Formation of lower fast-spread oceanic crust: a structural and geochemical study of troctolites in the Hess Deep Rift (East Pacific Rise)

Progress in Earth and Planetary Science

Research Article

Norikatsu Akizawa¹  Shoji Arai²  Benoît Ildefonse³  Marguerite Godard³ 

[1] Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, 277-8564, Kashiwa, Chiba, Japan;School of Natural Sciences, Macquarie University, Balaclava Road, 2109, Sydney, NSW, Australia;Department of Earth Sciences, Kanazawa University, 920-1192, Kakuma, Kanazawa, Japan;Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France;

关键词: IODP expedition 345;    Lower oceanic crust;    Fractional crystallization;    Mid-ocean ridge basalt;    Porous melt migration;    Melt-mantle interaction;   

DOI  :  10.1186/s40645-023-00560-4

 received in 2022-10-24, accepted in 2023-06-01,  发布年份 2023

来源: Springer

【 摘 要 】

Troctolites were recovered during Integrated Ocean Drilling Program Expedition 345 at the Hess Deep Rift, next to fast-spreading East Pacific Rise. These troctolites are divided into three groups based on textural differences: coarse-grained (1–10 mm in length) troctolite, fine-grained (~ 2 mm in length) troctolite, and skeletal olivine-bearing troctolite. All troctolites exhibit a magmatic fabric. The major-element compositions of olivine, plagioclase, and clinopyroxene in the troctolites are intermediate between those of Hess Deep gabbros and harzburgites. The trace-element compositions of olivine, plagioclase, and clinopyroxene in the troctolites overlap with those of troctolites from slow-spread crust, but they record no petrographic evidence indicating assimilation of mantle peridotite. Thermodynamic calculation for mineral chemistry showed that fractional crystallization of melt is the dominant process responsible for the formation of the troctolites. The fine-grained troctolite was crystallized with high crystallization rate resulting from hot melt injection into colder wall gabbro. In contrast, interactions between the unsolidified troctolite containing interstitial melt and newly injected melt resulted in the formation of the skeletal olivine-bearing troctolite. While our results demonstrate that the troctolites exhibit multiple melt injections and partial dissolution of a troctolite precursor, fractional crystallization is the dominant process for the creation of the lower crust in the Hess Deep Rift.

【 授权许可】

CC BY   
© The Author(s) 2023

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