Mantle and Crustal Contributions to the Mount Girnar Alkaline Plutonic Complex and the Circum-Girnar Mafic-silicic Intrusions of Saurashtra, Northwestern Deccan Traps

Continental flood basalt (CFB) provinces of the world are made up of vast mafic lava fields, along with large dyke-sill swarms and plutonic complexes (e.g. Macdougall, 1988; Mahoney & Coffin, 1997, and references therein). The mafic lavas are dominantly tholeiitic basalts and basaltic andesites. However, alkaline mafic and evolved lavas and intrusions (such as of alkali basalt, basanite, nephelinite, syenite) are also often found, either in close association with the tholeiitic lavas (e.g. Mahoney et al., 1985; Talusani, 2010; Haase et al., 2019) or geographically separated from the tholeiitic suites (e.g. Simonetti et al., 1998; Chatterjee, 2021). The tholeiitic and alkaline mafic magmas have been interpreted to reflect different degrees of partial melting of the same mantle source, or as derived from different mantle sources (e.g. Mahoney et al., 1985; Melluso et al., 2006; Haase et al., 2019). Dyke-sill swarms and plutonic complexes in CFB provinces contain a large number of individual intrusions and typically show considerable compositional diversity, with ultramafic rocks, gabbros, diorites, syenites, and granophyres well represented. The dyke swarms of the Palaeogene North Atlantic Igneous Province are world-famous, and plutonic complexes in the province (such as Skye, Mull, and Ardnamurchan in western Scotland or Skaergaard in east Greenland) are where many well-established ideas in igneous petrology were developed and tested (e.g. Harker, 1904; Wager & Deer, 1939; McBirney, 1975; Brooks, 2011). A plutonic complex comparable to these, though much less internationally known, is the Girnar plutonic complex in the northwestern Deccan Traps CFB province. Composed of gabbros and diorites, with innumerable dykes of nepheline syenites and lamprophyres, it was recognised early as an excellent site to study magmatic differentiation (e.g. Fedden, 1884; Mathur et al., 1926). The complex intrudes tholeiitic lava flows, and a large silicic ring dyke and many mafic dyke-sill intrusions intrude these lava flows in the region surrounding the complex. These varied rock units therefore provide an excellent opportunity to understand the petrogenesis of tholeiitic, alkaline and silicic magmatism and their potential relationships in a CFB province. We achieve this understanding by combining geological field relationships, petrography and mineral chemistry, and whole-rock geochemistry (including Sr-Nd-Pb isotopic data).