Cratonic eclogite xenoliths - formation and evolution of the subcontinental lithospheric mantle

The most extensive evidence for the evolution of the primitive crust is preserved at the base of the continental roots (140 to 200 km depth). However, this is completely inaccessible and hard to evaluate, except through the study of mantle xenoliths brought to the surface by kimberlite magmas. Most mantle xenoliths undergo kimberlitic/carbonaceous metasomatism prior to their entrapment, altering their primary composition. Despite a very complex history and a very low abundance (180 nodules), sampled in four main localities from the Siberian (Obnazhennaya, Udachnaya) and South African (Jagersfontein, Roberts Victor) cratons. Major and trace element compositions have been analysed in representative bimineralic (garnet (gt)-omphacite (cpx)), coesite-, kyaniteand corundum-bearing eclogites. Metasomatized eclogites (Type I) have a higher alkali- (Na2O in garnet and K2O in omphacite) and LREE, LILE-content. Non-metasomatized (Type II) eclogites include two main compositional groups, derived from different protoliths. The first group (Type IIA) is typically more magnesian, enriched in LREE and has δ18O values from 3.73 to 7.50 ‰, with positive Sr anomalies and corresponding to a low pressure-temperature layer. The whole-rock composition is consistent with a basaltic protolith. The second group (Type IIB) is more sodic and aluminous, depleted in LREE and has δ18O values of 2.35 to 3.59 ‰, corresponding to equilibrium at high pressure and temperature. The whole-rock trace element composition is consistent with a pyroxenitic protolith. Eclogites that contain coesite, kyanite and corundum (coe-ky-cor) are typically characterized by jadeite-rich clinopyroxenes with positive Eu and Sr anomalies and grossular-rich garnets with corresponding positive Eu and negative Sr anomalies. Additionally, corundum-bearing samples are overall LREE-depleted. Pressure-temperature estimates indicate coe-ky-cor-bearing eclogites equilibrated in the lowermost part of the cratonic keel, and the reconstructed whole-rock trace element composition corresponds to a very depleted gabbroic protolith. Corundum-bearing eclogites often show topotactic exsolution textures hosted in omphacite, consisting of a more calcic garnet ± kyanite/zoisite. Based on Si, Al and Mg diffusion profiles it can be inferred that exsolution was controlled by chemical exchange in an isochemical system. Similarly, an interpretation can be made for the variable HREE fractionation of intermediate composition between the exsolutions and the host omphacite, as evidence for intermineral partitioning. The formation of zoisite (1.7 % H2O) from a precursor clinopyroxene requires a significant amount of hydrogen (as H+ , OH- or H2O) incorporated in omphacite at mantle conditions. Calculated water content of omphacite, based on Fourier transform infrared spectrometry (FTIR) analyses, varies from ~930—1410 to ~1100—1680 ppm by weight H2O, according to different absorption coefficients. Primary garnets are typically anhydrous (<7 ppm H2O), whereas coarse exsolutions contain between 165—1950 ppm H2O. Reconstructed estimates for whole-rock water content (~310—890 ppm H2O) for the Obnazhennaya eclogites are significantly higher than those of the surrounding peridotites. The variability of δ18O in garnet among 41 xenoliths, shows a bi-modal distribution with median values at 3.57 ‰ and 5.68 ‰ and strong correlation (r = 0.96) between garnet and omphacite. The δ18O values and the reconstructed whole-rock trace element compositions indicate an oceanic crustal protolith for mantle eclogite xenoliths. This is consistent with the subduction of a hydrothermally altered, basaltic to websteritic sequence of an incompatible-element-depleted oceanic crust. Furthermore, although eclogites represent a small fraction of the upper mantle, they may be an important water reservoir at the base of the cratonic root. High water content in the lithospheric mantle would have major consequences for the longevity of the cratonic keel, forphysical and chemical properties in minerals, partial melting, mantle rheology and electrical conductivity and the global water cycle

Xenolites éclogitiques cratoniques - Origine et évolution du manteau lithosphérique sous-continental

