The U-Th-REE-Nb(Ta)-polymetallic mineralization is generally related to either the silica-undersaturated syenites,the silica-oversaturated alkaline/peralkaline granites or igneous carbonatites.In this study,the author...The U-Th-REE-Nb(Ta)-polymetallic mineralization is generally related to either the silica-undersaturated syenites,the silica-oversaturated alkaline/peralkaline granites or igneous carbonatites.In this study,the authors report a new mineralization type,which is related to the magmatic-hydrothermal albitite(with mineral assemblage predominated by albite with volume content>90%),as exemplified by the Chachaxiangka deposit in Qinghai Province of China.The Chachaxiangka deposit is the first albititerelated U-Th-REE-Nb deposit recognized in China and the mineralization can be divided into 3 types:the vein-type,the disseminated veinlet type and breccia type,of which the former 2 are predominant.Three mineralization stages can be identified according to the detailed mineralogical analyses,including the magmatic stage,main hydrothermal mineralization stage and post-ore stage.By comprehensive analyses of the mineralogical,major and trace element compositions,the authors suggest that the albitite vein is magmatic-hydrothermal in origin and both the magmatic evolution and overprint of the hydrothermal fluids play important roles in the formation of the albitite and related polymetallic mineralization.Phase separation between the silicate melt and carbonate/phosphate melt might take place in the magmatic stage,yet the immiscibility between the silicate melt and chloride-dominated fluids is the most important mechanism for the REE mineralization and also causes the Nb-Th re-mobilization and enrichment.The red color of the albitite aplite vein is an eye-catching prospecting mark in the field and more mineralization can be expected at depth and in the surrounding areas.The discovery of the new albitite type U-Th-REENb mineralization give rise to new ideas during future U-Th-REE-Nb exploration,not only in the Qaidam-Altun belt,but also other areas across China.展开更多
Gneisses with anatectic characteristics from the Liansan island in the Sulu UHPM(ultra-high pressure metamorphic)belt were studied for petrography,titanite U-Pb dating and mineral geochemistry.Three origins of garnets...Gneisses with anatectic characteristics from the Liansan island in the Sulu UHPM(ultra-high pressure metamorphic)belt were studied for petrography,titanite U-Pb dating and mineral geochemistry.Three origins of garnets are distinguished:metamorphic garnet,peritectic garnet and anatectic garnet,which are formed in the stages of peak metamorphism,retrograde anatexis and melt crystallization,respectively.The euhedral titanite has a high content of REE and high Th/U ratios,which is interpreted as indicating that it was newly-formed from an anatectic melt.The LA-ICP-MS titanite U-Pb dating yields 214-217 Ma ages for the titanite(melt)crystallization.The distribution of trace elements varies in response to the different host minerals at different stages.At the peak metamorphic stage,Y and HREE are mainly hosted by garnet,Ba and Rb by phengite,Sr,Nb,Ta,Pb,Th,U and LREE by allanite and Y,U and HREE by zircon.During partial melting,Y,Pb,Th,U and REE are released into the melt,which causes a dramatic decline of these element contents in the retrograde minerals.Finally,titanite absorbs most of the Nb,U,LREE and HREE from the melt.Therefore,the different stages of metamorphism have different mineral assemblages,which host different trace elements.展开更多
本文报道了柴北缘大陆型超高压变质带沙柳河地区发现的蛇绿岩型地幔橄榄岩,其原始矿物组合为橄榄石+斜方辉石+铬铁矿。方辉橄榄岩中识别出两个世代的橄榄石,第一世代橄榄石(OI^1)残晶发育扭折带,化学成分与现代大洋地幔橄榄岩的橄榄石一...本文报道了柴北缘大陆型超高压变质带沙柳河地区发现的蛇绿岩型地幔橄榄岩,其原始矿物组合为橄榄石+斜方辉石+铬铁矿。方辉橄榄岩中识别出两个世代的橄榄石,第一世代橄榄石(OI^1)残晶发育扭折带,化学成分与现代大洋地幔橄榄岩的橄榄石一致,第二世代橄榄石(OI^2)Fo 值高达94～97,其内部含有细小的流体包裹体,是第一世代橄榄石蛇纹石化后再次变质的产物。斜方辉石残晶的成分具有高 Al 和 Ca 的特征,与大洋地幔橄榄岩中斜方辉石的成分一致。温压条件的估算反映该橄榄岩体属于典型的尖晶石相方辉橄榄岩。其围岩是由堆晶辉长岩变质的条带状蓝晶石榴辉岩,二者构成了大洋蛇绿岩套的下部层位,并且与区内具有 N-MORB 和 OIB 性质的榴辉岩共生。这些特征表明该方辉橄榄岩应代表洋壳下伏地幔橄榄岩,从而揭示大陆造山带从早期的大洋俯冲消亡到大陆俯冲碰撞的完整过程。展开更多
