Structural interpretation of the Rukwa Rift, Tanzania

Geophysics ◽  
1988 ◽  
Vol 53 (6) ◽  
pp. 824-836 ◽  
Author(s):  
John W. Peirce ◽  
Lev Lipkov
Keyword(s):  
Gravity Data ◽  
Normal Fault ◽  
Gravity Models ◽  
Fault System ◽  
Rift System ◽  
Assistance Program ◽  
Density Control ◽  
Half Graben ◽  
Alluvial Material ◽  
Petroleum Development

The Rukwa Rift lies between Lakes Tanganyika and Malawi in the western limb of the East Africa rift system. Because little was known about the rift's structure or hydrocarbon potential, Petro‐Canada International Assistance Corporation completed a 2150 station gravity survey as part of an assistance program for the Tanzanian Petroleum Development Corporation. The survey covered an area 165 km × 375 km, which included the entire rift valley and lake plus regional control on either side. Outcrops of Carboniferous‐Triassic conglomerate, coal, and limestone, as well as Cretaceous sandstone, occur along the southwestern edge of the rift. The younger section is presumed to be dominated by alluvial material. In the absence of any density control, the gravity data were modeled using clastic sedimentary fill, which yields minimum depth estimates. Alternate models with more shale in the section have also been tried. A rift model with two shale pulses corresponding to interrift times yielded maximum depths of about 10 km. An all‐shale model failed to converge because of insufficient mass contrast. The final interpretation was based on the gravity models and aeromagnetic data acquired in an earlier survey. The Rukwa Rift is a half‐graben bounded to the northeast by a listric normal fault (strike 130 degrees) with 7 km of throw. A younger fault system forms the southwestern side of the valley and creates a major structure with 3 km of relief. The divergent strike of the younger faulting appears to be related in some way to right lateral shear in the Rukwa region. The Rukwa Rift has all the elements needed to be considered highly prospective for oil from a lacustrine source. There is strong evidence to suggest that the history of the Rukwa Rift is long and complex, providing ample opportunity for establishment of such an environment. The analogy of the Sudan rifts and the reports of oil seeps elsewhere in the western rift system support such a hypothesis. All the other elements of structure, reservoir, seal, maturation, and timing can be reasonably inferred from the available information. Of course, seismic and drilling are needed to provide firm stratigraphic control to confirm these inferences.

Tectonic framework of the Barra de São João Graben, Campos Basin, Brazil: Insights from gravity data interpretation

2014 ◽  
Vol 2 (4) ◽  
pp. SJ65-SJ74 ◽  
Author(s):  
Leandro B. Adriano ◽  
Paulo T. L. Menezes ◽  
Alan S. Cunha
Keyword(s):  
Gravity Data ◽  
Shear Zones ◽  
Data Interpretation ◽  
Fault System ◽  
Magnetic Data ◽  
Southeastern Brazil ◽  
Rift System ◽  
Seismic Line ◽  
Structural Framework ◽  
Campos Basin

The Barra de São João Graben (BSJG), shallow water Campos Basin, is part of the Cenozoic rift system that runs parallel to the Brazilian continental margin. This system was formed in an event that caused the reactivation of the main Precambrian shear zones of southeastern Brazil in the Paleocene. We proposed a new structural framework of BSJG based on gravity data interpretation. Magnetic data, one available 2D seismic line, and a density well-log of a nearby well were used as constraints to our interpretation. To estimate the top of the basement structure, we separated the gravity effects of deep sources from the shallow basement (residual anomaly). Then, we performed a 2D modeling exercise, in which we kept fixed the basement topography and the density of the sediments, to estimate the density of the basement rocks. Next, we inverted the residual anomaly to recover the depth to the top of the basement. This interpretation strategy allowed the identification of a complex structural framework with three main fault systems: a northeast–southwest-trending normal fault system, a northwest–southeast-trending transfer fault system, and an east–west-trending transfer fault system. These trends divided the graben into several internal highs and lows. Our interpretation was corroborated by the magnetic anomalies. The existence of ultradense and strongly magnetized elongated bodies in the basement was interpreted as ophiolite bodies that were probably obducted by the time of the shutdown of the Proterozoic Adamastor Ocean.

