STRATIGRAPHIC AND TECTONIC RELATIONSHIPS OF THE PALEOZOIC PORTION OF WRANGELLIA

Wrangellia is one of the largest and most exotic of the Cordilleran terranes, yet details of its internal stratigraphy and of its relationships with adjacent terranes is limited. Recent mapping combined with new geochemical and isotopic age information (igneous and detrital) of Wrangellia in southwest Yukon has improved knowledge of its geology and allows for comparison with other parts of the terrane in Alaska and British Columbia.

The majority of Wrangellia in Yukon occurs in a southeast-tapering wedge between the Denali and Duke River faults, where it comprises late Paleozoic volcanic rocks and associated sedimentary rocks, overlain by Triassic flood basalt, carbonate and marine siliciclastic rocks. The Duke River fault separates Wrangellia from the Alexander terrane in the south. To the north, across the Denali fault, Wrangellia is juxtaposed next to rocks of the Windy-McKinley and Yukon-Tanana terranes and igneous and metamorphic rocks of the Coast Plutonic complex. Current models suggest that Wrangellia and the Alexander terrane are stitched together by a Middle Pennsylvanian pluton and probably evolved together in late Paleozoic time. This shared history suggests that at least part of Wrangellia may have been built upon a portion of the Alexander terrane. New detrital zircon analyses from Permian-Triassic rocks of Wrangellia, however, do not show any similarities between the two terranes. Instead, Wrangellia appears to show some detrital signatures that are common to the Taku terrane, a succession of strongly deformed and metamorphosed rocks in southeast Alaska, and with portions of the Yukon-Tanana terrane.

Comparison of Wrangellia along strike between Alaska and British Columbia indicates differences in stratigraphy and ages. New geochemical data from the Pennsylvanian Station Creek Formation of Wrangellia in Yukon suggests a period of back-arc basin development prior to initiation of arc activity. This is in contrast with Wrangellia stratigraphy in Alaska but may be similar to rocks if Vancouver Island in British Columbia. The differences in the stratigraphy of Wrangellia along strike suggest that prior to the Triassic Wrangellia comprised disparate tectonic entities or, at the very least, encompassed a large area of variable tectonic environments.