EGU22-446
https://doi.org/10.5194/egusphere-egu22-446
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Magmatic evolution of Girnar volcano-plutonic complex of Deccan Traps, India: Sr-Nd-Pb-Hf isotopic evidence of multiple sources

Mahesh Halder1, Debajyoti Paul2, and Andreas Stracke3
Mahesh Halder et al.
  • 1Department of Earth Sciences, Indian Institute of Technology Kanpur, Kanpur 208016, India (maheshh@iitk.ac.in)
  • 2Department of Earth Sciences, Indian Institute of Technology Kanpur, Kanpur 208016, India (dpaul@iitk.ac.in)
  • 3Westfälische Wilhelms-Universität, Institut für Mineralogie, Münster, Germany (eastra_01@uni-muenster.de)

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/SmN ~5.0 to 7.8), whereas the tholeiitic gabbro and basalt show a relatively flat LREE pattern (La/SmN ~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 (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) 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.

How to cite: Halder, M., Paul, D., and Stracke, A.: Magmatic evolution of Girnar volcano-plutonic complex of Deccan Traps, India: Sr-Nd-Pb-Hf isotopic evidence of multiple sources, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-446, https://doi.org/10.5194/egusphere-egu22-446, 2022.

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