Navegando por Autor "Jalowitzki, Tiago Luis Reis"
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Item Dense hydrated Mg-silicates in diamond : implications for transport of H2O into the mantle.(2024) Carvalho, Luísa D. V.; Stachel, Thomas; Luth, Robert W.; Locock, Andrew J.; Pearson, D. Graham; Steele-MacInnis, Matthew; Stern, Richard A.; Nestola, Fabrizio; Cipriano, Ricardo Augusto Scholz; Jalowitzki, Tiago Luis Reis; Fuck, Reinhardt AdolfoWater in Earth’s upper mantle is a minor and yet critically important component that dictates mantle properties such as strength and melting behavior. Minerals with stoichiometric water, such as those of the humite group, are important yet poorly characterized potential reservoirs for volatiles in the upper mantle. Here, we report observation of hydroxyl members of the humite group as inclusions in mantle-derived diamond. Hydroxylchondrodite and hydroxylclinohumite were found coexisting with olivine, magnesiochromite, Mg- bearing calcite, dolomite, quartz, mica, and a djerfisherite-group mineral in a diamond from Brazil. The olivine is highly forsteritic (Mg# 97), with non–mantle- like oxygen isotope composition (δ 18O +6.2‰), and is associated with fluid inclusions and hydrous minerals—features that could be inherited from a serpentinite protolith. Our results constitute direct evidence for the presence of deserpentinized peridotitic protoliths in subcratonic mantle keels, placing important constraints on the stability of hydrous phases in the mantle and the origin of diamond- forming fluids.Item Mantle metasomatism and refertilization beneath the SW margin of the São Francisco Craton, Brazil.(2023) Rodrigues, Rodrigo Antonio de Freitas; Gervasoni, Fernanda; Jalowitzki, Tiago Luis Reis; Bussweiler, Yannick; Berndt, Jasper; Botelho, Nilson Francisquini; Queiroga, Gláucia Nascimento; Castro, Marcos Paulo de; Silva, Sebastiao William da; Araujo, Brunno Abilio Ciriaco; Oliveira, Ítalo Lopes de; Klemme, StephanA suite of kimberlite-hosted mantle xenoliths from the Catalao ̃ region, southwestern margin of the São Francisco Craton (SFC), Brazil, consists of spinel lherzolites (type I and II) and garnet-phlogopite wehrlites. The chemical composition of these xenoliths provides evidence of enrichment and refertilization of the SFC lithosphere which were caused by distinct metasomatic agents. Garnet-phlogopite wehrlites have porphyroclastic textures and were equilibrated between 1005 and 1010 ◦C and 2.9–3.0 GPa (~99 km). They record metasomatism caused by carbonatite and proto-kimberlite melts. Type I spinel lherzolite contains spinel-pyroxene symplectites indicating garnet destabilization due to variations of the P-T conditions. The minerals in this rock were equilibrated between 975 and 990 ◦C and their chemical compositions contain evidence for carbonatite metasomatism. High-Cr and low-Al clinopyroxene of garnet-phlogopite wehrlites and type I spinel lherzolite have high Mg#, Ca/Al, La/YbN, Zr/Hf ratios, and high Sr contents, coupled with low to intermediate Ti/Eu and Ti/Nb, which also suggests that they were formed by carbonatite melt. These geochemical features, together with the presence of carbonate inclusions in the olivines, corroborate the interaction with carbonatite melt. The low-Ti-Cr phlogopite (Phl1), which is restricted to only the garnet-phlogopite wehrlites, was probably produced through the release of volatiles components from the carbonatite melt that reacted with garnet porphyroclasts. Furthermore, metasomatic reactions involving garnet-phlogopite wehrlites and a proto-kimberlite melt formed high-Ti-Cr phlogopite (Phl2), consuming the original phlogopite (Phl1). Phl2 occurs as rims around Phl1, as isolated flakes around garnets, and in the matrix of wehrlites. Therefore, we assume that the proto-kimberlite metasomatism responsible for generation of Phl2 occurred prior to the eruption of the host kimberlite magma. Conversely, type II spinel lherzolites (876–915 ◦C; ~1.5 GPa) contain evidence of metasomatic reactions with silicate melts. These samples have high cpx/opx ratios (1.10–2.93) with low-Cr and high-Al clinopyroxene, and depleted incompatible trace element compositions. Some clinopyroxene crystals, however, show some enrichment in light rare earth elements (LREE), large ion lithophile elements (LILE), and Ti. Their low Ca/Al, La/YbN, and Zr/Hf, low Sr contents, high Ti/Eu and Ti/Nb, and a strong positive correlation of Ti with the other high field strength elements (HFSE) and LREE, may indicate that these clinopyroxene crystals were formed by refertilization caused by a silicate melt that was depleted in incompatible elements. Overall, these metasomatic processes suggest a pervasive refertilization of the cratonic lithosphere where the typically depleted peridotites of cratonic regions were replaced by a pyroxene-rich lithology.Item Subcretion of altered oceanic crust beneath the SW São Francisco Craton, Brazil : a stable isotope study on diamonds and their inclusions.