Greenstone belts contain several clues about the evolutionary history of primitive Earth.Here,we describe the volcano-sedimentary rock association exposed along the eastern margin of the Gavião Block,named the No...Greenstone belts contain several clues about the evolutionary history of primitive Earth.Here,we describe the volcano-sedimentary rock association exposed along the eastern margin of the Gavião Block,named the Northern Mundo Novo Greenstone Belt(N-MNGB),and present data collected with different techniques,including U–Pb–Hf–O isotopes of zircon and multiple sulfur isotopes(^(32)S,^(33)S,^(34)S,and ^(36)S)of pyrite from this supracrustal sequence.A pillowed metabasalt situated in the upper section of the N-MNGB is 3337±25 Ma old and has zircon with ε_(Hf)(t)=2.47 to1.40,Hf model ages between 3.75 Ga and 3.82 Ga,and δ^(18)O=+3.6‰to+7.3‰.These isotopic data,together with compiled whole-rock trace element data,suggest that the mafic metavolcanic rocks formed in a subduction-related setting,likely a back-arc basin juxtaposed to a continental arc.In this context,the magma interacted with older Eoarchean crustal components from the Gavião Block.Detrital zircons from the overlying quartzites of the Jacobina Group are sourced from Paleoarchean rocks,in accordance with previous studies,yielding a maximum depositional age of 3353±22 Ma.These detrital zircons have ε_(Hf)(t)=5.40 to0.84,Hf model ages between 3.66 Ga and 4.30 Ga,and δ^(18)O=+4.8‰to+6.4‰.The pyrite multiple sulfur isotope investigation of the 3.3 Ga supracrustal rocks from the N-MNGB enabled a further understanding of Paleoarchean sulfur cycling.The samples have diverse isotopic compositions that indicate sulfur sourced from distinct reservoirs.Significantly,they preserve the signal of the anoxic Archean atmosphere,expressed by MIF-S signatures(Δ^(33)S between1.3‰to+1.4‰)and a Δ^(36)S/Δ^(33)S slope of0.81 that is indistinguishable from the so-called Archean array.A BIF sample has a magmatic origin of sulfur,as indicated by the limited Δ^(34)S range(0 to+2‰),Δ^(33)S~0‰,and Δ^(36)S~0‰.A carbonaceous schist shows positive Δ^(34)S(2.1‰–3.5‰)and elevated Δ^(33)S(1.2‰–1.4‰)values,with corresponding negative Δ^(36)S between1.2‰to0.2‰,which resemble the isotopic composition of Archean black shales and suggest a source from the photolytic reduction of elemental sulfur.The pillowed metabasalt displays heterogeneous Δ^(34)S,Δ^(33)S,and Δ^(36)S signatures that reflect assimilation of both magmatic sulfur and photolytic sulfate during hydrothermal seafloor alteration.Lastly,pyrite in a massive sulfide lens is isotopically similar to barite of several Paleoarchean deposits worldwide,which might indicate mass dependent sulfur processing from a global and well-mixed sulfate reservoir at this time.展开更多
Multiple sulfur isotopes （32S, 335, 345, 365） and oxygen isotopes （160, 180） in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The δ345 values of Beijing aerosol samples range from 1.68%o ...Multiple sulfur isotopes （32S, 335, 345, 365） and oxygen isotopes （160, 180） in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The δ345 values of Beijing aerosol samples range from 1.68%o to 12.57%o with an average value of 5.86%0, indicating that the major sulfur source is from direct emission during coal combustion. The c5180 values vary from -5.29%0 to 9.02%0 with an average value of 5.17%o, revealing that the sulfate in Beijing aerosols is mainly composed of the secondary sulfate. The main heterogeneous oxidation of SO2 in atmosphere is related to H202 in July and August, whereas H202 oxidation and Fe3＋ catalytic oxidation with SO2 exist simultaneously in September and October. Remarkable sulfur iso- tope mass-independent fractionation effect is found in Beijing aerosols, which is commonly attributed to the photochemical oxidation of SO2 in the stratosphere. In addition, thermochemical reactions of sulfur-bearing compounds might be also a source of sulfur isotope anomalies based on the correlation between A335 and CAPE.展开更多
