Ip t M s clapter the wtmchamical studies carsf@ oat

on the calc-silicate m a s are psesented. ~t is well b o r n

f r o m lii~i? classioa;l works of' Ihe early petroLogists 1U@

Cross, Idiisltis, rirsson, dashislgtm, (4s- art& SZggli, that

the petrocWmiwf studies on rocks offer vaP..uable cslues regard-

fag their petm&enesist In the case of metmorphZc rocksz

these studies M i m t e not only ths nature of parant rooks,

lut also %he raetmmlic ohaxgas that Look place i n the evo1u-

t iw o f tih6 mcksl GhZs comct ion 50 ~8pms@nt$ti"fpe

sslnplea of ~a;Lo-sUioate moks wrem artalg7sfsd. Q- SolLow&g the

rapib aethods of W y s L s groposed bg 3ugt2.m a d l3mwook ( 1 9 ~ )

Thesfif rack aaal;pses, &rig wit& 4 W y s e s of o&a-silicate

roaks a9na;lgsM %y tihe gm~ious woul&aw fkca tLw waa, lnv.e3sti~ts$

ti&@ p ~ m t zl~thor* am pmsented 14 TaIb3.e 11. &oh a f th@s@

W y s @ s is omputed t o obtah the C ~ I * i ? + i l f . M O ~ (Cross et; a l e ,

1908), the Pasis c~mposZtiaa (NrlgfSli, 19203, tb E f i i g U ~aZtres

f~J,g&Li ., 1980 $ arrd %la@ 08- fli~lue3s ( D m *, Z913 ) . &act& of

tW &m$oal tualgaes is akso r@a&au&-e;ed afwr W aettM8 of

mLte (1959) t o aagfat %her cbm;kctix3, aoapsitioa a l tb@ ~ ~ 8 4 %

Table I1

Chemical malsses of calo-silAzate m&s

Total l00.2$, 99 .96 99.85 99~92 99,61 99 ,61

s f l ioa te rock, silicate m k , s f l i c a t s rook, sUls3ah rOak, oiliaate m k , sfflaat8 mlrl

7. sf3liaata rock, 30sm (67), Bpisakhapatdnam Dt . 8. &la - siliwte mctk, %ma (19), Vfsakbmtnam D t , 9. Cslo - siLA~atie rook, uhipuupalle (26) h ~ b Dt. 20 W& - sUcraLe m ~ k , 13ev&a (30), V i s a k b ~ ~ ~ z t a a m at, 12. Oda - sflSxtat@ rwk, mWm ($I)# ViatdCbgaUw D t r 12, - silicate roakIr, G ~ o r a ~ a l a s a (S), &Akdalam~ at.

la. Calc - sU&aate rook, Gariv%df (36), Vlsakhapat~lara distriat 14. OaLo a silicate mctk, JigrLrarn (43 1, Srfkakulam d is t r lo t 15. !2alc .- sLLi~ata rook, Konfsa. f 521, Vlsakhasatmm &&trial 16. tlale - ailLcette rookt KoBla~ahsa (56 ) + Vis&hapaZ;nam Clt . 17. Calo 1 ~LlFaaZie rook, $&Wambsa (571, SriLcakulaar ClistrlcO 28. Ef;jl;LC - ~ i l k ~ r a t e soak, Nara$aracappav&s~ { T 5 ) , 8 r ~ l a n z ijt

190 C a l o - siUaate m k , P a l l - (79 ) , i3rika&u3-arn Dt;, 80, Calo - s i L h a t e rock, Petdd-aaa (83}, SsUakuha DL* 21. ealc - s21Ssate w k , i?-valLasa (851, &UakuLm DL (

22 w Gab - sllkoate me, PaiEdfva2.aset ( 87 f , Sr&&lam 33% a 3 r 0913.a r* 81510608 m k , Batmle3. ( 9 2 ) ) X;risU Dt. 24. Oa1.a - s9Z%~a% soak, 73aja;gyapata (921, 3rUWculm Dtl

' WB&% r P. ?m~ti&srlm.

