Zircon U-Pb geochronology, geochemistry and Hf isotopes of Shenglikou muscovite monzogranite in northern margin of Qaidam Basin

This paper is the result of geological survey engineering.

Objective There are a large number of early Paleozoic granites distributed in the northern margin of Qaidam Basin. However, there are few research data on the existence of magmatic activities in the stage of deep subduction and early collision with the continent, which restricts the understanding of the tectonic background evolution in the northern margin of Qaidam Basin.

Methods Zircon U-Pb geochronology, petrochemistry and Hf isotope of muscovite monzogranite in the east of Shenglikou are studied.

Results LA-ICP-MS zircon U-Pb dating shows that the age of muscovite monzogranite is (433 ± 6) Ma (MSWD = 0. 026), which is the product of middle Silurian magmatism. Geochemical characteristics show that the rocks are rich in silicon (SiO₂=76.33%-76.99%) and alkali (K₂O+Na₂O=7.28%-8.19%), high K₂O, K₂O / Na₂O>1, low Mg (MgO=0.21%-0.29%) and Mg ^# (Mg ^#=23.29-30.17), A/CNK(1.12-1.19), belonging to the strongly peraluminous calc alkaline rock series. The rocks are relatively enriched in Rb, Th, U and other large ion lithophile elements, and depleted in Nb, Ta, Ti, P and some Ba, Sr and other large ion lithophile elements (LILE). The REE distribution curve is right dipping, showing obvious negative Eu anomaly(δEu=0.32-0.63). Hf isotope of zircon ε_Hf(t)=–5.2-–16.0, and the corresponding Hf isotopic crustal model ages T_DM2=1.86-2.20 Ga.

Conclusions The study of geochemistry and isotope shows that the muscovite monzogranite is S-type granite, which originated from the remelting and reconstruction of Paleoproterozoic crust. Based on the comprehensive comparison of the formation age of muscovite monzogranite and the regional high-pressure ultra-high pressure metamorphic age, combined with the study of petrochemistry and isotope, it is considered that the muscovite monzogranite in the east of Shenglikou was formed in the collision stage of the high-pressure ultra-high pressure metamorphic belt in the northern margin of Qaidam Basin.