New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase m...New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.展开更多
New attention has been given to the resources of rare earth minerals over the last years. The natural shortage of these elements in the Earth’s crust and trade restrictions recently imposed by China, motivated the Br...New attention has been given to the resources of rare earth minerals over the last years. The natural shortage of these elements in the Earth’s crust and trade restrictions recently imposed by China, motivated the Brazilian Government to encourage new projects by inserting the exploitation of rare earths in the National Mining Plan, which deals with industry strategic issues in the country, helping to reduce current importation. The incentives can be in the choice of future targets for mineral exploration and for the development of laboratory studies and pilot scale processing tests.展开更多
The Red River Shear Zone (RRSZ), which extends from eastern Tibet to the South China Sea, plays a central role in the hypothesis that strike\|slip extrusion of Indochina accommodated a significant portion of Indo\|Asi...The Red River Shear Zone (RRSZ), which extends from eastern Tibet to the South China Sea, plays a central role in the hypothesis that strike\|slip extrusion of Indochina accommodated a significant portion of Indo\|Asian convergence. The massifs of the RRSZ, the only known mid\|crustal section exposed through a transform plate boundary, contain high\|grade metamorphic rocks that are believed to have been plastically deformed in a left\|lateral sense during the mid\|Tertiary. While the history of diachronous transtension along the RRSZ was previously obtained for temperatures below the brittle\|ductile transition from argon thermochronometry, the precise timing of high temperature deformation and the magnitude of strain have not been directly determined. This is a significant limitation to testing the extrusion model as magnetic anomalies from the South China Sea, interpreted to be a pull apart basin at the SE termination of the RRSZ, specifically predict that slip occurred between 35～17Ma at a rate of 3～5cm/a.展开更多
In May 2018,the primetime news casted a shocking report saying that radon concentration on a certain model of bed mattress found to be as high as 2200 Bq/m3.After a humble,the Nuclear Safety and Security Commission(NS...In May 2018,the primetime news casted a shocking report saying that radon concentration on a certain model of bed mattress found to be as high as 2200 Bq/m3.After a humble,the Nuclear Safety and Security Commission(NSSC)of Korea confirmed that significant amount of thoron gas is emanated from several mattress models marketed by a company claiming beneficial health effects of negative ions.Laboratory analysis showed that some internal fabric sheets of those mattresses contain high concentration of Th-232.It was revealed that the manufacture treated the material with so-called‘negative ion powder’procured from the market and NSSC found that its radioactive content is the monazite powder.Although measurements with reliable instruments resulted in somewhat lower values,the tentative but conservative estimates of doses to the users are still remarkable,ranging from a few to 14 mSv a year.Most of the affected models have been marketed from 2010 but earlier models,with lower thorium content,were supplied from 2006.As many as 88,000 mattresses have been produced.The manufacturer with help of the government,recalled all the affected models and separated the radioactive internals.A large amount of waste is waiting for the government decision on disposal method.Similar problems were identified in other consumer products including latex mattresses and pillows imported,hot pads,and several models of sanitary or health-aid goods.These episodes called for revisiting NORM control strategy in Korea.展开更多
文摘New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.
文摘New attention has been given to the resources of rare earth minerals over the last years. The natural shortage of these elements in the Earth’s crust and trade restrictions recently imposed by China, motivated the Brazilian Government to encourage new projects by inserting the exploitation of rare earths in the National Mining Plan, which deals with industry strategic issues in the country, helping to reduce current importation. The incentives can be in the choice of future targets for mineral exploration and for the development of laboratory studies and pilot scale processing tests.
文摘The Red River Shear Zone (RRSZ), which extends from eastern Tibet to the South China Sea, plays a central role in the hypothesis that strike\|slip extrusion of Indochina accommodated a significant portion of Indo\|Asian convergence. The massifs of the RRSZ, the only known mid\|crustal section exposed through a transform plate boundary, contain high\|grade metamorphic rocks that are believed to have been plastically deformed in a left\|lateral sense during the mid\|Tertiary. While the history of diachronous transtension along the RRSZ was previously obtained for temperatures below the brittle\|ductile transition from argon thermochronometry, the precise timing of high temperature deformation and the magnitude of strain have not been directly determined. This is a significant limitation to testing the extrusion model as magnetic anomalies from the South China Sea, interpreted to be a pull apart basin at the SE termination of the RRSZ, specifically predict that slip occurred between 35～17Ma at a rate of 3～5cm/a.
文摘In May 2018,the primetime news casted a shocking report saying that radon concentration on a certain model of bed mattress found to be as high as 2200 Bq/m3.After a humble,the Nuclear Safety and Security Commission(NSSC)of Korea confirmed that significant amount of thoron gas is emanated from several mattress models marketed by a company claiming beneficial health effects of negative ions.Laboratory analysis showed that some internal fabric sheets of those mattresses contain high concentration of Th-232.It was revealed that the manufacture treated the material with so-called‘negative ion powder’procured from the market and NSSC found that its radioactive content is the monazite powder.Although measurements with reliable instruments resulted in somewhat lower values,the tentative but conservative estimates of doses to the users are still remarkable,ranging from a few to 14 mSv a year.Most of the affected models have been marketed from 2010 but earlier models,with lower thorium content,were supplied from 2006.As many as 88,000 mattresses have been produced.The manufacturer with help of the government,recalled all the affected models and separated the radioactive internals.A large amount of waste is waiting for the government decision on disposal method.Similar problems were identified in other consumer products including latex mattresses and pillows imported,hot pads,and several models of sanitary or health-aid goods.These episodes called for revisiting NORM control strategy in Korea.
