Orogenesis from Subducting Thick Crust and Evidence from Alaska

2013 ◽  
pp. 337-349 ◽  
Author(s):  
Geoffrey A. Abers
Keyword(s):  
Thick Crust

scholarly journals No mafic layer in 80 km thick Tibetan crust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gaochun Wang ◽  
Hans Thybo ◽  
Irina M. Artemieva
Keyword(s):  
Seismic Data ◽  
P Wave ◽  
Indian Plate ◽  
Low Velocity ◽  
Crustal Earthquakes ◽  
Tectonic Processes ◽  
P Wave Velocity ◽  
Juvenile Crust ◽  
Mafic Lower Crust ◽  
Thick Crust

AbstractAll models of the magmatic and plate tectonic processes that create continental crust predict the presence of a mafic lower crust. Earlier proposed crustal doubling in Tibet and the Himalayas by underthrusting of the Indian plate requires the presence of a mafic layer with high seismic P-wave velocity (Vp > 7.0 km/s) above the Moho. Our new seismic data demonstrates that some of the thickest crust on Earth in the middle Lhasa Terrane has exceptionally low velocity (Vp < 6.7 km/s) throughout the whole 80 km thick crust. Observed deep crustal earthquakes throughout the crustal column and thick lithosphere from seismic tomography imply low temperature crust. Therefore, the whole crust must consist of felsic rocks as any mafic layer would have high velocity unless the temperature of the crust were high. Our results form basis for alternative models for the formation of extremely thick juvenile crust with predominantly felsic composition in continental collision zones.

An earthquake-explosion reversed refraction line in the Peninsular Ranges of southern California and Baja California Norte

1982 ◽  
Vol 72 (4) ◽  
pp. 1195-1206
Author(s):  
F. Alejandro Nava ◽  
James N. Brune
Keyword(s):  
Sierra Nevada ◽  
High Velocity ◽  
Southern California ◽  
Baja California ◽  
Crustal Thickness ◽  
Arrival Times ◽  
Narrow Zone ◽  
Peninsular Ranges ◽  
Thick Crust

abstract An approximate reversed refraction profile has been obtained for the center of the Peninsular Ranges of southern California and Baja California Norte using arrival times from Corona blasts to obtain the NW-SE profile, and arrival times from the well-located Pino Solo earthquake of 17 July 1975 to obtain the reversing SE-NW profile. The results indicate a relatively high-velocity crust, with P velocities of 6.57 to 6.95 km/sec, similar to the high velocities found by Hadley and Kanamori (1979). A crustal thickness of about 40 km was found for the axis of the Peninsular Ranges, significantly greater than was found by Hadley and Kanamori (1979) for the average crustal thickness of the northern part of the province. This suggests that the thick crust may be confined to a relatively narrow zone along the axis of the province. The crustal thickness found here is approximately 10 km less than found for the deeper crust of the Sierra Nevada (Bateman and Eaton, 1967; Pakiser and Brune, 1980).

Explaining the thick crust in Paraná basin, Brazil, with satellite GOCE gravity observations

2013 ◽  
Vol 45 ◽  
pp. 209-223 ◽  
Author(s):  
Patrizia Mariani ◽  
Carla Braitenberg ◽  
Naomi Ussami
Keyword(s):  
Paraná Basin ◽  
Parana Basin ◽  
Thick Crust

Scaling laws for stagnant-lid convection with a buoyant crust

2021 ◽  
Vol 228 (1) ◽  
pp. 631-663
Author(s):  
Kyle Batra ◽  
Bradford Foley
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Thermal Evolution ◽  
Crustal Thickness ◽  
Plate Motion ◽  
Crustal Layer ◽  
Lithospheric Thickness ◽  
Thin Crust ◽  
Mantle Temperature ◽  
Thick Crust

SUMMARY Stagnant-lid convection, where subduction and surface plate motion is absent, is common among the rocky planets and moons in our solar system, and likely among rocky exoplanets as well. How stagnant-lid planets thermally evolve is an important issue, dictating not just their interior evolution but also the evolution of their atmospheres via volcanic degassing. On stagnant-lid planets, the crust is not recycled by subduction and can potentially grow thick enough to significantly impact convection beneath the stagnant lid. We perform numerical models of stagnant-lid convection to determine new scaling laws for convective heat flux that specifically account for the presence of a buoyant crustal layer. We systematically vary the crustal layer thickness, crustal layer density, Rayleigh number and Frank–Kamenetskii parameter for viscosity to map out system behaviour and determine the new scaling laws. We find two end-member regimes of behaviour: a ‘thin crust limit’, where convection is largely unaffected by the presence of the crust, and the thickness of the lithosphere is approximately the same as it would be if the crust were absent; and a ‘thick crust limit’, where the crustal thickness itself determines the lithospheric thickness and heat flux. Scaling laws for both limits are developed and fit the numerical model results well. Applying these scaling laws to rocky stagnant-lid planets, we find that the crustal thickness needed for convection to enter the thick crust limit decreases with increasing mantle temperature and decreasing mantle reference viscosity. Moreover, if crustal thickness is limited by the formation of dense eclogite, and foundering of this dense lower crust, then smaller planets are more likely to enter the thick crust limit because their crusts can grow thicker before reaching the pressure where eclogite forms. When convection is in the thick crust limit, mantle heat flux is suppressed. As a result, mantle temperatures can be elevated by 100 s of degrees K for up to a few Gyr in comparison to a planet with a thin crust. Whether convection enters the thick crust limit during a planet’s thermal evolution also depends on the initial mantle temperature, so a thick, buoyant crust additionally acts to preserve the influence of initial conditions on stagnant-lid planets for far longer than previous thermal evolution models, which ignore the effects of a thick crust, have found.

