Plate-Driven Micro-Hotspots and the Evolution of the Dragon Flag Melting Anomaly, Southwest Indian Ridge
Plate-Driven Micro-Hotspots and the Evolution of the Dragon Flag Melting Anomaly, Southwest Indian Ridge
复制标题
板块驱动的微热点和西南印度洋中脊龙旗融化异常的演化
DOI：
10.1016/j.epsl.2019.116002
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发表时间：
2020
影响因子：
5.3
通讯作者：
Dick H.J.B.
中科院分区：
文献类型：
--
作者：
Yu Xing;Dick H.J.B.
微观热点代表了在超低速扩张的西南印度洋脊（SWIR）与地幔热点无关的过量火山活动，但集中在地幔中的熔体流动，宽火山间距，和/或增加地幔肥力。个别微热点可以反映区域地幔肥力的变化，同时影响100公里的山脊，或极端熔体集中在孤立的部分地区异常厚的岩石圈。龙旗熔融异常喷发出同位素中等贫化的低钾拉斑玄武岩，是前者的最佳例子：一座位于50.5°E的巨大山脊中心火山。它远离Crozet，位于V形轨迹的顶点，该轨迹由向西北和东南方向延伸约400 km的101 km的隆起海底组成，表明在1011 -8 Ma时突然发生了过度火山活动。这种趋势与热点框架的预测相反，具有不一致的地球化学。位于东经14.7°的窄门火山是众多微热点之一，代表了被长的无岩浆脊部分所包围的孤立的大型火山中心。它也位于一个向东的V形测深趋势的顶点，但喷发大量的碱性玄武岩。这两个微热点品种是一个数量级小于威尔逊的经典热点，并没有固定在热点参考框架。它们可以生长并长时间保持静止，或相互自由迁移;由不断变化的板块构造应力场驱动。龙旗，代表在熔体供应增强的延长期内板块重组。窄门，另一方面，代表过度的火山活动，由于极深的熔体集中的低度熔体从一个异常广泛的地区在地幔中的一个孤立的火山段，厚岩石圈帽熔化在很深。为了约束的起源的微观热点的六个例子进行了评估，在其主要和同位素组成，以前的板块历史，深度和程度的熔融和构造背景。这包括新的主要，微量元素和重同位素数据的龙旗超段，和未公布的数据约瑟夫梅耶斯和窄门段。
Micro hotspots represent excess volcanism at the ultraslow spreading Southwest Indian Ridge (SWIR) unrelated to mantle hotspots, but to focused melt flow in the mantle, wide volcano spacing, and/or increased mantle fertility. Individual micro hotspot can reflect variations in regional mantle fertility, simultaneously affecting 100's of km of ridge, or extreme melt focusing to isolated segments in regions with unusually thick lithosphere. The Dragon Flag melting anomaly, erupting isotopically moderately depleted low-K tholeiite, is the best example of the former: an enormous ridge-centered volcano at 50.5°E. It is far from Crozet, and lies at the apex of a V-shaped trace consisting of ∼1 km anomalously elevated seafloor that extends ∼400 km to the northwest and southeast, indicating a sudden onset of excess volcanism at ∼11-8 Ma. This trend is opposite to that predicted by the hotspot framework, with inconsistent geochemistry. Narrowgate at 14.7°E is one of many micro hotspots that represent isolated large volcanic centers bounded by long amagmatic ridge sections. It also lies at the apex of an eastward V-shaped bathymetric trend, but erupts large volumes of alkali basalt.Both micro hotspot varieties are an order of magnitude smaller than Wilson's classic hotspots, and are not fixed in the hotspot referenced frame. They can grow and remain stationary for extended periods, or migrate freely with respect to each other; driven by the evolving plate tectonic stress field. Dragon Flag, represents a plate reorganization during a prolong period of enhanced melt supply. Narrowgate, on the other hand represents excess volcanism due to extreme deep melt focusing of low degree melt from an unusually wide region in the mantle to an isolated volcanic segment where thick lithosphere caps melting at great depth. To constrain the origins of the micro hotspots six examples are evaluated in terms of their major and isotopic composition, prior plate history, depth and extent of melting and tectonic context. This includes new major, trace element, and heavy isotope data for the Dragon Flag Supersegment, and unpublished data for the Joseph Mayes and Narrowgate segments.