Thermal and petrological consequences of melt migration within mantle plumes
Thermal and petrological consequences of melt migration within mantle plumes
复制标题
地幔柱内熔体迁移的热学和岩石学后果
DOI：
10.1098/rsta.1993.0004
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
C. Rosemberg
中科院分区：
文献类型：
--
作者：
G. Ceuleneer;M. Monnereau;M. Rabinowicz;C. Rosemberg
地幔柱核心预期的高温和高熔融度实际上在热点熔岩的喷发温度中没有表现，也没有表现在其玻璃的成分中，这仅限于玄武质领域。这一悖论的解决方案是寻找在地幔柱熔融区内的熔体迁移过程。在瑞利数为106的三维对流计算允许估计可能的温度，熔体分数和应力场内的羽流。可以区分两个具有不同熔体迁移模式的区域。深度范围从熔融区底部（150 km）到约80-100 km的较低区域，第一次熔融部分在次水平矿脉网络中重新分布，并响应于陡峭的水平温度梯度进行对流。该过程能够非常有效地使熔化区域内的温度均匀化。地幔柱中心和周围地幔之间的高温（300 °C）对比在这个区域的顶部可以降低到几十度。高压相的分级结晶将强烈地改变熔体的组成，因为它朝向熔化区域的外围循环。第二个上部区域，在那里，近垂直的矿脉方向将使熔体向地表快速迁移成为可能，延伸到岩石圈的底部。由于羽流温度在接近平均上地幔温度的值附近的缓冲，即使在脊上热点的情况下，该上部区域内的绝热熔融程度也不会大大超过正常扩展中心下方的绝热熔融程度。在热点喷发的熔岩可能是由于这些低压熔体（玄武岩）与高度演化的液体（可能具有金伯利岩至碱性亲和力）以各种比例混合而成，这些液体是由熔融区底部产生的高压熔体部分的分离结晶而产生的。这种情况下，可以解释低喷发温度和镁含量的热点熔岩，尽管复杂的高压，从而高温，历史证明了一些地球化学趋势。
The high temperatures and high degrees of melting expected in the core of mantle plumes have virtually no expression in the eruption temperatures of hotspot lavas, nor in the composition of their glasses, which is restricted in the basaltic field. A solution to this paradox is looked for in the melt migration processes within the melting region of mantle plumes. Three dimensional convective calculations at Rayleigh number of 106 allow estimates of the possible temperature, melt fraction and stress fields within a plume. Two regions with different melt migration patterns can be distinguished. A lower zone ranging in depth from the base of the melting region (150 km) to around 80—100 km where the first melt fraction is redistributed in a sub-horizontal vein network and convects in response to the steep horizontal temperature gradient. This process is able to homogenize the temperature within the melting region very efficiently. The high (300 °C) temperature contrast between the centre of the plume and the surrounding mantle can be reduced to a few tens of degrees at the top of this zone. Fractional crystallization of high pressure phases will strongly modify the composition of the melt as it circulates toward the periphery of the melting region. A second upper zone, where the sub-vertical vein orientation will make possible rapid melt migration toward the surface, extends to the base of the lithosphere. Due to the buffering of the plume temperature around a value close to the mean upper mantle temperature, the degree of adiabatic melting within this upper zone will not greatly exceed that beneath normal spreading centres, even in the case of on-ridge hotspots. The lavas erupted at hotspots are likely to result from the mixing in various proportions of these low pressure melts (basalts) with the highly evolved liquids (possibly with kimberlitic to alkalic affinities) resulting from fractional crystallization of the high-pressure melt fractions produced at the base of the melting region. This scenario could account for the low eruption temperatures and Mg contents of hotspot lavas, in spite of a complex high pressure, and thus high temperature, history evidenced by some geochemical trends.
影响因子：
3.9
作者：
MCKENZIE, D;BICKLE, MJ
通讯作者：
BICKLE, MJ