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1
Jourdin, F., O. Francis, P. Vincent, and P. Mazzega. "Some results of heterogeneous data inversions for oceanic tides." Journal of Geophysical Research: Solid Earth 96, B12 (November 10, 1991): 20267–88. http://dx.doi.org/10.1029/91jb00426.
2
Sun, L. Charles. "Data Inter-Operability Driven by Oceanic Data Assimilation Needs." Marine Technology Society Journal 33, no. 3 (January 1, 1999): 55–66. http://dx.doi.org/10.4031/mtsj.33.3.7.
Анотація:
An interactive data access and retrieval system, developed at the U.S. National Oceanographic Data Genter (NODG) and available at <ext-link ext-link-type="uri" href="http://www.node.noaa.gov">http://www.node.noaa.gov</ext-link>, is presented in this paper. The purposes of this paper are: (1) to illustrate the procedures of quality control and loading oceanographic data into the NODG ocean databases and (2) to describe the development of a system to manage, visualize, and disseminate the NODG data holdings over the Internet. The objective of the system is to provide ease of access to data that will be required for data assimilation models. With advances in scientific understanding of the ocean dynamics, data assimilation models require the synthesis of data from a variety of resources. Modern intelligent data systems usually involve integrating distributed heterogeneous data and information sources. As the repository for oceanographic data, NOAA’s National Oceanographic Data Genter (NODG) is in a unique position to develop such a data system. In support of the data assimilation needs, NODG has developed a system to facilitate browsing of the oceanographic environmental data and information that is available on-line at NODG. Users may select oceanographic data based on geographic areas, time periods and measured parameters. Once the selection is complete, users may produce a station location plot, produce plots of the parameters or retrieve the data.
3
Chen, Shan-Tai, Shung-Lin Dou, and Wann-Jin Chen. "A Data Mining Approach to Rainfall Intensity Classification Using TRMM/TMI Data." Journal of Advanced Computational Intelligence and Intelligent Informatics 12, no. 6 (November 20, 2008): 516–22. http://dx.doi.org/10.20965/jaciii.2008.p0516.
Анотація:
The systematic approach we propose for classifying oceanic rainfall intensity during the typhoon season consists of two major steps – 1) identifying the rain areas and 2) classifying rainfall intensity intonormalandheavyfor these areas. The heterogeneous hierarchical classifier (HHC), an ensemble model we developed for accurately identifying heavy rainfall events, consists of a set of base classifiers. The base classifiers are independently constructed through heterogeneous data mining approaches such as artificial neural networks, decision trees, and self-organizing maps. The meteorological satellite Tropical Rainfall Measuring Mission (TRMM) microwave imager (TMI) data from 2000 to 2005 are used to create the classification models. TRMM precipitation radar (PR) data and rain gauge data from Automatic Rainfall and Meteorological Telemetry System (ARMTS) measurement are used as ground truth data to evaluate models. Two thirds of the dataset is used for model training and one third for testing. Experimental results show that the proposed model classifies rainfall intensity highly accurately and outperforms previously published methods.
4
Yi, Shuang, and Kosuke Heki. "Heterogeneous oceanic mass distribution in GRACE observations and its leakage effect." Geophysical Journal International 221, no. 1 (January 10, 2020): 603–16. http://dx.doi.org/10.1093/gji/ggaa022.
Анотація:
SUMMARY Signal leakage between the land and ocean is a challenge in using Gravity Recovery and Climate Experiment (GRACE) observation data to study global mass redistributions. Although the leakage occurs in both directions, more attention has been paid to the land-to-ocean leakage and less to the ocean-to-land leakage. Here, we show that the ocean-to-land leakage is non-uniform and non-negligible and propose a new forward modelling method to fully consider bi-directional leakages with the help of the global Ocean ReAnalysis System ORAS5. This observation-driven model could significantly reduce the variations in ocean grids and thus decrease the ocean-to-land leakage. The results with different treatment of the ocean signal leakage are compared. We find that failing to consider the ocean-to-land leakage will cause an underestimation of ∼20 per cent in the seasonal variation and will introduce a bias of several giga-tons in the secular trend. Although the uniform and non-uniform model have similar results in the global average of seasonal mass variations, the non-uniform ocean model is necessary in most places, especially near the Arctic Ocean, the Sea of Japan and the Gulf of Carpentaria. Despite these achievements, we also point out that there is still much room for improvement in ocean mass models, particularly in long-term trends. Our results indicate the importance of the ocean-to-land leakage correction in the mass estimation in coastal land areas using the GRACE data.
5
Sokolov, S. D., G. Ye Bondarenko, A. K. Khudoley, O. L. Morozov, M. V. Luchitskaya, M. I. Tuchkova, and P. W. Layer. "Tectonic reconstruction of Uda-Murgal arc and the Late Jurassic and Early Cretaceous convergent margin of Northeast Asia–Northwest Pacific." Stephan Mueller Special Publication Series 4 (September 17, 2009): 273–88. http://dx.doi.org/10.5194/smsps-4-273-2009.
Анотація:
Abstract. A long tectonic zone composed of Upper Jurassic to Lower Cretaceous volcanic and sedimentary rocks is recognized along the Asian continent margin from the Mongol-Okhotsk fold and thrust belt on the south to the Chukotka Peninsula on the north. This belt represents the Uda-Murgal arc, which was developed along the convergent margin between Northeast Asia and Northwest Meso-Pacific. Several segments are identified in this arc based upon the volcanic and sedimentary rock assemblages, their respective compositions and basement structures. The southern and central parts of the Uda-Murgal arc were a continental margin belt with heterogeneous basement represented by metamorphic rocks of the Siberian craton, the Verkhoyansk terrigenous complex of Siberian passive margin and the Koni-Taigonos Late Paleozoic to Early Mesozoic island arc with accreted oceanic terranes. At the present day latitude of the Pekulney and Chukotka segments there was an ensimatic island arc with relicts of the South Anyui oceanic basin in a backarc basin. Accretionary prisms of the Uda-Murgal arc and accreted terranes contain fragments of Permian, Triassic to Jurassic and Jurassic to Cretaceous (Tithonian–Valanginian) oceanic crust and Jurassic ensimatic island arcs. Paleomagnetic and faunal data show significant displacement of these oceanic complexes and the terranes of the Taigonos Peninsula were originally parts of the Izanagi oceanic plate.
6
Piontkovski, S. A., I. A. Minsky, and Ya V. Meger. "LONG-TERM VARIABILITY OF OCEANIC ZOOPLANKTON BIOMASS." Водные биоресурсы и среда обитания 6, no. 3 (2023): 52–65. http://dx.doi.org/10.47921/2619-1024_2023_6_3_52.
Анотація:
Numerous scientific publications are dedicated to the analysis of long-term variability of zooplankton biomass in oceanic and neritic zones of the World Ocean. The number of these publications keeps growing with the availability of new data. Relevance of this research can be attributed to the crucial role of zooplankton biomass in the spatio-temporal and trophic structure of aquatic ecosystems. Inter-annual fluctuations of zooplankton biomass affect the catch volumes of small pelagic fish. This research is aimed at identification of statistically valid long-term trends of the World Ocean zooplankton biomass, which involves the analysis of the data from databases and published articles describing such variability. Regional and international databases (namely COPEPOD, HOT, JGOFS, ODATE and others), which are available in the form of CDs, archived materials, and online, have been used. For the time series of the biomass across 21 areas of the World Ocean (Pacific, Indian, Atlantic Oceans and internal seas), the regression analysis has been conducted, which made it possible to estimate the parameters of linear monotonic trends. Based on bivariate spatial autocorrelation functions, the areas within which the trends are statistically homogeneous have been identified. A comparative study of long-term variability of zooplankton biomass, phytoplankton biomass, primary production, and the total live biomass of the pelagic World Ocean is presented. It is shown that the spatial distribution of positive, negative and neutral trends of zooplankton biomass on the World Ocean scale is heterogeneous. The negative monotonic trends of zooplankton biomass are found to be prevailing (in 1980–2010s); the regression parameters describing them are presented.
7
Boev, Blažo, Vladica Cvetković, Dejan Prelević, Kristina Šarić, and Ivan Boev. "EAST VARDAR OPHIOLITES REVISITED: A BRIEF SYNTHESIS OF GEOLOGY AND GEOCHEMICAL DATA." Contributions, Section of Natural, Mathematical and Biotechnical Sciences 39, no. 1 (July 2, 2018): 51. http://dx.doi.org/10.20903/csnmbs.masa.2018.39.1.119.
Анотація:
The study reports and synthesizes the available geological and geochemical data on the East Vardar ophiolites comprising most known occurrences from the South Apuseni Mountains in Romania to the tip of the Chalkidiki Pen-insula in Greece. The summarized geological data suggest that the East Vardar ophiolites are mostly composed of the magmatic sequences, whereas the mantle rocks are very subordinate. The members of the magmatic sequences are characterized by the presence of abundant acid and intermediate volcanic and intrusive rocks. The age of these ophio-lites is paleontologically and radiometrically constrained and these data suggest that the East Vardar ophiolite formed as a short-lived oceanic realm that was emplaced before the uppermost Kimmeridgian. A relatively weak adakitic affinity is shown by intra-ophiolitic acid and intermediate rocks in many East Vardar provinces. It can be taken as evidence that the subduction of the young and hot slab, most likely along the earlier spreading ridge has occurred. A paleo-tectonic reconstruction consisting of four stages is proposed. It involves: a) an early/mid-Jurassic north-northeastward subduction of the West Vardar oceanic plate; b) the formation of a mid-Jurassic volcanic arc and a narrow back-arc oceanic stripe of East Vardar behind it; c) the mid-/Upper Jurassic initiation of East Vardar subduc-tion along the ridge axis, and d) complex and heterogeneous emplacement of the East Vardar ophiolites. So far avail-able data allow for having relatively clear ideas about the origin and evolution of the East Vardar ophiolites. Howev-er, in order to provide better understanding of all aspects of its evolution we need to answer additional questions re-lated to the true structural position of the East Vardar ophiolites slices in Serbia, the exact nature of subduction that caused back-arc spreading (intraoceanic vs subduction under continent?) and the full significance of the adakitic sig-nature shown by rocks in the East Vardar provinces other than Demir Kapija.
8
Kotowski, Alissa J., and Whitney M. Behr. "Length scales and types of heterogeneities along the deep subduction interface: Insights from exhumed rocks on Syros Island, Greece." Geosphere 15, no. 4 (June 24, 2019): 1038–65. http://dx.doi.org/10.1130/ges02037.1.
