5 research outputs found
The Origin of Iddingsite Veins in Olivine from the Nakhlite Meteorites:New Insights from Analogy with CM Carbonaceous Chondrites and Terrestrial Basalts
The nakhlite meteorites are samples
of a ~1300 million year old martian clinopyroxenite
lava flow or sill [1, 2]. These rocks contain secondary
minerals including hydrous silicates, carbonates, sulphates
and Fe-(hydr)oxides that formed by watermediated
alteration of the igneous body [3, 4]. A prerequisite
for understanding the nature of the aqueous
system from which these minerals formed, including
water/rock ratio, the provenance of solutes and its longevity,
is knowing whether the secondary minerals
formed by replacement of primary igneous components
(minerals and glasses), or by cementation of pores that
were opened by fracturing. A replacive origin would
suggest low water/rock ratios with solutions being
close to saturation with respect to secondary minerals,
and does not require a pre-existing network of pores
for fluids to gain access to mineral grain interiors. An
origin by cementation would suggest that solutes had
been sourced by dissolution of other parts of the
nakhlite parent rock or the martian crust and were introduced
by fluid flow under relatively high water/rock
ratio conditions; a means of fracturing the rock is also
required.<p></p>
Here we have sought to answer the question of
whether olivine-hosted veins in the nakhlites formed by
cementation or replacement by comparing the microstructures
of veins in the nakhlite Lafayette with veins
in olivine grains from type I chondrules in Murchison
(CM2 carbonaceous chondrite). We also draw on previously
published work on ‘iddingsite’ veins in olivine
from terrestrial basalts.<p></p>
Martian Igneous Activity and Fluid-Based Alteration:Chronological Constraints from 40Ar/39Ar Analyses of the Nakhlites
The nakhlites are a group of mafic
igneous rocks that crystallized on Mars at ca. 1.3-1.4
Ga [1-5]. They are amongst the least shocked Martian
meteorites, with cumulate igneous textures (Fig. 1) and
thus provide a crucial record of igneous activity and
fluid-rock interaction on the red planet.
Crystallization of the nakhlites. Understanding the
original structure of the nakhlite source is crucial for
using these stones to explore Martian igneous processes.
In particular, are the different nakhlites from a single
thick and differentiated lava flow/sill [6; 7], or do
they instead represent magmatically related – but distinct
– flows/intrusions? If the various meteorites are
derived from separate units, then there will be differences
in crystallization ages within the nakhlite suite –
which may be identified if these differences are sufficiently
large relative to the attainable precision of radioisotopic
dating techniques. Some studies [e.g., 5] appear
to resolve age differences between different
stones, and we aim to test the single vs. multiple unit
hypotheses via application of detailed 40Ar/39Ar stepheating
of six nakhlites.<p></p>
Alteration of the nakhlites, and the timing of waterrock
interaction. In addition to primary magmatic
minerals and glasses, the nakhlites contain secondary
minerals including clays and carbonates that were precipitated
by Martian aqueous fluids prior to impact
ejection (Fig. 2) [8-10]. When did this alteration occur?
