Mid-ocean-ridge rhyolite (MORR) eruptions on the East Pacific Rise lack the fizz to pop

Eruptions on the Alarcon Rise segment of the northern East Pacific Rise (23.55°N, 108.42°W) at 2500−2200 m below sea level (mbsl) produced the most compositionally diverse volcanic suite found along the submarine mid-ocean-ridge (MOR) system, offering an opportunity to compare mafic through silicic eruption styles at the same abyssal depth. Eruption styles that formed evolved volcanic rocks on the submarine MOR have not been studied in detail. The prevalence of lava flows along the MOR indicates that most eruptions are nonexplosive, but some volcaniclastic characteristics suggest that explosive styles also occur. Higher viscosities in intermediate (103–5 Pa·s) versus mafic (101 Pa·s) lavas on Alarcon Rise correspond with larger, more brecciated pillows, while highly viscous rhyolite lavas (106–7 Pa·s) formed rugged domes mostly composed of autoclastic breccia. Although high H2O contents (1.5–2.1 wt%), abundant volcaniclasts, and vesicularities up to 53% in rhyolite might imply eruption explosivity, limited fine-grained ash production and dispersal indicate an effusive origin. Higher viscosities of MOR rhyolite (MORR) magma and small eruption volumes, compared to MOR basalt (MORB), limit bubble coalescence and rapid magma ascent, two likely prerequisites for deep-marine eruption explosivity. This idea is supported by widespread dispersal of basaltic ash, but very limited production and dispersal of silicic ash on Alarcon Rise

Oceanic Zircon Records Extreme Fractional Crystallization of MORB to Rhyolite on the Alarcon Rise Mid-Ocean Ridge

The first known occurrence of rhyolite along the submarine segments of the mid-ocean ridge (MOR) system was discovered on Alarcon Rise, the northernmost segment of the East Pacific Rise (EPR), by the Monterey Bay Aquarium Research Institute in 2012. Zircon trace element and Hf and O isotope patterns indicate that the rhyolite formed by extreme crystal fractionation of primary mid-ocean ridge basalt (MORB) sourced from normal to enriched MOR mantle with little to no addition of continental lithosphere or hydrated oceanic crust. A large range in zircon ϵHf spanning 11 ϵ units is comparable to the range of whole rock ϵHf from the entire EPR. This variability is comparable to continental granitoids that develop over long periods of time from multiple sources. Zircon geochronology from Alarcon Rise suggests that at least 20 kyr was needed for rhyolite petrogenesis. Grain-scale textural discontinuities and trace element trends from zircon cores and rims are consistent with crystal fractionation from a MORB magma with possible perturbations associated with mixing or replenishment events. Comparison of whole rock and zircon oxygen isotopes with modeled fractionation and zircon-melt patterns suggests that, after they formed, rhyolite magmas entrained hydrated mafic crust from conduit walls during ascent and/or were hydrated by seawater in the vent during eruption. These data do not support a model where rhyolites formed directly from partial melts of hydrated oceanic crust or do they require assimilation of such crust during fractional crystallization, both models being commonly invoked for the formation of oceanic plagiogranites and dacites. A spatial association of highly evolved lavas (rhyolites) with an increased number of fault scarps on the northern Alarcon Rise might suggest that low magma flux for ∼20 kyr facilitated extended magma residence necessary to generate rhyolite from MORB

Geology of the Alarcon Rise, Southern Gulf of California

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

Geology of the Alarcon Rise, Southern Gulf of California

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

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

Repeat bathymetric surveys at 1-metre resolution of lava flows erupted at Axial Seamount in April 2011

At sites with frequent submarine volcanic activity, it is difficult to discern between new and pre-existing lava flows. In particular, the distribution of the fissures from which lava erupts, the routes taken by lava flows and the relationship between the new flows and the pre-existing seafloor bathymetry are often unclear. The volcanic and hydrothermal systems of Axial Seamount submarine volcano in the Pacific Ocean have been studied intensively since eruptions were detected in 1998 (refs 1, 2) and 2011 (ref. 3). Here we combine pre- and post-eruption bathymetric surveys³⁻⁸ with 1-m lateral resolution and 0.2-m vertical precision, to precisely map the extent and thickness of the lava flows, calculate the volume of lava and unambiguously identify eruptive fissures from the April 2011 eruption. Where the new lava flows extend beyond the boundaries of the repeated surveys, we use shipboard multibeam surveys to map the flows with lower resolution. We show that the eruption produced both sheet and lobate flows associated with high eruption rates and low-eruption-rate pillow mounds. We find that lava flows erupted from new as well as existing fissures and tended to reoccupy existing flow channels. This reoccupation makes it difficult to map submarine flows produced during one eruption without before-and-after bathymetric surveys.Keywords: tectonics and geodynamics, Volcanology, Structural geology, mineralogy and petrolog

Consistent phenological shifts in the making of a biodiversity hotspot: the Cape flora

