ORIGINAL PAPER Geochemical investigation of a semi-continuous extrusive basaltic section from the Deccan Volcanic Province, India: implications for the mantle and magma chamber processes Kopparapu Vijaya Kumar • Chakradhar Chavan • Sariput Sawant • K. Naga Raju • Prachiti Kanakdande • Sangita Patode • Krishna Deshpande • S. K. G. Krishnamacharyulu • T. Vaideswaran • V. Balaram Received: 6 April 2009 / Accepted: 22 October 2009 / Published online: 12 November 2009 Ó Springer-Verlag 2009 Abstract Spatial and temporal variations in the geo- chemistry of an extrusive basaltic section of Deccan traps record progressive changes in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present work we have carried out detailed field, petrographic, density and mag- netic susceptibility, and geochemical investigations on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow magma chambers in CFB magmatism. Four for- mations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed–Ambajogai area with increasing elevation. Our studies indicate that: (1) the Karanja Formation repre- sents a major magma addition, as indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al 2 O 3 , Na 2 O, K 2 O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimi- lation fractional crystallization, crystal-laden magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence of olivine gabbro–leucogabbro–oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration for the Gangakhed– Ambajogai section basalts is *2 kbar (*6 km depth); (5) petrophysical parameters act as proxies for magmatic pro- cesses; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the DVP; (7) parental basalts to some of the red boles, consid- ered as formation boundaries, might represent small degree partial melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance of mapping specific strati- graphic intervals in limited areas to understand mantle and magma chamber processes relevant to CFB magmatism. Keywords Continental flood basalts Á Deccan Á Petrography Á Petrophysics Á Geochemistry Á Dynamic melting Á Magma chambers Introduction to processes controlling erupted basalt compositions in continental flood basalt provinces Most erupted basaltic lavas in continental flood basalt (CFB) provinces do not represent mantle-derived primary melt compositions, but are end products of complex magma chamber processes (Cox 1980; Farnetani et al. Communicated by T.L. Grove. K. Vijaya Kumar (&) Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2215, USA e-mail: vijay_kumar92@hotmail.com K. Vijaya Kumar Á S. Patode Á K. Deshpande Á S. K. G. Krishnamacharyulu School of Earth Sciences, SRTM University, Nanded 431606, Maharashtra, India C. Chavan Á S. Sawant Á K. Naga Raju Á P. Kanakdande Á V. Balaram Geochemistry Division, NGRI, Hyderabad 500007, Andhra Pradesh, India T. Vaideswaran Op. Andhra Pradesh, Geological Survey of India, Southern Region, Bandlaguda, Hyderabad 500068, Andhra Pradesh, India 123 Contrib Mineral Petrol (2010) 159:839–862 DOI 10.1007/s00410-009-0458-6