Lithosphere ratios

Williams RW, Collerson KD, Gill JB, Deniel C (1992) High Th/U ratios in subcontinental lithospheric mantle mass spectrometric measurement of Th isotopes in Gaussberg lamproites. Eartli Planet Sci Lett 111 257-268... 

Indexes o and s define the ratio of the carbon isotopes in the sample and in the standard. A lithospheric carbonate material was accepted as standard. The closest to this zero point value belongs to standard sample NBS-19 (1.95%c). There are some other standard samples NBS-22 oil (—29.74%c), NBS-18 calcium carbonate (— 5.01%c). Usually 813C values for plants are in the range ( 15%o) to (— 30%c), and for oil (— 20%c) to ( 36%c). Atmospheric methane has the lowest content of 13C. Its 813C value is approximately —47%o. 

Case 2 Continuous deformation vertically averaged strain. The second and third models take a radically different viewpoint of continental deformation single faults are not important but rather add up to appear continuous over long lengthscales. These models use continuum mechanics to describe the lithosphere as a viscous fluid and consider the ratio of stresses arising from buoyancy forces following crustal thickening and horizontal plate... 

For special geochemical investigations, isotope ratios of other elements, such as B, N, Si, K and Se are also determined. The measurement of the distribution of the natural radioelements U and Th and their daughter nuclides in minerals, sediments, oil, water and the air gives information about the genesis of the minerals, sediments and oils, and about the processes taking place in the lithosphere, the hydrosphere and the atmosphere. The nuclear methods of dating will be discussed in chapter 16. 

Rehk per M., Halliday A. N., Alt J., Eitton J. G., Zipfel J., and Takzawa E. (1999) Non-chondritic platinum-group element ratios in oceanic mantle lithosphere petrogenetic signature of melt percolation Earth Planet. Sci. Lett. 65, 65-81. 

Niobium and tantalum are roughly interpolated between thorium and lanthanum in the Iherzolites, but the Nb/Ta values are variable. Lenoir et al. (2001) have revealed an abrupt change in the Nb/Ta ratio across the Ronda recrystallization front (Van der Wal and Vissers, 1993, 1996), from subchondritic values (—10) in the spinel tectonite domain ( ahead of the front) to near-chondritic (—16) in the granular domain ( behind the front). They tentatively ascribed this observation to a change from lithospheric conditions, under which Nb-Ta would be dominantly controlled by very small amounts of titanium oxides precipitated from volatile-rich small-volume melts (Bodinier et al., 1996), to more astheno-spheric conditions, under which the titanium oxides would be dissolved into basaltic partial melt and Nb-Ta redistributed between silicate phases. The harzburgites are systematically enriched in niobium and tantalum relative to... 

Calculated bulk rock trace-element systematics of eclogites have wider implications for mantle recycling models and bulk silicate earth mass balance. The subchondritic Nb/Ta, Nb/La, and Ti/Zr of both continental cmst and depleted mantle require the existence of an additional reservoir with superchondritic ratios to complete the terrestrial mass balance. Rudnick et al. (2000) have shown that rutile-bearing eclogites from cratonic mantle have suitably superchondritic Nb/Ta, Nb/La, and Ti/Zr such that if this component formed 1 -6% by weight of the bulk silicate earth, this would resolve the mass imbalance. This mass fraction far exceeds the likely mass of eclogite in the continental lithosphere and so the material is proposed to reside in the lower mantle, possibly at the core-mantle boundary. 

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