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Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea.

ABSTRACT: Volcanism is the surface expression of magma intrusion, crystallization, assimilation and hybridization processes operating throughout the crust over a range of time periods. Many magmas, including those erupted at subduction zones, have complex textures that reflect these processes. Here, we use textural and geochemical characteristics of calcic amphiboles to help identify multiple ingredients of subduction zone magmatism at Mt Lamington volcano, Papua New Guinea. Our approach uses existing trace element partitioning schemes to calculate the compositions of amphibole equilibrium melts (AEMs). The AEM compositions show that Mt Lamington andesites and plutonic enclaves are dominated by fractionation of amphibole?+?plagioclase?+?biotite, with assimilation of plagioclase and zircon. Magnesiohastingsite crystals in the andesite and diktytaxitic mafic enclaves reflect multiple episodes of recharge by more primitive, geochemically variable melts. The andesite also contains clots with rounded grains and melt on grain boundaries. These features indicate slow crystallization, and the retention of melt films could significantly enhance the potential for remobilization of crystals by infiltrating melts or during magma mixing. Variations in crystallization conditions could thus significantly affect the mush microstructure. We suggest that this could result in a significant bias of the volcanic record towards the preferential incorporation of more slowly cooled plutonic material from the lower crust or from more thermally mature plumbing systems. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

SUBMITTER: Humphreys MCS

PROVIDER: S-EPMC6335478 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea.

Humphreys M C S MCS Zhang J J Cooper G F GF Macpherson C G CG Ottley C J CJ

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 20190201 2139

Volcanism is the surface expression of magma intrusion, crystallization, assimilation and hybridization processes operating throughout the crust over a range of time periods. Many magmas, including those erupted at subduction zones, have complex textures that reflect these processes. Here, we use textural and geochemical characteristics of calcic amphiboles to help identify multiple ingredients of subduction zone magmatism at Mt Lamington volcano, Papua New Guinea. Our approach uses existing tra ...[more]

PMID: 30966932

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Project description:BackgroundSince 2004, the Global Fund-supported National Malaria Control Programme of Papua New Guinea (PNG) has been implementing country-wide free long-lasting insecticidal net (LLIN) distribution campaigns. In 2009, after the first distribution, only 32.5% of the population used a LLIN, mainly due to an insufficient number of nets available. This study investigated changes in mosquito net ownership and use following the continued free distribution of LLINs across PNG.MethodsFive villages from each province and 30 households from each village were randomly sampled in a country-wide household survey in 2010/11. A structured questionnaire administered to household heads recorded information on mosquito net ownership and use alongside household characteristics. Revised ownership and access indicators were applied in the analysis to reveal coverage gaps.ResultsThe survey covered 1,996 households in 77 villages. Ownership of at least one LLIN was reported by 81.8% of households, compared to 64.6% in 2009 (P?=?0.002). Sufficient LLINs to cover all household members (one net per two people) were found in 41.3% of the households (21.4% in 2009, P?<?0.001). Of all household members, 61.4% had access to a LLIN within their household (44.3% in 2009 P?=?0.002), and 48.3% slept under a LLIN (32.5% in 2009, P?=?0.001). LLIN use in children under five years amounted to 58.2%, compared to 39.5% in 2009 (P?<?0.001). Significant regional differences in coverage and changes over time were observed. A recent LLIN distribution was a key determinant of LLIN ownership (adj. OR?=?3.46) while families in high quality houses would frequently not own a LLIN (adj. OR?=?0.09). Residents were more likely to use LLINs than household guests (OR?=?2.04).ConclusionsRepeated LLIN distribution has led to significant increases in mosquito net ownership and use with few regional exceptions. Additional nets are required in areas where access is low, while major efforts are required to encourage the use of existing nets in region where access is high but use remains low. Complementary vector control approaches should also be considered in such settings.

Project description:BackgroundMale circumcision (MC) is a well-established component of HIV prevention in countries with high HIV prevalence and heterosexually driven epidemics. Delivery and monitoring of MC programs are reliant on good quality MC data. Such data are often generated through self-reported MC status surveys. This study examined self-reported MC status in comparison with genital photographs from men in Papua New Guinea (PNG).MethodsThis retrospective non-interventional study collated self-reported MC status data from the 'acceptability and feasibility of MC' study at 4 sites in PNG during 2010-2011. Participants reported their MC status based on an 8-category photographic classification covering the range of foreskin cutting practices in PNG. Genital photographs of 222 participants from this study were independently classified by 2 investigators. The 8-category photographic classification was simplified into a 3 category classification of 'no cut', 'straight cut' and 'round cut' before comparing for agreement between self-reporting and investigator assessment using Cohen's Kappa measure.ResultsUsing the 3-category classification, there was 90.6% (201/222) agreement between self-assessment and investigator classification (? value 0.805). Of the discordant 9.4% (21/222), 3.6% (8/222) self-classified as having a cut foreskin (5 straight cut; 3 round cut) while investigators classified as having no cut; 4.1% (9/222) self-classified as having no cut while investigators classified them as having had a cut (6 straight cut; 3 round cut) and 1.8% (4/222) self-classified as having a round cut while investigators classified as having a straight cut. Given the great variety of foreskin cutting practices and appearances, feasible explanations are suggested for two-thirds (13/21) of these discordant results.ConclusionsThis study demonstrates a high level of agreement between self-reporting and investigator assessment of MC status in PNG and suggests self-reporting of MC status to be highly reliable among men in PNG.

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Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea.

Publications

Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea.

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