Temporal Constraints on Geomagnetic Filed Behavior From High-Precision 40Ar/39Ar Geochronology

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

This project seeks to improve the paleomagnetic record through acquisition of precise 40Ar/39Ar age determinations coupled with magnetic measurements of lava flows that record in detail the behavior of the geodynamo. Three problems will be addressed: (1) The duration and temporal fine-structure of the Matuyama-Brunhes reversal process will be probed using many new incremental-heating data from lava flow sequences in Chile, Tahiti, Hawaii, and Washington that apparently were erupted at different times during the reversal. (2) Five volcanic areas in the southern hemisphere will be developed as new recording sites in a globally balanced array designed to measure paleosecular variation of the magnetic field over the past 5 million years. The new geochronology will play an important role in determining the periods and polarity states recorded by the lavas essential to modeling time-averaged behavior of the magnetic field. (3) The frequency, timing, duration, and geographic extent of reversal attempts are important observational constraints on modeling the geodynamo. Accordingly, we will expand efforts to verify the timing and geographic extent of at least three polarity events or subchrons in the late Matuyama chron. These include the recently proposed Punaruu (1.10 Ma) and Santa Rosa (0.92 Ma) events, and the Kamikatsura event (0.90 Ma). Laser fusion and incremental-heating of sanidine phenocrysts from silicic lava flows in New Mexico and California will provide the needed age resolution and spatial coverage.