(a) What are transform and transcurrent faults? Illustrate them using neat sketches. (10 marks) (b) Discuss the different types…

(a) Transform and transcurrent faults (10 marks)

A transform fault is a strike-slip fault that is itself a plate boundary, joining two offset ridge, trench or ridge–trench segments (a conservative margin). Slip is constant along the active segment and stops abruptly at the boundary junctions, beyond which the trace continues only as an inactive fracture zone. The slip sense is opposite to the apparent offset of the ridge (San Andreas Fault, Romanche fracture zone).

A transcurrent fault is a large strike-slip fault within a plate. It does not end at a plate boundary; slip dies out towards its tips or is taken up by folds and thrusts, and the slip sense agrees with the offset of markers (Great Glen Fault, Karakoram Fault).

Thus a transform fault is a plate boundary with constant slip, whereas a transcurrent fault is an intra-plate structure with dying-out slip.

(b) Types of plate boundaries and mid-oceanic ridges (10 marks)

Plate boundaries are of three kinds. Divergent: plates move apart, magma rises and new oceanic lithosphere forms (Mid-Atlantic Ridge, East African Rift). Convergent: one plate is subducted (ocean–ocean, Mariana arc; ocean–continent, Andes) or continents collide (Himalaya), giving trenches, volcanic arcs, deep earthquakes and fold mountains. Transform: plates slide past without creating or destroying lithosphere (San Andreas Fault).

Note on mid-oceanic ridges. They form a continuous submarine mountain chain about 65,000 km long, rising 2–3 km above the ocean floor, with a central rift valley. They are sites of spreading, pillow-basalt volcanism, shallow earthquakes and hydrothermal vents, and are offset by transform faults. The ocean floor becomes older and more sediment-covered away from the crest, with symmetrical magnetic stripes. Spreading rates range from about 2 cm/yr (Atlantic) to over 10 cm/yr (East Pacific Rise).

(c) Types of unconformities and their significance (10 marks)

An unconformity is a surface of erosion or non-deposition separating younger from older rocks.

• Angular unconformity: horizontal younger strata rest on tilted or folded older strata truncated by erosion.
• Disconformity: younger and older strata are parallel, separated by an irregular erosion surface.
• Nonconformity: sedimentary strata rest on eroded igneous or metamorphic rocks.
• Paraconformity: parallel strata with a flat, non-erosional break, recognised from fossils.

Significance. An unconformity records a hiatus with uplift, erosion and later subsidence or sea-level rise, often marked by a basal conglomerate. Angular unconformities record orogenic movements and are used to divide the stratigraphic record; missing strata hamper correlation. Unconformities also guide palaeogeography and host uranium ores (Athabasca) and hydrocarbon traps, and the Archaean–Cuddapah nonconformity marks the ancient Indian shield.

(d) Geomorphic provinces of the Indian subcontinent and their significance (10 marks)

The subcontinent has five major provinces. (1) The Himalayan mountain belt: young fold-thrust mountains, with the Greater, Lesser and Sub-Himalaya (Siwaliks) separated by the MCT, MBT and HFT. (2) The Indo-Gangetic-Brahmaputra plain: an alluvial foreland basin of thick Quaternary sediments. (3) The Peninsular plateau: an ancient shield of Archaean–Proterozoic rocks, with the Aravalli, Satpura, Western and Eastern Ghats and the Deccan Traps. (4) The coastal plains and deltas. (5) The islands (Andaman–Nicobar, Lakshadweep).

Significance. The Himalaya record the India–Eurasia collision and active tectonics; the plain holds groundwater and buried foredeep sediments; the plateau holds iron ore, manganese, gold, Gondwana coal and bauxite; the coastal basins hold hydrocarbons (Krishna–Godavari, Cambay) and beach placers; the Andaman arc records subduction.

(e) Resolutions in remote sensing and their significance (10 marks)

Resolution is the ability of a sensor to record detail.

• Spatial: the smallest ground area resolved (pixel size or IFOV), for example Landsat 30 m and Cartosat-2 about 1 m. It controls the scale of mapping, from regional lineaments to individual outcrops.
• Spectral: the number and narrowness of wavelength bands, from multispectral (Landsat-8, 11 bands) to hyperspectral (Hyperion, 220 bands). It allows minerals such as clays and alunite to be identified from absorption features in the SWIR.
• Radiometric: the sensitivity to differences in radiance, given by the number of bits (8-bit = 256 levels, 12-bit = 4096). It separates rocks of similar reflectance.
• Temporal: the revisit interval (Landsat 16 days, Sentinel-2 5 days), used to monitor landslides, floods, volcanic activity and shoreline change.

There is normally a trade-off between spatial, spectral and temporal resolution.