内蒙古阿如罕敖包花岗闪长岩年代学和地球化学及其对古亚洲洋演化的启示  

Chronology and geochemistry of the Aruhan granodiorite in Inner Mongolia and their implications for the evolution of the Paleo-Asian Ocean

作　　者：程天赦 杨文静[2] 张学斌[2] 滕超 杨欣杰 陈喜庆 肖登 吴荣泽[2] 周长红[2] CHENG Tian-she;YANG Wen-jing;ZHANG Xue-bin;TENG Chao;YANG Xin-jie;CHEN Xi-qing;XIAO Deng;WU Rong-ze;ZHOU Chang-hong(Cores and Samples Center of Natural Resources,China Geological Survey,Sanhe 065201,China;Tianjin Institute of Geological Survey,Tianjin 300191,China)

机构地区：[1]自然资源实物地质资料中心,河北三河065201 [2]天津市地质调查研究院,天津300191

出　　处：《岩石矿物学杂志》2024年第5期1218-1234,共17页Acta Petrologica et Mineralogica

基　　金：中国地质调查局三级项目(DD20242250,DD20221814,[2010]矿评01-19-01)。

摘　　要：内蒙古西乌旗阿如罕敖包花岗闪长岩体出露于贺根山缝合带中东段南侧。阿如罕敖包花岗闪长岩LA-ICP-MS锆石U-Pb测年结果为332±3~327±1 Ma,显示其形成于早石炭世;岩石具有高硅(SiO2含量为65.20%~68.27%)、富钠(Na_(2)O/K_(2)O值为2.56~4.35)、高铝(Al_(2)O_(3)含量为15.61%~17.35%,A/CNK值为1.02~1.17)、低镁(MgO含量为1.16%~1.61%,Mg^(#)值为29.54~41.75)等特征;稀土元素总量较低(ΣREE=44.73×10^(-6)~88.11×10^(-6))、轻重稀土元素分馏明显[LREE/HREE=6.75~10.18,(La/Yb)N=6.65~13.85]、铕无明显异常(δEu=0.79~1.07);高Sr(Sr含量为472×10^(-6)~552×10^(-6))、低Yb(Yb含量为0.86×10^(-6)~1.13×10^(-6))、低Y(Y含量为7.29×10^(-6)~11.42×10^(-6))、高Sr/Y值(Sr/Y=43.45~75.68)。岩石地球化学特征显示阿如罕敖包花岗闪长岩具有典型高Si岛弧型埃达克岩(O型)的特征,形成于活动大陆边缘弧环境,其源岩可能是俯冲洋壳+大洋沉积物的部分熔融与上覆地幔橄榄岩发生反应的产物,在形成过程中发生了结晶分异和壳源物质的混染。本次发现可能佐证了古亚洲洋贺根山洋盆中东段在早石炭世尚未闭合。结合区域研究成果,本文初步认为古亚洲洋贺根山洋盆在早石炭世可能存在双向俯冲消减,这与前人认为古亚洲洋贺根山洋盆向北单向俯冲消减的观点不同。The Aruhan granodiorite intrusion in Xiwuqi,Inner Mongolia,is exposed along the central and eastern parts of the Hegenshan suture zone.LA-ICP-MS zircon U-Pb dating shows that the ages of the granodiorite are ran-ging from 332±3 to 327±1 Ma,suggesting emplacement during the Early Carboniferous.The Aruhan granodiorite is characterized by high contents of SiO_(2)(65.20%to 68.27%),Al_(2)O_(3)(15.61%to 17.35%),Sr(472×10^(-6)to 552×10^(-6))and low contents of MgO(1.16%to 1.61%),Yb(0.86×10^(-6)to 1.13×10^(-6)),Y(7.29×10^(-6)to 11.42×10^(-6)),with Na_(2)O/K_(2)O and Sr/Y ratios ranging from 2.56 to 4.35 and 43.45 to 75.68,respectively.The total REE is low(44.73×10^(-6)to 88.11×10^(-6)),the fractionation of REE is significant[(La/Yb)N=6.65~13.85],and the anomaly of Eu(δEu=0.79 to 1.07)is not obvious.The geochemical characteristics of the whole-rock indicate that the Aruhan granodiorite belongs to typical high-SiO 2 island arc adakites(O-type)series,formed in an environment of active continental marginal arc.The source of the maga might be the product of partial melting of subducting oceanic crust with oceanic sediments,which reacts with overlying mantle peridotite.Crystalli-zation differentiation and contamination by crustal materials might occurre during its emplacement.This discovery may support the fact that the central and eastern parts of the Hegenshan Ocean was not yet closed during the Early Carboniferous.Combined with the regional research,we preliminarily believe that the Hegenshan Ocean may have undergone bidirectional subduction and abatement during the Early Carboniferous,which is different from the previ-ous view that the Hegenshan Ocean underwent unidirectional subduction and abatement northward only.

关 键 词：贺根山缝合带 埃达克岩 贺根山洋盆双向俯冲 早石炭世 活动大陆边缘弧 花岗闪长岩 西乌旗 

分 类 号：P581[天文地球—岩石学] P588.12[天文地球—地质学]