The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the f...The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the first appraisal of intermediate magmatism(diorite,monzonite,and monzodiorite)found in the Borjuri Pluton of Mikir Massif,which is the eastern extension of AMGC.The diorites are strongly metaluminous and exhibit enriched LREE([La/Yb]N=1.63–7.37)with respect to HREE([Gd/Yb]N=1.95–2.27).The studied rocks do not show any mineralogical or textural indication of metamorphism.Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting.The lower Mg#(33.49–38.69),low Cr(below detection limit),and Ni(27–41 ppm)contents along with elemental ratios such as Rb/Sr(0.32–0.95),La/Nb(0.49–4.21),and Nb/Ce(0.11–0.64)suggest a crustal source for the diorites.Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials.The P–T conditions of diorite emplacement(7.4 kbar,688℃)were calculated using the amphibole-plagioclase geothermobarometer.Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime.The Borjuri Pluton is in close proximity with the Kathalguri Pluton,which has been reported as a product of PanAfrican magmatism.In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites,we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.展开更多
The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons var...The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons varies from each other not only in major element content, aluminium saturation index, but also in ∑REE, δEu, and LREE/HREE, （La/Yb）N, （La/Sm） N and （Gd/Yb） N ratios. Uranium mineralization is mainly hosted by strong peraluminous granites, which has undergone intense fluid-rock interaction, and their REE compositions are characterised by M-type tetrad effects and lower ∑REE, δEu value, LREE/HREE, （La/Yb） N, （La/Sm） N and （Gd/Yb） N ratios.展开更多
基金DST-SERB grant vide Project No.CRG/2020/002635CSIR-JRF fellowship No.09/1236(11154)/2021-EMR-I。
文摘The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the first appraisal of intermediate magmatism(diorite,monzonite,and monzodiorite)found in the Borjuri Pluton of Mikir Massif,which is the eastern extension of AMGC.The diorites are strongly metaluminous and exhibit enriched LREE([La/Yb]N=1.63–7.37)with respect to HREE([Gd/Yb]N=1.95–2.27).The studied rocks do not show any mineralogical or textural indication of metamorphism.Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting.The lower Mg#(33.49–38.69),low Cr(below detection limit),and Ni(27–41 ppm)contents along with elemental ratios such as Rb/Sr(0.32–0.95),La/Nb(0.49–4.21),and Nb/Ce(0.11–0.64)suggest a crustal source for the diorites.Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials.The P–T conditions of diorite emplacement(7.4 kbar,688℃)were calculated using the amphibole-plagioclase geothermobarometer.Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime.The Borjuri Pluton is in close proximity with the Kathalguri Pluton,which has been reported as a product of PanAfrican magmatism.In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites,we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.
文摘The Guidong granitic complex is constituted by Luxi pluton, Xiazhuang pluton, Maofeng pluton, Sundong pluton, Aizi pluton and Siqian pluton, which intruded in Indosinian and early Yanshanian Periods. These plutons varies from each other not only in major element content, aluminium saturation index, but also in ∑REE, δEu, and LREE/HREE, （La/Yb）N, （La/Sm） N and （Gd/Yb） N ratios. Uranium mineralization is mainly hosted by strong peraluminous granites, which has undergone intense fluid-rock interaction, and their REE compositions are characterised by M-type tetrad effects and lower ∑REE, δEu value, LREE/HREE, （La/Yb） N, （La/Sm） N and （Gd/Yb） N ratios.
