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

The Acatlán Complex straddles a highpressure 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 paleo geo graphic 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 Ceno zoic (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.