Hydration due to high-T brittle failure within in situ oceanic crust, 30°N Mid-Atlantic Ridge

Michibayashi, K.; Hirose, Takehiro; Nozaka, Toshio; Harigane, Yumiko; Escartı́n, J.; Delius, H.; Linek, M.; Ohara, Yasuhiko

doi:10.1016/j.epsl.2008.08.033

Cited by 26 publications

(29 citation statements)

References 26 publications

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“…Recovery from the corresponding 5 m interval was very low (17%), and the core obtained was all fault rock. A study of that core and the Expedition 305 logging data [Michibayashi et al, 2008] indicate that the fault is centered at 746 mbsf and that the permeability of the fault rock is high, relative to the adjacent gabbroic rock. Higher permeability means locally increased pore water.…”

Section: 1002/2013gl058111mentioning

confidence: 99%

Geophysical signatures of past and present hydration within a young oceanic core complex

Blackman

Slagle

Guèrin

et al. 2014

Geophysical Research Letters

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Borehole logging at the Atlantis Massif oceanic core complex provides new information on the relationship between the physical properties and the lithospheric hydration of a slow-spread intrusive crustal section. Integrated Ocean Drilling Program Hole U1309D penetrates 1.4 km into the footwall to an exposed detachment fault on the 1.2 Ma flank of the mid-Atlantic Ridge, 30°N. Downhole variations in seismic velocity and resistivity show a strong correspondence to the degree of alteration, a recorder of past seawater circulation. Average velocity and resistivity are lower, and alteration is more pervasive above a fault around 750 m. Deeper, these properties have higher values except in heavily altered ultramafic zones that are several tens of meters thick. Present circulation inferred from temperature mimics this pattern: advective cooling persists above 750 m, but below, conductive cooling dominates except for small excursions within the ultramafic zones. These alteration-related physical property signatures are probably a characteristic of gabbroic cores at oceanic core complexes.

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Section: 1002/2013gl058111mentioning

confidence: 99%

Geophysical signatures of past and present hydration within a young oceanic core complex

Blackman

Slagle

Guèrin

et al. 2014

Geophysical Research Letters

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“…The thickness of fault rocks cannot be more than 15 m, as gabbros occur within 20 m of the seafloor, suggesting significant thinning compared with the south wall. However, the fault zone may also be expressed by several zones of breccia within the upper 120 m of Holes U1309B and U1309D and by a deeper zone at around 700 meters below seafloor (mbsf ) (Expedition 304/305 Scientists, 2006;Expedition Scientific Party 2005a, 2005bMichibayashi et al, 2008). Detailed paleomagnetic studies on cores from Hole U1309D Figure F2.…”

Section: Central Dome Of Atlantis Massifmentioning

confidence: 99%

Expedition 357 summary

Früh-Green¹,

Orcutt²,

Green³

et al. 2017

Proceedings of the International Ocean Discovery Program

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Contents AbstractInternational Ocean Discovery Program (IODP) Expedition 357 successfully cored an east-west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge (MAR) to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. The primary goals of this expedition were to (1) examine the role of serpentinization in driving hydrothermal systems, sustaining microbial communities, and sequestering carbon; (2) characterize the tectonomagmatic processes that lead to lithospheric heterogeneities and detachment faulting; and (3) assess how abiotic and biotic processes change with variations in rock type and progressive exposure on the seafloor. To accomplish these objectives, we developed a coring and sampling strategy centered on the use of seabed drills-the first time that such systems have been used in the scientific ocean drilling programs. This technology was chosen in the hope of achieving high recovery of the carbonate cap sequences and intact contact and deformation relationships. The expedition plans also included several engineering developments to assess geochemical parameters during drilling; sample bottom water before, during, and after drilling; supply synthetic tracers during drilling for contamination assessment; acquire in situ electrical resistivity and magnetic susceptibility measurements for assessing fractures, fluid flow, and extent of serpentinization; and seal boreholes to provide opportunities for future experiments.Seventeen holes were drilled at nine sites across Atlantis Massif, with two sites on the eastern end of the southern wall (Sites M0068 and M0075), three sites in the central section of the southern wall north of the Lost City hydrothermal field (Sites M0069, M0072, and M0076), two sites on the western end (Sites M0071 and M0073), and two sites north of the southern wall in the direction of the central dome of the massif and Integrated Ocean Drilling Program Site U1309 (Sites M0070 and M0074). Use of seabed drills enabled collection of more than 57 m of core, with borehole penetration ranging from 1.30 to 16.44 meters below seafloor and core recoveries as high as 74.76% of total penetration. This high level of recovery of shallow mantle sequences is unprecedented in the history of ocean drilling. The cores recovered along the southern wall of Atlantis Massif have highly heterogeneous lithologies, types of alteration, and degrees of deformation. The ultramafic rocks are dominated by harzburgites with intervals of dunite and minor pyroxenite veins, as well as gabbroic rocks occurring as melt impregnations and veins, all of which provide information about early magmatic processes and the magmatic evolution in the southernmost portion of Atlantis Massif. Dolerite dikes and basaltic rocks represent the latest stage of magmatic activity. Overall, the ultramafic rocks recovered ...

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“…Other ultramafic intervals are tens of centimeters to ~3 m thick, with dunite and harzburgite only recovered above 224 mbsf. A fault zone at 750 mbsf (Michibayashi et al, 2008) is also associated with a significant local drop in seismic velocity, and below it resistivity increases rapidly. This is one of the faults where a small deviation in borehole fluid temperature was confirmed during Exp.…”

Section: Highlighted Initial Resultsmentioning

confidence: 99%

“…Paleomagnetic results indicate that at least the upper 400 m, and likely the full 1.4-km section, of Hole U1309D has rotated a minimum of 45° counterclockwise about a horizontal axis that parallels the rift valley (Morris et al, 2009). Seven narrow fault zones (several centimeters to a few meters in scale) within the interval 100-1100 mbsf were documented within the core and by earlier logging data (Blackman et al, 2006;Hirose and Hayman, 2008;Michibayashi et al, 2008). But the limited extent of these faults might imply that they did not dominate the development of the OCC.…”

Section: Logging Operationsmentioning

confidence: 98%

Scientific Drilling

Blackman

Slagle

Harding

et al. 2013

Scientific Drilling

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Integrated Ocean Drilling Program (IODP) Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP). Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800-1400 meters below seafloor (mbsf) portion of the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offset now extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution.

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Hydration due to high-T brittle failure within in situ oceanic crust, 30°N Mid-Atlantic Ridge

Cited by 26 publications

References 26 publications

Geophysical signatures of past and present hydration within a young oceanic core complex

Geophysical signatures of past and present hydration within a young oceanic core complex

Expedition 357 summary

Scientific Drilling

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