Cenozoic volcanism and extension in northwestern Mesa Central, Durango, México

Resumen

The Santiago
Papasquiaro region is located in the northwest portion of the Mesa
Central and is characterized by Tertiary Sierra Madre Occidental
lithology. Geologic mapping and dating of key units using U-Pb laser
ablation method on zircons has identified three different
lithostratigraphic groups. These include: (1) early Eocene felsic
volcanic rocks, consisting of the Antigua ignimbrite [51.75
+0.35/-0.45 Ma]; (2) late Eocene - early Oligocene felsic to
intermediate volcanic rocks, consisting of the Altamira ignimbrite
[38.8 ± 1.0 Ma], El Cazadero andesite [ages of 37.2 +0.30/-0.40 Ma
and 35.95 +0.45/-0.5 Ma], a dioritic intrusion, the Venadita
rhyolite, Puente Negro ignimbrite [34.0 +0.50/-0.70 Ma], Los Fresnos
ignimbrite and Balín ignimbrite [33.2 +0.50/-0.20 Ma]; and (3) late
Oligocene to Quaternary sedimentary and volcanic mafic rocks
comprising the Santiago sedimentary formation, basalts equivalent to
Metates Formation and Neogene to Quaternary continental
non-consolidated deposits. Within the studied area, the main
volcanic pulse of the Sierra Madre Occidental volcanic province
corresponds to the second group, which lasted ca. 5 Ma. Older rocks
are represented by a single outcrop of the Antigua ignimbrite, and
the younger units are mainly continental clastic sediments
intercalated with sporadic mafic alkaline volcanic rocks that record
a major change in the tectonic regime. Extension that began in late
Eocene - Oligocene gradually tilted the late Eocene – early
Oligocene volcanic sequence and formed the NNW-trending Santiago
Papasquiaro half-graben, which is the northernmost and earliest
structure of the Río Chico-Otinapa graben. NW-striking faults of the
San Luis-Tepehuanes fault system were synchronous with the
development of the Santiago Papasquiaro half-graben. The deformation
propagated gradually to the south, forming the NNW Río Chico-Otinapa
graben by the early-middle Miocene, and to the east-southeast in the
Santiaguillo graben. A recent minor extensional deformation
accommodated by NE-striking faults was probably related to seismic
deformation of the Nuevo Ideal zone, approximately 40 km southeast
of the study area.