Mantle temperature

The diffusion of U and Th within a solid is, in general, very slow due to their large size and charge (Van Orman et al. 1998). Even at mantle temperatures, it is expected that a solid will not fully equilibrate with the surrounding phases (fluid, melt or other solid phases) if solid diffusion controls the equilibration. As yet, there have been no direct determinations of diffusion coefficients for any other decay chain element. 

A two-color pyrometer has been used along with the phase-Doppler anemometer to simultaneously measure the local velocity and size of kerosene droplets and the temperature of burning soot mantle in a swirl burner.[648] The measurements were conducted within the flame brush that develops in the shear layer of a swirl-stabilized, gas-supported kerosene flame with a swirl number of about 0.19 and potential heat releases of 10.6 and 15.5 kW, respectively. The results showed that the maximum burning fraction of the droplets occurs adjacent to the region denoted as gas flame but the value ranges from 20 5 to 40 5% depending on the axial station, and decreases sharply across the shear layer. The flame mantle temperature was found to be independent of droplet diameter, which agrees with previous results in the literature. 

Advancement reactions were performed using electric heating mantles. Temperatures of the resin, mantle/beaker interface, and mantle interior were recorded via thermocouples. Reaction mixtures were not protected from atmospheric oxygen. The advancement reaction was initiated at 120 C using O.IZ (weight/weight) triphenylphosphine. 

On somewhat smaller runs it may he more convenient to effect heating by the use of a wax or Wood s metal bath or an electric mantle. A hath or mantle temperature of 200° is sufficient for optimum 3neld. The reaction may froth vigorously if heated too rapidly or if the fumaramide is impure. 

Given the opposing signs of the Clapeyron slopes of the primary phase transitions associated with these seismic discontinuities, any elevated mantle temperatures associated with thermal plumes may be expected to yield thinning of the transition zone (Figure 2), via depression of the 410 and uplift of 660 (Shen et al., 1998 Bina, 1998c Lebedev et al., 2002). Some global and... 

The small magnitude of oxygen isotope fractionation at mantle temperatures and pressures, together with the constancy of peridotite oxygen isotope compositions make oxygen isotopes a powerful tool for identifying recycled crustal... 

Sobolev S. V., Zeyen H., Granet M., Achauer U., Bauer C., Werling F., Altherr R., and Fuchs K. (1997) Upper mantle temperatures and lithosphere-asthenosphere system beneath the French Massif Central constrained by seismic, gravity, petrologic, and thermal observations. Tectonophysics 275, 143-164. 

The thermal stability of antigorite is clearly insufficient to stabilize it at normal mantle temperatures and hence limits it to a role of supplying water in subducting slabs (Ulmer and Trommsdorff, 1995, 1999 Peacock, 2001),... 

Figure 23 Mantle potential temperature (°C) versus age (Ga) showing thermal evolution models for the upper mantle. The dashed line is a model for whole-mantle convection, and the solid line shows the trace of maximum upper-mantle temperatures in a model of transient layered convection with periodic mantle overturn (Davies, 1995, 1998). The large circles show estimates for average mantle lithosphere. Lithosphere labels are as in Figure 21.

Figure 5 Schematic pressure (P) versus temperature (r) diagram showing melting paths for adiabatically ascending mantle. Melting contours are evenly spaced for illustration only. The two paths are for two different mantle temperatures. The further a mantle parcel ascends, the greater the extent of melting (Langmuir et al, 1992) (reproduced by permission of American Geophysical Union from /. Geophys. Res., 1992, 77, 183-280).

The discussion above regarding variations in extents and pressures of melting from region to region, and the conclusion that these systematics result, to first order, from regional variations in mantle temperature is based on an examination of... 

The closed-system model is also used to justify the assumption that the solid mantle source is in secular equilibrium before melting begins. This will be the case if the mantle has acted as a closed system for more than about five half-lives of the longest-lived daughter product perturbed in the most recent event. As mentioned above, is not fractionated from at mantle temperatures and so Th (t]/2 75 kyr) constrains the time... 

Incompatible trace elements are only of limited use in distinguishing between volcanic successions formed in back-arc basins and those formed in oceanic plateaus (Table 3). However, the lower mantle temperature below a back-arc basin (Tp—1,280 °C) compared to a mantle plume (Tp> 1,400 °C) results in the eruption of few high-MgO lavas. An additional consequence of this lower mantle temperature is that back-arc basin lavas generally possess lower Ni and Cr contents for a given Mg number than oceanic plateau lavas (Figure 14(b)). Furthermore, because of their proximity to active subduction sites, back-arc basin sequences are also more likely to contain abundant volcaniclastic horizons than oceanic plateaus. 

What does the secular variation of lithosphere composition tell us about mantle temperatures ... 

Secular variation in the compositions of sulxjontinental lithosphere probably results from declining mantle temperatures. 

This result is confirmed when we consider the sensitivity of these results to the various hypotheses, using the alternatives previously described. Changing the surrounding mantle temperature Tx> slightly modifies the temperature profile (because of the scaling to the distance from the symmetry axis to the solidus), but has only a minute effect on voi atid It does change the... 

---