tectonic features
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2021 ◽  
Author(s):  
Anna Gülcher ◽  
Laurent Montési ◽  
Taras Gerya ◽  
Jessica Munch

In the absence of global plate tectonics, mantle convection and plume-lithosphere interaction are the main drivers of surface deformation on Venus. Among documented tectonic structures, circular volcano-tectonic features known as coronae may be the clearest surface manifestations of mantle plumes and hold clues to the global Venusian tectonic regime. Yet, the exact processes underlying coronae formation and the reasons for their diverse morphologies remain controversial. Here, we use 3D thermomechanical numerical simulations of impingement of a thermal mantle plume upon the Venusian lithosphere to assess the origin and diversity of large Venusian coronae. The ability of the mantle plume to penetrate into the Venusian lithosphere results in four main outcomes: lithospheric dripping, short-lived subduction, embedded plume and plume underplating. During the first three scenarios, plume penetration and spreading induce crustal thickness variations that eventually lead to a final topographic isostasy-driven topographic inversion from circular trenches surrounding elevated interiors to raised rims surrounding inner depressions, as observed on many Venusian coronae. Different corona structures may represent not only different styles of plume-lithosphere interactions, but also different stages in evolution. A morphological analysis of large existing coronae leads to the conclusion that least 37 large coronae (including the largest Artemis corona) are active, providing evidence for widespread ongoing plume activity on Venus.


Author(s):  
Pavla Hrubcová ◽  
Václav Vavryčuk

AbstractThe Tonga subduction zone in the south-west Pacific is the fastest convergent plate boundary in the world with the most active mantle seismicity. This zone shows unique tectonic features including Samoan volcanic lineament of plume-driven origin near the northern rim of the Tonga subducting slab. The proximity of the Samoa hotspot to the slab is enigmatic and invokes debates on interactions between the Samoa plume and the Tonga subduction. Based on long-term observations of intermediate and deep-focus Tonga earthquakes reported in the Global Centroid Moment Tensor (CMT) catalog, we provide novel detailed imaging of this region. Accurate traveltime residua of the P- and S-waves recorded at two nearby seismic stations of the Global Seismographic Network are inverted for the P- and S-wave velocities and their ratio and reveal their pronounced lateral variations. In particular, they differ for the southern and northern parts of the Tonga subduction region. While no distinct anomalies are detected in the southern Tonga segment, striking low-velocity anomalies associated with a high Vp/Vs ratio are observed in the northern Tonga segment close to the Samoa plume. These anomalies spread through the whole upper mantle down to depths of ~ 600 km. Together with the fast extension of the northern back-arc Lau Basin, slab deformation and geochemical enrichment in the northern Tonga region, they trace deep-seated magmatic processes and evidence an interaction of the Tonga subduction with the Samoa plume.


Author(s):  
A. Yu. Kosmacheva ◽  
M. O. Fedorovich

We present the interpretation of 2D seismic data in the Vilyui hemisyneclise located in the Republic of Sakha (Yakutia). The model identifies structural and tectonic features and tectonic development history of the Mesozoic deposits in the Vilyui hemisyneclise. Structure contour maps for the reflecting horizons of the Mesozoic are qualitatively the same. Traced faults attenuate at various stratigraphic levels. The structures of the hemisyneclise are known to be formed during the Cretaceous stage of development.


2021 ◽  
pp. 6-13
Author(s):  
Dmitry Ivanov ◽  
Alexander Tolstov ◽  
Vyacheslav Ivanov

This paper describes the tectonic features of the Alakit-Markha kimberlite field, regional factors of kimberlite magmatism control in this area, structural and tectonic preconditions for kimberlite pipe prospecting. The paper highlights kimberlite pipe formation features and the role of tectonics in this process. The most promising areas are those related to low-amplitude negative structures (e.g. depressions), especially transverse low-amplitude complications of the opposite sign for the main plicative structure: for antiforms (elevations), these are saddle-shaped depressions, and antiform elevations are for synforms (depressions).


2021 ◽  
pp. 181-200
Author(s):  
Charles W. Rovey ◽  
Damon J. Bassett ◽  
Matthew P. McKay

ABSTRACT A succession of Ordovician and Mississippian carbonates, separated unconformably, is exposed across the southern flank of the Ozark Dome in southwest Missouri. Deposits of both periods exemplify typical facies of the Midwestern United States: carbonate tidal-flat assemblages for the Early Ordovician and carbonate shelf environments for the Early–Middle Mississippian. The basic stratigraphic sequence of these deposits has been known for over a century, but interesting features remain to be addressed. Thin discontinuous sandstones are present within the Early Ordovician Cotter Dolomite, but the informal Swan Creek sandstone member seems anomalous. This sandstone can exceed 5 m in thickness and is fairly continuous across southwest Missouri. Most Ordovician sandstones in Missouri mark major transgressions above regional unconformities, but not the Swan Creek, and there is no obvious source of the sand. Therefore, we hypothesize that the Swan Creek represents reworked eolian dunes blown across the broad peritidal environment. Clastic sandstone dikes, apparently sourced from the Swan Creek, cut across beds of Cotter Dolomite near faults. We propose that these dikes are evidence of local faulting and seismicity during the Early Ordovician. Early and Middle Mississippian limestones comprise a sequence of shelf deposits, although mud mounds and other facies changes near the Missouri-Arkansas line mark the edge of the Mississippian shelf and the transition to a ramp setting. Early Mississippian carbonate deposition was interrupted by a short and localized influx of siliciclastic sediment comprising the Northview Formation. The Northview has additional characteristics consistent with a river-dominated deltaic deposit, which we suggest as its origin. If correct, this hypothesis implies that the history of tectonic features in the Midwest is more complicated than yet known. Finally, facies changes within and between the local Mississippian formations may record an early crustal response to the impending Ouachita orogeny farther to the south.


