REPEATED PALEOZOIC THRUSTING AND ALLOCHTHONEITY OF PRECAMBRIAN BASEMENT, NORTHERN TASMANIA

Stratigraphic and structural relationships in northern Tasmania sugges t a deformation sequence involving west-directed Cambrian and Devonian thrusting with imbrication of Precambrian basement, the Cambrian ocea nic suite and the Ordovician continental margin overlap sequences. Sec tion balancing requires a depth to detachment of 510 km and a total sh ortening on the order of 80 km, with at least half of this displacemen t attributable to the Late Cambrian deformation. Major faults are the Lorinna, Round Mountain, Mole Creek and Golden Valley Thrusts. The sma ller Precambrian massifs of northern Tasmania (Forth and Badger Head M assifs) represent the basal parts of major west-vergent thrust sheets which were emplaced in the Late Cambrian. Emplacement of these Cambria n thrust sheets warped the foreland upward causing exposure of the Tye nnan and Rocky Cape Massifs. East-west folding followed by southwest v ergent thrusting dominated Devonian deformation in northern Tasmania. The Devonian event redeformed the earlier Cambrian thrust structures, emplaced the Badger Head, Golden Valley, Mersey River and Forth Baseme nt Massifs (basement slices) and carried the East Tasmania Terrane on to the underlying West Tasmania Terrane basement in a piggyback fashio n above the Devonian thrust sheets. Later east-southeast vergent Devon ian thrusting within the Dial Range requires that the Rocky Cape Basem ent massif is also somewhat allochthonous, perhaps in the manner of th e foreland basement uplifts of the Rocky Mountains of the United State s.