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ABSTRACT Pal ghat Gap is the only major breach within the Western Ghats, and constitutes a very conspicuous geomorphic feature in the landscape of Peninsular India. Widely contrasting and contradicting hypotheses exist on its origin, advocating marine and fluviatile erosion, crustal upwarp and consequent development of joints and fractures, as wel I as tectonic processes such as block faulting. This clearly shows that the origin of the Palghat Gap is still a controversy, and evinces further geological interest. The present study was initiated in this backdrop, with the prime object of elucidating the geologic setting and metamorphic evolution of a segment of the Palghat Gap with contrasting geological features. Geological mapping of the study area (about 100 km 2 ) in 1 : 2S , 000 s ca le, comprising a part of the Gap proper and a par t of . i ts northern flank within Kerala, reveals the presence of two distinct rock units: 1. Garnet-biotite- sillimanite !. graphite gneisses (khondalite sensu stricto ), ubiquitously associated with calc granulites and crystalline limestones, with a subordinate group of sillimanite-free gneisses and pockets of cordierite-bearing gneisses, towards the flank, and ,., .:.. Fissile migmatitic exposed rocks comprising biotite and biotite-hornblende gneisses showing discontinuous and boudinaged bands of amphibolites and associated granites and pegmatites occurring within them.
Page 1 and 2: GEOLOGY, METAMORPHISM AND TECTONIC
Page 3: Acknowledgement Abstract Chapter I
Page 8 and 9: abundant proportions. Geochemical d
Page 10: quartz normative tholeiitic origin.
Page 13 and 14: al kal i f e 1 dspar, is reflected
Page 16: occurrence), is estimated to be 530
Page 20 and 21: associated with the closing stages
Page 22 and 23: Fig.l Landsat (MS S band 4) ima(1e
Page 24 and 25: the suggested presence of a wide sh
Page 27 and 28: opposite origin of features valleys
Page 30: careful perusal of the available ge
Page 37: and hornblende gneisses containing
Page 40: are interbanded with quartzo-feldsp
Page 46 and 47: l of joints (horizontal and oblique
Page 48 and 49: Fig . 14 & IS Fig.14 Fig.IS Amphibo
Page 50: Fig.16 Fig.17 Boudins of gneisses.
Page 56 and 57:
closures of an earlier generation (
Page 58 and 59:
symmetrical folds (Fig. 24) • In
Page 60:
Fig.25 Boudins of amphibolite folde
Page 66 and 67:
Fig . 31 Cross - folding of open me
Page 68 and 69:
CHAPTER I I I PETROGRAPHY Petrograp
Page 71 and 72:
Fig.32 Fig.33 Fig.34 Fig.35
Page 74:
Fig.36 Fig.37 Fig.38 Fig.39
Page 78 and 79:
Fig. 40 Fig. 41 Fig. 42 Fig. 43 & 4
Page 80 and 81:
Fig. 45 Fig. 46 Fig. 47 BEl of cord
Page 82 and 83:
quartzofeidspathic augens. Kinked a
Page 84 and 85:
Fig. 48 Fig. 49 Fig. 50 Fig. 51 Rea
Page 88:
clinopyroxene, possibly suggesting
Page 91:
Labradoritel as indicated by mlcrop
Page 94:
Fig . 56 Fig . 57 Fig.58 Fig.59
Page 98 and 99:
Fig. 60 Quartz grain completely sur
Page 101:
grains are inequigranuiar with cren
Page 104 and 105:
Fig.64 F1 g.65 F1g.66 • O· 'l "'
Page 108 and 109:
Fig. 68 Coarse biotite flakes trans
Page 110:
111.5 AMPHIBOLITES These are medium
Page 113 and 114:
Fig.72 Fig. 73 Fig.74 Fig.75
Page 115 and 116:
appear to corrode amphiboles. Alter
Page 117:
Fig. 76 Fig. 77 Fig. 78 Fig. 79 Per
Page 120 and 121:
Fig. 80 Fig. 81 Fig. 82 Pegmatite s
Page 122:
st"uctures are noticed in a few sec
Page 126 and 127:
-----------------------------------
Page 129:
sympathetically with K wt% while, K
Page 136:
132 negative correlations with 5i02
Page 140:
TABLE.7 (Contd .. ) b. TRACE ELEMEN
Page 152 and 153:
distinct positive trends of TiDZ' Z
Page 156 and 157:
corresponding values for Group I I
Page 158 and 159:
C -=O
Page 161 and 162:
TABLE. 10 RESULTS OF MAJOR AND TRAC
Page 170 and 171:
espect i ve I y) reported by Condie
Page 172 and 173:
lV.S.a AMPHIBOLITE Six samples of a
Page 175:
° N ;x:: 12 -+ ON o Z 8 tS • , I
Page 182:
TABLE.12 c NORMATIVE COMPOSITION OF
Page 190 and 191:
Qz Ab (0 ) Or An An ( b ) 186 Fig.
