Tectonic evolution of the Rio Grande Rise - Walvis Ridge hotspot twins inferred from magnetic anomaly and seismic reflection data

虽然陆地上的熔岩火山喷发，比如夏威夷岛上的火山喷发，令人敬畏，可能会造成重大的财产破坏，而且看起来很壮观，但与海底熔岩喷发相比，它们喷发的物质数量微不足道。海底火山喷发的熔岩量是如此之大，以至于整个海底（占地球表面的70%以上）都被海洋中脊或“热点”火山喷发的熔岩所覆盖，这两种火山都从地幔中喷出熔融物质并将其带到地表。这类被称为“热点”的火山是由局部的、持续的地幔物质上涌产生的，可以喷出大量的熔岩，形成大型火成岩省。随着地球构造板块的移动，随着时间的推移，这些热点产生了线性火山链，可以用来推断板块运动的距离、方向和速度。其中最具代表性的是太平洋的夏威夷-皇帝链，它显示了从大约8100万年到现在的年龄变化，以及一串简单的海山。南大西洋的沃尔维斯山脊是另一个。然而，与夏威夷岛链不同的是，沃尔维斯岭更为复杂，其时间跨度可追溯到1.3亿年前。本研究的重点是了解沃尔维斯海脊的形成和演化，以及它与姊妹省里约热内卢大隆起的关系，后者位于中大西洋海脊的东侧。这两个火成岩省曾经是一个整体，但在白垩纪晚期，大约8500万年前，一次裂谷事件将它们分开了。这一事件是由中大西洋海岭的重组和起源热点从海岭轴线向西移动造成的，在那里岩浆活动继续，沃尔维斯海岭增加了额外的海底火山。最近的证据表明，在这次分裂中，大西洋中脊形成了一个微板块。为了检验这一假设并更好地了解南大西洋是如何演变的，一支地球物理考察队将前往沃尔维斯岭地区，收集磁异常、测深和地震数据。新的磁场数据将用于推断大西洋中脊过去的位置和海底的年龄，这是重建板块边界的关键数据集。测深数据将显示海底特征的形态和结构，并使微孔板块假说得以检验。这项工作的更广泛影响包括与德国和巴西科学家的国际合作。它还提供了一个重要的地震现场调查，将用于帮助确定钻井位置和钻孔，为即将到来的nsf资助的国际海洋发现计划探险，帮助确保其成功。此外，该项目有一个大型的学生培训部分，其中8至10名学生将出海，获得学分，并接受地球物理和航海技术和技术方面的培训。与公众的接触将通过博客和邮轮项目网站以及从船上向休斯顿大学本科生的实时广播来完成。有关邮轮及其发现的新闻也将发布，以激发公众对该项目和科学的兴趣。沃尔维斯山脊（Walvis Ridge）从大西洋东南部非洲板块的海底升起，其持续时间约为1.3亿年，具有突出的准线性形状，是地球上最重要的热点火山轨迹之一，因为它是印度-大西洋热点参考框架的基石。这个特征被认为是来自非洲边缘的地幔柱的产物，这是一个大的、低剪切速度的省份，它有一个双胞胎，里约热内卢大隆起，一个横跨大洋的南美板块上的玄武岩高原。这两个大火成岩省可能是在晚白垩纪期间在大西洋中脊形成的。但是，当热点在6000万至7000万年前离开山脊时，岩浆活动仍在继续，但仅限于沃尔维斯山脊。由于它的准线性几何形状，沃尔维斯岭通常被建模为一个单一的、年龄递进的热点的痕迹。然而，沿着它的痕迹对火山进行的放射性年龄测定并不完全符合热点模型，年轻的海底火山分散在一些较老的海底火山中。沃尔维斯岭海山的地球化学证据表明，大约6000万至7000万年前，沃尔维斯径迹分裂成3个子径迹。最近对该地区构造结构的研究表明，在板块边界重组过程中，沃尔维斯岭和里约热内卢大隆起火成岩省之间可能形成了微板块，可能破坏了热点时代的进展，导致复杂的火山建筑形态和时代关系。由于目前南大西洋海底的地球物理数据很少，而大西洋中脊两侧板块的构造运动是我们板块运动模型的关键，因此我们将进行为期48天的地球物理研究，收集磁、地震和水深数据，以解决沃尔维斯脊与里约热内卢大隆起之间的关系。该项目的目标是了解这两个大火成岩省是如何形成和演化的。磁异常数据将绘制构造重组发生地区的C34-C30等时线，以及目前尚未绘制和定义磁异常的地区。识别这些异常及其几何形状是确定过去脊位和检验微孔板块假说的关键。地震和测深数据将检查沃尔维斯山脊上瓦尔迪维亚河岸地区的结构和形态，因为该河岸是主要的里约热内卢0大隆起高原的孪生兄弟。在巡航中收集的地震数据也将作为即将到来的国际海洋发现计划（IODP）考察的关键地点特征数据，该考察将在沃尔维斯岭钻探六个地点。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Although volcanic eruptions of lavas on land, like those on the island of Hawaii, are awe-inspiring, can cause significant destruction of property, and are spectacular to watch, they are insignificant in terms of the amount of erupted material when compared to eruptions of lava on the seafloor. The volume of lava from seafloor volcanic eruptions is so great that the entire floor of the oceans, over 70% of Earth's surface, is covered by lavas erupted from mid-ocean ridges or "hotspot" volcanoes, both of which tap molten material from the mantle and bring it to the surface. The class of volcanoes called "hotspots" arise from localized, persistent upwelling of mantle material and can erupt voluminous amounts of lava creating large igneous provinces. As Earth's tectonic plates move, over time, these hotspots create linear volcanic chains that can be used to infer the distance, direction, and rates of plate motion. The most iconic of these is the Hawaiian-Emperor chain in the Pacific Ocean, which exhibits an age progression from ~81 million years to the present along with a simple string of seamounts. The Walvis Ridge in the South Atlantic Ocean is another. Unlike the Hawaiian chain, however, the Walvis Ridge is more complex and spans a time that goes back ~130 million years. This research focuses on understanding the formation and evolution of the Walvis Ridge and its relation to its sister province, the Rio Grande Rise, which occurs on the eastern side of the Mid-Atlantic Ridge. These two igneous provinces were once a single entity, but during the late Cretaceous, ~85 million years ago, there was a rifting event that split them apart. This event resulted from reorganization of the Mid-Atlantic Ridge and movement of the originating hotspot off the ridge axis to the west where its magmatism continued and additional seafloor volcanoes were added to the Walvis Ridge. Recent evidence suggests that, during this breakup a microplate formed at the Mid-Atlantic Ridge. To examine this hypothesis and to better understand how the South Atlantic evolved, a