The Dunde iron-zinc polymetallic deposit is one of large iron deposits occurred in the Awulale Metallogenetic Belt,Western Tianshan(NW-China).This study reports new geochronology and geochemistry for granite in the Du...The Dunde iron-zinc polymetallic deposit is one of large iron deposits occurred in the Awulale Metallogenetic Belt,Western Tianshan(NW-China).This study reports new geochronology and geochemistry for granite in the Dunde mining area in order to constrain the tectonicmagmatic activities and metallogenesis of this region.Granites in the southwest of Dunde mining area are mainly syenogranites intruded into volcanics of the Dahalajunshan Formation in the Early Carboniferous,and they are far from the area where ore bodies and mineralized altered rocks are widely developed.LA-ICP-MS U–Pb zircon dating indicates that Dunde syenogranite was at 306.8±1.0 Ma,which could constrain the upper limit of metallogenic age for this deposit.The Dunde granites are high SiO_(2)(73.41–80.07 wt%),high differentiation index(D.I.=89.7–95.0),weakly peraluminous to metaluminous(A/CNK=0.94–1.08),and they are enriched in LILE and LREE and depleted in Eu,Ba,Sr and P_(2)O_(5),indicating that they belong to highly fractionated Ⅰ-type granite.Based on εHf values(+9.2 to+10.5)for zircon and high εNd(-t)values(+4.7 to+5.8)for whole-rock,and the two-stage model ages for 601–735 Ma,suggest that the magma source could be the juvenile lower crust.Combined with regional geological setting,the 306.8 Ma Dunde granites are formed in post-collision extensional tectonic setting.展开更多
The present study deals with the possibilities of applying the zircon saturation thermometry, which is based on the equilibrium between the zircon crystals and the melt, to strongly altered volcanic ashes—bentonites....The present study deals with the possibilities of applying the zircon saturation thermometry, which is based on the equilibrium between the zircon crystals and the melt, to strongly altered volcanic ashes—bentonites. It proposes an alternative to a widely used method of calculating magma temperature from Zr content and major component composition(Boehnke in Chem Geol351:324–333, 2013), that is not suitable for bentonites, as most of the major components have been largely altered in these rocks. For calculating source magma temperatures in strongly altered volcanic ashes, the exponential function from the Zr(ppm)/Al_(2)O_(3)(%) ratio with compositional corrections from the TiO_(2)/Al_(2)O_(3) ratio was found applicable. The idea to use the ratios of these elements is based on the low mobility of these elements in the earth’s surface conditions. Temperatures of magma, forming in the partial melting process, are assessed from the bulk rock composition. Pre-eruption temperatures were estimated from the composition of fine fractions of bentonites. The accuracy of the new method was established from comparison with the method by Boehnke et al.(Chem Geol 351:324–333,2013). The difference between the two methods was mostly less than ± 30° to ± 50°. The comparison with the magma temperature, estimated from the sanidine composition,revealed 13° lower values on average. Although the proposed method for estimating the source magma temperatures is less precise than the method of accounting for detailed rock compositions, it can be used in strongly altered rocks, where other methods are not usable. The new method still enables differentiation between felsic source magmas originating at low or high temperatures. Early Palaeozoic bentonites in the Baltic Basin can be divided,according to the source magma temperatures, into two types:(1) Low temperature(650–790 ℃), containing potassium-rich sanidine and abundant biotite(S type),(2)high temperature(770–850 ℃) with sodium-rich sanidine and scarce biotite(I type).展开更多
