Deep-water Trenches Research Articles

Coseismic and Tectonic Time-Scale Deformations of an Island Arc Based on Studies of East Coast of Kamchatka Peninsula (Far East, Russia)

Geologic structure of the late Holocene accumulative marine terrace on the coast of Kamchatka Bay (Kamchatka Peninsula) has been studied. The ages and relative hypsometric position of beach ridges composing the terrace allowed us to identify two types of vertical movements of the coast: periodic fast (coseismic) and slow time-scale uplift or subsidence. Large-amplitude vertical coseismic movements (up to 1‒2 meters) occur on average once in about 1200‒1300 years, and slow movements occur at an average rate from a fraction of a millimeter to about 2 mm per year. Coseismic motions represent relaxation of elastic deformations accumulated during the interseismic interval of the seismic cycle, neither exceed them nor accumulate. Slow motions set the general trend of vertical deformations of the coast. It is assumed that the subsiding central parts of the eastern bays of Kamchatka Peninsula (Avachinsky, Kronotsky and Kamchatsky) and depressions between the eastern peninsulas (Kronotsky, Shipunsky) and the main massif of Kamchatka form an arc-parallel extension zone, which is nearest to the deep-water trench, and that extension is caused by the migration of the subducted part of the Pacific plate toward the Pacific Ocean. Under the eastern Shipunsky and Kronotsky peninsulas, the arc-normal extension of the earth’s crust of the Kamchatka segment of the Kuril-Kamchatka island arc is replaced by a zone of transverse compression.

ПРОДОЛЬНЫЕ СДВИГИ В ОСТРОВНОЙ ДУГЕ ПРИ НОРМАЛЬНОМ ПОДДВИГЕ ОКЕАНИЧЕСКОЙ ПЛИТЫ: ПРИМЕР КАМЧАТКИ

Crustal deformation in Kamchatka since the Middle Pleistocene is driven by two processes: transverse extension as a result of its eastern part displacement towards the ocean following the submerged part of the oceanic plate, and transverse shortening just north of the subduction zone as the Komandor block of the Aleutian arc gets closer to Kamchatka. The areas of differently directed movements and deformations of Kamchatka are separated by the left-lateral horizontal flexure appearing in plan as curved uplifts of the Eastern Range, the deep water trench, and consequently, the axis of the East volcanic belt. Kinematically, the flexure replaces the expected transverse left-lateral strike-slip fault between the two differently deformed parts of Kamchatka. The revealed right-lateral displacements along the longitudinal faults in the northern part of the uplift of the Eastern Range in Kamchatka result from bedding-plane slip in the flexure limb. The high alluvial terrace of the Kamchatka River, displaced landforms, and faulted layers of the soil-pyroclastic cover were dated by the tephrochronological method. Age determinations imply that the recurrence of displacements along the faults of the flexure is about once every 3-5 thousand years, and the average rate of lateral displacements during the second half of the Holocene is about 1 mm per year. Comparison of the fault movement rates and the maximum value of the accumulated lateral displacement of the Kamchatka River valley suggest that horizontal movements began no later than the second half of the Middle Pleistocene. This also means that the Kamchatka River valley already existed at that time, and its antecedent part was formed when down-cutting into the bedrock of the uplifting Eastern Range. The total amount of displacement along the faults of the flexure since the second half of the Middle Pleistocene is estimated at about 1 km. On the whole, the results suggest the possibility of lateral movements along longitudinal faults in an island arc with the oceanic plate direction being normal to it.

Парамуширское землетрясение 25 марта 2020 г. Mw = 7.4

The strong Mw = 7.4 earthquake occurred on March 25, 2020 in the region of Northern Kuril Islands, with its epicenter on the ocean side of the Kuril-Kamchatka deep-water trench, to the east from its axis. The earthquake was felt on all the Kuril Islands, South and East Kamchatka, the maximum shaking was recorded in Severo-Kurilsk with intensity I = VI–VII. Distinct tsunami wave was also registered. In the article, this earthquake and its tectonic position are discussed in the context of the seismicity of the Kuril-Kamchatka arc. The actions of duty shifts in earthquake processing are described, and a detailed description of macroseismic effects is given. The results of the analysis of peak ground motion amplitudes, focal mechanisms and models of the source, tsunami propagation features are also shown. Coseismic displacements revealed by GNSS observation data are presented and compared with model data. Peculiarities and stages of the aftershock process are discussed and the size of the source area is estimated.

