Magnetic fabrics from sheeted dikes reveal regional magma flow patterns, and the spacing and dimensions of ophiolite magma-chambers, Troodos ophiolite, Cyprus

Abstract

Orientation-distributions of crystals were determined for 1289 specimens of the Sheeted Dike Complex of the Troodos ophiolite, located on the island of Cyprus. These were inferred from anisotropy of magnetic susceptibility (AMS). From these data the dispersion of magmatic flow fabrics with a mild tectonic overprint were recognized. The study area (~400km2) is located to the east of Mt. Olympus, and adjacent to a fossil transform fault (STTFZ) that was responsible for shearing of dikes and a change in their orientation from predominantly north-south to east-west as the fault is approached. The predominantly magmatic AMS fabrics blend a flow-aligned paramagnetic component from mafic silicates with a ferromagnetic component from titanomagnetites. The inclination of magma-flow axes varies from near vertical to near horizontal throughout the area with predominantly steep magma flow regions separated from regions with predominantly shallow magma-flow. Fast Fourier Transform (FFT) analysis of steep-flow region spacing shows that the magma chambers that fed the dikes were point-source with minimal along-axis extent, and very short lived. FFT wavelength calculations suggest that they may have been spaced approximately every 4km along the ridge, and every 100,000 to 250,000 years in time. These results imply localized magma chambers, thereby supporting the slow-spreading origin of the Troodos crust, and refine models for slow-spreading ridge processes to include a point-source magma delivery system between magma reservoirs and the sheeted dike complex.