TECTONICS OF EXOTIC TERRANES IN SOUTHEASTERN NEW ENGLAND
Southeastern New England is underlain by at least four different exotic geologic terranes. The juxtaposition and eventual collision of these terranes with North America led to the Acadian and Alleghanian orogenies in the mid- and late Paleozoic. By integrating studies in structure, petrology, and geochemistry, we are working to develop a picture of these terranes prior to their collision with North America. We are also investigating the plate tectonic processes by which these terranes were accreted to North America to better understand the resulting orogenies.
THE AVALON TERRANE OF SOUTHEASTERN NEW ENGLAND
The Avalon terrane consists of several tectonically separable blocks and units ranging in age from late Proterozoic to Pennsylvanian that have been deformed by at least two, and possibly four, late Precambrian and Paleozoic orogenic events. Preliminary research suggests that the collision of the Avalon Superterrane with North America was responsible for the Acadian orogeny in the rest of the northern Appalachians. However, the part of the Avalon terrane now making up southeastern New England was emplaced in the early stages of or prior to the Acadian orogeny. Ongoing research by graduate students is clarifying our understanding of the Avalon terrane and its origin. Additional research is related to understanding the sequence of tectonic events in this terrane, interpreted as a volcanic arc that lay off the coast of Gondwana, and to developing correlations of this terrane with those of West Africa, western and central Europe, and southern Britain and Ireland.
MYLONITE ZONES OF SOUTHERN NEW ENGLAND
Zones of severe brittle to ductile deformation separate many of the terranes in the eastern Appalachians. A better understanding of these complexly deformed zones will lead to a better understanding of the movements and processes of terrane accretion. Recently, we have been doing detailed analysis of the terrane boundary between the Avalon and Nashoba Terranes in southeastern New England marked by faults such as the Bloody Bluff Fault and Burlington Mylonite Zone. Here, protoliths of the mylonitic rocks include a range of plutonic and volcanic units. By understanding the movement directions recorded in the mylonites and dating unmylonitized igneous rocks using electron microprobe dating in situ monazite grains, we are able to establish controls on the accretionary history of this part of the Appalachians. Research includes detailed mapping, petrographic, structural and geochemical studies. This research offers an exciting opportunity to become involved in solving complex and significant structural, stratigraphic and tectonic problems that shed light on the processes of terrane accretion in the Appalachians and its extensions in Europe.
REGIONAL BEDROCK AND FRACTURE CHARACTERIZATION STUDIES IN THE NASHOBA TERRANE, MASSACHUSETTS
The Nashoba Terrace is highly metamorphosed ancient arc-back-arc complex lies west of the Avalon terrace in Southeast New England. With support from the U.S. Geological Survey, three students are currently mapping the bedrock of the enigmatic terrane at a scale of 24,000 to allow for a detailed analysis of its origin, metamorphic and accretionary history. In addition, the major terrane boardering an intraterrane fault zone is being studied in detail to diciper its timing and direction of motion. Further, since bedrock fractures provide most of the gorundwater resources in this region, detailed fracture maps and analysis are also being undertaken. These combined studies not only help to answer fundamental questions about the Nashoba Terrace but provide environmental and hydrological data to help meet societial needs.
ASSEMBLY AND DISPERSAL OF SUPERCONTINENTS
Many of the wide ranging research projects of the Department have as their goal an understanding and reconstruction of some aspect of the assembly and breakup of supercontinents. Evidence from the Northern Appalachians and from the other circum-Atlantic continents bears on aspects of the assembly and dispersal of the supercontinents Rodinia, Gondwana and Pangea.
GEOGRAPHIC INFORMATION SYSTEMS (GIS) IN THE ANALYSIS OF REGIONAL GEOLOGICAL/ENVIRONMENTAL PROBLEMS
The Department has an Arc/Info based GIS capability as part of our computer facilities. We are exploring the use of this powerful tool in solving geological and environmental problems. The tremendous amount of available data and the ability to display it graphically on a geographical basis is already leading to exciting new research possibilities in regional geological and tectonic applications as well as in a variety of other research areas.
