ISSN 0001-4370, Oceanology, 2008, Vol. 48, No. 2, pp. 239–249. © Pleiades Publishing, Inc., 2008. Original Russian Text © E.P. Lelikov, T.A. Emel’yanova, B.V. Baranov, 2008, published in Okeanologiya, 2008, Vol. 48, No. 2, pp. 260–270.
MARINE GEOLOGY
Magmatism of the Submarine Vityaz Ridge (Pacific Slope of the Kuril Island Arc) E. P. Lelikova, T. A. Emel’yanovaa, and B. V. Baranovb a
Il’ichev Pacific Oceanological Institute, Far East Division, Russian Academy of Sciences, Vladivostok, Russia e-mail:
[email protected] b Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia e-mail:
[email protected] Received February 11, 2006; in final form, March 5, 2007
Abstract—Original results of igneous rock studies are presented. The rocks were dredged during a marine expedition (cruise 37 of R/V Akademik M.A. Lavrent’ev in August–September, 2005) in the region of the submarine Vityaz Ridge and Kuril Arc outer slope. Several age complexes (Late Cretaceous, Eocene, Late Oligocene, Miocene, and Pliocene–Pleistocene) are recognizable on the Vityaz Ridge. These complexes are characterized by a number of common geochemical features since all of them represent the formations of island arc calc-alkali series. At the same time, they also have individual features reflecting different geodynamic settings. The outer slope of the Kuril Arc demonstrates submarine volcanism. The Pliocene–Pleistocene volcanic rocks dredged here are similar to the volcanites of the Kuril-Kamchatka Arc frontal zone. DOI: 10.1134/S0001437008020112
INTRODUCTION In 2005, the Pacific Oceanological Institute (FED RAS) and the Institute of Oceanology (RAS) carried out a marine expedition (cruise 37 of R/V Akademik M.A. Lavrent’ev in the framework of the project “The Structural Study of the Central Kuril–Kamchatka Island Arc as a Potential Center of Catastrophic Tsumamigenic Earthquakes.” The purpose of this expedition was the study of the Central Kuril seismic “gap” and an operative assessment of the tectonic situation in the seimoactive zone of the frontal arc slope between Urup Island in the southwest and Paramushir Island in the northeast [5]. In this area, geophysical studies (gravity and marine magnetic surveys, continuous seismic profiling) were accompanied by dredging of the rocks constituting the basement and sedimentary cover. Vasil’ev et al. [3] were the first to study the basement rocks in the southern part of the area. They defined the Lesser Kuril Anticline composed of tuffstones, tuffaceous siltstones, porphyrites and their tuffs, and tuff breccias and tuff conglomerates. These rocks are similar to their counterparts from the Matakotan and Malye Kurily formations of Shikotan Island dated by faunal fossils as the Late Cretaceous (Campanian– Maestrichtian) [9]. In addition to terrigenous rock, the latter author noted gabbroids and dolerites typical of the Lesser Kuril and Shikotan intrusive complexes, gray and pink granites, aplites, felsite–porphyries, and diorites. Unfortunately, paper [3] is lacking data on the geochemical composition of igneous rocks, which prevents their correct comparison with our materials.
The purpose of the geological studies during cruise 37 of R/V Akademik M.A. Lavrent’ev was dredging of steep slopes of submarine rises and canyon walls to obtain their constituting rocks, identification of the acoustic basement and sources of geophysical anomalies, and the study of the geological structure and evolution history of the submarine Vityaz Ridge. Dredging was conducted at 19 stations within three areas: Vityaz, Diana, and Bussol (Fig. 1). These works yielded a representative rock collection largely consisting of volcanites and subordinate granites. This paper is dedicated to an analysis of these rocks. The main attention is paid to the petrogeochemical characteristics of igneous rocks. The paper represents a first step in the geochemical study of the Vityaz Ridge. METHODS During the cruise, geochemical samples were obtained by a cylindrical dredge 60 cm in diameter run by a standard ship winch. Dredging was carried out in steep sediment-free areas of the sea bottom defined by echo sounding and continuous seismic profiling. The position of the dredging sites was determined using two marine satellite navigation receivers of the Global Positioning System (GPS): Garmin GPS 120 and Garmin GPS 128. The rocks dredged were documented and sampled for the subsequent treatment and laboratory studies. Taking into consideration the wide distribution of icerafted material in this region, only rock fragments that met the criteria of their bedrock origin were sampled.
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150° 1
151° 2
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Fig. 1. Location of dredging stations (triangles) and areas (rectangles) in the study region. The numbers are shown only for the stations whose rocks are discussed in the paper. Areas: (1) Bussol, (2) Diana, (3) Vityaz. The stars designate the following: 1—submarine volcanoes from the catalog in [1] (gray coloration); 2—submarine volcanoes discovered during cruise 37 of R/V Akademik M.A. Lavrent’ev (black coloration). The dashed line marks the position of the volcanic front after [1]. The depth contours are drawn with a step of 1000 m.
These criteria are the following: the angular shape of the rock fragments with fresh chipped surfaces, which indicate their breaking away from bedrocks, and the prevalence of rocks with a uniform petrographic composition, which indicates their origin from a single volcano–magmatic system. The laboratory treatment of the rocks included their petrographic study under a microscope; chemical analysis by the wet chemistry method; identification of REE and trace elements by the ICP-MS method using an
ICP-MS Elan DRC II Perkin Elmer analyzer (USA) with a sensitivity up to 10–11 in the Innovation–Analytical Center of the Institute of Tectonics and Geophysics (FED RAS); and determination of the radioisotopic ages of volcanic rocks at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM RAS). During the latter procedure, the content of radiogenic argon was measured with an MI-1201 IG mass-spectrometer by the isotopic dilution method using 38Ar as a tracer and the K content was determined OCEANOLOGY
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using the method of flame spectrophotometry using a modified FPA-01spectrometer. The accuracy of the measurements was controlled by the systemic determinations of the 40Arrad contents in the standard samples “biotite70A,” muscovite “P-207,” and muscovite “Bern-4M” and by the measurements of the isotopic composition of air argon. The constants λK = 0.581 × 10–10 year–1, λβ = 4.962 × 10–10year–1, and 40K = 0.01167 (atm. %) were used in the calculations. BOTTOM MORPHOLOGY The study area consists of two parts: the inner volcanic arc represented by the Greater Kuril Ridge and the outer arc corresponding to the submarine Vityaz Ridge. The latter is separated from the Greater Kuril Ridge by an interarc trough and is subdivided into the southern and northern plateaus: between Simushir and Rasshua islands, the ridge is undistinguishable in the bottom topography. The studies were carried out in three areas confined to the Vityaz Ridge and outer slope of the Greater Kuril Ridge east of Simushir Island (Fig. 1). The Vityaz area is located in the southwestern extremity of the northern plateau. Its slope consists of two steps separated by a relatively steep slope 1500– 2000 m high. It is located at an average approximate depth of 200 m with a distinct tendency to dipping in the southern direction toward the deep-sea trench down to depths of 750–1000 m. The surface of the step is flattened, which implies wave abrasion during the period of the low sea-level standing in the Holocene. West- and southwestward, the step grades into a steep bench up to 1500 m high. The latter is crossed by numerous canyons with heads in the flattened summit of the ridge. The canyons extend in the latitudinal direction and represent fault-line structures. Three stations in the canyons and the bench yielded fresh igneous rock fragments (stations 14, 17, and 19 in Fig. 1). The second step is located at depths of 1500–200 m. Its southern part hosts two small ridges approximately 25 km long and several smaller rises. The ridges extend in the near-latitudinal direction, being separated by a depression approximately 1900 m deep. The crests of the ridges are acute-angled with minimal water depths of 600 and 1200 m above its southern and northern segments, respectively. Three dredging stations are located in this area (stations 22—24 in Fig. 1). The Diana area is confined to the outer slope of the ridge east of Simushir Island and covers sea depths from 1000 to 5000 m. A remarkable feature of the slope is represented by several small ridges oriented in the northwestern direction (Fig. 2). The bathymetric survey revealed two small seamounts in the axial part of the ridge. Their heights vary from 250–300 to 1000–2000 m in the upper and lower parts of the slope, respectively. The shape of these seamounts allows them to be interpreted as submarine volcanic edifices. Dredging at one OCEANOLOGY
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of these mounts provided bedrocks (station 25 in Figs. 1, 2). The Bussol area comprises the summit of the southern plateau; its northwestern and northeastern slopes; and, partly, the Bussol Graben. The area is highly differentiated with depths varying from 1000 m above the plateau to >5000 m at the Bussol Graben bottom. The summit consists of two steps, one of which (northeastern) is subsided relative to the other to form a system of second-order steps each up to several tens of meters high. The steps are oriented in the near-meridional direction and correspond to tectonic fractures. They cross the plateau summit to continue at its northwestern and southeastern slopes in the form of canyons with an incision depth of approximately 500 m. The Bussol Graben is oriented in the general northwestern direction orthogonally to the island slope of the Kuril Arc. Its southwestern wall forms a very steep slope of the Vityaz Ridge with a depth gradient of 4000 m. The northeastern wall is gentler with a depth increment of 1500 m. The graben bottom consists of individual depressions separated by low rises. Dredging was carried out on the slopes and summit of the southern plateau (Fig. 1). PETROGRAPHIC CHARACTERISTICS OF IGNEOUS ROCKS Volcanic rocks are found at several dredging stations (14, 17, 19, 20, 22–26, 37) in all the study areas, while granites were dredged only in the Vityaz area (stations 17, 19) (Fig. 1). Their comprehensive examination, which included radioisotopic age determination (Table 1), petrographic and geochemical analyses of the volcanites, and their comparison with the volcanites from the Kuril island arc and Sea of Okhotsk, allowed them to be divided into several different-age complexes: Late Cretaceous, Eocene, Late Oligocene, Early Miocene, and Pliocene–Pleistocene. The Late Cretaceous Volcano–Plutonic Complex This nomplex includes several samples from station 17 (water depth of 1900 m) located on the northwestern slope of the northern plateau of the Vityaz Ridge, where they occur within the Upper Cretaceous volcanogenic– terrigenous sequence, and rhyolites from the Bussol area (station 37, water depth of 1950 m). All of them are similar to the rocks constituting the Late Cretaceous dacite–rhyolite complex developed on the rises of the central Sea of Okhotsk [4], which provides grounds for defining the Late Cretaceous volcanic complex in the Vityaz Ridge. Granites–porphyries from Station 19 (water depth of 1900 m) are also referred to this complex. Biotite–hornblende dacites (station 17) are porphyric rocks consisting of plagioclase (An42 40–50%), hornblende (15%), biotite (10%), and accessory minerals (up to 3–5%): titanomagnetite, leucoxene, apatite,
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–4
00
153°00′
–4
– 4000
152°30′
0
– 3000
46°30′
152°36′ E
Fig. 2. Bathymetric chart of the Diana area. The depth contours are drawn with a step of 100 m. Arrows indicate rounded mounts interpreted as small volcanic edifices. Other symbols are as in Fig. 1. The location of the area is shown in Fig. 1.
and zircon. Phenocrysts (30−35%) of plagioclase, hornblende, and biotite are developed in the micropoikilitic feldspar matrix. Rhyolites (station 37) are composed of andesine and oligoclase (40–50%), potassium feldspar (30–35%), quartz (20%), and accessory minerals: leucoxene (7%), apatite, topaz, and monazite. Phenocrysts (25–30%) from 0.8 to 2.5 mm across are represented by plagioclase, potassium feldspar, and quartz. The ground mass is spherolitic variolitic quartz–feldspar in composition. The rocks are subjected to propilitization and enclose nest-shaped accumulations of ore (sulfide) minerals (5−10%) and secondary minerals (25%): chlorite, sericite, and carbonate. Biotite–hornblende granite–porphyries (station 19) are massive rocks with porphyric aggregates (40–45%) 3–6 mm across, which are represented by oligoclase crystals (25–30%), potassium feldspar (10–15%), quartz (20–25%) grains, biotite (up to 7%) and hornblende with biotite, and actinolite developing after the
latter. The microgranite matrix is composed of oligoclase, quartz, potassium feldspar, and biotite. The Eocene complex. The rocks of this complex are developed in the northwestern slope of the Vityaz Ridge northern plateau, where they are represented by andesitic tuffs and moderately acid ignimbrites (station 14, water depth of 1570 m, and station 17) and granite–porphyries (station 17). Psephitic–psammitic crystal-lithic basaltic andesite tuffs (station 14) consist of clasts (60–80%) 0.8 to 6.0 mm across represented by dominant andesites (45%), subordinate basalts (10%) and plagioclases (15%), rare clinopyroxene (5%), orthopyroxene (5%), brown hornblende, magnetite (8–10%), and apatite. The matrix is composed of brownish volcanic ash. The texture of the rocks is psephitic–psammitic crystal-lithic, and the structure is massive. Moderately acid ignimbrites (station 17) consist of clasts (15%) 0.4–2.5 mm in size represented by zoned plagioclase (An52, 10−20%), dacite, and andesite (2–5%). OCEANOLOGY
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Table 1. Radioisotopic age determinations of the igneous rocks from the Vityaz Ridge Ordered number
± σ, ppm
40Ar rad
Age ± 1.6σ, My B.P.
Sample number
Latitude, N
Longitude, E
Dredging interval, m
K% ± σ, %
1
Lv-37-19-3
47°42.908'
154°22.670'
1800–1500
3.80 ± 0.04
19.8 ± 0.2
74 ± 2
2
Lv-37-14-4
47°57.019'
154°20.066'
1450–1200
1.92 ± 0.02
6.78 ± 0.09
50.2 ± 1.6
3
Lv-37-17-11
47°42.690'
154°23.208'
1770–1500
4.46 ± 0.05
15.41 ± 0.16
49.2 ± 0.15
4
Lv-37-17-8
47°42.690'
154°23.208'
1770–1500
3.45 ± 0.04
11.45 ± 0.10
47.2 ± 1.4
5
Lv-37-24-2
47°16.015'
154°06.770'
1900–1700
2.23 ± 0.03
4.29 ± 0.11
27.5 ± 1.6
6
Lv-37-37-6
45°33.784'
151°33.306'
2200–1900
0.82 ± 0.015
0.607 ± 0.013
10.7 ± 0.6
7
Lv-37-25-1
46°56.958'
152°53.644'
1870–1600
0.30 ± 0.015
0.034 ± 0.003
1.6 ± 0.3
Note: Samples: (1, 3) granite–porphyries, (2) basaltic andesite, (4) ignimbrite, (5) trachytic tufflava, (6) andesite, (7) basalt.
The matrix is composed of sintered particles of fresh volcanic glass, which are curved in a capricious manner around crystal and rock fragments. There are also fiammes 0.8–4.0 mm long. The texture and structure are ignimbritic and pseudofluidal, respectively. Biotite–hornblende granite–porphyries (station 17) are similar to the Late Cretaceous granites but differ from them by the lower content of phenocrysts (up to 30%) also represented by plagioclase (25–30%), potassium feldspar (20–25%), quartz (20–25%), biotite (up to 8%), and hornblende, by a more basic plagioclase (andesine), and bya micropegmatitic texture of the matrix. The Late Oligocene Volcanic Complex It is represented by tufflavas of trachytes, trachytic and rhyolitic tuffs, and sintered trachyrhyolitic tuffs. All these rocks were dredged from the northwestern slope of the northern plateau of the Vityaz Ridge (stations 17, 20, water depth of 1350 m; stations 23, 24, water depths of 1900–1800 m). Trachytic tufflava (station 24). Fragments from 0.5 to 2.5 mm across constitute 20% of the rock and are represented by trachytes, subordinate basalts, rhyolites, acid plagioclase, and quartz. The matrix (up to 70−80%) is trachytic lava consisting of microlites or laths of albite, potassium feldspar, and brownish volcanic glass. The texture and structure of the rocks are crystal-lithic trachytoid and fluidal, respectively. Silty crystal-lithic trachytic tuffs (stations 20, 23) are composed of clasts 0.3 to 2.5 mm across, which constitute up to 40% of the rock and are represented by trachytes (15–20%), acid plagioclase and potassium feldspar (10–15%), quartz, (5%), hornblende, and darkcolored minerals entirely replaced by boulingite. The pelitic ash matrix is locally replaced by hydromica (8−10%). The rock texture is silty crystal-lithic; the matrix is pelitic to, locally, microlepidoblastic; and the structure is pseudofluidal. OCEANOLOGY
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Trachyrhyolites (station 23) are amygdaloid porphyric rocks with a fluidal structure composed of albite (40–45%), potassium feldspar (30–35%), clinopyroxene (10%), and orthopyroxene (5–7%). Phenocrysts (30–35%) 0.7 to 4.0 mm in size are represented by albite, potassium feldspar, and ortho- and clinopyroxene. The trachytoid matrix is composed of albite and potassium feldspar laths. Secondary alteration is reflected in the pseudomorphic replacement of orthopyroxene (8–10%) by boulingite and amygdules filled with quartz and chlorite. Sintered psammitic crystal–vitric trachyrhyolitic tuff (station 17) consists of clasts (35–40%) 0.3 to 3.0 mm in size represented by quartz (10–15%); plagioclase An35 (10%); biotite (10%); hornblende (2–3%); and accessory magnetite (3–5%), zircon, apatite, and tourmaline. The matrix consists of volcanic glass particles of capricious shapes locally replaced by microgranoblastic quartz–feldspar aggregates. The texture and structure of the rock are psammitic crystal-vitric and pseudofluidal, respectively. The Miocene Volcanic Complex Based on radioisotopic measurements (Table 1), the andesitic block dredged from the southeastern slope of the southern plateau of the Vityaz Ridge (Bussol area, station 37, water depth 1950 m) is attributed to this complex. Bipyroxene–plagioclase andesites (station 37) are massive highly seriate rocks composed of plagioclase An60 (40–45%), clinopyroxene (20–25%), orthopyroxene (10–15%), volcanic glass (5–15%), and magnetite (3–5%). Phenocrysts (from 0.3 to 3.0 mm across, 35−45%) represented by plagioclase, olivine, clinopyroxene, and magnetite are submerged into the tholeiitic or hyalopilitic matrix.
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K2O + Na2O, wt % 8 24-2
Trachybasalts
Trachyandesites
7
Rhyolites
17-8
Trachyandesitic basalts Trachybasalts
6 5
17-13
B 37-6
A
1 2 3 4 5 6
4 17-2
3
22-1 19-2 Dacites
25-1 Andesites
2
Basalts
1 45
50
Andesitic basalts
55
60
65
70
75 SiO2,
80 wt %
Fig. 3. Alkali–silica diagram [10] compiled for the Cenozoic volcanites of the Vityaz Ridge. 1—Pliocene–Pleistocene; 2—Miocene; 3—Oligocene; 4—Eocene; 5—volcanites from the frontal zone of the Kuril island arc; 6—volcanites from the Kuril Basin. The straight line designates trends of volcanites: (A) frontal zone of the Kuril island arc; (B) Kuril Basin.
The Pliocene–Pleistocene Volcanic Complex It is characterized by the basalts that originate from the northwestern part of the Diana area (station 25, water depth of 1870 m). Based on radioisotopic age measurements (Table 1), they are attributed to this complex. Olivine–clinopyroxene–plagioclase basalts (station 25) are massive rocks with a glomeroporphyritic texture and tholeiitic matrix. They are composed of plagioclase An65 (30–35%), clinopyroxene (titanoaugite) (25−30%), olivine (chrysolite) (15%), volcanic glass (10%), and magnetite (6%). Phenocrysts (35%) 1–4 mm in size are represented by olivine, plagioclase, and clinopyroxene, while the matrix consists largely of plagioclase laths with clinopyroxene, magnetite, and volcanic glass developed in interstices. In the Vityaz area, dredging at selected stations brought fresh basalts and andesites compositionally similar to the volcanites from the Diana area; they are attributed to the Pliocene–Pleistocene complex. Clinopyroxene–plagioclase basalts (station 17) representing porous rocks with the hyalopiitic matrix are composed of zoned plagioclase An66 (35–40%) and clinopyroxene (augite) (10–15%), which form phenocrysts (45–50%) 0.4 to 2.0 mm across, volcanic glass (25–30%), and magnetite (1–3%). The matrix consists of fresh volcanic glass and rare plagioclase microlites. Clastic lavas of clinopyroxene–plagioclase andesites (station 22, water depth of 1750 m) are composed of angular or splintered clasts (40%) from 0.3 to
2.0 mm across of plagioclase An55 (20–25%), clinopyroxene (10–15%), and magnetite (10%). The matrix is represented by fresh moderately acid (andesitic) volcanic glass with rare plagioclase microlites. The rock texture and structure are crystal and massive, respectively; the matrix texture is hyaline. Amphibole–bipyroxene–plagioclase andesites (station 19, water depth of 1900 m) are porous glomeroporphyritic rocks with phenocrysts (45%) from 0.5 to 3.5 mm across represented by zoned plagioclase An62 (20–25%), augite (10%), hypersthene (8–10%), hornblende (3–5%), and magnetite (5%). The hyalopilitic matrix consists of fresh volcanic glass and rare plagioclase microlites. PETROGEOCHEMICAL CHARACTERISTICS OF ROCKS The geochemical analysis was largely performed for Pleistocene volcanites first discovered in the Diana area and on the northern plateau of the Vityaz Ridge. They are represented by basalts and andesites, which are characterized by elevated contents of Al2O3 (16.68– 18.20%) and CaO (6.34–9.37%), medium total alkalinity (2.09–4.61%) with a prevalence of Na2O over K2O, and low concentrations of TiO2 (<1%) and K2O (0.32– 0.90%) (Table 2). All these features allow them to be classed with high-alumina high-Ca, and moderately potassic rocks of normal-alkalinity volcanic series. In the alkalinity–silica diagram, data points of these rocks are located along the trend characterizing the volcanites from the frontal zone of the Kuril Arc (Fig. 3). The Pliocene–Pleistocene volcanites are characterized by moderate to elevated concentrations of Rb (from 3.80 to 25.05 ppm) and Sr (from 266.59 to 739.06 ppm), while alkaline Late Oligocene rocks demonstrate higher Rb (from 29.9 to 153.84 ppm) and lower Sr (from 151.23 to 572.94 ppm) contents. The rocks from all the complexes are characterized by lowered concentrations of Fe group elements (Co, Cr, Ni) (Table 2, Fig. 4). The Ni/Co value in them is <1.5, which is typical of volcanites from island arcs [8]. In addition, all the rock types show low Nb concentrations, which form the corresponding (Nb) minimum in the diagram of trace elements (Fig. 4) characteristic of volcanites from the Kuril Arc [2]. Such concentrations of large-ion lithophile and siderophile elements in the Pliocene–Pleistocene volcanites from the Vityaz Ridge point to their island-arc origin and to their similarity with rocks from the frontal zone of the Kuril Arc. The subalkali volcanites of the Late Oligocene complex are characterized by elevated LREE concentrations, a slightly fractionated spectrum of the REE distribution, and low La/Sm and La/Yb values normalized with respect to the chondrite standard, which range from 1.91 to 3.54 and from 3.48 to 8.60, respectively. The volcanites of the Pliocene–Pleistocene complex demonstrate a slightly fractionated REE distribution OCEANOLOGY
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Table 2. Contents of petrogenic (wt %), trace, and rare earth elements (ppm) in the magmatic rocks from the Vityaz Ridge 37-19-3
37-14-4
37-17-8
37-17-11
37-17-13
37-23-7
37-23-11
1
2
3
4
5
6
7
SiO2
72.94
55.92
63.92
74.96
74.22
–
–
TiO2
0.19
0.89
0.29
0.19
0.24
–
–
Al2O3
14.35
16.17
14.79
12.89
13.65
–
–
Fe2O3
1.18
4.84
2.44
0.94
1.17
–
–
FeO
0.98
4.27
2.41
0.98
0.91
–
–
MnO
0.05
0.15
0.035
0.04
0.034
–
–
MgO
0.44
4.72
1.48
0.18
0.36
–
–
Sample/element
CaO
0.92
4.09
1.77
0.92
–
–
Na2O
4.20
3.57
3.81
3.63
3.17
–
–
K2O
3.89
1.59
4.00
4.71
3.89
–
–
P2O5
0.03
0.40
0.068
0.05
0.063
–
–
L.O.I.
0.41
3.00
4.87
0.11
0.55
–
–
Sum
99.58
99.61
99.88
99.60
100.37
–
–
H2O
0.05
0.45
–
0.05
0.05
–
–
Rb
138.83
33.24
–
219.54
153.84
2.98
29.90
Sr
92.71
686.78
–
65.04
161.23
55.31
194.63
Ba
718.60
–
1235.68
801.37
31.92
105.68
Zr
42.18
66.65
–
48.81
59.99
66.40
61.71
Nb
20.32
2.03
–
7.58
6.09
0.81
2.50
Y
24.86
19.98
–
20.81
14.45
10.02
16.88
Co
1.43
38.96
–
1.02
3.72
8.74
7.15
Cr
8.65
34.03
–
2.55
7.72
58.35
29.00
Ni
–
17.37
–
0.93
5.78
5.28
17.28
V
5.65
278.89
–
6.29
29.36
132.66
120.73
La
37.34
11.69
–
34.18
19.74
6.96
9.72
Ce
78.15
29.48
–
74.74
41.71
19.32
22.81
Pr
8.47
3.87
–
7.82
4.60
2.26
2.80
Nd
30.30
17.21
–
28.54
17.53
10.19
12.01
Sm
5.79
3.96
–
4.99
3.48
2.27
2.70
Eu
0.43
1.16
–
0.40
0.52
0.60
0.75
Gd
6.21
4.44
–
5.17
3.55
2.54
3.31
1341.2
211
Tb
0.82
0.65
–
0.65
0.47
0.34
0.47
Dy
4.90
3.99
–
3.97
2.76
2.12
3.02
Ho
0.94
0.81
–
0.79
0.53
0.40
0.63
Er
2.76
2.28
–
2.43
1.57
1.13
1.88
Tm
0.39
0.33
–
0.33
0.22
0.15
0.26
Yb
2.73
2.19
–
2.41
1.56
1.10
1.90
Lu
0.39
0.35
–
0.34
0.22
0.15
0.29
Hf
1.32
1.60
–
1.72
2.14
1.75
1.42
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Table 2. (Contd.) 37-24-2
37-37-6
37-25-1
37-17-2
37-22-1
37-19-2
8
9
10
11
12
13
Sample/element SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 L.O.I. Sum H2O Rb Sr Ba Zr Nb Y Co Cr Ni V La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf
57.00 0.59 16.31 3.19 4.30 0.05 4.47 1.86 4.90 2.53 0.03 4.48 99.71 – 47.82 572.94 1032.5 91.85 1.98 15.53 17.71 30.04 30.92 139.35 8.45 19.63 2.52 11.58 2.75 0.92 3.31 0.46 2.90 0.58 1.72 0.23 1.62 0.24 2.19
58.32 0.99 16.43 4.96 3.64 0.17 3.29 6.47 3.14 0.80 0.20 1.73 100.14 0.76 15.13 380.73 173.03 69.26 1.51 22.29 19.20 11.41 9.63 284.30 7.90 19.61 2.59 12.74 3.41 1.10 4.31 0.62 4.18 0.87 2.59 0.35 2.48 0.35 1.74
52.2 0.81 18.20 3.01 6.30 0.20 4.81 9.37 3.57 0.38 0.083 0.69 99.62 0.05 4.03 313.72 317.81 37.39 0.29 16.24 25.71 30.22 16.34 380.39 2.38 6.60 0.99 5.42 1.76 0.68 2.51 0.42 2.91 0.64 1.88 0.28 1.92 0.29 0.96
52.90 0.91 17.19 2.62 7.00 0.18 5.25 9.24 2.63 0.36 0.28 1.09 99.65 0.05 3.80 266.59 – 46.87 0.40 24.00 29.70 20.58 10.77 361.33 3.03 9.49 1.28 7.08 2.30 0.80 3.38 0.55 3.86 0.85 2.53 0.36 2.48 0.37 1.07
60.94 0.68 16.68 2.92 4.27 0.16 3.29 6.89 2.75 0.90 0.072 0.57 100.09 0.05 16.37 356.61 241.35 90.66 0.61 23.83 17.98 19.26 4.29 257.58 4.88 13.63 1.93 9.57 2.73 0.77 3.62 0.58 4.05 0.87 2.61 0.38 2.77 0.43 2.35
61.90 0.51 17.40 2.53 3.08 0.19 2.85 6.34 3.00 0.32 0.19 1.34 99.65 0.05 25.05 533.25 390.00 101.00 1.65 17.87 11.87 36.58 6.50 108.57 10.06 23.25 2.94 12.73 2.82 0.84 3.29 0.46 3.09 0.65 1.96 0.29 2.14 0.34 2.28
Note: Samples: (1, 4) granite–porphyries, (2) basaltic andesite tuff, (3) ignimbrite, (5) trachyrhyolitic tuff, (6) trachyrhyolite, (7) trachytic tuff, (8) trachytic tufflava, (9, 13) andesite, (10, 11) basalt, (12) clastic andesite lava. Age complexes: (1) Late Cretaceous, (2–4) Eocene, (5−8) Late Oligocene, (9) Miocene, (10–13) Pliocene–Pleistocene, (−) no data. OCEANOLOGY
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MAGMATISM OF THE SUBMARINE VITYAZ RIDGE 1000 100
10
1 V
Cr
Co
Ni
Cu
Zn
Pb
Y
Mo
Zr
0.1
247
LV 37-14-4 LV 37-17-2 LV 37-25-1 LV 37-17-11 LV 37-17-13 LV 37-19-2 LV 37-19-3 LV 37-37-6 LV 37-22-1 LV 37-23-7 LV 37-23-11 LV 37-24-2
Fig. 4. Diagram illustrating the distribution of trace elements in the magmatic rocks from the Vityaz Ridge. The sample numbers are the same as in Table 2. Age complexes: Late Oligocene (samples LV37-17-13, LV37-23-7, LV37-23-11, LV37-24-2); Eocene (sample LV37-14-4); Pliocene–Pleistocene (samples LV37-17-2, LV37-19-2, LV37-22-1, LV37-25-1).
Rock/chondrite
1000 LV 37-17-13 LV 37-23-7 LV 37-23-11 LV 37-24-2 LV 37-14-4 LV 37-17-2 LV 37-19-2 LV 37-22-1 LV 37-25-1 LV 37-37-6 LV 37-17-11 LV 37-19-3
100
10
1
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf
Fig. 5. Diagram illustrating the REE distribution in the magmatic rocks from the Vityaz Ridge. The sample numbers are the same as in Table 2. Age complexes: Late Oligocene (samples LV37-17-13, LV37-23-7, LV37-23-11, LV37-24-2); Eocene (sample LV37-14-4); Pliocene–Pleistocene (samples LV37-17-2, LV37-19-2, LV37-22-1, LV37-25-1).
and elevated LREE concentrations as well, although their values are lower as compared with the Late Oligocene complex. Therefore, the Pliocene–Pleistocene volcanites are characterized by a gentler REE distribution trend (Fig. 5) and lower La/Sm and La/Yb values (0.82–2.23 and 0.83–3.19, respectively). The petrogeochemical properties of Pliocene–Pleistocene volcanites from the Vityaz Ridge indicate their belonging to the calc-alkaline series of island arcs and similarity with the volcanites from the frontal zone of the Kuril–Kamchatka Arc. Granite–porphyries constitute likely magmatic bodies intruding into the late Cretaceous and Eocene volcanogenic complexes. According to their chemical composition, they correspond to subalkali leucogranites with the sum alkali contents exceeding 8%. According to the K2O content and its ratio with SiO2, they belong to the volcano–plutonic association of potassic rocks and are characterized by high K/Rb values. Their data OCEANOLOGY
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points in the K/Rb–Rb diagram fall into the field of subvolcanic granitoids of the andesite–dacite–rhyolite formation together with the Late Cretaceous granites of the Sea of Okhotsk [7]. The granites are enriched in LREE, which makes them similar to the Eocene and Late Oligocene volcanites, as well as exhibit the presence of an Eu minimum inherent to most of these volcanites (Fig. 5). In terms of the content and distribution patterns of the main trace elements, they are analogous to volcanites. The granites are slightly different from the latter by higher Lm/Sm and La/Yb values (4.03−4.28 and 9.29–9.63, respectively) and lower Ni concentrations (Fig. 4). DISCUSSION The geological studies helped to reveal several different-age volcanogenic complexes, which reflect the evolution stages of the Vityaz Ridge.
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LELIKOV et al.
The following data provided grounds for recognizing the Late Cretaceous volcanic complex. By the typical set of rocks and their mineral composition, the volcanites dredged from the Vityaz Ridge are similar to the rocks of the Late Cretaceous dacite–rhyolite complex from the rises of the central Sea of Okhotsk and belong to the products of marginal continental volcanic belts [4]. They are elements of the Late Cretaceous–Early Paleogene volcanogenic–terrigenous sequence that constitutes the basement of the ridge. The terrigenous component of this sequence is represented by siliceous rocks and silty sandstones. Tuffaceous–siliceous rocks from station 14 yielded Late Cretaceous–Early Paleogene radiolarians (determinations by O.L. Smirnova, Pacific Oceanological Institute). By their composition, the rocks are similar to the Upper Cretaceous Lesser Kuril Formation of Shikotan Island [9]. In addition, the radioisotopic data on shallow subvolcanic granites enclosed in this complex provide additional evidence for their age (Table 1). Nevertheless, further radioisotopic studies of volcanogenic rocks are needed for the eventual solution of the problem related to their stratigraphic position in the section. The volcanites of the Eocene and Miocene complexes are characterized by restricted distributions and are distinguished based on radioisotopic data. Granites likely form small intrusions in the volcano–plutonic complexes and are similar to volcanites with respect to their geochemical characteristics. The Late Oligocene volcanic complex is represented by subalkali rocks: trachytes, trachyrhyolites, and their tuffs, which are similar in their geochemical specialization to the Late Oligocene–Early Miocene trachyandesites of the Sea of Japan [6]. Similar to the Late Cretaceous volcanites, they are constituents of terrigenous–volcanogenic complexes with the terrigenous component represented by polymictic, greywacke, and tuffaceous sandstones; silty argillites; and conglomerates. They are characterized by the massive structure, prevalence of coarse- to medium-grained inequigranular varieties, low disintegration degree, poor sorting, low roundness degree of detrital material, occurrence of plant remains, and red coloration of conglomerates. All these features provide grounds to interpret them as having been formed in shallow-water and subaerial sedimentation settings with an insignificant transport of detrital material from the provenances and low accumulation rates. Silty argillites from station 17 yielded the Late Oligocene spores-and-pollen complex (determination by N.K. Vagina, Pacific Oceanological Institute). The occurrences of ignimbrites and sintered tuffs in the Eocene and Late Oligocene volcanic complexes are also indicative of their formation in subaerial settings. The Pliocene–Pleistocene volcanites were found at most of the dredging stations in the Vityaz and Diana areas. In the latter area, dredging brought andesites dated at 1.6 My B.P. The material obtained, combined
with the data on the bottom relief and anomalous magnetic field, implies a volcanic origin of these mountains. Until recently, only three submarine volcanoes were known in the frontal zone of the Kuril Arc located on both sides of the Bussol Strait [1] (Fig. 1). Based on the distribution of on-land volcanoes, it is assumed that the volcanic front extends along the southeastern boundary of the Kuril island arc. The submarine volcanoes of the Diana area are located approximately 50 km seaward from the volcanic front. Such a remoteness of the submarine volcanic edifices from the volcanic front is probably explained by the peculiar structure of this island arc segment. It was established [5] that this area is crossed by numerous faults, which indicates its formation under an extensional regime. Precisely these faults serve as feeding channels for the volcanic edifices of the Diana area. The development of the Pliocene–Pleistocene complex in the Vityaz area is debatable. No morphological features similar to the morphostructures in the Diana area, which can be interpreted as young volcanic edifices, are established in the area in question. The basalts attributed to this complex are dredged from slopes of rises together with older rock varieties. These basalts are similar to the volcanites from the Diana area and substantially differ from the intermediate and acid tuffs developed in other age complexes. This served a basis for attributing the basalts and andesites from the Vityaz area to the Pliocene–Pleistocene complex. CONCLUSIONS During cruise 37 of R/V Akademik M.A. Lavrent’ev, dredging was carried out on seamounts southeast of Simushir Island (Diana area) and on the submarine Vityaz Ridge (Vityaz and Bussol areas). These studies revealed a young volcanic zone in the Diana area, the formation of which is explained by the particular structure of this segment of the Kuril island arc. Dredging on the Vityaz Ridge provided volcanic rocks belonging to several complexes. The Late Cretaceous volcanites and intrusive rocks form a single volcano–plutonic complex that constitutes the geological basement of this structure. Cenozoic volcanites belong to the Eocene, Late Oligocene, Miocene, and Pliocene– Pleistocene complexes. Discrimination of the latter complex in the Vityaz Ridge is problematic and needs further studies. All the igneous rocks examined are characterized by a number of common geochemical properties and classed with the calc-alkali series of island arcs, while the Pliocene–Pleistocene rocks are similar to the volcanites from the frontal zone of the Kuril Arc. Each of these complexes reflects an independent stage in the evolution of the Vityaz Ridge and coincides with similar stages in other segments of the continent–ocean transition zone, which indicates the unity of the tectonic processes that form this zone. OCEANOLOGY
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MAGMATISM OF THE SUBMARINE VITYAZ RIDGE
ACKNOWLEDGMENTS The program was supported by the Ministry of Science of the Russian Federation. This study was supported by the Russian Foundation for Basic Research (project no. 06-05-96108), by the Far East Division of the RAS (project no. 06-Sh-A-07-258), and by the Federal Targeted Program “The World Ocean.”
4.
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7.
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8.
2. A. Yu. Antonov, “Matter Zonation of the Quaternary Volcanism of the Kuril Island Arc and New Petrogenetic Consequences,” Litosfera, No. 1, 22–44 (2006). 3. B. I. Vasil’ev, E. G. Zhil’tsov, and A. A. Suvorov, Geological Structure of the Southwestern Part of the Kuril
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5. 6.
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Island Arc–Trench System (Nauka, Moscow, 1979) [in Russian]. T. A. Emel’yanova, Volcanism of the Sea of Okhotsk (Dal’nauka, Vladivostok, 2004) [in Russian]. N. P. Laverov, S. S. Lappo, L. I. Lobkovskii, et al., “The Central Kuril Gap: Structure and Seismic Potential,” Dokl. Akad. Nauk 408 (6), 1–4 (2006). E. P. Lelikov and E. P. Terekhov, “Alkaline Volcanites of the Floor of the Sea of Japan,” Tikhookean. Geol., No. 2, 71–77 (1982). E. P. Lelikov and A. N. Malyarenko, Granitoid Magmatism of the Marginal Seas of the Pacific Ocean (Dal’nauka, Vladivostok, 1994) [in Russian]. B. G. Lutts, Geochemistry of Oceanic and Continental Magmatism (Nedra, Moscow, 1980) [in Russian]. K. F. Sergeev, Tectonics of the Kuril Island System (Nauka, Moscow, 1976) [in Russian]. R. W. Le Maitre, P. Bateman, A. Dudek, et al., A Classification of Igneous Rocks and Glossary of Terms (Blackwell, Oxford, 1989).
