Abstract
Introduction
Present investigation
Geologic setting
Prevolcanic rocks
Early intermediate-composition rocks (Conejos Formation)
Vent facies
Volcaniclastic facies
Upper lava unit
Ash-flow sheets
Tuff of Rock Creek
Treasure Mountain Tuff
Lower tuff
La Jara Canyon Member
Middle tuff
Ojito Creek Member
Ra Jadero Member
Upper tuff
Younger ash-flow sheets and interlayered lavas
Masonic Park Tuff
Fish Canyon Tuff
Carpenter Ridge Tuff
Wason Park Tuff
Snowshoe Mountain Tuff
Interlayered lava flows
Sheep Mountain Andesite
Huerto Andesite
Volcanics of Table Mountain
Lavas and related rocks of the Platoro caldera complex
Rhyodacite of Fisher Gulch
Summitville Andesite
Andesite of Summit Peak
Volcanics of Green Ridge
Rhyolite unit
Andesite-rhyodacite unit
Porphyritifc rhyodacite unit
Rhyodacite of Park Creek
Quartz latite of South Mountain
Rhyolite of Cropsy Mountain
Volcaniclastic rocks (Los Pinos Formation)
Intrusive rocks
Granitic intrusions
Alamosa River stock
Cat Creek stock
Jasper stock
Bear Creek stock cluster
Other stocks
Porphyro-aphanitic intrusions
Andesitic rocks
Rhyodacitic rocks
Quartz latitic and rhyolitic rocks
Late basalt and rhyolite (Hinsdale Formation)
Basaltic lavas
Rhyolitic lavas and tuffs
Mixed lavas
Surficial deposits
Structural evolution
Pre-Tertiary structures
Tertiary volcanic structures
San Juan caldera cluster
Platoro caldera
Premonitory volcanism
Ash-flow eruptions and caldera collapse
Resurgent uplift
Postresurgence volcanism
Summitville caldera
Arcuate faulting
Topographic wall
Postcollapse volcanism
Caldera-related regional faulting
Rio Grande fault zone
Pass Creek-Elwood Creek-Platoro fault system
Late Cenozoic extensional faulting
Alteration and mineralization
Summitville district
Stunner and Gilmore districts
Platoro district
Jasper area
Crater Creek area
Cat Creek area
Economic significance
Petrologic evolution
References cited
Index.