摘要
大别造山带是三叠纪华南陆块俯冲于华北陆块之下所形成的陆-陆碰撞造山带,在早白垩世发育强烈的碰撞后岩浆作用。侵位于宿松群高压变质岩石中的大量中—基性脉岩是认识大陆板块深俯冲过程的壳幔相互作用和折返过程中岩石圈构造响应的重要载体之一。报道了有关宿松地体中—基性脉岩的岩石学和地球化学研究结果,探讨了其成因特征和源区演化。结果表明:中—基性脉岩总体具有安粗岩的性质,主量元素含量变化较大,SiO2质量分数介于48.45%~61.37%,偏基性脉岩具有偏高的MgO、Cr、Ni含量;所有脉岩样品的微量元素和稀土元素组成均一,大离子亲石元素和轻稀土元素相对富集,重稀土元素和高场强元素亏损;脉岩样品都具有相对富集的同位素组成特征,包括较高的初始N(^(87)Sr)/N(^(86)Sr)值(0.706 3~0.710 9),较低的εNd(t)值(-22.7^-15.1);初始Pb同位素比值也相对偏低,初始N(^(206)Pb)/N(^(204)Pb)值为15.858 5~17.196 7,初始N(207Pb)/N(^(204)Pb)值为15.207 2~15.332 1,初始N(^(208)Pb)/N(^(204)Pb)值为36.814 4~37.633 8,这些特征暗示岩浆源区具有扬子板块下地壳物质的显著贡献。总之,中—基性脉岩具有高Sr含量和低Y、Yb含量,与埃达克质岩组成类似,可能指示宿松地体早白垩世中—基性脉岩的形成与增厚的造山带岩石圈拆沉及其和地幔的相互作用有关。
Dabie orogenic belt is a typical continental collision belt by Triassic subduction and collision between Yangtze Block and North China Block.It is characterized by not only the largest exposure of Triassic ultrahigh-pressure metamorphic rocks in the world,but also the most profound occurrence of post-collisional Cretaceous igneous rocks.Early Cretaceous intermediatemafic dykes,intruding into high-pressure metamorphic rocks of Susong terrene of Dabie orogenic belt,are important for understanding the process of mantle-crustal interaction during the deepsubduction of the continental block and the tectonic respondence in the uplift.The petrological and geochemical characteristics of these intermediate-mafic dykes were presented,and the petrogenesis and geological implications were discussed.The results show that the intermediate-mafic dykes are mainly latite in composition;they have varied compositions in major elements(e.g.,mass fractions of SiO2are48.45%-61.37%),and basic dyke samples show relatively high mass fractions of MgO,Cr and Ni;all the dyke samples display homogeneous characteristics in trace element and rare earth element compositions,such as enrichment in large ion lithophile elements(LILE)and light rare earth elements(LREE),and obvious depletion in high field strength elements(HFSE,e.g.,Nb,Zr and Ti)and heavy rare earth elements(HREE).Isotopic compositions indicate that magma sources of the intermediate-mafic dykes are relatively enriched with the characteristics of initial N(^(87)Sr)/N(^(86)Sr)(0.706 3-0.710 9)andεNd(t)(-22.7--15.1);the initial Pb isotopic ratios are low with N(^(206)Pb)/N(^(204) Pb)of 15.858 5-17.196 7,N(^(207)Pb)/N(^(204)Pb)of 15.207 2-15.332 1,and N(^(208)Pb)/N(^(204)Pb)of 36.814 4-37.633 8,indicating the contribution of lower crustal materials of Yangtze Block.In general,the Early Cretaceous intermediate-mafic dykes in Susong terrene have high Sr,low Y and Yb contents,being comparable to typical adakite,implying that the generation of these dykes would be related to the delamination of thickened orogenic lower crust and the relative interaction with upper mantle.
出处
《地球科学与环境学报》
CAS
2016年第6期835-848,共14页
Journal of Earth Sciences and Environment
基金
国家自然科学基金项目(40973042
41090372)
中央高校基本科研业务费专项资金项目