Cracking at the magma–hydrothermal transition: evidence from the Troodos Ophiolite, Cyprus

Gillis, K. M.; Roberts, Michael D.

doi:10.1016/s0012-821x(99)00087-4

Cited by 90 publications

(112 citation statements)

References 45 publications

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“…This agrees with the Troodos ophiolite study [Gillis and Roberts, 1999], where a large metamorphic aureole has been observed in sheeted dikes at the margins of a gabbronorite intrusion. In the part of the Oman RZSDC devoid of late magmatic intrusions, there is no evidence of any reheating, except on a centimeter scale at the margin of a dike.…”

Section: Rzsdc In Domains Affected By Ridge Segmentationsupporting

confidence: 91%

“…[45] In RZSDC from ridge segmentation domains, the large magmatic intrusions can induce by reheating a local contact metamorphism, as described around a gabbronorite intrusion in Troodos [Gillis and Roberts, 1999;Gillis and Coogan, 2002]. Conversely, in our RZSDC where no such intrusions are observed, reheating to HT conditions can be induced only along the protodikes emplaced in the hotter, basal part of the RZSDC (Figure 10a).…”

Section: Rzsdc In Domains Affected By Ridge Segmentationmentioning

confidence: 91%

“…[3] The RZSDC has recently raised interest with petrological studies in Cyprus [Gillis and Roberts, 1999;Gillis, 2002;Gillis and Coogan, 2002] and in Oman [MacLeod and Yaouancq, 2000], following earlier descriptions of the RZSCD by Pallister and Hopson [1981] and Rothery [1983]. More general studies have been conducted by Coogan et al [2003] and in Oman ophiolite, by MacLeod and Rothery [1992] and by Nicolas and Boudier [1991], whose comprehensive structural study is expanded here.…”

Section: Introductionmentioning

confidence: 99%

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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: Rzsdc In Domains Affected By Ridge Segmentationsupporting

confidence: 91%

Section: Rzsdc In Domains Affected By Ridge Segmentationmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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Root zone of the sheeted dike complex in the Oman ophiolite

Nicolas

Boudier

Koepke

et al. 2008

Geochem Geophys Geosyst

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“…Fluid inclusions studies of oceanic layer 3 rocks indicated these fluids could be trapped at temperatures of up to 700øC [Vanko, 1988]. There is also evidence from the Troodos ophiolite [Gillis and Roberts, 1999] that fluids might penetrate to higher temperatures.…”

Section: Discussion and Summarymentioning

confidence: 99%

Thermal effects of gabbro accretion from a deeper second melt lens at the fast spreading East Pacific Rise

Chen¹

2001

J. Geophys. Res.

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Abstract. Motivated by recent observations, a ridge model has been developed which includes both a shallow melt lens and a second deeper melt lens above the Moho to assess the thermal effect of the gabbro accretion from the lower melt lens at the fast spreading East Pacific Rise. Modeling results argue for a limited role of the lower melt lens in constructing the layer 3 gabbros. If significant (>10%) amount of the layer 3 gabbros is emplaced near the Moho, then the liberated latent heat during crystallization would generate a large "molten" section of the lower crust due to the inability of cold seawater to penetrate into this hot/ductile region. A large molten section of the lower crust is not consistent with recent seismic tomographic results of the East Pacific Rise. Thus it is likely that the amount of the gabbro being emplaced from the lower melt lens at the EPR is significantly less than that suggested by Oman ophiolite studies, such a lower melt lens is short-lived, or a large portion of the sill intrusions observed at Oman was emplaced at a few kilometers off axis (>3-4 km).

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“…The lowermost dikes and upper gabbros have been identified as the conductive boundary layer between the magma chambers and the axial high-temperature hydrothermal systems and as the subsurface reaction zone where downwelling fluids acquire black-smoker chemistry (Alt, 1995;Alt et al, 1996a;Vanko and Laverne, 1998;Gillis et al, 2005). However, extensive regions of this style of alteration or zones of focused discharge are poorly known, and information from ophiolites may not be applicable to in situ ocean crust (Richardson et al, 1987;Schiffman and Smith, 1988;Bickle and Teagle, 1992;Gillis and Roberts, 1999). Drilling beyond the boundary between the lower dikes and upper gabbros will help trace recharge fluid compositions, estimate hydrothermal fluid fluxes (e.g., Teagle et al, 1998Teagle et al, , 2003Gillis et al, 2005), and integrate the thermal requirements of hydrothermal alteration in sheeted dikes and underlying gabbros with the magmatic processes in the melt lens.…”

Section: Expedition 309/312 Scientists Site 1256mentioning

confidence: 99%

Site 1256

2006

Proceedings of the IODP

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Cracking at the magma–hydrothermal transition: evidence from the Troodos Ophiolite, Cyprus

Cited by 90 publications

References 45 publications

Root zone of the sheeted dike complex in the Oman ophiolite

Root zone of the sheeted dike complex in the Oman ophiolite

Thermal effects of gabbro accretion from a deeper second melt lens at the fast spreading East Pacific Rise

Site 1256

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