Cenozoic geology of the Yolomécatl-Tlaxiaco area, Northwestern Oaxaca, Southeastern Mexico: Stratigraphy, structure and regional significance

• Published in: Journal of South American earth sciences Vol. 72; pp. 191 - 226
• Main Authors: Ferrusquía-Villafranca, Ismael, Ruiz-González, José E., Torres-Hernández, José Ramón, Anderson, Thomas H., Urrutia-Fucugauchi, Jaime, Martínez-Hernández, Enrique, García-Villegas, Felipe
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2016
• Subjects: Cenozoic; Oaxaca; Sierra Madre del Sur; Southeastern Mexico; Stratigraphy; Structure; Volcanism; Sierra Madre del Sur; Oaxaca; Southeastern Mexico; Stratigraphy; Cenozoic; Structure; Volcanism
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2016.09.005

The Yolomécatl-Tlaxiaco Area, lies in the rugged Sierra Madre del Sur (SMS) of northwestern Oaxaca (YOTLA), southeastern Mexico. Within the area Cenozoic units unconformably overlie metamorphic, clastic and carbonate rock units of Late Paleozoic to Cretaceous ages as well as the Mixteco/Oaxaca Terrane boundary. The Cenozoic sequence, emphasized herein, includes from botton to top: (1) basal, calcilithitic Early Tertiary Tamazulapam Conglomerate, (2) andesitic lava flows of Nduayaco “Group,” (3–4) Epiclastic/pyroclastic strata composing Yolomécatl Formation (∼40.3 ± 1.0 Ma), and Tayata Pyroepiclastics (5) Early Oligocene (∼32.9 Ma), felsic, pyroclastic Nundichi “Group,” (6) Late Oligocene (∼27.7 ± 0.7 Ma) andesitic lava flows of Nicananduta “Group” containing intercalations of unit (7) ?Chilapa Formation (largely lacustrine). Quaternary deposits unconformably overlie the sequence. The structural record includes NNW-SSE folds in the Mesozoic units, and one in Tayata Pyroepiclastics, as well as numerous fractures/faults of diverse types, whose pattern seems to roughly define four geographic/structural domains, NW, SW, S, and E. The Tertiary sequence records four magmatic and six deformational events: Pre-Late Eocene Extension accommodated by the Tamazulapam fault, along which magma of the Nduayaco “Group” moved upward. The next episode is the earliest Late Eocene extension recorded by the Yucuxaco-Santa Cruz Tayata fault was followed by accumulation of Yolomécatl Formation, Tayata Pyroepiclastics, and synsedimentary emplacement of tuff sheets at ∼40.3 ± 1.0 Ma. After this date, left lateral transpression emplaced a Teposcolula Limestone block over Nduayaco “Group” and ?Yolomécatl Formation, whereas the Tayata Pyroepiclastics was folded into an open anticline. Movement along the Yucuxaco-Santa Cruz Tayayata fault suite influenced accumulation of the Nundichi “Group” strata ca. ∼32.9 Ma. Subsequent ENE-WSW extension affected the Nundichi “Group,” partly placing it in contact with Jurassic limestone blocks. Finally, ca. 27.7 Ma, the Nicananduta “Group” was emplaced. The discrimination of YOTLA's Cenozoic magmatic/deformational events correlates well with that of events previously recognized in the SMS, and to the north along the southwestern margin of North America. However, significant differences persist in terms of number, characterization, age and duration of events that cannot be resolved at present. Anyway, differences are expected due to the inherent diachronic nature of magmatism and deformation across SMS, and the fact that the events reported here took place inland, not around the Mixteco/Oaxaca Terranes block, where most events of these kinds occurred. [Display omitted] •The lithostratigraphic characterization of the Yolomécatl-Tlaxiaco area is presented.•The stratigraphic record allows to identify 4 magmatic and 6 deformational events.•Such events broadly coincide with those already known for the Sierra Madre del Sur.