Gravity field, surface topography, and volcanic complexes of Kamchatka and its junction with the Aleutian arc

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ScienceDirect Russian Geology and Geophysics 59 (2018) 780–802 www.elsevier.com/locate/rgg

Gravity field, surface topography, and volcanic complexes of Kamchatka and its junction with the Aleutian arc N.L. Dobretsov a,b,*, A.N. Vasilevskiy a,b a

A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia Received 10 November 2017; accepted 18 December 2017

Abstract The paper deals with interpretation of global digital maps of gravity anomalies and surface topography for the northwestern Pacific and Kamchatka regions. A transformation procedure is suggested to reveal subtle features of surface topography against high elevation contrasts. Gravity data (free-air and Bouguer anomalies) have important implications for the evolution of the circum-Pacific region and the problems of volcanism and geodynamics in subduction zones. The patterns of gravity anomalies and transformed topography interpreted jointly with onshore and offshore geological data can make a basis for tectonic paleoreconstructions of upper crust and lithospheric mantle structures. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: tectonics; geodynamics; volcanoplutonic complexes; free-air and Bouguer gravity anomalies; integrated interpretation; Kamchatka; Aleutian arc

Introduction Tectonic reconstructions and synthesis rely largely on databases and World maps of both marine and continental gravity field (Andersen and Knudsen, 2016; Andersen et al., 2010; Bonvalot et al., 2012). We referred to these data when discussing the Late Cenozoic structure of the Eurasia/India– Australia junction from the Himalayas to the Northern Baikal region (Dobretsov et al., 2016a), as well as the Devonian, Late Paleozoic, and Late Cenozoic tectonic frameworks and surface topography of Gorny Altai (Dobretsov et al., 2017). In the present paper, gravity data are used to study the structure of Kamchatka and northwestern Pacific, which is a key region for understanding the circum-Pacific evolution and subduction-related volcanism and geodynamics (Dobretsov, 2010; Dobretsov et al., 2012, 2015, 2016b). Gravity data for this region have been of quite a limited use, actually restricted to the book on the Tolbachik fissure eruption of 2012–2013, Chapter 1 (Gordeev and Dobretsov, 2017). As we show below, interpreted jointly with transformed seafloor topography data, the gravity data are highly informative as to the tectonic and geodynamic history of the region

* Corresponding author. E-mail address: [email protected] (N.L. Dobretsov)

comprising the Kurile–Kamchatka arc and the adjacent areas of the Pacific and the Okhotsk Sea.

Methods We used digital maps of gravity anomalies and elevations, as well as printed geophysical and geological maps. Comparison of geophysical and geological data acquired in different ways is a common procedure in interpretation of gravity anomalies, which becomes much easier if electronic data are available. By varying color codes in the electronic maps of surface topography and gravity anomalies one can highlight different features and spatial relations of effects from the same process or analyze different processes. This is a valuable advantage as geological processes not always leave clearly detectable imprints in the gravity and elevation patterns because (i) events of different ages may superpose one upon another and (ii) the same process may be more or less prominent in different parts of the territory depending on the crust thickness and rheology, lithology, etc. Varying the color scale actually extends the dynamic range of digital mapping for better correlation with other data. Additionally we performed the windowed 2D Laplacian of elevations image to obtain better images of features hidden in digital gravity and topography maps. Procedures of this kind

1068-7971/$ - see front matter D 201 8, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.201 + 8.07.005

N.L. Dobretsov and A.N. Vasilevskiy / Russian Geology and Geophysics 59 (2018) 780–802

are used broadly for edge detection in processing of images acquired by machine vision systems. The transformation was applied to detect subtle topography features in digital maps, irrespective of the intensity of topography shaping processes. Note that formalized transformations of measured fields require special caution to avoid artifacts. For better checks, we carefully tuned the procedure parameters and compared the transformed and initial data. The next step for improving further the efficiency of electronic maps may be to use correlation functions for formalized comparison of different data in sliding windows. This transformation requires still more caution and fine tuning to handle maps of different types. As a preliminary step, we have studied correlation relationships between elevation contrasts and intensities of free-air and Bouguer gravity anomalies, in order to understand the contribution value of terrain to the gravity pattern. The gravity field is presented as maps of free-air and Bouguer anomalies. The free-air anomalies are borrowed from the DTU15 model (Andersen and Knudsen, 2016) based on spaceborne data, including advanced satellite altimetry and surface surveys which provide precise estimates of the gravity field over offshore areas and commensurate onshore data. The anomalies have been mapped at two scales in different projections. In the generalized 40° × 50° map of the northwestern Pacific (Fig. 1), the gravity highs are in blue and the lows are in red or yellow, to highlight trenches and troughs. The 18° × 14° map of Kamchatka uses red and brown-yellow for the highs but blue for the lows (Figs. 1, 2), to better image volcanic areas. The map of Bouguer anomalies (Fig. 3), based on the EIGEN-6C4 global model available at the ICGEM website (Förste et al., 2014), displays anomalies in the classical Bouguer reduction. It assumes homogeneous layers with the densities 2.67 g/cm3 (continental crust) and 1.645 g/cm3 (marine sediments) and is obtained for a spherical earth using the DTM2006 terrain model (Pavlis et al., 2007). The map is restricted to the surroundings of Kamchatka and images subtle offshore features (Fig. 3). The Bouguer anomalies had been used broadly for local and regional geological applications before free-air anomalies to a resolution of 10–20 km became available. Free-air anomalies are poorly suitable for local problems because of strong terrain effects which require Bouguer correction for exploration applications. However, the correction that reduces terrain effects in free-air anomalies leads to strong negative correlation with averaged elevations, which is especially notable on the regional scale. The Bouguer anomalies (Fig. 3) are inversely proportional to elevations (Fig. 4), and the correlation (Fig. 5a, c, e) is higher for averaged elevations (Fig. 5c, e), due to isostasy, than without averaging (Fig. 5a). However, the respective correlation with free-air anomalies (Fig. 5b, d, f) is very low: the coefficient R2 decreases from 0.29 to 0.15 and even 0.09 as the averaging radius increases from 10 to 100 km (10 km corresponds to nonaveraged elevations, according to the resolution of the maps). Thus, the free-air gravity appears to be a promising tool to study regional

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geology: being not related directly to terrain, it provides a more faithful record of the density pattern than the Bouguer gravity controlled by crust thickness and surface topography. In addition to the common map of elevations for Kamchatka (Fig. 4), we used a map of transformed topography (Fig. 6). Subtle analysis of the land and seafloor topography was made using the 2D Laplacian operator (divergence of lateral height/depth gradients) in a sliding window (Glukhmanchuk and Vasilevskiy, 2013). The window radius depended on the chosen scale of the heterogeneous surface and periodicity of variations in its geometry estimated preliminarily with the periodogram of surface topography to reduce transformation artifacts. The periodogram analysis is illustrated in Fig. 7 for the area (white box in Fig. 6) used further (Fig. 8) for detailed comparison with the previous results (Lomtev, 2017). The seafloor topography is shown by contour lines in Fig. 7: at 500 m in the panel a and 100 m in b. Small spacing of contour lines makes the map more informative in some areas but unreadable in others, and is thus poorly suitable for terrain mapping. The 2D Laplacian is presented in Fig. 7c, d with a color code. For simplicity, the Laplacian values are normalized to the maximum for the study area. The contour lines in Fig. 7d are better readable than in the panels b and c due to the color choice. The Laplacian traces well the topography variations (local curvature) irrespective of depth and slope, which is evident in the cross sections along profiles I–I′ and II–II′ in Fig. 7e, f. According to our experience of mapping for the whole region (Fig. 6), the topography transformation approach is especially successful for offshore areas. Specifically, it resolves circular volcanic features on the seafloor (calderas, volcanoes, and domes), as well as flat trench bottom and island arc slope (fore-arc basins) zones. The results were compared with geological and geophysical data, with reference to geological and tectonic maps (Bogdanov and Chekhovich, 2002; Shapiro et al., 2008; and oters), which allowed identifying tectonic settings and placing more rigorous constraints on the boundaries revealed in the gravity and transformed topography maps. The junction between the Kamchatka and Aleutian trenches was used as a test site for which a detailed map was compiled using data of continuous multichannel reflection profiling (Lomtev, 2017).

