Research

Eruption Timescales

This project exploits a new method that I have developed, called magnetic geothermometry. The method can determine the amount of time that an intrusion or magmatic conduit was actively supplied with magma (dike, sill, pluton, etc.). The method uses a combination of paleomagnetic data, geochemical data, and thermal modeling. Since it does not rely on radioactive decay or chemical diffusion, it can be applied equally to young (<1 Ma, or active) and old (>2 Ga) magmatic systems.

I’m applying this technique to shallow dikes of the Columbia River Basalts, in order to determine their eruption timescales. The duration of LIP eruptions has major implications for the mechanisms of mass extinction and paleoclimate modeling.

Mafic Terranes of Northern Alaska

Interior and northern Alaska is host to abundant mafic and ultramafic rocks. These units collectively cover 38,000 km3, the same area as Switzerland or Maine. However, very few geochemical analyses exist for these rocks, despite their prevalence.

This project aims to geochemically characterize these rocks, in order to better inform tectonic models of the region.

Baffin Flood Basalt Eruption Tempo

The flood basalts of southeastern Baffin Island (North Atlantic Igneous Province) are famous among isotope geochemists for their high 3He/4He ratios. However, these rocks are too primitive to date via 39Ar/40Ar or any other means yet developed. Therefore the age of these basalts is very poorly constrained. In addition, very little paleomagnetic data exists from this unit.

The goal of this project is to use paleomagnetic and geochemical data to determine which chron these basalts were erupted during, and to use secular variation in the data (or lack thereof) to roughly determine the amount of time between eruption of each flow.

39Ar/40Ar Geochronology of Altered Basalts

The Columbia River Basalts have been dated by 39Ar/40Ar geochronology, and more recently by U-Pb Zircon geochronology from interbedded ash deposits. These two methods disagree significantly, and the U-Pb results are now widely accepted as ‘correct’.
However, nobody knows why erroneous 39Ar/40Ar ages were measured in these rocks. The goal of this project is to geochemically and magnetically characterize CRB basalts of varying degrees of alteration. These same samples will then be dated 39Ar/40Ar to determine the link between alteration and age, and to determine which geochemical or magnetic indicators will show that a sample can yield a ‘correct’ age.

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.

However, a reexamination of these data found that they are not up to modern standards (only NRMs reported in many cases), and should not be relied on for any tectonic interpretations.

The goal of this project is to re-sample the Eocene Tyee formation of the Oregon Coast Range, to test the rotation hypothesis. Preliminary results suggest that these sediments do not pass the fold test, and therefore do no preserve a primary remanence.

Goat Rocks Volcanic Complex

This project is focused on the volcanostratigraphy, mapping, and magnetostratigraphy of the Goat Rocks volcanic complex in Washington. This eroded Cascade Arc composite volcano was active from 0.5-3.2 Ma, and deep erosion provides a look inside a young arc volcanic center.

Several geomagnetic reversals and excursions are preserved here, and a portion of the project aims to find these reversals and refine their age.

Uplift of Steens Mountain

Steens Mountain is a very large and prominent topographic feature in southeastern Oregon. You should drive to the top if you’re ever in the area, the view cannot be overstated. This is the source region of the Steens Basalts, the oldest member of the Columbia River flood basalts. The eastern face of the mountain was created by a prominent basin and range normal fault. However, the timing of fault activation and topographic uplift is not known.

This project uses thermochronologic, structural, stratigraphic, and paleomagnetic data to determine the uplift history of Steens Mountain. Preliminary data suggests that uplift was already underway by 15 Ma but significant uplift did not occur until after 10 Ma.

Antarctic Peninsula Paleomagnetism

The history of the geomagnetic field over Antarctica is poorly constrained. This is due to a lack of samples, which is obviously due to the remote location.
This project uses hundreds of cores from the Antarctic peninsula to better characterize the declination, inclination, and intensity of the magnetic field over the Antarctic Peninsula over the last ~5 Ma.

In addition, magnetic and geochemical data are being used to refine the volcanostratigraphy and magma supply rates of the James Ross Island Volcanic Group.

Contact:
biasi@caltech.edu

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