A high-pressure folded klippe at Tehuitzingo on the western margin of an extrusion zone, Acatlan Complex, southern Mexico

作者：Galaz E Gonzalo; Keppie J Duncan; Lee James K W; Ortega Rivera Amabel

来源：Gondwana Research, 2013, 23(2): 641-660.

DOI：10.1016/j.gr.2012.04.011

• Acatlan Complex
• Extrusion
• P-T-t high-pressure metamorphism
• Tectonics
• Geochronology

High-pressure (HP) rocks at Tehuitzingo, on the western margin of the HP belt within the Paleozoic Acatlan Complex (southern Mexico), occur in a klippe that was thrust over low-grade clastic rocks. The youngest detrital zircon cluster in the low-grade rocks yielded U-Pb ages of 481 +/- 16 Ma, which provide an older limit for deposition. The HP rocks are composed of metabasites, serpentinite, granite (482 +/- 3 Ma) and mica schist (youngest concordant detrital zircon: 433 +/- 3 Ma). The schist and granite are inferred to be high-grade equivalents of lower Paleozoic, low-grade rocks exposed elsewhere in the Acatlan Complex, from which they are inferred to have been removed by subduction erosion. Mineral analyses indicate that the subducted rocks underwent HP metamorphism and polyphase deformation at depths of similar to 50 km (similar to 16 kbar and 750 degrees C: eclogite facies). Subsequent retrogression passed through epidote-amphibolite to greenschist fades, which was synchronous with W-vergent thrusting over the low-grade clastic rocks. Deposition of the low-grade rocks and thrusting are bracketed between either 481-329 Ma (Ordovician-Mississippian), and was followed by F-3 synformal folding. Cooling through ca. 385 degrees C is indicated by 329 +/- 1 and 316-317 +/- 2 Ma, Ar-40/Ar-39 muscovite plateau ages in HP rocks, which are 5-17 my younger than those of the adjacent Piaxtla eclogites suggesting younger exhumation. The petrology, P-T conditions and ages of the Piaxtla Suite is consistent with an extrusion channel within the Acatlan Complex along the active western margin of Pangea during the Carboniferous. Detrital zircon populations in the low-grade psammite (ca. 481, 520-650, 720, 750, 815, 890, 1050 and 2750 Ma) and the HP schist (ca. 457-480, 534, 908, 954-1150, 1265, 1845 and 2035 Ma) indicate derivation from the Ordovician Acatlan granitoids, Neoproterozoic Brasiliano orogens, 900-750 Ma Goias arc (Amazonia), 1-1.3 Ma Oaxaquia, and more ancient sources in Oaxaquia/Amazonia.

• 出版日期2013-3