(2023) Carvalho, Luísa D. V.; Stachel, Thomas; Pearson, Graham; Timmerman, Suzette; Stern, Richard A.; Jalowitzki, Tiago Luis Reis; Cipriano, Ricardo Augusto Scholz; Fuck, Reinhardt AdolfoThe presence of diamonds of lherzolitic, eclogitic and websteritic paragenesis in proximal alluvial deposits on the southwestern edge of the Sao ̃ Francisco Craton documents the incorporation of subducted oceanic crust and associated metasomatism through slab dehydration fluids affecting the local SCLM. To better constrain the subduction-association of diamond substrates and metasomatic events, we conducted a combined study of the δ13C-δ15N-[N] characteristics of 81 diamonds and the δ18O values of four of their eclogitic garnet inclusions. Diamond carbon isotope compositions range from − 25.5 to +0.5‰, with 13C-depleted diamonds (≤ − 7‰) being exclusively of eclogitic/websteritic paragenesis while the 13C-enriched (≥ − 2‰) tail of the distribution is related to diamonds with lherzolitic inclusions. Nitrogen isotope values range from − 14.2 to +25.5‰, with about half of the values being positive. A general absence of coherent trends in δ13C-δ15N-[N] across growth zones implies that diamond formation did not occur under fluid-limited conditions. Instead, the observed heterogeneity in carbon and nitrogen isotope compositions reflects contributions of distinct source reservoirs hosted in both altered oceanic crust and Earth’s mantle. Nitrogen contents peak around a δ15N value of − 3.5‰, indicating that more N-rich fluids, presumably representing a primitive endmember composition, have a mantle-like δ15N signature. While positive and negative δ15N values occur equally near the δ13C mantle value (− 5 ± 2‰), 13C-depleted diamonds have nitrogen isotope compositions skewed towards positive values. 13C depletion and 15N enrichment is a signature of biogenic carbonates/organic matter and low-T clays in uppermost, basaltic sections of oceanic crust that experienced low-temperature seawater alteration prior to subduction. Correspondingly, the oxygen isotope compositions of eclogitic garnet inclusions fall in a restricted range between +5.5‰ to +7.0‰. For three of the four samples, the stable isotope signatures of inclusions and host diamonds display perfect agreement, with the intensity of seawater alteration signatures, in the form of garnet inclusion 18O enrichment and host diamond 13C depletion and 15N enrichment, increasing together. For the fourth sample, the δ18O signature of the garnet inclusion (+5.5‰) and δ13C-δ15N signatures of the diamond host (− 25 and + 19‰, respectively) are decoupled. While the mantle-like δ18O signature indicates a diamond substrate derived from deeper levels in oceanic crust (e.g., deep sheeted dikes), the diamond-forming fluids must have originated from sources that originally resided near the sea water interface. A viable mode of mixing such disparate isotopic signatures is the interaction of diamond-forming fluids derived from shallow oceanic crust altered at low-temperatures with eclogitized substrates originally formed in deeper levels of oceanic crust. This process likely occurred during diamond formation in a tectonic subduction m ́elange, which juxtaposes deeper and shallower levels of oceanic crust. In the lithospheric mantle above the subcreted oceanic slab, the elevated carbon isotope and highly variable nitrogen isotope compositions of diamonds formed in lherzolitic substrates likely relate to devolatilization and/or melting of principally oceanic sediments containing marine carbonates and clays and subsequent mixing with mantle-derived volatile components. In combination, our diamond and inclusion stable isotope data provide insight into multiple processes that promote diamond formation both inside subducted slabs accreted to the São Francisco cratonic keel and in adjacent subcontinental lithospheric mantle.