Page 194:
TABLE.13 RESULTS OF MAJOR AND TRACE
Page 204 and 205:
fn pegmatites, al I the end-member
Page 211 and 212:
206 in cordierite- bearing assembla
Page 214:
TABLE. 17 HICROPROBE ANALYSES OF PL
Page 217:
TABLE. 18 Rock type Anal. No. SiOZ
Page 226 and 227:
Based on the classification of Gire
Page 228 and 229:
223 resul ting in temperatures lowe
Page 230:
Exchange thermometers as a group ar
Page 234:
temperature. Revised form of this e
Page 239 and 240:
1/3 Mg3AIZSi301Z + CaFeSiZ06 = 1/3
Page 242 and 243:
237 composition of coexisting felds
Page 244 and 245:
such as garnet result in temperatur
Page 246 and 247:
Holdaway, 1976 and Perchuk & Lavren
Page 249:
VI.4. GEOBAROMETRY 244 Reconstructi
Page 255 and 256:
+ 2 (3300-1. 5T) 4 2 Gt (XMg + (XMg
Page 257 and 258:
252 & Wood (1979), Martignole & Sis
Page 262:
257 modelling of activity compositi
Page 269 and 270:
TABLE.21 contd .... 4000 5000 6000
Page 273:
268 TABLE.23 Garnet-biotite, Two-fe
Page 279:
and 1989) barometers, yield pressur
Page 284:
TABLE.27 MODEL PRESSURE ESTIMATED F
Page 291 and 292:
isolated and azonal clusters and ar
Page 294:
Freezing-heating experiments:- Micr
Page 306:
ate of tectonic vertical exposure a
Page 312 and 313:
esolving the discrepancies and inco
Page 314 and 315:
does not always hold good especiall
Page 320:
315 magmatic cycles, it is reasonab
Page 325:
ims is consistent with a reduction
Page 329 and 330:
transition from ITD into an essenti
Page 331:
along with the microtextural eviden
Page 334 and 335:
APPENDIX 1.1 OUTLINE OF THE PROCEDU
Page 336 and 337:
standard (O.OlN) using Barium diphe
Page 339 and 340:
model TP 2d. to give pellets of 40
Page 342 and 343:
1 .L. • Abbey, 337 S.(1977) Studi
Page 344 and 345:
33·9 23. Bingen,B., Demaiffe, D. a
Page 348 and 349:
343 67. England. P.C. and Thompson,
Page 352 and 353:
L09. Hansen. E.C., Newton. R.C. and
Page 354 and 355:
130. Hoisch. D,T. (1989). geothermo
Page 356 and 357:
151. Johnson. C.A., Essene E.J. (19
Page 358 and 359:
172. Lamb, W . M . , Valley, metamo
Page 361 and 362:
208. N ageswara Rao, J . and Sr in
Page 363:
228. Odom. A.L. (1982) Isotopic age
Page 367:
271. Reddy. A.G.B.. Mathew. M.P ..
Page 372 and 373:
j23. Subramanian. A.P. (1956) Miner
Page 374 and 375:
345. Wedepohl. K.H. (1969) composit
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