The document summarizes the intrusive rocks found in Kerala, India. It describes various basic and ultrabasic intrusions such as gabbro bodies along the Bavali lineament. It also discusses acidic and alkaline intrusions such as the Ezhimala Pluton granite suite and Peralimala pluton syenite. Pegmatites are also briefly covered. In summary, the document outlines the different types of intrusive rocks found in Kerala ranging from basic to acidic compositions and discusses their locations and characteristics.

1. SEMINAR
INTRUSIVES OF KERALA
Presented By
Snehamol P S
M.Sc. Geology ,First year

2. GEOLOGY OF KERALA
◦ Rock type of Kerala belongs to four major age groups such as : Archean, Proterozioc,
Crataceous and Cenozoic.
◦ State comprises of :
* an assemblage of migmatites, meta-sedimentary and meta- igneous rocks (Khondalite-
Charnockite assemblages) towards south
*Migmatite, grunerite, amphibolite, calc- granulites and granites towards the centre
*Granulite schists and gneisses and gneisses intruded by alkaline plutons constitute the
northern most part
◦ Tectonically region can be divided into Precambrian and Tertiary tectonic provinces

3. Intrusives of Kerala
◦ After the deposition/emplacement and regional metamorphism of Precambrian basement
rocks,a period of quiescence in the geologic record of Kerala
◦ This was interrupted by the emplacement of a number of intrusives of basic and ultrabasic,
acidic and alkaline affinities of different ages.
◦ Dolerite dykes were emplaced later.

4. Basic and ultrabasic rocks
◦ Kartikulam
◦ Adakkathodu
◦ Karrang
◦ Attapady shear zone
◦ Idamalayar fault
◦ Melathumuzhi
◦ Perinthitta

6. ◦ Gabbro bodies along the Bavali lineament oriented in an E-W direction in an ellipsoidal shape.
◦ Medium to coarse grained and foliation are prominent.
◦ Mafic minerals aligned in E-W direction.
◦ Gabbro bodies close to Bavali fault are extensively migmatised.
◦ Composed of plagioclase(An45), Clinopyroxene, Hornblende and Biotite with minor amounts of magnetite
&Ilmenite.
◦ Increase in modal percentage of hornblende, gabbro shifts towards diorite composition.

7. ◦ Kartikulam
Gabbro body.
Aligned along the Bavali fault zone in Kannur district; westward extension of Moyar lineament.
Occupies an area of 45km2 with a length of 10 km.
Adakkathodu
Meta gabbro body
Extends 8km
Includes minor patches of anorthositic differentiates and diorites

8. Attappady shear zone
◦ Marked by the occurrence of a host of basic and ultrabasic rocks.
◦ Consist peridotite, pyroxenite, gabbro, leuco-gabbro and anorthosite.
◦ Dominent members are pyroxenite and gabbro.
◦ Magnesite mineralisation is observed along the fractures of peridotite body.
◦ Gabbro bodies are known from various localities along the IDAMALAYAR FAULT- Sholayar,North of
Ottappalam.
◦ Ultrabasic rocks of dunite composition has been reported from Punalur(age of 1630 m.y),along a minor
shear zone parallel to the AKSZ.

9. Perinthatta Anorthosite
◦ Anorthosite are non-layered & highly deformed with very coarse grained plagioclase laths(2-5cm)
◦ They are aligned in E-W direction.
◦ Series of mafic to felsic intrusives associated with Bavali shear zone &Wayanad schist belt.
◦ Anorthosite massif emplaced within charnockites and pyroxene granulites,within the proximity of
Ezhimala Pluton.
◦ Lamprophyre dykes and sills of different size described from close to the southern flank of Palghat Gap.
◦ They are post-deformational and contains biotite & feldspar with K2O enriched

10. Acidic and alkaline Intrusives
◦ Late- Proterozoic – early Paleozoic magmatic activity manifested by the emplacement of
acidic and alkaline intrusives along the major lineaments.
◦ This event consistent with the Pan-African magmatic activity.
◦ The prominent granite/syenite plutons are :
◦ Angadimomogar
◦ Ezhimala
◦ Peralimala

11. ◦ Kalpatta
◦ Ambalavayal.
◦ Tovarimala.
◦ Vellingirimala.
◦ Wadakkancheri.
◦ Sholayar.
◦ Pariyaram.
◦ Mannapra.
◦ Munnar.
◦ Kizhakkancheri.
• Chengannur.
• Punalur.
• Host of small bodies within
migmatised gneisses of north
kerala.
• Palghat gap area.
• Idukki-Munnar region.

12. Ezhimala Pluton
◦ Emplaced within Sargur –equivalent sequence of Kannur.
◦ It’s a differentiated suite with a continuous compositional range from gabbro-granophyre-granite or
gabbro tonalite-trondhjemite granite suite.
◦ Located SW of Ezhimala, close to WNW end of Bavali lineament.
◦ Elongated in NNW-SSE with maximum exposure length of 6 km and width of 3 km.
◦ Host rock – gneisses with enclaves of sillimanite – kyanite schists,quartzite and metamorphosed
ultramafic rocks (Manantoddy formation)
◦ East &south part of the pluton – gabbro grading into leuco-gabbro.

13. ◦ Northern end- contains rafts and xenoliths of mylonitic and well banded quartzite,quartz-mica
schist, vein quartz and fine grained amphibolite.
◦ Appears granite cut through the gabbro.
◦ Major minerals-Quartz, plagioclase, K-feldspar.
◦ Accessory minerals – Chlorite, Fe-Ti oxides, epidote, biotite & carbonate.
◦ Micropegmatitic and micrographic textures.

