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Petrogenesis and Source Characteristics of Alkaline Plutons in Tamil Nadu, South India: Evidence for Enriched Lithospheric Mantle
706
RODINIA, GONDWANA AND ASIA
Mishra. B., Pandya, K. L. and Maejima, W. (1997) Alluvial fan sedimentation in the Cretaceous Athgarh Gondwana basin, Orissa, India. J. Sed. SOC.Japan, No. 46, pp. 3-14.
Raja Rao, C. S and Mitra, N. D. (1978) Sedimentation and tectonics of Gondwana basins of Peninsular India. 3rd Regional Conf. on Geol. Min. Resources of South East Asia, pp. 85-90.
Petrogenesis and Source Characteristics of Alkaline Plutons in Tamil Nadu, South India: Evidence for Enriched Lithospheric Mantle T. Miyazaki’, H. Kagamil, V. Ram Mohan2, K. Shuto3and T. Morikiyo4 Graduate School of Science and Technology,Niigata University, Niigata 950-2181, Japan Department of Geology, University of Madras, Chennai - 600 025, India Department of Geology, Faculty of Science, Niigata University, Niigata 950-2181, Japan Department of Geology, Faculty of Science, Shinshu University, Matsumoto 390-8621, Japan
In the northern part of the South Indian granulite terrain in Tamil Nadu, a number of alkaline plutons comprising saturated syenite, pyroxenite and carbonatite have been reported (Rajesh and Santosh, 1996). These plutons are located along a major NE-SW trending lineament (Grady, 1971). Along one such lineament, the alkaline complexes of Yelagiri, Sevattur and Samalpatti have intruded into the country rocks comprising epidote hornblende gneiss. The Sevattur and Samalpatti are associated with carbonatite and form alkali-carbonatite complexes. This region is also important to understand the crustal formation on the periphery of the Dharwar craton. The age of the alkaline magmatism reported from Yelagiri, Sevattur and Samalpatti indicate late Proterozoic alkaline magmatic activity in this region (Moralev et al., 1975; Kumar and Gopalan, 1991; Schleicher et al., 1997; Kumar et al., 1998; Miyazaki et al., 2000). The existence of alkali metal and LREE enriched subcontinental upper mantle has been recognized under this region (e.g., Kumar et al., 1998; Schleicher et al., 1998; Miyazaki et al., 2000). Kumar et al. (1998) showed that this enriched mantle had existed as sub-continental lithospheric mantle and had been a closed-system since about 2.5-2.6 Ga. Rb-Sr whole-rock isochron ages of the Yelagiri and Sevattur silicate rocks yield ages of 750-800 Ma, indicating their contemporaneous nature with other alkaline plutons in northern part of Tamil Nadu. Pressure and temperature estimations indicate that the Yelagiri and Sevattur syenites were emplaced at about 15-20 km depth at temperatures of about 750-850°C. Close spatial relationship, similarities in age, and mineralogical, geochemicaland isotopic characteristics of these plutons strongly suggest their close genetic relationship, although minor mineralogical, geochemical and isotopic variations are observed between the Yelagiri and Sevattur syenites indicating open system behaviour. The initial Sr and Nd isotope ratios of the Sevattur carbonatites suggest their derivation from alkali and LREE enriched mantle source. However, the syenites of the Yelagiri and Sevattur plutons have distinctly different isotopic characteristics from the Sevattur carbonatites, represented by their low initial Nd isotope ratios (Miyazaki et al., 2000). Contrasting isotopic compositions along with the geochemical
variations within and between the silicates and carbonatites argue against their derivation from conjugate immiscible liquid. Instead, it is considered that the carbonatites evolved from primitive carbonate liquid produced directly by low-degree melting of carbonated mantle peridotite (Harmer, 1999). Combined geochemical and isotopic characteristics of the Yelagiri and Sevattur syenites indicate that the syenitic magmas were generated from mantle-derived alkali basaltic magmas. Based on low Mg# and low Cr and Ni concentrations of the Yelagiri and Sevattur syenites, the alkali basaltic magmas are considered to have