Igneous Petrology — DU B.Sc. (Hons.) Geology Previous Year Question Papers

1. Answer the following : 9×2=18 (a) An intrusive igneous rock composed of crystals that are large enough to see with the naked eye is said to exhibit a .................. texture. (b) Crust plus the more rigid portion of the uppermost mantle together is called ................. . (c) Based on the total alkali vs. silica classification, what are the two distinct group of magma ? (d) Fluid flux induced melting primarily occurs along which type of plate boundary ? (e) (f) (g) (h) (i) The texture in which phenocrysts are present in glassy groundmass is called .................. . In the divariant fields, the degree of freedom is ............... . Ophitic texture is commonly observed in : (iii) Rhyolite. Elements whose partition coefficient is less than one is called ................ Name the coarse-grained (plutonic) rock consisting primarily of sodic plagioclase and hornblende : (iii) Gabbro 2. Answer the following : 6+6+6 (a) Phase and component in the igneous phase diagram. (b) Equilibrium melting and Fractional melting. (c) Rapakivi and Spinifex textures. 3. Given below is the isobaric T-X phase diagram for solid solution with eutectic : Or-Ab phase diagram. Answer the following questions : 8+4+6 (a) Describe the crystallization of melt with initial bulk compositions of Describe the texture that will develop with initial bulk compositions of a and i. What is the effect of pressure on the T-X phase diagram for the alkali feldspars phase diagram ? 4. Answer the following : 6+6+6 (a) Congruent and incongruent melting. (b) Lever rule and Phase rule. (c) High field strength (HFS) and large ion lithophile (LIL) elements. 5. Describe the following in detail : 9+9 (a) Factors responsible for mantle melting and magma generation. (b) Describe the various processes of magma differentiation. 6. Describe the following in detail : 6+6+6 (a) Tholeiitic and alkaline magma. (b) Differences between island and continental arc magmatic suites. (c) Volcanism associated with hotspots. 7. Answer the following : 12+6 (a) Briefly describe the different physical properties of magma. (b) Define major, minor and trace elements. 8. Answer the following : 6+6+6 (a) Primary magma and derivative magma (b) I-type and S-type granite. (c) Classification of granite based on the aluminum saturation index (ASI).