Abstract
The Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km2 area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite and quartz veins.
The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock, alkali pyroxenite, ijolite-melteigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite, volcanic tuff, phosphatic rock and chert breccia.
The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits with falling temperature into two immiscible fractions—one ultimately crystallises as alkali pyroxenite/ijolite and the other as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process). Isotopic studies (δ18O and δ13C) on carbonatites of Samchampi have indicated that the δ13C of the source magma is related to contamination from recycled carbon.
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References
Acharyya S K, Mitra N D and Nandi D R 1986Geol. Surv. Mem. 119 6–12
Appleyard E C 1974Lithos 7 149–169
Appleyard E C and Williams S E 1981TMPM Tschermaks Min. Pet. Mitt. 28 81–97
Bagdasarov Yu A 1997Geochim. International 35({na1}) 7–16
Bailey D K 1974 Nephelinites and Ijolites. In:The Alkaline Rocks (ed) H Sorensen (London: John Wiley Interscience) 53–66
Barth T F W and Ramberg I B 1966 The Fen Circular Complex. In:Carbonatites (eds) O F Tuttle and J Gittins (London: John Wiley Interscience) 225–257
Beccaluva L, Barbieri M, Born H, Brotzu P, Coltorti M, Conte A, Garbarino C, Gomes C B, Macclotta G, Morbidelli M, Ruberti E, Siena F and Traversa G 1992J. Petrol. 33(6) 1371–1404
Chattopadhyay N and Hashmi S 1984Rec. Geol. Surv. India 113 24–33
Currie K L 1976Geol. Surv. Can. Bull. 239 228pp
Deer W A, Howie R A and Zussman J 1963Rock-forming Minerals2 Chain silicates. (London: Longmas) 379pp
Deines P 1989 In:Carbonatite Genesis and Evolution (ed) K Bell (London: Unwin Hyman) 301–359
Erickson R L and Blade L V 1963US Geol. Surv. Prof. Paper 425 95pp
Freestone I C and Hamilton D L 1980Contrib. Miner. Petrol. 73 105–117
Gold D P 1966Miner. Soc. India IMA Volume (eds) M N Viswanathiah and P R J Naidu 83–91
Gomes C B, Ruberti E and Morbidelli L 1990J.S. Am. Earth Sci. 3 51–63
Gupta A K and Yagi K 1980 Petrology and genesis of Leucite bearing rocks, (Berlin: Springer Verlag) 252pp
Heinrich E W 1966The Geology of Carbonatites. (Chicago: Rand McNally) 555pp
Kent R W, Storey M and Saunders A D 1992Geology 20 891–894
Kjarsgaard B A and Hamilton D L 1988Miner. Mag. 52 43–55
Koster Van Gross A P and Wyllie P J 1966Amer. J. Sci. 264 234–255
Koster Van Gross A P and Wyllie P J 1968Amer. J. Sci. 266 932–967
Koster Van Gross A P and Wyllie P J 1973Amer. J. Sci. 273 465–487
Kumar D, Mamallan R, Srinivasan B, Jain S K and Krishnamurthy P 1989Explo. and Res. for Atomic Minerals 2 183–199
Leake B E 1978Can. Miner. 16 501–520
LeBas M J 1977Carbonatite-Nephelinite Volcanism, (London: Wiley Interscience) 347pp
LeBas M J 1987Geol. Soc. London Spl. Publ. 30 53–83
LeBas M J 1989Mem. Geol. Soc. India 15 137–144
Lee W and Wyllie P J 199229th IGC, Kyoto, Japan 11-8-10 0-9 1296 (Abs.)
Nag S 1983N. Jb. Miner. Abh. 147 217–227
Nag S, Chakravorty P S, Smith T E and Huang C H 1984Geol. J. 19 57–76
Nag S, Sengupta S K and Chawade M P 1993Rec. Geol. Surv. India 126(4) 24–26
Nockolds S R 1954Bull. Geol. Amer. 65 1007–1032
Peacock M A 1931J. Geol. 39 54–67
Pichler H and Schmitt-Riegraf C 1997Rock-forming Minerals in Thin Sections (London: Chapman & Hall) 220pp
Platt R G and Edgar A 1971J. Geol. 80 224–236
Sengupta S K, Rehman S and Nag S 1996 Regional Seminar on Development of Geological Research in Northeast India. Guwahati University, April 1996 (Abs.)
Sengupta S K, Ray J S, Rehman S and Nag S 1997International Symposium on Isotopes of Solar System. PRL, Ahmedabad, November 1997 (Abs.)
Shapiro L and Brannock W W 1962US Geol. Surv. Bull. 1141-A 56pp
Srinivasan V 1977J. Geol. Soc. India 48 598–604
Streckeisen A L 1967N. Jb. Miner. Abh. 107 144–240
Sutherland D S 1966Proc. Geol. Soc. London 1629 20–23
Treiman A H and Schedl A 1983J. Geol. 91 437–447
Verwood W J 1978Annual Rep. of Geophys. Lab. Washington 77 767–774 In: LeBas M J1987
Viladkar S G 1984India Mineralogist 130–135
Viladkar S G 1991N. Jb. Miner. Abh. 162(2) 201–213
Viladkar S G and Wimmenauer W 1992Chem. Erde. 52 277–291
Wimmenauer W 1966 The eruptive rocks and carbonatites of Kaiserstuhl, Germany. In:Carbonatites (eds) O F Tuttle and J Gittins (London: John Willey Interscience) 183–204
Yoder H S and Kushiro I 1969Amer. J. Sci. 267 558–582
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Nag, S., Sengupta, S.K., Gaur, R.K. et al. Alkaline rocks of Samchampi-Samteran, District Karbi-Anglong, Assam, India. Proc. Indian Acad. Sci. (Earth Planet Sci.) 108, 33–48 (1999). https://doi.org/10.1007/BF02840823
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DOI: https://doi.org/10.1007/BF02840823