Modeling results The map of free-air gravity anomalies for the northwestern Pacific (Fig. 1) synthesizes data first published by Gordeev and Dobretsov (2017) and images clearly the structure of oceanic and back-arc basin areas, with the Aleutian, Kurile– Kamchatka, Japan, and Izu-Bonin trenches around the Pacific plate. The plate has a rhomb-shaped pattern of its marginal uplifts, which likely represents its deformation before the subduction front. It comprises superposed volcanic structures of two types (Fig. 1): circular edifices (8) and the Emperor chain of volcanoes (7) that become progressively younger

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Fig. 1. Gravity field (free-air anomalies) of the northwestern Pacific, with reference to database of Andersen et al. (2014). Box (dashed line) frames the area of detailed study enlarged in Figs. 2–5; black lines are boundaries of zones, blocks, and plates according to tectonic models of Bogdanov and Chekhovich (2002) and Khanchuk et al. (2006). Numerals in circles (1–9) are structures in back-arc basins (see text for explanation). Volcanoes in the Emperor chain become younger southward (blue arrow). Purple heavy line separates Asia and North America (Barents Sea block).

southward, from 86–83 to 43–45 Ma (Duncan and Keller, 2004), and trace the motion of the plate over the Hawaii plume. The volcanoes in the chain are surrounded with gravity lows possibly produced by ash and pyroclastics of early eruptions maintained by the plume activity (Gordeev and Dobretsov, 2017). The circular edifices, 30 to 300 km in diameter, group into three fields: (a) Obruchev rise in the northern plate corner, from 48° to 52° N, near the end of the Emperor chain (Figs. 2, 3, 5); (b) a field between 48° and 40° N that also meets the Emperor chain; (c) an NE field (8 in Fig. 1) between 30° and 40° N which may correspond to the Shatsky rise and result from Early Cretaceous (125–120 Ma) plume activity (Ernst, 2014; Pirajno, 2000). The three fields, together with the volcanic centers on the Okhotsk Sea plate (5), may represent a single superplume (Bogdanov and

Chekhovich, 2002; Bogdanov and Dobretsov, 2002). This hypothesis is discussed separately below. The Pacific plate and the volcanic arcs are separated from the continental masses of Asia and North America (the boundary between the two continents is shown by a purple line on the extension of the Aleutian trench in Fig. 1) by back-arc basins and related structures (1–6 in Fig. 1 and Fig. 6 below). The Bonin (Shikoku) basin (1a in Fig. 1) is similar in its structural pattern to the Pacific plate part adjacent to the trench. The trench and the Rioke belt (1b in Fig. 1) at the northern border of the basin reach the Japan Sea basin (2 in Fig. 1) farther in the north and have a mosaic strike-slip structure consisting of several pull-apart basins with sediments, marked by gravity lows to –100 mGal separated by small rhomb-shaped volcanic uplifts that correspond to gravity

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Fig. 2. Gravity field (free-air anomalies) of Kamchatka and its surroundings, with reference to DTU15 model (Andersen and Knudsen, 2016). Heavy lines are fault boundaries (as in Figs. 3, 4); thin lines are structures of the Pacific plate and the Commander basin. EV, Emperor volcanic belt; CKD, Central Kamchatka depression.

highs to + 120 mGal. In the northern Japan Sea, there is a single 250 × 50 km large rhomb-shaped basin, which meets a collage of eleven small pull-apart basins in the south, possibly recording a fan-shape (rotational) spreading. Pure rotational opening is reconstructed in the Commander basin (4 in Fig. 1) shown in Figs. 2–4, 6. The South Kurile basin (3 in Fig. 1) likewise has a triangular shape, with cross faults and stepped boundaries on the side of the arc. It possibly opened by the rotation mechanism as well, but its northern one third may have been shifted to the south by the motion of the Okhotsk block, which makes the core of the Okhotsk plate. The Okhotsk plate itself and the Tatar strait (5 and 6 in Fig. 1, respectively) have quite a complicated structure. Note that the fault pattern of the plate is fan-shaped in the area of Hokkaido and Tatar strait but transversal within the Okhotsk block, and resembles oceanic structures in the northern Pacific plate (52°–44° N). The Okhotsk block may be of oceanic (Bogdanov and Chekhovich, 2002; Bogdanov and Dobretsov, 2002) or continental origin, still under debate. All structures at the junction of the Aleutian and Kamchatka trenches are considered in detail within the area between 62° and 48° N (box in Fig. 1) enlarged in Figs. 2–5, in terms of the gravity field (Figs. 2, 3) and the mapped raw (Fig. 4) and transformed (Fig. 6) surface topography.

The free-air gravity field (Fig. 2) provides a faithful image of the Pacific plate, the SE to NW Kamchatka and Aleutian trenches, the triangular Commander basin, and the volcanic belts of the Northern Kuriles and Kamchatka, with their possible extension into the Koryak plateau adjacent to the Okhotsk plate. The volcanic structures of the Pacific plate and the Commander basin are prominent in the gravity map (Figs. 2, 3) but are almost mute in the map of surface topography (Fig. 4). They are of two types in the northern Pacific plate (Fig. 2): (i) the Hawaii-type volcanoes of the Emperor chain in the southeast (EV in Fig. 2) surrounded by flats likely made up of thick ash layers, which are marked by gravity highs and lows (to –150 mGal), respectively; (ii) circular (oval) volcanic edifices within the low Obruchev rise (Fig. 2) and the Zenkevich elongate rise in front of the Kamchatka trench, which appear as poorly contrasting features detectable against zero (yellow) or slightly negative background gravity. The larger or smaller gravity highs may record variable heights of the edifices (from low hills to high mounts on the rise near the Kamchatka and Aleutian trench junction). Their volcanic origin, though negated in some models (Lomtev, 2017), is evident in structural contours in Figs. 2, 3 and 6. In the Bouguer gravity field of Kamchatka and its surroundings (Fig. 3), the Commander basin and the Pacific plate, as

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Fig. 3. Gravity field (Bouguer anomalies) of Kamchatka and its surroundings, with reference to model EIGEN-6C4 (Förste et al., 2014), from ICGEM website. Heavy lines are fault boundaries in trenches and areas of northwestern Pacific, Commander basin, and adjacent slopes of Kamchatka (according to Fig. 2, with reference to Figs. 4 and 6). Thin lines contour volcanic edifices in the Pacific plate.

well as a complex pattern of trenches are quite prominent while the structures of the Kamchatka arc and the Okhotsk plate are worse pronounced than in Fig. 2. Gravity highs in the southwestern Pacific plate (Fig. 3) reach 400–450 mGal and may record thick mafic crust beneath volcanoes (detectable in Fig. 2 but especially well seen in Fig. 6). The northeastern plate part corresponds to the northwestern end of the Emperor chain of Hawaii-type volcanoes marked by gravity highs (200 mGal at the summits, 250 mGal in the center, 300 mGal at the foot, and 350 mGal around). As imaged in Fig. 2, the chain seems not to reach the Aleutian trench and turn to the east where it is truncated by the Aleutian strike-slip fault. However, Fig. 3 clearly shows it as a single chain with similar anomalies, though the volcanoes in the northeastern end are smaller and have no gravity lows around, i.e., no traces of ash fallout. According to reconstructions by Duncan and Keller (2004), the earliest eruptions of the Hawaii volcanoes occurred about 85–90 Ma and were moderately explosive, like those of the third and modern stages of volcanism. The suggested reconstructions of the Hawaii chain as far as its junction with the Aleutian arc and on to the Kamchatsky Mys Peninsula appear to be generally valid (Duncan and Keller, 2004; Gorbatov et al., 2001; Portnyagin et al., 2005).

The Commander basin is marked by banded anomalies of the same magnitude as the Hawaii-type volcanoes (250 mGal, locally up to 300 mGal) but they are surrounded by 150 mGal zones with 100 mGal rims. Note that the rims highlight well the stepped displacements associated with uneven opening in this local spreading zone (see below). The volcanic belts and most of the Okhotsk block correspond to small Bouguer anomalies around 0 to +50 mGal (Fig. 3) which record poorly the area structure. However, the nearly zero gravity is evidence of isostatic equilibrium, without notable variations in the lithospheric mantle. The gravity pattern of the Commander basin (Figs. 2, 3, north of the Commander rise) consists of several elongate weak highs parallel to the Commander and Alfa strike-slip faults. This structure is presented as angular extension in our model (Fig. 1) which agrees with that of Avdeiko et al. (2002, 2007). The axial line is not shown in Figs. 2 and 3 but is reconstructed in Figure 10 (basin 3) where parallel transform faults and a spreading line like the one of the Bonin (Shikoku) (1 in Fig. 1) and West Philippine basins (see below, Fig. 15). Parallel lines show arc extension structures (1 in Fig. 1) that increase in distance from 0 at the triangle corner at ~60° N and 170° E to 2 × 250 cm near the Alfa strike-slip fault along the Pacific–North America boundary.

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Fig. 4. Surface topography of Kamchatka and its surroundings. Heavy lines are as in Figs. 2, 3; thin lines in the trench and on the slope are drawn with reference to Fig. 6. 1, slab edge distant from the junction with the Aleutian trench at the depth 200 km, 2, contour of presumable slab edge detached about 10 Myr ago at the same depth.

