摘要
西准噶尔巴尔雷克山南部的石炭系黑山头组火山岩主要由灰-灰紫色（气孔）杏仁状安山岩、杏仁状玄武安山岩组成，属亚碱性系列。LA-ICP-MS锆石U-Pb年龄为349±8Ma，MSWD=0．14（95％置信度），时代属早石炭世。Mg#介于23．82～50．45，全碱含量（NazO＋K2O=3．74％～8．02％）较高且相对富钠，轻稀土（LREE）相对富集[（La／Yb）Ν=2．87～13．41]且分馏较好[（La／Sm）Ν值均大于1（1．46～3．41）]，重稀土分馏较差[（Od／Yb）Ν=1．46～3．48]。仅部分样品有微弱的负铕异常（δEu=0．82～1．47）。大离子亲石元素（LILE）Ba、Th、K、Sr相对富集，其中Ba、K的富集尤为明显，高场强元素（HFSE）Νb、Ta相对亏损，Ti轻微亏损，Zr、Hf略富集。地球化学特征表明其为俯冲带流体交代岩石圈地幔的产物，综合分析认为其形成于活动大陆边缘环境。黑山头组火山岩时代的确定及构造环境信息为进一步认识西准噶尔巴尔雷克一带的构造演化提供了新的证据。
The volcanic rocks of the Heishantou Formation in the area of Barleik, West Junggar, consist of gray purple （vesicular） almond andesite and almond shaped basaltic andesite, belonging to sub-alkaline series. High-precision LA-ICP-MS zircon U-Ph dating shows that the rocks formed at the age of 3498Ma, with MSWD=0.14 （95% conf.）, suggesting an age of Early Carboniferous. These rocks are characterized by moderate Mg#（23.82～50.4）, relatively high alkali （Na2O ＋ K2O= 3.74%～8.02%）, and relative enrichment in Na, enrichment in LREE [（La/Yb）N=2.87～13. 41] and well fractionated [（La/Sm）N = 1.46～3.41], and weak HREE fractionation [（Gd/Yb）N =1.46～3.48]. Only part of the samples shows weak negative Eu anomalies （δEu=0.82～1.47）. Large ion lithophile elements （LILEs, eg. , Ba, Th, K and Sr） are relatively enriched, especially Ba and K, and high field-strength elements （HFSEs, eg., Nb, Ta, and Ti） are depleted, but Zr and Hf slightly enriched. Geochemical features indicate that the volcanic rocks are the products of metasomatism between subduction-zone fluids and lithospheric mantle. Comprehensive analysis indicates that the volcanic rocks derived from active continental margin. The determination of the age and tectonic environment information of volcanic rocks from the Heishantou Formation provides new evidence for further understanding of the tectonic evolution in the area of Barleik in West Junggar.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2013年第3期343-352,共10页
Acta Geologica Sinica
基金
国土资源大调查项目(编号XJZBKD2008-04)资助的成果