As the clays contain potassium, they are amenable
to K-Ar and 40Ar/39Ar dating. K-Ar data from Lafayette
suggests the alteration phases formed between 0
to 670 Ma [11]. We consider further the timing of alteration
using our 40Ar/39Ar data.<p></p>
Global matrix 2.0:Report card grades on the physical activity of children and youth comparing 38 countries
The Active Healthy Kids Global Alliance organized the concurrent preparation of Report Cards on the physical activity of children and youth in 38 countries from 6 continents (representing 60% of the world's population). Nine common indicators were used (Overall Physical Activity, Organized Sport Participation, Active Play, Active Transportation, Sedentary Behavior, Family and Peers, School, Community and the Built Environment, and Government Strategies and Investments), and all Report Cards were generated through a harmonized development process and a standardized grading framework (from A = excellent, to F = failing). The 38 Report Cards were presented at the International Congress on Physical Activity and Public Health in Bangkok, Thailand on November 16, 2016. The consolidated findings are summarized in the form of a Global Matrix demonstrating substantial variation in grades both within and across countries. Countries that lead in certain indicators often lag in others. Average grades for both Overall Physical Activity and Sedentary Behavior around the world are D (low/poor). In contrast, the average grade for indicators related to supports for physical activity was C. Lower-income countries generally had better grades on Overall Physical Activity, Active Transportation, and Sedentary Behaviors compared with higher-income countries, yet worse grades for supports from Family and Peers, Community and the Built Environment, and Government Strategies and Investments. Average grades for all indicators combined were highest (best) in Denmark, Slovenia, and the Netherlands. Many surveillance and research gaps were apparent, especially for the Active Play and Family and Peers indicators. International cooperation and cross-fertilization is encouraged to address existing challenges, understand underlying determinants, conceive innovative solutions, and mitigate the global childhood inactivity crisis. The paradox of higher physical activity and lower sedentary behavior in countries reporting poorer infrastructure, and lower physical activity and higher sedentary behavior in countries reporting better infrastructure, suggests that autonomy to play, travel, or chore requirements and/or fewer attractive sedentary pursuits, rather than infrastructure and structured activities, may facilitate higher levels of physical activity.</p
Global matrix 2.0:Report card grades on the physical activity of children and youth comparing 38 countries
The Active Healthy Kids Global Alliance organized the concurrent preparation of Report Cards on the physical activity of children and youth in 38 countries from 6 continents (representing 60% of the world's population). Nine common indicators were used (Overall Physical Activity, Organized Sport Participation, Active Play, Active Transportation, Sedentary Behavior, Family and Peers, School, Community and the Built Environment, and Government Strategies and Investments), and all Report Cards were generated through a harmonized development process and a standardized grading framework (from A = excellent, to F = failing). The 38 Report Cards were presented at the International Congress on Physical Activity and Public Health in Bangkok, Thailand on November 16, 2016. The consolidated findings are summarized in the form of a Global Matrix demonstrating substantial variation in grades both within and across countries. Countries that lead in certain indicators often lag in others. Average grades for both Overall Physical Activity and Sedentary Behavior around the world are D (low/poor). In contrast, the average grade for indicators related to supports for physical activity was C. Lower-income countries generally had better grades on Overall Physical Activity, Active Transportation, and Sedentary Behaviors compared with higher-income countries, yet worse grades for supports from Family and Peers, Community and the Built Environment, and Government Strategies and Investments. Average grades for all indicators combined were highest (best) in Denmark, Slovenia, and the Netherlands. Many surveillance and research gaps were apparent, especially for the Active Play and Family and Peers indicators. International cooperation and cross-fertilization is encouraged to address existing challenges, understand underlying determinants, conceive innovative solutions, and mitigate the global childhood inactivity crisis. The paradox of higher physical activity and lower sedentary behavior in countries reporting poorer infrastructure, and lower physical activity and higher sedentary behavior in countries reporting better infrastructure, suggests that autonomy to play, travel, or chore requirements and/or fewer attractive sedentary pursuits, rather than infrastructure and structured activities, may facilitate higher levels of physical activity.</p
Top 10 International Priorities for Physical Fitness Research and Surveillance Among Children and Adolescents: A Twin-Panel Delphi Study.
The measurement of physical fitness has a history that dates back nearly 200 years. Recently, there has been an increase in international research and surveillance on physical fitness creating a need for setting international priorities that could help guide future efforts. This study aimed to produce a list of the top 10 international priorities for research and surveillance on physical fitness among children and adolescents. Using a twin-panel Delphi method, two independent panels consisting of 46 international experts were identified (panel 1 = 28, panel 2 = 18). The panel participants were asked to list up to five priorities for research or surveillance (round 1), and then rated the items from their own panel on a 5-point Likert scale of importance (round 2). In round 3, experts were asked to rate the priorities identified by the other panel. There was strong between-panel agreement (panel 1: r  = 0.76, p < 0.01; panel 2: r  = 0.77, p < 0.01) in the priorities identified. The list of the final top 10 priorities included (i) "conduct longitudinal studies to assess changes in fitness and associations with health". This was followed by (ii) "use fitness surveillance to inform decision making", and (iii) "implement regular and consistent international/national fitness surveys using common measures". The priorities identified in this study provide guidance for future international collaborations and research efforts on the physical fitness of children and adolescents over the next decade and beyond. [Abstract copyright: © 2022. Crown.