The Commander rise does not bear explicit signatures of volcanism, which is confirmed by onland observations. It rather resembles a strongly deformed thrust sheet in the Koryak upland (like the one between 60° and 62° N and 163°–170° E in Fig. 2). The Kamchatka trench and adjacent sedimentary basins are weakly pronounced in both gravity (Figs. 2, 3) and topography (Fig. 4) maps but are prominent in the map of transformed topography (Fig. 6), which is discussed below and compared with bathymetry and seismic data (Lomtev, 2017). The volcanic belts of Northern Kuriles and Kamchatka are well detectable in the maps of gravity (Fig. 2) and topography (Figs. 4, 6). The Northern Kurile belt of volcanic islands grades into the belt of Southern Kamchatka which, after some displacement, extends into the Eastern belt (from the Avacha and Kozelsk to Gamchen-Kronotsky volcanoes) superposed over a Cretaceous volcanic arc. The Klyuchevskoy group of volcanoes (Nikolka to Shiveluch) within the Central Kamchatka depression (CKD) is positioned en-echelon to the arcs. The volcanic belt of the Central Range separated by CKD from the Eastern belt and the Klyuchevskoy group of volcanoes is clearly traceable in Figs. 2, 4, and 6, but only Fig. 6 displays well its structure (1 in Fig. 6). CKD is currently a rift basin, but in the Miocene it may have been part of a

paleotrench; trench remnants track its position prior to collision with the Kronotsky arc. Below we proceed to correlations with historic geological data in order to check this hypothesis and study details of volcanic belts. Note in conclusion that the Kurile arc borders the extension zone of the South Kurile basin (Figs. 1, 2). The rhombic structures, shown in Fig. 2 together with the cross faults and the stepped Okhotsk boundary of the Kurile arc, originate at 54.5° N and continue as far as the Shelikhov gulf (7). They are similar to extension basins 2, 3, and 4 in Fig. 1, but their extension nature has no solid proof yet. As in the case of the Commander basin, they require further study in the context of the Pacific plate motion and the rotation of the Okhotsk and Bering subplates. The map of transformed elevations (2D Laplacian) has provided more reliable implications for the structure of the region. The results are correlated below with geological and other geophysical data. Geological correlations and the structure of the Kamchatka trench and the Pacific plate The area of the northern Kamchatka trench and its junction with the Aleutian trench (Fig. 8, enlarged area of white box

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Fig. 5. Correlation of elevations and gravity anomalies in the Kamchatka region. a, c, e, Elevations and Bouguer anomalies; b, d, f, elevations and free-air anomalies. Averaging radiuses: 5 km for a, b, 50 km for c, d, 100 km for e, f. Black dashed lines show linear regression; R2 is coefficient of deformation (in linear regression model).

in Fig. 6), comprises two sedimentary basins (3 in Fig. 8): the Kamchatka basin at the junction of the Kurile and Aleutian trenches (near the Kamchatsky Mys Peninsula) and the Kronotsky basin in the gulf of the same name between the Kronotsky and Shipun Peninsulas. Flat valleys on the trench bottom have similar contours (dashed line in Fig. 8) in the

Kamchatsky and Kronotsky basins, increasing slightly towards the Kamchatka coast, and join narrower sedimentary lenses along the trench axis. There is also a system of en-echelon elongate and oval rises, possibly, serpentinite protrusions (shown in the geological-morphological map of the area from (Lomtev, 2017), Fig. 2).

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Fig. 6. Transformed topography that records surface curvature (normalized Laplacian, see text). White box corresponds to the area of Fig. 8. Numerals 1, 2 in circles mark volcanic belts of Central (1) and Eastern (2) Ranges, 7 marks Shelikhov junction.

Scarps with local sedimentary lenses in sections across the island arc slope of the Kamchatka trench (Fig. 9) were interpreted (Lomtev, 2017 and Fig. 4 therein) as vertical faults of uncertain origin. However, such systems are most often considered as thrusts of an accretionary wedge (Baranov et al., 2002), like the one consisting of five sheets under a fore-arc (below) and a back-arc (above) basins in a section across the Kurile island arc reported by Zonenshain and Kuzmin (1993 and Fig. 30 therein). Similar thrust sheets composed of sedimentary material with volcanic and serpentinite lenses were reported from other trenches as well (Dobretsov, 2010; Dobretsov and Kirdyashkin, 1992; Magee and Zobak, 1993; Shipley et al., 1994). Therefore, we have reinterpreted the scarps (Fig. 9) as bases of low-angle thrusts (4 to 6 sheets) in an accretionary wedge. Such wedge of variable thickness, with serpentinite lenses and protrusions, is shown in Fig. 10 as banded structures at the arc slope base. Thus, the rises within the trench may be serpentinite lenses and protrusions on an island arc slope of the Kamchatka trench (Lomtev, 2017, Fig. 2). Serpentinite lenses and diapirs were studied in detail in the Bonin trench (Hasegawa et al., 2009; Kogiso et al., 2009). Sediments and serpentinites jointly produce gravity lows along the trench axis (Figs. 1, 2), but the contribution of serpentinite is hard to constrain; it may be approximately equal to that of sedimentary lenses (Lomtev, 2017, Fig. 2).

Thus, the structure of the Pacific plate, the Commander basin, the trenches and the island arc slope have been interpreted (Fig. 10) using the transformed topography map (Fig. 6), as well as the data of Figs. 8 and 9. This interpretation is more detailed and spatially uniform than the earlier one (Pushcharovsky and Neprochnov, 1984). The gravity and topography data presented in Figs. 1–4, 6 and synthesized in Fig. 10 provide a faithful image with uniformly distributed information on both continental and oceanic parts of the region because satellite data have the same resolution for onshore and offshore areas. Furthermore, satellite surveys make basis for a representative database which will be updated every four years and become an indispensable tool for geological and geophysical studies of the Earth. The maps of gravity anomalies and transformed topography, compared with onland (Fig. 11–14) and marine (the test site of Figs. 8, 9) geological data, are applicable as a basis for tectonic reconstructions of both crustal and lithospheric mantle structures. However, additional methodological studies are required for deeply eroded areas where transitional crust–mantle layers are exposed. In any case, geological and partly geophysical data are indispensable for full understanding of the structure and evolution of subduction and collision zones.

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Fig. 7. 2D Laplacian of topography image in area framed by white box from Fig. 6 (enlarged in Fig. 8). a, b, Seafloor topography is shown as depth contour lines at 500 m (a) and 100 m (b); c, d, 2D Laplacian; contour lines in panel d correspond to those in b; e, f: cross sections and 2D Laplacian of elevations image along profiles I–I′ and II–II′ (red lines in panels a, d).

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Fig. 8. Northern Kamchatka trench and its junction with Aleutian trench, after (Lomtev, 2017). 1, profiles, their numbers and points (PR, profile collected by R/V Pegas; B, profile collected by R/V Barglett); 2, trench axes; 3, sedimentary basins on island arc slope; 4, scarps. Numerals stand for: 1, Obruchev rise; 2, margin flats; 3, oceanward trench sides; 4a–4d, submarine extension of Kamchatsky Mys (4a), Kronotsky (4b), and Shipun (4c) Peninsulas and seamounts of Kronotsky gulf (4d); 5, Kamchatka (5a) and Zhupan (5b) canyons; 6, upper (a) and lower (b) boundaries of island arc slope. Dashed lines are boundaries of elevation zones from Fig. 6.

Evolution of volcanic belts, collisional structures and sedimentary basins The inferred tectonic and geodynamic framework of the North Kurile and Kamchatka volcanic belts is illustrated with Fig. 11, modified after a figure from (Shapiro et al., 2008). The cited paper and Fig. 11 are based on previous studies of structures produced by collisions of the Kamchatka arc with those of Valagina and Kronotsky (Bogdanov et al., 1987; Mitrofanov, 1977; Solov’ev, 2005; Solov’ev et al., 2002, 2004; Zinkevich et al., 1993), as well as on migration of the two arcs as recorded by paleomagnetic data (Kovalenko, 2003; Levashova et al., 2000; Pecherskiy and Shapiro, 1996; Pech-

erskiy et al., 1997; Shapiro, 1995; Shapiro et al., 2004; Stavskiy et al., 1988) and by U–Pb, Ar–Ar, and fission-track thermochronology of zircons (Bindeman et al., 2010; Hourigan et al, 2009; Solov’ev, 2005; Solov’ev et al., 2004). The collision with the Valagina arc in the north of Kamchatka is recorded in the large Vatyna and Lesnaya thrusts (Fig. 11), where the Valagina paleoarc is thrust upon the Middle Cretaceous–Paleocene Omgon–Ukelayat flysch terrane of the North Asian craton passive margin. Details of this structure were shown in Fig. 2 from Shapiro et al. (2008). The autochthonous block is composed of strongly deformed but weakly metamorphosed clastic flysch of the Lesnaya Group (Ukelayat Group, according to (Mitrofanov, 1977)), which are

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Fig. 9. Sections across Kamchatka trench based on continuous reflection profiling data, modified after (Lomtev, 2017). 1, Acoustic basement (AB); 2, boundaries: a, lithological, b, formations; 3, thrusts. Numerals in circles are trench (1 and 2) and lower (3) and upper (4) sedimentary sequences on island arc slope. AB, Thickness of sedimentary pile consisting of 4–6 tectonic sheets.

