Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

K. Soman ¹, N. G. K. Nair ², V. N. Golubyev ³, M. M. Arakelyan ³

Affiliations
1 Department of Geology, Friendship University, Moscow, RU
2 Centre for Earth Science Studies, Trivandrum 695010, IN
3 IGEM, Academy of Sciences, Moscow, USSR, RU

Abstract

K/Ar mica age of chrysoberyl-bearing pegmatites from four localities of Trivandrum district, Kerala ranges from 445 to 474 m.y., with a mean around 460 m.y. There is a close agreement between the ages of the concordant and cross-cutting pegmatites, between muscovite and biotite ages, as also between various size fractions. Chrysoberyl occurs within feldspars in association with quartz and muscovite. Since the formation of chrysoberyl-quartz association requires a higher pressure or temperature, the reported age would indicate the time of emplacement of the chrysoberyl-bearing pegmatites at the closing phase of a major tectonomagmatic event. It is interesting to note that these pegmatites of south-western India are younger compared to those of other localities viz., Rajasthan, Bihar. Nellore and Mysore.

Full Text

     

N. G. K Nair ¹, K. Soman ¹, M. Santosh ¹, M. M. Arakelyants ², V. N. Golubyev ²

Affiliations
1 Centre for Earth Science Studies, Trivandrum 695010, IN
2 IGEM, Academy of Sciences, Moscow, USSR, RU

Abstract

Biotite separates from three granite plutons in the Northern part of the Kerala region, namely, Kalpatta. Ambalavayal and Thaluru yield K-Ar ages of 512±20 m.y., 560±30 m.y. and 710±20 m y. respectively. The age data are comparable with those reported for similar granitic intrusives of the south Indian region.

Full Text

   

K. Soman ¹, N. G. K. Nair ¹, A. V. Druzhinin ²

Affiliations
1 Centre for Earth Science Studies, Trivandrum 695 010, IN
2 Peoples Friendship University, Moscow, RU

Abstract

Recent investigations prove that the southern part of Kerala and the adjoining areas further to the south in Tamil Nadu constitute a chrysoberyl-pegmatite field in the granulite terrain of southwestern India. Gem stones like chrysoberyl and its varieties, sapphire, topaz and zircon are mostly derived from pegmatites, though some come from the alluvial beds also. Chrysoberyl-pegmatites occur in a predominantly garnet-sillimanite ± graphite gneissic terrain with intermittent bands of garnet-biotite gneiss and enderbites. Geochronological data reveal that the pegmatites were emplaced 445-474 m.y. ago. Fluid inclusion studies show that the pegmatite minerals contain liquid carbon dioxide and give an entrapment temperature of 500-570°C. CO₂ densities permit a pressure estimate of 250 Mpa and more, which is also consistent with the sillimanite-andalusite and quartz-chrysoberyl associations in the pegmatites. The similarities in geology, the ages of pegmatites and granites and also the mineral composition of pegmatites of southwestern India and the alluvial gem gravels of Sri Lanka suggest that the al1uvial gem beds of Sri Lanka may also be of pegmatitic origin.

Full Text

     

D. Thomas ¹, M. Lalithambika ¹, K. Soman ²

Affiliations
1 Regional Research Laboratory, Pappanamcode. Trivandrum, IN
2 Centre for Earth Science Studies, Trivandrum 695031, IN

Abstract

SEM and DT A investigations of the clays from the famous clay mine at Kundara show that kaolinite and halloysite constitute the clay minerals, and that halloysite is transformed into well-crystalline kaolinite. This indicates that kaolinite formation is preceded by the formation of halloysite in the weathering crust at Kundara. This finding is consistent with the recent experimental results of halloysite-kaolinite transformation.

Full Text

   

Narayanaswamy ¹, K. Soman ¹

Affiliations
1 Centre for Earth Science Studies, Trivandrum 695031, IN

Abstract

Description and size data are presented for zircons separated from Precambrian rocks of south Kerala, comprising garnet-sillimanite-graphite gneiss (khondalite), charnockite, garnet-biotite gneiss and garnet-Quartz-feldspar neosome.

Zircons from khondalite are rounded, do not show much overgrowth features and are typical of granulites of sedimentary parentage. Zircons in charnockite show unimodal frequency curves and self-nucleated RMA nature. suggestive of magmatic origin. Those from garnet-biotite gneisses do not show any linear. RMA trends, and the terminally rounded zircons in them do not show any angle between length and c-axis suggesting a mixed source. Zircons from garnet-quartz-feldspar neosome show features, suggestive of migmatitic origin.

Keywords

Zircon Morphology, Petrology, Igneous and Metamorphic, Kerala Khondalite-Charnockite.

Full Text

     

K. Soman ¹, K. G. Thara ¹, M. M. Arakelyants ², V. N. Golubyev ³

Affiliations
1 Centre for Earth Science Studies, Trivandrum 695031, IN
2 IGEM, Academy of Sciences, Moscow 109017, RU
3 IGEM, Academy of Sciences, Moscow 109017, IN

Abstract

Of the three styles of deformation recognised in the Palghat Gap area, the D₃ period is conspicuous with a major pegmatite emplacement phase, associated with the migmatization event. Dating of mica from pegmatites belonging to this stage (both concordant and cross-cutting) has yielded ages ranging from 484 to 512 m.y. The pegmatite emplacement is suggested to be towards the closing stage of a retrogressive metamorphic event, associated with crustal uplift in the Palghat Gap region, which laid the tectonic frame-work for the formation of the gap later.

