ABSTRACT We report on a geophysical study of maar volcanoes in the Auckland Volcanic Field which was performed in 1975, whose results remain relevant. Modelled gravity and magnetic anomalies indicate that substantial funnel-shaped magnetised basaltic bodies underlie the mud-filled craters at Onepoto and Orakei Basin. These bodies may represent magma that solidified within the craters after initial explosive eruptive phases that involved direct interaction between magma and surface or near-surface water. The estimated volume of residual magnetised basalt beneath the crater is roughly equal to the ejected quantity of basalt at Onepoto and about 3 times larger at Orakei. Magnetic anomaly data show that the Lake Pupuke crater also partially filled with basaltic material after an explosive phase than in turn followed an initial effusive eruptive phase. In contrast, there is no magnetic indication of a substantial magnetised basaltic body beneath Tank Farm crater, so it appears that magma supply ceased at the end of the explosive phase.

中文翻译：

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奥克兰火山场 Onepoto、Orakei、Pupuke 和 Tank Farm maar 火山结构和形成的地球物理限制

摘要 我们报告了 1975 年对奥克兰火山场中的玛珥火山进行的地球物理研究，其结果仍然具有相关性。模拟的重力和磁异常表明，在 Onepoto 和 Orakei 盆地充满泥浆的陨石坑下方存在大量漏斗状磁化玄武岩体。这些物体可能代表了在初始爆发性喷发阶段之后在火山口内凝固的岩浆，这些阶段涉及岩浆与地表或近地表水之间的直接相互作用。陨石坑下方剩余磁化玄武岩的估计体积大致等于 Onepoto 喷出的玄武岩数量，而 Orakei 则大约大 3 倍。磁异常数据显示，在爆发阶段之后，普普克湖火山口也部分充满了玄武岩物质，而在最初的喷发阶段之后。