CONTACT-METAMORPHISM AND PARTIAL MELTING OF PELITIC ROCKS IN THE AUREOLE OF THE LARAMIE ANORTHOSITE COMPLEX, MORTON PASS, WYOMING

Supracrustal and granitic rocks, metamorphosed to amphibolite facies in the late Archean, were thermally metamorphosed by the successive intrusions of the Laramie Anorthosite Complex at about 1.4 Ga. Pelitic compositions formed granulite-like rocks that show clear evidence of partial melting, uncomplicated by any later metamorphism. Calculation of the displaced equilibria corresponding to low-variance pelitic assemblages across the aureole yields minimum temperatures in the range of 650° to 800°C at a pressure of about 3 ± 0.5 kb and a (H2O) <1. -from Authors