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Plate Tectonic Model for the Evolution of the Eastern Bering Sea Basin

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Plate Tectonic Model for the Evolution of the Eastern Bering Sea Basin Plate tectonic model for the evolution of the eastern Bering Sea Basin ALAN K. COOPER } DAVID W. SCHOLL T U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 MICHAEL S. MARLOW ABSTRACT Watts and Weissel, 1975) have been pro- orientation of the magnetic lineations in the posed for the crustal generation by exten- eastern Bering Sea Basin. The eastern Bering Sea Basin, composed sion. These basins are commonly associated of the Aleutian and Bowers Basins, is with high heat-flow values (Sclater, 1972; GEOMORPHIC AND flanked to the north by Mesozoic foldbelts Matsuda and Uyeda, 1971), positive re- GEOLOGIC SETTING that probably represent zones of plate sub- gional gravity anomalies (Packham and duction in Mesozoic time. Present plate Falvey, 1971; Watts and Talwani, 1974), Major bathymetric features of the eastern subduction occurs 400 to 1,000 km farther layered oceanic crustal sections (Karig, Bering Sea Basin include two large aseismic south, at the Aleutian Trench. North-south 1971), and low-amplitude magnetic ridges, Bowers Ridge and Shirshov Ridge magnetic lineations that formed at an anomalies that trend in a direction sub- (Fig. 1), and the flat abyssal floors of the oceanic spreading ridge, probably in parallel with the active island arc (Uyeda Aleutian and Bowers Basins. Bowers Ridge Mesozoic time (117 to 132 m.y. ago), have and Vacquier, 1968; Karig, 1970; Watts extends in a broad arc, nearly encircling been identified in the Aleutian Basin. The and Weissel, 1975). Bowers Basin, from the central Aleutian orientation and age of those anomalies can The hypothesis of crustal generation by Ridge to near the southern end of Shirshov be explained by reconstructing Kula- extension within the marginal basins may Ridge. Shirshov Ridge, in contrast to Bow- Farallon Pacific plate motions during late not explain the formation of all marginal ers Ridge, is a linear feature that separates Mesozoic—early Tertiary time. basins, in particular, the eastern Bering Sea the Aleutian and Komandorsky Basins. In Mesozoic time, subduction of the Kula Basin. As in the Philippine Basin (Ben Av- The Aleutian Ridge is the southern bar- plate occurred north of the Aleutian Trench raham and others, 1972), the magnetic rier behind which sediment has ponded in near the present location of the Bering Sea lineations within the Aleutian and Bowers the Bowers and Aleutian Basins. The oldest continental margin. At about 70 m.y. B.P. Basins (Cooper and others, 1976a, 1976b) rocks recovered from the Aleutian Ridge (Late Cretaceous), the zone of subduction trend at a large angle to the active island are of Eocene or possibly Paleocene age shifted south to the present location of the arc. Other geophysical measurements in the (Scholl and others, 1975; Schmidt, 1973). Aleutian Trench, thereby trapping a frag- eastern Bering Sea Basin, such as heat flow Marlow and others (1973) and Scholl and ment of oceanic plate imprinted with (Foster, 1962; Langseth and von Herzen, others (1975) proposed that the Aleutian north-south magnetic lineations within the 1970; Langseth and Horai, in prep.), grav- Ridge was built over a period of 10 to 20 eastern Bering Sea Basin. A stable basin ity (Kienle, 1971), and regional magnetic m.y., probably by submarine volcanism. framework has prevailed behind the Aleu- data (Cooper and Scholl, 1974; Regan and Volcanism began in Late Cretaceous or ear- tian arc since early Tertiary time. others, 1975) are atypical of the active ex- liest Tertiary time; by Eocene time, the tensional basins. Shor (1964), Scholl and ridge stood above sea level and had approx- INTRODUCTION Buffington (1970), and Scholl and others imately attained its present size. (1975) have suggested that, unlike the ex- The Bering Sea Basin is bounded on the The Bering Sea Basin is a marginal basin tensional marginal basins, the Bering Sea north and east by the Bering Sea continental of the North Pacific perimeter. The eastern Basin is founded upon trapped oceanic margin (Bering Shelf—Kamchatka Penin- part of the Bering Sea Basin includes the crust. Further support for this concept has sula; Fig. 1). Late Mesozoic structural two abyssal basin areas, the Aleutian Basin been presented by Cooper and others trends of the Pacific foldbelt in southern and Bowers Basin (Fig. 1), that are east of (1976b), who identified the magnetic linea- Alaska appear to bend northwestward Shirshov Ridge. There are numerous tec- tions in the Aleutian Basin (Fig. 2). These (Burk, 1965) at the tip of the Alaska Penin- tonic models for the evolution of these and north-trending anomalies appear to be sula near Sanak Island (lat 56°N, long other marginal basins in the southwestern sea-floor spreading