Post-Laramide and pre-Basin and Range deformation and implications for Paleogene (55–25 Ma) volcanism in central Mexico: A geological basis for a volcano-tectonic stress model
Résumé
At central-eastern Mexico, in the Mesa Central province, there are several ranges that were formed after the K/T Laramide compression but before the Basin and Range peak extensional episodes at middle–late Oligocene. Two important volcano-tectonic events happened during this time interval, 1) uplift of crustal blocks exhuming the Triassic–Jurassic metamorphic sequence and formation of basins that were filled with red beds and volcanic sequences, and 2) normal faulting and tilting to the NE of these blocks and fanglomerate filling of graben and half-graben structures. The first event, from late Paleocene to early Eocene, was related to NNE and NNW oriented dextral strike-slip faults. These faults were combined with NW–SE en echelon faulting in these blocks through which plutonism and volcanism occurred. The second event lasted from early Oligocene to early Miocene and coincided with Basin and Range extension. Intense volcanic activity occurred synchronously with the newly-formed or reactivated old fault systems, producing thick sequences of silicic pyroclastic rocks and large domes. Volcano-tectonic peaks occurred in three main episodes during the middle–late Oligocene in this part of Mexico, at about 32–30 Ma, 30–28 Ma, and 26–25 Ma. The objectives of this work is to summarize the volcano-tectonic events that occurred after the end of the Laramide orogeny and before the peak episodes of Basin and Range faulting and Sierra Madre Occidental Oligocene volcanism, and to discuss the influence of these events on the following Oligocene–Miocene volcano-tectonic peak episodes that formed the voluminous silicic volcanism in the Mesa Central, and hence, in the Sierra Madre Occidental. A model based upon geological observations summarizes the volcanic-tectonic evolution of this part of Mexico from the late Paleocene to the Early Miocene.