Petrogenesis And Tectonic Implications Of Late Neoarchean Crust Rocks In Western Shandong Province

In recent years,additional lines of evidence from geology and zircon chronology constraints in addition to zircon Lu-Hf isotope data and whole-rock Sm-Nd isotope data,and other evidence indicate that 2.56-2.50Ga is an important period of mantle magmatic activity in the eastern part of the western Shandong Province.The samples of the supracrustal rocks from Yanlingguan-Liuhang area and Zhangjiapo area are divided into two groups according to lithology and geochemistry.The A type of the metamorphic acid rock has higher SiO₂?67.33-70.81 wt.%,The average of 69.07wt.%?,Al₂O₃?13.85-15.63 wt.%?,MgO?1.29-2.16 wt.%?,Mg#?53-42,The average of 48?,the original rock of calcium alkaline rhyolitic-dacite,high SiO₂ and and low MgO,Mg#is similar to Archean TTG,as well as the regulation of the late Neoarchean TTG similar REE distribution pattern;In addition,the depletion of Nb,Ta and Ti is similar to that of typical island-arc volcanic rocks.it was formed by partial melting of subduction plate,combined with?_Hf?t₂=2550Ma?is-3.64,corresponding single-stage model age(T_DM)is 3120Ma and the zircon Hf crustal residence age distribution is3461Ma,indicating that there may be modification of ancient crustal materials during rock formation.the B type of the metamorphic acid rock SiO₂?65.80-65.98 wt.%,The average of 65.89 wt.%?,Al₂O₃?14.34-15.38 wt.%?,MgO?2.27-3.02 wt.%?,Mg#?50-57,The average of 54?,are calc-alkaline rhyolite-dactie.the A?B type of the metamorphic acid rock is high Mg#and MgO and Archean TTG,become acidic rock SiO₂>60 wt.%,and high Sr/Y and low content of Y,can be compared with high si adakite,and with more high si adakite similar REE distribution pattern,and both belong to the scope of high si adakite,it may be the product of the overlying mantle peridotite metasomatized the slab-derived melts;the second group of sedimentary rock?Biotite quartz schist?source rock of clay minerals to graywacke,mainly derived from the felsic source area,formed in a continental margin arc environment.According to the data from LA-ICP-MS zircon U-Pb,it shows that the formation ages of the A?B type of the metamorphic acid rock are both 2550 Ma,and the part provenance ages of the metamorphic sedimentary rock may be 2570 Ma,and the sedimentary ages may not be earlier than 2526 Ma.Based on the previous data and the data in this paper,it is concluded that the evolution stage of the late Neoarchean can be divided into two stages:2560-2530Ma is the subduction extrusion environment,the subducted partial melting of oceanic plate,and the subduction melt metasomatic overlying peridotite forms the metamorphic acid rock,which is subduction environment.2525-2500Ma:This stage is the extension environment,In the context of the plume,It forms shell-source granite,Comatite and mafic rocks.