JG vol. 118, no. 1 2010 Tuesday Oct 27 2009 01:03 PM/80097/MILLERD CHECKED Application of Foreland Basin Detrital-Zircon Geochronology to the Reconstruction of the Southern and Central Appalachian Orogen Hyunmee Park, David L. Barbeau Jr., Alan Rickenbaker, Denise Bachmann-Krug, and George Gehrels1 Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina 29208, U.S.A. (e-mail: [email protected]) ABSTRACT q1 We report the U-Pb age distribution of detrital zircons collected from central and southern Appalachian foreland basin strata, which record changes of sediment provenance in response to the different phases of the Appalachian orogeny. Taconic clastic wedges have predominantly ∼1080–1180- and ∼1300–1500-Ma zircons, whereas Acadian clastic wedges contain abundant Paleozoic zircons and minor populations of 550–700- and 1900–2200-Ma zircons q2 consistent with a Gondwanan affinity. Alleghanian clastic wedges contain large populations of ∼980–1080-Ma, ∼2700- Ma, and older Archean zircons and fewer Paleozoic zircons than occur in the Acadian clastic wedges. The abundance of Paleozoic detrital zircons in Acadian clastic wedges indicates that the Acadian hinterland consisted of recycled material and possible exposure of Taconic-aged plutons, which provided significant detritus to the Acadian foreland basin. The appearance of Pan-African/Brasiliano- and Eburnean/Trans-Amazonian-aged zircons in Acadian clastic wedges suggests a Devonian accretion of the Carolina terrane. In contrast, the relative decrease in abundance of Paleozoic detrital zircons coupled with an increase of Archean and Grenville zircons in Alleghanian clastic wedges indicates the development of an orogenic hinterland consisting of deformed passive margin strata and Grenville basement. The younging-upward age progression in Grenville province sources revealed in Taconic through Allegh- anian successions suggest a reverse unroofing sequence that indicates at least two cycles of Grenville zircon recycling. Online enhancements: appendix, data file. Introduction Sediments derived from orogenic hinterlands and 1981; Gehrels et al. 1995; Fedo et al. 2003). Modern adjacent quiescent cratons accumulate in foreland techniques of U-Pb geochronology using laser ab- basins that develop in response to tectonic loading lation–multicollector–inductively coupled plasma- caused by subduction, continental collision, and/ mass spectrometry (LA-MC-ICP-MS) now allow or terrane accretion (Jordan 1995; DeCelles and Gi- rapid inexpensive determination of ages (Black et les 1996). In the case of orogenic systems with suf- al. 2004; Gehrels et al. 2006). In this article, we use ficiently diverse sediment sources, spatial and tem- such data to address persistent questions relating poral variations in foreland basin sediment to the tectonic development of the southern and provenance data can provide insight into the ki- central segments of the Paleozoic Appalachian nematics of deformation, landscape evolution, and orogen. sediment dispersal (Cawood and Nemchin 2001; The Appalachian hinterland is partially com- McLennan et al. 2001). In recent years, U-Pb geo- posed of a complex mosaic of terranes that were chronology of individual detrital zircons has be- amalgamated to the Laurentian margin during mul- come one of the most useful approaches for iden- tifying sediment sources in basins (Gaudette et al. tiple phases of collision and related magmatism throughout Paleozoic time (fig. 1; Horton et al. 1989; Sinha et al. 1989; Hatcher 2005). Existing Manuscript received May 15, 2009; accepted August 4, 2009. 1 Arizona LaserChron Center, Department of Geosciences, analyses of Appalachian detrital-zircon composi- University of Arizona, Tucson, Arizona 85721. tions indicate that sediments derived from hinter- [The Journal of Geology, 2010, volume 118, p. 000–000] ᭧ 2010 by The University of Chicago. All rights reserved. 0022-1376/2010/11801-00XX$15.00. DOI: 10.1086/648400 CHECKED 1 CHECKED 2 P A R K E T A L . Figure 1. Simplified map of the Appalachian foreland basin and hinterland (modified from Millici and Witt 1988; Hatcher et al. 2004). land accreted terranes are relatively minor in com- such sediment should provide important data for parison to those originally derived from Grenville the evaluation of Appalachian tectonic models, and related rocks that occur pervasively in the east- several of which remain poorly constrained or con- ern Laurentian subsurface (Eriksson et al. 2004; troversial. Here we report single-grain detrital-zir- Thomas et al. 2004; Becker et al. 2005). Despite the con U-Pb and Pb-Pb crystallization ages from 15 small sizes of these non-Grenville populations, samples of Upper Ordovician to Mississippian JG vol. 118, no. 1 2010 Tuesday Oct 27 2009 01:03 PM/80097/MILLERD CHECKED Journal of Geology T E C T O N I C D E V E L O P M E N T O F T H E A P P A L A C H I A N O R O G E N CHECKED 3 sandstones collected along the central and southern of the Iapetus Ocean (Drake et al. 1989). This