1 Ma East Pacific Rise oceanic crust and uppermost mantle exposed by rifting in Hess Deep (equatorial Pacific Ocean)

Francheteau, Jean; Armijo, Rolando; Cheminée, J. L.; Hékinian, Roger; Lonsdale, Peter; Blum, N.

doi:10.1016/0012-821x(90)90160-y

Cited by 175 publications

(167 citation statements)

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“…The results of these dive programs showed that a complete, relatively fresh, crustal section (consisting of volcanics, sheeted dikes, and minor gabbros) is exposed along the scarps that bound the rift valley. Similar; but more dismembered, sections of the EPR oceanic crust (including lavas, dikes, gabbros, and peridotites) are exposed on the floor of the Hess Deep Rift Valley and along the intra-rift ridge (Francheteau et al, 1990;Hekinian et al, 1993). Two alternative rifting models have been proposed for the formation of the Hess Deep Rift Valley and the emplacement of deep crustal rocks at shallow levels in the oceanic crust (see fig.…”

Section: Geologic and Tectonic Overviewmentioning

confidence: 99%

“…1). Hess Deep, the deepest part (>5400 meters below seafloor [mbsf]) of this rift valley, is the result of deep faulting associated with the westward propagation of the east-west trending Cocos-Nazca spreading center that is opening up the eastern flank of young oceanic crust (0.5-1 Ma) created at the fast-spreading equatorial East Pacific Rise (EPR) (Lonsdale, 1988;Francheteau et al, 1990). A major, faultbounded, intra-rift ridge, approximately 8 km wide and 25 km long, with a flattened crest and an oval dome shape has formed between the Hess Deep and the northern scarp that bounds the valley.…”

Section: Geologic and Tectonic Overviewmentioning

confidence: 99%

“…1990; Francheteau et al, 1992) and an Alvin dive program in 1989 (Karson et al, 1992). The results of these dive programs showed that a complete, relatively fresh, crustal section (consisting of volcanics, sheeted dikes, and minor gabbros) is exposed along the scarps that bound the rift valley.…”

Section: Geologic and Tectonic Overviewmentioning

confidence: 99%

“…The formation of magnetite during the hydration process may also play a crucial role in contributing to marine magnetic anomalies as well as providing a source of hydrogen and methane to hydrothermal fluids. It is thus important to understand the controls on seawater penetration into the mantle and to determine the active or passive role of serpentinization; that is whether extensional structures are required for serpentinization processes to occur or whether ser-pentinite protrusions and diapirism are required for structures to form (e.g., Bonatti, 1976;Boillot et al, 1980;Francheteau et al, 1990). Fundamental to understanding the processes of serpentinization is the determination of the depth and temperature of seawater penetration, which in turn may shed light on the relative timing of serpentinization in the overall tectonic history of ocean basins.…”

Section: Introductionmentioning

confidence: 99%

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Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Früh-Green¹,

Plas²,

Lécuyer³

1996

Proceedings of the Ocean Drilling Program, 147 Scientific Results

106

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Leg 147 of the Ocean Drilling Program recovered sections of the East Pacific Rise lower crust and shallow mantle ( l Ma), tectonically exposed at the western end of the Cocos-Nazca propagator of the Hess Deep Rift Valley. These rocks record a polyphase history of hydrothermal alteration and provide new constraints on the depth and mechanisms of hydrothermal circulation at fast-spreading ridges. A complex sequence of harzburgite-dunite-troctolite-gabbro recovered at Site 895 is considered to be the result of processes of melt migration and wall-rock reaction close to the mantle/crust boundary. The peridotites are extensively serpentinized (50%-100%) and are cut by multiple generations of fracture-filling veins. In the gabbros, progressive alteration under greenschist to zeolite facies conditions is characterized by tremolite + chlorite + diopside + anorthjte ± prehnite assemblages in the least altered samples, and incipient rodingitization to prehnite + hydrogrossular + zeolite + clays as Cataclastic deformation and veining increases.Oxygen isotope ratios of mineral separates from the gabbros and peridotites from Site 895 show a depletion in I8O relative to mantle values and are consistent with high-temperature exchange with aqueous fluids. Dunite/harzburgite ratios of chlorite, serpentine, and tremolite, together with δ' 3 C values of CO 2 extracted from completely serpentinized dunites, suggest at least two, but possibly three, components of the hydrothermal fluids: hydrothermally altered seawater; magmatic volatiles; and H 2 released during serpentinization. These data combined with structural data imply that penetration of seawater and high-temperature hydrothermal alteration produced a low 18 O shallow mantle sequence at some distance off-axis of the East Pacific Rise, but at an early stage in the propagation of the Cocos-Nazca rift and formation of the Hess Deep Rift Valley. Mineral assemblages in the gabbroic rocks and the presence of antigorite at Hess Deep, combined with oxygen isotope ratios, suggest that faulting associated with the Cocos-Nazca propagator enhanced seawater penetration and hydrothermal alteration at temperatures above 350°C in this segment of the East Pacific Rise oceanic lithosphere. The results of this study suggest that seawaterperidotite interactions and high-temperature serpentinization processes may be an important contribution to the overall 18 Obudget in the oceanic lithosphere nd may represent a significant sink for mantle CO 2 and source of H 2 .

