GLG 301 Lecture 16: 301-2017-Summary 16
Document Summary
See also dynamic earth booklet on d2l under supplementary material. Divergent plate boundaries: divergent plate boundaries are initiated by rifting (break-up) of continents. For example, east african rift and gulf of aden/red sea system. In michigan, keweenaw (mid-continent) rift at 1 ga: mid-ocean ridge axis. If spreading continues you develop a new ocean with a mid- ocean ridge. Considerable heat is lost through hydrothermal circulation. Black smokers due to contact of water with 1000 c magma/rock and pick up of heavy metals: structure of the oceanic crust. Initially based on seismic refraction (velocity of seismic waves in the rock see later) data. Gross scale layering well defined: total thickness of 7 1 km and sharp moho (the boundary between the crust and mantle where seismic velocities (and presumably chemical composition) changes abruptly. Sedimentary layer (layer 1) increases in thickness away from ridge: average ~0. 4-0. 6 km, thicker near passive margins (>
