8 research outputs found
Geology of the Alarcon Rise, Southern Gulf of California
Abstract Meter-scale AUV bathymetric mapping and ROV sampling of the entire 47 km-long Alarcon Rise between the Pescadero and Tamayo transforms show that the shallowest inflated portion of the segment hosts all four active hydrothermal vent fields and the youngest, hottest, and highest effusion rate lava flows. This shallowest inflated part is located ~1/3 of the way between the Tamayo and Pescadero transforms and is paved by a 16 km2 channelized flow that erupted from 9 km of en echelon fissures and is larger than historic flows on the East Pacific Rise or on the Gorda and Juan de Fuca Ridges. Starting ~5 km south of the Pescadero transform, 6.5 km of the Alarcon Rise is characterized by faulted ridges and domes of fractionated lavas ranging from basaltic andesite to rhyolite with up to 77.3 wt % SiO2. These are the first known rhyolites from the submarine global mid-ocean ridge system. Silicic lavas range from \u3e11.7 ka, to as young as 1.1 ka. A basalt-to-basaltic andesite sequence and an andesite-to-dacite-to-rhyolite sequence are consistent with crystal fractionation but some intermediate basaltic andesite and andesite formed by mixing basalt with dacite or rhyolite. Magmatism occurred along the bounding Tamayo and Pescadero transforms as extensive channelized flows. The flows erupted from ring faults surrounding uplifted sediment hills inferred to overlie sills. The transforms are transtensional to accommodate magma migration from the adjacent Alarcon Rise.
Plain Language Summary This study combines 1 m resolution bathymetry collected using an autonomous underwater vehicle, with chemical compositions of precisely located lava samples and ages of lava flows determined from short sediment cores collected using a remotely operated vehicle. The objective was to determine the history of an entire 47 km long segment of the global mid-ocean ridge system. The ridge segment studied is named the Alarcon Rise and is located at the mouth of the Gulf of California. The Rise is bounded to the north and south by strike-slip faults that offset the Rise from adjacent segments of the spreading ridge system. Such faults are usually thought to be parallel to the direction of seafloor spreading, but these have an oblique component to their movement that makes space for magma to be injected along the faults where it uplifts hills of sediment and sometimes erupts. Most lavas erupted along midocean ridges are basalts, but some highly unusual silica-rich lavas were identified by their rough surface texture and sampled. These lavas include the most silica-rich ones found along the entire global submarine mid-ocean ridge system. They formed, not by melting of nearby continental crust, but from common basalt by extreme amounts of crystallization of minerals, leaving a small volume of remaining high-silica magma. The complete mapping and closely spaced sampling along the Rise show that old ideas indicating a central point of magma delivery from the underlying mantle for each ridge segment followed by shallow transport of the magmas along the ridge are supported by the central distribution of (1) hydrothermally active sites, (2) the youngest, hottest, most fluid lava flows, and (3) the most voluminous lava flows that accumulate to form the shallowest portion of the ridge segment. The study shows how magmas are transported at shallow depths along the ridge and even around the corners in the adjacent faults
Geology of the Alarcon Rise, Southern Gulf of California
Meterâscale AUV bathymetric mapping and ROV sampling of the entire 47 kmâlong Alarcon Rise between the Pescadero and Tamayo transforms show that the shallowest inflated portion of the segment hosts all four active hydrothermal vent fields and the youngest, hottest, and highest effusion rate lava flows. This shallowest inflated part is located âŒ1/3 of the way between the Tamayo and Pescadero transforms and is paved by a 16 km2 channelized flow that erupted from 9 km of en echelon fissures and is larger than historic flows on the East Pacific Rise or on the Gorda and Juan de Fuca Ridges. Starting âŒ5 km south of the Pescadero transform, 6.5 km of the Alarcon Rise is characterized by faulted ridges and domes of fractionated lavas ranging