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.
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.
17.
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
23.
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.
25.
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.
