l la lb lc ld le lf lg lh li ll lm lo lp lr ls lt lu lv lw lx ly lz

Перевод: lithosphere

литосфера

Тезаурус:

1. On the other hand, the Orbiter has established that most, perhaps all, of the Cytherean surface is close to isostatic equilibrium, which indicates that there may be a fairly thin lithosphere plus an asthenosphere, and this raises the possibility of considerable geological activity.
2. Later scientists thought that a succession of "heat waves" arising from radioactive decay in subsurface materials, and by the gravitational collapse of the solid lithosphere, was responsible for sweating out most of the water vapour.
3. Mantle lithosphere endmember: model 1; Os , -20; Os, 200pg per g; Nd , -5; Nd, 50g per g: model 2; Os , -20; Os, 200 pg per g, Nd , -10; Nd, 50g per g: model 3; Os , -20; Os, 500pg per g; Nd , -10; Nd, 50g per g.
4. The Pb isotope data for other islands located in areas of old lithosphere, Fernando de Noronha, Cape Verdes and the oceanic Cameroon line (Fig. 1), tend to be only slightly high in 206 Pb/ 204 Pb for a given 207 Pb/ 204 Pb (Fig. 2 c ), as expected given the lower average U/Pb ratios of lavas from these islands (Fig. 3 a ).
5. The central Atlantic is an ideal location in which to study the relationships between the lithosphere and isotopic compositions in basalts because the range in lithospheric age is large, there are no recent subduction zones nearby and the area is well away from the effects of the Dupal anomaly in the Southern Hemisphere.
6. These signatures are more readily attributed to source regions within the continental lithosphere, and there are strong indications that it is often the mantle lithosphere that contributes isotopically "enriched" (low- 143 Nd/ 144 Nd) material.
7. The theory of plate tectonics states that the outer layer of the earth, the lithosphere (-; 100 km thick) comprises a small number of (relatively) rigid plates which are separated by narrow zones along which most tectonic, seismic and volcanic activity is concentrated.
8. The sources of the Cameroon line, Trinidade and Madeira magmas have clearly resided in the upper mantle since the oceanic lithosphere was formed, and have not been displaced laterally by asthenospheric flow relative to the lithosphere since that time.
9. Whatever the exact mechanism for U/Pb fractionation, it seems to occur at shallow depths in the mantle at about the time of formation of the local oceanic lithosphere.
10. There are objections, however, to models that propose cold, refractory mantle lithosphere as an important source of basaltic magma.
11. We therefore interpret the isotope data for these two regions as indicating that the high U/Pb ratios of the lavas are also features of the source, with the age of U/Pb fractionation being comparable to the age of the lithosphere.
12. Sr i (initial 87 Sr/ 86 Sr) and Nd i (initial 143 Nd/ 144 Nd) data ( ref. 28 and N.P., M.P.A. and A. Halliday, manuscript in preparation) are consistent with, but do not prove, derivation from an enriched continental lithosphere similar to that identified in Chile.