McLennan, S. M., Bock, Barbara, Compston, W., Hemming, S. R. and McDaniel, D. K. (2001) Detrital zircon geochronology of Taconian and Acadian foreland sedimentary rocks from New England. Journal of Sedimentary Research, 71 (2). pp. 305-317. DOI 10.1306/072600710305.

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Abstract

U-Pb ages of detrital zircons in lower Paleozoic sedimentary
rocks from New England permit evaluation of the relationships
between tectonic activity and provenance of foreland sediments deposited
in response to the Taconian and Acadian orogenies. The Lower
Cambrian Poughquag Quartzite was deposited on the Laurentian passive
margin. Poughquag detrital zircons (n 5 40) are mostly concordant
to slightly discordant with 207Pb*/206Pb* ages of 1.67–0.87 Ga
and are consistent with a provenance from the nearby Grenville Structural
Province. Two Poughquag zircon grains record 206Pb*/238U ages
of about 0.64 Ga and 0.55 Ga and could have been derived from riftrelated
magmatic rocks. The Middle Ordovician Austin Glen Member
of the Normanskill Formation and Lower Silurian Shawangunk Formation
represent clastic-wedge sedimentation in the Laurentian foreland
deposited in response to the Taconian orogeny (ca. 470–430 Ma).
Zircons from these units (n 5 41 for Austin Glen, n 5 29 for Shawangunk)
are also predominantly of Grenville age (207Pb*/206Pb* ages
of 1.46–0.94 Ga). One zircon from the Austin Glen records an age of
3.29 Ga, consistent with derivation from North American Archean terranes.
No zircon from either unit (or reported in the literature) can be
interpreted as recording an Ordovician (Taconian) age. Devonian Catskill
‘‘redbeds’’ represent synorogenic to postorogenic foreland sedimentation
associated with the Acadian orogeny (ca. 400–360 Ma). Zircons
from one sample (n 5 45) are all near concordant and have a
bimodal age distribution. Approximately 60% of grains have 207Pb*/
206Pb* ages of 1.23–1.00 Ga and the other 40% have 206Pb*/238U ages
of 0.47–0.42 Ga. Very different proportions of Precambrian and Paleozoic
ages are seen in the Catskill sample if zircons are selected on
the basis of size or optical clarity, and this observation highlights the
possibility of sampling bias if detrital zircons are not randomly selected
for U-Pb analysis. The 0.47–0.42 Ga population is consistent with derivation
from rocks crystallized during the Taconian orogeny. No analyzed
zircon in this sample records an unambiguous Devonian (Acadian)
age. Accordingly, during early Paleozoic evolution of the Laurentian
foreland basins in New England, detrital zircons do not appear
to record contemporaneous orogenic activity but instead are restricted
to recycling of the preexisting continental margin. It is possible that
substantial topography (e.g., accretionary prism) impeded sediment
transport from the active orogen to the foreland basin.

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