New Interpretation of Some Laccolithic Mountains and Its Possible Bearing on Structural Traps for Oil and Gas

Abstract

Each of the five Henry Mountains consists of nearly symmetrical dome, several miles in diameter and a few thousand feet high. Their flanks are wrinkled by radial anticlinal noses, each a mile or two long and a few thousand feet wide. At the center of each dome is a stock, and evidence is presented to show that physical injection of the stocks produced the domes. The anticlinal noses were produced by elongate laccoliths injected radially from the stocks. Igneous cores exposed at the centers of large domes at numerous localities in the United States and other countries have been interpreted generally as mushroom-shaped laccoliths and many of the domes have not been tested for oil and gas, perhaps because the arched strata are breached by erosion and the older strata were thought to pass undisturbed beneath the intrusion. Recent studies in the Henry Mountains, however, indicate that these domes may be produced by stocks as well as by laccoliths and it is suggested that oil or gas may be trapped on the flanks of such domes in oil-bearing regions in much the same way as oil and gas are trapped on the sides of salt domes.