(a) Examine the recent views on mountain building process and divide the world mountains on the basis of their genesis. 20 (b)…

Mountain building, climate zonation and ocean-floor morphology are expressions of plate tectonics, mantle dynamics and surface processes.

Part (a): Mountain building Recent views treat mountain building as a lithosphere-scale process, moving beyond static fold theory to dynamic plate-tectonic and mantle-driven models. Sea-floor spreading at mid-ocean ridges, slab pull (negative buoyancy of sinking lithosphere) and slab suction (mantle-flow drag at a trench) control plate motions; convergence at trenches is mainly driven by slab pull, while suction modifies trench dynamics. The Wilson cycle explains how rifting opens basins, spreading widens them, subduction consumes crust, and collision builds orogens. Genetically, world mountains divide into fold mountains from convergence/collision (Himalayas, Alps), block/horst mountains from faulting (Vosges, Black Forest), volcanic mountains from subduction or plume activity (Cascade Range), and relict mountains from erosion of older orogens (Aravallis, Urals). Recent advances refine this: mantle plume dynamics, delamination of dense lithosphere, and critical taper wedge mechanics explain crustal thickening, exhumation, magmatism and seismicity. Delamination can produce rapid uplift without direct collision, while critical taper theory links wedge stability to basal friction, fluid pressure and sediment load. Collisional Himalayan-type orogens differ from accretionary Andean-type margins in plate convergence, slab angle, crustal addition and topographic response. The examined finding is that mountain building is not a single process but a spectrum of lithospheric responses to plate forces, mantle flow, slab dynamics and crustal strength.

Part (b): Köppen latitudinal distribution Köppen climates show latitudinal zonation modified by continentality, relief, monsoons and oceans. The pattern reflects pressure belts: ITCZ, subtropical highs, westerlies and polar easterlies. Equatorial Af, Am and Aw occur roughly 0–20°; Af has rain in every month, Am has a short dry season offset by very heavy monsoon rain, and Aw has a distinct winter dry season as the ITCZ and the subtropical high shift with the seasons. Dry B climates are azonal: BWh/BSh occur in subtropical dry regions such as the Sahara and Australia, while BSk/BWk occur in mid-latitude continental interiors such as Central Asia, Patagonia and the Great Basin. C climates extend from about 25–30° to 60° in both hemispheres: Cfa/Cwa can occur near 25–30°, Cfb/Cwb and Csa/Csb dominate mid-latitudes, and Cfb can reach about 60°N. Monsoon reversal in Asia explains Cwa and Dwa. D climates are mainly northern-hemisphere, extending to about 70°N, with Dfa/Dfb/Dfc/Dfd and monsoon Dwa/Dwb; they are essentially absent in the Southern Hemisphere because of limited land area. ET and EF occupy polar regions, roughly 60–90°.

Part (c): Indian Ocean bottom topography The sketch below shows the main ridges, plateaus, basins, trenches and sediment fans.

The Central Indian Ridge and Carlsberg Ridge form the mid-ocean ridge system, segmented by transform faults. The Ninety East Ridge is a north-south trending aseismic hotspot trace, not a transform-fault remnant. The Chagos-Laccadive Ridge is associated with the Réunion hotspot, while the Mascarene Plateau lies in the SW. The Wharton Basin occupies the east. The Sunda Trench, of which the Java Trench is a segment, marks active subduction in the eastern periphery; the Makran trench/subduction zone in the NW Arabian Sea is the other major active margin, forming an accretionary prism. The western sector otherwise lacks broad marginal trenches. Asymmetrical sediment fans from the Ganga-Brahmaputra and Indus systems thicken near their mouths and thin offshore because monsoon currents and river discharge deposit sediment unevenly.

Plate tectonics unifies these themes: ridge spreading and subduction shape mountains and trenches, mantle plumes and slab dynamics modify orogens, latitude and pressure belts organise Köppen climates, and the Indian Ocean floor records spreading, subduction, plumes and sedimentation.