长白山天池火山粗面玄武岩的喷发历史与演化

Eruption history and magma evolution of the trachybasalt in the Tianchi volcano,Changbaishan.

本文新提出的年代学和岩石化学结果,进一步从天池火山与区域火山活动的关系,论述了天池火山造盾、造锥历史和岩浆结晶分异转型的时间约束,早更新世早期(2Ma前)开始粗面玄武岩的造盾,早更新世晚期(约1Ma)粗面玄武岩向粗安岩、粗面岩演化,中更新世是粗面岩造锥的主阶段,到了晚更新世(约0．1Ma)粗面岩向碱流岩演化。在中—晚更新世来自地壳岩浆房的粗面岩、碱流岩造锥过程中,来自地幔的粗面玄武岩浆喷发活动始终没有间断过。由于来自地幔粗面玄武质岩浆持续向地壳岩浆房补给,所以天池火山是一座长寿命的火山。岩浆的结晶分异作用和混合作用是天池火山岩浆演化的两个最重要过程,前者形成天池火山双峰式火山岩分布特征,后者成为天池火山喷发的触发机制。天池火山在晚更新世—全新世碱流质岩浆主喷发期兼有少量玄武质粗安岩、粗安岩或粗面质岩浆的交替喷出,揭示了天池火山的地壳岩浆房熔体的分层结构特点,由于来自地幔粗面玄武质岩浆注入地壳岩浆房,导致不同层位岩浆的扰动和混合作用,触发天池火山的喷发。

In this paper we report new chronological data and chemical analysis results on the Tianchi Volcano, and provide further constrains on the eruption history and the changes of magma types of the shield-forming stage and the cone-forming stage. At the beginning of the early Pleistocene （ca. 2Ma）, the Tianchi Volcano started the trachybasaltic activity of the shield-forming stage, and then the trachybasaltic magma changed to the trachytic and trachyandesitic magmas at the end of the early Pleistocene （ ca. 1Ma） ; the cone-forming stage of trachyte mainly occurred in the middle Pleistocene, and the trachyte magma changed to the pantelleritic magma at the late Pleistocene （ca. 0. 1Ma）. In the middle-late Pleistocene, volcanic activity of the trachyte and pantellerite from the crustal chamber dominated the cone-forming stage, but the episodic volcanism of the trachybasalt from the mantle chamber also occurred. Since the mantle chamber supplied trachybaslt influx from below to the crsutal chamber, the Tianchi Volcano is a long-life volcano. Fractional crystallization and magma mixing were two important processes in the Tianchi Volcano, the former determined the bimodal characteristics of the volcanic rocks, and the latter triggered the volcanic eruption. In the late Pleistocene and the Holocene, volcanic activity of pantellerite dominated the Tianchi Volcano, with episodic activity of basaltic trachyandesite, trachyandesite and trachyte throughout the cone-forming stage. This fact indicated that there is a multi-layered magma chamber system beneath the Tianchi Volcano. The trachybasalte influx from the mantle chamber disordered the magma layers and caused the magma mixing, then triggered the eruptions.