geophysical expedition will go to the Walvis Ridge area and collect magnetic anomaly, bathymetry, and seismic data. The new magnetic data will be used to infer past locations of the Mid-Atlantic Ridge and the age of the seafloor, a crucial data set for making plate boundary reconstructions. Bathymetry data will show the morphology and structure of seafloor features and enable testing of the microplate hypothesis. Broader impacts of the work include international collaboration with German and Brazilian scientists. It also provides an important seismic site survey that will be used to help site drilling locations and boreholes for an upcoming NSF-funded International Ocean Discovery Program expedition, helping ensure its success. In addition, the project has a large student training component in which eight to ten students will go to sea, earn academic credit, and be trained in geophysical and sea-going technology and techniques. Outreach to the public will be done via blogs and a cruise project website as well as real-time broadcasts from the ship to University of Houston undergraduate classes. News releases about the cruise and its findings will also be generated to stimulate public interest in the project and science. With its ~130 million-year duration and prominent quasi-linear shape, the Walvis Ridge, which rises from the seafloor on the African plate in the southeast Atlantic Ocean, is one of the Earth's most important hotspot volcanic tracks because it serves as a keystone for the Indo-Atlantic hotspot reference frame. This feature is considered the product of a mantle plume arising from the edge of the African, large, low-shear velocity province and has a twin, the Rio Grande Rise, a basaltic plateau across the ocean on the South American plate. These two large igneous provinces likely formed together at the Mid-Atlantic Ridge during the Late Cretaceous. But, when the hotspot drifted off the ridge ~60-70 million years ago, magmatism continued but only on the Walvis Ridge. Due to its quasi-linear geometry, the Walvis Ridge is usually modeled as the trace of a single, age-progressive hotspot. However, radiometric age dating of volcanoes along its trace do not all fit with the hotspot model, with younger submarine volcanoes being dispersed among some of the older ones. Geochemical evidence of Walvis Ridge seamounts shows that ~60-70 million years ago, the Walvis track split into three sub-tracks. Recent studies of tectonic fabrics from the area suggest that a microplate may have formed between the Walvis Ridge and Rio Grande Rise igneous provinces during plate boundary reorganization, potentially disrupting the hotspot age progression and resulting in complex volcanic edifice morphologies and age relations. Because current geophysical data of the seafloor in the South Atlantic are sparse and the tectonic movement of the plates on both sides of the Mid-Atlantic Ridge is key to our models of plate motion, a 48-day geophysical that will collect magnetic, seismic, and bathymetric data will be carried out to resolve the relations between the Walvis Ridge and Rio Grande Rise. Goals of the project are to understand how these two large igneous provinces formed and evolved. Magnetic anomaly data will map isochrons C34-C30 in the area where the tectonic reorganization occurred and where magnetic anomalies are presently poorly mapped and defined. Identification of these anomalies and their geometry is key to defining past ridge positions and testing the microplate hypothesis. Seismic and bathymetric data will examine the structure and morphology of Valdivia Bank area on the Walvis Ridge as this bank is the twin of the main Rio Grande Rise plateau. Seismic data collected on the cruise will also serve as critical site characterization data for an upcoming International Ocean Discovery Program (IODP) expedition that is set to drill six locations on Walvis Ridge.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.