anomalies, which can 165°W, Fig. 1) and may connect with a and western Pacific (Beloussov and be correlated with the Ml to M13 series of foldbelt of similar age underlying nearly Ruditch, 1961; Karig, 1971; Packham and the Mesozoic magnetic time scales of Lar- undeformed and thick Cenozoic sedimen- Falvey, 1971; Sleep and Toksôz, 1971; son (1974), Larson and Chase (1972), and tary rocks in the outer part of the Bering Watts and Weissel, 1975; Scholl and Hilde (1973). Shelf (Scholl and Buffington, 1970; Scholl others, 1975). The mechanism presently fa- In this paper, we have reconstructed the and others, 1975; M. S. Marlow, D. W. vored for basins of the western Pacific in- late Mesozoic and early Tertiary history for Scholl, and E. C. Buffington, in prep.). volves extensional rifting of the marginal the eastern Bering Sea Basin to explain the Along the northwestern boundary of the basin and seaward migration of the adja- origin of the present magnetic anomaly pat- basin, Mesozoic eugeosynclinal rocks simi- cent volcanic island arc. Both asymmetric tern. Plate models based on the relocated lar to those of southern Alaska (Burk, (one-limb) spreading (Packham and Falvey, positions of the Kula, Farallon, Pacific, and 1965) form the core of the adjacent Koryak 1971) and symmetric (two-limb) spreading North American plates are presented that Mountains in eastern Siberia (Fig. 1). These (Karig, 1971; Sclater and others, 1972; are consistent with the postulated age and foldbelts, especially the buried Mesozoic Geological Society of America Bulletin, v. 87, p. 1119-1126, 4 figs., August 1976, Doc. no. 60805. 1119 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/8/1119/3443964/i0016-7606-87-8-1119.pdf by guest on 02 October 2021 176 172° 168° 60° 168° 172° 176° 180° 176° 172° Figure 1. Index map of the eastern Bering Sea Basin. Bathymetry from Scholl and others (1974). Transverse Mercator projection. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/8/1119/3443964/i0016-7606-87-8-1119.pdf by guest on 02 October 2021 age of the lineations (Larson, 1974) increases from east (Ml, 117 m.y.) to west (M13, 132 m.y.)- Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/8/1119/3443964/i0016-7606-87-8-1119.pdf by guest on 02 October 2021 1122 COOPER AND OTHERS foldbelt paralleling the outer shelf, have 140 160 180 160 140 120 been interpreted as resulting from Mesozoic plate convergence along the northern Ber- Q TRIPLE POINT ing Sea margin (Scholl and Buffington, O DSDP HOLE 183 1970; Scholl and others, 1975; M. S. Mar- N NO. AMERICAN PLATE low, D. W. Scholl, and E. C. Buffington, in prep.). F FARALLON PLATE In summary, the eastern Bering Sea Basin P PACIFIC PLATE is bordered on two sides by Mesozoic fold- K KULA PLATE belts of eastern Siberia and the Bering Shelf, which may be continuous, and on a third M1 p side by the Aleutian island arc of presuma- M 13^ bly Late Cretaceous and early Tertiary age. LARSON (74) MESOZOIC The flat abyssal basin floor and the underly- ANOMALY SEQUENCE ing flat sedimentary layers of Cenozoic or DIRECTION AND RATE OF possibly older age suggest a relatively stable o PLATE MOTION (cm/yr) tectonic environment since at least early 140 160 180 160 140 120 Tertiary time (Scholl and others, 1975). (a) 140 160 180 160 140 120 PLATE RECONSTRUCTIONS 140 160 160 160 140 120 rr -i i r 60 - l^si-.N - 60 The entrapment of older oceanic litho- . /. J \ // /> ^ M** V y/h vV;. sphere in the eastern Bering Sea Basin dur- 45 -M. Wj 45 ing Late Cretaceous or early Tertiary time t" " can best be visualized by reconstructing the K * • 30 r V// 30 positions of the Kula, Farallon, Pacific, and F X North American lithospheric plates. Two 15 wsy/r v 15 independent models based on different re- M1 ^ construction techniques and covering 0 ? 0 slightly different time periods are presented p \ here. The first model illustrates reconstruc- 15 • 15 tions that are based on paleomagnetic data 30 " 80 MY 30 such as paleomagnetic pole positions and -1.1- J i .. i . .i. marine magnetic anomalies. The second, 140 160 180 160 140 120 140 160 180 160 140 120 and somewhat more speculative, model is (b) (c) in part based on plate motion derived from 150 120 90 60 postulated hot-spot traces. In all recon- 90 120 150 180 structions it is assumed that the Bering Sea is presently part of the North American plate and that it has been attached to the North American plate since at least Late Cretaceous time (Churkin, 1973). Model 1. Paleomagnetic Data Three reconstructions of plate positions in the Pacific Basin area at 38, 80, and 110 m.y. B.P. (early Tertiary, Late Cretaceous, and Early Cretaceous) are shown in Figure 3. The reconstruction at 38 m.y. (Fig. 3b), from Atwater and Molnar (1973), is made by using magnetic lineation data in the North Atlantic, South Pacific, and Indian Oceans to obtain the relative position of the North American and Pacific plates.
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