Mathematics – Logic
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..528a&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 528
Mathematics
Logic
Angola, Anorthosite, Canada, Greenland, Intrusion, Metamorphism (Geology), Petrology, Textures, Geochronology, Lunar Rocks, Recrystallization, Strontium Isotopes, Tectonics
Scientific paper
The significance of textural analysis in anorthosite research has been emphasized by some petrologists. Textural features of anorthositic rocks can provide important information about their petrogenesis and subsequent evolution. In this work, preliminary results on a petrographic study of terrestrial anorthositic rocks from Canada, Southwestern Angola, and Greenland are presented and discussed in a comparative context with their lunar analogs. Terrestrial anorthositic masses show evidence of anorogenic emplacements. Geological and geophysical evidence suggests that large slabs of norite-gabbro composition are associated with tectonic thrusts. On the other hand, their Sr-87/Sr-86 ratios are generally lower than 0.703, in agreement with being derived from a noritic mantle source. Observations suggest that most terrestrial anorthosites have not formed by processes of magmatic differentiation but during long, retrograde metamorphic conditions producing deformation, cataclasis, grain comminution, and recrystallization throughout several orogenic episodes. Due to the lack of information on field relations among pristine lunar anorthosites, it is difficult to make direct comparisons with their terrestrial analogs about their modes of emplacement. However, their textural resemblance suggests that they were formed by similar processes. Tectonic activity may have favored the intrusion of anorthositic masses in the lunar protocrust in a way similar to the terrestrial case. Thus, a large diveristy of pressure and temperature regimes can be envisioned to occur at different emplacement locations. As magma crystallization proceeds, new intruding bodies may collide with previously formed crustal materials and may thus facilitate recrystallization and granulation of precursor igneous suites. These conditions are not unlike those achieved upon continental collisions in the terrestrial examples, and therefore a similar evolution of such akin rock types can be expected.
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