High-pressure reactive melt stagnation recorded in abyssal pyroxenites from the ultraslow-spreading Lena Trough, Arctic Ocean
Pyroxenites are an essential component in petrological and geochemical models for melt formation at mid-ocean ridges and ocean islands. Despite their rarity, their origin has been widely discussed and various processes have been invoked for their formation. Here, we present a detailed study of the m...
| Published in: | Journal of Petrology |
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| Main Authors: | , , , , , |
| Format: | Text |
| Language: | unknown |
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LSU Digital Commons
2014
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| Subjects: | |
| Online Access: | https://digitalcommons.lsu.edu/geo_pubs/976 https://doi.org/10.1093/petrology/egt073 https://digitalcommons.lsu.edu/context/geo_pubs/article/1975/viewcontent/976.pdf |
| Summary: | Pyroxenites are an essential component in petrological and geochemical models for melt formation at mid-ocean ridges and ocean islands. Despite their rarity, their origin has been widely discussed and various processes have been invoked for their formation. Here, we present a detailed study of the microtextures and major, minor and trace element compositions of relatively fresh pyroxenites and associated harzburgites from the ultraslow-spreading Lena Trough, Arctic Ocean. Microtextural and geochemical characteristics suggest an origin by magmatic assimilation-fractional crystallization with a high ratio of mass crystallized to mass assimilated.The major element compositions of pyroxenes suggest that this process occurred at high pressures (>0.7 GPa), although interstitial plagioclase in two of the pyroxenites indicates that melt-rock reaction continued at lower pressures.The parental melt to the pyroxenites was most probably depleted mid-ocean ridge basalt similar to basalts from the North Lena Trough and westernmost Gakkel Ridge; basalts from the Central LenaTrough cannot have functioned as parental melts. The melt was generated close to the garnet-spinel facies transition by variable degrees of partial melting and reacted with the local refractory harzburgite. Pyroxenites from this study provide further evidence, together with plagioclase-bearing and vein-bearing peridotites, for significant melt stagnation below the Lena Trough that occurred over a range of depths, either continuously or stepwise. Comparison with abyssal pyroxenites reveals common characteristics, suggesting that, consistent with results of high-pressure crystallization experiments, they mark the onset of (reactive) crystallization of melts passing through the deeper parts of the mid-ocean ridge plumbing system. © The Author 2013. Published by Oxford University Press. All rights reserved. |
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