Tecolote volcano, Pinacate volcanic field (Sonora, Mexico): A case of highly explosive basaltic volcanism and shifting eruptive styles

Explosive basaltic eruptions have been documented in monogenetic volcanic fields, and recognizing the scales of their explosivity is important for understanding the full range of basaltic volcanism. Here we reconstruct one of the youngest eruptions in the Pinacate volcanic field (Sonora, Mexico) and estimate the volumes of the lava flows, scoria cone, and tephra units. The source vent of the eruption is Tecolote volcano (27 ± 6 ka, 40Ar/39Ar). There were two distinct episodes of tephra production, Tephra Unit 1 (T1) followed by Tephra Unit 2 (T2). T1 and T2 show different dispersal patterns, with T1 dispersed in an approximately circular pattern and T2 dispersed oblately trending SE and NW of the vent. Based on column height reconstructions and deposit characteristics, the T1-producing eruption was subplinian (15–18 km plume), with a calculated mass eruption rate ranging between 1.0 ± 0.6 × 107 kg/s and 2.2 ± 1.2 × 107 kg/s and corresponding durations between 79 ± 54 min and 38 ± 26 min, respectively. The T2-producing eruption was violent Strombolian (11 km plume) with a calculated mass eruption rate of 3.2 ± 1.4 × 106 kg/s and resulting duration of 193 ± 78 min. In addition to the two tephra units, Tecolote volcano produced seven morphologically distinct lava flows. The majority of lava volume production occurred before—and partly contemporaneously with—tephra production, and five small-volume lava flows were emplaced after pyroclastic activity terminated, indicating shifting and simultaneous eruptive styles. Of the total 0.23 km3 dense rock equivalent (DRE) erupted volume, the lava flows constitute the majority (0.17 km3 DRE), with 0.041 km3 DRE volume for the cone and a combined 0.026 ± 0.005 km3 DRE volume for the two tephra units. The geochemistry of the samples is consistent with that determined for other Pinacate rocks, which show a trend most similar to that of ocean island basalts and appears characteristically similar to other volcanic fields of the Basin and Range province.