扬子板块北部古被动大陆边缘的地球化学特征

本文初次提出扬子板块北部古被动大陆边缘的地球化学特征是:a、裂陷早期阶段,发育碱性双峰式火山岩,但在裂陷的晚期和移离的早期阶段,发育碱性而不具双峰特征的火山岩、岩脉群;b、发育具两类不同地球化学特征的砂页岩,裂陷阶段形成的砂页岩与活动大陆边缘形成的砂页岩具相似的地球化学特征,移离阶段所形成的砂页岩才真正具被动大陆边缘砂页岩的地球化学特征。

Geochemical Characteristics of Ancient Passive Continental Margin of the Northern Yangtze Plate

The ancient Passive continental margin of the northern Yangtze plate was developed through Late Proterozoic-Middle Ordovician rifting and Middle Ordovician-Late Silurian drifting. This paper deals with the geochemical characteristics of the ancient passive continental margin of the northern Yangtze plate.a. The volcanic rocks developed at the early stage of rifting are alkalic and bimodal, while the volcanic rocks, dikes and swarms formed during the late stage of rifting to the early stage of drifting are not bimodal, although alkalic.b. Sandstones and shales formed during the evolution of this continental margin show two different geochemical characteristics. The sandstones and shales produced in the rifting stage are geochemically similar to those of active continental margins. Only do those rocks produced in the drifting stage possess the geochemical characteristics of sandstones and shales of a passive continental margin.