Total Alkali Silica map of the Squillace pluton (central Calabria, Italy): a new automated mapping procedure via kriging interpolation technique

The geological maps of crystalline basement complexes are usually based on field mapping techniques coupled withpetrographical investigations of representative samples. Nevertheless, the coarse and often uneven grain size ofgranitoid rocks commonly require expensive and time-consuming analyses of a large number of thin sections for agiven sample, in order to obtain reliable rock classifications necessary to map different lithological units. Geochemicalclassifications of granitoid rocks, supported by field and petrographic observations, are increasingly being used becausethey represent the average compositions of much greater rock volumes and because they are comparatively faster andless expensive.In this work we present the automated production of a geochemical-based lithological map, obtained through theapplication of Total Alkali Silica (TAS) parameters (Middlemost, 1994), thanks to the implementation of a newalgorithm for ESRI ArcGIS® 10.1.This new algorithm is largely based on the use of kriging interpolation technique (Oliver et al., 1990), aimed tominimize the relative weight of an uneven data distribution in areas with complex boundary surfaces of interpolation.Obtained results allowed a detailed TAS-based lithological map of the investigated plutonic body to be obtained (i.e.Squillace pluton), significantly comparable with a previous traditional field-based map (Caggianelli, 1989).The adopted methodology permitted to also obtain a set of distribution maps of chemical elements and of otherspecific parameters of petrological interest, able to easily visualize trends useful to better understand the processes ofgenesis, emplacement, interaction and evolution of plutonic bodies, even where contacts are masked by sedimentary orsoil covers, with a degree of reliability numerically quantifiable.