Wallacean and Melanesian Islands Promote Higher Rates of Diversification within the Global Passerine Radiation Corvides.

The complex island archipelagoes of Wallacea and Melanesia have provided empirical data behind integral theories in evolutionary biology, including allopatric speciation and island biogeography. Yet, questions regarding the relative impact of the layered biogeographic barriers, such as deep-water trenches and isolated island systems, on faunal diversification remain underexplored. One such barrier is Wallace's Line, a significant biogeographic boundary that largely separates Australian and Asian biodiversity. To assess the relative roles of biogeographic barriers-specifically isolated island systems and Wallace's Line-we investigated the tempo and mode of diversification in a diverse avian radiation, Corvides (Crows and Jays, Birds-of-paradise, Vangas, and allies). We combined a genus-level data set of thousands of ultraconserved elements (UCEs) and a species-level, 12-gene Sanger sequence matrix to produce a well-resolved supermatrix tree that we leveraged to explore the group's historical biogeography and the effects of the biogeographic barriers on their macroevolutionary dynamics. The tree is well resolved and differs substantially from what has been used extensively for past comparative analyses within this group. We confirmed that Corvides, and its major constituent clades, arose in Australia and that a burst of dispersals west across Wallace's Line occurred after the uplift of Wallacea during the mid-Miocene. We found that dispersal across this biogeographic barrier was generally rare, though westward dispersals were two times more frequent than eastward dispersals. Wallacea's central position between Sundaland and Sahul no doubt acted as a bridge for island-hopping dispersal out of Australia, across Wallace's Line, to colonize the rest of Earth. In addition, we found that the complex island archipelagoes east of Wallace's Line harbor the highest rates of net diversification and are a substantial source of colonists to continental systems on both sides of this biogeographic barrier. Our results support emerging evidence that island systems, particularly the geologically complex archipelagoes of the Indo-pacific, are drivers of species diversification. [Historical biogeography; island biogeography; Melanesia; molecular phylogenetics; state-dependent diversification and extinction.].

A New, Morphologically Cryptic Species of Fanged Frog, Genus Limnonectes (Amphibia: Anura: Dicroglossidae), from Mindoro Island, Central Philippines

We describe a new species of fanged frog (genus Limnonectes) from Mindoro and Semirara Islands, of the Mindoro Pleistocene Aggregate Island Complex, of the central Philippines. Although morphologically indistinguishable from its closest relative, Limnonectes acanthi, of the Palawan faunal region, the two species can be readily diagnosed on the basis of spectral (dominant frequency) and temporal (pulse number and structure) properties of their advertisement calls, and their allopatric insular geographic ranges on permanently separate geological platforms which have not been connected by dry land in the recent geological past—all of which we interpret as congruent and independent lines of evidence supporting our recognition of two independently evolving evolutionary lineages (species). Ribosomal RNA mitochondrial gene sequences were used to provide genetic identification of specimens and estimate phylogenetic relationships; genetic divergences between Palawan and Mindoro faunal regions exceed those estimated among other, uncontroversial, phenotypically distinct Philippine species with equivalent levels of allopatry and biogeographic isolation. The recognition of the new species further emphasizes the degree to which even well-studied Philippine landmasses still harbor unrecognized biodiversity, and suggests that other widespread Philippine fanged frogs should be scrutinized for non-traditional diagnostic character differences (mate-recognition signal divergence, ecological differences, larval characteristics, life-history trait variation), especially when their geographic ranges span the archipelago's permanent, deep-water trenches, which define its well-characterized Pleistocene Aggregate Island Complexes.

FPGA Based Tsunami Wave Propagation Calculator

The authors continue to use hardware acceleration to calculate tsunami wave propagation in a few seconds at modern PC. The goal of this work is to develop original implementation the FPGA-based algorithm for nested-grids computations of tsunami wave propagation. The FPGA-based Calculator, for regular grid has been proposed and numerically tested earlier. Use of the nested grid approach makes it possible to calculate wave propagation almost until the shore line. Numerical tests are based on the real digital bathymetry at southern part of Japan. Mesh step variation of the gird is from 180 m to just 7 m. Realistic shape of the initial sea surface displacement at tsunami source was used. The detailed distribution of wave height maxima around and inside the Onahama port have been issued as a result of tsunami generated by a model source located along the Japan deep-water trench. The superfast FPGA calculator provides an opportunity to obtain the calculated wave parameters inside ports and harbours even before arrival of tsunami wave.

