Palaeomagnetic evidence of Miocene and Pliocene rotational deformations of the Aegean Area

Abstract

We present results from recent analyses of seismic refraction and sea-floor microseismicity studies in the Pacific and Atlantic oceans which lend support to the hypothesis that processes responsible for the construction of ophiolite suites are similar to phenomena extant at mid-ocean ridges. Seismicity at fast-spreading ridges is characterized by very low magnitude (0–1) and shallow (<2–3 km) microearthquakes and long-term oscillations or harmonic tremor. A detailed seismic-refraction experiment on a fast-spreading portion of the East Pacific Rise supports the hypothesis of the existence of a crustal magma chamber. Analyses of these data indicate that the chamber is largely unperturbed by the presence of conjugate spreading centres and the inverted delta-shaped zone of partial melt is characterized by a half width in excess of 6 km. Finally, a new approach for obtaining upper-crustal velocities when applied to data characterized by the presence of shear waves provides several counter-examples to the hypothesis that the shallow crust evolves with time.