Exploring and sampling the world's mid-ocean ridges
Mid-ocean ridge basalts: the Earth's most voluminous volcanic rocks
On a volumetric basis, basaltic lavas erupted under the ocean at mid-ocean ridges are the most important products of terrestrial volcanism. What we have learned from mid-ocean basalts (MORB's) has had tremendous implications for our understanding of large-scale geodynamic and tectonic processes operating within the Earth's core, mantle, and crust.
When studying a group of related igneous rocks, an important issue to ascertain is the amount of compositional variation that characterizes the dataset. This is of particular importance for the study of MORB's. Are MORB's relatively uniform in composition, perhaps suggesting partial melting from uniform source materials in the mantle followed by uniform modification by magmatic processes? Alternatively, does the global MORB dataset exhibit significant compositional variation, perhaps suggesting important differences in source materials, melting conditions, or subsequent magmatic processes? A related issue is whether geochemical variation in the MORB dataset is a function of geographic location (e.g., position along the mid-ocean ridge system). This may have important implications for lateral variations in composition, temperature, or pressure within the Earth's mantle. Keep these larger issues in mind as you work through the following exercise.