Геологическое развитие северной части Срединно-Курильского прогиба по данным сейсмофациального анализа

The model of geological evolution of an interarc basin, which is the north-east ending of Mid Kuril trough located on the continental slope of Kuril-Kamchatka trench, was constructed. Seismic facies analysis was first applied to define sedimentation conditions in a deep water trench. The analysis was based on the 2D CDP reflection seismic data obtained by Dalmorneftegeophysica JSC in 2014. According to the modeling results, the basin began to form in the Late Cretaceous and passed several stages. Initial subsidence of a local crust area of the incipient basin changed over to its further separation from the adjacent waters of the Sea of Okhotsk and Pacific Ocean by various volcanic formations framing its contour. The basin waters and the Pacific Ocean waters merged as a result of subsidence and submersion of volcanic structures on the east basin framing at the final stage during the Oligocene-Middle Miocene. This subsidence is directly related to the global processes associated with Kuril-Kamchatka ocean trench appearance such as inherent crust subsidence along valley bottom line accompanied by increase in inclination angle of its flanks. It was concluded that the trench origination time approximately corresponds to the Oligocene-Middle Miocene boundary.

Insights Into Insular Isolation of the Bull Shark, Carcharhinus leucas (Müller and Henle, 1839), in Fijian Waters

The bull shark (Carcharhinus leucas) is a large, mobile, circumglobally distributed high trophic level predator that inhabits a variety of remote islands and continental coastal habitats, including freshwater environments. Here, we hypothesize that the barriers to dispersal created by large oceanic expanses and deep-water trenches result in a heterogeneous distribution of the neutral genetic diversity between island bull shark populations compared to populations sampled in continental locations connected through continuous coastlines of continental shelves. We analyzed 1,494 high-quality neutral single nucleotide polymorphism (SNP) markers in 215 individual bull sharks from widespread locations across the Indian and Pacific Oceans (South Africa, Indonesia, Western Australia, Papua New Guinea, eastern Australia, New Caledonia, and Fiji). Genomic analyses revealed partitioning between remote insular and continental populations, with the Fiji population being genetically different from all other locations sampled (FST = 0.034–0.044, P < 0.001), and New Caledonia showing marginal isolation (FST = 0.016–0.024, P < 0.001; albeit based on a small sample size) from most sampled sites. Discriminant analysis of principal components (DAPC) identified samples from Fiji as a distinct cluster with all other sites clustering together. Genetic structure analyses (Admixture, fastStructure and AssignPOP) further supported the genetic isolation of bull sharks from Fiji, with the analyses in agreement. The observed differentiation in bull sharks from Fiji makes this site of special interest, as it indicates a lack of migration through dispersal across deep-water trenches and large ocean expanses.

Фациальный состав, геохимические особенности и геодинамические обстановки образования позднеэмсских островодужных комплексов зоны Главного Уральского разлома на Южном Урале

The facial and geochemical peculiarities of the Late Emsian island arc complexes of the Main Urals Fault Zone (Southern Urals) are considered. The results of geodynamic reconstructions are given. It was shown that the rock composition of the complexes formed in three geodynamic settings: 1) on the island arc slope of the deep-water trench, 2) within the frontal island arc, and 3) in the junction zone of the northern edge of the frontal island arc and back-arc basin. The facies of the island arc slope include serpentinite-clastic edaphogenic breccias containing Co-Cu-massive sulfide mineralization and polymictic olistostrome. Volcanogenic strata and intrusive formations represent the frontal arc. Low-Ti magmatites belonging mainly to the tholeiitic and boninitic series and having a metallogenic specialization for massive sulfide mineralization dominate in the southern areas of the suture zone. Moderate-Ti magmatites of the tholeiitic composition, productive on Au-Cu-porphyry mineralization, are distributed in the northern regions. A gold-bearing volcano-intrusive association has formed in the junction zone of the northern edge of the frontal island arc and back-arc basin, where moderate-Ti rocks of tholeiitic and transitional from tholeiitic to calc-alkaline composition dominate. It is assumed that the differences in the geochemical characteristics and metallogenic specialization of the Late Emsian magmatites are associated with the changes in the geodynamic conditions of magma formation and ore genesis along and across the strike of the island arc system.