exposed in tectonic windows (Shamanka and Vatanvaam domes) and are thrust over by the ~5 km thick Upper Cretaceous Valagina Formation siliciclastic and volcanic rocks. The Valagina rocks spread as far as the northern Olutor Range where they make up the uppermost thrust sheet of the Koryak upland (Bogdanov et al., 1987; Shapiro, 1995). The thrust (its both autochthon and allochthon parts) lies under the clastic sediments of the Pustoretsk–Parapolsky (N–Q) and Ilpin–Pakhachi (Pg2–N) troughs. The oldest Late Paleogene ages of the sediments suggest that the collisional thrusts and folds formed within a short time span of 45 to 50 Ma (Shapiro et al., 2008). The Upper Cretaceous–Paleogene volcanic-sedimentary rocks that extend from the Goven Peninsula and Karaginsky

island through the Ozernyi Peninsula, into the ranges of Kumroch, Valagina, and Ganaly (between Quaternary volcanics of the eastern belt and the Klyuchevskoy group of volcanoes, Fig. 11) may also belong to the Valagina paleoarc. These complexes were interpreted jointly as the Eastern Kamchatka (EK) terrane which was compared with the Olutor (or Parana, Pa) and Southern Kamchatka (SK) terranes (Kovalenko, 2003). The SK terrane consists of Upper Cretaceous–Paleocene fault-bounded lenses (often considered as concordant stratigraphic units) in the southern Sredinnyi (Central) Range (Fig. 11) east of exposed metamorphic rocks. They include the Irunei volcanic-siliciclastic complex of chert, tuff, and basaltic and andesitic lavas; the Kirganik Formation of mafic and intermediate tuff and lava; the volcanic-sedimen-

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Fig. 10. Synthetic map based on gravity, topographic (Figs. 2–4) and geological data. 1, Pacific seafloor with volcanoes (a) and deformation pattern between them (b); 2, volcanoes of Emperor chain surrounded by ash deposits; 3, deepwater basins (numerals 1–3 in circles stand for South Kurile (1), Shelikhov (2) (a), and Commander (3) basins (b)); 4, trenches with flat bottom (a), island arc slope of accretionary wedge (b), and oceanward trench sides (c); 5, Commander block; 6, sedimentary basins on the island arc slope and lenses in trench; 7, core of Okhotsk plate (a) and framing of mixed composition and origin (b); 8, suture of collision with the Valagina arc and with granite gneiss domes, 9, fragments of Valagina arc; 10, fragments of Kronotsky arc; 11, Pleistocene–Quaternary Central Range (1), Klyuchevskoy (2), Eastern (3), and Southern Kamchatka and Northern Kurile (4) volcanic belts (numerals in squares); 12, Omolon (OM) cratonic terrane (a) and Viligin block (b) with thick continental crust (Fig. 16); 13, Cretaceous–Paleogene fold belts; 14, Central Kamchatka depression; 15, main faults.

tary Kvakhona Formation; the siliciclastic Kheivan and Stopolnikov Formations; the Kamchatka Group and the Khozgon Formation of clastics with metagabbro and metaophiolite lenses, which span a paleontologically constrained interval from the Late Jurassic–Early Cretaceous to the

Eocene, often with large overlaps (Bondarenko, 2004; Grechin, 1979; Zinkevich et al., 1993). According to paleomagnetic data (Kovalenko, 2003), the Eastern Kamchatka, Southern Kamchatka, and Parana terranes were located between 50° and 40° N in the Late Cretaceous

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Fig. 11. Simplified tectonics of Kamchatka and southern Koryakia, complemented after (Shapiro et al., 2008). 1–5, subaerial volcanic belts: Eastern Kamchatka (1, N to Present) and Central Kamchatka (Central Range, 2, Pg3 to Present), Western Kamchatka (Kinkil) (3), Apuka–Vyvenka, N2–(?) (4), Cherepanov, Pg1–2 (5); 6–9, sedimentary basins: Western Kamchatka, Pg–N (6), Central Kamchatka depression and its possible extension to the Olutor Range (7), Ilplin–Pakhachi basin, Pg1–N1 (8), Pustoretsk–Parapolsky basin, N–Q (9); 10–15, basement terranes: Omgon–Ukelayat terrane, clastic deposits of continental slope (10), Valagina island arc, K2–P1 (11), Vetlova–Goven accretionary wedge (12), Kronotsky island arc, K2–Pg (13), metamorphic collisional rocks of granite gneiss domes and Ganaly uplift (14), Northern Koryakia terranes (15); 16, large thrust (suture) zones, numerals in circles: Vatyna (1), Lesnaya (2), Andrianovka (3), Goven (4), Karaga (5), Vetlova (6), Grechishkin (7), Valagina (8); 17, axes of deep-water trenches (a), paleotrenches (b), and other faults (c). Lines for offshore areas are from Figs. 6 and 8.

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(83–75 Ma), against 62°–54° N at present, i.e., 12°–14° farther to the south, and formed a chain with the Southern Kamchatka terrane in the north and the Parana terrane in the south. The collision occurred around 55 Ma, or at 45 Ma according to (Hourigan et al., 2009; Solov’ev, 2005), at least for the Vatyna and Lesnaya thrusts (Fig. 11). The collision zone of the Southern Kamchatka terrane in the southern Central Range includes metamorphic domes (blocks?) and has a complicated structure and a long history. The age and origin of the metamorphic rocks have been a subject of discussions. Specifically, zircons from the Kolpakova Group gneiss and migmatite are 45 to 52 Ma the youngest (Hourigan et al., 2009), while no zircons younger than 50 Ma have been found in other clastic sequences of the Eastern and Southern Kamchatka terranes and in the Ukelayat flysch. Thus, 45–48 Ma may be the age of high-temperature metamorphism (migmatites). The Kolpakova Group, Khozgon Formation, and Kamchatka Group clastics, and the Ukelayat flysch contain zircons with ages in a range of 65 to 150 Ma (corresponding to the Cretaceous evolution of the Valagina arc), as well as older zircons. The older ages are 200–300 Ma (Jurassic–Permian), 1900–2000 Ma (prominent peak, a few zircons from the Khozgon Formation and Kolpakova Group rocks); and 1700–2100 Ma (prominent and broad peak, zircons from the Ukelayat flysch). Zircons of the latter age range record sediment transport from the Omolon or Okhotsk blocks detached from the East Asian plate (Khanchuk, 1985; Khanchuk et al., 2006). The metamorphic domes of the Southern Kamchatka terrane underwent a complex evolution since 50 Ma, such as the Khangar dome in the upper reaches of the Krutogorova, Kvakhona, and Andrianovka Rivers (Fig. 5 in (Shapiro et al., 2008) and Fig. 12 in this study, updated after (Tararin et al., 2015), complemented by Dobretsov). The core of the dome is composed of gneisses and volcanics of the Khangar volcano, as well as the Khozgon Formation lens of phyllite and metabasaltic rocks, and is surrounded by granitic plutons of two complexes. They are mainly Oligocene diorite and granodiorite in the north and the Krutogorova complex of gneiss granite (Pg1–2 ?) in the south, both including 30–36 Ma diorite, gabbro and monzonite of the Lavkinsky pluton (Tararin et al., 2015). The outermost zone of the dome consists mostly of Cretaceous sediments. The dome structure mapped in Fig. 12, and its rocks of different ages, record the Cenozoic history of the Kamchatka island arc, from 45–52 Ma (zircons in the Kolpakova gneiss, see above), through 30–35 Ma (Lavkinsky gabbro), to the Holocene (volcanics). The Kolpakova Group may have an older age (Litvinov et al., 1999; Richter, 1995), but the dome is young (Hourigan et al., 2009; Tararin et al., 2015). The core of the Kola dome (and the Kola pluton) in Kamchatka is composed of the Kolpakova Group migmatite and migmatitic gneiss (as in the Khangar dome); the synform of gneiss granites contains a semicircular body of the Khozgon phyllite and metasandstone with metamorphic picritic basalt sills which make up the northern slope of the Khangar dome (Tararin et al., 2015). A sill-like body of layered gabbro

