Abstract
Far-field deformation in the upper plate of many ancient and modern convergent margins is commonly attributed to flat-slab subduction processes. Recent studies have suggested that the high topography of the central Alaska Range (Alaska, USA), for example, is the far-field deformational response to Neogene shallow subduction processes in southern Alaska. In this study, we analyze six stratigraphically controlled detrital zircon samples from Miocene–Pliocene sandstone of the Tanana foreland basin to evaluate the temporal and spatial links between exhumation of the central Alaska Range and shallow subduction. The Tanana basin, located north of the central Alaska Range, contains ∼2 km of Neogene strata. Lower Miocene strata from the basin have detrital zircon ages with dominant Precambrian populations. These grain ages are attributed to sediment derivation from the Yukon composite terrane source area located at the northern edge and north of the Alaska Range. During the early–middle Miocene the provenance of the Tanana basin switched to a distinctly Mesozoic source signal. These Mesozoic-age grains are attributed to sediment derived from source areas within and south of the Alaska Range. The early–middle Miocene change in provenance from predominantly Precambrian to Mesozoic sediment sources, in the context of previously published basin analysis studies, is interpreted to represent the onset of Neogene uplift of the central Alaska Range. The timing of exhumation of the central Alaska Range is important not only for understanding the tectonics of the highest mountain range in North America, but additionally because recent modeling studies predict that this range is one of the first expected products of Neogene flat-slab subduction along the southern Alaska convergent plate boundary. Results of our study provide a needed chronologic framework to fully evaluate the temporal and spatial upper plate responses to shallow subduction processes.
