RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES5002, doi:10.2205/2005ES000190, 2005
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Figure 4 |
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Figure 5 |
[26] The common features of the hard-rock series are: (1) the siliceous volcanic composition of its lower part and the volcanogenic terrigenous composition of its upper part; (2) the combination of Tholeiite and subalkaline basalts in its lower and middle parts and the predominance of alkaline basalt, up to picritic ones, in the upper part; (3) the association of siliceous and carbonate rocks with the formation of jasper-limestone flyschoid alternation; (4) the predominance of quartz-jasper and low-quartz feldspar with albitophyre-andesite-basalt clastic material. The radiolaria finds restrict the age of this rock sequence to the Middle Jurassic (Bathonian)-Early Cretaceous interval.
[27] The Utesna rock sequence has a chaotic structure because of widely developed olistostromes and imbricate dislocation zones grading to melange. The olistoliths are dominated by hard rocks. The sandstones vary from arkose to graywacke ones, which suggests different sources the clastic material, both oceanic and continental. The high-quartz rocks are typical of the turbidites, and occur as olistoliths in the olistostromes.
[28] The thickness of the slabs is not lower than 1 km, the total tectonic thickness of the accretion rock complex may be equal to or higher than 4-5 km, which is a typical value for accretion prisms. The radiolaria assemblages from the olistoliths and from the matrix date this rock complex Aptian-Cenomanian.
[29] The structural pattern of the Utesna rock sequence allows one to rank it as the Middle Cretaceous accretion rock complex that had accumulated during the accretion of the oceanic volcanic plateau or of some submarine volcanic mountains to the Asian continental margin. The presence of high-quartz and quartz feldspar sandstones in the turbidites, and of exotic Permian limestones in the olistostromes, suggests that this accretionary prism originated south of its modern position, in the vicinity of the outcrops of the old accretionary rock complexes or of large continental blocks of the Asian margin (for instance, the Northern and Southern Kitakami terrains of the Northern Honshu Island), unknown in the vicinity of South Sakhalin.
[30] The Evstafiev Formation is composed of siltstone, sandstone, tuffstone, and the members of their flyschoid interbedding. The lower part of this formation is dominated by siliceous aleuropelite with siliceous sandstone interbeds. Up the sequence the silica content declines, the rocks grow more tuffaceous, the rock sequence being dominated by flyschoid members with gradational bedding. The sandstones of this formation are distinguished by a low quartz content, being dominated by acid-intermediate igneous rock particles. The maximum thickness of this formation is 2600 m. The scarce Campanian-Maestrichtian radiolaria and the remnants of Late Cretaceous inocerams restrict the age of these rocks to Late Cretaceous. The specific structure of this formation suggests that its rocks had accumulated in the axial part of a deep-sea trench or in the lower part of its internal slope under the conditions of the eastward progradation of some forearc trough.
[31] This terrain has a scale-overthrust, intricately folded divergent structure which was shaped during several tectonic stages and is distinguished by the submeridional strike of its melanges and en-echelon overthrusts (see I-I in Figure 5).
[32] The overthrusts and melanges of eastern vergence controlled the growth of the tectonic thickness of the Utesna rock sequence and its thrusting over the Late Cretaceous turbidites in the eastern direction. The overthrusts and terrigenous melanges of the western vergence are developed mainly in the field of the Evstafiev rock development. In the central part of the peninsula they controlled the overthrusting of the Utesna and Scalnaya rock sequences in the western direction. The melange inclusions are composed mainly of siliceous rocks, the matrix being similar to the Late Cretaceous turbidites.
[33] The Ozerskii Terrain consists of six lithostratigraphic units embracing the time interval from the Late Permian to Paleocene, inclusive. It shows a persistent tectonic and stratigraphic sequence which was studied most thoroughly in the Chaika subterrain.