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(Yurchik complex) is present also in the Ganaly dome southeast of the Khangar dome. The primary assemblage of garnet–biotite (+kyanite and staurolite) in the Kolpakova migmatites and migmatitic plagiogneiss became replaced by an assemblage of biotite–cordierite (+sillimanite and feldspar). A similar contact metamorphic reaction was observed also around the Lavkinsky pluton and the Yurchik gabbro. The latest synmetamorphic granitic veins contain only andalusite coexisting with cordierite (Tararin et al., 2015). This succession records transition from syncollisional kyanite-facies metamorphism to late collisional adiabatic decompression, growth of domes and emplacement of the Lavkinsky mafic rocks that heated up the thermal domes. The highest temperature to 800 °C was inferred from granulites coexisting with layered gabbro and peridotite in the Ganalsky dome (Kuzmin et al., 2003). The Khangar and Kola domes in Kamchatka can be compared with their counterparts in the Chukchi Peninsula and Gorny Altai, in order to check their collisional origin. Metamorphics in three collisional domes of the Chukchi Peninsula reach amphibolite or sometimes granulite facies in the core and are of epidote–amphibolite to greenschist facies on the limbs; the metamorphic rocks are surrounded with coexisting collisional and subduction granitoids on the dome periphery (Akinin and Calvert, 2002; Akinin and Voroshin, 2006; Natalin et al., 1999). As in the case of Kamchatka, the Chukchi area had a complex history: (1) collision (132– 115 Ma or 121–108 Ma) recorded in kyanite-facies rocks formed at 6–8 kbar and T = 500–700 °C; (2) growth of domes (108–90 Ma) with adiabatic decompression and formation of andalusite–sillimanite and cordierite assemblages, and synmetamorphic intrusions of granites; (3) exhumation and activity of circular faults (88–75 Ma). This sequence of events shows that the Chukchi and Kamchatka accretionary-subduction systems shared a similar ~50 Myr long evolution. Similar domes formed in the Cretaceous within the Brooks Range collisional belt in Alaska (Khain et al., 2009; Toro et al., 2002). Trends of this kind were observed in many collisional structures (Reverdatto et al., 2017), as well as in zoned metamorphic complexes of southern and southeastern Gorny Altai (Dobretsov et al., 2017), where metamorphism evolved in three phases, while the late phase (when domes and circular faults completed their formation) was concurrent with plutonism (Buslov et al., 2013; Kruk, 2015). The signatures of collision with the Kronotsky arc were studied only within the peninsulas of eastern Kamchatka (Fig. 13). The volcaniclastic rocks of the Kronotsky island arc are exposed in the Kamchatsky Mys, Kronotsky, and Shipun Peninsulas; they have Late Cretaceous to Eocene ages, like the Valagina arc, though ophiolites may be Jurassic (Khotin and Shapiro, 2006; Osipenko and Krylov, 2001). Peridotites of Soldat Mount in Kamchatsky Mys (Batanova et al., 2014) lie over serpentinite melange dipping westward and meet the Pikezh Formation siliceous clastics and the Smagin Formation silisiclastic and volcanic rocks with lenses of gabbro and parallel dikes (indicating spreading) in the west. The dikes

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Fig. 12. Simplified geology of the northern Central Kamchatka metamorphic dome and Khangar volcano, compiled with reference to (Tararin et al., 2015). 1, alluvium; 2, Quaternary volcanics of Khangar caldera (andesite, dacite, felsic pumice); 3, mafic and felsic metamorphic siliciclastic-volcanic rocks (a) and gabbro and metasandstone (b) of Khimki complex, K2 hm; 4, Kamchatka complex, upper sequence (Kheivan Formation), K1–2 hv, phyllite, schists, and metamorphic sandstone; 5, Andrianovka complex, K1–2 an, mafic and ultramafic amphibole, amphibole–plagioclase, and epidote–amphibole–plagioclase schists and phyllitic schists; 6, Kamchatka complex, lower sequence, K1–2 km, biotite, garnet–biotite, garnet–staurolite–biotite and garnet–staurolite–mica schsits; 7–9, Kolpakova complex, K1–2 kl: 7, upper sequence of alternated amphibolite, garnet amphibolite, clinopyroxene–amphibole mafic shcists, garnet–biotite–amphibole plagiogneiss and quartzite, kyanite-bearing plagiogneiss; 8, middle of garnet–mica plagiogneiss, migmatites; 9, lower sequence of kyanite-bearing garnet–mica plagiogneiss, migmatite, less often amphibolite and garnet amphibolite, quartzite; 10, Lavkinsky plutonic complex, P3–N1, of undifferentiated diorite, granodiorite, monzonite, quartz syenite; 11, Kola plutonic complex, K1–2 of massive and gneissic biotite granite and granodiorite; 12, Krutogorova plutonic complex, K1–2 of gneissic biotite and garnet–biotite granite and granodiorite; 13, synmetamorphic leucocratic granite and pegmatite; 14, thrusts and large faults; 15, hornblende; 16, boundary of Khangar volcano; 17, geological boundaries. Inset show area of study.

were assigned to back-arc and subduction (Khotin and Shapiro, 2006; Tsukanov et al., 2004) or spreading (Batanova et al., 2014; Osipenko and Krylov, 2001) settings according to the compositions of gabbro and plagiogranites. The age of the Smagin Formation was estimated as Albian–Cenomanian (93–112 Ma) from radiolarians (Boyarinova et al., 1999; Zinkevich et al., 1993), while the Pikezh Formation is Turonian–Campanian. Island arc rocks contact with (lie under?) the Oligocene– Miocene Tyushev Formation clastics that were shed from the Kronotsky arc and deposited in the back-arc or fore-arc basins. There is an accretionary complex deposited from 50 to 15 Ma between the Valagina and Kronotsky arcs, which is composed of several units: the Middle–Upper Eocene Stanislav Formation, the Paleocene–Lower Eocene Vetlova Formation, and fragments of the Tyushev Formation (Oligocene–Miocene). A younger accretionary complex is present on the slope of the

Kamchatka trench (Figs. 8–10 and Fig. 14). Thus, the fragment of the Kronotsky island arc may be a very large lens (olistolith), about 600 km long, in the upper island arc slope. Extension of the Kronotsky arc to Karaginsky island and the Olutor Range requires separate consideration.

Discussion and conclusion The Cenozoic history of volcanic and collisional events in the Kurile–Kamchatka arc was as sketched in Fig. 14, modified after (Solov’ev et al., 2004). The early collision phase of the Kamchatka–Okhotsk block included several episodes (Bogdanov and Chekhovich, 2002). Early Eocene, around 60–55 Ma: N–S motion of the Valagina arc parallel to the Emperor Range leading to its collision with the northeastern margin of Asia and thrusting

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Fig. 13. Simplified tectonics of southeastern Kamchatka, modified after (Shapiro, 1995; Solov’ev, 2005, with author’s additions). 1, deposits of Central Kamchatka depression (N2–Q), dashed line contours zone of Klyuchevskoy group of volcanoes along Kumroch Range; 2, Eastern Kamchatka volcanic belt (Pliocene–Quaternary); 3, Central Kamchatka volcanic belt (Oligocene–Quaternary); 4, Oligocene–Miocene clastic deposits; 5, volcanics of Valagina plaeoarc and its clastic sedimentary cover (K2–Pg); 6–7, Eastern Kamchatka accretionary wedge: clastic deposits of Stanislav (Pg2) and Vetlova (Pg1–2) groups (6), clastic deposits of Tyushev Formation, Pg3–N1 (7); 8, volcanic-sedimentary rocks of Kronotsky island arc, K2–Pg1 (a) and their possible extension into the submarine slope part (b); 9, sedimentary basins (a) and accretionary wedge of island slope (b) (Figs. 6–8); 10, flat part of trench and boundary of present subduction zone; 11, faults (a) and thrusts (b) and their possible extension.

upon the latter (Fig. 14a). The formation of collisional structures, such as the Lesnaya thrust and granite gneiss domes in the southern Central Range, had completed around 45 Ma. At that time, the Pacific plate began subducting beneath the newly formed Kamchatka arc having redirected the subduction beneath the Kronotsky arc. All these events were induced by the 60° rotation of the Pacific plate (from N–S to NW) and the respective stress changes at the boundaries of the adjacent plates (Fig. 14b). Middle–Late Eocene (40–35 Ma): subduction of the Pacific plate beneath the thickened crust of Kamchatka; Stanislav Formation deposition; convergence of the Kronotsky and Kamchatka arcs (Fig. 14c). Oligocene–Middle Miocene (30–15 Ma): continuing subduction beneath the Kamchatka arc; growth of the accretionary wedge maintained by erosion of the Vetlova Group; deposition of the Tyushev Formation on the slopes of the Kronotsky rise (extinct arc) (Fig. 14d). Middle–Late Miocene (15–7 Ma): collision of the Kronotsky and Kamchatka arcs; erosion of the Tyushev Formation

and related supply of material shed from the Kronotsky rise slopes into the accretionary wedge. Judging by a long belt in the Kamchatka volcanism in the same time interval (from 15–17 to 5 Ma), it was a major collision event accompanied by reorientation of subduction toward the ocean and the onset of the Commander basin opening (Fig. 14e). Thus, the volcanic belt of the Central Range was a front (main) belt from 45 to 15 Ma, till the Kamchatka–Kronotsky arc collision, and currently has turned into a back structure. Most of caldera volcanoes and large stratovolcanoes are no longer active, but new small volcanoes are appearing which erupt alkaline and subalkaline basalts in group or fissure modes (Figs. 6, 10). The felsic and mafic compositions of magmatism (felsic volcanics + alkaline basalts) coexist only in Icha volcano and its southern surroundings (Bindeman et al., 2010; Dobretsov et al., 2016b; Perepelov, 2014). Spreading in the Commander basin, which has similar Eocene–Upper Cretaceous volcanics of the Kronotsky paleoarc and the Olutor Range on its two sides, was an important event, apparently, a consequence of the collision. It may have

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Fig. 14. Collisional events, modified after (Solov’ev et al., 2004). Not to scale. Events a–e are described in text. 1, oceanic crust; 2, thin continental crust of Western Kamchatka; 3, Valagina paleoarc and respective terrane in the Kamchatka structure; 4, Kronotsky paleoarc; 5–8, clastic complexes: Lesnaya and Ukelayat (5), Stanislav (6); Vetlova (7), Tyushev (8); 9, modern accretionary wedge (Figs. 5, 10); 10, possible spreading center; 11, active volcanism.

