闽西南晚中生代四方岩体同位素年代学、地球化学及其构造意义  

Geochronology and geochemical characteristics in late Mesozoic Sifang pluton,southwestern Fujian, and their s ignificance

作　　者：毛建仁[1] 陶奎元[1] 李寄嵎[2] 谢方贵[1] 许乃政[1] 

机构地区：[1]南京地质矿产研究所,南京210016 [2]台湾大学地质系

出　　处：《岩石学报》2002年第4期449-458,共10页Acta Petrologica Sinica

基　　金：原地矿部项目 (编号 :地科专 96-0 2 );中国地质调查局地质调查项目 (编号:199910 2 0 110 0 0 3 )资助

摘　　要：闽西南地区四方岩体主要由花岗闪长岩和花岗闪长斑岩组成 ,花岗闪长岩单颗粒锆石 U-Pb年龄为 10 7.8±1.2 Ma,角闪石 Ar-Ar年龄为 10 4.8± 0 .8Ma,形成于早白垩世。岩体是在伸展拉张构造环境下以快速冷却 (50～ 60℃ / Ma)侵位的 ,岩石相对富 Na2 O,A / CNK<1,具壳 -幔混合源 I型花岗岩特征。岩石富 K、Rb、Th、U、L REE,贫 Ti、Nb、Ta、Sr,具火山弧/活动大陆边缘钙碱性岩系的特征。 (87Sr/ 86Sr) i为 0 .70 63 5～ 0 .70 898,εNd(t)为 -5.2 4～ -3 .69,TDM为 1.3 3～ 1.2 1Ga。岩石主要由幔源岩浆与中下地壳物质部分熔融形成的花岗质岩浆的混合形成的。与闽东沿海地区相比 ,晚中生代时闽西南地区总体处于与华南软流圈地幔上涌有关的伸展拉张构造环境 ,但由玄武岩浆底侵作用引发的壳幔作用并不强烈。Sifang pluton in southwestern Fujian is composed of granodiorite and granodiorite porphyry. The Pb-206/U-238 ages of zircon in granodiorite are 107.7 Ma and 108.0 Ma, respectively. The Ar-40-Ar-39 plateau and anti-isochron ages of hornblende in granodiorite are 104.8 +/- 0.8 Ma and 104.5 +/- 0.8 Ma, respectively. These data suggest that Sifang pluton was formed in Early-Cretaceous. It was emplaced under the higher cooling velocity (50similar to60degreesC/Ma) setting. The granodiorites are enriched in Na2O relatively, while possess feature of I-type granite of crust-mantle mixing sources. They are enriched moderately in K, Rb, U, Th LREE and depleted in Ti, Nb, Ta, Sr with higher (La/Yb)(n) and LREE/HREE ratios. They are characterized by Sr-Nd isotopic compositions with (Sr-87/Sr-86)(i) = 0. 70635similar to0. 70898, (epsilonNd)(t)= -5.24similar to-3.69 and T-DM = 1.33similar to1.21 Ga. They were formed by mixing of the partial melting granitic magma of crust-derived material and mantle-derived basic magma. The studying area was situated in the extensional tectonic environment under the upwelling of asthenosphere mantle in South China generally, but underplating was not so strong. The intermediate-acid magmatism in the Early-Cretaceous was closely related to the mineralization.

关 键 词：同位素 地球化学 花岗闪长岩 年代学 热演化史 构造环境 福建 

分 类 号：P588.122[天文地球—岩石学] P597[天文地球—地质学]