Mid-ocean ridge eruptive vent morphology and substructure: Evidence for dike widths, eruption rates, and evolution of eruptions and axial volcanic ridges
Mid-ocean ridge eruptive vent morphology and substructure: Evidence for dike widths, eruption rates, and evolution of eruptions and axial volcanic ridges
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DOI：
10.1029/96jb02275
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发表时间：
1996-12-10
影响因子：
3.9
通讯作者：
Smith, DK
中科院分区：
文献类型：
--
作者：
Head, JW;Wilson, L;Smith, DK
中大西洋海脊(MAR)内谷底轴向火山脊的高分辨率侧扫声纳数据揭示了它们的建筑元素的细节。我们建立了岩脉玄武岩喷发的定量模型，并将这些喷发的预测结果与观测到的形态特征进行了比较。气体出溶的抑制、岩浆破坏的缺乏以及热液效应的共同作用，减缓了海底岩脉中岩浆的上升速度，增强了冷却，导致沿岩脉最宽的地方喷发更加迅速地集中。据预测，堤坝最初会从裂隙喷口喷发，形成一条条隆起的山脊；活动集中到几个相邻的喷口会产生一连串的隆起的块状丘陵，并可能增加单一喷口的渗漏速度，从而产生小的海山。据预测，最宽的堤坝将产生长达几公里的平稳水流，这应该会在邻近的低谷形成池塘。在冰岛和蛇绿岩杂岩中，根据体积通量和在海底观察到的岩脉宽度所隐含的流动长度预测的建筑物规模与观察到的特征的尺寸在数量上是一致的。根据典型的MAR扩张率，预计每40年大约有一次岩脉侵位事件；由于并非所有的岩脉都到达地表，实际的平均喷发间隔将超过这一时间间隔。在一般的堤防就位事件之间，MAR堤坝应该会固化。东太平洋隆起(EPR)上的堤防侵位事件更频繁，因此新堤坝更有可能重新占据未完全固化的老堤坝的位置。MAR轴向火山脊的形态与以板层流为主的EPR的形态差异归因于平均而言，沿EPR的岩墙较宽，喷发频率更高。
High-resolution side scan sonar data of Mid-Atlantic Ridge (MAR) inner valley floor axial volcanic ridges reveal details of their architectural elements. We develop quantitative models for basaltic eruptions from dikes and compare the predicted products of these eruptions with the observed morphologic features. Inhibition of gas exsolution, lack of magma disruption, and hydrothermal effects combine to decrease the rise speed of magma in submarine dikes and enhance cooling, leading to more rapid centralization of eruptions along-the widest places in the dike. Dikes are predicted to initially feed eruptions from fissure vents, producing lines of hummocky ridges; centralization of activity to several adjacent vents produces chains of hummocky bulbous mounds and can enhance the effusion rate at a single vent to produce small seamounts. The widest dikes are predicted to produce smooth flows up to several kilometers in length, which should pond in adjacent lows. Edifice sizes predicted on the basis of volume fluxes, and flow lengths implied by the widths of dikes observed on the seafloor, in Iceland and in ophiolite complexes, are in quantitative agreement with the dimensions of observed features. Each ridge is made up of the products of a variety of these individual dike-emplacement and extrusive events involving various dike widths, cooling times, and eruption durations On the basis of typical MAR spreading rates, about one dike emplacement event would be expected every 40 years; since not all dikes reach the surface, the actual mean interval between eruptions will exceed this. MAR dikes should solidify between average dike emplacement events. Dike emplacement events are more frequent on the East Pacific Rise (EPR) and thus new dikes are more likely to reoccupy the sites of incompletely solidified older dikes. Differences between the morphology of the MAR axial volcanic ridge and the sheet flow dominated EPR are attributed to on average wider dikes erupting with greater frequency along the EPR.