U-Pb detrital zircon and geochemical provenance study of Precambrian low-grade metasedimentary rocks from eastern Kansas and western Missouri

Abstract

U-Pb analyses of single detrital zircons and bulk geochemical analyses were conducted to test the idea that pre-Late Cambrian, low-grade metasedimentary rocks from the basement of eastern Kansas and western Missouri were derived, in part, from elastic sedimentary rocks of the 1.1- 1.2 Ga Midcontinent Rift. The 1.1-1.2 Ga arkosic rift sediments were proposed to have been eroded off of the Nemaha Uplift, and transported and deposited in structurally controlled basins in eastern Kansas and western Missouri.

Geochemical provenance and tectonic setting analyses of the metasedimentary rocks indicate derivation from average upper continental crust source rocks from an intracratonic setting. Enrichment in Cr, Ti, Co and Ni concentrations relative to elastic rocks of the Midcontinent Rift suggests a minor (<5%) mafic source input not seen in the rift derived elastic rocks.

U-Pb detrital zircon data extracted from the pre-Late Cambrian lowgrade elastic metasedimentary rocks place a maximum age of deposition for one well at 1.0 Ga and for another well at 620 Ma. A minimum age limit is provided by the Late Cambrian-Early Ordovician Reagan and Lamotte sandstones that unconformably overlie the elastic rocks.

Additional provenance ages from the low-grade metasedimentary rocks range from 1.60-1.83 Ga. Provenance ages derived from the elastic rocks of the Midcontinent Rift System range in age from 1.1-1.2; 1.3-1.5; and 1.7-1.8 Ga. No zircons of the age range 1.1-1.2 and 1.3-1.5 Ga were found in the elastic metasedimentary rocks studied here, and only a few zircons fell in the age range 1.7-1.8 Ga. The majority of the zircons fell in the age range 1.6-1.7 Ga, a range not represented in the elastic rocks of the Midcontinent Rift system. Provenance ages derived from the low-grade metasedimentary rocks are not consistent with those derived from elastic rocks of the Midcontinent Rift System, and in fact, argues against the idea that the metasedimentary rocks were derived from elastic rocks of the Midcontinent Rift System.