Geology 2023 Paper I 50 marks Describe

Q4

(a) What is a Shear Zone ? Describe the different Shear Sense indicators. (20 marks) (b) Enumerate the Shepard's classification of coast's and briefly describe the marine cycle of erosion along a shoreline of submergence. (15 marks) (c) Describe the different types of volcanoes based on mode of the eruption and its associated products. Add a note on positive and negative relief features associated with volcanoes. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) अपरूपण क्षेत्र क्या है ? विभिन्न प्रकार के अपरूपण अभिदिशा सूचकों का वर्णन कीजिए । (20 अंक) (b) तटों का 'शेपर्ड' वर्गीकरण लिखें और तटरेखा के निमज्जन के साथ सागरीय चक्र के अपरदन का संक्षिप्त वर्णन कीजिए । (15 अंक) (c) उद्गार की विधि और उससे सम्बन्धित उत्पादों के आधार पर विभिन्न प्रकार के ज्वालामुखियों का वर्णन करें । ज्वालामुखियों से सम्बन्धित सकारात्मक एवं नकारात्मक उच्चावच (रिलीफ) विशेषताओं पर टिप्पणी कीजिए । (15 अंक)

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Directive word: Describe

This question asks you to describe. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The question demands descriptive treatment across three distinct geological domains. Allocate approximately 40% of time/words to part (a) given its 20 marks weightage, with ~30% each to parts (b) and (c). Structure with brief definitions first, followed by systematic elaboration of types/indicators, and conclude with integrated field examples where possible. For part (a), begin with shear zone definition and kinematic framework, then detail shear sense indicators with sketches; for (b), enumerate Shepard's classification first, then explain the marine cycle on submerged shorelines; for (c), classify volcanoes by eruption mode and products, then address relief features in the note.

Key points expected

  • Part (a): Definition of shear zone as ductile to brittle-ductile deformation zone with concentrated strain; kinematic vorticity and non-coaxial flow concepts
  • Part (a): Shear sense indicators including S-C fabrics, C' shear bands, asymmetric porphyroclasts (δ-type, σ-type), mica fish, rotated clasts, pressure shadows, and bookshelf gliding
  • Part (b): Shepard's classification based on primary and secondary factors: coasts of submergence, emergence, neutral, compound; further subdivision by tectonic setting and lithology
  • Part (b): Marine cycle of erosion on submerged shorelines: stages of youth (cliffs, wave-cut platforms), maturity (bays, headlands, sea caves, arches, stacks), old age (reduced relief, marine planation)
  • Part (c): Volcano classification by eruption mode: Hawaiian (effusive, basaltic), Strombolian (moderate explosive, scoria), Vulcanian (viscous, ash-laden), Plinian (cataclysmic, pumice), Pelean (nuées ardentes, domes); associated products for each
  • Part (c): Positive relief features: volcanic cones, shield volcanoes, stratovolcanoes, lava domes, volcanic necks; Negative relief features: calderas, craters, maars, volcanic depressions, fissure eruptions

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precise definitions of shear zones with kinematic framework; accurate Shepard's classification hierarchy; correct volcano-eruption associations with specific product characteristics; no conflation of marine erosion stagesBasic definitions correct but kinematic concepts vague; Shepard's classification incomplete or confused with other schemes; volcano types listed but eruption-product linkages weak; marine cycle stages jumbledFundamental errors in defining shear zones as faults; wrong classification basis; volcano types confused with vent types; marine cycle described as subaerial erosion cycle
Diagram / cross-section20%10Clear labeled diagrams for S-C fabric relationships, asymmetric porphyroclast geometry with shear sense arrows; coastal profile showing wave-cut platform, cliff, sea stack sequence; volcanic cross-sections contrasting shield vs. stratovolcano morphology with eruption columnsDiagrams present but poorly labeled or missing critical features like shear direction indicators; coastal diagrams lack stage differentiation; volcano diagrams generic without eruption style illustrationNo diagrams or irrelevant sketches; diagrams without labels; incorrect geometries (e.g., symmetric porphyroclasts showing no shear sense)
Field evidence20%10Specific Indian examples: Singhbhum shear zone, Aravalli shear zones for (a); Kerala-Karnataka submerged coasts, Gulf of Khambhat for (b); Barren Island (active), Narcondam, Deccan Traps flood basalts for (c); mentions field criteria like stretching lineations, groove castsGeneric field references without specific locations; Indian examples missing or incorrect; conflates similar features across different settingsNo field examples; fabricated locations; confuses shear zones with thrust belts or rift zones
Quantitative reasoning15%7.5Mention of strain rates, vorticity numbers (Wk ~0.75-1 for simple shear); approximate coastal retreat rates; volcano explosivity index (VEI) correlation with eruption types; viscosity-magma composition relationships (10^2-10^6 Pa·s range)Vague references to 'high' or 'low' strain/viscosity without magnitudes; no quantitative framework for coastal erosion ratesNo quantitative parameters; incorrect orders of magnitude; confuses intensive and extensive properties
Indian / economic relevance20%10Economic significance of shear zones (Au-Cu mineralization in Dharwar, Kolar gold fields); coastal hazards and management (tsunami vulnerability of submerged coasts); volcanic soil fertility (Deccan Traps black cotton soils), geothermal potential, volcanic hazards mitigation; sustainable coastal zone managementMention of economic aspects without specificity; generic statements about mineralization or soil fertility without linking to specific Indian depositsNo economic or applied relevance discussed; misses opportunity to connect to Indian mining, agriculture, or disaster management

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