Date of Award
1993
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Aluminosilicate mineral assemblages, with more than 30% Al{dollar}\sb2{dollar}O{dollar}\sb3{dollar} and less than 2% CaO+Na{dollar}\sb2{dollar}O+K{dollar}\sb2{dollar}O, occur on the western flank of the Cargo Muchacho Mountains, southeastern California. The aluminosilicate mineral assemblages are shallow-dipping tabular zones locally more than 100 m in total thickness. From bottom to top, they are: (a) the Feldspar Zone, with quartz-oligoclase-K-feldspar-biotite-epidote-magnetite, (b) the Muscovite Zone, with quartz-muscovite-biotite-magnetite-tourmaline-apatite, and (c) the Kyanite Zone, with quartz-kyanite-muscovite-magnetite-rutile-tourmaline-apatite (with or without andalusite, pyrophyllite, staurolite, lazulite, and specularite) occur in the Kyanite Zone.;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.;Bulk rock and mineral compositions vary regularly from quartzofeldspathic gneiss of the Tumco Formation into the Kyanite Zone. Bulk rock Al{dollar}\sb2{dollar}O{dollar}\sb3{dollar}, TiO{dollar}\sb2{dollar}, P{dollar}\sb2{dollar}O{dollar}\sb5{dollar}, Ga and V increase from the gneiss across the Feldspar and Muscovite Zones, into the Kyanite Zone, whereas the transition metal oxides and alkali and alkaline earth oxides decrease in this same direction. Feldspar and mica become more aluminous, suggesting bulk rock control on mineral composition. The paragonite content of muscovite increases, and Fe/(Fe+Mg) of biotite decreases into the Kyanite Zone. Tourmaline is schorldravite, with a low uvite component, and with increasing Fe from core to rim. The compositions of biotite and tourmaline, in conjunction with the transition from biotite-bearing assemblages to magnetite-bearing assemblages are consistent with progressive oxidation from the feldspar-bearing assemblages into the kyanite-bearing assemblages.;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{dollar}\sp\circ{dollar}C, and suggest the source for the fluids was likely the 173-160 Ma metaluminous-peraluminous intrusive suite.
Recommended Citation
Owens, Eric Olinder, "Magmatism, Deformation And Mesothermal Metasomatism: Interpretation Of Aluminosilicate Mineral Assemblages In The Cargo Muchacho Mountains, Southeastern California" (1993). Digitized Theses. 2199.
https://ir.lib.uwo.ca/digitizedtheses/2199