The use of correspondence analysis and principal component analysis as a tool for deducing metamorphic mineral crystallization in Mn-rich lithologies

Principal component analysis (PCA) and correspondence analysis (CA) have been used to identify several critical mineral crystallization factors during metamorphism of Mn-rich lithologies from the Iberian Massif, Spain. Three types of variables have been considered in the system: mineralogical variables, bulk composition variables and one physical variable (oxygen fugacity). PCA was applied to the compositional variables to obtain four components, which were used as new compositional variables. These, together with the mineralogical and physical variables, were treated in the CA. The plot of the variables on the factor 1-factor 2 plane reveals that tephroite crystallization is controlled by a compositional variable representing low values of ratio Si/(Mn+Fe) in the rocks. Moreover, it is possible to deduce from this plot the importance of high oxygen fugacity conditions for the crystallization of piemontite. The third factor shows that the crystallization of spessartine does not require very restrictive physical-chemical conditions.