14. ◦ Gabbro showing subophitic texture; contains wedge shaped plagioclase laths, cpx interlocked with
plagioclase and hornblende
◦ accessory minerals- Biotite,apatite &epidote
GEOCHEMISTRY
◦ Represent a product of fractional crystallization at higher levels.
◦ Cotectic crystallisation of quartz and feldspar possible.
◦ Age – 678 Ma for granite and granophyre

15. Peralimala pluton
◦ Exposed in the western part of Wayanad schist belt.
◦ Length about 20 km and width about 4 km.
◦ Enveloped to the north &south by migmatitic gneisses occupies the core portion of a tight isoclinal
antiformal fold.
◦ Medium grained rock with grey colour with pink K-feldspar.
◦ Major mineral- K-feldspar
minor minerals – plagioclase, albite- oligoclase, hornblende ,aegerine augite & quartz.
accessory minerals – Sphene,apatite, zircon ,calcite.
◦ Age – 750 ±40 Ma.
◦ Formed in a rift –related tectonic setting where alkaline magmatism is possible as in East African Rift
Valley System

16. Ambalavayal granite
◦ Intrusive into biotite gneisses of Wayanad.
◦ Spatially related to Moyar lineament .
◦ E-W elongated body, covering an area of 25 km2 .
◦ Dominent mineral phase – perthitic K-feldspar interlocked with quartz.
mafic minerals – greenish hornblende and biotite
accessory minerals- S phene, epidote, monazite, apatite, calcite & Fe-Ti oxides.
◦ Age - 595±20 Ma.

18. Kalpatta granite
◦ Occurs as an elliptical stock among migmatitic gneisses and charnockites.
◦ Covers an area of about 50 km2
◦ Medium to coarse grained graey biotite granite
◦ Numerous veins of aplite and pegmatite of 5-15cm width traverse the granite.
◦ Eastern contact is faulted.
◦ Three textural varieties are distinguished : porphyritic, coarse &fine
◦ Composed of K-feldspar ,plagioclase and quartz in a hypidiomorphic granular texture.

19. ◦ Dominent mineral- microcline(perthitic) ,biotite(mafic)
accessory- sphene,apatite,,zircon
◦ This pluton is localised along the western part of Moyar lineament.
◦ Distinguished by its grey colour and presence of biotite
◦ Age – 765 Ma.K – Ar biotite age is 512±20 Ma.
◦ Latter thought to be a thermally reset age ,correlatable with the 500 Ma regional tectono-
thermal event in South India.

20. Pariyaram granite
◦ Intrusive into charnockite rocks.
◦ Covers 35km2.
◦ Bounded by 2 sub parallel lineaments .
◦ Sharp contact with the country rock.
◦ Medium grained rock with pink feldspar, quartz & hornblende.
◦ Geochemically classified as granodiorite

21. Munnar granite
◦ In munnar area two period of granite emplacement was noticed.
◦ First period : thinly foliated,pink,medium grained gneissic granite containing biotite ,
magnetite and hornblende as mafic phase.
◦ Occurs as overturned, doubly plunging ,cross folded brachy structure.
◦ Second period : massive ,medium –coarse grained granite,emplaced pre-syn kinematic with
the broad open WNW-ESE to E-W trending folds.
◦ Cross cutting linear bodies possibly represent the third phase of emplacement.
◦ Host migmatitic gneisses are of pink and grey varieties.pink variety contains augen of K-
feldspar ,grey variety rich in biotite.

22. ◦ Major minerals- K-feldspar,plagioclase, quartz.
accessory minerals- biotite, sphene, apatite, zircon.
◦ The regional tectonic setting of the area described by Katz would suggest that Munnar –
Periyar lake area is the SW extension of Madurai aulacogen.
◦ Age – 740 ±30 Ma

24. Chengannur granite
◦ A linear body emplaced within charnockite –cordierite gneiss sequence in the margin of
Achankovil shear zone.
◦ Concordant body.
◦ Maximum breadth around chengannur and towards west it disappears below the coastal
sedimentaries or it truncated by faults parallel to the coast.
◦ Occupies an area of over 110km2 .
◦ Major minerals – perthitic K-feldspar, plagioclase, quartz, hornblende
accessory minerals- magnetite, ilmenite, apatite,zircon.
◦ Age – 550 Ma.

26. Angadimogar granite
◦ Occurs within migmatitic terrain.
◦ Major minerals – quartz, K-feldspar, plagioclase ,hornblende
accessoryminerals – zircon, sphene, riebeckite,acmite
◦ Age - 638±24 Ma.

27. Pegmatites of south Kerala
◦ Classified into two ;
#simple pegmatites –consist quartz, feldspar, biotite,garnet,apatite,monazite
#complex pegmatites- consist additionally beryl, muscovite, tourmaline, sillimanite,
andalusite, chrysoberyl, cordierite, corundum.
◦ Localities –
◦ Venjaramoodu, Vamanapuram, Bonnacord &in parts of Thiruvananthapuram ,age;460Ma.
◦ Punalur ;age -539±15 Ma

28. Reference
◦ Soman,K., (2004) GEOLOGY OF KERALA.Geological society of India, Bangalore.
◦ Santhosh,M., Nair,N.G.K.,Thampi,P.K.,(1983),Alkali granite-syenite – carbonatite
association in Munnar Kerala,India;implications for rifting,alkaline magmatism and liquid
immiscibility.