Invited reviewEpisodicity and the dance of late Mesozoic magmatism and deformation along the northern circum-Pacific margin: north-eastern Russia to the Cordillera
Introduction
The large-scale plate tectonic history of the northern circum-Pacific margin, which experienced 1000’s of km of oceanic subduction from the Mesozoic to the present (Engebretson et al., 1985; Shephard et al., 2013), argues in compelling fashion that subduction played the greatest role in shaping the geology and distribution of most of the magmatic belts found in this region (Figure 1, Figure 2). However, important differences exist between the Russian, Alaskan and Cordilleran sectors of this margin despite their shared history of subduction. The most obvious of these differences is the Cenozoic development of back-arc basins along the Russian and western Alaskan margins, but not along the Cordilleran or easternmost Alaska sectors of the margin (Fig. 1). The opening of the Arctic Ocean basins in Cretaceous to Cenozoic time (Fig. 1) resulted in translation of microplates southward towards the Pacific margin during seaward migration of subduction zones (Miller et al., 2018b), adding complexity to the history of this part of the margin. There are additional significant differences in the age and style of deformation along this margin: While all parts of the margin have a varied history of terrane accretion, shortening-related tectonics dominated the Cordilleran margin in the Mesozoic, while extension or neutral tectonics presided along much of the Alaskan and Russian margin (e.g., Miller and Hudson, 1991; Miller et al., 2002; Akinin et al., 2009a).
Magmatic belts are one of the first-order results of subduction along a continental margin. They are generally well preserved in the geologic record making their map distribution, geochronology, geochemistry and relationship to country rock deformation amenable to study. A considerable number of the Jurassic to Quaternary magmatic belts of NE Russia correspond to age equivalent belts in adjacent Alaska and the North American Cordillera (Figure 2, Figure 3A–D). These magmatic belts, and the events they record, are the topic of this summary paper, organized in three parts. The first part focuses on the Jurassic to recent magmatic history of NE Russia, with special attention to the Cretaceous. Cenozoic magmatism, which developed during the step-out of subduction to the Aleutians and Kamchatka (Figure 1, Figure 2), is discussed only briefly as it has been better studied and summarized by others. The second part of the paper provides a comparison of the timing and nature of magmatism in Russia to magmatism and deformation in Alaska and the Cordillera. The third part of the paper includes a discussion of the possible plate tectonic controls that have led to the observed differences in the tectonic settings of magmatism through time along the length of the northern circum-Pacific margin. We stress that this summary is preliminary in nature because it is based on incomplete, but rapidly expanding data sets. It builds upon previous syntheses of available data (Miller et al., 2002, Miller et al., 2018b; Akinin et al., 2009a; Akinin and Miller, 2011) and relies greatly on the compilation and interpretation of Alaskan and Canadian magmatism by Nelson et al., (2013). The well-documented timing of deformation in the Canadian Cordillera, described as a series of punctuated events related to the westward motion of North America (Monger and Gibson, 2019), forms the basis for comparing the synchronized but contrasting styles of deformation in Russia to those of the Cordillera, leading to the understanding that these are likely linked to the absolute motion of the continental plates with respect to their subduction zones.
Section snippets
Methods and databases
New geologic mapping, increased availability and precision of geochronologic techniques, the advent of large U-Pb detrital zircon data sets, coupled with major and trace element geochemical and isotopic analyses (Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8) have all led to an improved database for the magmatic belts in Russia. In order to compare magmatic and tectonic histories (Fig. 3A–D), we constructed chronostratigraphic charts for the different sectors of the margin (Plate 1
Part 2. Comparison of Russian magmatic belts to magmatism in Alaska and the Cordillera
This section draws some key comparisons between the distribution, nature and tectonic setting of the NE Russian magmatic belts discussed above with those of Alaska and the northern Cordillera using the simplified locations and tectonic settings for magmatism through time in Figure 3A–D and making use of the comparison chart for timing of events compiled in Plate 1.
Compilations of Mesozoic U-Pb ages from Northeast Russia and Alaska (Fig. 8) show significant magmatic activity in the various
Part 3: Plate tectonic setting of north Pacific magmatism
Figure 9 utilizes GPlates software (Müller et al., 2016) to place the history of northern circum-Pacific magmatism in the context of a model for plate motions from the latest Jurassic (150 Ma) to the Cenozoic (40 Ma) (Shephard et al., 2013). The model uses an absolute frame of reference which is based on the Indo-African hotspots between 100-0 Ma (O’Neill et al., 2005) and the true polar wander-corrected paleomagnetic reference frame for earlier times (Steinberger and Torsvik, 2008). Note that
Summary and conclusions
The increasingly extensive data on the age and geochemistry of magmatic rocks of North East Russia allow a clearer delineation of their space-time evolution. Subduction- related magmatic belts track the evolution of the paleo-Pacific margin of Siberia, indicating that this margin stepped outward with time by the accretion of terranes and by extension, including the tectonic re-arrangement of parts of Arctic Russia due to opening of the Arctic Ocean. The Verkhoyansk-Kolyma orogen and Brooks
Declaration of Competing Interest
We do not believe we have any conflicts of interest.
Acknowledgements
Research associated with this paper was funded by NSF Tectonics Awards 0948673 and 1624582 to Elizabeth Miller and in part by the CALE International Project (P.I. Victoria Pease, Stockholm University). Fieldwork and associated travel costs and the collection of analytical data were supported by the Russian Foundation for Basic Research (RFBR) and the U.S. Civilian Research and Development Foundation award number RUG1-2994-MA-11 to Vyacheslav Akinin and Elizabeth Miller. The compilation of
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