Late acquisition of “primary” remanence in some fresh basalts: A cause of spurious paleomagnetic results

Although rarely reported, the principal magnetic carrier associated with rocks of basaltic composition can be titanomagnetite (Fe3−xTixO4) very rich in titanium (x>.75). If not oxidized during cooling, such a pristine magnetic carrier will possess a Curie temperature too low to insure the acquisition of a stable thermoremanent magnetization (TRM). A stable chemical remanent magnetization (CRM) ultimately may be acquired through room temperature oxidation of the titanomagnetite to titanomaghemite; however, such a process can occur during a time interval far removed from that of initial cooling. A case study is presented which dramatically illustrates the spurious nature of paleomagnetic results associated with such an occurrence.