摘要
内蒙古中部苏尼特左旗南东地区出露的早古生代花岗岩类岩石和玄武-安山岩序列,对于限定苏尼特左旗岛弧演化以及兴蒙造山带在该地区的构造演化具有重要意义。花岗岩类岩石主要由花岗闪长岩和花岗岩组成,LA-ICP-MS锆石UPb测年结果显示其形成于晚奥陶世-早志留世(441～449Ma)。花岗岩类岩石表现出高硅(Si O2=69. 60%～77. 36%)、铝(Al_2O_3=12. 70%～15. 40%),低镁(MgO=0. 19%～0. 81%)、铁(Fe2O3=0. 94%～3. 49%)的特征。此外,花岗岩类岩石εHf(t)值介于-0. 81～+5. 64之间,且二阶段模式年龄介于1119～1478Ma之间,这表明其主要来源于新生地壳的部分熔融。玄武-安山岩SiO2含量介于49. 13%～57. 82%之间,并具有较高的镁(MgO=3. 31%～6. 57%)、铁(Fe2O3=6. 54%～9. 63%)含量,且Zr/Hf比值(35. 4～37. 6)与原始地幔相应值接近,再结合该火山岩高铝(Al2O3=16. 77%～18. 34%)、高钠(Na2O=3. 46%～5. 05%)、高Th/Ce比值(0. 12～0. 25)以及Sr正异常等特征,表明其来源于俯冲交代的地幔楔的部分熔融。本次研究的所有火成岩样品均属于钙碱性系列,并表现出富集大离子亲石元素(Rb、Th、K等)和轻稀土元素,亏损高场强元素(Nb、Ta、Ti、P等)的特征。此外,其Rb/Zr比值(0. 07～1. 0)以及Nb(4. 24×10-6～15. 17×10-6)含量与正常大陆弧接近,结合前人已报道的年代学以及地球化学资料,表明苏尼特左旗东南地区早古生代火成岩与古亚洲洋向北的俯冲演化有关。
The Early Pale0zoic granitic rocks and volcanic sequence outcropped in the southeastern Sonid Zuoqi area of central Inner Mongolia are important significances in constraining the tectonic evolution of the Sonid Zuoqi arc and even the Inner Mongolia-Da Hinggan Orogenic Belt. In this study,we present new zircon U-Pb ages,precise whole-rock geochemistry of major and trace elements and Hf isotope compositions for these granitic rocks and basaltic-andesite sequences. The LA-ICP-MS zircon U-Pb dating results indicate that the granitic rocks are formed in Late Ordovician and Early Silurian（ 441 - 449 Ma）. The granitic rocks are dominated in granites with minor granodiorites,which are characterized by high abundances of Si O2（ 69. 60% - 77. 36%） and Al2 O3（ 12. 70% -15. 40%）,low MgO（ 0. 19% - 0. 81%） and Fe2 O3（ 0. 94% - 3. 49%） contents. In addition,the granitic rocks yield slightly negative to positive εHf（ t） values（-0. 81 - ＋ 5. 64） and young Hf two-stage model（ tDM2） ages（ 1119 - 1478 Ma）. The petrological and geochemical analyses reveal that the primary magma that formed the granitic rocks was possibly originated from the partial melting of predominant juvenile crustal materials with subordinate Mesoproterozoic continental crust. The basaltic-andesite sequences are composed of basalt,trachyandesite and andesite. They are featured by low Si O2 content（ 49. 13% - 57. 82%）,high MgO（ 3. 31% -6. 57%） and Fe2 O3（ 6. 54% - 9. 63%） contents. In addition,the Zr/Hf ratios（ 35. 4 - 37. 6） of the basaltic-andesite sequences are close to those of primitive mantle. Moreover,the basaltic-andesite sequences exhibit high abundances of Al2 O3（ 16. 77% - 18. 34%）and Na2 O（ 3. 46% - 5. 05%）,positive Sr anomaly and high Th/Ce ratios（ 0. 12 - 0. 25）. Such features suggest that the basalticandesite magma could be derived from the partial melting of metasomatized mantle wedge. All of the studied igneous rocks belong to calc-alkaline series,exhibit enrichment of large ion l
作者
唐建洲
张志诚
陈彦
姬泽佳
杨金福
TANG JianZhou;ZHANG ZhiCheng;CHEN Yan;JI ZeJia;YANG JinFu(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,Peking University,Beijing 100871,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第10期2973-2994,共22页
Acta Petrologica Sinica
基金
国家重点研发计划(2017YFC0601302)
"973"项目(2013CB429801)联合资助
