Sending the answers to Busfar questions on my presentation.
Q:1)
Figure 2 shows a large lateral velocity variation in the upper mantle. The
author suggests that these differences could be a reflection of the
temperature variation within the asthenosphere. Could there be other factors
that contribute to the velocity variation within the asthenosphere?
A:1)
I tend to believe that lateral variation in density, which could be caused
by physical compression or simply chemical change of the mantle’s content,
would contribute to the variation of P-wave velocity.
My Response
What I think, that these chemical changes also come from temperature variation like when oceanic (basaltic) crust tend to subduct beneath some oceanic / continental crust down to mantle, due to temperature and pressure, it goes under metamorphism and changes to high density eclogite. So these density variations in these depths are also because of temperature variations.
Q:2)
The article suggests that western North America (e.g., from the Canadian
shield to the Pacific plate margin) contains the largest mantle-velocity
gradient on Earth. If this is true, what do you think causes this
phenomenon?
A:2)
This is most likely, or at least largely, due to the nature of the
geological setting in the Rocky Mountains area where there is a dramatic
change in the lithosphere density going from fast, cratonic, cold, and dense
lithosphere mainly on the east to slow, orogenic, hotter, and less dense
lithosphere mainly on the west. This abrupt change in the nature of the
lithosphere over a relatively (relative to other parts of the world) short
distance causes this unique situation where the lithosphere’s velocity
varies dramatically.
My Response
I agree
Q:3)
What do you think is the origin of the high velocity lower crustal layer?
A:3)
It could be due to the intrusion of other high density materials during the
Proterozoic Eon. Other possibilities include that it had a more complex
origin than currently assumed, or concentration of refractory residues of
partial melting.
My Response
I agree
