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granulite terrains. Enrichment of almandine from core to rim is also expressed in chemical terms by a lower XMg' Garnet in calc granulites are remarkably high in grossular content (59-61 %) while, almandine is distinctly low at 36-38 mo I %. Individual grains of biotite show the effect of re- distribution of elements during retrogression. The general Mg-enrichment trends observed in biotite from matrix to contact zones - to inclusions indicate chemical exchange with host garnets and is well illustrated also by plots of Al iv Vs. Mg/(Mg + Fe) and XMg Vs. Ti, where the matrix biotite composition corresponds to the Fe-rich varieities (Mg:Fe < 2:1l while, the rims and especially the inclusions tend towards Mg-rich (Mg:Fe > 2:1) or phlogopite composition. On the basis of their increasing Mg and decreasing Ti and Fe concentrations (atomic proportions), three groups of biotite (biotite I, I I and I I I ) have been distinguished, an assumption which goes well with the petrographic evidences too. The al kal i feldspars are characterised by small Ca (0.013 p.f.u, average) and Fe (0.004 p.f.u, average). Anorthite content of alkali feldspar is largely controlled by the rock chemistry, especially the Na20/(Na20 + K20) ratio of the host rocks. Towards plagioclase contacts, 'Or' increases and , Ab' shows a corresponding decrease. Higher Fe concentrations in perthites of granites, compared to matrix
al kal i f e 1 dspar, is reflected in the higher temperature estimates for the former. Plagioclase grain is unzoned and exhibits more or less a uniform composition. In sillimanite-bearing and absent- metapelitic rocks, plagioclase composition corresponds to oligoclase and in cordierite-bearing rocks, it becomes albitic. reported. In calc granulites, an andesine composition is Cordierites are Mg-rich (8.43 wt % MgO) and contain appreciable amounts of FeO also (7.84 wt %). They are relatively poor in Na and K « 0.03 p.f.u and 0.001 p.f.u respectively) and Mn is reported only in trace amounts « 0.004 p.f.u). XFe shows a slight decrease from core to rim. Clinopyroxene of calc granulites shows a wide variation from hedenbergitic to diopsidic composition. The large variation in Mg/(Mg + Fe) and Ca/(Ca + Fe + Mg) of the two sets of clinopyroxene implies that the mechanism of equilibration was a combination of cation exchange and solution regrowth. More specifically, the change in composition may be related to the incomplete re-equil ibration during decrease in temperature (from 808 to 775°C) and a pressure drop from 4.39 to 2.20 Kbars, whereby the clinopyroxene changed by diffusion processes, diopsidic composition. towards a
Page 1 and 2: GEOLOGY, METAMORPHISM AND TECTONIC
Page 3: Acknowledgement Abstract Chapter I
Page 6: Field investigations indicate that
Page 9 and 10: mineralogy of K-feldspar (46 modal
Page 14: Amphiboles of both the calc granuli
Page 19 and 20: through syn to post-thickening magm
Page 21 and 22: CHAPTER I INTRODUCTION Palghat Gap
Page 23 and 24: Fig.2(a) A view of a part of the Pa
Page 25: Narayanaswamy,1954), paucity of myl
Page 28: of movement. Aeromagnetic data of R
Page 34: Bounded by the Western Ghats, the K
Page 39 and 40: Fig.5 Coarsening of sillimanite in
Page 43: and a proven vertical extent of mor
Page 47 and 48: F1g.12 Hornblende - biotite gneiss
Page 49 and 50: of 0.75 m, along NE-SW trending fra
Page 52: direction of fracture planes. Withi
Page 57 and 58: Fig.21 Rootless isoclinal folds (F
Page 59 and 60: Fig.23 Isoclinal folds axial plane.
Page 62:
Pig . 27 Concordant pegmatite belon
Page 67 and 68:
The tectonic framework of the area
Page 69:
inclusions of plagioclase as wel I
Page 72:
the reaction:- G.rossularite + Sill
Page 77 and 78:
TABLE:- 1 MICROPROBE ANALYSES OF SI
Page 79 and 80:
Fig.43 .Fig.40
Page 81 and 82:
Fi g.44 Fig.45 Fig.46 Fig . 47
Page 83 and 84:
where biotite is almost completely
Page 85:
.Fig. 48 Fig.49 Fig.SO Fig . Sl
Page 90 and 91:
Fig.52 Fig.53 Fig.54 Fig.55 B6
Page 93 and 94:
Fig. 56 Fig. 57 Fig. 58 Fig. 59 Cal
Page 97 and 98:
Magnetite is present ubiquitously a
Page 99:
Fig.60 Fig.61 Fig.62 Fig.63 • O.S
Page 103 and 104:
Fig. 64 Fig. 65 Fig. 66 Fig. 67 Bri
Page 105:
Biotite gneiss is typically a coars
Page 109 and 110:
Fig.6B Fig.69 Fig.lO Fig.71 l e::..
