Collision tectonics of the Wanni and Highland complexes in Sri Lanka

XIV

Note

the significant

shift

in 6’BO from

Collision tectonics of the Wanni and Highland complexes in Sri Lanka

> + 20?6~

to + 15.3% and also the shaft In 613C (Hoffbauer and Spiering, 1994). Thus, the indications are that the Eppawala carbonate rock is not a carbonatite but a marble which has been intruded lighter and

by

granite

and

rendered

due to the interaction fluids

which

derived

is very

from

much

isotopically

between the

the marble

granitic

in evidence

dolomitic

have

marble

produced

such

as

diopside,

phlogopite,

and

chalcopyrite

metasomatizing

granite

in

including

of carbonate

rock

Thus the intense greatly

to

to as a skarn as that

deposit

two

granite

to

the

552

Ma and 556

It is most

granitic

intrusion

likely

means

the age of the

Eppawala

took

Eppawala region

place

that

while

of Eppawala

thus

belong

namely,

the

located

close

1994). to the

dated

(Holzl

that

the

at the

at

al.,

et

the

Eppawala

age,

i.e. about

this is most

probably

mineralization time

of

the

1994) same

M9

in the

time

(Precambrian

Zone 3) the Ml 3 metamorphism (Hapuarachchi,

be same

been

apatite

during

so

is not known

(Hapuarachchi,

area

west

have

is of the same

550 Ma, which

metamorphism

and

be referred

Ma respectively

1994).

which

granite granites,

deposit

at

at Eppawala.

occurrences,

and Tonigala

Eppawala

to have

skarn

may

intrusion

in the

complex

was in progress

The apatite

deposit

may

Pan-African.

REFERENCES Hapuarachchi, D. J. A. C. 1994. Professional Paper 63~. Hoernes, E. et al. 1994. Precambrian Research 66, 183-198. Hoffbauer, R. and Spiering, 8. 1994. Precambrian Research

66,

Osaka City University, Japan

of

amphibolite

an

(Vijayan from

(Cooray,

1994). and

WC

(AG),

of the

325349.

Holzl, S. et al. 1994. Precambrian Research 66, 123-149. Jayawardena, D. E. de S. 1976. Geological Survey Dept. Colombo 2, Economical Bulletin 3, 4 1 p.

between

and

west

which

1994).

The relationship

still obscure. area

near

WC and HC, as well are carried Structural

the

and the

latter

between

(BDchel,

WC and HC is field studies

boundary

as structural

and kinematic field

in and around

between

studies

Kurunegala

areas.

of WC

The deformational

Dn-5

(banding Dn-3

a southward

(east-west

trending in the

folds),

showing

east-west

(asymmetric

folds),

area,

while

(earlier

a southward

structures

(asymmetric Dn Dn + 1

and Dn + 2 (local shear

Dn-2

trending

by

showing

vergence),

upright

Kurunegala

and foliation),

structures

Dn-1

major

Dn-4

formed

structures

an eastward

trending

the earliest

and foliation),

vergence), showing

(north-south

out and

sequences

from

(structures

Dn-2 (asymmetric

structures

carried

Gadaladeniya-Aranayake

folds),

flattening),

of WC, based

were

of the following

to the latest: (recumbent

analyses

observations,

the

are composed

(banding

Sri Lanka.

out In this study.

on detailed

zones)

in five boundary

by a thrust

the

the The

to form

the

this, detailed

surrounding

are

into

is exposed

over

To clarify

which

respectively

complexes.

WC and HC in central is superposed

later

VC),

is considered

WC,

synforms

former

terrain

amphibolite-

to east,

HC and VC are separated

of the

an

Wanni

eastern

are

terrain

facies

is subdivided

eastern

gneiss

facies

complex:

the

East

and are composed

granulite HC)

of gneisses

WC), a granulite

complex:

western

fragments

high-grade

to

complex: terrain

Arena

the

in Sri Lanka

doubly-plunging

rocks

it to

distributed

a part

apatite.

and its age would

The age of the Eppawala but

the

appears

deposit

for the granitic

Galgamuwa

for

carbonate

converting apatite

the

process

metasomatism

account

the

thus

Eppawala

bodies

from

widely (Wanni

of

Precambrian

distributed

the marble

derived

metasomatism

modified

Eppawala the

skarn-like

chlorine

is one

Lanka

facies

pyrite,

metasomatic

and

Srr

(Highland

biotite,

between

fluids

a complex fluorine

tremolite,

including

These

to

minerals

actinolite,

by the reaction

and

appears with

hornblende,

and apatite.

are formed

deposit

granite

bodies

sulphides,

of Geosciences, Osaka 558,

Gondwana.

