Concordant paleomagnetic directions from the Tehuantepec Isthmus: Constraints on the Neogene evolution of the North American-Caribbean plate boundary

We report paleomagnetic data for Miocene igneous rocks of the southeastern Tehuantepec Isthmus region, Mexico. Thermal and alternating field demagnetization reveal predominantly normal polarity magnetization, interpreted as primary TRM. The overall mean direction (Dec = 355.6[deg], Inc = 36.5[deg], K = 36.4, a95 = 9.3[deg], N = 8 sites) is statistically indistinguishable from the expected direction, calculated using the North American reference pole. This result indicates that significant rotation or displacement of the Tehuantepec region relative to the craton has not occurred since 13 Ma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31328/1/0000237.pd

Palaeomagnetism and magnetostiatigraphy of Triassic strata in the Sangre de Cristo Mountains and Tucumcari Basin, New Mexico, USA

We report palaeomagnetic data and a composite magnetic polarity sequence for Middle and Upper Triassic rocks assigned to the Anton Chico Member of the Moenkopi Formation and Chinle Group, respectively, exposed along the eastern flank of the Sangre de Cristo Mountains and in the Tucumcari Basin of eastern and northeastern New Mexico. Thermal demagnetization isolates a well-defined, dual polarity, characteristic magnetization, carried in most cases by haematite and interpreted as an early acquired chemical remanent magnetization (CRM). Characteristic magnetizations from 74 palaeomagnetic sites (one site = one bed) are used to define a magnetic polarity sequence, which we correlate with previously published Triassic data obtained from both marine and non-marine rocks. Preliminary correlation suggests that the resolution of magnetostratigraphic data derived from continental strata is not necessarily of lesser quality than that from marine rocks. On the basis of the magnetostratigraphic data, a profound unconformity is believed to separate lower-middle Norian and upper Norian-Rhaetian strata of the Chinle Group. Palaeomagnetic poles derived from selected sites in steeply dipping (> 85°) strata for the Middle Triassic (Anisian, ∼240 Ma: 50°N 121°E; N = 8), late Carman-early Norian (∼225 Ma: 53°N 104°E; N = 16), and late Norian-Rhaetian (∼208 Ma: 59°N 77°E; N = 8) are in relatively good agreement with previously published data for the Moenkopi Formation and Chinle Group and related strata in southwest North America. None the less, comparison with palaeomagnetic poles obtained from gently dipping or flat-lying Triassic strata from this study (Anisian, 46°N 112°E; N = 13; late Carnian, 54°N 87°E; N =12) and previously published Triassic poles in southwest North America suggest that a modest ‘apparent rotation’ not greater than about 5° affects declinations from steeply dipping rocks. The distribution of palaeomagnetic poles indicates ∼25° (angular distance) of apparent polar wander between about 240 and 208 Ma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73972/1/j.1365-246X.1996.tb05646.x.pd

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

Propiedades magnéticas y petrofábrica de unidades volcánicas terciarias de Ia región de Arandas-Atotonilco, Jalisco, México

