A Detailed Bathymetric Study of Tectonic and Magmatic Processes at the Extremely Slow-Spreading Gakkel Ridge

摘要：Gakkel脊是北极洋中脊扩展中心，是全球洋中脊（MOR）系统中扩展最慢的部分。地幔熔融模型预测，当扩张速度小于15-20 mm/a时，熔体产量和地壳厚度将显著减少。极慢的扩张速度和沿Gakkel Ridge的扩张速度梯度使其成为地幔熔融和地壳生成的重要端元约束模式。MORs的扩展涉及这两方面。适应板块分离的岩浆伸展和机械伸展的平衡和相互作用随着伸展速率（和熔体有效性）的变化而变化，从而产生不同的脊轴和脊翼形态。因此，低扩张速率和低熔体产量可能影响地壳厚度以及火山活动和断裂的沿轴分布。最近，Gakkel Ridge被两个项目研究，使用了非常不同的平台和仪器。SCICEX项目使用一艘美国海军潜艇获取重力、高分辨率侧扫描和中低分辨率测深数据，这些数据距离Gakkel山脊轴线50公里，长度为600公里。AMORE项目使用两艘破冰船在Gakkel脊轴处获取高分辨率测深、岩石样本和地震折射数据。测深数据绘制了约1000公里的山脊轴线，但仅限于裂谷底和裂谷壁。首席调查员应AMORE首席调查员的邀请，分析和解释AMORE测深数据，并建立岩石样本的详细构造背景。该项目将主要基于高分辨率AMORE水域水深测量数据和sciex侧扫描数据。研究的目标是确定和表征Gakkel Ridge裂谷内的火山和构造地貌，将水深测量的性质和分布与伸展过程联系起来，并确定这些过程如何沿着山脊变化，以及它们如何相互作用以适应Gakkel Ridge极慢的扩张速度下的板块分离。要解决的假设包括：在极缓慢扩张的Gakkel山脊上，火山活动采取什么形式？在火山活动广泛分布的西部火山区，个别小型火山特征的形式、分布和规模是否存在显著差异？- Gakkel岭的构造活动以什么形式出现？断层沿轴线的倾斜度、倾斜度、长度和间距是否存在差异？西部火山带和其他岩浆活动较少的山脊之间的断层有什么不同？在山脊的东部，断层的性质是否在靠近火山中心时发生了变化？如果发生了变化，是如何发生的？在山脊与开口方向正交的地区，断层的性质与在山脊斜向的地区不同吗？-火山和构造过程是如何相互作用，形成沿Gakkel岭的观测形态的？在没有火山作用的情况下，伸展和岩石圈的形成是如何发生的？更广泛的影响：本科生将通过Lamont Doherty地球观测站（LDEO）的暑期实习计划参与这项研究。这是一个由nsf赞助的项目，本科生在LDEO科学家的指导下花一个夏天的时间完成一个项目。最后，他们写了一篇摘要，并就他们的研究发表了一篇美国地球物理联合会（AGU）式的“演讲”。通常情况下，实习生会在全国会议上展示他们的工作，或者与导师共同撰写论文。这个项目非常成功地将本科生引入了一个学术研究环境，大多数人决定继续攻读地球科学研究生院。

ABSTRACTCochranOPP-0352642Intellectual Merit: Gakkel Ridge, the mid-ocean ridge spreading center in the Arctic, is the slowest spreading portion of the global mid-ocean ridge (MOR) system. Mantle melting models predict that melt production and crustal thickness should decrease significantly at spreading rates of less than 15-20 mm/a. The extremely slow spreading rate and the gradient in spreading rate along the Gakkel Ridge make it an important end member constraining models of mantle melting and crustal generation. Extension at MORs involves both. The balance and interplay of magmatic and mechanical extension of accommodating plate separation varies as a function of spreading rate (and melt availability) to produce the differing ridge axis and ridge flank morphology. Thus, the low spreading rate and low melt production may affect the crustal thickness and along-axis distribution of volcanism and faulting. Recently the Gakkel Ridge was studied by two programs using very different platforms and instrumentation. The SCICEX program used a U.S. Navy submarine to obtain gravity, high-resolution sidescan and low- to moderate-resolution bathymetry data out to 50 km from the axis for 600 km along the Gakkel Ridge. The AMORE project used two icebreakers to obtain high-resolution bathymetry, rock samples and seismic refraction data at the Gakkel Ridge axis. The bathymetry data maps the ridge axis for ~1000 km, but is confined to the rift valley floor and walls. The Principal Investigator was invited by AMORE Principal Investigators to analyze and interpret the AMORE bathymetry data and to establish the detailed tectonic context of their rock samples. The project will be primarily based on the high-resolution AMORE swath-bathymetry data and the SCICEX sidescan data. The goals of the research are to determine and characterize volcanic and tectonic landforms within the Gakkel Ridge rift valley, relate the nature and distribution of the bathymetry to extensional processes, and to establish how these processes vary along the ridge and how they interact to accommodate plate separation at the extremely slow spreading rates of the Gakkel Ridge. Hypotheses to be addressed include: -What form does volcanic activity take at the extremely slow spreading Gakkel Ridge? Are theresignificant differences in the form, distribution and size of individual small scale volcanic features in the western volcanic zone where volcanism is widespread and the rest of the ridge where it occurs at widely spaced volcanic centers?-What form does tectonic activity take at the Gakkel Ridge? Are there differences in the dip, throw, length and spacing of faults along the axis? How does faulting differ between the western volcanic zone and the rest of the ridge where magmatism is rarer? In the eastern portion of the ridge, does the nature of faulting change approaching the volcanic centers and if so, how? Does the nature of faulting in areas where the ridge is orthogonal to the opening direction differ from where it is oblique?-How do volcanic and tectonic processes interact to produce the observed morphology along the Gakkel Ridge? How does extension and lithospheric creation occur in the absence of volcanism?Broader Impacts: Undergraduate students will be involved in this research through Lamont Doherty Earth Observatory (LDEO)'s Summer Internship program. This is an NSF-sponsored program in which undergraduates spend the summer working on a project under the mentorship of an LDEO scientist. At the end they write an abstract and present an American Geophysical Union (AGU) -type" talk on their research. Not infrequently, interns present their work at national meetings or coauthor papers with their mentors. This program has been very successful in introducing undergraduates to an academic research environment and the majority decide to go on graduate school in the Earth sciences.