a5. t f a h - s i l j i~~ l t e me&, 'hdti ( T O 6 ) , 8rikak;ulam Dt. 26. C a b - slkLaate rock, ' k l p ~ l a a & a m (107), #@st GoBavarf. Dt. 27. 02~3.~1 - s iP loa te mole, tTpp&avalasa (108) , S r W m ut . 28. ;'&a - sill+aate mok, Vija$aw&a'(114), Krish~ ate 89. C3dc - silioatre m k , Vis~eanatbpmm (11 6a) , f 3 r i b k t k l a m Dt . 30 . Irala - ai l ieate soakt VisWanaBhprpram ( 116b), Sr$k&mlatn at.

maks hs presented Sn Ta'bJe 12. Tha :.I*k.*iJ. norms, basis

malebules, NigglS mluss ard the f ) sw vduas are present&

ia TilbZes 13 m& 14. The various vdues obtained & r~llow3.ng

diflferent startdaxtk methods sf calcuZatiosl have Wen plotte& i~

the oorrespondiag t r i l iwar Biawms fFigs* 30, 31, 32, 33$ 34,

55 and 36) wi%h a view to draw tangibpe cowlusions tgJ.th mgarrt

to the pt35rogsxsssis of' the socks,

A gem& of %be chertdml, data of the oalc-silioate

r~c fks ~r@sen%Qd Isi Tab10 11, indicates &hat Wt?i~ am a l l

aWaot;srSW I@ aaess CaQ QvW the SIB of M@ FerO

gmereiE riohnwss ia Si08. Tns Jug oontent of %ha rooks is

found to vary s i p i f l ~ a n l l y , raaglng fm aWut 36 pep c w t

t o 70 MS ca t . lh the ma$osity of the asalyses, the mxitmt

of' SLOB ia near amt 50 gar asat. llla geueral rtchaess o f

rsUitra i n tikame rocks is mPfec%ts# clearly S;t %heir & ~ s

(Ttab3.e 2 ) (T~abI8 13), W h am ohar~f,ctarbed 5pr %he

oaapLete diwmae of' Uai;lemahrat;aB 3~in8rd~ W freguat

pmiag%ms sf ~aarnts~ 3- We rocks, wMah m mhtitLv@L..

PWP ~UiiXt, [W;$8@5jl 26 34))

are &been% Wpum ei ttle pmwcance ol w e s s COZ, % U h flmres

B@oalculateia, chemical analyses o f c a b - silicate rocks f o'btalned by assuming all aa arxd ~ d g were or ig i aa l l y pmsant as

oarbonatest

Table 1% (c~ntf iusd)

Ta'bZe 12 (continued)

Table 12 (coutuuedj

T a b l e 12 (co;ntiaued)

104

TabZe 13

~'.I*B .a. m a s an& basis corngodtion of a&-silicate mobs

TaUe 13 [continued)

Tabfe 14

P3f ggli values mr c a l e silicate ma&

ACF values f b s aalc-siliciate mats

A 10 *8 9.5 0 13.3 16r? 14cS 0

0 55.9 55.9 81 -1 54.8 55.2 52 '8 59.7

P 29 03 34 .Q 18 *9 31 *9 28.1 82 *3 40 *b

Table 14 (cont-ed)

Niggli ~ a l u e s for calc-silicate racks.

8 9 10 11 12 13 14

&OF values of ode-silioate racks.

15.9 12.3 8 -5 20 13 12 .S 7' *4 12 s 4

62.3 58 00 55 * I 57 *5 52.3 58.3 56 *O

21 08 29 .? 36 94 32 .2 35 *2 54 -3 32 *6

Table 14 (corktZnued)

Bfggli values of c&L~rsilioat@ rocks.

- a f

C

alk

C

Alk

O l s a n n values of oa.la-silieate m a s

16.63 16.43 15*8Q 16*?9 15*96 16e69 15.70

2.03 3. a57 1 e 8 0 1 a99 1 *6l 1 *48 I*&

11056 12*00 12.40 11-22 12.48 11.85 12*%0

Table 14 (continued)

Miggll values o f calc-silicate rocks.

