Eruption Timescales
The goal of this research project is to determine how long an individual flood basalt eruption lasts, as this has large implications for CO2 and other volatile fluxes to the atmosphere during these events. To do this, I invented a new method called magnetic geothermometry (MGT). MGT uses a combination of petrology, paleomagnetism, and thermal modeling to constrain the active lifetime of any igneous intrusion. Long-lived intrusions will transfer significant amounts of heat into the surrounding wall-rock, while short-lived intrusions will transfer much less heat. In the wall rock, magnetite can be paleomagnetically reset and geochemically altered from this heating, and these changes are particularly sensitive to the duration of heating. By measuring the degree of paleomagnetic resetting and geochemical reordering in wall-rock magnetites, I can determine which intrusions are relatively short- or long-lived. I then construct thermal models of the intrusion to quantify how long it must have been active to produce the observed effects in the wall rock. I applied MGT to feeder dikes of the Columbia River flood basalts and determined that these dikes were transporting magma for less than a few years in most cases. This intensely focused high effusion-rate activity implies that global volatile and CO2 emissions reached several orders of magnitude above ‘steady state’ during eruptions. Thus, it is plausible major climate perturbations could arise from the eruption of a single flood basalt flow.
Cascade Volcanics
This project is focused on refining the age of the two most recent geomagnetic reversals (Brunhes-Matuyama and Matuyama-Gauss) using lavas from the Goat Rocks volcanic complex in Washington. This complex hosts several extinct volcanic centers which together provide most of the volcanic complexity that the Cascades have to offer (polygenetic to monogenetic, explosive to effusive, basaltic to rhyolitic). The composite volcano was active from 0.5-3.2 Ma and deep glacial erosion provides a look inside the volcanic center. Accurate age determination of these reversals is critical to correlation and dating of quaternary volcanics, sediments, and archeological artifacts worldwide.
Oregon Coast Range Rotation
The Coast Range of Oregon is thought to have rotated ~60 degrees into its current position since the Eocene. This is largely based on paleomagnetic data gathered in the 1960s and 70s, which are not up to modern standards (no demagnetization was performed in many cases). I collected and analyzed ~600 paleomagnetic cores from the Eocene Tyee Formation of the Oregon Coast Range to test the rotation hypothesis. I was unable to reproduce the results of earlier studies, despite using more sensitive magnetometers and more modern demagnetization techniques. My results suggest that these sediments do not preserve a primary paleomagnetic direction and should not be relied upon for any tectonic interpretations.
Baffin Flood Basalt Eruption Tempo
The flood basalts of southeastern Baffin Island (North Atlantic Igneous Province) probably represent the earliest magmas from the Iceland mantle plume. They are famous among isotope geochemists for their high 3He/4He ratios and primitive geochemistry. However, these rocks have not been dated via any modern geochronological technique, and have poorly characterized stratigraphy, physical volcanology, and surface distribution. This project uses 40Ar/39Ar geochronology, mapping, volcanostratigraphy, petrological modeling, and paleomagnetism to establish the age, eruptive tempo, emplacement mechanisms, and paleoclimate impacts of this flood basalt. Based a variety of evidence for rapid eruption, I found that all the exposed basalts likely erupted between 61.7- 62 Ma over a ~2500-year timespan. This suggests that they are responsible for the hyperthermal ‘Latest Danian Event’, a period of rapid global warming. Finally, these results also date the onset of rifting between western Greenland and the rest of the North American craton at this latitude.
Contact:
biasi@dartmouth.edu
Joe Biasi 