La Yeguada volcanic vomplex in the Republic of Panama: An assessment of the geologic hazards using 40Ar/39Ar geochronology

La Yeguada volcanic complex is one of three Quaternary volcanic centers in Panama. To assess potential geologic hazards, new samples were analyzed using argon analysis (40Ar/39Ar), and obtained the following: the most recent eruption occurred approximately 32,000 years ago at the Media Luna cinder cone; the youngest dated eruption from the main dome complex occurred 357 ± 19 ka, producing the Castillo dome unit; Cerro Picacho, a separate dacite dome 1.5 km east of the main complex is 4.47 ± 0.23 Ma; and the El Satro Pyroclastic Flow unit surrounds the northern portion of the volcanic complex is 11.26 ± 0.17 Ma. No Holocene (10,000 years ago to present) activity is recorded at the La Yeguada volcanic complex and therefore, it is unlikely to produce another eruption. The main geologic hazard at the La Yeguada volcanic complex is from landslides coming off the many steep slopes

Temporal evolution of long-lived magmatic systems: the Chachani volcano complex, south of Perù

The Chachani Volcanic Complex (CVC) is an extensive (~289±10 km3) assemblage of spatially, temporally and genetically related major and minor eruptive centers. The c. 1.2 Myr-long activity suggests that the CVC is a long-lived volcanic system characterized by semi-persistent activity and short periods of quiescence. The stratigraphy, Ar/Ar and U/Pb chronology, spatial distribution along lineaments, and the degree of landform preservation help distinguish two groups of edifices in the CVC. The ‘old’ edifice group is characterized by large stratovolcanoes and small dome coulees. This group has been built between

Cardiorespiratory Fitness Diminishes the Effects of Age on White Matter Hyperintensity Volume

White matter hyperintensities (WMHs) are among the most commonly observed marker of cerebrovascular disease. Age is a key risk factor for WMH development. Cardiorespiratory fitness (CRF) is associated with increased vessel compliance, but it remains unknown if high CRF affects WMH volume. This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 (mean age = 65.36 years, SD = 3.92) who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume (beta = .32, p = .015). However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants (beta = -.25, p = .040). Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults

Correlation of ignimbrites using characteristic remanent magnetization and anisotropy of magnetic susceptibility, Central Andes, Bolivia

Large ignimbrite flare-ups provide records of profound crustal modification during batholith formation at depth. The locations of source calderas and volumes and ages of the eruptions must be determined to develop models for the tectonomagmatic processes that occur during these events. Although high-precision isotopic ages of the ignimbrites are critical, less expensive and more rapid techniques, such as paleomagnetism, can extend the temporal information from dated outcrops. Paleomagnetic and rock magnetic data, including characteristic remanent magnetization (ChRM) and anisotropy of magnetic susceptibility (AMS), from the Altiplano-Puna Volcanic Complex of the Central Andes reliably identify calderas and eight associated Mio-Pliocene ignimbrites. ChRM results indicate a larger between-site error for most ignimbrites, in comparison to within-site scatter. Part of this dispersion may be due to tumescence/detumescence associated with the caldera-forming eruptions, but most of the effect is probably due to the recording of paleosecular variation during cooling and vapor-phase crystallization of the thick ignimbrites. AMS data identify the source calderas for four ignimbrites and provide limits on possible post-emplacement rotations of the deposits. AMS data indicate significant topographic control on inferred flow directions, implying that the flows were dense and/or of low mobility

Evolution of a long-lived volcanic complex: the Chachani case study (south Peru)

The study of numerous individual volcanoes carried out in the Central Andean Volcanic Zone over the past 20 years has provided information to better understand active volcanism in the Peruvian Andes. However, large-sized, dormant volcanic complexes remain much less understood due to their complexity or because the impact of individual active volcanoes on populated areas has led researchers to prioritize their study on the most recent composite cones. Large, long-lived volcanic complexes have not yet been considered in volcanological studies in Peru, although they belie a rich history of eruptive activity that may be more recent than previously thought. The Chachani Volcanic Complex (CVC) is one of the few Andean volcanic complexes in which the relationships between stratigraphy, chronology and compositional changes are considered to understand the compositional evolution of a long-lived magmatic system

Cronoestratigrafía del volcanismo con énfasis en ignimbritas desde hace 25 Ma en el SO del Perú – Implicaciones para la evolución de los Andes centrales

El sur del Perú representa el segundo campo ignimbrítico de los Andes con un área que sobrepasa los 25 000 km2 y volúmenes de casi 5000 km3. Se prresenta la extensión, la estratigrafía y la cronología de 12 ignimbritas que afloran en el área de los cañones profundos de los Ríos Ocoña–Cotahuasi–Marán y Colca (OCMC). La cronología de las ignimbritas a lo largo de los últimos 25 Myr está basada en 74 dataciones 40Ar/39Ar and U/Pb. Antes de 9 Ma, ocho ignimbritas con gran volumen fueron producidas cada 2.4 Myr. Después de 9 Ma, el periodo de reposo entre cada ignimbrita de volumen pequeño a moderado ha disminuido hasta 0.85 Myr. Esta cronología de las ignimbritas y de las lavas del Neógeno y Cuaternario ayuda a revisar la nomenclatura de las formaciones volcánicas utilizadas para la Carta Geológica Nacional. Además las unidades volcánicas identificadas son herramientas para reconstruir la evolución geológica del flanco occidental de los Andes Centrales durante su levantamiento desde hace 25 Ma. Junto con la cronoestratigrafía de estas unidades, datos geomorfológicos obtenidos en las cuencas y sobre otros depósitos de los cañones OCMC ayudan a precisar la historia de la incisión del flanco occidental de los Andes Centrales desde hace 25 Ma. Finalmente la cronología de depósitos de avalancha de escombros y de terrazas rocosas basada en cosmogénicos (Be10) permite precisar la evolución de los cañones durante el Pleistoceno y el Holoceno