Osam values o f calc-silicate mlrs.

S 16096 16.63 17.69 15*54 16.38 16.38 16.76

A1 2,12 1 *97 1.19 1.45 1 *69 1-88 0 090

F 10.92 11 040 11 el2 13.01 11*95 19.74 12.34

114

Table 14 (continued)

Niggli values o f cdc-silicate roUls.

29 30 31 32 33 34

a1 10.96 10.97 14.34 14 el8 14.36 11 '27

3% 26.16 30 a 2 6 29 -10 27 *54 29 014 11 -76

C 60 050 55-82 52 -32 52.19 52 .40 75.75

alk 2.38 2 -95 4.24 6 -09 4 .I0 3 .22

3 *21 1 a 8 5 1.80 1 089 1 *80 6 044

0s- values of c d c - silicate rocks.

&OF vzlluss o f wLci-sbf;Lcate rocks,

A 9.8 10 13. $2 -5 14.2 55.2 11 e 8

C 6% *P 56e9 52 *2 52*5 52 *6 75 w 7

F 29 sQ 33 r 0 35 *5 33.3 34 *2 12.5

as caL~ite o r seapolite by coasumin~; s ignif izant mounts of

(la00 As much of the UaO in the mok requires no j i O Z Tor the

Eberal formatioa, these rocks are free f k o m uu%essaWrut&

mberals Fnspf t e of contairifi~g low co~tsut o f s i l i ca 8 iw%hm

factor t h a t is fespousible fbr the abseuee of undersaturated

rnherals isl Wlese rooks 9s the low content oi' alkalies, ~ U c h

m ~ ~ i m high miowts of siLica fttr the fbmatiort of feldsgm8

Hexti t a 9102, r5aB flgums promineatly in tb chemical hat aF

WWG ID its caateat m a a W t 18 per ceut t o 36 per otmt.

CaO maW$ enters j lnto tihe styucture;~ of' aiupsiae- salite,

wolbs2;aa9te, cdczi%, pla&oc2aset scapalite gmssul;ks,

The ~ 1 9 ~ oontent generally rages Fmm a b u t 6 to 13 per cent,

al%h~y;t.1 IJ1 a f @ w rooks it ao~isti.t;u%es Lass toh OB% par cent

of" t h ~ m k s * This ox5de mainly exlters i n to tihe stmctiums of

feX$~~l j i , saapoliZie a'n8 grossulasl Tha sumof%gd axid NO

i o m d abrrut 8 per c012tl d.thbtr&h En a 9 % ~ analyses they maker

Less tJnezrr 2 per mat of the rnGEi~* These uxidss a2oag w i t &

%% a.a& gno, occurrisg in small amounts, enter mainly &to

the stvructjure of pgmxena* 'The cowrtents of Ha20 anb KZO are

gasraeraly low, eaah of %ha r t l W g 8bouL arne w r c a t of the

~ W k s s ThtQ W"Ei.P B U ~ A L ~ %he s ~ P v G ~ U P X ~ of f'@l&s~JU?s EWX

acspollte TiOZand P205, occurrbi; irz mall amounts, geaeraUy

fti&m out as sghene arid apaiiite raspectiveix+ *The genera3

a a h y 0 . m ~ ~ p t u r e o f the rows is jszciieatsd from tile low c o b

Lents of' H20 in all the ~ a a l g ~ e s . 'SAG conteist o f GO2, which

r a g e s 2t-o~ abut 1 t o 12 par cent, enters i~tr> the struc turns

of calcite and soapalite.

ia attmgt Fs aow aa&e Lo connpare tifie sll-1 composition

(Table 2 ) tne norrnaative comngositiou (TabJe 13) of tW calc-

sUic;ate mcks. Ixz comgut5a.g the nomrztivs minesrals

C.S.F.V. o2eLsaPfieatioa has been e~ployed* dhm %h@ c,I,P,%,

nom w a s ar3.~nafLy dszlsed i t w a s Latw&e& znt Is ua& mclu-

sSveiy for lgrieous rooks* In meeat gears m m y $etrologists,

particularly lkm tmeriaa am3 3uroge, extended the 9. X.p .1.

