Magnetism and Magmatism

September 1, 2015 ” Magnetism, Magmatism & Ice: traveling to the South Pole to understand magnetic field reversals”.

Presented by Mike Cheadle, Assoc. Prof., Univ. of Wyoming

The Earth magnetic field extends from the Earth’s core to where it meets the solar wind, a stream of charged particles emanating from the Sun. Periodically the field reverses its direction, but our understanding of these field reversals is limited, because there has n’t been a reversal during human history.  Some argue that a reversal could lead to significant consequences for human society, although the effects will likely be manageable.  The geological record provides one way to better our understanding of these reversals and Mike Cheadle will present his research on the evidence for the strength and rate of reversals recorded by the Dufek layered mafic intrusion in Antarctica, which is arguably the second largest frozen magma chamber known on the Earth.  He’ll also recount his experiences of travelling via the South Pole and working on “the ice” in Antarctica.

The Dufek layered mafic intrusion is ~180 million years old and covers an area of 50,000 km2 corresponding to 20% of the area of the state of Wyoming or greater than ten times the size of a Yellowstone super volcano magma chamber.  This single, frozen magma chamber likely fed one or more volcanoes and records a style of magmatism that hasn’t been seen during human history.  The intrusion is revealed by two 1.7km high mountain ranges that rise above the Antarctic ice sheet with no vegetation or soil covering the rocks.  This near 100% exposure permits study of the intimate details of magma chamber processes and allows geologists to address the still unanswered question of “how do large magma chambers work?”  Further, because the intrusion is so large and so cooled very slowly from 12000C, it acts much like a tape recorder, recording many reversals of the Earth’s magnetic field during a period of time when the field was much weaker than today and the reversals were more numerous.  Mike will explain how geologists use the rocks to provide information about both the magmatic processes involved in the formation of the Dufek intrusion, discuss the constraints the rocks place on the timescale, strength and nature of magnetic field reversals and explain a little about camping and studying geology on the Antarctic ice sheet.