Geologic significance of regional gravity and magnetic anomalies in the East‐Central midcontinent

1982 ◽  
Author(s):  
W. J. Hinze ◽  
E. G. Lidiak ◽  
Jon E. Reed ◽  
G. R. Keller ◽  
L. W. Braile ◽  
...  
Keyword(s):  
Magnetic Anomalies ◽  
East Central ◽  
Gravity And Magnetic ◽  
Regional Gravity

scholarly journals GRAVITY AND MAGNETIC SIGNATURE OF THE TRANSBRASILIANO LINEAMENT IN THE EAST-CENTRAL PORTION OF THE PARNAÍBA BASIN, NORTHEASTERN BRAZIL

2017 ◽  
Vol 35 (1) ◽  
Author(s):  
Thuany Patrícia Costa de Lima ◽  
Emanuel Ferraz Jardim de Sá ◽  
Fernando Antonio Pessoa Lira Lins ◽  
Alex Francisco Antunes ◽  
José Antônio De Morais Moreira
Keyword(s):  
Shear Zone ◽  
Potential Field ◽  
Field Data ◽  
Magnetic Anomalies ◽  
Northeastern Brazil ◽  
Central Portion ◽  
East Central ◽  
Potential Field Data ◽  
Gravity And Magnetic ◽  
Parnaíba Basin

ABSTRACT. The Transbrasiliano Lineament (TBL) corresponds to a NE-trending mega shear zone of late Neoproterozoic age with an extensive segment underneath the Parnaíba Basin (northeastern Brazil); the Eopaleozoic to Mesozoic section of the basin evidence the lineament’s brittle reactivation events. This paper presents a case study of TBL in the east-central portion of Parnaíba Basin with a special concern to the characterization of pre-Silurian grabens in the basement. The approach involves the interpretation of potential field data and seismic reflection line based on a plastic dextral transcurrent mega shear zone model. The gravity anomaly belts display a curvilinear shape joining the NE trend of the TBL, in accordance to a dextral S-C pair. A retrogressive stage with narrower ductile-brittle dextral structures controlled the opening of pull-apart grabens. Magnetic anomalies seem to be related to these late structures. The integration of the map analyses, seismic interpretation and 2D gravity modeling led to the conclusion that the sources causing the gravity and magnetic anomalies in the basin result from mass variations related to anisotropies of the crystalline basement and crustal heterogeneities, such as granite plutons, metasedimentary belts, shear zones and pre-Silurian grabens. The delimitation of grabens underneath the Parnaíba Basin suffers severe restrictions when solely interpreted based on potential field data. Keywords: gravity forward modeling, Transbrasiliano Lineament, magnetic anomaly. RESUMO. O Lineamento Transbrasiliano (LTB) corresponde a uma megazona de cisalhamento com direção NE, de idade Neoproterozoica, com um extenso segmento subjacente à Bacia do Parnaíba; a seção Eopaleozoica a Mesozoica da bacia evidencia seus eventos de reativação. Este trabalho aborda o LTB na porção centro-leste da Bacia do Parnaíba, com especial atenção à caracterização de grabens pré-Silurianos do embasamento. A abordagem envolve interpretações de dados de métodos potenciais e de linha sísmica de reflexão baseadas em um modelo de megazona de cisalhamento plástica transcorrente dextral. As faixas de anomalias gravimétricas exibem uma geometria curvilínea, aproximando-se em direção ao trend NE do Lineamento Transbrasiliano, em consonância a um par S-C dextral. Um estágio retrogressivo com estruturas dúcteis-frágeis mais estreitas controlaram a abertura de grabens pull-apart. As anomalias magnéticas imageam essas estruturas tardias. A integração da análise de mapas de anomalia, interpretação sísmica e modelagem gravimétrica 2D permite concluir que as fontes causadoras das anomalias gravimétricas e magnéticas na bacia resultam de variações de massa relacionadas a heterogeneidades crustais e às anisotropias do embasamento cristalino, tais como plútons graníticos, faixas de metassedimentos e zonas de cisalhamento, com contribuição subordinada dos grabens pré-Silurianos. A delimitação desses grabens subjacentes à Bacia do Parnaíba sofre severas restrições quando interpretadas unicamente com base nos dados de métodos potenciais. Palavras-chave: modelagem gravimétrica direta, Lineamento Transbrasiliano, anomalia magnética.

