Why can continental crust displace more of the mantle than oceanic crust?
The reason continental crust can displace more of the mantle than oceanic crust has to do with its thickness and buoyancy. Continental crust is significantly thicker than oceanic crust, averaging around 30-40 kilometers compared to oceanic crust's average thickness of only 7 kilometers. This greater thickness means that continental crust extends deeper into the mantle.
Additionally, continental crust is less dense or more buoyant than oceanic crust. It primarily consists of less dense granite and sedimentary rocks, while oceanic crust is predominantly composed of denser basaltic rock. The difference in density creates a buoyancy effect that allows the continental crust to "float" higher on the denser mantle below.
To understand this concept, you can use the principle of isostasy. Isostasy is the equilibrium maintained by Earth's crust on the semi-fluid mantle beneath it. The thicker and less dense continental crust "floats" higher on the denser mantle, effectively displacing a larger volume of the mantle compared to the thinner and denser oceanic crust.
So, in summary, the combination of greater thickness and higher buoyancy of continental crust allows it to displace more mantle than oceanic crust.