RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES5002, doi:10.2205/2005ES000190, 2005

The Cretaceous-Paleogene Geodynamics of South Sakhalin

[103]  As follows from our analysis of the South Sakhalin terrains, the rocks composing them had accumulated from the end of the Paleozoic to the middle of the Paleogene, yet the structural shaping of the Hokkaido-Sakhalin fold system began only during the second half of the Early Cretaceous, from the time when the structural features of the continent-ocean transition zone began to form. The history of the tectonic evolution of the region included five structural rearrangements associated with changes in the kinematics of the oceanic plates, with the rearrangement of the continent-ocean boundary, and with the accretion-collision processes that operated in the Asia-Pacific transition zone.

Triassic-Jurassic.
As follows from most of the paleotectonic reconstructions available, an open oceanic basin had existed during the pre-Cretaceous segment of the geologic record of the East Asia margin, east of the modern outline of the continent [Khanchuk et al., 1988; Maruyama et al., 1997; Mazarovich and Richter, 1985; Melankholina, 1988; Parfenov et al., 1999; Rozhdestvenskii, 1993; Zonenshain et al., 1990, to name but a few]. The limited paleomagnetic data available for the Mesozoic oceanic rocks of Japan and NE Russia [Sokolov et al., 1997; Zonenshain et al., 1990] suggest their accumulation at low equatorial latitudes with their subsequent displacement in the northern direction. This is also proved by the Tethyan complexes of the Triassic, Jurassic, and Early Cretaceous radiolarians found in the siliceous rocks of the Tonin-Aniva and Ozerskii terrains.

[104]  As follows from the reconstructions of the oceanic plates [Engebretson et al., 1985; Maruyama et al., 1997], the Farallon-Izanagi spreading range moved along the East Asian margin during the time of 220-180 Ma. Since that time to almost the middle of the Late Cretaceous (85 Ma), the Izanagi plate interacted with the continental margin. During the Triassic and Jurassic a large volcanic oceanic plateau was formed on the Izanagi plate in association with the Central-Pacific plume activity, known as the Sorachi Plateau [Kimura et al., 1994; Maruyama et al., 1997] and as the Okhotsk Plateau [Bogdanov and Dobretsov, 2002], and believed to have been associated with the central Pacific plume activity.

Early Cretaceous.
At the beginning of the Early Cretaceous the Rebun-Moneron island arc was formed, possibly, because of a change in the vector and velocity of the Izanagi plate movement. The position of this island arc is still not clear. Proceeding from the changes in the heavy mineral associations of the Early Cretaceous sedimentary rocks of Sikhote Alin, South Korea, and Southwest Japan, Nechaev et al. [1997] assumed that the island arc of that time had formed at the latitude of South Japan and might have extended in the northeastern direction away from the continental margin with the geodynamic environment changing from that of the continental margin to intraoceanic.

[105]  The Izanagi plate moved at that time at the highest velocity (30.0 cm year-1 ) in the northwestern direction (see Figure 10), which caused its rapid orthogonal subduction under the island arc. Its subduction was stopped by the underplating of the large blocks of the above-mentioned oceanic plateau at the end of the Neocomian (possibly during the Hauterivian-Barremian). The high velocity of the Izanagi plate movement (20.7 cm year-1 ) caused the detachment of the arc rocks from their basement, as well as of the accretion prism with the fragments of the accreted plateau. All of these rock components continued their passive movement along the continental margin as the constituents of the oceanic plate. This was facilitated by a change in the direction of the Izanagi plate motion from the northwestern to the northern at the beginning of the Aptian without any changes in the velocity of their movement.

