The magnetization of oceanic crust: contribution to knowledge from the Troodos, Cyprus, ophiolite

An extensive study of a segment of the Troodos, Cyprus, ophiolite using both outcrop and drill-core samples, and extending from the sediment–extrusive interface through sheeted dikes to cumulate ultramafics, has allowed a number of key questions regarding the magnetization of oceanic crust to be addressed. These include the number of strongly magnetized intervals with depth, their lateral variability and controls on their occurrence. Comparison has also been made with the section in Ocean Drilling Program (ODP) hole 504B, and a reinterpretation of its constructional setting is offered.Two strongly magnetized intervals occur in the area studied. The upper is in the extrusive sequence, extends on average from 0.2 to 0.6 km depth, and has a thickness of ~0.4 km. Here magnetization is dominated by remanence. The lower interval extends from the lowest level at which flows occur with dikes (average depth = 0.9 km) into the Sheeted Complex (average depth = 1.2 km) and has a thickness of 0.3 km. Here magnetization is dominantly induced. No other strongly magnetized intervals occur in the section. The extent of dike intrusion is closely related to the position of the lower limit of the high-remanence layer and to the occurrence of the high induced magnetization layer. In both cases the replacement of primary magnetite, which can carry a strong remanence, by magnetically soft secondary magnetite appears to be the controlling process.Comparison of the Troodos and hole 504B magnetization profiles shows close similarity in the upper, remanence-dominated magnetic interval. The absence of the deeper interval of high induced magnetization in the hole 504B profile is interpreted as meaning that sheeted dikes have not been penetrated by the drill hole.