Dawn-Ann Trebilcock HBSc thesis abstract
Different types of iron oxides occur in the oceanic rocks, found in the ophiolites of Cyprus, at different stages of alteration at varying depths and distances from the fossil spreading axes. The distinct Curie temperatures and susceptibilities are identified by tests done on the Curie Balance and the susceptibility-temperature apparatus, respectively.
Cyprus provides a perfectly exposed ophiolite and various parts to study the ocean floor structure of part of the Cretaceous Neotethys Sea. The ocean floor structure is generally as follows: a harzburgite and lherzolite mantle at its core, an overlying, discontinuous gabbroic complex, succeeded by a large sheeted dike complex topped by pillowed volcanics and a sedimentary succession. The Troodos ophiolite is thought to have had three fossil spreading axes that were of intermediate spreading rate, around 50 to 150mm/year.
From Troodos there were six mantle sequence rocks and eight sheeted dike complex rocks used in the Curie balance. Nine of the Troodos mantle rocks and ten from the sheeted dike complex were used for the low temperature (77K to 300K) susceptibility variations with temperature experiments. The high temperature (300K to 900K) susceptibility variations with temperature experiments involved five Troodos mantle specimens and five sheeted dike complex specimens. From Akamas eight samples were used in the Curie balance, ten in the low temperature susceptibility experiments and five used in the high temperature susceptibility variations with temperature tests.
It is concluded that the sheeted dike complex underwent more alteration than the mantle sequence rocks of Troodos and Akamas. The Akamas ophiolite mantle sequence shows more oxides to indicate more alteration when compared to the Troodos mantle sequence rocks. In the mantle sequence, magnetite is the most common with a Curie temperature of 582°C in the Curie balance and a range of 855K (582°C) to 885K (612°C) in the susceptibility versus temperature apparatus. TM60 is found in both the Troodos and Akamas mantle sequence rocks, but more frequently in the Akamas specimens.
In the sheeted dikes, TM60 was found to be fairly constant in the high temperature susceptibility experiments. The unblocking temperature for titanomagnetite, TM60 was established to be in the range of 410K to 440K. The unblocking temperatures for magnetite were between 850K (577°C) and 890K (617°C). The more often a specimen was heated, the more pronounced the presence of the magnetite became. Specimens would start out with three to five transitions and after one or two more heating treatments all transitions were removed except the Tc for magnetite. The Tc would also decrease in temperature by small increments after each heating. Two samples from the sheeted dike complex in Troodos ophiolite was heated and one from the Akamas mantle sequence.