腾冲活火山的岩浆演化

The Magmatic Evolution of the Active Volcano in the Tengchong Area

腾冲火山活动分老期(包括上新世、早更新世和中更新世)和新期(中更新世—全新世,包括马鞍山、黑空山和打鹰山),代表性火山岩分别是玄武岩、英安质熔结凝灰岩、玄武质粗安岩和粗安岩,均属于高钾钙碱性火山岩。新期马鞍山、黑空山、打鹰山火山活动至少可以追溯到中更新世,岩浆成分从中更新世粗面玄武岩—玄武质粗安岩演化到晚更新世—全新世粗安岩。它们有一共同的岩浆源(或岩浆房),岩浆形成演化与壳幔作用和岩浆房内的辉石分离结晶作用有关。根据岩浆演化趋势,现在腾冲活火山之下岩浆房中的岩浆将向更富碱和富硅的粗面质或流纹质岩浆演化。

Tengchong volcanic activity is divided into the old period (including Pliocene, Early Pleistocene and Middle Pleistocene) and new period (Middle Pleistocene—Holocene, in which the activities of the Maanshan, Dayingshan and Heikongshan Volcanos started to occur. The representative volcanic rocks are basalt, dacitic welded tuff, basaltic trachyandesite and trachyandesite, all belonging to a high-potash calc-alkaline volcanic rock suite. Volcanic activities of the Maanshan Volcano, Dayingshan Volcano and Heikongshan Volcano were traced back at lest to the Middle Pleistocene. The magmas evolved from trachybasalt-basaltic trachyandesite of the Middle Pleistocene to trachyandesite of the Late Pleistocene—Holocene. They are origined from a comagma source (or magma chamber). The genesis and evolution of magmas are related to the crustal-mantle interaction and pyroxene crystallization differentiation within the magma chamber. The trend of the magmatic evolution shows that the magmas beneath the magma chamber of the active volcano in the Tengchong region tends to becom even more alkaline and silicic magmas of trachyte or rhyolite.