Gravity anomalies and associated tectonic features over the Indian Peninsular Shield and adjoining ocean basins

The Afar triangle is bordered, to the west, by a seismic belt running along and on top of the escarpment. Seventy-five percent of the seismic energy of the area is released along this belt. The epicentre distribution along the western escarpment coincides either with major north-south marginal tectonic features or with cross-rift faulting. A second epicentre lineation runs at N 15° E through central Afar. To the south-east, in the region of the Gulf of Tadjura, epicentre locations offer no distinct lineation. The sum of the free-air gravity anomalies over Afar is almost zero; Bouguer values are generally negative and strictly proportional to elevation. Absolute Bouguer positive values are found only over volcanic centres and along the northeastern coast; their maximum does not compare with the positive values found over the nearby Red Sea trough. Evidence based on attenuation and dispersion of seismic surface waves and on gravity profiles suggests a continental crustal structure of relatively ‘standard’ thickness under the Afar triangle.

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Geophysical characteristics of the Tornquist Fan area, northwest Trans-European Suture Zone: indication of late Carboniferous to early Permian dextral transtension

Geological Magazine ◽

10.1017/s0016756897007267 ◽

1997 ◽

Vol 134 (5) ◽

pp. 597-606 ◽

Cited By ~ 79

Author(s):

HANS THYBO

Keyword(s):

Gravity Anomalies ◽

Late Carboniferous ◽

Border Zone ◽

Early Permian ◽

Subsequent Formation ◽

Consolidated Crust ◽

Basement High ◽

Formed Part ◽

Tectonic Features ◽

Strike Slip Movement

The Tornquist Fan is a northwestward widening splay of late Carboniferous–early Permian fault zones in the region of Denmark emanating from the Teisseyre-Tornquist Zone in northern Poland. The crust–mantle boundary shows an undulating topography which correlates with the main tectonic features of the area. Zones of high average velocity through the consolidated crust coincide with pronounced positive Bouguer gravity anomalies in the deep basins and in the border zone of the shield. Less pronounced, similar correlation to gravity is found for the thickness of the lower crust, whereas the thickness of the upper crust in parts is inversely related to the gravity anomalies. Some magnetic anomalies appear to be related to the gravity anomalies. The positive features are interpreted as magmatic bodies that formed during late Carboniferous to early Permian transtensional movement along the faults of the Tornquist Fan, which explains pull-apart structures in the area and the Ringkøbing-Fyn basement High. The magmatism has strong implications for the subsequent formation of the regional Mesozoic basins. Localized dextral strike-slip movement on the Teisseyre-Tornquist Zone became distributed over the Tornquist Fan, which formed part of the rigid Baltic Shield and was situated at the northwestern end of this major, long-reaching Central European zone. As defined by late Cretaceous–early Tertiary compressional inversion structures, the Sorgenfrei-Tornquist Zone cuts across the Tornquist Fan area.

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Geophysical interpretation of tectonic features in Bangladesh

Journal of Nepal Geological Society ◽

10.3126/jngs.v18i0.32205 ◽

1998 ◽

Vol 18 ◽

pp. 135-141

Author(s):

Mohammad Nurul Hasan ◽

Md. Noor Islam ◽

Salma Begum

Keyword(s):

Gravity Data ◽

Gravity Anomalies ◽

Bengal Basin ◽

Tectonic Feature ◽

North East ◽

Hilly Region ◽

Hinge Zone ◽

Surma Basin ◽

Seismic Sections ◽

Tectonic Features

Bangladesh occupies the major part of the Bengal basin. It is mainly a plain fluvi-dieltaic land. Except the eastern and northeastern Tertiary hilly region, the whole country is covered with thick Quaternary sediments. Tectonic features in Bangladesh, except the eastern and northeastern hilly structures, are hidden under thick cover of sediments. Gravity anomalies dearly show the locations of major subsurface tectonic features of the country, namely a) Himalayan foredeep, b) Rangpur platform, c) Hinge zone, d) Surma basin and e) Bengal foredeep. Magnetic anomalies and the seismic sections also support the gravity results. Shape, extent and depth of the tectonic features in Bangladesh are interpreted from geophysical data, particularly from the gravity data supported by available geological and drilling information. Interpretation shows that the Rangpur platform, situated in the northwestern Bangladesh, is the shallowest subsurface tectonic feature in the country. The northern part of the Rangpur platform slopes down to the Himalayan foredeep and the southern part to the Hinge zone. The Surma Basin, containing very thick sediments, lies in north-east corner of the country; and the Bengal foredeep, the most extended tectonic feature, occupies the southern deltaic part of the country. The Fold Belt, the only exposed tectonic feature, lies in the eastern and northeastern hilly region of the country.

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