IDK TBH Flashcards
What happens between the boundary between upper mantle and lower mantle?
Pooling of subducted slab material on the boundary between the upper and lower mantle
What happens when it breaks?
Once it breaks through the upper mantle, the material becomes less buoyant and sinks quickly
What have scientists discovered about broken subducted plates?
They discovered that broken subducted slabs may ‘avalanche’ all the way to the core-mantle boundary (CMB)
What makes up most of the lower mantle? What does it transform to?
Perovskite makes up most of the lower mantle and can transform into a denser form called post-perovskite where slabs arrive at the core mantle boundary
What has seismic imaging in the lowermost mantle revealed?
Seismic imaging of the lowermost mantle reveals widespread high S-wave velocity anomalies between the LLSVPs
What is this consistent with?
These are consistent with accumulations of old dense slabs as also asserted by satellite gravity data
What are slab graveyards?
Slab ’graveyards’ are an accumulation of slabs on the core-mantle boundary because things like the Farallon plate has sunk and accumulated over hundreds of millions of years
Where have they accumulated?
Slab graveyards have accumulated around the Pacific plate
How then can the graveyards produce high shear wave velocity anomalies and the LLSVPs low shear-wave velocity anomalies?
Shear wave velocity increases greatly with increasing rigidity but decreases somewhat with increasing density
LLSVPs are characterised by low shear wave velocity because they are denser and hotter- and therefore less rigid- than the surrounding mantle
Slab graveyards are denser but colder- and therefore much more rigid- than the average mantle material, so that shear wave velocities increase overall
