DETRITAL ZIRCON GEOCHRONOLOGY ACROSS THE CHOPAWAMSIC FAULT, WESTERN PIEDMONT OF VIRGINIA, AND ITS BEARING ON EARLY PALEOZOIC TECTONIC DEVELOPMENT IN THE SOUTHERN APPALACHIANS
Samples from the pre-Ordovician Pt display various peak modes from 1.00 – 1.25 Ga; almost all analyses in these samples span from c. 500 Ma to c. 1.6 Ga. These results support a Laurentian provenance for the Pt.
Metasedimentary samples from the Middle to Late Ordovician Ct are dominated by detrital zircons between 450 – 470 Ma; these ages likely represent recycled debris from adjacent volcanic rocks in the Ct. However, one sample from the Ct displays a sub-population of Proterozoic zircons ranging from 600 Ma to 1.2 Ga; this set provides the only indication of any basement input to these samples. Zircons from 600 – 800 Ma may reflect the influence of a peri-Gondwanan crustal basement to the Ct.
Samples from the Arvonia successor basin, which unconformably overlies the Ct, display dissimilar detrital inputs. A sample from the Bremo quartzite exhibits peak modes at c. 460 Ma and 1.01 Ga, while a sample from the Buffards Formation consists mostly of Middle Silurian, c. 425 Ma, detrital zircons. The age disparities between these two samples may reflect a transition in sediment provenance from underlying older terranes (potential input from both Ct and Pt) to the introduction of contemporaneous magmatism to the Arvonia depositional system. A sample from a smaller unit of metasedimentary rocks (Storck area) previously interpreted to be related to the Arvonia basin displays a wide distribution of detrital ages ranging from 500 Ma to 2.25 Ga, with principal modes at c. 525 Ma, 605 Ma, 945 Ma and 1.14 Ga; it is uncertain how or if this sample may be related to the Arvonia basin, but the distribution of detrital ages is consistent with input from a Gondwanan source.