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

虽然人们对洋壳的性质研究了几十年，但由于缺乏几百万年前形成的地壳的数据，许多问题仍然没有答案。地壳的海洋盆地可达2亿年。在年龄上，地球最大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到700万年之后。如果是的话，能维持多久？最近的工作表明，旧地壳上的不规则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，一个大洋扩张段的行为在岩浆活动和构造裂谷的数量上有多长？该项目将使用地震成像来测量从大西洋中脊到7000万年前地壳的性质，大西洋中脊是今天新地壳形成的地方。扩张中心西侧的老地壳这些数据将回答有关海洋地壳演化的问题，并将提供有关综合海洋发现计划未来海底钻探可以安全完成的信息，以解决有关海洋化学在长期尺度上演变的问题。现场实验将作为研究生和早期职业科学家的培训平台。一所大学网络中的前退伍军人将参与研究的各个方面。来自地壳增生速度低于30毫米/年或年龄超过8 Ma的地震和钻井岩心数据尤其稀少。这排除了评估是否海洋地壳层2A地震速度达到7.5 Ma的成熟值，或者相反，他们继续演变到更老的年龄？不可能知道缓慢扩展地壳的地震结构在岩浆段中是否均匀，或者是否存在不均匀性并与过去扩展速率的变化有关。该项目提供了地球物理数据，用于连续描述从活跃扩张中心到形成至~70 Ma的地壳的缓慢至中等扩张洋壳的特征，包括1 500公里的地震反射数据和在5个地点配置的海底地震仪折射数据，这些地点将用于未来的科学钻探。由此产生的数据将解决以下问题：大洋地壳在百万年时间尺度上的演变、缓慢扩张海脊随时间的演变和稳定性，以及通过今后的钻探，热液对全球地球化学循环的贡献。

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.