Collaborative Research: Mesozoic to Present-Day Tectonics of Northeast Russia: A Cooperative Research Program with the Yakut Science Center and NEISRI

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Abstract This award provides supports to continue a cooperative research program between the University of Alaska Fairbanks, Michigan State University, the Yakut Science Center (YSC, Yakutsk, Russia), and the Northeast Interdisciplinary Scientific Research Institute (NEISRI, Magadan, Russia) which was initiated in 1990. The research program is interdisciplinary, using paleomagnetism, geochronology, geochemistry, seismology and structural geology to study the Mesozoic to Cenozoic tectonic history of northeastern Russia from the edge of the Siberian platform up to, and including, the Okhotsk-Chukotka volcanic belt (OCVB). The study area includes the zone of Mesozoic accretion of terranes of both Arctic and Pacific origins and the present-day plate boundary between North America (NA) and Eurasia (EU). So far, this cooperative project has detected an age progression among Mesozoic granites, identified a widespread paleomagnetic overprint in the northwestern Kolyma Structural Loop (KSL), and obtained previously published paleomagnetic data for the region. Earthquake focal mechanisms, based on regional and teleseismic data, reveal that crustal shortening in the region, driven by the opening of the Arctic Ocean is being relieved by the extrusion of the Okhotsk (OK) plate to the southeast. To expand understanding of the KSL, this project will focus on its southeastern end, where formations similar to those studied in the northeastern part of the loop turn from a southeasterly strike to a northeasterly one. This region also lies along the NA-OK plate boundary and fault traces and seismically generated features are visible in low resolution satellite images. The next phase of work will involve two transects by NEISRI and the YSC along the Kolyma and Indigirka Rivers, and analysis the samples collected. These transects cross the Kular-Nera slate belt, the Omulevka composite terrane, the Il'in-Tas formation, or their along-strike equivalents. These units represent, according to one model, the Late Jurassic forearc, arc, and back-arc deposits of the Uyandina-Yasachnaya island arc which was located on or near the edge of the Kolyma-Omolon superterrane (K-OS); this model, however, is still open to considerable debate, especially relating to the polarity of subduction. The primary objectives here are to determine the age and polarity of the Uyandina arc, the relationship between the K-OS and the Viliga shelf terrane, the extent of the paleomagnetic overprint, whether oroclinal bending occurs, the age and paleolatitude of the Late Cretaceous OCVB, the detailed tectonics and location of the NA-OK plate boundary, and the crustal structure of the region. Resolution of these problems will aid in constraining the tectonic evolution of northeast Russia, which has implications for the tectonics of the North Pacific and the Arctic Ocean. In particular, this work will aid in determining the timing and methodology of the isolation of the Arctic basin which has impact on paleoclimatology. The seismic studies will help in constraining the amount of crustal thickening resulting from compression and aid in wave propagation studies and nuclear test- ban monitoring.