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.

Integrated Geophysical Interpretation of Kerio Valley Basin Stratigraphy, Kenya Rift

2016 ◽  
Author(s):  
Godfred Osukuku ◽  
Abiud Masinde ◽  
Bernard Adero ◽  
Edmond Wanjala ◽  
John Ego
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Fault System ◽  
Magnetic Data ◽  
Data Sets ◽  
Seismic Profiles ◽  
The West ◽  
Seismic Reflection Data ◽  
Basement Rocks ◽  
Western Side

Abstract This research work attempts to map out the stratigraphic sequence of the Kerio Valley Basin using magnetic, gravity and seismic data sets. Regional gravity data consisting of isotactic, free-air and Bouguer anomaly grids were obtained from the International Gravity Bureau (BGI). Magnetic data sets were sourced from the Earth Magnetic Anomaly grid (EMAG2). The seismic reflection data was acquired in 1989 using a vibrating source shot into inline geophones. Gravity Isostacy data shows low gravity anomalies that depict a deeper basement. Magnetic tilt and seismic profiles show sediment thickness of 2.5-3.5 Km above the basement. The Kerio Valley Basin towards the western side is underlain by a deeper basement which are overlain by succession of sandstones/shales and volcanoes. At the very top are the mid Miocene phonolites (Uasin Gishu) underlain by mid Miocene sandstones/shales (Tambach Formation). There are high gravity anomalies in the western and southern parts of the basin with the sedimentation being constrained by two normal faults. The Kerio Valley Basin is bounded to the west by the North-South easterly dipping fault system. Gravity data was significantly of help in delineating the basement, scanning the lithosphere and the upper mantle according to the relative densities. The basement rocks as well as the upper cover of volcanoes have distinctively higher densities than the infilled sedimentary sections within the basin. From the seismic profiles, the frequency of the shaley rocks and compact sandstones increases with depths. The western side of the basin is characterized by the absence of reflections and relatively higher frequency content. The termination of reflectors and the westward dip of reflectors represent a fault (Elgeyo fault). The reflectors dip towards the west, marking the basin as an asymmetrical syncline, indicating that the extension was towards the east. The basin floor is characterized by a nearly vertical fault which runs parallel to the Elgeyo fault. The seismic reflectors show marked discontinuities which may be due to lava flows. The deepest reflector shows deep sedimentation in the basin and is in reasonable agreement with basement depths delineated from potential methods (gravity and magnetic). Basement rocks are deeper at the top of the uplift footwall of the Elgeyo Escarpment. The sediments are likely of a thickness of about 800 M which is an interbed of sandstones and shales above the basement.

scholarly journals Exploiting Aeromagnetic and Gravity Data Interpretation to Delineate Massif Deposits of Rehamna Area (Western Meseta-Morocco)

2021 ◽  
Vol 54 (2C) ◽  
pp. 13-28
Author(s):  
Kawtar Benyas
Keyword(s):  
Gravity Data ◽  
Precious Metals ◽  
Data Interpretation ◽  
Structural Features ◽  
Magnetic Data ◽  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Geological Structures ◽  
Magnetic Signatures ◽  
First Vertical Derivative

The analysis of the magnetic signatures and gravity gradient values of the Rehamna Massif south of the Moroccan Western Meseta by using Geosoft Oasis Montaj 7.0.1 software, allowed us to detect several useful anomalies to be exploited and which are related to magmatic bodies and structural features within the study area. These data were analyzed by applying several techniques, including the horizontal gradient filters combined with the first vertical derivative. Subsurface structures; such as geological boundaries, faults, dykes and folds, were visualized as lineaments on geophysical maps, then results were compared with structural features provided by previous studies in the region. Thus, the Rehamna Massif structural map shows sets of linear features which may represent faults or boundaries of geological structures, which can be either faults or boundaries of geological structures, and they are mostly oriented in the directions: N-S, NNE-SSW, NE-SW, E-W with the predominance of the NNE-SSW to NE-SW directions. In addition, the super position of the minerals bearing beds or formations were distinguished from gravity and magnetic data processing results. Some of the recognized anomalies are related to the existence of precious metals which belong to the granitic bodies within the study area.

