Plagioclase classification

If one considers a granitoid rock containing essential amounts of quartz (QZ), plagioclase AN, AB), alkali feldspar (KS) and biotite (67) that requires classification, an appropriate composition matrix (C), where FM = Fe+Mg, is ... 

Classification of such a rock would employ the quartz (QZ)-plagioclase (PL)-alkali feldspar AF) Streckeisen ternary diagram, and so geochemical parameters describing the proportions of quartz, plagioclase and alkali feldspar can be obtained using the 7 matrix ... 

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. 

Table 4.2 Usts partition coefficients" jfof dace elements betwe a range of rock-foi ing minerals and andesitic liquids (57-63 wt % StOj in the TAS classification). A summary of the REE values is given in Figure 4,9. Many published sources of partition Coefficients treat andesites and basalts together and a comparison of Figures 4.1 and 4.2 shows that the partition coefficients for the REE are similar in basaltic and andesitic liquids. Values for garnet, the pyroxenes and the value for Eu in plagioclase, however, are higher in andesites than in basalts. REE partition coefficients for hornblende are higher in andesites than basalts, but are comparable between andesites and basaltic andesites. Values for the REE in the pyroxenes vary between published sources this may in part be due to compositional effects.

Fig. 3.21 The classification of plutonic igneous rocks by Streckeisen (1967, 1976) is based on the modal abundances of quartz (Q), alkali feldspar (including albite, An < 5%) (A), and plagioclase (An >5%) (P). The fields have been numbered in order to identify the rock types that correspond to them 1. quartz, 2. alkali granite, 3. granite, 4. granodiorite, 5a. quartz diorite (trondhjemite), 5b. quartz diorite (tonalite), 6. alkali syenite, 7a. quartz syenite, 7b. syenite, 8a. quartz monzonite (adamellite), 8b. monzonite, 9a. monzodiorite, 9b. monzogabbro, 10. diorite/gabbro (Adapted from Streckeisen 1967)...

Fig. 5.17 The plutons of Hope Granite that intruded the metasedimentary basement rocks of the Shackleton-Glacier area are collectively referred to as the Queen Maud batholith. The modal concentrations of Quartz (Q), alkali feldspar (A), and plagioclase (P) are used to classify a representative collection of the Hope Granite from this area (see also Fig. 3.21, Appendix 3.6.1). The distribution of data points indicates that the Hope Granite consists of granite (field 3), granodiorite (field 4), and quartz diorite (field 5) (Data by Wade and Cathey (1986) and classification of plutonic igneous rocks by Streckeisen (1967))...

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