lithospheric plates

Click image to enlarge

Photo Credit: NASA Goddard Space Flight Center 
Used with permission.

Lithospheric plates are the plates that comprise the fractured surface of the earth. Lithospheric plates are of two types: continental plates comprised mostly of granitic-type rock rich in silica and aluminum (also called "sial") and oceanic plates comprised mostly of basaltic-type rocks rich in magnesium and aluminum (also called "sima"). Earthquake and volcanic activity is common along the boundaries of lithospheric plates.