A variety of geological studies involving Upper Paleozoic strata, conducted during the mid-twentieth century, produced a preliminary stratigraphic nomenclature for Carboniferous and Permian sedimentary rocks in New Mexico, and a general understanding of the lithostratigraphy, age and distribution of these rock units. Ongoing investigations by geologists from the NMBGMR, universities, museums, and industry are aimed at refining this understanding. For example, strata pertaining to the Pennsylvanian System are often poorly delineated and/or subdivided on geologic maps, due in large part to their lithostratigraphic complexity and a loosely defined stratigraphic nomenclature. Progress has been made during the past 15 years toward improving the stratigraphic nomenclature for Upper Paleozoic strata in New Mexico, and documenting stratigraphic patterns, both of which should provide a better foundation for ongoing and future studies of these rocks.
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.
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.
In 1972, geophysicist Dan McKenzie was among the first to recognize that patterns of fault block motion along the active zone of continental collision in Eurasia are best explained in terms of rigid microplates that act as dies or indenters. Indenters, such as Arabia, bulldoze the less rigid (plastic) crustal domains ahead into folded welts (e.g. Iran) and push some blocks aside (e.g. Turkey). The geometry of deformation around indenters is controlled by the shape of the impinging rigid face and to the boundary conditions of the surrounding plastic rocks at depth. As a working hypothesis, Chamberlin and Anderson (1989) suggested that structural patterns in the Laramide Zuni uplift are much smaller but otherwise quite similar to indentation-extrusion domains observed between India and south China.
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!
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 Rio Grande rift of central New Mexico is dominated by NNW- to NE-striking normal faults of Late Oligocene to Quaternary age. Crustal extension is distributed across many subparallel fault blocks. Fault traces commonly show abrupt changes in strike, often bifurcate, and occasionally step over to adjacent faults along transverse ramps (e.g. Chamberlin et.al, 1994a; Chamberlin and Harrison, 1996). Based on observations of striated fault surfaces most rift faults are apparently dip-slip to slightly oblique-slip normal faults. There is generally little or no evidence of significant strike slip faulting in areas of high-angle normal faulting. However, minor lateral slip may occur where a north or south propagating fault tip is deflected by a preexisting basement shear zone oriented at a high angle to the propagating rift fault (Chamberlin, 2000). Broad zones of lateral shear may be accommodated by a combination of minor vertical axis rotations and distributed oblique-slip normal faulting in which the dip-slip component is dominant.
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 Magdalena radial dike swarm (MRDS) is a large diameter (200- 250 km) radial array of basaltic-andesite dikes of Oligocene age broadly focused on the large volume (7000 km3) Socorro-Magdalena caldera cluster (SMCC) of the central Rio Grande rift. Five large overlapping calderas of the SMCC range in age from 32.5 to 24.7 Ma and show a pattern of migrating to the southwest over a distance of about 80 km during a period of about 8 million years.
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.
