Geochemical Characteristics of Karamay Jurassic Basalts and Implication on Crust-Mantle Interaction
详细信息
- 责任者：Chen Shuangshuang (State Key Laboratory of Geological Processes and Mineral Resources ; Faculty of Earth Sciences ; China University of Geosciences ; Wuhan 430074 ; China) ; Su Yuping
- 刊名：Geochimica
- 出版年：2013
- 卷期：42(1)
- 关键词：玄武岩 ; basalts ; 新疆 ; Xinjiang
- 页码：p.29-45
- 图表：illus., 5 tables, 81 refs.
- 分类号：0801
- issnNo：ISSN0379-1726
- isbnNo：CN44-1398/P
摘要
Mesozoic-Cenozoic deep lithospheric process in the northern Xinjiang has been much concerned but not studied in detail.In this paper,systematic studies on Karamay Jurassic basalts in the Western Junggar were carried out,including field geology,petrography,whole-rock major and trace elements,Sr-Nd isotope,zircon U-Pb geochronology and Hf isotope.These basalts unconformably overlie rocks of the Early Carboniferous Tailegula Formation,and show obvious columnar jointing,massive structure and porphyritic texture.The phenocryst minerals are mainly composed of Ca-rich plagioclase,augite,olivine,and siderite for some samples and the groundmass displays intergranular and intersertal texture.They belong to alkaline series(σ=3.87–4.68),and are strongly enriched in large ion lithophile elements(such as Rb,Ba,K) and light rare earth elements,with no Eu anomaly(δEu=1.02–1.06).They also have a relatively low positive εNd(t) values(+2.95–+3.02) and high(87Sr/86Sr)i values(0.7048–0.7049),demonstrating their mantle source is similar to that of OIB-type basalts.These basalts may be produced by low degree of partial melting in the garnet lherzolite stability field at depths of more than 80 km.Zircon from the Karmay basalts yielded a U-Pb concordant age of(357.3±5.1) Ma,similar to the age of their country rocks from the Tailegula Formation,indicating that the zircons were inherited from early magmatism.Quite different from the late Palaeozoic island-arc and post-collisional mafic volcanic rocks,the Jurassic basalts were derived from relatively less depleted mantle source in a stable intraplate tectonic environment.This mantle source was related to metasomatism of enriched melt,which were produced by metamorphic remelting of the subducting slab and sinking lithosphere.
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