broken the folded (?) paleoarc continuing as the submerged Bowers Range. Fan-shaped opening itself is not a unique event. Another such example is known from the Philippine Sea basin (Fig. 15) where opening reached ~1000 km at 58–50 Ma and a maximum of 3850 km at 25 Ma (Hall et al., 1995), i.e., the average spreading rate for the 30 Myr time span was 130 km/Ma. Assuming the same opening rate for the Commander basin which is about 550 km wide along the Alfa fault, the onset of spreading can be timed at 4 Ma (~5 Ma at slightly slower early spreading). The West Philippine spreading stopped after 25 Ma, and the oceanic lithosphere began sinking rapidly into the subduction zone. The area consumed by subduction for 25 Ma approached the amount of opening (see the reconstruction for 5 Ma), while the zone of active spreading rotated 60°–65° clockwise and moved 3500 km relative to the China continent (black arrow line in Fig. 15, panel of 5 Ma). This analogy

should be taken into account when discussing the evolution of the Commander basin. Note that the genetic series of back-arc extension structures (1 to 7 in Fig. 1) ends in this basin. In conclusion, it is pertinent to compare our modeling results (Fig. 10) with the crust thickness model (Fig. 16) of Nurmukhamedov et al. (2016). Kamchatka has an intermediate type of crust, with its thickness being 30 km over most of the Kamchatka territory, including the areas of the Vatyna and Lesnaya thrusts and reaching 40–43 km in a few areas. They are: the zone of metamorphics and granite gneiss domes along the maximum compression axis; farther in the north, where dacites and ignimbrites occupy the largest area and dacites contain xenoliths of metamorphic rocks (Davydova, 2014; Perepelov, 2014); and beneath the Klyuchevskoy group of volcanoes (40 km).

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797 Fig. 15. Reconstructions for Cenozoic events in Philippine plate, modified after (Hall et al., 1995). Dashed lines shows extended (50– 25 Ma) and then subducted (25– 5 Ma) parts of oceanic plate. Black arrow line in panel for 5 Ma is migration path of the southeastern plate corner. Black lines for 25 Ma mark extension structures similar to those of Commander basin.

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Fig. 16. Thickness of Kamchatka continental crust, from CMP reflection profiling data, complemented after (Nurmukhamedov et al., 2016). 1, regional seismic reflection and MTS profiles of 1986–2006 and their numbers; 2, reference profile of 2007–2010; 3, segment of profile 8–8′, reacquired after Olutor earthquake; 4, source area of Olutor earthquake of 2006 (a), instrumental epicenter (b) of main shock; 5, crust thickness contour lines; 6, I–I, II–II, DSS profiles (Anosov, 1978); III–III, onshore–offshore DSS profile; 7, outcrops of metamorphic rocks and granite gneiss domes; 8, outcrops of Omolon block (Khanchuk et al., 2006); 9, Pustoretsk–Parapolsky basin; 10, Vatyna–Andrianovka collisional sutures, from (Fig. 11).

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Fig. 17. Seismic tomography for Klyuchevskoy group of volcanoes (Koulakov et al., 2016). Panels on the left: anomalies Vs in slices at depths 10, 30, 50, and 70 km; gray lines are lenses with melt (magma reservoirs) at different depths, as well as slices at 10 km at base of andesite (a) and basalt (b) edifices. Panels on the right: slice in VP, VS anomalies and VP/VS ratios; black lines show slab top and accretionary wedge.

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Thus, the crust produced by subduction-related volcanism proper is within 30 km thick and is thicker (to 43 km) in zones of collision, with granite gneiss domes, and still thicker (50 km) in Early Precambrian metamorphic cratonic blocks, such as the Omolon and Olutor blocks (Fig. 16). The lithospheric and asthenospheric structure below 100 km, with magma sources, the slab, and the suprasubduction mantle, are poorly detectable in gravity data but can be imaged by seismic tomography, which is of low resolution for Kamchatka trough. It is important in the future to obtain a detailed section from the Kamchatsky Mys Peninsula to the Okhotsk coast. The petrological, chemical, and seismic tomography aspects of subduction magmatism were discussed by Dobretsov et al. (2012, 2015), and a multistage system of magma reservoirs (Fig. 17) was modeled for volcanoes of the Klyuchevskoy group and Kizimen (Koulakov et al., 2011, 2016). A 50– 10 km long and 10–15 km thick zone of melting exists at the slab boundary. Basaltic melts are generated in a reservoir at the depth 50–70 km where hot (1400–1500 °C) suprasubduction mantle undergoes melting under the effect of rising andesitic melts. The depths to the melting zone are 50 km beneath volcanoes, 70 km at a distance of 30 km farther in the north, and 30 km (main reservoir) between Kizimen and Udina volcanoes; smaller melt lenses occur at shallower depths beneath volcanoes: e.g., two distinct lens-shaped zones at 10 km under basaltic and andesitic volcanoes. It is also important to detect a deep residual slab block which subducted before 15 Ma from a paleotrench beneath the Central Kamchatka basin. It is shown in Fig. 4, together with the northern boundary of the present slab, at a depth of 200 km beneath Shiveluch volcano, 220 km far from the Kamchatka/Aleutian trench junction. Assuming subduction at 7 cm/yr (70 km/Ma), with projection correction, its onset may be estimated at ~5 Ma. Seismic tomographic images (Koulakov et al., 2016) reveal a weak anomaly with a straight boundary at the depth 200 km (Fig. 4) parallel to the paleotrench in the CKD, located at the same distance of 230–250 km (in the horizontal projection). This may be the plate edge that continued sinking 5 Myr more after the subduction had stopped. These estimates, although obtained with assumptions and simplifications, appear reasonable as three different events fall at 5 Ma: the onset of the Commander basin spreading; renewal of stationary subduction simultaneously with the opening; and detachment and “freezing” of the slab 5 Myr after the cessation of subduction. Thus, it became possible to reconstruct the succession of events in the history of the Kurile–Kamchatka zone and to outline further research objectives. The next step may consist in physical (including experimental) modeling for zones of this kind (Castro and Gerya, 2008; Dobretsov and Kirdyashkin, 1992; Foley et al., 2000; Gerya, 2011; Portnyagin et al., 2015). The value of electronic gravity and topography databases for comprehensive geological and tectonic reconstructions is worth a special note. Synthesized data of the transformed

topography map for the Pacific plate, the Commander basin, the trenches, and the island arc slopes, as well as detailed seismic images of the northern Kamchatka trench and its surroundings, provided a detailed and spatially uniform description for the structure of the Pacific plate and volcanic belts within its limits which has updated and extended the previous knowledge. The joint interpretation of the gravity and transformed topography data, along with onshore and offshore geology, has demonstrated high efficiency in tectonic reconstructions, for both upper crust and lithospheric mantle structures. The manuscript profited much from constructive criticism by the reviewers A.A. Duchkov and V.V. Yarmolyuk. The study was supported by grant 14-17-00430 from the Russian Science Foundation and was performed as part of the basic project run by the Laboratory of Seismic Tomography at the Institute of Petroleum Geology and Geophysics (Novsibirsk).

References Akinin, V.V., Calvert, A.T., 2002. Cretaceous mid-crustal metamorphism and exhumation of the Koolen gneiss dome, Chukotka Peninsula, northeastern Russia, in: Miller, E.L., Grantz, A., Klemperer, S.L. (Eds.), Tectonic Evolution of the Bering Shelf–Chukchi Sea–Arctic Margin and Adjacent Landmasses. Geol. Soc. Am. Spec. Pap. 360, pp. 147–166. Akinin, V.V., Voroshin, S.V., 2006. Integrated geochronology and GIS database for analysis of the magmatic history of northeastern Asia. Tikhookeanskaya Geologiya 25, 39–50. Andersen, O.B., Knudsen, P., 2016. Deriving the DTU15 Global high resolution marine gravity field from satellite altimetry. Abstracts, ESA Living Planet Symposium. Prague, Czech Republic. Andersen, O.B., Knudsen, P., Berry, P., 2010. The DNSC08GRA global marine gravity field from double retracked satellite altimetry. J. Geodesy 84 (3), 191–199, doi:10.1007/s00190-009-0355-9. Anosov, G.I., Bikkenina, S.K., Popov, A.A., Sergeev, K.F., Utnasin, V.K., Fedorchenko, V.I., 1978. Deep Seismic Soundings in Kamchatka [in Russian]. Nauka, Moscow. Avdeiko, G.P., Popruzhenko, S.V., Palueva, A.A., 2007. The tectonic evolution and volcano-tectonic zonation of the Kuril–Kamchatka islandarc system. Geotectonics 36 (4), 312–327. Avdeiko, G.P., Savelyev, D.P, Palueva, A.A., Popruzhenko, S.V., 2007. Evolution of the Kurile–Kamchatkan volcanic arcs and dynamics of the Kamchatka–Aleutian junction, in: Eichelberger, J., Godeev, E., Izbekov, P., Lees, J. (Eds.), Volcanism and Subduction. The Kamchatka Region. Geophysical Monograph, 173, American Geophysical Union, Washington, DC, pp. 41–60. Baranov, B., Wong, H.K, Dozorova, K., Karp, B., Lüdmant, T., Karnaukh, V., 2002. Opening geometry of the Kurile Basin (Okhotsk Sea) as inferred from structural data. The Island Arc 11 (3), 206–219. Batanova, V.G., Laskovskaya, Z.E., Savelieva, G.N., Sobolev, A.V., 2014. Peridotites from the Kamchatsky Mys: evidence of oceanic mantle melting near a hotspot. Russian Geology and Geophysics (Geologiya i Geofizika) 55 (12), 1395–1403 (1748–1758). Bindeman, I.N., Leonov, V.L., Isbekov, P.E., Ponomareva, V.V., Wats, K.E., Shipley, N.K., Perepelov, A.B., Bazanova, I.I., Jicha, B.R., Singer, B.S., Schimin, A.K., Portnyagin, M.V., Chen, C.H., 2010. Large-volume silicic volcanism in Kamchatka. Ar–Ar and U–Pb ages, isotopic and geochemical characterictics of major pre-Holocene caldera-forming eruptions. J. Volcanol. Geotherm. Res. 1, 57–80. Bogdanov, N.A., Chekhovich, V.D., 2002. The collision of the West Kamchatka and Okhotsk Sea plates. Geotektonika, No. 1, 72–85.

