Rocks magmatic

Middlemost, E. A. K. (1985), Magmas and Magmatic Rocks, Longman, London. 

Reaction conditions are thought to be such that chemical equilibrimn is probably attained between the fluid phase and the magmatic rocks. One of the important high-temperatme chemical reactions that basalt undergoes is... 

Fig. 2. Correlation between a field of rocks compositions of the bimodal complex and the fields of intraplate magmatic rocks in the Central Asia and typical magma sources by primary isotope compositions of Sr and Nd. Fields of rocks explore bimodal complex -1, Early Mesozoic -2 and Late Mesozoic -3 of Central Asia. Correlation trend of basalt composition of the bimodal series of the Early Mesozoic Mongol - Transbaikalian region (Yarmolyuk et al. 2002) -4. At drawing of the diagram we used the data from the work (Magma types, 2006). PREMA and BSE values (Zindler Hart 1986), Siberian plume (Sharma etal. 1992).

Yarmolyuk, V.V. et al. 2002. Tectono-magmatic zoning, sources of magmatic rocks and geodynamics of the Early Mesozoic Mongol-Transbaikalian region. Geotectonics, 4, 42-63. 

Microlithofacial classification of the sandstones is based on Dott s classification modified by Pettijohn et al. (1972). They are mostly arenites and subarkose and quartz wackes (rare sublithic, sporadically lithic and arkosic). Quartz is the main component of the sandstones (about 60-70 vol. percent). Feldspars (6 vol. percent) are mostly represented by potassium feldspars with plagioclases in lesser amounts. Some micas (muscovite and biotite) and chlorites are observed. Mica content of arenites reaches 3 vol. %, but is higher in the wackes. Heavy minerals present include zircon, sphene, rutile and apatite. Magmatic rocks (volcanic more than Plutonic) are predominant among lithoclasts (about 2 vol. %), but some metamorphic and sedimentary clasts being present too. 

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. 

Tab. 15.2 Average magnetite and ilmenite content (g kg ) of magmatic rocks (Data from Wede-pohl, 1969)...

In summary, the composition of Fe-Ti oxides in magmatic rocks provides the pet-rologist with important information about the oxygen fugacity and temperature and also the silicon activity of the magma. It also has a strong effect on the magnetic properties of these phases (see Chap. 6 7). 

Gibbsite, a mineral more and more frequently identified in the early stages of rock weathering (especially magmatic rocks) is usually not important in river sediments but has been noted in small quantities over large areas in deep sea sediments (Griffin, et al., 1968 Biscay, 1965). 

Data enabling comparisons of the compositional differences of sedimentary zeolites of different origin are scarce. Such comparisons have been mostly between zeolites from magmatic rocks and those from sedimentary rocks, independent of the genetic type of the latter (1). The studies of Coombs and Whetton (2), which compared the specific features of analcime in metamorphic and unaltered sedimentary rocks, are evidence of the capabilities of this approach. Clinoptilolites belonging to different groups—alkaline basins of the United States (la), true sedimentary rocks... 

Fig. 2.2. A) TAS classification diagram of Tuscany magmatic rocks. Note that TAS nomenclature applies to volcanic rocks only. The dashed line divides the subalkaline and alkaline fields (Irvine and Baragar 1971). B) AQ vs. K20/Na20 diagram for mafic rocks (MgO > 3 wt%) of the Tuscany Province. For definition of AQ see Chap. 1.

Fig. 2.3. Variation diagrams of MgO vs. selected major and trace elements and 87Sr/86Sr for magmatic rocks of the Tuscany Province. Symbols as in Fig. 2.2.

Fig. 2.4. Sr, Nd (A) and Pb (B) isotopic composition of Tuscany magmatic rocks. Symbols as in Fig. 2.2. Composition of other Italian magmatic provinces are shown or comparison.

Fig. 2.10. SiC>2 vs. K20/Na20 diagram for Tuscany magmatic rocks. Solid arrows indicate mixing between mafic magmas, and between these and crustal anatectic melts. Dashed arrows indicate fractional crystallisation and unmixing (Monte -catini leucocratic veins).

Table 2.2. Representative compositions of Tuscany magmatic rocks. Numbers in parentheses refer to data obtained on distinct though similar rock samples from the same locality as those analysed for the other elements. Source of data 1) Vollmer (1977) 2) Hawkesworth and Vollmer (1979) 3) Poli et al. (1984) 4) Giraud et al. (1986) 5) Peccerillo et al. (1988) 6) Pinarelli (1991) 7) Conticelli and Peccerillo (1992) 8) Poli (1992) 9) Prosperi-ni (1993) 10) Westerman et al. (1993) 11) Innocenti et al. (1997) 12) De Astis et al. (2000) 13) Conticelli et al. (2002) 14) Dini et al. (2002) 15) Gasperini et al. (2002) 16) Author s unpublished data.

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