Late Cenozoic Volcanism in Marie Byrd Land: Assessing Petrogenetic and Eruptive Mechanisms by Comparitive Studies of Analogs

玛丽·伯德地的火山位于南极洲太平洋沿岸，位于西经110度到140度之间，是环太平洋火环的一部分。O它们形成于过去的3000万年（Ma）；但每一个都只有不到3万年的寿命，而且它们是由各种各样的岩石组成的。不像火山带其他地方的火山是由于板块碰撞而形成的，玛丽伯德地火山是在一个裂口环境中形成的，在这个环境中，地壳一直在拉伸、破裂，慢慢上升，形成一个大圆顶，现在直径约300英里，最高点海拔9000英尺。古老的火山位于圆顶的中心附近，随着圆顶的增长，火山活动向圆顶的边缘转移，现在的活火山就在那里。因此，这些火山的起源似乎涉及到熔化和地壳内部变形之间的相互作用，熔化产生了远在地壳以下的原始熔岩，而地壳内部的变形似乎控制了熔岩流向地表的过程。当熔岩到达地表并在南极西部冰盖下喷发时，它会产生水火山沉积物，这些沉积物提供了在人类活动影响气候之前冰盖大小变化的记录。在高河山，这些岩石似乎记录了过去30万年里至少1000英尺范围内冰位的多次波动，这表明冰盖对气候变化反应迅速。可以想象，对温室气体变暖的类似反应可能导致海平面上升20英尺。该奖项由美国国家科学基金会极地项目办公室资助，支持的工作将集中在以下问题上：(1)是什么导致了大约70-90英里深度的玄武岩熔岩的融化，以及隆起和拉伸与这一过程有什么关系？(2)什么过程导致玄武岩在上升到地表时改变了成分，从而产生了玛丽·伯德地火山的多样性？(3)从火山沉积物中我们可以了解到冰盖的历史及其对温室效应的脆弱性？该奖项支持一项比较岩石学研究，以便在世界其他地方表现出不同风格或发展阶段的类似火山省的背景下了解玛丽伯德地的火山岩。该奖项支持对三个这样的地区进行比较研究：(1)维多利亚地的火山，位于玛丽伯德地以西约1000英里处，位于南极西部裂谷的一部分，其变形和火山活动的历史有些不同。(2)苏格兰西北部6000 - 6500万年前的火山，这些火山已经被侵蚀得足够深，暴露出地下火山管道。(3)冰岛冰下喷发产生的火山，包括活火山Grimsvotn，它在瓦塔纳冰川下最近喷发时产生了类似于Takahe火山的水火山沉积物。这些研究很重要，因为它们将有助于理解(1)地球内部深层过程和地壳变形之间的相互作用如何控制裂谷环境中火山的发展，以及(2)南极西部冰盖的过去行为如何被用作其未来稳定性的关键。

9720411 LeMasurier The volcanoes of Marie Byrd Land lie along the Pacific coast of Antarctica between 110 degrees and 140 degrees west longitude, and are part of the circum-Pacific ORing of Fire.O They have formed during the past 30 million years (Ma); but each has had an individual lifetime of less than 3 Ma, and they are made up of a wide variety of rock types. Unlike volcanoes elsewhere in the Ring of Fire, which have formed as a result of plate collision, Marie Byrd Land volcanoes have formed in a OriftO environment where the earthOs crust has been stretching, fracturing, and slowly rising to form a large dome that is now about 300 miles in diameter and 9,000 feet above sea level at its crest. Older volcanoes are found near the center of the dome, and as the dome grew, volcanic activity shifted toward the edge of the dome, where the now active volcanoes are located. The origin of these volcanoes thus appears to involve an interplay between melting, that produces the original lava far below the crust, and deformation within the crust, that seems to control what happens to the lava on its way to the surface. When the lava reaches the surface, and is erupted under the West Antarctic ice sheet, it produces hydrovolcanic deposits that provide a record of how the size of the ice sheet varied before climate was influenced by human activity. At Mt. Takahe these rocks appear to record multiple fluctuations in ice level, through a range of at least 1,000 ft. within the past 300,000 years, suggesting that the ice sheet responds readily to climatic change. A similar response to greenhouse warming could, conceivably, lead to a 20 foot rise in sea level. This award, funded by the Office of Polar Programs at the National Science Foundation, supports work that will focus on the following questions: (1) What has caused melting at roughly 70-90 miles depth to produce basalt lava, and how have uplift and stretching been related to this process? (2) What processes h ave caused the basalt to change composition as it rises to the surface, producing the variety among volcanoes in Marie Byrd Land? (3) What can we learn from hydrovolcanic deposits about the history of the ice sheet and its vulnerability to greenhouse warming? This award supports a comparative petrological study to understand the volcanic rocks of Marie Byrd Land in the context of similar volcanic provinces elsewhere in the world that exhibit different styles or stages of development. This award supports comparative studies of three such regions: (1) The volcanoes of Victoria Land, about 1000 miles west of Marie Byrd Land, in a part of the West Antarctic rift that has had a somewhat different history of deformation and volcanism. (2) The 60-65 million year old volcanoes in NW Scotland, which have been eroded deeply enough to expose subsurface volcanic conduits. (3) Volcanoes produced by subglacial eruptions in Iceland, including the active volcano Grimsvotn, which has produced hydrovolcanic deposits like those at Mt. Takahe during its recent eruptions under the glacier Vatanajokull. These studies are important because they will contribute to an understanding of (1) how the interplay between deep internal processes and crustal deformation within Earth can control the development of volcanoes in a rift environment, and (2) how the past behavior of the West Antarctic ice sheet can be used as a key to its future stability.