RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES5002, doi:10.2205/2005ES000190, 2005
[7] The southwestern area of Hokkaido is occupied by the Oshima Terrain [Kiminami et al., 1992] which is often compared with the Middle Jurassic (Berriasian) terrains of the accretionary prisms of the Central Sikhote-Alin area and with those of the Honshu Island (Samarka, North Kitakimi, and Mino-Tamba) [Golozubov, 2004; Isozaki, 1996; Maruyama, 1997].
[8] The more eastern area is occupied by the Rebun-Kobato linear island-arc terrain, which is often included in the Oshima Terrain [Kiminami et al., 1986; Niida and Kito, 1986]. This terrain is dominated by Tholeiite andesite and basalt, as well as by volcanic sedimentary rocks, dated Berriasian-Barremian in the Kobato Mountains in the west of Hokkaido [Nagata et al., 1986] and Valanginian-Barremian in the Rebun Island [Ikeda and Komatsu, 1986].
[9] The axial part of Hokkaido is usually referred to as the Sorachi-Iezo tectonic belt which shows the complex tectonic relations between the pre-Barremian oceanic volcanogenic siliceous rocks (Sorachi Group), the Hauterivian (?) - Barremian - Paleocene flysch, turbidite, and shallow-sea sediments of the Iezo Supergroup, their metamorphic analogs, and numerous serpentinite melange with ophiolite and high-pressure rock slices (Kamuikotan metamorphic belt). In this paper they are treated as independent tectonic units which satisfy the definition of a terrain [Parfenov et al., 1999; Sokolov, 2003], namely, the Iezo Barremian-Paleocene turbidite terrain, the Sorachi (pre-Barremian oceanic plateau), and the Kamuikotan Cretaceous-Early Eocene subduction-type metamorphic terrain.
[10] The Idonnappu suture zone (belt) is the eastern restriction of the Central Hokkaido terrains. It consists of steeply standing slabs of turbidite, olistostrome, and melange, which grow younger eastward from Barremian-Albian to Campanian-Danian, and also of large oceanic basalt slabs of different origin [Kiyokawa, 1992; Ueda et al., 1994]. The suture zone shows shear deformations, the earliest of them being ranked as left lateral with eastern vergence [Kiyokawa, 1992]. The Idonnappu zone is usually interpreted as a Cretaceous accretion, yet, the wide development of shear zones of different time periods, as well as the structured pattern of the melange and the linear pattern of the entire structural feature suggest its shear origin, the presence of large ophiolite allochthons allowing one to rank it as a suture-type structural feature.
[11] The Hidaka Terrain corresponds to the Late Cretaceous-Early Eocene accretion prism, composed of turbidite and east-vergence terrigenous melange zones [Kiminami et al., 1992]. The orientation of the paleocurrents and the composition of the turbidite suggest that the clastic material had been derived from the side of the continental margin. The positions and origin of the eastern boundaries of this terrain are still a matter discussion.
[12] The Tokoro Terrain [Kanamatsu et al., 1992; Kiminami et al., 1992; Sakakibara et al., 1986, 1993; Tajika, 1988] is composed of Campanian-Early Eocene hemipelagic rocks and tuff turbidite (Yubetsu Group), of Upper Cretaceous and Lower Paleocene conglomerates and turbidites (Saroma Group), and of Middle-Late Jurassic to Cenomanian siliceous volcanic rocks of oceanic islands (Nikoro Group). The Saroma and Yubetsu Groups are known to be treated as the rocks of the fore-arc trough or as those of the accretion prism, which had accumulated under the conditions of the Mezopacific oceanic plate subduction under the ensimatic island arc [Kanamatsu et al., 1992; Kiminami et al., 1986, 1992; Kimura, 1996]. In the southern part of the terrain the accretion rocks are overlain with an angular unconformity by a Middle-Late Eocene neoautochthon and were crowded, along with latter, during the Early-Middle Miocene in the course of the Nemuro island arc collision [Bazhenov and Burtman, 1994; Kimura, 1996].
