漠河盆地东南部中生代火山岩年代学与地球化学研究  

Chronology and geochemistry of Mesozoic volcanic rocks from southeastern Mohe Basin

作　　者：郭宏宇[1] 孙德有[1] 孙如江[1] 苟军[1] 杨东光[1] 敬海鑫 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《世界地质》2015年第1期55-66,共12页World Geology

基　　金：中国地质调查局项目(1212011121081);中国核工业地质局项目(ddy2011002)联合资助

摘　　要：漠河盆地东南部中生代火山岩地层主要由光华组和甘河组组成,锆石U--Pb定年结果确定两组火山岩分别形成于128-125 Ma和126-120 Ma。光华组流纹岩高硅富碱、贫钙铁镁;轻重稀土分馏较明显[w（La/Yb）N=13.01-17.99],铕异常中等（δEu=0.49-0.67）;富集大离子亲石元素Rb、K、Th、U,亏损高场强元素Nb、Ta、P、Ti;锆石εHf（t）值为-2.5-3.0,两阶段Hf模式年龄为989-1 130 Ma;岩浆源区为中元古代末期的地壳物质。甘河组粗安岩和玄武粗安岩富碱高钾,镁指数较大（Mg#≈48）;稀土元素配分曲线为轻稀土富集的右倾型[w（La/Yb）N=12.67-23.21],铕异常不明显（δEu=0.77-0.91）;富集Rb、Ba、K、Th、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素;锆石εHf（t）值为-1.2-4.1;岩浆源区为俯冲流体交代过的岩石圈地幔,岩浆经历了一定程度分离结晶作用。Mesozoic volcanic rocks in southeastern Mohe Basin include those from the Guanghua Formation and Ganhe Formation. Zircon U--Pb ages indicate that they were formed in 128 - 125 Ma and 126 - 120 Ma,respectively. Guanghua Formation corresponding to rhyolite in chemical composition,is rich in silicon and alkalis,poor in calcium,ferrum and magnesium,relatively significant fractionation of HREE and LREE [w（ La / Yb）N=13. 01 - 17. 99] and middle Eu anoalies（ δEu = 0. 49 - 0. 67）,LILE（ Rb,K,Th,U） and depleted in HSFE（ Nb,Ta,P,Ti）; The εHf（ t） values range from- 2. 5 to 3. 0,and the corresponding tDM2 vary from 989 Ma to1 130 Ma. The magma could be derived from partial melting of crustal material during late Mesoproterozoic. The Ganhe Formation corresponding to trachyandesites and basaltic trachyandesites in chemical composition,is characterized by high potassium,rich alkali and high M values（ Mg#≈48）,enriched in LREE [w（ La /Yb）N= 12. 67 -23. 21] with weak Eu anoalies（ δEu = 0. 77 - 0. 91）,depleted in HFSE（ Nb,Ta,P,Ti） and relatively rich in LILE（ Rb,Ba,K,Th,U）; The εHf（ t） values range from- 1. 2 to 4. 1. The geochemical data suggest that the magma could be derived from partial melting of lithosphere mantle metasomatized by subduction fluids,and proba-bly experienced a degree of fractional crystallization.

关 键 词：火山岩 锆石年龄 地球化学 岩石成因 漠河盆地 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]