Table of Contents
Interaction of Tectonic Plates
- Major geomorphological features such as fold and block mountains, mid-oceanic ridges, trenches, volcanism, earthquakes etc. are a direct consequence of the interaction between various Tectonic Plates (lithospheric plates).
- There are three ways in which the plates interact with each other.
Types of Tectonic Plate Boundaries (Jose F. Vigil. USGS, via Wikimedia Commons)
Tectonic Plates: Divergent, Convergent and Transform Boundaries (nps.gov R.J. Lillie. 2005. Parks and Plates)
Watch the video for quick and better understanding
Divergence forming Divergent Edge or the Constructive Edge
- In this kind of interaction, the plates diverge (move away from each other).
- Mid-ocean ridges (e.g. Mid-Atlantic Ridge) are formed due to this kind of interaction.
- Here, the basaltic magma erupts and moves apart (seafloor spreading).
- On continents, East African Rift Valley is the most important geomorphological feature formed due to the divergence of African and Somali plates.
- Divergent edges are sites of earth crust formation (hence the name constructive edge), and volcanic earth forms are common along such edges.
- Earthquakes (shallow focus) are common along divergent edges.
Convergence forming Convergent Edge or Destructive Edge
- In this kind of interaction, two lithospheric plates collide against each other.
- The zone of collision may undergo crumpling and folding, and folded mountains may emerge (orogenic collision). Himalayan Boundary Fault is one such example.
- When one of the plates is an oceanic plate, it gets embedded in the softer asthenosphere of the continental plate, and as a result, trenches are formed at the zone of subduction.
- Near the convergent edge a part of the crust is destroyed, hence the name Destructive Edge.
- The subducted material gets heated, up and is thrown out forming volcanic island arc and continental arc systems and a dynamic equilibrium is achieved.
Transcurrent Edge or Conservative Edge or Transform Edge
- In this kind of interaction, two plates slide past against each other, and there is no creation or destruction of landform but only deformation of the existing landform.
- In oceans, transform faults are the planes of separation generally perpendicular to the mid-oceanic ridges.
- San Andreas Fault (Silicon Valley lies dangerously close to the faultline) along the western coast of USA is the best example for a transcurrent edge on continents.
- The Indian plate includes Peninsular India and the Australian continental portions.
- The subduction zone along the Himalayas forms the northern plate boundary in the form of continent-continent convergence.
- In the east, it extends through Rakinyoma Mountains (Arakan Yoma) of Myanmar towards the island arc along the Java Trench.
- The eastern margin is a spreading site lying to the east of Australia in the form of an oceanic ridge in SW Pacific.
- The Western margin follows Kirthar Mountain of Pakistan. It further extends along the Makrana coast (Pakistan and Iranian coasts) and joins the spreading site from the Red Sea rift (Red Sea rift is formed due to the divergence of Somali plate and Arabian plate) south-eastward along the Chagos Archipelago (Formed due to hotspot volcanism).
- The boundary between India and the Antarctic plate is also marked by an oceanic ridge (divergent boundary) running in roughly W-E direction and merging into the spreading site, a little south of New Zealand.
Topography of Indo-Australian Plate. The boundaries are conspicuous.
- India was a large island situated off the Australian coast. The Tethys Sea separated it from the Asian continent till about 225 million years ago.
- India is supposed to have started her northward journey about 200 million years (Pangaea broke).
- About 140 million years ago, the subcontinent was located as south as 50◦ S latitude.
- The Tethys Sea separated the Indian plate and the Eurasian plate.
- The Tibetan block was a part of the Asiatic landmass.
- India collided with Asia about 40-50 million years ago causing rapid uplift of the Himalayas (the Indian plate and the Eurasian plate were close to the equator back then).
- It’s thought that India’s coastline was denser and more firmly attached to the seabed, which is why Asia’s softer soil was pushed up rather than the other way around.
- The process is continuing, and the height of the Himalayas is rising even to this date.
- The northward movement of the Indian tectonic plate pushing slowly against the Asiatic plate is evident by the frequent earthquakes in the region.
- During the movement of the Indian plate towards the Asiatic plate, a major event that occurred was the outpouring of lava and formation of the Deccan Traps (shield volcano).
- The shield volcanism started somewhere around 60 million years ago and continued for a long period.
1) Polar fleeing force relates to:
- Revolution of the Earth
- Rotation of the earth
2) Which one of the following is not a minor plate?
3) Which one of the following facts was not considered by those while discussing the concept of sea floor spreading?
- Volcanic activity along the mid-oceanic ridges.
- Stripes of normal and reverse magnetic field observed in rocks of ocean floor.
- Distribution of fossils in different continents.
- Age of rocks from the ocean floor.
4) Which one of the following is the type of plate boundary of the Indian plate along the Himalayan mountains?
- Ocean-continent convergence
- Divergent boundary
- Transform boundary
- Continent-continent convergence
Answers: 1: b); 2: d); 3: c) & 4: d)
Answer in about 30 words.
- What were the forces suggested by Wegener for the movement of the continents?
- How are the convectional currents in the mantle initiated and maintained?
- What is the major difference between the transform boundary and the convergent or divergent boundaries of plates?
- What was the location of the Indian landmass during the formation of the Deccan Traps?
Answer in about 150 words
- What are the evidences in support of the continental drift theory?
- Bring about the basic difference between the drift theory and Plate tectonics.
- What were the major post-drift discoveries that rejuvenated the interest of scientists in the study of distribution of oceans and continents?