2005ES000190-fig13
Figure 13
[106]  As mentioned above, the Aptian-Albian time witnessed the large-scale left-lateral movements of the Meso-Paleozoic terrains of different types along the Asian margin with the formation of a huge collage and the combination of the Tethyan and transitional biogeographical provinces [Golozubov, 2004; Maruyama et al., 1997; Tazava, 1993]. The shear-type deformations and huge displacements were typical not only of the perioceanic structural features, but also of the Jurassic accretion-type rock complexes, such as the Mino-Tamba, Northern Kitakami, and Oshima ones. The fragments of the Early Cretaceous island-arc system and of the oceanic plateau were spread along the Asian margin over hundreds to a few thousands of kilometers and produced the Rebun-Kobato, Moneron, and Sorachi terrains. The Izanagi Plate seems to have experienced oblique subduction under the continental margin in different segments of its boundary with the latter, or its transform-type movements. Accretion-type rock complexes, similar to those of the Tonin-Aniva Terrain, accumulated in areas of the subduction environment. Turbidites of subarkose composition, might have accumulated in the areas of the transform-type boundary at the expense of the erosion of the Jurassic accretion-type rocks, as well as of the continental terrain deposits. Active shear-type movements continued during the Cenomanian, as the Izanagi Plate moved along the East Asian continental margin. Moving along with it was the oceanic ridge which separated the Izanagi and Pacific oceanic plates (see Figure 13a).

[107]  The global left-lateral movements resulted in the formation of an extensive suture which had inherited the Early Cretaceous convergent boundary and could be traced by the fragments of the accretion-type Northern and Southern Chichibu and Kurosegawa terrains and of the subduction-type Mikabu and Sambagawa terrains of Southwest Japan. The granitoid magmatism of the Rioke Belt developed with some delay in the rear of this structural feature [Isozaki, 1996; Miyashiro, 1975]. Earlier, it was interpreted as a high-temperature and low-pressure metamorphic belt, forming a pair with the Sambagawa high-pressure metamorphic belt. According to this view, the Sambagawa Terrain and the metamorphic accretion-type terrains, conjugated with it, were "pressed" in the zone of transregional strike-slip faults, whereas the Rioke granite belt was formed as a syncollision tectono-magmatic structural feature. This is proved by the intensive transformation of the granitoids to gneiss and by their tectonic position. As follows from [Maeda and Kagami, 1996; Maruyana et al., 1997], the formation of the syntectonic granitoids and the low-pressure metamorphism might have been associated also with the development of the Izanagi-Pacific oceanic ridge along the continental margin. As follows from the age of the igneous rocks (100 pm 5 million years), the peak of this tectonic activity can be placed at the end of the Early Cretaceous.

[108]  The left-lateral strike-slip movements involved the whole of the continental margin. Its Jurassic-Early Cretaceous accretion structure experienced repeated lateral doubling with the formation of large saw-shaped protrusions in the NE direction [Golozubov, 2004]. One of these protrusions was formed by the Abakuma, North and South Kitakami, and Oshima terrains of Southeast Japan. It can be supposed that the formation of this doubling zone might have been accompanied by the Aptian-Albian alkaline volcanic activity of the Kem Terrain along its continental side. At the same time the Rebun-Kobato, Moneron, and Sorachi terrains were displaced along the oceanic side of the protrusion and accreted at the end of the Early to the beginning of the Late Cretaceous, having occupied the position close to the modern one, adding the abundant volcaniclastic material to the synchronous turbidite sediments of the southern segment of the Iezo-West Sakhalin Trough. The latter originated as a circum-shear turbidite depression which grew larger in the northern direction and overlapped the Sorachi Plateau accreted segments. The eastern segments of this plateau continued to move to the north and were subducted in the oblique subduction zone (Figure 13b).

Late Cretaceous.
As the Izanagi-Pacific Ridge had moved along the East Asia margin, the Pacific oceanic plate had been interacting with the latter. During the Late Cretaceous the geodynamic environment in the transition zone changed notably, although was still controlled by the oblique subduction of the oceanic plate. The accreted pre-Late Cretaceous terrains were overlain by the East Sikhote Alin continental margin volcanic belt and by the Iezo-West Sakhalin forearc basin grading eastward to a deep-sea trench.

