Precise U‐Pb Zircon Constraints on the Earliest Magmatic History of the Carolina Terrane

Abstract

The early magmatic and tectonic history of the Carolina terrane and its possible affinities with other Neoproterozoic circum-Atlantic arc terranes have been poorly understood, in large part because of a lack of reliable geochronological data. Precise U-Pb zircon dates for the Virgilina sequence, the oldest exposed part, constrain the timing of the earliest known stage of magmatism in the terrane and of the Virgilina orogeny. A flow-banded rhyolite sampled from a metavolcanic sequence near Chapel Hill, North Carolina, yielded a U-Pb zircon date of 632.9 +2.6/-1.9 Ma. A granitic unit of the Chapel Hill pluton, which intrudes the metavolcanic sequence, yielded a nearly identical U-Pb zircon date of 633 +2/-1.5 Ma, interpreted as its crystallization age. A felsic gneiss and a dacitic tuff from the Hyco Formation yielded U-Pb zircon dates of 619.9 +4.5/-3 Ma and 615.7 +3.7/-1.9 Ma, respectively. Diorite and granite of the Flat River complex have indistinguishable U-Pb upper-intercept dates of 613.9 +1.6/-1.5 Ma and 613.4 +2.8/-2 Ma. The Osmond biotite-granite gneiss, which intruded the Hyco Formation before the Virgilina orogeny, crystallized at 612.4 +5.2/-1.7 Ma. Granite of the Roxboro pluton, an intrusion that postdated the Virgilina orogeny, yielded a U-Pb upper intercept date of 546.5 +3.0/-2.4 Ma, interpreted as the time of its crystallization. These new dates both provide the first reliable estimates of the age of the Virgilina sequence and document that the earliest known stage of magmatism in the Carolina terrane had begun by 633 +2/-1.5 Ma and continued at least until 612.4 +5.2/-1.7 Ma, an interval of approximately 25 m.yr. Timing of the Virgilina orogeny is bracketed between 612.4 +5.2/-1.7 Ma and 586+/-10 Ma (reported age of the upper Uwharrie Formation). The U-Pb systematics of all units studied in the Virgilina sequence are simple and lack any evidence of an older xenocrystic zircon component, which would indicate the presence of a continental-type basement. This observation, together with the juvenile Nd isotopic character of the Virgilina volcanic arc sequence, suggests that the oldest part of the Carolina terrane was built on oceanic crust away from a continental crustal influence.

Detrital Zircon Geochronology Across the Chopawamsic Fault, Western Piedmont of North-Central Virginia: Implications for the Main Iapetan Suture in the Southern Appalachian Orogen

“…6). Neoproterozoic to Early Cambrian detrital zircon grains in the Storck sample are consistent with derivation from the peri-Gondwanan microcontinent of Carolinia which includes potential detrital zircon sources of the Virgilina (630 -610 Ma; Samson et al 1995;Wortman et al 2000) and Albemarle (575 -532 Ma; Hibbard et al 2002) magmatic sequences. Furthermore, the Neoproterozoic to Early Cambrian population present in the Storck sample is similar to the detrital signature observed in metasedimentary samples from Carolinia .…”

Neoproterozoic?Early Paleozoic evolution of peri-Gondwanan terranes: implications for Laurentia-Gondwana connections

“…However, initial Nd values of +0.5 to +5.9 and T DM model ages of 0.7-1.1 Ga from ca. 635-610 Ma volcanic rocks of the Virgilina sequence Wortman et al 2000) suggest that Carolina, like Avalonia, was formed from juvenile peri-Rodinian crust and was located outboard from the northern Gondwanan margin until at least 700 Ma.…”

U-Pb Zircon Ages and Pb Isotope Geochemistry of Gold Deposits in the Carolina Slate Belt of South Carolina

“…The Middle Cambrian magmatic arc in North Carolina is interpreted as having a Grenville-type crustal root (Mueller et al, 1996), consistent with a genetic connection to Laurentia (Samson et al, 1990 Pb (<15.48;Samson, 1995;Wortman et al, 2000) that are too low to match the compositions of sulfides from gold deposits of South Carolina ( Pb (Sinha et al, 1994) than the most radiogenic sulfides in the gold deposits (Fig. 12).…”

“…An older sequence (ca. 650-600 Ma) was built on oceanic crust and was derived mainly from juvenile and mantle sources (Samson, 1995;Samson et al, 1995;Fullagar et al, 1997;Wortman et al, 2000). The younger metavolcanic rocks (ca.…”