Downloaded 67 times
More Related Content
Similar to Introduction to Geochemistry of Igneous Rocks
Introduction to Geochemistry of Igneous Rocks
- 1. Introduction To Geochemistryof Igneous Rocks
- 2. Igneous Rocks • Igneousrocks are formed through the colling and solidification of magma or lava. • The magma can be derived form partial melts of existing rocks neither a planets mantle or curst .
- 3. Why rocks aremelts? • Typically the meltin is caused by one or more of the three processes. • An increase in temperature, • A decrease in pressure, • A change in composition,
- 4. Solidification into rocksoccurs either below the surface as intrusive rocks. If on the surface , extrusive rocks
- 5. Chemistry of igneousrocks: • The chemical composition of magma determines which minerals and how much of each will crystallize when an igneous rocks forms. • Magma contains : • Silicon • Oxygen
- 6. Igneous rocks arerocks composed By • Primarily by silicate minerals as; Quartz, plagioclase ,feldspar, potassium feldspar, amphibole, pyroxene, biotite and olivine. A magma that is rich in silica, aluminium, potassium, and sodium will crystallize that contain those elements (feldspar and quartz)
- 7. magma rich in ironand magnesium and calcium will contain • Dark colour fero-magneium minerals, • pyroxene • Amphibole • olivine and biotite.
- 8. Chemical analysis byweight % of oxides • e.g Si, O, Mg, Na • Where siO2 is most abundent elements. Based on amount of silica. Igneous rocks are classified into four groups . Which are in order of decreasing silica content.
- 9.
- 10. FELSIC ROCKS • Rckswith a silica content of 65% or more (by weight) are cconsidered to be silica rich. • The remaicning 25% to 35% of these rocks id mostly ; • Aluminium oxide (Al2O3) • Sodium oxide (Na2O) • Potasium (K2O)
- 11. Small amount of calcium(CaO) Magnesium (Mgo) Iron (Feo and Fe2O3)
- 12. These are calledfelsic rocks silica rich igneous rocks with a relatively hig content of potassium and sodium
- 13. FEL----SIC Fel feldspar Sic silica Feldsparcrystallize from the K , Na ,Al Silica from silicon oxides ‘
- 14. INTERMEDIATE ROCKS • Rocks witha silica content of between 55% to 65% are classified as intermediate rocks
- 15. Chemistry of intermediateIgneous rocks • Rocks contain significant amounts (30 to 50%) Of dark ferromagnesium minerals Like pyroxene amphibole Light colored plagioclase feldspar and small amount of quartz.
- 16. Diorites • The coursegrained intermediate rocks.about half of the mineral grains are dark in colour and the other half are white.
- 17. Andesite • Fine grainedand medium grey or greenish grey .
- 18. Rhyolite • Is afine grained extrusive felsic rocks
- 19. Granite • Is thecoarse grained intrusive equivalent of rhyolite
- 20. Mafic rocks • Rockswith a silica content of between 45% and 55% by weight are considered as silica- poor. • The remaining is composed mainly of the oxides of aluminum, calcium, magnesium and iron.
- 21. • Rocks inthis group are called mafic silica-deficient igneous rocks with a relatively high content of magnesium, iron and calcium. • The mafic term comes from magnesium and ferum the latin word for iron.
- 22. Chemistry of Maficrocks • Mafic rocks are made up of ; • Grey plagioclase • Feldspar And the ferromagnesium minerals • Pyroxene and • olivine Tend to be dark color.
- 23. Gabbro • Mafic magmathat cool slowly beneth the surface form the coarse grained intrusive rock called as gabbro
- 24. Basalt • If magmaerupts on the surfaces, it forms the dark fine grained extrusive rocks called as basalt.
- 25. Ultramafic Rocks • Ansultra-mafic rocks is one that contain less than 45% silica and rich in iron, magnesium and clacium.
- 26. Chemistry of ultramaficRocks • Ultramafic rocks are composed entirely of the ferromagnesium minerals : • Olivine and pyroxene • No feldspar and quartz are present. • Most ultramafic rocks comes form mantle rather than form the earth’s crust .
- 27. Komatite • The volcanicultramafic rocks is ver rare, ultramafic extrusive rocks are mostly resdricted to the very early history of the earth.
- 28. Peridote • The coarsegraine intyusive rocks is composed of olivine and pyoxene and is the most abundant ultramafic rocks.
- 29. INTRUSIVE IGNEOUS ROCKS •Intusive igneous rocks crystallize below earth’s surface and the slow cooling that occur there allows large crustals to form • Examples of intrusice ingeous rocks • Diorite • Gabbro • Granite pegmatite • peridotite