Character, distribution, and tectonic significance of accretionary terranes in the Central Alaska Range
Authors: Jones David L. , Silberling N. J. , Gilbert Wyatt , Coney Peter 
Published: February 2008

The central part of the Alaska Range near Mount McKinley is composed of nine separate tectonostratigraphic terranes that were accreted in southern Alaska during late Mesozoic time. These terranes now form long, linear, fault‐bounded belts that are subparallel to the Denali fault on the north but oblique to the fault on the south. The postaccretion right lateral offset along the Denali fault system is about 200 km. From north to south the major terranes are (1) Yukon‐Tanana terrane, metasedimentary and metavolcanic rocks, mostly undated, but including rocks of known late Paleozoic age; polymetamorphosed with terminal events in late Mesozoic, (2) Pingston terrane, isoclinally folded Upper Triassic deep‐water silty limestone, quartzite, and carbonaceous slate, folded with upper Paleozoic phyllite, chert, tuff, and minor limestone, (3) McKinley terrane, upper Paleozoic flysch, chert, and minor limestone, intruded by large gabbro sills and dikes and overlain by thick piles of Triassic porphyritic pillow lava; the top of the section is thick sequence of upper Mesozoic conglomerate, flysch, chert, and phyllite, (4) Dillinger terrane, very thick sequence of strongly folded lower Paleozoic micaceous sandstone (turbidites), graptolitic shale, and deep‐water limestone, locally overlain unconformably by Jurassic fossiliferous sandstone or Triassic (?) pillow basalt, (5) Windy terrane, heterogeneous assemblage of serpentinite, basalt, tuff, and chert (= ophiolite?) with Paleozoic and Mesozoic flysch and blocks of mid‐Paleozoic fossiliferous limestone, (6) Mystic terrane, predominantly upper Paleozoic flysch and conglomerate, but also includes lower Paleozoic graptolitic shale, pillow basalt, and shallow‐water limestone, and upper Paleozoic fossiliferous limestone, sandstone, chert, and undated pillow basalt, (7) Chulitna terrane, Upper Devonian ophiolite overlain by upper Paleozoic chert, volcanic conglomerate, limestone, and flysch, capped by Lower Triassic limestone and Upper Triassic red beds, basalt, and interbedded basalt and limestone; later Mesozoic rocks are sandstone, chert, and argillite, (8) Westfork terrane, Jurassic chert, sandstone, conglomerate, and Triassic (?) and Jurassic crystal tuff, (9) Broad Pass terrane, upper Paleozoic chert, tuff, and argillite, with blocks of Devonian and older limestone locally associated with serpentinite. These diverse terranes, of mixed oceanic and continental affinities, are now juxtaposed to form a complex sequence of folded and faulted rootless nappes. Major suture zones between them are occupied by intensely deformed upper Mesozoic flysch. All of the terranes differ markedly from Wrangellia, the southermost coherent accreted terrane in Alaska. Paleomagnetic measurements from Triassic rocks prove that Wrangellia originated near the equator, probably in the southern heimsphere. Paleolatitudes for terranes in the central Alaska Range are not yet determined, but other lines of evidence (biogeographic and lithologic) suggest large‐scale northern transport for some terranes.