云南白马寨镍矿区煌斑岩^(40)Ar-^(39)Ar定年和地球化学特征  

^(40)Ar-^(39)Ar dating and geochemical characteristics of lamprophyres in the Baimazhai nickel deposit,Yunnan province.

作　　者：管涛[1] 黄智龙[1] 许成[1] 张振亮[1] 严再飞[1] 陈觅[1] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学重点实验室

出　　处：《岩石学报》2006年第4期873-883,共11页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(G1999043203);中国科学院知识创新工程项目(KZCX2-101)资助.

摘　　要：云南白马寨镍矿区煌斑岩全部为云煌岩。两个样品的^(40)Ar/^(39)Ar定年结果分别为32．46±0．62Ma和32．01±0．60Ma,表明矿区煌斑岩为哀牢山断裂带新生代早期高钾岩浆活动的产物。在化学组成上,矿区煌斑岩具有高M值[100×Mg/ (Mg+Fe^(2+))](67．42～86．35)、高ALK(K_2O+Na_2O为7．01%～9．81%)、富钾(K_2O/Na_2O为1．66～2．64)、富大离子亲石元素(如Sr、Rb、Ba等)和LREE、明显的Ta、Nb、Ti负异常的特征。Sr-Nd同位素具有高(^(87)Sr/^(86)Sr)_0比值(0．70625～0．70912)和低ε_(Nd) (-5．22～-3．68)的特征,位于EM1和EM2地幔端元之间,有更靠近EM2的趋势。元素和同位素地球化学特征表明矿区煌斑岩的源区为交代富集地幔,进一步判别表明源岩处于尖晶石相方辉橄榄岩和石榴石相二辉橄榄岩的混合线上,以尖晶石相方辉橄榄岩为主。源区交代富集的矿物既有金云母,也有角闪石。岩浆演化过程中经历了橄榄石+斜长石±磷灰石±铁钛氧化物的结晶分异。岩浆形成于大陆弧的构造背景,俯冲的陆壳和古特提斯洋壳对富集的源区均有贡献。白马寨镍矿区煌斑岩和哀牢山断裂带新生代早期其它高钾岩浆岩具有相近的年代、一致的地球化学特征,表明它们具有相似的源区,受控于相同的构造背景。Lamprophyres in the Baimazhai nickel deposit are classified as minettes. The dating results of two samples are 32.46 ± 0.62Ma and 32, 01 ± 0.60Ma, respectively, which indicate they are products of early pulse of Cenozoic potassic magmatism in the Ailaoshan fault belt. As to chemical composition, the lamprophyres have high M value [ 100 Mg/（ Mg ＋ Fe^2＋ ） ] （67.42 - 86, 35 ） , with enriched ALK （ the content of K2O ＋ Na2O range from 7.01% to 9.81% ）, potassium （ the ratios of K2O/Na2O range from 1.66 to 2.64） , large ion lithophile elements （ e, g, Sr, Rb, Ba, etc ） and LREE, and show marked negative Ta-Nb-Ti anomalies. The Sr-Nd isotopic data pose the characteristics of high （^87Sr/^86 Sr）0 （0. 70625 - 0. 70912 ） and lowεNd （ - 5. 22 - -3. 68 ） , and lie between EMI and EM2 end members, especially near EM2. All these characteristics show that the lamprophyres were derived from a metasomatized enriched mantle source region. Further identification show the source rock lie between spinel harzburgite and garnet lherzolite and is dominated by the former, and metasomatized enriched minerals in the source region include phlogopite and amphibole. The magma predominantly evolved through fractional crystallization of olivine ＋ plagioclase ＋ apatite ＋ Ti-Fe oxides. The lamprophyres formed in continental arc tectonic setting. Both subducted continental and ancient Tethyan oceanic crust contributed to enriched mantle source region. The lamprophyres coincide with other early pulse of Cenozoic potassic magmatic rocks in the Ailaoshan fault belt in age and geochemical characteristics, which indicate they were derived from similar mantle source region and formed in the same tectonic setting.

关 键 词：煌斑岩 ^40Ar/^39Ar定年 地球化学特征 成因 白马寨 云南 

分 类 号：P588.137[天文地球—岩石学] P597.3[天文地球—地质学]