Origins of Carbon and Nitrogen in Mantle Xenolith

Abstract

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.