Quartz porphyry veins and granite porphyry veins are developed in the Dubi
area of Zhengxiangbai Banner, Inner Mongolia, and are structurally located in
the Bainaimiao island arc belt on the northern margin of the North China
craton. Through LA-ICP-MS zircon U-Pb dating, the diagenetic ages of the quartz
porphyry and granite porphyry are (127.8±2.1) and
(128.8±0.7) Ma, respectively, and both are products of the Early Cretaceous
magmatism. Petro-geochemically, the quartz porphyry is rich in silica (w(SiO2) 76.06%-77.20%) and
potassium (w(K2O)
4.66%-6.48%), high TFeO/MgO ratio (10.42-12.55), higher 10000Ga/Al ratio
(2.71-3.27), low w(CaO)(0.58%-0.70%).
w(Al2O3) is 11.63%-12.67%, and the aluminum saturation
index(A/CNK) is 1.08-1.15. The granite porphyry is rich in silica (w(SiO2) 70.67%-71.88%) and
potassium (w(K2O)
5.83%-6.45%), high TFeO/MgO ratio (10.91-12.10), higher 10000Ga/Al ratio
(2.64-3.03), and low w(CaO)
(0.33%-0.44%). w(Al2O3)
is 14.47%-15.14%, and the aluminum saturation index is 1.14-1.16. Their REE
distribution curves show “seagull”
right-leaning pattern with obvious
negative Eu anomalies. They are relatively rich in Rb, Th, K, Zr, Hf etc., and
depleted in Sr, Ba, Ti, P, etc., indicating the characteristics of aluminous
A-type granite. The zircon εHf(t)
values of quartz porphyry and granite porphyry are -1.56-1.85 and -0.87-2.14, respectively, and the two-stage model
ages(TDM2) are 1 281-1 067 Ma and 1 240-1 046 Ma, respectively, indicating that
the two rocks are the products of mixed
materials from the crust and mantle. Combined with the regional tectonic
evolution, it is considered that the quartz porphyry and granite porphyry were
formed in the intraplate extensional environment during the thinning of the
Early Cretaceous lithosphere on the northern margin of the North China craton.