Crustal xenolith magnetic properties and long wavelength anomaly source requirements

Abstract

Granulite xenoliths, probable components of the lower continental crust, are a primary source of information about the magnetization of the lower crust. Magnetization values for lower crustal xenoliths from three tectonic settings (converging plate margin, rift valley, and continental intraplate region) demonstrate that metabasic rocks in the granulite facies have magnetization values consistent with magnetizations inferred for modeled sources of long wavelength anomalies. Measured Curie points for granulite xenoliths are near 560‐570°C except for those from rift zones and other regions where anhydrous, probably reducing lower crustal conditions exist in a steep geothermal gradient. In samples from the reducing environments Curie points <300°C are measured. The lower crust could be the most magnetic crustal layer. Satellite magnetic anomalies may serve to delineate magnetization provinces which may be related to the tectonic and chemical evolution of continents.