Earth and Planetary Sciences ETDs

Publication Date

7-14-1971

Abstract

Precambrian rocks in the Florida Mountains have a long and complex history of orogeny and epeirogeny. The oldest recorded event is regional metamorphism (amphibolite facies) of sedimentary and igneous rocks which are intruded by granite. Following a long period of erosion, diamictite was deposited on a deeply weathered surface of igneous and metamorphic rocks.

At least 3,000 feet of Paleozoic strata is preserved above the Precambrian rock1s. The Paleozoic strata are mostly shelf carbonates; the Bliss Formation and the Devonian Percha Shale are the only major Paleozoic elastic units present. From Cambrian through Mississippian time the Florida Mountains area was part of a stable shelf lying south of the trans­continental arch. In Pennsylvanian time the shelf was epeirogenically deformed into a number of basins and uplifts and the Florida Mountains area was a shelf, or at times a low positive area, between the Orogrande Basin on the north­east and the Pedrogosa Basin on the south. Marine shelf conditions also prevailed during Permian Wolfcamp time.

During Mesozoic time, the Florida Mountains area was a southeast extension of the Burro uplift, or of the more extensive Deming axis. Triassic and Jurassic rocks are absent. An unnamed Lower Cretaceous (?) conglomerate overlies Ordovician El Paso limestone, indicating extensive early Mesozoic erosion. A Mesozoic(?) syenitic pluton is intrusive into the Precambrian and Paleozoic rocks and is probably genetically related to this uplift.

Northward-yielding thrust faults and high-angle re­verse faults developed in the Florida Mountains in Late Cretaceous-Early Tertiary (Laramide) time. Horizontal yield­ing on the order of several thousand feet is indicated. The thrust faults generally are subparallel to bedding and show tectonic elimination of strata as well as repetition. The thrust and steep reverse faults cut or deform rocks as young as the Lower Cretaceous conglomerate and syenitic intrusive of probable Mesozoic age. The faults are overlain by the Lobo Formation of Tertiary(?) age and are therefore con­sidered to be of Laramide tectonic origin.

The thrust faults in the Florida Mountains are inter­preted as a southeastern continuation of the Cordilleran foldbelt. These faults mark the northern erosional limit of thrusting associated with Late Cretaceous-Early Tertiary de­formation of the Mexican geosyncline on the south.

With respect to Laramide deformation, the preorogenic rocks in the Florida Mountains and southwest New Mexico range in age from Precambrian to Lower Cretaceous. Analysis of the structures within these rocks allows definition of the contact between the deformed foldbelt and its foreland to the north­east. The foreland is deformed in the Saxonic or Germano-type while Alpino-type deformation characterizes the foldbelt. Yielding along the margin of the foldbelt is northward toward the foreland. Some of the Cretaceous and Tertiary rocks of southwest New Mexico, including the Mojado, Ringbone and Hidalgo Formations may represent synorogenic detritus and volcanics derived from the deformed and uplifted Mexican geosyncline to the south. Postorogenic rocks, include the Tertiary Lobo Formation, Tertiary andesite agglomerate and tuff, Tertiary rhyolitic rocks, the Santa Fe-Gila Formation, and Quaternary alluvium and basalt flows.

Following Laramide thrusting and erosion in the Florida Mountains the elastic Lobo Formation was deposited unconformably on the Precambrian, the Paleozoic, the syenitic intrusive rocks, and the thrust faults. The Lobo Formation is disconformably overlain by Tertiary andesite agglomerate and tuff which are in turn cut by rhyolite dikes.

In Miocene time the present mountains were formed by block faulting along range-marginal faults. The block form­ing the Florida Mountains was uplifted vertically at least 4,000 feet relative to surrounding basins. Quaternary and Tertiary gravel and alluvium, eroded from the uplift, surround the mountains and fill adjacent valleys.

Degree Name

Earth and Planetary Sciences

Level of Degree

Doctoral

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Lee A. Woodward

Second Committee Member

J. Paul Fitzsimmons

Third Committee Member

Sherman Alexander Wengerd

Language

English

Document Type

Dissertation

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