THE TEMPORALITY OF ANORTHOSITES

• DOI: 10.3749/canmin.48.4.711
• Publication Date: 2010-10-07T12:14:20Z
• Authors: L. D. Ashwal
• Keywords: Temporality

The compositions, textures, associated rocks and tectonic environments of anorthosites allow categorization into six different types, some which show distinct age-restrictions in terrestrial planetary history. Primordial, Archean Proterozoic are distinctly restricted time space. Those layered mafic intrusions ophiolites no apparent time-restrictions. Primordial form the bulk lunar crust possibly that Mercury, probably formed response to accretion. No surviving this nature has yet been found on Earth. Calcic (>An80) megacrystic entirely Archean, where they with volcanic greenstone belts, may have by accumulation An-rich plagioclase from ultramafic magmas; high H2O content parental melts explain calcic temporality might be linked komatiitic magmatism. Massif-type anorthosite is most abundant occurs as small plutons huge composite batholiths almost Proterozoic, although vast majority were emplaced between ~1000 ~1800 Ma. Compositions (An50±10), textures (lathy plagioclase) settings (emplaced continental rather than oceanic crust) effectively distinguish anorthosites. Their restriction related unique supercontinental configurations. Incomplete preservation or insufficient depth erosion unlikely explanations for degree non-unformitarianism therefore implied.