Research On Magmatic Origin, Evolution Mechanism And The Relation With Formation Of Cu-Polymetallic Deposit In The Middle-Segment Of Nanjing-Zhenjiang

The middle-segment of Nanjing-Zhenjiang is located in the junction between the northeastern margin of Yangtze Block and the southeastern margin of North China Block, experienced multi-stages tectonic movement. Yanshanian magmatism is the main geological type in the research region which has close relation with the formation of Cu-polymetallic deposit.Basee on geological investigation, optical microscopic observation, X-ray diffraction, microprobe analysis, silicate content analysis, REE and trace elements geochemical analysis are used to study the petrologic and geochemical characteristics of complex instrusives and mineralogical properties of plagioclase in Anjishan, Funiushan, Xiyinkeng, Hongshuidang, Tongshan, Xiashu, furthermore, magmatic origin, evolution mechanism, geotectonic setting and the relationship between the complex intrusives and formation of Cu-polymetallic deposit are discussed. Conclusions are drawn as follows:(1) Six complex instrusives are characterized by rich in silicon, potassium and sodium, low in magnesium and aluminium-oversaturated which reveal the instrusives belong to high potassic calc alkaline series. Moreover, six complex instrusives are enriched in light REEs, Rb, La and depleted heavy REEs, Ti, Y, Yb, Nb and Ta. The fractionation degree of light REEs is obviously higher than heavy REEs, positive Eu anomaly and negative Ce anomaly is revealed by REE-element counts. All above are similar with adakite. It shows that the complex intrusives in the research region have the same origin and intrude at the same time, belong to I-type granites. The results suggest that the crystallization differentiation degree of Anjishan, Funiushan and Tongshan instrusives is higher than the instrusives in Xiyinkeng and Hongshuidang.(2) Collision of Yangtze Block and North China Block make crustal thickening and lithosphere delamination, then mantle upwell caused lower crust melting partly. Primary magma formed after hornblende (±garnet) deriving from the mixsure of partial melting lower crust and mantle, and intruded upward along deep fault in the post-collisional extensional envirnment. Finaly experiencing crystallization differentiation and assimilation-contamination, the complex instrusives formed.(3) Comprehensive research on location, lithological combination, rock-forming temperature and pressure, denudation degree and metallogenic element (Cu, Pb, Zn) contents of six complex instrusives, it is considered that Anjishan, Funiushan, Tongshan instrusives are the main targets to prospect Cu-polymetallic deposit.