Mantle xenoliths from Tallante (Betic Cordillera, Spain) include samples recording a peculiar distinct style of metasomatism that induced orthopyroxene, plagioclase, phlogopite and amphibole crystallization and generated “hydrous” opx-rich mantle domains. The latter are locally crosscut by felsic veinlets containing plagioclase and orthopyroxene ± quartz ± phlogopite ± amphibole. The observed parageneses and available Sr-Nd-Hf isotopic data suggest that metasomatic agents were related to recycling of crust components within the mantle, plausibly in connection with subduction processes occurred during the Cenozoic Betic orogenic cycle. In this study we investigated representative samples of composite xenoliths consisting of peridotite crosscut by felsic veins (varying in size from centimetric to millimetric) and unveined peridotites, measuring the 18O/16O ratios of the constituent minerals by laser fluorination. Results show that the narrow O-isotope compositional “typical” of mantle rocks, and the limited oxygen isotope fractionation at mantle temperatures, make oxygen isotopes a powerful tool for identifying recycled crustal material in the mantle. Orthopyroxene and plagioclase of the centimetric vein show delta18O values of +9.8 and +10.6‰, respectively, whereas clinopyroxene of the surrounding peridotite country rock has delta18O= +6.2‰. Plagioclase of two distinct millimetric felsic veins show delta18O of 7.6 and 7.3‰. The delta18O values significantly higher than typical mantle ones provide insights to the genesis of the Cenozoic subduction-related magmas of the Betic region that include silica-oversaturated calcalkaline (s.l.) and lamproite products, possibly resolving source vs. shallow level crustal contamination of the magmatic rocks. Moreover, the different O-isotope composition recorded in veinlets characterized by different thickness could provide insights into diffusion-assisted O-isotope requilibration of mantle rocks, thus constraining the time for “crust digestion” into the mantle.

The oxygen isotopic composition of xenoliths from Tallante (Southern Spain): evidence for crust recycling into the mantle

BIANCHINI, Gianluca
2011

Abstract

Mantle xenoliths from Tallante (Betic Cordillera, Spain) include samples recording a peculiar distinct style of metasomatism that induced orthopyroxene, plagioclase, phlogopite and amphibole crystallization and generated “hydrous” opx-rich mantle domains. The latter are locally crosscut by felsic veinlets containing plagioclase and orthopyroxene ± quartz ± phlogopite ± amphibole. The observed parageneses and available Sr-Nd-Hf isotopic data suggest that metasomatic agents were related to recycling of crust components within the mantle, plausibly in connection with subduction processes occurred during the Cenozoic Betic orogenic cycle. In this study we investigated representative samples of composite xenoliths consisting of peridotite crosscut by felsic veins (varying in size from centimetric to millimetric) and unveined peridotites, measuring the 18O/16O ratios of the constituent minerals by laser fluorination. Results show that the narrow O-isotope compositional “typical” of mantle rocks, and the limited oxygen isotope fractionation at mantle temperatures, make oxygen isotopes a powerful tool for identifying recycled crustal material in the mantle. Orthopyroxene and plagioclase of the centimetric vein show delta18O values of +9.8 and +10.6‰, respectively, whereas clinopyroxene of the surrounding peridotite country rock has delta18O= +6.2‰. Plagioclase of two distinct millimetric felsic veins show delta18O of 7.6 and 7.3‰. The delta18O values significantly higher than typical mantle ones provide insights to the genesis of the Cenozoic subduction-related magmas of the Betic region that include silica-oversaturated calcalkaline (s.l.) and lamproite products, possibly resolving source vs. shallow level crustal contamination of the magmatic rocks. Moreover, the different O-isotope composition recorded in veinlets characterized by different thickness could provide insights into diffusion-assisted O-isotope requilibration of mantle rocks, thus constraining the time for “crust digestion” into the mantle.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1507513
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