Principal Results

Party, Shore-Based Contributors Shipboard Scientific

doi:10.2973/odp.proc.ir.120.108.1989

Cited by 3 publications

(12 citation statements)

References 11 publications

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“…It lies in a 15 Ma old crust that formed at the EPR with a full spreading rate of >200 mm/a [Wilson, 1996] [8] The total crustal thickness at Site 1256 is estimated at 5-5.5 km [Swift et al, 2008]. The crustal seismic structure is characterized by upper Layer 2 velocities of 4.5-5 km/s, and Layer 2-3 transition lying at 1200-1500 m subbasement [Shipboard Scientific Party, 2003b].…”

Section: Geological Setting and Basement Stratigraphymentioning

confidence: 99%

“…Primary igneous features include magmatic fabrics, laminations, flattened vescicles, folds, shear-related structures, and late magmatic veins. Magmatic ductile and brittle-ductile structures are mostly concentrated near the top and bottom parts of lava pond in Hole 1256C, and interpreted as being due to flow kinematics [Shipboard Scientific Party, 2003b;Crispini et al, 2006]. On the basis of structural and microstructural features, the lava pond in Hole 1256C has been divided into five structural units [Crispini et al, 2006], which partly coincide with the magmatic units as defined by Wilson et al [2003].…”

Section: Geological Setting and Basement Stratigraphymentioning

confidence: 99%

“…Felsic veins and felsic interstitial areas from the lava pond are composed of quartz, alkali feldspar, apatite, Fe-rich clinopyroxene, and minor brown micas [Shipboard Scientific Party, 2003b;Laverne et al, 2007;Umino, 2007]. The peculiar distribution of these late magmatic felsic veins might be explained by a mechanism such as buoyant instabilities of a residual, less dense melt [e.g., Geshi, 2001] migrating toward the upper part of a lava flow.…”

Section: Fracture Distributionmentioning

confidence: 99%

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Deformation pattern in a massive ponded lava flow at ODP‐IODP Site 1256: A core and log approach

Tartarotti

Fontana

Crispini

2009

Geochem Geophys Geosyst

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A complete “in situ” section of upper oceanic crust, from extrusive lavas, through dikes into gabbros has been recently drilled for the first time in 15 Ma old crust created at the superfast spreading East Pacific Rise (EPR). The upper igneous basement cored at Ocean Drilling Program (ODP)–Integrated Ocean Drilling Program (IODP) Holes 1256C and 1256D consists of sheet flows and massive flows, including a ponded lava flow unit (“lava pond”) interpreted as a thick lava flow delivered off‐axis and accumulated in a topographic depression. Fine‐scale structural analysis shows that the lava pond is much less fractured than the deeper lavas, probably as the effect of structure spacing that is larger than in the underlying lava flows. In Hole 1256D, structures are mainly subhorizontal in the lava pond and become steeper downhole, toward the sheeted dike complex. This reflects the distance of the lava pond from the stress field produced by the intrusion of dikes at depth, inducing mostly subvertical eruptive fractures and fracture network, and the distance of the site from active rifting at the EPR. Contrasting structural patterns in the lava pond and in the deeper parts of the drilled section are reflected in contrasting physical properties patterns, as obtained by shipboard and downhole logging data. Electrical resistivity, compressional velocity, and bulk density are generally higher, whereas natural radioactivity and neutron porosity are lower in the lava pond than in the deeper hole. The occurrence of a thick massive lava flow at the top part of the volcanic section affects the deformation pattern of the entire drilled crust and, consequently, its permeability regime which, in turn, controls the geometry and distribution of hydrothermal circulation and basalt alteration.

