CHARACTERISTIC DETRITAL ZIRCON POPULATIONS OF THE EASTERN LAURENTIAN MARGIN IN THE APPALACHIANS

We compiled 7534 concordant U–Pb detrital zircon data from the literature for eight geographic domains along the eastern Laurentian margin from Newfoundland, Canada to Alabama, USA, to test whether variations exist along strike, and to provide a reference database for future U–Pb detrital zircon studies. Data are from Neoproterozoic–Devonian units in the northern Appalachians and from Neoproterozoic–Permian units in the southern Appalachians. Samples containing significant ~700–500 Ma and ~2200–2000 populations were excluded. These populations do not have substantial Laurentian sources. They are most likely derived from Gondwanan material, which is characterized by large Pan-African/Brasiliano (~700–500 Ma) and substantial Transamazonian/Eburnian (~2200–2000 Ma) zircon populations. Gondwanan material forms a major source for detrital zircon in the Appalachians, because Gondwanan-derived terranes form the outboard terranes along the entire eastern Laurentian margin since their mid-Paleozoic accretion, and Gondwana collided with Laurentia during the late Paleozoic formation of supercontinent Pangea.

The general Laurentian margin detrital zircon signature is highly consistent along the entire length of the Canadian and US Appalachians. The Precambrian signature is characterized by a small ~2.7 Ga population and a major ~1.9–0.9 Ga Ma population that peaks at ~1.2–1.0 Ga. Analysis of only Neoproterozoic to Cambrian units yielded the same Precambrian signature. Detrital zircon populations are from the Archean craton (~2.7 Ga population), Paleoproterozoic orogens (~1.9–1.6 Ga), the Granite-Rhyolite province (~1.5–1.4 Ga), the Elzevir block and Grenville province (~1.3–0.9 Ga). The Mesoproterozoic populations vary in size depending on proximity to the ~1.5–1.4 Ga Granite-Rhyolite province, the ~1245–1225 Ma Elzevir block and the ~1.2–0.9 Ga Grenville province. A middle Ordovician zircon population varies in size along strike depending on input from the Taconic orogenic belt, but is strongest in the Northern Appalachians. Because of the general along-strike consistency in detrital zircon age populations, the compilation of all U-Pb detrital zircon data can be used in future U–Pb detrital zircon studies as an indicator for eastern Laurentian margin sources.