Geology topics

Alejandro Hinojosa-Corona

Publications and source records attributed to Alejandro Hinojosa-Corona.

3 recordsLinked to original sources

USGS2026

Self-similar vent clustering in the Pinacate volcanic field (Sonora, Mexico and Arizona, United States)

The spatial distribution of vents in a distributed volcanic field may provide clues about the geometry of the volcanic field’s plumbing system. Distributed volcanism is characterized by magma feeders that are independent of one another, scattered over wide areas, and active for relatively short times (typically less than one hundred years). On the other hand, focused volcanism results in large volcanic edifices, forming central or shield volcanoes that are active for tens of thousands of years or longer. Whether distributed or focused, the form of volcanism may depend on several factors: magma fluxes at depth; magma composition, temperature, and viscosity; and crustal stress and strain states. Over time, some volcanic fields may shift from focused to distributed volcanism. Located in northwestern Sonora, Mexico, and southwestern Arizona, United States, the Pinacate volcanic field is made up of lava flows, 8 maars, and more than 400 cinder cones. It has been active for approximately 2 million years. The oldest features in the field are large-volume lava flows that constructed Sierra El Pinacate (known locally and referred to herein as the Santa Clara shield volcano) and formed the base of the field. Later activity took the form of monogenetic cones and maars, produced by high-alkali basalts with an ocean-island basalt chemical signature. The plumbing system of the Pinacate volcanic field, along with its relations with the structural setting of the area, are analyzed here in terms of the spatial distribution of vents, vent morphology, and main structural trends of the morphologic lineaments in the area. The spatial analysis of vents identified three clusters. The largest cluster (cluster 1) is in the north-northwest portion of the volcanic field, whereas the smallest cluster (cluster 2), formed by younger cones, is on the east side of the volcanic field. The southern cluster (cluster 3) is mainly located over the Santa Clara shield volcano. Self-similar clustering analysis was performed on the whole volcanic field, as well as on the two larger clusters (clusters 1 and 3); cluster 2 was not analyzed individually due to the small number of vents. The self-similar clustering analysis indicated that the dataset containing all the vents in the volcanic field and the dataset containing only the vents in cluster 1 (the largest cluster) have magma storage at approximately 17 kilometers (km) depth. The vents of cluster 3 indicate storage at approximately 9 km depth. The fractal exponent characterizing the self-similar clustering of cluster 3 (1.5905) is lower than the fractal exponent of cluster 1 (1.7252), implying that cluster 1 formed after cluster 3. The available absolute ages of volcanic products in the Pinacate volcanic field indicate a middle to early Pleistocene age for the vents in cluster 3, and younger ages (late Pleistocene to Holocene) for cluster 2. The cone morphology is equivocal for defining relative ages of the clusters; nevertheless, the spatial distribution of the best-preserved cones implies that northwest-southeast, north-south, and northeast-southwest trends are linked to the development of the volcanic field. Lineament mapping, as well as the shape, elongation, and orientation of inferred feeder dikes, indicates that the Pinacate volcanic field formed along a northwest-southeast, regional-scale dextral transtensional shear zone and southwestward shallowing of the Mohorovičić discontinuity to 18–20 km.

Arizona, Sonora↗

USGS2025

Blue carbon stocks along the Pacific Coast of North America are mainly driven by local rather than regional factors

Coastal wetlands, including seagrass meadows, emergent marshes, mangroves, and temperate tidal swamps, can efficiently sequester and store large quantities of sediment organic carbon (SOC). However, SOC stocks may vary by ecosystem type and along environmental or climate gradients at different scales. Quantifying such variability is needed to improve blue carbon accounting, conservation effectiveness, and restoration planning. We analyzed SOC stocks in 1,284 sediment cores along >6,500 km of the Pacific coast of North America that included large environmental gradients and multiple ecosystem types. Tidal wetlands with woody vegetation (mangroves and swamps) had the highest mean stocks to 1 m depth (357 and 355 Mg ha −1 , respectively), 45% higher than marshes (245 Mg ha −1 ), and more than 500% higher than seagrass (68 Mg ha −1 ). Unvegetated tideflats, though not often considered a blue carbon ecosystem, had noteworthy stocks (148 Mg ha −1 ). Stocks increased with tidal elevation and with fine (<63 μm) sediment content in several ecosystems. Stocks also varied by dominant plant species within individual ecosystem types. At larger scales, marsh stocks were lowest in the Sonoran Desert region of Mexico, and swamp stocks differed among climate zones; otherwise stocks showed little correlation with ecoregion or latitude. More variability in SOC occurred among ecosystem types, and at smaller spatial scales (such as individual estuaries), than across regional climate gradients. These patterns can inform coastal conservation and restoration priorities across scales where preserving stored carbon and enhancing sequestration helps avert greenhouse gas emissions and maintains other vital ecosystem services.

Pacific Coast of North America↗

USGS2020

An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress

The moment magnitude 7.2 El Mayor−Cucapah (EMC) earthquake of 2010 in northern Baja California, Mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults. These faults have been exhumed from depths of 6−10 km since the late Miocene based on low-temperature thermochronology, synkinematic alteration, and deformational fabrics. Coseismic slip of 1−6 m of the EMC event was accommodated by fault zones that displayed the full spectrum of architectural styles, from simple narrow fault zones (<100 m in width) that have a single high-strain core, to complex wide fault zones (>100 m in width) that have multiple anastomosing high-strain cores. As fault zone complexity and width increase the full spectrum of observed widths (20−200 m), coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays. Thus, the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long-term history of slip on the faults at deeper levels of the seismogenic crust. We find that factors such as protolith, normal stress, and displacement, which control gouge production in laboratory experiments, also affect the architectural complexity of natural faults. Fault zones developed in phyllosilicate-rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo-feldspathic granitoid rocks. We hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad, multi-stranded fault zones. Fault orientation also strongly affects fault zone complexity, which we find to increase with decreasing fault dip. We attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting. The conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone, promoting complex branching and development of multiple high-strain cores. Overall, we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress.

Baja California↗