The Study Of Petrological Geochemistry Of Hypabyssal Intrusive Rocks From Subsea Tunnel In Jiaozhou Bay In Qingdao And Adjacent Districts

Jiaozhou Bay lies in the joint of eastern Jiaonan lift and Jiaolai basin. It is of important geological significance for its particular tectonic settings, to discussing the petrological geochemistry of hypabyssal intrusive rocks in this area and rebuilding regional geological evolution.This paper reports the result of geochemistry data of twenty three samples from Jiaozhou Bay in Qingdao and adjacent districts using the technology of thin section and polarization micro-image analysis, bulk rocks chemistry analysis, ICP-AES and ICP-MS. The samples are syenitic porphyry and granite porphyry and lamprophyre which are classified in two types:acid rocks and intermediate-mafic rocks,belonging to shoshonitic and high-K calc-alkaline lava series. From early to late, the order of emplacement is volcanic rocks, plutonic intrusive rocks, hypabyssal intrusive rocks(granite porphyry→syenitic porphyry→lamprophyre).The acid rocks are alkalic feldspar granite, they have higher silicon, alkli and lower iron, magnesium. They are enriched in LILE and LREE, REE patterns are right-leaned, (La/Yb)N=9.22~27.37 ,δEu =0.16~0.97. They have the same characteristic with A-type granite which is emplacement in post-orogenic entironment . The magma is derived from lower crust and formed by the process of fractional crystallization paired with assimilation.The intermediate-mafic rocks comprise of latite, basalt latite, trachybasalt and basalt with higher LILE , lower HFSE, right-leaned REE patterns and positive Ce anomaly. All characters above show that the magma is derived from upper mantle altered by subduction; mantle source may be the combination of lower curst of Yangtze plate and upper mantle of North China plate. The lower crust and upper mantle of Yangtze plate have separated by high-speed subduction. The rocks are the product of the lower degrees of partial melting of mantle magma.