Protolith

The crustal residence age DM of sediments formed at time t, i.e., the mean age of their continental protolith is defined as... 

The Kokchetav Massif of northern Kazakhstan is a very large, fault-bounded metamorphic complex of Late Proterozoic-Paleozoic protolith age, surrounded by the Caledonian rocks of the Ural-Mongolian fold belt. The Kokchetav UHP and HP belt runs NW-SE extending at least 150 km long and 17 km wide. This massif has attracted much interest since the discovery of metamorphic diamonds. It is the first locality where microdiamonds were found within metamorphic rocks derived from crustal material. 

The isotope composition of metamorphic rocks is mainly controlled by three factors, besides the temperature of exchange (1) the composition of the pre-metamorphic protolith, (2) the effects of volatilization with increasing temperatures and (3) an... 

Menzies M. A. and Dupuy C. (1991) Orogenic massifs Protolith, process and provenance. J. Petrol. (Orogenic Iherzolites and mantle processes) (sp. vol.), 1-16. 

Jerde E. A., Taylor L. A., Crozaz G., Sobolev N. V., and Sobolev V. S. (1993) Diamondiferous eclogites from Yakutia, Siberia evidence for a diversity of protoliths. Contrib. Mineral. Petrol. 114, 189—192. 

The dolomite observed by Stachel et al. (1998) was a single-phase inclusion. The presence of dolomite within the stability field of diamond requires a protolith in which the exchange reaction Mg2Si20s + CaMg(C03)2 = CaMgSi20g + 2 MgCOs is prevented from occurring by the absence of orthopyroxene. 

Figure 16 Volatile content as a function of depth for two hydrothermally altered harzburgitic (ophicarbonate) protoliths, shown for three geotherms. Constructed from P-T projections in Kerrick and ConnoUy (1998). Protolith mineralogy is (a) antigorite - - brucite - - calcite and (b) antigorite - - talc - - calcite. Hot, intermediate, and cold refer to geotherms illustrated in Figure 15. Shaded sub-arc region after Kerrick and...

Figure 10 shows major-element oxides versus Mg for off-craton and oceanic mantle, as well as some estimated compositions for primitive mantle (Table 1). As expected from the normative plots, the two sets of mantle compositions have distinct trends for all oxides. Previous models for primitive upper mantle have a range in Mg from 89 to 90, and Figures 9 and 10 show that the oceanic and off-craton trends also converge within this range. Assuming that the off-craton and abyssal mantle trends are due primarily to melt extraction from a common protolith, then the intersection of the trends should provide a good estimate for the composition of fertile upper mantle for major elements. 

If the fertile mantle protolith to oceanic and subcontinental mantle is nonchondritic in refractory elements, and if the bulk silicate Earth is chondritic in refractory elements, then a complimentary reservoir must exist elsewhere, presumably buried in the deep lower mantle and isolated from mantle convection (e.g., Anderson, 1989 Kellogg et al., 1999 Albarede and van der HUst, 1999). The primitive upper mantle could have acquired a superchondritic ratio as a consequence of crystal fractionation in a magma ocean, or perhaps by extraction of an early crust with low CaO/AbOs. 

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