摘要
东昆仑西段夏日哈木地区出露一套鄂拉山组火山岩,其成因对古特提斯洋演化过程具有重要的指示意义。通过对其进行锆石U-Pb年代学、Hf同位素和全岩主、微量元素、Sm-Nd同位素等研究确定其形成时代、岩石成因及其构造意义。安山岩中锆石的^(206)Pb/^(238)U加权平均年龄为223±2Ma,属于晚三叠世。岩石具有较低的SiO_(2)(59.45%~63.10%)和Mg^(#)值(28~51)、较高的Al_(2)O_(3)(16.19%~17.66%)和K_(2)O含量(1.42%~3.50%),表现为弱过铝高钾钙碱性系列。岩石具有富集轻稀土和大离子亲石元素,亏损高场强元素的特征,结合全岩ε_(Nd)(t)值(-4.3~-3.1)和锆石ε_(Hf)(t)值(-3.4~+1.1),表明其可能来源于受富集地幔熔体底侵的古老下地壳部分熔融。结合区域地质资料,认为这些安山岩形成于碰撞后伸展环境,而古特提斯洋在晚三叠世已关闭。本文研究结果也说明在造山带研究中需谨慎利用火成岩的岛弧性质来判断其俯冲环境这一构造属性。
The volcanic rocks of the Elashan Formation exposed in the Xiarihamu area,western segment of East Kunlun Orogenic Belt,are of great significance for studying the evolution of the Paleo-Tethys Ocean.Detailed zircon U-Pb,Hf isotope,whole-rock geochemistry and Sm-Nd isotope analyses upon the andesites in Xiarihamu area are conducted to determine their formation ages and petrogenesis,and discuss the tectonic significance.The results show that the zircon ^(206)Pb/^(238)U weighted average age of the andesites is 223±2Ma,belonging to the Late Triassic.The andesites have low SiO_(2)(59.45%~63.10%)contents and Mg^(#)values(28~51),high Al_(2)O_(3)(16.19%~17.66%)and K_(2)O(1.42%~3.50%)contents,suggesting a weak peraluminous,high-potassium calcium alkaline series.Furthermore,they are enriched in LREE and LILE contents,and depleted in HFSE,with whole-rock ε_(Nd)(t)and zircon ε_(Hf)(t)values of-4.3~-3.1 and-3.4~+1.1,respectively.All these characteristics show that the andesites were derived from partial melt of an ancient lower crust which was also influenced by underplating of an enriched lithospheric mantle magma.Based on regional geological data,it is suggested that the andesites in Xiarihamu area are related to Paleo-Tethys evolution and formed in a post-collisional extensional setting instead of a compressive setting.The results of this paper also indicate that it should be careful to identify a subduction environment by using the island arc characteristics of igneous rocks in the orogenic belt.
作者
段雪鹏
孟繁聪
张帮禄
王宗起
于晓飞
DUAN XuePeng;MENG FanCong;ZHANG BangLu;WANG ZongQi;YU XiaoFei(Development and Research Center,China Geological Survey,Beijing 100037,China;China University of Geosciences,Beijing 100083,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第11期3341-3358,共18页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41272052、42072049)
中国地质调查局项目(121201102000150005-08、D20221649、DD202211692)联合资助.
