Extensive young silicic volcanism produces large deep submarine lava flows in the NE Lau Basin
Extensive young silicic volcanism produces large deep submarine lava flows in the NE Lau Basin
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DOI：
10.1007/s00445-018-1211-7
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发表时间：
2018-03
影响因子：
3.5
通讯作者：
R. Embley;Kenneth H. Rubin
中科院分区：
文献类型：
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作者：
R. Embley;Kenneth H. Rubin
新的实地观测表明，位于萨摩亚西南约 200 公里处的 NE Lau 盆地的多个地点最近喷发了大面积（高达约 402 平方公里）非晶体玻璃状英安岩熔岩。这一体积重大且分布广泛的海底英安岩熔岩流的发现将硅质喷发火山活动的范围扩展到深海海底。尽管在大型硅质海山 Niuatahi 的侧翼发现了几个熔岩流场，但在海山以北很远的地方发现了两个最大的熔岩场和几个较小的熔岩流场（“北部熔岩流场”）。这些油田最北端的最远端位于 Niuatahi 火山口中心以北 60 公里处。我们估计，从可能的喷发口到熔岩流远端的熔岩流长度范围从几公里到超过 10 公里。较浅、靠近喷口区域的摄像机拖曳显示出复杂的熔岩形态，包括吻合的管状枕状流和绳状表面、内生圆顶和/或山脊，其中一些具有“折痕状”挤压脊，以及具有挤压结构的膨胀裂片。一个2 × 1.5公里、30米深的凹陷可能是其中一个熔岩流场的喷发中心。 Lau 熔岩流场似乎以推定的高渗流率喷发，并且可能因推定的高岩浆水含量和/或高喷发温度而导致粘度降低，这与喷发成分 (~ 66% SiO2) 和玻璃状低结晶度基质结构一致。北部熔岩流场内的大面积范围（236 km2）和相对较小的成分变化范围（对于 wt% Si02%，σ= 0.60）意味着在 NE Lau 盆地的上地幔或下地壳中存在大量可喷发的分异熔体。在该地点，火山活动可能受到弧后区域长期伸展引起的深部地壳断裂的控制。在从太古宙到中新世的古代序列中以及在当今海底扩张中心小批量地描述了表现出类似形态的海底英安岩流。这项研究表明，在适当的条件下，现代海底可以喷发大量的硅质熔岩。
New field observations reveal that extensive (up to ~ 402 km2) aphyric, glassy dacite lavas were erupted at multiple sites in the recent past in the NE Lau basin, located about 200 km southwest of Samoa. This discovery of volumetrically significant and widespread submarine dacite lava flows extends the domain for siliceous effusive volcanism into the deep seafloor. Although several lava flow fields were discovered on the flank of a large silicic seamount, Niuatahi, two of the largest lava fields and several smaller ones (“northern lava flow fields”) were found well north of the seamount. The most distal portion of the northernmost of these fields is 60 km north of the center of Niuatahi caldera. We estimate that lava flow lengths from probable eruptive vents to the distal ends of flows range from a few km to more than 10 km. Camera tows on the shallower, near-vent areas show complex lava morphology that includes anastomosing tube-like pillow flows and ropey surfaces, endogenous domes and/or ridges, some with “crease-like” extrusion ridges, and inflated lobes with extrusion structures. A 2 × 1.5 km, 30-m deep depression could be an eruption center for one of the lava flow fields. The Lau lava flow fields appear to have erupted at presumptive high effusion rates and possibly reduced viscosity induced by presumptive high magmatic water content and/or a high eruption temperature, consistent with both erupted composition (~ 66% SiO2) and glassy low crystallinity groundmass textures. The large areal extent (236 km2) and relatively small range of compositional variation (σ= 0.60 for wt% Si02%) within the northern lava flow fields imply the existence of large, eruptible batches of differentiated melt in the upper mantle or lower crust of the NE Lau basin. At this site, the volcanism could be controlled by deep crustal fractures caused by the long-term extension in this rear-arc region. Submarine dacite flows exhibiting similar morphology have been described in ancient sequences from the Archaean through the Miocene and in small batches on present-day seafloor spreading centers. This study shows that extensive siliceous lavas can erupt on the modern seafloor under the right conditions.