N-isotope composition of the primitive mantle compared to diamonds

作者：Jia Yiefei^*; Kerrich Robert

来源：Lithos, 2015, 233: 131-138.

DOI：10.1016/j.lithos.2015.02.009

• Nitrogen
• Isotopes
• Primitive mantle
• Crust
• Recycle
• Neoarchean

The nitrogen isotopic composition of the Earth's primitive mantle is controversial. Chromium-isotopic ratios of various terrestrial minerals and rocks, and chondritic meteorites are consistent with the silicate Earth being a mixture of enstatite and carbonaceous chondrites. From their relative proportions and N-isotope compositions we estimate that the bulk primitive mantle delta N-15 is -7 +/- 3 parts per thousand. The negative value, as also evidenced by mantle-derived oceanic basalts and diamonds, is an intrinsic long-term feature of Earth's mantle. Some enstatite chondrite-like delta N-15 values down to -24%. measured in very rare diamonds could be interpreted as a heterogeneous mantle. delta N-15 values in oceanic island basalts derived from the deep mantle have three components: deep mantle of similar to-9 parts per thousand consistent with estimate, recycled sediments of about 15 parts per thousand, and atmospheric N incorporated from groundwater and/or subducted atmospheric N (Mohapatra and Murty, 2000a; Chem. Geol. 164,305-320). Some enriched delta N-15 values in MORB and OIB result from degassing fractionation. Shift of the upper mantle from an initial -7 parts per thousand to -5 parts per thousand by the Neoarchean can be explained by a combination of sediment recycling through subduction and upper mantle magma degassing processes.

• 出版日期2015-9-15
• 单位Saskatoon; CSIRO; Saskatchewan