Sedimentary cover determination and structural architecture from gravity data: East of Suez Area, Sinai, Egypt

2022 ◽  
Vol 15 (1) ◽  
Author(s):  
Mostafa El-Sehamy ◽  
Ahmad Mostafa Abdel Gawad ◽  
Tarek Aly Aggour ◽  
Orabi Hussien Orabi ◽  
Hekmat Fawzy Abdella ◽  
...  
2019 ◽  
Author(s):  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Ingo Grevemeyer ◽  
Dietrich Lange ◽  
Martin Thowart ◽  
...  

Abstract. The Ligurian Basin is located in the Mediterranean Sea to the north-west of Corsica at the transition from the western Alpine orogen to the Apennine system and was generated by the south-eastward trench retreat of the Apennines-Calabrian subduction zone. Late Oligocene to Miocene rifting caused continental extension and subsidence, leading to the opening of the basin. Yet, it still remains enigmatic if rifting caused continental break-up and seafloor spreading. To reveal its lithospheric architecture, we acquired a state of the art seismic refraction and wide-angle reflection profile in the Ligurian Basin. The seismic line was recorded in the framework of SPP2017 4D-MB, the German component of the European AlpArray initiative, and trends in a NE-SW direction at the centre of the Ligurian Basin, roughly parallel to the French coastline. The seismic data recorded on the newly developed GEOLOG recorder, designed at GEOMAR, are dominated by sedimentary refractions and show mantle Pn arrivals at offsets of up to 70 km and a very prominent wide-angle Moho reflection. The main features share several characteristics (i.e. offset range, continuity) generally associated with continental settings rather than documenting oceanic crust emplaced by seafloor spreading. Seismic tomography results are augmented by gravity data and yield a 7.5–8 km thick sedimentary cover which is directly underlain by serpentinised mantle material at the south-western end of the profile. The acoustic basement at the north-eastern termination is interpreted to be continental crust, thickening towards the NE. Our study reveals that the oceanic domain does not extend as far north as previously assumed and that extension led to extreme continental thinning and exhumation of sub-continental mantle which eventually became serpentinised.


2020 ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo

Abstract The Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activities. It is, however, difficult to understand the overall tectonic character of the region due to a thick sedimentary cover. We report the first finding of Neogene basin inversion in southwest Japan by estimating the depth and structure of the basement surface in the Mikawa Bay Region by analyzing gravity data. Our gravity basement map and two-dimensional density-structure model automatically determined using the genetic algorithm revealed a half-graben bounded on the south by the north-dipping Utsumi Fault. The motion of the Utsumi Fault, which inverted from normal faulting during the Miocene to recent reverse faulting, indicated the inversion of the half-graben. The timing of the inversion of the fault motion, i.e., the reverse faulting of the Miocene normal fault, can be compared with an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the southwestern part of the Nishi–Mikawa Plain is considered to have formed as a result of the backthrust of the Utsumi Fault under inversion tectonics. If the Takahama Fault is indeed the backthrust fault of the Utsumi Fault, the root of the Takahama Fault may be deep such that the Takahama Fault is seismogenic and linked to the 1945 Mikawa earthquake.


Author(s):  
P. Clariana ◽  
R. Soto ◽  
C. Ayala ◽  
A. M. Casas-Sainz ◽  
T. Román-Berdiel ◽  
...  

AbstractA new gravity survey (1164 gravity stations and 180 samples for density analysis) combined with two new geological cross sections has been carried out in a sector of the Central Pyrenees in order to improve the characterization of basement and cover architecture. From North to South, the study area comprises the southern half of the Axial Zone and the northernmost part of the South-Pyrenean Zone. New gravity data were combined with previous existing databases to obtain the Bouguer and residual anomaly maps of the study area. The two cross sections, oriented NNE–SSW, were built from field data and previous surficial and subsurface data and cross the La Maladeta plutonic complex. The residual anomaly map shows values ranging from −18 to 16 mGal and anomalies mainly oriented N120E. The two 2.5D modelled cross sections show similar observed gravity curves coinciding with similar interpreted structural architecture. Data show a gravity high oriented N120E coinciding with the Orri basement thrust sheet and an important gravity depression, with the same orientation, coinciding with the leading edge at depth of the Rialp basement thrust sheet and interpreted as linked to a large subsurface accumulation of Triassic evaporites. The volume at depth of the La Maladeta and Arties granites has been constrained through gravity modelling. This work highlights that the combination of structural geology and gravity modelling can help to determine the structural architecture of an orogen and localize accumulations of evaporites at depth.


2020 ◽  
Author(s):  
Ruth Soto ◽  
Pilar Clariana ◽  
Conxi Ayala ◽  
Antonio M. Casas-Sainz ◽  
Teresa Román-Berdiel ◽  
...  

