Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture ...Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture and consists of feldspar （Or55Ab43 to Or25Ab71）, ferro-pargasite/ferro-pargasite horn-blende, hastingsite, pyroxene （Wo47, En5, Fs46）, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene （Wo47-50, En22-39, Fs12e31） set in a groundmass matrix of alkali feldspar （Or99Ab0.77 to Or1.33Ab98）, titanite and magnetite. In comparison to AFS-1, higher elemental concentra-tions of Ba, Sr and PREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is w1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.展开更多
Luku alkali syenite is distributed throughout the southern end of the Hongge basic-ultrabasic intrusion in Panzhihua,Sichuan,SW China.Using LA-ICP-MS,the alkali syenite intrusion yielded a zircon U-Pb age of_(2)64.5&#...Luku alkali syenite is distributed throughout the southern end of the Hongge basic-ultrabasic intrusion in Panzhihua,Sichuan,SW China.Using LA-ICP-MS,the alkali syenite intrusion yielded a zircon U-Pb age of_(2)64.5±1.6 Ma,concordant with the ages of the E’meishan large igneous province(260 Ma).The intrusion displayed silica-saturated,Al-adequate and alkali-rich signatures,with SiO_(2)62.07%-64.04%,Al_(2)O_(3)16.26%-16.79%and Na_(2)O+K_(2)O 9.17%-9.91%(averaging 9.31%).The rock falls into the alkaline zone on the SiO_(2)-A.R.diagram,as well as in the potassium zone on the K_(2)O-Na_(2)O diagram,indicating a potassium alkaline rock.The rock has a low total REE concentration and showed enrichment in LREE(LREE/HREE=7.06-7.95),typical negative Eu anomalies(δEu=0.73-0.80),trace element deficiencies in LILEs(Ba,K,Sr,Zr)and enrichment in HFSEs(Th,U,Nd,Sm,Ta and Nb),displaying crust and mantle element information.Zircons show a strong positive Ce anomaly and negative Eu anomaly,similar to the characteristics of crustal source magmatic zircon,however the(Lu/Gd)N ratio ranges from 1.48 to 3.17,and the(Yb/Sm)N ratio ranges from 38.49 to 77.15,which are similar to the characteristics of mantle-derived magmatic zircon.In the La/Yb-δEu correlation diagram,the data plots near the boundary between crust type and crust-mantle type.From the combined‘trinity’spatiotemporal relationship of Indosinian intermediate-acid alkali intrusive rocks in the Panxi area with E’meishan basalt and basic-ultrabasic intrusive rocks,the regional tectonic evolution and the partial melting model of the most intraplate magma sources,we believe that the Luku alkali syenite in Sichuan was formed from the partial melting of a crust-mantle source material,due to underplating of the mantle plume basic magma.展开更多
基金financial support from Department of Science and Technology, New Delhi in the form of research grant (ESS/16/295/2006) to KRH and NVCR is acknowledged
文摘Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture and consists of feldspar （Or55Ab43 to Or25Ab71）, ferro-pargasite/ferro-pargasite horn-blende, hastingsite, pyroxene （Wo47, En5, Fs46）, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene （Wo47-50, En22-39, Fs12e31） set in a groundmass matrix of alkali feldspar （Or99Ab0.77 to Or1.33Ab98）, titanite and magnetite. In comparison to AFS-1, higher elemental concentra-tions of Ba, Sr and PREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is w1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.
基金This work was supported by the China Geological Survey(Grant Nos.DD20189501 and DD20190446).
文摘Luku alkali syenite is distributed throughout the southern end of the Hongge basic-ultrabasic intrusion in Panzhihua,Sichuan,SW China.Using LA-ICP-MS,the alkali syenite intrusion yielded a zircon U-Pb age of_(2)64.5±1.6 Ma,concordant with the ages of the E’meishan large igneous province(260 Ma).The intrusion displayed silica-saturated,Al-adequate and alkali-rich signatures,with SiO_(2)62.07%-64.04%,Al_(2)O_(3)16.26%-16.79%and Na_(2)O+K_(2)O 9.17%-9.91%(averaging 9.31%).The rock falls into the alkaline zone on the SiO_(2)-A.R.diagram,as well as in the potassium zone on the K_(2)O-Na_(2)O diagram,indicating a potassium alkaline rock.The rock has a low total REE concentration and showed enrichment in LREE(LREE/HREE=7.06-7.95),typical negative Eu anomalies(δEu=0.73-0.80),trace element deficiencies in LILEs(Ba,K,Sr,Zr)and enrichment in HFSEs(Th,U,Nd,Sm,Ta and Nb),displaying crust and mantle element information.Zircons show a strong positive Ce anomaly and negative Eu anomaly,similar to the characteristics of crustal source magmatic zircon,however the(Lu/Gd)N ratio ranges from 1.48 to 3.17,and the(Yb/Sm)N ratio ranges from 38.49 to 77.15,which are similar to the characteristics of mantle-derived magmatic zircon.In the La/Yb-δEu correlation diagram,the data plots near the boundary between crust type and crust-mantle type.From the combined‘trinity’spatiotemporal relationship of Indosinian intermediate-acid alkali intrusive rocks in the Panxi area with E’meishan basalt and basic-ultrabasic intrusive rocks,the regional tectonic evolution and the partial melting model of the most intraplate magma sources,we believe that the Luku alkali syenite in Sichuan was formed from the partial melting of a crust-mantle source material,due to underplating of the mantle plume basic magma.