2021 ◽  
Vol 62 (08) ◽  
pp. 947-963
Author(s):  
V.A. Kontorovich ◽  
A.E. Kontorovich ◽  
A.Yu. Kalinin ◽  
L.M. Kalinina ◽  
V.V. Lapkovskii ◽  
...  

Abstract —The paper considers the seismogeologic, structural, and tectonic features of Neoproterozoic–Paleozoic and Mesozoic sedimentary complexes in the Arctic regions of the Siberian Platform. Based on the results of deep drilling, the geologic structure of the study area was analyzed, and the key sections of Neoproterozoic–Paleozoic deposits of the Anabar–Khatanga and Lena–Anabar oil and gas areas (OGA) were compiled. Analysis of geological and geophysical materials showed the existence of a sedimentary basin up to 14–16 km in thickness on the continental margin of the Siberian Platform, with five regional seismogeologic megacomplexes in its section: Riphean, Vendian, lower–middle Paleozoic, Permian, and Mesozoic. Based on the results of a complex interpretation of CDP seismic-survey and deep-drilling data, a structural and tectonic analysis was performed, structural maps were compiled for all reference stratigraphic levels, and a conclusion has been drawn about the similarity of the structural plans of the Riphean top and overlying sedimentary complexes. Using a structural map along the Permian top, a tectonic map of the study area was compiled, which corresponds to the current state of study. The results of numerical modeling of the salt diapir formation processes are presented, and the types of anticlinal structures, potential oil- and gas-promising objects, are considered.


2021 ◽  
Vol 9 ◽  
Author(s):  
Jean-Charles Schaegis ◽  
Valentin Rime ◽  
Tesfaye Kidane ◽  
Jon Mosar ◽  
Ermias Filfilu Gebru ◽  
...  

Lake Afdera is a hypersaline endorheic lake situated at 112 m below sea-level in the Danakil Depression. The Danakil Depression is located in the northern part of the Ethiopian Afar and features an advanced stage of continental rifting. The remoteness and inhospitable environment explain the limited scientific research and knowledge about this lake. Bathymetric data were acquired during 2 weeks expeditions in January/February 2016 and 2017 using an easily deployable echosounder system mounted on an inflatable motorized boat. This study presents the first complete bathymetric map of the lake Afdera. Bathymetric results show that the lake has an average depth of 20.9 m and a total volume of 2.4 km3. The maximum measured depth is 80 m, making Lake Afdera the deepest known lake in Afar and the lowest elevation of the Danakil Depression. Comparison with historical reports shows that the lake level did not fluctuate significantly during the last 50 years. Two distinct tectonic basins to the north and the south are recognized. Faults of different orientations control the morphology of the northern basin. In contrast, the southern basin is affected by volcano-tectonic processes, unveiling a large submerged caldera. Comparison between the orientation of faults throughout the lake with the regional fault pattern indicates that the lake is part of two transfer zones: the major Alayta–Afdera Transfer Zone and the smaller Erta Ale–Tat’Ali Transfer Zone. The interaction between these Transfer Zones and the rift axis forms the equivalent of a developing nodal basin which explains the lake’s position as the deepest point of the depression. This study provides evidence for the development of an incipient transform fault on the floor of the Afar depression.


2021 ◽  
Vol 40 (2) ◽  
pp. 461-502
Author(s):  
A. M. C. ŞENGÖR

The very first scientific paper by the great Austrian geologist Eduard Suess (1831–1914), the dean of geologists internationally during his lifetime, treats the graptolites of Bohemia (the ‘Barrandian’). This paper and most of his subsequent papers on palaeontology are accompanied by superb drawings of his observations in which Suess took great care not to insert himself between Nature as he perceived it in the framework of the knowledge of his day and his readers. In his drawings, he exercised what the great German geologist Hans Cloos later called ‘the art of leaving out’. This meant that in the drawings, the parts not relevant to the discussion are left only in outline, whereas parts he wished to highlight are brought to the fore by careful shading; but even the parts left only in outline are not schematic, instead they are careful reconstructions true to Nature as much as the material allowed it. This characteristic of Suess’ illustrations is seen also in his later field sketches concerning stratigraphy and structural geology and also in his depiction of the large tectonic features of our globe representing a guide to his manner of thinking. His illustrations in his early palaeontological work foreshadowed the later global geologist’s approach to our planet (and the Moon!) as a whole.


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