African orogeny events. Whereas clinopyroxene, amphibole, titanite and apatite fractionation seems to have affected the nephelinite, nepheline syenite and syenite, carbonatite is affected by fractionation of calcite, dolomite, ankerite, pyroxene, apatite, magnetite, mica, and pyrochlore. Trace elements and Sr-Nd-Pb-C-O isotopic compositions of these ARCs strongly suggest a subcontinental lithospheric mantle source, that is enriched either by distribution of subducted crustal material or by metasomatism of mantle-derived fluids, for the generation of ARCs. Despite some isotopic variability that can result from crustal contamination, a trend showing enrichment in 87 Sr/ 86 Sr i (0.702 to 0.708) and depletion in ε Nd(i) (-1.3 to -14.1) over a 2 Gyr duration indicates temporal changes in the lithospheric/ asthenospheric source of ARCs, due to periodic enrichment of the source by mantle-derived fluids. ARC generation starts in an intracontinental rift setting (beginning of Wilson cycle). These early-formed ARCs are carriedto 100 km depths during continental collision (termination stage of Wilson cycle) and undergo extensive

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The ca. 66 Ma Girnar Complex of the Deccan Traps consists of various mafic to silicic rocks and provides a unique setting for understanding the dynamics of magma chamber processes. The intrusive alkaline rocks in Girnar are diorites/monzodiorites and contain syenite/nepheline syenite veins. Several (alkaline) mafic dykes cut the alkaline rocks. These rocks are surrounded by intrusive tholeiitic gabbro and extrusive basaltic flows and a silicic (SiO2 >65 wt.%) ring dyke at the outer margin of the complex. The tholeiitic gabbro and basaltic lavas have relatively flat light rare earth element (REE) patterns (La/SmN ~0.8 to 1.8) with positive Eu anomalies of 1.1-1.3. The tholeiitic basalts formed by 3-5% partial melting of an incompatible element depleted mid-ocean ridge basalts (MORB)-like source. Accumulating ca. 20-30% of (olivine, orthopyroxene, clinopyroxene, and plagioclase) crystals from the tholeiitic melt generated the tholeiitic gabbro. The alkaline rocks display enriched light REE patterns (La/SmN ~5.0 to 7.8) consistent with (~9%) partial melting of a spinel lherzolite source, different from the MORB-like source for tholeiitic rocks. The subsequent 58-72% fractional crystallization of olivine, clinopyroxene, plagioclase, orthoclase, spinel, and apatite mineral assemblage formed the alkaline rocks. Reverse and oscillatory zoning in plagioclase (An30 to An50) phenocrysts of the silicic rocks suggest that convective movement of crystals in a magma chamber led to initial crystallization of high-An plagioclase in the hotter zone of the magma chamber, followed by addition of low-An plagioclase in cooler regions of the magma chamber. Pressure estimates from shattered (xenocryst or antecryst) clinopyroxene crystals in silicic rocks give a minimum value of 450 MPa. Ti-in-quartz geothermometry gives a crystallization temperature between 690 °C to 1080 °C. The distinct isotopic composition of the silicic rocks (87Sr/86Sri = 0.7204-0.7275, εNd(i) = -6.8 to -7.3, 206Pb/204Pbi = 18.74-19.02, 207Pb/204Pbi = 15.76-15.79, 208Pb/204Pbi = 39.63-40.03, εHf(i) = -6.0 to -7.3) further indicates that the silicic rocks assimilated 7 to 9% granitic basement rocks. Overall, therefore, the Girnar Complex started to form with the emplacement of mafic rocks (both alkaline and tholeiitic) in the central part along a reactivated fault lineament and silicic rocks along the concentric marginal fault. Petrography, mineral chemistry, and whole-rock geochemical and Sr-Nd-Pb-Hf isotope ratios of the Girnar Complex rocks indicate that despite the close spatial association of tholeiitic gabbro and basalt, alkaline rocks, and silicic rocks, these rocks originated from multiple sources and evolved in a complex magma drainage and storage network in a continental setting of the Deccan Large Igneous Province (LIP).

<p>Close spatial association of plutonic and volcanic rocks in Large Igneous Provinces is very rare. Occurrence of various mafic rocks (syeno-diorite, gabbro, basalt and mafic dyke) and silicic rocks in the Girnar volcano-plutonic complex of Deccan Traps provides a unique opportunity to understand complex petrogenetic processes. Alkaline rocks (syeno-diorite and mafic dyke) display an enriched LREE pattern (La/Sm<sub>N </sub>~5.0 to 7.8), whereas the tholeiitic gabbro and basalt show a relatively flat LREE pattern (La/Sm<sub>N </sub>~0.8 to 1.8) with a positive Eu anomaly (1.1 to 1.3). Trace elements modelling of alkaline rock compositions are consistent with their origin by 5–9% partial melting of a spinel lherzolite source, with the melt experiencing 74–88% fractional crystallization. Tholeiitic gabbro and basalt could be generated from 20% and ~5% melting of a depleted MORB source, respectively. Distinct isotopic composition of silicic rocks (<sup>87</sup>Sr/<sup>86</sup>Sr<sub>i </sub>= 0.7204–0.7275, ε<sub>Nd(i)</sub> = −6.8 to −7.3, <sup>206</sup>Pb/<sup>204</sup>Pb<sub>i </sub>= 18.74–19.02, <sup>207</sup>Pb/<sup>204</sup>Pb<sub>i </sub>= 15.76–15.79, <sup>208</sup>Pb/<sup>204</sup>Pb<sub>i </sub>= 39.63–40.03, ε<sub>Hf(i) </sub>= −6.0 to −7.3) indicate an origin from melting of a crustal source contaminated with (≤5%) mantle-derived mafic melts. The presence of shattered clinopyroxene crystals in silicic rocks and variation in Ti content of quartz are attributed to a sudden release of pressure during magma ascent. The Girnar Complex is emplaced in a reactivated fault lineament where mafic rocks (both alkaline and tholeiitic) were uplifted by several kilometers after its formation in a shallow magma chamber. Silicic rocks were emplaced along the concentric marginal fault of the Girnar Complex, synchronously or just after this uplift event.</p>