Thick crust beneath the Ordos plateau: Implications for instability of the North China craton

2012 ◽  
Vol 357-358 ◽  
pp. 366-375 ◽  
Author(s):  
Chun-Quan Yu ◽  
Wang-Ping Chen ◽  
Jie-Yuan Ning ◽  
Kai Tao ◽  
Tai-Lin Tseng ◽  
...  
Keyword(s):  
North China Craton ◽  
North China ◽  
The North ◽  
Ordos Plateau ◽  
Thick Crust

A new species ofTriptolemma(Porifera: Pachastrellidae) from the Pacific Ocean with a revision of the genus

2010 ◽  
Vol 91 (2) ◽  
pp. 329-338 ◽  
Author(s):  
Marco Bertolino ◽  
D. Pica ◽  
G. Bavestrello ◽  
N. Iwasaki ◽  
B. Calcinai
Keyword(s):  
New Species ◽  
Pacific Ocean ◽  
Chemical Dissolution ◽  
Typical Pattern ◽  
Etching Mechanism ◽  
The Pacific ◽  
The Pacific Ocean ◽  
First Time ◽  
A New Species ◽  
Thick Crust

A new species,T. strongylatasp. nov. is described on the basis of material collected from the Pacific Ocean. The new species is characterized by the presence of sinuous strongyles. Moreover the incomplete description ofT. simplex(Sarà, 1959) is implemented on the basis of new abundant material allowing, for the first time, the complete description of the skeleton of aTriptolemmaspecies and the detecting of the presence of monaxonic spicules in the spicular complement of the genus. The skeleton is composed of a thick crust of disorderly arranged mesotriaenes and scattered microscleres, supported by diverging spicule tracts formed by oxeas towards the surface. Both species were recorded associated to boring sponges(SpiroxyaandCliona)in excavations of the calcareous scleraxis of precious corals or in organogenic concretions. In the cavities where the tissue ofTriptolemmawas recorded the wall of the excavation partially lost its typical pattern characterized by ovoid scars and became irregularly eroded. Our hypothesis is thatTriptolemmainsinuates inside the erosions produced by other sponges and it is able to enlarge them by an etching mechanism based on chemical dissolution only.

A discussion concerning the floor of the northwest Indian Ocean - Geophysical studies of the Seychelles Bank

1966 ◽  
Vol 259 (1099) ◽  
pp. 227-239 ◽  
Keyword(s):  
Indian Ocean ◽  
Magnetic Anomaly ◽  
Seismic Refraction ◽  
Central Area ◽  
Magnetic Anomalies ◽  
Gravity Measurements ◽  
Northern Edge ◽  
Mohorovičić Discontinuity ◽  
Granite Mass ◽  
Thick Crust

Geological studies of the islands on the Seychelles Bank, and the results of seismic refraction experiments made on the bank, are reviewed. They show that the crust is of continental type under the centre of the bank. Gravity measurements confirm that the thick crust extends to the northern edge of the bank and show that the Mohorovicic discontinuity slopes upward at an angle of about 19° under the peripheral cliff. Large narrow magnetic anomalies occurring in the central area of the bank are ascribed to minor intrusions of dolerite found in the Precambrian granites, and it is suggested that the edge of this area may mark the limit of the granite mass. Magnetic anomaly profiles of the Mascarene Ridge are similar to those over the Seychelles Bank and could result from a similar structure.

Pignot. Ringworm symptomatology and therapy. Presse Med., No. 20, 10.III 1937)

1937 ◽  
Vol 33 (7) ◽  
pp. 936-936
Author(s):  
V. Dembskaya
Keyword(s):  
Hair Shaft ◽  
Thick Crust

To better see the diseased hair, you need to put your head between the shadow and the light so that the latter glides over it. Sometimes the hair that is affected by shingles is hidden under crusts. These scabs make it easier to find affected hair. With a microsporion, the hair appears to be covered with frost, with an endosporion, it looks like a comma, its fragments are deeply embedded in a thick crust. These signs relate to an already developed disease. A hair affected by microsporion looks like a glass rod dipped in glue and dumped in the sand under the microscope. With endotrichophytosis, it is all permeated with spore filaments, resembling a bag filled with nuts, and the parasite does not spread beyond the epidermis of the hair shaft. With kerion, parasites are found that are very reminiscent of microsporion, but they are even smaller, which is why they were called microids. As with microsporion, they form, as it were, a case around the hair with the only difference that here the spores lie in the form of threads, and not in the form of a mosaic. In much rarer cases, there are parasites of the endo-exotrix type, which fill the interior of the hair and at the same time go beyond the epidermis, forming around it, as it were, a case of very large spores (megaspores).

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