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TitleGeophysical structure of the Troodos Ophiolite from downhole logging
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AuthorSalisbury, M H; Christensen, N I; Vine, F J; Smith, G C; Eleftheriou, S
SourceCyprus crustal study project: initial report, hole CY-4; by Gibson, I L (ed.); Malpas, J (ed.); Robinson, P T (ed.); Xenophontos, C (ed.); Geological Survey of Canada, Paper no. 88-9, 1989 p. 331-349, (Open Access)
Mediapaper; on-line; digital
RelatedThis publication is contained in Gibson, I L; Malpas, J; Robinson, P T; Xenophontos, C; (1989). Cyprus crustal study project: initial report, hole CY-4, Geological Survey of Canada, Paper no. 88-9
File formatpdf
Lat/Long WENS 33.0500 33.1000 34.9500 34.8833
Subjectsgeophysics; igneous and metamorphic petrology; ophiolites; oceanic crust; pillow lavas; seismic velocities; magnetic susceptibility; magnetic field; densities; porosity; resistivity; igneous rocks; geophysical surveys; basalts; volcanic rocks; pyroxenites; gabbros; geophysical logging; gamma ray logging; temperature; lithology; Troodos Ophiolite Cmplx; Cretaceous
Illustrationsgeophysical logs; location map; drillcore diagram; depth profiles
Released1989 12 01; 2016 10 13
AbstractVelocity (Vp and Vs), density, porosity, natural gamma, resistivity , total magnetic field and magnetic susceptibility logs demonstrate that the Troodos ophiolite complex is geophysically similar to the oceanic crust. Insitu velocities (Vp) range from 3.2-3.5 km/s in the pillow basalts (Layer 2A) and then increase gradually through the pillow basalt/dike transition and the sheeted dikes (Layer 2B) to classic Layer 3 velocities (6.7-6.9 km/s) in the gabbros while Vs averages 2.1 km/sin the pillow basalts and rises to values of 3.2-3 .5 km/s in the gabbros. In the pyroxenites, Vp increases only slightly (to 7.0 km/s) but Vs rises to 4.0 km/s. The porosity and natural gamma radiation decrease from averages of 20% and 30 API units, respectively, in the pillow basalts to negligible values in the gabbros, while the formation density and resistivity increase from 2.2 to 2.95 g/cm3 and from I 0 to 20K-50K ohm-mover the same interval, suggesting that seawater penetrates no deeper than the base of the dikes. Aside from Ys, the only property which changes at the gabbro/pyroxenite boundary is density, which increases abruptly to 3.1 g/cm3 The magnetic susceptibility increases steadily from 0.5 x 10-3 S.I. units in the pillow basalts to 4 x 10-3 units at the 50% dike/50% gabbro transition, below which it decreases abruptly to 0.5 x 10-3 units. Since resistivity increases by an order of magnitude at the same depth and Vp increases rapidly from 5.75 to 6.4 km/s at this depth and then increases steadily to 6.8 km/s within the next few hundred meters, we interpret the dike/gabbro transition as the Layer 2/3 boundary of the oceanic crust.