摘要
报道了西藏自治区拉萨地块中部仁错地区的念青唐古拉岩群中变质辉长岩的锆石U-Pb定年结果和岩石地球化学资料以及锆石Hf同位素组成.LA-ICP-MS和SIMS锆石U-Pb定年结果表明,变质辉长岩原岩形成于新元古代早期（约925 Ma）,这是目前拉萨地块乃至整个青藏高原内部最古老的基性岩浆记录.全岩地球化学资料显示,变质辉长岩具有类似典型大洋中脊玄武岩（N-MORB）的地球化学特征,并有部分岛弧拉斑玄武岩（IAT）的亲缘性.变质辉长岩锆石具有明显正的？Hf（t）值（8.26~13.7）和年轻的Hf模式年龄（TDM=933~1205 Ma）,表明变质辉长岩原岩的岩浆来自于亏损的地幔源区.综合这些资料可知,变质辉长岩可能代表了新元古代早期的洋壳残片,这为深入理解青藏高原前寒武纪的构造演化的研究提供了重要信息.
In the past decades, a lot of studies have been focused on the amalgamation between the Indian and Eurasian continents in the Tibetan Plateau during the Cenozoic. However, little attention was paid to the Precambrian evolution of the Tibetan Plateau though it has the same important scientific significance to those of the Cenozoic. Numerous Precambrian rocks occur in the Lhasa terrane such as the Nyainqentanglha and Nyingchi Groups, and they are commonly considered to be the Precambrian basement of the Lhasa terrane. The Nyainqentanglha Group is one of the most important Precambrian rocks in the Tibetan Plateau, and it plays a key role in understanding the Precambrian tectonic evolution of the plateau. The Nyainqentanglha Group is composed of a suit of tectonic slices with different sizes and ages, including meta-sedimentary, meta-volcanic and meta-basic-acid intrusive rocks. In this paper, we reported new zircon U-Pb ages and Hf isotope, and whole-rock major and trace element compositions for meta-gabbro from the Nyainqentanglha Group in the Ren Co area, north-central Lhasa terrane, Tibet. Zircon LA-ICP-MS and SIMS U-Pb dating yielded weighted mean 206Pb/238 U ages of 930.9±7.3 and 925.2±6.2 Ma, respectively. Zircons from the meta-gabbro exhibit pudding, fan-shaped or slight zoning structure and high Th/U ratios（0.73–31.6）, indicating that these zircons are of magmatic origin. Thus these ages represent the crystallization age of the protoliths of meta-gabbro. This is the oldest ages of the mafic magmatic rocks in the Lhasa terrane, as well as within the Tibetan Plateau. The meta-gabbros contain low Si O2 concentrations（47.83wt%–49.32wt%） and show the sub-alkaline basalt features in the Si O2 versus Zr/Ti O2 diagram. The chondrite-normalized rare earth element（REE） and primitive-mantle-normalized trace element multi-element patterns indicate that these rocks can be divided into two groups. The REE and trace element patterns of both groups are similar to those of N-type mid-ocean ridge basalts（N
出处
《科学通报》
EI
CAS
CSCD
北大核心
2016年第19期2176-2186,1-2,共11页
Chinese Science Bulletin
基金
国家自然科学基金(41522204
41502216)
中国地质调查局项目(12120113093900
12120115026901)资助
