Serpentine, from peridotite

The geological process of the formation of serpentine from peridotite probably involves the synthesis of carbon compounds under FTT conditions (see Sect. 7.2.3). The hydrogen set free in the serpentinisation process can react with CO2 or CO in various ways. The process must be quite complex, as CO2 and CO flow through the system of clefts and chasms in the oceanic crust and must thus pass by various mineral surfaces, at which catalytic processes as well as adsorption and desorption could occur. 

Peridotite Olivine (serpentinous, from which 10 % invariable olivine) -70... 

Rocks consisting essentially of olivine alone are known as dunites, the name coming from the occurrence of this rock in the Dun mountains of New Zealand. In the United States, this mineral is found in North Carolina, South Carolina, and Georgia, where corundum is associated wtith the dunite in commercial quantities. The olivine of peridotites alters readily to the mineral serpentine, often to such an extent that the rock itself is called a serpentine. As mentioned above, the pendotites may contain chromite or other valuable minerals, often to such an extent that they may be commercially exploited, for nickel, platinum, and precious garneL... 

Abe N. (2001) Petrochemistry of serpentinized peridotite from the Iberia Abyssal Plain (ODP Leg 173) its character intermediate between sub-oceanic to sub-continental upper mantle. In Non-volcanic Rifting of Continental Margins Evidence From Land and Sea. Spec. Publ. (eds. R. C. L. Wilson, R. B. Whitmarsh, H. P. J. Taylor, andN. Froitzheim). Geological Society of London, vol. 187, pp. 143-159. 

Bowin C. O., Nalwalk A. J., and Hersey J. B. (1966) Serpentinized peridotite from the north wall of the puerto rico trench. Geol. Soc. Am. Bull. 77, 257-269. 

Dehydration, or more generally, devolatilization of the oceanic crust is a process that combines continuous and discontinuous reactions in a variety of heterogeneous bulk compositions. In addition, within a vertical column—the sedimentary, mafic, and serpentinized peridotite layers— each experience a significant thermal gradient. The result is a continuous, but not constant, production of a fluid or melt, with the rate of mobile phase production generally decreasing with depth. Peaks in the volatile flux result from significant discontinuous reactions. However, despite the continuous fluid flux, trace elements may not necessarily be released continuously. 

MORE melting and dehydration in serpentinized peridotite was illustrated in Section 3.17.5.4. Here, an example of the effects on trace-element transfer as a function of fluid rock ratios is illustrated. The layered structure of the oceanic lithosphere may cause the fluid rock ratio in the sedimentary layer to be greater than one (as fluids from the underlying mafic and peridotitic layers must rise through the sediments). Thus, some of the trace elements (e.g., beryllium, thorium) commonly considered to be only efficiently mobilized by melts could also be quite effectively mobilized by fluids, if the entire subducted lithosphere is considered. 

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