Continental crust relationships

Hofmann, A. W. (1988). Chemical differentiation of the Earth the relationship between mantle continental crust, and oceanic crust. Earth Planet. Sci. Letters, 90,... 

Relationship between the trace elemental composition of phytoplankton, continental crust and seawater. Phytoplankton and crustal abundances are normalized to phosphorus (ppm trace metal ppm P). Seawater trace elements abundances are normalized to phosphate (ppb trace metal ppb P as phosphate). Source-. From Quigg, A., et al. (2003). Nature 425, 291-294. 

Figure 3 Crust-mantle differentiation patterns for the decay systems Rb-Sr, Sm-Nd, Lu-Hf, and Re-Os. The diagram illustrates the depletion-enrichment relationships of the parent-daughter pairs, which lead to the isotopic differences between continental crust and the residual mantle. For example, the Sm/Nd ratio is increased, whereas the Rb/Sr ratio is decreased in the residual mantle. This leads to the isotopic correlation in mantle-derived rocks plotted in Figure 4(a). The construction is similar to that used in Figure 2, but D values have been adjusted slightly for greater clarity.

Figures 4-6 show the isotopic compositions of MORBs from spreading ridges in the three major ocean basins. Figures 4(b) and 5(a) also show isotope data for marine sediments, because these are derived from the upper continental crust and should roughly represent the isotopic composition of this crust. In general, the isotopic relationships between the continental and oceanic crust are just what is expected from the elemental parent-daughter relationships seen in Figure 3. The high Rb/Sr and low Sm/Nd and Lu/Hf ratios of continental materials relative to the residual mantle are reflected by high Sr/ Sr and low " Nd/ " Nd and Hf/ Hf ratios (not shown).

McLennan S. M. (2001b) Relationships between the trace element composition of sedimentary rocks and upper continental crust. Geochem. Geophys. Geosys. 2 (article no. 2000GC000109). 

Figure 16 Plot of versus Th/Sc ratio for deep-sea turbidites according to tectonic setting of deposition (a) and according to quartz content (b). Also shown are compositions of various geochemical reservoirs (from Taylor and McLennan, 1985) and mixing relationships between average island arc andesite and upper continental crust (after...

The two layers in continental lithosphere represent extreme end-members in the compositional spectrum of magmatic rocks and each forms through independent processes. Archaean continental crust has an allochthonous relationship to underlying lithospheric mantle. 

The simplest way of thinking about the relationship between the continental crust and mantle is to use a three reservoir box model, in which an initial primitive mantle composition (reservoir 1) is progressively differentiated through time into a depleted mantle reservoir (reservoir 2) and the continental crust (reservoir 3). This simple approach provides a good explanation of the Nd- and Sr-isotope compositions of the mantle and crust. On a Nd-Sr isotope plot, crustal compositions are complementary to the mantle isotopic array (Fig. 4.21a) relative to the composition of the primitive mantle. Expressing the Nd-isotope data in a slightly different manner, an eNd versus time... 

These relationships indicate that about 53 % of the mantle was involved in the formation of the continental crust and remaining 46% was not. A subject of continuing discussion... 

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