Zircon U-Pb Age and In-situ Muscovite Rb-Sr Isochron Age of Alkaline Volcanic Rocks in the Beifeng Abyss of the Chukchi Margin in the Arctic Ocean and Their Geotectonic Implications
The Chukchi Margin is located at the core of the Amerasia Basin in the Arctic Ocean.As an underwater highland,it extends from the Alaska-Chukchi continental shelf to the Amerasia Basin.The study of the Chukchi Margin is crucial for reconstructing the plate tectonic evolution of the Arctic region.However,its crustal nature,origin,and evolution are not yet clear.In this study,detailed analyses were conducted on an alkaline volcanic rock sample obtained from the slope of the Beifeng Abyss Plain in the Chukchi Margin.We used the mineral automatic quantitative analysis(TIMA)method to study its lithological characteristics,determined the U-Pb isotope ages of 119 zircon grains in the samples by LA-ICP-MS,and simultaneously measured the Rb-Sr isochron age of in-situ microcrystalline muscovite in the sample thin sections using LA-ICP-MS technology.The results show that the ages of the 119 zircon grains can be roughly divided into four groups:94-636 Ma,929-1369 Ma,1655-2040 Ma,and 2439-2735 Ma.Combined with previous studies on the U-Pb ages of metamorphic zircons obtained in the Chukchi Margin and the ages of detrital zircons in the Canadian Arctic region,it was found that the zircon grains captured in the second,third,and fourth groups might have originated from the basement of the Canadian Arctic Islands.The Th/U ratios of the young zircon grains in the first group were all relatively high,indicating typical magmatic zircon.The average age of the youngest 6 zircon grains is 100.9±1.2 Ma,which roughly represents the formation age of the alkaline volcanic rock.The in-situ muscovite Rb-Sr isochron age of the sample thin section obtained from the test is 72±17 Ma.The relationship between this age and the youngest zircon age in the sample corresponds to the phenomenon that muscovite is mostly vein-like and metasomatic to alkaline rocks under microscope.Therefore,the vein-like muscovite in the sample may be the product of later submarine tectonic-hydrothermal activities.The zircon and muscovite ages obtained in this study confirm,from the perspective of geological ages,that the Amerasia Basin was formed by the separation of the Alaska-Chukchi microplate from the margin of the North American plate during the Early Cretaceous and has undergone later submarine tectonic-hydrothermal superimposition.
Amerasia Basin of the Arctic OceanChukchi Marginzircon U-Pb datingin-situ Rb-Sr dating of muscovitetectonic evolution of the Arctic region
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