The 300±20 Ma anomalously radioactive trachytes of Wadi El Kareim, central Eastern Desert, are a significant example of U-mineralization related to the alkaline volcanics in Egypt. Extensive portable gamma-ray sp...The 300±20 Ma anomalously radioactive trachytes of Wadi El Kareim, central Eastern Desert, are a significant example of U-mineralization related to the alkaline volcanics in Egypt. Extensive portable gamma-ray spectrometric data has been utilized to identify geological factors controlling uranium mobility in the geological units along the three detailed study locations of Kab Al-Abyad, South Wadi(W) Al-Tarafawy and W. Al-Farkhah; their eT h/eU ratios averaging around 4.1, 3.7 and 5.6 respectively. Quantitative analysis with the integration of mobility maps and geological studies suggest two systems controlling U-migration within the geological units(confined system and unconfined system). In the confined system, the syngenetically formed U have experienced mobility after leaching and are redistributed in the presence of an incorporation carrier during transportation(probably as carbonate complexes). Then the retardant for uranium is achieved by sorption or by coprecipitation with the aid of Fe oxy-hydroxide, and finally the formation of immobile secondary U-bearing minerals takes place along a lithogeochemical trap. In contrast to the confined system, the unconfined one is basically lacking the lithogeochemical trap which influences the final accumulation of U-bearing minerals. The radioactivity of the trachyte rocks arises from the radioactive minerals uranophane and betauranophane with U-and/or Th-bearing minerals samarskite, Th-rich REE silicates, monazite and allanite.展开更多
The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has bee...The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.展开更多
The Yusishan deposit is a newly found leptynite-type niobium and tantalum(Nb-Ta)deposit,which is located in the Eastern Altun of Gansu Province.The leptynite of the Neoproterozoic Aoyougou Formation occurs more than 1...The Yusishan deposit is a newly found leptynite-type niobium and tantalum(Nb-Ta)deposit,which is located in the Eastern Altun of Gansu Province.The leptynite of the Neoproterozoic Aoyougou Formation occurs more than 10 km long and 3 km wide.In this paper,we carried out a detailed study of the leptynite and related mineralization.The U-Pb dating of zircon reveals ages of 831±5 Ma and 790±5 Ma for the unmineralized leptynite and 491±4 Ma and 455±4 Ma for the mineralized leptynite.The petrographic and geochemical evidence identified the protolith of the leptynite as alkalin e volcanic rocks that erupted during Neoproterozoic at ca.830 Ma.At ca.490 Ma,the tectono-magmatic and metamorphic event triggered remobilization and enrichment of Nb-Ta as well as other critical metals(REE,Zr,Hf etc)with the formation of industry orebodies in the leptynite strata.The Yushishan deposit presents many similarities with the alkaline volcanic rocks related rare metal deposits in the south Qinling of China and the Brochman,Toogni and Southern Peak Range deposits in Australian.We therefore propose that the Yushishan deposit is a new type(sub-type)of Nb-Ta deposit and termed as leptynite type that represents the metamorphic counterpart of the alkaline volcanic rocks related rare metal deposits.展开更多
We present the disaster-forced biological evolution model as a general framework that includes Darwinian ＂phylogenic gradualism＂, Eldredge-Gould＇s ＂punctuated equilibrium＂, mass extinctions, and allopatric, parap...We present the disaster-forced biological evolution model as a general framework that includes Darwinian ＂phylogenic gradualism＂, Eldredge-Gould＇s ＂punctuated equilibrium＂, mass extinctions, and allopatric, parapatric, and sympatric speciation. It describes how reproductive isolation of organisms is established through global disasters due to supernova encounters and local disasters due to radioactive volcanic ash fall-outs by continental alkaline volcanism. Our new evolution model uniquely highlights three major factors of disaster-forced speciation： enhanced mutation rate by higher natural radiation level, smaller population size, and shrunken habitat size （i.e., isolation among the individual pop- ulations）. We developed a mathematical model describing speciation of a half-isolated group from a parental group, taking into account the population size （Ne）, immigration rate （m）, and mutation rate （μ）. The model gives a quantitative estimate of the speciation, which is consistent with the observations of speciation speed. For example, the speciation takes at least 105 generations, if mutation rate is less than 10 3 per generation per individual. This result is consistent with the previous studies, in which μ is assumed to be 10 3-10-5. On the other hand, the speciation is much faster （less than l0S generations） for the case that μ is as large as 0.1 in parapatric conditions （m 〈 μ）. Even a sympatric （m ~ 1 ） speciatiou can occur within 103 generations, if mutation rate is very high （μ- 1 mutation per individual per generation）, and if Ne 〈 20-30. Such a high mutation rate is possible during global disasters due to supernova encounters and local disasters due to radioactive ash fall-outs. They raise natural radiation level by a factor of 100-1000. Such rapid speciation events can also contribute to macro-evolution during mass extinction events, such as observed during the Cambrian explosion of biodiversity. A similar rapid speciation （though in a much smaller scale） also has been undergoing in cichlid fishes and great African apes in the last several tens of thousand years in the current African rift valley, including the origin of humankind due to the radioactive ash fall-outs bv continental alkaline volcanism.展开更多
The volcanic rocks from Baiyingaolao Formation in the northeastern Hailar Basin are mainly composed of rhyolite and trachydacite. U-Pb dating of zircon shows these volcanic rocks formed in Early Cretaceous( 128--124 M...The volcanic rocks from Baiyingaolao Formation in the northeastern Hailar Basin are mainly composed of rhyolite and trachydacite. U-Pb dating of zircon shows these volcanic rocks formed in Early Cretaceous( 128--124 Ma). Geochemical data indicate that they are sub-alkaline series in composition and rich in alkali and potassium. All samples have similar rare earth element patterns characterized by high total rare earth elements contents( ∑REE = 113. 96 × 10- 6-204. 33 × 10- 6),significant fractionation of heavy and light rare earth elements( ∑LREE / ∑HREE = 3. 10-4. 52) with middle negative Eu anomalies( δEu = 0. 46-0. 76).The trace elements are characterized by enrichment in large-ion lithophile elements such as K,Rb,LREE and depletion in high field strength elements e. g. Nb,Ta,HREE,P and Ti,while enriched in Th and U. Rhyolite and trachydacite contain low initial87 Sr /86 Sr ratios( 0. 704 9--0. 7 053) and positive εNd( t) values( ca. 4.15). These data suggest that the magma of rhyolite and trachydacite were derived from mafic lower crust newly accreted from mantle,with the evolutional trend of comagmatic fractional crystallization.展开更多
文摘The 300±20 Ma anomalously radioactive trachytes of Wadi El Kareim, central Eastern Desert, are a significant example of U-mineralization related to the alkaline volcanics in Egypt. Extensive portable gamma-ray spectrometric data has been utilized to identify geological factors controlling uranium mobility in the geological units along the three detailed study locations of Kab Al-Abyad, South Wadi(W) Al-Tarafawy and W. Al-Farkhah; their eT h/eU ratios averaging around 4.1, 3.7 and 5.6 respectively. Quantitative analysis with the integration of mobility maps and geological studies suggest two systems controlling U-migration within the geological units(confined system and unconfined system). In the confined system, the syngenetically formed U have experienced mobility after leaching and are redistributed in the presence of an incorporation carrier during transportation(probably as carbonate complexes). Then the retardant for uranium is achieved by sorption or by coprecipitation with the aid of Fe oxy-hydroxide, and finally the formation of immobile secondary U-bearing minerals takes place along a lithogeochemical trap. In contrast to the confined system, the unconfined one is basically lacking the lithogeochemical trap which influences the final accumulation of U-bearing minerals. The radioactivity of the trachyte rocks arises from the radioactive minerals uranophane and betauranophane with U-and/or Th-bearing minerals samarskite, Th-rich REE silicates, monazite and allanite.
基金funded by the Open Foundation of the Beijing SHRIMP Center (DDC15-016)the Applied Basic Research Program Youth Project of Yunnan Province (2016DF031)the National Basic Research Program of China (2015CB452605)
文摘The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.
