Below are recent summer research projects completed by students studying Geology at Pomona College.

2019

Interpreting the Geologic History of the Tuulikki Mons Region, Venus

Mattea Horne ’22; Advisor: Eric Grosfils

We mapped Tuulikki Mons, a ~500 km diameter Venusian volcano, and its vicinity in order to constrain its geologic history and interactions with the surrounding environment. The data used consisted primarily of Magellan radar backscatter and topography imagery of the surface. We identified key geologic features and units in ArcGIS, mapping their extent as they related to our primary goal. Using basic geological principles, including superposition and cross-cutting relationships, we identified significant stages (e.g. material units, deformation) characterizing the volcano’s placement in the regional stratigraphy (order of events). We found that the units defining Tuulikki Mons (Dark Basal Flows, Digitate Flows, and Dark Summit Material) were younger than the surrounding regional plains units. However, several other volcanic centers nearby overlap in age with Tuulikki Mons, indicating concurrent activity and hence a pulse of regional volcanic activity. We then used a numerical finite element model of Tuulikki in COMSOL Multiphysics to assess crustal flexure as a result of the volcano’s load. By varying lithospheric elastic thickness, we reproduced a flexural moat and arch preserved to the west of the volcano for an elastic thickness of 25 km, in agreement with predictions for the region previously reported in the literature.

2017

Titanite Geochronology of the Sierras

Grace Hruska ’18; Advisor: Jade Lackey

Sierra Nevada batholiths and neighboring plutons have been previously dated using Zircon-geochronology methods but have yet to be studied utilizing titanite until now. Titanite (CaTiSiO5), is an accessory mineral found in calc-alkaline plutons that can be used to calculate the ages of plutonic batholiths. Titanite has an unusual crystal structure that takes up uranium (U), zircon (Zr) and rare earth elements (REE), and has low diffusivity rates of U. Unlike zircon, titanite has a high closure temperature of 650-700 C which indicates that it cooled before zircons, this information can then be used to calculate cooling rates of granitic rocks. Methodology included selection of magmatic and metamorphic titanite grains, mounting grains onto an epoxy puck, SEM imaging and measurement of isotope concentrations with ICP-MS. Results from age calculation have yet to be fully analyzed for calculation of cooling rates and relationship of previously zircon-dated rocks. We need to reduce a few of the data sets and interpret them but preliminary findings suggests that the young Eastern Sierra titanites have good dating systematics, a sufficient amount of common lead, and can be used to determine cooling rates.
Funding Provided By: Department Funding

Trace elements in the San Gabriel streams

Olivia Mendoza ’20; Advisor: Jade Lackey

Trace elements are depicted at different concentration levels depending on the discharge levels at each stream. The goal of this project was to investigate trace metal levels in the San Gabriel mountains following a high rainfall year. We sampled water from 24 different sites in 6 different streams and ponds, using the US Fish and Wildlife Service water sampling protocol. Old USGS data showed us that elements such as arsenic had higher concentrations during lower discharge years, we wanted to find similar patterns with silver, aluminum, beryllium, zinc, and other elements that indicate geological processes. We sampled at places that had interesting settings such as landslide zones, fault areas, and springs. Samples were run through an inductively coupled plasma mass spectrometer (ICP-MS) to determine trace element levels. Some elements, including strontium and tin, had high levels in all sites sampled. In contrast, zinc levels were high in two of the six streams and zero in all others. Manganese and aluminum levels also varied by stream, but these differences could be due to variation in sampling methodology. We then compared our own data do historical data on trace element levels and water flow rates. We are still in the process of comparing high rainfall years to lighter rainfall years in our specific zones but our data has already shown us that sampling techniques, heavy debris zones, and springs indicate massively different trace level element concentrations.
Funding Provided By: Department Funding