基金the Brazilian National Council for Scientific and Technological Development(CNPq)for financial support(grants 163459/2013-4 and 202267/2014-8 for G.S Teles and 305053/2014-0 for F.Chemale Jr.)the Australian Research Council(ARC)(grant DP140103393 for T.R.Ireland)。
文摘Greenstone belts contain several clues about the evolutionary history of primitive Earth.Here,we describe the volcano-sedimentary rock association exposed along the eastern margin of the Gavião Block,named the Northern Mundo Novo Greenstone Belt(N-MNGB),and present data collected with different techniques,including U–Pb–Hf–O isotopes of zircon and multiple sulfur isotopes(^(32)S,^(33)S,^(34)S,and ^(36)S)of pyrite from this supracrustal sequence.A pillowed metabasalt situated in the upper section of the N-MNGB is 3337±25 Ma old and has zircon with ε_(Hf)(t)=2.47 to1.40,Hf model ages between 3.75 Ga and 3.82 Ga,and δ^(18)O=+3.6‰to+7.3‰.These isotopic data,together with compiled whole-rock trace element data,suggest that the mafic metavolcanic rocks formed in a subduction-related setting,likely a back-arc basin juxtaposed to a continental arc.In this context,the magma interacted with older Eoarchean crustal components from the Gavião Block.Detrital zircons from the overlying quartzites of the Jacobina Group are sourced from Paleoarchean rocks,in accordance with previous studies,yielding a maximum depositional age of 3353±22 Ma.These detrital zircons have ε_(Hf)(t)=5.40 to0.84,Hf model ages between 3.66 Ga and 4.30 Ga,and δ^(18)O=+4.8‰to+6.4‰.The pyrite multiple sulfur isotope investigation of the 3.3 Ga supracrustal rocks from the N-MNGB enabled a further understanding of Paleoarchean sulfur cycling.The samples have diverse isotopic compositions that indicate sulfur sourced from distinct reservoirs.Significantly,they preserve the signal of the anoxic Archean atmosphere,expressed by MIF-S signatures(Δ^(33)S between1.3‰to+1.4‰)and a Δ^(36)S/Δ^(33)S slope of0.81 that is indistinguishable from the so-called Archean array.A BIF sample has a magmatic origin of sulfur,as indicated by the limited Δ^(34)S range(0 to+2‰),Δ^(33)S~0‰,and Δ^(36)S~0‰.A carbonaceous schist shows positive Δ^(34)S(2.1‰–3.5‰)and elevated Δ^(33)S(1.2‰–1.4‰)values,with corresponding negative Δ^(36)S between1.2‰to0.2‰,which resemble the isotopic composition of Archean black shales and suggest a source from the photolytic reduction of elemental sulfur.The pillowed metabasalt displays heterogeneous Δ^(34)S,Δ^(33)S,and Δ^(36)S signatures that reflect assimilation of both magmatic sulfur and photolytic sulfate during hydrothermal seafloor alteration.Lastly,pyrite in a massive sulfide lens is isotopically similar to barite of several Paleoarchean deposits worldwide,which might indicate mass dependent sulfur processing from a global and well-mixed sulfate reservoir at this time.
基金supported by National Natural Science Foundation of China(Grant Nos.41240025 and 41373023)Start-up Foundation of the Ministry of Education for Overseas Returnees(Grant No.2012s001)Prospective Researching Project of Industry-University-Research of Jiangsu Province(Grant No.BY2013007-03)
文摘Multiple sulfur isotopes （32S, 335, 345, 365） and oxygen isotopes （160, 180） in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The δ345 values of Beijing aerosol samples range from 1.68%o to 12.57%o with an average value of 5.86%0, indicating that the major sulfur source is from direct emission during coal combustion. The c5180 values vary from -5.29%0 to 9.02%0 with an average value of 5.17%o, revealing that the sulfate in Beijing aerosols is mainly composed of the secondary sulfate. The main heterogeneous oxidation of SO2 in atmosphere is related to H202 in July and August, whereas H202 oxidation and Fe3＋ catalytic oxidation with SO2 exist simultaneously in September and October. Remarkable sulfur iso- tope mass-independent fractionation effect is found in Beijing aerosols, which is commonly attributed to the photochemical oxidation of SO2 in the stratosphere. In addition, thermochemical reactions of sulfur-bearing compounds might be also a source of sulfur isotope anomalies based on the correlation between A335 and CAPE.