Se reportan los resultados de un estudio combinado de paleomagnetismo, propiedades magnéticas, observaciones con microscopio óptico en laminas delgadas y superficies pulidas, microscopio electrónico de barrido (SEM) y anisotropia de susceptibilidad magnética (ASM) en varias unidades volcánicas de la región de Arandas-Atotonilco, Los Altos de Jalisco, México. La mineralogía magnética y estados de dominio se estiman de las mediciones de susceptibilidad magnética, dirección e intensidad de la magnetización remanente natural (NRM), coeficientes Q, espectros de coercitividades y de temperaturas de bloqueo, curvas termomagnéticas (temperaturas de Curie), variación de la susceptibilidad en función de bajas temperaturas (temperatura de nitrógeno líquido ), curvas de magnetización isotermal (lRM), desmagnetización por campos alternos (CA) de la IRM de saturación, curvas de magnetización remanente anhisteretica (ARM), es magnetización por CA de la ARM de saturación, pruebas de Lowrie-Fuller de estado de dominio magnético y pruebas de magnetización remanente viscosa. Las características de flujo y petrofábrica se determinan a partir de los datos de ASM. Las direcciones de flujo estimadas de observaciones de campo correlacionan con las direcciones de los ejes de susceptibilidad mínimos. Las intensidades de magnetización de cada sitio y de todos los sitios siguen una distribución logarítmico normal. En general, la mineralogía magnética y los estados de dominio son de naturaleza compleja en los diferentes flujos. Las diferencias y similitudes en y entre las varias unidades se discuten en términos de los parámetros magnéticos e indicadores de estado de dominio. Los experimentos de determinación de paleointensidades se discuten en términos de los datos sobre estado de dominio, en particular en referenda a los datos de temperaturas de Curie, espectro de temperaturas de bloqueo y variación de la susceptibilidad con bajas temperaturas

Large-scale rotations of the Chortis Block (Honduras) at the southern termination of the Laramide flat slab

Paleogeographic reconstructions place the Chortis block adjacent to southern Mexico in the Late Cretaceous and earlier time, forming the tectonically disturbed southwestern tip of the North American plate. This study assesses the relative motion between Chortis and North America during the Laramide orogeny, later development of the North America-Caribbean plate boundaries. We carried out paleomagnetic analysis of rotations and latitudinal displacement using a total of 90 sites from the Átima Limestone and the Valle de Ángeles Formation redbeds sampled at seven localities in Honduras. Two secondary but ancient magnetizations post-date Late Cretaceous folding at most localities. The oldest magnetization is a ChRM of high laboratory unblocking temperature in the redbeds (> 650 °C), and a moderate temperature in the limestones (500–600 °C). This component is WNW directed at five localities, varying somewhat in declination, having a consistent moderate positive inclination (mean I = 39.7°; α95 = 6.8°, n = 53 sites). The age of the ChRM is bracketed between 85 and 63 Ma, based on youngest zircon age and the age of a cross-cutting dike. An intermediate unblocking temperature component present in both units (Dec = 146.2°, Inc = − 28.5°; k = 13.1, α95 = 6.8°, n = 37 sites), is interpreted as an overprint. The ChRM indicates an average counterclockwise rotation of 55.4 ± 5.7°, with respect to the expected direction. The younger overprint was acquired between ~ 50 and 15 Ma; its mean is also discordant with the expected North America direction, implying some Neogene rotation of Chortis. Abundant late Albian-Turonian zircons in Valle de Ángeles redbeds explicitly require extending the Laramide arc along western Mexico into Chortis. A reconstruction of Chortis south of Mexico that takes into account 55 degrees of rotation shows a gap between both continental blocks at about 70 Ma. We propose a model where this gap formed by back-arc extension creating the Late Cretaceous Chontal basin at the southern termination of the Laramide flat-slab

Paleomagnetism of the Acatlan terrane, southern Mexico: evidence for terrane rotation

232 drill samples were collected from 33 sites from the Acatlan Terrane, southern Mexico. The medium-grade metamorphosed basement rocks (schists, granitoid, greenstones) showed magnetic directions that are randomly distributed and no meaningful results could be obtained. However, late Paleozoic red beds, the Ordovician (?) Totoltepec Granite and the early Paleozoic (?) Tecomate Limestone (metamorphosed in Acadian times) give coherent paleomagnetic directions. The samples responded well to thermal demagnetization but not to alternating field demagnetization. The ages of the magnetizations are reasonably bracketed between Carboniferous and Jurassic. Compared with data from the North American craton and from the Oaxaca terrane, conclusive evidence for major north-south displacements of the Acatlan terrane is not present, but significant clockwise rotations of the terrane with respect to the craton and the adjacent Oaxaca terrane are quite evident. These rotations occurred during the Jurassic or Early Cretaceous.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27809/1/0000214.pd