青海都兰县三色沟铅锌矿区变质岩原岩恢复

Geochemistry and protolith restoration of the metamorphic rocks from the Sansegou Pb-Zn mining district in Dulan, Qinghai

关键词:  变质岩  原岩恢复  构造环境  青海都兰县

Key words:  metamorphic rock  protolith restoration  tectonic setting  Dulan in Qinghai

摘要:

对研究区变质岩的岩石学、地球化学研究表明,金水口群中-深变质岩原岩的为一套以火山岩为主的火山-沉积组合。火山岩主要为晶屑凝灰岩、岩屑凝灰岩、角砾凝灰岩、凝灰质砂岩等,属钙碱性岩系。沉积岩为泥灰岩。火山岩构造环境应属活动大陆边缘。

Abstract:

The examination of petrology and geochemistry of the metamorphic rocks from the Sansegou Pb-Zn mining district in Dulan, Qinghai has mirrored that the protolith of the Jinshuikou Group mesometamorphic to hypometamorphic rock series are assembled by a succession of volcanic-dominated volcanic-sedimentary associations containing volcanic rocks, volcanic rocks intercalated with sedimentary rocks, and sedimentary rocks. The volcanic rocks consist of crystal tuff, lithic tuff, breccia tuff and tuffaceous sandstone, indicating the calc-alkaline rock series. The sedimentary rocks are made up of marl. The tectonic setting of the volcanic rocks should belong to the active continental margin, and eruption depths range between 120 and 250 km, with an average of 180 km. The metamorphic rocks are characterized by SiO₂ contents ranging from 59.32 to 79.43%, Al₂O₃ contents from 12.21 to 16.8%, σ values from 0.18 to 2.64, AR values from 1.53 to 3.54, TiO₂ contents from 0.08 to 0.88%, ΣREE (not including Y) from 92.44 to 337.33, LREE from 81.10 to 305.48, and HREE from 9.59 to 55.65. The LREE and HREE are highly differentiated, and the HREE are heavily depleted. The REE distribution patterns display right-leaning curves. δEu values vary between 0.2 and 1.04, whereas δCe values vary between 0.81 and 0.86.