岩石学报  2017, Vol. 33 Issue (12): 3873-3896   PDF    
“壳-幔”混合成因高Ba-Sr花岗质岩浆演化——以华北克拉通中部带老山和狐偃山岩体为例
王亚莹1 , 曾令森1 , 陈福坤2 , 蔡剑辉3 , 阎国翰4 , 侯可军3 , 王倩3     
1. 大陆构造与动力学重点实验室, 中国地质科学院地质研究所, 北京 100037;
2. 中国科学技术大学地球与空间科学学院, 合肥 230026;
3. 中国地质科学院矿产资源研究所, 北京 100037;
4. 北京大学地球与空间科学学院, 北京 100871
摘要:锆石U-Pb年龄显示华北克拉通中部带西缘老山杂岩体和狐偃山正长岩形成时间接近(128.7~125.4Ma),代表华北克拉通中部带早白垩世岩浆活动。系统的地球化学研究显示两岩体具有如下特征:(1)SiO2含量中等(57.3%~69.8%),高K2O(3.0%~8.2%)和Na2O(4.3%~6.4%)含量,低MgO(0.2%~1.4%)、CaO、TiO2和P2O5含量;(2)富集大离子亲石元素(Ba、Sr、K)和LREEs,亏损高场强元素(Nb、Ta、Zr、Hf)和HREEs。全岩地球化学特征(如高Ba、Sr含量和K/Rb比值,低Rb、Y含量)与高Ba-Sr花岗岩相符;(3)根据主量元素,相容元素(Cr、Co、Ni、V)和微量元素(Ba、Sr)特征,研究样品可分为2组:组1具有高Ba特征,Sr(87Sr/86Sr(t)=0.7049~0.7053)和Nd(εNdt)=-11.5~-9.7)同位素组成均一,经历了以黑云母为主的分离结晶作用;组2具有低Ba特征,Sr(87Sr/86Sr(t)=0.7051~0.7070)和Nd(εNdt)=-18.7~-14.8)同位素组成更加富集且分散,经历了角闪石,斜长石及磷灰石、磁铁矿和榍石等矿物分离结晶。2组样品不同的源区组分和分离结晶组合会显著改变岩浆中特征微量元素(Ba、Sr、Rb)含量和比值(Sr/Y、Nb/Ta、Dy/Yb)。本文研究表明华北克拉通中部带岩石圈地幔富集机制主要与元古代东、西陆块向中部带碰撞拼合时俯冲板块派生流体交代作用有关,该区中生代破坏机制为古太平洋板块俯冲所引起的碰撞后伸展背景下富集岩石圈地幔减压熔融、底侵至下地壳并引起"壳-幔"岩浆相互作用所形成的大规模深部岩浆抽取。
关键词: 高Ba-Sr花岗岩     岩石圈地幔交代作用     “壳-幔”岩浆混合     华北克拉通破坏    
The evolution of high Ba-Sr granitoid magmatism from "crust-mantle" interaction: A record from the Laoshan and Huyanshan complexes in the central North China Craton
WANG YaYing1, ZENG LingSen1, CHEN FuKun2, CAI JianHui3, YAN GuoHan4, HOU KeJun3, WANG Qian3     
1. Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;
2. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;
3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;
4. School of Earth and Space Sciences, Peking University, Beijing 100871, China
Abstract: Zircon U-Pb ages show that both Laoshan complex and Huyanshan syenite in the western part of the central North China Craton formed around 128.7~125.4Ma, representing the Early Cretaceous magmatism in the Central North China Craton (CNCC). Systemtic geochemsty data of this tow rocks show that (1) moderate SiO2(57.3%~69.8%), high K2O (3.0%~8.2%) and Na2O (4.3%~6.4%), low MgO (0.2%~1.4%), CaO, TiO2 and P2O5 contents; (2) enrichment of LILEs (Ba, Sr, K) and REE, depletion of HFSEs (Nb, Ta, Zr, Hf) and HREEs. Their whole rock geochemical characteristics, such as high Ba, Sr contents and K/Rb ratios, low Rb and Y contents, are consistent with high Ba-Sr granites; (3) Samples in this paper can be divided into two groups according to their major elements, compatible elements (Cr, Co,