Early Miocene shortening in the lower Comondú Group in Baja California Sur (México)

Bonini, Marco; Cerca, Mariano; Moratti, Giovanna; López‐Martínez, Margarita; Corti, Giacomo; Gracia‐Marroquín, Diego

doi:10.1016/j.tecto.2017.05.032

Cited by 3 publications

(4 citation statements)

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“…Inversion of these fault‐slip data yields subhorizontal E‐to‐ENE‐oriented extension directions (azimuth 064°–081°; Table ). Interestingly, the fault damage zone contains closely‐spaced shear planes and is intruded locally by steep trydimite veins (Bonini et al, ) (Site 10). Slickensides collected on mesoscopic faults along a minor fault splay in the footwall of the El Carrizal fault indicate instead a subhorizontal ~NE‐oriented extension direction (azimuth 040°) (Site 11; Figure ).…”

Section: Results From the Western Rift Boundarymentioning

confidence: 99%

“…The oldest evidence of extensional deformation in the southern Gulf of California is documented in the southernmost Baja California Peninsula, where the activity of the (syn‐subduction) E‐dipping Los Cabos detachment is thought to have initiated at ~17.5 to 17 Ma (Bot et al, ). This extensional deformation is permissibly constrained by a short‐lived episode of shortening (~21–19.4 Ma) that has been identified in the same region, although north of Los Cabos, thereby suggesting that extension must have started no earlier than 19.4 Ma (Bonini et al, ). The region north of La Paz is characterized by Late Oligocene to Middle Miocene volcaniclastic, epiclastic, and sedimentary deposits of the Comondú Group (Hausback, ) (Figure ).…”

Section: Regional Tectonic Historymentioning

confidence: 87%

“…The Comondú deposits are generally subdivided into lower (~26–19 Ma), middle (~19–15 Ma), and upper (~14–12 Ma) stratigraphic units (Dorsey & Burns, ; Drake et al, ; Hausback, ; Umhoefer et al, ). For convenience, in this study the Comondú Group has been distinguished into ‘lower’ and ‘upper’ stratigraphic units, which are separated by a regional unconformity likely produced by the aforementioned shortening episode (Bonini et al, ). In particular, the ‘upper’ stratigraphic unit of this study lumps the San Juan Tuff as well as the middle (~19–15 Ma) and upper (~14–12 Ma) Comondú Group of Drake et al ().…”

Section: Regional Tectonic Historymentioning

confidence: 99%

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Strain partitioning in highly oblique rift settings: Inferences from the southwestern margin of the Gulf of California (Baja California Sur, México)

et al. 2019

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This study aims to analyze the modalities of strain accommodation within a highly oblique rift, taking the Gulf of California as a prototype. Rifting in the Gulf of California is accomplished by intra-Gulf strike-slip (transform) faults, and mostly dip-slip displacement on the rift-margin faults. We have collected fault-slip data and samples for radiometric dating at selected sites in southeastern Baja California, which is host to the southwestern margin of the rift. We have identified three styles of faulting, particularly (1) WSW-dipping normal faults, (2) E-ENE-dipping normal faults, and (3) steep NNE-NE-trending left-lateral faults. The E-ENE-dipping normal faults define the western margin of the Gulf of California rift and are most likely coeval (late Miocene to recent) with both the~NNE-NE-trending left-lateral faults and some of the WSW-dipping faults. Fault-slip data have often been collected on potentially active Gulf of California rift-margin faults, which invariably display dominant dip-slip kinematics (generally with minor dextral component). Distribution of extension directions determined from stress inversion of brittle fault kinematic data indicates a peak of 080°-090°, which is strikingly similar to the orientations of T axes from earthquake focal mechanisms of both rift-margin normal/faults and intra-Gulf strike-slip faults. These findings suggest that this stretching may have been occurring throughout the protracted rift history. Furthermore, highly oblique rifts do not show across-rift variations in the orientation of local extension, which is instead typical of continental rifts with lower obliquity.

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Section: Results From the Western Rift Boundarymentioning

confidence: 99%

Section: Regional Tectonic Historymentioning

confidence: 87%

Section: Regional Tectonic Historymentioning

confidence: 99%

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Strain partitioning in highly oblique rift settings: Inferences from the southwestern margin of the Gulf of California (Baja California Sur, México)

et al. 2019

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“…Experiments were made by step-heating the samples, increasing the laser power from 1 to 14 watts and measuring the isotopic composition of argon released during each step. More details of the 40 Ar-39 Ar technique are explained in Ochoa-González, Carreon-Freyre, Cerca, and López-Martínez (2015) and Bonini et al (2017). The age was calculated for each individual fraction adding individual steps in accordance with Hall (1981).…”

Section: Ar-39ar Geochronologymentioning

confidence: 99%

The Eocene-Oligocene Nanchititla dike swarm, eastern Michoacán, México

et al. 2019

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We present a geologic map for the Eocene-Oligocene Nanchititla mafic dike swarm consisting of over 140 NNW-SSE trending dike segments; whose emplacement was influenced by the left-lateral transtensional deformation regime prevailing in southern México during the Cenozoic. The hosting rock is a mechanically heterogeneous continental sedimentary sequence interbedded with volcanic rocks. Interaction among magma and host rock promoted the formation of dike-sill systems, segmentation and sinuous intrusions. Dike thickness observed is between 1 and 45 m with a peak in the range from 1 to 5 m. Six giant dikes of more than 30 m thick were documented. The 80% of the dikes have porphyritic textures rich in plagioclase phenocrysts with size ranging from 0.5 to 2.5 cm. New and compiled 40Ar-39Ar ages constrain the swarm emplacement between 30 and 34.5 Ma, whereas plagioclase phenocrysts entrained by the magma have older ages between 35 and 42 Ma.

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