[34] The bases of both subterrains include the tectonic slabs of the Albian-Cenomanian subarcose turbidite of the Gorbusha Sequence, which is underlain by the Vavai melange and is comparable in terms of its sandstone composition with the coherent turbidite of the Tonin-Aniva Terrain (Figures 4 and 5). This rock sequence is composed of quartz-feldspar sandstone, siltstone, and members of their flyschoid intercalation with gradation stratification. The bottom of this rock sequence is dominated by sandstone with acid effusive and granite clastics (up to 35-40%), whereas the top is composed of sandstone with albitite-jasper and basaltic andesite composition of the fragments. The thickness of these rocks is higher than 1000 m.
[35] The subarkose turbidites are overlain by a tectonic layered oceanic rock complex composed of the Velikan, Yunona, and Kedrov rock sequences. The contacts between these rock sequences are stratigraphically concordant but deformed by faults.
[36] The Velikan rock sequence is complicated by metabasats, clastic hyalobasalt lavas and hyaloclastites with subordinate jasper layers at the top. In terms of their mineral and chemical compositions, the basalts are ranked as oceanic Tholeiite, and in terms of their minor elements, they resemble MOR basalts. The Late Permian-Middle Triassic (Anisian) age of these rocks was proved by the rare radiolarias found in the jasper interbeds. This rock sequence is more than 300 m thick.
[37] The Yunona rock sequence (Middle Triassic-Jurassic) is the main marker of the Ozerskii Terrain because of its permanent jasper composition. The jasper includes phthanite layers, radiolarites, and siliceous argillites in the upper part of this rock sequence, and occasional basalt lenses. The rock sequence of the Tunaicha subterrain (Yunona Mt. area) is ranked as a stratotypical one and has been subdivided into stages using 15 radiolarian complexes [Bragin, 1986, 1991]. The Triassic rocks have a thickness of 80-100 m. The Jurassic rocks are 170-200 m thick, the total thickness of this rock sequence being 300 m.
[38] The Kedrov rock sequence is composed of tuffaceous siliceous rocks in its lower part, which grade facially from tuffaceous silicite to cherty tuffite rocks with tuff members and subalkaline basalt lenses. The upper tuffaceous-terrigenous part of this rock sequence varies from site to site in the amounts of tuff, tuffaceous siliceous and terrigenous rocks and in the number of their flyschoid interbedding. The petrochemical features of the basalts suggest their oceanic, intraplate origin.
[39] The Upper Tithonian-Albian age of this rock sequence was determined using abundant radiolaria and more rare rudists and trigoniids. The thickness of this rock sequence varies from 800-850 m in the Chaika subterrain to 500 m in the Tunaicha one.
[40] The upper structural level in the Chaika Subterrain is occupied by the Chaika rock sequence which rests on the oceanic rock complex in argillaceous melange zones and is composed of tuffaceous turbidite and flysch of tuffaceous origin. Large rootless slabs of these rocks have been found in the Vavai melange. The rocks of this sequence show the vertical upward replacement of the hemipelagic deposits by thick-bedded terrigenous, very thick-bedded tuffaceous terrigenous rock members, with the markers of varicolored tuffaceous siltstone and tuffite, and tuffaceous-silty-sandy flyschoid members with olistostrome horizons in the top of the rock sequence. The olistoliths include both subalkaline and tholeitic oceanic basalts, and island-arc calcalkaline and Tholeiite basalts. This rock sequence varies from 850 m to 1100 m in thickness. Its psammites are low in quartz, contain some basaltic andesite clastic material, and correspond in their composition to ensimatic island arc sandstones. The rocks of this terrain contain abundant Campanian-Maestrichtian and Paleocene radiolarians and Early Paleogene spores and pollen.
