s for the hornblende are given in Table 4(b), which shows that some hornblende crystals are rich in CaO and other rich in Na2O, except one sample with high TiO2 content (3.62 wt%). Basta (1988) [21] indicated that the primary hornblende in the younger gabbros of Sinai are rich in TiO2 (>1.5%) while the secondary hornblende is poor in TiO2.

On Si vs. (Na + Ka) diagram (Figure 5(d)) according to Leak (1978) [22] , the majority of samples plot in the ferroan pargastic hornblende field and one sample plot in tschermakitic field.

3.4.3. Plagioclases

Plagioclase is ubiquitous mineral in all the studied samples. The mineral compositions are given in Table 4(c). Or-Ab-An ternary diagram (Figure 5(e)) according to Deer et al. (1992) [19] shows that the studied plagioclase analyses plot in the labradorite (An 63) and bytownite (An 76) fields.

In conclusion the gabbro of the studied area are pertain to the Egyptian younger gabbros (Takla et al., 1981 [3] ) because they contains fresh pyroxene, brown hornblende and fresh plagioclase. The younger gabbro of the studied area is produced from calc-alkaline magma in continental setting similar to the younger gabbros of Samut-Atud (El Mansi, 1996) [6] .

4. Conclusions

The study of the younger gabbros in wadi Shianite area is classifieds into: pyroxene hornblende gabbronorite,

(a) (b)(c) (d)(e)

Figure 5. Mineral analyses of selected mineral phase of the younger gabbros. (a) Q-J diagram (Morimoto et al. 1988); (b) CaSiO3-MgSiO3-FeSiO3 diagram (Deer et al. 1992); (c) Al2O3-TiO2 diagram (La Bas, 1962); (d) Si ? (Na + K) digram ( Leak, 1978); (e) Or-Ab-An diagrame (Deer et al. 1992).

hornblende gabbro and anorthosite. Pyroxene hornblende gabbronorite is the predominant type; it has hypidiomorphic granular texture and less common porphyritic texture. It consists of plagioclases, pyroxenes (hypersthenes and augite), brown hornblende and biotite. Hornblende gabbro is a coarse to medium grained rock composed of plagioclase, brown hornblende and biotite. Opaque and apatite are accessories. Anorthosite is idiomorphic and granular. It is composed mainly of plagioclase and diallage.

From the study of the opaque mineralogy it is cleared that the opaque minerals in the younger gabbros range from 1% to 11%. They are composed mainly of ilmenite and magnetite. The opaque minerals indicate that they are belonging to younger gabbros of Egypt (Takla, 1971 [1] ; and Basta and Takla, 1974) [2] .

Geochemically, the studied gabbros are similar to the younger gabbros of Egypt (Takla et al., 1981 [3] ). They are sub alkaline formed in a continental arc setting. The pyroxene chemistry (augite) indicates that the host rocks are sub alkaline similar to conclusion reached from the whole-rock geochemistry.

Cite this paper

Magdy S.Basta, (2015) Petrology and Geochemical Characteristic of the Younger Gabbros of Wadi Shianite Area, Southeastern Desert, Egypt. Open Journal of Geology,05,577-588. doi: 10.4236/ojg.2015.58052

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