Paper Number: 220
Petrology and Geochemistry of Chintalapalle lamproite , Eastern Dharwar Craton, Southern India.
Pankaj, Praveer.1, Kumar, Alok.2and Rao, K.K.3
1Geological Survey of India, FTC, SU:AP&T, Hyderabad, India. prpankaj@gmail.com
2Geological Survey of India, Project Diamond, Hyderabad, India
3Geological Survey of India, NMH-II office, Seminary hills, Nagpur,Maharashtra, India
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A new lamproite has been reported in Eastern Dharwar Craton in Chintalpalle village, Mahbubnagar district, Telangana. Megascopically the lamproite is, fine-grained, highly altered, grey, hard and compact, carbonatised, containing rounded to elliptical pseudomorphs of microphenocrysts of feldspar and platy to fibrous potassic richterite in a groundmass of carbonate, chlorite, apatite and sphene.
It is ultrapotassic i.e., K2O/Na2O >3wt% and peralkaline nature with K2O+Na2O/Al2O3>0.7 wt%. The Chintalapalle lamproite together with those of Krishna, Vattikod, Ramadugu and Cuddapah Basin lamproites shows a large regional framework of mantle magmatism emplaced in and around the Cuddapah basin.
Petrographic studies reveal the presence of porphyritic texture comprising microphenocrysts of sanidine and richterite set in a groundmass rich in carbonate, and chlorite with rutile and titanite as accessory phases.
This Lamproite is characterized by low SiO2 (43.48 – 44.96%), low Al2O3 (6.49-6.54%), Fe2O3 (9.82-10.07%), high MgO (11.53 –12.18%), high TiO2 (3.44-3.48%), high K2O(3.51-3.67%) with moderate content of Na2O (1.09-1.12%). The lamproite shows elevated levels of Ba (395-494ppm), Ni (356-381ppm), Cr (329-350pm) and Sc (15-1.9) ppm.
Figure 1: Spider plot (Nakamura 1974) of REE data of Chintalpalle lamproite compared with other Indian and West Kimberley Lamproites.
The LREE enrichment varies between 250-350 with respect of Chondrite (Nakamura, 1974) and the chondrite normalized REE plot indicates that this lamproite compares well with other Indian and West Kimberley lamproites(Figure-1). Geochemical characteristics such as high Mg#(56.40-57.87), abundance of compatible elements (Ni, Cr and Co), and low HREE contents imply a refractory mantle source that had experienced previous melt extraction (e.g. Mitchell and Bergman 1991). High (La/Yb)n varying between 49.68-55.17 and low HREE contents also imply generation of the lamproite magma by small degrees of partial melting from an enriched (metasomatised) mantle source within the garnet stability field.
References:
[1] Chalapathi Rao et al.(2004). Journal of Petrology.45(5):907-948
[2] Chalapathi Rao et al.(2014). Lithos.196-197:150-168
[3] Jia et al. (2003).Earth and Planetary Science Letters.215:43-56
[4] Mitchell R.H. and Bergman S.C. (1991) Petrology of lamproites. Plenum Press. 447