Sr and O isotopic characteristics of porphyries in the Qinling molybdenum deposit belt and their implication to genetic mechanism and type

A great deal of Mesozoic hypobatholithic granites and hypabyssal porphyries develop in the Qinling Mountains. The former has long been regarded as transformation type (or S-type), and the latter associated with Mo-mineratization regarded as syntexis type (or I-type) granitoids. Statistics show that Sr-I and delta O-18 of hypabyssal porphyries respectively range from 0.705' to 0.714, and from 7.2 parts per thousand to 12.1 parts per thousand, agreeing with those of hypobatholithes (Sr-I=0.705-0.710, delta O-18 = 6.1 parts per thousand- 10.4 parts per thousand), which indicates that they share similar material sources and petrogenic mechanism. Based on analysis of lithological, mineralogical and geochemical characteristics of these granitoids and on study of their petrogenic tectonic background and regional geophysical data, live argue that both the shallow-seated porphyries and deep-seated batholithes were the products of Mesozoic collision between South China and North China paleocontinents. Subsequently, all these grantitoids should be attributed to collision type.