Collaborative Research: Evolution of South Atlantic Oceanic Crust: A Seismic Transect

虽然海洋地壳的性质已经研究了几十年，但由于缺乏数百万年前形成的地壳的数据，许多问题仍然没有得到解答。由于海洋盆地中地壳的年龄高达200万年，地球上最大的构造板块的历史仍有待研究。关键问题与地壳和海洋之间的化学交换有关——这种交换是否会持续超过7英里，如果会，持续多久？最近的研究表明，古老地壳上不规则的海底可能是地热循环的场所，将物质从地壳转移到海洋。另一个基本问题是，从岩浆活动和构造裂谷的数量来看，一个海洋扩张段以同样的方式运行多久？这个项目将使用地震成像技术来测量从大西洋中脊（今天新地壳形成的地方）到扩张中心西侧70英里的旧地壳的地壳性质。这些数据将回答有关海洋地壳演化的问题，并将为“综合海洋发现计划”（Integrated Ocean Discovery Program）未来在何处可以安全完成海底钻探提供信息，以解决有关长期海洋化学演化的问题。实地实验将成为研究生和早期职业科学家的培训平台。大学网络中的前退伍军人将参与研究的各个方面。在小于30mm /年或小于8ma的地壳中，地震和钻探岩心的数据尤其稀少。这就排除了对海洋地壳2A层地震速度是否在7.5 Ma达到成熟值的评估，或者它们是否继续演化到更老的时代？我们不可能知道在一个岩浆段中，缓慢扩张的地壳的地震结构是否均匀，或者是否存在非均质性，并与过去扩张速度的变化有关。该项目提供了从活动扩展中心到地壳形成至~70 Ma的缓慢到中等扩展的海洋地壳的连续特征的地球物理数据，包括1500公里的地震反射数据和在未来科学钻探目标的5个地点配置的海底地震仪折射数据。由此得到的数据将解决有关海洋地壳在数百万年时间尺度上的演化、缓慢扩张的山脊随时间的演化和稳定性，以及通过未来的钻探，热液对全球地球化学循环的贡献等问题。

Although the nature of oceanic crust has been studied for decades, many questions remain unanswered, owing to a paucity of data from crust formed more than a few million years ago. With ocean basins containing crust up to 200 m.y. in age, the history of Earth's largest tectonic plates remain to be studied. Key questions relate to chemical exchange between the crust and ocean-- does this continue beyond 7 m.y. or not, and, if so, for how long? Recent work shows that irregular seafloor on older crust can be the site of geothermal circulation that transfers material from crust to ocean. Another fundamental question is how long does an oceanic spreading segment behave in the same way- in terms of amount of magmatic activity versus tectonic rifting?This project will use seismic imaging to measure the properties of the crust from the Mid-Atlantic Ridge, where new crust forms today, out to 70 m.y. old crust on the western flank of the spreading center. These data will answer questions about oceanic crustal evolution and they will provide information about where future seafloor drilling by the Integrated Ocean Discovery Program could be safely accomplished, to address questions about the evolution in ocean chemistry over long time scales. The field experiment will serve as a training platform for graduate students and early career scientists. Former veterans in a university network will be involved in aspects of the research.Seismic and drill core data from crust accreted at less than 30 mm/yr, or older than about 8 Ma are particularly sparse. This precludes assessment of whether oceanic crustal Layer 2A seismic velocities reach mature values in 7.5 Ma, or instead do they continue to evolve to older ages? Its not possible to know if the seismic structure of slow-spread crust is uniform in a magmatic segment, or if heterogeneity exists and is associated with a past change in spreading rate. This project provides geophysical data for a continuous characterization of slow-to-intermediate spread oceanic crust from the active spreading center to crust formed up to ~70 Ma, including 1500 km of seismic reflection data and collocated ocean bottom seismometer refraction data at 5 sites targeted for future scientific drilling. The resulting data will address questions about the evolution of oceanic crust on million-year timescales, the evolution and stability of slow-spreading ridges over time and, via future drilling, hydrothermal contributions to global geochemical cycles.