Geochemical characteristics of precious metal-bearing carbonaceous sequences from the eastern Bureya Massif

This paper reports the geochemical characteristics of PGE- and Au-bearing carbonaceous shales of the Sutyr and Kimkan sequences from the eastern Bureya Massif in the Russian Far East. The weakly altered shales are chemically close to the average upper crustal shale (NASC) but differ in the lower contents of iron, manganese, magnesium, phosphorus, calcium, and REE. According to the discrminant diagrams, these sediments are similar to the modern sediments accumulated under the influence of the continental terrigenous runoff, suprasubduction volcanism, and seawaters, which suggest their relation either with the deep-water trench near the active continental margin or with the central part of the marginal sea. The iron-rich sedimentary rocks of the Kimkan Sequence, including the Kimkan iron ore, are characterized by a positive Eu anomaly, which probably indicates their rift origin. The superimposed hydrothermal alterations of the Sutyr Sequence, including sericitization, sulfidization, and formation of quartz veinlets, were accompanied by the removal of silica and the input of potassium, LREE, and MREE with the formation of a well expressed Eu anomaly. The rocks from the weakly altered to metalliferous sediments of the Kimkan Sequence show a decrease in alkalis and especially in potassium. The carbon isotope composition of the Sutyr shales corresponds to that of the biogenic carbon (δ13CVPDB from −20.7 to −23.7‰). The shales of the Kimkan Sequence have a heavier carbon isotope composition (δ13CVPDB from −15.6 to −19.1‰), which may indicate either partial carbon influx from an endogenous source or its formation during decarbonatization in the presence of iron.

Petrochemical characteristics of carbonaceous shales in the eastern Bureya massif and their precious-metal mineralization

Some geological, petrochemical, and geochemical characteristics of carbonaceous shales as a new unconventional natural source of gold and PGE are considered by the example of the Kimkan and Sutyr’ units of the Bureya massif (southern Far East, Russia). It is shown that shales of the units belong to the terrigenous-carbonaceous and siliceous-carbonaceous formations. They accumulated in deep-water trenches, and the active continental margin was probably their main provenance. The carbonaceous terrigenous-sedimentary units and precious-metalores in them show specific petrochemical characteristics different for complexes with predominantly PGE and gold mineralization. According to these characteristics, carbonaceous complexes with high Fe contents, low total contents of alkalies, and high K/Na ratios are promising for PGE-rich ores. Gold ores are usually localized in black-shale strata with high total contents of alkalies and low K/Na. In this respect, the shales and Fe-ores of the Kimkan unit obviously contain high-PGE mineralization, while the rocks of the Sutyr’ unit can bear gold deposits. We assume that the PGE mineralization is genetically related to the formation and transformation of carbonaceous rocks. At the same time, most of gold in the carbonaceous shales is native and is not related to carbon; it is present in mineral assemblages resulted from superimposed sulfidization and silicification.

Oil and gas potential of continental margins of the Pacific Ocean

Oil and gas basins (OGB) of active and transform margins of the Pacific Ocean are discussed. Their western and eastern parts differ substantially in the evolution, tectonic pattern, and scope of resources. In the west, marginal seas incorporated into the Cenozoic geodynamic system of deep-water basins (marginal seas) and conjugate island arcs exhibit a greater oil and gas potential (hereafter, petroleum potential) as compared to the eastern margin bounded by a deep-water trench and transformed into the framing with OGBs only in separate sectors. The abundance of siliceous rocks influenced the formation and accumulation of oil and gas in the Pacific region. The most part of hydrocarbon accumulations is related to organogenic edifices and channels of shelf fans. Oil and gas fields confined to fans on slopes of deep-water troughs of active and transform margins are also known. Proceeding from the global practice, significant petroleum potential in Russia is associated with back-arc seas of the Pacific. The poorly studied deep-water basins on slopes are worthy of special attention.