[13] The Nemuro Terrain is exposed in the southeast of the Hokkaido Island and extends as far as the islands of the Minor Kuril Arc [Kiminami, 1983; Kiminami et al., 1992; Melankholina, 1988]. The eastern part of the terrain is composed of Campanian-Late Eocene tuff turbidite and flysch with dolerite sills and island-arc volcanic flows. The western part of the terrain, contacting the Tokoro Terrain, is composed of Campanian-Middle Miocene flysch, turbidite, and conglomerates, and does not contain any effusive rocks. The compositions of the turbidites and volcanic rocks suggest their accumulation in the environment of an ensimatic volcanic arc. The results of the paleomagnetic studies carried out in the eastern part of the terrain [Bazhenov and Burtman, 1994] suggest the arc was formed in a low-latitude region and that its accretion to the continental margin took place only in the Early-Middle Eocene.
[14] The main specific feature of the subdivision of Hokkaido into tectonic regions was the fact that the western and central terrains, including the Hidaka accretion terrain, were ranked as the structural features produced by the subduction of the Paleo-Mezopacific oceanic plates under the continental margin. The origin of the eastern terrains is explained by the subduction of opposite polarity. Most of the authors associate their origin with the subduction of the oceanic crust under the inferred Sea of Okhotsk microcontinent [Jolivet, 1986; Kiminami, 1983; Kiminami et al., 1986, 1992, to name but a few]. However, some geologists suggest that the Tokoro and Nemuro terrains were formed in the environment of an ensimatic island arc [Bazhenov and Burtman, 1994; Bazhenov et al., 2001; Kimura, 1996].
[15] The tectonic units of Central Hokkaido extend conventionally into South Sakhalin, whereas the eastern terrains are believed to be unique for Hokkaido, or are correlated with the eastern segment of Central Sakhalin.
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Figure 2 |
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Figure 3 |
[16] The Moneron Terrain is interpreted as the northern continuation of the Rebun-Kobato Neocomian island-arc terrain. Its structure was studied in the Moneron Hole [Piskunov and Khvedchuk, 1976], which penetrated the three-kilometer sequence of island-arc tholeitic and calc-alkaline volcanic rocks ranging from intermediate to basic compositions, and including thin members of volcanogenic sedimentary rocks. This volcanic rock complex is layered tectonically into several members with a Cretaceous-Paleocene age range, which are combined irregularly in different parts of the rock sequence, and grouping generally into the following four age intervals: 141, 118, 103-86, 77-59 Ma.
[17] The Aptian-Maestrichtian turbidite and the Paleocene coastal-marine and paralic coal-bearing rocks of the West Sakhalin Terrain, totaling more than 6 km in thickness, correlate confidently with the rocks of the Iezo Terrain. The stratigraphic and tectonic specifics of this terrain were discussed in detail in literature [Governmental Geological Map, 2001; Melankholina, 1973, 1988; Zyabrev, 1984, 1987, 1992]. The eastern flank of this terrain is poorly metamorphozed at the contact with the Susunai Terrain of metamorphic rocks. In the SE direction the distal turbidite facies are crushed in the Merei shear zone and transformed to mylonite. The Upper Cretaceous-Paleocene terrigenous rocks of the West Sakhalin terrain are overlain by Eocene-Oligocene deposits, with a hidden stratigraphic unconformity in the west, and with a distinct angular unconformity in the east [Governmental Geological Map, 2001; Zharov et al., 2004]. In the north-western part of their outcrop, these rocks are cut by a belt of Paleocene biotite rhyolite dikes of subduction-collision origin. It follows that the West Sakhalin terrain is a fragment of the Aptian-Paleocene continental margin trough, bounded in its flanks by deep long-lived fold zones. The closure and inversion of this trough is clearly seen at the Cretaceous-Paleogene boundary.
