COOLIDGE AND LOONGANA-001 - A NEW CARBONACEOUS CHONDRITE GROUPLET

Petrographic and bulk compositional data suggest the existence of a ne w grouplet of carbonaceous chondrites consisting of Coolidge and Loong ana 001. Coolidge is a carbonaceous chondrite find from Kansas, USA, p reviously considered a metamorphosed CV chondrite. Loongana 001 is a r ecent find from Western Australia. It has a high matrix/chondrule mode l abundance ratio, 1-2 vol% refractory inclusions and high refractory lithophile abundance ratios (approximately 1.35x CI), indicating that it is a carbonaceous chondrite. Coolidge and Loongana 001 have many co mpositional and petrographic similarities. They have refractory elemen t abundances in the range of CV chondrites, significantly higher than those in the CR chondrites. They have similar volatile element abundan ce patterns showing low volatile element abundances relative to both C R and CV chondrites. Coolidge and Loongana 001 have similar chondrule dimensions and shapes, oxidation states and opaque mineral assemblages . They are also similar in petrologic type (3.8-4) and shock stage (S2 ). Although both Coolidge and Loongana 001 may be related to the CV cl an, they are not CV chondrites, nor are they formed by metamorphism of a CV precursor. They are distinctly different in composition from CV chondrites and their chondrules are smaller and have a much lower abun dance of coarse-grained chondrule rims. Coolidge and Loongana 001 cons titute a distinct carbonaceous chondrite grouplet.