This Aliwula area in paper reports lithologic features, K-Ar age and geochemical data of riebeckite granophyres from the southern Da Hinggan Mts., aiming to reveal the petrogenesis of riebeckite granophyres. K- Ar age...This Aliwula area in paper reports lithologic features, K-Ar age and geochemical data of riebeckite granophyres from the southern Da Hinggan Mts., aiming to reveal the petrogenesis of riebeckite granophyres. K- Ar age of riebeckite granophyres is 126± 2 Ma, implying that the riebeckite granophyres formed in the Early Cretaceous. The granophyres are rich in riebeckites and with a lot of melt-fluid inclusion in its quartz pheno- crysts. The granophyres are characterized by extensive enrichment in Si02, FeO, and （Na20 ＋ K20） and de- pletion in MgO and CaO, strong negative Eu anomalies and strong positive Ce anomalies. Additionally, the rie- beckite granophyres not only have high total REE contents and display enrichment of HFSEs （for example Zr, Hf, Nb, Ta）, but also are strong in depletion of LILEs （ e. g. Ba, Sr） as well as high Ga/A1 ratios. Primitive mantle-normalized REE pattern significantly displays REE M-W tetrad effect. REEs fractionate evidently and highly enrich in LREE, but are uneven distribution in the rocks. Taken together, we conclude that the riebeck- ite granophyres are similar to typical A-type granite, which could be derived from stretching environments in the Early Cretaceous. The granophyres originated from residual melt which underwent highly differentiation process, and were formed in magmatic-hydrothemal transition stage at last.展开更多
Homret Ghannam alkali feldspar granite(HGAFG)in the central Eastern Desert(CED)of Egypt represents a distinctive example of late Neoproterozoic magmatism in the Arabian-Nubian Shield(ANS).This study integrates field o...Homret Ghannam alkali feldspar granite(HGAFG)in the central Eastern Desert(CED)of Egypt represents a distinctive example of late Neoproterozoic magmatism in the Arabian-Nubian Shield(ANS).This study integrates field observations,petrography,mineral chemistry(EMPA),and whole-rock geochemistry to investigate its petrogenesis,geodynamic evolution,and rare-metal potential.HGAFG comprises two cogenetic varieties,alkali feldspar granite and riebeckite-bearing granite,hosting rare-metal minerals such as zircon,fluorite,columbite and apatite.HGAFG exhibits diagnostic A-type geochemical characteristics,including high SiO₂contents(73.81-77.86 wt%),metaluminous to mildly peralkaline composition(ASI:0.92-1.03),enrichment in HFSE(Zr≈791.80 ppm,Nb≈68.12 ppm,Y≈90.81 ppm)andΣREE(103.40-475.57 ppm),and pronounced negative Eu anomalies(Eu/Eu^(*)=0.07-0.20).Zircon saturation thermometry yields high crystallization temperatures(TZr≈908.87℃)and low emplacement pressures(1.46 kbar)under reducing conditions(ƒO_(2)≈−11.5).The mineralogical and geochemical results reveal that HGAFG originated from a hybrid,fluorine-rich magma generated by anatexis of lower crust,followed by extensive fractional crystallization,during late post-collisional extension associated with lithospheric delamination.The reduced nature and fluorine enrichment of HGAFG magma promoted the mineralization of Nb-Ta-REE phases,highlighting its significance as a fertile,high-temperature product of the terminal magmatic stage in ANS evolution.展开更多
文摘This Aliwula area in paper reports lithologic features, K-Ar age and geochemical data of riebeckite granophyres from the southern Da Hinggan Mts., aiming to reveal the petrogenesis of riebeckite granophyres. K- Ar age of riebeckite granophyres is 126± 2 Ma, implying that the riebeckite granophyres formed in the Early Cretaceous. The granophyres are rich in riebeckites and with a lot of melt-fluid inclusion in its quartz pheno- crysts. The granophyres are characterized by extensive enrichment in Si02, FeO, and （Na20 ＋ K20） and de- pletion in MgO and CaO, strong negative Eu anomalies and strong positive Ce anomalies. Additionally, the rie- beckite granophyres not only have high total REE contents and display enrichment of HFSEs （for example Zr, Hf, Nb, Ta）, but also are strong in depletion of LILEs （ e. g. Ba, Sr） as well as high Ga/A1 ratios. Primitive mantle-normalized REE pattern significantly displays REE M-W tetrad effect. REEs fractionate evidently and highly enrich in LREE, but are uneven distribution in the rocks. Taken together, we conclude that the riebeck- ite granophyres are similar to typical A-type granite, which could be derived from stretching environments in the Early Cretaceous. The granophyres originated from residual melt which underwent highly differentiation process, and were formed in magmatic-hydrothemal transition stage at last.
文摘Homret Ghannam alkali feldspar granite(HGAFG)in the central Eastern Desert(CED)of Egypt represents a distinctive example of late Neoproterozoic magmatism in the Arabian-Nubian Shield(ANS).This study integrates field observations,petrography,mineral chemistry(EMPA),and whole-rock geochemistry to investigate its petrogenesis,geodynamic evolution,and rare-metal potential.HGAFG comprises two cogenetic varieties,alkali feldspar granite and riebeckite-bearing granite,hosting rare-metal minerals such as zircon,fluorite,columbite and apatite.HGAFG exhibits diagnostic A-type geochemical characteristics,including high SiO₂contents(73.81-77.86 wt%),metaluminous to mildly peralkaline composition(ASI:0.92-1.03),enrichment in HFSE(Zr≈791.80 ppm,Nb≈68.12 ppm,Y≈90.81 ppm)andΣREE(103.40-475.57 ppm),and pronounced negative Eu anomalies(Eu/Eu^(*)=0.07-0.20).Zircon saturation thermometry yields high crystallization temperatures(TZr≈908.87℃)and low emplacement pressures(1.46 kbar)under reducing conditions(ƒO_(2)≈−11.5).The mineralogical and geochemical results reveal that HGAFG originated from a hybrid,fluorine-rich magma generated by anatexis of lower crust,followed by extensive fractional crystallization,during late post-collisional extension associated with lithospheric delamination.The reduced nature and fluorine enrichment of HGAFG magma promoted the mineralization of Nb-Ta-REE phases,highlighting its significance as a fertile,high-temperature product of the terminal magmatic stage in ANS evolution.
