The recognition of the magnesian andesitic series（MA）in the Precambrian granitic rocks in western Shandong Province and the continental crustal growth

Abstract：Based on 39 SHRIMP and LA-ICP-MS Zircon U-Pb ages, 192 petrochemical data, and two representative age frameworks, this paper suggests a preliminary scheme of the age framework for the early Precambrian granites in western Shandong Province, i.e., three stages of （1）early-middle Neoarchean（2741～2612 Ma）,（2）Late Neoarchean（2563～2500 Ma）, and（3）early Paleoproterozoic（2494～2435 Ma）, which correspond to three rock assemblages and the evolutional trends of （1）T1T2G1 with trondhjemitic trend,（2）T1T2G1G2QM with both trondhjemitic and calc-alkaline trends,（3）G2QM with calc-alkaline trend. On the basis of both SiO2-MgO and SiO2-FeO/MgO relations, most of T1T2G1 having the magnesian andesitic rock (MA) characteristics is considered to have been formed in the oceanic subduction setting. It is thought that three stages of granitic rock assemblages might have been formed in island-arc, continental marginal arc, and continental collisional settings, respectively, and probably represented the compositions of immature, semi-mature, and mature continental crust, respectively. Thus, the granitic rocks have recorded the process of the formation of the continental crust.