Eppawala

scapolite,

magnetite

and

at

skarn-like

Department

intrusion

in the

area (Jayawardena, 1976). Interaction between the intrusive the

Y. TANI

vergence

upright showing

Dn-3

asymmetric folds),

and Dn-1

an eastward

vergence), Dn (north-south trending upright folds), Dn + 1 (en echelon veins showing a dextral shear sense), and Dn + 2 (east-west trending folds) from the earliest to the latest in the GadaladeniyaAranayake area. On the other hand, structural and kinematic analyses of HC that were carried out in the Kegall-Peradeniya area show the following deformational sequence from the earliest to the latest:

Dn-3

(banding

and

foliation),

Dn-2

xv

(asymmetric

structures

showing

material.

a southward

This

vergence), Dn-1 (asymmetric structures an eastward vergence), Dn (north-south

showing trending

surrounded

upright

showing

Eastern

folds),

a dextral

Dn + 1 (en echelon

shear sense

Dn + 2 (east-west Shear

sense

folds,

trending

and

S-C

such

following

two

southward

asymmetric observed

Together

the

in this

WC were

enclosing These

suggest

Lankan piled

directions.

This were

regimes

during

Garnet

HC and a topMa

and kinematics that

Sri

by the movement present terrains

convergent

Pan-African

period.

amounts

along

boundary of

GBG

that

the

garnet

Sri Lanka

P. 1994.

Journal

Geological

5, 41-57.

of migmatitic Eastern

rocks in Tekkali,

Ghats,

T. YAMAMOTO,’

India

A. T. RAO’

and

M. YOSHIDA’ ‘Department

of Geoscience, Osaka City University, Osaka 558 Japan 2Department of Geology, Andhra University, Visakhapatnam, 530003 India

leucosome

coronal

rims

Ti-rich

of garnet

which

of garnet

Furthermore,

the

zoning

in most minerals

that

might

have

When

hypersthene

considered

or

as a residue,

Bt + Qtz

+ PI +

and Montel,

Opx

event

absense indicates

uplifted

quickly.

garnet

in

the

GBG + melt

may promote

partial

melting and produced the migmatitic appearance. So far as the occurrence is concerned, the concept of dehydration melting seems reasonable. On the other hand, it has not yet been sure whether this migmatitic rocks were created by in situ melting or not. The possibility that this leucosome is a derived channel of the main plutonic body remains to be solved by future study. Our on going project aims to evaluate all these alternatives by further field and

geochemical

works. REFERENCES

In Tekkali, South

Srikakulum

India,

hundreds

many

rock

is

granite

of quarries

100 km*. Light mined

district,

companies

Pradesh, are running

in an area approximately

grayish-blue and

Andhra

sold

coloured as

migmatitic

a construction

is

reaction:

+ Grt + Kfs

1994)

that this

cooling

of compositional this massif

of

between

indicates

an isobaric

and

textures

especially

from

provides

pressure

Reaction

and plagioclase, 1989).

that

This texture about

quartz,

suffered

to that

suggesting with

from

conditions. with

in minor

be xenocrystic.

information

temperature

(Vielzeuf

Study

may

uniform

similar thus

composition

(IBC) (Harley,

Society

a “greasy” has

also occurs

in GBG (Py,,Alm,,Sps,Grs,,).

garnet

a charnockitic

leucosome-mesosome

in the

exhibits

important

mafic

interstitial

exhibit

and has a composition

has a different

rock type

39-57.

the

Hypersthene lamellae

not

(Py,,Alm,,Sps,Grs,),

orthopyroxene

Btichel, G. 1994. Precambrian Research 66, 77-94. Cooray, P. G. 1994. Precambrian Research 66, 3-20. Kleinschrodt, R. 1994. Precambrian Research 66,

does

has

of An,,.

REFERENCES

KrGner, A. and Jaeckel,

leucosome

composition

that

the

the

Ma (Kroner

indicate

by the

plagioclase,

plagioclase

of the Precambrian formed

Although

of

of

granoblastic

and clinopyroxenes.

and

570-550

different

indicates

structure

Sri Lanka

tectonic

two

consist

across

as massive

number show

appearance

is characterized

having

fundamental of

study,

large enclaves

this

over VC with

Structures

in this

ortho-

cuts

also occurs

it

hand,

at about

and

biotite, is

HC with and

700-800

thrusted

WC

texture

leucosome

which

assemblage,

movement,

megastructure nappe

that over

On the other

1994).

clarified

data

and the kinematic

of

(garnet

The

as net-veins

enclaves.

geochronological

of gneissic

association

orthopyroxene

leucosome.

occurs

outcrops

vergence,

(Kleinschrodt, of WC

mainly

in the

GBG) and orthopyroxene-bearing

HC.

at about

altogether

eastward

gneiss:

coarse-grained

eastward

southward

to-the

biotite

by the

minor

a later

study

1994).

with

in WC and

a top-to-the and Jaeckel,

the

biotite

rocks

lithology

are comprised

and

to HC and thrusted

possibly

and show

main

characterized

garnet,

massif

belt.

rocks

the GBG. The leucosome

allochthonous occured

in

mobile

an earlier

so far, the structural

analyses

Ghats

The migmatitic

a migmatitic

the

kinematics:

gneisses

with

published

were

the areas

different

of the

as asymmetric

is

metasedimenta’ry

series),

mesosome

megacrysts,

movement,

movement

and

fabrics,

WC and HC throughout

(khondalite

folds).

indicators,

asymmetric

boudinage

veins

and local shear zones),

area by

Harley, S. L. 1989. Geological Magazine Veilzeuf, D. and Montel, J. M. 1994. Mineralogy

Petrology

117,

375-393.

126,

215-247.

Contributions