Dr. Matthew Heizler (geochronologist) has just been awarded a three year grant from the NSF tectonics division to study the "Great Unconformity" exposed in western North America. An unconformity is a span of time for which no rock record is represented because it has been eroded away or because sediment was never deposited. The Great Unconformity was coined by John Wesley Powell during his epic run of the Colorado River through the Grand Canyon, AZ in 1876. Here he noticed that deformed ancient metamorphic rocks were covered by much younger undeformed sedimentary rocks. New Mexico has some of the best exposures of the contact between these very old Precambrian rocks (1.7 billion years) and younger sediments (300 million years) of anywhere in North America.
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.
PhD. Student, Drew Levy, from the University of Nevada-Reno received an award for his proposal and will be working with Dr. Matthew Heizler.
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 Tibetan plateau is a product of the most dramatic tectonic event of recent geological history: the collision of the Indian sub-continent with Eurasia. In spite of the topographic and tectonic implications of the plateau, the mechanisms for its uplift remain controversial. The controversy is in large part a result of poorly constrained uplift history. Types of evidence that have been adduced for the uplift history include paleoecological date, cooling histories of plutonic and igneous rocks, and geomorphic interpretations. Some lines of evidence indicate relatively gradual uplift since the mid-Tertiary, while others support rapid acceleration of uplift during the latest Cenozoic, with the greatest portion during the Quaternary.
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.
The depositional age of the Gatuña Formation in the Pecos Valley of southeastern New Mexico is poorly constrained, with estimates that vary from as old ca. 13 Ma at its base to as young as ca. 100 ka at its highest levels. As part of geologic mapping program efforts, we are applying detrital sanidine Ar-Ar geochronology and detrital zircon U-Pb geochronology to more tighlty bound the depositional age and duration of these alluvial deposits and their context within the late Cenozoic paleo-landscape of the ancestral Pecos River.
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.
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.
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.
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).