[41] The Late Cretaceous-Early Paleogene rocks of the Tunaicha Subterrain have an aleuropelite and argillite composition and include rare flyschoid horizons and interlayers of tuffaceous sandstone in the eastern part of this subterrain. In some sections aleuropelite replaces the siliceous terrigenous rocks of the Kedrov rock sequence. These rocks are less than 650 m in thickness. This rock sequence was dated using scarce Late Cretaceous inocerams, Campanian-Maestrichtian radiolarians, and poor Early Paleogene spore and pollen spectra.
[42] The upper structural levels of the Chaika Subterrain are occupied by a zonal quartz diorite-granodiorite intrusion (Okhotsk Massif) and by the accompanying dike series of contrasting composition ranging from microdiorite to rhyolite and alkaline microgranite. These rocks have been classified as the Okhotsk diorite-granodiorite complex consisting of two phases. Ranked as the early phase are the rocks of this massif and the holocrystalline microdiorite and granodiorite porphyry dikes cutting only the Chaika rocks. They are composed of island-arc diorite and granodiorite, and their petrochemistry proves their ensimatic origin. The rocks of the second phase are acid and alkaline dikes cutting the rocks of the Okhotsk Massif, the dikes of the first phase, and the deposits of the Yunona, Kedrov, and Chaika rock sequences. The rocks of the second phase are fairly similar to those of the granite-syenite suite and correspond to the intermediate, subduction-collision, granitoids that had been formed during the collision of the island arcs with the continental structural features. The results of the K-Ar and zircon track dating restrict the ages of the early rocks to Paleocene-Early Eocene (63.5-48.5 Ma) and those of the second phase to Middle Eocene (45 Ma). The secondary alterations of the rocks were dated Miocene-Oligocene (37.4-22.3 Ma) and are believed to have been associated with the rise of the granites to the ground surface.
[43] The Ozerskii Terrain has a more ordered structural pattern, compared to the Tonin-Aniva one, and is distinguished by its differently oriented structural elements and by the deformation style of the Chaika and Tunaicha subterrains.
[44] The Chaika Subterrain has a steeply standing slab structure of the western and southwestern vergence and consists of three slab packages, namely, the Gorbusha, Velikan, and Okhotsk (see III-III in Figure 5).
[45] The lower, Gorbusha slab package is composed of the subarcose turbidite of the Gorbusha rock sequence, overturned to the southwest. The Velikan slab package rests on the Gorbusha slab package along a melange zone with the slabs of the Gorbusha sandstone and volcanic siliceous rocks, comparable with the hard rocks of the Tonin-Aniva Terrain in terms of their age, lithology, and geochemistry. At the base of the Velikan package, the Velikan basalts are deformed to large, SSE-overturned folds and are broken tectonically into slabs, as thick as 100-150 m. The jasperoid rocks of the Yunona rock sequence compose the bulk of this tectonic package and are deformed to large recumbent and diving folds with the spans of their limbs measuring up to a few hundred meters. The northern limbs show the growth of the jasperoid rock sequence at the expense of the tuffaceous siliceous of the Kedrov rock sequence. The total thickness of this oceanic rock complex is not larger than 1.2 km, the total thickness of this slab package being larger than 3.5 km.
[46] The Velikan slab package is overlain, via the zone of scaly schist and tectonite, by the Okhotsk slab package composed of the Chaika tuffaceous terrigenous rock sequence cut by the granitoids of the Okhotsk Complex. The dikes of the first phase of the Okhotsk Complex were emplaced before the formation of the plate structure of the subterrain, whereas the rocks of the second stage showed their subduction-collision geochemical properties. This suggests their origin at the early collision stages and dates this subterrain formation not older than 45 Ma.
[47] The Tunaicha Subterrain has a slab-overthrust and north-dipping nappe-fold structure and is composed of slab and nappe packages, where the Mesozoic oceanic and Late Cretaceous-Paleocene rock complexes are superposed (Figure 5, II-II and III-III). The nappes are separated by the zones of terrigenous and, occasionally, serpentinite melange and were deformed in the southern part of this subterrain by the formation of tectonic windows, where the subarkose turbidites of the Gorbusha rock sequence, or the melanged rocks of the Tonin-Aniva Terrain, are exposed (Figures 4 and 5). The Tunaicha Subterrain includes the Yunona and Kazachka packages of slabs and nappes, which occupy the frontal and rear positions, respectively.
