Collaborative Research: The Transition from Rifting to Seafloor Spreading at the Western Tip of the Cocos-Nazca Rift

在洋中脊的研究中，一个长期存在的问题是它们是如何形成和演化的。我们对赤道东太平洋加拉帕戈斯群岛三重结的研究考察将描述从最初的裂谷到海底扩张的转变，以及与之相关的脊轴分割的发展。在该地区，科科斯-纳斯卡裂谷西端断裂成东太平洋隆起东翼~0.5 Ma的增厚地壳，可以研究裂谷向岩浆海底扩张过渡的各个阶段。为了研究与裂谷尖端距离的沿轴变化，我们将收集地球物理数据，包括形态、重力和磁场变化、用于化学分析的岩石样本和用于识别热液活动的水柱数据。我们关于海洋裂谷的发现将补充正在进行的大陆裂谷背景下这些过程的研究。研究区从科科斯-纳斯卡扩张中心的裂陷起始位置向东延伸至赫斯深裂陷岩浆扩张成核，再到岩浆完全扩张，呈现出裂陷和分段的起始、发展的递进阶段。将收集多波束测深、重力和磁数据，以重建从最初的裂谷到海底扩张的构造演化，特别是随着它们的发展，分段和偏移特征的变化。对沿扩展轴和流线采集的岩石样品进行化学分析，将有助于揭示地幔熔融和熔体输送系统的演化及其与构造分割的关系。研究生和本科生（杜克大学和麻省理工学院/WHOI）将参与邮轮和岸上研究，获得宝贵的航海经验，并学习进行合作研究。此外，我们将在这项工作的基础上开发活动，用于少数民族中学女生的年度科学浸入式课程。

A long-standing question in the study of mid-ocean ridges focuses on how they initiate and evolve. Our research cruise to the Galapagos Triple Junction in the eastern equatorial Pacific Ocean will characterize the transition from initial rifting to seafloor spreading, and the associated development of ridge axis segmentation. In this region, the western tip of the Cocos-Nazca Rift is breaking into ~0.5 Ma crust accreted on the east flank of the East Pacific Rise, and each stage in the transition from rifting to magmatic seafloor spreading can be studied. In order to examine along-axis changes as a function of distance from the rift tip, we will collect geophysical data on morphology, gravity and magnetic variations, rock samples for chemical analyses, and water column data for identifying hydrothermal activity. Our findings on oceanic rifting will complement on-going studies of these processes in continental rift settings. Our study area extends eastward from the site of initial rifting of the Cocos-Nazca spreading center to nucleation of magmatic spreading at the Hess Deep rift, to full magmatic spreading, thus exhibiting progressive stages in the initiation and development of rifting and segmentation. Multibeam bathymetry, gravity, and magnetic data will be collected to reconstruct the tectonic evolution from initial rifting through seafloor spreading, and in particular, changes in segment and offset characteristics as they develop. Chemical analysis of rock samples collected along the spreading axes and along flow lines will shed light on the evolution of mantle melting and melt delivery systems and their relationship to the tectonic segmentation. Graduate and undergraduate students (Duke and MIT/WHOI), will participate in the cruise and on-shore research, gaining valuable seagoing experience and learning to conduct collaborative research. In addition, we will develop activities based upon this work for use in a yearly science-immersion program for minority, middle school girls.