Enlarged Perivascular Spaces are Negatively Associated with Montreal Cognitive Assessment Scores in Older Adults

Emerging evidence suggests that enlarged perivascular spaces (ePVS) may be a clinically significant neuroimaging marker of global cognitive function related to cerebral small vessel disease (cSVD). We tested this possibility by assessing the relationship between ePVS and both a standardized measure of global cognitive function, the Montreal Cognitive Assessment (MoCA), and an established marker of cSVD, white matter hyperintensity volume (WMH) volume. One hundred and eleven community-dwelling older adults (56–86) underwent neuroimaging and MoCA testing. Quantification of region-specific ePVS burden was performed using a previously validated visual rating method and WMH volumes were computed using the standard ADNI pipeline. Separate linear regression models were run with ePVS as a predictor of MoCA scores and whole brain WMH volume. Results indicated a negative association between MoCA scores and both total ePVS counts (P ≤ 0.001) and centrum semiovale ePVS counts (P ≤ 0.001), after controlling for other relevant cSVD variables. Further, WMH volumes were positively associated with total ePVS (P = 0.010), basal ganglia ePVS (P ≤ 0.001), and centrum semiovale ePVS (P = 0.027). Our results suggest that ePVS burden, particularly in the centrum semiovale, may be a clinically significant neuroimaging marker of global cognitive dysfunction related to cSVD

Astronomical and Tectonic Influences on Climate and Deposition Revealed Through Radioisotopic Geochronology and Bayesian Age-Depth Modeling of the Early Eocene Green River Formation, Wyoming, USA

The Wilkins Peak Member (WPM) of the Green River Formation in Wyoming, USA, comprises alternating lacustrine and alluvial strata that preserve a record of terrestrial climate during the early Eocene climatic optimum. We use a Bayesian framework to develop age-depth models for three sites, based on new 40Ar/39Ar sanidine and 206Pb/238U zircon ages from seven tuffs. The new models provide two- to ten-fold increases in temporal resolution compared to previous radioisotopic age models, confirming eccentricity-scale pacing of WPM facies, and permitting their direct comparison to astronomical solutions. Starting at ca. 51 Ma, the median ages for basin-wide flooding surfaces atop six successive alluvial marker beds coincide with short eccentricity maxima in the astronomical solutions. These eccentricity maxima have been associated with hyperthermal events recorded in marine strata during the early Eocene. WPM strata older than ca. 51 Ma do not exhibit a clear relationship to the eccentricity solutions, but accumulated 31%–35% more rapidly, suggesting that the influence of astronomical forcing on sedimentation was modulated by basin tectonics. Additional high-precision radioisotopic ages are needed to reduce the uncertainty of the Bayesian model, but this approach shows promise for unambiguous evaluation of the phase relationship between alluvial marker beds and theoretical eccentricity solutions

Water Exchange Rate across the Blood-Brain Barrier Is Associated with CSF Amyloid-β 42 in Healthy Older Adults

INTRODUCTION: We tested if water exchange across the blood-brain barrier (BBB), estimated with a noninvasive magnetic resonance imaging (MRI) technique, is associated with cerebrospinal fluid (CSF) biomarkers of Alzheimer\u27s disease (AD) and neuropsychological function. METHODS: Forty cognitively normal older adults (67–86 years old) were scanned with diffusion‐prepared, arterial spin labeling (DP‐ASL), which estimates water exchange rate across the BBB (kw). Participants also underwent CSF draw and neuropsychological testing. Multiple linear regression models were run with kw as a predictor of CSF concentrations and neuropsychological scores. RESULTS: In multiple brain regions, BBB kw was positively associated with CSF amyloid beta (Aβ)42 concentration levels. BBB kw was only moderately associated with neuropsychological performance. DISCUSSION: Our results suggest that low water exchange rate across the BBB is associated with low CSF Aβ42 concentration. These findings suggest that kw may be a promising noninvasive indicator of BBB Aβ clearance functions, a possibility which should be further tested in future research

Frontal White Matter Integrity in Adults with Down Syndrome with and without Dementia

Adults with Down syndrome (DS) are at high risk for developing Alzheimer\u27s disease after the age of 40 years. To detect white matter (WM) changes in the brain linked to dementia, fractional anisotropy (FA) from diffusion tensor imaging was used. We hypothesized that adults with DS without dementia (DS n = 10), DS with dementia (DSAD n = 10) and age matched non-DS subjects (CTL n = 10) would show differential levels of FA and an association with scores from the Brief Praxis Test and the Severe Impairment Battery. WM integrity differences in DS compared with CTL were found predominantly in the frontal lobes. Across all DS adults, poorer Brief Praxis Test performance correlated with reduced FA in the corpus callosum as well as several association tracts, primarily within frontoparietal regions. Our results demonstrate significantly lower WM integrity in DS compared with controls, particularly in the frontal tracts. DS-related WM integrity reductions in a number of tracts were associated with poorer cognition. These preliminary results suggest that late myelinating frontal pathways may be vulnerable to aging in DS