UPSC Geology 2021 — Paper II

This multi-part question requires approximately 150 words per sub-part (10 marks each). For (a), begin with Hermann-Mauguin notation rules, derive 4/mmm as the symbol, and sketch stereographic projection with symmetry elements and {hkl} faces. For (b), draw the Diopside-Anorthite binary phase diagram, trace crystallization path, and identify ophitic/subophitic texture. For (c), contrast Bowen's reaction series with mineral examples. For (d), define terms with Indian examples (Tamil Nadu charnockites for prograde; retrograde chloritization) and explain metasomatism. For (e), outline Folk's allochem/matrix classification with limestone types. Allocate ~3 minutes per part with 30-40 seconds for diagrams.

• (a) Hermann-Mauguin notation: rotation axes as digit (1-6), mirror planes as 'm', centre of symmetry as /m; derived symbol 4/m 2/m 2/m or 4/mmm; stereographic projection showing 4-fold axis vertical, 2-fold axes horizontal/diagonal, mirror planes as great circles, centre as small circle, and {hkl} form as 8 faces in general position
• (b) Binary phase diagram of Diopside-Anorthite system with eutectic at ~1270°C, 40% An; crystallization path for Di70An30 melt showing initial diopside crystallization at liquidus, composition moving to eutectic, final solid as mixture of diopside + anorthite; texture: ophitic or subophitic with large diopside enclosing anorthite laths
• (c) Continuous reaction series: plagioclase feldspar (Ca-rich to Na-rich) with gradual compositional change; Discontinuous series: olivine → pyroxene → amphibole → biotite with distinct mineral changes at specific temperatures; named for gradual vs. abrupt phase transitions
• (d) Prograde metamorphism: increasing P-T conditions (e.g., Tamil Nadu granulites); Retrograde: decreasing P-T with rehydration/reaction (e.g., garnet to chlorite); Metasomatism: chemical alteration by fluid infiltration (e.g., fenitization at Sivamalai, Tamil Nadu)
• (e) Folk's classification based on allochems (intraclasts, oolites, fossils, peloids) and matrix (micrite vs. sparite); categories include biosparite, micrite, intramicrite, oosparite; significance for porosity/permeability in carbonate reservoirs

This descriptive question requires systematic exposition across three parts: spend approximately 40% of effort on part (a) given its 20 marks, covering all six silicate classes with structural formulas and examples; allocate 35% to part (b) for precise optical definitions, measurement procedure, and labeled microscope sketches; and 25% to part (c) for crystallographic twin definitions and feldspar twinning types. Begin with clear definitions, proceed with structured classification/tables, and conclude with Indian mineral occurrences where relevant.

• Part (a): Six silicate classes with correct Si:O ratios (nesosilicates 1:4, sorosilicates 2:7, cyclosilicates 1:3, inosilicates single chain 1:3/double chain 4:11, phyllosilicates 2:5, tectosilicates 1:2) and shared oxygen counts (0, 1, 2, 2-3, 3, 4 respectively)
• Part (a): Representative Indian examples for each class (e.g., zircon/olivine, epidote, beryl, pyroxene/amphibole, mica, quartz/feldspar)
• Part (b): Precise definition of birefringence as difference between highest and lowest refractive indices (δ = nγ - nα or nε - nω)
• Part (b): Definition of extinction angle as angle between vibration direction of slower ray and crystal edge/trace of cleavage
• Part (b): Step-by-step measurement procedure: oriented grain selection, stage rotation to extinction positions, angle recording from both sides, calculation of acute angle
• Part (c): Clear distinction between twin plane (mirror plane), twin axis (rotation axis), and composition plane (common boundary)
• Part (c): Feldspar twin types: Carlsbad, Baveno, Manebach, albite, pericline with their crystallographic elements

The directive 'discuss' requires a critical examination with balanced coverage across all three sub-parts. Allocate approximately 40% effort to part (a) given its 20 marks and multi-component nature (magma generation, grain size-cooling relationship, and magmatic differentiation processes), 40% to part (b) for four metamorphic textures with sketches, and 20% to part (c) for migmatite definition and granite origin. Structure with brief introductions for each part, systematic development of concepts, and integrated conclusions showing linkages between igneous and metamorphic processes.

