【摘要】 四川牦牛坪稀土矿床与稀土矿化时空密切共生的碳酸岩-正长岩碱性杂岩体的成岩时代为喜山期,碳酸岩呈脉状沿正长岩岩体中心侵入。两者具有相似的²⁰⁶Pb/²⁰⁴Pb和²⁰⁸Pb/²⁰⁴Pb比值,但碳酸岩²⁰⁷Pb/²⁰⁴Pb比值变化较大,且低于正长岩。这种差异并不能归因于地壳物质的混染作用,而是反映了地幔源区的特征。在Pb、Sr和Nd同位素图解中,矿区碳酸岩和正长岩显示低Pb,高Sr同位素的特征,部份碳酸岩Pb同位素落在MORB内,而Sr和Nd同位素明显不同于MORB,相对接近洋岛玄武岩的Ⅰ型富集地幔（EM1）。喜山扬扬子板块呈楔形体插入龙门山地壳之中,受挤压的中下部地壳向前陆深处发生俯冲,并延伸至攀西裂谷顶部富集地幔体中,被交代的富集地幔经不同程度的和不连续的部份熔融作用形成碱性岩浆,整个演化过程导致了源区成份的不均一性。更多还原

【Abstract】 The carbonatite-syenite complexes in the Maoniuping REE deposit, Sichuan province, which are spatially and temporallyassociated with rare earth mineralization, were emplaced at the time of Himalayan. They show similar ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pbratios, but the carbonatites show large spread in ²⁰⁷Pb/²⁰⁴Pb ratios and lower than those for syenites. This reflects the characteristics oftheir mantle source, rather than crustal contamination. In Sr-Nd-Pb diagrams, the carbonatites and syenites are characterized by lowerPb and higher Sr isotopic ratios. The Pb isotopes for carbonatites are plotted to the range of the MORB, while the Sr and Nd isotopesare different to the MORB, relatively close to the EM1 of the OIB. The Yangtze plate was penetrated as a wedge into the crust atLongmenshan during the Himalayan period. The extruded middle and lower crust onwards subducted and extended into the enrichedmantle in the top of the Panxi rift. This was followed by variable degrees and discrete partal melting of the metasomatized enrichedmantle to produce alkali magma. The whole evolutionary process resulted in inhomogeneity of the mantle source.更多还原