Limitations of ophiolite complexes as models for the magnetic layer of the oceanic lithosphere

We propose that only those ophiolite complexes whose magnetic properties and metamorphic grade correspond to comparable stratigraphic units of in‐situ oceanic crust should be used for modeling the magnetic properties of the oceanic lithosphere. Because drilling of the igneous oceanic crust by the Deep Sea Drilling Project (DSDP) has penetrated a maximum of 0.6 km, only the upper extrusives (pillow basalts and associated flows) of an ophiolite complex can be used in this direct comparison. Previously published and new data of submarine basalts are used for establishing minimum constraints for the magnetic properties of the extrusive rocks of ophiolite complexes. These criteria are: 1) initial Curie points (T_c) should be between 100° ‐ 450°C (for T_c ⪞ 200° C the saturation magnetization versus temperature curves should be irreversible); 2) (intensity of magnetization) > 1×10⁻⁴ gauss (1×10⁻¹ Am⁻¹); 3) (ratio of remanent to induced magnetization) > 1; 4) alteration of the upper extrusives should not exceed zeolite facies metamorphism. These necessary but not sufficient criteria were applied to five ophiolite complexes, of which only two satisfied all the requirements. The remaining ophiolite complexes were probably subjected to a metamorphic event either during or subsequent to their original emplacement as part of the oceanic lithosphere.