摘要
对华北东南缘荆山花岗岩进行了锆石U-Pb定年、微量元素和Hf同位素分析,全岩主微量元素和Sr-Nd同位素分析.LA-ICP-MS锆石U-Pb定年结果表明,荆山花岗岩形成于晚侏罗世(160.9±0.8~161.6±1.5 Ma).残留锆石的U-Pb年龄主要为三叠纪和新元古代,分别与大别-苏鲁造山带超高压变火成岩的变质年龄和原岩年龄一致.这些花岗岩为钙碱性-高钾钙碱性,具有弧型的微量元素分布特征和富集的Sr-Nd-Hf同位素组成,即高的全岩(^(87)Sr/^(86)Sr)i比值(0.7080~0.7091),低的ε_(Nd)(t)值(-15.6~-13.5)和锆石ε_(Hf)(t)值(-23.1~-9.5),对应的两阶段Nd-Hf模式年龄主要为古元古代.这些锆石U-Pb同位素年代学和地球化学特征与大别-苏鲁造山带超高压变火成岩一致,表明它们之间存在成因联系.特别地,残留锆石新元古代和三叠纪U-Pb年龄是俯冲华南陆壳的标志性特征.因此,荆山花岗岩是俯冲华南陆壳部分熔融的产物,华南陆壳是三叠纪大陆碰撞过程中进入华北地壳之中的.这些花岗岩具有低的Rb含量、高的Sr和Ba含量,低的Rb/Sr比值以及低的全岩锆饱和温度和锆石Ti温度(~700℃),表明它们源于俯冲华南陆壳低温加水部分熔融,可能与侏罗纪古太平洋板块俯冲于中国东部之下有关.
In this paper it presents a combined study of zircon U-Pb ages,trace elements and Hf isotopes,and whole-rock majortrace elements and Sr-Nd isotopes for the Jingshan granites from the southeast margin of the North China block(NCB).LA-ICPMS zircon U-Pb dating yielded Late Jurassic ages of 160.9±0.8 to 161.6±1.5 Ma.Relict zircons have U-Pb ages of mainly Triassic and Neoproterozoic,in agreement with metamorphic and protolith ages for the ultrahigh-pressure(UHP)meta-igneous rocks in the Dabie-Sulu orogenic belt,respectively.These granites are calc-alkaline to high-K calc-alkaline,and exhibit arc-type trace element features and enriched Sr-Nd-Hf isotope compositions,i.e.high whole-rock(^(87)Sr/^(86)Sr)i ratios of 0.7080 to 0.7091,lowε_(Nd)(t)values of-15.6 to-13.5 and zirconε_(Hf)(t)values of-23.1 to-9.5,with two-stage Nd-Hf model ages mainly of Paleoproterozoic.These zircon U-Pb geochronological and geochemical characteristics are consistent with those of the UHP metaigneous rocks in the Dabie-Sulu orogenic belt,indicating a genetic link between them.In particular,the Neoproterozoic and Triassic U-Pb ages of relict zircons are characteristic features of the subducted continental crust of the South China block(SCB).Therefore,the Jingshan granites are the product of partial melting of the subducted SCB continental crust,which would be incorporated into the crust of the NCB during the Triassic continental collision.These granites have low Rb contents,high Sr,Ba contents,and thus low Rb/Sr ratios,and low zirconium saturation and Ti-in-zircon temperatures(~700℃),suggesting their derivation from low-temperature partial melting of the subducted SCB continental crust with water addition,which might be related to the subduction of the paleo-Pacific plate beneath eastern China in the Jurassic.
作者
杨阳
孙国超
赵子福
Yang Yang;Sun Guochao;Zhao Zifu(CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;CAS Center for Excellence in Comparative Planetology,Hefei 230026,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2021年第6期1993-2015,共23页
Earth Science
基金
中国科学院战略性先导科技专项(No.XDB41000000).
关键词
荆山花岗岩
华北东南缘
大别-苏鲁造山带
俯冲华南陆壳
岩石学
地球化学
Jingshan granite
southeast margin of North China block
Dabie-Sulu orogen
subducted continental crust of South China block
petrology
geochemistry
