GEOCHRONOLOGY AND GEOCHEMISTRY OF ALLEGHANIAN AND 'ATYPICAL' ALLEGHANIAN GRANITES IN THE CAROLINA TERRANE, SOUTHERN APPALACHIANS: IMPLICATIONS FOR SOURCES AND TERRANE ACCRETIONARY HISTORY

The Carolina Terrane in the southern Appalachians is host to a large number of granitic intrusions. The majority of these plutons intruded during the Alleghanian Orogeny (330 Ma to 300 Ma) in the south central Appalachians. These granites typically have ¹⁴⁷Sm/¹⁴⁴Nd ratios lower than 0.12, often unusually low compared to average world-wide granites. Juxtaposed along with the Alleghanian granites are a few plutons which are geochemically different from plutons of known Alleghanian age. They have higher ¹⁴⁷Sm/¹⁴⁴Nd ratios compared to the majority of the known Alleghanian plutons and their bulk REE concentration is also significantly lower (ƩREE = 120 ppm) than the Alleghanian plutons (ƩREE = 178 ppm). Three such granites, namely the Cloud's Creek Granite, Newburry granite and Lake Murray granite gneiss, yielded ages of 414.9+2.1/-1.7 Ma, 414±3 Ma and 421+4/-2.9 Ma respectively. Similar undated granites intruding into the Carolina Terrane that are geochemically similar to the known Silurian-Devonian intrusions hence have the potential to be Silurian-Devonian rather than Alleghanian in age. In order to test if these geochemically ‘atypical' Alleghanian plutons are indeed Silurian-Devonian in age, we dated a subset of both geochemically typical Alleghanian as well as ‘atypical' Alleghanian granites using the LA-ICPMS technique. Four granites of typical Alleghanian chemical characteristics, namely the Batesburg granite, Wise granite, Lexington granite and Merriweather granite were confirmed as Alleghanian in age. The three geochemically ‘atypical' plutons (the Steven's Creek granite, Falls Lake Gneiss and Clark Hill granite) are either Alleghanian but display significant chronological complexity, or are in fact not Alleghanian but nor are they Silurian Devonian. Zircons from the Steven's Creek granite had Grenvillian (~1 Ga) cores consistent with a significant Laurentian source component. The Clarks Hill granite and the Falls Lake granites on the other hand, yielded Neoproterozoic ages, which is more characteristic of the host Carolina Terrane and hence are likely to be younger, native components of the Carolina Terrane. A comparative study of these and other geochemically typical and ‘atypical' Alleghanian plutons might shed important insight into the accretionary history of the Carolina Terrane.