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

在大洋中脊的研究中，一个长期存在的问题集中在它们是如何形成和演化的。我们对赤道太平洋东部加拉帕戈斯三叉路口的研究巡航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段的发展。在该地区，科科斯-纳斯卡裂谷西端正在裂解为东太平洋隆起东侧约0.5 Ma的地壳，可以研究从裂谷向岩浆海底扩张过渡的各个阶段。为了研究随着距离裂谷尖端的距离而发生的沿轴变化，我们将收集关于形态、重力和磁力变化的地球物理数据、用于化学分析的岩石样本以及用于识别热液活动的水柱数据。我们在大洋裂谷方面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。研究区域从科科斯-纳斯卡扩张中心的初始裂谷部位向东延伸到赫斯深裂谷的岩浆扩张成核，再到完全的岩浆扩张，表现出裂谷和裂解作用的启动和发展的渐进阶段。将收集多波束测深、重力和磁性数据，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。沿扩张轴和流线采集的岩石样品的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段的关系。研究生和本科生(杜克大学和麻省理工学院/WHOI)将参加邮轮和岸上研究，获得宝贵的海上经验并学习开展协作研究。此外，我们将在这项工作的基础上开展活动，用于每年为少数民族中学女孩举办的科学沉浸计划。

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.