摘要
浙江上侏罗-下白垩统火山沉积岩系发育良好，分布广泛，约占全省面积的三分之二，前人统称其为“中生界火山沉积岩岩系”。长期以来对于这套厚度巨大岩系的时代、划分与对比看法颇不一致，其中尤以浙东和浙西的对比问题争论较多。近年来。
Volcano-sedimentary series of the Upper Jurassic to the Lower Cretaceous are extensively developed in Zhejiang Province.But ages and stratigraphic correlation concerning these rocks have long been a controversial problem.Systematic sampling has been made of volcanic rocks of the Laocun,Haungjian,Shouchang and Moshishan Formations in western Zhejiang considered thus far as the late Jurassic.Isotopic age determinations show that U-Th-Pb zircon ages are approximately concordant with Rb-Sr isochron ages,whereas K-Ar biotite ages and K-Ar isochron ages are all slightly-lower.It can therefore be established that the ages of volcanic rocks mentioned above range from 134 + 6 to 122 + 2 m.y.,corresponding to the '' transitional period'' from Jurassic to Cretaceous.It can also be concluded that the rocks have not undergone apparent epigenetic metamorphism.The initial isotopic ratio (Sr87/Sr86) is about 0.7089-0.7121,on the basis of which it may be postulated that the volcanic magma seems to have originated from the upper mantle with contamination by sialic materials subsequent to differentiation.For age determinations of such acid volcanics,Rb-Sr isochron method is considered more suitable in view of its following advantages: the reliability of results; wide applicability to different samples; smaller sample requirement and the possibility for further studies involving petrogenesis by use of initial Sr87/Sr86 ratio.
出处
《地球化学》
CAS
1979年第1期1-12,共12页
Geochimica
