Development of Detachment Faults at Intermediate Magma Supply

人们现在认识到，长寿命(滑脱)断裂和核心杂岩的形成是常见的，占沿中大西洋海脊(MAR)北部2500公里延伸的约50%。拆离断层不仅可以研究下洋壳和上地幔的结构，而且还改变了我们对洋壳的组成和结构、流体流动、热液喷发和相关生态的看法。但许多关键问题仍然存在：为什么一个断层继续延伸，滚动形成一个核心复合体，而另一个断层在延伸一小段时间后停止？滑脱断层的形成是否与整体和/或局部岩浆预算有关？相邻的拆卸是否相连？这个项目的目标就是试图回答这些问题。具体地说，1)约束控制中段滑脱断裂形成、演化和连接的过程；2)研究沿山脊轴线的岩浆供应与滑脱断裂形成的关系。在3月份北纬16.5度附近选定的研究区域戏剧性地展示了靠近中轴线的新的中段拆离断层中断了一个更长、更老且仍然活动的拆离断层的整体发展，而拆离距离轴线更远。PIS计划获得区域多波束测深和地磁数据，以了解向外扩展到5 Ma的历史。高分辨率多波束测深、磁力、CTD和光学传感器数据将从自主水下航行器(AUV)哨兵收集，照片将从WHOI Towcam收集。这些数据将被用来描述拆离断层及其终端的特征，评估它们在哪里活动，并研究它们可能如何沿着轴线连接。这些数据还将使人们能够评估地轴上火山活动的性质。疏浚计划将证实通过对基底的地幔、深成或火山起源、地壳结构在整个地区如何变化的测深分析所作出的推断，并将确定区域岩浆供应在拆离断层形成过程中保持不变的程度，以及与当地岩浆供应变化的可能关系。这项工作将对拆离断层的形成及其与岩浆供应的关系的模型施加强烈的约束。广泛的影响：拟议的研究解决了在AGU Chapman会议上由社区确定的几个问题：大洋岩石圈的拆离：变形、岩浆作用、流体流动和生态系统？对于推动我们对洋脊缓慢扩展的断层的理解至关重要。该项目包括J·埃斯卡廷及其研究生(巴黎IPGP)和H·周(同济大学，中国)参与的国际合作的一部分。三名麻省理工学院/世界卫生组织联合项目的学生将获得航海经验，其中两名学生将收集有助于他们博士论文的数据。朱和来自美国马里兰州的两名本科生将参加这次邮轮。

It is now recognized that long-lived (detachment) faults and the formation of core complexes are common, accounting for ~50% of the extension along 2500 km of the northern Mid-Atlantic Ridge (MAR). Not only do detachment faults allow the architecture of the lower ocean crust and upper mantle to be examined, but they change the way we think about the very composition and structure of ocean crust, fluid flow, and hydrothermal venting and associated ecology. But many critical questions remain: Why does a fault continue to extend, rolling over to form a core complex, while another stops after extending only for a short time? Is detachment fault formation associated with overall and/or local magma budget? Are adjacent detachments linked? The goal of this project is to try to answer these questions. In particular, to 1) constrain the processes controlling the formation, evolution, and linking of mid-segment detachment faults and; 2) examine the relationship between magma supply along the ridge axis and detachment fault formation. the chosed study area near 16.5 degrees N at the MAR presents a dramatic demonstration of a new mid-segment detachment fault near to the axis interrupting the overall development of a longer, older and still active detachment fault whose breakaway is farther off-axis. The PIs plan is to obtain regional multibeam bathymetry and magnetic data to understand the spreading history out to 5 Ma. High-resolution multibeam bathymetry, magnetic, CTD and optical sensor data will be collected from the autonomous underwater vehicle (AUV) Sentry, and photographs from the WHOI Towcam. These data will be used to characterize the detachment faults and their terminations, assessing where they are active and examining how they might link along the axis. The data also will allow assessment of the nature of volcanism at the axis. A dredging program will confirm the inferences made from bathymetric analysis as to the mantle, plutonic or volcanic origin of basement, how crustal architecture varies across the region, and will establish the degree to which the regional magma supply has been constant over detachment fault formation and possible relationships to local magma supply variations. This work will place strong constrains on models for detachment fault formation and its relationship to magma supply.Broader Impacts: The proposed study addresses several issues identified by the community at the AGU Chapman Conference ?Detachments in Oceanic Lithosphere: Deformation,Magmatism, Fluid Flow, and Ecosystems? as critical to move forward our understanding of faulting at slow-spreading mid-ocean ridges. The project has a component of international cooperation through the participation of J. Escartin and his graduate student (IPGP, Paris) and H. Zhou (Tonji University, China). Three MIT/WHOI Joint Program students will receive sea-goingexperience, and two of them will collect data that will contribute to their PhD theses. W. Zhu and two undergraduate students from U. Maryland will participate on the cruise.