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Abstract <p>The discovery of a new type of rock on the lunar surface, spinel anorthosite, has prompted interest to the petrogenesis of spinel-bearing rocks. We searched for and studied Mg–Al spinel in lunar highland meteorites Dhofar 025, Dhofar 311, and NWA 11303 and experimentally modeled spinel anorthosite formation as a result of equilibrium crystallization of possible post-impact melts of troctolite and troctolitic anorthosite. It was established that the impact-induced formation of spinel anorthosite requires rapid crystallization of troctolitic anorthosite melt. Spinel is mainly present in the meteorites as monomineralic fragments produced by rock disintegration during impact processes. Such rocks are spinel-containing troctolites and, possibly, deep-seated rocks of the lunar crust, known as spinel cataclasites, which are present as fragments in Dhofar 025 and Dhofar 311. A single fragment of spinel anorthosite was found in NWA 11303, but it differs in mineralogy from the rocks that were predicted from the Chandrayaan-1 orbital spectral data. The similarity of spinel compositions from different rock types does not allow us to identify reliably the sources of Mg–Al spinel fragments in lunar breccias. The investigation of the mineral composition and structural features made it possible to trace the main stages of the evolution of spinel-bearing mineral assemblages in impact melts of highland composition, which are manifested in shock-induced melting at grain boundaries, development of rims at the contact of spinel fragments with impact melt, and formation of rounded zonal grains at the final stage.</p>

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Formation and Evolution of Spinel Anorthosite on the Moon: Experiment and Observation on Lunar Highland Meteorites Dhofar 025, Dhofar 311, and NWA 11303

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  • 发表日期：

    2026年1月1日

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  • L. A. Lakhmanova,
  • S. I. Demidova,
  • V. G. Butvina,
  • M. A. Golunova,
  • P. Y. Plechov,
  • P. G. Bukhtiyarov,
  • K. V. Van,
  • G. S. Nikolaev

摘要

Abstract

The discovery of a new type of rock on the lunar surface, spinel anorthosite, has prompted interest to the petrogenesis of spinel-bearing rocks. We searched for and studied Mg–Al spinel in lunar highland meteorites Dhofar 025, Dhofar 311, and NWA 11303 and experimentally modeled spinel anorthosite formation as a result of equilibrium crystallization of possible post-impact melts of troctolite and troctolitic anorthosite. It was established that the impact-induced formation of spinel anorthosite requires rapid crystallization of troctolitic anorthosite melt. Spinel is mainly present in the meteorites as monomineralic fragments produced by rock disintegration during impact processes. Such rocks are spinel-containing troctolites and, possibly, deep-seated rocks of the lunar crust, known as spinel cataclasites, which are present as fragments in Dhofar 025 and Dhofar 311. A single fragment of spinel anorthosite was found in NWA 11303, but it differs in mineralogy from the rocks that were predicted from the Chandrayaan-1 orbital spectral data. The similarity of spinel compositions from different rock types does not allow us to identify reliably the sources of Mg–Al spinel fragments in lunar breccias. The investigation of the mineral composition and structural features made it possible to trace the main stages of the evolution of spinel-bearing mineral assemblages in impact melts of highland composition, which are manifested in shock-induced melting at grain boundaries, development of rims at the contact of spinel fragments with impact melt, and formation of rounded zonal grains at the final stage.