Publication Date:
2016-11-18
Description:
A new multidimensional classification scheme consistent with the chemical classification of the International Union of Geological Sciences (IUGS) is proposed for the nomenclature of High-Mg altered rocks. Our procedure is based on an extensive database of major element (SiO 2 , TiO 2 , Al 2 O 3 , Fe 2 O 3 t , MnO, MgO, CaO, Na 2 O, K 2 O, and P 2 O 5 ) compositions of a total of 33868 (920 High-Mg and 32948 “Common”) relatively fresh igneous rock samples. The database consisting of these multinormally distributed samples in terms of their isometric log-ratios was used to propose a set of 11 discriminant functions and 6 diagrams to facilitate High-Mg rock classification. The multinormality required by linear discriminant and canonical analysis was ascertained by a new computer program DOMuDaF. One multidimensional function can distinguish the High-Mg and Common igneous rocks with high percent success values of about 86.4% and 98.9%, respectively. Similarly, from 10 discriminant functions the High-Mg rocks can also be classified as one of the four rock types (komatiite, meimechite, picrite, and boninite), with high success values of about 88% to 100%. Satisfactory functioning of this new classification scheme was confirmed by seven independent tests. Five further case studies involving application to highly altered rocks illustrate the usefulness of our proposal. A computer program HMgClaMSys was written to efficiently apply the proposed classification scheme, which will be available for online processing of High-Mg igneous rock compositional data. Monte Carlo simulation modelling and mass-balance computations confirmed the robustness of our classification with respect to analytical errors and post-emplacement compositional changes. This article is protected by copyright. All rights reserved.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
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Geosciences
,
Physics
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