2017/11/29 by Margaret D. Thompson, Jahandar Ramezani, Anne M. Grunow +1
Earth and Planetary Sciences · Computer Science · #Geological and Geochemical Analysis #Geochemistry and Geologic Mapping #High-pressure geophysics and materials
paper · doi:10.1086/694867
Mid-Paleozoic alkalic plutons and associated volcanic rocks in a northeast-trending belt transecting the southeastern New England segment of “West” Avalonia are well known for their anorogenic, “within-plate” geochemical signatures, yet poor age control has obscured the tectonic setting of this magmatism. Although studied in the past by pioneers of mineralogy and petrology, this group of rocks currently stands out as the only northern Appalachian unit on the lithotectonic map of the Appalachian orogen as having “uncertain tectonic affinity.” New high-precision zircon geochronology derived from weighted-mean 206Pb/238U dates by the chemical abrasion–TIMS method establish the following crystallization ages for members of mid-Paleozoic alkalic suite: 426.00 ± 0.50–423.93 ± 0.51 Ma for the Cape Ann Pluton, 411.96 ± 0.52 Ma for the Wampatuck rhyolite associated with the 411.58 ± 0.50 Ma Quincy Granite, 377.97 ± 0.44 Ma for the Peabody Granite, and 377.74 ± 0.44 Ma for the Wenham Monzonite (2σ total errors). A date of 422.99 ± 0.51 Ma was also obtained from the Newbury Volcanic Complex located in the Ganderian Putnam-Nashoba terrane that formed the mid-Paleozoic Laurentian margin in southeastern New England. The new geochronology is integrated with a compilation of published U-Pb dates and paleomagnetically determined paleolatitudes to examine the history of within-plate magmatism during West Avalonia’s northward drift from Gondwana to collision with Laurentia and to assess possible intraplate mechanisms for recurrent bimodal alkalic activity in the same zone for more than 70 My.