thumbnail

The crystal structure and thermal history of orthopyroxene from lunar anorthosite 15415

Earth and Planetary Science Letters

By:
, , and

Links

  • The Publications Warehouse does not have links to digital versions of this publication at this time
  • Download citation as: RIS

Abstract

A single crystal of untwinned orthopyroxene from lunar anorthosite sample 15415, with composition (Mg1.14Fe0.80Mn0.02Ca0.04)(Si1.97Al0.03)O6, has a unit cell in space group Pbca with a = 18.310(15) A ??, b = 8.904(10) A ??, c = 5.214(7) A ??, containing 2 formula units. A set of 742 counter-measured intensity data made with MoK?? radiation has been used to refine the crystal structure in isotropic thermal mode to R = 0.116. Anisotropic refinement led to R = 0.092, but thermal parameters are distorted by non-random errors resulting from poor crystal texture. The resulting structure is in close agreement with that obtained by Ghose [9] for a hypersthene from Greenland. A parameter q, which gives (MgqFe1-q) for cation site M(1) and (Mg1.14-qFeq-0.18Ca0.04) for site M(2), was included in the least-squares analysis, yielding q = 0.90(1). This orthopyroxene has the high degree of cation order expected of pyroxenes subjected to Apollonian metamorphism at lower than 500-600??C. No evidence exists for a subsequent thermal event of sufficient intensity to disorder the pyroxene. On the basis of previous laboratory studies of argon-release patterns of lunar plagioclase and order-disorder kinetics of terrestrial pyroxenes, we attribute the reported isotopic age (3.9-4.1 AE) to cessation of metamorphism, perhaps caused by impact excavation. ?? 1978.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The crystal structure and thermal history of orthopyroxene from lunar anorthosite 15415
Series title:
Earth and Planetary Science Letters
Volume
37
Issue:
3
Year Published:
1978
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Earth and Planetary Science Letters
First page:
476
Last page:
484