from basaltic andesite to rhyolite with up to 77.3 wt % SiO2. These are the first known rhyolites from the submarine global midâocean ridge system. Silicic lavas range from \u3e11.7 ka, to as young as 1.1 ka. A basaltâtoâbasaltic andesite sequence and an andesiteâtoâdaciteâtoârhyolite sequence are consistent with crystal fractionation but some intermediate basaltic andesite and andesite formed by mixing basalt with dacite or rhyolite. Magmatism occurred along the bounding Tamayo and Pescadero transforms as extensive channelized flows. The flows erupted from ring faults surrounding uplifted sediment hills inferred to overlie sills. The transforms are transtensional to accommodate magma migration from the adjacent Alarcon Rise
Geology of the Alarcon Rise, Southern Gulf of California
Meterâscale AUV bathymetric mapping and ROV sampling of the entire 47 kmâlong Alarcon Rise between the Pescadero and Tamayo transforms show that the shallowest inflated portion of the segment hosts all four active hydrothermal vent fields and the youngest, hottest, and highest effusion rate lava flows. This shallowest inflated part is located âŒ1/3 of the way between the Tamayo and Pescadero transforms and is paved by a 16 km2 channelized flow that erupted from 9 km of en echelon fissures and is larger than historic flows on the East Pacific Rise or on the Gorda and Juan de Fuca Ridges. Starting âŒ5 km south of the Pescadero transform, 6.5 km of the Alarcon Rise is characterized by faulted ridges and domes of fractionated lavas ranging from basaltic andesite to rhyolite with up to 77.3 wt % SiO2. These are the first known rhyolites from the submarine global midâocean ridge system. Silicic lavas range from \u3e11.7 ka, to as young as 1.1 ka. A basaltâtoâbasaltic andesite sequence and an andesiteâtoâdaciteâtoârhyolite sequence are consistent with crystal fractionation but some intermediate basaltic andesite and andesite formed by mixing basalt with dacite or rhyolite. Magmatism occurred along the bounding Tamayo and Pescadero transforms as extensive channelized flows. The flows erupted from ring faults surrounding uplifted sediment hills inferred to overlie sills. The transforms are transtensional to accommodate magma migration from the adjacent Alarcon Rise
GeomorfologĂa tectĂłnica de una falla normal activa de bajo ĂĄngulo en las Sierras CucapĂĄ y El Mayor, Baja California, Mexico
EvoluciĂłn del sistema de fallas mioceno-cuaternarias sobre la margen oriente de Laguna Salada, Baja California, MĂ©xico
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Hydrothermal vent fields discovered in the southern Gulf of California clarify role of habitat in augmenting regional diversity.
Hydrothermal vent communities are distributed along mid-ocean spreading ridges as isolated patches. While distance is a key factor influencing connectivity among sites, habitat characteristics are also critical. The Pescadero Basin (PB) and Alarcón Rise (AR) vent fields, recently discovered in the southern Gulf of California, are bounded by previously known vent localities (e.g. Guaymas Basin and 21° N East Pacific Rise); yet, the newly discovered vents differ markedly in substrata and vent fluid attributes. Out of 116 macrofaunal species observed or collected, only three species are shared among all four vent fields, while 73 occur at only one locality. Foundation species at basalt-hosted sulfide chimneys on the AR differ from the functional equivalents inhabiting sediment-hosted carbonate chimneys in the PB, only 75 km away. The dominant species of symbiont-hosting tubeworms and clams, and peripheral suspension-feeding taxa, differ between the sites. Notably, the PB vents host a limited and specialized fauna in which 17 of 26 species are unknown at other regional vents and many are new species. Rare sightings and captured larvae of the 'missing' species revealed that dispersal limitation is not responsible for differences in community composition at the neighbouring vent localities. Instead, larval recruitment-limiting habitat suitability probably favours species differentially. As scenarios develop to design conservation strategies around mining of seafloor sulfide deposits, these results illustrate that models encompassing habitat characteristics are needed to predict metacommunity structure