Origin of Syntilting Remagnetizations in Deformed Mississippian Carbonates, Southern Canadian Rockies

The purpose of this study is to test for a connection between the timing of remagnetization relative to folding and the style of deformation/strain within Mississippian carbonates in folds with variable geometries from the southern Canadian Rockies. Understanding how strain effects the timing of acquisition of secondary magnetizations in fold and thrust belts is important since they are commonly used in structural applications as well as dating diagenetic events. Folds in the Canadian fold and thrust belt contain a widespread characteristic remanent magnetization (ChRM) with northerly declinations and steep down inclinations that reside in magnetite based on rock magnetic results. Preliminary tilt test results suggest the ChRM is syntilting on one fold which has a steep, thinned front limb, whereas results from moderately dipping limbs of another fold suggest a pretilting ChRM. One hypothesis for the difference in the tilt test results is that more intense strain in the steep limb may have altered an original pretilting into a syntilting ChRM. This will be tested by detailed strain analysis in future studies. Field relationships and petrographic analysis suggests a stratigraphic control on the ChRM which is common in dolomitized zones. The ChRM is interpreted as a chemical remanent magnetization (CRM). The presence of degraded hydrocarbons in the rocks and geochemical data (radiogenic ⁸⁷Sr /⁸⁶Sr values) are consistent with either hydrocarbons and/or evolved basinal fluids as the agent(s) of remagnetization. An intermediate temperature (unblocked by 320°C) reversed component that is late syntilting/post-tilting is also observed and has been confirmed to reside in pyrrhotite based on low temperature rock magnetic experiments . It is interpreted to be related to alteration by fluids which moved along fractures produced during deformation.