[48] The articulation of the Chaika and Tunaicha subterrains was mapped in the area southeast of the Tunaicha Lake, being hidden, to a great extent, under the Cenozoic sediments. The northern part of the Chaika Subterrain is deformed by a system of sublatitudinal reverse faults and strike-slip thrust faults, which followed the structural style of the Tunaicha Subterrain. The upper, oceanic and island-arc, slabs of the Chaika subterrain are curved to the northeast, whereas the lower Gorbusha slab is turned, together with the Vavai melange, under the Tunaicha Subterrain, residing in its basement. The northwestern flank of the Okhotsk Massif is most highly eroded and is cut off in the north by the NE-striking faults. North of these faults, the rocks of the Tunaicha Subterrain do not show any indications of hornfels development, the granitoid boulders being restricted to the Oligocene-Lower Miocene conglomerates of the neoautochthon, and being absent in its Upper Eocene basal conglomerates. This suggests that the structural connection of these subterrains might have taken place at the Eocene-Oligocene boundary or during the Early Oligocene with the displacements of the granitoids to the surface. This agrees with the absence of the Late Eocene neoautochthon in the junction zone of these terrains, which can be explained by its erosion.
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Figure 6 |
[49] This subterrain is basically composed of black plicated, as well as green and blue, schists, with the high predominance of the former, all of them being known as the Krasnoselskaya metamorphic rock series. These rocks contain abundant Na-amphibole of the crossite-riebeckite series and some local Na-pyroxene and lawsonite. The blue schists trace the synmetamorphic faults and are accompanied by small serpentinite and talcite protrusions. As follows from their petrogeochemical characteristics, the greenschists developed mainly after the oceanic intraplate subalkaline basalts and, to a lesser extent, after the MOR Tholeiite basalts.
[50] The riebeckite schists showed their ages to be 67, 77, and 85 million years. Proceeding from the Early Cretaceous-Cenomanian age of the initial rocks for the black shale (spores, pollen, and radiolarians) and from the Paleocene-Eocene age of their diaphthoresis (see below), the formation of these metamorphic rocks was dated Late Cretaceous.
[51] The Sokolskaya metamorphic rock series is represented by the amphibolite composing slabs in the serpentinite melange and in the areas underlain by the rocks of the Krasnoselskaya metamorphic rock series, and also by the lawsonite-glaucophane schists and eclogite-like metasomatic rocks developed after amphibolite. As follows from the petrogeochemical data available, the protoliths of the amphibolite were the alkaline and subalkaline igneous rocks of interoceanic rises and more rarely MOR basalts.
[52] The glaucophanized amphibolites and eclogite-like rocks were K-Ar dated 133-135 million years, whereas the amphibolite showed an older 206 Ma age [Egorov, 1969]. The amphibole-bearing schists were dated 90-92 Ma and seem to have formed after amphibolites were included into the late Cretaceous Subterrain.
[53] The metabasalts of the Annino rock sequence occur as sheets at the bases of all tectonic rock packages and as slabs in the melange zones. These rock sequences were classified into two types. The rocks of one of them are developed in the central part of the subterrain and are represented by the alternation of MOR Tholeiite metabasalts and metahyaloclastites with scarce quartzite lenses (Figure 6). The rocks of the second type are developed in the southern part of this subterrain and are represented by intraplate subalkaline and alkaline intraplate metabasalts, hyaloclastites, and tuff breccias with microquartzite layers and occasional limestone lenses. These rocks are not more than 700 m thick. They were dated Triassic-Jurassic proceeding from the K-Ar dating of the metabasalts (177-179 Ma) and from the age of the overlying Onega rocks.
