Rocks chemistry

Bulk rock chemistry of hydrothermally altered midoceanic ridge basalt has been well studied and used to estimate the geochemical mass balances of oceans today (Wolery and Sleep, 1976 Humphris and Thompson, 1978 Mottl, 1983). In contrast, very few analytical data on hydrothermally altered volcanic rocks that recently erupted at back-arc basins are available. However, a large number of analytical data have been accumulated on the hydrothermally altered Miocene volcanic rocks from the Green tuff region in the Japanese Islands which are inferred to have erupted in a back-arc tectonic setting (section 1.5.3). 

The Pebble Limited Partnership has provided drill core geology and rock chemistry, which were used to create a geologic and geochemical cross sections along the line of the 2007 soil traverse - a... 

Bulk-rock chemistry (major and minor elements)... 

Sapienza G, Scribano V (2000) Distribution and representative whole-rock chemistry of deep-seated xenoliths from the Iblean Plateau, south-eastern Sicily, Italy. Per Mineral 69 185-204... 

Ernst W. G. and Piccardo G. B. (1979) Petrogenesis of some Eigurian peridotites 1. Mineral and bulk-rock chemistry. Geochim. Cosmochim. Acta 43, 219-237. 

Orthopyroxene Clinopyroxene Spinel Garnet Plagioclase Amphibole Mica Thermobarometry Bulk Rock Chemistry... 

Taylor L. A. and Neal C. R. (1989) Eclogites with oceanic crustal and mantle signatures from the Bellsbank kimberlite, South Africa Part 1. Mineralogy, Petrography, and whole rock chemistry. J. Geol. 97, 551-567. 

Clintonite. Clintonite is the trioctahedral brittle mica with ideal composition of Ca(Mg2Al)(SiAl3)Oio(OH)2. This structure violates the Al-avoidance principle of Loew-enstein (1954). It crystallizes in H20-saturated Ca-, Al-rich, Si-poor systems under wide P-T conditions. Clintonite, usually found in metasomatic aureoles of carbonate rocks, is rare in nature because crystallization is limited to environments characterized by both alumina-rich and silica-poor bulk-rock chemistry and very low CO2 and K activities (Bucher-Nurminen 1976 Olesch and Seifert 1976 Kato et al. 1997 Grew et al. 1999). The IM polytype and IMj sequences are the most common forms. The 2Mi form is rare (Akhundov et al. 1961) and no 3T forms have been reported. Many IM crystals are twinned by 120° rotation about the normal to the 001 cleavage. Such twinning causes extra spots on precession photographs that simulate an apparent three-layer periodicity (MacKinney et al. 1988). 

Many authors have suggested the dependence of the composition of igneous micas on factors such as bulk host-rock chemistry, oxygen fugacity, H2O fugacity, and (other) fluid activity (e g. Arima and Edgar 1981 Barton 1979 Edgar and Arima 1983 Speer... 

Because of the lack of relevant chemical and structural data on smectites from pelitic sediments and early diagenetic rocks, further research is needed to determine if the path toward and along one of these two series is pre-determined by the previously available (detrital or authigenic) smectites. In other words do transitional dioctahedral-trioctahedral smectites exist in common sediments Moreover or alternatively, are the fates of the two divergent prograde series controlled by local changes of the fluid and rock chemistries ... 

Accuracy is about getting the right answer. It is an estimate of how close our measured value is to the true value. Knowing the true value can be very difficult but it is normally done by reference to recommended values for intemadonal geochemical reference standards (see for example Govindaraju, 1984 Abbey, 1989). It is of course possible to obtain precise, but inaccurate, results, For most geological studies precision is more important than small differences in absolute concentration, for provided the data have all been obtained in the same laboratory the relative differences in rock chemistry can be used to infer geochemical processes. 

Diagrams on which rock chemistry can be plotted together with experimentaily determined phase boundaries... 

Applications to (a) Contamination of magmas by the continental crust The expression crustal contamination contamination can have a number of different meaning. Most normally it means the contaminadon of mantle derived melts by continental crust after they have left the source region (Hawkesworth and van Calsteren, 1984). However, it can also be used in the sense of a mantle source region, from which magmas are derived which was contaminated by crustal material at some dme in the past by, for example, the incorporation of subducted sediment into the mande. One of the problems for geochemists is that it is not always easy to discriminate between the two processes on the basis of rock chemistry. 

The principal emphasis in this book is on whole-rock chemistry the equally large area of mineral chemistry has only been touched upon tangendally. Furthermore, it has not been possible to cover some of the more novel and esoteric techniques currendy being applied to geochemical invesdgadons. 

Following emplacement or eruption, igneous rocks may be chemically modified, either by outgassing or by interaction with a fluid. The outgassing of igneous rocks chiefly affects the stable isotope chemistry whereas interaction with a fluid may affect all aspects of the rock chemistry. Ideally, igneous rocks selected for chemical analysis are completely fresh, but sometimes this cannot be achieved. For example,... 

Additionally one has to include in the budget still permanent CO2 degassing (unknown value) from the crust (accepting the deep carbon hypothesis). There is also no doubt that degassed CH4 is partly a product of deep rock chemistry (cf Eq. 2.4-2.7). 

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