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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Basaltic lava domes, lava lakes, and volcanic segmentation on the southern East Pacific Rise
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Basaltic lava domes, lava lakes, and volcanic segmentation on the southern East Pacific Rise

机译：东太平洋上升带南部的玄武岩熔岩穹顶，熔岩湖和火山分段

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Meter-scale DSL-120 sonar mapping and coregistered Argo II photographic observations reveal changes in eruptive style that closely follow the third-order structural segmentation of the ridge axis on the southern East Pacific Rise, 17 degrees 11'-18 degrees 37'S. Near segment ends we observe abundant basaltic lava domes which average 20 m in height and 200 m in basal diameter and have pillow lava as the dominant lava morphology. The ubiquity of pillow lava suggests low effusion rate eruptions. The abundance of lava domes suggests that the fissure eruptions were of sufficient duration to focus and produce a line of volcanic edifices. Near segment centers we observe fewer but larger lava domes, voluminous drained and collapsed lava lakes, and smooth lobate and sheet lava flows with very little pillow lava. The abundance of sheet flows suggests that high effusion rate eruptions are common. Fewer lava domes and large lava lakes suggest that fissure eruptions do not focus to point sources. This pattern was observed on eight third-order ridge segments suggesting that a fundamental volcanic segmentation of the ridge occurs on this scale. The third-order segment boundaries also correlate with local maxima in the seismic axial magma chamber reflector depth throughout the study area and decreased across-axis width of the region of seismic layer 2A thickening along the one segment where sufficient cross-axis seismic lines exist. The geochemically defined magmatic segment boundaries in the study area match the locations of our volcanic segment boundaries, although rock sampling density is not adequate to constrain the variation across all the third-order volcanic segments chat we identify. These observations suggest that variation in the processes of crustal accretion along axis occurs at a length scale of tens of kilometers on superfast spreading (>140 km/Myr full rate) mid-ocean ridges. [References: 96]
机译：米级DSL-120声纳测绘和共同注册的Argo II摄影观测揭示了喷发形式的变化，该变化紧随东南太平洋南部上升脊（17度11'-18度37'S）上脊轴的三阶结构分段。在段末端附近，我们观察到丰富的玄武岩熔岩穹顶，平均高度为20 m，基径为200 m，并且以枕状熔岩为主要熔岩形态。枕头熔岩的普遍存在表明低渗出速率。丰富的熔岩穹顶表明裂隙喷发的持续时间足以集中并产生一系列的火山构造。在分段中心附近，我们观察到较少但较大的熔岩穹顶，大量排干和倒塌的熔岩湖，光滑的叶状和片状熔岩流以及很少的枕状熔岩。大量的表层流表明高渗出率是普遍现象。较少的熔岩穹顶和较大的熔岩湖表明裂隙喷发并未集中于点源。在八个三阶山脊段上观察到这种模式，表明在该规模上发生了山脊的基本火山分段。三阶分段边界还与整个研究区域的地震轴向岩浆室反射器深度中的局部最大值相关，并且沿着一个存在足够横轴地震线的分段增加了​​地震层2A区域加厚的横轴宽度。尽管研究区的岩石采样密度不足以限制我们确定的所有三阶火山岩段的变化，但在研究区域中由地球化学定义的岩浆段边界与我们的火山岩段边界的位置匹配。这些观察结果表明，在超快扩散（> 140 km / Myr全速率）中洋海脊上，沿地壳增生过程的变化发生在几十公里的长度尺度上。 [参考：96]

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