Magma Dynamics at Mid-Ocean Ridges by Noble Gas Kinetic Fractionation: Assessment of Magmatic Ascent Rates and Mantle Composition
Magma Dynamics at Mid-Ocean Ridges by Noble Gas Kinetic Fractionation: Assessment of Magmatic Ascent Rates and Mantle Composition
复制标题
通过惰性气体动力学分馏研究大洋中脊的岩浆动力学：岩浆上升速率和地幔成分的评估
DOI：
10.1016/j.epsl.2005.10.018
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
M. Martelli
中科院分区：
文献类型：
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作者：
A. Paonita;M. Martelli
尽管它在了解洋壳形成和火山喷发风格的相关影响，在洋中脊的岩浆动力学知之甚少。在这里，我们提出了一种新的方法来评估上升率的洋中脊玄武岩（MORB）岩浆，以及他们的前和sin-eruptive动力学。它是基于这样的想法，即上升的岩浆可以达到一个可变的程度的CO2过饱和熔体和动力学分馏之间的稀有气体在囊泡在其上升速率通过地壳。为了量化这种关系，我们使用了MORB熔体中多组分气泡生长的模型，该模型是通过扩展Proussevitch和Sahagian [A.A. Proussevitch，D.L. Sahagian，岩浆中气泡生长的动力学和能量学：分析公式和数值模拟，J. Geophys。103（1998），18223-18251.]到CO2-He-Ar气体混合物。经过适当的参数化，我们已将其应用于已公布的数据套件具有所需的功能（玻璃从皮托海山和大西洋中脊）。我们的研究结果强调，所调查的MORB岩浆显示出非常不同的上升速率范围：缓慢上升的爆裂岩石形成的岩浆穿过地壳（0.01-0.5米/秒），略快的速度充满活力的渗出（0.1-1米/秒），高达1-10米/秒的速度落在熔岩渗出和夏威夷活动之间的边缘。在一个单一的管道系统内，非常不同的岩浆动力学突出了小尺度上洋壳压缩应力的巨大差异。还可以获得关于脊系统如何工作的限制以及岩浆源的特征。我们的模型显示了如何测量熔体中的溶解气体浓度和在同一样品中的囊泡的挥发性成分是至关重要的，在认识到的动力学效应和明确评估岩浆动力学。应努力将所研究的样品正确地置于其采集地的火山海底沉积物序列中。还需要加强对含气莫尔岩浆的一些物理性质的了解，主要是惰性气体的扩散系数，以更高的置信度描述多组分气泡的生长。
Despite its impact in understanding oceanic crust formation and eruptive styles of related volcanism, magma dynamics at mid-ocean ridges are poorly known. Here, we propose a new method to assess ascent rates of mid-ocean ridge basalt (MORB) magmas, as well as their pre- and sin-eruptive dynamics. It is based on the idea that a rising magma can reach a variable degree of both CO2supersaturation in melt and kinetic fractionation among noble gases in vesicles in relation to its ascent rate through the crust. To quantify the relationship, we have used a model of multicomponent bubble growth in MORB melts, developed by extending the single-component model of Proussevitch and Sahagian [A.A. Proussevitch, D.L. Sahagian, Dynamics and energetics of bubble growth in magmas: analytical formulation and numerical modeling, J. Geophys. Res. 103 (1998), 18223–18251.] to CO2–He–Ar gas mixtures. After proper parameterization, we have applied it to published suites of data having the required features (glasses from Pito Seamount and mid-Atlantic ridges). Our results highlight that the investigated MORB magmas display very different ranges of ascent rates: slow rises of popping rock forming-magmas that cross the crust (0.01–0.5 m/s), slightly faster rates of energetic effusions (0.1–1 m/s), up to rates of 1–10 m/s which fall on the edge between lava effusion and Hawaiian activity. Inside a single plumbing system, very dissimilar magma dynamics highlight the large differences in compressive stress of the oceanic crust on a small scale. Constraints on how the systems of ridges work, as well as the characteristics of the magmatic source, can also be obtained. Our model shows how measurements of both the dissolved gas concentration in melt and the volatile composition of vesicles in the same sample are crucial in recognizing the kinetic effects and definitively assessing magma dynamics. An effort should be made to correctly set the studied samples in the sequence of volcanic submarine deposits where they are collected. Enhanced knowledge of a number of physical properties of gas-bearing MOR magmas is also required, mainly noble gas diffusivities, to describe multicomponent bubble growth at a higher confidence level.