Developments in Brief : Granite Formation Theory May Change

Two University of California, Berkeley, geologists have discovered a new region of granite running through the western slopes of the Sierra Nevada that may alter current thinking about the creation of granite deposits.

According to George Brimhall and Jay Ague, analysis of ore samples from more than 400 sites in the Sierra in the last three years shows that granite can be produced under conditions other than those previously known.

Geological theory is that granite is formed by the interaction between molten material, or magma, from the Earth’s interior and the thick continental rock of the Earth’s crust as the magma is pushed toward the surface. The researchers say that the new find shows that similar interactions are possible where the crust is thinner.

The area where the deposit was discovered once was part of the ocean floor and has a richer supply of the ores needed to create granite, Brimhall and Ague said. They said the 20-mile-wide band containing granite is the first large occurrence of true granite found on the western side of the Sierra.

Brimhall is a professor and chairman of geology and geophysics at Berkeley. Ague is a geology graduate student. They presented their findings last week in San Antonio at the Geological Society of America’s annual meeting.