Abstract
Abstract The tectonomagmatic evolution of eastern Chukotka, NE Russia, is important for refining the onset of Pacific plate subduction, understanding the development of the Amerasia Basin, and constraining Arctic tectonic reconstructions. Field mapping and strategic sample collection provide relative age constraints on subduction-related continental arc magmatism in eastern Chukotka. Ion microprobe U–Pb zircon ages provide absolute constraints and identify five magmatic episodes ( c. 134, 122, 105, 94 and 85 Ma) separated by three periods of uplift and erosion ( c. 122–105, 94–85 and post-85 Ma). Volcanic rocks in the region are less contaminated than their plutonic equivalents which record greater crustal assimilation. These data, combined with xenocrystic zircons, reflect the self-assimilation of a continental arc during its evolution. Proto-Pacific subduction initiated by c. 121 Ma and arc development occurred over c. 35–50 myr. Crustal growth was simultaneous with regional exhumation and crustal thinning across the Bering Strait region. Ocean–continent subduction in eastern Chukotka ended at c. 85 Ma. The timing of events in the region is roughly synchronous with the inferred opening of the Amerasia Basin. Simultaneous arc magmatism, extension and development of the Amerasia Basin within a back-arc basin setting best explain these coeval tectonic events.
Highlights
Many studies have carefully documented the formation of deep-seated, syn-extensional metamorphic core complexes and gneiss domes associated with N-S crustal stretching across the Bering Strait in the Late Cretaceous (e.g. Akinin et al, 2009a and references therein), but few have focused on the igneous history recorded by the superb exposures of magmatic rocks in far eastern Chukotka described here. 84 Our investigation of Cretaceous igneous rocks in eastern Chukotka, based on several seasons of geological field mapping and systematic sampling in the Provideniya-Chaplino region (Fig. 1), defines fundamental cross-cutting and map relationships, and provides absolute age constraints from high-spatial resolution secondary ion-mass spectrometry (SIMS)
We studied exposures 223 around Tkachen Bay
The final stage of magmatism occurred at 85 Ma – there is no record of younger arc magmatism in the Provideniya-Chaplino region. 769 A significant part of the punctuated magmatic history documented here can be correlated 770 across the Bering Strait, but in Alaska the upper-crustal successions are absent
Summary
7 1- Department of Geological Sciences, Stockholm University, Sweden. 8 2- Department of Geological and Environmental Sciences, Stanford, University, Stanford, California, USA. 10 3- MapTect LLC, Athens, Georgia, USA. 11 4- Geological Institute, Russian Academy of Sciences, Moscow 119017, Russia. 12 5- North East Interdisciplinary Science Research Institute, Russian Academy of Sciences, Magadan, Russia. 14 6- Department of Geology, University of Georgia, Athens, Georgia, USA
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