FLUIDIZATION MODEL FOR INTRACONTINENTAL COLLISION AND ITS METALLOGENIC SIGNIFICANCE: THEORETICAL INFERENCE AND EVIDENCES FROM GOLD DEPOSITS, THE EASTERN QINLING MOUNTAINS
Chen Yanjing(Department of Geology, Peking University, Beijing, 100871)
Intracontinental collision and fluidization remain to be well studied although they have become the forward research fields since 1980′s. In the light of metallogenic and petrogenic model for collisional orogenesis proposed by Chen (1991, 1992), this paper, through theoretical deduction, advances a fluidization model for intracontinental collision. During intracontinental subduction, fluids were produced by reworking, metamorphism and magmatism in turn as the subducting slab descending. The fluids showed clear spatial zonation, which results in regular zonations in element distribution, petrogenesis, mineralization and alteration. At the early compressing stage of the intracontinental subduction, fluids were derived mainly from deep secretion (reworking, metamorphism and magmatism), whereas at the late extension stage, fluids were characterized as shallow down going meteoric water; consequently, at the middle compression to extension transition stage, fluids should be the mixed deep secreted and shallow meteoric ones. To testify the rationality of this fluid evolution model for intracontinental collision, the author takes the eastern Qinling mountains, a typical intracontinental collisional orogenic belt, as an example because the metallogenic geology, geochemistry, space and time of gold deposits have been verified consistent with the intracontinental collision occurred most intensively in Mesozoic. The oxygen and hydrogen isotopic analyses and the thermometric data for ore forming fluids of several representative gold deposits show that the feature, source and evolution of the ore forming fluids extremely agree with the theoretical model for fluidization in intracontinental collision.