been highly differentiated within lower-crustal magma chamber before emplacement. Generally, it is known that carbonatites and associated silicate rocks have similar initial Sr and Nd isotope ratios, even though they have diverse petrogenesis. However, recent comprehensive isotopic studies of carbonatites and their associated silicate rocks show that there are several alkaline-carbonatite complexes with wide isotopic variation in the associated silicate rocks, as observed in the Yelagiri and Sevattur plutons (e.g., Harmer, 1999). Models, such as AFC or binary mixing with crust material, cannot explain the wide isotopic variations in the Yelagiri and Sevattur syenites; therefore these isotopic variations are considered to reflect isotopic heterogeneity of enriched mantle. Trace element distribution diagrams of the Yelagiri and Sevattur syenites are characterized by pronounced enrichment in LIL and large negative Nb anomaly, indicating subduction related signature of their source mantle. In the northern part of South Indian granulite terrain, geochemical and isotopic signatures of other mantle-derived intrusive rocks with different ages from ca. 2.5 Ga to ca. 0.75 Ga also indicate the existence of enriched mantle (Kumar and Gopalan, 1991; Jayananda et al., 1995; Radhakrishna et al., 1995; Reddy et al., 1995; Kumar et al., 1998; Schleicher et al., 1998). Moreover, trace element characteristics of these rocks also show their subduction related signature. It is considered that the enriched mantle was formed by subduction-related geological processes, as hinted by Kumar et al. (1998), which probably occurred at a convergent margin along the southern and/or southeastern edge of the Dharwar craton, and survived convective disruption in the mantle, as Gondwana Research, V. 4,No. 4,2001
RODINIA, GONDWANA AND ASIA
sub-continental lithospheric mantle, from early Proterozoic until at least 750-800 Ma ago.
References Grady, J.C. (1971) Deep main faults in South India. J. Geol. SOC.India, V. 12, pp. 56-62. Harmer, R.E. (1999) The petrogenetic association of carbonatite and alkaline magmatism: constraints from the Spitskop complex, South Africa. J. Petrol., v. 40, pp. 525-548. Jayananda, M., Martin, H., Peucat, J. J . and Mahabaleswar, B. (1995) Late Archaean crust-mantle interactions: geochemistry of L E E enriched mantle derived magmas. Example of the Closepet batholith, southern India. Contrib. Mineral. Petrol., v. 119, pp. 314-329. Kumar, A. and Gopalan, K. (1991) Precise Rb-Sr age and enriched mantle source of the Sevattur carbonatites, Tamil Nadu, South India. Curr. Sci., v. 60, pp. 653-655. Kumar, A,, Charan, S.N., Gopalan, K. and Macdougall, J.D. (1998) A long-lived enriched mantle source for two Proterozoic carbonatite complexes from Tamil Nadu, southern India. Geochim. Cosmochim. Acta, v. 62, pp. 515-523.
707
Miyazaki, T., Kagami, H., Shuto, K., Morikiyo, T., Ram Mohan, V. and Rajasekaran, K.C. (2000) Rb-Sr geochronology, Nd-Sr isotopes and whole-rock geochemistry of Yelagiri and Sevattur syenites, Tamil Nadu, South India. Gondwana Res., v. 3, pp. 39-53. Moralev, V.M., Voronovski, S.N. and Borodin, L.S. (1975) New findings about the age of carbonatites and syenites from southern India. USSR Acad. Sci., v. 222, pp. 46-48. Rajesh, H.M. and Santosh, M. (1996) Alkaline magmatism in Peninsular India. Gondwana Res. Group Mem., No. 3, pp. 91-115. Reddy, B.M., Janardhan, A.S. and Peucat, J.J. (1995) Geochemistry, age and origin of alkaline and ultramafic rocks of Salem, Tamil Nadu, South India. J. Geol. SOC.India, v. 45, pp. 251-262. Schleicher, H., Todt, W., Viladkar, S.G. and Schmidt, F. (1997) Pb/Pb age determinations on Nuwania and Sevattur carbonatites of India: evidence for multi-stage histories. Chem. Geol., v. 140, pp. 261273. Schleicher, H., Kramm, U., Pernicka, E., Schidlowski, M., Schmidt, F., Subramanian, V., Todt, W. and Viladkar, S.G. (1998) Enriched subcontinental upper mantle beneath southern India: evidence from Pb, Nd, Sr and C - 0 isotopic studies on Tamil Nadu carbonatites. J. Petrol., v. 39, pp. 1765-1785.
