Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6440628 | Lithos | 2015 | 8 Pages |
Abstract
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 δ15N is â 7 ± 3â°. 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 δ15N values down to â 24â° measured in very rare diamonds could be interpreted as a heterogeneous mantle. δ15N values in oceanic island basalts derived from the deep mantle have three components: deep mantle of ~â 9â° consistent with estimate, recycled sediments of about 15â°, and atmospheric N incorporated from groundwater and/or subducted atmospheric N (Mohapatra and Murty, 2000a; Chem. Geol. 164, 305-320). Some enriched δ15N values in MORB and OIB result from degassing fractionation. Shift of the upper mantle from an initial â 7â° to â 5â° by the Neoarchean can be explained by a combination of sediment recycling through subduction and upper mantle magma degassing processes.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Yiefei Jia, Robert Kerrich,