The Yukon–Tanana terrane: Part of North America at ∼ 215 Ma from paleomagnetism of the Taylor Mountain batholith, Alaska

Abstract

The massive unmetamorphosed 212 Ma Taylor Mountain batholith underlies ∼ 648 km 2 of the Yukon–Tanana terrane (YTT) in east-central Alaska, and intrudes klippen thrust sheets of the Fortymile River assemblage and the Chicken Metamorphic Complex. Structural evidence indicates that the batholith is neither tilted nor rotated about a vertical axis. Paleomagnetic analysis of 295 specimens from 24 sites in the batholith and cross-cutting mafic dikes isolates a stable primary characteristic remanent magnetization in magnetite with unblocking temperatures of 500 to 585 °C that places the batholith's paleopole at 61.4°N, 102.2°E ( N = 17, α 95 = 5.2°) on the North American apparent polar wander path (APWP) at 215 ± 5 Ma (1 σ). The Taylor Mountain paleopole alone and all YTT paleopoles together show that the YTT has been a para-autochthonous part of the North American margin since the Late Triassic. Further, the Intermontane Belt (IMB) paleopoles are distinct from the North American and YTT paleopoles prior to the mid Eocene and provide two APWP segments. One IMB segment includes the Quesnel, Cache Creek, Eastern Coast Belt, and northern Stikine terranes, and the second more-speculative IMB segment includes the central and southwestern Stikine and Methow terranes. This analysis supports tectonic models for the northern Cordillera in which the IMB terranes were obducted onto North America during the Late Cretaceous to mid Eocene, co-eval with the Laramide orogeny.