The Sergipano Orogenic System(SOS)in southern Borborema Province(NE Brazil)hosts voluminous Neoproterozoic plutonism related to the Brasiliano/Pan-African Orogeny.This paper presents comprehensive whole-rock geochemic...The Sergipano Orogenic System(SOS)in southern Borborema Province(NE Brazil)hosts voluminous Neoproterozoic plutonism related to the Brasiliano/Pan-African Orogeny.This paper presents comprehensive whole-rock geochemical data,titanite U-Pb ages,and the first combined zircon U-Pb and Lu-Hf isotope results for plutonic rocks from the MacururéDomain to constrain their sources,petrogenesis,and tectonic setting.Three magmatic episodes are recognized and record the evolutionary stages of the orogen.(i)Early-collisional magmatism(643–628 Ma)comprises gabbros and diorites with minor tonalites characterized by well-developed tectonic foliation and evidence of solid-state deformation.These rocks are magnesian,high-K calc-alkaline,LILE-and LREE-enriched and provide subchondriticε_(Hf)(t)values(6.5 to4.7)and Orosirian Hf-T^(C)_(DM)model ages(1.83–1.94 Ga).Such features indicate derivation from a lithospheric mantle source metasomatized by incorporating crustal components through subduction processes prior to magma generation,possibly related to the Rhyacian Orogeny(2.20–1.96 Ga).Extensive mixing/mingling between basaltic and crust-derived magmas took place at lower crustal depths,producing coeval hybrid diorites and quartz-diorites.(ii)Syn-collisional magmatism(630–624 Ma)encompasses biotite-and muscovite-bearing granodiorites and monzogranites,preserving their structures parallel to the schistosity of the country rocks.These rocks are leucocratic,weakly metaluminous to peraluminous,and contain abundant surmicaceous enclaves.Petrographic features and geochemical composition suggest an origin related to the partial melting of graywacke protoliths with a subordinate igneous component.(iii)Late-collisional magmatism(625–600 Ma)includes undeformed and isotropic monzonites and granodiorites,which truncate the regional foliation.These rocks are consistently metaluminous and magnesian,showing affinities with the high-K calc-alkaline to shoshonite series.Trace element modeling with subchondriticε_(Hf)(t)values(8.3 to4.1)and Paleoproterozoic Hf-T^(C)_(DM)model ages(1.77–2.03 Ga)demonstrate that reworking of ancient lower mafic crust played an important role at this time.The integration of our data with previously published results leads us to conclude that the geodynamic evolution of the SOS along the western Gondwana margin is better explained by large-scale lithospheric extension followed by basin inversion and continental collision.展开更多
The Elogo complex is a greenstone belt portion located on the Eastern edge of the Archean Congo craton at the junction with the Paleoproterozoic to Neoproterozoic Sembe Ouesso basin. This study was carried out on this...The Elogo complex is a greenstone belt portion located on the Eastern edge of the Archean Congo craton at the junction with the Paleoproterozoic to Neoproterozoic Sembe Ouesso basin. This study was carried out on this complex to determine the context of the placement of basaltic rocks. Metaluminous tholeiitic basalts (basic and ultrabasic), calc-alkaline basalts, andesitic basalts, and peraluminous calc-alkaline dacites represent greenstones. Tholeiitic and calc-alkaline basalts come from deep enriched and depleted mantle sources, including garnet in fusion residues [Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> > 16 (16.5 to 35.12) and in some samples between 12.45 to 14.48;CaO/Al<sub>2</sub>O<sub>3</sub> 1 (1.04 to 1.35) in ten samples and (Gb/Yb)<sub>PM</sub> > 1]. The calc-alkaline dacites come from a shallow depleted mantle source [Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> > 16;CaO/Al<sub>2</sub>O<sub>3</sub> 1]. Tholeiitic and calc-alkaline basalts have a negative Rb, Ba, Ce, and Nb anomaly without negative Ti anomaly, positive Ta, Pb anomalies, and a lack of significant REE [(La/Yb)n = 0.36 to 0.97 and 1 to 2.15;(Ce/Yb)n = 0.27 to 0.96 and 1.04 to 1.72, respectively] fractionation. High