摘要
新特提斯洋在晚白垩世末期(68Ma左右)的构造演化一直饱受争议。西藏松多地区晚白垩世末期弧岩浆岩包括花岗斑岩和二长花岗岩。锆石定年结果显示,二长花岗岩和花岗斑岩年龄均为68Ma。松多花岗斑岩和二长花岗岩的Si O_2含量为68.5%~80.6%,K_2O含量为4.1%~6.5%,P2O5含量为0.011%~0.058%。花岗斑岩Mg#值较低,为11.3~19.0,二长花岗岩Mg~#值为24.2~43.5。花岗斑岩和二长花岗岩样品均显示轻稀土元素富集、重稀土元素亏损和明显的Eu(δEu=0.15~1.21)负异常。两者均富集大离子亲石元素Rb、Th、U、K、Pb等,亏损高场强元素Nb、Ta、Ti。花岗斑岩εHf(t)值为-0.9^+2.9,二阶段模式年龄T_(DM)~C在955~1196Ma之间;二长花岗岩εHf(t)值为-17.1^+7.9(只有1个点为负值),二阶段模式年龄在633~2219Ma之间。最终认为,松多地区晚白垩世末期二长花岗岩和花岗斑岩岩浆源区为新生下地壳,但花岗斑岩更靠近古老下地壳。结合区域资料,认为新特提斯洋在晚白垩世末期68Ma左右属于洋脊俯冲结束阶段。
The tectonic evolution of the Neo-Tethys Ocean in the last phase of Late Cretaceous around 68Ma has been controversial.This paper firstly reports the last phase of Late Cretaceous arc igneous rocks in the Sumdo area of Tibet.They consist of granite porphyry and monzogranite.Zircon dating results show that the age of granite porphyry and monzogranite is 68Ma.The granite porphyry and monzogranite have the data SiO2(68.5%~80.6%),K2O(4.1%~6.5%),and P2O5(0.011%~0.058%).The granite porphyry contains low Mg#values(11.3~19.0),and the monzogranite has high Mg#values(24.2~43.5).The granite porphyry and monzogranite show light REE enrichment,heavy REE depletion,and obvious negative Eu anomalies.They both are enriched in large-ion lithophile elements such as Rb,Th,U,K and Pb,and depleted in high-field-strength elements such as Nb,Ta and Ti.The granite porphyry hasεHf(t)values ranging between-0.9 and+2.9,corresponding to TDMC model ages 955~1196Ma.TheεHf(t)values of the monzogranite are-17.1^+7.9,with only one point being negative,corresponding to TDMC model ages 633~2219Ma.The authors have thus drawn the conclusion that the magma source of the granite porphyry and monzogranite in the Songdo area was new lower crust,but the granite porphyry was closer to the ancient lower crust.Combined with regional data,the authors hold that the Neo-Tethys Ocean belongs to the end stage of ocean ridge subduction in the last phase of Late Cretaceous around 68Ma.
作者
刘金恒
解超明
范建军
王明
罗安波
高忠维
王斌
曾孝文
LIU Jinheng;XIE Chaoming;FAN Jianjun;WANG Ming;LUO Anbo;GAO Zhongwei;WANG Bin;ZENG Xiaowen(College of Earth Science,Jilin University,Changchun 130061,Jilin,China)
出处
《地质通报》
CAS
CSCD
北大核心
2018年第8期1477-1491,共15页
Geological Bulletin of China
基金
中国地质调查局项目<冈底斯-喜马拉雅铜矿资源基地调查>(编号:DD20160015)
<班公湖-怒江成矿带铜多金属矿资源基地调查>(编号:DD20160026)
国家自然科学基金项目<藏北聂荣微陆块新元古代-寒武纪构造演化>(批准号:41402190)
<青藏高原羌塘南部埃迪卡拉纪地层研究>(批准号:41602230)
关键词
松多地区
晚白垩世末期
弧岩浆岩
新特提斯洋
洋脊俯冲
sumdo area
last phase of Late Cretaceous
arc igneous rocks
Neo-Tethys Ocean
ocean ridge subduction
