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DOI	10.1016/j.epsl.2019.116048
	How do detachment faults form at ultraslow mid-ocean ridges in a thick axial lithosphere?
	Bickert M.; Lavier L.; Cannat M.
发表日期	2020
ISSN	0012821X
卷号	533
英文摘要	Slow-spreading mid-ocean ridges develop large offset normal faults, or detachments, that exhume mantle-derived peridotites to the seafloor. Successive detachments that flip polarity (flip-flop detachments) have been documented in corridors of nearly amagmatic spreading at the eastern Southwest Indian Ridge (SWIR). The depth of earthquake hypocenters supports the existence of a very thick axial lithosphere with a brittle lid thicker than 20 km. This is also consistent with our petrological observations on dredged peridotites from the area (plagioclase-free, spinel-bearing dynamically recrystallized assemblages in shear zones) that reveal high stress (80–270 MPa) and high temperature (>800 °C) deformation combining brittle and ductile mechanisms. Thermo-mechanical models using strain dependent cohesion weakening to localize deformation do not produce detachments for a brittle lithosphere thicker than 20 km. Here, we explore two other weakening mechanisms observed in situ, and for which we have temperature constraints from rock sampling: serpentinization (at T<350 °C) and grain size reduction by dynamic recrystallization (at T∼800–1000 °C). Serpentinization and more generally hydrous alteration minerals have been shown to localize strain at detachment-dominated slow-spreading ridge locations. Here we show that grain size reduction due to dynamic recrystallization also occurs in peridotites from the eastern SWIR. Our models explore the effect of implementing these weakening mechanisms separately or together in an amagmatic spreading context, of varying the threshold conditions for their activation, and the thermal conditions on-axis. We show that serpentinization alone does not produce flip-flop detachments, while grain size reduction alone does, albeit with unrealistically high associated topographic relief. Combining the two, we observe the activation of several modes of axial deformation: horst mode, spider mode, and long or short-lived flip-flop detachments. Flip-flop detachment faulting, once initiated, can be activated over long periods of time, with fault topography and offsets that are consistent with geological observations in the eastern SWIR nearly amagmatic study area. The transition between these modes appears to depend on the amount and location of serpentine that has been produced in previous stages of faulting. © 2019 Elsevier B.V.
关键词	deformation microstructure detachment fault grain size reduction mantle lithosphere Southwest Indian Ridge
英文关键词	Chemical activation; Deformation; Dynamic recrystallization; Dynamics; Feldspar; Flip flop circuits; Grain size and shape; Serpentine; Size determination; Structural geology; Submarine geology; Topography; Deformation microstructure; Detachment fault; Grain-size reduction; Mantle lithosphere; Southwest Indian Ridge; Faulting; deformation mechanism; detachment fault; formation mechanism; grain size; lithospheric structure; mantle structure; mid-ocean ridge; oceanic lithosphere; Indian Ocean; Southwest Indian Ridge; Araneae
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202489
推荐引用方式 GB/T 7714	Bickert M.,Lavier L.,Cannat M.. How do detachment faults form at ultraslow mid-ocean ridges in a thick axial lithosphere?[J],2020,533.
APA	Bickert M.,Lavier L.,&Cannat M..(2020).How do detachment faults form at ultraslow mid-ocean ridges in a thick axial lithosphere?.Earth and Planetary Science Letters,533.
MLA	Bickert M.,et al."How do detachment faults form at ultraslow mid-ocean ridges in a thick axial lithosphere?".Earth and Planetary Science Letters 533(2020).