Research

I study periods of volcanic activity which are either protracted (such as at a major volcanic center) or brief (such as at a monogenetic volcano). Paleomagnetism records fine-scale variation in the geomagnetic field which allows brief episodes to be delineated at a finer scale than geochronological methods. Tying the two together for an absolute time picture is important. Paleomagnetic data and precise geochronological data are helpful in delinating relative and absolute timing vis-a-vis "single" intrusions and more obviously polyphase complexes. My work in this area takes place in California at both distributed shield volcanoes of the Cascade Volcanic Arc as well as at the Clear Lake Volcanic Field. I have also worked in Utah (Henry Mountains), Wyoming (Yellowstone), Colorado, and Oregon in volcanoes and hypabyssal intrusions from all periods within the Phanerozoic.

I also have interest in the paleomagnetism of flows and intrusions of large igneous provinces from the Miocene to the Proterozoic. Both polarity and secular variation of the geomagnetic field are useful to correlate flows, define tectonic deformation, and meter time. I have worked on these questions in Oregon, Washingon, and Idaho, as well as internationally in India.

Mafic dyke swarms infest Precambrian cratons. These swarms have a variety of favorable characteristics that make them ideal for paleomagnetic studies (Halls, 2008). Additionally, geochronological constraints on these dykes create a "bar code" that can be compared to other cratons. Unraveling the generational history of these dyke swarms with multiple methods at a variety of scales is the best tool for the quantitative assessment of Proterozoic paleogeographical reconstructions. My work in this area has been focused on mafic dykes in the cratons of India and Antarctica.

Large-scale remagnetization has severely impacted the early Paleozoic paleomagnetic record in North America (McCabe and Elmore, 1989; Geissman and Harlan, 2002; Torsvik et al., 2012). The unique spatiotemporal circumstances surrounding these remagnetizations deserve closer scrutiny with both paleomagnetism and geochronology. The implication of such pervasive remagnetization for Precambrian paleomagnetism through repeated assembly and dispersal of supercontinents may be under-appreciated. My work in this area has taken place in Southern Colorado (Cambrian intrusive centers) and Western New York (Devonian black shales).

Sometimes, late at night, a sleepless mind ponders the big questions: how does paleomagnetism relate to deep-Earth processes, can quality criteria be updated for modern paleomagnetists, and does GAD exist? These questions can - and have been - tackled through a variety of methods. My work in this area ranges from thinking to doing, with current work focusing on the utility of random walks to paleomagnetism.