基金financially supported by projects from the National Natural Science Foundation of China(No.42030811)the Ministry of Science and Technology(MOST)National Key R&D Program of China(No.2017YFC0602405)the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(No.MSFGPMR03-2)。
文摘The Yusishan deposit is a newly found leptynite-type niobium and tantalum(Nb-Ta)deposit,which is located in the Eastern Altun of Gansu Province.The leptynite of the Neoproterozoic Aoyougou Formation occurs more than 10 km long and 3 km wide.In this paper,we carried out a detailed study of the leptynite and related mineralization.The U-Pb dating of zircon reveals ages of 831±5 Ma and 790±5 Ma for the unmineralized leptynite and 491±4 Ma and 455±4 Ma for the mineralized leptynite.The petrographic and geochemical evidence identified the protolith of the leptynite as alkalin e volcanic rocks that erupted during Neoproterozoic at ca.830 Ma.At ca.490 Ma,the tectono-magmatic and metamorphic event triggered remobilization and enrichment of Nb-Ta as well as other critical metals(REE,Zr,Hf etc)with the formation of industry orebodies in the leptynite strata.The Yushishan deposit presents many similarities with the alkaline volcanic rocks related rare metal deposits in the south Qinling of China and the Brochman,Toogni and Southern Peak Range deposits in Australian.We therefore propose that the Yushishan deposit is a new type(sub-type)of Nb-Ta deposit and termed as leptynite type that represents the metamorphic counterpart of the alkaline volcanic rocks related rare metal deposits.
基金supported by Grants-in-Aid for Scientific Research(23224012) from the Japanese Ministry of Education, Science,Sports,Technology,and Culture
文摘We present the disaster-forced biological evolution model as a general framework that includes Darwinian ＂phylogenic gradualism＂, Eldredge-Gould＇s ＂punctuated equilibrium＂, mass extinctions, and allopatric, parapatric, and sympatric speciation. It describes how reproductive isolation of organisms is established through global disasters due to supernova encounters and local disasters due to radioactive volcanic ash fall-outs by continental alkaline volcanism. Our new evolution model uniquely highlights three major factors of disaster-forced speciation： enhanced mutation rate by higher natural radiation level, smaller population size, and shrunken habitat size （i.e., isolation among the individual pop- ulations）. We developed a mathematical model describing speciation of a half-isolated group from a parental group, taking into account the population size （Ne）, immigration rate （m）, and mutation rate （μ）. The model gives a quantitative estimate of the speciation, which is consistent with the observations of speciation speed. For example, the speciation takes at least 105 generations, if mutation rate is less than 10 3 per generation per individual. This result is consistent with the previous studies, in which μ is assumed to be 10 3-10-5. On the other hand, the speciation is much faster （less than l0S generations） for the case that μ is as large as 0.1 in parapatric conditions （m 〈 μ）. Even a sympatric （m ~ 1 ） speciatiou can occur within 103 generations, if mutation rate is very high （μ- 1 mutation per individual per generation）, and if Ne 〈 20-30. Such a high mutation rate is possible during global disasters due to supernova encounters and local disasters due to radioactive ash fall-outs. They raise natural radiation level by a factor of 100-1000. Such rapid speciation events can also contribute to macro-evolution during mass extinction events, such as observed during the Cambrian explosion of biodiversity. A similar rapid speciation （though in a much smaller scale） also has been undergoing in cichlid fishes and great African apes in the last several tens of thousand years in the current African rift valley, including the origin of humankind due to the radioactive ash fall-outs bv continental alkaline volcanism.
文摘The volcanic rocks from Baiyingaolao Formation in the northeastern Hailar Basin are mainly composed of rhyolite and trachydacite. U-Pb dating of zircon shows these volcanic rocks formed in Early Cretaceous( 128--124 Ma). Geochemical data indicate that they are sub-alkaline series in composition and rich in alkali and potassium. All samples have similar rare earth element patterns characterized by high total rare earth elements contents( ∑REE = 113. 96 × 10- 6-204. 33 × 10- 6),significant fractionation of heavy and light rare earth elements( ∑LREE / ∑HREE = 3. 10-4. 52) with middle negative Eu anomalies( δEu = 0. 46-0. 76).The trace elements are characterized by enrichment in large-ion lithophile elements such as K,Rb,LREE and depletion in high field strength elements e. g. Nb,Ta,HREE,P and Ti,while enriched in Th and U. Rhyolite and trachydacite contain low initial87 Sr /86 Sr ratios( 0. 704 9--0. 7 053) and positive εNd( t) values( ca. 4.15). These data suggest that the magma of rhyolite and trachydacite were derived from mafic lower crust newly accreted from mantle,with the evolutional trend of comagmatic fractional crystallization.
