Drilling to Gabbro in Intact Ocean Crust

Wilson, Douglas S.; Teagle, D. A. H.; Alt, Jeffrey C; Banerjee, Neil R.; Umino, Susumu; Miyashita, Sumio; Acton, Gary D; Anma, Ryo; Barr, S. R.; Belghoul, Akram; Carlut, Julie; Christie, David M.; Coggon, Rosalind M.; Cooper, Kari M.; Cordier, Carole; Crispini, Laura; Durand, S. Rodriguez; Einaudi, F.; Galli, Laura; Gao, Yongjun; Geldmacher, Jörg; Gilbert, Lisa A.; Hayman, Nicholas W.; Herrero‐Bervera, Emilio; Hirano, Nobuo; Holter, Sara; Ingle, Stéphanie; Jiang, Shijun; Kalberkamp, Ulrich; Kerneklian, Marcie; Koepke, Jürgen; Laverne, Christine; Lledo, Haroldo L.; Maclennan, John; Morgan, Sally; Neo, Natsuki; Nichols, Holly; Park, Sung Hyun; Reichow, Marc K.; Sakuyama, Tetsuya; Sano, Takashi; Sandwell, R.W.; Scheibner, Birgit; Smith-Duque, Chris E.; Swift, Stephen A.; Tartarotti, Paola; Tikku, A. A.; Tominaga, Masako; Veloso, Eugenio E.; Yamasaki, Toru; Yamazaki, Shusaku; Ziegler, Christa L

doi:10.1126/science.1126090

Cited by 241 publications

(267 citation statements)

References 48 publications

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“…Two features seem particularly characteristic. The IODP and Oman RZSDC have a comparable $100 m thickness if, according to Wilson et al [2006], the top gabbros from the gabbro unit are represented by the last meters of the core. Most textures observed in the Hole 1256D also match those in Oman, as illustrated by the comparison of ophitic gabbros (Figures 15a and 15b; see also for Troodos ophiolite [Gillis and Coogan, 2002]).…”

Section: Rzsdc In Domains Affected By Ridge Segmentationmentioning

confidence: 99%

“…[47] On the basis of the observation of prograde mineral reactions in the granoblastic dikes, the ''granoblastic'' textures are ascribed by Teagle et al [2006] and Wilson et al [2006] to ''contact metamorphism by underlying gabbro intrusions.'' 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.…”

Section: Rzsdc In Domains Affected By Ridge Segmentationmentioning

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 Segmentationmentioning

confidence: 99%

Section: Rzsdc In Domains Affected By Ridge Segmentationmentioning

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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“…[3] There are two methods of accessing subsurface ocean crust: deep crustal drilling [Alt et al, 1996;Wilson et al, 2006] and submersible investigations of tectonic escarpments, also known as ''tectonic windows'' [Karson, 2002;Karson et al, 2002aKarson et al, , 2002bPockalny et al, 2004]. The most recently investigated Pacific-crust tectonic window is the Pito Deep Rift (PDR), where in situ ocean crust generated at the SEPR is exposed along escarpments with kilometer-scale relief (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Crustal faults exposed in the Pito Deep Rift: Conduits for hydrothermal fluids on the southeast Pacific Rise

