The evolution of mid-ocean ridge magma chambers and the growth of slow-spreading oceanic crust

大洋中脊岩浆室的演化和缓慢扩张的洋壳的生长

基本信息

批准号：
NE/H020004/1
负责人：
Cornelis Lissenberg
金额：
$ 6.13万
依托单位：
CARDIFF UNIVERSITY
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FH020004%2F1
关键词：
evolution mid ocean ridge magma

项目摘要

Oceanic crust covers nearly two thirds of the Earth's surface. It is generated at mid-ocean ridges by the solidification of magmas formed in the upwelling mantle. These magmas are stored in magma chambers below the ridge axis, where they crystallise to yield the lower oceanic crust. The heat provided by magma input and crystallisation drives seafloor hydrothermal systems, which control ocean chemistry through lithosphere-hydrosphere exchange, and provide energy for chemosynthetic ecosystems. Recovered sections of lower oceanic crust have provided much information on crustal accretion mechanisms, but the key element of time has remained largely unconstrained due to the absence of precise dating tools. As a result, the temporal evolution of the accretion process has remained enigmatic. This is critical, however, not only for understanding formation of a large part of the Earth's crust, but also for understanding the controls on hydrothermal circulation. Our recent work has demonstrated that U-Pb zircon dating techniques are now of sufficient precision to allow us to resolve the temporal evolution of magma chambers and relationships with crustal cooling (Lissenberg et al., Science, 2009), showing that zircon growth may occur over a significant time span (>100 ka) within individual mid-ocean ridge plutons. As a result, we now have a tool to reconstruct the relationships between time, temperature and magma chemistry. This proposal seeks to further develop this tool and greatly expand its scientific application by applying it to samples from the lower oceanic crust recovered from the Vema Lithospheric Section (11 degrees N, Mid-Atlantic Ridge). Combining high-precision zircon dating with trace element analyses, we will reconstruct how long magma chambers along this ridge segment were active, how they evolved over time and how quickly they cooled. This will provide an unprecedented view of the evolution of mid-ocean ridge magmatic systems over time. The pattern of the age variation of the samples with distance from the spreading ridge will constrain where magma was delivered to the crust. This allows a test of our hypothesis that slow-spreading oceanic crust forms in two fundamentally different modes, one dominated by symmetric spreading and melt delivery at shallow levels (inferred for Vema), and the other by asymmetric spreading, detachment faulting and deep magma emplacement.

海洋壳覆盖了地球表面的近三分之二。它是通过固化上升地幔中形成的岩浆的固化在海脊中产生的。这些岩浆存储在山脊轴下方的岩浆腔中，在那里它们结晶以产生下海洋壳。岩浆输入和结晶提供的热量驱动了海底水热系统，该系统通过岩石圈 - 水圈交换来控制海洋化学，并为化学合成生态系统提供能量。回收的较低海洋壳的部分提供了有关地壳积聚机制的大量信息，但是由于缺乏精确的约会工具，时间的关键要素在很大程度上仍然不受限制。结果，积聚过程的时间演变仍然存在神秘。但是，这不仅对于理解地球大部分地壳的形成，而且对于理解水热循环的控制而言至关重要。我们最近的工作表明，U-PB锆石约会技术现在已经足够精确，可以使我们能够解决岩浆腔室的时间演变以及与地壳冷却的关系（Lissenberg等，Science，Science，2009），表明可能发生氧化锆的生长在各个中山脊岩内的大量时间跨度（> 100 ka）中。结果，我们现在有了一种工具来重建时间，温度和岩浆化学之间的关系。该提案旨在进一步开发该工具，并通过将其应用于从岩石岩岩层（11度N，中大西洋山脊）中回收的下海洋壳的样品，从而大大扩展其科学应用。将高精度的锆石约会与痕量元素分析相结合，我们将重建沿这个山脊段沿山脊段的岩浆腔，它们如何随着时间的流逝以及它们冷却的速度而变化。随着时间的流逝，这将为中山山脊岩浆系统的演变提供前所未有的观点。样品的年龄变化模式与距离山脊距离的距离将限制岩浆被输送到地壳的地方。这允许测试我们的假设，即以两种根本不同的模式形成缓慢的海洋壳，一种由对称扩散和融化的层次（可推断为VEMA），另一个由不对称扩散，不对称的扩散，分离的断层和深层岩浆覆盖。