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Study of gravity signature across the floating basement of Bundelkhand granite using 3D Euler deconvolution, source edge detection technique and various gravity gradient analyses

Ghosh Gopal K.

Acta Geophysica

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2022

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Vol. 70, no 4

1519--1537

EN

Bundelkhand granitic massif (BGM) encompasses various granitic plutonism in early Proterozoic age which contains granitic sample of massif within the age 2560±106 m.y. The Bundelkhand granitic massif is formed by various granitic upward intrusions. The gravity data suggest that it exhibits low gravity over the higher-gravity zone inside the Bundelkhand massif. It is suggested that due to the tectonic activity gravity variation takes place and the Bundelkhand granitic massif formed. Younger intrusive dykes, metasedimentary and gneissic rocks, older enclaves of metabasic, are supposed to be present in the zone. The present study has been carried the interpretation of gravity signature using various gravity gradient analyses of Bouguer gravity data in the Bundelkhand granitic belt which is one of the floating basement areas. The various gravity derivatives are analyzed, and it suggests about the source edge locations and the delineation pattern. Three-dimensional Euler deconvolution analysis has been carried out using specified structural index (SI) and different window sizes (WS). Apart from this, tilt derivative (Tilt), horizontal tilt derivative (TDX), analytical signal (ASA), total horizontal derivatives (THDR) and source edge detection (SED) have been studied. These various derived results are superimposed with one another map, and the results are correlated for understanding various lineament pattern including different strike and dip direction and different source depth locations. The integrated results look well correlated and provide value addition to get some geological consequences and better understanding the study area.

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Delineation of major subsurface structural features and source depth locations using 3-D Euler deconvolution of gravity data at north-eastern part of India

Ghosh Gopal K.

Acta Geophysica

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2022

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Vol. 70, no 5

2033--2044

EN

The convergence of different major tectonic plates, namely the Eurasian, Indian and Sunda plates, may be the cause of the Assam Syntaxis due to the tectonic interaction between the Himalayan and the Indo-Burman ranges. The study covers the area between latitude 23°–28° N and longitude 88°–96° E and has experienced various types of earthquakes in the recent past. Seismic activity occurs in and around the Shillong Plateau, Mikir Hills, Arakan-Yoma Fold Belt, Naga Hills, parts of the Bengal Basin, lower and upper Brahmaputra valley, and the Mishmi Hills of the Himalayan foothills. Still, part of the study area is extremely unreachable and a limited number of thrust-faults have been identified from field geological studies and GIS maps received from the various sources. In this paper, an attempt has been made to study the delineation of thrust-fault locations using available ground gravity data of northeastern India with the help of a three-dimensional Euler deconvolution technique using the least squares method. Gravity data suggest an undulating nature throughout the area; however, high gravity values are observed at the Bengal Basin and Shillong Plateau, whereas lower gravity values are observed at Brahmaputra and Assam valley, Indo-Burman Range and Molasse Basin. The Shillong Plateau has high gravity with high elevation, whereas the Bengal Basin has high gravity with low elevation. This means that certain tectonic resettlement takes place in the Shillong Plateau, which causes the higher gravity anomaly. The use of Euler deconvolution with the help of a structural index plays a major role in gaining a better understanding of thrust-fault delineation and provides a mappable solution in this area. In this study, source depth estimation using 3- dimensional Euler deconvolution has been carried out by applying a range of structural index and window sizes. The different combinations of structural index and window size during the Euler deconvolution process generates several solutions including some unwanted spurious noise. To remove this noise, unrealistic solutions are discarded by applying filtering criteria to obtain the desired acceptable depth. The results derived using 3-dimensional Euler deconvolution correlate well with the previous finding of thrust-fault delineation. The present study validates the thrust-fault boundaries as well as providing additional thrust-fault settings in the complex tectonic area. The gravity data interpretation appears to offer a reasonable approach for source depth estimation and structural boundary identification.

3

Interpretation of gravity anomaly to delineate thrust faults locations at the northeastern part of India and its adjacent areas using source edge detection technique, tilt derivative and Cos(θ) analysis

Ghosh Gopal K.

Acta Geophysica

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2019

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Vol. 67, no. 5

1277--1295

EN

The Northeast India and its adjacent areas converge among the three diferent plates, viz. Eurasia, India and Sunda plates. The tectonic interaction of Northeast India and underlying dynamics of the Himalayas as well as the Indo-Burma Ranges might cause the Assam Syntaxis. The area of study is located between latitude 23°–28°N and longitude 88°–96°E and situated in one of the most seismically active tectonic provinces in the world with seismic zone-V. This area had demonstrated several thrust faults activities and tectonic evident accomplishments during the recent past. The complicated geotectonic setups inspirits various smaller magnitude earthquakes, and the current seismicity shows seismic activities are still enduring in the Shillong Plateau, Arakan-Yoma fold belt, Bengal Basin, Naga Hills, Mikir Hills, Upper–Lower Brahmaputra Valley and Mismi Hills of Himalayan foothills. It is imperative to obtain wide-ranging learning tectonic confguration, thrust faults delineation for improved geoscientifc study. Parts of the areas are extremely unreachable, and very limited thrust faults were marked by studying GIS map received from the various agencies and feld geological study. During the past studies, most of the prominent lineaments/thrusts are marked; however, many active and hidden thrust faults are still unidentifed. Seismic data can provide better information about the thrust faults locations, but due to small number of seismic data, the information is not adequate. In this paper, attempt has been made to study and reinterpret the available ground gravity data of northeastern parts of India for understanding thrust fault locations using various applications of gravity derivatives like analytical signal, horizontal gravity gradient, tilt derivative, horizontal tilt angle derivative and Cos(θ) analysis. Source edge detection technique has also been premeditated to categorize thrust fault locations. It is understandable that the low gravity is observed at Assam Valley which contributed sediment accumulations and higher gravity anomaly observed at Shillong Plateau and Bengal Basin containing denser formations. Bouguer gravity data is used after isostatic correction assuming Airy’s isostasy root depth model and frst-order trend removal using least square technique. The derived thrust fault locations from the present study are superimposed with the existing thrust-fault locations for correlation. Some additional thrust faults are narrated which are not previously mapped. It is also suggested that Brahmaputra Thrust, Dauki Fault, Naga Thrust, Disang Thrust and Kopili Fault have key responsibility for high seismicity and tectonic movement causing upliftment and depression that encouraged some anticlockwise rotation in the area.