This study is based on the most complete existing collection of cratonic eclogites (> 180 nodules), from the Siberian and South African cratons. Non-metasomatized Type IIA eclogites are typically more magnesian, LREE-enriched, with δ18O values of 3.7-7.5 ‰, positive Sr anomalies and corresponding to a low pressure-temperature (PT) layer. The whole-rock composition is consistent with a basaltic protolith. Type IIB eclogites are morsodic and aluminous, LREE-depleted, with δ18O values of 2.3-3.6‰, corresponding to equilibrium at high-PT. The whole-rock trace element composition is consistent with a pyroxenitic protolith. Coesite, kyanite and corundum-bearing eclogites ypically have jadeite-rich clinopyroxenes witlpositive Eu and Sr anomalies and grossular-rich gamets with corresponding positive Eu and negative Sr anomalies. PT-estimates indicate coe-kycor-bearing eclogites equilibrated in the lowermost part of the cratonic keel and reconstructed whole-rock trace element composition corresponds to a very depleted gabbroic protolith. This is consistent with the subduction of a hydrothermally altered, basaltic to websteritic sequence of an incompatible-element-depleted oceanic crust.Calculated water content of omphacite is a minmum estima te of ~930-1410 ppm by weight H2O and reconstructed estimates for whole-rock watercontent ~310-890 ppm HO) for the Obnazhennaya eclogites are significantly higher than those of the surrounding peridotites. Thus, mantle eclogite may be an important water reservoir at the base of the cratonic root, with major consequences for cratonic keel, longevity mantle rheology and global water cvcleCette étude est basée sur la collection la plus complète d'éclogites cratoniques (> 180 nodules), provenant des cratons sibériens et sud-africains.Les éclogites non-métasomatisés de type IIA sont plus magnésiennes, enrichis en LREE, avec des valeurs de δ18O, de 3,7-7,5 ‰, des anomalies positives en Sr et correspondant à une couche à basse pression-température (PT). La composition de la roche totale est un protolithe basaltique. Les éclogites de type IIB sont plus sodiques et alumineux, appauvris en terres rares, avec des valeurs de δ18O de 2,3-3,6 ‰, correspondant à l'équilibre à haute PT. La composition de la roche totale correspond au protolithe pyroxénitique. Les éclogites à coésite, disthène ou corindon ont des clinopyroxènes riches en jadéite, avec des anomalies positives en Eu et Sr et des grenats riches en grossulaire, avec des anomalies positive en Eu et négatives en Sr. Les estimations de PT indiquent que les éclogites à co-ky-cor ont été équilibrées dans la partie la plus basse de la quille cratonique et la composition de la roche totale correspondant à un protolithe gabbroïque très appauvri, cohérente avec la subduction d'une séquence basaltique à websteritique d'une croûte océanique altérée, appauvrie en éléments incompatibles.L'estimation minimum d'eau dans l'omphacite d'Obnazhennaya est de ~930-1410 ppm d'H20 et pour la roche totale de ~310-890 ppm H2O, significativement supérieures aux péridotites environnantes. Ainsi, les éclogites du manteau peuvent être un important réservoir d'eau à la base de la racine cratonique, avec des conséquences majeures pour la longévité de la quille cratonique, la rhéologie du manteau et pour le cycle global de l'eau

Subduction relics in the subcontinental lithospheric mantle evidence from variation in the δ18O value of eclogite xenoliths from the Kaapvaal craton

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Subduction relics in the subcontinental lithospheric mantle evidence from variation in the δ18O value of eclogite xenoliths from the Kaapvaal craton

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Kyanite-bearing eclogite xenoliths from the Udachnaya kimberlite, Siberian craton, Russia

Xenoliths brought up by kimberlite magmas are rare samples of otherwise inaccessible lithospheric mantle. Eclogite xenoliths are found in most cratons and commonly show a range of mineral and chemical compositions that can be used to better understand craton formation. This study focuses on five new kyanite-bearing eclogites from the Udachnaya kimberlite pipe (367±5 Ma). They are fine-to coarse-grained and consist mainly of “cloudy” clinopyroxene (cpx) and garnet (grt). The clinopyroxene is Al,Na-rich omphacite while the garnet is Ca-rich, by contrast to typical bi-mineral (cpx+grt) eclogites that contain Fe- and Mg-rich garnets. The Udachnaya kyanite eclogites are similar in modal and major element composition to those from other cratons (Dharwar, Kaapvaal, Slave, West African). The kyanite eclogites have lower REE concentrations than bi-mineral eclogites and typically contain omphacites with positive Eu and Sr anomalies, i.e. a “ghost plagioclase signature”. Because such a signature can only be preserved in nonmetasomatised samples, we infer that they were present in the protoliths of the eclogites. It follows that subducted oceanic crust is present at the base of the Siberian craton. Similar compositions and textures are also seen in kyanite eclogites from other cratons, which we view as evidence for an Archean, subduction-like formation mechanism related to craton accretion. Thus, contrary to previous work that classifies all kyanite eclogites as type I (IK), metasomatized by carbonatite/kimberlitic fluids, we argue that some of them, both from this work and those from other cratons, belong to the non-metasomatized type II (IIB). The pristine type IIB is the nearest in composition to protoliths of mantle eclogites because it contains no metasomatic enrichments

