Formation of large summit troughs along the East Pacific Rise as collapse calderas: An evolutionary model

Lagabrielle, Yves; Cormier, Marie-Hélène

doi:10.1029/1999jb900015

Cited by 42 publications

(47 citation statements)

References 79 publications

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“…06OA-20a varitextured ophitic gabbro, pl ($1 mm) zoned and altered, interstitial clinopyroxene (5 to 10 mm), grading into brown, then green amphibole. [Hooft et al, 1997;Lagabrielle and Cormier, 1999;Garel et al, 2002]. Conversely, a rise of the melt lens would result in an assimilation of its roof, as also envisaged by Coogan et al [2003].…”

Section: Wadi Gaz Section: Microprobe Analysismentioning

confidence: 99%

Root zone of the sheeted dike complex in the Oman ophiolite

Nicolas

Boudier

Koepke

et al. 2008

Geochem Geophys Geosyst

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[1] In the Oman ophiolite crustal section, a contact zone between the gabbro unit and the volcanics and diabase sheeted dikes, called the root zone of the sheeted dike complex, has been recently mapped at a fine scale in a selected area. The Oman ophiolite is derived from a fast spreading ridge which had a melt lens located between the main gabbro unit and the root zone of the sheeted dike complex. With a few exceptions accounted for, this horizon has a fairly constant thickness, $100 m, and a crude internal pseudo-stratigraphy. At the base of the root zone are isotropic ophitic gabbros interpreted as a thermal boundary layer. This layer is transitional between the magmatic system of the melt lens, convecting at 1200°C, and a high-temperature (<1100°C) hydrothermal system, convecting within the root zone. Above this level, the isotropic gabbros have been, locally, largely molten due to an influx of seawater, at $1100°C, thus generating varitextured ophitic and pegmatitic gabbros. These latter gabbros constitute the upper part of the root zone and are associated with trondjhemitic intrusions as screens in the lower sheeted dikes. Diorites and trondjhemites were also generated by hydrous melting, at temperatures below 1000°C. The whole root zone is a domain of very sharp average thermal gradient ($7°C/m). At the top of the root zone, a new thermal boundary layer, with diabase dikes hydrated in amphibolite facies conditions, separates the preceding high-temperature convective system from the well-known greenschist facies (<450°C) hydrothermal system operating throughout the sheeted dike complex, up to the seafloor. The isotropic gabbros near the base of the root zone are intruded by protodikes with distinctive microgranular margins and an ophitic center. Protodike swarms are exceptional because, intruding a medium at $1100°C, they are largely destroyed by dike-in-dike intrusions and by hydrous melting. However, they demonstrate that this zone was generated by melt conduits issued from the underlying melt lens. Each dike of the sheeted dike complex is thus fed by one protodike. As this zone has been recently drilled by IODP in the eastern Pacific Ocean, a brief comparison is proposed.

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Section: Wadi Gaz Section: Microprobe Analysismentioning

confidence: 99%

Root zone of the sheeted dike complex in the Oman ophiolite

Nicolas

Boudier

Koepke

et al. 2008

Geochem Geophys Geosyst

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“…We have reinvestigated the geological site previously studied by Caroff et al (1997). In this zone, known for its strong magma budget (e.g., Carbotte et al, 1997;Hussenoeder et al, 2002), the variable across-strike ridge profile is a sensitive indicator of a cyclic magma supply (Lagabrielle and Cormier, 1999). Thus, the configuration of this site is particularly adequate for the application of our new geochemical approach.…”

Section: Introductionmentioning

confidence: 98%

A geochemical approach to model periodically replenished magma chambers: Does oscillatory supply account for the magmatic evolution of EPR 17–19°S?

Rannou

Caroff

Cordier

2006

Geochimica et Cosmochimica Acta

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“…Troughs, 500 to 1800 m wide, with a maximum vertical relief of 110 m, are observed along 15-20% of the ridge. They occur only along ridge segments with large cross-sectional areas, indicative of a time-averaged robust magma supply, and are not observed along segments with a reduced axial area [Lagabrielle and Cormier, 1999]. The vertical relief of the troughs tends to be maximum where the magma sill is shallowest, and minimum at segment ends where the magma sill is not detected.…”

mentioning

confidence: 98%

“…These observations are not consistent with a model in which large summit troughs fo:'m by rifting of the brittle upper crust during amagmatic extension. Rather, it has been proposed that they represent elongated collapse calderas that form when the central part of the magma reservoir (including the melt sill) deforms and compacts in response to stretching during periods of low magma supply [Lagabrielle and Cormier, 1999].…”

mentioning

confidence: 99%

Extensional faulting and caldera collapse in the axial region of fast spreading ridges: Analog modeling

Lagabrielle¹,

Garel²,

Dauteuil³

et al. 2001

J. Geophys. Res.

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Abstract. The axial high of the East Pacific Rise (EPR) is bounded by ridge-parallel lateral grabens that develop 2-8 km off-axis. These troughs appear to lengthen away from the ridge crest, suggesting that tectonics is active at least 10 km away from the axis. Along 15-20% of the length of the ridge the axial high is notched by a summit trough 500 to 1800 m wide. These large axial troughs represent elongated collapse calderas that form when the EPR magma reservoir (comprising the melt lens and the underlying crystal mush zone) deforms and compacts during periods of waning magma supply under continuous stretching. We report the results of analog experiments performed in order to constrain the tectonic-magmatic evolution of the crestal region of fast spreading ridges and more particularly the possible link that may exist between the development of axial caldera and the creation of lateral grabens along the crestal region. We used inflatable elongated balloons filled with water as an analog of the magma reservoir. The balloon is capped with a silicone layer representing hot rocks below the brittle-ductile transition and is covered by a sand layer representing the brittle crust. The sand surface was given a dome shape that approximates the morphology of a fast spreading ridge. Mobile walls activated by a stepping motor allowed us to conduct the deflation experiments during continuous extension. Combination of deflation and extension leads to the creation of two lateral depressions and one axial trough. The lateral depressions are controlled by normal faults, while the central trough is delineated by reverse faults. During balloon deflation, tectonic extension is accommodated away from the axis due to the presence of the ductile silicone layer, whereas the deflation of the axial reservoir is accommodated by the collapse of the overlaying brittle crust. This accounts (1) for the development of axial troughs as collapse calderas, and (2) for the ubiquitous formation of lateral grabens of the flanking tectonic province in response to the deformation of the crystal mush.

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Formation of large summit troughs along the East Pacific Rise as collapse calderas: An evolutionary model

Cited by 42 publications

References 79 publications

Root zone of the sheeted dike complex in the Oman ophiolite

Root zone of the sheeted dike complex in the Oman ophiolite

A geochemical approach to model periodically replenished magma chambers: Does oscillatory supply account for the magmatic evolution of EPR 17–19°S?

Extensional faulting and caldera collapse in the axial region of fast spreading ridges: Analog modeling

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