COMPARISON OF DETRITAL ZIRCON AGE AND PROVENANCE PATTERNS BETWEEN THE BELT BASIN AND CA. 1.52–1.43 GA METASEDIMENTARY SUCCESSIONS IN SOUTHWESTERN LAURENTIA AND THEIR TECTONIC SIGNIFICANCE

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 beginning as early as ca. 1.52 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 and quartz litharenite of the White Ledges Formation. In northern New Mexico, schist and quartzite of the Pilar and Piedra Lumbre Formations and metaconglomerate of the Marquenas Formation were deposited between ca. 1.52 and 1.45 Ga. Successions at both localities are penetratively deformed and were metamophosed at depths of 6 to 15 km. Abundant ca. 1.6–1.5 Ga detrital zircon in the Yankee Joe, Blackjack, and Piedra Lumbre Formations suggest non-Laurentian provenance from sources to the west. The Pilar Formation preserves interbedded ca. 1.52–1.49 Ga metatuff layers that record magmatic events not represented in western Laurentia. Locally derived detritus including boulders and cobbles of ca. 1.45 Ga metarhyolite and the absence of ca. 1.5-1.6 Ga detritus in the Marquenas Formation suggests that exotic sources no longer contributed to the basin. The localization of basin sources was possibly in response to thermal uplift driven by widespread plutonism and the onset of regional orogenesis ca. 1.45 Ga. Published data suggest similar provenance patterns in the Belt Supergroup, with a change from abundant 1.6–1.5 Ga non-Laurentian detrital zircon in the ca. 1.47–1.45 Ga lower units to predominately Laurentian detritus in the ca. 1.44–1.37 Ga Missoula Group. Our working model for the southwest involves sedimentation as early as 1.52 Ga in response to either rifting or renewed convergence in southern Laurentia. Basin closure, deformation and metamorphism occurred between 1.45 and 1.40 Ga, associated with the formation of regional thrust systems that coincide with an inferred crustal province boundary. The ca. 1.45–1.44 Ga change in provenance from exotic to local sources observed in both the southwestern and Belt successions suggest that orogenesis in Arizona and New Mexico might have changed sediment dispersal patterns throughout a broad region of western Laurentia.