Deciphering the origin(s) of H and Cl in Apollo 15 quartz monzodiorites: Evidence for multiple processes and reservoirs

Thomas J. Barrett, Katharine L. Robinson, Jessica J. Barnes, G. Jeffrey Taylor, Kazuhide Nagashima, Gary R. Huss, Ian A. Franchi, Mahesh Anand, David A. Kring

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Apollo 15 quartz monzodiorites (QMDs) are reported to contain some of the most deuterium-depleted apatite found in lunar samples. In this study, apatite from six Apollo 15 QMDs, including three samples from 15405 not previously investigated, were analyzed for their H and Cl isotopes. Apatite in 15405 are extremely 2H (or D)-poor, with δD values ranging from −658 ± 53 to −378 ± 113‰, comparable to apatite data from related samples 15403 and 15404. In addition to new H isotope data, the first Cl-isotope data for lunar QMDs are presented. Apatite in 15405 and related samples are enriched in 37Cl with respect to Earth, with measured δ37Cl values ranging from +13 to +37‰. These values are within the reported δ37Cl range for KREEP-rich samples. The fact that the Cl isotopic composition of apatite in QMDs are similar to those in other lunar lithologies, but the H isotopic data are distinct and unique, provides possible further evidence for the existence of a D-poor reservoir in the lunar interior. Raman spectroscopy of the silica polymorph in sample 15405 reveals it to be a mixture of quartz and cristobalite. Based on available experimental data on the stability of various silica phases over a range of pressure and temperature regime, a deep-seated origin in the crust for QMDs may be possible which would support an endogenous origin of the H-Cl isotope systematics of the QMDs. The role of impact-induced transformation of silica phases and its contributing towards low D/H ratio in apatite, however, cannot be ruled out.

Original languageEnglish (US)
Pages (from-to)192-206
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume358
DOIs
StatePublished - Oct 1 2023

Keywords

  • Apatite
  • Apollo 15
  • Chlorine
  • Hydrogen
  • Moon
  • NanoSIMS
  • Quartz monzodiorites

ASJC Scopus subject areas

  • Geochemistry and Petrology

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