Al-rich objects in ordinary chondrites: Related origin of carbonaceous and ordinary chondrites and their constituents

摘要: Ca-Al-rich inclusions (CAIs), common constituents of carbonaceous chondrites, have been studied extensively because they contain refractory, high-temperature minerals, suggesting that formed at high temperatures during the early history solar system. Few CAIs previously discovered in ordinary chondrites. Here we describe 169 Al-rich objects (arbitrarily defined as having ≥ 10 wt.% Al2O3) from 24 types 3 and 4 five regolith breccias containing unequilibrated material, unique meteorite Kakangari, a few 5 6 Based on shape texture, divide into chondrules (round, with igneous textures), irregularly-shaped (similar to type F spinel-rich complex CAIs), fragments (probably inclusions). For descriptive purposes, further subdivide compositional subgroups, although are entirely transitional. Conclusions: 1. a) wide-spread, albeit rare, chondrites similar (except coarse-grained ones) thus providing strong support for related origin their constituents, 2. b) independent, freely-floating, molten droplets cooled rather rapidly, 3. c) chondrules, like Mg-Fe-rich by melting millimeter- submillimeter-sized dust-balls. In case dust-balls consisted largely mixtures variable amounts least two solid precursor materials, one refractory-rich other volatile-rich. Phases which interpret unmelted relicts some these this model, 4. d) The wide ranges bulk compositions volatile-rich ones, yet complete transition between them, existence transitional composition suggest all processes. Differences result mixing different proportions refractory-, volatile-, (and other) materials were then melted, 5. e) Most show no indication once origin. Secondary alteration has probably changed original mineral assemblage. Mainly entered refractory gas, reacted constituents, produced secondary phases. Rims both decomposition reaction gas well accretion, 6. f) Coarse-grained found Allende not observed