Luke Beranek and colleagues from Idaho State & Australian National University have published a new article in Lithosphere.
Long-lived accretionary orogens like the North American Cordillera are built sequentially over tens to hundreds of millions of years. Although field evidence for the oldest mountain-building events in such convergent settings can be obscured by younger tectonism, ancient sedimentary rocks are known to be important archives of early-orogen evolution. This paper reports new data from ancient sandstones to investigate the earliest plate convergence in the northern U.S. Rocky Mountains, which culminated in the Antler orogeny and early growth of the North American Cordillera. The oldest convergent margin sandstones demonstrate stratigraphic ties with lithospheric blocks to the west that were juxtaposed against the Cordilleran margin ~20 m.y. prior to the Antler orogeny. These lithospheric blocks now reside in British Columbia, California, and Oregon, but are far-travelled and probably have origins near northern Europe. The Antler orogeny was likely a non-collisional mountain-building event that featured sinistral-oblique deformation and foreland basin sedimentation inboard of a west-facing arc system.