Cosmogenic dating techniques have been successfully applied to dating of geomorphically-young surfaces, such as glacial moraines, beach terraces, and basaltic lava flows that have intact surface features, and hence have undergone little erosion (e.g. Phillips et al., 1997a and b; Phillips et al, in review, Dunbar and Phillips, 1996; Zreda et al., 1991, 1993; Zreda, 1994; Anthony and Poths, 1992, Laughlin et al., 1994). These techniques rely on measurement of cosmogenic nuclides that begin to build up as soon as a rock is exposed to cosmic rays. Therefore, cosmogenic techniques can be applied to dating of any surface that is composed of material that was not exposed to cosmic rays prior to formation of the surface, and has been exposed more-or-less continuously since. In the case of an extrusive volcanic rock, buildup of cosmogenic nuclides begins when the rock is erupted, so measurement of the ratio of a cosmogenic isotope to a non-cosmogenic isotope can provide an estimate of eruption age (Phillips et al., 1986).
New Mexico is home to many hundreds of volcanoes that erupted during the last several million years. However, the exact timing of these eruptions has proven difficult to determine by many previous studies. An ongoing NSF-funded project, led by NM Bureau of Geology researcher Matthew Zimmerer, examines the timing of eruptions during the last 500,000 years in order to understand the patterns of volcanism in space and time. This information provides the foundation for an assessment of volcanic hazards in New Mexico.
Volcanic ash and associated aerosol layers in glacier ice offer a uniquely complete record of explosive volcanism. Investigation of these layers, both in bare ice areas of and in ice cores offers insight into eruptive processes, local and regional ice flow processes, and the impact of eruptions on global systems (climate and ozone depletion). The Antarctic ice sheet is an ideal place to preserve a record of volcanic eruptions. The combination of chemical fingerprinting of glass shards, and chemical analysis of volcanic aerosols associated with tephra layers in Antarctic blue ice allows establishment of a high-resolution chronology of local and distant volcanism that can help understand patterns of significant explosive volcanism, atmospheric loading, and climatic effects associated with volcanic eruptions.
Currently seeking a graduate student to work on minor mid-Cenozoic igneous occurrences in eastern New Mexico, which form a patchy discontinuous belt representing the most distal periphery of Cordilleran magmatism emplaced approximately 50-200 km east of the closest major alkaline magmatic centers. They have received little attention and present excellent opportunities for exciting fieldwork, novel research, and impactful student mentorship. Initial reconnaissance of these igneous rocks is building towards holistic studies addressing basic aspects of these occurrences through mapping, petrography, geochemistry, and geochronology. This work will lead to bigger questions on the relationship between these peripheral intrusions and more major alkaline magmatic centers, exhumation and heat flow histories recorded in these rocks, and significance for tectonics of paleo-plate dynamics of the SW US Cordilleran margin!
Masters of Science student, Karissa Vermillion, from New Mexico State University received an award for her proposal and will be mentored by Dr. Jake Ross.
The New Mexico Geochronology Research Laboratory (NMGRL) is a participant in the “Awards for Geochronology Student Research” program (AGeS2 ). AGeS2 grants are funded by the National Science Foundation Earthscope program, in conjunction with the Geological Society of America, and are designed to link students with geochronology laboratories to facilitate in depth student understanding of geochronology methods with hands on experience ultimately leading to publication of new data.
The Jemez Mountains volcanic field, in northwestern New Mexico, has been active for at least the past 16.5 million years, and has produced a large number of explosive and effusive volcanic eruptions during that time. Volcanic ash from the Jemez Mountains volcanic field provides a temporal record of the young eruptions from the caldera and many such deposits have been recognized in a number locations in New Mexico. The ash is present as thick deposits near the eruptive source, and as thinner deposits interbedded in ancestral Rio Grande river sediments at greater distances from the vent.
Directly dating the timing of deformation remains a challenging task. An ongoing collaboration seeks to establish U-Pb dating of titanite grains involved in ductile deformation as a promising new deformation chronometer by applying this technique to Laramide-age shear zones in Joshua Tree National Park.
Pre-Cordilleran rocks of western North America are predominantly composed of inboard, more stratigraphically coherent assemblages and more outboard assemblages with tectonostratigraphic histories obscured by extensive deformation, magmatism, and metamorphism. Inboard assemblages generally represent autochthonous deposits of the western Laurentian continental margin that formed in response to the breakup of the Rodinian supercontinent whereas outboard packages define a tectonic collage representing westward continental growth since mid-Paleozoic time . Detrital zircon U-Pb geochronology of metasedimentary strata across western North America has revealed varied sedimentary sources from both within and without the Laurentian craton that shift through time and space.
Actually, its bacteria and elephants and monkeys and humans, oh my! Geochronology (the determination of a rock's age) has a wide variety of applications; one of which is placing absolute age constraints on evolution. The New Mexico Geochronology Research Laboratory mainly focuses on projects in New Mexico and the Southwestern USA. However, in a role that fulfills its broader commitment to the scientific community, projects are undertaken from throughout the world. Recent collaborations with geologists, archeologists, and biologists have lead to exciting advances in our understanding of
Mammal evolution in South America, including a refinement of when North American and South American critters began walking the present land bridge between the continents,
When humans arrived in Java, Indonesia, and
Confirmation that bacteria have lived in salt crystals found near the WIPP site in New Mexico for more than 200 million years
Publication and/or submission of these findings are being recognized in internationally acclaimed journals such as the Proceedings of the National Academy of Sciences, Nature, Science, and Geology.
