松辽盆地改造残留的古火山机构与现代火山机构的类比分析

现代火山机构形态有盾状、锥状和穹状，可按喷发样式进一步划分为7种类型。据此分类，在松辽盆地周缘剖面及其北部徐家围子断陷区可识别出4类火山机构：盾状火山机构，由喷溢相熔岩组成，可夹有薄层爆发相火山碎屑岩；层火山机构，由互层的熔岩与火山碎屑岩组成，喷溢相与爆发相交替的序列明显；火山碎屑锥，几乎全部由火山碎屑（熔）岩组成，爆发相为主；熔岩穹丘由高粘度的流纹质、英安质熔岩堵塞火山口后缓慢挤出形成，喷溢相和侵出相发育，兼有火山通道相。盆地内埋藏火山机构最小坡度为3°，最大坡度为25°，底部直径为2～14 km，分布面积为4～50 km²，火山岩厚度为100～600 m；总体上呈现出数目多、个体规模小、受区域大断裂控制、具裂隙式-多中心喷发、彼此相互叠置的特征。火山岩岩性和岩相是控制松辽盆地古火山机构类型及形态的主要因素。

Analogy of Volcanic Edifices between Modern Volcanoes and Ancient Remnant Volcanoes in Songliao Basin

Modern volcanoes can be classified as three main forms in shape (Shield-shape, cone-shape and dome-shape) and seven different types. In surrounding sections and northern faulted depression in the Songliao Basin, there are mainly four types of volcanoes such as shield volcano, composite volcano, pyroclastic cone and lava dome. Shield volcanoes are built almost entirely of fluid lava flows, with little explosive pyroclastics. Composite volcanoes are built of flow layers alternating with pyroclas-tics, thus the alternate sequence of effusive and explosive facies is well developed. Pyroclastic cones, the simplest type of volcano, consist of particles and blobs of congealed lava from a single vent, mainly of explosive facies. Lava domes are formed by relatively small, bulbous masses of the lava which is too viscous to flow long distance, therefore, the lava piles over and around its vent by extrusion. Eruption patterns here mainly include effusive, extrusive and volcanic vent facies. In the Songliao Basin the buried volcanic edifices is characterized by slope angle ranging from minimum 3° to maximal 25°, bottom diameter from 2 to 14 kilometers and volcanic rock thickness from 100 to 600 meters. The buried volcanic edifices may cover an area of 4 to 50 sq. kilometers for each. As a whole, buried volcanoes of the northern Songliao Basin appear numerous, individually small and are controlled by regional faults. They are normally featured with crack and multi-central type eruptions, volcanic products of different vents commonly pile up each other. Volcanic lithology and lithofacies are the main factors that control the types and forms of the volcanic apparatus in the Songliao Basin.