Plate Tectonics
Lithospheric Plates · 7 Major & Minor Plates · Plate Motion Mechanisms (28 Micro-Realms)
The Grand Unifying Theory of Geology (1967)
In 1967, McKenzie and Parker and independently W.J. Morgan synthesized Continental Drift and Seafloor Spreading into Plate Tectonics. A tectonic plate is a massive, irregularly-shaped slab of solid Lithosphere (Crust + top mantle, $5\text{–}200\text{ km}$ thick) that moves horizontally as a rigid unit over the ductile Asthenosphere.
I. Lithospheric Plates & The 1967 Plate Tectonic Synthesis
1967 Founding Trio
- Formulated in 1967 (NCERT)
- McKenzie, Parker & Morgan
- Unified drift & spreading
Lithospheric Plate
- Massive irregular solid slab
- Crust + top solid mantle
- Moves as a single rigid unit
5–100 vs 200 km Thickness
- $5\text{–}100\text{ km}$ in oceanic parts
- About $200\text{ km}$ in continental
- Thickest under ancient cratons
Oceanic vs Continental Plate
- Wholly or mostly whichever dominates
- Pacific: Largely oceanic plate
- Eurasian: Continental plate
Asthenosphere Glide
- Plates move horizontally
- Over plastic Asthenosphere
- Continent is passive passenger!
J. Tuzo Wilson (1965)
- Coined the term "Plates"
- Identified Transform Faults
- Linked ridges & trenches
Seven Major Plates
- 7 Major plates (NCERT)
- Account for ~94% of surface
- Surrounded by ridges/trenches
II. The Seven Major Lithospheric Plates (NCERT Classification)
I. Antarctica Plate
- Antarctica + surrounding ocean
- Ringed by divergent ridges
- Almost stationary polar cap
II. North American Plate
- N. America + W. Atlantic floor
- Separated from S. America
- Along Caribbean islands
III. South American Plate
- S. America + W. Atlantic floor
- Rifts from Mid-Atlantic Ridge
- Converges with Nazca plate
IV. Pacific Plate
- Largest plate on Earth
- Almost entirely oceanic SIMA
- Bordered by Ring of Fire
V. India–Australia–NZ Plate
- Peninsular India + Australia
- Plus New Zealand & Indian Ocean
- Collides north with Eurasia
VI. African Plate
- Africa + Eastern Atlantic floor
- Up to Mid-Atlantic Ridge
- Splitting along East African Rift
VII. Eurasian Plate
- Eurasia + adjacent oceanic floor
- Predominantly continental plate
- Excludes India & Arabia
III. Important Minor Plates (NCERT Prelims Location Matrix)
1. Cocos Plate
- Between Central America
- And Pacific Plate (NCERT)
- Subducts under Mexico/C. America
2. Nazca Plate
- Between South America
- And Pacific Plate (NCERT)
- Subducts to form Andes
3. Arabian Plate
- Mostly Saudi Arabian landmass
- Rifted from Africa (Red Sea)
- Collides into Zagros (Iran)
4. Philippine Plate
- Between Asiatic & Pacific plate
- Bounded by Mariana Trench
- Diamond-shaped oceanic plate
5. Caroline Plate
- Between Philippine & Indian plate
- North of New Guinea (NCERT)
- Western Pacific microplate
6. Fuji Plate
- North-East of Australia
- Southwest Pacific basin
- Active back-arc spreading
Other Key Minor Plates
- Juan de Fuca (Cascadia NW US)
- Caribbean & Scotia plates
- Burma, Sunda, Somali plates
IV. Plate Motion Mechanisms (Convection, Ridge Push, Slab Pull)
Quake Belts = Boundaries
- Plate interiors are quiet
- Quakes & volcanoes trace edges
- Defines plate outlines
Euler Pole Rotation
- Plates move on a sphere
- Rotate around an Euler Pole
- Speed increases away from pole
Mantle Convection Cells
- Heated material rises, spreads
- Cools & sinks back down
- Mobile rock beneath rigid plates
Ridge Push Force
- Buoyant elevated MOR crest
- Gravitational sliding down flanks
- Pushes young plate outward
Slab Pull (Strongest Driver)
- Cold dense oceanic slab sinks
- Drags trailing plate into trench
- Fastest plates have long trenches
Basal Drag & Suction
- Asthenosphere shear coupling
- Trench rollback suction
- Modulates plate velocity
Hotspot Reference Tracks
- Stationary deep mantle plumes
- Plate moves over blowtorch
- Hawaiian & Réunion chains
Core Distinctions
Wegener's Continental Drift: Only the continents (SIAL) move, ploughing through a stationary ocean floor. Plate Tectonics: It is not the continent that moves alone—continents are part of a Lithospheric Plate (Crust + top mantle, $5\text{–}200\text{ km}$), and the entire plate moves over the Asthenosphere.
2. Why Atlantic Floor is Split Across 4 Major PlatesBecause the Mid-Atlantic Ridge is the plate boundary! The Western Atlantic floor belongs to the North & South American plates, while the Eastern Atlantic floor belongs to the Eurasian & African plates.
3. NCERT Minor Plate Locations (Frequent Prelims Match-the-Following)• Cocos: Central America $\leftrightarrow$ Pacific
• Nazca: South America $\leftrightarrow$ Pacific
• Caroline: Philippine $\leftrightarrow$ Indian (North of New Guinea)
• Fuji: North-East of Australia
The 7 Major Plates (NCERT)
Complete Global Lithospheric Division