摘要
伊犁地块阿腾套山地区发育一套富钠碱长花岗斑岩,样品富钠贫钾(Na2O/K2O=1.85),低Al2O3(12.01%)、Sr(21.4×10-6),高Y(36.7×10-6)、Yb(4.46×10-6),轻重稀土分馏程度低(LaN/YbN=3.83),Eu负异常强烈(δEu=0.19),具有极其亏损的Hf同位素组成(εHf(t)=+7.3^+15.1),其特征与低压型TTG相同。同时样品低MgO(0.47%)和Mg#(26),是新生的贫钾玄武质陆壳在低压条件下部分熔融的产物。按An-Ab-Or标准矿物分类方法,样品位于奥长花岗岩区域,在讨论TTG时应将奥长花岗岩的概念扩大到包含富钠碱长花岗岩。样品具有很高的锆石饱和温度(900℃),结合区域资料,形成于弧后拉张环境。锆石U-Pb年龄为366.4±1.6Ma,属泥盆纪末期。在伊犁-中天山地块南缘持续出露有志留纪-石炭纪弧岩浆岩,而阿腾套山弧后地区岩浆作用集中于早石炭世,花岗斑岩样品是泥盆纪末期伊犁地块南部由弧向弧-盆体系转换的关键记录。
A suite of sodium-rich alkali-feldspar granite porphyries outcrop in Atengtao Mountain,Yili Block.The sample is rich in sodium and poor in potassium (Na2O/K2O=1.85),with extremely depleted Hf isotopic composition,similar to TTG series.Meanwhile,it is characterized by low Al2O3 (12.01%),Sr (21.4×10-6),MgO (0.47%),Mg# (26),high Y (36.7×10-6),Yb (4.46×10-6) contents and weakly fractionation of LREE and HREE (LaN/YbN=3.83) and apparently negative Eu anomaly (δEu=0.19),which is a product of the partial melting of a new potassium-poor basaltic continental crust under low-pressure conditions.According to the An-Ab-Or normative classification,the sample belongs to trondhjemite.We suggest that the concept of trondhjemite should be extended to include sodium-rich alkali-feldspar granites when discussing TTG group.The sample has a very high zircon saturation temperature (900℃),combined with regional data,which is generated in a back-arc extension place.That the zircon U-Pb age is 366.4±1.6 Ma reveal the granite porphyries were emplaced at the end of the Devonian.In the south margin of Yili-Central Tianshan Block,arc magmatic rocks were produced during Silurian to Carboniferous,while the magmatism in the back-arc area of the Atengtao Mountain was concentrated in the Early Carboniferous.The Latest Devonian granite porphyries should be the critical records for the transformation of the South Yili Block from arc to arc-basin system.
作者
滕明耀
谢德胜
罗耀清
王伟宁
TENG Ming-yao;XIE De-sheng;LUO Yao-qing;WANG Wei-ning(School of Earth Science and Resources,Chang'an University,Xi'an 710054,Chinag;No.9 Geological Party,Bgmerd of Xinjiang,Urumqi 830000,China)
出处
《世界有色金属》
2019年第24期182-185,共4页
World Nonferrous Metals
基金
区域地质调查项目(T16-1-LQ02)
