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      Evidence for Multi-stage Melt Transport in the Lower Ocean Crust: Atlantis Bank Gabbroic Massif (IODP Hole U1473A, SW Indian Ridge)

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          The architecture of lower oceanic crust at slow- and ultraslow-spreading ridge is diverse, yet the mechanisms that produce this diversity are not well understood. Particularly, the 660-km2 gabbroic massif at Atlantis Bank (Southwest Indian Ridge) exhibits significant compositional zonation, representing a high magma supply end member for accretion of the lower ocean crust at slow and ultraslow-spreading ridges. We present the petrographic and geochemical data of olivine gabbros from the 809-meter IODP Hole U1473A at Atlantis Bank gabbroic massif. Structurally, the upper portion of U1473A consists of a ∼600-meter shear zone; below this, the hole is relatively undeformed, with several minor shear zones. Olivine gabbros away from the shear zones have mineral trace element compositions indicative of high-temperature reaction with an oxide-undersaturated melt. By contrast, olivine gabbros within shear zones display petrographic and chemical features indicative of reaction with a relatively low-temperature, oxide-saturated melt. These features indicate an early stage of primitive to moderately evolved melt migration, followed by deformation-driven transport of highly evolved Fe-Ti-rich melts to high levels in this gabbroic massif. The close relationship between shear zones and the reaction with oxide-saturated melts suggests that syn-magmatic shear zones provide a conduit for late-stage, Fe-Ti-rich melt transport through Atlantis Bank lower crust. This process is critical to generate the compositional zonation observed. Thus, the degree of syn-magmatic deformation, which is fundamentally related to magma supply, plays a dominant role in developing the diversity of lower ocean crust observed at slow- and ultraslow-spreading ridges.

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          Author and article information

          Journal of Petrology
          Oxford University Press (OUP)
          August 10 2020
          [1 ]State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
          [2 ]University of Chinese Academy of Sciences, Beijing, China
          [3 ]Department. of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole Massachusetts, USA
          [4 ]Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
          [5 ]CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China
          [6 ]State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
          © 2020




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