REARRANGEMENT OF STRESSED MINERALS OF QUARTZ MONZONITE PLUTONS TO TRICLINIC-SHAPED ORTHOCLASE PORPHYROBLASTS

Quartz monzonites (QM) contrast with other granitic rocks in hosting porphyroblasts of orthoclase and quartz of Papoose Flat (PF) types. At PF, strong evidences document role of mild stress in kinetics of post-emplacement rearrangement of minerals in pluton and country rocks (Dickson, 1995, 2005). Timing at PF was from megacrystals in border facies of granitic and meta-sedimentary rocks thinned and foliated during gravitational sliding shortly after emplacement of pluton. Late-stage stress may account for occurrences in other western U.S. plutons. Whole crystals of monoclinic orthoclase contain hour-glass inclusions, concentric layers, and triclinic outer shapes [faces (001) to (010) differ 3 to 5 deg. from 90 deg.]. Triclinic shaped orthoclase crystals are in the Lincoln porphyry, Colorado (Goldsmith and Laves, 1962). PF-type crystals are crooked to the eye, mostly untwined, simple in habit, and show the same forms and textures. Replacement is by disequilibrium reactions driven by excess energy along temperature-pressure-compositional gradients (TPX) (Dickson, 2000). Mild stress rearranged minerals by a facile process akin to annealing. Reaction cells absorb country rocks by cycling energies of liquefaction in dissolving and precipitating reactions. Cells modify compositions from different mineral solubilities along TPX gradients and exchanges with host rocks; they evolve toward granitic compositions and lower densities. Stress by buoyant low density QM bodies just after emplacement would permeate plutons and host rocks, causing fluid coated minerals to rearrange to crooked crystals with PF textures.