• Part (a): Magma generation mechanisms—decompression melting, flux melting, and heat transfer; relationship between cooling rate and grain size (coarse phaneritic vs. fine aphanitic textures); fractional crystallization (Bowen's reaction series) and assimilation as differentiation processes
• Part (a): Clear explanation of how rapid surface cooling produces glassy/vitreous textures while slow intrusive cooling yields coarse-grained rocks; mention of porphyritic textures indicating two-stage cooling
• Part (b): Four metamorphic structures/textures with sketches—foliation (slaty cleavage, schistosity, gneissic banding), lineation, porphyroblasts, and granoblastic texture; origin linked to directed pressure, recrystallization, and metamorphic grade
• Part (b): Additional textures like augen, mylonitic, or hornfelsic with appropriate genetic contexts; sketches showing 3D orientation of platy minerals in foliation and rotated porphyroblasts
• Part (c): Definition of migmatite as mixed rock with melanosome (dark) and leucosome (light) components; migmatization as evidence for in-situ granite formation through anatexis and melt segregation
• Part (c): Connection between migmatites and granites via the 'granite problem'—demonstrating transition from metamorphic to igneous realms; reference to metatexis vs. diatexis and field evidence from high-grade terranes

The directive 'describe' demands systematic, detailed exposition with clear illustrations. Allocate approximately 40% effort to part (a) on provenance given its 20 marks, 40% to part (b) on facies models requiring detailed sketches, and 20% to part (c) on sedimentary structures. Structure as: brief introduction defining key terms → detailed treatment of each sub-part with diagrams for (b) → integrated conclusion linking provenance-facies-palaeocurrent for basin analysis.

• Part (a): Definition of provenance (source area characteristics) and genetic classification of quartz (monocrystalline vs. polycrystalline, undulatory vs. non-undulatory extinction for metamorphic vs. plutonic sources), feldspars (K-feldspar vs. plagioclase indicating acid vs. intermediate igneous sources; freshness vs. alteration for transport distance), and lithic fragments (sedimentary, metamorphic, volcanic lithics indicating recycled orogenic sources)
• Part (a): Application of QFL and Qm-F-Lt ternary diagrams for provenance discrimination (continental block, magmatic arc, recycled orogen fields per Dickinson et al.)
• Part (b): Definition of sedimentary facies model as a generalised summary of facies characteristics and associations in a specific depositional environment, emphasizing predictability and Walther's Law
• Part (b): Meandering river facies succession: channel lag (coarsest, basal scours) → point bar (upward-fining, trough cross-beds, lateral accretion surfaces) → levee (fine sand, ripples) → crevasse splay (sheet sandstones) → floodplain (mudstone, paleosols, root traces); with neat labelled cross-section showing lateral migration
• Part (c): Genesis and palaeocurrent significance of four structures: (i) trough cross-bedding (3D dunes, bipolar in tidal, unidirectional in fluvial), (ii) tabular cross-bedding (2D dunes, migration direction), (iii) ripple marks (current ripples vs. wave ripples, flow direction from steeper lee side), (iv) parting lineation (upper flow regime, parallel to flow), (v) flute casts (turbidity currents, flow direction from bulbous to tapered end)
• Part (c): Indian examples: Siwalik molasse provenance (Himalayan uplift), Gondwana fluvial facies (Damodar valley), Bhander sandstone palaeocurrents (Vindhyan basin)

This multi-part question requires precise time allocation: spend ~25% on (a) for correct weighted average calculation using area-weighted grade formula; ~20% each on (b)-(e) for concise 150-word responses. For (a), apply Σ(W×L×%Pb)/Σ(W×L); for (b), emphasize Gondwana stratigraphy and coking coal significance; for (c), contrast gravity with magnetic/electrical methods; for (d), explain substitution vs. interstitial entry; for (e), link Milankovitch cycles to eustatic changes and industrial-era thermal expansion.

• (a) Correct application of weighted average formula: Σ(W×L×%Pb)/Σ(W×L) = (21×7.1 + 18.75×7.5 + 30×6.9 + 43.75×8.9)/(21+18.75+30+43.75) = 7.73% Pb
• (b) Jharia coal: Lower Gondwana (Barakar Formation), bituminous rank, high volatile matter, premier coking coal reserve of India, challenges of coal fires and subsidence
• (c) Geophysical methods: gravity, magnetic, seismic, electrical; gravity detects density contrasts for massive sulphide bodies, chromite, and iron ore deposits
• (d) Trace element definition (<0.1%): substitution (diadochy, coupled substitution), interstitial sites, surface adsorption, fluid inclusions
• (e) Late Pleistocene: 120m lower at LGM (~20 ka), Milankovitch forcing, ice-volume equivalent sea level; anthropogenic rise 3.3mm/yr post-industrial, thermal expansion + glacier melt

The directive 'explain' demands clear exposition with cause-effect reasoning across all three parts. Allocate approximately 40% of time/words to part (a) given its 20 marks, 35% to part (b), and 25% to part (c). Structure as: brief introduction on mineral resource significance → systematic treatment of (a) with genetic classification → (b) with policy framework and mineral categories → (c) with manganese specifics → concluding synthesis on India's mineral security.

