The Plutonic Foundation of a Slow-Spreading Ridge

Dick, H. J.; Robinson, Paul T.; Meyer, Peter S

doi:10.1029/gm070p0001

Cited by 18 publications

(6 citation statements)

References 45 publications

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“…Note that clinopyroxene is replaced by brown amphibole in the crystallization sequence, likely due to diffusion of water from the gabbro into the dike. however, exists between oxide enrichment and mylonitic deformation (e.g., Figures S4d to S4f), with local oxide segregations found along foliation planes and magmatic contacts (First observed in Hole 735B by Dick, Meyer, et al, 1991, Dick, Schouten, et al, 1991a, 1991b, and Dick et al, 1992, and subsequently Agar and Lloyd at 23°N during ODP Leg 153). There are, 27 ultramylonite shear zones in the hole, 19 of which correlate with magnetic susceptibility peaks, while most remaining peaks correlate with the presence of a mylonite.…”

Section: Structural Geologymentioning

confidence: 96%

Dynamic Accretion Beneath a Slow‐Spreading Ridge Segment: IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex

et al. 2019

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809 deep IODP Hole U1473A at Atlantis Bank, SWIR, is 2.2 km from 1,508‐m Hole 735B and 1.4 from 158‐m Hole 1105A. With mapping, it provides the first 3‐D view of the upper levels of a 660‐km2 lower crustal batholith. It is laterally and vertically zoned, representing a complex interplay of cyclic intrusion, and ongoing deformation, with kilometer‐scale upward and lateral migration of interstial melt. Transform wall dives over the gabbro‐peridotite contact found only evolved gabbro intruded directly into the mantle near the transform. There was no high‐level melt lens, rather the gabbros crystallized at depth, and then emplaced into the zone of diking by diapiric rise of a crystal mush followed by crystal‐plastic deformation and faulting. The residues to mass balance the crust to a parent melt composition lie at depth below the center of the massif—likely near the crust‐mantle boundary. Thus, basalts erupted to the seafloor from >1,550 mbsf. By contrast, the Mid‐Atlantic Ridge lower crust drilled at 23°N and at Atlantis Massif experienced little high‐temperature deformation and limited late‐stage melt transport. They contain primitive cumulates and represent direct intrusion, storage, and crystallization of parental MORB in thinner crust below the dike‐gabbro transition. The strong asymmetric spreading of the SWIR to the south was due to fault capture, with the northern rift valley wall faults cutoff by a detachment fault that extended across most of the zone of intrusion. This caused rapid migration of the plate boundary to the north, while the large majority of the lower crust to spread south unroofing Atlantis Bank and uplifting it into the rift mountains.

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Section: Structural Geologymentioning

confidence: 96%

Dynamic Accretion Beneath a Slow‐Spreading Ridge Segment: IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex

et al. 2019

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“…Hydrothermal olivine has not been previously reported, to our knowledge, from altered sheeted dikes, but has been reported from ultramafic rocks drilled at IODP Site 735B (Dick et al., 1992). The most extensive studies of alteration of sheeted dikes recovered from intact oceanic crust comes from scientific oceanic drilling at Hole 504B and 1256D (Figure 1).…”

Section: Resultsmentioning

confidence: 74%

Active Basalt Alteration at Supercritical Conditions in a Seawater‐Recharged Hydrothermal System: IDDP‐2 Drill Hole, Reykjanes, Iceland

Zierenberg

Friðleifsson²,

Elders

et al. 2021

Geochem Geophys Geosyst

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The goal of the Iceland Deep Drilling Program (IDDP) is to investigate the feasibility of producing electric power from supercritical geothermal fluids whose chemical properties are shaped by reaction with the host rocks (Friðleifsson et al., 2014). The IDDP-2 penetrated a geochemical analog for basalt-hosted seafloor hydrothermal systems that produce black smokers. Seawater-rock interaction at mid-ocean ridges is the dominant source of thermal and chemical exchange between the lithosphere and the hydrosphere, yet

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“…Thus, positive identification of and discrimination between hydrothermal and late-magmatic origins for many veins is difficult. Of note, a ptygmatically folded zircon-bearing trondhjemite vein in amphibole gneiss at ~27 mbsf suggested an anatectic origin to Dick et al (1992), and thus a possible example of our Type II veins.…”

Section: Introductionmentioning

confidence: 88%

Silica‐Rich Vein Formation in an Evolving Stress Field, Atlantis Bank Oceanic Core Complex

Dick

Urann

et al. 2020

Geochem Geophys Geosyst

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Drilling 809‐m Hole U1473A in the gabbro batholith at the Atlantis Bank Oceanic Core Complex (OCC) found two felsic vein generations: late magmatic fractionates, rich in deuteric water, hosted by oxide gabbros, and anatectic veins associated with dike intrusion and introduction of seawater‐derived volatiles. Microtextures show a change from compressional to tensional stress during vein formation. Temperatures and oxidation state were obtained from amphibole‐plagioclase and oxide pairs in the adjacent gabbros. Type I veins generally have reverse shear‐sense, with restricted ΔFMQ, high Mt/Ilm ratios, and low‐amphibole Cl/F indicating deuteric fluids. They formed during percolation and fractionation of Fe‐Ti‐rich melts into the primary olivine gabbro. Type II veins are usually hosted by olivine gabbro, occur at dike contacts and the margins of normal‐sense shear zones. They are undeformed or weakly deformed, with highly variable ΔFMQ, low Mt/Ilm ratios, and high‐amphibole Cl/F, indicating seawater‐derived fluids. The detachment fault on which the gabbro massif was emplaced rooted near the base of the dike‐gabbro transition beneath the rift valley. The ingress of seawater volatiles began at >800°C and penetrated at least ~590 m into the lower crust during extensional faulting in the rift valley and adjacent rift mountains. The sequence of the felsic vein formation likely reflects asymmetric diapiric flow, with a reversal of the stress regime, and a transition from juvenile to seawater‐derived volatiles. This, in turn, is consistent with fault capture leading to the large asymmetries in spreading rates during OCC formations and heat flow beneath the rift mountains.

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The Plutonic Foundation of a Slow-Spreading Ridge

Cited by 18 publications

References 45 publications

Dynamic Accretion Beneath a Slow‐Spreading Ridge Segment: IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex

Dynamic Accretion Beneath a Slow‐Spreading Ridge Segment: IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex

Active Basalt Alteration at Supercritical Conditions in a Seawater‐Recharged Hydrothermal System: IDDP‐2 Drill Hole, Reykjanes, Iceland

Silica‐Rich Vein Formation in an Evolving Stress Field, Atlantis Bank Oceanic Core Complex

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