[109]  The process of the oblique subduction was accompanied by the left-lateral movements of the Early Cretaceous prism with the subduction and high-pressure metamorphism of the lower structural levels (West Susunai Subterrain). The upper structural levels experienced crowding and were thrust over the fore-arc turbidite and trench sediments. To sum up, the active continental margin of the Andean type existed in the east of Asia during the early half of the Late Cretaceous. Its accretion-type structural features were formed in the environment of the oblique subduction of the Pacific Plate.

[110]  The Early Campanian time witnessed the reorganization of the Asia-Pacific ocean convergent boundary. A system of intraoceanic island arcs was formed in the northwestern part of the Meso-Ppacific Ocean at a latitudinal distance of up to 2000-3000 km from the continental margin [Bazhenov et al., 2001, 2002; Kovalenko and Chernov, 2003]. The compilation of the paleomagnetic data available for the Campanian-Early Paleogene island-arc rocks of Hokkaido, South Sakhalin, Kamchatka, and Koryakia shows that the island-arc systems had a NE strike, generally orthogonal to the movement of the Pacific Plate. The southwestern flank of the island arc garland, closest to the East Asian continental margin, was occupied by the Tokoro Arc. This arc developed at the leading edge of the Pacific plate which moved, at the end of the Cretaceous, in the NW direction at a rate of 13.1 cm year-1 [Engebretson et al., 1985]. The subduction zone was directed to the ocean, and the arc moved closer to the continental margin, together with the overhanging oceanic plate. Northeast of the Tokoro Arc, supposedly following the same kinematic model, the East Sakhalin island arc [after Zonenshain et al., 1990], or the Patience island arc [after Khanchuk, 1993; Parfenov et al., 1999], was formed and included in the early Paleogene into the accretion-collision structure of the East Sakhalin composite terrain. As to the further reconstruction and substantiation of the early collision of the Patience Arc with the continental margin, we have to admit that this margin had been advanced northwest relative to the Tokoro Arc and joined it along a transform fault (Figure 13b).

[111]  The space between the ensimatic arcs and the continental margin was occupied by the microplates of the marginal seas, representing large Paleo-Meso-Pacific segments. The Velikan plate identified in this region (Figure 12b) experienced subduction in the Campanian-Maestrichtian both under the continental margin and under the Tokoro Arc, which contributed to the rapid convergence of these structural features.

[112]  To sum up, at the end of the Late Cretaceous the environment of the active Andean-type continental margin coexisted with the environment where the continental-margin and intraoceanic subduction zones existed together with epioceanic marginal seas being located between them. The latter situation has no analogs, yet can be compared conventionally with the modern Polynesian or Philippine Sea situation [Bazhenov et al., 2001, 2002; Kovalenko and Chernov, 2003; Melankholina, 2000].

2005ES000190-fig14
Figure 14
Paleocene.
During the Early Paleogene, the collision of the Patience Arc with the continental margin resulted in the formation of the East Sakhalin composite accretion-collision terrain, and the convergent boundary bordering the continent was reconstructed again. The changes of its configuration were associated with the impossibility of the further oblique subduction in the Central Sakhalin area and with the still acting compression in the northern direction, caused by the movement of the Velikan Plate. These movements resulted in the Early Paleocene transformation of the Late Cretaceous oblique subduction zone to a left-lateral shear zone with the folding of the West Susunai Subterrain and the inversion of the West Sakhalin fore-arc basin (Figure 14a). A sublatitudinal underthrust zone was formed during the Paleocene at the southern flank of the east Sakhalin composite terrain. Subducted along this zone were the marginal marine rocks of the Velikan Plate. The western flank of the subduction zone (East Susunai subterrain) was superposed over the Cretaceous subduction zone producing a trench-trench connection.

[113]  It should be noted that almost simultaneously, namely, from the end of the Paleocene to the beginning of the Eocene, the collision of the Achaivayam-Valaga ensimatic island arc with the continental margin rearranged the convergent margin with the formation of a new subduction zone dipping under the continent and extending in the direction of South Sakhalin [Konstantinovskaya, 1999, 2003].