Distribution Patterns of Gold Deposits in the Archaean Manica-Mutare-Odzi Greenstone Belt S. Mondlane'/*,P. Dirks1, H. Jelsma' and T. Blenkinsopl University of Zimbabwe, Geology Departmenf, 167 MP, Mount Pleasant, Harare, Zimbabwe Eduardo Mondlane University, Geology Department, PO. Box 257, Maputo, Mozambique The Manica - Mutare - Odzi (MMO) greenstone belt in West Mozambique and East Zimbabwe is a late Archaean linear structure that was intruded by the Penhalonga granodiorite at ca. 2.74 Ga. The ENE-trending belt comprises ultramafic metavolcanic rocks along the margins and coarse clastic metasedimentary rocks in the central zone. Rock units are intensely folded and a regional penetrative foliation has developed. Fold axes generally plunge shallowly either to the east or to the west and parallel the regional mineral lineation. The MMO greenstone belt has produced ca. 84 tonnes of Au (Forster et al., 1996) mainly from shear zone hosted, fault hosted and quartz vein hosted deposits. Mineralization follows corridors, which seem to control the localisation of the deposits. Fry analysis helps to define the underlying structural directions controlling the distribution of gold deposits, which may not be directly obvious otherwise. This is done by enhancing linear trends in an X - Y data points. Fry analysis was used to determine the spatial relationships of gold deposits. The input data were extracted from existing records (geological maps, bulletins and mine reports) of mine positions. Sixty out-of 243 deposits were field checked during the present study and were found to be within a maximum offset range of ca. 100 meters in Latitude and ca. 50 meters in Longitude. This offset is deemed acceptable, as it is not known exactly at what point the previous location was taken (main shaft or adit entrance, first adit, etc.). The Fry analysis is applied to sectors of the belt (Manica, Mutare and Odzi) for all deposit types. The method has been repeated for gold deposits grouped by type (fault/shear zoneGondwana Research, V. 4, No. 4, 2001
hosted (112 deposits), quartz vein (170 deposits), stratabound/ contact reefs (22 deposits), and stock work/disseminated (20 deposits) and finally for the deposits grouped according to sulphide paragenesis. When grouping the deposits by sulphides, deposit type and region (Manica, Mutare or Odzi) linear patterns that might be subdued when applying the Fry analysis to all deposit types at the same time can be revealed. The results interpreted visually and compared to structural and lineament analysis from satellite images suggest that gold mineralization in the MMO greenstone belt clusters repeatedly in corridors of about 5 km wide and generally oriented ENE-WSW, NW-SE or N-S. These corridors are not evident on the geological -structural maps of the area, suggesting an underlying control by deepseated structures without surface expression. Interpretation of the translation maps shows that the ENE-WSW direction is related to the structural trend of the MMO greenstone belt. The NW-SE and N-S directions are persistent at deposit type level of analysis, except for the contact reef and stratabound deposits, which only show the NE-SW direction. The NE-SW direction, in the all deposit type analysis, is masked by the structural trend of the belt. The stockwork and disseminated deposits, show NW-SE as the main direction in the translation maps. The shear zones and fault-hosted deposits are generally aligned NE-SW and NW-SE directions, probably forming conjugate sets. In addition an E-W direction is evident in the Odzi section of the belt while a N-S direction is evident in the Manica and Mutare sections of the belt. The quartz vein hosted deposits are more diffuse and show different orientations,
RODINIA, GONDWANA AND ASIA
Mishra. B., Pandya, K. L. and Maejima, W. (1997) Alluvial fan sedimentation in the Cretaceous Athgarh Gondwana basin, Orissa, India. J. Sed. SOC.Japan, No. 46, pp. 3-14.
