| The Caroline Terrane (CT) consists of metamorphosed arc-related volcanic, plutonic, and sedimentary rocks. The CT is subdivided into two belts, the Charlotte Belt (CB) and the Carolina Slate Belt (CSB), separated by broad transition zone (CB-CSB transition zone). The primary lithotypes are felsic metavolcanic rocks, metamorphosed mafic flows and dikes, aluminous Ms-schist and Sill-Kfs-schist, and metapelites. Mineralogical variations within the CB-CSB transition zone and the CSB reflect variations in metamorphic conditions. Felsic rocks preserve three assemblages; F1 (Qtz + Pl(An15–20) + Kfs + Mgt ± Bt ± Hbl), F2 (Qtz + Ab + Kfs + Ms(phengitic) + Bt + Ep + Ttn), and F3 (Qtz + Ab + Kfs + Ms(phengitic) + Grt + Bt + Ep + Ttn). Mafic lithologies also display three distinct assemblages; M1 (Amp + P1(An30–50) + Ilm + Mgt ± Qtz), M2 (Amp + P1(An20–40) + Chl + Ep + Ilm ± Qtz) and M3 (Na-Amp + Ab + Ep ± Qtz).; Metamorphic P-T conditions were determined for M1 and M2 mafic lithologies and F3 felsic lithologies. P-T conditions in mafic lithologies were found using the empirical Holland and Blundy (1994) geothermometers and by calculating the P-T positions of relevant equilibria. For F3 lithologies, metamorphic conditions were found using garnet—phengite Fe-Mg exchange thermometry (Hynes and Forest, 1988), modeling garnet forming equilibria, and through multiequilibria techniques. P-T grids calculated for both mafic and felsic rocks support the thermobarometric calculations. These procedures revealed the presence of three lithotectonic blocks; (1) a low pressure block recording upper amphibolite to granulite facies conditions (T = 650–725°C, P = 4.6 kbar), (2) a high pressure black recording amphibolite to eclogite facies conditions (T = 625–730°C, P = 9.6–15 kbar, and (3) a greenschist facies block (T ≈ 400°C, P ≈ 5–8 kbar). Mineral zonation patterns, inclusion relationships, and phase equilibria constraints indicate clockwise P-T paths for the low and high pressure blocks. The metamorphic conditions preserved in the CT record the Neoproterozoic collision of two separate volcanic arcs, the present day CB and CSB. These events took place while the two arcs were part of the peri-Gondwanan subduction system. Thus, the metamorphic conditions preserved in the CT and the collision they record, suggest a more complex tectonic setting for the peri-Gondwanan subduction system than has been proposed previously. |
