Isotopic constraints on the origin of Appalachian mafic complexes

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ID: 294028
1984
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Abstract
Proto-Atlantic oceanic crust identified among the mafic and ultramafic rocks of the Appalachians. Sm-Nd mineral isochrons for the Baltimore Mafic Complex, Maryland (BMC) yield an age of 490 + or - 20 my, interpreted as the igneous crystallization age. BMC whole-rock samples do not define isochrons and have initial isotopic compositions of -6.4 < epsilon Nd (T) < -2.2, +51 < epsilon Sr (T) + 115. epsilon Nd (T) and epsilon Sr (T) are anti-correlated. This is not the signature of depleted mantle and oceanic crust but is similar to old continental crust. BMC is mafic continental intrusion, possibly subduction related, which was contaminated with old continental crust during emplacement. Whole-rock samples from the Thetford Mines Complex, Que. (TMC), do not define isochrons and have -1.5 < epsilon Nd (T) < +4.2, +2.6 < epsilon Sr (T) < +114. These data do not in any way reflect the signature of normal oceanic crust. The TMC is chemically and isotopically similar to a class of ophiolites that have affinities to modern boninites. The Chunky Gal Amphibolite, North Carolina, Lake Chatuge Complex, North Carolina, and Hazen9s Notch Amphibolite, Vermont were found to have a depleted mantle signature with +5 < epsilon Nd (T) < +8 and may be fragments of oceanic crust. The Webster-Addie body, North Carolina, has epsilon Nd (T) approximately -1, epsilon Sr (T) approximately +30 and is not isotopically similar to oceanic crust or the other North Carolina mafic bodies analyzed. Appalachian mafic rocks have diverse origins.--Modified journal abstract.
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openalex_W2120208585 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors H.F. Shaw, G. J. Wasserburg
Journal american journal of science
Year 1984
DOI
10.2475/ajs.284.4-5.319
URL
https://doi.org/10.2475/ajs.284.4-5.319
Keywords Keywords not found

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