Background The best documented survival responses of organisms to past climate change on short (glacial-interglacial) timescales are distributional shifts. Despite ample evidence on such timescales for local adaptations of populations at specific sites, the long-term impacts of such changes on evolutionary significant units in response to past climatic change have been little documented. Here we use phylogenies to reconstruct changes in distribution and flowering ecology of the Cape flora - South Africa's biodiversity hotspot - through a period of past (Neogene and Quaternary) changes in the seasonality of rainfall over a timescale of several million years. Results Forty-three distributional and phenological shifts consistent with past climatic change occur across the flora, and a comparable number of clades underwent adaptive changes in their flowering phenology (9 clades; half of the clades investigated) as underwent distributional shifts (12 clades; two thirds of the clades investigated). Of extant Cape angiosperm species, 14-41% have been contributed by lineages that show distributional shifts consistent with past climate change, yet a similar proportion (14-55%) arose from lineages that shifted flowering phenology. Conclusions Adaptive changes in ecology at the scale we uncover in the Cape and consistent with past climatic change have not been documented for other floras. Shifts in climate tolerance appear to have been more important in this flora than is currently appreciated, and lineages that underwent such shifts went on to contribute a high proportion of the flora's extant species diversity. That shifts in phenology, on an evolutionary timescale and on such a scale, have not yet been detected for other floras is likely a result of the method used; shifts in flowering phenology cannot be detected in the fossil record

Geologic history of the summit of Axial Seamount, Juan de Fuca Ridge

Multibeam (1 m resolution) and side scan data collected from an autonomous underwater vehicle, and lava samples, radiocarbon-dated sediment cores, and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on Axial Seamount’s summit and upper rift zones. The maps show 52 post-410 CE lava flows and 20 precaldera lava flows as old as 31.2 kyr, the inferred age of the caldera. Clastic deposits 1–2 m thick accumulated on the rims postcaldera. Between 31 ka and 410 CE, there are no known lava flows near the summit. The oldest postcaldera lava (410 CE) is a pillow cone SE of the caldera. Two flows erupted on the W rim between ~800 and 1000 CE. From 1220 to 1300 CE, generally small eruptions of plagioclase phyric, depleted, mafic lava occurred in the central caldera and on the east rim. Larger post-1400 CE eruptions produced inflated lobate flows of aphyric, less-depleted, and less mafic lava on the upper rift zones and in the N and S caldera. All caldera floor lava flows, and most uppermost rift zone flows, postdate 1220 CE. Activity shifted from the central caldera to the upper S rift outside the caldera, to the N rift and caldera floor, and then to the S caldera and uppermost S rift, where two historical eruptions occurred in 1998 and 2011. The average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions.Keywords: Lava flows, Juan de Fuca Ridge, Geologic, Mapping, Axial Seamoun

The Economic Benefits Resulting from the First 8 Years of the Global Programme to Eliminate Lymphatic Filariasis (2000–2007)

Lymphatic filariasis (LF), commonly known as ‘elephantiasis’, is one of the world's most debilitating infectious diseases. In 83 countries worldwide, more than 1.3 billion people are at risk of infection with an estimated 120 million individuals already infected. A recent publication reviewing the health impact of the first 8 years of the Global Programme to Eliminate Lymphatic Filariasis (GPELF) demonstrated the enormous health benefits achieved in populations receiving annual mass drug administration (MDA), as a result of infection prevented, disease progression halted, and ancillary treatment of co-infections. To date, however, no studies have estimated the economic value of these health benefits, either to the individuals or the societies afflicted with LF. Our study estimates that US$21.8 billion will be gained among individuals benefitting from just the first 8 years of the Global Programme, and an additional US$2.2 billion will be saved by the health systems of endemic countries. Treating endemic populations is possible at very low cost – particularly because of the generous drug donations from two pharmaceutical companies – but results in enormous economic benefits. Findings from this study yield a much clearer understanding the GPELF's full economic impact and strengthen the conviction that it is a ‘best buy’ in global health

Creatine Monohydrate and Conjugated Linoleic Acid Improve Strength and Body Composition Following Resistance Exercise in Older Adults

Aging is associated with lower muscle mass and an increase in body fat. We examined whether creatine monohydrate (CrM) and conjugated linoleic acid (CLA) could enhance strength gains and improve body composition (i.e., increase fat-free mass (FFM); decrease body fat) following resistance exercise training in older adults (>65 y). Men (N = 19) and women (N = 20) completed six months of resistance exercise training with CrM (5g/d)+CLA (6g/d) or placebo with randomized, double blind, allocation. Outcomes included: strength and muscular endurance, functional tasks, body composition (DEXA scan), blood tests (lipids, liver function, CK, glucose, systemic inflammation markers (IL-6, C-reactive protein)), urinary markers of compliance (creatine/creatinine), oxidative stress (8-OH-2dG, 8-isoP) and bone resorption (Ν-telopeptides). Exercise training improved all measurements of functional capacity (P<0.05) and strength (P<0.001), with greater improvement for the CrM+CLA group in most measurements of muscular endurance, isokinetic knee extension strength, FFM, and lower fat mass (P<0.05). Plasma creatinine (P<0.05), but not creatinine clearance, increased for CrM+CLA, with no changes in serum CK activity or liver function tests. Together, this data confirms that supervised resistance exercise training is safe and effective for increasing strength in older adults and that a combination of CrM and CLA can enhance some of the beneficial effects of training over a six-month period. Trial Registration. ClinicalTrials.gov NCT0047390