Three Dimensional Magma Dynamics in Large Sills

该奖项支持一个项目，研究南极洲干谷地区岩床的就位和凝固，并将其历史与复活节岛和留尼汪岛上类似的片状岩浆体进行比较。 如果能通过直接观察了解片状岩浆体侵位和凝固的三维历史，就能在理解地球演化方面取得巨大进展。 板状岩浆体很可能是形成大洋和大陆地壳的主要原因。 例如，在洋脊之下，相对狭窄（约1 - 4公里），薄（100 - 300米）的岩浆带或岩床通过就位和凝固过程之间的微妙平衡提供了洋壳的基本结构，构成了地球表面的60%。 底侵玄武质岩浆和高位侵入花岗质岩浆的基本相似的凝固过程，通过早期岩浆的再活化和分选，对大陆地壳的输送和塑造起了很大作用。 然而，由于两个简单的原因，学习片状岩浆的动态历史被证明是非常困难的：缺乏大量连续的岩石暴露，缺乏广泛的，清晰的内部标记来揭示凝固的时间和空间历史。 在大型的、众所周知的层状侵入体中，内部层状构造是丰富的，但几乎没有岩浆充填的性质和风格的迹象（例如，填充是周期性的还是稳定的？在离散点还是沿着沿着慢的还是快的？ 等）。 世界各地的许多大型地下室大致显示了充填是如何发生的，但很少显示任何内部指示或标记，详细说明充填和固化过程本身。 当一个标记，如大的，独特的，以前形成的晶体的痕迹的形式，确实发生了，它很少可以追溯到三维由于穷人的自然曝光。 南极洲的地下室基石改变了这一切。 它厚（300米）、大（大于5，000立方公里）、暴露度极高，最重要的是带有明显的内部标记，呈大（1 - 6毫米）斜方辉石晶体舌的形式。此外，这种斜方辉石舌的厚度，晶体大小和位置的系统变化，反映了填充位置和填充本身的速度。 这个天体及其三维动力学的记录很可能被证明是片状岩浆系统的“罗塞塔石碑”。 它具有根本的重要性，是这个项目的核心。 从这项研究中也很可能获得在洋脊之下形成洋壳结构的详细过程。 而陆壳通过凝固前缘不稳定性和透镜体的产生而孕育的种子也在基底岩床中清晰可见。 作为一项比较研究，在复活节岛的熔岩中寻找证据也很可能确立这一过程在火山系统中的重要性。

This award supports a project to study the emplacement and solidification of sills in the Dry Valleys region of Antarctica and to compare their histories to similar sheet-like magma bodies on Easter Island and Reunion Island. If the three-dimensional history of emplacement and solidification of sheet-like magmatic bodies could be learned through direct observation, a great advance could be made in understanding the evolution of Earth. Sheet-like bodies of magma may well be responsible for delivering and shaping both the oceanic and continental crusts. Beneath ocean ridges, for example, relatively narrow (~1 - 4 kilometers), thin (100 - 300 meters) ribbons or sills of magma deliver, through a delicate balance between emplacement and solidification processes, the basic structure of the oceanic crust, which forms some 60% of Earth's surface. And basically similar solidification processes in sheets of underplating basaltic magma and high-level invading granitic magma go a long way to delivering and shaping the continental crust through remobilization and sorting of earlier magmas. Learning the dynamic history of sheet-like magmas has, however, proven exceedingly elusive for two simple reasons: lack of vast continuous rock exposures and lack of extensive, clear internal markers to reveal the temporal and spatial history of solidification. Internal layerings are plentiful in the large, well known layered intrusions, but there is little sign of the nature and style of magma filling (e.g., was filling periodic or steady? at discrete points or along fissures? slow or fast? etc.). The many large diabase sills throughout the world broadly show how filling occurred, but rarely do they show any internal indicators or markers detailing the filling and solidification processes themselves. And when a marker, as in the form of trails of large, distinct, previously formed crystals, does occur it rarely can be traced out in three dimensions due to poor natural exposures. T he Basement Sill of Antarctica changes all this. It is thick (300 meters), vast (greater than 5,000 cubic kilometers), superbly exposed, and above all carries a distinct internal marker in the form of a tongue of large (1 - 6 millimeters) orthopyroxene crystals. Moreover, this orthopyroxene tongue varies systematically in thickness, crystal size, and position within the sill reflecting both the filling locations and the rate of filling itself. The documentation of this body and its three dimensional dynamics may well prove to be the "Rosetta Stone" of sheet-like magmatic systems. It is of fundamental importance and is central to this project. The detailed processes that give rise beneath ocean ridges to the structure of the oceanic crust also may well be gained from this study. And the seeds of initiation of continental crust, through Solidification Front Instability and the production of silicic lenses, is also clear in the Basement Sill. As a comparative study, a search for evidence in the lavas of Easter Island may well also establish the importance of this process in volcanic systems.