INVITED SPEAKER: TECTONIC CONNECTIONS BETWEEN DEFORMED AND METAMORPHOSED CA. 1.49–1.43 GA METASEDIMENTARY SUCCESSIONS IN SOUTHWESTERN LAURENTIA

Detrital zircon data indicate that metasedimentary rocks formerly correlated with 1.7–1.6 Ga successions in southwestern Laurentia are actually Mesoproterozoic, requiring a previously unrecognized interval of basin development and closure beginning as early as ca. 1.49 Ga. In central Arizona, ca. 1.49–1.43 Ga schist and quartzite of the Yankee Joe and Blackjack Formations overlie 1.66 Ga ash-flow tuffs of the Redmond Formation and orthoquartzite of the White Ledges Formations. In northern New Mexico, ca. 1.49–1.45 Ga quartzite of the Piedra Lumbre Formation overlies 1.70 Ga quartzite and schist of the Ortega, Rinconada, and Pilar Formations. These relationships require discontinuities of at least 170 m.y. in the Hess Canyon Group of Arizona and 210 m.y. in the Hondo Group of New Mexico. There is no obvious stratigraphic break within the successions at either locality, and both are penetratively deformed and underwent regional metamorphism at greenschist to upper amphibolite facies. Deformation and metamorphism in northern New Mexico also affected the <1.46 Ga Marquenas Formation, comprising sheared and folded pebble to boulder conglomerate and quartzite. Patterns of 1.49–1.43 Ga deposition and provenance suggest that basin development was localized along the Jemez lineament, which is a candidate for the lithospheric suture zone between the Yavapai and Mazatzal accretionary provinces. Abundant detrital zircon with ages between 1.6 and 1.5 Ga in the Yankee Joe, Blackjack, and Piedra Lumbre Formations suggest that sediment was derived from non-Laurentian sources to the southwest that are no longer present. Our working model involves sedimentation in reactivated Paleoproterozoic basins as early as 1.49 Ga in response to either rifting or renewed convergence in southern Laurentia. Basin closure and accompanying deformation and metamorphism occurred between 1.45 and 1.40 Ga and involved the formation or reactivation of regional brittle and ductile thrust systems that cross and might actually represent the fundamental suture zone between accretionary provinces. Basin development and sedimentation were contemporaneous with granitic magmatism in the midcontinent but generally preceded widespread ca. 1.4 Ga A-type granitic magmatism in southwestern Laurentia.