The layers in the cumulate gabbro have less silica but are richer in iron and magnesium than the upper portions of the crust.
In addition, he noticed that they had unique shapes, occurred in a predictable sequence across their trends, and could be correlated across the fracture zones.
Three-dimensional diagram showing crustal generation and destruction according to the theory of plate tectonics; included are the three kinds of plate boundaries—divergent, convergent (or collision), and strike-slip (or transform).
The age of the oceanic crust does not go back farther than about 200 million years.
These areas include, among others, Newfoundland and the Pacific Coast Ranges of California, the island of Cyprus in the Mediterranean Sea, and the mountains in Oman on the southeastern tip of the Arabian Peninsula.
Ophiolites reveal the structure and composition of the oceanic crust in astonishing detail.