摘要
滇西地区位于特提斯构造域东南缘,其新生代岩浆活动是地质学界研究的重点之一。前人对滇西地区新生代花岗岩的成因及动力学背景的认识存在争议。本文选取临沧花岗岩岩基北部昌宁和云县两地出露的新生代二长花岗岩开展锆石U-Pb年代学、全岩主微量元素和锆石Hf同位素研究。结果表明昌宁二长花岗岩的年龄约为46Ma;岩石属于钙碱性系列,具有富钾、低钙和准过铝质的特点;富集轻稀土元素和大离子亲石元素,相对亏损高场强元素;ε_(Hf)(t)值为-4.93~-2.20,二阶段模式年龄为1.43~1.26Ga。地球化学和同位素分析结果指示其具埃达克质岩石的特征,起源于增厚的古老下地壳部分熔融。云县二长花岗岩的年龄约为27Ma;岩石属于高钾钙碱性系列,具有低镁,强过铝质特征;富集轻稀土元素和大离子亲石元素,相对亏损高场强元素;ε_(Hf)(t)值为-5.97~-2.34,二阶段模式年龄为1.99~1.26Ga。地球化学和同位素分析结果指示其具高分异S型花岗岩的特征,由地壳中变泥质岩石经白云母脱水熔融所形成。结合区域地质资料,本文认为由于俯冲的新特提斯板片回撤导致岩石圈地幔发生对流减薄,使得软流圈物质上涌从而诱发增厚的古老下地壳部分熔融,由此形成了昌宁二长花岗岩,随后新生代大规模走滑剪切活动所衍生的剪切加热诱发地壳脱水熔融,进而形成了云县二长花岗岩。
The western Yunnan is tectonically located in the southeastern margin of the Tethys tectonic domain,with intensive Cenozoic magmatism.The understanding of the genesis and dynamic background of the Cenozoic granites in this area remains controversial.We conducted zircon U-Pb geochronology,whole-rock major and trace elements,and zircon Hf isotope analyses upon the Cenozoic Changning and Yunxian monzogranites in the northern part of the Lincang granite batholith.The results show that the Changning monzogranites crystallized at~46Ma.Geochemically,they belong to calc-alkaline series,and characterized by high potassium and low calcium contents with A/CNK ratios ranging from 1.07 to 1.08,and enriched in light rare earth elements and large ion lithophile elements relative to high field strength elements.Theε_(Hf)(t)values range from-4.93 to-2.20,with the two-stage model ages from 1.43Ga to 1.26Ga,belonging to adakitic affinity.The source rocks of the monzogranites are originated from partial melting of the thickened ancient lower crust.By contrast,the Yunxian monzogranites is formed at~27Ma.They belong to strongly peraluminous sereies and featured by high-K calc-alkaline with low magnesium contents,and enriched in light rare earth elements and large ion lithophile elements and depleted in high field strength elements.Theε_(Hf)(t)values and two-stage model ages(t DM2)of analysized samples range from-5.97 to-2.34 and 1.99Ga to 1.26Ga respectively.The sources rocks of this pluton are of highly differentiated S-type granite characteristics,and are generated by dehydration melting of metapelitic rocks.Combined with regional geological data,we propose a two-stage model to explain the formation of these monzogranites:(1)due to the rollback of the subducted Neo-Tethys slab,the lithospheric mantle underwent convective thinning,inducing asthenosphere upwelling and partial melting of the thickened ancient lower crust and formed the Changning monzogranites;(2)subsequently,the shear heating which derived from the large-scale strike-slip shearing activities in the Cenozoic induced dehydration melting of the continental crust and generated the Yunxian monzogranites.
作者
班丁
李刚
刘正宏
王晨
徐仲元
董晓杰
李文庆
玄雨菲
BAN Ding;LI Gang;LIU ZhengHong;WANG Chen;XU ZhongYuan;DONG XiaoJie;LI WenQing;XUAN YuFei(College of Earth Sciences,Jilin University,Changchun 130061,China;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources,Changchun 130061,China;Nanjing Center,China Geological Survey,Nanjing 210016,China)
出处
《岩石学报》
北大核心
2025年第7期2388-2411,共24页
Acta Petrologica Sinica
基金
国家自然科学基金项目(91955205)资助.
