Vertical density structure of oceanic crust and upper mantle. Free‐air gravity inversion

2001 ◽  
Author(s):  
Vsevolod I. Egorov ◽  
Yuri P. Goryachev
Keyword(s):  
Oceanic Crust ◽  
Upper Mantle ◽  
Gravity Inversion ◽  
Density Structure ◽  
Crust And Upper Mantle ◽  
Free Air ◽  
Vertical Density ◽  
Free Air Gravity

Gravitationally induced stresses at structural boundaries

1980 ◽  
Vol 17 (9) ◽  
pp. 1286-1291 ◽  
Author(s):  
A. K. Goodacre ◽  
H. S. Hasegawa
Keyword(s):  
Upper Mantle ◽  
Gravity Anomalies ◽  
Positive Anomaly ◽  
Crust And Upper Mantle ◽  
Free Air ◽  
Induced Stresses ◽  
Free Air Gravity ◽  
Free Air Anomaly ◽  
Structural Boundary ◽  
High Seismicity

Prominent gravity anomalies, consisting of paired positive-negative belts, occur in Canada at structural boundaries between geological provinces. The associated anomalous masses produce what are termed gravitationally induced stresses. These stresses may contribute to the failure of rocks along preexisting faults, or other zones of weakness. In the case of a typical structural boundary, failure at shallow depths in the crust is likely to occur in the region outlined by the negative gravity anomaly, whereas failure deeper within the crust and upper mantle may occur beneath the positive anomaly. Along the lower St. Lawrence valley, good spatial correlation is found between regions of high seismicity and those negative free-air anomaly areas which are adjacent to prominent free-air gravity highs. It is suggested that in a heavily faulted region, such as the lower St. Lawrence valley, gravitationally induced stresses may be a contributing factor to the production of earthquakes in regions which are otherwise already close to failure.

A suite of alkali basalts and gabbros associated with the Hare Bay Allochthon of western Newfoundland

1977 ◽  
Vol 14 (3) ◽  
pp. 346-356 ◽  
Author(s):  
R. A. Jamieson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Upper Mantle ◽  
Ultramafic Rocks ◽  
Alkali Basalts ◽  
Crust And Upper Mantle ◽  
Bay Area ◽  
Close Proximity ◽  
Thrust Sheets

The Hare Bay Allochthon of northwestern Newfoundland consists of a series of sedimentary, volcanic, metamorphic, and ultramafic rocks which was emplaced over a Cambro-Ordovician continental margin as several thrust sheets. It probably represents a continental margin sequence overridden by oceanic crust and upper mantle. The Partridge Point gabbro, Cape Onion volcanics, and Ireland Point Volcanics, which now occur in the Maiden Point, Cape Onion, and St. Anthony tectonic slices respectively, appear to be closely related on petrographic and chemical grounds. Olivine, titanaugite, kaersutite, and plagioclase indicate that these rocks formed as a single suite of hydrous alkali basalts, possibly as part of a seamount near a continental margin. This relationship provides a link between the lower sedimentary and the upper igneous-metamorphic structural slices of the allochthon and implies that most of the transported rocks in the Hare Bay area evolved in close proximity to each other.

Variation in young oceanic crust and upper mantle structure

1982 ◽  
Vol 87 (B10) ◽  
pp. 8435 ◽  
Author(s):  
Joseph F. Gettrust ◽  
Kazuo Furukawa ◽  
William B. Kempner
Keyword(s):  
Oceanic Crust ◽  
Upper Mantle ◽  
Mantle Structure ◽  
Crust And Upper Mantle ◽  
Upper Mantle Structure

scholarly journals Density structure and isostasy of the lithosphere in Egypt and their relation to seismicity

2018 ◽  
Author(s):  
Mikhail K. Kaban ◽  
Sami El Khrepy ◽  
Nassir Al-Arifi
Keyword(s):  
Red Sea ◽  
Upper Mantle ◽  
Nile Delta ◽  
Western Desert ◽  
Integrative Model ◽  
Joint Analysis ◽  
Density Structure ◽  
Crust And Upper Mantle ◽  
Gravity Field Model ◽  
Northern Red Sea

Abstract. A joint analysis of the new satellite-terrestrial gravity field model with the recent data on the crustal structure and seismic tomography model was conducted to create an integrative model of the crust and upper mantle; and to investigate the relation of the density structure and the isostatic state of the lithosphere to the seismicity of Egypt. We identified the distinct fragmentation of the lithosphere of Egypt into several blocks. This division is closely related to the seismicity patterns in this region. The relatively dense and strong lithosphere in the Nile Delta limits the seismic activity within this area, while earthquakes are mainly associated with the boundaries of this block. In the same way, the relatively strong lithosphere in the Suez Isthmus and northern Mediterranean prevents the Gulf of Suez from opening further. The central part of Egypt is generally characterized by an increased density of the mantle, which extends to the Mediterranean at a depth of 100 km. This anomaly deepens southward to Gilf El Kebir and eastward to the Eastern Desert. The average density of the crystalline crust is generally reduced in this zone, indicating the increased thickness of the upper crust. The low-density anomaly under the northern Red Sea is limited to 100–125 km, confirming the passive origin of the extension. Most of the earthquakes occur in the crust and uppermost mantle in this structure due to the hot and weak upper mantle underneath. Furthermore, an asymmetric lithosphere structure is observed across the Northern Red Sea. The isostatic anomalies show the fragmentation of the crust of Sinai with the high-density central block. Strong variations of the isostatic anomalies are correlated with the high level of seismicity around Sinai. This tendency is also evident in the North Red Sea, east of the Nile Valley, and in parts of the Western Desert.

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