STONE 6: Artificial Sedimentary Meteorites in Space

The STONE 6 experiment demonstrated the survivability of carbonaceous and microfossiliferous martian analogue sediments during atmospheric re-entry. Doped endoliths died but their carbonised cells remained

Constraining Absolute Plate Motions Since the Triassic

The absolute motion of tectonic plates since Pangea can be derived from observations of hotspot trails, paleomagnetism, or seismic tomography. However, fitting observations is typically carried out in isolation without consideration for the fit to unused data or whether the resulting plate motions are geodynamically plausible. Through the joint evaluation of global hotspot track observations (for times <80 Ma), first‐order estimates of net lithospheric rotation (NLR), and parameter estimation for paleo–trench migration (TM), we present a suite of geodynamically consistent, data‐optimized global absolute reference frames from 220 Ma to the present. Each absolute plate motion (APM) model was evaluated against six published APM models, together incorporating the full range of primary data constraints. Model performance for published and new models was quantified through a standard statistical analyses using three key diagnostic global metrics: root‐mean square plate velocities, NLR characteristics, and TM behavior. Additionally, models were assessed for consistency with published global paleomagnetic data and for ages <80 Ma for predicted relative hotspot motion, track geometry, and time dependence. Optimized APM models demonstrated significantly improved global fit with geological and geophysical observations while performing consistently with geodynamic constraints. Critically, APM models derived by limiting average rates of NLR to ~0.05°/Myr and absolute TM velocities to ~27‐mm/year fit geological observations including hotspot tracks. This suggests that this range of NLR and TM estimates may be appropriate for Earth over the last 220 Myr, providing a key step toward the practical integration of numerical geodynamics into plate tectonic reconstructions

Protecting Clinical Trial Participants and Protecting Data Integrity: Are We Meeting the Challenges?

Susan Ellenberg discusses alternative approaches towards evaluating data as it accumulates in clinical trials, and to protecting the integrity and preventing undue risks to participants, as the trial continues

Community infrastructure and repository for marine magnetic identifications

Magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary data set from which the age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined. Although these identifications are an invaluable resource, their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize, host, and update these interpretations. We have developed an open-source, community-driven online infrastructure as a repository for quality-checked magnetic anomaly identifications from all ocean basins. We provide a global sample data set that comprises 96,733 individually picked magnetic anomaly identifications organized by ocean basin and publication reference, and provide accompanying Hellingerformat files, where available. Our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions, for both experts and nonexperts alike. To further enhance the existing repository and strengthen its value, we encourage others in the community to contribute to this effort

Deep lithospheric structures along the southern central Chile Margin from wide-angle P-wave modellilng

Crustal- and upper-mantle structures of the subduction zone in south central Chile, between 42 degrees S and 46 degrees S, are determined from seismic wide-angle reflection and refraction data, using the seismic ray tracing method to calculate minimum parameter models. Three profiles along differently aged segments of the subducting Nazca Plate were analysed in order to study subduction zone structure dependencies related to the age, that is, thermal state, of the incoming plate. The age of the oceanic crust at the trench ranges from 3 Ma on the southernmost profile, immediately north of the Chile triple junction, to 6.5 Ma old about 100 km to the north, and to 14.5 Ma old another 200 km further north, off the Island of Chiloe. Remarkable similarities appear in the structures of both the incoming as well as the overriding plate. The oceanic Nazca Plate is around 5 km thick, with a slightly increasing thickness northward, reflecting temperature changes at the time of crustal generation. The trench basin is about 2 km thick except in the south where the Chile Ridge is close to the deformation front and only a small, 800-m-thick trench infill could develop. In south central Chile, typically three quarters (1.5 km) of the trench sediments subduct below the decollement in the subduction channel. To the north and south of the study area, only about one quarter to one third of the sediments subducts, the rest is accreted above. Similarities in the overriding plate are the width of the active accretionary prism, 35-50 km, and a strong lateral crustal velocity gradient zone about 75-80 km landward from the deformation front, where landward upper-crustal velocities of over 5.0-5.4 km s&lt;SU-1&lt;/SU decrease seaward to around 4.5 km s&lt;SU-1&lt;/SU within about 10 km, which possibly represents a palaeo-backstop. This zone is also accompanied by strong intraplate seismicity. Differences in the subduction zone structures exist in the outer rise region, where the northern profile exhibits a clear bulge of uplifted oceanic lithosphere prior to subduction whereas the younger structures have a less developed outer rise. This plate bending is accompanied by strongly reduced rock velocities on the northern profile due to fracturing and possible hydration of the crust and upper mantle. The southern profiles do not exhibit such a strong alteration of the lithosphere, although this effect may be counteracted by plate cooling effects, which are reflected in increasing rock velocities away from the spreading centre. Overall there appears little influence of incoming plate age on the subduction zone structure which may explain why the M-w = 9.5 great Chile earthquake from 1960 ruptured through all these differing age segments. The rupture area, however, appears to coincide with a relatively thick subduction channel

