Magnetic Properties of the Lower Oceanic Crust from Hess Deep (IODP Expedition 345)

Abstract:

Hess Deep is located at a tectonic window created by rifting of the Cocos-Nazca into East Pacific Rise crust. IODP Expedition 345 drilled into this window to recover lower oceanic crust primitive plutonic rock lithologies such as gabbros, troctolites, and olivine gabbronorites.

Differences in ferromagnetic carriers impact the ferromagnetic properties and the contribution of oceanic crust to magnetic anomalies. 57 samples have been magnetically examined using low-temperature magnetic remanence, hysteresis properties, and low field susceptibility. Results show varying properties based on lithology and alteration processes.

Secondary processes such as metamorphism, hydrothermal alteration and cataclasis can alter the magnetic history and properties of these once primitive rocks. The least altered samples consistently show pure stiochemetric magnetic magnetite as the main ferromagnetic carrier. Whereas, altered samples may contain multiple ferromagnetic carriers, such as pyrrhotite and magnetite.