USE OF A GEOCHEMICALLY DIVERSE PCA TRAINING SET TO ASSESS THE TECTONIC SETTING OF THE WICHITA GRANITE GROUP, SOUTHWESTERN OKLAHOMA

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 (Southern Oklahoma Aulacogen).This study uses multivariate statistics to confirm that the WGG are similar to other extension-related granites.

Principal component analysis (PCA) compared the WGG to a training set of well-defined and recent analyses of granites taken from 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 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 Fe₂O_3T, MgO, Al₂O₃, SiO₂, the alkali oxides,P₂O₅ and Y. The WGG PCA most greatly differed from arc granites, followed by orogenic examples. The Coastal Maine complexes produced wide, individually-distinct scatter that partially overlapped with the WGG in all three principal components. WGG showed the strongest PC-space 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 of China.