spe423-21 page 437 437 Geological Society of America Special Paper 423 2007 Vestige of the Rheic Ocean in North America: The Acatlán Complex of southern México R. Damian Nance* Department of Geological Sciences, 316 Clippinger Laboratories, Ohio University, Athens, Ohio 45701, USA Brent V. Miller Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843, USA J. Duncan Keppie <BIO>Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México D.F., México J. Brendan Murphy Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, Canada, B2G 2W5 Jaroslav Dostal Department of Geology, St. Mary’s University, Halifax, Nova Scotia, Canada, B3H 3C3 ABSTRACT The Acatlán Complex of southern México comprises metasedimentary and metaigneous rocks that represent the vestige of a Paleozoic ocean. Juxtaposed against granulite-facies gneisses of Mesoproterozoic (ca. 1 Ga) age, the complex has previ- ously been related to the Iapetus Ocean and interpreted to preserve a tectonostrati- graphic record linked to that of the Appalachian orogen: (1) Cambro-Ordovician deposition of a trench or forearc sequence (the Petlalcingo Group: the Magdalena, Chazumba, and Cosoltepec Formations) and an oceanic assemblage (the Piaxtla Group), (2) polyphase Late Ordovician–Early Silurian deformation (the Acatecan orogeny) during which the Piaxtla Group underwent eclogite-facies metamorphism synchronous with megacrystic granitoid emplacement, (3) deposition of the arc-relat- ed Tecomate Formation and intrusion of megacrystic granitoid plutons during the Devonian, and (4) deformation under greenschist-facies conditions during the Late Devonian Mixtecan orogeny. However, recent structural, geochronological, and geochemical studies have shown that (1) the Cosoltepec Formation is bracketed between ca. 455 Ma and the latest Devonian and may be part of a continental rise prism with slivers of oceanic basalt; (2) the Magdalena and Chazumba Units represent a clastic wedge assemblage *E-mail: nance@ohio.edu. Nance, R.D., Miller, B.V., Keppie, J.D., Murphy, J.B., and Dostal, J., 2007, Vestige of the Rheic Ocean in North America: The Acatlán Complex of southern México, in Linnemann, U., Nance, R.D., Kraft, P., and Zulauf, G., eds., The evolution of the Rheic Ocean: From Avalonian-Cadomian active margin to Allegh- enian-Variscan collision: Geological Society of America Special Paper 423, p. 437–452, doi: 10.1130/2007.2423(21). For permission to copy, contact editing@ geosociety.org. ©2007 Geological Society of America. All rights reserved.