N.L. Dobretsov and A.N. Vasilevskiy / Russian Geology and Geophysics 59 (2018) 780–802 Bogdanov, N.A., Dobretsov, N.L., 2002. The Okhotsk volcanic oceanic plateau. Geologiya i Geofizika (Russian Geology and Geophysics) 43 (2), 101–114 (87–99). Bogdanov, N.A., Vishnevskaya, V.S., Kepezhinskas, P.K., Sukhov, N.A., Fedorchuk, A.V., 1987. Geology of the Southern Koryak Upland [in Russian]. Nauka, Moscow. Bondarenko, G.E., 2004. Mesozoic Tectonic and Geodynamic History of the Northern Circum-Pacific Region. Author’s Abstract. Doctor Thesis. Moscow. Bonvalot, S., Balmino, G., Briais, A., Kuhn, M., Peyrefitte, A., Vides, N., Biancale, R., Gabalda, G., Moreauc, G., Reinguin, F., Sarraih, M., 2012. World Gravity Map: Surface Free-air Anomaly, 1:50,000,000 Map. BGI-CGMW-CNES-IRD, Paris, ISBN 978. Boyarinova, M.E., Veshnyakov, N.A., Korkin, A.G., Saveliev, D.P., 1999. State Geological Map of the Russian Federation. East Kamchatka Series. Sheets 0-58-XXVI, XXXI, XXXII. Explanatory Note [in Russian]. VSEGEI, St. Petersburg. Buslov, M.M., Geng, H., Travin, A.V., Otgonbaator, D., Voitishek, A.E., 2013. Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area. Russian Geology and Geophysics (Geologiya i Geofizika) 54 (10), 1250–1271 (1600–1627). Castro, A., Gerya, T.V., 2008. Magmatic implications of the wedge plumes: experimental study. Lithos 103, 138–148. Davydova, M.Yu., 2014. Origin and Evolution of Magmas at the Uksichan Volcanic Center (Centrali Range of Kamchatka). Author’s Abstract, Candidate Thesis. Vladivostok. Dobretsov, N.L., 2010. Petrology, geochemistry, and geodynamics of subduction magmatism. Petrologiya, No. 1, 1–24. Dobretsov, N.L., Kirdyashkin, A.G., 1992. Subduction zone dynamics: models of an accretional wedge. Ofioliti 17, 155–164. Dobretsov, N.L., Koulakov, I.Yu., Litasov, Yu.D., 2012. Migration paths of magma and fluids and lava compositions in Kamchatka. Russian Geology and Geophysics (Geologiya i Geofizika) 53 (12), 1253–1275 (1633–1661). Dobretsov, N.L., Koulakov, I.Yu., Litasov, K.D., Kukarina, E.V., 2015. An integrate model of subduction: contributions from geology, experimental petrology and seismic tomography. Russian Geology and Geophysics (Geologiya i Geofizika) 56 (1–2), 13–38 (21–55). Dobretsov, N.L., Buslov, M.M., Vasilevsky, A.N., Vetrov, E.V., Nevedrova, N.N., 2016a. Cenozoic history of topography in southeastern Gorny Altai: thermochronology, resistivity and gravity records. Russian Geology and Geophysics (Geologiya i Geofizika) 57 (11), 1525–1534 (1937–1948). Dobretsov, N.L., Simonov, V.A., Kotlyarov, A.V., Kulakov, R.Yu., Karmanov, N.S., 2016b. Physicochemical parameters of crystallization of melts in intermediate suprasubduction chambers (by the example of Tolbachik and Ichinskii Volcanoes, Kamchatka Peninsula). Russian Geology and Geophysics (Geologiya i Geofizika) 57 (7), 993–1015 (1265–1291). Dobretsov, N.L., Buslov, M.M., Rubanova, E.S., Vasilevsky, A.N., Kulikova, A.V., Bataleva, E.A., 2017. Middle–Late Paleozoic geodynamic complexes and structure of Gorny Altai and their record in gravity data. Russian Geology and Geophysics (Geologiya i Geofizika) 58 (11), 1277–1288 (1617–1632). Duncan, R.A., Keller, R.A., 2004. Radiometric ages for basement rocks from the Emperor seamount, ODP leg 197. Geochem., Geophys., Geosyst. 5, 1–13. Ernst, R., 2014. Large Igneous Provinces. Cambridge University Press. Foley, S.F., Barth, M.G., Jenner, G.A., 2000. Rutile/melt partition coefficient for trace elements and an assessment on the influence of rutile on the trace element characterisations of subduction zone magmas. Geochim. Cosmochim. Acta 64, 933–938. Förste, Ch., Bruima, S.L., Abrikosov, O., Lemoine, J.-M., Marty, J.-C., Flechtner, F., Balmino, G., Barthelmes, F., Biancale, R., 2014. EIGEN6C4. The latest combined global gravity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and GRGS. Toulouse GFZ Data Services, http:.doi.org/10,5880/icgem, 2015.1. Gerya, T., 2011. Future directions in subduction modelling. Geodynamics 52 (5), 344–378. Glukhmanchuk, E.D. Vasilevskiy, A.N., 2013. Description of fracture zones based on the structural inhomogeneity of the reflector deformation field.

