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

极慢扩展加克尔海脊构造和岩浆过程的详细水深研究

• 批准号: 0352642
• 负责人: James Cochran
• 金额: $ 17.46万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-04-01 至 2008-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0352642&HistoricalAwards=false
• 关键词: Detailed; Bathymetric; Study; Tectonic; Magmatic

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.

知识点：加克尔海岭是北极洋中脊扩张中心，是全球洋中脊（莫尔）系统中扩张最慢的部分。 地幔熔融模型预测，当扩张速率小于15-20 mm/a时，熔融产物和地壳厚度将显著减少。极慢的扩张速率和沿着的扩张速率梯度使其成为制约地幔熔融和地壳生成模式的重要端元。MORs的扩展涉及两者。调节板块分离的岩浆和机械延伸的平衡和相互作用作为扩展速率（和熔体可用性）的函数而变化，以产生不同的脊轴和脊侧面形态。因此，低的扩张速率和低的熔体生产可能会影响地壳厚度和火山作用和断裂作用的沿轴分布。最近，Gakkel Ridge由两个使用非常不同的平台和仪器的程序进行了研究。SCICEX计划利用美国海军潜艇获取沿加克尔海岭沿着、距轴线50公里范围内的重力、高分辨率侧扫和中低分辨率测深数据。AMORE项目使用两艘破冰船在Gakkel海岭轴获取高分辨率测深数据、岩石样本和地震折射数据。测深数据绘制了约1 000公里的海脊轴线，但仅限于裂谷谷底和壁。首席研究员应AMORE首席研究员的邀请，分析和解释AMORE测深数据，并确定岩石样本的详细构造背景。该项目将主要以高分辨率AMORE条带测深数据和SCICEX侧扫数据为基础。这项研究的目的是确定加克尔海脊裂谷内的火山地貌和构造地貌并确定其特征，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海脊变化，以及它们如何相互作用，以适应加克尔海脊极慢扩张速度下的板块分离。要解决的假设包括：-什么形式的火山活动采取在极其缓慢的扩展Gakkel岭？在火山活动广泛的西部火山带和火山活动分布在火山中心的山脊的其余部分，个别小规模火山特征的形式、分布和大小是否存在显著差异？加克尔海岭的构造活动是什么形式的？断层沿着轴的倾角、落差、长度和间距是否存在差异？断层作用在西部火山带和其他岩浆活动较少的山脊之间有何不同？在海脊的东部，断层的性质是否在接近火山中心时发生变化？如果是，是如何变化的？在脊与开口方向垂直的区域和脊倾斜的区域，断层的性质是否不同？火山和构造过程是如何相互作用而产生沿着加克尔海岭观测到的地貌的？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：本科生将通过拉蒙多尔蒂地球观测站（LDEO）的夏季实习计划参与这项研究。这是一个由NSF赞助的项目，本科生在一位LDEO科学家的指导下，利用暑假从事一个项目。最后，他们写了一个摘要，并提出了一个美国地球物理联盟（AGU）类型的”谈话，他们的研究。实习生经常在国家会议上介绍他们的工作，或与导师共同撰写论文。该计划在将本科生引入学术研究环境方面非常成功，大多数人决定继续攻读地球科学研究生院。