There are two generations of white micas in retrograded coesite-bearing eclogite from the Yangkou area near Qingdao, eastern China. The secondary phengite developed along the folliations in eclogite is the majority of...There are two generations of white micas in retrograded coesite-bearing eclogite from the Yangkou area near Qingdao, eastern China. The secondary phengite developed along the folliations in eclogite is the majority of the white micas. Nd and Sr isotopic disequilibriums between garnet and retrograded omphacite as well as secondary phengite have been observed. Consequently, the Rb-Sr ages ((193±4) Ma-(195±4) Ma) given by the tie lines of the secondary phengite + garnet or whole rock may predate the formation time of the phengite. The Rb-Sr age of (183±4) Ma given by the secondary phengite + retrograde omphacite is much closer to the formation time of the phengite indicating the retrograde age of eclogite instead of a cooling age of eclogite at 500℃.展开更多
The studies of seismic tomography and wide-angle reflection have been carried out to reveal the velocity structUrebeneath the eastern Dabie orogenic belt. The result from the seismic tomography shows the high velocity...The studies of seismic tomography and wide-angle reflection have been carried out to reveal the velocity structUrebeneath the eastern Dabie orogenic belt. The result from the seismic tomography shows the high velocity bodiesmight be positioned to a depth of only about 1 .5 km below sea level within the Dabie ultra-high pressure metamorphic (UHPM) belt; the fan-profile shows the Shuihou-Wuhe fault, the demarcation between the South Dabieand the North Dabie, slopes to the south-west at a dip angle of about 45° in the bottom of upper crust. The wideangle reflection shows the middle crustal boundaries and the complex features from the lower crust.展开更多
基金This study was financially supported by the National Key R&D Program of China(2016YFE0206300)Natural Science Foundation of China(41772082)+1 种基金China Geological Survey(DD2016013601)China Nuclear Geological Bureau(201654).Colleagues from No.203 Research Institute of Nuclear Industry are greatly appreciated for their field support.
文摘The U-Th-REE-Nb(Ta)-polymetallic mineralization is generally related to either the silica-undersaturated syenites,the silica-oversaturated alkaline/peralkaline granites or igneous carbonatites.In this study,the authors report a new mineralization type,which is related to the magmatic-hydrothermal albitite(with mineral assemblage predominated by albite with volume content>90%),as exemplified by the Chachaxiangka deposit in Qinghai Province of China.The Chachaxiangka deposit is the first albititerelated U-Th-REE-Nb deposit recognized in China and the mineralization can be divided into 3 types:the vein-type,the disseminated veinlet type and breccia type,of which the former 2 are predominant.Three mineralization stages can be identified according to the detailed mineralogical analyses,including the magmatic stage,main hydrothermal mineralization stage and post-ore stage.By comprehensive analyses of the mineralogical,major and trace element compositions,the authors suggest that the albitite vein is magmatic-hydrothermal in origin and both the magmatic evolution and overprint of the hydrothermal fluids play important roles in the formation of the albitite and related polymetallic mineralization.Phase separation between the silicate melt and carbonate/phosphate melt might take place in the magmatic stage,yet the immiscibility between the silicate melt and chloride-dominated fluids is the most important mechanism for the REE mineralization and also causes the Nb-Th re-mobilization and enrichment.The red color of the albitite aplite vein is an eye-catching prospecting mark in the field and more mineralization can be expected at depth and in the surrounding areas.The discovery of the new albitite type U-Th-REENb mineralization give rise to new ideas during future U-Th-REE-Nb exploration,not only in the Qaidam-Altun belt,but also other areas across China.
