A GEOCHEMICAL AND PETROGRAPHIC ANALYSIS OF THE ECHO POND PLUTON, VT

A group of syn- to post-collisional Devonian plutons in the Northeast Kingdom of Vermont is representative of a significant period of magmatism that occurred after the main phase of the Acadian Orogeny between approximately 390 and 360 Ma. The dates of the Acadian Orogeny are poorly constrained and the tectonic history near the end of the Acadian Orogeny is poorly understood. The study of these plutons using modern techniques of geochemistry and age-dating is an important step toward gaining a better understanding of the tectonic processes occurring at the end of the Acadian Orogeny.

The focus of this study is the Echo Pond Pluton, a member of a group of plutons collectively known as the Northeast Kingdom Batholith. Our work has confirmed the presence of four distinct zones in the Echo Pond Pluton, based on rock type: mafic zones in the southern and northeastern areas of the pluton containing quartz-amphibole gabbro and diorite, a zone of granodiorite and granite that constitutes the central portion of the pluton, and a small zone of porphyritic granodiorite and granite containing rounded quartz grains in the east-central part of the pluton. The pluton intrudes the meta-sedimentary rocks of the Gile Mountain Formation. Quartz veins, granite dikes, and xenoliths are common at gradational contacts with the surrounding country rock. Previous workers used isotopic data to suggest that both mantle and crustal components played a role in the evolution of the Echo Pond Pluton. ICP-AES analysis of major, minor, and trace elements and ICP-MS analysis of rare earth elements will build upon this work, leading to more detailed conclusions about the magmatic evolution of the pluton.

Few studies have addressed the Echo Pond Pluton specifically, and little is known about its magmatic origin. Moreover, a precise age for the Echo Pond Pluton has not been obtained. The use of U-Pb dating of zircon, petrography, and modern methods of geochemical analysis will further constrain the dates of Acadian magmatism in Vermont and contribute to a more complete understanding of the magmatic origin and tectonic processes that led to the emplacement of the Echo Pond Pluton. This study hopes to accomplish this and provide a foundation for future study of the final stages of the Acadian Orogeny in Vermont.