Microseismicity of the frontal Hellenic arc according to OBS observations

Five ocean bottom seismographs (OBS) of the pop-up and tethered types were installed southeast of the island of Crete at depth ranging from 1700 to 4000 m, and worked continuously for one week (July 2–9, 1988). Some one thousand microearthquakes with local magnitude M L from approximately 0 to 1.9 were registered. A total of 105 quakes were recorded by three or more instruments. Foci of these microearthquakes in the earth's crust and upper mantle are concentrated off the eastern flank of Crete along the contact between two blocks of the Hellenic arc. The en-echelon arrangement of the Pliny and Strabo deep-water trenches to the south of Crete is accompanied by a twofold Benioff zone. The seismic zones dip under the Hellenic arc with the same angle of 60° and are also en-echelon. The Strabo zone is probably the younger with a maximum focal depth of 70 km against 120 km for Pliny zone. Seismic activity in the crust beneath the island is revealed to extend along the entire slope of the Pliny trench, but there is a principal maximum of activity at ±5 km, a minimum at 15–20 km, and a second maximum at 20–30 km. These findings are in agreement with results from OBS observations made to north of Crete in 1987.

Tectonic Evolution of Pacific Ocean: ABSTRACT

In accordance with the lithosphere plate theory, the western part of the Pacific Ocean was occupied by an oceanic basin prior to the disintegration of Pangea. Linear magnetic anomalies and DSDP data indicate that the oldest oceanic crust is Late Jurassic in age. Little is known about the boundaries of the proto-Pacific plate and its fragments in the western part of the Pacific Ocean, but it is obvious that the oceanic crust fragments of this age occur along the western rim of the basin from the Koryak Mountains in Asia to eastern Australia as well as in various foldbelts on the east in Alaska and the Klamath Mountains. The most intensive tectonic movements and spreading within the Pacific Ocean, accompanied by subduction along both sides of the oceanic plate, occurred nea the end of the Jurassic (Kimmeridgian-Tithonian) and during Early Cretaceous time (Aptian-Albian). A result was the formation of the Kula plate with tectonic nappes which stand as such submarine dome rises as the Shatsky Rise, Manihiki Plateau, Hess Rise, and Campbell Plateau, characterized by double thicknesses of oceanic crust. By comparing differences in Albian-Aptian facies, between the east Pacific Ocean and the west, it is possible to assume that shallow-water depths characterized the east, while the west was the site of a deep-water abyssal plain. Albian subsidence, in the eastern part of the ocean, coincided with tectonic uplift in the west and with the initiation of subduction along the East Asian volcanic belt. Island arcs and trenches, formed at the end of the Cretaceous, caused oceanward migration of the subduction zones. This detached the Bering Sea and Philippine plates from the margin of the oceanic plate. Tertiary spreading along the East Pacific Rise was compensated by subduction under South America and within the deep-water trenches. Spreading in marginal seas during Oligocene-Miocene time resulted in the formation of back-arch basins, compression within the framework of island arcs and thrusting of the arcs onto the oceanic crust. Convergence of arcs may be explained by rapid oceanward displacement within marginal seas, and local movement along transform faults significantly affected the evolution of the Pacific Ocean and the distribution of mineral deposits within the oceanic basin and on the continental shelf. End_of_Article - Last_Page 959------------

Morphology and tectonics of oceanic deepwater trenches and the problem of “Benioff zones”

Morphology and tectonics of oceanic deepwater trenches and the problem of “Benioff zones”

AQUATIC NATURAL SPATIAL COMPLEXES OF THE EARTH

A senior Soviet physical geographer calls for a single classification of the earth's natural territorial complexes, including not only land areas, which have been the focus of research in landscape science, but also the earth's water areas. The vertical tier structure of natural complexes is proposed as the basis for such a classification: complexes with a constant structure (terrestrial, aquatic, glacial) and complexes with a variable structure (terrestrial-aquatic, terrestrial-glacial and aquatic-glacial). The class of aquatic natural complexes is further broken down into a subclass of oceanic complexes and a subclass of inland aquatic complexes (lakes and rivers). Oceanic complexes might be broken down further in terms of conventional morphologic elements—coastal zone, continental shelf, continental slope, seabed and deep-water trenches.