c la~s iMoa t i an t o the metaaosphlc rocks also* dskola 12952)

axpz4essetd %be op&ion %bat %Be Born o f L h C r I.P.%* & L S S ~ ~ ~ . C E L -

$Lon is ars f&ezhli%ed mZneral corngosfifon aost oLosaly aigrseing

with modes of %he @met-A-sa ntetamrgU mcks ~msJa uader

%he aoaditfons a f g~fmxsa~-W@83s 4:m28rs a~ l i l ~al t luUts faoieas.

&a the ea;l~-aLL&bt~3 rooks ua&etr pmsmt s$um are cowldererd

hy tihe a u % b Zo btlrloag $0

hportant dif'f'emuces a m noted betweea thn3 m o d a l m ~ e m l s

and the nosmatiive mbemls o f these rocks. The oxfitles that

U&B up p1ai;iocbse and calcite ia the norm are m&sented Fn

the made by pla&oc~e,scapolite acd calcite. :i mall mount

of" gmssulas whii:h is ofbexs. foulla in the modes, is absent in

the noms, By combinin& mall a u n t s oF the normative rnherds,

plagkoclase aha viollastordte, the formation o f gmssuhr,

alone; w i t h some quartz aan be conceived. TiOZ, v i ~ b h flmms

uut,by combiaSng with FeO, as ilmenite tihe aoms, is

representea as sph@ne ia the mcdes,if it is coasi&ered to taka

Fn a l i t t l e quantity of CaO mand SiOZ fbr its fomat i~n . #M.le

W i n g cornparisom beeween me nodes arzd tihe mms it mst be

remabrad that nornative n.tn%rals ase repre8el22i0d ia farus

of wei&t pementagas, &fl@ modal mUc?ra,ls are arns;F;ed i n

tams of' mime pame~l.tages, It is also t o *ee rroted that L b

sum af tbe nnjxteds the noms is very awrQ $DO par cenSr,

wharsas the sun of %be m i n e d s of" the 10ads l s e x a c t l ~ IOQ p w

cent. E80 figures out as a constituent o f the nonos, &@raas

i t f3rxI.s rma glace in the modes r Afier rn-6 d.10~13~ f%r

th$ vwfous discrepancies %hat em cause difP1wacss in tihe

a W awld aorm;ztfws oomgasfZ;ioxl of the rocks, i t is obsw~ed

~/fb AX .hIK :r"diagram af"PSIgg1Z i3.920) - 2 % ~ c r h f u ~ i a d analyses o r 2% oalcs-sf l l F c & t e

rucks, whose a/% Yaluas rail&@ Z2om 1 -5 to

2-3 are plo+tsd AKA the iliaiii;ram. 2be p l o t s

Pall 5.n the f i e U of' WmSsahe ,acLlraer+ts.

