We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals(titanite,calzirtite,anatase,baddeleyite and pyrochlore)of a ...We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals(titanite,calzirtite,anatase,baddeleyite and pyrochlore)of a newly discovered Late Cretaceous kimberlite(U-Pb zircon age 90.0±1.3 Ma;2σ)named Osvaldo Franca 1,located in the Alto Paranaíba Igneous Province(APIP),southeastern Brazil.Pyrope grains are lherzolitic(Lherz-1,Lherz-2 and Lherz-3),harzburgitic(Harz-3)and wehrlitic(Wehr-2).The pyrope xenocrysts cover a wide mantle column in the subcratonic lithosphere(66–143 km;20–43 kbar)at relatively low temperatures(811–875°C).The shallowest part of this mantle is represented by Lherz-1 pyropes(20–32 kbar),which have low-Cr(Cr_(2)O_(3)=1.74–6.89 wt.%)and fractionated middle to heavy rare earth elements(MREE-HREE)pattern.The deepest samples are represented by Lherz-2,Lherz-3,Harz-3,and Wehr-2 pyropes(36–43 kbar).They contain high-Cr contents(Cr_(2)O_(3)=7.36–11.19 wt.%)and are characterized by sinusoidal(Lherz-2 and Wehr-2)and spoon-like(Lherz-3 and Harz-3)REE patterns.According to their REE and trace elements,pyrope xenocrysts have enriched nature(e.g.,Ce and Yb vs.Cr_(2)O_(3)),indicating that the cratonic lithosphere has been affected by a silicate melt with subalkaline/tholeiite composition due to their low Zr,Ti and Y concentrations.Besides minerals with typical kimberlitic signatures,such as ilmenite and zircon,the exotic compositions of phlogopite and ulvöspinel suggest an enriched component in the magma source.The formation of rare mineral phases with strong enrichment of light-REE(LREE)and high field strength elements(HFSE)is attributed to the late-stage kimberlitic melt.We propose a tectonic model where a thermal anomaly,represented by the low-velocity seismic anomaly observed in P-wave seismic tomography images,supplied heat to activate the alkaline magmatism from a metasomatized cratonic mantle source during the late-stages of Gondwana fragmentation and consequent South Atlantic Ocean opening.The metasomatism recorded by mineral phases is a product of long-lived recycling of subducted oceanic plates since the Neoproterozoic(Brasiliano Orogeny)or even older collisional events,contributing to the exotic character of the Osvaldo Fran?a 1 kimberlite,as well as to the cratonic lithospheric mantle.展开更多
Current palaeoclimatic reconstructions for the R＆#237;o de la Plata region during the latest Pleistocene （30,000 e10,000 yr BP） propose dry conditions, with rainfall at the Last Glacial Maximum amounting to one-thi...Current palaeoclimatic reconstructions for the R＆#237;o de la Plata region during the latest Pleistocene （30,000 e10,000 yr BP） propose dry conditions, with rainfall at the Last Glacial Maximum amounting to one-third of today＇s precipitation. Despite the consequential low primary productivity inferred, an impressive megafauna existed in the area at that time. Here we explore the influence of the flooding from a huge extinct system of water bodies in the Andean Altiplano as a likely source for wet regimes that might have increased the primary productivity and, hence, the vast number of megaherbivores. The system was reconstructed using specifically combined software resources, including Insola, Global Mapper v13, Surfer and Matlab. Changes in water volume and area covered were related to climatic change, assessed through a model of astronomical forcing that describes the changes in insolation at the top of the at-mosphere in the last 50,000 yr BP. The model was validated by comparing its results with several proxies （CH4, CO2, D, 18O） from dated cores taken from the ice covering Antarctic lakes Vostok and EPICA Dome C. It is concluded that the Altiplano Lake system drained towards the southeast in the rainy seasons and that it must have been a major source of water for the Paran＆#225;-Plata Basin, consequently enhancing primary productivity within it.展开更多
An“explosive extratropical cyclone”is an atmospheric phenomenon that occurs when there is a very rapid drop in central atmospheric pressure.This phenomenon,with its characteristic of rapidly lowering the pressure in...An“explosive extratropical cyclone”is an atmospheric phenomenon that occurs when there is a very rapid drop in central atmospheric pressure.This phenomenon,with its characteristic of rapidly lowering the pressure in its interior,generates very intense winds and for this reason it is called explosive cyclone,bomb cyclone.With gusts recorded of 116 km/h,atmospheric phenomenon-“cyclone bomb”(CB)hit southern Brazil on June 30,the beginning of winter 2020,causing destruction in its influence over.One of the cities most affected was Chapecó,west of the state of Santa Catarina.The satellite images show that the CB generated a low pressure(976 mbar)inside it,generating two atmospheric currents that moved at high speed.In a northwest-southeast direction,Bolivia and Paraguay,crossing the states of Parana and Santa Catarina,and this draft that hit the south of Brazil,which caused the destruction of the affected states.Another moving to Argentina,southwest-northeast direction,due to high area of high pressure(1022 mbar).Both enhanced the phenomenon.展开更多
