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This Article Figures Only Full Text Full Text (PDF) All Versions of this Article: B26597.1v1 121/11-12/1678    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Ortega-Obregon, C. Articles by Ortega-Rivera, A. GeoRef GeoRef Citation

Geology and geochronology of Paleozoic rocks in western Acatlán Complex, southern Mexico: Evidence for contiguity across an extruded high-pressure belt and constraints on Paleozoic reconstructions

Carlos Ortega-Obregon¹, J. Duncan Keppie^1,, J. Brendan Murphy², J.K.W. Lee³ and Amabel Ortega-Rivera⁴

¹ Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autonoma de México, Mexico D.F. 04510, Mexico
² Department of Earth Sciences, Saint Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
³ Department of Geology and Environmental Sciences, Queens University, Kingston, Ontario K7L3NG, Canada
⁴ Instituto de Geología, Estación Regional del Noroeste, Apartado Postal 1039, Universidad Nacional Autonoma de México, Hermosillo, Sonora 83000, Mexico

Correspondence: E-mail: duncan{at}servidor.unam.mx

The Acatlán Complex straddles a high-pressure belt previously interpreted as either: (1) a suture zone within the Iapetus or the Rheic oceans, which would have a contrasting geological record across the suture; or (2) a tectonic slice extruded into the upper plate, which would imply contiguity across the complex. Distinguishing between these hypotheses is critical to paleogeographic reconstructions. Examination of the western Acatlán Complex reveals the following: (1) deposition of clastic rocks between 654 and 464 Ma; (2) intrusion of bimodal Ordovician bodies at ca. 464 Ma; (3) high-grade deformation with cooling through 400 °C by ~360–335 Ma; (4) deposition of clastic rocks and pillow lavas after ~350–400 Ma; (5) deformation accompanied by greenschist facies metamorphism at ca. 335 Ma; (6) deposition of clastic and bimodal volcanic rocks at ca. 327 Ma; (7) ~320–270 Ma subgreenschist deformation; (8) deposition of the Middle-Upper Permian sedimentary rocks; and (9) intrusion of a 61 ± 1 Ma diorite followed by early Cenozoic (Laramide) ENE folding and faulting. Zircon ages (~350–400, 570–505, 827–890 Ma, 0.9–1.3 Ga) suggest both local and Amazonian sources with deposition above a local Mesoproterozoic (Oaxacan) basement on the southern margin of the Rheic Ocean. This geological record is very similar to that of the eastern Acatlán Complex, which supports the extrusion hypothesis, a model that may be applicable to other orogens.