基金supported by funds from the National Natural Science Foundation of China(Grant Nos.42172067,41972064,U1906207)the SDUST Research Fund。
文摘Gneisses with anatectic characteristics from the Liansan island in the Sulu UHPM(ultra-high pressure metamorphic)belt were studied for petrography,titanite U-Pb dating and mineral geochemistry.Three origins of garnets are distinguished:metamorphic garnet,peritectic garnet and anatectic garnet,which are formed in the stages of peak metamorphism,retrograde anatexis and melt crystallization,respectively.The euhedral titanite has a high content of REE and high Th/U ratios,which is interpreted as indicating that it was newly-formed from an anatectic melt.The LA-ICP-MS titanite U-Pb dating yields 214-217 Ma ages for the titanite(melt)crystallization.The distribution of trace elements varies in response to the different host minerals at different stages.At the peak metamorphic stage,Y and HREE are mainly hosted by garnet,Ba and Rb by phengite,Sr,Nb,Ta,Pb,Th,U and LREE by allanite and Y,U and HREE by zircon.During partial melting,Y,Pb,Th,U and REE are released into the melt,which causes a dramatic decline of these element contents in the retrograde minerals.Finally,titanite absorbs most of the Nb,U,LREE and HREE from the melt.Therefore,the different stages of metamorphism have different mineral assemblages,which host different trace elements.
文摘本文报道了柴北缘大陆型超高压变质带沙柳河地区发现的蛇绿岩型地幔橄榄岩,其原始矿物组合为橄榄石+斜方辉石+铬铁矿。方辉橄榄岩中识别出两个世代的橄榄石,第一世代橄榄石(OI^1)残晶发育扭折带,化学成分与现代大洋地幔橄榄岩的橄榄石一致,第二世代橄榄石(OI^2)Fo 值高达94～97,其内部含有细小的流体包裹体,是第一世代橄榄石蛇纹石化后再次变质的产物。斜方辉石残晶的成分具有高 Al 和 Ca 的特征,与大洋地幔橄榄岩中斜方辉石的成分一致。温压条件的估算反映该橄榄岩体属于典型的尖晶石相方辉橄榄岩。其围岩是由堆晶辉长岩变质的条带状蓝晶石榴辉岩,二者构成了大洋蛇绿岩套的下部层位,并且与区内具有 N-MORB 和 OIB 性质的榴辉岩共生。这些特征表明该方辉橄榄岩应代表洋壳下伏地幔橄榄岩,从而揭示大陆造山带从早期的大洋俯冲消亡到大陆俯冲碰撞的完整过程。
基金This work was supported by the State Key Basic Research Development Program (Grant No. G1999075503) and the National Natural Science Foundation of China (Grant No. 49794042).
文摘There are two generations of white micas in retrograded coesite-bearing eclogite from the Yangkou area near Qingdao, eastern China. The secondary phengite developed along the folliations in eclogite is the majority of the white micas. Nd and Sr isotopic disequilibriums between garnet and retrograded omphacite as well as secondary phengite have been observed. Consequently, the Rb-Sr ages ((193±4) Ma-(195±4) Ma) given by the tie lines of the secondary phengite + garnet or whole rock may predate the formation time of the phengite. The Rb-Sr age of (183±4) Ma given by the secondary phengite + retrograde omphacite is much closer to the formation time of the phengite indicating the retrograde age of eclogite instead of a cooling age of eclogite at 500℃.
文摘The studies of seismic tomography and wide-angle reflection have been carried out to reveal the velocity structUrebeneath the eastern Dabie orogenic belt. The result from the seismic tomography shows the high velocity bodiesmight be positioned to a depth of only about 1 .5 km below sea level within the Dabie ultra-high pressure metamorphic (UHPM) belt; the fan-profile shows the Shuihou-Wuhe fault, the demarcation between the South Dabieand the North Dabie, slopes to the south-west at a dip angle of about 45° in the bottom of upper crust. The wideangle reflection shows the middle crustal boundaries and the complex features from the lower crust.
