 46-54

Abstract

The Quartz Alkali-feldspar Plagioclase Feldspathoid diagram, better known as the Streckeisen diagram, is the reference tool used for the classification of plutonic rocks cropping out on Earth's surface. To facilitate the methodical calculations and analysis procedures for a correct plutonic lithotype nomenclature, a new computer tool (Auto-QAPF Plutonic) is here provided. This tool follows the official guidelines provided by the IUGS and reaches the specific rock name using mineral modal amounts together with chemical data if available, adding some other information such as the colour index prefixes (leuco- and mela-) or the special rock nomenclatures (e.g., trondhjemite), when useful. Finally, we focussed our attention to enriching the rock-type nomenclature with the specific textural features of the sample, using a stepwise controlled procedure consisting in the application of ArcGIS-based toolboxes able to extrapolate automatically the grain boundary of the rock constituents. This is in order to get more advanced information together with the rock nomenclature, such as the mineral grain size distribution as well as the occurrence of a potential fabric anisotropy (e.g., S-L fabrics). informatic implementation of plutonic rock classification, accompanied by the automatic extrapolation of fabric parameters opens up the possibilities to the Earth science teachers of the high schoolto face a complex aspect of the geosciences, as the rock nomenclature in a speedy and easy way facilitating the process of acquiring learners

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