Understanding how Earth’s earliest granitic batholiths came to be: Structural geology of the 3.5-3.2 Ga East Pilbara craton, Western Australia

Author: Nick Roberts (PhD expected 2021)

I am a 5th year PhD Student working with Basil Tikoff on a unique structural geology problem—how Paleoarchean granitic domes were emplaced to form some of Earth’s earliest continental crust. My field area is a block of Paleoarchean crust on the northern coast of Western Australia called the Pilbara craton.

Today, granitic domes form in a variety of tectonic settings, from continental extension (think metamorphic core complexes in the Basin and Range in the US West), to continental collisional settings (Pyranese, Himalayas). Almost nothing is known about the tectonic setting of the ancient granitic domes of the Pilbara craton—not even whether Plate Tectonics existed. My job as a structural geologist is to document the deformation associated with these domes and to reconstruct the history of dome emplacement. The ultimate goal of this research is to understand the processes that led to the creation of a bimodal crust on earth—where thin, dense crust defines ocean basins while thick, more buoyant crust defines the continents.

I have gone to Australia three times to do fieldwork and collect samples for analysis here at UW-Madison. For the past six months, I have been working with two UW-Madison undergrads, Rex and Casey. Together, the three of us did extensive sample collecting and mapping in a particularly deformed zone in the Pilbara craton during the summer of 2018. Rex and Casey were there for 6 weeks of the 3-month field season and mapped a few areas as part of their senior theses.

Structural geology is not all fieldwork. Since the field season ended in August, Rex, Casey and I have been processing the hundreds of rocks samples we have collected. Processing includes reorienting all rocks into their original orientation, cutting rocks into small billets for thin sections, and drilling 1-inch cores for magnetic measurements. We’ve analyzed a few of our thin sections on the scanning electron microscope and presented this work at the 2018 American Geophysical Union.

I am passionate about geology, especially the study of how rocks in the middle to lower crust accommodate deformation at the regional and micro scales. I am more than happy to chat with students about careers, grad school, or anything else!

-Nick Roberts

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