Tectonic rotations of dikes in fast-spread oceanic crust exposed near Hess Deep

Oceanic crust that initially formed at the fast-spreading (130 mm/yr) East Pacific Rise at ~1 Ma is exposed in the walls of Hess Deep rift at the northern edge of the Galapagos microplate. Steep fault scarps expose a dismembered vertical sequence of pillow basalts, sheeted diabase dikes and gabbroic rocks. Diabase dikes in these units are dominantly vertical; however, extensive outcrops of steeply to moderately dipping dikes exist in some places. The nonvertical attitude of the dikes may be the result of tectonic rotations attending sea-floor spreading at the East Pacific Rise or the result of complex rotations of fault blocks during the opening of the Hess Deep rift at ~0.65 Ma. -Authors