Date of Award
Master of Science - Geology
Dr. Chris Barker
Dr. Liane Stevens
Dr. LaRell Nielson
Dr. C.J. Aul
Preliminary investigation of the Bullard Peak metamorphic series (BPMS) in the northwestern Wind Mountain quadrangle within the Burro Mountains of southwestern New Mexico suggests a possible previously unidentified shear zone, prompting detailed (1:12,000) geologic mapping and collection of structural data. The study area has a complex tectonic history, including 1) ~1.65 Ga metamorphism during accretion of the Mazatzal terrane to Laurentia’s southern margin; 2) ~1.4 Ga intrusion of Granite and Rhyolite Province granitoids; 3) significant uplift during the formation of the Ancestral Rockies (~300 Ma) and the Rocky Mountains (~70-50 Ma); and 4) inversion tectonics with reactivation of compressional faults as normal and strike-slip faults during extension related to the formation of the Basin and Range and the Rio Grande Rift starting at ~37 Ma.
Evidence for northeast (031o; N31oE) shearing during accretion of the Mazatzal Province is recorded by southwest plunging (211o; S31oW) lineations with top-to-the-northeast shear sense. Average foliation planes in the BPMS are oriented 061o/39o (N61oE, 39oSE). Multiple folding events affected the region, likely starting during the accretion of the Mazatzal Province. Folds formed during this event are expected to be northwest verging. Abundant folding may have occurred during the intrusion of granitoids of the Granite and Rhyolite Province. These folds would have varying
orientations caused by stress regimes formed by intruding batholiths changing orientation based on their geometry. The final folding event was caused by oblique faulting in the region. Associated fault drag folds have axial planar orientations similar to the faults that caused them. The ductile deformation seen in the BPMS is most likely a result of northeast accretion of the Mazatzal Province and intrusion of granitoids of the Granite and Rhyolite Province.
Some of the faults with slickensides in the area are strike-slip (both dextral and sinistral) with a component of oblique-slip (normal or reverse) motion. The mean vector of the mapped faults is 054o/26o (N54oE, 26oSE). The faults have two dominant orientations, northeast-southwest and northwest-southeast, making up 76% of all faults recorded. The complex pattern of faulting in the region produced previously unmapped positive flower structures, two in outcrop and one on a map scale. Two dominant trends, northeast-southwest and northwest-southeast, are expressed in the faulting and help create the complex fault system seen in the Burro Mountains. The northwest-southeast trending faults probably formed during the uplift of the Ancestral Rocky Mountains and have been reactivated during Mesozoic rifting, the Laramide orogeny, and Basin and Range extension. The northeast-southwest trending faults most likely formed as joints during uplift of the Ancestral Rocky Mountains or the Laramide orogeny. This fault system produced the positive flower structures when the faults were reactivated during the Laramide orogeny or Basin and Range extension.
Angelloz, Jensen Kohl, "Structural Analysis of the Northwest Wind Mountain Quadrangle, New Mexico: Proterozoic Shearing to Cenozoic Brittle Faulting in the Burro Mountains" (2017). Electronic Theses and Dissertations. 134.
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