Keywords

Geochronology, Palghat Gap, Pegmatites, Kerala.

Full Text

     

K. Soman ¹

Affiliations
1 Center for Earth Science Studies, Trivandrum - 695 031, IN

Abstract

No Abstract.

Full Text

   

K. Soman ¹, Narayanaswamy ², W. R. Van Schmus ³

Affiliations
1 Centre for Earth Science Studies, Trivandrum-695 031, IN
2 Centre for Earth Science Studies, Trivandrum-695 031
3 Department of Geology, University of Kansas, Lawrence, Kansas 66045, US

Abstract

South Kerala in southwestern India offers interesting khondalite-charnockite assemblages suitable for detailed multidisciplinary case studies on granulite petrogenesis. Arrested chamockite formation is also characteristic of the terrain. Absolute ages of the khondalites are poorly constrained; we have obtained limited U-Pb zircon data for various rock types of south Kerala khondalite belt. Zircons from khonddite sensu-stricto and garnet-biotite gneiss of possible sedimentary origin give a concordia upper-intercept apparent age of ca. 2200 Ma, suggesting that the khondalites contain detrital material that is atleast Early Proterozoic in age; the data yield a tower intercept apparent age of ca. 400-600 Ma, but it is not clear if this represents new zircon growth andepisodic Pb loss at that time (preferred) or is an artifact of norrnal diffusive loss of radiogenenic Pb. Zircons from retrograded granulitic gneisses have zircon upper-intercept apparent ages of ca. 1550 Ma, indicating either a younger protolith age or, more probably, greater radiogenic Pb loss during subsequent migmatite-grade metamorphism that caused retrogression of the granulite. Since all the zircon populations are complex, more detailed anaIyses will need to be pursued to resolve age relationships of these rocks with greater certainty. Monazite from a retrograded granulitic gneiss, yields a concordant age of ca. 520 Ma; this age is probably related to late Proterozoic-Early Cambrian regional thermal event in south Kerala and is correlative with a similar event in Sri Lanka.

Keywords

Geochronology, Zircons, Granulites, Kerala.

Full Text

     

K. Soman ¹

Affiliations
1 Centre for Earth Science Studies, Akkulam, Thiruvananthapuram - 695 03 1, IN

Abstract

Coastal environments constitute a critical national and global resource that suffers widespread degradation due to human impacts. Because of their resource potential and opportunities, coasts are over populated. Unmindful exploitation of coastal resources and discharge of effluents/pollutants result in resource depletion and lead to multiple user conflicts in the coasts. Damage to life and property due to natural hazards adds to the woes of the coasts. In order to make good of the degradation, destruction and multiple user conflicts affecting the resource-rich coasts and to ensure sustainability of this rich resource base, 'Integrated Coastal Zone Management" (ICZM) programmes were implemented in various countries with great success. In India too, the notification ol' 199 1 on 'Coastal Regulation Zone' was one such exercise, sans scientific backing in working out the setback line/regulation zones. Earmarking a uniform, static 500 m 'regulation zone' from the high tide line, irrespective of the diverse nature of the coastline, the ecosystems and vulnerability to natural hazards has rendered it an unscientific effort. Considering the multitude of problems being faced by the Indian coasts, their contrasting geomorphologic features and vulnerability to natural hazards, it is prudent to work out the setback lines by the local geoscientific fraternity and to draft plans for their sustainable management at par with global standards. Lessons from recent tsunami hit along the Indian coast have accelerated the pace of thinking in this line in India.

Keywords

Coastal Regulation Zone, Setback Line, Geomorphology, Continental Shelf, And ICZM Pixel.

Full Text

     

K. Soman ¹

Affiliations
1 Center for Earth Science Studies, Thiruvananthapuram-695 031, IN

Abstract

No Abstract.

Full Text

   

K. Soman ¹

Affiliations
1 Centre for Earth Science Studies Thiruvananthapuram - 695 031, IN

Abstract

No Abstract.

Full Text

   

P. K. Raman ¹, K. S. Rao ², K. Soman ³

Affiliations
1 Flat # 202, 'Narmisam 'Srinagar Colony PO Hyderabad - 500 073, IN
2 Flat # 401, Srinilaya Estate Ameerpet, Srinagar Colony P O Hyderabad - 500 073, IN
3 Centre for Earth Science Studies Thiruvananthapuram, IN

Abstract

No Abstract.

Full Text

   

K. Soman

Abstract

No Abstract.

Full Text

   

K. Soman ¹

Affiliations
1 Centre for Earth Science Studies, Akkulam, Trivandrum - 695 031, IN

Abstract

No Abstract.

Full Text

   

K. Soman ¹, Mahamaya Chattopadhyay ¹, K. G. Thara ²

Affiliations
1 Centre For Earth Science Studies, Trivandrum, IN
2 Institute of Land Management, Trivandrum, IN

Abstract

No Abstract.

Full Text

   

K. Soman

Abstract

No Abstract.

Full Text