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

洋中脊研究中的一个长期问题是，洋中脊是如何形成和演变的。我们对赤道东太平洋的加拉帕戈斯三联点的研究巡航将描述从初始裂谷到海底扩张的过渡，以及脊轴分段的相关发展。在这一区域，可可-纳斯卡裂谷西端正在断裂成东太平洋海隆东侧增生的~0.5 Ma地壳，可以研究裂谷向岩浆海底扩张过渡的各个阶段。 为了研究沿轴向的变化与距裂谷尖端距离的函数关系，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确定热液活动的水柱数据。我们对海洋裂谷作用的研究结果将补充正在进行的大陆裂谷背景下的这些过程的研究。我们的研究区向东延伸，从网站的初始裂谷的Cocos-Nazca扩张中心的Hess深裂谷的岩浆扩张的成核，以充分的岩浆扩张，从而表现出渐进的阶段，在开始和发展的裂谷和分段。将收集多波束测深、重力和磁力数据，以重建从最初裂谷到海底扩张的构造演化，特别是分段和偏移特征在其发展过程中的变化。对沿着伸展轴和沿着流线采集的岩石样品进行化学分析，将有助于阐明地幔熔融和熔融输送系统的演化及其与构造分段的关系。 研究生和本科生（杜克和麻省理工学院/WHOI）将参加巡航和岸上研究，获得宝贵的航海经验，并学习进行合作研究。此外，我们将根据这项工作开发活动，用于少数民族中学女生的年度科学沉浸计划。

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.