801

Russian Geology and Geophysics (Geologiya i Geofizika) 54 (1), 82–86 (106–112). Gorbatov, A., Fukao, Y., Widiyantoro, S., Gordeev, E., 2001. Seismic evidence for a mantle plume ocean wards of the Kamchatka–Aleutian trench junction. Geophys. J. Int. 146 (2), 282–288, doi: 10.1046/j.0956540x.2001.01439.x. Gordeev, E.I., Dobretsov, N.L. (Eds.), 2017. The Tolbachik Fissure Eruption of 2012–2013 [in Russian]. Nauka, Novosibirsk. Grechin, V.I., 1979. Upper Cretaceous volcanic-sedimentary rocks of different structural zones of Kamchatka, in: Sedimentation and Volcanism in Synclinal Basins [in Russian]. Nauka, Moscow, pp. 130–149. Hall, R., Fuller, M., Ali, J.R., Anderson, C.D., 1995. The Philippine Sea Plate: Magnetism and reconstructions, in: Taylor, B., Natland, J. (Eds.), Active Margins and Marginal Basins of the Western Pacific. American Geophysical Union, Geophysical Monograph 88, pp. 371–404. Hasegawa, A., Nakajima, J., Uchida, N., Ocada, T., Zhao, D., Matsuzawe, T., Umino, N., 2009. Plate subduction, and generation of earthquakes and magmas in Japan as inferred from seismic observation: an overview. Gondwana Res. 16 (3), 370–400. Hourigan, J.R., Brandov, M.T., Solov’ev, A.V., Kirmasov, A.B., Stevenson, J., Reiners, P.W., 2009. Eocene arc–continent collision and crustal consolidation in Kamchatka, Russian Far East. Am. J. Sci. 309, 333–396. ICGEM: International Centre for Global Earth Models. http:/icgem.gfzpotsdam.de/home. Khain, V.E., Filatova, N.I., Polyakov, I.D., 2009. Tectonics, Geodynamics, and Petroleum Potential of the East Arctic Seas and Adjacent Landmasses [in Russian]. Nauka, Moscow. Khanchuk, A.I., 1985. Evolution of Precambrian Continental Crust in Island Arc Systems of East Asia [in Russian]. DVNC AN SSSR, Vladivostok. Khanchuk, A.I., Goryachev, N.A., Rodionov, S.M. (Eds.), 2006. Geodynamics, Magmatism, and Metallogeny of Eastern Russia [in Russian]. Dalnauka, Vladivostok, Book 1. Khotin, M.Yu., Shapiro, M.N., 2006. Ophiolites of the Kamchatskiy Cape (East Kamchatka): structure, composition, and tectonic setting. Geotektonika, No. 6, 61–89. Kovalenko, D.V., 2003. Paleomagnetism of Geological Complexes in Kamchatka and South Koryakia [in Russian]. Nauchnyi Mir, Moscow. Kogiso, T., Omori, S., Maruyama, S., 2009. Magma genesis beneath Northern Japan arc: a new perspective on subduction zone magmatism. Gondwana Res. 16, 441–457. Kruk, N.N., 2015. Continental crust of Gorny Altai: stages of formation and evolution: indicative role of granitoids. Russian Geology and Geophysics (Geologiya i Geofizika) 56 (8), 1097–1113 (1403–1423). Koulakov, I.Yu., Dobretsov, N.L., Bushenkova, N.A., Jakovlev, A.V., 2011. Slab shape in subduction zones beneath the Kurile–Kamchatka and Aleutian arcs based on regional tomography results. Russian Geology and Geophysics (Geologiya i Geofizika) 52 (6), 650–665 (830–851). Koulakov, I.Yu., Kukarina, E.V., Gordeev, E.I., Chebrov, V.N., Vernikovskiy, V.A., 2016. Magma sources in the mantle wedge under volcanoes of the Klyuchevskoy group and Kizimen based on seismic tomography modeling. Russian Geology and Geophysics (Geologiya i Geofizika) 57 (1), 82–94 (109–124). Litvinov, A.F., Patoka, M.G., Markovskiy, B.A., 1999. Map of Mineral Deposits of Kamchatka. Scale 1:5,000,000 [in Russian]. VSEGEI, St. Petersburg. Levashova, N.M., Shapiro, N.M., Beniyamovskiy, V.N., Bazhenov, M.L., 2000. Reconstruction of the tectonic history of the Kronotskaya island arc (Kamchatka), from paleomagnetic and geological data. Tektonika, No. 2, 65–84. Lomtev, V.L., 2017. Structure of the northern Kurile–Kamchatka trench and its surroundings. Vestnik SVNC DVO RAN, No. 2, 30–40. Magee, M.E., Zobak, M.D., 1993. Evidence for a weak interplate thrust fault along the Northern Japan subduction zone and implication for the mechanics of thrust faulting and fluid expulsion. Geology 21 (9), 809–812. Mitrofanov, N.P., 1977. The Vatyn nappe in the Central Koryak folded zone. Geologiya i Geofizika (Soviet Geology and Geophysics) 18 (4), 144–150 (118–122).

802

N.L. Dobretsov and A.N. Vasilevskiy / Russian Geology and Geophysics 59 (2018) 780–802

Natalin, B.A., Amato, J.M., Toro, J., Wright, J.E., 1999. Paleozoic rocks of northern Chukotka Peninsula, Russian For East: implications for the tectonics of the Arctic region. Tectonics 18, 977–1003. Nurmukhamedov, A.G., Nediadko, A.G., Rakitov, V.A., Lipatiev, M.S., 2016. Lithosphere boundaries in Kamchatka, from earthquake converted waves. Vestnik KRAUNC. Nauki o Zemle 29 (1), 35–52. Osipenko, A.B., Krylov, K.A., 2001. Chemical heterogeneity of mantle peridotites in ophiolites of East Kamchatka: causes and geodynamic implications, in: Petrology and Metallogeny of Mafic and Ultramafic Complexes of Kamchatka [in Russian]. Nauchnyi Mir, Moscow, pp. 138– 158. Pavlis, N.K., Factor, J.K., Hoimes, S.A., 2007. Terrain-related gravimetric quantities computed for the next EGM, in: Gravity Field of the Earth, Proc. 1st Int. Symp. Int. Gravity Field Service. Harita Dergisi Spec. Issue 18, Istanbul, pp. 318–323. Pecherskiy, D.M., Shapiro, M.N., 1996. Paleomagnetism of Upper Cretaceous and Paleogene volcanic series of East Kamchatka: Evidence for absolute motions of ancient subduction zones. Izv. RAN, Fizika Zemli, No. 2, 31–55. Pecherskiy, D.M., Levashova, N.M., Shapiro, M.N., Bazhenov, M.L., Sharonova, Z.V., 1997. Paleomagnetism of Paleogene volcanic series of the island arc. Tectonophysics 273, 219—237. Perepelov, A.B., 2014. Cenozoic Volcanism of Kamchatka during Events of Tectonic Setting Change. Author’s Abstract, Doctor Thesis. IGC, Irkutsk. Pirajno, F., 2000. Ore Deposits and Mantle Plumes. Kluwer Acad. Publ. Portnyagin, M.V., Saveliev, D.P., Hornle, C., 2005. Cretaceous oceanic plume basalts of East Kamchatka: mineral chemistry of spinel and ore potential of magmas. Petrologiya 13 (6), 626–645. Portnyagin, M.V., Duggen, S., Hauff, F., Mironov, N., Bindeman, I., Thirlwall, M., Hoernle, K., 2015. Geochemistry of the Late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems. J. Volcan. Geotherm. Res. 307, 133–155, doi: 10.1016/j.jvolgeores.2015.08.015. Pushcharovsky, Yu.M., Neprochnov, Yu.P. (Eds.), 1984. The Seafloor Structure in the Northwestern Pacific (Geophysics, Magmatism, Tectonics) [in Russian]. Nauka, Moscow. Reverdatto, V.V., Likhanov, I.I., Polyanskiy, O.P., Sheplev, V.S., Kolobov, V.Yu., 2017. Nature and Models of Metamorphism [in Russian]. Izd. SO RAN, Novosibirsk. Richter, A.V., 1995. The metamorphic complex of the Central Range in Kamchatka. Geotektonika, No. 1, 71–78.

Shapiro, M.N., 1995. Late Cretaceous Achaivayam–Valaga volcanic arc (Kamchatka) and plate motion in the Northern Pacific. Geotektonika, No. 1, 58–70. Shapiro, M.N., Solov’ev, A.V., Garver, J.I., Shcherbinina, E.A., Ledneva, G.V., Brandon, M., 2004. Age of the terrigenious rocks of northeastern Karaginskiy Island (Eastern Kamchatka). Stratigr. Geol. Correl. 12 (2), 188–198. Shapiro, M.N., Solov’ev, A.V., Hourigan, J.K., 2008. Lateral variations of tectonic structures in the zone of Eocene collisions between an island arc and the continent (Kamchatka). Geotektonika, No. 6, 1–21. Shipley, T.H., Moore, G.F., Bangs, N.C., Moore, J.C., Stoffa, P.L., 1994. Seismically inferred dilatancy distribution, north Barbados Ridge decollement. Geology 22, 411–414. Solov’ev, A.V., 2005. Tectonics of West Kamchatka, from fissure track thermochronolgy and structural analysis, in: West Kamchatka: Mesozoic Geological History [in Russian]. Nauchnyi Mir, Moscow, pp. 163–194. Solov’ev, A.V., Shapiro, M.N., Garver, J.I., 2002. Lesnaya thrust sheet, North Kamchatka. Geotektonika, No. 6, 45–59. Solov’ev, A.V., Shapiro, M.N., Garver, J.I., Lander, A.V., 2004. Formation of the East Kamchatkan accretionary prism based on fission-track dating. Geologiya i Geofizika (Russian Geology and Geophysics) 45 (11), 1237–1247 (1292–1302). Stavskiy, A.P., Chekhovich, V.D., Kononov, M.V., Zonenshain, L.P., 1988. Palinspastic plate tectonic reconstructions of the Anadyr–Koryak region. Geotektonika, No. 6, 32–42. Tararin, I.A., Badredinov, Z.G., Chubarov, V.I., 2015. Petrology and Metallogeny of Metamorphic and Metasomatic Complexes of Central and East Kamchatka [in Russian]. Dalnauka, Vladivostok. Toro, J., Gans, P.B., Mc Gellant, W.C., Dumitru, T.A., 2002. Deformation and exhumation of the mount Igikpak region, Central Brooks Range, Alaska. Geol. Soc. Am. Spec., Pap. 300, pp. 111–132. Tsukanov, N.V., Luchitskaya, M.V., Skolotnev, S.G., Kramer, V., Seifert, V., 2004. New data on the structure and composition of gabbroids and plagiogranites from the Late Cretaceous ophiolite complex of the Kamchatsky Mys Peninsula (Eastern Kamchatka). Dokl. Earth Sci. 397 (5), 632–635. Zinkevich, V.P., Konstantinovskaya, E.A., Tsukanov, N.V., Rikhter, A.V., Sobolev, A.V., Kamenetsky, V.S., Danyushevsky, L.M., 1993. Accretionary Tectonics of Eastern Kamchatka [in Russian]. Nauka, Moscow. Zonenshain, L.P., Kuzmin, M.I., 1993. Paleogeodynamics [in Russian]. Nauka, Moscow.

Editorial responsibility: D.V. Metelkin