Classic Concepts and New Directions: Exploring 125 Years of GSA Discoveries in the Rocky Mountain Region

The Rocky Mountain Region has been the subject of continuous, exhaustive scientific work since the first organized geologic trips to the area began in the 1860s. Despite almost 150 years of scrutiny, the region's magnificent geology continues to challenge, perplex, and astound modern geoscientists. It is a testing ground for geologists and for big geologic ideas. This volume, prepared for the 2013 GSA Annual Meeting in Denver, Colorado, serves both as a progress report on what we have learned over those years of study and a guide to forthcoming scientific questions about the region. The guide's fourteen chapters, which span the region's 1.7-billion-year history, give a retrospective glimpse of early geologic ideas being forged, bring the latest mapping and analytical results from classic locations, and introduce techniques that will form the bedrock of our geologic understanding in the years to come.
From ignimbrite to batholith, northeastern San Juan Mountains, Colorado: Bonanza, Cochetopa Park, and North Pass calderas Available to Purchase
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Published:January 01, 2013
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CiteCitation
Peter W. Lipman, William C. McIntosh, Matthew J. Zimmerer, 2013. "From ignimbrite to batholith, northeastern San Juan Mountains, Colorado: Bonanza, Cochetopa Park, and North Pass calderas", Classic Concepts and New Directions: Exploring 125 Years of GSA Discoveries in the Rocky Mountain Region, Lon D. Abbott, Gregory S. Hancock
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Abstract
The Southern Rocky Mountain volcanic field contains widespread andesite and dacitic lavas erupted from central volcanoes; associated with these are ~26 regional ignimbrites (each 150–5000 km3) emplaced from 37 to 23 Ma, source calderas as much as 75 km across, and subvolcanic plutons. Exposed plutons vary in composition and size from small roof-zone exposures of porphyritic andesite and dacite to batholith-scale granitoids. Calderas and plutons are enclosed by one of the largest-amplitude gravity lows in North America. The gravity low, interpreted as defining the extent of a largely concealed low-density silicic batholith complex, encloses the overall area of ignimbrite calderas, most of which lack individual geophysical expression. Initial ignimbrite eruptions from calderas aligned along the Sawatch Range at 37–34 Ma progressed southwestward, culminating in peak eruptions in the San Juan Mountains at 30–27 Ma. This field guide focuses on diverse features of previously little-studied ignimbrites and caldera sources in the northeastern San Juan region, which record critical temporal and compositional transitions in this distinctive eastern Cordilleran example of Andean-type continental-margin volcanism.
- andesites
- batholiths
- breccia
- calderas
- Cenozoic
- Chaffee County Colorado
- Colorado
- continental margin
- field trips
- granites
- gravity anomalies
- guidebook
- Gunnison County Colorado
- igneous rocks
- ignimbrite
- intrusions
- magma chambers
- magmas
- Neogene
- North America
- Paleogene
- plutonic rocks
- plutons
- pyroclastics
- road log
- Rocky Mountains
- Saguache County Colorado
- San Juan Mountains
- Sawatch Range
- Tertiary
- tuff
- U. S. Rocky Mountains
- United States
- volcanic features
- volcanic rocks
- volcanism
- Cochetopa Park Caldera
- Bonanza Caldera
- North Pass Caldera
- Saguache Creek Tuff