MINERAL GEOCHEMISTRY OF MANTLE XENOLITHS AND THEIR HOST LAMPROPHYRES, WESTERLY, RHODE ISLAND

The goal of this project is to examine the differences in mineral chemistry between mantle xenoliths and their ultramafic volcanic host rock, lamprophyres from Westerly, Rhode Island. Understanding the differences between the two will help produce a better picture of the sub-continental lithospheric mantle during the late-stage rifting of the last supercontinent, Pangea. These lamprophyres intruded into the Narragansett Pier granite and the Westerly granite units. During the breakup of Pangea, a succession of shallow mafic intrusions that range from lamprophyres to dolerites were emplaced throughout New England, but the lamprophyres do not directly relate to the dolerites. These ultramafic dikes are alkali-rich, volatile-rich, rocks derived from direct partial melting of the Earth’s mantle. Both the lamprophyre and xenoliths are filled with minerals pyroxene and olivine but previous researchers (Maute et al., 2017) found there are differences in the Nd, Sr, Hf, and Pb isotope geochemistry between the xenoliths and the lamprophyres. This project will use the Electron Microprobe (EPMA) facility at Rutgers University to chemically analyze the minerals from both the xenoliths and their host lamprophyres and look for zonation indicative of magmatic processes. Additionally, these analyses will provide a better understanding of the pressure and temperature conditions of their formation in the mantle. The results will provide invaluable information about the mantle itself and present insight into the deep-seated tectonic activity and the conditions during the end of Pangea’s rifting sequence in southeastern New England.