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The Caltepec fault zone: Exposed roots of a long-lived tectonic boundary between two continental terranes of southern México

By
Mariano Elías-Herrera
Mariano Elías-Herrera
1
Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Deleg. Coyoacán, México, D.F., 04510, México
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Fernando Ortega-Gutiérrez
Fernando Ortega-Gutiérrez
1
Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Deleg. Coyoacán, México, D.F., 04510, México
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José Luís Sánchez-Zavala
José Luís Sánchez-Zavala
1
Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Deleg. Coyoacán, México, D.F., 04510, México
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Consuelo Macías-Romo
Consuelo Macías-Romo
1
Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Deleg. Coyoacán, México, D.F., 04510, México
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Amabel Ortega-Rivera
Amabel Ortega-Rivera
2
Centro de Geociencias, Universidad Nacional Autónoma de México (UNAM), Campus Juriquilla, Querétaro, Qto., 76230, México
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Alexander Iriondo
Alexander Iriondo
2
Centro de Geociencias, Universidad Nacional Autónoma de México (UNAM), Campus Juriquilla, Querétaro, Qto., 76230, México
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Published:
January 01, 2007

The Caltepec shear zone is a dextral transpressional tectonic boundary between the Oaxacan and Acatlán Complexes, which are crystalline basements of the Zapo-teco and Mixteco terranes in southern México, respectively. The terrane boundary (2–6 km wide) reveals protracted and polyphase tectonic activity from at least Early Permian to the present. The major tectonothermal event in the Caltepec fault zone was related to the oblique collision of the metamorphic complexes during the amalgamation of Pangea. An anatectic leucosome and the resulting syntectonic granite (Cozahuico Granite) in the fault zone yielded U-Pb zircon ages of 275.6 ± 1.0 Ma and 270.4 ± 2.6 Ma, respectively. The initial 87Sr/86Sr ratios (0.70435–0.70686) and Sm-Nd model ages (TDM) (1.0–1.6 Ga) for the Cozahuico Granite and leucosome indicate a magmatic mixture that originated from melted Proterozoic crust and a component of depleted mantle. The Leonardian age of the cover (Matzitzi Formation) and a 40Ar/39Ar cooling age (muscovite) of 268.59 ± 1.27 Ma for mylonitic mica schist at the base of the thrust imply high cooling rates (∼180 °C/Ma) and uplift during the Permian. The adjacent sedimentological record indicates intense tectonic reactivation during Early Cretaceous, Paleogene, and Neogene along the long-lived Caltepec fault zone, alternating with periods of relative tectonic quiescence during Triassic, Jurassic, and Mid-Cretaceous times. The trend of the Caltepec fault zone parallel to the Oaxaca fault, 50 km to the east, is interpreted as part of a synchronous and dynamically coupled tectonic system that has been releasing tectonic stresses associated with the rupture of Pangea and the evolution of the Pacific margin of southern México from Jurassic to Holocene times.

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GSA Special Papers

Geology of Me´xico: Celebrating the Centenary of the Geological Society of Me´xico

Susana A. Alaniz-Álvarez
Susana A. Alaniz-Álvarez
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Ángel F. Nieto-Samaniego
Ángel F. Nieto-Samaniego
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Geological Society of America
Volume
422
ISBN print:
9780813724225
Publication date:
January 01, 2007

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