• Part (a): Modern genetic classification of mineral deposits (magmatic, hydrothermal, sedimentary, metamorphic, residual, mechanical) with clear hierarchical structure
• Part (a): Residual concentration deposits: lateritic nickel (Sukinda), bauxite (Panchpatmali), iron ore (Singhbhum); explanation of tropical weathering, iron/alumina enrichment, silica removal
• Part (a): Mechanical concentration deposits: placer gold (Kolar paleoplacers), beach placers (monazite in Kerala-Tamil Nadu coast), cassiterite; explanation of density-based sorting in fluvial/marine environments
• Part (b): Premise of National Mineral Policy 2019: security of supply, sustainable mining, private sector participation, scientific exploration, minimal environmental impact
• Part (b): Strategic minerals (rare earth elements, lithium, cobalt—Chhattisgarh REE belts); Critical minerals (copper, tungsten, molybdenum—Malanjkhand, Degana); Essential minerals (iron, manganese, bauxite, coal—Odisha, Jharkhand belts)
• Part (c): Mode of occurrence: bedded/stratiform deposits in Dharwar Supergroup, associated with iron formations; syngenetic-sedimentary origin with later supergene enrichment
• Part (c): Distribution: Balaghat (Madhya Pradesh)—largest producer, high-grade ore; Nagpur-Bhandara (Maharashtra); Keonjhar, Sundergarh (Odisha); Dharwar (Karnataka); Vizianagaram (Andhra Pradesh)
• Part (c): Uses: ferromanganese in steelmaking (deoxidizer, sulfur control), dry cell batteries, chemical industry, aluminum alloying; India's 7th largest global reserves but import dependence for battery-grade manganese

The directive 'state' in part (a) demands precise, factual presentation of cosmic abundance characteristics and estimation bases. Allocate approximately 40% of time/words to part (a) given its 20 marks, 20% to part (b), and 40% to part (c). Structure as: brief introduction linking cosmochemistry to mineral chemistry and petroleum geology; three distinct sections for each sub-part with clear sub-headings; and a concluding synthesis on how elemental abundance governs mineral formation and hydrocarbon source rock potential.

• Part (a): Characteristic features of cosmic abundance — H and He dominance (~98% by mass), even-odd atomic number pattern, iron peak at Z=26, exponential decrease with atomic number, and rarity of Li-Be-B due to nuclear instability
• Part (a): Bases of estimation — spectroscopic analysis of stellar atmospheres, meteorite composition (especially CI chondrites), solar wind measurements, and cosmic ray abundance data
• Part (b): Types of chemical bonds with mineral examples — ionic (halite, NaCl), covalent (diamond, C), metallic (native Au, Cu), van der Waals (graphite, phyllosilicates), hydrogen bonds (ice, kaolinite), and mixed bonding in silicates
• Part (c): Western Indian oil fields — Mumbai High (Bombay High) fractured basement and carbonate reservoirs, Cambay Basin rift-related Tertiary sediments, and Kutch-Saurashtra region with Mesozoic and Tertiary sequences
• Part (c): Structural controls — listric faults, rollover anticlines, and stratigraphic traps in Mumbai High; rift graben geometry in Cambay Basin with Eocene-Oligocene source rocks

The directive 'describe' demands systematic, detailed exposition with factual precision. Allocate time proportionally: ~20% (200 words) for part (a) on Himalayan catchment mismanagement, ~40% (400 words) for part (b) covering radioactive waste classification and disposal protocols, and ~40% (400 words) for part (c) on waterlogging mechanisms and reclamation techniques. Structure each part with definition-cause-effect-solution sequencing; use sub-headings for clarity. Conclude with integrated remarks on sustainable development.

• Part (a): Deforestation, slope destabilization, and reduced infiltration in Himalayan catchments (e.g., Uttarakhand) increase runoff velocity and sediment load, amplifying downstream flood risk in Indo-Gangetic plains
• Part (a): Specific unscientific practices—unregulated road cutting, terracing failures, and encroachment on river channels—disrupt natural drainage buffers
• Part (b): Classification of radioactive wastes by activity level (low, intermediate, high) and half-life; distinction between spent fuel and reprocessed wastes
• Part (b): Disposal methods: near-surface engineered facilities for low-level waste, deep geological repositories (granite, salt dome, basalt) for high-level waste, and vitrification processes
• Part (c): Definition of waterlogging as saturation of root zone above field capacity; causes including excessive irrigation, poor drainage, and impermeable subsurface layers
• Part (c): Remedial measures: biological (afforestation, crop rotation), mechanical (tile drainage, vertical drainage), and chemical (gypsum application, leaching) for salinity reclamation
• Integration: Link between catchment mismanagement and groundwater recharge patterns affecting regional waterlogging potential