[54] The Onega rock sequence is represented by microquartzite layers and quartzite-like schists, developed after siliceous and siliceous-argillaceous rocks, which are replaced upward by green and black paramorphic schists developed after tuff, tuffaceous siltstone, and silty pelite. This rock sequence is more than 700 m thick. The rocks were dated Jurassic-Lower Cretaceous proceeding from the scarce radiolarians found in the siliceous rocks and from the spore and pollen remains found in the black paraschists.
[55] The Zhukovka rock sequence is widespread in the central part of the terrain, along its contact with the West Susunai Subterrain. This rock sequence is represented by the coarse alternation of siliceous shale and tuffaceous silicite, varicolored metahyaloclastite and phyllite developed after the tuffite and tuffaceous siltstone, and slabs of poorly metamorphic subalkaline metabasalts of intraplate origin. The petrogeochemistry of the metabasalts and the total appearance of this rock sequence make it similar to the Lower Cretaceous hard rock sequences of the Tonin-Aniva Terrain. This rock sequence has a maximum thickness of 970 m. The siliceous shale was found to contain Cretaceous spores and pollen. This rock sequence was dated Early Cretaceous.
[56] The Shuya rock sequence is composed of alternating phyllites, and phyllitic sandstones with lenses of quartz-like schist, quartzite, green para- and orthoschists, and limestone. Some of these rock sequences show a chaotic structure and seem to be of olistostrome origin. The quartzite-like schists originated after high-quartz sandstones, whereas the metajaspers and cryptogranular quartzite, found in the Annino and Onega rock sequences, are not characteristic here. Found in the schists were Albian-Late Cretaceous palynological complexes, containing Devonian relict spores.
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Figure 7 |
[58] The synmetamorphic structure of the East Susunai Subterrain varies in the northern direction from the northeastern one, formed by the tectonic slabs of different dips, to the sublatitudinal one, controlled by the overthrust sheets of southern vergence, and emphasized by the Sima metamorphozed terrigenous melange. The age of this melange becomes younger northward from 64.5 to 54 million years. This subterrain shows at least four structural styles of different ages estimated using the age of its micas. The early structural elements of the NNE strike had originated in the course of the subduction of the volcanic siliceous rocks under the West Susunai Subterrain at the end of the Cretaceous (68 Ma) and of their swell-like folding during the deformation of the Cretaceous subduction zone at the beginning of the Paleocene (64 Ma). The main synmetamorphic sublatitudinal structural style reflects the tectonic stratification of these structural features and their subduction in the northern direction in the Paleocene-Early Eocene (61-54 million years). The late metamorphic structural style was associated with the upthrusting of the whole Susunai Terrain in the SE direction during the Middle-Late Eocene (43.5 Ma).
[59] The Vavai melange zone is traceable over a distance of about 70 km, with its width ranging from 5 km to 8 km, from the Sea of Okhotsk coast to the western flank of the Tonin-Aniva Peninsula, where, together with the structural features of the Tonin-Aniva and Ozerskii terrains, it is cut off by the shear faults of the Merei suture zone (Figure 4). Over its total length, the Vavai melange includes tectonic lenses of serpentinite, ophiolite gabbroids, and zones of serpentinite melange, which allow one to interpret it as a suture structural feature. Its southeastern extension is marked by the outcrops of melange rocks with small serpentinite protrusions and gabbroid lenses at the protruding capes of the Sea of Okhotsk coast. The melange includes the slabs of the Middle Cretaceous accretion rocks, the rocks of the Meso-Pacific crust, and the Campanian-Paleocene island-arc rocks.
[60] The structure and structural styles of the Vavai melange in the eastern and western parts of the peninsula differ markedly and generally repeat the structural specifics of the subterrains of the Ozerskii Terrain. The imbricate structure of the Vavai suture zone is overlain, in the northern part of the peninsula, by a Late Eocene-Oligocene neoautochthon. In the south of the peninsula the melange rocks are metamorphosed to hornfels at the contact with the Middle Eocene-Early Oligocene syncollision granites.
