| Aluminosilicate mineral assemblages, with more than 30% Al;Bulk rock and mineral compositions vary regularly from quartzofeldspathic gneiss of the Tumco Formation into the Kyanite Zone. Bulk rock Al;Mineral paragenesis, the fracture and vein occurrence of the minerals, and mineral equilibria in the zones of alumino-silicate mineral assemblages indicate development via early pervasive replacement by oxidizing, low to moderate pH fluids which removed most major cations from the Kyanite and Muscovite Zones. Cross-cutting S-C fabrics containing alumino-silicate mineral assemblages suggest pervasive replacement evolved to later shear zone-hosted replacement. Mineral equilibria indicate pressures and temperatures of aluminosilicate formation at about 5 Kb and 550;The host rocks are find grained quartzofeldspathic gneiss of the Tumco Formation, and Jurassic intrusive rocks. The latter are 173 Ma quartz diorite, a 173-160 Ma metaluminous to peraluminous suite of hornblende-biotite granodiorite, granite porphyry, and muscovite-biotite granite, and post-160 Ma pegmatite and aplite. Emplacement of the 173-160 Ma series coincided with deformation along low angle shear zones, and was accompanied by late magmatic albitization and muscovitization. Cross cutting relationships indicate development of the aluminosilicate assemblages occurred during the emplacement of the 173-160 Ma intrusive suite. |
