Rb-Sr age of the Sivamalai alkaline complex,Tamil Nadu |
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| Authors: | T V Subba Rao B L Narayana K Gopalan |
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| Institution: | (1) National Geophysical Research Institute, 500007 Hyderabad, India |
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| Abstract: | The Sivamalai alkaline complex comprises ferro-, pyroxene-hornblende- and nepheline-syenites. Field relations show that the
nepheline syenites followed the emplacement of non-feldspathoidal syenites. Mineralogical data on the syenite suite have been
reviewed. The Sivamalai alkaline rocks are not strongly enriched in rare-earth elements like most miaskites. Rb-Sr isotopic
analyses of a suite of six samples from the various members of the complex define an isochron corresponding to an age of 623
±21 Ma (2σ) and initial Sr ratio of 0.70376 ±14 (2σ). This is consistent with a model of fractional crystallization of a parent magma
derived from an upper mantle source with apparently no isotopic evidence for more than one magma source for the complex. The
Sivamalai alkaline complex represents a Pan-African alkaline magmatic event in the southern granulite terrane of Peninsular
India. |
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| Keywords: | Sivamalai alkaline complex Rb-Sr whole-rock isochron initial strontium ratio fractional crystallization rare-earth element abundances |
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