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doi:10.2204/iodp.sp.345.2012

Cited by 4 publications

(7 citation statements)

References 107 publications

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“…The highest priority for drilling at Hess Deep was to sample one or more 100 to ≥250 m long sections of primitive gabbroic rock. The Expedition 345 Scientific Prospectus (Gillis et al, 2012) identified three primary drill sites (proposed Sites HD-01B-HD-03B), with the intention that if coring was proceeding well in the first or second sites, it would be continued as long as possible in order to capitalize on good drilling conditions and obtain the longest possible continuous sample. Site survey data in conjunction with on-bottom observations collected during the expedition were used to plan specific hole locations in the vicinity of proposed Sites HD-01B-HD-03B.…”

Section: Drilling Strategymentioning

confidence: 99%

“…These approaches included the possible deployment of a standard reentry cone, deployment of a free-fall funnel (FFF) or "nested" FFFs, bare rock hole without installation of a seafloor structure, and bare rock installation of a reentry cone with a short entry pup. In addition, the experiences of previous hard rock drilling expeditions were reviewed for best practices (see "Operations plan" in the Expedition 345 Scientific Prospectus [Gillis et al, 2012] for more details).…”

Section: Drilling Strategymentioning

confidence: 99%

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Expedition 345 summary

Gillis¹,

Snow²,

Klaus³

et al. 2014

Proceedings of the IODP

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Integrated Ocean Drilling Program (IODP) Hess Deep Expedition 345 was designed to sample lower crustal primitive gabbroic rock that formed at the fast-spreading East Pacific Rise (EPR) in order to test competing models of magmatic accretion and the intensity of hydrothermal cooling at depth. The Hess Deep Rift was selected to exploit tectonic exposures of young EPR plutonic crust, building upon results from Ocean Drilling Program Leg 147 as well as more recent submersible, remotely operated vehicle, and nearbottom surveys. The primary goal was to acquire the observations required to test end-member crustal accretion models that were in large part based on relationships from ophiolites, in combination with mid-ocean ridge geophysical studies. This goal was achieved with the recovery of primitive layered olivine gabbro and troctolite with many unexpected mineralogical and textural relationships, such as the abundance of orthopyroxene and the preservation of delicate skeletal olivine textures. Site U1415 is located within the Hess Deep Rift along the southern slope of the intrarift ridge between 4675 and 4850 m water depths. Specific hole locations were selected in the general area of the proposed drill sites (HD-01B-HD-03B) using a combination of geomorphology, seafloor observations, and shallow acoustic subbottom profiling data. A total of 16 holes were drilled. The primary science results were obtained from coring of two ~110 m deep reentry holes (U1415J and U1415P) and five single-bit holes (U1415E and U1415G-U1415I). Despite deep water depths and challenging drilling conditions, reasonable recovery for hard rock expeditions (15%-30%) was achieved at three 35-110 m deep holes (U1415I, U1415J, and U1415P). The other holes occupied during this expedition included three failed attempts to establish reentry capability (Holes U1415K, U1415M, and U1415P) and six jet-in tests to assess sediment thickness (Holes U1415A-U1415D, U1415F, and U1415L). Olivine gabbro and troctolite are the dominant plutonic rock types recovered at Site U1415, with minor gabbro, clinopyroxene oikocryst-bearing gabbroic lithologies, and gabbronorite. These rocks exhibit cumulate textures similar to those found in layered mafic intrusions and some ophiolite complexes. All lithologies are primitive, with Mg# between 76 and 89, falling within the global range of primitive oceanic gabbros. Spectacular modal and grain size layering was prevalent in >50% of the recovered core, display

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Section: Drilling Strategymentioning

confidence: 99%

Section: Drilling Strategymentioning

confidence: 99%

Expedition 345 summary

Gillis¹,

Snow²,

Klaus³

et al. 2014

Proceedings of the IODP

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“…Moho Expedition 345 Preliminary Report Figure F3. Schematic representation of the predictions of the general depth trends of latent heat release, bulk Mg#, strain rate, cooling rate, hydrothermal fluid flux, fluid temperature, and intensity of high-temperature (HT) alteration for the end-member "gabbro glacier" (with mainly conductive cooling of the lower crust) and "sheeted sill" (with convective cooling of the lower crust) models (from Gillis et al, 2012). Figure F4.…”

Section: Lower Gabbromentioning

confidence: 99%

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2014

IODP Preliminary Report

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“…The question whether the entire crust or only the extrusive part above the melt lens is cooled by hydrothermal circulation strongly influences geochemical fluxes and fluid-rock interactions. Exclusive supramelt lens hydrothermal flow results in lower mass and energy fluxes as well as limited fluid-rock interactions [Gillis et al, 2012], whereas deep convective cooling implies crustal-scale hydrothermal alteration and possibly sufficiently high fluid circulation temperatures to cause hydrous remelting of the lower crust [Koepke et al, 2005]. Estimates of lower crustal cooling rates from Oman yield inconclusive results ranging between extensive hydrothermal circulation and close to conductive cooling at different sections of the ophiolite [Coogan et al, 2002;VanTongeren et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

“…A recent study of cooling rates from the upper section of the lower crust at the East Pacific Rise (EPR) reports near conductive cooling for the first few hundreds of meters of lower oceanic crust [Faak et al, 2015]. Although some of these observations seem to favor conductive cooling of the lower crust, field evidence from Oman [Bosch et al, 2004;Nicolas and Mainprice, 2005] and seismic methods [Crawford and Webb, 2002;Dunn et al, 2000] support deep hydrothermal circulation [Gillis et al, 2012]. In addition, a hybrid shallow on-axis and deep off-axis hydrothermal flow scheme that is found in 3-D simulations can reconcile some of these observations [Hasenclever et al, 2014], which further support the concept of pervasive crustal-scale fluid flow.…”

Section: Introductionmentioning

confidence: 99%

Modes of crustal accretion and their implications for hydrothermal circulation

Theissen-Krah

Rüpke

Hasenclever

2016

Geophysical Research Letters

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Hydrothermal convection at mid‐ocean ridges links the ocean's long‐term chemical evolution to solid earth processes, forms hydrothermal ore deposits, and sustains the unique chemosynthetic vent fauna. Yet the depth extent of hydrothermal cooling and the inseparably connected question of how the lower crust accretes remain poorly constrained. Here based on coupled models of crustal accretion and hydrothermal circulation, we provide new insights into which modes of lower crust formation and hydrothermal cooling are thermally viable and most consistent with observations at fast‐spreading ridges. We integrate numerical models with observations of melt lens depth, thermal structure, and melt fraction. Models matching all these observations always require a deep crustal‐scale hydrothermal flow component and less than 50% of the lower crust crystallizing in situ.

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Cited by 4 publications

References 107 publications

Expedition 345 summary

Expedition 345 summary

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Modes of crustal accretion and their implications for hydrothermal circulation

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