Анотація:
Abstract We use structural and microstructural observations from exhumed subduction-related rocks exposed on Syros Island (Cyclades, Greece) to provide constraints on the length scales and types of heterogeneities that occupy the deep subduction interface, with possible implications for episodic tremor and slow slip. We selected three Syros localities that represent different oceanic protoliths and deformation conditions within a subduction interface shear zone, including: (1) prograde subduction of oceanic crust to eclogite facies; (2) exhumation of oceanic crust from eclogite through blueschist-greenschist facies; and (3) exhumation of mixed mafic crust and sediments from eclogite through blueschist-greenschist facies. All three localities preserve rheological heterogeneities that reflect metamorphism of primary lithological, geochemical, and/or textural variations in the subducted protoliths and that take the form of brittle pods and lenses within a viscous matrix. Microstructural observations indicate that the matrix lithologies (blueschists and quartz-rich metasediments) deformed by distributed power-law viscous flow accommodated by dislocation creep in multiple mineral phases. We estimate bulk shear zone viscosities ranging from ∼1018 to 1020 Pa-s, depending on the relative proportion of sediments to (partially eclogitized) oceanic crust. Eclogite and coarse-grained blueschist heterogeneities within the matrix preserve multiple generations of dilational shear fractures and veins formed under high-pressure conditions. The veins commonly show coeval or overprinting viscous shear, suggesting repeated cycles of frictional and viscous strain. These geologic observations are consistent with a mechanical model of episodic tremor and slow slip (ETS), in which the deep subduction interface is a rheologically heterogeneous distributed shear zone comprising transiently brittle (potentially tremor-genic) sub-patches within a larger, viscously creeping interface patch. Based on our observations of outcrop and map areas of heterogeneous patches and the sizes, distributions, and amounts of brittle offset recorded by heterogeneities, we estimate that simultaneous brittle failure of heterogeneities could produce tremor bursts with equivalent seismic moments of 4.5 × 109–4.7 × 1014 N m, consistent with seismic moments estimated from geophysical data at active subduction zones.
9
Srivastava, Rohit, and Ruchita Shah. "Study of Monsoonal Features Using Regional Climate Model over Heterogeneous Monsoon Dominated Region." E3S Web of Conferences 101 (2019): 03004. http://dx.doi.org/10.1051/e3sconf/201910103004.
Анотація:
Global warming is an increase in average global temperature of the earth which lead to climate change. Heterogeneity in the earth-atmosphere system becomes difficult to capture at low resolution (1°x1°) by satellite. Such features may be captured by using high resolution model such as regional climate model (0.5°x 0.5°). This type of study is quite important for a monsoon dominated country like India where Indo-Gangetic Plains (IGP) faces highest heterogeneity due to its geographic location. Present study compares high resolution model features with satellite data over IGP for monsoon season during a normal rainfall year 2010 to understand the actual performance of model. Almost whole IGP simulates relative humidity (RH) with wide range (~50-100%), whereas satellite shows it with narrow range (~60-80%) during September, 2010. Thus model is able to pick the features which were missed by satellite. Hence further model simulation extends over India and adjoining oceanic regions which simulates data of southwest monsoon with high (~70-100%) RH, high (~0.4-0.7) cloud fraction (CF) and low (~80-200 W/m2) outgoing longwave radiation (OLR) over Arabian Sea during June, 2010. Such type of study can be useful to understand heterogeneity at regional scale with the help of high resolution model generated data.
10
Lücke, O. H., and I. G. Arroyo. "Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data." Solid Earth Discussions 7, no. 3 (July 14, 2015): 1941–77. http://dx.doi.org/10.5194/sed-7-1941-2015.
Анотація:
Abstract. The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry is presented based on three-dimensional density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into Northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. To the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a terminal depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.
11
Lücke, O. H., and I. G. Arroyo. "Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data." Solid Earth 6, no. 4 (October 29, 2015): 1169–83. http://dx.doi.org/10.5194/se-6-1169-2015.
Анотація:
Abstract. The eastern part of the oceanic Cocos Plate presents a heterogeneous crustal structure due to diverse origins and ages as well as plate-hot spot interactions which originated the Cocos Ridge, a structure that converges with the Caribbean Plate in southeastern Costa Rica. The complex structure of the oceanic plate directly influences the dynamics and geometry of the subduction zone along the Middle American Trench. In this paper an integrated interpretation of the slab geometry in Costa Rica is presented based on 3-D density modeling of combined satellite and surface gravity data, constrained by available geophysical and geological data and seismological information obtained from local networks. The results show the continuation of steep subduction geometry from the Nicaraguan margin into northwestern Costa Rica, followed by a moderate dipping slab under the Central Cordillera toward the end of the Central American Volcanic Arc. Contrary to commonly assumed, to the southeast end of the volcanic arc, our preferred model shows a steep, coherent slab that extends up to the landward projection of the Panama Fracture Zone. Overall, a gradual change in the depth of the intraplate seismicity is observed, reaching 220 km in the northwestern part, and becoming progressively shallower toward the southeast, where it reaches a maximum depth of 75 km. The changes in the terminal depth of the observed seismicity correlate with the increased density in the modeled slab. The absence of intermediate depth (> 75 km) intraplate seismicity in the southeastern section and the higher densities for the subducted slab in this area, support a model in which dehydration reactions in the subducted slab cease at a shallower depth, originating an anhydrous and thus aseismic slab.
12
Johnston, Stephen T., James K. Mortensens, and Philippe Erdmer. "Igneous and metaigneous age constraints for the Aishihik Metamorphic suite, southwest Yukon." Canadian Journal of Earth Sciences 33, no. 11 (November 1, 1996): 1543–55. http://dx.doi.org/10.1139/e96-117.
Анотація:
The pericratonic Aishihik metamorphic suite occurs outboard of accreted oceanic and oceanic-arc terranes in southwest Yukon. It consists of a structurally lower unit of feldspathic quartz mica schist and a heterogeneous upper unit of carbonaceous quartzite, micaceous quartzite, marble, and metaigneous rods. The metaigneous rocks include volcanic protoliths and crystallized between 351.5 ± 2.0 and 343.8 ± 0.8 Ma, suggesting correlation of the upper unit with the Nasina assemblage. The lower unit may be correlative with the pre-Mississippian Nisling assemblage. The metaigneous rocks and Early Jurassic plutons are characterized by inherited zircon components with Early Protcrozoic average ages. The Aishihik faatholitfa, a quartz diorite magmatic arc pluton, intruded the metamorphic suite at 186.0 ± 2.8 Ma at a depth of about 30 km. The batholith and metamorphic suite were intruded discordant, high-level (<6 km depth) plutons of the Long Lake plutonic suite, which crystallized at [Formula: see text] Ma. These data, together with cooling ages, require rapid exhumation of the Aishihik metamorphic suite at about 186 Ma. Exhumation coincided with the deposition of a molasse across the oceanic Whitehorse Trough, suggesting that the west margin of the trough lay above the pericratonic belt prior to and during uplift. Cooling ages of 160–165 Ma indicate a second burial and heating event, probably linked to the obduction of the Cache Creek terrane. Subsequent erosion, recorded by molasse of the Tantalus Group, and associated isostatic rebound resulted in exhumation and slow cooling through Middle Jurassic time.
13
Zhang, Shane, Hongda Wang, Mengyu Wu, and Michael H. Ritzwoller. "Isotropic and azimuthally anisotropic Rayleigh wave dispersion across the Juan de Fuca and Gorda plates and U.S. Cascadia from earthquake data and ambient noise two- and three-station interferometry." Geophysical Journal International 226, no. 2 (April 13, 2021): 862–83. http://dx.doi.org/10.1093/gji/ggab142.
Анотація:
SUMMARY We use data from the Cascadia Initiative (CI) amphibious array and the USArray Transportable Array to construct and compare Rayleigh wave isotropic and azimuthally anisotropic phase speed maps across the Juan de Fuca and Gorda Plates extending onto the continental northwestern United States. Results from both earthquakes (28–80 s) as well as ambient noise two- and three-station interferometry (10–40 s) are produced. Compared with two-station interferometry, three-station direct wave interferometry provides >50 per cent improvement in the signal-to-noise ratio and the number of dispersion measurements obtained, particularly in the noisier oceanic environment. Earthquake and ambient noise results are complementary in bandwidth and azimuthal coverage, and agree within about twice the estimated uncertainties of each method. We, therefore, combine measurements from the different methods to produce composite results that provide an improved data set in accuracy, resolution and spatial and azimuthal coverage over each individual method. A great variety of both isotropic and azimuthally anisotropic structures are resolved. Across the oceanic plate, fast directions of anisotropy with 180° periodicity (2ψ) generally align with palaeo-spreading directions while 2ψ amplitudes mostly increase with lithospheric age, both displaying substantial variations with depth and age. Strong (>3 per cent) apparent anisotropy with 360° periodicity (1ψ) is observed at long periods (>50 s) surrounding the Cascade Range, probably caused by backscattering from heterogeneous isotropic structures.
14
Lei, Ming, Zhengfu Guo, Wenbin Zhao, Maoliang Zhang, and Lin Ma. "Coexisting Late Cenozoic Potassic and Sodic Basalts in NE China: Role of Recycled Oceanic Components in Intraplate Magmatism and Mantle Heterogeneity." Lithosphere 2020, no. 1 (September 1, 2020): 1–28. http://dx.doi.org/10.2113/2020/8875012.
Анотація:
Abstract This study presents an integrated geochemical study of the Wudalianchi-Erkeshan potassic basalts and Halaha sodic basalts of NE China, and uses these data to further our understanding of the petrogenetic relationships between the coeval potassic and sodic basalts in this region. The potassic basalts with high concentrations of K2O have arc-like trace-element compositions and enriched Sr-Nd-Hf isotopic compositions with unradiogenic 206Pb/204Pb values (16.77–16.90). In contrast, the sodic basalts with high concentrations of Na2O have OIB-like trace-element compositions and depleted Sr-Nd-Hf isotopic compositions with radiogenic 206Pb/204Pb values (18.27–18.40). These data suggest that the potassic and sodic basalts were derived from mixed depleted mid-ocean-ridge basalt mantle (DMM) and enriched mantle source end-members, where the enriched end-members are ancient sediment for the potassic basalts and Pacific oceanic crust for the sodic basalts. The combined geophysical and geochemical data indicate that these two enriched end-members are located in the mantle transition zone. We propose that partial melting of upwelling asthenospheric mantle comprising ambient DMM and recycled materials shifting from the ancient sediment to the Pacific oceanic crust could have produced the coeval potassic and sodic basalts in NE China. The proposed mantle sources for the potassic and sodic basalts indicate that the upper mantle beneath NE China was highly heterogeneous during late Cenozoic.
15
Matsuno, Tetsuo, Kiyoshi Baba, and Hisashi Utada. "Probing 1-D electrical anisotropy in the oceanic upper mantle from seafloor magnetotelluric array data." Geophysical Journal International 222, no. 3 (May 6, 2020): 1502–25. http://dx.doi.org/10.1093/gji/ggaa221.
Анотація:
SUMMARY Electrical anisotropy in the oceanic upper mantle can only be imaged by seafloor magnetotelluric (MT) data, and arguably provides important clues regarding the mantle structure and dynamics by observational determinations. Here, we attempt to probe the electrical (azimuthal) anisotropy in the oceanic mantle by analysing recent seafloor MT array data from the northwestern Pacific acquired atop 125–145 Ma seafloor. We propose a method in which an isotropic 1-D model is first obtained from seafloor MT data through an iterative correction for topographic distortions; then, the anisotropic properties are inferred as deviations from the isotropic 1-D model. We investigate the performance of this method through synthetic forward modelling and inversion using plausible anisotropic 1-D models and the actual 3-D bathymetry and topography of the target region. Synthetic tests reveal that the proposed method will detect electrical anisotropy in the conductive upper mantle or electrical asthenosphere. We also compare the performance of the proposed scheme by using two rotational invariant impedances and two topographic correction equations. The comparison reveals that using different rotational invariants and correction equations provides relatively consistent results, but among the rotational invariants, the sum of squared elements (ssq) impedance yields better recovered results for topographically distorted data than the determinant impedance. An application of the method to seafloor MT array data sets from two areas in the northwestern Pacific reveals the possible presence of two layers of electrical anisotropy in the conductive mantle (<100 Ω-m) at depths of ∼60–200 km. The anisotropy is estimated to be more intense in the shallower layer for both areas. On the other hand, the estimated anisotropic azimuth (defined as the most conductive direction) and the depth to the interface between the two layers are different between the two array areas separated by a small horizontal distance of ∼1000 km in spite of their similar seafloor ages. The most conductive directions are aligned neither with the current absolute plate motion direction nor with the fastest direction of seismic azimuthal anisotropy. The inferred electrical anisotropy features may result from array-scale (∼1000 km) mantle dynamics, such as small-scale convection, which might affect the electrical and seismic properties differently, although there remains the possibility that some portions of these features are explained by laterally heterogeneous mantle structures.
16
Gregory, Emma P. M., Satish C. Singh, Milena Marjanović, and Zhikai Wang. "Serpentinized peridotite versus thick mafic crust at the Romanche oceanic transform fault." Geology 49, no. 9 (June 3, 2021): 1132–36. http://dx.doi.org/10.1130/g49097.1.
Анотація:
Abstract The crust beneath transform faults at slow-spreading ridges has been considered to be thin, comprising a thin mafic layer overlying serpentinized peridotite. Using wide-angle seismic data, we report the presence of a Moho at ∼6 km depth and a low-velocity anomaly extending down to 9 km beneath the 20-km-wide Romanche transform valley floor in the equatorial Atlantic Ocean. The low crustal velocities above the Moho could be due to either highly serpentinized mantle peridotite or fractured mafic rocks. The existence of clear Moho reflections and the occurrence of a large crustal-depth rupture during the 2016 magnitude 7.1 earthquake suggest that the crust likely consists of fractured mafic material. Furthermore, the presence of low velocities below the Moho advocates for extensive serpentinization of the mantle, indicating that the Moho reflection is unlikely to be produced by a serpentinization front. The crust to the north of the transform fault likely consists of mafic material, but that in the south appears to be more amagmatic, possibly containing serpentinized peridotite. Our results imply that the transform fault structure is complex and highly heterogeneous, and thus would have significant influence on earthquake rupture and alteration processes.
17
LAPIERRE, H., D. BOSCH, A. NARROS, G. H. MASCLE, M. TARDY, and A. DEMANT. "The Mamonia Complex (SW Cyprus) revisited: remnant of Late Triassic intra-oceanic volcanism along the Tethyan southwestern passive margin." Geological Magazine 144, no. 1 (December 21, 2006): 1–19. http://dx.doi.org/10.1017/s0016756806002937.
Анотація:
Upper Triassic volcanic and sedimentary rocks of the Mamonia Complex in southwestern Cyprus are exposed in erosional windows through the post-Cretaceous cover, where the Mamonia Complex is tectonically imbricated with the Troodos and Akamas ophiolitic suites. Most of these Upper Triassic volcanic rocks have been considered to represent remnants of Triassic oceanic crust and its associated seamounts. New Nd and Pb isotopic data show that the whole Mamonia volcanic suite exhibits features of oceanic island basalts (OIB). Four rock types have been distinguished on the basis of the petrology and chemistry of the rocks. Volcanism began with the eruption of depleted olivine tholeiites (Type 1) and oceanic island tholeiites (Type 2) associated with deep basin siliceous and/or calcareous sediments. The tholeiites were followed by highly phyric alkali basalts (Type 3) interbedded with pelagic Halobia-bearing limestones or white reefal limestones. Strongly LREE-enriched trachytes (Type 4) were emplaced during the final stage of volcanic activity. Nd and Pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources. Fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts. The trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions. This is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes. The correlations observed between incompatible elements (Nb, Th) and εNd and Pb isotopic initial ratios suggest that the Mamonia suite was derived from the mixing of a depleted mantle (DMM) and an enriched component of High μ (μ = 238U/204Pb, HIMU) type. Models using both Nd and Pb isotopic initial ratios suggest that the depleted tholeiites (Type 1) derived from a DMM source contaminated by an Enriched Mantle Type 2 component (EM2), and that the oceanic tholeiites (Type 2), alkali basalts (Type 3) and trachytes (Type 4) were derived from the mixing of the enriched mantle source of the depleted tholeiites with a HIMU component. None of the Mamonia volcanic rocks show evidence of crustal contamination. The Upper Triassic within-plate volcanism likely erupted in a small southerly Neotethyan basin, located north of the Eratosthenes seamount and likely floored by oceanic crust.
18
Müller, R. D., and T. C. W. Landgrebe. "The link between great earthquakes and the subduction of oceanic fracture zones." Solid Earth Discussions 4, no. 2 (September 26, 2012): 1229–80. http://dx.doi.org/10.5194/sed-4-1229-2012.
Анотація:
Abstract. Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more) recurrence times of giant earthquakes. We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude ≥ 8) subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones. We use a computational recommendation technology, a type of information filtering system technique widely used in searching, sorting, classifying, and filtering very large, statistically skewed data sets on the internet, to demonstrate a robust association and rule out a random effect. Fracture zone-subduction zone intersection regions, representing only 25% of the global subduction coupling zone, are linked with 13 of the 15 largest (magnitude (Mw ≥ 8.6) and half of the 50 largest, magnitude ≥ 8.4) earthquakes. In contrast, subducting volcanic ridges and chains are only biased towards smaller earthquakes (magnitude < 8). The associations captured by our statistical analysis can be conceptually related to physical differences between subducting fracture zones and volcanic chains/ridges. Fracture zones are characterized by laterally continuous, uplifted ridges that represent normal ocean crust with a high degree of structural integrity, causing strong, persistent coupling in the subduction interface. Smaller volcanic ridges and chains, not have a relatively fragile heterogeneous internal structure and are separated from the underlying ocean crust by a detachment interface, resulting in weak coupling and relatively small earthquakes, explaining the observed dichotomy.
19
Müller, R. D., and T. C. W. Landgrebe. "The link between great earthquakes and the subduction of oceanic fracture zones." Solid Earth 3, no. 2 (December 5, 2012): 447–65. http://dx.doi.org/10.5194/se-3-447-2012.
Анотація:
Abstract. Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more) recurrence times of giant earthquakes. We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude ≥ 8) subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones. We use a computational recommendation technology, a type of information filtering system technique widely used in searching, sorting, classifying, and filtering very large, statistically skewed data sets on the Internet, to demonstrate a robust association and rule out a random effect. Fracture zone–subduction zone intersection regions, representing only 25% of the global subduction coupling zone, are linked with 13 of the 15 largest (magnitude Mw ≥ 8.6) and half of the 50 largest (magnitude Mw ≥ 8.4) earthquakes. In contrast, subducting volcanic ridges and chains are only biased towards smaller earthquakes (magnitude < 8). The associations captured by our statistical analysis can be conceptually related to physical differences between subducting fracture zones and volcanic chains/ridges. Fracture zones are characterised by laterally continuous, uplifted ridges that represent normal ocean crust with a high degree of structural integrity, causing strong, persistent coupling in the subduction interface. Smaller volcanic ridges and chains have a relatively fragile heterogeneous internal structure and are separated from the underlying ocean crust by a detachment interface, resulting in weak coupling and relatively small earthquakes, providing a conceptual basis for the observed dichotomy.
20
Peyve, A. A., S. Yu Sokolov, A. A. Razumovsky, A. N. Ivanenko, I. S. Patina, V. A. Bogolyubskiy, I. A. Veklich, and A. P. Denisova. "Relation between Magmatic and Tectonic Processes in the Formation of the Oceanic Crust to the South of the Charlie Gibbs Fracture Zone (North Atlantic)." Геотектоника, no. 1 (January 1, 2023): 48–74. http://dx.doi.org/10.31857/s0016853x23010058.
Анотація:
The article presents new data on the structure and relationship of tectonic and magmatic processes during the formation of the Mid-Atlantic Ridge between the Charlie Gibbs and Maxwell fracture zones in the North Atlantic. It is shown that this region is characterized by significant reduction in volcanism, which leads to the excavation of low crustal and upper mantle rocks to the surface. Both individual inland oceanic complexes of the most varied configurations and extended sublatitudinal ridges composed of plutonic rocks are formed. Our analysis showed that this formation setting existed for at least 14‒16 Ma. The formation of most internal oceanic complexes is associated not only with tectonic factors, but also with the serpentinization of peridotites, which leads to a decrease in density, an increase in volume, and, as a result, to the emergence of large ultrabasic massifs, including separated blocks of gabbroids, dolerites, and basalts. Numerous zones of sliding, crushing, abrasion and deformation of rocks indicate tectonic movements. The study region is characterized by numerous non-transform displacements of different amplitudes, which are formed under conditions when relative displacements of oceanic lithosphere segments are realized in wide areas undergoing shear and extension deformations. The morphology of the emerging tectonic-magmatic structures of the region is determined by tectonic factors. The exceptions are cases when the volumes of melts entering the surface in a short period of time are significantly higher than the average for a certain segment of the rift valley. The analysis performed shows the presence within the region of sources of magnetic anomalies that are heterogeneous in nature, both of volcanic origin and associated with manifestations of superimposed tectonic activity.
21
Foppa, Nando, Stefan Wunderle, David Oesch, and Florian Kuchen. "Operational sub-pixel snow mapping over the Alps with NOAA AVHRR data." Annals of Glaciology 38 (2004): 245–52. http://dx.doi.org/10.3189/172756404781814735.
Анотація:
AbstractThis study is part of research activities concentrating on the real-time application of the U.S. National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) sensor for snow-cover analysis of the European Alps. For mapping snow cover in heterogeneous terrain, we implement the widely used linear spectral mixture algorithm to estimate snow cover at sub-pixel scale. Principal component analysis, including the reflective part of AVHRR channel 3, is used to estimate fractions of “snow” and “not snow” within a pixel, using linear mixture modeling. The combination of these features leads to a fast, simple solution for operational and near-real-time processing. The presented algorithm is applied on the European Alps on 17 January 2003 and successfully maps snow at sub-pixel scale. The detailed snow-cover information makes it easy to recognize the complex topography of the Alps, more so than with either a classic binary map or a Moderate Resolution Imaging Spectroradiometer (MODIS) snow product. The sub-pixel algorithm reasonably identifies snow-cover fractions in regions and at altitudes where neither the classic binary map nor the MODIS algorithm detects any snow. Differences concerning the snow distribution are found in forested areas as well as in the lowest-elevation zones. The algorithm substantially improves snow mapping over complex topography for operational and near-realtime applications.
22
Shkodzinsky, V. "The nature of the evolution of magmatism in the history of the Earth." Vestnik of geosciences, no. 4 (June 30, 2023): 4–13. http://dx.doi.org/10.19110/geov.2023.4.1.
Анотація:
Numerous evidences of hot heterogeneous accretion of the Earth have been obtained. According to these data, the Early Precambrian crystalline complexes and acidic crust were resulted from emerging residual melts formed by low-pressure compression fractionation of the bottom parts of the early magmatic ocean. The rise of residual melts from various layers of the magmatic ocean, crystallized from top to bottom, caused the evolution of magmatism of ancient platforms from acidic to basic, then to alkaline-ultrabasic and kimberlite. The warming of the mantle by the initially hot core led to the appearance of a direct geothermal gradient in it at the end of the Neoproterozoic and to the beginning of the rise of mantle plumes. Under their influence, oceanic and subduction environments were formed. Magmas in them are formed as a result of frictional and decompression melting of the differentiates of the magmatic ocean.
23
Roda, Manuel, Maria Iole Spalla, Marco Filippi, Jean-Marc Lardeaux, Gisella Rebay, Alessandro Regorda, Davide Zanoni, Michele Zucali, and Guido Gosso. "Metamorphic Remnants of the Variscan Orogeny across the Alps and Their Tectonic Significance." Geosciences 13, no. 10 (October 6, 2023): 300. http://dx.doi.org/10.3390/geosciences13100300.
Анотація:
Lithospheric slices preserving pre-Alpine metamorphic imprints are widely described in the Alps. The Variscan parageneses recorded in continental, oceanic, and mantle rocks suggest a heterogeneous metamorphic evolution across the Alpine domains. In this contribution, we collect quantitative metamorphic imprints and ages of samples that document Variscan tectonometamorphic evolution from 420 to 290 Ma. Based on age distribution and metamorphic imprint, three main stages can be identified for the Variscan evolution of the Alpine region: Devonian (early Variscan), late Devonian–late Carboniferous (middle Variscan), and late Carboniferous–early Permian (late Variscan). The dominant metamorphic imprint during Devonian times was recorded under eclogite and HP granulite facies conditions in the Helvetic–Dauphinois–Provençal, Penninic, and eastern Austroalpine domains and under Ep-amphibolite facies conditions in the Southalpine domain. These metamorphic conditions correspond to a mean Franciscan-type metamorphic field gradient. During the late Devonian–late Carboniferous period, in the Helvetic–Dauphinois–Provençal and central Austroalpine domains, the dominant metamorphic imprint developed under eclogite and HP granulite facies conditions with a Franciscan field gradient. Amphibolite facies conditions dominated in the Penninic and Southalpine domains and corresponded to a Barrovian-type metamorphic field gradient. At the Carboniferous–Permian transition, the metamorphic imprints mainly developed under amphibolite-LP granulite facies conditions in all domains of the Alps, corresponding to a mean metamorphic field gradient at the transition between Barrovian and Abukuma (Buchan) types. This distribution of the metamorphic imprints suggests a pre-Alpine burial of oceanic and continental crust underneath a continental upper plate, in a scenario of single or multiple oceanic subductions preceding the continental collision. Both scenarios are discussed and revised considering the consistency of collected data and a comparison with numerical models. Finally, the distribution of Devonian to Triassic geothermal gradients agrees with a sequence of events that starts with subduction, continues with continental collision, and ends with the continental thinning announcing the Jurassic oceanization.
24
Aoyama, Michio, and Katsumi Hirose. "Artificial Radionuclides Database in the Pacific Ocean: HAM Database." Scientific World JOURNAL 4 (2004): 200–215. http://dx.doi.org/10.1100/tsw.2004.15.
Анотація:
The database “Historical Artificial Radionuclides in the Pacific Ocean and its Marginal Seas”, or HAM database, has been created. The database includes90Sr,137Cs, and239,240Pu concentration data from the seawater of the Pacific Ocean and its marginal seas with some measurements from the sea surface to the bottom. The data in the HAM database were collected from about 90 literature citations, which include published papers; annual reports by the Hydrographic Department, Maritime Safety Agency, Japan; and unpublished data provided by individuals. The data of concentrations of90Sr,137Cs, and239,240Pu have been accumulating since 19571998. The present HAM database includes 7737 records for137Cs concentration data, 3972 records for90Sr concentration data, and 2666 records for239,240Pu concentration data. The spatial variation of sampling stations in the HAM database is heterogeneous, namely, more than 80% of the data for each radionuclide is from the Pacific Ocean and the Sea of Japan, while a relatively small portion of data is from the South Pacific. This HAM database will allow us to use these radionuclides as significant chemical tracers for oceanographic study as well as the assessment of environmental affects of anthropogenic radionuclides for these 5 decades. Furthermore, these radionuclides can be used to verify the oceanic general circulation models in the time scale of several decades.
25
Caley, T., D. M. Roche, C. Waelbroeck, and E. Michel. "Constraining the Last Glacial Maximum climate by data-model (<i>i</i>LOVECLIM) comparison using oxygen stable isotopes." Climate of the Past Discussions 10, no. 1 (January 10, 2014): 105–48. http://dx.doi.org/10.5194/cpd-10-105-2014.
Анотація:
Abstract. We use the fully coupled atmosphere-ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 yr). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice-sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data-model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data-model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a trong mean annual cooling between the LGM and present (> 6°C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data-model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and present are not spatially homogenous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data-model comparison support a heterogeneous cooling of few degrees (2–4°C) in the LGM Ocean.
26
Ahmad, Iftikhar, M. E. A. Mondal, Md Sayad Rahaman, Rajneesh Bhutani, and M. Satyanarayanan. "Archean granitoids of the Aravalli Craton, northwest India." Geological Society, London, Special Publications 489, no. 1 (2020): 215–34. http://dx.doi.org/10.1144/sp489-2018-195.
Анотація:
AbstractThe Archean granitoids of the Aravalli Craton (NW India) are represented by orthogneisses (3.3–2.6 Ga) and undeformed granitoids (c. 2.5 Ga). Here we present whole-rock geochemical (elemental and Nd-isotope) data of the granitoids from the Aravalli Craton with an aim of understanding the evolution of the continental crust during the Archean. These Archean granitoids have been classified into three compositional groups: (1) TTG – tonalite–trondhjemite–granodiorite; (2) t-TTG – transitional TTG; and (3) sanukitoids. Based on the geochemical characteristics, it is proposed that the TTGs have formed from the partial melting of subducting oceanic plateau. The t-TTG formed owing to reworking of an older continental crust (approximately heterogeneous) in response to tectonothermal events in the craton. For the formation of the sanukitoids, a two-stage petrogenetic model is invoked which involves metasomatization of the mantle wedge, followed by slab breakoff and asthenospheric upwelling, which leads to the melting of asthenosphere and the metasomatized mantle wedge. It is also proposed that subducted sediments contributed to the genesis of sanukitoid magma.
27
Caley, T., D. M. Roche, C. Waelbroeck, and E. Michel. "Oxygen stable isotopes during the Last Glacial Maximum climate: perspectives from data–model (<i>i</i>LOVECLIM) comparison." Climate of the Past 10, no. 6 (November 10, 2014): 1939–55. http://dx.doi.org/10.5194/cp-10-1939-2014.
Анотація:
Abstract. We use the fully coupled atmosphere–ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 years). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data–model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data–model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a strong mean annual cooling in the area south of Iceland and Greenland between the LGM and present (> 6 °C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data–model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and the present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and the present are not spatially homogeneous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data–model comparison supports a heterogeneous cooling of a few degrees (2–4 °C) in the LGM Ocean.
28
McFerren, G., and T. van Zyl. "GEOSPATIAL DATA STREAM PROCESSING IN PYTHON USING FOSS4G COMPONENTS." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B7 (June 22, 2016): 931–37. http://dx.doi.org/10.5194/isprs-archives-xli-b7-931-2016.
Анотація:
One viewpoint of current and future IT systems holds that there is an increase in the scale and velocity at which data are acquired and analysed from heterogeneous, dynamic sources. In the earth observation and geoinformatics domains, this process is driven by the increase in number and types of devices that report location and the proliferation of assorted sensors, from satellite constellations to oceanic buoy arrays. Much of these data will be encountered as self-contained messages on data streams - continuous, infinite flows of data. Spatial analytics over data streams concerns the search for spatial and spatio-temporal relationships within and amongst data “on the move”. In spatial databases, queries can assess a store of data to unpack spatial relationships; this is not the case on streams, where spatial relationships need to be established with the incomplete data available. Methods for spatially-based indexing, filtering, joining and transforming of streaming data need to be established and implemented in software components. This article describes the usage patterns and performance metrics of a number of well known FOSS4G Python software libraries within the data stream processing paradigm. In particular, we consider the RTree library for spatial indexing, the Shapely library for geometric processing and transformation and the PyProj library for projection and geodesic calculations over streams of geospatial data. We introduce a message oriented Python-based geospatial data streaming framework called Swordfish, which provides data stream processing primitives, functions, transports and a common data model for describing messages, based on the Open Geospatial Consortium Observations and Measurements (O&M) and Unidata Common Data Model (CDM) standards. We illustrate how the geospatial software components are integrated with the Swordfish framework. Furthermore, we describe the tight temporal constraints under which geospatial functionality can be invoked when processing high velocity, potentially infinite geospatial data streams. The article discusses the performance of these libraries under simulated streaming loads (size, complexity and volume of messages) and how they can be deployed and utilised with Swordfish under real load scenarios, illustrated by a set of Vessel Automatic Identification System (AIS) use cases. We conclude that the described software libraries are able to perform adequately under geospatial data stream processing scenarios - many real application use cases will be handled sufficiently by the software.
29
Verma, Neeharika, Steven Lohrenz, Sumit Chakraborty, and Cédric G. Fichot. "Underway Hyperspectral Bio-Optical Assessments of Phytoplankton Size Classes in the River-Influenced Northern Gulf of Mexico." Remote Sensing 13, no. 17 (August 24, 2021): 3346. http://dx.doi.org/10.3390/rs13173346.
Анотація:
High inflows of freshwater from the Mississippi and Atchafalaya rivers into the northern Gulf of Mexico during spring contribute to strong physical and biogeochemical gradients which, in turn, influence phytoplankton community composition across the river plume–ocean mixing zone. Spectral features representative of bio-optical signatures of phytoplankton size classes (PSCs) were retrieved from underway, shipboard hyperspectral measurements of above-water remote sensing reflectance using the quasi-analytical algorithm (QAA_v6) and validated against in situ pigment data and spectrophotometric analyses of phytoplankton absorption. The results shed new light on sub-km scale variability in PSCs associated with dynamic and spatially heterogeneous environmental processes in river-influenced oceanic waters. Our findings highlight the existence of localized regions of dominant picophytoplankton communities associated with river plume fronts in both the Mississippi and Atchafalaya rivers in an area of the coastal margin that is otherwise characteristically dominated by larger microphytoplankton. This study demonstrates the applicability of underway hyperspectral observations for providing insights about small-scale physical-biological dynamics in optically complex coastal waters. Fine-scale observations of phytoplankton communities in surface waters as shown here and future satellite retrievals of hyperspectral data will provide a novel means of exploring relationships between physical processes of river plume–ocean mixing and frontal dynamics on phytoplankton community composition.
30
Billi, Andrea, Claudio Faccenna, Olivier Bellier, Liliana Minelli, Giancarlo Neri, Claudia Piromallo, Debora Presti, Davide Scrocca, and Enrico Serpelloni. "Recent tectonic reorganization of the Nubia-Eurasia convergent boundary heading for the closure of the western Mediterranean." Bulletin de la Société Géologique de France 182, no. 4 (July 1, 2011): 279–303. http://dx.doi.org/10.2113/gssgfbull.182.4.279.
Анотація:
Abstract In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian (W-Africa) northward subduction beneath Eurasia, subduction has almost ceased, as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic reflection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the convergent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two back-arc oceanic basins (Algerian-Liguro-Provençal and Tyrrhenian basins) and it is now mainly active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provençal, Algerian, and Alboran (partly) margins. Onset of compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins following a similar propagation of the cessation of the subduction, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced on the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to really start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. Part of the contractional deformation may have shifted toward the north in the Liguro-Provençal basin possibly because of its weak rheological properties compared with those of the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are strongly heterogeneous along the boundary. These features prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred to follow a Wilson Cycle (at a small scale) with the following main steps : (1) northward Nubian subduction with Mediterranean back-arc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive onset of compression, from west to east, in the former back-arc domain and consequent basin inversion (since ~8–10 Ma); (4) possible future subduction of former back-arc basins.
31
Reyes, Javier, Luis E. Lara, Vanessa Sutherland, Nicolás Aguirre, Carlos Orellana, Folkmar Hauff, and Kaj Hoernle. "Tracing the Origin and Magmatic Evolution of the Rejuvenated Volcanism in Santa Clara Island, Juan Fernández Ridge, SE Pacific." Minerals 14, no. 5 (May 19, 2024): 524. http://dx.doi.org/10.3390/min14050524.
Анотація:
Oceanic intraplate volcanoes sometimes experience late-stage eruptive activity known as rejuvenated volcanism, and contrasting interpretations for its petrogenesis depend on the compositional characteristics. In the Juan Fernández Ridge (JFR), a volcanic chain approximately 800 km in length emplaced on the Nazca Plate, some subaerial occurrences of rejuvenated volcanism have been recognized on the Robinson Crusoe and Santa Clara Islands, both part of the same deeply eroded shield volcano complex. This study aims to understand the origin and magmatic evolution of rejuvenated volcanism on Santa Clara Island, emplaced after ~2.15 Ma of quiescence above the shield sequence, mainly via the analysis of unpublished geochemical and isotopic data. Field reconnaissance identified two nearly coeval rejuvenated sequences on Santa Clara Island: Bahía W (BW) and Morro Spartan (MS), both formed by basanitic and picro-basaltic lava flows with brecciated levels and local intercalations of sedimentary and pyroclastic deposits. In comparison to the chemical signature of the preceding shield-building stage (comprised mainly of basalts and picrites), the two rejuvenated sequences exhibit a notable enrichment in incompatible elements, but the Sr, Nd, and Pb isotopes are very similar to the FOZO mantle endmember, with an apparent additional contribution of HIMU and EM1 components. The geochemistry of lavas revealed the involvement of various processes, including contamination by ultramafic xenoliths, high-pressure fractional crystallization of olivine and clinopyroxene, and potential partial assimilation of oceanic lithospheric components. While the oceanic lithosphere has been considered as a potential source, the isotopic data from Santa Clara lies outside of the mixing curve between depleted mantle (DM, here represented by the North Chile Rise and the East Pacific Rise) and the previous shield stage, suggesting that a lithospheric mantle is not the primary source for the rejuvenated stage volcanism. Therefore, we favor an origin of the rejuvenated volcanism from the mantle plume forming the JFR, supported by similarities in isotopic signatures with the shield stage and high values of 208Pb/204Pb (only comparable to San Félix—San Ambrosio in the vicinity of JFR), implying the presence of a regional source with radiogenic 208Pb/204Pb isotope ratios. In addition, isotopic variations are subparallel to the mixing line between HIMU and EM1 components, whose participation in different proportions might explain the observed trends. In conclusion, we propose that the source of the rejuvenated volcanism on Santa Clara Island is a heterogeneous mantle plume, the same one that fed the shield stage. The rejuvenated volcanism is derived from a secondary melting zone away from the main axis of the plume.
32
Geersen, Jacob, Andrea Festa, and Francesca Remitti. "Structural constraints on the subduction of mass-transport deposits in convergent margins." Geological Society, London, Special Publications 500, no. 1 (December 19, 2019): 115–28. http://dx.doi.org/10.1144/sp500-2019-174.
Анотація:
AbstractThe subduction of large and heterogeneous mass-transport deposits (MTDs) is discussed to modify the structure and physical state of the plate boundary and therewith exert an influence on seismicity in convergent margins. Understanding which subduction-zone architectures and structural boundary conditions favour the subduction of MTDs, primarily deposited in oceanic trenches, is therefore highly significant. We use bathymetric and seismic reflection data from modern convergent margins to show that a large landslide volume and long runout, in concert with thin trench sediments, increase the chances for an MTD to become subducted. In regions where the plate boundary develops within the upper plate or at its base (non-accretionary margins), and in little-sedimented trenches (sediment thickness <2 km), an MTD has the highest potential to become subducted, particularly when characterized by a long runout. On the contrary, in the case of a heavily sedimented trench (sediment thickness >4 km) and short runout, an MTD will only be subducted if the thickness of subducting sediments is higher than the thickness of sediments under the MTD. The results allow identification of convergent margins where MTDs are preferentially subducted and thus potentially alter plate-boundary seismicity.
33
Weidner, Elizabeth, Larry Mayer, and Thomas C. Weber. "Direct measurements of gas flux at seep sites using a broadband split-beam echosounder." Journal of the Acoustical Society of America 154, no. 4_supplement (October 1, 2023): A92. http://dx.doi.org/10.1121/10.0022903.
Анотація:
Measurement of methane gas flux from oceanic seep sites is challenging, given the ephemeral nature and the heterogeneous spatial distribution of seeps. Acoustic systems offer a solution, as they make synoptic measurements of the water column, and the gas bubbles are strong acoustic scatterers. Here, we present a method to directly estimate gas flux using a calibrated broadband split-beam echosounder. The vertical range resolution of the broadband system facilitates discrimination of individual bubbles in the acoustic record. By comparing measurements of bubble target strength to an analytical scattering model, bubble radii can be directly measured from the acoustic data. Concurrently, split-aperture processing allows for the precise tracking of bubbles as they rise from the seafloor for measurement of bubble rise velocity. Together, the observations of bubble radius and rise velocity offer a measure of gas flux, requiring nothing more than a vessel transiting over a seep site. Application of this method to seep data collected on the East Siberian Arctic Shelf shows good agreement between resulting measurements of bubble radii (0.68–8.40 mm) with those made using optical sensors, and bubble rise velocities (4–36 cm/s) are consistent with published measurements and models. Extrapolating from single bubbles measurements, our estimates of regional methane flux (2.9 × 104 kg/year) suggest that carbon emissions in this region may be lower than previously believed.
34
Kaneshima, Satoshi. "Seismic scatterers in the lower mantle near subduction zones." Geophysical Journal International 219, Supplement_1 (May 28, 2019): S2—S20. http://dx.doi.org/10.1093/gji/ggz241.
Анотація:
SUMMARY We investigate the global distribution of S-to-P scatterers in the shallow to mid-lower mantle beneath subduction zones, where deep seismicity extends down to the bottom of the upper mantle. By array processing broadband and short period waveform data obtained at seismic networks, we seek anomalous later phases in the P coda within about 15–150 s after direct P waves. The later phases usually arrive along off-great circle paths and significantly later than S-to-P conversion from the ‘660 km’ discontinuity, often show positive slowness anomalies relative to direct P, and do not show a conversion depth that is consistent among nearby events. They are thus adequately regarded as scattered waves, rather than conversion at a global horizontal discontinuity. The S-to-P scattered waves often show amplitudes comparable to ‘S660P’ waves, which indicates that a spatial change in elastic properties by several percent occurs at the scatterers as abruptly as the post-spinel transformation and should arise from compositional heterogeneity. We locate prominent S-to-P scatterers beneath Pacific subduction zones and beneath southern Spain. Nearly half of 137 S-to-P scatterers located in this study and previous studies by the authors are shallower than 1000 km, and the number of scatterers decreases with depth. Scatterers deeper than 1800 km are rare and mostly weak. We examine relations between the locations of the scatterers and recently subducted slabs inferred from seismic tomography. The scatterers of mid-mantle depths, deeper than about 1000 km, are located distant from tomographic slabs. On the other hand, the majority of shallower scatterers are located beneath the slabs rather than near their fastest portions, which would indicate that chemically heterogeneous materials are not extensively entrained within thickened and folded slabs when the slabs impinge on the lower mantle. We also find scatterers near the locations where basaltic rocks of recently subducted oceanic crust are expected to exist, which suggests that oceanic crust is not delaminating when slabs impinge on the lower mantle.
35
Dey, Sukanta, Sibani Kumari Nayak, Aniruddha Mitra, Keqing Zong, and Yongsheng Liu. "Mechanism of Paleoarchean continental crust formation as archived in granitoids from the northern part of Singhbhum Craton, eastern India." Geological Society, London, Special Publications 489, no. 1 (2020): 189–214. http://dx.doi.org/10.1144/sp489-2019-202.
Анотація:
AbstractMany Paleoarchean cratons display a gradual change from early sodic tonalite–trondhjemite–granodiorite magmatism to late K-rich granitoid magmatism; the geodynamic significance of this change is debatable though. This contribution presents field, geochemical and zircon U–Pb age and Hf isotope results of four different 3.32–3.25 Ga granitoid bodies from the northern part of Singhbhum Craton to investigate their petrogenesis and role in crustal evolution. The granitoids range in composition from tonalites to trondhjemites, derived from intracrustal melting at low- to medium-pressure conditions. The source was mainly low-K mafic rock. The granitoids show intrasuite fractional crystallization. These sodic granitoids represent the last stage of granitoid magmatism in the Singhbhum Craton which formed contemporaneously with K-rich granitoids occurring in other parts of the craton. This fact suggests that, contrary to the popular notion (of only potassic granitoids), both sodic and potassic granitoids could form at the terminal phase of cratonization, implying reworking of heterogeneous (mafic to tonalite) crust. A combination of evidence from geochemical data, secular change in granitoid composition, structural pattern and rock association of the Singhbhum Craton reflects that recurring mantle plume-related mafic–ultramafic magma emplacement in an oceanic plateau setting and attendant crustal melting can explain the Paleoarchean crustal evolution pattern.
36
Pipera, K., A. Koroneos, T. Soldatos, G. Poli, and G. Christofides. "Origin of the High-K Tertiary magmatism in Northern Greece: Implications for mantle geochemistry and geotectonic setting." Bulletin of the Geological Society of Greece 47, no. 1 (September 5, 2013): 416. http://dx.doi.org/10.12681/bgsg.11017.
Анотація:
Tertiary plutonic and volcanic rocks cropping out in the Rhodope Massif (N. Greece) are studied using existing and new geochemical and isotopic data. Most of these rocks belong to the post-collisional magmatism formed as part of the prolonged extensional tectonics of the Rhodope region in Late Cretaceous– Paleogene time. This magmatism is considered to be of mantle origin; however, the character of the mantle source is controversial. Rock bulk chemistry and compositional variations show magmas with calc-alkaline to high-K calc-alkaline and shoshonitic features associated with magmatism at convergent margins. Initial 87Sr/86Sr, 143Nd/144Nd ratios, Pb isotopes and REE composition of the mafic rocks indicate mainly an enriched mantle source, even if some rocks indicate a depleted mantle source. Low- and High-K mafic members of these rocks coexist indicating a strongly heterogeneous mantle source. The High-K character of some of the mafic rocks is primarily strongly related to mantle enrichment by subduction-related components, rather than crustal contamination. The geochemical characteristics of the studied rocks (e.g Ba/Th,Th/Yb,Ba/La, U/Th, Ce/Pb) indicate that primarily sediments and/or sediment melts, rather than fluid released by the subducted oceanic crust controlled the source enrichment under the Rhodope Massif.
37
Harnois, Luc, and John M. Moore. "Geochemistry of two metavolcanic arc suites from the Central Metasedimentary Belt of the Grenville Province, southeastern Ontario, Canada." Canadian Journal of Earth Sciences 28, no. 9 (September 1, 1991): 1429–43. http://dx.doi.org/10.1139/e91-126.
Анотація:
Samples of two subalkaline metavolcanic suites, the Tudor formation (ca. 1.28 Ga) and the overlying Kashwakamak formation, have been analysed for major elements and 27 trace elements (including rare-earth elements). The Tudor formation is tholeiitic and contains mainly basaltic flows, whereas the Kashwakamak formation is calc-alkaline and contains mainly andesitic rocks with minor felsic rocks. The succession has been regionally metamorphosed to upper greenschist – lower amphibolite facies. Trace-element abundances and ratios indicate that rocks of the Tudor and Kashwakamak formations are island-arc type. Geochemical modelling using rare-earth elements, Zr, Ti, and Y indicates that the Tudor volcanic rocks are not derived from a single parental magma through simple fractional crystallization. Equilibrium partial melting of a heterogeneous Proterozoic upper mantle can explain the trace-element abundances and ratios of Tudor formation volcanic rocks. The intermediate to felsic rocks of the Kashwakamak formation appear to have been derived from a separate partial melting event. The data are consistent with an origin of the arc either on oceanic crust or on thinned continental crust, and with accretion of the arc to a continental margin between the time of extrusion of Tudor volcanic rocks and that of Kashwakamak volcanic rocks.
38
Furman, Tanya, Barry B. Hanan, Megan Pickard Sjoblom, Biltan Kürkcüoğlu, Kaan Sayit, Erdal Şen, Pinar Alıcı Şen, and Tekin Yürür. "Evolution of mafic lavas in Central Anatolia: Mantle source domains." Geosphere 17, no. 6 (November 4, 2021): 1631–46. http://dx.doi.org/10.1130/ges02329.1.
Анотація:
Abstract We present new Sr-Nd-Pb-Hf isotopic data on mafic lavas from the Sivas, Develidağ, Erciyes, and Erkilet volcanic complexes in central Turkey and Tendürek in eastern Turkey to evaluate the mantle sources for volcanism in the context of the geodynamic evolution of the Anatolian microplate. Early Miocene through Quaternary volcanism in Western Anatolia and latest Miocene through Quaternary activity in Central Anatolia were dominated by contributions from two distinct source regions: heterogeneous metasomatized or subduction-modified lithosphere, and roughly homogeneous sublithospheric ambient upper mantle; we model the source contributions through mixing between three end members. The sublithospheric mantle source plots close to the Northern Hemisphere reference line (NHRL) with radiogenic 206Pb/204Pb of ∼19.15, while the other contributions plot substantially above the NHRL in Pb isotope space. The lithospheric source is heterogeneous, resulting from variable pollution by subduction-related processes likely including direct incorporation of sediment and/or mélange; its range in radiogenic isotopes is defined by regional oceanic sediment and ultrapotassic melts of the subcontinental lithospheric mantle. The geochemical impact of this contribution is disproportionately large, given that subduction-modified lithosphere and/or ocean sediment dominates the Pb isotope signatures of mafic Anatolian lavas. Subduction of the Aegean or Tethyan seafloor, associated with marked crustal shortening, took place throughout the region until ca. 16–17 Ma, after which time broad delamination of the thickened lower crust and/or the Tethyan slab beneath Central Anatolia allowed for sediment and/or mélange and slab-derived fluids to be released into the overlying evolving modified mantle. Aggregation of melts derived from both mantle and lithospheric domains was made possible by upwelling of warm asthenospheric material moving around and through the complexly torn younger Aegean-Cyprean slab that dips steeply to the north beneath southern Anatolia.
39
Prouteau, Gaelle, Rene C. Maury, Manuel Pubellier, Joseph Cotten, and Herve Bellon. "Le magmatisme post-collisionnel du Nord-Ouest de Borneo, produit de la fusion d'un fragment de croute oceanique ancre dans le manteau superieur." Bulletin de la Société Géologique de France 172, no. 3 (May 1, 2001): 319–32. http://dx.doi.org/10.2113/172.3.319.
Анотація:
Abstract Magmatic activity linked to syn- or post-collisional zones leads to the emplacement of remarkably heterogeneous rocks: calc-alkaline, high-K calc-alkaline or shoshonitic series variably contaminated by continental crust; anatectic granites and ignimbrites derived from the latter; and finally alkali potassic to ultrapotassic basalts [Harris et al., 1990; Pearce et al., 1984, 1990; Arnaud et al., 1992; Benito et al., 1999]. The main sources of these magmas are either the upper mantle (sub-oceanic or subcontinental) frequently metasomatized by hydrous fluid originating from the subducted slab; or the continental crust, which can act as a contaminant [Benito et al., 1999; Miller et al., 1999] or melt directly [Harris et al., 1990; Zingg et al., 1990]. The purpose of the present paper is to document the role of a third source: the subducted oceanic crust, as evidenced by the occurrence of Miocene adakites in Sarawak (NW Borneo). The studied rocks have been sampled from western Sarawak (fig. 1), and their location is shown on the geological map [Tan, 1982] of figure 2. They mostly occur as stocks, dykes and sills which crosscut the Paleozoic to Miocene sedimentary units. Two kinds of intrusions can be distinguished. High-K calc-alkaline to medium-K calc-alkaline diorites and microdiorites occur in the northern part of the studied area, in Salak Island and Santubong Peninsula. Microtonalites and dacites occur near Kuching and in the southern part of Sarawak (Kuap and Bau areas). Whole-rock K-Ar data (table I) demonstrate that these two associations are of different ages: high-K calc-alkaline diorites were emplaced during the Lower Miocene (22.3 to 23.7 Ma), whereas the microtonalites and dacites are younger by ca. 8 Ma or more (Middle to Upper Miocene, 14.6 to 6.4 Ma). Major and trace element data (table II) show that the Lower Miocene diorites display all the usual characteristics of subduction-related magmas. The Middle to Upper Miocene microtonalites and dacites share some of these characteristics, but in addition they display typical adakitic features: SiO 2 -rich (65.5-70%) and sodic (Na 2 O/K 2 O>2) character (table II and figure 3); lack or rare occurrence of pyroxenes, usually replaced by early-crystallized (near-liquidus) amphiboles (table III); very low Y and HREE contents, consistent with the presence of residual garnet in their source, and leading to characteristically high La/Yb and Sr/Y ratios (fig. 4, 5). Their titanomagnetite-hemoilmenite associations reflect equilibrium features [Bacon and Hirschman, 1988] indicating moderate temperatures (<900 degrees C) and highly oxidizing (NNO+1) crystallization conditions [Ghiorso and Sack, 1991]. The Lower Miocene Sarawak diorites are typically subduction-related from a geochemical point of view. They likely derive from the evolution of island-arc basaltic magmas, which themselves originated from the partial melting of upper mantle peridotites previously metasomatized by hydrous fluids expelled from the subducting oceanic slab [Tatsumi et al., 1986; Tatsumi, 1989]. The origin of the Middle-Upper Miocene adakitic microtonalites and dacites is different. According to previous studies, they likely derive from the partial melting of metabasalts (garnet amphibolites or eclogites) from subducted oceanic crust [Defant and Drummond, 1990; Defant et al., 1991, 1992; Drummond et al., 1996; Maury et al., 1996; Martin, 1993, 1999]. Their position in the hybrid tonalite+peridotite system [Caroll and Wyllie, 1989] shows that they crystallized within the garnet stability field and likely interacted with the upper mantle during their ascent (fig. 7). This feature is not consistent with their genesis through melting of metabasalts accreted at the base of the Borneo continental crust. In addition, the less evolved Sarawak adakites display mineralogical and geochemical features remarkably similar to those of the 1991 Mt Pinatubo dacite, the experimental petrology of which has been extensively studied at low [2 kbar; Scaillet and Evans, 1999; Rutherford and Devine, 1996] to medium pressures [4 to 20 kbar; Prouteau et al., 1999]. Such dacitic magmas are not in equilibrium with garnet at pressures lower than or equal to 20 kbar, which rules out their derivation from metabasalts tectonically or magmatically accreted to the base of the North Borneo continental crust. We propose, instead, that they originated from the partial melting of basalts from a fragment of oceanic lithosphere within the upper mantle. Like the adakites of Central Mindanao, Philippines [Sajona et al., 1994, 1997 and 2000; Maury et al., 1996] and those from Aird Hills, Papua-New Guinea [Smith et al., 1979; Defant and Drummond, 1990] the Sarawak adakites represent potential markers of the occurrence at depth of oceanic crust slivers, which could be much more common in collision zones than previously thought.
40
FAGHIH, ALI, TIMOTHY KUSKY, and BABAK SAMANI. "Kinematic analysis of deformed structures in a tectonic mélange: a key unit for the manifestation of transpression along the Zagros Suture Zone, Iran." Geological Magazine 149, no. 6 (June 29, 2012): 1107–17. http://dx.doi.org/10.1017/s0016756812000295.
Анотація:
AbstractKinematic analysis of mélange fabrics provides critical information concerning tectonic processes and evaluation of the kinematics of ancient relative plate motion. Systematic kinematic analysis of deformed structures within a tectonic mélange exposed along the Zagros Suture Zone elucidates that this zone is an ancient transpressional boundary. The mélange is composed of a greywacke and mudstone matrix surrounding various lenses, blocks and ribbons of radiolarian chert, limestone, sandstone, pillow lava, tuff, serpentinite, shale and marl. The deformation fabrics of the mélange suggest that the mélange units were tectonically accreted at shallow levels within a subduction complex, resulting in layer-parallel extension and shearing along a NW–SE-trending suture that juxtaposes the Afro-Arabian continent to the south and the Central Iranian microcontinents to the north. The tectonic mélange is characterized by subhorizontal layer-parallel extension and subsequent heterogeneous non-coaxial shear resulting in alternating asymmetric and layer-parallel extensional fabrics such as P–Y fabrics and boudinaged layers. Kinematic data suggest that the mélange formed during oblique subduction of the Neo-Tethys oceanic lithosphere in Late Cretaceous time. Kinematic shear sense indicators reveal that the slip direction (N9°E to N14°E) during accretion-related deformations reflects the relative plate motion between the Afro-Arabian continent and Central Iranian microcontinents during Late Cretaceous to Miocene times.
41
Whalen, J. B., K. L. Currie, and O. van Breemen. "Episodic Ordovician-Silurian plutonism in the Topsails igneous terrane, western Newfoundland." Transactions of the Royal Society of Edinburgh: Earth Sciences 78, no. 1 (1987): 17–28. http://dx.doi.org/10.1017/s0263593300010920.
Анотація:
ABSTRACTThe Topsails igneous terrane of western Newfoundland contains several intrusive and volcanic suites underlain and separated by screens of older intrusive rocks. The heterogeneous Hungry Mountain complex yielded U-Pb zircon upper and lower intercept ages of 2090 ± 75 Ma and 467 ± 8 Ma, demonstrating a significant inherited component of Aphebian age, while an adjacent suite of relatively massive granodioritic to granitic rocks yielded a slightly discordant U-Pb zircon age of 460 ± 10 Ma. The 438 ± 8 Ma age of the Rainy Lake complex, a suite of island arc type intrusive rocks, suggests it forms part of a Silurian magmatic episode, which also included Springdale Group bimodal volcanics (429 ± 4 Ma), and peralkaline granite and subvolcanic porphyries which intrude the Springdale Group (429 ± 3 Ma and 427 ±3 Ma, respectively). Most igneous units contain a slight component of inherited zircon, but initial 87Sr/86Sr ratios (average 0·704) are similar to calculated ‘Bulk Earth’ values at this time.Available data suggest that the Topsails terrane formed an oceanic tract with active volcanic island arcs when obduction commenced in early Ordovician time. The subsequent magmatic history, including the major but short-lived early Silurian magmatism, can be directly or indirectly related to obduction processes, including over-riding of the Topsails terrane by ophiolitic allochthons. There is no evidence of any Acadian (Devonian) igneous activity in the Topsails terrane.
42
NIMIS, Pier Luigi, Stefano MARTELLOS, Daniel SPITALE, and Juri NASCIMBENE. "Exploring patterns of commonness and rarity in lichens: a case study from Italy (Southern Europe)." Lichenologist 50, no. 3 (May 2018): 385–96. http://dx.doi.org/10.1017/s0024282917000731.
Анотація:
AbstractThis paper, based on data from the latest checklist of Italy, analyzes the distribution patterns of rare and common lichen species within biogeographically homogeneous versus heterogeneous areas of Italy, and the relationships with some main drivers of rarity and commonness. The following data were used: 1) commonness-rarity values of 2565 species in nine ecoregions; 2) frequency of 353 nationally rare and 387 nationally common species in 21 administrative regions. The following functional and ecological traits were considered: growth form, photobiont(s), type of reproduction, substrata, bioclimatic range, ecological indicator values for aridity and eutrophication, and poleophoby. Within each ecoregion, rare species by far outweigh common species but about one third of these are common in other ecoregions. At the level of regional floras, rarity is significantly associated with epiphytic substrata, non-trebouxioid photobionts and high air humidity, while commonness is associated with saxicolous substrata, trebouxioid photobionts and eutrophication. Rarity seems to mainly depend on two factors, bioclimate (many rare species are outside the limit of their bioclimatic optima) and reduced availability of suitable habitats (e.g. old-growth forests), while commonness is mainly related to disturbance (eutrophication, creation of drier habitats). Most of the nationally rare lichens belong to an oceanic-suboceanic element with tropical affinities or to a small set of continental species with their optima in the dry steppe biome, which suggests that many rare species can persist in microrefugia, that is sites with microclimates that support small populations of species beyond the boundaries of the climatic limits of their main distributions.
43
Picazo, Suzanne M., Tanya A. Ewing, and Othmar Müntener. "Paleocene metamorphism along the Pennine–Austroalpine suture constrained by U–Pb dating of titanite and rutile (Malenco, Alps)." Swiss Journal of Geosciences 112, no. 2-3 (September 13, 2019): 517–42. http://dx.doi.org/10.1007/s00015-019-00346-1.
Анотація:
Abstract We present in situ rutile and titanite U–Pb geochronology for three samples from the Ur breccia, which forms the boundary between the Malenco unit and the Margna nappe (Eastern Central Alps) near Pass d’Ur in southeast Switzerland. These sampled both oceanic brecciated material and a blackwall reaction zone in contact with a micaschist and serpentinized peridotite. Peak temperatures during Alpine metamorphism in these units were ~ 460 ± 30 °C. Textural observations combined with new geochronological data indicate that rutile and titanite both grew below their closure temperatures during Alpine metamorphism. We present a technique to calculate the most precise and accurate ages possible using a two-dimensional U–Pb isochron on a Wetherill concordia. Rutile from two samples gave a U–Pb isochron age of 63.0 ± 3.0 Ma. This age conflicts with previous 39Ar–40Ar data on heterogeneous amphiboles from which an age of 90–80 Ma was inferred for the high pressure part of the Alpine evolution, but is consistent with K–Ar ages and Ar–Ar ages on phengitic white mica. Titanite from three samples gave a U–Pb isochron age of 54.7 ± 4.1 Ma. This age is consistent with Rb–Sr isochron ages on mylonites along and in the footwall of the Lunghin–Mortirolo movement zone, a major boundary that separates ductile deformation in the footwall from mostly localized and brittle deformation in the hangingwall. Our ages indicate a Paleocene rather than upper Cretaceous metamorphism of the Pennine–Austroalpine boundary and permit at most ~ 15 Myr, and possibly much less, between the growth of rutile and titanite.
44
Akimoto, Hajime, Tatsuya Nagashima, Jie Li, Joshua S. Fu, Dongsheng Ji, Jiani Tan, and Zifa Wang. "Comparison of surface ozone simulation among selected regional models in MICS-Asia III – effects of chemistry and vertical transport for the causes of difference." Atmospheric Chemistry and Physics 19, no. 1 (January 16, 2019): 603–15. http://dx.doi.org/10.5194/acp-19-603-2019.
Анотація:
Abstract. In order to clarify the causes of variability among the model outputs for surface ozone in the Model Intercomparison Study Asia Phase III (MICS-Asia III), three regional models, CMAQ v.5.0.2, CMAQ v.4.7.1, and NAQPMS (abbreviated as NAQM in this paper), have been selected. Detailed analyses of monthly averaged diurnal variation have been performed for selected grids covering the metropolitan areas of Beijing and Tokyo and at a remote oceanic site, Oki. The chemical reaction mechanism, SAPRC99, used in the CMAQ models tended to give a higher net chemical ozone production than CBM-Z used in NAQM, agreeing with previous studies. Inclusion of the heterogeneous “renoxification” reaction of HNO3 (on soot surface)→NO+NO2 only in NAQM would give a higher NO concentration resulting in a better agreement with observational data for NO and nighttime O3 mixing ratios. In addition to chemical processes, the difference in the vertical transport of O3 was found to affect the simulated results significantly. Particularly, the increase in downward O3 flux from the upper layer to the surface after dawn was found to be substantially different among the models. Larger early morning vertical transport of O3 simulated by CMAQ 5.0.2 is thought to be the reason for higher daytime O3 in July in this model. All three models overestimated the daytime ozone by ca. 20 ppbv at the remote site Oki in July, where in situ photochemical activity is minimal.
45
Karabil, Sitar, Eduardo Zorita, and Birgit Hünicke. "Mechanisms of variability in decadal sea-level trends in the Baltic Sea over the 20th century." Earth System Dynamics 8, no. 4 (November 17, 2017): 1031–46. http://dx.doi.org/10.5194/esd-8-1031-2017.
Анотація:
Abstract. Coastal sea-level trends in the Baltic Sea display decadal-scale variations around a long-term centennial trend. In this study, we analyse the spatial and temporal characteristics of the decadal trend variations and investigate the links between coastal sea-level trends and atmospheric forcing on a decadal timescale. For this analysis, we use monthly means of sea-level and climatic data sets. The sea-level data set is composed of long tide gauge records and gridded sea surface height (SSH) reconstructions. Climatic data sets are composed of sea-level pressure, air temperature, precipitation, evaporation, and climatic variability indices. The analysis indicates that atmospheric forcing is a driving factor of decadal sea-level trends. However, its effect is geographically heterogeneous. This impact is large in the northern and eastern regions of the Baltic Sea. In the southern Baltic Sea area, the impacts of atmospheric circulation on decadal sea-level trends are smaller. To identify the influence of the large-scale factors other than the effect of atmospheric circulation in the same season on Baltic Sea sea-level trends, we filter out the direct signature of atmospheric circulation for each season separately on the Baltic Sea level through a multivariate linear regression model and analyse the residuals of this regression model. These residuals hint at a common underlying factor that coherently drives the decadal sea-level trends in the whole Baltic Sea. We found that this underlying effect is partly a consequence of decadal precipitation trends in the Baltic Sea basin in the previous season. The investigation of the relation between the AMO index and sea-level trends implies that this detected underlying factor is not connected to oceanic forcing driven from the North Atlantic region.
46
Chamberlain, K. J., J. Barclay, K. J. Preece, R. J. Brown, and J. P. Davidson. "Lower Crustal Heterogeneity and Fractional Crystallization Control Evolution of Small-volume Magma Batches at Ocean Island Volcanoes (Ascension Island, South Atlantic)." Journal of Petrology 60, no. 8 (August 1, 2019): 1489–522. http://dx.doi.org/10.1093/petrology/egz037.
Анотація:
Abstract Ocean island volcanoes erupt a wide range of magmatic compositions via a diverse range of eruptive styles. Understanding where and how these melts evolve is thus an essential component in the anticipation of future volcanic activity. Here we examine the role of crustal structure and magmatic flux in controlling the location, evolution and ultimately composition of melts at Ascension Island. Located in the South Atlantic, Ascension Island is an ocean island volcano that has produced a continuum of eruptive compositions from basalt to rhyolite in its 1 Myr subaerial eruptive history. Volcanic rocks broadly follow a silica-undersaturated subalkaline evolutionary trend, and new data presented here show a continuous compositional trend from basalt through trachyte to rhyolite. Detailed petrographic observations are combined with in situ geochemical analyses of crystals and glass, and new whole-rock major and trace element data from mafic and felsic pyroclastic and effusive deposits that span the entire range in eruptive ages and compositions found on Ascension Island. These data show that extensive fractional crystallization is the main driver for the production of felsic melts for Ascension Island, a volcano built on thin, young, oceanic crust. Strong spatial variations in the compositions of erupted magmas reveal the role of a heterogeneous lower crust; differing degrees of interaction with a zone of plutonic rocks are responsible for the range in mafic lava compositions, and for the formation of the central and eastern felsic complexes. A central core of nested, small-scale plutonic, or mush-like, bodies inhibits the ascent of mafic magmas, allowing sequential fractional crystallization within the lower crust, and generating felsic magmas in the core of the island. There is no evidence for magma mixing preserved in any of the studied eruptions, suggesting that magma storage regions are transient, and material is not recycled between eruptions.
47
Hertwig, A., W. V. Maresch, and H. P. Schertl. "Jadeitite and Related Rocks in Serpentinite Mélanges from the Rio San Juan Complex, Dominican Republic: Evidence for Both Isochemical Replacement and Metasomatic Desilication of Igneous Protoliths with Fluid-Assisted Jadeite Growth." Russian Geology and Geophysics 62, no. 5 (May 1, 2021): 496–524. http://dx.doi.org/10.2113/rgg20204265.
Анотація:
Abstract —This study presents an overview of the systematic petrography, mineralogy, and geochemistry of jadeitite and jadeite-rich rocks found as blocks in the serpentinite mélanges of the Rio San Juan Complex (RSJC) of the northern Dominican Republic. The RSJC is one of the remnants of the subduction/accretionary complex of the Great Caribbean Arc that once spanned the gap between North and South America, moved relatively eastward to its present position as the Lesser Antilles island arc, and left collisional fragments along the two continental margins. Our systematic collection of heterogeneous samples ranges from jadeitite s.str. (sensu stricto) with ≥90 vol.% jadeite to quartz-rich rocks with jadeite and lawsonite. Two suites of rock types can be recognized. In the matrix-quartz-free rock suite, albite is the principal vein-filling or interstitial phase. Quartz is present only as inclusions in the cores of some jadeite crystals. In the matrix-quartz-bearing rock suite, quartz is abundant and albite is relatively rare. The first-order question concerning jadeite-rich rocks is whether jadeite precipitated from a high-pressure aqueous fluid (“vein precipitation” or “P-type”) or whether the jadeite-rich rock formed through comprehensive metasomatic replacement of an igneous protolith (“R-type”). Some examples occur as discordant veins and are clearly P-type. For most, however, classification has been equivocal. The systematic data on the petrography and whole-rock chemistry of jadeite rocks from the RSJC presented in this paper leads to significant clarification. A major argument against R-type genesis is that the metasomatic mass transfer required to produce jadeitite and jadeite-rich rocks from any normal igneous protolith is prohibitively complex. Using whole-rock, major-element compositions, we show that many members of the matrix-quartz-bearing rock suite from the RSJC can be derived by isochemical HP/LT metamorphism of normal oceanic plagiogranites subducted together with oceanic crust. Isocon analysis shows, furthermore, that more jadeite-rich rock types and also members of the matrix-quartz-free suite can be derived from such plagiogranites primarily by straightforward desilication, a realistic scenario in a serpentine-rich environment. The quartz inclusions found in jadeite crystals of the matrix-quartz-free suite corroborate a genetic path in which the plagioclase in a plagiogranite protolith reacts to jadeite + quartz. Later desilication and the formation of albite in the Si-undersaturated rock matrix leave tell-tale quartz inclusions as relics in jadeite crystals.
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Moulin, Maryline, Frauke Klingelhoefer, Alexandra Afilhado, Daniel Aslanian, Philippe Schnurle, Hervé Nouzé, Marina Rabineau, Marie-Odile Beslier, and Aurélie Feld. "Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – I. Gulf of Lion’s margin." Bulletin de la Société Géologique de France 186, no. 4-5 (July 1, 2015): 309–30. http://dx.doi.org/10.2113/gssgfbull.186.4-5.309.
Анотація:
Abstract The conjugate margins system of the Gulf of Lion and West Sardinia (GLWS) represents a unique natural laboratory for addressing fundamental questions about rifting due to its landlocked situation, its youth, its thick sedimentary layers, including prominent palaeo-marker such as the MSC event, and the amount of available data and multidisciplinary studies. The main goals of the SARDINIA experiment, were to (i) investigate the deep structure of the entire system within the two conjugate margins: the Gulf of Lion and West Sardinia, (ii) characterize the nature of the crust, and (iii) define the geometry of the basin and provide important constrains on its genesis. This paper presents the results of P-wave velocity modelling on three coincident near-vertical reflection multi-channel seismic (MCS) and wide-angle seismic profiles acquired in the Gulf of Lion, to a depth of 35 km. A companion paper [part II – Afilhado et al., 2015] addresses the results of two other SARDINIA profiles located on the oriental conjugate West Sardinian margin. Forward wide-angle modelling of both data sets confirms that the margin is characterised by three distinct domains following the onshore unthinned, 33 km-thick continental crust domain: Domain I is bounded by two necking zones, where the crust thins respectively from ~30 to 20 and from 20 to 7 km over a width of about 170 km; the outermost necking is imprinted by the well-known T-reflector at its crustal base; Domain II is characterised by a 7 km-thick crust with « anomalous » velocities ranging from 6 to 7.5 km/s; it represents the transition between the thinned continental crust (Domain I) and a very thin (only 4–5 km) “atypical” oceanic crust (Domain III). In Domain II, the hypothesis of the presence of exhumed mantle is falsified by our results: this domain may likely consist of a thin exhumed lower continental crust overlying a heterogeneous, intruded lower layer. Moreover, despite the difference in their magnetic signatures, Domains II and III present the very similar seismic velocities profiles, and we discuss the possibility of a connection between these two different domains.
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Martin, C., and A. P. Dickin. "Styles of Proterozoic crustal growth on the southeast margin of Laurentia: evidence from the central Grenville Province northwest of Lac St.-Jean, Quebec." Canadian Journal of Earth Sciences 42, no. 10 (October 1, 2005): 1643–52. http://dx.doi.org/10.1139/e05-052.
Анотація:
The southeast margin of Laurentia was a very long lived active continental margin, part of whose history is recorded in the Grenville Province of the Canadian Shield. Within this province, Nd-isotope mapping can be used to define the boundaries between terranes with a variety of crustal formation ages and can also distinguish between crustal growth by oceanic and continental-arc magmatism. The former gives rise to large terranes with homogeneous Nd-isotope signatures and well-defined boundaries, whereas the latter leads to areas with heterogeneous Nd-isotope signatures. One of the best examples of continental-arc magmatism in the Grenville Province is provided by the region northwest of Lac St.-Jean, Quebec. Eighty new Nd-isotope analyses are used (along with aeromagnetic data) to divide this area into three blocks, bounded by abrupt changes in Nd model age. The western block consists almost exclusively of tonalitic grey gneisses with Archean model ages. The eastern block is composed almost exclusively of gneisses with Nd model ages of 1.61.5 Ga and tonalitetrondhjemitegranodiorite-type chemistry. In contrast, the central block has a wide range of Nd-isotope signatures and more alkaline major element chemistry characteristic of an ensialic arc. The εNd values in this block correlate with distance southeast of the Allochthon Boundary Thrust, suggesting that ensialic arc magmas suffered diminishing contamination in a southeastward direction by old Laurentian crust. A subduction-flip model is proposed, whereby north-dipping subduction under the continental margin followed the accretion of a Mesoproterozoic arc terrane to the Laurentian craton.
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Lemenkova, Polina. "Seafloor and Ocean Crust Structure of the Kerguelen Plateau from Marine Geophysical and Satellite Altimetry Datasets." Geomatics 3, no. 3 (August 10, 2023): 393–426. http://dx.doi.org/10.3390/geomatics3030022.
Анотація:
The volcanic Kerguelen Islands are formed on one of the world’s largest submarine plateaus. Located in the remote segment of the southern Indian Ocean close to Antarctica, the Kerguelen Plateau is notable for a complex tectonic origin and geologic formation related to the Cretaceous history of the continents. This is reflected in the varying age of the oceanic crust adjacent to the plateau and the highly heterogeneous bathymetry of the Kerguelen Plateau, with seafloor structure differing for the southern and northern segments. Remote sensing data derived from marine gravity and satellite radar altimetry surveys serve as an important source of information for mapping complex seafloor features. This study incorporates geospatial information from NOAA, EMAG2, WDMAM, ETOPO1, and EGM96 datasets to refine the extent and distribution of the extracted seafloor features. The cartographic joint analysis of topography, magnetic anomalies, tectonic and gravity grids is based on the integrated mapping performed using the Generic Mapping Tools (GMT) programming suite. Mapping of the submerged features (Broken Ridge, Crozet Islands, seafloor fabric, orientation, and frequency of magnetic anomalies) enables analysis of their correspondence with free-air gravity and magnetic anomalies, geodynamic setting, and seabed structure in the southwest Indian Ocean. The results show that integrating the datasets using advanced cartographic scripting language improves identification and visualization of the seabed objects. The results include 11 new maps of the region covering the Kerguelen Plateau and southwest Indian Ocean. This study contributes to increasing the knowledge of the seafloor structure in the French Southern and Antarctic Lands.