Mesozoic and Cenozoic tectonic growth of southern Alaska: A sedimentary basin perspective

Abstract

Mesozoic and Cenozoic sedimentary strata exposed throughout southern Alaska contain a rich archive of information on the growth of collisional continental margins through the processes of terrane accretion, magmatism, accretionary prism development, and subduction of oceanic spreading ridges. Two major collisional events define the tectonic growth of southern Alaska: Mesozoic collision of the Wrangellia composite terrane and Cenozoic collision of the Yakutat terrane. The sedimentary record of these two collisional events can be summarized as follows. (1) Middle Jurassic volcaniclastic and sedimentary strata represent shallow-marine deposition in narrow subbasins adjacent to the volcanic edifice of the south-facing, intraoceanic Talkeetna arc. (2) Late Jurassic syndepositional regional shortening resulted in thick sections of conglomerate in proximal parts of both retroarc and forearc basins. In distal retroarc depocenters, fine-grained turbidite sedimentation commenced in a series of basins that presently extend for Ͼ2000 km along strike. This time interval also marked cessation of magmatism and rapid exhumation of the Talkeetna oceanic arc. We interpret these observations to reflect initial oblique collision, younging to the northwest, of the Wrangellia composite terrane with the continental margin of western North America. (3) During Early Cretaceous time, Jurassic retroarc basin strata were incorporated into an expanding north-verging thrust belt, and sediment was bypassed into more distal collisional retroarc basins located within the suture zone. Compositional data from these collisional basins show that the Wrangellia composite terrane was exhumed to deep stratigraphic levels. Detrital zircon ages from strata in these basins record some sediment derivation from source areas with North American continental margin affinity. Our data clearly show that the Wrangellia composite terrane and the former continental margin were in close proximity by this time. Accretion of this oceanic terrane and associated basinal deposits marked one of the largest additions of juvenile crust to western North America. The collision of the Wrangellia composite terrane also resulted in a change in subduction parameters that eventually prompted development of a new south-facing arc system, the Chisana arc. Construction of this arc was contemporaneous with renewed forearc basin subsidence and sedimentation. (4) Late Early Cretaceous to early Late Cretaceous time was characterized by regional deformation of retroarc collisional basin strata by south-verging thrust faults that are part of a regional thrust belt that

Thermochronology of the Talkeetna intraoceanic arc of Alaska: Ar/Ar, U‐Th/He, Sm‐Nd, and Lu‐Hf dating

“…A klippe of arc plutonic rocks south of the Border Ranges fault zone in the Klanelneechena area [Winkler et al, 1981] has been correlated with the Talkeetna arc. The Talkeetna arc is overlain by a sequence of Jurassic to Oligocene sedimentary and volcanic rocks and intruded by a variety of Late Cretaceous to Oligocene rocks reflecting Jurassic through Recent plate convergence [Plafker et al, 1994;Trop and Ridgeway, 2007]. [5] This study builds on an existing geochronology data set that is examined in detail later in the paper.…”

Arc and Slab-Failure Magmatism in Cordilleran Batholiths I – The Cretaceous Coastal Batholith of Peru and its Role in South American Orogenesis and Hemispheric Subduction Flip

“…In Alaska, rocks of the Valanginian-Cenomanian Kahiltna basin were metamorphosed and thrust northward at ~74 Ma, coincident with development of the Campanian-Maastrichtian Cantwell basin, a thrust-top basin formed during the deformation caused by the accretion of Wrangellia to the paleo-Alaskan margin along a well-defined geophysical and detrital zircon provenance break (Ridgway et al 2002;Trop and Ridgway 2007;Hults et al 2013). Late CretaceousEarly Tertiary northward-vergent thrusts and folds also deformed Early Cretaceous features in northern Alaska, including apparent basement duplexing in the Brooks Range (Moore et al 1997).…”

Summary of fossil fuel and geothermal resource potential in the Railbelt energy region

“…An oceanic plate (currently the Pacific Plate), has been subducting northwestward beneath the continental crust of Alaska since early Jurassic time (~200 million years) (Trop and Ridgway, 2007;Amato and others, 2007). Voluminous magma was intruded into the overriding continental crust and partially expelled to the surface during several cycles of volcanic events lasting millions of years (Reed and Lanphere, 1969;Wilson, 1985;Amato and others, 2007).…”

“…The Nenana basin is also known as the Tanana basin (e.g. Trop and Ridgway, 2007) or Middle Tanana basin (Ehm, 1983;Stanley and others, 1990).…”

“…However, broad, low-lying areas of the greater basin are covered by Quaternary surficial deposits, limiting direct examination of the stratigraphy. The source of these sediments is interpreted to change over time; the older Usibelli Group was deposited by streams that flowed southward from the ancient YukonTanana uplands, whereas the Nenana Gravel was deposited by streams flowing north out of the Alaska Range following major uplift in late Cenozoic time (e.g., Stevens, 1971;Buffler and Triplehorn, 1976;Wahrhaftig, 1987;Stanley and others, 1992;Trop and Ridgway, 2007).…”