ABSTRACT
The picrobasalts and basalts are a chemically coherent group of volcanic rocks that erupted throughout geologic time. The meimechites are a rare group of rocks that are chemically akin to the komatiites. Basaltic rocks are continually being extruded from or intruded into the 65 000 km long, segmented, mid-oceanic ridge system. The basaltic rocks collected from mid-oceanic ridges seldom crystallise under equilibrium conditions. The introduction of a huge, possibly 2000 km in diameter, plume-head beneath a lithospheric plate is likely to cause thermal erosion at its base and doming, stretching and fracturing of the overlying rocks. Experimental studies have revealed that eutectic-like partial melting of typical upper mantle source rocks such as lherzolite yields the common types of primitive picrobasaltic and basaltic magmas. The rocks of the Main Lava Series from Skye in the Inner Hebrides of Scotland are a well-known and historically important group of rocks.