Raja Rao, C. S and Mitra, N. D. (1978) Sedimentation and tectonics of Gondwana basins of Peninsular India. 3rd Regional Conf. on Geol. Min. Resources of South East Asia, pp. 85-90.
Petrogenesis and Source Characteristics of Alkaline Plutons in Tamil Nadu, South India: Evidence for Enriched Lithospheric Mantle T. Miyazaki’, H. Kagamil, V. Ram Mohan2, K. Shuto3and T. Morikiyo4 Graduate School of Science and Technology,Niigata University, Niigata 950-2181, Japan Department of Geology, University of Madras, Chennai - 600 025, India Department of Geology, Faculty of Science, Niigata University, Niigata 950-2181, Japan Department of Geology, Faculty of Science, Shinshu University, Matsumoto 390-8621, Japan
In the northern part of the South Indian granulite terrain in Tamil Nadu, a number of alkaline plutons comprising saturated syenite, pyroxenite and carbonatite have been reported (Rajesh and Santosh, 1996). These plutons are located along a major NE-SW trending lineament (Grady, 1971). Along one such lineament, the alkaline complexes of Yelagiri, Sevattur and Samalpatti have intruded into the country rocks comprising epidote hornblende gneiss. The Sevattur and Samalpatti are associated with carbonatite and form alkali-carbonatite complexes. This region is also important to understand the crustal formation on the periphery of the Dharwar craton. The age of the alkaline magmatism reported from Yelagiri, Sevattur and Samalpatti indicate late Proterozoic alkaline magmatic activity in this region (Moralev et al., 1975; Kumar and Gopalan, 1991; Schleicher et al., 1997; Kumar et al., 1998; Miyazaki et al., 2000). The existence of alkali metal and LREE enriched subcontinental upper mantle has been recognized under this region (e.g., Kumar et al., 1998; Schleicher et al., 1998; Miyazaki et al., 2000). Kumar et al. (1998) showed that this enriched mantle had existed as sub-continental lithospheric mantle and had been a closed-system since about 2.5-2.6 Ga. Rb-Sr whole-rock isochron ages of the Yelagiri and Sevattur silicate rocks yield ages of 750-800 Ma, indicating their contemporaneous nature with other alkaline plutons in northern part of Tamil Nadu. Pressure and temperature estimations indicate that the Yelagiri and Sevattur syenites were emplaced at about 15-20 km depth at temperatures of about 750-850°C. Close spatial relationship, similarities in age, and mineralogical, geochemicaland isotopic characteristics of these plutons strongly suggest their close genetic relationship, although minor mineralogical, geochemical and isotopic variations are observed between the Yelagiri and Sevattur syenites indicating open system behaviour. The initial Sr and Nd isotope ratios of the Sevattur carbonatites suggest their derivation from alkali and LREE enriched mantle source. However, the syenites of the Yelagiri and Sevattur plutons have distinctly different isotopic characteristics from the Sevattur carbonatites, represented by their low initial Nd isotope ratios (Miyazaki et al., 2000). Contrasting isotopic compositions along with the geochemical
variations within and between the silicates and carbonatites argue against their derivation from conjugate immiscible liquid. Instead, it is considered that the carbonatites evolved from primitive carbonate liquid produced directly by low-degree melting of carbonated mantle peridotite (Harmer, 1999). Combined geochemical and isotopic characteristics of the Yelagiri and Sevattur syenites indicate that the syenitic magmas were generated from mantle-derived alkali basaltic magmas. Based on low Mg# and low Cr and Ni concentrations of the Yelagiri and Sevattur syenites, the alkali basaltic magmas are considered to have been highly differentiated within lower-crustal magma chamber before emplacement. Generally, it is known that carbonatites and associated silicate rocks have similar initial Sr and Nd isotope