GEO 330 Lecture Notes - Lecture 18: Nakhlite, Lherzolite, Diogenite
31 Mar 2018
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Ci, cm, co, cv, ck, cr, ch: ordinary chondrites. Iron meteorites (main groups: ia, iia, iib, iiia, iiib, iva, others. It is an orthopyroxenite and is not classified as a shergottite, nakhlite, or chassignite: nwa7034 is an impact breccia with an age of ~2gy. Snc meteorites -- shergottites: two main types of shergottites -- basalts and lherzolites. Both lithologies have similar mineralogies, but lith. Indicates variable degrees of interaction of initial magma with crust: lherzolitic shergottites contain olivine and chromite grains enclosed by large orthopyroxene crystals, with small amounts of maskelynite, pigeonite, augite, whitlockite, and chromite filling the intersticies. Lherzolites are defined by the presence of olivine and both orthopyroxene (opx) and clinopyroxene (cpx) Orthopyroxene -- (mg, fe)2 si2o6: fe-mg minerals have more mg than basaltic shergottites, chromites are strongly zoned, indicating either: Mixing of different magma sources: unlike basaltic shergottites, lherzolites are plutonic rocks and have true cumulus textures.
