Alteration processes

Another alteration process is alkylation which is used to produce higher octane aviation gasoline and petrochemical feedstock for explosives and synthetic rubber. An isomerization process is also used to produce more material as an alkylation feedstock. 

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Within each chondrite class there are petrographic grades that relate to alteration processes that occurred within the meteorite parent body. The... 

The reaction of seawater with country rocks is also a possible but unlikely explanation. Tertiary volcanic sediments in the vicinity of Kuroko deposits are altered and tend to have lost both Ca and Sr (Farrell and Holland, 1983). The ratio of Sr loss to Ca loss is roughly equal to the Sr/Ca ratio in seawater. If seawater was the altering medium, its Sr/Ca ratio was probably not strongly affected by the alteration process. The 87sr/86si- ratio would be intermediate between an initial value of 0.7088 and ca. 0.740 — the Sr/ Sr ratio of unaltered Tertiary volcanics of the Hokuroku basin. It is unlikely, therefore, that this type of alteration can account for the Sr content and for the isotopic composition of Sr in the anhydrites at the upper end of the trend line in Fig. 1.49. On the other hand, mixing of seawater with solutions which have a Sr/Ca ratio much smaller than that of seawater could have led to the deposition of Kuroko anhydrites. 

Honnoretz, J., Laveme, C., Hubberten, H.W., Emmermann, R. and Muehlenbachs, K. (1983) Alteration processes in layer 2 basalts from deep sea drilling project Hole 504B, Costa Rica Rift. Initial Rep. Deep Sea Drill. Proj., 55, 509-542. 

Seyfried, W.E. Jr. (1987) Experimental and theoretical constraints on hydrothermal alteration processes at midocean ridges. Ann. Rev. Earth Planet. Sci., 15, 317-335. 

Meteorites on Mars. Meridiani Planum is the first Iron meteorite discovered on the surface of another planet, at the landing site of the Mars Exploration rover Opportunity [359]. Its maximum dimension is 30 cm (Fig. 8.38). Meteorites on the surface of solar system bodies can provide natural experiments for monitoring weathering processes. On Mars, aqueous alteration processes and physical alteration by Aeolian abrasion, for example, may have shaped the surface of the meteorite, which therefore has been investigated intensively by the MER instruments. Observations at mid-infrared wavelengths with the Mini-TES... 

In an altered process to prepare 2,4-dichlorophenoxybutyric acid, the lactone was added to the other components, and soon after, the reaction temperature reached 165°C, higher than the usual 160°C. Application of cooling failed to check the... 

FIGURE 57-6 Central sensitization of dorsal horn neurons and a loss of inhibition after nerve injury result in altered processing of sensory input. ATP activates microglia through the P2X4 receptor. The resulting release of cytokines contributes to the development of pain through a mechanism of action that is, as yet, unknown. 

Large-scale hydrogeochemical mapping - insight into alteration processes and prospectivity mapping... 

A miniaturized MB spectrometer MIMOS II was developed for the robotic exploration of Mars, where it provided fundamental information about mineralogical composition and alteration processes, helped to classify rocks and soils, aided geologic mapping, was instrumental in assessing habitability of past and present environments, and identified potential construction resources for future human explorers. The applicability of the instrument as a process monitor for oxygen production and prospecting tool for lunar ISRU has been demonstrated. The characterization of air pollution sources and the study of mixed-valence materials as a function of depth in soil are examples of terrestrial in situ applications. MIMOS lla with additional XRF capability will open up new applications. 

The depositional environment of the oil source rocks, its thermal evolution, and secondary alteration processes are the most important factors, which determined the composition of crude oil. 

For the steady-state situation, chlorine dioxide emissions are measured when altering process variables such as concentration, temperature and production capacity. These measurements result in a number of relationships, plotted in Figs 25.2 and 25.3, with respect to the hypochlorite installation. 

The above-discussed equilibria are of fundamental importance for an understanding of alteration processes, with special emphasis on the role of pH in water-rock interaction events. 

Interaction between late-stage alteration processes, possibly related to the... 

The dolomitic rocks were affected by an alteration process evidenced by a bleaching of the rock at its base (Jones Rehnfeldt 2001). The primary copper mineralisation is associated solely with the bleached portion of this dolomitic layer. Occasionally traces of copper oxides are observed in the basal conglomerate. 

Leitch, C.H.B. Lentz, D.R. 1994. The gresen approach to mass balance constraints of alteration systems methods, pitfalls, examples. In Lentz, D.R., ed) Alteration and Alteration processes associated with Ore-forming systems. Geological Association of Canada, Short Course Notes, 11, 161-192. Lentz, D.R. 1995. Preliminary evaluation of six in-house rock geochemical standards from the Bathurst Camp, New Brunswick. New Brunswick Department of Natural Resources and Energy, Minerals and Energy Division, Miscellaneous Report 18, p. 81-89. 

On the basis of their high temperature of formation, it could be expected that magmatic rocks exhibit relatively small differences in isotopic composition. However, as a resnlt of secondary alteration processes and the fact, that magmas can have a crnstal and a mantle origin, the variation observed in isotopic composition of magmatic rocks can actnally be quite large. 

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