Quartet Mountain Lamprophyres and crustal xenoliths: new insights into the Mesoproterozoic metamorphic history of northwestern Laurentia

The Quartet Mountain Lamprophyres are Early Cambrian ultramafic dykes that crosscut Proterozoic sedimentary strata in the Wernecke Mountains, east-central Yukon. They were derived from low-degree partial melting of a light REE-enriched garnetiferous upper mantle and have near-chondritic Nd530 values of -1.5 to 1.9. The lamprophyres co ntain xenoliths derived from the crust and upper mantle. SHRIMP U-Pb isotopic analysis of zircon from five xenoliths identified ages of metamorphism, at 1.60 Ga, 1.27 Ga and 1.15 Ga. The 1.60 and 1.27 Ga events were likely caused by nearby, documented events of metasomatism and magmatism. The 1.15 Ga metamorphism correlates with scattered igneous and metamorphic ages from the northern and central North American Cordillera, the Grenville orogen and the Sibao orogen of South China. The 1.15 Ga event in northwestern Cordillera is thought to reflect crustal heating in an extensional regime generated by the oblique convergence of the Yangtze Craton with western Laurentia.