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Mesozoic tectonics of the Maria Fold and Thrust Belt and McCoy Basin
Publications (thesis will soon be available in PDF format)
Mesozoic tectonics of the Maria Fold and Thrust Belt and McCoy Basin: A transect through an ancient orogenic belt and synorogenic basin
For my Ph.D. project, I am studying Mesozoic tectonics of the Jurassic-Cretaceous Maria Fold and Thrust Belt (MFTB) and McCoy Basin in southeastern California. My advisor for this project is Karl Karlstrom. My Ph.D. committee includes Karl E. Karlstrom, Yemane Asmerom, Louis A. Scuderi, Stephen J. Reynolds, and Thomas D. Hoisch. This project will integrate approaches from structural geology, geochronology, and GIS to try to unravel the geologic evolution of this key piece of the Cordilleran puzzle.
My
work in this extremely fascinating geologic locale began in 2004, when I studied
Paleozoic rocks of the Big Maria syncline (Figure 1) for my master's thesis
project. The syncline is named for the Big Maria Mountains in
southeastern California, and is macroscopic (several kilometers long) nappe. The syncline is composed of rocks of Precambrian,
Paleozoic and Mesozoic age (through the Jurassic period) and consists of an
upright, relatively unattenuated lower limb, and an overturned, extremely
attenuated upper limb. My investigation found that Paleozoic rocks in the upper
limb are attenuated from 3-11% of original thickness, individual units are
locally attenuated to less than 1% of original thickness, and that the average
degree of attenuation of the upper limb is to approximately 8% of original
thickness (Figure 2). Paleozoic rocks in the syncline are
stratigraphically correlative to the classic cratonal sequence of the Grand
Canyon and individual units are assigned names from the Grand Canyon.
As part of my Ph.D. research, I have been
conducting investigations to decipher the structural evolution of the syncline
and the highly deformed Big Maria Mountains (BMM). I have done this work in
collaboration with Steve Reynolds at Arizona State University and have been
assisted by undergraduate students Jeff Geier and Bryan MacFarlane. Preliminary
work has demonstrated that three deformation events, D1,
D2, and D3
have been recognized in the BMM. The first
deformation event was a multi-stage progressive deformation event defined by a
foliation (S1)
subparallel to bedding, tight to isoclinal folds, sheath folds, and that formed
the Big Maria syncline and similar structures exposed in the BMM and other
ranges in the MFTB.
S1
overprints all units in the syncline except for Cretaceous leucogranite dikes.
Preliminary structural analysis suggests these structures were formed by
east-southeast-directed (reverse and dextral) compressional shear and is likely
the mid-crustal ductile expression of Sevier Foreland Thrust Belt deformation. D2
thrust Jurassic and Precambrian crystalline rocks over Paleozoic and Mesozoic
cratonal rocks and imbricate attenuated sections. This event is responsible for
large south-to-southwest-directed shear zones. The MFTB is distinguished from
the rest of the Foreland Thrust Belt by highly deformed and metamorphosed
cratonal rocks and these south-directed shear zones. D3 refolded the syncline into upright, tight folds
with NW-trending axes and is defined by a pervasive SW-dipping cleavage (S2),
which overprints the Cretaceous leucogranite dikes. D3
is likely the result of NE-directed folding and thrusting
related to deformation during the Laramide Orogeny.
The Maria Fold and Thrust Belt (MFTB), named for
the Big and Little Maria Mountains of southeastern California, is a roughly
east-west trending tectonic regime characterized by predominately south-facing
folds and thrust faults observed in several ranges throughout west-central
Arizona and southeastern California (Figure 3, from Laubach and others, 1989). The MFTB lies directly north of
and structurally above an east-west trending belt of exposures of
Jurassic-Cretaceous McCoy Mountains Formation (MMF) that define the McCoy Basin.
For my Ph.D. research, I plan to examine a key portion of the MFTB and McCoy Basin in the Palen and McCoy Mountains of SE California. The area I will examine is one of the few places in the region where the transition from the MFTB to the McCoy Basin is clearly exposed. I will perform detailed structural analysis at key locations in the MFTB and McCoy Basin, including the exposed contact between these terranes at Palen Pass, deformed rocks in the BMM, low-grade metamorphosed rocks in the McCoy Mountains, and the southern boundary between the MMF and Precambrian and Jurassic crystalline rocks at the Mule Mountains Thrust. I will examine structural fabrics in the field, collect samples for microstructural analysis, and obtain crystallization ages for key igneous rocks. I will then compare and synthesize my results with other work done in the region to propose a model for the tectonic evolution for this key part of the North American Cordillera.
In July 2005 I did work with Karl Karlstrom on the Ojo Caliente quadrangle for the New Mexico Statemap Project, an initiative of the New Mexico Bureau of Geology & Mineral Resources, a division of New Mexico Tech. For this project, I wrote descriptions for the Precambrian units, helped with the correlation of Quaternary terraces of the Rio Ojo Caliente and created a river profile with older terrace profiles, did a structural analysis of Precambrian granite dikes, and created a cross section of the La Madera syncline and Cerro Colorado antiform.
In June and July 2006 did work with Karl on the La Madera quadrangle to the north. For this project, I wrote unit descriptions of Precambrian units, helped further develop a regional Precambrian stratigraphy, drew a geologic cross section emphasizing the main syncline in the La Madera quadrangle, extended the river profile of the Rio Ojo Caliente to include the Rio Tusas and Rio Vallecitos, extended correlation of Quaternary terraces along the river system, added canyon wall data at the various constrictions of each river to help constrain incision history, and assisted in compilation and final drafting of the geologic map.
Salem, A.C., 2005, Structural geology and stratigraphy of Paleozoic rocks of the
Big Maria syncline, southeastern California, M.S. thesis,
Arizona State University, Tempe, 163 p.
Salem, A.C., and Reynolds, S.J., 2005, Structural evolution of the Big Maria
syncline: a kinematic analysis of ductile deformation and extreme attenuation in
the Maria Fold and Thrust Belt: Geological Society of America Abstracts with
Programs, v. 37, no. 7, p. 211.
Salem, A.C., Reynolds, S.J., Geier, J., and Karlstrom, K.E., 2006, Structural
evolution of the Big Maria syncline, southeastern California, Geological Society
of America Abstracts with Programs, Backbone of the Americas Conference: From
Patagonia to Alaska, Mendoza, Argentina (April 3-7, 2006)
Pending publications
Koning, D., and seven others (8th author), 2005, Geologic map of the Ojo Caliente Quadrangle, Rio Arriba and Taos Counties, New Mexico, 1:24,000, New Mexico Bureau of Geology and Mines, New Mexico Tech, Socorro.