Nb/Th (2 to 10) and Nb/U (1.82 to 26) ratios and low La/Ta (5 to 27) ratios are characteristic of divergent margin magmatic sources. Tholeiitic and calc-alkaline basalts correspond to an extensive back-arc basin-type tectonic setting. Calc-alkaline andesitic basalts and dacites show positive Ba, U, Th, K, La, Ce, Pb, and Li anomalies and negative Nb, Ta, and Ti anomalies reflecting crustal contamination and hydrothermal alteration in a compressive tectonic context as a volcanic arc in a subduction regime marking the interruption of the meso-neoarchean Elogo’s opening. Elogo’s opening and closing are probably associated with the emplacement of the greenstone of the meso-neoarchean Gabon Belinga group and the relics of the Mesoarchean greenstones of the Cameroun Ntem complex.展开更多
The Weining Beishan area of Ningxia Hui Autonomous Region is located at on the western edge of the Helanshan tectonic belt,which is a tectonic joint among Alxa Block,Ordos Block,and North Qilian orogenic belt.However,...The Weining Beishan area of Ningxia Hui Autonomous Region is located at on the western edge of the Helanshan tectonic belt,which is a tectonic joint among Alxa Block,Ordos Block,and North Qilian orogenic belt.However,the tectonic evolution of this area remains unclear due to the lack of magmatic information.This paper conducted researches on geochronology,geochemistry,and Sr-Nd-Hf isotopes of the diorite porphyrites exposed in the Weining Beishan area.The zircon U-Pb dating yields two ages of 145.0±1.1 and 146.2±1.5 Ma,and the whole-rock geochemical data indicate that the diorite porphyrites are metaluminous to weakly peraluminous and high-K calc-alkaline series.The characteristics of highly initial^(87)Sr/^(86)Sr ratios(0.70816 to 0.71047),negativeε_(Nd)(t)(−8.9 to−8.4),and negativeε_(Hf)(t)(−13.8 to−21.2)indicate that the diorite porphyrites originated from partial melting of the middle-lower ancient crust related to the North China Craton.Combined with the regional geology,we suggested that partial melting was triggered by a tectonic activity of deep faults cutting through the crust under the regional stress transformation from compressing to extension during the Late Jurassic–Early Cretaceous,which is probably related to the westward subduction of the Paleo-Pacific Plate.展开更多
基金supported by Special Fund for Basic Scientific Research of Central Colleges,Chang’an University(Grant No.:300102279210)the Natural Science Foundation of Shaanxi Province(Grant No.:2019JQ-690)the geological and mineral survey evaluation project of China Geological Survey(Grant No.:DD20190065).
文摘The Dunde iron-zinc polymetallic deposit is one of large iron deposits occurred in the Awulale Metallogenetic Belt,Western Tianshan(NW-China).This study reports new geochronology and geochemistry for granite in the Dunde mining area in order to constrain the tectonicmagmatic activities and metallogenesis of this region.Granites in the southwest of Dunde mining area are mainly syenogranites intruded into volcanics of the Dahalajunshan Formation in the Early Carboniferous,and they are far from the area where ore bodies and mineralized altered rocks are widely developed.LA-ICP-MS U–Pb zircon dating indicates that Dunde syenogranite was at 306.8±1.0 Ma,which could constrain the upper limit of metallogenic age for this deposit.The Dunde granites are high SiO_(2)(73.41–80.07 wt%),high differentiation index(D.I.=89.7–95.0),weakly peraluminous to metaluminous(A/CNK=0.94–1.08),and they are enriched in LILE and LREE and depleted in Eu,Ba,Sr and P_(2)O_(5),indicating that they belong to highly fractionated Ⅰ-type granite.Based on εHf values(+9.2 to+10.5)for zircon and high εNd(-t)values(+4.7 to+5.8)for whole-rock,and the two-stage model ages for 601–735 Ma,suggest that the magma source could be the juvenile lower crust.Combined with regional geological setting,the 306.8 Ma Dunde granites are formed in post-collision extensional tectonic setting.
