Potential field and bathymetric investigation of the Monowai volcanic centre, Kermadec Arc: implications for caldera formation and volcanic evolution
Potential field and bathymetric investigation of the Monowai volcanic centre, Kermadec Arc: implications for caldera formation and volcanic evolution
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克马德克弧莫诺瓦伊火山中心的位场和测深调查：对破火山口形成和火山演化的影响
DOI：
10.1093/gji/ggt512
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发表时间：
2014
影响因子：
2.8
通讯作者：
Paulatto M
中科院分区：
文献类型：
--
作者：
Paulatto M
位于汤加-Kermadec弧上的Monowai火山中心由一个玄武岩-安山质海底成层火山和邻近的破火山口组成。最近的调查表明，它是活跃的，但对它的结构和演变知之甚少。在这里，我们提出了一个综合分析的条带测深和势场数据从Monowai，在巡航SO 215期间获得的R/V索内，在2011年4月至6月。Monowai破火山口与20-25 mGal布格重力异常高和广泛的正磁异常有关。沿沿着破火山口边缘和成层火山山顶观测到高达+1400和-800 nT的短波长磁异常。布格重力异常数据的反演表明，破火山口高是由一个埋藏的致密体造成的，该致密体由一个从3至6公里深延伸的主要单元和一个位于Monowai破火山口边缘下方并从海底延伸到主要单元顶部的较浅的环形结构组成。我们估计平均密度对比度约为+450 kg m−3，相当于2650-2850 kg m−3的密度，表明是镁铁质成分。环形构造被解释为一组环形岩墙，主要单元为凝固或部分凝固的岩浆房系统（Monowai岩体）。主单元的体积估计为200-300 km 3。观测到的磁异常与Bruhnes磁极内的岩浆侵入相一致。对条带测深数据的分析表明，Monowai位于一个20公里宽的地堑内，这是一个雁行式左阶地垒和地堑系统的一部分，跨越弧和弧后的长度。Monowai破火山口垂直于裂谷方向被拉长，这表明它受到区域应力状态的影响。地貌分析表明，破火山口由一个单一的崩溃结构，其复杂的形状和多个环形断层可以归因于长期活动和多个崩溃事件。目前尚不清楚目前在莫诺维火山锥的喷发是直接从一个小的底层岩浆房，或从邻近莫诺维岩体的岩浆体横向进料。然而，在其侧翼的放射状裂缝脊的观察表明，一个浅层岩浆体可能最近已被侵位在山顶下，导致膨胀和形成拉伸裂缝。
The Monowai volcanic centre, located on the Tonga-Kermadec Arc, consists of a basaltic–andesitic submarine stratovolcano and adjacent caldera. Recent surveys have shown that it is active, but little is known about its structure and evolution. Here we present a combined analysis of swath bathymetry and potential field data from Monowai, acquired during cruise SO215 on the R/V Sonne, in 2011 April–June. The Monowai caldera is associated with a 20–25 mGal Bouguer gravity anomaly high and a broad positive magnetic anomaly. Short-wavelength magnetic anomalies of up to +1400 and –800 nT are observed along the caldera rim and on the summit of the stratovolcano. Inversion of the Bouguer gravity anomaly data shows that the caldera high is caused by a buried dense body consisting of a main unit extending from 3 to 6 km depth, and a shallower ring structure that underlies the rim of Monowai caldera and extends from the seafloor to the top of the main unit. We estimate the average density contrast to be about +450 kg m−3, corresponding to a density of 2650–2850 kg m−3, suggesting a mafic composition. The ring structure is interpreted as set of ring dykes and the main unit as a solidified or partly solidified magma chamber system (the Monowai pluton). The volume of the main unit is estimated to be 200–300 km3. The observed magnetic anomalies are consistent with magmatic intrusion within the Bruhnes magnetic polarity. Analysis of the swath bathymetry data shows that Monowai is located inside a 20-km-wide graben, part of an en-echelon, left-stepping horst and graben system that spans the length of the arc and backarc. The Monowai caldera is elongated perpendicular to the direction of rifting, suggesting that it is affected by the regional stress regime. Geomorphological analysis suggests that the caldera consists of a single collapse structure and that its complex shape and multiple ring faults can be attributed to prolonged activity and multiple collapse episodes. It remains unclear whether the current eruption at the Monowai cone is fed directly from a small underlying magma chamber, or laterally from a magma body adjacent to the Monowai pluton. However, observation of radial fissure ridges on its flanks suggests that a shallow magma body may have been recently emplaced beneath the summit causing inflation and the formation of extensional cracks.
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