Venus tesserae feature layered, folded, and eroded rocks

Geology ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 81-85 ◽  
Author(s):  
Paul K. Byrne ◽  
Richard C. Ghail ◽  
Martha S. Gilmore ◽  
A.M. Celâl Şengör ◽  
Christian Klimczak ◽  
...  
Keyword(s):  
Normal Faults ◽  
Tectonic Deformation ◽  
Thrust Faults ◽  
Linear Features ◽  
Future Studies ◽  
Sedimentary Sequences ◽  
Geographically Dispersed ◽  
Terrain Type

Abstract Tesserae on Venus are locally the stratigraphically oldest units preserved on the planet. These regions are characterized by pervasive tectonic deformation including normal faults, grabens, thrust faults, and folds. In multiple tesserae, sets of (often highly) curved, parallel linear features are also present. These features strongly resemble terracing in layered volcanic or sedimentary sequences on Earth having arcuate or sinuous outcrop patterns that follow undulating topography. Should this analogy hold for Venus, then these outcrop patterns imply some erosion of the tessera units in which these strata occur; radar-dark materials filling proximal lows might be deposits of that eroded material. This outcrop pattern is seen in geographically dispersed tessera units, so the preservation of layering could be common for this terrain type. If so, then tesserae record the culmination of volcanic and/or sedimentary deposition, folding, and erosion—complex geological histories that should be considered in future studies of this enigmatic terrain.

scholarly journals The structural evolution of the Albula Pass region, Graubünden, eastern Switzerland: the origin of the various vergences in the structure of the Alps

2016 ◽  
Vol 53 (11) ◽  
pp. 1279-1311 ◽  
Author(s):  
A.M. Celâl Şengör
Keyword(s):  
Early Cretaceous ◽  
Sedimentary Rocks ◽  
Structural Evolution ◽  
Normal Faults ◽  
Thrust Faults ◽  
The South ◽  
The Future ◽  
Structural Fabric ◽  
The Alps ◽  
Entire Ensemble

The Albula Pass region lies between the Lower Austroalpine Err Nappe and the Middle Austroalpine Silvretta Nappe. They will be treated here as the frame of the non- to gently metamorphic sedimentary units between the two during the Alpide times. Sedimentation started on a metamorphic Hercynian basement during the latest Carboniferous(?) and continued into the Permian. Then a sequence from the Alpine Buntsandstein to the medial Jurassic to early Cretaceous Aptychenkalk (=Maiolica) and radiolarites were deposited in an environment of rifting and subsidence. The succeeding Palombini clastics were laid down after the Aptychenkalk and mark the onset of shortening in the Alpine realm. The initial structures that formed were at least two north-dipping normal faults which formed before the deposition of the Jurassic sedimentary rocks. When shortening set in, the first structure that came into being was the south-vergent Elalbula Nappe, bending the normal faults into close antiforms. It became further dismembered into two pieces creating parts of the future Ela and Albula nappes in the Albula region. This motion was later reversed, when the entire ensemble became bulldozed by the immense body of the Silvretta Nappe along numerous, closely spaced thrust faults, some of which only very locally followed horizontal bits of the old normal faults, but in principle they determined their own course. No evidence for westerly motion could be identified, although microstructures in the structural fabric were not studied. The reason for this may be the pre-orogenic fabric in the bounding tectonic units.

scholarly journals GEOPHYSICAL STUDIES AND TECTONISM OF THE HELLENIDES

2017 ◽  
Vol 43 (1) ◽  
pp. 32 ◽  
Author(s):  
J. Makris
Keyword(s):  
Upper Mantle ◽  
Aegean Sea ◽  
Velocity Model ◽  
Normal Faults ◽  
Tectonic Deformation ◽  
Flow Density ◽  
Crust And Upper Mantle ◽  
The North ◽  
Deep Seismic Soundings ◽  
Western Greece

