A mantle plume is a narrow, localized column of abnormally hot, buoyant rock that rises through the Earth’s mantle from the core-mantle boundary (approx. 2,900 km deep).
Characteristics of Mantle Plumes
Mushroom-shaped structure – Broad head and narrow tail.
Temperature– Plumes are 100-300°C hotter than the surrounding ambient mantle.
Buoyant upwelling due to lower density.
Stationary relative to moving plates – Forms volcanic chains.
Basalts derived from plumes show distinct isotopic and chemical signatures compared to mid-ocean ridge basalts. Eg- high MgO concentrations
Role of mantle plumes in plate tectonics
Plumes provide evidence of vertical convection within mantle.
Intraplate Volcanism (Hotspots) – Mantle plumes create volcanic activity away from plate boundaries. Eg- Hawaiian Island chain formed over a Pacific plate hotspot.
Formation of Volcanic Island Chains – As tectonic plates move over stationary plumes, a chain of volcanoes forms. Eg- Hawaiian-Emperor Seamount Chain
Continental Flood Basalts – Plume head eruption can cause massive basalt outpourings. Eg- Deccan Traps in India (~66 million years ago).
Plate Breakup and Rifting – Mantle plumes can weaken lithosphere, initiating continental rifting.
East African Rift System.
Role in breakup of Gondwana
Thermal Uplift of Lithosphere – Hot plume material causes crustal doming before volcanic eruption.
Recent research suggests that the intense thermal weakening caused by a plume can cause a tectonic plate to collapse under its own weight, potentially initiating a new subduction zone.
Plume activity and plate motion together form an integrated framework for understanding Earth’s tectonic evolution.
2025 – Discuss how the changes in shape and sizes of continents and ocean basins of the planet take place due to tectonic movements of the crustal masses. (15)
The Theory of Plate Tectonics, developed in the late 1960s, is based on earlier ideas of continental drift (Alfred Wegener) and seafloor spreading (Harry Hess). It states that the lithosphere is divided into rigid plates that move over the semi-fluid asthenosphere and modify the shape, size, and distribution of continents and ocean basins
Changes in the shape and size of continents and ocean basins due to tectonic movements
Divergent Plate Movement – Increase in ocean basin size and breakup of continents.
Plates move apart → magma rises and solidifies to form a new oceanic crust.
Causes seafloor spreading and widening of oceans.Eg- Expansion of the Atlantic Ocean along the Mid-Atlantic Ridge. (2.5 cm per year.)
Continental rifting leads to fragmentation of landmasses.
East African Rift valley
Formation of Linear Seas- Eg- Red Sea due to drifting of Arabian Plate away from the African Plate.
Convergent Plate Movement – Shrinking of oceans and enlargement/upliftment of continents.
Ocean-Continent Convergence
Denser oceanic plate subducts, leading to
formation of trenches and volcanic mountain chains.
Reduction in ocean basin area
Eg- Nazca Plate subducting under the South American Plate to form the Andes Mountains and the Peru-Chile Trench.
The Pacific Ocean is currently shrinking due to subduction along the “Ring of Fire”.
Continent-Continent Convergence – Collision causes fold mountain formation and crustal thickening. Eg- Himalayas formed after closure of the Tethys Sea.
Transform Plate Movement – Change in Continental Configuration
Lateral sliding of plates causes horizontal displacement of landforms. Eg- San Andreas Fault.
Modifies coastlines and continental margins.
It also leads to periodic assembly and break-up of supercontinents such as Pangaea.
These tectonic processes not only remodel the Earth’s surface but also influence climate, ocean circulation, biodiversity, and natural resource distribution.
