Ammonium concentration and nitrogen isotope composition in metasedimentary rocks from different tectonometamorphic units of the European Variscan Belt

Geochemistry of fluid discharges from Peteroa volcano (Argentina-Chile) in 2010–2015: Insights into compositional changes related to the fluid source region(s)

“…do not allow to clearly discriminate between crustal and magmatic sources. Such a positive isotopic signature is indeed typical of 1) N 2 produced by thermal decomposition of organic material buried in sedimentary material (Jenden et al, 1988;Fischer et al, 2002;Snyder et al, 2003;Inguaggiato et al, 2004) likely involved in the subduction process, and/or 2) low-grade metamorphism affecting NH 4 fixed in the crystal lattices of K-rich minerals (micas and K-feldspars) of crystalline rocks (e.g., Honma and Itihara, 1981;Mingram and Brauer, 2001).…”

The evolution of Earth's biogeochemical nitrogen cycle

“…Metamorphism can increase sedimentary nitrogen isotope ratios by preferential volatilization of isotopically light NH 3 or N 2 (Bauersachs et al, 2009;Bebout et al, 1999;Bebout and Fogel, 1992;Boyd and Phillippot, 1998;Haendel et al, 1986;Jia, 2006;Mingram and Bräuer, 2001;Palya et al, 2011). However, the overall effect is variable and not always expressed (Busigny et al, 2003;Plessen et al, 2010;Yui et al, 2009), which prohibits precise corrections.…”

Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

“…Anaerobic degradation of organic matter during early diagenesis retains the initial ␦ 15 N value or decreases ␦ 15 N only to a slight extent (less than 2‰) (Freudenthal et al, 2001;Möbius et al, 2010;Robinson et al, 2012). On the other hand, although thermal metamorphism can increase C/N ratios to hundreds and even thousands, ␦ 15 N values might only increase to a small extent, depending on metamorphic grade, with increases of ∼1-2‰ at greenschist facies and of ∼3-4‰ at amphibolite facies (Bebout and Fogel, 1992;Jia, 2006;Mingram and Bräuer, 2001). As the ␦ 15 N bulk values from our studied successions are unlikely to have been modified significantly by post-depositional thermal alteration because of high H/C ratio values having been measured at the nearby coeval Yanwutan-Lijiatuo section (Guo et al, 2007b), nitrogen isotopic shifts if any caused by thermal alteration should be expressed consistently through the section in such a limited stratigraphic interval.…”