Page 112 and 113:
Fig. 72 Fig. 73 Fig. 74 Fig. 75 Sie
Page 114 and 115:
Opaques constitute 0 to 6 modal per
Page 116 and 117:
(X= yel lowish green, Y= brownish g
Page 119 and 120:
11 1.7 PEGMAT I TE Pegmatites are u
Page 121 and 122:
Fig.BO Fig.Bl Fig .B2 UI
Page 125 and 126:
Average values of CaO/MgO ratios fo
Page 127:
proportion in the first two varieti
Page 135 and 136:
TABLE. 6 COMPOS I T ION OF KHONDAL
Page 138:
wt % of type I I varieties. Oxidati
Page 150:
.£.=1-5-2-3 fm c -=1-0-1-5 fm - -
Page 153:
assemb I ages (Goldsmith & Newton,
Page 157 and 158:
TABLE.9 ( c ) NIGGLI PARAMETERS ---
Page 159:
Fig.93 a). In the AlkFM diagram on
Page 162:
elements, CaO, t FeO , TiOZ and MgO
Page 171 and 172:
Rb depleted and Sr enriched nature
Page 173:
TABLE 11.a MAJOR ELEMENT ANALYSES O
Page 178:
their genesis. Amphibolites interla
Page 187:
granites, compared to hornblende-pr
Page 191:
low « 3.Z wt %), with slightly hig
Page 199:
Enrichment of almandine towards rim
Page 205:
!Table.1S). On the basis of their i
Page 212:
2C7 tempera'ture of the former. Com
Page 216 and 217:
cordierite-bearing rocks fall close
Page 219:
TABLE.l9 HICROPROBE ANALYSES OF CLI
Page 227 and 228:
The static involving changes fluid
Page 229 and 230:
to minerals with the largest grain
Page 232:
227 b. Garnet-Cordierite:- Holdaway
Page 237:
thermometric calculations is:- = [-
Page 240:
235 formulae of Raheim & Green (197
Page 243 and 244:
238 100-300 C C compared to other s
Page 245 and 246:
specified P-T conditions. However,
Page 247:
al ka I i feldspar upon cool ing. r
Page 254 and 255:
pressure-dependent equilibria: CaAI
Page 256 and 257:
Cpx and ()(CaMgSi 0 2 = 2 6 pyroxen
Page 258:
253 Bhattacharya & Sen (1985) provi
Page 268 and 269:
TABLE.21 contd ... 4000 GAR CORE-BT
Page 270:
265 TABLE.21 (b) GARNET-CORDIERITE
Page 278 and 279:
TABLE.24 b CROSSINGS OF GPAQ P-T LI
Page 281:
TABLE.25 (contd •.• ) Temperatu
Page 288:
283 which yield data on the process
Page 292:
Fig.124 H 2 0-rich inclusions Ca )
Page 297:
292 carbonic inclusion densities se
Page 309:
low density C02 rich fluids in rift
Page 313 and 314:
J08 sequences, the success in datin
Page 315:
deformation stage, would represent
Page 323:
318 ear lies t recognisable planar
Page 328 and 329:
323 to effect the quasi-isochemical
Page 330 and 331:
The rapid extension of continental
Page 333 and 334:
flanks (2) development of fissile m
Page 335 and 336:
330 extracted with Hydrochloric aci
Page 337:
Estimation of CaO and MgO 332 Twen"
Page 340:
spectrometer while measuring the co
Page 343 and 344:
13. Balasundaram, M. S . ( 1953) .
Page 345:
340 34. Boyd, F.R. and England, J.L
Page 349:
77. Fonarev,V.I. and Konilov, A.N.
Page 353 and 354:
119. Heier, K.S. (1962) amphibolite
Page 355 and 356:
141. Hutcheon, I., Froese. E, Gordo
Page 357 and 358:
162. Krauskopf, K.S. (1979) Introdu
Page 359:
185. MacDonald, G.A. (1968) Composi
Page 362 and 363:
218. Newton, R.C., Charlu, T.V. and
Page 366 and 367:
261. Raith. H.. Raase. P .. Ackerma
Page 371 and 372:
313. Srikantappa. C.and Prakash Nar
Page 373 and 374:
335. Urey, H.C. (1947). the thermod
Page 375:
357. Wood, B. J . ( 1976) . The par
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