Upper Mississippi Valley and Sweetwater Mississippi Valley-type districts, United States of America: Timing of mineralization and dolomitization from paleomagnetism.

摘要

Paleomagnetic analyses of 359 specimens from 33 sites in the Upper Mississippi Valley (UMV) Zn-Pb district and 382 specimens from 27 sites in the Sweetwater Ba-F-Zn district were done to determine the timing of fluid flow responsible for dolomitization and Mississippi Valley-type (MVT) mineralization. Ordovician limestones and dolostones host the midcontinental UMV district mineralization. Paleomagnetic measurements suggest that their characteristic remanent magnetization (ChRM) is carried mostly by pyrrhotite with minor magnetite, giving an Early Permian (282 +/- 10 Ma) secondary chemical remagnetization age. Also, ChRM paleoinclinations from mineralized blocks suggest that the dolomitization and mineralization events were about coeval. The Sweetwater district lies in the Appalachian Valley and Ridge province of eastern Tennessee and its mineralization is hosted by Lower Ordovician carbonates.;The paleomagnetic age dates for the above two MVT districts record the observed widespread regional chemical remagnetization events from fluid flow related to the Carboniferous---Early Permian Ouachitan/Alleghenian orogeny. (Abstract shortened by UMI.)