GEOPHYSICAL AND PETROLOGIC ADVANCES IN UNDERSTANDING THE TAUNTON-BELT WEDGE, AN ARCHEAN TERRANE WITHIN THE MINNESOTA RIVER VALLEY SUBPROVINCE OF THE SUPERIOR CRATON, NORTH-CENTRAL U.S.A.

Abstract

The Taunton-belt wedge, defined herein, is an unexposed fault-bounded Archean terrane located within the Morton block of the Minnesota River Valley (MRV) subprovince of the Superior Craton. It is bounded on the north by the Yellow Medicine shear zone (YMSZ), a prominent regional structure that extends from the west margin of the Paleoproterozoic Penokean orogen in Minnesota to the east margin of the Paleoproterozoic Trans-Hudson orogen in South Dakota. The south boundary of the wedge is a less distinct curving fault zone that splays west–southwest from the YMSZ in south-central Minnesota and rejoins it in eastern South Dakota. The interior geology of the wedge is poorly known, owing to continuous cover of the Precambrian basement by Phanerozoic strata and Pleistocene glacial deposits. Regional aeromagnetic and ground gravity mapping indicate a broad belt of mafic metavolcanic and related rocks in roughly the northern half of the wedge, and many granitoid intrusions in the southern half. Geophysical signatures characteristic of layered gneiss, such as those observed over known gneiss elsewhere in the Morton block, are minor to absent.