Evaluating mechanisms for the formation, propagation and evolution of volcanic rifts and margins

在盘古大陆分裂的过程中，大量岩浆涌出并填满了裂缝。在短短几十万年的时间里，可能爆发了多达一千万立方千米的玄武岩，岩浆可能引发了大陆的破裂。地质学家将这些大规模喷发的地区定义为大火成岩省。埃塞俄比亚高原是一个年轻的火山省的例子，而位于曼哈顿哈德逊河对面的帕利塞德是一个从纽芬兰延伸到巴西的2亿年前的火山省的一部分。近年来，科学家们收集的数据提供了证据，证明在大多数大陆裂谷边缘的近海埋有厚厚的熔岩堆，而在近海的熔岩可能与在陆地上绘制的地图所估计的一样多。这个项目的重点是使用数值模型来模拟和理解岩浆侵入和挤压对大陆分裂和由此产生的大陆边缘结构的影响。人们对这些类型的岩浆作用如何影响碳氢化合物的生成和保存越来越感兴趣。本项目支持培养1名博士后研究员和1名研究生。在大多数裂谷边缘的近海发现的厚厚的火山流层，被称为向海倾斜反射层（SDRs），是火山边缘的一个决定性特征。然而，这些特征的形成以及地幔柱作为形成特别提款权的熔岩来源的潜在贡献仍然是一个有争议的话题。该项目考虑了羽流是否与火山裂谷传播一致的大规模问题。观察表明，裂谷从裂谷的远端传播到中心，受到羽流影响的地区，这使人们质疑需要羽流来引发火山裂谷的想法，比如那些产生了大部分大西洋边缘的火山裂谷。该项目的主要假设是，沿裂谷迅速演变的火山活动模式可以调和羽流概念和观测到的裂谷传播方向。要验证这一假设，就需要考虑火山活动是如何沿着一条数千公里长的火山裂谷产生的。这项研究使用中等低分辨率的地幔流动和熔融三维模型来考虑地幔柱物质如何沿着早期裂谷扩散。研究的第二个主要部分是岩浆裂谷发育的二维截面模型。将评估岩浆侵入和火山作用对裂谷形成的影响，特别是对特别提款权的发展和快速沉降的影响。初步模型认为，在SDR形成后，如果下地壳能够流入一个伸展的地壳区域，则会产生快速沉降。新模型将允许对以前的概念模型进行定量测试，特别是那些涉及SDR形成期间演化裂谷的热量和密度结构的横向变化的模型。

Massive volumes of magma poured out and filled in the split during the breakup of the supercontinent Pangea. As much as ten million cubic kilometers of basalt may have erupted in just a few hundred thousand years, and the magma may have triggered the rupture of the continent. Geologists define these areas of massive eruptions as Large Igneous Provinces. The Ethiopian Plateau is an example of a younger volcanic province, while the Palisades on the opposite side of the Hudson River from Manhattan is part of a of a 200-million-year-old volcanic province that stretches from Newfoundland to Brazil. In recent years, scientists have collected data that provide evidence of thick piles of lavas buried just offshore of most rifted continental margins, and as much lava may be offshore as what is estimated from mapping on land. This project is focused on using numerical models to simulate and understand the way magma intrusion and extrusion influence the breakup of continents and the structure of the resulting continental edges. There is growing interest in how these types of magmatic processes affect the generation and preservation of hydrocarbons. The project supports the training of a post-doctoral researcher and a graduate student.The thick sequences of volcanic flows found offshore of most rifted margins, termed Seaward Dipping Reflectors (SDRs), are a defining feature of volcanic margins. However, the formation of these features and the potential contribution of mantle plumes as a source of the lavas that form SDRs remain a topic of controversy. This project considers the large-scale question of whether plumes are consistent with volcanic rift propagation. Observations suggesting that rifts propagate from the distal end of rifts to the central, plume-affected areas has called into question the idea that plumes are needed to initiate volcanic rifts such as those that produced most of the Atlantic margins. The primary hypothesis of this project is that a rapidly evolving pattern of volcanism along a rift can reconcile the plume concept and the observed rift propagation directions. Testing this hypothesis requires consideration of how volcanism is fed along a several thousand kilometer-long volcanic rift. This study uses moderately low-resolution 3-D models of mantle flow and melting to consider how plume material might spread along an incipient rift. The second, and main, component of the study focuses on 2-D cross-sectional models of magmatic rift development. The effect of magma intrusion and volcanism on rift formation and particularly on the development and the rapid subsidence of SDRs will be assessed. Preliminary models produce fast subsidence after SDR formation if the lower crust can flow into a region of stretching crust. The new models will allow quantitative testing of previous conceptual models, particularly those involving lateral variability in the thermal and density structure of an evolving rift during SDR formation.