REMAGNETIZATION BY BASINAL FLUIDS - TESTING THE HYPOTHESIS IN THE VIOLA LIMESTONE, SOUTHERN OKLAHOMA

Migration of orogenic or basinal fluids is a recently invoked mechanis m to explain the widespread presence of late Paleozoic secondary magne tizations in the rocks of North America. Paleomagnetic and geochemical results from the Ordovician Viola Limestone in southern Oklahoma are evaluated to assess the role of basinal fluids in leading to secondary magnetizations in the unit. The Viola Limestone contains what we inte rpret to be a pervasive Pennsylvanian synfolding magnetization residin g in magnetite and a localized Permian magnetization which resides in hematite and occurs in alteration zones around mineralized veins. Both secondary magnetizations are interpreted as chemical remanent magneti zations (CRM) based on low burial temperatures and the presence of aut higenic magnetic phases. The relative proportion of the Permian CRM in hematite gradually decreases whereas the magnetite CRM increases with distance from the veins. Fluid inclusion and Sr isotope studies indic ate that the vein mineralization (calcite with Mississippi-Valley-type oxides and sulfides) precipitated from basinal fluids which were warm , saline, and radiogenic. The radiogenic Sr-87/Sr-86 values of the lim estones in the alteration zones, and the fact that there is more signi ficant alteration closer to the veins suggests that the basinal fluids were also responsible for alteration in the limestones. The coinciden ce of the geochemical and remagnetization trends suggests that the Per mian CRM dates the migration of basinal fluids through the veins. Geoc hemical results from the Viola Limestone containing the pervasive CRM indicate that it is relatively unaltered with no evidence for basinal fluids. The lack of evidence for basinal fluids suggests that other me chanisms for the origin of the pervasive CRM need to be tested. The re sults of this study indicate that flow of basinal fluids was focused i n veins and only locally altered the host limestone.