GATE GG-1 Igneous petrology PYQs & Answers — Page 4

Questions 31–37 of 37. Imported answers require independent review unless marked reviewed.

Choose the CORRECT combination for the following four statements.

Statement I: Anhydrous partial melting of peridotites produces basic magma. Statement II: Hydrous melting of peridotites produces andesitic magma. Statement III: Congruent melting of minerals produces liquids of compositions identical to the minerals. Statement IV: Incongruent melting of minerals produces liquids of different compositions and new solids.

Your answerChoose one option.

All the four statements I to IV are correct.

Statements I, II and III are correct but statement IV is incorrect.

Statements I and II are correct but statements III and IV are incorrect.

All the four statements I to IV are incorrect.

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A hypothetical garnet peridotite composed of 60% olivine, 25% orthopyroxene, 10% clinopyroxene and 5% garnet undergoes 10% batch melting described by

where F is degree of melting and D is bulk partition coefficient. The ratio of Ce in the melt to the original rock will be ________. (round off to 2 decimal places). (The K_D values of Ce for olivine, orthopyroxene, clinopyroxene and garnet are 0.01, 0.003, 0.10 and 0.02, respectively)

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A melanocratic porphyric rock containing phenocrysts of biotite, with feldspar restricted to the groundmass, is called

Your answerChoose one option.

trachyte.

dacite.

andesite.

lamprophyre.

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In the hypothetical isobaric ternary liquid projection diagram given below, solid phases A, B, C, D and E exist in equilibrium with liquid. The reaction taking place at the isobaric invariant point W is

Diagram for Geology and Geophysics question 37

Your answerChoose one option.

Liquid (at W) = B + D + E

Liquid (at W) = A + B + D

Liquid (at W) + E = B + D

Liquid (at W) + B + D = E

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A basic magma has an initial nickel concentration of 300 ppm. Olivine crystals from this magma by equilibrium crystallization (Case I) or fractional crystallization (Case II). Then, the absolute value of the difference between the nickel concentrations of the liquids remaining after 25% crystallization in these two cases is ____________. (Use K

olivine-melt = 10).

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The given T–X diagram shows the phase relations in olivine solid solution at 1 bar pressure. If ‘P’ is the initial position of melt, the proportion of melt at 1500°C is ________ %.

Diagram for Geology and Geophysics question 36

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The modal abundance in an ultramafic rock and the partition coefficients of lutetium (Lu) in clinopyroxene, orthopyroxene, olivine and plagioclase are tabulated below. The bulk distribution coefficient of lutetium (D̄Lu) in the ultramafic rock is __________.

Mineral	Modal abundance (%)	Partition coefficient
Clinopyroxene	45	0.506
Orthopyroxene	40	0.42
Olivine	10	0.045
Plagioclase	05	0.019

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GATE GG-1 Igneous petrology PYQs

Question 34

Question 54

Question 10

Question 37

Question 47

Question 36

Question 40