<p>Cenozoic contractional deformation in the Central Pyrenees generated several basement thrust sheets involving Paleozoic rocks and decoupled Mesozoic and Cenozoic cover units detached on the main décollement level, the Triassic evaporites. The overall geometry and structural architecture of the chain have already been established based on numerous geological and geophysical data obtained during several decades. This work aims to validate the overall accepted geometry of the Central part of the chain by the construction of six serial cross-sections constrained by gravity data and 2.5D gravity modelling. The study area comprises the southern half of the Axial Zone between La Maladeta and Andorra-Mont Louis granites and its southern leading edge as well as the northernmost part of the South-Pyrenean Zone.</p><p>New gravity data were acquired and combined with previous existing databases to obtain Bouguer anomaly and residual anomaly maps of the study area. Six serial gravity-constrained cross sections have been built using available geological maps, previous published works, new geological and gravity data and 2.5D gravity modelling. Density values for gravity modelling were derived from 231 laboratory measurements of rock samples collected in the field from non-weathered outcrops that include all rock types outcropping in the study area. The residual anomaly map shows a good correlation between basement thrust sheets and gravity highs whereas negative anomalies seem to correspond to (1) Mesozoic basins, (2) Triassic evaporites and (3) Late Variscan igneous bodies. The 2.5D gravity modelling along the six cross sections highlights: (i) strong along-strike variations on the gravity signal due to lateral differences of the surficial and subsurface occurrence of Triassic evaporites, (ii) different geometry at depth of the Late Variscan igneous bodies outcropping in the study area and (iii) geometric lateral variations of the basement thrust sheets and their relationship with the Mesozoic-Cenozoic units.</p>


2011 ◽  
Vol 48 (6) ◽  
pp. 1065-1089 ◽  
Author(s):  
M.D. Thomas ◽  
M. Pilkington ◽  
R.G. Anderson

The ability of airborne sensors to image the magnetic signatures of prospective Quesnel terrane rocks through ubiquitous Quaternary glacial sedimentary cover in central British Columbia helps target new areas for mineral exploration. Newly acquired high-resolution data provide new perspectives on the nature and probable areal distribution of many geological units, revealing detail and information unattainable by conventional geological mapping. In combination with gravity data, these magnetic data indicate the presence of a granitic intrusion and a development of Nicola Group volcanic rocks, both potential hosts for porphyry- and (or) vein-type mineralization, under younger Tertiary volcanic cover. At a finer scale, magnetic patterns and fabrics permit discrimination between volcanic rocks of the Tertiary Chilcotin and Kamloops groups, and detection of subtle compositional and (or) structural variations within the groups. Contacts between volcanic cover and basement rocks and between basement units are more accurately defined, significantly reducing locally the areal extent of volcanic cover and opening up more ground for exploration. The high resolution of features in images of magnetic vertical derivatives reveals the Naver pluton to be more complex than currently mapped, comprising several integral elements, one of which may be a large roof pendant. Internal subdivisions of the Thuya batholith are defined, and annular marginal phases are proposed within two large granodioritic intrusions. Several new intrusions are proposed within the extensive, mainly sedimentary Devonian–Triassic terrain northeast of Kamloops, internal composition variation is suggested for some larger mapped intrusions, and areas underlain by some intrusions are enlarged.


2020 ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo

Abstract The Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activities. It is, however, difficult to understand the overall tectonic character of the region due to a thick sedimentary cover. We report the first finding of Neogene basin inversion in southwest Japan by estimating the depth and structure of the basement surface in the Mikawa Bay Region by analyzing gravity data. Our gravity basement map and two-dimensional density-structure modeling revealed a half graben bounded on the south by the north-dipping Utsumi Fault. The motion of the Utsumi Fault, which inverted from normal faulting during the Miocene to recent reverse faulting, indicated the inversion of the half graben. The timing of the inversion of the fault motion, i.e. the reverse faulting of the Miocene normal fault, can be compared with an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the southwestern part of the Nishi–Mikawa Plain is considered to have formed as a result of the backthrust of the Utsumi Fault under inversion tectonics. If the Takahama Fault is indeed the backthrust fault of the Utsumi Fault, the root of the Takahama Fault may be deep such that the Takahama Fault is seismogenic and linked to the 1945 Mikawa earthquake.


1997 ◽  
Vol 134 (5) ◽  
pp. 661-667 ◽  
Author(s):  
C. KRÓLIKOWSKI ◽  
Z. PETECKI

A new gravity model of the crustal structure of the Trans-European Suture Zone in the northwestern Poland has been constructed. The Bouguer anomaly map, obtained after stripping off the three-dimensional gravity effect of the sedimentary cover down to the Zechstein formations, is characterized by a 50 mGal gravity anomaly. We have assumed that the short-wavelength components derive from upper crustal intrusions and the long-wavelength components reflect crustal thickness and lateral heterogeneity which are strongly supported by the new seismic data along the LT-7 geotraverse. Quantitative modelling of gravity data along three profiles crossing the area indicate the presence of anomalous masses within the Lower Palaeozoic sequence, mainly along the Teisseyre-Tornquist Zone. Two of the profiles crossing the long-wavelength ‘stripped’ gravity high suggest the existence of a zone of 35 km crust above a dense upper mantle along the Teisseyre-Tornquist Zone. The extent of the zone can be determined based on the Bouguer anomalies interpretation.


2020 ◽  
Author(s):  
Michał Jakubowicz ◽  
Steffen Kiel ◽  
James Goedert ◽  
Jolanta Dopieralska ◽  
Zdzislaw Belka

<p>Stratigraphic and structural context of the early evolution of the Cascadia convergent margin, following major subduction reconfiguration associated with accretion of the igneous Siletzia terrane at 50−45 Ma, remains insufficiently understood. Here, we have applied a novel approach that uses combined Nd, Sr and stable isotope analyses of ancient methane-seep carbonates to constrain the early hydrogeological regime of the Cascadia margin. Analyses included the oldest-known seep deposits of Cascadia, formed during mid-Eocene time (42.5−40.5 Ma). A combination of exceptionally high ε<sub>Nd</sub> and low <sup>87</sup>Sr/<sup>86</sup>Sr signatures observed in these carbonates consistently point to former interactions between the seeping fluids and mafic, igneous constituents of the forearc basement. Moderately negative δ<sup>13</sup>C<sub>carbonate</sub> values imply thermogenic origin of hydrocarbons at three out of four studied seeps, with likely contribution of biogenic methane at a single, landward-most site. When combined with structural constraints, the recorded signals point to discharges of fluids originating from deep portions of the young subduction wedge, and their channeled ascent through the Siletzia terrane. The results document the presence of a fluid expulsion system indicative of active convergence prior to maturation of typical arc magmatism in the Cascades at 40 Ma. The exceptionally pronounced role of exotic, <sup>143</sup>Nd-enriched, <sup>87</sup>Sr- and <sup>18</sup>O-depleted fluids recorded for early Cascadia reflects its distinctive structural architecture, including the relatively thin sedimentary cover of the young forearc, its extensional tectonics, and the near-trench position of the volcanic terrane that the descending plate-derived fluids must have migrated through prior to reaching the seafloor. </p>


2020 ◽  
pp. jgs2020-193
Author(s):  
Simone Teloni ◽  
Chiara Invernizzi ◽  
Stefano Mazzoli ◽  
Pietro Paolo Pierantoni ◽  
Vincenzo Spina

A seismic sequence that affected the Durrës region in late 2019 to early 2020 sheds new light into the structural architecture and active tectonic setting of the northern outer Albanides. Stress inversion analysis using the focal mechanisms confirms that the area is dominated by ENE trending, horizontal maximum compression. Seismogenic sources consist mainly of ENE dipping thrust faults roughly parallel to the coastline. Hypocentre distribution indicates that most of the earthquakes, including the Mw = 6.4 main shock, nucleated within the basement, while only some of the shallow aftershocks tend to cluster around the deeper portion of previously identified seismogenic structures within the sedimentary cover. Our results, unravelling for the first time the fundamental role of deeply rooted, crustal ramp-dominated thrusting in seismogenesis, imply a profound reconsideration of the seismotectonic setting of the region in view of a correct assessment of seismic hazard in this densely populated area of Albania.


2020 ◽  
Vol 224 (2) ◽  
pp. 923-944 ◽  
Author(s):  
Yunus Levent Ekinci ◽  
Çağlayan Balkaya ◽  
Gökhan Göktürkler ◽  
Şenol Özyalın

SUMMARY Aegean Graben System is a significant member of the complex geology of western Turkey. The depths to the metamorphic basement reliefs in two major grabens have been reported by many geophysical studies. However, the sediment thicknesses of these graben basins still remain controversial due to the findings differing from each other. Thus, we have inverted the gravity data of the sedimentary cover–metamorphic basement using a stochastic derivative-free vector-based metaheuristic named differential evolution algorithm (DEA). This is the first application of DEA adapted to the basement relief depth problem. Model parametrizations have been achieved by discretizing the basins using a group of juxtaposed vertical blocks. Before the inversion studies, mathematical nature of the inverse problem has been investigated via prediction cost function/error energy maps for some block pairs using a hypothetical basin model. These maps have shown the resolvability characteristic of the block thicknesses on such inversion problem. Parameter tuning studies for the optimum mutation constant/weighting factor have been performed to increase the efficiency of the algorithm. The synthetic data have been successfully inverted via the tuned control parameter and some smoothing operators. Probability density function (PDF) analyses have shown that the best solutions are within the confidence interval limits without uncertainties. In the field data case, long-wavelength anomalies caused by both crustal and deeper effects have been removed from the complete Bouguer anomalies through 2-D finite element method using the element shape functions. Some profiles extracted from the residual gravity anomaly map have been used for the inversion and obtained results have shown that the maximum depths to the metamorphic basement reliefs in the grabens are shallower than the findings of the previous studies. Information obtained from the lithological logs drilled in the grabens has supported our results. Moreover, PDF analyses have indicated the reliability of the obtained solutions without uncertainties.


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