Mineralogical and chemical modification of components in CV3 chondrites: Nebular or asteroidal processing?

Abstract

— Calcium‐ and aluminum‐rich inclusions (CAIs), chondrules, dark inclusions and matrices in certain CV3 carbonaceous chondrites appear to have been modified by different degrees of late‐stage alteration processes that caused significant variations in mineralogy and chemistry. Some chondrules and CAIs are rimmed with fayalitic olivine. Metal in all components may be oxidized and sulphidized to magnetite, Ni‐rich metal and sulfides. Silicates in all components are aqueously altered to different degrees to phyllosilicates. Primary minerals in some CAIs experienced Fe‐alkali‐halogen metasomatism forming nepheline, sodalite, wollastonite, hedenbergite and other secondary minerals. In CV3 chondrites with metasomatized CAIs, nepheline, sodalite, etc. are also present in chondrule mesostases and in matrices. McSween's (1977b) reduced subgroup of CV3 chondrites generally shows minimal alteration of all components and may represent the unaltered precursors for the oxidized CV3 chondrites, which generally show major alteration. Most studies have been focused on specific components in CV3 chondrites and have not considered possible relationships between alteration processes. We infer from the correlated occurrences of the alteration features that they were closely related in time and space and review nebular and asteroidal models for their origins. We prefer an asteroidal model.

Oxygen isotope evidence regarding the formation of spinel-bearing chondrules

“…The O isotopic compositions of mesostasis in A1 show the values near the TF line. The values of mesostasis may not preserve the O isotope ratio of chondrule melt at solidification, but result from O isotopic exchange during aqueous alteration in the parent body because the Allende meteorite shows evidence of the aqueous alteration [13,14].…”

Primitive FeNi metal grains in CH carbonaceous chondrites formed by condensation from a gas of solar composition

“…, Rs [Kallemeyn et al, 1996], COs [Brearley, 1993;McSween, 1977], CKs [Geiger and Bischoff, 1995], CVs [Krot et al, 1995], CMs and CIs [Zolensky and McSween, 1988]). …”

Phase Equilibrium Investigation for CaO-SiO₂-5wt.%MgO-20wt.%Al₂O₃-TiO₂ System Relevant to Ti-bearing Slag System

“…The Al-Ti diopside phase is one of the most common phases presented in Ti-bearing slag system and is characterized by the high solubility of Al 2 O 3 and TiO 2 . [34][35][36][37][38][39][40] In Fig. 2(f), four phases equilibria are detected for sample K15 at 1 300°C, except for the equilibrium phases mentioned for sample K12, the pseudobrookite solid solution phase with the fomula of (MT 2 , AT) ss is found, as marked in Fig.…”