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Section: Geologic and Tectonic Overviewmentioning

confidence: 99%

Section: Geologic and Tectonic Overviewmentioning

confidence: 99%

Section: Geologic and Tectonic Overviewmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Früh-Green¹,

Plas²,

Lécuyer³

1996

Proceedings of the Ocean Drilling Program, 147 Scientific Results

106

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“…The rift exhumed deep levels of oceanic lithosphere generated at the East Pacific Rise and make it one of the rare places where the lower oceanic crust and uppermost mantle of a fast spreading ridge are exposed ( Fig. 1) (Searle and Francheteau, 1986;Lonsdale, 1988;Searle, 1989;Francheteau et al, 1990). ODP Leg 147 drilled such rocks for the first time (ODP Leg 147 Shipboard Scientific Party, 1993;Mével et al, 1993).…”

Section: Logging For Tectonics In Hess Deepmentioning

confidence: 99%

Constraints on the Geometry and Fracturing of Hole 894G, Hess Deep, from Formation MicroScanner Logging Data

Célérier¹,

Macleod²,

Harvey³

1996

Proceedings of the Ocean Drilling Program, 147 Scientific Results

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Ocean Drilling Program Hole 894G, sited on a small horst within Hess Deep, was drilled in lower oceanic crust that was generated at the East Pacific Rise and then rifted by the propagating Cocos/Nazca divergent plate boundary. Difficult drilling conditions in fractured gabbros resulted in a washed-out hole.Despite these unfavorable circumstances, open-hole logs from the Formation MicroScanner (FMS) tool string provide strong constraints on the fracture orientations and suggest a few directions of preferential enlargement. These results were obtained because five logging passes were recorded to compensate for the expected low data quality by redundancy and because the now classical analysis of FMS data has been adapted to this situation of multiple passes and washed out borehole.An east enlargement direction is thought to be related to the east-west strike of the dense network of fractures observed both in cores and on the FMS resistivity images, and an east-northeast enlargement direction may be the result of drill pipe wear along the borehole plunge direction. Additional east-southeast to south-southeast and north-northeast enlargements may reflect the influence of either the Nazca-Galapagos or the Cocos-Nazca plate boundary state of stress, respectively. However, the interpretation of these poorly defined directions remains uncertain.The analysis of the FMS resistivity images shows mainly east-west striking and southward dipping fractures and very few north-south trending features. This suggests a strong Cocos-Nazca control on brittle deformation in the Hess Deep. The distribution of orientation of the fractures identified on the FMS images is very similar to that obtained from core veins reoriented relative to paleomagnetic north. Matching the two sets requires that the remanent magnetization direction points north-northwest. The preferred interpretation of this result is a vertical-axis component of tectonic rotation of 30° to 40° counterclockwise.

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Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties

Dekkers

Heslop

Herrero‐Bervera

et al. 2014

Geochem Geophys Geosyst

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We analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6 44.1' N, 91 56.1' W) on the Cocos Plate in 15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

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1 Ma East Pacific Rise oceanic crust and uppermost mantle exposed by rifting in Hess Deep (equatorial Pacific Ocean)

Cited by 175 publications

References 27 publications

Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Petrologic and Stable Isotope Constraints on Hydrothermal Alteration and Serpentinization of the EPR Shallow Mantle at Hess Deep (Site 895)

Constraints on the Geometry and Fracturing of Hole 894G, Hess Deep, from Formation MicroScanner Logging Data

Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties

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