The birth of the Beringia Arc: A mid-Cretaceous continental volcano-plutonic belt stretching from Russia to Alaska

Cretaceous igneous rocks exposed in the Bering Strait region from the Russian Far East across Seward Peninsula to the Yukon-Koyukuk basin and the Ruby-Farewell terrane of Alaska lack a unifying model for their formation. We present 47 new U-Pb zircon, titanite, and baddeleyite ages from magmatic rocks. The older group consists of 115−102 Ma plutons and volcanic rocks, including ultrapotassic rocks, found in northeastern Russia, islands in the Bering Sea, and on the Seward Peninsula of Alaska. The younger group includes 102−70 Ma plutonic rocks and dikes from the Yukon-Koyukuk basin and on the Seward Peninsula as well as the volcanic rocks of the vast Okhotsk-Chukotka belt in eastern Russia. Many have elevated alkalis and the subalkaline rocks plot in the calc-alkaline field. Most of the rocks with <65 wt% SiO2 are alkaline, whereas more siliceous rocks are generally subalkaline with Nb and Ta troughs, consistent with arc chemistry. Sr and Nd isotopes plot near bulk earth for the most primitive samples, and there is a trend toward more negative εNd and more positive initial 87Sr/86Sr with higher SiO2, which we interpret to indicate varying degrees of crustal contamination of subduction-related parental magmas. Nd model ages average to ca. 800 Ma. We created a tectonic model in GPlates in which collision of island arcs with the continent in the Late Jurassic−Early Cretaceous was followed by a new north-dipping subduction zone, establishing an Andean-type arc system at least 2200 km long. We call this magmatic belt the Beringia Arc. It lasted from 115 Ma to at least 70 Ma before subduction either rolled back or jumped to the south. The Beringia Arc system was coeval with the continental arc represented by the Okhotsk-Chukotka volcanic belt in northeastern Russia that mainly formed from 98 Ma to 80 Ma. This study links the abundant mid-Cretaceous plutonic rocks of the Bering Strait region into a single model of generation in a continental arc.