SHRIMP U-PB GEOCHRONOLOGY OF ZIRCON AND TITANITE AND 40AR/39AR OF HORNBLENDE AND MUSCOVITE FROM MESOPROTEROZOIC ROCKS OF THE WESTERN BLUE RIDGE, GREAT SMOKY MOUNTAINS NATIONAL PARK AREA, TN AND NC

New SHRIMP U-Pb geochronologic data from zircon and titanite and 40Ar/39Ar of hornblende and muscovite define igneous and metamorphic events of Mesoproterozoic and Paleozoic age in the western Blue Ridge province. The Mesoproterozoic rocks include migmatitic gneiss and metagranitoids. Post-Paleozoic uplift and erosion exposed these rocks in the cores of two domes and two antiforms and along several thrust faults. Migmatitic biotite gneiss and hornblende-biotite gneiss contain isolated pods of calc-silicate granofels, amphibolite, and ultramafic rocks. The metamorphosed granitoids include moderately foliated, fine-grained, leucocratic metagranite and megacrystic metagranite, and weakly foliated metagranodiorite and porphyritic metagranite. Crystallization ages of the metagranitoids are temporally correlative with three magmatic intervals (M) recognized in the Blue Ridge of northern VA. The oldest event is represented by crystallization of the granitic leucosome at 1194±8 Ma in migmatitic gneiss in the Ela dome. Igneous protoliths of metagranitoids of the Bryson City dome and Dellwood antiform crystallized at 1167±6 and 1160±8 Ma, respectively, and correspond to M1. A younger foliated metagranite in the Dellwood antiform was emplaced at 1116±14 Ma and corresponds to M2. Less deformed megacrystic metagranite (1045±6 Ma, Ela dome), metagranodiorite (1037±5 Ma, along the Greenbrier fault), and porphyritic metagranite (1022±4 Ma, Ravens Fork antiform), are representatives of M3. Weak foliations in the rocks of M3 suggest a major deformation event occurred before 1045 Ma. This episode is probably associated with the Ottawan orogeny that affected Grenvillian rocks elsewhere in the eastern U.S. and Canada. Subsequent partial melting and deformation of probable Taconian age is recorded in the Ela dome by crystallization of titanite at 443± 7 Ma in the 1194±8 Ma leucosome and a 440 Ma 40Ar/39Ar hornblende (hbl) cooling age from hornblende gneiss, and a 450 Ma 40Ar/39Ar hbl cooling age from amphibolite in the Dellwood antiform. Mississippian 40Ar/39Ar muscovite cooling ages from the Mesoproterozoic and Neoproterozoic cover rocks show that they were subsequently deformed under retrograde greenschist-facies conditions during the Alleghanian orogeny.