摘要
本文通过对扬子陆块北缘上两地区二长花岗岩年代学、Hf同位素及地球化学研究,限定其形成时代、物质来源以及所处的大地构造环境。LA-ICP-MS锆石U-Pb测年结果表明上两地区二长花岗岩形成于新元古代早期,年龄为909±5Ma。锆石Hf同位素显示二长花岗岩的ε_(Hf)(t)既有正值也有负值,在-6^+3.4之间,变化较大。tDM2变化于1570~2156Ma,平均值为1802Ma,当ε_(Hf)(t)为最小负值-6.0时,tDM2为2156Ma。表明其物源主要是约1800Ma新生地壳的部分熔融,混染了部分古老地壳。地球化学显示,二长花岗岩的SiO_2含量较高,平均值达75.46%,均属亚碱性系列,且均为铝质过饱和(A/CNK=0.93~1.29);轻稀土富集,微量元素原始地幔蛛网图中显示富集大离子亲石元素(LILE)、具有明显的Nb、Ta负异常,并具有与上部陆壳非常相似的蛛网图曲线,在花岗岩的构造环境判别图解中落入弧花岗岩区,其应是扬子陆块北缘大陆边缘弧岩浆的产物。
In this paper, the geochronology, Hf isotope and geochemistry of the monzonitic granites of the Shangliang area in the northern margin of Yangtze block are used to study the age, material source and tectonic environment. U-Pb dating of LA-ICPMS shows that the monzonitic granitoids were formed in the early Neoproterozoic （ca. 909 ± 5 Ma）. The Hf isotopes of the zircons show that the εHf （t） of the monzonitic granites is both positive and negative and varies widely from -- 6 to ＋ 3.4. tDM1 ranges from 1375 Ma to 1803 Ma, with an average value of 1522 Ma, whereas tDM2 varies from 1570 Ma to 2156 Ma with an average value of 1802 Ma. When CHf（t） is the minimum negative value of --6.0, tDM2 is 2156 Ma, Indicating that the source is mainly about 1800 Ma partial melting of the new crust, mixed with some ancient crust. Geochemistry shows that the monzogranite has high SiO2 content, with an average value of 75.46%, suggesting it belongs to the sub-alkaline series with aluminum supersaturation（A/CNK=0.93- 1.29）. Rare earth elements distribution shows LREE enrichment and trace elements primitive mantle spider diagram shows enrichment of LILE, obvious negative anomalies of Nb and Ta, and a similar spider curve to that of the upper crust. The discrimination diagram of the tectonic setting of the granite show that the granite falls into the arc granite region, suggesting that it should be the product of continental margin magmatic arc in the northern margin of the Yangtze plate.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2018年第1期65-76,共12页
Acta Geologica Sinica
基金
中国地质调查局项目(编号12120115024601
DD20160016
DD20160017)
国家自然科学基金项目(编号41272091)联合资助成果