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Section: Geological Setting and Basement Stratigraphymentioning

confidence: 99%

Section: Geological Setting and Basement Stratigraphymentioning

confidence: 99%

Section: Fracture Distributionmentioning

confidence: 99%

See 1 more Smart Citation

Deformation pattern in a massive ponded lava flow at ODP‐IODP Site 1256: A core and log approach

Tartarotti

Fontana

Crispini

2009

Geochem Geophys Geosyst

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“…Interestingly, borehole geophysical measurements also revealed increasing pore pressures and increasing thermal gradients up to 100°C/km around the main fault [Kemerer and Screaton, 2002]. A flow of warm fluids has been detected above the Moresby detachment (site 1108), likely explaining the pore pressure and temperature anomalies [Shipboard Scientific Party, 1999a].…”

Section: Summary Of Odp Leg 180 Resultsmentioning

confidence: 95%

“…These veins also occur as vertical extensional joints cutting across the fresh gabbro at the bottom of the hole. The whole sequence recovered at site 1117 defines a 100 m thick fault zone in which brittle brecciation and veining is progressively overprinted by ductile shearing toward the fault [Shipboard Scientific Party, 1999a]. Mylonites are themselves crosscut by a later stage of veining associated to a final brittle deformation [Roller et al, 2001].…”

Section: Summary Of Odp Leg 180 Resultsmentioning

confidence: 99%

Hydrothermal fluid venting along a seismogenic detachment fault in the Moresby rift (Woodlark basin, Papua New Guinea)

Famin

Nakashima

2005

Geochem Geophys Geosyst

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[1] We investigate the conditions of hydrothermal alteration occurring along an active, seismogenic normal fault dipping <30°in the Moresby rift (Woodlark basin, Papua New Guinea). Petrological and fluid inclusion studies were conducted in the samples recovered from the Ocean Drilling Program leg 180 that cored the footwall, scarp, and hanging wall of the fault. Chemical analyses of the thermodependent Si-Al substitutions in chlorites show that synrift alteration is coeval with a temperature rise from 200°C to 300°C in the footwall of the detachment, whereas no thermal event is recorded in the hanging wall. In the same samples, fluid inclusions indicate that footwall rocks followed an isothermal exhumation path from 5-7 km to the subsurface. Taken together, the results strongly suggest that the +100°C temperature rise results from the upward migration of H 2 O-NaCl fluids expelled by dehydrating metamorphic rocks from the lower crust. Fluid release began with the onset of detachment faulting and is still actively occurring nowadays. The fact that low-angle earthquakes also occur now at 5-7 km along the fault suggests that the dehydration of the metamorphic rocks and the subsequent circulation of hot hydrothermal fluids may be responsible for the weakening of the middle crust and the formation of a detachment in the Moresby rift.Components: 9370 words, 7 figures, 1 table.

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Influence of sedimentation, local and regional hydrothermal circulation, and thermal rebound on measurements of seafloor heat flux

Hutnak

Fisher

2007

J. Geophys. Res.

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[1] We quantify the influence of environmental processes on measurements of seafloor heat flux with a new one-dimensional thermal model that includes time-varying sedimentation and boundary conditions, represents several scales of hydrothermal and transient conductive processes within basement, and allows fluid seepage through accumulating sediments. Variations in basement thermal conductivity, the extent of hydrothermal mixing in upper basement, and fluid seepage through sediments each influence seafloor heat flux by 2-8%. Conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by !5-10%, even after several to several tens of million years. The new models indicate that thermal rebound takes much longer than suggested by earlier (analytical) calculations, mainly because earlier models did not account for the heat capacitance of the conductive lithosphere. Application of the new model to 3.5-3.6 Ma seafloor on the eastern flank of the Juan de Fuca Ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100-200 ka, following the burial of numerous basement outcrops. Application of the new model to the eastern flank of the East Pacific Rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values. Model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor, even where there is little evidence at present for ridge-flank hydrothermal circulation.Citation: Hutnak, M., and A. T. Fisher (2007), Influence of sedimentation, local and regional hydrothermal circulation, and thermal rebound on measurements of seafloor heat flux,

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Principal Results

Cited by 3 publications

References 11 publications

Deformation pattern in a massive ponded lava flow at ODP‐IODP Site 1256: A core and log approach

Deformation pattern in a massive ponded lava flow at ODP‐IODP Site 1256: A core and log approach

Hydrothermal fluid venting along a seismogenic detachment fault in the Moresby rift (Woodlark basin, Papua New Guinea)

Influence of sedimentation, local and regional hydrothermal circulation, and thermal rebound on measurements of seafloor heat flux

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