The Granitic Layer of the Earth's Crust

Comparison of crustal structure of the deep basins of the Caspian, Black, and Mediterranean Seas indicates the similarities of the main characteristics: great Bouger anomalies, the absence of a 'granitic' layer, a thick sedimentary layer with a relatively smooth interface, aseismicity. However, each of the above-mentioned basins (or even different parts of one deep basin) has its peculiarities, which indicates a very complicated tectonic development of the entire Caspian–Mediterranean zone.

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A study of the Earth's crust near Gauribidanur in Southern India

Bulletin of the Seismological Society of America ◽

10.1785/bssa0610030671 ◽

1971 ◽

Vol 61 (3) ◽

pp. 671-683

Author(s):

S. K. Arora

Keyword(s):

Epicentral Distance ◽

Earth’S Crust ◽

Seismic Events ◽

Travel Times ◽

Geological Features ◽

Local Earthquake ◽

First Arrival ◽

Earth's Crust ◽

Relative Differences ◽

Granitic Layer

abstract A hypothetical two-layered model has been evolved for the Earth's crust near Gauribidanur. The model is found to be consistent with the local earthquake and rockburst data obtained at Gauribidanur seismographic array. Sixty-seven well-recorded seismic events have been studied for this purpose. First arrival conditions for some of the phases in a “near-source” (epicentral distance Δ ≦ 10°) seismogram have been derived and subsequently made use of in establishing the nature of the first arriving phases pertaining to the available data. Thickness of the top granitic layer and the depth of Moho below this layer are found to be about 16 km and 19 km, respectively. Observed velocities are 5.67, 6.51 and 7.98 km/sec for P phases, and 3.46, 3.96 and 4.61 km/sec for the corresponding S phases. Values of the crustal parameters given by this study have been used in estimating the relative differences in travel times corresponding to various observed phases. These travel times may improve the precision with which earthquakes in this region could be located. Typical geographical and geological features of the region are also briefly described.

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Negative Gravity Anomalies over Acid “Intrusions” and their Relation to the Structure of the Earth's Crust

Geological Magazine ◽

10.1017/s0016756800065444 ◽

1953 ◽

Vol 90 (4) ◽

pp. 257-267 ◽

Cited By ~ 18

Author(s):

M. H. P. Bott

Keyword(s):

Country Rock ◽

Gravity Anomalies ◽

Igneous Rocks ◽

Earth’S Crust ◽

Density Contrast ◽

Magmatic Origin ◽

Bouguer Anomalies ◽

Sample Density ◽

Earth's Crust ◽

Granitic Layer

AbstractThe results of gravity surveys over various exposed and buried acid intrusions are summarized. Some sample density determinations are discussed. It is found that the acid intrusions considered are almost invariably associated with negative Bouguer anomalies, which are certainly often caused by direct density contrast between the less dense acid intrusive, and the denser country rock. This has two immediate implications. (1) Large negative Bouguer anomalies over “granites” may suggest magmatic origin. (2) These gravity anomalies, supported by seismological and seismic evidence, and the petrological distribution of igneous rocks, lead to the postulation of a denser “metasedimentary” layer overlying the “granitic” layer. The bearing of this on the mechanism of intrusion is briefly discussed.

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