摘要
海南岛屯昌地区侵入岩由花岗闪长岩、花岗岩及少量辉绿-闪长玢岩(脉)、镁铁质包体组成。本文报道了这些侵入岩的锆石LA-ICPMS U-Pb定年结果和地球化学组成,定年结果显示岩石形成于早白垩世晚期(~107 Ma)。地球化学特征显示,花岗闪长岩和花岗岩具有高的SiO2、Al2O3含量以及高的Sr含量和Sr/Y比值,低的Y和Yb含量,Eu异常不明显等,属于埃达克质岩。屯昌埃达克质岩具有比较均一的Sr、Nd同位素组成(ISr=0.7082~0.7096,εNd(t)=-6.55^-3.85)。镁铁质岩脉和包体则显示了稍低的ISr(0.7064~0.7086)和变化的εNd(t)(-5.10^+0.13)。埃达克质岩的锆石原位Hf同位素组成为:(176Hf/177Hf)i=0.28257~0.28277,εHf(t)=-4.86^+2.09,相应的两阶段模式年龄TDM2变化于1.09 Ga和1.54 Ga之间。闪长玢岩脉的(176Hf/177Hf)i=0.28257~0.28264,εHf(t)=-4.94^-2.42,TDM2=1.38~1.55 Ga,类似于埃达克质岩。屯昌埃达克质岩很可能由新底侵的玄武质下地壳物质部分熔融所形成,俯冲的古太平洋板块在早白垩世晚期(约107 Ma)的后撤作用所导致的软流圈上涌为地壳熔融提供了热源。
The Tunchang intrusive rocks consist of granodiorites, granites and minor, diabase-diorite porphyry dikes and mafic enclaves. This paper presents new zircon LA-ICPMS U-Pb age and geochemical data of these intrusive rocks. The age results show that the Tunchang intrusive rocks were generated in Late Early Cretaceous （~107 Ma）. Both granodiorites and granites are geochemically similar to adakites, e.g., high SiO2, Al2O3, Sr and Sr/Y values, low Y and Yb contents, and negligible Eu anomalies. The Tunchang aidakitic rocks have
homogeneous ISr （0.7082-0.7096） and εNd（t） （？6.55- ？3.85）, and limited ranges for （176Hf/177Hf）i （0.28257-
0.28277）, εHf（t） values （？4.86- ＋2.09） and TDM2 （1.09-1.54 Ga）. However, the mafic dikes and enclaves have
slightly low ISr （0.7064-0.7086） and variable εNd（t） （？5.10- ＋0.13） values. The mafic dike have （176Hf/177Hf）i =
0.28257-0.28264, εHf（t） = ？4.94- ？2.42, TDM2 = 1.38-1.55 Ga, which are similar to those of the adakitic rocks.We suggest that the Tunchang adakitic rocks were likely generated by partial melting of newly underplated basaltic lower crust as a result of asthenosphere upwelling due to Late Early Cretaceous （~107 Ma） rollback of subducted Paleo-Pacific plate.
出处
《地球化学》
CAS
CSCD
北大核心
2010年第6期497-519,共23页
Geochimica
基金
中国科学院知识创新工程重要方向项目(KZCX2-YW-128
KZCX1-YW-15-2)
国家自然科学基金(40721063)
广东省自然科学基金(7006313)
关键词
埃达克质岩
底侵作用
花岗岩
海南岛
华南
adakitic rocks
underplating
granite
Hainan Island
South China