Hayman

Karson

2009

Geochem Geophys Geosyst

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[1] The escarpments that bound the Pito Deep Rift (northeastern Easter microplate) expose in situ upper oceanic crust that was accreted $3 Ma ago at the superfast spreading ($142 mm/a, full rate) southeast Pacific Rise (SEPR). Samples and images of these escarpments were taken during transects utilizing the human-occupied vehicle Alvin and remotely operated vehicle Jason II. The dive areas were mapped with a ''deformation intensity scale'' revealing that the sheeted dike complex and the base of the lavas contain approximately meter-wide fault zones surrounded by fractured ''damage zones.'' Fault zones are spaced several hundred meters apart, in places offset the base of the lavas, separate areas with differently oriented dikes, and are locally crosscut by (younger) dikes. Fault rocks are rich in interstitial amphibole, matrix and vein chlorite, prominent veins of quartz, and accessory grains of sulfides, oxides, and sphene. These phases form the fine-grained matrix materials for cataclasites and cements for breccias where they completely surround angular to subangular clasts of variably altered and deformed basalt. Bulk rock geochemical compositions of the fault rocks are largely governed by the abundance of quartz veins. When compositions are normalized to compensate for the excess silica, the fault rocks exhibit evidence for additional geochemical changes via hydrothermal alteration, including the loss of mobile elements and gain of some trace metals and magnesium. Microstructures and compositions suggest that the fault rocks developed over multiple increments of deformation and hydrothermal fluid flow in the subaxial environment of the SEPR; faults related to the opening of the Pito Deep Rift can be distinguished by their orientation and fault rock microstructure. Some subaxial deformation increments were likely linked with violent discharge events associated with fluid pressure fluctuations and mineral sealing within the fault zones. Other increments were linked with the influx of relatively fresh seawater. The spacing of the faults is consistent with fault localization occurring every 7000 to 14,000 years, with long-term slip rates of <3 mm/a. Once spread from the ridge axis, the faults were probably not active, and damage zones likely played a more significant role in axial flank and off-axis crustal permeability.

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“…The base of the SDC is defined by the uppermost gabbroic intrusion at 1404.6 mbsf (Wilson et al, 2006). Recovery within the SDC was highly variable but averaged <12%.…”

Section: Downhole Distribution Of Chilled Marginsmentioning

confidence: 99%

Data report: microstructure of chilled margins in the sheeted dike complex of IODP Hole 1256D

Hayman¹,

Anma²,

Veloso³

2009

Proceedings of the IODP

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Chilled margins were recovered from the sheeted dike complex (SDC) of superfast (>200 mm/y)-spreading East Pacific Rise-spread crust during drilling of Integrated Ocean Drilling Program Hole 1256D on the Cocos Plate. The chilled margins contain stretched spherules, oriented plagioclase laths, grain-size segregation, and color banding. These rheomorphs locally crosscut veins but are elsewhere crosscut by veins. Electron microprobe investigations found that the chilled margins comprise dispersed micrometerscale minerals and veins including chlorite, actinolite, quartz, anhydrite, sphene, calcite, sphalerite, K-feldspar (adularia and/or orthoclase), magnetite, pyrite, and chalcopyrite. Though many of these phases are present throughout the SDC, anhydrite and calcite have not been previously recognized >100 m below the SDClava transition zone, and, with one exception, K-feldspar has not been previously identified in Hole 1256D core. Microstructures include quartz clasts surrounded by anhydrite, K-feldspar veins and clasts cut or surrounded by chilled margin material, and lenses of ductily deformed sphene. Some of the crosscutting relationships and distribution of mineral phases could be explained by hydrothermal alteration that occurred roughly simultaneously with dike intrusion. IntroductionDuring Integrated Ocean Drilling Program (IODP) Expedition 312, the structural geology team was impressed by the microstructure of chilled margins recovered from the sheeted dike complex (SDC) of the Pacific crust drilled in Hole 1256D. Microstructures and crosscutting relationships within and around the chilled margins led the structure team to postulate that the fracturing and hydrothermal alteration of the chilled margins occurred more or less during dike intrusion. If so, the microstructures are evidence for weakening of the crust by elevated fluid pressure (Harper and Tartarroti, 1996;Umino et al., 2008) and provide a mechanism for the generation of hydrothermal plumes at the seafloor by diking (Delaney et al., 1998).The purpose of this data report is to summarize shipboard observations of the SDC chilled margins and to present new, higher resolution data on the microstructures, mineralogy, and compositions of the dike margins. We review shipboard hand sample and thin section studies and present new backscatter electron images (BSEI)

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Drilling to Gabbro in Intact Ocean Crust

Cited by 241 publications

References 48 publications

Root zone of the sheeted dike complex in the Oman ophiolite

Root zone of the sheeted dike complex in the Oman ophiolite

Crustal faults exposed in the Pito Deep Rift: Conduits for hydrothermal fluids on the southeast Pacific Rise

Data report: microstructure of chilled margins in the sheeted dike complex of IODP Hole 1256D

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