扬子板块北缘神门地区铁船山组凝灰质流纹岩岩石学特征及成因探讨  

Petrological characteristics and genesis of tuffaceous rhyolite of Tiechuanshan Formation in Shenmen area,Northern margin of the Yangtze Plate

作　　者：王健[1] 严冰[1] 王鑫鋆 廖怡 Wang Jian;Yan Bing;Wang Xinyun;Liao Yi(College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu 610059,Sichuan,China;Sichuan Chuanhe Nuclear Geological Engineering Co.,Ltd,Chengdu 610052,Sichuan,China;The 9th Geological Brigade Of Sichuan Province,Deyang 618000,Sichuan,China)

机构地区：[1]成都理工大学地球与行星科学学院,四川成都610059 [2]四川川核地质工程有限公司,四川成都610052 [3]四川省第九地质大队,四川德阳618000

出　　处：《陕西地质》2024年第2期11-25,共15页Geology of Shaanxi

基　　金：国家重点研发计划(编号:2023YFC2906802)。

摘　　要：扬子板块北缘新元古代岩浆岩分布范围较广,种类较多,并受多期岩浆-构造热活动影响明显。铁船山组凝灰质流纹岩具斑状和霏细结构,发育流纹构造。凝灰质流纹岩地球化学特征表明,属钙碱性系列火山岩,其经历了一定程度的分异演化,岩浆源区岩石以陆壳组分为主。ΣREE(138 ppm~181 ppm)与陆壳平均值接近,K_(2)O的变化范围为在2.42 wt.%~3.23 wt.%;具有弱的负Eu异常,Eu/Eu*变化范围为0.50~0.64,Mg^(#)值较低(36.8~45),暗示加厚下地壳来源的特征。轻重稀土元素比值的变化范围为3.61~4.23,表明轻重稀土元素存在明显的分馏,(La/Sm)N的变化范围为2.53~4.75,表明轻稀土分馏程度较强、富集程度较高,(La/Yb)N的变化范围为2.67~3.73,表明其形成于陆壳底部高压力下源区岩石脱水熔融的地质环境,微量元素比值指示为壳源且更接近下地壳。结合源区判别,神门地区凝灰质流纹岩具有典型的岛弧花岗岩的地球化学特征,为俯冲挤压背景下岛弧环境的产物。The Neoproterozoic magmatic rocks in the northern margin of the Yangtze plate exhibit a wide distribution range and a high degree of diversity,and are significantly affected by multi-stage magmatic-tectonic thermal activities.The tuffaceous rhyolite of the Tiechuanshan Formation exhibits porphyritic and fine structure,developing rhyolite structure in the process.The geochemical characteristics of tuffaceous rhyolite indicate that it belongs to the calc-alkaline series of volcanic rocks,which have undergone a certain degree of differentiation and evolution.The rocks in the magma source area are primarily composed of continental crust.The ΣREE(138 ppm~181 ppm)is in close proximity to the average value of the continental crust,and the range of K_(2)O is 2.42 wt.%~3.23 wt.%.There is a weak negative Eu anomaly,with an Eu/Eu*range of 0.50~0.64,and the Mg^(#)value is low(36.8~45),which collectively suggests the characteristics of a thickened lower crust source.The ratio of light and heavy rare earth elements varies from 3.61 to 4.23,indicating the presence of notable fractionation between these two groups of elements.The range of(La/Sm)N is 2.53~4.75,indicating that the degree of fractionation of light rare earth is significant and the degree of enrichment is high.The variation range of(La/Yb)N is 2.67~3.73,indicating that it is formed in the geological environment of dehydration and melting of rocks in the source area under high pressure at the bottom of the continental crust.The ratio of trace elements suggests that the source is the crust and that the formation is more closely related to the lower crust.In light of the source discrimination diagram of tuffaceous rhyolite in the Shenmen area,it can be posited that the tuffaceous rhyolite was formed as a result of partial melting of the new mafic lower crust,which may have been influenced by fluid metasomatism of the subducted slab.When considered alongside the source discrimination diagram of tuffaceous rhyolite in the Shenmen area,the tuffaceous rhyolite in the Shen

关 键 词：扬子板块北缘 凝灰质流纹岩 铁船山组 地球化学 构造环境 岩石成因 

分 类 号：P581[天文地球—岩石学] P595[天文地球—地质学]