Motuoapa Peninsula, located in the southeast of the Taupo Volcanic Centre, New Zealand, is dominated by a silicic pyroclastic cone and overlaying lavas. The pyroclastic succession has not been recognised and studied before, and its thickness and sedimentological characteristics indicate completely different eruption mechanisms than proposed for the other pyroclastic successions within the central Taupo Volcanic Zone. Here, we present the results of field mapping and sedimentological characterisation of accessible pyroclastic deposits, and complement these data with combined U-Th and (U-Th)/He zircon geochronology providing first constraints on the succession's crystallization and eruption history.

(U-Th)/He zircon eruption ages of 77.2 ± 6.3, 81.3 ± 9.2 and 34.5 ± 3.1 ka indicate that volcanic activity in the Motuoapa Peninsula occurred in two distinct eruptive episodes that were separated by ca. 45 kyrs. The earlier rhyolitic eruption at ca. 80 ka is inferred to have commenced in a shallow subaqueous environment. Its lowermost succession includes breccias and tuff breccias sourced from an extruding lava dome by autobrecciation, quench-fragmentation and localised debris flows. With gradual emergence of the growing volcanic pile, explosive hydrovolcanic activity became dominant, constructing an emergent cone by pyroclastic density currents and fall-out. The lack of exotic/accidental clasts, along with an abundance of low-vesicularity rhyolitic juvenile fragments, suggests fragmentation driven by magma-water interaction, which predominantly occurred at shallow depths within the outgassed part of the ascending magma. The frequency and thickness of ash-dominated units increases upwards, suggesting a gradual increase in explosive energy of tephra jets. The final phase of the rhyolitic activity was dominated by emplacement of viscous lava that breached the crater rim and flowed onto the SE sector of the pyroclastic cone. The remnant of the Motuoapa pyroclastic cone, along with the bedded structure of deposits that comprise fallout and surge-dominated units, appears very similar to Surtseyan tuff cones and silicic tuff/pumice cones described elsewhere. A dacitic eruption that produced a nearby lava dome at ca. 35 ka, represents a significantly younger event that occurred after substantial erosion of the earlier pyroclastic cone. The Motuoapa Peninsula deposits most likely record the evolution of a subaqueous silicic eruption, where hydrovolcanism played a fundamental role on subaerial pyroclastic cone formation in a terrestrial environment with abundant surface water availability. The similarities between the environment of the Taupo area today and the area during the Motuoapa activity at ca. 80 ka may provide an analogue model for future subaqueous eruptions in the region.

位于新西兰陶波火山中心东南部的Motuoapa半岛以硅质火山碎屑锥和覆岩熔岩为主。火山碎屑演替以前​​尚未得到认识和研究，其厚度和沉积学特征表明与陶波火山中部地区其他火山碎屑演替所提出的喷发机制完全不同。在这里，我们介绍了可获取的火山碎屑矿床的田间制图和沉积学特征，并结合了U-Th和（U-Th）/ He锆石地质年代学对这些数据进行了补充，从而为演替的结晶和喷发历史提供了首个限制条件。

（U-Th）/ He锆石的喷发年龄分别为77.2±6.3、81.3±9.2和34.5±3.1 ka，表明Motuoapa半岛的火山活动发生在两个不同的喷发事件中，两者之间相隔约20年。45公斤。早于约5年的流纹状喷发。推测80 ka是在浅水水下环境中开始的。它的最低层序包括角砾岩和凝灰岩角砾岩，这些角砾岩和角砾岩角砾岩是从挤压的熔岩穹顶通过自缩水，急冷碎片和局部泥石流而产生的。随着不断增长的火山桩的出现，爆炸性的火山活动变得占主导地位，通过火山碎屑密度流和沉降构造了一个爆发锥。缺乏异国情调/偶然的碎屑，以及大量的低泡状流纹质流质幼年碎屑，表明由岩浆-水相互作用驱动的碎裂，它主要发生在上升岩浆脱气部分的浅层深度。灰分占主导地位的单位的频率和厚度向上增加，这表明特非拉喷气机的爆炸能量逐渐增加。流变活动的最后阶段主要是粘性熔岩的侵入，该熔岩冲破了火山口的边缘并流入了火山碎屑锥体的东南部。Motuoapa火山碎屑锥体的残留物，以及包括沉降物和涌浪为主的单元的沉积物的层状结构，与其他地方描述的Surtseyan凝灰岩锥体和硅质凝灰岩/浮石锥体非常相似。一次大火山喷发，在大约2米处产生了附近的熔岩穹顶。35 ka代表发生在较早的火山碎屑岩大量侵蚀后发生的年轻得多的事件。Motuoapa半岛沉积物最有可能记录了水下硅质喷发的演变，在该环境中，水热作用在地下环境中具有丰富的地表水可利用性对地下热碎屑锥的形成起着重要作用。今天陶波地区的环境与约莫图帕地区活动期间的地区之间的相似之处。80 ka可能为该地区未来的水下喷发提供一个模拟模型。