Correlation Analysis Method and its Application to Interpretation of Regional Gravity and Magnetic Anomalies in Eastern Xinjiang, China

2012 ◽  
Vol 546-547 ◽  
pp. 628-633
Author(s):  
Chun Guan Zhang ◽  
Bing Qiang Yuan ◽  
Yu Hong Li
Keyword(s):  
Correlation Analysis ◽  
Junggar Basin ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Analysis Method ◽  
Contributing Factors ◽  
Gravity And Magnetic ◽  
Metamorphic Basement ◽  
Correlation Analysis Method ◽  
Regional Gravity

Based on detailed analysis of Bouguer gravity anomaly and magnetic anomaly by reduced to the pole, this paper uses correlation analysis method to analyze regional gravity and magnetic anomalies of different filter scales, including filter scales of 50km, 90km, and 130km, and then discusses the contributing factors of local gravity and magnetic anomalies in eastern Xinjiang. The results show that regional gravity and magnetic anomalies are cogenetic anomalies in some areas, such as Hangou, and northern Lamamiao, Jingrquan, and western Qijiaojing, gravity and magnetic anomalies are allogenic anomalies in other areas. The study reveals that regional negative gravity anomalies are chiefly caused by Cenozoic – Mesozoic with larger thickness and lower density, and regional positive magnetic anomalies are mainly caused by Precambrian metamorphic basement with stronger magnetic property uplifting in Turpan – Hami and Santanghu basin. Mantle substances uplifting mainly cause regional positive gravity and magnetic anomalies in Junggar basin. Regional positive gravity anomalies are mainly caused by Pre-Mesozoic with higher density uplifting, and regional negative magnetic anomalies are chiefly caused by sedimentary formation and intermediate acidity rock with larger thickness and weaker magnetism and Precambrian metamorphic basement.

A DIRECT COMPUTATION OF GRAVITY AND MAGNETIC ANOMALIES CAUSED BY 2- AND 3-DIMENSIONAL BODIES OF ARBITRARY SHAPE AND ARBITRARY MAGNETIC POLARIZATION BY EQUIVALENT‐POINT METHOD AND A SIMPLIFIED CUBIC SPLINE

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 610-622 ◽  
Author(s):  
Chao C. Ku
Keyword(s):  
Arbitrary Shape ◽  
Gaussian Quadrature ◽  
Magnetic Anomalies ◽  
Cubic Spline ◽  
The Body ◽  
Point Method ◽  
Magnetic Polarization ◽  
3 Dimensional ◽  
Equivalent Point ◽  
Gravity And Magnetic

A computational method, which combines the Gaussian quadrature formula for numerical integration and a cubic spline for interpolation in evaluating the limits of integration, is employed to compute directly the gravity and magnetic anomalies caused by 2-dimensional and 3-dimensional bodies of arbitrary shape and arbitrary magnetic polarization. The mathematics involved in this method is indeed old and well known. Furthermore, the physical concept of the Gaussian quadrature integration leads us back to the old concept of equivalent point masses or equivalent magnetic point dipoles: namely, the gravity or magnetic anomaly due to a body can be evaluated simply by a number of equivalent points which are distributed in the “Gaussian way” within the body. As an illustration, explicit formulas are given for dikes and prisms using 2 × 2 and 2 × 2 × 2 point Gaussian quadrature formulas. The basic limitation in the equivalent‐point method is that the distance between the point of observation and the equivalent points must be larger than the distance between the equivalent points within the body. By using a reasonable number of equivalent points or dividing the body into a number of smaller subbodies, the method might provide a useful alternative for computing in gravity and magnetic methods. The use of a simplified cubic spline enables us to compute the gravity and magnetic anomalies due to bodies of arbitrary shape and arbitrary magnetic polarization with ease and a certain degree of accuracy. This method also appears to be quite attractive for terrain corrections in gravity and possibly in magnetic surveys.

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