Post-tholeiite rifting and genesis of ultramafic lamprophyres at ~65 Ma in the Deccan Large Igneous Province, India

• DOI: 10.5194/egusphere-egu24-4288
• Publication Date: 2024-03-08T13:34:41Z
• Authors: Anshika Singh; Ashish Dongre
• Keywords: Ultramafic rock; Deccan Traps

Small-volume alkaline magmatism has now garnered due attention in geosciences, wherein these rocks provide essential information about deep mantle processes, geochemical composition, and the prevailing geodynamics. The continental of deep-seated ultramafic lamprophyres (UML) is spatially temporally linked with breakup rifting. Additionally, they have gained significant terms mineralization. Deccan hosts one most extensive peculiar suites lamprophyre complexes India, this holds valuable geological to unveil geodynamic processes implications on enrichment/depletion SCLM during times. present research delves into mineral whole-rock compositions paleomag dating from West Coast Alkaline Complex (WCAC) Large Igneous Province. study for relation Réunion plume, associated main phase tholeiite magmatism, initiation rifting western Indian subcontinental margin, separation Seychelles subcontinent, as well role lithosphere thinning triggering magmatism. WCAC are principally composed olivine phlogopite phenocrysts/ macrocryst embedded a mesostasis carbonate, clinopyroxene, olivine, nepheline, spinel, melilite groundmass. presence titanian aluminous phlogopite, Al-enriched spinels high Fe2+/(Fe+Mg) ratios characteristic features lamprophyres. They primitive, undersaturated silica (SiO2: 38.43 – 38.99), rich MgO (up 10 wt. %), TiO2 4.2 light rare earth elements. Mineral genetic classification schemes demonstrate resemblance lamprophyres.  High LREE/HREE (La/Yb= 75-82) ratios, similar UMLs reported globally, low Ba/Rb Rb/Sr exhibit predominance amphibole source. Geochemical investigations inarguably trace their genesis back enriched garnet lherzolite mantle, metasomatised by silicate carbonate veins. show compositional similarity global damtjernites derivation moderate pressure depth (3-4 GPa) corresponding 90-100 km thick lithospheric mantle. Paleomagnetic studies support intrusion lamprophyres, predominantly chron C29n, thereby substantiating radiometric eruption age at ~65 Ma. Seismic tomography models reveal current thickness approximately 50 beneath WCAC, suggesting delamination after 65 UML resulted rift, which ultimately led subcontinent Seychelles. impetus behind emplacement dykes intricately tied passive external plate boundary forces, surpassing influence Reunion plume. presumably occurred other continued response greater plate-tectonic stresses region persistent weakness.