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.

scholarly journals The key role of conjugate fault system in importing earthquakes into the eastern flank of the Red Sea

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Ali K. Abdelfattah ◽  
Chokri Jallouli ◽  
Mohamed Fnais ◽  
Saleh Qaysi ◽  
Hassan Alzahrani ◽  
...  
Keyword(s):  
Focal Mechanism ◽  
Red Sea ◽  
Vital Role ◽  
Fault System ◽  
Magnetic Data ◽  
Rift System ◽  
Stress Regime ◽  
Focal Mechanism Solutions ◽  
Eastern Flank ◽  
Conjugate Fault

AbstractThis study aims to synthesize seismic observations with gravity and magnetic data and to suggest a new scenario on the development of the Harrat Lunayyir (HL) tectonic system on the eastern Red Sea coastline, Saudi Arabia. Gravity and aeromagnetic anomalies distinctly mapped the NE and NW trends, while the InSAR data depict a small NW–SE graben and an NW–SE dyke. High-resolution relocations, which are well-consistent with the focal mechanism solutions for events with magnitudes greater than 3.0, admit two distinctly fault styles of different orientations. Thus, leading to the NE and NW fault planes’ reactivation related to the Precambrian basement faults and the Red Sea rift system, respectively. The spatiotemporal distributions of epicenters and focal mechanism solutions suggest a new seismic deformation scenario of the 2009 earthquake seismic activity. The low static frictions of 0.2–0.35 obtained from the stress inversion indicates reactivation of preexisting faults in the respective seismogenic zones. The obtained results give rise to a swarm-like sequence of tectonic implications, two activated fault styles differently oriented, and an NE conjugate fault system inherited in the region, which plays a vital role in transferring the ambient stress regime into the Red Sea’s eastern flank.

Integrated gravity and seismic interpretation in the Norman Range, Northwest Territories, Canada

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. B107-B112 ◽  
Author(s):  
Donald C. Lawton ◽  
J. Helen Isaac
Keyword(s):  
Northwest Territories ◽  
Structural Model ◽  
Gravity Data ◽  
Velocity Model ◽  
Data Interpretation ◽  
Deformation Model ◽  
Geologic Mapping ◽  
Seismic Line ◽  
Depth Migration ◽  
Reflection Seismic

We integrate the interpretation of gravity data acquired across the Norman Range near Norman Wells, Northwest Territories, Canada, with geologic mapping and the processing and interpretation of a 2D reflection seismic line. Our purpose is to determine which of two contrasting structural models of deformation is supported by both gravity and seismic data. Interpretation of the gravity data implies that the more likely structural model is that of thin-skinned deformation with a low-angle thrust fault having a décollement within Upper Cambrian evaporites. We use this structural model to guide the development of a velocity model for prestack depth migration of the seismic line. Interpretation of the processed seismic line supports the thin-skinned deformation model.

scholarly journals Mapping Main Structures and Related Mineralization of the Arabian Shield (Saudi Arabia) Using Sharp Edge Detector of Transformed Gravity Data

Minerals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 71
Author(s):  
Ahmed M. Eldosouky ◽  
Reda A. Y. El-Qassas ◽  
Luan Thanh Pham ◽  
Kamal Abdelrahman ◽  
Mansour S. Alhumimidi ◽  
...  
Keyword(s):  
Saudi Arabia ◽  
Gold Mineralization ◽  
Gravity Data ◽  
Shear Zones ◽  
Fault Zones ◽  
Gold Deposits ◽  
Fault System ◽  
Arabian Shield ◽  
Potential Field Data ◽  
Najd Fault System

Saudi Arabia covers most of the Arabian Peninsula and is characterized by tectonic regimes ranging from Precambrian to Recent. Using gravity data to produce the lateral boundaries of subsurface density bodies, and edge detection of potential field data, a new subsurface structural map was created to decipher the structural framework controls on the distribution of gold deposits in Saudi Arabia. Moreover, we detected the relationships between major structures and mineral accumulations, thereby simultaneously solving the problem of edge detectors over complex tectonic patterns for both deeper and shallower origins. Analytic signal (ASg), theta map (TM), TDX, and softsign function (SF) filters were applied to gravity data of Saudi Arabia. The results unveil low connectivity along the Najd fault system (NFS) with depth, except perhaps for the central zones along each segment. The central zones are the location of significant gold mineralization, i.e., Fawarah, Gariat Avala, Hamdah, and Ghadarah. Moreover, major fault zones parallel to the Red Sea extend northward from the south, and their connectivity increases with depth and controls numerous gold mines, i.e., Jadmah, Wadi Bidah, Mamilah, and Wadi Leif. These fault zones intersect the NFS in the Midyan Terrane at the northern part of the AS, and their conjugation is suggested to be favorable for gold mineralization. The SF maps revealed the boundary between the Arabian Shield and Arabian Shelf, which comprises major shear zones, implying that most known mineralization sites are linked to post-accretionary structures and are not limited to the Najd fault system (NFS).

scholarly journals Análise Geológico-Estrutural do Cinturão Sunsás na Região de Nova Brasilândia - Sudeste de Rondônia

2000 ◽  
Vol 27 (2) ◽  
pp. 65 ◽  
Author(s):  
JOÃO LUIZ LUFT JR ◽  
GILMAR RIZZOTTO ◽  
FARID CHEMALE JR ◽  
EVANDRO FERNANDES DE LIMA
Keyword(s):  
Shear Zones ◽  
Data Interpretation ◽  
Relative Movement ◽  
Structural Framework ◽  
Northern Portion ◽  
Southern Border ◽  
Orogenic Cycle ◽  
Geological Units ◽  
Central South ◽  
Radiometric Data

The present study is on structural framework of geological units exposed in the Paulo Saldanha topographic sheet situated in the Nova Brasilândia region, Rondônia State. These units outcrops in southwestern portion of Amazonic Craton formed by mobile belts of Mesoproterozoic ages, represented by 1.4 Gy Rondonian and 1.0 Gy Sunsás Orogenic Provinces. The main rocks of study area comprises, in its central portion, the Nova Brasilândia Metaplutonic-volcanic-sedimentary Sequence formed by ortho- and para-derived rocks metamorphosed in upper amphibolites facies, represented by metaturbidites with major intercalation’s of amphibolites and local migmatized granitoid lenses. In southernmost portion, this sequence are dominantly formed by metagabros and amphibolites, with small granitoid bodies of Granito Rio Branco unit highly tectonized by a syn-transpressive regime (D1). At central-south portion, outcrop the Suite Intrusiva Rio Pardo formed by granodiorites syn- to post-transcurrent shear zones, emplaced through spaces generated by transtrative regime (D2) of Rio Branco Transcurrent Shear Zone. All of above units were hard tectonized during Sunsás Orogeny markink the last important period of lithospheric accretion to the southern border of the Amazonic Craton NW-SE and E-W structures strongly control the lithostratigraphic boundaries of Nova Brasilândia Sequence, and Rio Branco and Rio Pardo units, all deformed by the transpressive and transtrative tectonic regime that characterize the Sunsás Orogeny. A hard metamorphic foliation (S1) characterize the NW-SE trending lineaments highly recorded in the metaturbidites of the central Paulo Saldanha sheet. These structures were rotated by E-W trending transcurrent shear zones with sinistral relative movement, formed by Rio Branco and Alvorada shear zones situated in central-southern and northern portion, respectively; and both constituted by milonitic foliation (S2) and stretching lineations (L2) best characterizes at central-southern portions by augengranites of Rio Branco unit. Radiometric data were obtained by U-Pb, Rb-Sr and Sm-Nd methods in the units of the Nova Brasilândia Sequence and from granitoids of Suite Granítica Rio Pardo and Granito Rio Branco. These data interpretation insert the Nova Brasilândia region around 1.1 Gy Sunsás Orogenic Cycle.

scholarly journals Multisource data integration for groundwater prospecting in Precambrian shear zones, Espírito Santo State (Southeastern Brazil)

2021 ◽  
Vol 60 (2) ◽  
pp. 124-139
Author(s):  
Marcos Eduardo Hartwig ◽  
César Augusto Moreira ◽  
Marilane Gonzaga De Melo
Keyword(s):  
Shear Zones ◽  
Southeastern Brazil ◽  
Tectonic Structures ◽  
Near Surface ◽  
Espírito Santo ◽  
Well Production ◽  
Structural Framework ◽  
Basement Rocks ◽  
Espirito Santo ◽  
Groundwater Prospecting

The Precambrian metamorphic rocks in the southern region of the Espírito Santo State(southeastern Brazil) is intercepted by ductile and brittle/ductile shear zones over which towns like Guaçuí, Marechal Floriano and Domingos Martins were established. In the years of 2014 to 2016 the Espírito Santo State faced the worst drought in the past 80 years. In situations like that, the only source of fresh water available is underground. Therefore, the purpose of this study was to integrate multisource data for groundwater prospecting and management. The study area comprises the central sectors of the Guaçuí and Batatal shear zones. Methodology involved the interpretation of stereo-pairs for the identification of lineaments, electrical resistivity surveys and geological fieldwork. The results were tentatively validated with available groundwater well production data. Six resistivity profiles with a total length of 2,400 m were surveyed and 15 outcrops were described across these structures. Results have shown that the structural framework of the shear zones is predominantly made of NW to NNW and NE to NNE-trending lineaments. The former is related to brittle tectonics and the latter coincides with the ductile Precambrian fabric of the crystalline basement rocks. A near-surface porous aquifer regarded to the regolith and recent unconsolidated sedimentary deposits presenting resistivity values < 1,372 Ohm.m and depths < 30 m have good potential for groundwater storage. However, results arenot conclusive about the hydrogeological significance of tectonic structures for groundwaterprospection in the study area.

BIOINDICATORS OF SEA-LEVEL FLUCTUATIONS IN SOUTHEASTERN BRAZIL: NEW DATA AND METHODOLOGICAL REVIEW

Radiocarbon ◽  
2021 ◽  
pp. 1-15
Author(s):  
Julia Caon Araujo ◽  
Kita Chaves Damasio Macario ◽  
Vinícius Nunes Moreira ◽  
Anderson dos Santos Passos ◽  
Perla Baptista de Jesus ◽  
...  
Keyword(s):  
Sea Level ◽  
Late Holocene ◽  
Data Interpretation ◽  
Progressive Increase ◽  
Southeastern Brazil ◽  
Recrystallization Process ◽  
Sea Level Changes ◽  
Sea Level Fluctuations ◽  
Data Gap ◽  
Current Zero

ABSTRACT The vermetidae fossils of Petaloconchus varians, formed by calcium carbonate, associated with their radiocarbon ages, are the most accurate indicators of paleo sea level due to their restricted occupation in the intertidal zone in the rocky shore. However, the recrystallization of minerals can affect these age calculations and, consequently, the interpretation of the data. The aim of this study is to present new indicators of paleo sea-level changes in Southeast Brazil for the last 6000 years contributing to fill the data gap for the late Holocene. The influence of the recrystallization process was successfully resolved using the CarDS protocol, enabling the separation of the original aragonite fraction by density, prior to radiocarbon dating. This avoids the rejuvenation of ages and ensures greater efficiency for data interpretation. Paleo sea-level indicators were able to show a progressive increase in sea level up to the transgressive maximum of 4.15 m in 3700 BP years, followed by a regression to the current zero. This regression seems to have in addition, here we reinforce the reliability of the use of fossil vermetids as indicators of sea-level fluctuations.

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