Onset of Alleghanian Orogen: Detrital – Zircon Signature from the Mississippian Strata in Southern and Central Appalachian
University of South Carolina, Department of Geosciences Columbia, South Carolina
Mississippian (350-290Ma) sandstone collected from northern Alabama and Pennsylvanian strata through the Appalachian basin, contains detrital –zircons originated from Superior (ca. 2.7Ga), Central-Plains, Mid-Continent and Pan-African provinces (1.6-1.9Ga) that are absent in Taconic (470-440Ma), Silurian (440-420Ma) and Acadian foreland basin (400-350Ma) samples since Neoproterozoic-early Ordovician (700-470Ma). Because the re-appearance of these zircons in Pennsylvanian foreland basin strata (320-290Ma) have been interpreted as evidence of sediment recycling of rift and passive-margin samples associated with uplift and exhumation caused by the Alleghanian orogeny, the our preliminary detrital-zircon data collected from Mississippian strata in northern Alabama suggest that the Alleghanian phase of Appalachian orogenesis may have begun 20-30 million years earlier than previously thought. This possibility is further supported by Visean Ar-Ar cooling ages recently recovered from southern Blue Ridge hangingwall samples. Thus, the objective of this research is to evaluate preliminary results from the southern Appalachians that the dominant Alleghanian orogeny was instigated in the Mississippian Period prior to the Pennsylvanian onset typically acknowledged by the modern Appalachian research community. For this purpose, this research extends to the Appalachian detrital-zircon database to include samples collected from Mississippian strata in the central and northern Appalachian foreland basin. Sandstones in Mauch-Chunk & Pennington Groups were collected from Virginia and West Virginia during summer 2007, and they are under sample preparation for analyzing detrital-zircon ages which is scheduled in the end of October 2007. The results expect to evaluate the spatial variation in the recycled-sediment orogenic proxy for the Alleghanian phase of the Appalachian orogeny.
AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid