Komandorsky Islands Research Articles

Uppermost Mantle Pn Velocity and Anisotropy Structures Beneath the Sakhalin–Kuril–Kamchatka Region

AbstractIn this study, we used the Pn tomography method to obtain detailed velocity and anisotropy structures of the uppermost mantle beneath Sakhalin–Kuril–Kamchatka region for improving the understanding of plate subduction, arc–arc collision, and volcanism. We found low Pn velocities beneath volcanoes and areas characterized by pronounced tectonic activity and high Pn velocities with strong anisotropy in the subducting plate. Low Pn velocity anomalies beneath southern Sakhalin connected the low‐velocity anomalies in the mantle and crust, indicating the ascent of fluid or melt, and may provide a magmatic source for the rear‐arc Rishiri volcano. In the absence of plate subduction, low‐velocity anomalies and north–south Pn anisotropy manifested beneath northern Kamchatka, revealing the lateral propagation of mantle flow beneath this northern region. We suggest that the eastern boundary of the slab window at the Kamchatka–Aleutian junction is likely to be located near the Komandorsky Islands.

Evidence of a Supershear Transition Across a Fault Stepover

AbstractSupershear earthquakes, propagating faster than the Earth's shear wave velocity, can generate strong ground motion at distances far from the ruptured fault. Despite the hazards associated with these earthquakes, the exact fault properties that govern their occurrence are not well constrained. Although early studies associated supershear ruptures with simple fault geometries, recent dynamic rupture models have revealed a supershear transition mechanism over complex fault geometries such as fault stepovers. Here we present the first observation of a supershear transition on a fault stepover system during the 2017 Mw 7.7 Komandorsky Islands earthquake. Using a high‐resolution back‐projection technique, we find that the earthquake's rupture velocity accelerates from 2.1 to 5.0 km/s between two offset faults, demonstrating the viability of a new supershear transition mechanism occurring in nature. Given the fault complexity of the Earth's transform plate boundaries, this result may improve our understanding of supershear rupture processes and their associated hazards.

Earthquake july 17, 2017, Mw = 7.8 near the Komandorsky islands and strong seismic manifestations in the western segment of Aleut island arc

The tectonic position, seismological characteristics and features of the aftershock process of the source of the strongest Near-Aleutian earthquake on July 17, 2017 on the Commander Islands with Мw = 7.8 are considered. The analysis showed that the seismic source according to the distribution of aftershock epicenters in the form of a linearly elongated narrow zone with a length of about 400 km almost completely occupied the northern slope of the Commander island elevation and was located in the Bering fault zone. It covered the whole of this seismic-generating zone up to the transverse structure to the west of the Near Islands (Attu is.). In accordance with the focal mechanisms solution and the nature of the displacements in the foci of the main shock, the strongest foreshocks and aftershocks, the shift in the source was an almost pure right-sided shift. The aftershock process of the July 17 earthquake developed quite enough inertly for an earthquake of such strength. In addition, it has two features in comparison with the aftershock processes of most of the Kuril-Kamchatka earthquakes: 1) low release of the cumulative scalar seismic moment (M0cum aft), which according to various estimates was from 0.75% to 1.0% of the seismic moment of the main shock (M0me); 2) a very slow increase in the deficit in the release of the seismic moment (M0). At the same time, the duration of the quasi-stationary phase of M0cum release in aftershocks, estimated at about ½ year and covering a significant part of the duration of the entire aftershock process of this earthquake, seems unusually long. These features of the aftershock process of the Middle Aleutian earthquake on July 17, 2017 distinguish it from the aftershock processes characteristic of most strong Kuril-Kamchatka earthquakes. In general, its source can be considered as a transform between the two Benioff zones – Aleutian and Kuril-Kamchatka, and not subduction, that is characterise the last two.

Earthquake july 17, 2017, Mw = 7.8 near the Komandorsky islands and strong seismic manifestations in the western segment of Aleut island arc

The tectonic position, seismological characteristics and features of the aftershock process of the source of the strongest Near-Aleutian earthquake on July 17, 2017 on the Commander Islands with Мw = 7.8 are considered. The analysis showed that the seismic source according to the distribution of aftershock epicenters in the form of a linearly elongated narrow zone with a length of about 400 km almost completely occupied the northern slope of the Commander island elevation and was located in the Bering fault zone. It covered the whole of this seismic-generating zone up to the transverse structure to the west of the Near Islands (Attu is.). In accordance with the focal mechanisms solution and the nature of the displacements in the foci of the main shock, the strongest foreshocks and aftershocks, the shift in the source was an almost pure right-sided shift. The aftershock process of the July 17 earthquake developed quite enough inertly for an earthquake of such strength. In addition, it has two features in comparison with the aftershock processes of most of the Kuril-Kamchatka earthquakes: 1) low release of the cumulative scalar seismic moment (M0cum aft), which according to various estimates was from 0.75% to 1.0% of the seismic moment of the main shock (M0me); 2) a very slow increase in the deficit in the release of the seismic moment (M0). At the same time, the duration of the quasi-stationary phase of M0cum release in aftershocks, estimated at about ½ year and covering a significant part of the duration of the entire aftershock process of this earthquake, seems unusually long. These features of the aftershock process of the Middle Aleutian earthquake on July 17, 2017 distinguish it from the aftershock processes characteristic of most strong Kuril-Kamchatka earthquakes. In general, its source can be considered as a transform between the two Benioff zones – Aleutian and Kuril-Kamchatka, and not subduction, that is characterise the last two.

Rupture Along 400 km of the Bering Fracture Zone in the Komandorsky Islands Earthquake (MW 7.8) of 17 July 2017

AbstractThe 17 July 2017 Komandorsky Islands MW 7.8 earthquake involved arc‐parallel right‐lateral patchy strike‐slip faulting along ~400 km of the Bering Fracture Zone (BFZ) in the westernmost Aleutian Islands back arc. The large size of the earthquake indicates that the BFZ serves regionally as the primary plate boundary extending from the Near Islands to Kamchatka, with the fore‐arc Komandorsky Sliver translating rapidly parallel to the Aleutian Trench. The slip distribution is determined by analysis of seismic, tsunami, and geodetic observations. Fault displacements of 4 to 8.5 m, mostly in the upper 15 km, but with localized extension to 20 to 30 km depth along a ~100 km long segment of the BFZ, are comparable to the possible slip deficit since the last major earthquakes in this region in 1849 and 1858, given an estimated 5.1 cm/yr rate between the Komandorsky Sliver and the Bering Plate.

Plate coupling and strain in the far western Aleutian arc modeled from GPS data

AbstractThe Aleutian and Kuril‐Kamchatka arcs meet at a triple junction of the Pacific (PAC), Bering (BER), and North American (NAM) plates. We invert GPS observations from the westernmost Aleutian (Komandorsky) Islands and Kamchatka for the fault locking depth and block motion in the far western Aleutian transform boundary. Three boundary models were considered: (1) only the Aleutian thrust fault without a trench‐normal component, (2) only a strike‐slip fault in the back arc north of the Komandorsky Islands, and (3) a rigid Komandorsky sliver bounded by the Aleutian and back‐arc faults. Observed velocities prefer Model 3, with a secular westward sliver velocity of 51 mm/a relative to NAM (two thirds of the total PAC‐NAM motion). The observed velocities are ~10% slower because of elastic strain from boundary faults. The best fitting locking depth of faults bounding the sliver is 12 km, which is similar to depths observed in diverse tectonic environments.

Contemporary Conditions and Key Trends in Development of Groups of Harbor Seals (Phoca vitulina stejnegeri) and Spotted Seals (Phoca largha) in the Bering and Medny Islands (Komandorsky Archipelago)

The present paper elaborates on the status of both harbor and spotted (largha) seal populations on the Komandorsky Islands. Local populations of these seals have doubled since the 1980s. The total population of harbor and spotted seals at both Bering and Medny Islands is now estimated to be 4000–4300 animals. Various methods of counting have been applied. A methodological approach to counting seals on the Komandorsky archipelago is described.

Paleomagnetic determination of paleolatitude and rotation of Bering Island (Komandorsky Islands) Russia: comparison with rotations in the Aleutian Islands and Kamchatka

Abstract. A paleomagnetic study was carried out on Paleogene sedimentary rocks from Bering Island, Komandorsky islands, located at the far western end of the Aleutian Island Arc. The age of these sediments has been debated at length, but the combination of magnetostratigraphy with the fossil record indicates that the base of the section is of early Eocene (approximately 55 Ma) and the top latest Eocene age. Paleomagnetic data were obtained from 260 samples from 60 individual bedding units. The combined data show a clockwise rotation R=26.3°±8.5°, F=8.1°±2.5° with respect to the North American Plate and R=38°±8.8°, F=8.7°±2.7° with respect to the Eurasian Plate. They also show a shallowing of the inclination which yields a paleolatitude of 53°, 12° south of its expected latitude. The shallowing may have a component due to compaction, but the wide variation in sampled lithologies, combined with internal consistency of the data set, would argue against the shallowing being significant. To compare these data with other Aleutian Arc data we compiled a comprehensive survey of all available data sets. Out of these we selected four islands for which the data passed basic reliability criteria, namely Umnak, Amlia, Amchitka and Medny islands. All four showed significant clockwise rotation with respect to both North American and Eurasian polar wander paths. Several mechanisms can generate the observed rotation, ranging from block rotation driven by oblique relative motion of the Pacific plate, through lateral transport along the curve of the arc, to whole-arc rotation about its eastern end. The distribution and age spread of the rotation data are insufficient to discriminate between mechanisms, but it seems likely that different mechanism may have operated at different times and in different locations.

Provenance of the Palaeocene‐Eocene clastic rocks of the Komandorsky Islands

The Palaeocene–Eocene sequence on the Komandorsky Islands is represented by sediments and minor volcanics with a total thickness of more than 3000 m. Sandstone, siltstone, mudstone, siliceous rocks and conglomerate, which have accumulated in the upper and middle parts of a deep‐water fan, prevail. All the debris was delivered from the north‐east, from the side of the contemporary Komandorsky basin in the Bering Sea. Products of volcanic denudation and fresh tephra dominate its composition. However, at some levels the sandstone contains fragments of jasper, quartzite, slate, schist, gabbro and granite as well as non‐volcanic quartz along with a volcanic component. The heavy minerals fraction of the sandstone contains considerable quantities of apatite, zircon, garnet and chromite, as well as pyroxenes, amphiboles and magnetite. The chemical composition of the garnet is specific to metamorphic rocks. A significant admixture of chromite is indicative of denudation from an ophiolite complex. The folded and partly metamorphosed pre‐Palaeogenic rocks were a source of these fragments. Their most likely source terrane was the Shirshov‐Bowers chain (Cretaceous palaeoarc). The Komandorsky block originally was the forearc part of the Aleutian arc where the latter was superimposed on the Shirshov‐Bauers chain. A subsequent north‐west displacement of forearc structures, in response to the transform fault at the boundary between the Pacific and North American plates, could have resulted in the separation of the Komandorsky block from its Early Palaeogene debris source area.

VOLCANOGENIC AND VOLCANICLASTIC RESERVOIR ROCKS IN MESOZOIC‐CENOZOIC ISLAND ARCS: EXAMPLES FROM THE CAUCASUS AND THE NW PACIFIC

Subduction of the Tethys oceanic plate beneath the Lesser Caucasus island are in the Late Creataceous — Eocene produced conditions favourable for the generation and accumulation of hydrocarbons. Subduction of crust in the Transcaucasus Massif led to the formation of various types of trap. Also, geothermal gradients here were high, resulting in the generation of hydrocarbons in shallow‐water sediments on the margins of the Massif, and their accumulation in both sedimentary and volcaniclastic reservoirs (e.g. in the Samgori‐Patardzeuli and Muradkhanly fields).The geodynamic setting of the NW margins of the Pacific Ocean was similar in the Neogene to that of the Transcaucasus Massif. Oceanic crust was subducted during the Oligo‐Miocene, and a series of inter‐are rifts were formed. The principal oilfields of Japan, where accumulations are resrvoired in volcaniclastic strata (Neogene‐Pleistocene) are located here. A possible analogue is the rift located in the southern East Kuril Basin, where the occurrence of petroleum has been inferred. Lithological studies of the Komandorsky Islands, eastern Kamchatka, the Kuril Islands and western Sakhalin indicate that the distribution of the reservoirs depends on the stage of evolution of the rifts and adjacent island arcs.

Magnesian andesite in the western Aleutian Komandorsky region: Implications for slab melting and processes in the mantle wedge

Research Article| May 01, 1995 Magnesian andesite in the western Aleutian Komandorsky region: Implications for slab melting and processes in the mantle wedge G. M. Yogodzinski; G. M. Yogodzinski 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14850 Search for other works by this author on: GSW Google Scholar R. W. Kay; R. W. Kay 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14850 Search for other works by this author on: GSW Google Scholar O. N. Volynets; O. N. Volynets 2Institute of Volcanic Geology and Geochemistry, Petropavlovsk, Kamchatka 683006, Russia Search for other works by this author on: GSW Google Scholar A. V. Koloskov; A. V. Koloskov 2Institute of Volcanic Geology and Geochemistry, Petropavlovsk, Kamchatka 683006, Russia Search for other works by this author on: GSW Google Scholar S. M. Kay S. M. Kay 3Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14850 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1995) 107 (5): 505–519. https://doi.org/10.1130/0016-7606(1995)107<0505:MAITWA>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G. M. Yogodzinski, R. W. Kay, O. N. Volynets, A. V. Koloskov, S. M. Kay; Magnesian andesite in the western Aleutian Komandorsky region: Implications for slab melting and processes in the mantle wedge. GSA Bulletin 1995;; 107 (5): 505–519. doi: https://doi.org/10.1130/0016-7606(1995)107<0505:MAITWA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The role of the subducting lithospheric slab in the genesis of mantle-derived (primitive) magmas is investigated through a study of volcanic rocks formed in the tectonically strike-slip–dominated western Aleutian arc. Two types of chemically and petrologically distinctive primitive andesites have been found among the Miocene–late Pleistocene–age volcanic rocks in the western Aleutians. These are termed the “Adak-type” and “Piip-type” magnesian andesites. Trace element and isotopic characteristics indicate that Adak-type magnesian andesites (adakites) formed principally as small percentage melts of the basaltic portion of the subducting oceanic crust, leaving a clinopyroxene-garnet-rutile residual mineralogy. The resulting slab melt signature (high La/Yb, Sr) distinguishes Adak-type magnesian andesites from all other Aleutian volcanic rocks. Primitive characteristics (high Mg#, Cr, Ni) and intermediate compositions (∼59% SiO2) of Adak-type magnesian andesites were acquired by interaction with peridotite and/or basalt in the mantle wedge. The absence of olivine phenocrysts from Adak-type magnesian andesites indicates that they were not equilibrated with peridotite and so are unlike Piip-type magnesian andesites, which appear to have equilibrated under low pressure and hydrous conditions in the subarc mantle. Piip-type magnesian andesites also contain a slab melt component, but reaction-equilibration with peridotite has lowered La/Yb and Sr to levels like those of common Aleutian volcanic rocks.Miocene-age calc-alkaline rocks of the Komandorsky Islands have chemical characteristics transitional between those of Adak-type magnesian andesites and common Aleutian volcanic rocks from the central and eastern arc. In a source mixture of depleted mantle wedge, slab melt, and sediment, the Komandorsky rocks have a relatively large contribution from the slab melt endmember. The strong slab melt signature among western Aleutian rocks is attributed to highly oblique convergence that produced a slow subduction path into the subarc mantle. Geochemically, the slab melt provided a high Sr, La/Yb, La/Ta, and low Ti/Hf endmember to the western Aleutian source mixture. The enhanced role for slab melting in the western Aleutians may be like that predicted for Archean systems and for modern systems where the subduction zone is warm. In this regard, Adak-type magnesian andesites are probably the appropriate analog to sanukitoids and other primitive andesitic rocks of Archean age. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleomagnetism of Paleogene rocks of the Central—East Kamchatka and Komanorsky Islands: tectonic implications

Paleomagnetic investigation of Paleocene—Eocene to Miocene rocks has been carried out at five localities in the Eastern Kamchatka and Komandorsky Islands. After thermal and af cleanings, consistent paleomagnetic directions were isolated for a number of formations. Data from the Kronotsky Peninsula and Medny Island passed both the fold and reversal tests and thus can be considered as reliable; other results are of lower quality. All the results were derived from sedimentary rocks, and thus the corresponding paleolatitudes may be biased due to inclination errors. A limited collection of basalts yielded inclination values systematically lower than those in sediments; this anomaly was tentatively explained by shape anisotropy. The correctness of paleolatitude estimations was thus left unproved. Several models of the Northern Pacific tectonic evolution were suggested and analyzed, but the authors failed to find a model that was fully compatible with paleomagnetic, kinematic and geological data

Magmatism of the westernmost (Komandorsky) segment of the Aleutian Island Arc

Four magmatic associations are distinguished in the westernmost (Komandorsky) segment of the Aleutian island arc: basalt-plagiorhyolite (45-28 Ma), trachybasalt-teschenite (27-16 Ma), diorite-granitoid (12.5–8.5 Ma) and dacite-rhyolite (0.7-0 Ma). The latter association is represented by the lavas of a recently discovered active submarine volcano (Piip volcano) about 40 km north of the Komandorsky Islands and 700 km west of the Quaternary center on Buldir Is. Detailed petrogeochemical data, including REE and 143Nd 144Nd and 87Sr 86Sr isotopic ratios, show that the parental melts of the Komandorsky Is. were of mantle origin and their sources remained isotopically homogeneous during the whole geological history of the Aleutian arc. 10Be concentrations in lavas of the Piip volcano (2.7 × 10 6 at/g) indicate subduction-related incorporation of young pelagic sediments in their magmatic sources or contamination of ascending melts by non-solidified sedimentary material directly beneath the volcano. The Komandorsky segment of the Aleutian arc evolved from a depleted arc tholeiitic series, through a markedly alkaline series to later calc-alkaline andesites and dacites, and finally to late-stage calc-alkaline dacites and rhyodacites erupted inboard of the older volcanic centers.

Seismicity and tectonics of the far Western Aleutian Islands

Study of focal mechanisms of earthquakes in the Near and Komandorsky Islands indicate that there are several distinct zones of tectonic activity. South of the Near Islands, normal faulting occurs in the trench east of 172°E and low-angle thrusting dominates the Aleutian ridge. Mechanisms indicate underthrusting as far west as Mednyy Island with strike-slip faulting restricted to the south and west of Beringa Island. A zone of northeast striking left-lateral faulting near 1645.°E is proposed to separate the Aleutian Ridge from Kamchatka Peninsula. This motion, as well as faulting north of the Komandorsky Islands, may be related to the existance of a buffer plate comprising the Aleutian Ridge in the Komandorsky Islands. Active subduction terminates near 173°E and the faulting north of the Komandorsky Islands may, in part, be due to the bouyancy of a remnant slab. Depth phase modelling indicates bulletin-reported depths are overestimated due to a misidentification of depth phases.

Summit Basins of Aleutian Ridge, North Pacific

The crestal region of the 2,200-km-long (and mostly submerged) Aleutian Ridge is commonly an irregular tableland or summit platform. Rising above this platform, which generally lies at a depth shallower than about 200 m, are the Aleutian and Komandorsky Islands. Deeper areas of the summit platform include elongate and roughly rectangular shaped basins. Three of the larger summit basins, Amukta and Amlia basins and Pratt depression, lie along the northern edge of the summit platform and are aligned geomorphically with the loci of late Cenozoic volcanic centers. These basins are underlain by thick, slightly deformed sequences of late Cenozoic beds. Amukta basin (171.7°W) and neighboring Amlia (173°W) basin have a combined area of about 4,700 sq km (1,800 sq mi), and their floors are covered by about 1,000 m of water. They are underlain by an estimated 4,000 m of gently folded late Miocene through Holocene beds. This estimate is based on interpretations of magnetic, gravimetric, and seismic-reflection data. The deposits are dislocated along normal and high-angle reverse faults (growth types), and deformation appears to be most severe adjacent to a prominent normal fault bordering the northern sides of these basins. The floor of Pratt depression (179°E), approximately 850 m deep, also may be underlain by a thick sequence of late Cenozoic beds. A major fault scarp borders this basin on the south. The summit basins are grabens or half-grabens that began to form near the end of the Miocene, but perhaps not until the Pliocene. Andesitic volcanism accompanied their formation, and, we suspect, the basins may have subsided in response to a slight distension of the ridge crest caused by the generation of deep-seated magmas. Contemporaneous with subsidence and faulting, the basins filled with erosional debris derived from the adjacent ridge crest. The crest is underlain by deformed, altered, and plutonically intruded sedimentary and igneous rocks of Eocene through early Miocene age. Volcanic ash and diatomaceous debris are probably important minor constituents of the late Cenozoic basin fills. Seismic-reflection records suggest that much of the detritus reaching the central areas of t e basins was transported there by turbidity currents. Gaps or outlets in the northern walls of Amlia and Amukta basins allowed some of this debris, especially that of Pleistocene age, to bypass the basin and excavate large submarine canyons in thick late Cenozoic beds underlying the ridge's northern insular slope. In contrast, Pratt depression, which does not have outlets, may include a thicker sequence of Pleistocene strata.