Alkali‐halogen metasomatism of the CM carbonaceous chondrites

• Published in: Meteoritics & planetary science Vol. 54; no. 12; pp. 3052 - 3063
• Main Authors: Lee, M. R., Cohen, B. E., King, A. J.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.12.2019
• Subjects: Aluminum; Anorthite; Calcite; Calcium; Calcium magnesium silicates; Carbonaceous chondrites; Chondrites; Diopside; High temperature; Inclusions; Iron; Meteors & meteorites; Perovskites; Serpentine; Sodalite
• DOI: 10.1111/maps.13405
• ISSN: 1086-9379

Meteorite Hills (MET) 01075 is unique among the CM carbonaceous chondrites in containing the feldspathoid mineral sodalite, and hence it may provide valuable evidence for a nebular or parent body process that has not been previously recorded by this meteorite group. MET 01075 is composed of aqueously altered chondrules and calcium‐ and aluminum‐rich inclusions (CAIs) in a matrix that is predominantly made of serpentine‐ and tochilinite‐rich particles. The chondrules have been impact flattened and define a foliation petrofabric. Sodalite occurs in a 0.6 mm size CAI that also contains spinel, perovskite, and diopside together with Fe‐rich phyllosilicate and calcite. By analogy with feldspathoid‐bearing CAIs in the CV and CO carbonaceous chondrites, the sodalite is interpreted to have formed by replacement of melilite or anorthite during alkali‐halogen metasomatism in a parent body environment. While it is possible that the CAI was metasomatized in a precursor parent body, then excavated and incorporated into the MET 01075 parent body, in situ metasomatism is the favored model. The brief episode of relatively high temperature water–rock interaction was driven by radiogenic or impact heating, and most of the evidence for metasomatism was erased by subsequent lower temperature aqueous alteration. MET 01075 is very unusual in sampling a CM parent body region that underwent early alkali‐halogen metasomatism and has retained one of its products.