Development of Detachment Faults at Intermediate Magma Supply

现在人们认识到，长期存在的（拆离）断层和核心复合体的形成是常见的，约占北方中大西洋海岭（MAR）沿沿着2500 km的50%。拆离断层不仅使我们能够研究下洋壳和上地幔的结构，而且改变了我们对洋壳的组成和结构、流体流动、热液喷口和相关生态的看法。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，而另一个断层只延伸了很短的时间就停止了？拆离断层的形成是否与总体和/或局部岩浆收支有关？相邻的determination是否连接？这个项目的目标就是试图回答这些问题。特别是，1）约束控制中段拆离断层的形成、演化和连接的过程; 2）检查沿着脊轴的岩浆供应与拆离断层形成之间的关系。在MAR的16.5度N附近选择的研究区域提供了一个新的中段剥离断层的戏剧性的演示，该断层靠近轴，中断了一个更长、更老且仍然活跃的剥离断层的整体发展，该剥离断层的分离离轴更远。PI计划获得区域多波束测深和磁力数据，以了解5 Ma的扩张历史。高分辨率多波束测深、磁、温深和光学传感器数据将从自主水下航行器哨兵收集，照片将从WHOI Towcam收集。这些数据将被用来描述剥离断层及其终端的特征，评估它们在哪里活动，并研究它们如何沿轴沿着连接。这些数据还将有助于评估地轴上火山活动的性质。疏浚计划将确认从测深分析中得出的关于基底的地幔、深成或火山起源的推断，以及地壳结构如何在整个区域内变化，并将确定区域岩浆供应在拆离断层形成过程中保持恒定的程度以及与当地岩浆供应变化的可能关系。这项工作将把强大的约束模型剥离断层的形成及其关系的岩浆supply.Broader影响：拟议的研究解决了几个问题，确定了社会在AGU查普曼会议？大洋岩石圈中的拆离作用：变形、岩浆作用、流体流动和生态系统？这对我们进一步理解缓慢扩张的洋中脊断层至关重要。该项目的一个组成部分是通过J. Escartin及其研究生（IPGP，巴黎）和H. Zhou（Tonji University，China）.三名麻省理工学院/WHOI联合项目的学生将获得航海经验，其中两人将收集数据，这将有助于他们的博士论文。W.朱和两名来自美国的本科生。马里兰州将参加巡航。

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.