浅谈山西省古元古代末期火山岩的构造背景

对山西古元古代末期火山岩的构造属性进行了研究,旨在为解决现今国内外关于古/中元古界(代)分界问题的分岐提供依据。该期火山岩角度不整合于具活动大陆边缘特征的结晶基底之上。无论是汉高山群(或小两岭组)还是西洋河群(—熊耳群),均呈SEE向展布,熔岩占绝对优势,偶见碎屑岩; 以裂隙(串珠状)宁静式溢流喷发为主,同期的基性侵入岩墙群为其岩浆上升的通道。岩性以安山岩-玄武安山岩为主,含少量玄武岩和流纹岩。岩石斑晶为辉石和斜长石,偶见角闪石和黑云母。岩石地球化学富大离子亲石元素和轻稀土元素,亏损高场强元素,w(Th)>w(Ta)。全岩εNd(t)值和εHf(t)值均为负值,在SiO₂-K₂O图解中以SH+HKCA系列为主,为钾质火成岩系列。该期火山岩是古元古代中晚期华北克拉通结晶基底的西部陆块与东部陆块碰撞拼合的延续,为后碰撞火山弧岩浆。

Brief discussion of tectonic environment of volcanic rocks in Late Paleoproterozoic of Shanxi Province

In this paper, the authors studied the construct properties of volcanic rocks in the Late Paleoproterozoic period of Shanxi Province, which aims to provide references for the disagreements about boundary between Paleoproterozoic and Mesoproterozoic. The volcanic extrusive rocks of this period are unconformable on the crystalline basement with the character of active continental margin. Both of the Hangaoshan Group (Xiaolangling Formation) and the Xiyanghe Group (-Xionger Group) are extending to SEE direction, and the lava is absolute dominant, with occasional clastic rocks. Besides, the lava is mainly composed of fissures (beaded) and peaceful overflow eruptions, and the corresponding basic intrusive rock group was rising channel for the magma. The lithology is mainly andesite-basaltic andesite, with the lithology is mainly andesite and basaltic andesite, with a small amount of basalt and rhyolite. The rock phenocrysts are pyroxene and plagioclase, and occasionally composed of hornblende and biotite. The geochemistry of the rocks is rich in large ion lithophile elements and light rare earth elements, and low in high field strength elements, with w(Th)>w(Ta). The εNd(t) and εHf(t) values of the whole rock are negative, which are dominated by SH+HKCA series in the SiO₂-K₂O diagram and potassic volcanic rocks series. It is a continuation of the collision and cohere between the western and eastern continental blocks of the crystalline basement of the North China Craton in the Late and Middle Paleoproterozoic, which are the post-collision volcani arc magma.