Stable isotope analysis of carbon and nitrogen in angrites

Abstract

Abstract-Angrites are a small group of ancient basaltic achondrites, notable for their unusual chemistry and extreme volatile depletion. No comprehensive study of indigenous light elements currently exists for the group. Measurement of the abundances and isotopic composition of carbon and nitrogen could provide information pertaining to the evolution of the angrite parent body. Bulk-sample stepped combustion analyses of five angrites and a glass separate from D'Orbigny were combined with earlier data and acid dissolution experiments of carbonates found in D'Orbigny to compile an inventory of indigenous carbon and nitrogen. Indigenous carbon combusted between 700°C and 1200°C, with abundances of 10-140 ppm and a mass-weighted d 13 C of À25 to À20& with the exception of D'Orbigny (d 13 C approximately À5&). Nitrogen was released at 850-1200 ºC, 1-20 ppm with a d 15 N À3& to +4&; again, D'Orbigny (d 15 N approximately +20 to +25&) was an exception. We interpret these components as largely indigenous and decoupled; the carbon in graphitic or amorphous form, while the nitrogen is present as a dissolved component in the silicates. No relationship with the textural sub-classification of angrites is apparent. We suggest that the angrite parent body contains a reservoir of reduced carbon and thus may have undergone a change in redox conditions, although the timing and mechanism for this remain unclear.

Simultaneous analysis of abundance and isotopic composition of nitrogen, carbon, and noble gases in lunar basalts: Insights into interior and surface processes on the Moon

“…In order to minimise any terrestrial contamination of the samples before analysis, the basalt powders were weighed out and transferred into 4 mm  4 mm clean platinum foil buckets in a Class 100 clean room (Pt foil cleaning methods are as described in Abernethy et al, 2013). Tweezers and spatulas used to transfer the basalt powders from their respective vials to the platinum buckets were cleaned before use, and wiped with acetone using lint-free cloths between uses with separate samples.…”

Precise carbon isotopic ratio analyses of micro amounts of carbonate and non‐carbonate in basalt using continuous‐flow isotope ratio mass spectrometry

“…Most analytical schemes for the carbon isotope analysis of different carbon species in basalt are based on a stepwise heating method. 1,2 Fuex and Baker, 3 however, made a pioneering investigation of carbon isotope ratios from a variety of igneous rocks. They first distinguished carbonate and non-carbonate carbon, and this work was followed by that of other researchers.…”

“…Due to signals contributing to the measured δ values from the tin capsule and/or the tin capsule plus quartz powder used, it is necessary to carry out a blank determination prior to the analyses of samples. The average peak area and δ value of the two blank measurements can be used to correct the data for blank contribution, as shown in (2) where δ blk corr is the blank corrected δ value of the sample; δ meas and δ blk are the determined raw δ value of the sample and δ value of the blank, respectively; and A meas and A blk are the peak areas of the sample and the blank, respectively.…”

Basaltic volcanism on the angrite parent body: Comparison with 4 Vesta

“…In an investigation of the light element content of a small subset of angrites, Abernethy et al. () found up to ~100 ppm in some of the samples, an order of magnitude more carbon than required for the bubble nucleation process. In an attempt to reconcile these findings with the McCoy et al.…”

“…A subset of the angrite data has been reported previously (Abernethy et al. ). Two separate families of volatile components were observed.…”