四川冕宁木落寨稀土矿床成岩成矿的^(40)Ar/^(39)Ar年代学研究  

^(40)Ar/^(39)Ar geochronology of rocks and ores from the Muluozhai REE deposit in Mianning County,Sichuan province.

作　　者：田世洪[1] 侯增谦[2] 袁忠信[1] 陈文[2] 谢玉玲[3] 费红彩[1] 尹淑苹[3] 衣龙升[3] 周肃[4] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]国土资源部同位素地质重点实验室 [3]北京科技大学土木与环境工程学院,北市100083 [4]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2006年第10期2431-2436,共6页Acta Petrologica Sinica

基　　金：国家杰出青年基金(编号:40425014);国家重点基础研究发展规划项目(编号:2002CG412610和 G1999043211);中国地质科学院重点开放实验室专项资金(编号:KL05-9);中国地质大学(北京)地质过程与矿产资源国家重点实验室资金(编号:GPMR0548)联合资助

摘　　要：杞落寨稀土矿床位于四川省冕宁县境内,雅砻江西侧。矿体产于英碱正长岩与变质辉绿岩和大理岩接触的构造破碎带中此前,英碱正长岩被认为形成于燕山期,但没有任何同位素年龄资料的报道本文通过^(40)Ar/^(39)Ar 快中子活化分析,得出英碱正长岩微斜长石的^(40)At/^(39)Ar 坪年龄为31.2±0.56Ma,等时线年龄为30.6±2.6Ma。矿石金云母的^(40)Ar/^(39)Ar 坪年龄为35.5±0.5Ma,等时线年龄为35±1Ma。微斜长石的年龄比金云母年龄偏小,是因为两者的 Ar 同位素封闭温度不同,前者约为170℃,而后者为350℃。两者年龄差较大表明在35.5～31.2Ma 之间,矿体和岩体均进入了较慢冷却阶段,冷却速率约为41.9℃/Ma。因此,木落寨矿床的矿石与英碱正长岩的形成年龄接近,均属新生代喜马拉雅期木落寨矿床成岩成矿年龄的确定,对于进一步了解该区域偏碱性火成岩的形成时代及拓宽区域稀土找矿远景,具有很大意义。The Muluozhai REE deposit is located in the Mianning County, Sichuan Province and at the western side of Yalongjiang River. The Muluozhai REE deposit is tectonically located on the northern Jinpingshan Mountains, a Cenozoic intracontinental orogenic belt in southwestern China, The orebodies occurred in the structural fracture zones and ore veins between the nordmarkite and metamorphic diabase or marble. The Muluozhai district, with an elevation more than 4000 m, is characterized by high mountain and dangerous roads and lower degree of geological research works and has no isotopic data reported on rocks and ores so far. The nordmarkite was previously considered to be formed during the Yanshanian. In this paper, we report ^40Ar^39Ar dating on microcline from nordmarkite and phlogopite in ores, which yielded a plateau age of 31.2 ±0. 56Ma and inverse isochronal age of 30. 6 ± 2.6Ma for microcline in nordmarkite, and a plateau age of 35.5 ± 0. 5Ma and inverse isochronal age of 35 ± 1Ma for phlogopite in ores, respectively. The different closed temperature of argon isotope system of microcline （ about 170℃ ） and phlogopite （350℃） resulted in the age of microcline younger than that of phlogopite. The relatively large differences suggested that both the orebodies and pluton were in a relatively slow cooling stage with a cooling rate of about 41.9℃/Ma during 35.5 - 31.2Ma. The results indicate that the ores and nordmarkite have identical formation ages, belonging to the Himalayan period. Confirmation of the diagenetic and metallogenic ages of the Muluozhai REE deposit is of great significance on understanding the formation ages of the regional igneous rocks and searching for REE mineral resources of the same kind.

关 键 词：^40Ar^-39Ar年龄 英碱正长岩 木落寨稀土矿床 四川冕宁 

分 类 号：P597.3[天文地球—地球化学] P618.7[天文地球—地质学]