Abstract
The Gerizhuotuo complex intrusion,a typical stitching plutonwith its long axis cutting regional structural lines,is significant in tectonic geochronology for providing an upper-age for the timing of plate collision.The zircon U-Pb dating results indicate that the pluton was formed in 227-224 Ma.Geochemically,porphyritic granite falls into the high-K calc-alkaline se-ries,with high Sr(479-573μg/g)and low Yb(1.03-1.20μg/g)and Mg#(48.7-51.8),being of the characteristics of ada-kitic rocks.The in situ zirconeHf (t)value varies from -2.40 to 2.98,which suggests that the primary magma was derived from partial melting of lower crustal materials.Diorite also shows high-K calc-alkaline affinitie,with a Ti/Yb ratio ranging from 1 930 to 2 178,Nb/Ta ratio ranging from 15.9 to 17.4.It is suggested that a mixture,between basaltic magma derived from partial melting of metasomatized mantle and acidic magma derived from crustal material,produced the dioritic magma.It is concluded that the pluton was formed in a post-collisional tensional environment.
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