col- Appalachians in Tennessee, West Virginia, Virginia, lision produced the Taconic foreland basin that is and Pennsylvania. The age distribution of detrital well preserved in northern New York and involved zircons from Pennsylvanian sandstones in the cen- uplift and carbonate deposition upon the forebulge tral and southern Appalachians are well established and the accumulation of black shales and turbidites (e.g., Becker et al. 2005) and can be used to evaluate in the foredeep (Bradley 1989, 2008). In the hinter- the provenance evolution of the Appalachian fore- land, the orogeny involved significant magmatic land basin together with our Ordovician to Missis- activity, penetrative deformation, and granulite- sippian samples. With these data, we examine the facies and kyanite-grade metamorphism at ∼465 history of terrane accretion and kinematic evolu- Ma (Hatcher 1987; Drake et al. 1989; Bradley 2008). tion of the central and southern Appalachians. The accreted terranes responsible for this defor- mation and sediment accommodation presumably included 450–470-Ma magmatic arcs preserved in Geological Background the Milton, Tugaloo, Potomac, and Chopawamsic The Appalachians are a 3,300-km-long orogen ex- terranes and ∼530-Ma rocks of the Smith River Al- tending from Newfoundland to Alabama that lochthon (fig. 1; Horton et al. 1989; Coler et al. formed through at least three Paleozoic orogenic 2000; Hibbard et al. 2003). In the study area, the events on the eastern margin of Laurentia (Wil- synorogenic clastic wedges associated with this Ta- liams 1978; Bradley 2008). Today the Appalachians conic deformation are represented by the Martins- consist of crystalline basement exhumed from the burg Formation, the Oswego Sandstone, and the underlying Grenville province in addition to vari- Juniata Formation (fig. 2). ably deformed and metamorphosed rift, passive Silurian to Early Devonian time in the Appala- margin, and foreland basin sedimentary rocks. chians was a period of orogenic quiescence between These rocks record the development of the Lauren- the Taconic and Acadian orogenies (Johnson et al. tian passive margin caused by breakup of the su- 1985; Ettensohn 1991). During this time, Upper Si- percontinent Rodinia and tectonic evolution as- lurian to Lower Devonian strata accumulated in sociated with opening and closing of Atlantic-realm the Appalachian foreland basin and are character- ocean basins (fig. 2). The breakup of Rodinia is re- ized by eustatically controlled sequences including corded in two pulses of magmatic activity, includ- the Tuscarora Sandstone, the Rose Hill Formation, ing a failed rifting event at ∼700–760 Ma and the and Keefer Sandstone of the Clinton Group; the opening of the Iapetus Ocean at ∼550–620 Ma (figs. McKenzie Formation; the Helderberg Group; and 2, 3; Aleinikoff et al. 1995; Walsh and Aleinikoff the Oriskany Sandstone in West Virginia and Vir- q3 1999; Cawood et al. 2001). The first magmatic ac- ginia (fig. 2; Johnson et al. 1985; Brett et al. 1990). tivity is preserved in the Mt. Rogers and Robertson The Devonian to Early Mississippian Acadian River formations of the Blue Ridge and is charac- orogeny is generally regarded as the result of the terized by bimodal igneous activity in an intracon- collision of the Avalonian microcontinent to the tinental rift system (fig. 3; Aleinikoff et al. 1995). margin of eastern Laurentia in the northern Ap- Evidence of the younger 550–620-Ma rifting event palachians, and the accretion of the Carolina ter- is widespread in the northern Appalachians in- rane in the southern and central Appalachians (Os- cluding the Pound Ridge Granite and the Catoctin berg et al. 1989; Wortman et al. 2000). These Formation of the central and southern Appalachi- collisions are also recorded by ∼384–423-Ma plu- ans (fig. 3; Aleinikoff et al. 1995; Rankin et al. tonism and the cratonward migration of northern 1997). Following the breakup of Rodinia, eastern Appalachian deformation front (Bradley et al. 2000). Laurentia accumulated 3–5 km of passive margin In comparison to widespread evidence of the Aca- sedimentary rocks represented by the Erwin, dian orogeny in the northern Appalachians, the Hampton, and Unicoi formations of the Chilhowee Acadian orogeny is poorly manifested in the south- Group, as well as the Shady Dolomite and the ern and central Appalachian hinterland outside of Rome and New Market formations in the central 374–382-Ma granitoid plutonism in the eastern and southern Appalachians (fig. 2; Diecchio 1986; Blue Ridge and late Acadian metamorphism in the Fichter 1986; Read 1989). Cat Square terrane (Horton et al. 1989; Osberg et This passive margin sedimentation was inter- al. 1989; Hatcher 2005). Acadian synorogenic de- rupted by the Taconic orogeny in the Middle Or- posits are known broadly as the Catskill clastic dovician, presumably caused by progressive colli- wedge and are present from New England to Geor- sion of an arc and continental fragments with the gia (Faill 1985; Osberg et al.