scholarly journals Half-graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

2020 ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo
Keyword(s):  
Gravity Data ◽  
Sedimentary Cover ◽  
Active Faults ◽  
Normal Fault ◽  
Gravity Modeling ◽  
Inversion Tectonics ◽  
Central Japan ◽  
Basin Inversion ◽  
Reverse Faulting ◽  
Half Graben

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.

scholarly journals Half graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

2020 ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo
Keyword(s):  
Gravity Data ◽  
Sedimentary Cover ◽  
Active Faults ◽  
Normal Fault ◽  
Gravity Modeling ◽  
Inversion Tectonics ◽  
Central Japan ◽  
Basin Inversion ◽  
Reverse Faulting ◽  
Half Graben

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.

scholarly journals Half graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

2020 ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo
Keyword(s):  
Gravity Data ◽  
Active Faults ◽  
Normal Fault ◽  
Japan Sea ◽  
Gravity Modeling ◽  
Inversion Tectonics ◽  
Central Japan ◽  
Basin Inversion ◽  
Reverse Faulting ◽  
Half Graben

Abstract The Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activity. It is, however, difficult to understand the overall tectonic character of the region due to the thick sediments in this region. We estimated the depth and the structure of the basement top in the Mikawa Bay Region through the analysis of gravity data, compiling publicly available gravity data and our own gravity measurements in the central part of the region. The gravity basement map shows the deepening of the basement top from the Nishi-Mikawa Plain to the Chita Peninsula. Two-dimensional modeling constrains the orientation of the Utsumi and Takahama faults. The fact that the basement top structure related to the Kou Fault is insignificant in the gravity data indicates that the geometry of the Kou Fault is small relative to that of the Utsumi Fault. The basement top structure from the Nishi-Mikawa Plain to the Chita Peninsula reveals a half graben structure bounded by the Utsumi Fault. The inverse motion of the Utsumi Fault, which underwent normal faulting during the Miocene followed by recent reverse faulting, is interpreted to reflect the inversion tectonics of the half graben. The timing of the inversion tectonics, i.e. the reverse faulting of the Miocene normal fault, can be compared to an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the center 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.

scholarly journals Recent Activity and Kinematics of the Bounding Faults of the Catanzaro Trough (Central Calabria, Italy): New Morphotectonic, Geodetic and Seismological Data

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 405
Author(s):  
Claudia Pirrotta ◽  
Graziella Barberi ◽  
Giovanni Barreca ◽  
Fabio Brighenti ◽  
Francesco Carnemolla ◽  
...  
Keyword(s):  
Scaling Laws ◽  
Normal Fault ◽  
Historical Earthquakes ◽  
Fault System ◽  
Normal Faults ◽  
The North ◽  
Seismological Data ◽  
Geomorphic Features ◽  
Half Graben ◽  
Fault Scarps

A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to define the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well defined. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data confirm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9.

Thermo-tectonic imaging of the Afro-Arabian Rift System

2020 ◽  
Author(s):  
Samuel Boone ◽  
Fabian Kohlmann ◽  
Maria-Laura Balestrieri ◽  
Malcolm McMillan ◽  
Barry Kohn ◽  
...  
Keyword(s):  
Low Temperature ◽  
Red Sea ◽  
Fission Track ◽  
Normal Fault ◽  
Eastern Africa ◽  
Fault System ◽  
Rift System ◽  
Gulf Of Aden ◽  
Apatite Fission Track ◽  
Continental Scale

<p>Low-temperature thermochronology has long been utilised in the Afro-Arabian Rift System (AARS) to examine exhumation cooling histories of normal fault footwalls and elucidate rifting chronologies where datable syn-rift strata and/or markers are absent. In particular, apatite fission track (AFT) and (U-Th)/He (AHe) analyses have constrained the timing and rate of rift-related, upper crustal thermal perturbations between ~30 and 120 °C (up to ~5 km depth). In turn, these provide insights into the spatio-temporal evolution of individual rift basins, morphotectonic rift shoulder development, normal fault system growth and, in some cases, the thermal influence of igneous intrusions and circulation of hot fluids. However, the relatively limited number of samples and confined areas generally involved in individual case studies have precluded insights into longer wavelength tectonic and geodynamic phenomena, such as regional denudation trends and the growth of topography due to plume impingement.</p><p>Here, we present a synthesis of >2000 apatite fission track (AFT) and ~1000 (U-Th)/He (AHe) analyses from the Eocene-Recent AARS collated using LithoSurfer, a new cloud-based geoscience data platform. This continental-scale low-temperature thermochronology synthesis, the first of its kind in Africa, provides novel insights into the upper crustal evolution of the AARS that were previously difficult to decipher from an otherwise cumbersome and intractably large dataset. The data record a series of pronounced episodes of upper crustal cooling related to the development of the Red Sea, Gulf of Aden and East African Rift System (EARS). They also provide insights into the inherited tectono-thermal histories of these regions which controlled the spatial and temporal distribution of subsequent extensional strain.</p><p>Thermochronology data trends along the AARS reflect a combination of rift maturity, structural geometry and geothermal regime, intrinsically linked to lithospheric architecture and magmatic activity. These relationships are best illustrated by contrasting the upper crustal thermal evolution of different AARS segments of varying age and complexity: for example, between the nascent Okavango, mature Ethiopian and evolved Red Sea rifts, wide (e.g. Turkana Depression) versus narrow (e.g. Main Ethiopian Rift) zones of deformation, between areas of transtensional (Dead Sea Transform), oblique (e.g. Gulf of Aden) and sub-orthogonal rifting (e.g. Malawi Rift), and the magmatic eastern versus amagmatic western branches of the EARS.</p><p>A regional interpolation of standardised thermal history models generated from the mined AFT, AHe and, in some cases, vitrinite reflectance data yield Mesozoic-recent heat maps, extrapolated to produce paleo-denudation and burial histories for eastern Africa and Arabia. Integrating these thermotectonic images with other regional datasets allows for the interrelationship between tectonic and dynamic topography development, the denudation history of the land surface, and sediment transport and deposition to be explored in new ways.</p><p> </p>

Kinematic evolution of a fold-and-thrust belt developed during basin inversion: the Mesozoic Maestrat basin, E Iberian Chain

2016 ◽  
Vol 155 (3) ◽  
pp. 630-640 ◽  
Author(s):  
MARINA NEBOT ◽  
JOAN GUIMERÀ
Keyword(s):  
Hanging Wall ◽  
Evolutionary Model ◽  
Normal Fault ◽  
Fault System ◽  
Rift System ◽  
Thrust Belt ◽  
Northern Margin ◽  
Kinematic Evolution ◽  
Fold And Thrust Belt ◽  
Maestrat Basin

AbstractThe Maestrat basin was one of the most subsident basins of the Mesozoic Iberian Rift system, developed by a normal fault system which divided it into sub-basins. Its Cenozoic inversion generated the N-verging Portalrubio–Vandellòs fold-and-thrust belt in its northern margin, detached in the Triassic evaporites. In the hinterland, a 40 km wide uplifted area, in the N–S direction, developed, bounded to the N by the E–W-trending, N-verging Calders monocline. This monocline is interpreted as a fault-bend fold over the ramp to flat transition of the E–W-trending, N-verging Maestrat Basement Thrust, and also indicates the transition from a thick-skinned (S) to a thin-skinned (N) style of deformation. This paper presents a kinematic evolutionary model for the northern margin of the basin and a reconstruction of the Maestrat Basement Thrust geometry, generated by the inversion of the Mesozoic normal fault system. It contains a low-dip ramp (9°) extended southwards more than 40 km, attaining a depth of 7.5 km. As this thrust reached the Mesozoic cover to the foreland, it propagated across the Middle Muschelkalk evaporitic detachment, generating a nearly horizontal thrust which transported northwards the supra-salt cover, and the normal fault segments within it, for c. 11–13 km. The displacement of the basement in the hanging-wall of the low-dip basement ramp generated the 40 km wide uplifted area, while the superficial shortening was accumulated in the northern margin of the basin – which contains the thinnest Mesozoic cover – developing the Portalrubio–Vandellòs fold-and-thrust belt.

scholarly journals Half-graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo
Keyword(s):  
Gravity Data ◽  
Sedimentary Cover ◽  
Active Faults ◽  
Normal Fault ◽  
Gravity Modeling ◽  
Inversion Tectonics ◽  
Central Japan ◽  
Basin Inversion ◽  
Reverse Faulting ◽  
Half Graben

AbstractThe 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.

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