(a) Discuss in detail the notion of 'continental drift' and the theories of plate tectonics as they relate to palaeogeography…

(a) Continental drift, plate tectonics and palaeogeography

Wegener’s continental drift proposed that continents once formed Pangaea and have drifted apart. Evidence included the jigsaw fit of South America and Africa, fossil correlations such as Glossopteris and Mesosaurus across Gondwana, and palaeoclimatic indicators like glacial striations and coal deposits in now tropical regions. The idea was initially rejected because no mechanism was accepted. Plate tectonics supplied mechanisms: mantle convection, slab pull, ridge push, and transform motion. Seafloor spreading, supported by young oceanic crust and symmetrical magnetic stripes, linked drift to plate tectonics. Divergent boundaries create oceanic crust at mid-ocean ridges; convergent boundaries consume it at trenches, producing subduction, collision and orogeny; transform boundaries accommodate lateral slip. This makes plate tectonics a dynamic framework: it explains not only present boundaries but also past reconstructions, rates of drift, and the timing of mountain building. Indian examples include the Himalayan collision zone where the Indian plate has converged with Eurasia, the Andaman-Nicobar subduction zone, and the diffuse Indo-Australian plate boundary, a broad zone of deformation rather than a simple transform. Palaeomagnetic data, including Apparent Polar Wander Paths from Deccan Trap basalts, support India’s northward movement and Gondwana reconstruction. India rifted from Antarctica and Australia about 130 Ma, from Madagascar about 88 Ma and from the Seychelles about 65 Ma, crossed the Réunion hotspot as the Deccan Traps erupted near 66 Ma, drifted north at up to 15–18 cm per year in the Late Cretaceous, and collided with Asia about 50 Ma. The Gondwana basins of the Damodar, Son-Mahanadi and Pranhita-Godavari valleys, with Glossopteris coal, are the Indian record of the southern supercontinent.

The Wilson cycle and supercontinent cycles—Rodinia, Gondwana, Pangea—show repeated assembly and breakup. Palaeogeography thus uses fit, fossils, climate, magnetics and plate kinematics to restore past positions, ocean basins and collision timing.

(b) Principles and classification of aerial photography

Aerial photography records the Earth’s surface from aircraft; related remote-sensing images use other platforms. Its principles include stereoscopic vision, which gives three-dimensional perception from overlapping images; parallax, the apparent displacement used to estimate heights and relief; scale, the ratio of image distance to ground distance; resolution, the ability to distinguish adjacent features; and overlap, usually 60 per cent longitudinal and 20 to 30 per cent lateral, needed for stereoscopy and coverage. Photo scale equals focal length divided by flying height above the ground.

Classification is by platform: terrestrial, aerial and space; by tilt: vertical (camera axis within about 3° of the vertical), low-oblique (horizon not shown) and high-oblique (horizon shown); by film or sensor: panchromatic, infrared and false-colour composite; and by scale: large, medium and small. These classifications help select the right image for structural mapping, lineament detection and thematic interpretation. In India, GSI aerial surveys have been used for geological mapping and mineral targeting, while Landsat and IRS satellite imagery have helped map lineaments in the Dharwar craton. Bhuvan integrates such datasets for geological and remote-sensing analysis.

(c) Linear structures of deformed rocks

Linear structures are elongated features in rocks. Primary lineations include flow lineation and current (parting) lineation or sole marks, formed during magmatic flow or deposition; they may be inherited and later deformed. Secondary lineations are deformational: fold axes, crenulation and intersection lineations, mineral and stretching lineations, mullions, rods, pencil structure and boudin axes. They are important strain markers and kinematic indicators: their orientation, plunge and associated asymmetry help determine the direction of shortening, extension and transport. A simple sketch would show a folded bed with a fold axis, a planar foliation cut by a mineral lineation, and boudinaged layers with long axes parallel to extension. In maps, lineaments may be mapped from aerial or satellite images, then verified in the field.

In India, lineations along the arcuate Singhbhum shear zone record its thrusting and shear sense, NE-SW trending fold-axis lineations in the Aravalli-Delhi fold belt follow the belt and lie normal to the shortening direction, and mineral lineations in the Kerala khondalite belt indicate transport direction during ductile shear. Together, these structures help reconstruct palaeostresses and plate-boundary evolution.