Petrofabric studies of eclogite, spinel-Websterite, and spinel-lherzolite Xenoliths from kimberlite-bearing breccia pipes in southeastern Utah and northeastern Arizona

Textural evidence, clinopyroxene fabric, and mineral assemblages of eclogite nodules from the kimberlite-bearing breccia pipes of the east Colorado plateau are consistent with an origin by metamorphic recrystallization of predominantly basic igneous rocks. The eclogites are divided into three fabric groups exhibiting linear, planar, and random fabrics. Clinopyroxenes follow similar orientation rules as amphiboles in metamorphosed crustal tectonites. Partial recrystallization of olivine and extensive postcrystalline strain in the pyroxenes of the lherzolites and the websterites are believed to be due to a modification of the original fabric under crustal conditions. The inferred structural history of the ultramafic nodules puts various constraints on petrologic models attempting to explain their origin.