Geology of Nisyros Volcano
Geology of Nisyros Volcano
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尼西罗斯火山地质
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发表时间：
2018
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通讯作者：
V. Dietrich
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作者：
V. Dietrich
这本书的核心在尼西罗斯火山的地质学这一章中找到。新的《尼塞罗斯岛(十二岛)地质图》的编制是解释尼西罗斯火山喷发历史的基础。这座高达698米的层状火山的火山构造以中央几乎圆形的火山口为标志，直径3.6公里，陡峭的岩壁落差300-400米。这一主要构造特征被两个共轭的大断层和三个小断层系统所横切。由于含钾矿物(如闪锌矿和黑云母)的稀有性以及其他岩石学和化学原因，准确的地质年代学数据仍然缺乏，因此喷发史只能基于32个可填图的喷发单元的详细岩石地层学的相对年龄。利用喷发序列、接触关系、碎屑沉积和夹层古土壤，划分了五个火山旋回。火山活动始于“早期屏蔽火山旋回”期间的浅海玄武岩-安山岩熔岩，演化为局部湖泊的陆上环境。逐渐地，复合层状火山形成了尼西罗斯岛的圆形，岛的北部和南部发生喷发，后者喷发出流纹岩熔岩。在东海岸，主要是爆炸性喷发产生了两个较大的由安山岩和英安岩组成的凝灰岩锥。在演化的层状火山阶段，玄武岩-安山岩和安山岩以熔岩和火山碎屑的形式从覆盖岛屿南部、西部和北部斜坡的几个较小的煤渣、飞溅和斯科石锥体中释放出来。“复合地层火山旋回”以岛北部一个大型英安岩穹隆的渗出而结束，导致北部斜坡的一个大穹顶坍塌入海。在未知的时间间隔下，大量流纹质火山碎屑岩从北部和南部喷发中心开始喷发，即“火山口喷发旋回”，随后是第一次火山口坍塌和随后向东南方向挤压的大量流纹岩熔岩流。最年轻的大爆发流纹岩喷发发生在距离北部中心一段未知的时间间隔之后，覆盖了北部和东部斜坡的主要浮石沉积，并引发了第二阶段的火山口坍塌。之后，在“后火山口喷发旋回”期间，大量流纹状岩浆涌出，使火山口西部充满了巨大的圆顶和水流，向西南部的大海延伸。从那时起，尼塞罗斯火山仍处于休眠阶段。辉长岩和闪长岩侵入岩等岩浆对应体以及镁铁质堆积体在深处产生了一个大型热液系统，至今仍非常活跃。
The heart of the book is found in this Chapter, the geology of Nisyros Volcano. The compilation of the new “Geological Map of the Island of Nisyros (Dodecanese Archipelago)” with cross sections serves as the basis for the interpretation of the eruptive history of Nisyros volcano. The volcano-tectonic structures of the 698 m high stratovolcano are marked by the central, almost circular caldera with a diameter of 3.6 km and a drop of 300–400m of its steep walls. This dominant structural feature is crosscut by two conjugate major and three minor fault systems. Since accurate geochronological data are still missing due to the rarity of potassium bearing minerals, such as sanidine and biotite as well as to other petrologic and chemical reasons, the eruptive history can only be based on relative ages of a detailed lithostratigraphy of thirty-two mappable eruptive units. A major division into five volcanic cycles has been devised using eruptive successions, contact relationships, epiclastic deposits and intercalated paleosols. Volcanic activity started with shallow submarine basaltic-andesitic lavas during the “Early Shield Volcano Cycles” evolving into a subaerial environment with local lacustrine lakes. Progressively, a composite stratovolcano built up the circular shape of Nisyros Island, with eruptions on the northern and southern part of the island, the latter with effusion of rhyolitic lava. Along the east coast, mainly explosive eruptions produced two larger tuff cones of andesitic and dacitic compositions. During an evolved stratovolcanic stage, basaltic-andesites and andesites were emitted as lavas and pyroclastics from several smaller cinder, spatter and scoria cones covering the southern, western and northern slopes of the island. The “Composite Stratovolcanic Cycles” ended with the effusion of a large dacitic dome in the northern part of the island, which generated a major dome collapse of the northern slopes into the sea. With an unknown time gap, voluminous eruptions of rhyolitic pyroclastics started from the northern and southern eruptive centers, “Caldera Eruptive Cycles”, followed by a first caldera collapse and successive voluminous rhyolitic lava flows, which extruded towards southeast. The youngest major explosive rhyolitic eruption occurred after an unknown time interval from a northern centre, covering the northern and eastern slopes with major pumice deposits and inducing a second-stage of the caldera collapse. Afterwards, during the “Post Caldera Eruptive Cycle”, voluminous effusions of rhyodacitic magma filled the western part of the caldera with large domes and flows that extend towards the sea, in the southwest. Since then, Nisyros Volcano remains in a dormant stage. Magmatic counterparts, such as gabbroic and dioritic intrusives, as well as mafic cumulates have generated a large hydrothermal system at depth, which is still highly active today.