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A Synthesis of Jurassic and Early Cretaceous Crustal Evolution Along

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A Synthesis of Jurassic and Early Cretaceous Crustal Evolution Along RESEARCH A synthesis of Jurassic and Early Cretaceous crustal evolution along the southern margin of the Arctic Alaska–Chukotka microplate and implications for defining tectonic boundaries active during opening of Arctic Ocean basins Alison B. Till U.S. GEOLOGICAL SURVEY, 4210 UNIVERSITY DRIVE, ANCHORAGE, ALASKA 99508, USA ABSTRACT A synthesis of Late Jurassic and Early Cretaceous collision-related metamorphic events in the Arctic Alaska–Chukotka microplate clarifies its likely movement history during opening of the Amerasian and Canada basins. Comprehensive tectonic reconstructions of basin open- ing have been problematic, in part, because of the large size of the microplate, uncertainties in the location and kinematics of structures bounding the microplate, and lack of information on its internal deformation history. Many reconstructions have treated Arctic Alaska and Chukotka as a single crustal entity largely on the basis of similarities in their Mesozoic structural trends and similar late Proterozoic and early Paleozoic histories. Others have located Chukotka near Siberia during the Triassic and Jurassic, on the basis of detrital zircon age popula- tions, and suggested that it was Arctic Alaska alone that rotated. The Mesozoic metamorphic histories of Arctic Alaska and Chukotka can be used to test the validity of these two approaches. A synthesis of the distribution, character, and timing of metamorphic events reveals substantial differences in the histories of the south- ern margin of the microplate in Chukotka in comparison to Arctic Alaska and places specific limitations on tectonic reconstructions. During the Late Jurassic and earliest Cretaceous, the Arctic Alaska margin was subducted to the south, while the Chukotka margin was the upper plate of a north-dipping subduction zone or a zone of transpression. An early Aptian blueschist- and greenschist-facies belt records the most profound crustal thickening event in the evolution of the orogen. It may have resulted in thicknesses of 50–60 km and was likely the cause of flexural subsidence in the foredeep of the Brooks Range. This event involved northern Alaska and northeasternmost Chukotka; it did not involve central and western Chukotka. Arctic Alaska and Chukotka evolved separately until the Aptian thickening event, which was likely a result of the rotation of Arctic Alaska into central and western Chukotka. In northeastern Chukotka, the thickened rocks are separated from the relatively little thickened continental crust of the remainder of Chukotka by the oceanic rocks of the Kolyuchin-Mechigmen zone. The zone is a candidate for an Early Cretaceous suture that separated most of Chukotka from northeast Chukotka and Alaska. Albian patterns of magmatism, metamorphism, and deformation in Chukotka and the Seward Peninsula may represent an example of escape tectonics that developed in response to final amalgamation of Chukotka with Eurasia. LITHOSPHERE; v. 8; no. 3; p. 219–237 | Published online 3 March 2016 doi: 10 .1130 /L471 .1 INTRODUCTION Nokleberg et al., 2000; Shepherd et al., 2013). In geologic studies of the Canada Basin summa- many models, opening of the Amerasian Basin rized in Grantz et al. (2011), Shepherd et al. Research in Arctic tectonics has blossomed was accomplished by movement of a large conti- (2013), and Gottlieb et al. (2014) support the in recent decades due to increased ease of access nental block called the Arctic Alaska–Chukotka rotational model for basin opening. However, to the region and consequent interest in develop- microplate or terrane (Fig. 1; Lawver et al., simple rigid rotation of the over 3000-km-long ment of natural resources. Despite substantial 2002; Grantz et al., 2011; Shepherd et al., 2013, Arctic Alaska–Chukotka microplate results in progress, uncertainties and controversies persist and references therein). The processes respon- significant overlap of the western end of the regarding the tectonic mechanisms responsible sible for movement of the microplate—via rota- micro plate with the continental crust of the for Mesozoic opening of the Amerasian Basin, tion, translation, or both—have been the subject Lomonosov Ridge (Fig. 1; Rowley and Lottes, a central feature of Arctic geography (Fig. 1). of ongoing debate (e.g., Carey, 1955; Hamilton, 1988; Miller et al., 2006; Pease, 2011). Internal New geophysical and geologic data collected 1970; Tailleur, 1973; Churkin and Trexler, 1980; deformation of the microplate by crustal exten- within the basin and its immediate borderlands Oldow et al., 1987; Smith, 1987; Grantz et al., sion could account for some of the size discrep- have been used to update tectonic models 1990; Lane, 1997; Lawver et al., 2002; Miller ancy (Miller et al., 2006; Miller and Akinin, (e.g., Grantz et al., 2011), but a broader geo- et al., 2006, 2008). 