Proterozoic Mountain Building and Collapse, Eastern Adirondacks, New York

Rocks of the Adirondack Mountains of New York represent a large dome-shaped uplift of the Precambrian basement of North America. These rocks record the assembly and breakup of the supercontinent, "Rodinia" that formed approximately 1 billion years ago. The formation and dispersal of this continent may have played a role in the evolution of life on Earth, the evolution of climate and the production of a snowball Earth, and in the development of important economic resources, including Rare Earth Element deposits. New data are significantly changing our understanding of the history of the Adirondack uplift. A major period of mountain-building, the 1180 million year Shawinigan orogeny, was previously unrecognized in the region, and one challenge involves recognizing and distinguishing the effects of this tectonism compared to the 1050 Million year Ottawan orogeny that was previously thought to dominate the geology of this region. The latest stages in the geologic history of the Adirondacks involved intrusion of extensive granite ("Lyon Mountain granite") and the development of shear zones that were important in the collapse of the mountains and in the uplift of the basement rocks. This research will involve modern structural, petrologic, and geochronologic analysis to characterize the geologic and tectonic history of the eastern Adirondack region, and further our understanding of mid crustal processes during mountain building and collapse. This work represents a new collaboration between the University of Massachusetts and Castleton State College, a predominantly undergraduate state college nearly adjacent to the Adirondack field area. In addition to the PIs, the research team will consist of undergraduates from Castleton State College and a graduate student from the University of Massachusetts. The graduate student will serve as a mentor for undergraduates from Castleton and a link between the two institutions. The collaboration will provide an ideal base for field research during all seasons of the year and it will provide access for Castleton undergraduates to a predominantly undergraduate state college nearly adjacent to the Adirondack field area. In addition to the PIs, the research team will consist of undergraduates from Castleton State College and a graduate student from the University of Massachusetts. The graduate student will serve as a mentor for undergraduates from Castleton and a link between the two institutions. The collaboration will provide an ideal base for field research during all seasons of the year and it will provide access for Castleton undergraduates to a research-oriented university and to research equipment. Finally, the eastern Adirondack Mountains are a popular destination for hiking, camping, and vacations. Student researchers will work to develop outreach materials and programs about the geology of the spectacular northeastern Adirondack region.

This research tests the hypothesis that there is a regionally extensive shear zone in the eastern Adirondacks in the vicinity of Whitehall, New York that accommodated the eastward unroofing of the Adirondack Mountains during orogenic collapse shortly after the culmination of the Ottawan orogenic event (ca. 1050 Ma). Preliminary in-situ monazite ages constrain the extensional shearing to 1050-1026 Ma, similar to those reported for the extensional movement on the Carthage-Colton shear zone in the NW Adirondacks. These data suggest that orogenic collapse following the Ottawan orogeny resulted in the formation of a two-sided metamorphic core complex or gneiss dome structure. This project will utilize in-situ high resolution monazite geochronology, in conjunction with detailed field mapping, structural and kinematic analysis, and metamorphic petrology in order to characterize the extent, kinematics, and timing of East Adirondack shearing and to integrate the shear zone into the overall tectonic history of the Adirondack Mountains. The Grenville orogen marks the culminating collision in the assembly of the supercontinent Rodinia. Post-collisional collapse of the Himalayan-scale Grenville orogen signaled the start of a new phase of rifting, passive margin development, and in the broadest sense, the Appalachian Wilson cycle. Major changes have been proposed in the character and age of tectonic events involved in the construction and collapse of the orogen. With the coming of Earthscope-US-Array and GeoPrisms it is critical to evaluate new models for this orogen that may have had a controlling influence on the geometry and character of the proto-Atlantic margin. The proposed research will involve detailed field mapping and structural/petrographic analysis in order to establish a chronologic framework for the development and overprinting relationships of fabrics and metamorphic mineral assemblages. Rocks related to each of the major stages of Adirondack orogenesis (Elsevirian, Shawinigan, AMCG plutonism, Ottawan, etc) are all in close proximity in the eastern Adirondacks. The project involves the use of thermobarometry and psuedosection analysis to delineate the Pressure-Temperature evolution of the crust during the orogenic events with particular focus on the late-stage shearing. A major portion of the work will involve in-situ monazite geochronology in order to place timing constraints on all parts of the history. Our ultimate goal is to place new constraints on the tectonic history of the Grenville Orogen, especially on the collapse and exhumation stages, and also to add to the evolving understanding of monazite behavior during metamorphism and deformation. This work will help to place the Adirondack massif within the context of gneiss domes and provide evidence about the role that this dome played in the collapse and exhumation of the orogen.