High temperature hydrothermal alteration and amphibole formation in Gakkel Ridge abyssal peridotites
نویسندگان
چکیده
Alteration mineral assemblages in abyssal peridotites offer insights into the temperature and pressure conditions during hydrothermal fluid circulation oceanic lithosphere. Abundant venting has been documented along ultraslow spreading Gakkel Ridge have extensively sampled from ridge, yet these not systematically evaluated for nature extent of their alteration. Here, we present an analysis alteration 40 19 dredges spanning ~600 km ridge within Sparsely Magmatic Eastern Volcanic Zones. We use a petrographic-based scoring system to assign rank each sample 1 (unaltered) 5 (altered) 0.5 step intervals, based on scale Birner et al. (2016). cover full range alteration, essentially unaltered completely serpentinized, but are generally moderately highly altered (average score 3.5). The is independent peridotite lithology different between two zones. Serpentine all samples, magnetite occurs samples with scores >2.5, 27% contain carbonate veins that cross-cut other minerals. In 20% tremolite + talc as rims around pyroxene, while chlorite haloes spinel. A gabbro-veined lherzolite also contains pargasite replacing later overprinting by tremolite-talc intergrowths. abundance tremolite, chlorite, much lower than reported talc-tremolite-chlorite schists core complexes, where flow through crust leads open-system behavior. At Gakkel, our petrological observations suggest was nearer closed-system conditions, which can be explained absence some sections ridge. Pseudosection modeling Perple_X, assumes behavior, indicates pyroxene reacts form at temperatures >500 °C, corresponding depths >20 Ridge. pargasitic amphibole requires >750 °C form. Overall, results peridotites, more lithospheric mantle regions lack significant crust, abundances relationships mafic involved • altered, except fresh dredges. Hydrothermal formed ± 33% samples. Fluid may occurred depth. One Ti-rich pargasite, suggesting °C. Late-stage
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ژورنال
عنوان ژورنال: Lithos
سال: 2021
ISSN: ['0024-4937', '1872-6143']
DOI: https://doi.org/10.1016/j.lithos.2021.106107