[61] The connection zone of the Susunai and West Sakhalin turbidite terrains can be ranked as the structural features discussed above. The synmetamorphic structure of the West Susunai subterrain was deformed along this zone during the Paleocene with the exhumation of the Early Cretaceous high-pressure schists and the low-pressure greenschist metamorphism of the West Sakhalin turbidites. West of this connection zone, the turbidites are cut by the Early Paleocene rhyolite of subduction-collision origin (Figure 3). These processes were synchronous with the closure of the West Sakhalin trough and operated in the tension field of the left-lateral strike-slip fault, the eastern flank of which was the Merei suture zone.
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Figure 8 |
[63] The Merei Zone was found to include three lithostratigraphic units, similar to the rocks of the same age in the conjugated terrains, and the zones of shale melange with various tectonic inclusions (Figure 8). The most widespread rock is the Late Cretaceous-Paleocene silty pelite similar to that of the upper rock unit of the Tunaicha Subterrain and to the rocks of the same age in the southern surroundings of the Susunai Ridge. The pre-Turonian rocks are separated into two tuffaceous terrigenous and siliceous-argillaceous rock sequences, developed in the southern and northern zones, respectively, and separated by terrigenous melange zones.
[64] The Lower Cretaceous tuffaceous-terrigenous rock sequence is represented by silty pelite with interlayers of highly quartzitic sandstone and silicic argillite and members of volcaniclastic and pyroclastic rocks. This rock sequence is intricately deformed marking a few structural styles, the main of which is represented by the combination of isoclinal and SE-overturned folds with their hinges dipping steeply (20-60o) to the southwest, by ubiquitous cleavage, and by slab-type faults of the NE strike, showing distinct indications of a left-lateral strike-slip fault.
[65] The Albian-Cenomanian siliceous-argillaceous rock sequence is composed of siliceous siltstone and argillite with interbeds of siliceous sandstone. These rocks are substituted downward by tuffaceous silicite, their upper parts containing aleuropelite members with marly sandstone interbeds and marl concretions. In the upper part of this rock sequence, Albian-Cenomanian radiolarians were found in the siliceous sandstones.
[66] The Late Cretaceous-Paleocene aleuropelite sequence was found to be represented by two types of the rock sequence. In the western part of the Merei Zone and at the Aniva Gulf coast, this rock sequence is composed of homogeneous silty pelite with occasional interlayers of graywacke sandstone beds. These rocks are transformed to dark-gray clay-like mylonite.
[67] In the eastern part of the Merei Zone this rock sequence rests (supposedly conformably) on the sequence of siliceous-argillaceous rocks. It is also composed of aleuropelite with marl concretions, yet includes the notable number of sandstone and tuffaceous sandstone interlayers, members of alternating normal sedimentary and tuffaceous rocks and occasional siliceous siltstone interbeds.
[68] The western and eastern segments of the Merei Zone differ in structure. The western segment is composed of mylonite bands, 1-2 km wide, developed after the Upper Cretaceous-Paleocene aleurolite of the West Sakhalin Terrain. The eastern segment of this zone is composed of steeply standing tectonic slabs of NE strike, composed of Cretaceous rocks of different formations and of melange, resembling that of the Ozerskii Terrain. Compared to the NE orientation of the slabs, the internal structure of this zone is characterized by the development of pre-Eocene left-lateral structural paragenesises, whereas the right-lateral shears are Neogene ones, have submeridional strikes, and inherited the structural heterogeneities inside and at the flanks of the suture zone. The comparison of the Cenozoic rocks, as well as of the structural and geophysical indications on both sides of the Merei Suture, suggested the magnitudes of the right-lateral movements to be 35-40 km.
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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