文摘The present study deals with the possibilities of applying the zircon saturation thermometry, which is based on the equilibrium between the zircon crystals and the melt, to strongly altered volcanic ashes—bentonites. It proposes an alternative to a widely used method of calculating magma temperature from Zr content and major component composition(Boehnke in Chem Geol351:324–333, 2013), that is not suitable for bentonites, as most of the major components have been largely altered in these rocks. For calculating source magma temperatures in strongly altered volcanic ashes, the exponential function from the Zr(ppm)/Al_(2)O_(3)(%) ratio with compositional corrections from the TiO_(2)/Al_(2)O_(3) ratio was found applicable. The idea to use the ratios of these elements is based on the low mobility of these elements in the earth’s surface conditions. Temperatures of magma, forming in the partial melting process, are assessed from the bulk rock composition. Pre-eruption temperatures were estimated from the composition of fine fractions of bentonites. The accuracy of the new method was established from comparison with the method by Boehnke et al.(Chem Geol 351:324–333,2013). The difference between the two methods was mostly less than ± 30° to ± 50°. The comparison with the magma temperature, estimated from the sanidine composition,revealed 13° lower values on average. Although the proposed method for estimating the source magma temperatures is less precise than the method of accounting for detailed rock compositions, it can be used in strongly altered rocks, where other methods are not usable. The new method still enables differentiation between felsic source magmas originating at low or high temperatures. Early Palaeozoic bentonites in the Baltic Basin can be divided,according to the source magma temperatures, into two types:(1) Low temperature(650–790 ℃), containing potassium-rich sanidine and abundant biotite(S type),(2)high temperature(770–850 ℃) with sodium-rich sanidine and scarce biotite(I type).
基金This study was financed in part by the Coordenação de Aper-feiçoamento de Pessoal de Nível Superior-Brazil(CAPES)-Finance Code 001The research was supported with funding from Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq,Jean-Michel Lafon-grants 312393/2020-2 and 42625/2018-7+1 种基金Maria de Lourdes Silva Rosa-grant 311023/2021-5and Herbet Conceição-grant 310740/2021-5).
文摘The Sergipano Orogenic System(SOS)in southern Borborema Province(NE Brazil)hosts voluminous Neoproterozoic plutonism related to the Brasiliano/Pan-African Orogeny.This paper presents comprehensive whole-rock geochemical data,titanite U-Pb ages,and the first combined zircon U-Pb and Lu-Hf isotope results for plutonic rocks from the MacururéDomain to constrain their sources,petrogenesis,and tectonic setting.Three magmatic episodes are recognized and record the evolutionary stages of the orogen.(i)Early-collisional magmatism(643–628 Ma)comprises gabbros and diorites with minor tonalites characterized by well-developed tectonic foliation and evidence of solid-state deformation.These rocks are magnesian,high-K calc-alkaline,LILE-and LREE-enriched and provide subchondriticε_(Hf)(t)values(6.5 to4.7)and Orosirian Hf-T^(C)_(DM)model ages(1.83–1.94 Ga).Such features indicate derivation from a lithospheric mantle source metasomatized by incorporating crustal components through subduction processes prior to magma generation,possibly related to the Rhyacian Orogeny(2.20–1.96 Ga).Extensive mixing/mingling between basaltic and crust-derived magmas took place at lower crustal depths,producing coeval hybrid diorites and quartz-diorites.(ii)Syn-collisional magmatism(630–624 Ma)encompasses biotite-and muscovite-bearing granodiorites and monzogranites,preserving their structures parallel to the schistosity of the country rocks.These rocks are leucocratic,weakly metaluminous to peraluminous,and contain abundant surmicaceous enclaves.Petrographic features and geochemical composition suggest an origin related to the partial melting of graywacke protoliths with a subordinate igneous component.(iii)Late-collisional magmatism(625–600 Ma)includes undeformed and isotropic monzonites and granodiorites,which truncate the regional foliation.These rocks are consistently metaluminous and magnesian,showing affinities with the high-K calc-alkaline to shoshonite series.Trace element modeling with subchondriticε_(Hf)(t)values(8.3 to4.1)and Paleoproterozoic Hf-T^(C)_(DM)model ages(1.77–2.03 Ga)demonstrate that reworking of ancient lower mafic crust played an important role at this time.The integration of our data with previously published results leads us to conclude that the geodynamic evolution of the SOS along the western Gondwana margin is better explained by large-scale lithospheric extension followed by basin inversion and continental collision.
