Remanence characteristics of gabbros from the MARK area; implications for crustal magnetization

Citation:
Gee, JS, Lawrence RM, Hurst SD.  1996.  Remanence characteristics of gabbros from the MARK area; implications for crustal magnetization. Proceedings of the Ocean Drilling Program, Scientific Results. 153:429-436.

Keywords:

05A, Igneous and metamorphic petrology, 920, anisotropy, Atlantic Ocean, deformation, igneous rocks, Kane fracture, Leg 153, magnetic susceptibility, magnetite, metasomatism, mid-atlantic ridge, North Atlantic, Ocean Drilling Program, ODP Site, oxides, paleomagnetism, peridotites, petrofabrics, plutonic, preferred orientation, rocks, serpentinization, structural analysis, ultramafics, zone

Abstract:

Although the general concept of linear magnetic anomalies generated by seafloor spreading processes is well established, the details of the source distribution responsible for these anomalies remain uncertain. We summarize here magnetic properties from variably altered and deformed olivine gabbro, gabbro, and less abundant troctolite, gabbronorite, and oxide gabbros sam- pled at four sites drilled on the western median valley wall of the Mid-Atlantic Ridge south of the Kane Fracture Zone. The overall mean natural remanent magnetization (NRM) intensity (1.54 ± 2.6 A/m) and Koenigsberger ratio (8.05 ± 15.2) for these samples suggest that lower crustal gabbros are a significant contributor to marine magnetic anomalies. However, dual magnetic polarities were recorded at all four sites, with apparent polarity reversals sometimes occurring over spatial scales of tens of cen- timeters. Detailed demagnetization and rock magnetic studies of one such interval suggest that the complex remanence, dual polarities, and the occurrence of spurious well-defined magnetization components are related to production of magnetite during high-temperature alteration and/or cooling in periods of opposite polarity. These complexities, if generally applicable to oce- anic gabbros, may reduce the integrated contribution from the gabbroic layer to marine magnetic anomalies.

Notes:

n/a

DOI:

10.2973/odp.proc.sr.153.042.1997