2008; Miller and Verzhbitsky, 2009). Separate graphic approach is required to account for all The Canada Basin is the part of the Amera- locations and tectonic histories for Chukotka of the tectonic elements that were active during sian Basin adjacent to Canada and Arctic Alaska and Arctic Alaska before basin opening have basin opening (e.g., Rowley and Lottes, 1988; (Fig. 1). The results of modern geophysical and been proposed and help to address this issue, LITHOSPHERE© 2016 Geological | Volume Society 8 of| AmericaNumber 3| |For www.gsapubs.org permission to copy, contact [email protected] 219 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/8/3/219/3045353/219.pdf by guest on 30 September 2021 TILL Timanide orogen (part) REGIONAL GEOLOGY GREENLAND Novaya Arctic Alaska–Chukotka Microplate Zemlya The Arctic Ocean basin is rimmed by blocks Taimyr Pearya Figure 1. Map of the Arctic of continental crust that had similar Neopro- Severnaya Ridge region showing the loca- Zemlya Axel Heiberg terozoic and early Paleozoic histories, based on RUSSIA Island tion of the Amerasian and igneous ages, detrital zircon age populations, Canada basins and the Arc- LomonosovAMERASIAN and affinities of early Paleozoic fauna (Fig. 1; tic Alaska–Chukotka micro- BASIN New Siberian CANADA plate. Also shown are the Kuznetsov et al., 2010; Pease, 2011; Dumou- Islands location of Neoproterozoic lin et al., 2011). These blocks are considered Canada and Lower Paleozoic rocks by some to be pieces of a dismembered Neo- Basin pole of Verkhoyansk rotation typically related to the proterozoic and earliest Paleozoic continent, Wrangel Tima nide orogen or Arc- such as Arctida (Shatskii, 1935; Kuznetsov, ARCTIC ALASKA- Island tida (Kuznetsov et al., 2010) Alaska 2006; Kuznetsov et al., 2010; Filatova and CHUKOTKA and the Timanide orogen Ch Khain, 2010), while others consider them to be MICROPLATE ukotk Arctic itself (Pease, 2011). Loca- a ALASKA tion of the pole of rotation dispersed parts of a large accretionary margin is from Grantz et al. (2011). related to the Timanide orogen of Baltica (Fig. 1; Patrick and McClelland, 1995; Dumoulin et al., 2002, 2011; Lorenz et al., 2008; Pease and Scott, Exposures of Neoproterozoic and lower Paleozoic rocks 2009; Amato et al., 2009; Miller et al., 2010a). typically related to the Timanide orogen or Arctida The Arctic Alaska–Chukotka microplate has Timanide orogen (part) an area comparable to that of Greenland (Amato et al., 2015) and is the largest of these crustal blocks (Fig. 1). On the Russian side, it includes but no suture has been identified between the addressed to create better tectonic models for the Chukotka, Wrangel Island, parts of the New two (e.g., Miller et al., 2006; Shepherd et al., opening of the Amerasian Basin: Siberian Islands, and the adjacent continental 2013; Amato et al., 2015). (1) Were Arctic Alaska and Chukotka sep- shelf (Fig. 1). On the North American side, it Additional uncertainty regarding the process arate crustal entities during opening of the includes Saint Lawrence Island, Seward Penin- of basin opening and migration of the Arctic Amerasian Basin? Can a structure be identified sula, the Brooks Range, and the North Slope of Alaska–Chukotka microplate arises from an within the Arctic Alaska–Chukotka microplate Alaska (Fig. 2). It is specifically the Neoprotero- incomplete understanding of the location and that delineates a boundary between the two zoic and early Paleozoic geology of the Seward evolution of Mesozoic tectonic boundaries and crustal blocks? Peninsula and the southern and western Brooks associated collision zones on the south and west (2) What information about crustal defor- Range that are similar to Chukotka and the other sides of the microplate (present coordinates; mation can be used to constrain the size of the crustal blocks in the Arctic (Churkin and Trex- e.g., Moore et al., 1994; Sokolov et al., 2002, Arctic Alaska–Chukotka microplate during the ler, 1980; Natal’in et al., 1999; Dumoulin et al., 2009; Amato et al., 2004, 2015; Pease, 2011). process of Amerasian or Canada Basin opening? 2002, 2011; Amato et al., 2014). These subduction zones, collisional zones, and (3) Can the metamorphic history of the Notably, little shared history has been docu- transform faults are important because they pre- southern Arctic Alaska–Chukotka microplate be mented for Arctic Alaska and Chukotka between sumably accommodated closure of ocean basins used to constrain the age and character of major the Permian and the Cretaceous. For example, south and west of the Arctic Alaska–Chukotka tectonic boundaries active during basin opening? most of central and western Chukotka is under- microplate as the Amerasian Basin opened. Evi- This paper addresses these three areas of lain by voluminous Triassic turbidites (Tuch- dence for subduction of the southern margin uncertainty in two ways. First, I present a syn- kova et al., 2009), while rocks of similar age in of Arctic Alaska (e.g., Till et al., 1988; Gott- thesis of the metamorphic and structural evo- western Arctic Alaska are shale rich and were schalk, 1990) was used to constrain some tec- lution of the southern margin of the Arctic deposited in starved basins on a continental shelf tonic models (e.g., Moore et al., 1994; Nokle- Alaska– Chukotka microplate.
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