Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge, Arctic Ocean

摘要: A high-resolution mapping and sampling study of the Gakkel ridge was accomplished during an international ice-breaker expedition to high Arctic North Pole in summer 2001. For this slowest-spreading endmember global mid-ocean-ridge system, predictions were that magmatism should progressively diminish as spreading rate decreases along ridge, hydrothermal activity be rare. Instead, it found magmatic variations are irregular, is abundant. 300-kilometre-long central amagmatic zone, where mantle peridotites emplaced directly axis, lies between abundant, continuous volcanism west, large, widely spaced volcanic centres east. These observations demonstrate extent melting not a simple function rate: temperatures at depth or chemistry (or both) must vary significantly along-axis. Highly punctuated absence offsets suggests first-order segmentation controlled by processes melt segregation. The strong focusing coupled with faulting may account for unexpectedly levels observed.