Three Dimensional Magma Dynamics in Large Sills

该奖项支持了一个研究南极洲干谷地区岩浆岩的就位和凝固的项目，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。如果可以通过直接观测了解片状岩浆体的三维就位和凝固历史，那么对地球演化的认识将取得很大进展。片状的岩浆体很可能是产生和塑造海洋和大陆地壳的原因。例如，在洋脊之下，相对狭窄（约1 - 4公里）、较薄（100 - 300米）的岩浆带或岩脉，通过侵位和凝固过程之间的微妙平衡，提供了海洋地壳的基本结构，构成了地球表面的60%左右。基本上，类似的固化过程在底板玄武岩岩浆片和高侵入的花岗质岩浆片中，通过早期岩浆的再活化和分选，在传递和塑造大陆地壳方面走了很长的路。然而，由于两个简单的原因，了解片状岩浆的动态历史非常难以捉摸：缺乏大量连续的岩石暴露，缺乏广泛、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，内部层状丰富，但很少有迹象表明岩浆填充的性质和风格（例如，填充是周期性的还是稳定的？）在离散点还是沿着裂缝？慢还是快？等等)。世界上许多大型辉绿岩岩样广泛地显示了充填是如何发生的，但很少显示任何内部指标或标记，详细说明充填和凝固过程本身。当一个标记，如先前形成的大而明显的晶体的痕迹，确实出现时，由于自然曝光不良，它很少能在三维空间中被追踪到。南极洲的基底岩改变了这一切。它很厚（300米），很大（超过5000立方公里），非常暴露，最重要的是，它的内部有一个明显的标志，就是一个大的（1 - 6毫米）正辉石晶体的舌状结构。此外，这种正辉石舌体在厚度、晶体大小和在底座内的位置上有系统的变化，反映了填充位置和填充本身的速度。这个天体和它的三维动力学的文件很可能被证明是片状岩浆系统的“罗塞塔石碑”。这是至关重要的，是这个项目的核心。在洋脊之下形成海洋地壳结构的详细过程也可能从这项研究中得到。通过凝固锋不稳定和硅透镜体的产生，大陆地壳起源的种子在基底岩中也很清楚。作为一项比较研究，在复活节岛的熔岩中寻找证据也可能很好地确定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.