VOLCANIC GEOLOGY AND ERUPTION FREQUENCY, SAO-MIGUEL, AZORES
VOLCANIC GEOLOGY AND ERUPTION FREQUENCY, SAO-MIGUEL, AZORES
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DOI：
10.1007/bf00301211
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发表时间：
1990-11-01
影响因子：
3.5
通讯作者：
MOORE, RB
中科院分区：
文献类型：
--
作者：
MOORE, RB
六个火山区组成了亚速尔群岛最大的岛屿圣米格尔岛。除最后一个部分为上新世外，其余均为第四纪。从西到东，这些区域是：（1）塞特西达德斯的粗面岩成层火山，（2）碱性玄武岩火山锥和熔岩流，含少量粗面岩，（3）阿瓜德波的粗面岩成层火山，（4）碱性玄武岩火山锥和熔岩流，含少量粗面岩和粗面石，（5）富尔纳斯的粗面岩成层火山，（6）Nordeste地盾。包括Povoação破火山口，由碱性玄武岩、粗面岩和粗面岩组成。新的放射性碳和K-Ar年龄增加了在最近对整个岛屿进行地质测绘期间获得的地层数据，并提供了更好的数据来解释喷发频率。在过去大约3000年的时间里，活跃地区的平均休眠间隔为：塞特西达德斯约400年，2区145年，阿瓜德保罗1150年，富尔纳斯370年。然而，塞特西达德斯的平均休眠间隔从过去两次爆发前的400年增加到约680年，而在过去四次爆发前，富尔纳斯的休眠间隔从370年减少到约195年。第4带的火山喷发在晚更新世和全新世早期大约每1000年发生一次，大约3000年没有发生。波瓦桑火山口截断了Nordeste地盾的一部分，可能形成于更新世中期至晚期。火山口形成于最晚更新世时期的三个较年轻的成层火山序列：外部Agua de Pau（46和26.5 ka之间），塞特Cidades（约22 ka），内部Agua de Pau（15.2 ka）和Furnas（约12 ka）。正断层是常见的，但许多被全新世粗面岩浮石掩埋。大多数断层走向西北或西北偏西，与特塞拉裂谷有关，特塞拉裂谷在圣米格尔最活跃的部分穿过塞特西达德斯和2区。一个主要的正断层使Nordeste熔岩移位150-250米，可能标志着一个祖先Terceira裂谷的位置。最近的地震活动（例如，在1980年代）一般都是分散的，但一些小的地震群发生在阿瓜德波的东北侧。
Six volcanic zones comprise São Miguel, the largest island in the Azores. All are Quaternary in age except the last, which is partly Pliocene. From west to east the zones are (1) the trachyte stratovolcano of Sete Cidades, (2) a field of alkali-basalt cinder cones and lava flows with minor trachyte, (3) the trachyte stratovolcano of Agua de Pau, (4) a field of alkali-basalt cinder cones and lava flows with minor trachyte and tristanite, (5) the trachyte stratovolcano of Furnas, and (6) the Nordeste shield, which includes the Povoação caldera and consists of alkali basalt, tristanite, and trachyte. New radiocarbon and K-Ar ages augment stratigraphic data obtained during recent geologic mapping of the entire island and provide improved data to interpret eruption frequency. Average dormant intervals for the past approximately 3000 years in the areas active during that time are about 400 years for Sete Cidades, 145 for zone 2, 1150 for Agua de Pau, and 370 for Furnas. However, the average dormant interval at Sete Cidades increased from 400 to about 680 years before each of the past two eruptions, and the interval at Furnas decreased from 370 to about 195 years before each of the past four eruptions. Eruptions in zone 4 occurred about once every 1000 years during latest Pleistocene and early Holocene time; none has occurred for about 3000 years. The Povoação caldera truncates part of the Nordeste shield and probably formed during the middle to late Pleistocene. Calderas formed during latest Pleistocene time at the three younger stratovolcanoes in the sequence: outer Agua de Pau (between 46 and 26.5 ka), Sete Cidades (about 22 ka), inner Agua de Pau (15.2 ka), and Furnas (about 12 ka). Normal faults are common, but many are buried by Holocene trachyte pumice. Most faults trend northwest or west-northwest and are related to the Terceira rift, whose most active segment on São Miguel passes through Sete Cidades and zone 2. A major normal fault displaces Nordeste lavas 150–250 m and may mark the location of an ancestral Terceira rift. Recent seismicity (e.g., in the 1980s) generally has been scattered, but some small earthquake swarms have occurred beneath the north-eastern flank of Agua de Pau.