Nance Presentation: Does Canadian Meguma Terrane Extend Into Southern Britain?

Ohio University faculty made an impact with 23 presentations at the Geological Society of America’s 125th Anniversary Annual Meeting & Exposition Oct. 27–30 in Denver.

Erica Neace, Dr. R. Damian Nance, James Briad, Brendan Murphy, Nicolle Dupius, & Robin Shail presented on DOES THE MEGUMA TERRANE EXTEND INTO SOUTHERN BRITAIN?. Nance is an Ohio University Distinguished Professor of Geological Sciences in the College of Arts & Sciences.

The Meguma terrane of southern Nova Scotia, Canada, is the only major lithotectonic element of the northern Appalachian orogen that has no clear correlatives elsewhere in the Appalachians and lacks firm linkages to the Caledonide and Variscan orogens of western and southern Europe. This is in contrast with its immediate peri-Gondwanan neighbor, Avalonia, which shows similarities to portions of Carolinia in the southern Appalachians and has been traced from the Rhenohercynian Zone of southern Britain eastward around the Bohemian Massif to the South Carpathians and western Pontides. At issue is the tendency in Europe to assign all peri-Gondwanan terranes (like Meguma) lying north of the Rheic suture to Avalonia, characterized by relatively juvenile basement and detrital zircon ages that include Mesoproterozoic populations, and those to the south of the suture to Cadomia, characterized by a more evolved basement and detrital zircons with ages that match Paleoproterozoic and older sources in the West African craton.

But while the unexposed basements of Avalonia and Meguma are thought to be isotopically similar, the Meguma sedimentary cover contains scarce Mesoproterozoic zircons. Hence, felsic magmas produced by crustal melting in the Meguma terrane (e.g. the ~370 Ma South Mountain Batholith) are isotopically more juvenile (εNd = -5 to -1, T_DM = 1.3 Ga) than the rocks they intrude (εNd -12 to -7, T_DM = 1.7 Ga) – a distinctive relationship also recognized for the Sierra Norte Batholith (~330 Ma; εNd = +1 to -3, T_DM = 0.9–1.2 Ga) and its Late Devonian host rocks (εNd = –5 to –11) in southern Spain, where it has been used to suggest the possible presence of Meguma basement beneath the South Portuguese Zone. Available data for the Cornubian batholith of SW England (~270-290 Ma; εNd = -5 to -7, T_DM = 1.3–1.8 Ga) and the Devonian metasediments it intrudes (εNd = –8 to –11) suggests this may also be true of that part of southern Britain (Rhenohercynian Zone) with which the South Portuguese Zone is traditionally correlated.