[114]  To sum up, the beginning of the Paleogene witnessed the extinction of the Cretaceous subduction zone, the migration of the convergence boundary to the south, and the formation of a new Paleogene continental margin, known as the Okhotsk one, at the latitude of the South Sakhalin plate.

[115]  The subduction of the Velikan Plate under the Tokoro Arc continued up to the Early Eocene, as indicated by the magmatic activity of the suprasubduction structural features and by the synchronous emplacement of fore-arc tuffaceous turbidite in the Tokoro Terrain [Kiminami et al., 1992].

Eocene-Oligocene.
The Middle Eocene time witnessed the largest structural rearrangement of the region as a result of the collision of the Tokoro Arc with the continental margin and the closure of the continental-margin epioceanic basin (Figure 14b). The arc-continental margin collision produced different effects and was responsible for the evolution along the collision zone as a result of the oblique convergence of the structural features and of the complex configuration of the continental margin.

[116]  In South Sakhalin the collision occurred from the end of the Middle Eocene to the Early Oligocene. Southward, in Hokkaido, the collision of the Tokoro and Hidaka terrains terminated only in the Oligocene, as follows from the ages of the syncollision intrusions [Maeda et al., 1990]. In the southern segments of the collision zone, the accretion-type rocks of the Tokoro and Hidaka terrains experienced progressive metamorphism with the formation of the Hidaka collision-type metamorphic terrain. The oldest synkinematic anatectic granites have been dated Early Eocene (56 Ma, Ar-Ar), [Komatsu et al., 1992; Osanai et al., 1994]. This suggests that the collision might have developed from the south to the north, concordantly with the convergence of the island-arc and continental margin structural features, yet, terminated more rapidly in the north.

[117]  The Aniva composite terrain, produced by the amalgamation of the accretion structural features, moved in the northern direction along the Idonnappu and Merei suture zones, and was finally included into the continental margin at the Eocene-Oligocene boundary, or at the beginning of the Oligocene, being located in the junction zone between the Okhotsk and proto-Japanese continental margins. Later the accretion-type structural features of Southeast Sakhalin and East Hokkaido were overlapped by the Late Eocene-Early Miocene neoautochthon.

[118]  The proto-Japan continental margin began to form synchronously with or slightly earlier than the Tokoro Arc and continental margin collision, that is, at the end of the Early-Middle Eocene. It was recorded in the slow inherited subsidence along the inverted Cretaceous basin and in the formation of the Middle-Late Eocene zone of calc-alkaline volcanism (proto-Japan volcanic arc), displaced eastward relative to the Cretaceous-Paleocene East Sikhote Alin Belt (Figure 14b). The specific geochemistry of the volcanic rocks suggests their suprasubduction origin and their association with some previously subducted Paleo-Mezopacific slab [Okamura et al., 1998; Yasnygina, 2004]. At the back of the volcanic zone, extension began in the later half of the Eocene or at the beginning of the Oligocene, and the proto-Tatar and Central Sea of Japan rift basins began to form, with plateau basalts residing at their continental shoulders. On the contrary, in front of the proto-Japan Arc, en-echelon upthrust-overthrust zones were formed, which marked the axes of the synsedimentation structural highs. The comparison of the specific structural and petrological features of the proto-Japan Arc and the adjacent structural features suggests their evolution as a result of the break or the abrupt curvature of the previously subducted slab of the oceanic crust and its subsequent "floating up" or rolling away toward the trench. These movements "shaped" the late metamorphic structural features in the Susunai Terrain and controlled the final exhumation of the metamorphic rocks.

[119]  The Okhotsk arc-trench system was being formed at that time in the area of the Sea of Okhotsk continental margin. Its frontal elements are preserved in the East Susunai and Tunaicha subterrains. Its Eocene-Oligocene volcanic rocks (46-26 Ma), marking the zone of the suprasubduction igneous activity, have been found in the southern part of Central Sakhalin and in its sea-floor extension, recorded in the Academy of Science Rise [Emel'yanova, 2003].


RJES

Citation: Zharov, A. E. (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.

Copyright 2005 by the Russian Journal of Earth Sciences

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