Direct ascent to the surface of asthenospheric magma in a region of convex lithospheric flexure
Direct ascent to the surface of asthenospheric magma in a region of convex lithospheric flexure
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DOI：
10.1080/00206814.2017.1379912
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发表时间：
2018-01-01
影响因子：
2.6
通讯作者：
Kato, Yasuhiro
中科院分区：
文献类型：
--
作者：
Sato, Yuki;Hirano, Naoto;Kato, Yasuhiro
大洋岩石圈应力场控制着海底小点火山的分布。然而，这些小点火山的喷发地点被认为是有限的岩石圈外隆的凹曲区域。在这里，我们提出了新的数据，最近确定的一个小斑点熔岩场的岩石圈的凸弯曲部分附近的俯冲带近海的日本东北部地区，包含80多个火山。这一地区的特点是强烈的碱性熔岩，喷发的凸弯曲的地区。对于以前报道的小斑点的凹曲区域，在喷发地点之下的岩石圈底部处于伸展状态，而岩石圈上部处于压缩状态。这种应力场的变化，从岩石圈下部到上部，导致上升岩脉在岩石圈中部停止，导致与周围橄榄岩的交代作用。岩石和捕虏晶的新地球化学数据表明，由于岩石圈上部的伸展机制和与周围地幔橄榄岩交代反应的程度降低，在凸曲区喷发的强碱性岩浆将更快地上升通过岩石圈中深部。结果表明，交代作用的程度和小点岩浆的成分变化主要受岩石圈应力场的控制。
The stress field of oceanic lithosphere controls the distribution of submarine petit-spot volcanoes. However, the eruption sites of these petit-spot volcanoes are considered to be limited to concavely flexed regions of lithosphere off the outer rise. Here, we present new data for a recently identified petit-spot lava field on a convexly flexed section of the lithosphere adjacent to the subduction zone offshore of northeast Japan in an area containing more than 80 volcanoes. This area is marked by strongly alkaline lavas that were erupted on the convexly flexed region. As for the concavely flexed region where the petit-spots previously reported, the base of the lithosphere beneath the eruption sites is under extension, whereas the upper part of the lithosphere is under compression. This change in the stress field, from the lower to upper lithosphere, causes ascending dikes to stall in the mid-lithosphere, leading to metasomatic interaction with the surrounding peridotite. The new geochemical data of rocks and xenocrysts presented in this study indicate that strongly alkaline magmas erupted on the convexly flexed region would have ascended more rapidly through the mid-depth of lithosphere because of the extensional regime of the upper lithosphere and decreasing the degree of metasomatic reaction with the surrounding mantle peridotite. The results indicate that the degree of metasomatism and the compositional variations of petit-spot magmas are controlled mainly by the stress field of the lithosphere.