$hat the modes Listed. ia -Cable 2 a e e e ~ L 0 5 6 l - y w i t & tihe noam

Ifstet! 3a Table 13*

The i41;SggXi values art #.I@ cale-silicate rooks am

grssented ia -table 14. ,wn; ttls J i g g U values c is rourrb t a

W mo8t @?txlmheut;, ruith i t s value mwia$ Pmra a&ut 47 to

79 per csslC~ The value of a&, sk1~url LS very Lorn, r w e s fmrn

abcrut 2 fro 6 par cent. Ykso aJ. values, showing siaif icmt

vwiatim, range ~ i ~ m aMut 9 t o 18 par o e ~ t , The v d u e of &,

wbieh, shows gm8raJl~ a less degrees o f tpwiaLi~n, wries Born

18 Bo 53 ps~n sent. Only in %he Gas@ of 3 arauses the value US

i~ nuoh 1 0 w ~ r . The a/& ra t io varias si&xLCLcwtL$ ;Era

I*44 $0 I,Im%e J&t?Ll %ha NZQgU. Y&U@S Uf3 j2LotLtid. &l tb

proper cross-sm tioas oF thr! itiwi tatr&etimn (ELgs. 30, 31,

cljZ 331, a11 tth~ gXots rn found. to a11 in the fLeU o f

HaP3a%sohe 9Bd&8122ileH i&i~3al&& t b t %ke gaxwnt mcks oi aszlc-

s i l ioa ts Pwk8 ax% aaZ~-@Ich sedlneatary racks*

3 % ~ 0- va1ue~ a f t b ~ ~a;Lc~~Xl j ica%e m u g wuch are

prji~awt~fd, m u e 54 rn p ~ o ~ t e l t ~yl, am. 641 ad- 35+ m tha

The chemical. anaLyses of d ca2c-siliccat@

Yrrc&Et W ~ O S @ ~ / fh Vt%h.l03 X'Jil&O 1YQTtl 2*3 $8 as a r e ~Sottsd the diagram* The plo-bs f a l Z

%ha field o r Ohen9sche Gedi.aenCle*

F I G . 33

Thu ah&ca*al a~~algrslis o 2 34 c d c -

sfltit~fale mcds wakgscc~ ape gloltscc3, 5 . a the

d 3 e n e a m * ~ C X K X L ~ 037 3h.a pLO"Gs f+xZlt. %LI the

e.mptrZvs TiaXCL + iiuixLla ts%f~@ ss %lS c?u l s i d , ~

the empt2ve fXe3.d-

The cklaiPoaJ, a a a L y s % . s of

34: cazc-si3icZcats rocks WaL~ssd axe

p30tted in the d .Aagpxm* AX& tlne

p l a t s Pa&& in %he amptAve 2XeXL-

119

;5 kl F t r i ang le o r Osamn f22.g. 34j, the lots of' ; g3. F vdues

of 19 arrauseu fd.1 &i the eruptive kltelc~ the plots of tb,

rmaJzliag andgses fall outsieZ~t the e,r;tgtive f i e u + Bcoomnt;

t o I t s m (1913), the g l o z ; ~ of J p values of all. k@eous

mckii, ax& tfitfjlr metmorphlte equival~hts , except a few abomal

types l ike c o W u ~ 1 - r i z h mcks arid pura ~ua r t z r f a id spa r socks,

fa11 in tha eruptive f%eld o f the &iagram, whweas the plods

oP ather roaks fall outside t;hs field. Zn tihe C R1, A3.k triangle

of Usurn ( E g , 351, thij plots of I: ,GI. &I& values of a l l the cale-

rsflicats rocks SaU ia the emp%ivs f i e l u 0,' the diagram*

doconking t o Osam (1913j, p10Ss of" t' al A l k ~ a l u a s of all

Z&rz@ous sacks mil tMls m@tmorpU@ wuivalents f a W &he

smptive fie=, wMreras t;Czs plots o f other rocks fall. outsUe

tha f i a U + IF %he views Of Qsaru? am tairea t o aorrect, t;he

g a ~ n t muk~ OP c t a L ~ ~ s i l i ~ a t e ~ O O B S nus t be aonsidered t o W of

ignews o r i g b . Butt;, the evr;idemes oolZected by Lhe author,

wM& will bs bisc3usst3d latar, in field as well as in %he

labomtory Sarlieab a t r@Tbi%@ sadiorentary xarenta@e to %has8

maks. It ia, th~refbre, cowlwkrsd Wzat trle S ~1 P C ill &lk

awams a2 O w n csrs naL sui taue h f'ixiw the waritage of

tihe oala- aLlioa%@ X W ~ B s

~ c c ~ p t @ the sedbentmy para tage o f talc- silicate

moks, it fs xlow proposed. t o cmpute tha ahmioil omposition

o f the parent socks. Tha metba followed t o caapute tlw

clat3~ical analysis of the parwt m l r oz" each caio- s i f icate roc&

is tlxo one outline& 'b57 'ihite (1969) ,?hila m w b g %this ealcu-

la t ian i t is assunnee2 tka.l; th@ metamo~sMsm t o w m h the c d a -

silicate rocks are subjeo ted is sssenthl ly FsochemicaL in

natwe, @ x c @ ~ % f o r %ha expu.LsL~n -02 ear?x,n dioxide in lare

amounts. It is a l s o aasumad th& whola o f ilaO and YgO were

gmse1~1G In the parent sack in. the roan of aar~m-bes. The

moutlZ; of sarbn dioxida ;iu each analysis is raised m%il its

molecular proportion eyuals thal; a? the sum 01 Gal) Exid HgO.

