A recent trend in sciences on mantle-derived materials, with special emphases on refertilization, rheology, and ophiolite problems: a report of the Fifth International Conference on Orogenic Lherzolite

Abyssal peridotites recovered directly from mid-ocean ridges (mid-ocean ridge peridotites hereafter) are generally interpreted to be formed as a residue after partial melting and melt extraction in the adiabatically upwelling mantle beneath mid-ocean ridges. Osmium and some other isotopic characteristics of some mid-ocean ridge peridotites, which were formed by partial melting events, are much older than present-day mid-ocean ridge systems (ancient melting residual peridotites) , however, suggesting ancient origins. Ancient melting residual peridotites might have been incorporated into the oceanic asthenosphere beneath mid-ocean ridges. If this is the case, the nature of the oceanic plate and its formation processes need to be reconsidered because the asthenospheric mantle, which has abundant ancient melting residual peridotites, is not sufficient to create basaltic oceanic crusts, followed by formation of the serpentinized peridotite crust by hydrothermal circulation along faults developed around the mid-ocean ridges by continuous spreading. Comprehensive geochemical studies on depleted mid-ocean ridge peridotites are required to detect and verify ancient melting residual peridotites from mid-ocean ridge peridotites. It is crucial to examine the effects of minor Os-rich phases on 187 Os / 188 Os isotopic compositions to understand the meaning of their model ages. Precise chemical analyses of fluid mobile elements including light elements, such as H, Li, Be, and B, on clinopyroxene, as well as orthopyroxene, provide clues about differences in geochemical signatures and thermal histories between present-day mid-ocean ridge residual peridotites and ancient melting residual peridotites.

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Origins of Carbon and Nitrogen in Mantle Xenolith

Takano

Ohkouchi

2015

Journal of Geography(Chigaku Zasshi)

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The mantle is one of the largest reservoirs of deeply buried carbon and nitrogen in the Earth. Currently, mantle xenolith, which potentially originated from indigenous mantle, is the sole sampling access for mantle material from which to understand the enigmatic deep carbon and nitrogen cycles. Based on Deines (2002) , there are three major origins of deep carbon in mantle xenolith: i) pristine mantle carbon, ii) sedimentary organic carbon, and iii) oceanic limestone, including inorganic carbon. We can estimate how those three end-members combine using the CO2 / 3 He indicator. In contrast, some laboratory-based experiments demonstrate abiotic formation of hydrocarbon (up to C32 n-alkane: McCollom and Seewald, 2006) and other relevant molecules during the Fischer-Tropsch Type reaction. We discuss the origins of carbon and nitrogen from the viewpoint of bulk geochemistry and molecular-specific organic geochemistry. Important concepts of the geochromatography of crustal fluid coupled with the mantle refertilization process need to be shared to obtain a further understanding of deep carbon and nitrogen dynamics.

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A recent trend in sciences on mantle-derived materials, with special emphases on refertilization, rheology, and ophiolite problems: a report of the Fifth International Conference on Orogenic Lherzolite

Cited by 5 publications

References 155 publications

Formation and evolution of the uppermost mantle of oceanic plate and island arc based on natural samples of ultramafic-mafic rocks

Formation and evolution of the uppermost mantle of oceanic plate and island arc based on natural samples of ultramafic-mafic rocks

Ancient Melting Residual Peridotites Producing Variable Source Mantle beneath Mid-ocean Ridges: Detection and Geodynamic Implications

Origins of Carbon and Nitrogen in Mantle Xenolith

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