Isotopic anomalies of Ne, Xe, and C in meteorites. III. Local and exotic noble gas components and their interrelations

Details Isotopic anomalies of Ne, Xe, and C in meteorites. III. Local and exotic noble gas components and their interrelations Isotopic anomalies of Ne, Xe, and C in meteorites. III. Local and exotic noble gas components and their interrelations

May 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988gecoa..52.1245m&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 52, Issue 5, pp.1245-1254

Computer Science

13

Scientific paper

Data on gas-rich separates from the Murray and Murchison C2 chondrites are reviewed, in order to characterize their noble-gas components. Revised compositions are obtained for Ne-A1 and Ne-A2, two subcomponents of "planetary" Ne: Ne 20 / Ne 22 = 8.86 ± 0.09, 8.46 ± 0.12; Ne 21 / Ne 22 = 0.0303 ± 0.0007, 0.0348 ± 0.0012. Ne-AI is associated with a special type of planetary Xe (Xe-P3). Both Ne-A1 and Xe-P3 closely follow Xe-HL, but are located in a separate carrier (C ) of high chemical but low thermal resistance (amorphous diamond?); they are present in C1, 2 and unmetamorphosed C3V chondrites, but not in metamorphosed Allende. A new composition is derived for Xe-S: 128/129/130/131/132 = 0.432 ± 0.006/0.119 ± 0.022/1/0.312 ± 0.016/2.030 ± 0.011. However, Xe 130 / Xe 132 ratios even in the most enriched samples do not exceed 0.31, suggesting that Xe-S occurs as part of a pseudocomponent, mixed with Xe-P and Xe-HL. A new planetary Xe component, Xe-P5, has been found in the 1300° fractions of several Murray separates; its carrier is colloidal and resistant to HF and HClO 4 but not H 3 PO 4 , and hence probably is an oxide mineral. A coarse (>2 m) spinel fraction from Murray contains fissiogenic Xe matching that from Pu 244 in isotopic composition, but the implied Pu 244 abundance of 1.2 ppb (14 × C 1) is surprisingly high. Less than 12% of the fissiogenic Xe can be from Cm 248 , which corresponds to an original ( Cm 248 / Pu 244 ) o 1.7 × 10 -3 . Murray CJ, a sample strongly enriched in Ne-E(H) and its SiC carrier, contains (2.2) × 10 -8 ml/g of presumably spallogenic Ne 21 ; a factor 4-6 more than expected from the recent cosmic-ray irradiation. Although a presolar irradiation of the SiC grains is a distinct possibility, more prosaic explanations, such as recoil of Ne 21 from adjacent spinel, must be ruled out first.

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