ratios, even though they have diverse petrogenesis. However, recent comprehensive isotopic studies of carbonatites and their associated silicate rocks show that there are several alkaline-carbonatite complexes with wide isotopic variation in the associated silicate rocks, as observed in the Yelagiri and Sevattur plutons (e.g., Harmer, 1999). Models, such as AFC or binary mixing with crust material, cannot explain the wide isotopic variations in the Yelagiri and Sevattur syenites; therefore these isotopic variations are considered to reflect isotopic heterogeneity of enriched mantle. Trace element distribution diagrams of the Yelagiri and Sevattur syenites are characterized by pronounced enrichment in LIL and large negative Nb anomaly, indicating subduction related signature of their source mantle. In the northern part of South Indian granulite terrain, geochemical and isotopic signatures of other mantle-derived intrusive rocks with different ages from ca. 2.5 Ga to ca. 0.75 Ga also indicate the existence of enriched mantle (Kumar and Gopalan, 1991; Jayananda et al., 1995; Radhakrishna et al., 1995; Reddy et al., 1995; Kumar et al., 1998; Schleicher et al., 1998). Moreover, trace element characteristics of these rocks also show their subduction related signature. It is considered that the enriched mantle was formed by subduction-related geological processes, as hinted by Kumar et al. (1998), which probably occurred at a convergent margin along the southern and/or southeastern edge of the Dharwar craton, and survived convective disruption in the mantle, as Gondwana Research, V. 4,No. 4,2001
RODINIA, GONDWANA AND ASIA
sub-continental lithospheric mantle, from early Proterozoic until at least 750-800 Ma ago.
References Grady, J.C. (1971) Deep main faults in South India. J. Geol. SOC.India, V. 12, pp. 56-62. Harmer, R.E. (1999) The petrogenetic association of carbonatite and alkaline magmatism: constraints from the Spitskop complex, South Africa. J. Petrol., v. 40, pp. 525-548. Jayananda, M., Martin, H., Peucat, J. J . and Mahabaleswar, B. (1995) Late Archaean crust-mantle interactions: geochemistry of L E E enriched mantle derived magmas. Example of the Closepet batholith, southern India. Contrib. Mineral. Petrol., v. 119, pp. 314-329. Kumar, A. and Gopalan, K. (1991) Precise Rb-Sr age and enriched mantle source of the Sevattur carbonatites, Tamil Nadu, South India. Curr. Sci., v. 60, pp. 653-655. Kumar, A,, Charan, S.N., Gopalan, K. and Macdougall, J.D. (1998) A long-lived enriched mantle source for two Proterozoic carbonatite complexes from Tamil Nadu, southern India. Geochim. Cosmochim. Acta, v. 62, pp. 515-523.
707
Miyazaki, T., Kagami, H., Shuto, K., Morikiyo, T., Ram Mohan, V. and Rajasekaran, K.C. (2000) Rb-Sr geochronology, Nd-Sr isotopes and whole-rock geochemistry of Yelagiri and Sevattur syenites, Tamil Nadu, South India. Gondwana Res., v. 3, pp. 39-53. Moralev, V.M., Voronovski, S.N. and Borodin, L.S. (1975) New findings about the age of carbonatites and syenites from southern India. USSR Acad. Sci., v. 222, pp. 46-48. Rajesh, H.M. and Santosh, M. (1996) Alkaline magmatism in Peninsular India. Gondwana Res. Group Mem., No. 3, pp. 91-115. Reddy, B.M., Janardhan, A.S. and Peucat, J.J. (1995) Geochemistry, age and origin of alkaline and ultramafic rocks of Salem, Tamil Nadu, South India. J. Geol. SOC.India, v. 45, pp. 251-262. Schleicher, H., Todt, W., Viladkar, S.G. and Schmidt, F. (1997) Pb/Pb age determinations on Nuwania and Sevattur carbonatites of India: evidence for multi-stage histories. Chem. Geol., v. 140, pp. 261273. Schleicher, H., Kramm, U., Pernicka, E., Schidlowski, M., Schmidt, F., Subramanian, V., Todt, W. and Viladkar, S.G. (1998) Enriched subcontinental upper mantle beneath southern India: evidence from Pb, Nd, Sr and C - 0 isotopic studies on Tamil Nadu carbonatites. J. Petrol., v. 39, pp. 1765-1785.
