9: Regional Al2SiO5 triple-point metamorphic rocks of northern New Mexico: A field trip to honor the career contributions of Lincoln Hollister to petrology and tectonics
Christopher G. Daniel, Christopher L. Andronicos, Ruth F. Aronoff, 2016. "Regional Al2SiO5 triple-point metamorphic rocks of northern New Mexico: A field trip to honor the career contributions of Lincoln Hollister to petrology and tectonics", Unfolding the Geology of the West, Stephen M. Keller, Matthew L. Morgan
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Proterozoic Al2SiO5 “triple-point” metamorphic rocks of north-central New Mexico are examined to honor the career contributions of Lincoln Hollister to petrology and tectonics, and to promote discussion of outstanding problems in metamorphic petrology. Hollister’s career began with studies of compositional zoning in garnet and staurolite, and interpreting the occurrence of coexisting Al2SiO5 polymorphs in British Columbia. These studies emphasized the kinetic and bulk composition controls of metamorphism. Hollister’s interest in the Al2SiO5 polymorphs led to his graduate student, Professor Jeff Grambling’s pioneering work that proposed the equilibrium occurrence of coexisting kyanite, sillimanite, and andalusite in the Truchas Peaks, New Mexico. Subsequently, polymetamorphism and the disequilibrium coexistence of kyanite, sillimanite, and andalusite have been proposed as alternate explanations for the occurrence of the polymorphs across the region.
Field stops in the Picuris Mountains and Tusas Mountains will visit classic metamorphic rock localities, which are the subject of debate regarding the equilibrium/disequilibrium nature of the regional “triple-point” metamorphism. The trip will examine Al2SiO5-bearing mineral assemblages to demonstrate the regional distribution of the polymorphs. Stops in the Picuris Mountains will examine andalusite ± cordierite, andalusite ± chloritoid, and kyanite + sillimanite + andalusite–bearing rocks. Field stops in the Tusas Mountains will show kyanite and sillimanite ± garnet–bearing assemblages. Garnet + biotite ± staurolite–bearing rocks are common in both areas and will be examined. Results of garnet, monazite, and zircon geochronology and their bearing on the P-T-t-D paths for the region and the timing of orogenesis will be discussed.
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Prepared in conjunction with the 2016 GSA Annual Meeting in Denver, Colorado, this volume contains sixteen guides to field trips in this rich geologic region. The four “Great Surveys” of the late 1800s ventured west to explore and document the region’s unknown natural resources and collect valuable geologic information. Many of the field guides in this volume, aptly titled Unfolding the Geology of the West, will cover the same hallowed ground as the early geologic expeditions. Organized into four sections, this volume spans some of the major subdisciplines of geology: (1) stratigraphy, sedimentology, and paleontology; (2) structure and metamorphism; (3) Quaternary landscape evolution; and (4) engineering and environmental geology.