华北克拉通大青山-集宁地区古元古代变质沉积岩的锆石氧同位素组成:SHRIMP微区原位分析  

Oxygen isotopic compositions of zircons from Paleoproterozoic metasedimentary rocks in the Daqingshan-Jining area,North China Craton: In situ SHRIMP analysis

作　　者：董春艳[1] 万渝生[1] 龙涛[1] 张玉海[1] 刘建辉[1] 马铭株[1] 颉颃强[1] 刘敦一[1] 

机构地区：[1]中国地质科学院地质研究所北京离子探针中心,北京100037

出　　处：《岩石学报》2016年第3期659-681,共23页Acta Petrologica Sinica

基　　金：国家"973"项目(2012CB416600);国家自然科学基金项目(41002062);中国地质调查局项目(1212010811033;12120113013700;121201121062)联合资助

摘　　要：在已获得锆石U-Pb年龄基础上,我们首次对孔兹岩带典型出露区大青山和集宁土贵乌拉地区古元古代变质沉积岩进行了锆石SHRIMP氧同位素研究。锆石具有复杂的内部结构和年龄分布。大青山地区古元古代早期变质沉积岩4个样品碎屑锆石的δ18O为5.52‰～7.11‰,部分重结晶锆石的δ18O为7.22‰～7.90‰,变质新生锆石的δ18O为6.37‰～8.31‰。大青山地区古元古代晚期变质沉积岩2个样品的锆石O同位素组成特征与古元古代早期的类似,另外2个样品的锆石O同位素组成与之不同,碎屑锆石、部分重结晶锆石和变质新生锆石的δ18O分别为6.26‰～10.80‰、9.00‰～11.20‰和9.66‰～11.90‰。集宁土贵乌拉地区古元古代晚期超高温变质沉积岩4个样品不存在碎屑锆石,变质锆石的δ18O变化范围为11.41‰～13.57‰。主要认识如下：1）大青山地区碎屑沉积物主要来自新太古代晚期-古元古代早期成熟度不高的TTG花岗质岩石物源区,与之相比,集宁土贵乌拉地区古元古代晚期超高温岩石的变质原岩成熟度更高;2）不同类型变质沉积岩变质新生锆石的δ18O和变质新生锆石与碎屑锆石的Δ18O存在明显区别,主要反映了岩石体系和变质流体的O同位素组成不同;3）大青山地区高角闪岩相-麻粒岩相变质沉积岩,重结晶锆石的O同位素完全重置,但U-Th-Pb体系未完全重置,集宁土贵乌拉地区超高温变质沉积岩的重结晶锆石O和U-Th-Pb同位素体系都完全重置。变质作用强度不同是主要原因。This paper reports for the first time the O isotope compositions for zircons from Paleoproterozoic metasedimentary rocks in the Daqinshan-Jining area,zircon U-Pb ages of which have mostly been reported elsewhere. The zircons show complex internal structures and age distributions. For four Early Paleoproterozoic metasedimentary rocks from the Daqingshan area,the detrital,partially recrystallized and metamorphic zircons have δ18O values of 5. 52‰ ～ 7. 11‰,7. 22‰ ～ 7. 90‰ and 6. 37‰ ～ 8. 31‰,respectively.The zircons of two Late Paleoproterozoic metasedimentary samples in the Daqingshan area are similar in O isotope composition to those from the Early Paleoproterozoic metasedimentary rocks. However,other two Late Paleoproterozoic metasedimentary samples have theδ18O values of detrital,partially recrystallized and metamorphic zircons being 6. 26‰ ～ 10. 80‰,9. 00‰ ～ 11. 20‰ and 9. 66‰ ～11. 90‰,respectively. Four Late Paleoproterozoic UHT metasedimentary samples in the Tuguiwula area of Jining contain no detrital zircons but have metamorphic zircons with δ18O values ranging from 11. 41‰ to 13. 57‰. Combined with early studies,we have arrived at conclusions as follows. 1） The Paleoproterozoic sediments in the Daqingshan area were mainly derived from the Late Neoarchean to Early Paleoproterozoic TTG rocks with low maturity. In contrast,the protolith of the Late Paleoproterozoic UHT metamorphic rocks in Tuguiwula shows a relatively high maturity. 2） Either δ18O of metamorphic zircons or Δ18O of metamorphic and detrital zircons show large variations in the metamorphic rocks,mainly due to the differences of rock types and metamorphic fluid. 3）In the high amphibolite facies-granulite facies metasedimentary rocks in the Daqingshan area,the recrystallized zircons show complete reset in O isotope,but not in U-Th-Pb system; in the UHT metasedimentary rocks in Tuguiwula of Jining,the recrystallized zircons show complete reset in both O isotope and U-Th-Pb system. This also indicat

关 键 词：锆石 氧同位素 SHRIMP 变质沉积岩 古元古代 华北克拉通 

分 类 号：P588.34[天文地球—岩石学] P597[天文地球—地质学]