Reports: UR856956-UR8: Post-Rift Tectonism on Circum-Atlantic Margins?

William H. Amidon, PhD, Middlebury College

The goal of our research is to identify the spatio-temporal pattern of tectonic rejuvenation in the northeastern U.S. and thus constrain possible mechanisms of uplift. We are doing this with a two-pronged approach involving: 1) changes in the provenance of detrital minerals in the Baltimore Canyon Trough, and 2) low-temperature thermochronology in onshore drill cores. The detrital approach will allow us to determine the origin of three sediment pulses over the last 150 million years, which are likely generated by tectonic uplift with the northeastern U.S.. The thermochronology approach will allow us to determine the specific exhumation history of several key locations in the northeastern U.S. Our work began with two senior thesis students in the 2016-2017 academic year and was followed up with the work of four undergraduate students during the summer of 2017 who received a stipend through the PRF grant.

On the detrital side we have completed U-Pb zircon dating of our original 5 samples from the COST-B2 core and 8 samples of modern river sediment from across the northeastern U.S.. These U-Pb zircon results suggest that the Miocene sediment pulse was likely derived from the Adirondack region, although these results await confirmation from analysis of other heavy mineral phases. This summer we obtained 12 new samples from the COST-B2 sediment core, and 3 new river samples and have completed mineral separation, mounting, and SEM analysis of those samples. At this point we have a partial dataset including mineral abundance and major element chemistry of most of the samples mentioned above. Next steps will be to undertake trace element analysis on specific mineral phases such as garnet and ilmenite, which have proved to be the most common detrital heavy minerals.

On the thermochronology side we have obtained samples from two deep drill cores. One is the 4700’ deep Moodus Deep Core from East Haddam, CT and the other from the 6500’ deep Sterling Hill Core from Franklin, NJ. These samples were obtained by a field trip to two different drill core repositories and also to the drill sites to collect complementary surface samples. Since collection in mid-July 2017 we have completed separations of apatite and zircon from both cores and are in the process of shipping samples out for apatite fission-track and apatite U-Th/He dating. Thus, we do not have new data or interpretations to report, but should have this by the end of calendar year 2018.

In summary, our first year has been quite productive but we have not yet generated enough data to draw preliminary interpretations. We are hopeful that our second year will bring some preliminary interpretations and allow us to focus our research accordingly for the final year of the project.