INTRUSIVE VOLCANIC ROCKS

BYT.VENKATESH,1ST YEAR,M.SC.GEOLOGY,DEPARTMENT OF GEOLOGY.

CONTENT• INTRODUCTION

• BATHOLITHS

• LACCOLITHS

• PHACOLITHS

• LOPOLITHS

• SILLS

• DYKES

• CONCLUSION

INTRODUCTION

there are two types rocks which is produced by the vulcanicity.they are,

1.extrusive rocks

2.intrusive rocks

INTRODUCTION

• Major intrusive rocks are,

• Batholiths,laccoliths,phacoliths,lopoliths,sills,dikes, etc.

• When gases & vapour are not erupted strongly,the ascending magmas to not erupt as lava rather these are intruded in below crustal surface and after solidification assume intrusive rocks.

BATHOLITH:

Description: It is a large, irregularly shaped reservoir of magma.Formation: Magma intrudes into a large

chamber beneath the surface of the earth. It cools and solidifies at a very slow rate there.

It is commonly composed of coarse-grained rocks (e.g., granite)

Batholith cools and solidifies, later to be exposed at the surface through erosion

LACCOLITH: Description: It is a dome like feature between bedding planes.

Formation: Magma intrudes between bedding planes, but its progression is blocked by a structure. The magma pushes up the rock layer above it. It cools and solidifies at a very slow rate there.

Acid rocks are more common than basic rocks in laccoliths.

PHACOLITH:

A phacolith is a pluton parallel to the bedding plane.

It is typically lens-shaped pluton that occupies either the crest of an anticline or the trough of a syncline.

In rare cases the body may extend as a sill from the crest of an anticline through the trough of an adjacent syncline, such as cross section.

LOPOLITH:A saucer- or lens-shaped body of intrusive

igneous rock, formed by the penetration of magma between the beds or layers of existing rock and subsequent subsidence beneath the intrusion.

It is believed that lopoliths are formed when magma which has intruded into the earth’s crust draws close to the earth’s surface and the sedimentary rock underlying the lopolith sinks in the area of the magma chamber.

SILLS:

Description: It is a horizontal sheet like feature between bedding planes.Formation: Magma intrudes between bedding

planes. It cools and solidifies at a very slow rate there.

Sills can be confused with solidified lava flows; however, there are several differences between them, i.e., intruded sills will show partial melting and incorporation of the surrounding country rock.

DYKES:Description: It is a vertical or diagonal wall like

feature cutting across bedding planes.

Formation: Magma intrudes into a line of weakness cutting across beddingplanes vertically or at an angle. It cools and solidifies at a very slow rate there.

Dikes can be either intrusive or sedimentary in origin. For example, when molten rock intrudes into a crack then crystallizes, it is an igneous dike. When sediment fills a pre-existing crack, it is a clastic dike.

CONCLUSION:

Intrusive vulcanicity occurs when the magma enters and solidifies in lines of weakness or chambers in the earth's crust.

Many mountain ranges, such as the Sierra Nevada in California, are formed mostly by intrusive rock, large granite (or related rock) formations.

REFERENCE:

https://en.wikipedia.org/wiki/Intrusionmyweb.facstaff.wwu.edu/talbot/cdgeol/

Igneous/IntrusivePhysical geography by K. Bharadhwaj.http://www.weebly.com/?

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