Geochronology, Petrology, and Geochemistry of the Jurassic White Mountain Batholith, New Hampshire

Tufts University, Medford MA

Investigators

Abstract

The White Mountains of New Hampshire are composed of metamorphic rocks formed during the formation of the supercontinent Pangea and igneous rocks emplaced and erupted during the subsequent opening of the Atlantic Ocean. The igneous rocks include granites (New Hampshire is known as the Granite State) and volcanic rocks that form spectacular cliff faces such as the iconic 'Old Man of the Mountain' in Franconia Notch State Park. The geologic trigger for this phase of magmatism, however, remains largely unknown. The PI will train undergraduate students at Tufts University to sample the rocks throughout the region in order to obtain chemical and age information that can be used to link the magmatism to a particular geologic process that gave rise to the New Hampshire we see today. The results will be disseminated in a series of peer-reviewed journal articles, and at professional scientific conferences. As a capstone to the project, the PI and students will develop a dedicated summer-long exhibition at the Museum of the White Mountains in Plymouth, New Hampshire in order to communicate the results to the general public. The exhibit will include examples of rocks and minerals (both large-scale slabs and microscope slides) that are typical of the region, videos of tectonic plate motions during the opening of the Atlantic, primers on geologic dating techniques, and trail guides for hikers interested in learning more about geology in the White Mountains. In this project, the PI and undergraduate students at Tufts University will focus on establishing a detailed geochronologic, petrologic, and geochemical dataset for the main phase of magmatism in the White Mountain Magma Series (WMMS), the White Mountain Batholith. The White Mountain Batholith (WMB) is composed of a series of porphyritic syenites, hornblende granites, biotite granites, and comendite (Na-rich rhyolite) tuffs. Recently published ages from Kinney et al. (2022) reveal that the WMB is not a monolithic pluton, but is instead composed of two distinct magmatic centers: the western batholith and the eastern batholith. Magmatism first initiated in the western portions of the batholith (198 -190 Ma) and then appears to jump to the eastern portions approximately 10 Myr later (184 - 180 Ma). The researcher's work will establish the timing of emplacement between various units and plutons, the depths of emplacement, and the petrogenetic relationships between each unit. Undergraduate student training is a central focus of this work and the PI will train a total of six undergraduate students at Tufts University on scientific research projects over the three year period. Students will obtain high precision U-Pb zircon ages for key sample localities across the batholith to constrain the timing of emplacement, as well as obtain whole rock major and trace element compositions and Rb-Sr and Sm-Nd isotopic compositions for each lithological unit in the western, eastern, and central batholiths. Their results will be an essential first step in distinguishing between various geodynamic scenarios for the origin of the WMMS. A summer-long dedicated exhibition at the Museum of the White Mountains (Plymouth, NH), and associated public lecture series, will provide a capstone to the project and allow the PI and students to communicate their results to the general public. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.