HR: 16:20h
AN: U54A-01    [Abstracts]
TI: The Acatlan Complex, Southern Mexico: Ordovician-Devonian Passive Margin on the Southern Rheic Ocean Margin and Carboniferous-Permian Subduction on Western Pangea
AU: * Keppie, J D
EM: duncan@servidor.unam.mx
AF: Instituto de Geología, Universidad Nacional Autónoma de México, Universidad Nacional Autónoma de México, Mexico, DF 04510, Mexico
AU: Ramos-Arias, M
EM: alfredogeo@yahoo.com.mx
AF: Instituto de Geología, Universidad Nacional Autónoma de México, Universidad Nacional Autónoma de México, Mexico, DF 04510, Mexico
AU: Morales-Gamez, M
EM: morzuz@yahoo.com
AF: Instituto de Geología, Universidad Nacional Autónoma de México, Universidad Nacional Autónoma de México, Mexico, DF 04510, Mexico
AU: Nance, R D
EM: nance@ohio.edu
AF: Department of Geological Sciences, 316 Clippinger Laboratories, Ohio University, Athens, OH 45701, United States
AU: Miller, B V
EM: bvmiller@tamu.edu
AF: Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, United States
AU: Murphy, J B
EM: bmurphy@stfx.ca
AF: Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada
AU: Dostal, J
EM: jdostal@SMU.CA
AF: Department of Geology, St. Mary's University, Halifax, NS B3H 3C3, Canada
AU: Ortega-Rivera, A
EM: amabel@servidor.unam.mx
AF: Instituto de Geologia, Universidad Nacional Autónoma de Mexico, Estación Regional del Noroeste, Apartado Postal 1039, Hermosillo, SON 83000, Mexico
AU: Lee, J W
EM: lee@geol.queensu.ca
AF: Department of Geology, Queens University, Kingston, ONT K7L 3NG, Canada
AB: New structural, geochronological and geochemical data from the Acatlan Complex of southern Mexico shows it preserves a history of Cambro-Ordovician rifting along the southern margin of the Rheic Ocean, followed by Devono-Carboniferous subduction and exhumation and development of a Permo-Triassic transtensional arc on the eastern Pacific margin. The oldest rocks are represented by low-grade, siliciclastics intruded by bimodal, rift- related, mafic and felsic plutons and continental rift tholeiitic dikes ranging in age from ca.480 to 440 Ma. Greenschist facies psammites and pelites containing detrital zircons as young as ca.360 Ma represent continental rise deposits that contain tectonic slices of mafic rocks with oceanic tholeiitic and alkalic affinities. Tectonically interleaved with these greenschist facies rocks are slices of high pressure eclogite with a continental rift tholeiitic protolith, blueschist mafic rocks, high grade rift-passive margin, metasedimentary rocks, ca.470-420 Ma granitoid rocks, and periarc serpentinite. Concordant U-Pb zircon data on one of these eclogites yields an age of ca.346 Ma interpreted as the age of metamorphism that was closely followed by rapid decompression migmatization and cooling through ca.350°C by ca.350 Ma (40Ar/39Ar muscovite data). Carboniferous to Middle Permian exhumation of these high grade rocks occurred after the amalgamation of Pangea and during: (1) deposition of continental to shallow marine rocks with two pulses of fault-related conglomerates in the lower Mississippian (Kinderhookian) and Lower Permian (Leonardian); (2) listric normal deformation under greenschist facies conditions dated at ca.347 Ma and ca.300 Ma (40Ar/39Ar muscovite and amphibole data, respectively), and associated with either core complex development or extrusion; (3) Permian arc magmatism that extends along the western margin of Pangea through Mexico; and (4) Permian, dextral transtensional deformation. The western margin of Pangea during the Triassic changes from rift and passive margin in northern Mexico to S-vergent thrust and associated clastic wedge in the Acatlan Complex consistent with oblique dextral convergence between the Pacific and Pangean plates.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8110 Continental tectonics: general (0905)
DE: 8157 Plate motions: past (3040)
DE: 8178 Tectonics and magmatism
SC: Union [U]
MN: 2007 Joint Assembly