TRIASSIC VOLCANISM AND MAGMATISM IN THE EASTERN ALASKA RANGE, ALASKA - THE MISSING LINK IN WRANGELLIA

Wrangellia is one of the largest accreted basaltic terranes within the Cordillera of western North America. Early researchers suggested that this exotic volcanic terrane formed in an oceanic plateau flood basalt setting. In fact, Wrangellia may represent one of the best exposed and preserved large scale examples of oceanic plateau flood basalts on earth yet it is still poorly understood. Past research was generally restricted to the easily accessible areas, particularily on Vancouver Island in the western portion of Wrangellia, and thus provided only the superficial characteristics of this volcanic province. Our research over the past 10 years in the eastern Wrangellia has confirmed a number of the earlier researchers findings; however, it has also disclosed a number new volcanological, geochemical, geochronological and metallogenic findings that will fundamentally change our understanding of Triassic volcanism/magmatism in Wrangellia, and oceanic plateau flood basalt provinces in general. This work has focused the attention of the exploration community on the importance of such volcanic environments when exploring for Ni-Cu-PGE deposits.

Geochronological investigations conducted during this study, and constrained paleontological data, reveal that the onset of Triassic magmatism began about 230.4 ± 2.3 Ma and was complete by 223 Ma. Although initial intrusive magmatism began as early as 230.4 ± 2.3 Ma volcanic activity did not begin until 226.4 ±2.0 Ma, and ended in the Late Carnian stage (223.4 Ma) of the Triassic. Therefore, a three million year time span for the Triassic volcanism and a seven million year history of Triassic magmatism for Wrangellia is fairly well contrained.

New mineralogical, petrological, geochemical, isotopic, and field relationships (pertinent to the diverse paleo-environments of volcanism) will be presented from our studies in the eastern Alaska Range, and compared with our new findings from studies conducted elsewhere in the terrane, Vancouver Island and the Yukon, in order to better understand this new volcanic/magmatic terrane. In addition, we will present for the first time a detailed account of one of the most important missing links in Wrangellia – Triassic picritic to ultramafic volcanism and the genetic association with Ni-Cu-PGE mineralization in eastern Wrangellia.