Collaborative Research: Mantle Melting and Crustal Genesis at the Slowest Spreading Rate: A Petrological Investigation of Gakkel Ridge, Arctic Ocean

AbstractOPP-99-11795MichaelOPP-99-12162DickOPP-99-12156GrahamOPP-00-00389LangmuirThe Gakkel海脊在全球洋脊系统中占有独特而重要的地位，因为它是：1)最慢的扩张海脊；2)最深的大洋海脊；3)极地幔成分可以直接采样的唯一地区；4)在一个独特的构造环境中，被大陆岩石圈包围。海脊的走向垂直于扩张方向，这导致极少的转换偏移量，它似乎是最冷的上地幔上方的海脊。这一特征的结合使大量关于洋壳形成的假说得到了检验。从岩石学上讲，加克尔山脊一直没有取样，很大程度上是因为北冰洋的永久冰盖使地球物理数据很难获得。海脊上的常年冰盖需要两艘破冰船协同工作，才能安全有效地进行探险。最近的发展使取样探险成为可能。从潜艇上收集的美国SCICEX水深测量、侧扫和重力数据为制定良好的采样计划提供了必要的背景数据。作为对InterRidge计划努力的回应，德国同事们已经准备好了一艘名为PolarSTEM的破冰船，进行为期50天的两艘船的国际探险，致力于研究Gakkel Ridge。美国还将提供一艘破冰船--新的USCG Healy。首席调查员将在加克尔山脊600公里处采集玄武岩、橄榄岩和相关岩石的样本。对这些岩石的详细地球化学研究与地壳和岩石圈厚度的地球物理估计相结合，可以生成超慢扩张条件下洋壳形成的定量模型。同时，在进行地下室取样时，将使用连接在疏浚(或取心)铁丝网和花环上的MAPR设备，作为热液调查进行勘察。这项调查将为加克尔山脊未来的热液和相关生物学研究奠定基础。最后，沿着Gakkel海岭进行采样和数据解释将使我们对北冰洋结壳的组成及其对北冰洋化学的影响有一个基本的了解。

AbstractOPP-99-11795MichaelOPP-99-12162DickOPP-99-12156GrahamOPP-00-00389LangmuirThe Gakkel Ridge occupies a unique and important place within the global system of ocean ridges because it is: 1) the slowest spreading ridge; 2) the deepest ocean ridge; 3) the sole region where polar mantle compositions can be sampled directly; and 4) in a unique tectonic setting surrounded by continental lithosphere in close proximity. The Ridge's strike is perpendicular to spreading direction which results in very few transform offsets and it appears to be the ridge above the coldest upper mantle. This combination of characteristics permits a large number of hypotheses of ocean crust formation to be tested. The Gakkel Ridge has been unsampled petrologically, largely due the permanent ice cover of the Arctic Ocean that makes geophysical data difficult to obtain. This perennial ice cover over the Ridge will require two icebreakers working in tandem to mount a safe and effective expedition. Recent developments make a sampling expedition possible. The U.S. SCICEX bathymetry, sidescan and gravity data collected from a submarine provide the necessary background data to plan a good sampling program. German colleagues, in response to InterRIDGE planning efforts, have in place ice breaker, Polarstem, for a two-ship, 50-day international expedition dedicated to study of the Gakkel Ridge. The United States will also provide an icebreaker, the new USCG Healy. The Principal Investigators will sample basalts, peridotites, and related rocks along 600 km of the Gakkel Ridge. Detailed geochemical study of these rocks along with geophysical estimates of crustal and lithospheric thickness can be combined to generate quantitative models of oceanic crust formation under ultra-slow spreading conditions. Concurrently, with the basement sampling, a reconnaissance will be carried out as a hydrothermal survey using MAPR devices attached to the dredging (or coring) wire and rosettes. The survey would be designed to lay the groundwork for future hydrothermal and related biological studies along Gakkel Ridge. Finally, sampling along Gakkel Ridge and interpretation of the data will provide a basic understanding of the makeup of Arctic Ocean crust, and its influence on Arctic Ocean chemistry.