滇西北衙富碱斑岩的特征及成因  

Characteristics and Origin of Alkali-rich Porphyries from Beiya in Western Yunnan

作　　者：徐受民[1] 莫宣学[1] 曾普胜[2] 张文洪 赵海滨[1] 赵寒冬[1] 

机构地区：[1]中国地质大学地球科学与资源学院 [2]云南财经大学资源环境系,云南昆明650221 [3]云南地矿资源股份有限公司北衙分公司,云南鹤庆671000

出　　处：《现代地质》2006年第4期527-535,共9页Geoscience

基　　金：国家重点基础研究计划项目(2002CB412603)

摘　　要：提供了与滇西北衙大型金矿床密切相关的富碱斑岩的主量元素及稀土和微量元素的分析数据，对富碱斑岩的成因、起源条件和源区类型进行了讨论。研究表明，北衙地区的富碱斑岩具有较高的SiO2（w（SiO2）〉68％）和Al2O3（w（Al2O3）=13．45％-15．22％），具有富集Sr（w（Sr）=365×10^-6-930×10^-6），亏损HREE（w（Yb）=0．64×10^-6-1．17×10^-6和Y（w（Y）=7．17×10^-6-12．25×10^-6），较高的w（Sr）／w（Y）、w（La）N／w（Yb）。比值，无明显的负Eu异常等特征，显示了与埃达克岩的某些相似性。然而，富碱斑岩低的w（MgO）、w（Cr）和埘（Ni），又与典型的埃达克岩有所不同。富碱斑岩产出的地质背景及岩石学和地球化学特征表明，富碱斑岩并非起源于俯冲的大洋板片，而是源于加厚地壳的底部，源区为榴辉岩相岩石。富碱斑岩显著富集Rb、Ba、Th、K，可能与俯冲大陆板片的脱水作用和流体的交代作用有关。产生富碱斑岩岩浆的动力学机制，与印度大陆板块和扬子大陆板块对“三江”的相向俯冲、金沙江-红河断裂带的走滑拉分及其诱发的软流圈上涌和流体交代作用有关。This paper presents petrological and geochemical data of Au-mineralization-related alkali-rich porphyries in the Beiya gold deposit and its adjacent regions, western Yunnan. Geochemically, the alkali-rich porphyries from Beiya have relatively high contents of SiO2 （ 〉 68% ） and Al2O3 （ 13.45% - 15.22% ）, high Sr/Y and （La/Yb）N ratios, enrichment in Sr （365 × 10^-6 - 930 ×10^-6） but depletion in Yb and Y （Yb： 0.64 × 10^-6 -1. 17 ×10^-6; Y： 7. 17 × 10^-6 -12.25 × 10^-6） , and weak Eu negative anomalies. All of those characteristics mentioned above indicate that alkali-rich porphyries from Beiya are somewhat similar to adakites in geochemistry. However, their lower contents of MgO, Cr and Ni are different from those of typical adakites. Petrological and geochemical characteristics of alkali-rich porphyries suggest that magmas might not be generated from subducted oceanic slab, but likely from the base of thickened crust, corresponding to eclogite-facies. High abundance of trace elements Rb, Ba, Th and K in alkali-rich porphyries may be attributed to fluid metasomatism. Dynamically, magma generation might be related to a face-to-face intra-continental subduction beneath Sanjiang blocks of the India continent versus the Yangtze continent, strike-slip movements of the Jinshajiang-Red River fault and tectonics-induced asthenospheric upwelling and metasomatism by fluids released from subducting slabs.

关 键 词：富碱斑岩 埃达克岩 下地壳 扬子大陆板块 北衙 滇西 

分 类 号：P588.1[天文地球—岩石学]