Water in clinopyroxene from the 2021 Geldingadalir eruption of the Fagradalsfjall Fires, SW-Iceland

Water content plays a significant role in magma genesis, ascent rate, and, ultimately, in the style and intensity of volcanic eruptions, due to its control on the density, viscosity and melting behaviour of silicate melts. A reliable method for determining the pre-eruptive magmatic water content is to use phenocrysts of nominally anhydrous minerals (NAMs) which can preserve water as hydrogen configurations in structural defects. The advantage of this method is that eruptive changes such as water loss during magma degassing may be experimentally reconstructed and analysed by infrared spectroscopy. Applying this to clinopyroxene crystals (n=17) from lava samples (n=7) from April 2021 of the Geldingadalir eruption, SW-Iceland, reveals parental water contents of 0.69 ± 0.07 to 0.86 ± 0.09 wt. % H2O. These values are higher than those expected for typical mid-ocean ridge basalts (MORB 0.3–0.5 wt. % on average) indicating a significant plume (OIB) contribution to the magma source. Moreover, such water concentrations would imply that water saturation in the ascending Geldingadalir magmas was attained only at very shallow levels within the plumbing system. This could explain the at times pulsating behaviour within the uppermost conduit system as being the result of shallow episodic water vapour exsolution in addition to the deep-sourced CO2 flux

Archean subduction relics in the cratonic root – evidence from eclogite xenoliths

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Genetic Characterization of Dilated Cardiomyopathy in Romanian Adult Patients

Dilated cardiomyopathy (DCM) represents a group of disorders affecting the structure and function of the heart muscle, leading to a high risk of heart failure and sudden cardiac death (SCD). DCM frequently involves an underlying genetic etiology. Genetic testing is valuable for risk stratification, treatment decisions, and family screening. Romanian population data on the genetic etiology of DCM are lacking. We aimed to investigate the genetic causes for DCM among Romanian adult patients at tertiary referral centers across the country. Clinical and genetic investigations were performed on adult patients presenting to tertiary hospitals in Romania. The genetic investigations used next-generation sequencing panels of disease-associated DCM genes. A total of 122 patients with DCM underwent genetic testing. The mean age at DCM diagnosis was 41.6 ± 12.4 years. The genetic investigations identified pathogenic or likely pathogenic variants in 50.8% of participants, while 25.4% had variants of unknown significance. Disease-causing variants in 15 genes were identified in people with DCM, with 31 previously unreported variants. Variants in TTN, LMNA, and DSP explained 75% of genetic causes for DCM. In total, 52.4% of patients had a family history of DCM/SCD. Left ventricular ejection fraction of <35% was observed in 41.9% of patients with disease-causing variants and 55% with negative or uncertain findings. Further genotype-phenotype correlations were explored in this study population. The substantial percentage (50.8%) of disease-causing variants identified in patients with DCM acknowledges the importance of genetic investigations. This study highlights the genetic landscape in genes associated with DCM in the Romanian population

Evaluation of Disease Activity in Inflammatory Bowel Disease: Diagnostic Tools in the Assessment of Histological Healing

Inflammatory bowel disease (IBD) comprises two types of chronic intestinal disorders: Crohn’s disease and ulcerative colitis. In long-standing ulcerative colitis disease activity, histological persistent inflammation has been linked to an increased risk of relapse, and long-term corticosteroid use, even when endoscopic remission is reached. In Crohn’s disease, the discontinuous nature of lesions and transmural inflammation have limited the standardized histological assessment. The current evidence from research proposes that besides clinical and endoscopic healing, the achievement of histological healing constitutes an endpoint to assess disease activity and remission in IBD patients concerning better long-term disease outcomes. Histological alterations may persist even in the absence of endoscopic lesions. For these reasons, new advanced techniques promise to revolutionize the field of IBD by improving the endoscopic and histologic assessment, disease characterization, and ultimately patient care, with an established role in daily practice for objective assessment of lesions. This review outlines the importance of including microscopic evaluation in IBD, highlighting the clinical benefits of a deep state of disease remission using validated diagnostic methods and scoring systems for daily clinical practice