Petrology, geochemistry, and geochronology of Proterozoic granitoid and related rocks of the northern Mummy Range, north-central Colorado

摘要

Detailed geologic mapping in the northern Mummy Range, north-central Colorado, reveals seven distinguishable igneous granitoid rock units intruded into a sequence of high-grade metamorphic host rocks. U-Pb dating of zircons from twelve samples indicates that these granitoids were emplaced during two separate periods of magmatism about 300 m.y. apart, one in the Paleoproterozoic and another in the Mesoproterozoic. Zircon dating confirms that all of this magmatic activity post-dated the peak of Paleoproterozoic metamorphism in this area.