Peridotites water content

Peslier A. H., Luhr J. F., and Post J. (2002) Low water contents in pyroxenes from spinel-peridotites of the oxidized, sub-arc mantle wedge. Earth Planet Sci. Lett. 201, 69-86. 

Murakami et al. (2002) studied a natural peridotite composition (with 7.5-13.5 wt.% H2O) at 25.5 GPa and 1,600-1,650 °C. They measured water contents in their run products by SIMS. They found magnesium-rich perovskite and ferropericlase to have —2,000 ppm H2O and calcium-rich perovskite to have —4,000 ppm H2O. A lower mantle consisting of 79 wt.% Mg-perovskite, 16 wt.% ferropericlase, and 5 wt.% Ca-perovskite could contain 2,100 ppm H2O, which when integrated over the mass of the lower mantle yields a reservoir —5 times greater than the oceans. They compare this to the transition zone, which can store nearly six oceans worth of water, despite its smaller volume, because of the greater solubility of water in wadsleyite and ringwoodite (—3.3 X 10" ppm and... 

Recent work on the effects of mantle metasomatism on water solubihty in nominally anhydrous minerals (Peslier et al. 2000) has shown that the (OH) contents of these minerals decrease during the increase in oxidation state accompanying metasomatism. This has the possible implication that the rheological strength of cratons actually increases as a result of metasomatism. The ubiquitous nature of metasomatism in cratonic peridotites (Menzies Hawkesworth 1987 Pearson 1999h) may have the result of providing additional strength to an already robust lithospheric keel. There are specific instances... 

Rocks, Soils, and Water The iodine content of most rocks varies, from 0.01-0.50 mg kg in ultramafic rocks (dunite, peridotites, pyroxenites) to 2-6 mg kg with the greatest amounts being found in shales that are rich in organic matter. Mafic rocks (basalt) store 0.08-0.50 mg I kg granite and gneisses 0.2-0.5 mg kg sandstones 0.5-... 

In summary, Mg-rich rocks (peridotites, serpentinites) enrich their surroundings with considerable amounts of rather specific trace elements such as Cr, Ni, V and Co. These elevated concentrations of trace elements, together with the lack of Ca and the often very surficial water circulation, lead to restricted plant growth. Ground waters are characterized by elevated Mg- and Ni- contents and often relatively high pH values. 

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