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Title: Enigmatic association of the carbonatite and alkali-pyroxenite along the Northern Shear Zone, Purulia, West Bengal: A saga of primary magmatic carbonatite
Authors: Chakrabarty A.
Sen A.K.
Published in: Journal of the Geological Society of India
Abstract: The Purulia carbonatite, 'carbonatite'-'alkali-pyroxenite'-'apatite- magnetite rock' association, is located at Beldih area of Purulia district, West Bengal and falls within the 100 km long Northern Shear Zone (NSZ). Published literature suggests that the Purulia carbonatite was formed by the process of liquid immiscibility from under-saturated silicate parent magma. However, no silica under-saturated rocks like ijolite, nepheline-syenite etc. is known from the area. The trace element geochemistry (Ba/La, Nb/Th, Nb/Pb and Y/Ce ratios in the present study) also does not support this view. Present study indicates that the Purulia carbonatite is enriched in ?REE and incompatible elements but the carbonatite is also poorer in Nb, Th and Pb compared to the world average of calicocarbonatites. The lower value of Nb is characteristics of carbo(hydro)thermal carbonatite where carbonatite is associated with alkali-pyroxenite and suggests probable origin of the carbonatite as carbothermal residua evolved from an unknown parentage. However, the field, petrographic and geochemical data indicate the genesis of this carbonatite from a primary carbonatitic magma of mantle decent. The 87Sr/ 86Sr ratio of the carbonatite and apatite separated from the carbonatite (?0.703) implies primary magmatic derivation of the Purulia carbonatite. Close similarity of the apatite of the apatite-magnetite rock with the mantle apatite (of type Apatite B) indicates that they are also of primary magmatic origin. The present work portrays a unique example where primary magmatic carbonatite is associated with the alkali-pyroxenite. © 2010 Geological Society of India.
Citation: Journal of the Geological Society of India (2010), 76(5): 403-413
Issue Date: 2010
Keywords: Carbonatite
Carbothermal residua
Liquid immiscibility
Mantle apatites
Northern Shear Zone
ISSN: 167622
Author Scopus IDs: 25121521500
Author Affiliations: Chakrabarty, A., Department of Earth Sciences, IIT Roorkee, Roorkee 247 667, India, Department of Geology, Durgapur Government College, Durgapur 713 214, India
Sen, A.K., Department of Earth Sciences, IIT Roorkee, Roorkee 247 667, India
Funding Details: Acknowledgements: AC acknowledges MHRD, CSIR (India) and ESKAS (Swiss Federal Commission scholarship, Switzerland) for providing scholarships for carrying out the work as part of his Doctoral programme. Help rendered by Prof. Christoph A. Heinrich, Prof. Albrecht von Quadt (ETHZ, Switzerland) and Dr. Pulok Mukherjee (WIHG, Dehradun) are thankfully acknowledged. The authors acknowledge the Director, Wadia Institute of Himalayan Geology, Dehradun for providing the ICP-MS facility. The funding provided by the CSIR, New Delhi for research project (no. 24(0286)/05/EMR-II) is gratefully acknowledged. Authors express sincere thanks to the anonymous reviewer for constructive suggestions to improve the manuscript.
Corresponding Author: Sen, A. K.; Department of Earth Sciences, IIT Roorkee, Roorkee 247 667, India; email:
Appears in Collections:Journal Publications [ES]

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