文摘We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals(titanite,calzirtite,anatase,baddeleyite and pyrochlore)of a newly discovered Late Cretaceous kimberlite(U-Pb zircon age 90.0±1.3 Ma;2σ)named Osvaldo Franca 1,located in the Alto Paranaíba Igneous Province(APIP),southeastern Brazil.Pyrope grains are lherzolitic(Lherz-1,Lherz-2 and Lherz-3),harzburgitic(Harz-3)and wehrlitic(Wehr-2).The pyrope xenocrysts cover a wide mantle column in the subcratonic lithosphere(66–143 km;20–43 kbar)at relatively low temperatures(811–875°C).The shallowest part of this mantle is represented by Lherz-1 pyropes(20–32 kbar),which have low-Cr(Cr_(2)O_(3)=1.74–6.89 wt.%)and fractionated middle to heavy rare earth elements(MREE-HREE)pattern.The deepest samples are represented by Lherz-2,Lherz-3,Harz-3,and Wehr-2 pyropes(36–43 kbar).They contain high-Cr contents(Cr_(2)O_(3)=7.36–11.19 wt.%)and are characterized by sinusoidal(Lherz-2 and Wehr-2)and spoon-like(Lherz-3 and Harz-3)REE patterns.According to their REE and trace elements,pyrope xenocrysts have enriched nature(e.g.,Ce and Yb vs.Cr_(2)O_(3)),indicating that the cratonic lithosphere has been affected by a silicate melt with subalkaline/tholeiite composition due to their low Zr,Ti and Y concentrations.Besides minerals with typical kimberlitic signatures,such as ilmenite and zircon,the exotic compositions of phlogopite and ulvöspinel suggest an enriched component in the magma source.The formation of rare mineral phases with strong enrichment of light-REE(LREE)and high field strength elements(HFSE)is attributed to the late-stage kimberlitic melt.We propose a tectonic model where a thermal anomaly,represented by the low-velocity seismic anomaly observed in P-wave seismic tomography images,supplied heat to activate the alkaline magmatism from a metasomatized cratonic mantle source during the late-stages of Gondwana fragmentation and consequent South Atlantic Ocean opening.The metasomatism recorded by mineral phases is a product of long-lived recycling of subducted oceanic plates since the Neoproterozoic(Brasiliano Orogeny)or even older collisional events,contributing to the exotic character of the Osvaldo Fran?a 1 kimberlite,as well as to the cratonic lithospheric mantle.
文摘Current palaeoclimatic reconstructions for the R＆#237;o de la Plata region during the latest Pleistocene （30,000 e10,000 yr BP） propose dry conditions, with rainfall at the Last Glacial Maximum amounting to one-third of today＇s precipitation. Despite the consequential low primary productivity inferred, an impressive megafauna existed in the area at that time. Here we explore the influence of the flooding from a huge extinct system of water bodies in the Andean Altiplano as a likely source for wet regimes that might have increased the primary productivity and, hence, the vast number of megaherbivores. The system was reconstructed using specifically combined software resources, including Insola, Global Mapper v13, Surfer and Matlab. Changes in water volume and area covered were related to climatic change, assessed through a model of astronomical forcing that describes the changes in insolation at the top of the at-mosphere in the last 50,000 yr BP. The model was validated by comparing its results with several proxies （CH4, CO2, D, 18O） from dated cores taken from the ice covering Antarctic lakes Vostok and EPICA Dome C. It is concluded that the Altiplano Lake system drained towards the southeast in the rainy seasons and that it must have been a major source of water for the Paran＆#225;-Plata Basin, consequently enhancing primary productivity within it.
文摘An“explosive extratropical cyclone”is an atmospheric phenomenon that occurs when there is a very rapid drop in central atmospheric pressure.This phenomenon,with its characteristic of rapidly lowering the pressure in its interior,generates very intense winds and for this reason it is called explosive cyclone,bomb cyclone.With gusts recorded of 116 km/h,atmospheric phenomenon-“cyclone bomb”(CB)hit southern Brazil on June 30,the beginning of winter 2020,causing destruction in its influence over.One of the cities most affected was Chapecó,west of the state of Santa Catarina.The satellite images show that the CB generated a low pressure(976 mbar)inside it,generating two atmospheric currents that moved at high speed.In a northwest-southeast direction,Bolivia and Paraguay,crossing the states of Parana and Santa Catarina,and this draft that hit the south of Brazil,which caused the destruction of the affected states.Another moving to Argentina,southwest-northeast direction,due to high area of high pressure(1022 mbar).Both enhanced the phenomenon.