文摘The Elogo complex is a greenstone belt portion located on the Eastern edge of the Archean Congo craton at the junction with the Paleoproterozoic to Neoproterozoic Sembe Ouesso basin. This study was carried out on this complex to determine the context of the placement of basaltic rocks. Metaluminous tholeiitic basalts (basic and ultrabasic), calc-alkaline basalts, andesitic basalts, and peraluminous calc-alkaline dacites represent greenstones. Tholeiitic and calc-alkaline basalts come from deep enriched and depleted mantle sources, including garnet in fusion residues [Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> > 16 (16.5 to 35.12) and in some samples between 12.45 to 14.48;CaO/Al<sub>2</sub>O<sub>3</sub> 1 (1.04 to 1.35) in ten samples and (Gb/Yb)<sub>PM</sub> > 1]. The calc-alkaline dacites come from a shallow depleted mantle source [Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> > 16;CaO/Al<sub>2</sub>O<sub>3</sub> 1]. Tholeiitic and calc-alkaline basalts have a negative Rb, Ba, Ce, and Nb anomaly without negative Ti anomaly, positive Ta, Pb anomalies, and a lack of significant REE [(La/Yb)n = 0.36 to 0.97 and 1 to 2.15;(Ce/Yb)n = 0.27 to 0.96 and 1.04 to 1.72, respectively] fractionation. High Nb/Th (2 to 10) and Nb/U (1.82 to 26) ratios and low La/Ta (5 to 27) ratios are characteristic of divergent margin magmatic sources. Tholeiitic and calc-alkaline basalts correspond to an extensive back-arc basin-type tectonic setting. Calc-alkaline andesitic basalts and dacites show positive Ba, U, Th, K, La, Ce, Pb, and Li anomalies and negative Nb, Ta, and Ti anomalies reflecting crustal contamination and hydrothermal alteration in a compressive tectonic context as a volcanic arc in a subduction regime marking the interruption of the meso-neoarchean Elogo’s opening. Elogo’s opening and closing are probably associated with the emplacement of the greenstone of the meso-neoarchean Gabon Belinga group and the relics of the Mesoarchean greenstones of the Cameroun Ntem complex.
文摘The Weining Beishan area of Ningxia Hui Autonomous Region is located at on the western edge of the Helanshan tectonic belt,which is a tectonic joint among Alxa Block,Ordos Block,and North Qilian orogenic belt.However,the tectonic evolution of this area remains unclear due to the lack of magmatic information.This paper conducted researches on geochronology,geochemistry,and Sr-Nd-Hf isotopes of the diorite porphyrites exposed in the Weining Beishan area.The zircon U-Pb dating yields two ages of 145.0±1.1 and 146.2±1.5 Ma,and the whole-rock geochemical data indicate that the diorite porphyrites are metaluminous to weakly peraluminous and high-K calc-alkaline series.The characteristics of highly initial^(87)Sr/^(86)Sr ratios(0.70816 to 0.71047),negativeε_(Nd)(t)(−8.9 to−8.4),and negativeε_(Hf)(t)(−13.8 to−21.2)indicate that the diorite porphyrites originated from partial melting of the middle-lower ancient crust related to the North China Craton.Combined with the regional geology,we suggested that partial melting was triggered by a tectonic activity of deep faults cutting through the crust under the regional stress transformation from compressing to extension during the Late Jurassic–Early Cretaceous,which is probably related to the westward subduction of the Paleo-Pacific Plate.
