These structures contain peridotites that are generally melt-depleted, although the Kaapvaal one has peridotites with excess orthopyroxene, and the Slave one shows increasing peridotite fertility with depth.  
These structures contain peridotites that are generally melt-depleted, although the Kaapvaal one has peridotites with excess orthopyroxene, and the Slave one shows increasing peridotite fertility with depth.  Early estimates of the thicknesses of these structures relied on surface heat flux measurements that have been superceded by xenolith geotherm analysis that yield boundary layer thicknesses of about 200 kilometers, disagreeing with seismic analyses that show high-velocity anomalies extending about 300 kilometers below these structures.  Orogenic belts and accreted terranes dating from the Phanerozoic surround these regions that have remained undisturbed for over a billion years.  For 10 points, continental shields are the exposed surfaces of what structures that are subdivided by age into Protons and Archons, and which represent the oldest, undisturbed parts of continental plates?
These structures contain peridotites that are generally melt-depleted, although the Kaapvaal one has peridotites with excess orthopyroxene, and the Slave one shows increasing peridotite fertility with depth.  
cratons [prompt on "continental shields" before mention in the question]