By constraining gravity modelling by Deep Seismic Soundings (DSS) and the Bouguer gravity field of Greece a 3-D density-velocity model of the crust and upper mantle was developed. It was shown that in the north Aegean Trough and the Thermaikos Basins the sediments exceed 7 km in thickness. The basins along the western Hellenides and the coastal regions of western Greece are filled with sediments of up to 10 km thickness, including the Prepulia and Alpine metamorphic limestones. The thickest sedimentary series however, were mapped offshore southwest and southeast of Crete and are of the order of 12 to 14 km. The crust along western Greece and the Peloponnese ranges between 42 and 32 km thickness while the Aegean region is floored by a stretched continental crust varying between 24 to 26 km in the north and eastern parts and thins to only 16 km at the central Cretan Sea. The upper mantle below the Aegean Sea is occupied by a lithothermal system of low density (3.25 gr/cm³) and Vp velocity (7.7 km/s), which is associated with the subducted Ionian lithosphere below the Aegean Sea. Isostasy is generally maintained at crustal and subcrustal levels except for the compressional domain of western Greece and the transition between the Mediterranean Ridge and the continental backstop. The isotherms computed from the Heat Flow density data and the density model showed a significant uplift of the temperature field below the Aegean domain. The 400°C isotherm is encountered at less than 10 Km depth. Tectonic deformation is controlled by dextral wrench faulting in the Aegean domain, while western Greece is dominated by compression and crustal shortening. Strike-slip and normal faults accommodate the western Hellenic thrusts and the westwards sliding of the Alpine napes, using the Triassic evaporates as lubricants.

scholarly journals Impact of basement thrust faults on low-angle normal faults and rift basin evolution: a case study in the Enping sag, Pearl River Basin

Solid Earth ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 2327-2350
Author(s):  
Chao Deng ◽  
Rixiang Zhu ◽  
Jianhui Han ◽  
Yu Shu ◽  
Yuxiang Wu ◽  
...  
Keyword(s):  
Growth Pattern ◽  
Northern South China Sea ◽  
Spatial Relationship ◽  
Normal Faults ◽  
Rift System ◽  
Nucleation Density ◽  
Thrust Faults ◽  
Pearl River Basin ◽  
Existing Structures ◽  
The Impact

Abstract. Reactivation of pre-existing structures and their influence on subsequent rift evolution have been extensively analysed in previous research on rifts that experienced multiple phases of rifting, where pre-existing structures were deemed to affect nucleation, density, strike orientation, and displacement of newly formed normal faults during later rifting stages. However, previous studies paid less attention to the extensional structures superimposing onto an earlier compressional background, leading to a lack of understanding of, e.g. the reactivation and growth pattern of pre-existing thrust faults as low-angle normal faults and the impact of pre-existing thrust faults on newly formed high-angle faults and subsequent rift structures. This study investigating the spatial relationship between intra-basement thrust and rift-related faults in the Enping sag, in the northern South China Sea, indicates that the rift system is built on the previously deformed basement with pervasive thrusting structures and that the low-angle major fault of the study area results from reactivation of intra-basement thrust faults. It also implies that the reactivation mode of basement thrust faults is dependent on the overall strain distribution across rifts, the scale of basement thrust faults, and the strain shadow zone. In addition, reactivated basement thrust faults influence the nucleation, dip, and displacement of nearby new faults, causing them to nucleate at or merge into downwards it, which is representative of the coupled and decoupled growth models of reactivated thrust faults and nearby new faults. This work not only provides insights into the growth pattern of rift-related faults interacting with reactivated low-angle faults but also has broader implications for how basement thrust faults influence rift structures, normal fault evolution, and syn-rift stratigraphy.

scholarly journals Basin inversion and structural architecture as constraints on fluid flow and Pb-Zn mineralisation in the Paleo-Mesoproterozoic sedimentary sequences of northern Australia

2020 ◽  
Author(s):  
George M. Gibson ◽  
Sally Edwards
Keyword(s):  
Oil And Gas ◽  
Sedimentary Basins ◽  
Normal Faults ◽  
Northern Australia ◽  
Tectonic Event ◽  
Basin Inversion ◽  
Petroleum Systems ◽  
Sedimentary Sequences ◽  
Structural Architecture ◽  
Migration Pathways

Abstract. As host to several world-class sediment-hosted Pb-Zn deposits and unknown quantities of conventional and unconventional gas, the variably inverted 1730–1640 Ma Calvert and 1640–1580 Ma Isa superbasins of northern Australia have been the subject of numerous seismic reflection studies with a view to better understanding basin architecture and fluid migration pathways. Strikingly similar structural architecture has been reported from much younger inverted sedimentary basins considered prospective for oil and gas elsewhere in the world. Such similarities suggest that the mineral and petroleum systems in Paleo-Mesoproterozoic northern Australia may have spatially and temporally overlapped consistent with the observation that basinal sequences hosting Pb-Zn mineralisation in northern Australia are bituminous or abnormally enriched in hydrocarbons. This points to the possibility of a common tectonic driver and shared fluid pathways. Sediment-hosted Pb-Zn mineralisation coeval with basin inversion first occurred during the 1650–1640 Ma Riversleigh Tectonic Event towards the close of the Calvert Superbasin with further pulses accompanying the 1620–1580 Ma Isa Orogeny which brought about closure of the Isa Superbasin. Mineralisation in all cases is hosted by the syn-inversion fraction of basin fill, contrary to most existing interpretations of Pb-Zn ore genesis where the ore-forming fluids are introduced during the rifting or syn-extensional phase of basin development. Syn-extensional normal faults of Calvert and Isa age are mutually orthogonal, giving rise to a complex compartmentalisation of sub-basins with predominantly NNW and ENE strikes. Basin inversion subsequent to 1640 Ma occurred overall in a transpressive tectonic regime linked to continent-continent collision accompanied by orogen-parallel extensional collapse and right-stepping strike-slip faulting.

scholarly journals CONTRASTING GEOMETRY BETWEEN ALPINE AND LATE- TO POSTALPINE TECTONIC STRUCTURES IN ANAFI ISLAND (CYCLADES)

2004 ◽  
Vol 36 (4) ◽  
pp. 1688 ◽  
Author(s):  
Konstantinos I. Soukis ◽  
Demetrios J. Papanikolaou
Keyword(s):  
Normal Faults ◽  
Thrust Faults ◽  
High Angle ◽  
Backarc Basin ◽  
Tectonic Structures ◽  
Extensional Deformation ◽  
Upper Miocene ◽  
Deformation Phase ◽  
Shear Sense ◽  
Shear Sense Indicators

A significant change is observed in the geometry of the major faults in Anafi Island from Ν to NE dip in the alpine structures to S to SW dip in the late to post-alpine. Several thrust faults dipping to the NE preserved at the central-eastern part of the island form a nappe pile of Cretaceous HT/LP metamorphic units emplaced over a parautochthonous nonmetamorphic flysch of partly Eocene age without development of metamorphic structures (deformation phase Di). The development of detachment normal faults dipping to the SW (deformation phase D2) deformed the previous thrusts together with the post alpine continental sedimentary sequence of Miocene age, occurring in the northern and western part of Anafi. Asymmetric to the SW folds are observed at the lower part of the Upper Miocene sediments as well as numerous shear sense indicators along the undulating surface of the detachment above the underlying alpine units. The deformation weakens towards the upper part of the Upper Miocene sediments. An intensely sheared molassic type formation of probable ?Oligocene-Early Miocene age was distinguished between the alpine units and the detached Upper Miocene sediments. High angle normal faults dipping to the SW deform all previous structures (D3). The extensional deformation phases D2 and D3 are related to the opening of the Cretan backarc basin during Tortonian - Early Pliocene.

Activity of the Funai Fault and Radiocarbon Age Offsets of Shell and Plant Pairs from the Latest Pleistocene to Holocene Sediments Beneath the Oita Plain, Western Japan

Radiocarbon ◽  
2017 ◽  
Vol 59 (6) ◽  
pp. 1737-1748 ◽  
Author(s):  
Toshimichi Nakanishi ◽  
Keiji Takemura ◽  
Hisanori Matsuyama ◽  
Shoichi Shimoyama ◽  
Wan Hong ◽  
...  
Keyword(s):  
Sedimentary Facies ◽  
River Channel ◽  
Fault System ◽  
Philippine Sea Plate ◽  
Normal Faults ◽  
Tectonic Deformation ◽  
Northern Coast ◽  
Braided River ◽  
Delta Front ◽  
Terrestrial Plant

AbstractBeppu Bay is located on east-central Kyushu, southwest Japan, and is characterized by hydrothermal activity, tectonic deformation, and recent volcanism under the influence of convergence of the Philippine Sea plate. This area, occupying the western portion of an arc-bisecting dextral fault system, is a tectonic depression that has existed since ca. 5 Ma. Sedimentary facies, mollusk assemblages, and radiocarbon (14C) ages of 25 terrestrial plant fragments and 16 marine carbonate shells from a 70-m drill core were determined to estimate the activity of the Funai Fault, which consists of normal faults along the southern margin of the tectonic basin. Based on the analysis, six sedimentary facies, namely braided river channel, estuary, prodelta, delta front, delta plain, and artificial soil, were identified. The vertical slip rate was calculated as 2.6–2.7 mm/yr based on displacements of the braided river channel sediments of the last glacial period and the base of Kikai-Akayoya tephra in the Holocene highstand sediments of this area. Reservoir ages during 6180–10,410 cal BP were determined from marine shell and terrestrial plant pairs from the sediments of the estuary, prodelta and delta front facies, and were correlated with values from a northern coast of Kyushu and the Korean Peninsula.

scholarly journals Fault evolution in the Potiguar rift termination, equatorial margin of Brazil

Solid Earth ◽  
2015 ◽  
Vol 6 (1) ◽  
pp. 185-196 ◽  
Author(s):  
D. L. de Castro ◽  
F. H. R. Bezerra
Keyword(s):  
Sedimentary Basins ◽  
Strike Slip ◽  
South Atlantic ◽  
Normal Faults ◽  
South American ◽  
Sedimentary Sequences ◽  
The North ◽  
Lateral Shearing ◽  
The Right ◽  
Fault Evolution

Abstract. The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify architecture of fault systems and to analyze the evolution of the eastern equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The basin is located along the NNE margin of South America that faces the main transform zone that separates the North and the South Atlantic. The Potiguar rift is a Neocomian structure located at the intersection of the equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide, and ~ 40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en echelon system of NW–SE- to NS-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by postrift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the equatorial margin in the Cretaceous and occurs not only at the rift termination but also as isolated structures away from the main rift. This study indicates that the strike-slip shearing between two plates propagated to the interior of one of these plates, where faults with similar orientation, kinematics, geometry, and timing of the major transform are observed. These faults also influence rift geometry.

Quaternary of Chile: The State of Research

1977 ◽  
Vol 8 (1) ◽  
pp. 2-31 ◽  
Author(s):  
Roland P. Paskoff
Keyword(s):  
Sea Level ◽  
Volcanic Activity ◽  
Current Knowledge ◽  
Climatic Changes ◽  
Normal Faults ◽  
Tectonic Deformation ◽  
Marine Fauna ◽  
Quaternary Volcanism ◽  
Central Chile ◽  
Sea Level Fluctuations

The aim of this paper is to present a summary of current knowledge about Quaternary climatic changes, sea level fluctuations, tectonic deformation, and volcanic activity in Chile. In the Andean highlands of the hyperarid desert, glaciers and lakes fluctuated repeatedly. Evidence of pluvial periods is not well documented in the marginal desert. On the contrary, pronounced climatic changes are recorded in semiarid Chile. In central Chile two or three major glacial advances have been identified, but they remained confined within the high Cordillera. In the longitudinal valley of the Lake Region geomorphic remnants of four glaciations have been described;14C dates are available for the last glaciation. The glacial history of the Fjord Region is still obscure. Whether Pleistocene climatic changes in the northern and southern part of Chile were synchronous or not is a problem which requires further investigation. Sea level fluctuations along the Chilean coast are in part ascribed to glacio-eustatic effects. They left striking sets of step-like marine terraces in northern and central Chile. From a paleontologic point of view the Pleistocene corresponds to a pronounced move toward isolation and endemic development of the marine fauna. The Quaternary tectonic tendency seems to be toward extension and not compression expected as sea-floor spreading compensation. Normal faults limiting uplifted, downwarped, and tilted blocks are common. Folds are rarely found. Northern Chile is characterized by an imposing chain of about 600 stratovolcanoes. They rest on Tertiary ignimbrites which cover thealtiplano. Quartz-bearing latite-andesites are predominant. Present volcanic activity is sporadic and weak. South of a conspicuous gap between 27 and 33°S, Quaternary volcanism reappears in the high Cordillera, and many volcanoes have erupted violently within historic times. Rocks are fundamentally andesite or basaltic andesite. Poorly sorted ashes including pumice clasts in the Central Valley south of Santiago are interpreted as volcanic mudflows of late Pleistocene age.

scholarly journals Fault evolution in the Potiguar rift termination, Equatorial margin of Brazil

2014 ◽  
Vol 6 (2) ◽  
pp. 2885-2913
Author(s):  
D. L. de Castro ◽  
F. H. R. Bezerra
Keyword(s):  
Sedimentary Basins ◽  
Strike Slip ◽  
Normal Faults ◽  
South American ◽  
Sedimentary Sequences ◽  
Lateral Shearing ◽  
Isolated Structures ◽  
The Right ◽  
Fault Architecture ◽  
Fault Evolution

Abstract. The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify fault architecture and to analyse the evolution of the eastern Equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The Potiguar rift is a Neocomian structure located in the intersection of the Equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide and ~40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en-echelon system of NW- to EW-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by post-rift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the Equatorial margin in the Cretaceous and occurs not only at the rift termination, but also as isolated structures away from the main rift.

scholarly journals Sol Hamed Ophiolitic Complex, Southern Eastern Desert, Egypt: Petrological, Economic Potentiality and Structural Implications

2019 ◽  
Author(s):  
Tarek Sedki ◽  
Shehata Ali ◽  
Haroun A. Mohamed ◽  
Rafat Zaki
Keyword(s):  
Gold Mineralization ◽  
Mantle Peridotite ◽  
Eastern Desert ◽  
Normal Faults ◽  
Thrust Faults ◽  
Alteration Zones ◽  
Quartz Veins ◽  
Basement Rocks ◽  
Depleted Mantle ◽  
Arc Setting

The Sol Hamed (SH) area is a part of the Arabian-Nubian Shield (ANS) ophiolites occurred within Onib-Sol Hamed suture zone in the southern Eastern Desert of Egypt. The ophiolitic assemblages in this area are represented by serpentinite, metagabbro and arc assemblages represented by metavolcanics. They later intruded by gabbroes and granites. Geochemically, the compatible trace elements (Cr=2426–2709 ppm, Ni=1657–2377 ppm and Co=117–167 ppm) enrichment in SH serpentinites indicate derivation from a depleted mantle peridotite source. They show affinity to the typical metamorphic peridotites. The normative compositions reflect harzburgitic mantle source. Their Al2O3 contents (0.05–1.02 wt. %) are akin to oceanic and active margin peridotites and Pan-African serpentinites. The Cr and TiO2 contents indicate supra-subduction zone (SSZ) environment. Their Al2O3/SiO2 and MgO/SiO2 ratios support the SSZ affinity and are similar to ANS peridotites with fore-arc setting. Moreover, their Al2O3 and CaO depletion is typical of fore-arc peridotites. Structurally, the area represents four deformational events can be well-known in the Neoproterozoic rocks (D1, D2, D3 and D4); D1: E–W thrust faults and related E–W (F1) folds; D2: NW–SE thrust faults and related NW–SE (F2) folds were formed; D3: conjugate NNW-trending sinistral and NNE-trending dextral transpression, as well as N–trending tight folds (F3) and D4: is E–W dextral strike-slip and dip-slip normal faults striking NNW–SSE to N–S and E–W may be related to Red Sea rifting. There are major three fault sets affected the area. The first set trend mainly NE-SW and is manifested in the volcanic-sedimentary assemblage and Gabal SH and have important role in mineralization. The second set trend E-W affecting all the basement rocks and disturbs the first fault set. The third set trend N-S affected all the rock units. Magnesite mineralization in SH serpentinites is cryptocrystalline formed due to hydrothermal alteration of the serpentinite host rocks. It is occur as snow-white veins and stock-works. These characteristics are typical of Kraubath type magnesite deposits. Gold mineralization is confined to malachite-bearing quartz veins, smoky quartz veins and alteration zones. Malachite-bearing quartz veins trending NW-SE cut through gabbroic rocks and exhibit mylonitic structure. They are fractured containing malachite and disseminated sulfide minerals. Smoky quartz veins trending NE-SW with SE steeply dipping intrude the meta-andesite. They are intensively sheared containing iron oxides in the fissures. The gold grades increase with arsenopyrite occurrences. On the other hand, the barren quartz veins are nearly vertical with E-W directions. Alteration zones with NW-SE trend and nearly vertical dip intrude metagabbros and metavolcanics. Hematite, limonite, goethite and fresh pyrite characterize these zones. They occur mainly neighboring the auriferous quartz veins.

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