[18] The Susunai Terrain is interpreted as the northern continuation of the Kamuikotan metamorphic terrain, being comparable with the latter both in the age of the metamorphism and in the tectonic position and internal structure. The metamorphic rocks of these terrains are more often interpreted as the deep levels of the Cretaceous accretion rocks, or as the surfaces of the Cretaceous subduction zones [Dobretsov et al., 1994; Kimura et al., 1992; Komatsu et al., 1992; Sakakibara and Ota, 1994]. As follows from another viewpoint [Richter, 1986], the metamorphic structure was formed as a result of the Maestrichtian-Paleocene metamorphism of the turbidites of the West Sakhalin terrain and its basement in the course of the obduction of the perioceanic structural features over the continental margin.
[19] A radically new interpretation of the geotectonic structure is offered in this paper for the Tonin-Aniva Peninsula (Figure 3). In contrast to the previous views, only the central and southern parts of the peninsula are comparable with the Khidaka Terrain and can be interpreted as the Tonin-Aniva Terrain of the continental-margin accretionary prism.
[20] The northern and northeastern parts of the peninsula are treated as the Ozerskii Terrain with its widely developed rocks of the Permian-Cenomanian oceanic crust of the Paleo- and Meso-Pacific Ocean and the fragments of the Campanian-Early Eocene ensimatic island-arc system and of the Late Cretaceous-Paleocene sedimentary cover of the epioceanic marginal sea. The Ozerskii Terrain was correlated with the Tokoro Terrain and was found to be the accretionary prism of the ensimatic island arc [Bazhenov et al., 2001, 2002; Zharov, 2003].
[21] The Tonin-Aniva and Ozerskii terranes are separated by the Vavai melange zone extending from the western part of the peninsula to its southeastern end. All over the boundary melange area, the structural features of the Ozerskii Terrain overlap the Tonin-Aniva Terrain, proving the allochthonous origin of the former.
[22] The Tonin-Aniva and Ozerskii terrains form the Aniva composite terrain [Zharov, 2003, 2004], the origin of which was dated Middle-Late Eocene, proceeding from the age of the Vavai melange and of the suturing collision granitoids.
[23] The Merei suture-type shear zone is the recently mapped tectonic element of the region, which is comparable in many respects with the Idonnappu suture zone. These structural features are controlled by extensive shear sutures, separate the Cretaceous-Early Paleogene accretion and turbidite terranes, and are accompanied, along the western flank, by the left-lateral en-echelon outcrops of high-pressure rocks and melanged ophiolites of the Kamuikotan and Susunai terrains.
[24] The comparison of the tectonic elements of South and Central Sakhalin shows that only one West-Sakhalin Terrain can be traced reliably in the northern direction. Its Late Cretaceous distal turbidites are replaced at the latitude of the northern part of the Gulf of Patience by proximal facies and grade further northward to coastal marine and paralic coal-bearing rocks [Melankholina, 1973, 1988; Zyabrev, 1987, 1992]. This suggests the discordant orientation of the modern boundaries of the terrain relative to the Late Cretaceous structure-facies zoning of the continental margin trough. The metamorphic and accretion-related rocks are widespread also in Central Sakhalin, east of the West Sakhalin Terrain. Identified among these rocks were the equivalents of the Tonin-Aniva Terrain and, less confidently, some tectonostratigraphic units of the Ozerskii and Susunai terrains [Khanchuk, 1993; Richter, 1986; Rozhdestvenskii, 1993, to name but a few]. However, the differences in the structure and tectonic positions of individual rock complexes, as well as the different Paleogene evolution of South and Central Sakhalin preclude any correct correlations. In this paper the metamorphic, accretion-type, and sea-margin rocks of Central Sakhalin are classified as the East-Sakhalin composite terrain of accretion-collision origin, which developed from the end of the Early Cretaceous to the Eocene, inclusive.
[25] Discussed below are the main lithologic and structural features of the Tonin-Aniva, Ozerskii, and Susunai terrains and of the Merei suture zone, which illustrate the tectonic types and collision structures of South Sakhalin, as well as, the models for the formation and evolution of the Cretaceous-Paleogene East Asian continental margin.
Citation: 2005), South Sakhalin tectonics and geodynamics: A model for the Cretaceous-Paleogene accretion of the East Asian continental margin, Russ. J. Earth Sci., 7, ES5002, doi:10.2205/2005ES000190.
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