The Superior craton represents the largest exposure of Archean crust on Earth and can offer insights into the long-term evolution of cratonic geotherms. U-Pb geo- and thermochronology of zircon and rutile from lower and mid-crustal xenoliths record lower crustal crystallization, metamorphism, and long-term cooling prior to surface exhumation within a Jurassic-aged kimberlite. Archean igneous zircon LA-ICPMS ages range from 2751 21 to 2341 41 Ma, indicating a prolonged record of zircon crystallization. Preliminary U-Pb LA-ICPMS rutile data has a far wider range of ages from 2660 140 to 324 17 Ma and are interpreted to record the long-term relaxation of the cratonic geotherm. Nitrogen aggregation data collected from diamonds exhumed within the Jurassic and a nearby older Proterozoic (~1.1 Ga) kimberlite pipe suggest at least two major diamond-forming events after craton formation. These data require that a thermal pulse caused by the Keweenawan Midcontinent Rift at ~1.1 Ga reverted the mostly high N-aggregated IaB diamonds to graphite but did not perturb the deep crust (~50 km depth). As the geotherm relaxed after the thermal pulse, the diamond stability window was reoccupied and a second diamond-forming event took place before later Jurassic eruption of poorly nitrogen-aggregated type IaA diamonds near Attawapiskat, Ontario. Maintenance of Archean rutile U-Pb cooling ages in middle-crustal amphibolite limits the magnitude of reheating.

With more than 70m of sea level equivalent ice stored in the polar ice sheets, sea level forecasting is heavily reliant on projections of ice sheet response to changes in global climate. One way that Earth scientists have approached this problem is to look back at past warm periods to determine how terrestrial ice mass changed in during previous climatic events. In Antarctic, however, there is an added complexity that 97.6% of the modern continent is covered by ice, which restricts access to the geologic record. Without terrestrial archives of Antarctic ice sheet evolution, it is challenging to parameterize the dominant processes that govern ice sheet sensitivity to climate and the environmental effects of ice loss. In this dissertation, I applied geochronologic, isotopic, elemental, and spectroscopic analyses to Antarctic subglacial chemical precipitates – a novel terrestrial record of basal conditions – to investigate the processes that link climate change, Antarctic ice motion, and the hydrologic system at the ice-bed interface. Collectively, this work expands our understanding of Antarctic evolution on centennial to millennial timescales and establishes Antarctic subglacial precipitates as climate archives analogous to speleothems.The first two chapters investigate the physical processes associated with subglacial hydrology and ice motion. By applying geochronologic and geochemical analyses to a group of precipitates that formed over tens-of-thousands of years during the Late Pleistocene, we showed that the continent-wide Antarctic subglacial hydrologic system responds rapidly (within 60 yrs.) to millennial-scale climate events, with more intense subglacial flushing during warm periods and diminished basal meltwater flow during cold periods. This close coupling between climate and subglacial hydrologic activity requires changes to Antarctic ice surface slope caused by hundreds of meters of thinning at the ice sheet margins. These studies provide evidence that the Antarctic gains and loses ice during millennial-scale climate cycles and indicate that subglacial meltwater flushing drive higher ice velocities that promote ice thinning and grounding line retreat. The latter chapters focus on the mechanisms that control the chemical composition of subglacial waters, to help discern the environmental effects of Antarctic ice loss on geologic timescales. The third chapter uses stable isotope measurements ( carbon and oxygen) on a suite of 49 subglacial precipitates to show that microbial activity mobilizes fossil carbon stored in rocks and sediment throughout the Antarctic continent. This respired CO2 drives a continent-wide silicate weathering cycle that mobilizes elements from the subglacial bedrock, which may play an important role in fertilizing the Southern Ocean ecosystem. Chapter 4 established 10 kyr record of trace metal cycling beneath the East Antarctic Ice Sheet (EAIS) measured in a subglacial precipitate that formed across glacial termination III. This record implies that climate modulated changes in subglacial flushing intensity regulate the mobilization of redox sensitive trace metals on geologic timescales.