gach a u d y s i a is then mcalcuiated t o w e %he sm of the wei&t

pemaatages of Lhd various oxides e ~ u a l t h e sumaat;faa of %ha

original malysis+ 248 mcaloulated cJne3~ica;L malgass of the

aalc-silicate rooks are presented ia Table 22 0

1% is belismd that tihe chsmical data pmmted Irr

Table 12 olosely lrpgroximatsts t h e cwaaloal aomgasition o f the

p a r a t roc3rs o f Che oalc-si3ioate socks. 1% is, &wevsr,

suggestecl that -the mter conteat o f the paren* rocks f s xucZa

mom than &at is Wlicated i33. the analyses* I t is &so

possibLe that th0 re la t ive pmpartior~s of k%D E'eZ03

m i g h t have signLTicarztly varied durbi; the course oi' metm~rphim.

<fhis factor is not t i s en in to account whilu r e c d o u l ~ t i q tb

chenzical malyses o f tha ca lc-s i l ica t~ mads Jm osdar to depict,

%ln@ chemical coapositioa of the parent mks. m e m ~ / @ ~ o ~ ratio of' the clxlc-4.liotzte m k s is fair12 high it is

likely that in the parent rocks of -trhs talc-silicata roaks,

wfiich were fosm@d W e r aeas aWspaerio oouditians, tixis m U o

nust "be r?ak@ law* a p 0 ~ ~ s a . i o f the chemioal data presentsd

Sr Ta%ie 12 Miaa t e s %hat %ha parent m u s o f the calolsiliczlte

rocks rara chmmteriz& By ~ O D t a S s l i m mainly m0, SLQ 2 CO 2

and subl.dinstely .klZOa, Y@ 11M B O . W o n (1958) progosea

the relatioWxtp betweerr, chemical coay;rosltion& m k t y p in

the ~ed&t~n%s lQ- a trbangtxlar ~OEkpo~i tk~n d i a g m ~ a i a h th

apioes are SiQg, 1 5 0 and ( ~ a , X&)GOa* >Yt%i the

moiFzLctulateB aSa63Hnical arra3,ysss of oitlct-silioate rocks, the

e&rnaber valu$s of Xason am omptf%lc D camputinie, 'tIrJ,ese

V&WQ, the 2%0 C)OXL$BD% ~LI 8 & ~ h 3.h@~~I.Cfd. W y 9 1 s I s m~&uler%eb

as BesOg and sbB@ to %ha Fap03 a m t a t * mes@ vaues

pr~s@ated TaUe 12 an& plotteSh In the tsiail&xhr co&p~si-

%Lou dfagxtwii of E$asOB ( ~ f g r 36) . Fmm the diagram it be

s e w t b L the ma j os i t y a f pJots o f t;he amlysss f a Z l t;b

@ charts* L$ f e ~ p l o i j ~ M L %a the i%32& of Umestorses and

The rwalcuJatad oham%cal a&gsas oi

34 00-silicate rooks a r u gsesenG fYz %ha

&Lagsamt X o s t o I the p3cots f a l l LXL %be ;C*lelih

CfXB'LlOvl $0 ~ @ B % o ~ X ~ S &Q~UXZI~%@S a& do!

sa~&s-t;onas and cher2ls.. A few plats faZZ A a

the3 22eM 02 sa.&stme~l arzd cherda anti a f e w

athers i a the fAe3.d. of limeatfpnes am% d~k~gn%t€%sl;

V A C A N T F l f L Q