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.
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 Laramide orogeny was a mountain building event that affected the US western interior during the Late Cretaceous to Paleogene (approximately 90–45 million years ago). Many of the iconic mountains and major oil and gas producing intermontane basins of the Rocky Mountains and Colorado Plateau, such as the Wind River range in Wyoming and the San Juan Basin here in New Mexico, formed during this time as Earth’s crust was compressed. The Laramide orogeny remains a major point of controversy, as it is difficult to explain how tectonism proceeded so far into the North American plate.
Despite recognition as one the most iconic volcanoes on the planet, there is still much to learn about Valles caldera in north-central NM. A new collaboration between researchers at the Bureau and from UT Austin is seeking to understand the events leading up to supereruptions. In particular, the team is studying the Cerro Toledo Formation, a group of volcanic domes and related ashes that erupted between the large caldera forming events at 1.61 and 1.23 million-years-ago.
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.
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.
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.
Two Bureau of Geology scientists, in collaboration with scientists at the United State Geological Survey, have discovered similarities between ground water systems that formed ore deposits 10 million years ago and modern ground water in the Rio Grande Rift. They reported their work in an invited presentation at the 2000 Annual Meeting of the Geological Society of America.
Dr. Virgil Lueth, mineralogist/ economic geologist, and Lisa Peters, senior lab associate at the New Mexico Geochronological Research Lab, have been studying the mineral jarosite in ore deposits from Chihuahua, Mexico, to Albuquerque.
