Estimate of confidence in paleomagnetic directions derived from mixed remagnetization circle and direct observational data

A method is presented for obtaining the direction and confidence oval for a paleomagnetic component at a site given a number of independently oriented samples, some of which give an estimate of the remanence direction, while others yield only remagnetization circles. Such mixed remagnetization circle-remanence direction data frequently characterise paleomagnetic sites carrying two remanence components where the component of interest is small and less dispersed compared to a more easily removed one. The method described maximises the amount of usable data per site and thus leads to an improved site direction estimate.           ARK: https://n2t.net/ark:/88439/y000446 Permalink: https://geophysicsjournal.com/article/149 &nbsp

Paleomagnetism and U-Pb geochronology of easterly trending dykes in the Dharwar craton, India: feldspar clouding, radiating dyke swarms and the position of India at 2.37 Ga

A U-Pb baddeleyite age of 2367 ± 1 Ma from a diabase dyke together with previously published age data, suggests that a major early Proterozoic dyke swarm cuts across the structural grain of the Archean Dharwar craton in India. Paleomagnetic data suggest the swarm is at least 300 km wide and 300 km long and has a fan angle of at least 30° with convergence to the west. It was originally emplaced at high latitudes, and together with the Widgiemooltha dykes of the Yilgarn block of Australia, may have been a segment of a larger radiating swarm related to a long-lived plume event that was active for about 50 My from 2418 to 2367 Ma. A regional change in the intensity of brown feldspar clouding in the dykes suggests that the Dharwar craton was tilted northwards, in harmony with previous observations on the structure and metamorphism of the Archean rocks. Towards the south the brown feldspar clouding becomes more intense and locally assumes a blacker, more "sooty" appearance. The black clouding, whose precise origins remain unknown, is accompanied by a remagnetization and appears to coincide closely with a region of carbonatite magmatism at ˜800 Ma, and with a shear zone and change in structural trend related to Pan-African deformation at ˜550 Ma. Paleomagnetic studies suggest that (i) the high coercivity part of the remanent magnetization is carried by magnetite exsolved within either brown or black clouded feldspars and (ii) as a more general observation, diabase with brown clouded feldspar can carry a primary magnetization but not if the clouding is black

Three-body non-additive forces between spin-polarized alkali atoms

Three-body non-additive forces in systems of three spin-polarized alkali atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio calculations. The non-additive forces are found to be large, especially near the equilateral equilibrium geometries. For Li, they increase the three-atom potential well depth by a factor of 4 and reduce the equilibrium interatomic distance by 0.9 A. The non-additive forces originate principally from chemical bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Quaternary tephra from the Valles caldera in the volcanic field of the Jemez Mountains of New Mexico identified in western Canada

A fine-grained, up to 3-m-thick tephra bed in southwestern Saskatchewan, herein named Duncairn tephra (Dt), is derived from an early Pleistocene eruption in the Jemez Mountains volcanic field of New Mexico, requiring a trajectory of northward tephra dispersal of 3c1500 km. An unusually low CaO content in its glass shards denies a source in the closer Yellowstone and Heise volcanic fields, whereas a Pleistocene tephra bed (LSMt) in the La Sal Mountains of Utah has a very similar glass chemistry to that of the Dt, supporting a more southerly source. Comprehensive characterization of these two distal tephra beds along with samples collected near the Valles caldera in New Mexico, including grain size, mineral assemblage, major-and trace-element composition of glass and minerals, paleomagnetism, and fission-track dating, justify this correlation. Two glass populations each exist in the Dt and LSMt. The proximal correlative of Dt1 is the plinian Tsankawi Pumice and co-ignimbritic ash of the first ignimbrite (Qbt1g) of the 1.24 Ma Tshirege Member of the Bandelier Tuff. The correlative of Dt2 and LSMt is the co-ignimbritic ash of Qbt2. Mixing of Dt1 and Dt2 probably occurred during northward transport in a jet stream