Granite comparison

The Early Cambrian Wichita Granite Group of southwestern Oklahoma is exposed as a dozen shallowly-emplaced sheet plutons that exhibit geochemistry typical of A-type magmas: they are ferroan, largely alkali-calcic, and exhibit within-plate trace element signatures. Prior studies connected these to Iapetan Rifting (i.e. the Southern Oklahoma Aulacogen).Recent work uses multivariate statistics to confirm that the WGG are similar to extension-related granites

Principal component analysis (PCA) is a statistical technique that constructs a matrix of new components from a set of multiple variables. Specifically, PCA can take large swaths of whole-rock geochemistry data and permit comparison on the basis of all chemical parameters. Comparing the values of significant components (generally, those that describe >10% of the variability), one can descriminate similarities or differences. This is not dissimlar from multicomponent assessments like AFM and Pierce Descrimination Diagrams, except it is able to use many more chemical parameters.. Unlike other multivariant comparisons, it should be noted that PCA distribution cannot be directly tied to magmatic evolution or process.

I compared the WGG to a training set of well-defined and recent analyses of granites taken from the GEOROC Compilation Files (2023-12-2JETOA_GRANITE_parts 1&2.csv: DIGIS Team). To construct a significant-but-manageable set, this study used 306 complete analyses of selected Phanerozoic granitoids from 15 “location” designations for the 10 common major-element oxides and 4 trace elements (Rb, Sr, Y, and Zr). Selections represented a range of Fe/Mg ratios and alkalinities across a-variety of tectonic settings: collisional arcs and orogenies, post-collisional and within-plate and extension, as well as a potentially oblique setting (Coastal Maine Magmatic Province). To this, the study added 89 complete analyses of the WGG. All individual primary components were z-scored based on the set average and deviation.

The resulting first 3 principal components covered 43, 22, and 12 % of the variance, and PC4 describes less than 10%. Dominant loadings (eigenvectors) included Fe2O3T, MgO, Al2O3, SiO2, the alkali oxides,P2O5 and Y. The WGG PCA most greatly differ from arc granites, followed by orogenic examples. The Coastal Maine complexes produced a wide, individually distinct scatter that joins with the WGG in all three principal components. WGG showed the strongest affinity with extensional granites from the Younger Ring Complexes, Nigeria, the Poyi Intrusion, Beishan, and post-collisional members of the Tasmanian Lachlan Fold Belt and the Hainan Island Granites in China.