Forms of Igneous Rocks (Igneous Bodies)

-


Concordant and Discordant Forms of Igneous Rocks 



Igneous intrusions are classified based on their relationship to the pre-existing rock layers (country rocks). These intrusions can either conform to or disrupt the layering of the surrounding rocks, giving rise to concordant and discordant forms.


---

Concordant Forms

Concordant intrusions occur when magma is injected along bedding planes or between layers of pre-existing rocks, aligning with the natural structure without significantly disturbing it.

1. Sills

Definition: Thin, horizontal sheets of magma that solidify parallel to the bedding planes.

Formation: Formed when magma intrudes between sedimentary or other layered rocks under low pressure.

Characteristics:

Typically uniform in thickness.

May vary in composition (basaltic sills are common).


---

2. Laccoliths

Definition: Dome-shaped intrusions where magma pushes the overlying layers upward, forming a convex structure.

Formation: Result from magma of high viscosity (e.g., granitic magma) that pools and lifts the overlying layers.

Characteristics:

Flat base and domed top.

Often associated with volcanic activity.

---

3. Lopoliths

Definition: Basin-shaped intrusions where the magma pools and causes the overlying layers to sag downward.

Formation: Typically formed by dense, mafic magma.

Characteristics:

Convex downward shape.

Large in size, often associated with layered mafic complexes.
---



Discordant Forms

Discordant intrusions occur when magma cuts across the bedding planes or layers of the country rock, disrupting their natural arrangement.

1. Dikes

Definition: Vertical or steeply inclined sheets of magma that cut across pre-existing rock layers.

Formation: Formed when magma forces its way through fractures or faults in the rock.

Characteristics:

Typically narrow but can be very long.

Often found in swarms (multiple dikes in a region).

---

2. Batholiths

Definition: Massive, irregularly shaped intrusions that form deep within the Earth's crust.

Formation: Result from the slow cooling and solidification of large volumes of magma.

Characteristics:

Extremely large (covering hundreds of square kilometers).

Composed mainly of granitic rock.

Often exposed at the surface due to erosion of overlying material.


---

3. Volcanic Necks (Plugs)

Definition: Hardened magma within the vent of an extinct volcano, exposed after the surrounding volcanic material is eroded.

Formation: Forms when magma solidifies within the throat of a volcano.

Characteristics:

Resistant to erosion.

Often steep and prominent.



---


Comments

Post a Comment

Popular posts from this blog

Minerals : Classification and Physical properties

-
Image
Mineral is a naturally occurring, homogeneous inorganic compound having fixed chemical composition and atomic structure formed due to inorganic processes of the Earth. Classification of Rock forming Minerals These are mainly of two types I Silicates Silicates again subdivided into 1. Ferromagnesian minerals i)  Olivine group of minerals ii) Pyroxene group of minerals iii) Amphibole group of minerals iv) Biotite 2. Non Ferromagnesian minerals i)  Feldspar group of minerals ii) Quartz group of minerals iii) Muscovite II Non Silicates Oxides Sulphides Sulphates Carbonates Physical Properties of Minerals Minerals are identified on the basis of following physical properties 1. Colour 2. Streak 3. Lustre 4. Fracture 5. Cleavage 6. Hardness 7. Specific Gravity 8. Form and structure  1. Colour The colour of a mineral depends on the absorption of some and reflectance of other of the coloured rays which constitute the white light. 2. Streak Streak of a miner...
Read more

Dam and its distribution

-
Image
What is a Dam? A dam is a barrier constructed across a river or stream to regulate, manage, or block the flow of water. It creates a reservoir, lake, or impoundment behind it, which can be used for various purposes. Dams are critical components of water resource management systems and contribute significantly to agriculture, industry, and urban development. --- Types of Dams 1. Gravity Dams: Built with concrete or stone, relying on their weight to hold back water (e.g., Bhakra Nangal Dam). 2. Embankment Dams: Made with earth or rockfill; these are cheaper and suitable for wide river valleys (e.g., Hirakud Dam). 3. Arch Dams: Curved dams designed to distribute water pressure (e.g., Idukki Dam). 4. Buttress Dams: Use supports or buttresses to hold back water. 5. Detention Dams: Designed to store water temporarily to control floods. --- Purposes of a Dam Dams serve various purposes that directly benefit humans and the environment. Below are detailed explanations of these purposes: 1. Irri...
Read more