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The Rajahmundry Trap Basalts(RTB) are erupted through fault-controlled fissures in the Krishna-Godavari Basin(K-G Basin) of Godavari Triple Junction,occurring as a unique outcrop sandwiched between Cretaceous and Tertiary sediments along the east coast of India.Detailed geochemical studies have revealed that RTB are mid-Ti(1.74-1.92) to high-Ti(2.04-2.81) basalts with a distinct quartz tholeiitic parentage.MgO(6.2-13.12 wt.%),Mg~#(29-50) and Zr(109-202 ppm) suggest that these basalts evolved by fractional crystallization during the ascent of the parent magma along deep-seated fractures.Moderate to high fractionation of HREE,as indicated by(Gd/Yb)N ratios(1.71-2.31) of RTB,suggest their generation through 3-5%melting of a Fe-rich mantle corresponding to the stability fields of spinel and garnet peridotite at depths of 60-100 km.Low K_2O/P_2O_5(0.26-1.26),high TiO_2/P_2O_5(6.74-16.79),La/Nb(0.89-1.45),Nb/Th > 8(8.35-13),negative anomalies at Rb reflect minimum contamination by granitic continental crust.(Nb/La)_(PM) ratios(0.66-1.1) of RTB are attributed to endogenic contamination resulted through recycling of subducted oceanic slab into the mantle.Pronounced Ba enrichment with relative depletion in Rb indicates assimilation of Infra- and Inter-trappean sediments of estuarine to shallow marine character.Geochemical compositions such as Al_2O_3/TiO_2(3.88-6.83),medium to high TiO_2(1.74-2.81 wt.%).positive Nb anomalies and LREE enrichment of these RTB attest to their mantle plume origin and indicate the generation of parent magma from a plume-related enriched mantle source with EM 1signature.Ba/Th(46-247),Ba/La(3.96-28.51) and Th/Nb(0.08-0.13) ratios suggest that the source enrichment process was marked by recycling of subduction-processed oceanic crust and lithospheric components into the mantle.Zr/Hf(37-41) and Zr/Ba(0.51-3.24) indicate involvement of an asthenospheric mantle source.The Rajahmundry basalts show affinity towards FOZO(focal zone mantle) and PSCL(post-Archaean subcontinental lithosphere) which reflect mixing between asthenospheric and lithospheric mantle components in their source.Origin of RTB magma is attributed to plume-lithosphere interaction and the upward movement of melt is facilitated by intrabasinal deep-seated faults in the K-G Basin.
The Rajahmundry Trap Basalts (RTB) are erupted through fault-controlled fissures in the Krishna-Godavari Basin (KG Basin) of Godavari Triple Junction, occurring as a unique outcrop sandwiched between Cretaceous and Tertiary sediments along the east coast of India. Betted geochemical studies have revealed that RTB are mid-Ti (1.74-1.92) to high-Ti (2.04-2.81) basalts with a distinct quartz tholeiitic parentage. MgO (6.2-13.12 wt.%), Mg ~ # (109-202 ppm) suggest these these basalts evolved by fractional crystallization during the ascent of the parent magma along deep-seated fractures. Moderate to high fractionation of HREE, as indicated by (Gd / Yb) N ratios (1.71-2.31) of RTB, suggest their generation through 3-5% melting of a Fe-rich mantle corresponding to the stability fields of spinel and garnet peridotite at depths of 60-100 km.Low K 2 O / P 2 O 5 (0.26-1.26), high TiO 2 / P 2 O 5 ( 6.74-16.79), La / Nb (0.89-1.45), Nb / Th> 8 (8.35-13), negative anomalies at Rb reflect minimum contamination by granitic c (Nb / La) _ (PM) ratios (0.66-1.1) of RTB are attributed to endogenic contamination resulted by recycling of subducted oceanic slab into the mantle. Pronounced Ba enrichment with relative depletion in Rbinduced assimilation of Infra-and Inter-trappean sediments of estuarine to shallow marine character. Geochemical compositions such as Al 2 O 3 / TiO 2 (3.88-6.83), medium to high TiO 2 (1.74-2.81 wt.%). Positive Nb anomalies and LREE enrichment of these RTB attest to their mantle plume origin and indicate the generation of parent magma from a plume-related enriched mantle source with EM 1signature.Ba/Th(46-247), Ba / La (3.96-28.51) and Th / Nb (0.08-0.13) ratios suggest that the source enrichment process was marked by recycling of subduction-processed oceanic crust and lithospheric components into the mantle. Zr / Hf (37-41) and Zr / Ba (0.51-3.24) indicate involvement of an asthenospheric mantle source. The Rajahmundry basalts show affinity towards FOZO (focal zone mantle) and PSCL (post-Archaean subcontinental lithosphere) which reflects mixing between asthenospheric and lithospheric mantle components in their source. Origin of RTB magma at attributed to plume-lithosphere interaction and the upward movement of melt is facilitated by intrabasinal deep-seated faults in the K-G Basin.