Endogenic Processes
Internal Heat Engine · Diastrophism (Orogeny vs. Epeirogeny) · Folding & Faulting · PVT Metamorphism (28 Micro-Realms)
The Internal Land-Building Engine (NCERT Chapter 6)
Powered by internal radioactivity, rotational and tidal friction, and primordial heat, Endogenic Processes are divided into Diastrophism and Volcanism. Diastrophism encompasses four distinct processes that move, elevate, or build up portions of the Earth's crust: 1) Orogenic processes (mountain building through folding), 2) Epeirogenic processes (continent building through uplift/warping), 3) Earthquakes, and 4) Plate Tectonics—all of which induce PVT (Pressure, Volume, Temperature) changes that drive metamorphism.
I. The Internal Energy Engine & Geothermal Gradients (NCERT)
3 Internal Heat Sources
- Energy emanates from within Earth
- Main force behind endogenic processes
- Three distinct generation processes
1. Radioactivity (Primary)
- Decay of $\text{U}^{238}, \text{Th}^{232}, \text{K}^{40}$
- Generates 50–80% of internal heat
- Concentrated in crust & mantle
2. Friction & 3. Primordial
- Rotational & tidal friction flexing
- Primordial heat from early accretion
- And iron core differentiation
Geothermal Gradients
- Rate of temperature increase w/ depth
- Coupled with upward heat flow
- Induces diastrophism & volcanism
Variable Crustal Strength
- Geothermal gradients are not uniform
- Crustal thickness & strength vary
- Action of endogenic forces is uneven!
Diastrophism & Volcanism
- Two main endogenic branches (NCERT)
- Diastrophism: Slow/sudden deformation
- Volcanism: Molten magma movement
Tectonic Uneven Relief
- Tectonically controlled original surface
- Is always uneven across the globe
- Provides raw relief for exogenic wear
II. Diastrophism: Orogeny vs. Epeirogeny (NCERT Core)
What is Diastrophism?
- All processes that move, elevate
- Or build up portions of Earth's crust
- Encompasses 4 specific processes
1. Orogenic Processes
- Greek "Oros" = Mountain building
- Acts through severe folding
- Deforms crust into high ranges
Long & Narrow Orogenic Belts
- Affects long and narrow belts
- Of the Earth's crust (NCERT)
- Alpine–Himalayan & Cordilleran
2. Epeirogenic Processes
- Greek "Epeiros" = Continent building
- Uplift or warping of large parts
- Of the Earth's crust (G.K. Gilbert)
Orogeny vs. Epeirogeny
SEVERE FOLD
SIMPLE WARP
- Orogeny: Severe deformation into folds
- Epeirogeny: Simple vertical deformation
- Tangential vs. Radial vector contrast
Emergence vs. Submergence
- Upward epeirogeny: Raised beaches
- Downward: Submerged coastal forests
- Cymatogeny: Broad undulating arching
Isostatic Vertical Rebound
- Buoyant equilibrium of crust on mantle
- Erosion unloading triggers uplift
- Fennoscandian post-glacial rise
III. Structural Mechanics: Folding, Faulting, Quakes & Plates
Anticlines & Synclines
- Ductile compressional rock bending
- Anticline: Upfolded arch crest
- Syncline: Downfolded trough basin
Fold Asymmetry Spectrum
- Symmetrical $\to$ Asymmetrical
- Overturned & Isoclinal (parallel limbs)
- Recumbent: Horizontal axial plane
Nappes & Thrust Sheets
- Recumbent fold shears along plane
- Rides tens of km over other rocks
- Kashmir & Garhwal Himalayan Nappes
Normal vs. Reverse Faults
- Normal: Tensional pull (crust lengthens)
- Reverse/Thrust: Compression (shortens)
- Strike-Slip: Lateral shear fault
Horsts & Grabens (Rifts)
- Horst: Upthrown block mountain
- Graben: Down-dropped rift valley
- Vosges–Rhine–Black Forest system
3. Earthquakes (Local)
- 3rd branch of Diastrophism (NCERT)
- Involving local relatively minor
- Sudden movements along faults
4. Plate Tectonics
- 4th branch of Diastrophism (NCERT)
- Involving horizontal movements
- Of lithospheric crustal plates
IV. Endogenic Volcanism, PVT Metamorphism & Indian Signatures
Endogenic Volcanism
- Movement of molten rock (magma)
- Onto or toward the Earth's surface
- Forms extrusive & intrusive forms
PVT Changes (NCERT)
- Pressure, Volume and Temperature
- Created by Orogeny, Epeirogeny,
- Earthquakes & Plate Tectonics
Induced Metamorphism
- Endogenic processes cause PVT shifts
- Which in turn induce metamorphism
- Of crustal rocks at depth (NCERT)
Orogenic Root Anatexis
- Deeply buried mountain roots
- Recrystallize into gneiss/migmatite
- Partial melt forms leucogranites
Indian Orogenic Belts
- Himalayas: Young Tertiary fold belt
- Aravallis: Ancient Precambrian fold
- Nallamala & Eastern Ghats folds
Indian Horst & Rift System
- Grabens: Narmada, Tapi, Damodar, Son
- Horst: Satpura Block Mountain
- Faulted Western Ghats escarpment
Indian Epeirogenic Shifts
& MUMBAI FOREST
- Emergence: Rann of Kutch, Kathiawar
- 1819 Allah Bund uplift (+6 m)
- Submergence: Princess Dock forest
Core Distinctions
All processes that move, elevate, or build up portions of the Earth's crust come under Diastrophism: 1) Orogenic processes (mountain building through severe folding of long, narrow belts), 2) Epeirogenic processes (continent building through uplift or warping of large parts), 3) Earthquakes (local, relatively minor movements), and 4) Plate Tectonics (horizontal movements of crustal plates).
2. Orogeny vs. Epeirogeny (UPSC Prelims Favourite)In the process of orogeny, the crust is severely deformed into folds along long, narrow belts (tangential compression). Due to epeirogeny, there may be simple deformation (radial vertical uplift, subsidence, or broad warping of large continental interiors).
3. The PVT → Metamorphism Chain (NCERT)Orogeny, epeirogeny, earthquakes, and plate tectonics cause Faulting and Fracturing of the crust. All these processes cause Pressure, Volume, and Temperature (PVT) changes, which in turn induce metamorphism of rocks.
Endogenic Processes Matrix
NCERT Chapter 6 Structural Summary