A DYNAMIC SWEAT CONFIGURATION FOR WESTERN COLUMBIA INFERRED FROM WERNECKE SUPERGROUP GEOCHRONOLOGY AND GEOCHEMISTRY

The late Paleoproterozoic Wernecke Supergroup in the Wernecke Mountains, Yukon, records a series of events that affected northwestern Laurentia (present coordinates), including extension and basin formation followed by orogenesis and terrane obduction. The Wernecke Supergroup was deposited after ca. 1.66 Ga on northwestern Laurentia in a subsiding marine environment. It is considered to be the distal correlative of the Muskwa, Athabasca, Thelon and Hornby Bay successions of Canada. Detritus is interpreted to have been derived mainly from Laurentia although the youngest detrital zircons and the geochemical signature of fine-grained siliciclastic rocks also suggest an exotic input. Possible non-Laurentian counterparts of the Wernecke Supergroup may be located in eastern Australia (Isan Supergroup, Willyama Supergroup, Tarcoola Formation) and the Yangtze craton of South China (Dahongshan-Dongchuan-Hondo groups).

Following extension, basin formation and deposition, the Wernecke Supergroup was deformed, metamorphosed and exhumed by the Racklan orogeny. During the latest stages of the orogeny the Wernecke Supergroup was tectonically overridden by a non-Laurentian terrane named Bonnetia and subsequently intruded by hydrothermal fluids responsible for widespread brecciation and IOCG mineralization to form the 1.599 Ga Wernecke Breccia. The brecciation led to the collapse and downward movement of fragments of the overlying terrane. Subsequent tectonic and erosional events denuded the region, leaving clasts of Bonnetia within the Wernecke Breccia as the only remnants of the volcano-plutonic province obducted onto the Wernecke Supergroup.

The Racklan orogeny is considered to be the northwestern Laurentian expression of the Isan and Olarian orogenies of Australia, the Mazatzal and Labradorian orogenies of southern USA and eastern Canada, the Gothian orogeny of Scandinavia, and the Quatro Cachoeiras orogeny of Brazil. This transcontinental orogenic belt represents a readjustment of the margins of the supercontinent Columbia at the Paleo-Mesoproterozoic boundary. All of the events recorded by the Wernecke Supergroup are compatible with a SWEAT configuration for western Columbia, where eastern Australia, Antarctica and South China were continuously repositioned along the Laurentian margin