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Q61. A garnet bearing charnockite has zoned zircon and monazite grains. Zircon cores have high Th/U while rims have low Th/U ratios. The correct inference is:
Monazite strongly partitions Thorium (Th) into its structure. When monazite crystallizes, it depletes the remaining melt of Th. Therefore, any zircon rims that grow afterward will naturally have a low Th/U ratio.
Q62. Mississippi valley type deposit is:
Mississippi Valley Type (MVT) deposits are epigenetic (formed after the host rock) lead-zinc concentrations found in carbonate sedimentary rocks.
Q63. Longshore current flows:
Longshore currents flow parallel to the shoreline. They are generated when waves approach the coast at an angle and undergo refraction, pushing water along the beach.
Q64. Some oceanic sediments and sedimentary rocks are listed below. Which one of these is correct in the increasing order of depth of deposition?
Lepidocyclina is shallow marine. Pteropods (aragonite) dissolve first (shallow CCD ~2000m). Globigerina (calcite) dissolves deeper (~4500m). Radiolarians (silica) survive past the CCD to the deepest abyssal plains.
Q65. Kimberlite magma originates from mantle at depths exceeding 100 km and emplaced through a thick continental crust without significant crustal assimilation. The reason is:
Kimberlites are rich in volatiles (CO2 and H2O) which drive extremely rapid, explosive ascent, preventing the magma from cooling or assimilating the surrounding crust.
Q66. Choose the correct option based on the following two statements: (A) 34S/32S ratio in co-existing sulfide minerals in equilibrium can be used as a geothermometer. (B) The fractionation factor of 34S/32S in coexisting phases depends on pressure.
Isotopic fractionation is highly dependent on temperature (making it a good geothermometer) but is virtually independent of pressure.
Q67. Sheet silicates are considered as trioctahedral if they have:
In sheet silicates, if the octahedral sites are occupied by divalent cations (like Mg2+ or Fe2+), all three available sites must be filled to balance the charge, making it 'trioctahedral' (e.g., Biotite).
Q68. Which one of the following statements about Manning velocity equation is correct?
In Manning's equation, Velocity is proportional to (Hydraulic Radius)^(2/3) and (Channel Slope)^(1/2). Since 2/3 > 1/2, Hydraulic Radius carries higher power.
Q69. Which one of the following pairs in Koeppen's classification of climates is NOT correctly matched?
In Koeppen's classification, 'B' stands for Dry/Arid climates (deserts and steppes). Polar climates are designated by the letter 'E'.
Q70. For a cubic mineral, the first few peaks in the XRD pattern have Miller indices 111, 200, 220, 222 and 311. From the systematic absences of peaks, the mineral may be inferred to have:
In a Face-Centred Cubic (FCC) lattice, diffraction peaks only occur when the Miller indices (h, k, l) are either ALL odd or ALL even. The given sequence perfectly matches this rule.