The present-day number of tectonic plates

The number of tectonic plates on Earth described in the literature has expanded greatly since the start of the plate tectonic era, when only about a dozen plates were considered in global models of present-day plate motions. With new techniques of more accurate earthquake epicenter locations, modern ways of measuring ocean bathymetry using swath mapping, and the use of space based geodetic techniques, there has been a huge growth in the number of plates thought to exist. The study by Bird (2003) proposed 52 plates, many of which were delineated on the basis of earthquake locations. Because of the pattern of areas of these plates, he suggested that there should be more small plates than he could identify. In this paper, I gather together publications that have proposed a total of 107 new plates, giving 159 plates in all. The largest plate (Pacific) is about 20 % of the Earth's area or 104 Mm (super 2) , and the smallest of which (Plate number 5 from Hammond et al. 2011) is only 273 km (super 2) in area. Sorting the plates by size allows us to investigate how size varies as a function of order. There are several changes of slope in the plots of plate number organized by size against plate size order which are discussed. The sizes of the largest seven plates is constrained by the area of the Earth. A middle set of 73 plates down to an area of 97,563 km (super 2) (the Danakil plate at number 80, is the plate of median size) follows a fairly regular pattern of plate size as a function of plate number. For smaller plates, there is a break in the slope of the plate size/plate number plot and the next 32 plates follow a pattern of plate size proposed by the models of Koehn et al. (2008) down to an area of 11,638 km (super 2) (West Mojave plate # 112). Smaller plates do not follow any regular pattern of area as a function of plate number, probably because we have not sampled enough of these very small plates to reveal any clear pattern. Copyright 2016 The Author(s) and Harrison

Reporting of social deprivation in musculoskeletal trials: an analysis of 402 randomised controlled trials

Background: Social deprivation is broadly defined as the restriction of access an individual has to social or cultural interactions due to poverty, discrimination or other disadvantages. While social deprivation is a widely acknowledged determinant of outcome in musculoskeletal conditions, it remains unclear how this is considered in the conduct and interpretation of musculoskeletal trials.  Aim: To determine the frequently to which measures of social deprivation are reported in trials recruiting people with musculoskeletal diseases.  Materials and Methods: We conducted a Pubmed search of randomised controlled trials published between 01 January 2019 and 01 June 2020. We included full-text papers of trials recruiting people with musculoskeletal diseases, irrespective of intervention type or origin. We extracted data relating to trial characteristics, setting, trial design, funding source and musculoskeletal disease. We extracted data on any reported social deprivation index or measure of social deprivation based on internationally adopted indicators. We analysed data descriptively to summarise the reporting of each social deprivation index and measure of social deprivation within trials.  Results: From 2133 potentially eligible citations, 402 were eligible. Mean age of participants was 51.7 years; 63% were female. Trials most frequently recruited people with spinal pain (24.6%) or osteoarthritis (10.0%). Two trials (0.5%) reported social deprivation indices/scores. When assessed by discrete measures of social deprivation, 164 trials (40.8%) reported one or more social deprivation measures. The most commonly reported measures were morbidity (20.2%), employment status (17.7%) and educational attainment (15.5%). Race (6.7%), ethnicity (6.2%) and annual salary (1.3%) were infrequently reported. One trial (0.3%) presented subgroup results by social deprivation measures.  Discussion and Conclusion: Social deprivation is inconsistently reported in musculoskeletal trials. Trialists should report baseline measures of social deprivation in trial reports and aid generalisability to target population, and to examine whether social deprivation might modify treatment effects of interventions for musculoskeletal conditions

Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs

Mantle plumes are thought to play a key role in transferring heat from the core\u2013mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji\u2013Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH4VSV) with thermo-mechanical calculations

In-situ evidence for dextral active motion at the Arabia-India plate boundary

International audienceThe Arabia-India plate boundary--also called theOwen fracture zone--is perhaps the least-known boundary among large tectonic plates1-6. Although it was identified early on as an example of a transform fault converting the divergent motion along the Carlsberg Ridge to convergent motion in the Himalayas7, its structure and rate of motion remains poorly constrained. Here we present the first direct evidence for active dextral strike-slip motion along this fault, based on seafloor multibeam mapping of the Arabia-India-Somalia triple junction in the northwest Indian Ocean. There is evidence for 12km of apparent strike-slip motion along the mapped segment of the Owen fracture zone, which is terminated to the south by a 50-km-wide pull-apart basin bounded by active faults. By evaluating these new constraints within the context of geodetic models of global plate motions, we determine a robust angular velocity for the Arabian plate relative to the Indian plate that predicts 2-4mmyr−1 dextral motion along the Owen fracture zone. This transformfault was probably initiated around 8 million years ago in response to a regional reorganization of plate velocities and directions8-11, which induced a change in configuration of the triple junction. Infrequent earthquakes of magnitude 7 and greater may occur along the Arabia-India plate boundary, unless deformation is in the formof aseismic creep

Astrometry and geodesy with radio interferometry: experiments, models, results

Summarizes current status of radio interferometry at radio frequencies between Earth-based receivers, for astrometric and geodetic applications. Emphasizes theoretical models of VLBI observables that are required to extract results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the achievements of VLBI during the past two decades in reference frames, Earth orientation, atmospheric effects on microwave propagation, and relativity.Comment: 83 pages, 19 Postscript figures. To be published in Rev. Mod. Phys., Vol. 70, Oct. 199