High silica magmas cause the most explosive and potentially destructive volcanic eruptions on Earth. Studies of volcanic rocks have shed light on the processes that occur in magma chambers prior to explosive eruptions. However, many of these processes have not been fully documented in intrusive magmatic rocks, some of which represent fossil magma chambers. My research is focused on identifying the plutons, or parts of plutons, that represent coherent fossil magma chambers and using these natural laboratories to study the processes that ultimately lead to eruption.

Outcrop of granite with enclave
Meter-scale granodioritic enclaves (dark rock) within the Golden Horn batholith. The enclaves represent hotter, less evolved magma that intruded into a crystal-rich granitic magma and cooled quickly. If you look closely you can see crystals that were entrained in the enclaves during intrusion.

Crystal-liquid separation is one of the fundamental processes that drives changes in magma composition. On a large-scale this process contributes to the differentiation of continental crust, while on the scale of an individual intrusion it can lead to a greater potential to dike or erupt. However, the timescales over which this process occurs over a range of crustal depths and magma SiO2 content remain largely unconstrained. Recently, I’ve become interested in better constraining these timescales. This research has involved work on crystal-liquid separation in large, upper-crustal, silicic magma reservoirs as well as quantifying the rates in layered mafic intrusions. I’m currently exploring techniques and potential localities to expand this research to the middle and lower crust.

Pluton differentiation timescale
Coupled geochronologic and geochemical constraints on the timescale of magmatic differentiation from alkaline basalt to quart monzonite in the Dariv Complex, Mongolia from Bucholz et al. (2017).

Large igneous provinces (LIPs) represent relatively short periods of voluminous basaltic magmatism. This magmatism is present throughout the geologic record and shares a temporal coincidence with many of Earth’s mass extinctions. However, the link between volcanism and extinction remains enigmatic. One proposed link is that volatiles released during LIP magmatism drive climate change. This hypothesis requires extremely high eruption rates coincident with and immediately preceding the mass extinction event. Over the past few years, I have worked to quantify eruption rates in two LIPs: the Deccan traps, which were emplaced coeval with the end-Cretaceous extinction and the accreted Siletzia oceanic plateau, which is not associated with paleoclimate change nor an extinction event. The eruption rates in these two provinces are markedly different, providing one possible explanation for this difference.

A weathering horizon on a basalt flow
Paleosol (red bole) between two basalt flows within the Deccan Traps. Here you can see the paleosol forming a thick mantle between the flows and filling voids in the flow top breccia of the lower flow.

In some continental rifts there is little magmatism and large areas of subcontinental lithospheric mantle are exhumed. However, the mechanism by which these rocks are exhumed remains controversial. Two of the main hypotheses are 1) the mantle is exhumed along large-scale detachment faults or 2) the mantle is exhumed during ultra-slow seafloor spreading. These two models make dramatically different predictions regarding the timing of mantle exhumation and magmatism on each margin. The detachment model predicts highly asymmetric record of exhumation and magmatism, while the ultra-slow seafloor spreading model requires a more symmetric record. Recently, I was able to work with a unique set of samples from ODP cores drilled along conjugate margins of the Jurassic-Cretaceous Newfoundland-Iberia rift, which I used to test these two hypotheses.

Diagram representing progressive rifting
Cartoon of mantle exhumation along a lithospheric-scale detachment fault prior to plate rupture and initial seafloor spreading from Eddy et al. (2017). This model may explain why magmatism and mantle exhumation was time-transgressive from east to west and the narrow region of exhumed mantle on the Newfoundland margin compared to the Iberia margin.