Geochronology and structural setting of Latest Devonian – Early Carboniferous magmatic rocks, Cape Kiber, northeast Russia

Abstract

Cape Kiber on the Arctic coast of Chukotka, northeast Russia, consists of a granite intruding Devonian (and older?) strata in the core of a large southeast trending anticline. These strata are structurally overlain by Carboniferous and younger strata. A U–Pb age of 351.4 ± 5.6 (2σ) Ma shows that the granite is Early Carboniferous in age. A large granite cobble extracted from a Carboniferous conglomerate produced a Late Devonian or Early Carboniferous U–Pb age of ∼355–361 Ma. Also, a deformed and altered granitic dyke yielded an age of 363.7 ± 5.7 (2σ) Ma. Major and trace elements suggest a syn-collisional (orogenic) setting. The granite’s (biotite) Ar release spectrum is reset. The granitic dyke also shows a disturbed Ar–Ar whole-rock spectrum implying an Early Cretaceous age (∼122–130 Ma) for closure of the Ar system. We interpret this as due to widespread greenschist metamorphism accompanying regional deformation of the Anyuy–Chukotka Fold Belt that accompanied closure of the South Anyuy Ocean. Regionally, this event predates deposition of Aptian and Albian strata and the eruption of Okhotsk–Chukotsk magmatic rocks. An Ar–Ar (biotite) plateau age of 96.4 ± 1.0 (2σ) Ma from a mildly deformed, lamprophyre dyke reflects intrusion in a setting of regional extension. Its deformation reflects a younger tectonic event. The record of Devonian–Carboniferous magmatism and early Carboniferous unroofing is younger and less complex than that of Arctic Alaska. However, evidence for Early Devonian (Caledonian) or Late Devonian (Ellesmerian) deformation could have been masked by intense Mesozoic deformation. Outcrop data and geochronology support and refine regional interpretations of Early Cretaceous deformation and mineral growth accompanying accretion of Chukotka to north Asia, followed by regional extension and subsequent convergent deformation.