Distribution Patterns of Gold Deposits in the Archaean Manica-Mutare-Odzi Greenstone Belt S. Mondlane'/*,P. Dirks1, H. Jelsma' and T. Blenkinsopl University of Zimbabwe, Geology Departmenf, 167 MP, Mount Pleasant, Harare, Zimbabwe Eduardo Mondlane University, Geology Department, PO. Box 257, Maputo, Mozambique The Manica - Mutare - Odzi (MMO) greenstone belt in West Mozambique and East Zimbabwe is a late Archaean linear structure that was intruded by the Penhalonga granodiorite at ca. 2.74 Ga. The ENE-trending belt comprises ultramafic metavolcanic rocks along the margins and coarse clastic metasedimentary rocks in the central zone. Rock units are intensely folded and a regional penetrative foliation has developed. Fold axes generally plunge shallowly either to the east or to the west and parallel the regional mineral lineation. The MMO greenstone belt has produced ca. 84 tonnes of Au (Forster et al., 1996) mainly from shear zone hosted, fault hosted and quartz vein hosted deposits. Mineralization follows corridors, which seem to control the localisation of the deposits. Fry analysis helps to define the underlying structural directions controlling the distribution of gold deposits, which may not be directly obvious otherwise. This is done by enhancing linear trends in an X - Y data points. Fry analysis was used to determine the spatial relationships of gold deposits. The input data were extracted from existing records (geological maps, bulletins and mine reports) of mine positions. Sixty out-of 243 deposits were field checked during the present study and were found to be within a maximum offset range of ca. 100 meters in Latitude and ca. 50 meters in Longitude. This offset is deemed acceptable, as it is not known exactly at what point the previous location was taken (main shaft or adit entrance, first adit, etc.). The Fry analysis is applied to sectors of the belt (Manica, Mutare and Odzi) for all deposit types. The method has been repeated for gold deposits grouped by type (fault/shear zoneGondwana Research, V. 4, No. 4, 2001
hosted (112 deposits), quartz vein (170 deposits), stratabound/ contact reefs (22 deposits), and stock work/disseminated (20 deposits) and finally for the deposits grouped according to sulphide paragenesis. When grouping the deposits by sulphides, deposit type and region (Manica, Mutare or Odzi) linear patterns that might be subdued when applying the Fry analysis to all deposit types at the same time can be revealed. The results interpreted visually and compared to structural and lineament analysis from satellite images suggest that gold mineralization in the MMO greenstone belt clusters repeatedly in corridors of about 5 km wide and generally oriented ENE-WSW, NW-SE or N-S. These corridors are not evident on the geological -structural maps of the area, suggesting an underlying control by deepseated structures without surface expression. Interpretation of the translation maps shows that the ENE-WSW direction is related to the structural trend of the MMO greenstone belt. The NW-SE and N-S directions are persistent at deposit type level of analysis, except for the contact reef and stratabound deposits, which only show the NE-SW direction. The NE-SW direction, in the all deposit type analysis, is masked by the structural trend of the belt. The stockwork and disseminated deposits, show NW-SE as the main direction in the translation maps. The shear zones and fault-hosted deposits are generally aligned NE-SW and NW-SE directions, probably forming conjugate sets. In addition an E-W direction is evident in the Odzi section of the belt while a N-S direction is evident in the Manica and Mutare sections of the belt. The quartz vein hosted deposits are more diffuse and show different orientations,