Earth and Planetary Sciences ETDs

Author

Amy Luther

Publication Date

8-1-2006

Abstract

The Sandia-Manzano-Los Pinos Mountains, on the eastern flank of the Rio Grande Rift, provide spectacular exposures of the Proterozoic Manzano thrust belt. This region is an important place to better characterize polyphase deformation and magmatism related to the assembly of Laurentia, particular the 1.65-1.60 Ga Mazatzal orogeny and the later 1.4 Ga thermo-tectonic event. This study focuses on the Los Pinos Mountains, near the southern end of the Manzano thrust belt, an area that has been only weakly overprinted by a later phase of Mesoproterozoic tectonism and is therefore an ideal place to characterize Paleoproterozoic deformational events. Building on a large amount of prior work to the north, this study allows for a complete cross section to be drawn for the Manzano thrust belt and for the development of a more complete stratigraphic understanding of the Manzano Group. Paleoproterozoic rocks of the northern Los Pinos Mountains contain three tectonic fabrics that have variable intensities, with the north-northeast-striking S2 being the dominant foliation. New mapping of the Los Pinos Mountains resulted in the recognition of a new macroscopic D2 anticline cored by the 1662 +/- 1 Ma (Shastri, 1992) Sevilleta Metarhyolite. Documentation of the overturned nature of much of the stratigraphy corrects the prior interpretation of Myers et al. *(1981). A NEW u-Pb zircon date of 1601 +4/-3 Ma (Jones, 2005) on the upper Blue Springs Rhyolite indicates that the Manzano Group records deposition from 1662-1600 Ma. Additional evidence supports the interpretation of synchronous D2 deformation and plutonism in the aureole of the 1655 +/- 3 Ma Los Pinos pluton (In agreement with Shastri, 1992) indicates that D2 (attributed to the Mazatzal orogeny) was a protracted event lasting from ~1655 Ma to some time after 1600 Ma. Reverse-sense west-side-up shearing on steeply west-dipping S2 was a progressive event which resulted in rotation of F2 folds. This shearing event is interpreted to be broadly synchronous with top-to-the-northwest thrusting elsewhere in the Manzano thrust belt, and hence suggests a bivergent Mazatzal orogeny.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Advisor

Karlstrom, Karl

First Committee Member (Chair)

Smith, Gary

Second Committee Member

Crossey, Laurie

Language

English

Document Type

Thesis

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