DSDP Hole 504B, the first reference section over 1 km through Layer 2 of the oceanic crust

Anderson, Roger N.; Honnorez, J.; Becker, Keir; Adamson, A. C.; Alt, Jeffrey C; Emmermann, Rolf; Kempton, Pamela D.; Kinoshita, Hajimu; Laverne, Christine; Mottl, Michael J.; Newmark, R. L.

doi:10.1038/300589a0

Cited by 203 publications

(128 citation statements)

References 19 publications

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“…The physical properties change significantly across the transition from volcanic rocks to sheeted dikes: the sonic velocities and resistivity increase sharply whereas bulk permeability and porosity drop by orders of magnitude (Anderson et al, 1982). Porosities and thermal conductivities decrease with depth in the dikes, and seismic velocity and resistivity gradients flatten out at about 1500 mbsf.…”

Section: Site 504mentioning

confidence: 99%

“…It is the only hole to penetrate through the volcanic section, altered at low temperatures, into the underlying hydrothermally altered sheeted dike complex. The site has become a reference section for the petrology, geochemistry, hydrothermal alteration, and magnetic and physical properties of the upper oceanic crust (Anderson et al, 1982;Becker et al, 1989;Dick, Erzinger, Stokking, et al, 1991;Alt, Kinoshita, Stokking et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

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Stable and Strontium Isotopic Profiles through Hydrothermally Altered Upper Oceanic Crust, Hole 504B

Alt¹,

Teagle²,

Bach³

et al. 1996

Proceedings of the Ocean Drilling Program, 148 Scientific Results

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Leg 148 penetrated 111m farther into Hole 504B, to a total depth of 2111 meters below seafloor (mbsf), and recovered diabase dikes similar to the immediately overlying rocks. Secondary mineralogy and whole-rock oxygen and strontium isotopic compositions were determined for samples from Leg 148. In addition, strontium isotopic analyses were performed on previously recovered samples of the lower dikes (1550-2000 mbsf). Trends observed in the lower dikes (1550-2000 mbsf) continue in the Leg 148 section (2000-2111 mbsf). These include the local presence of magnesiohornblende and secondary calcic plagioclase and high Ti contents of amphiboles. Cu, Zn, and S contents of the more altered rocks are low, and whole-rock δ 18 θ values of 33%350°C) and greater extents of recrystallization than in the upper dikes. All of the data for the new Leg 148 section are consistent with the rocks being a continuation of a subsurface reaction zone, where metals and sulfur are leached from the crust by hydrothermal fluids and transported to form metal sulfide mineralizations on or within the crust or vent into seawater.Sr contents of the lower sheeted dikes (1550-2111 mbsf) are generally 48-62 ppm, and whole-rock 87 Sr/ 86 Sr ratios range from 0.70265 to 0.70304, only slightly elevated relative to fresh MORB values. The rocks were altered by seawater-derived hydrothermal fluids, with little change in the Sr concentrations of the rocks. Although amphibole is the most abundant secondary phase, the Sr isotopic composition of the rocks is probably dominated by the abundance of secondary plagioclase. The 87 Sr/ 86 Sr ratios of hydrothermal fluids were higher than measured in variably recrystallized (10%-80%) whole rocks. The seawater component of hydrothermal fluids increased through time, as documented by 87 Sr/ 86 Sr ratios of 0.7028-0.7034 for amphibole and chlorite, to 0.7035-0.7038 for vein epidotes. The latter values record the composition of upwelling black smoker-type endmember hydrothermal fluids at Site 504.The low 87 Sr/ 86 Sr ratios for the lower dikes differ from the uniformly high ratios of the thoroughly recrystallized sheeted dikes from the Troodos ophiolite. The oceanic dikes interacted with much smaller volumes of seawater than the ophiolitic rocks and apparently to a lesser extent. These differences are in some way related to the contrasting tectonic setting, mineralogy, and chemical composition of ophiolites compared to in situ ocean crust.

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Section: Site 504mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Stable and Strontium Isotopic Profiles through Hydrothermally Altered Upper Oceanic Crust, Hole 504B

Alt¹,

Teagle²,

Bach³

et al. 1996

Proceedings of the Ocean Drilling Program, 148 Scientific Results

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“…Extrusive layer thicknesses estimated in ophiolites range from 400 to 1600 m [1,42]. In contrast, estimates of extrusive thicknesses from oceanic scarps are only -300-500 m [43][44][45][46] while at DSDP Hole 504B the extrusive section is less than 600 m thick [16], comparable to layer 2A thicknesses determined from off-axis seismic data ( Table 1). The extrusive-dike transition zone (defined as the vertical depth from 20% to 70% sheeted dikes) is quite thin in ophiolite sections (Table 2), a few tens of meters to 100-200 m [1,47,48].…”

Section: £££ Hooft Et Al J Earth and Planetary Science Lerrers 14mentioning

confidence: 79%

“…The extrusive-dike transition zone (defined as the vertical depth from 20% to 70% sheeted dikes) is quite thin in ophiolite sections (Table 2), a few tens of meters to 100-200 m [1,47,48]. Oceanic scarps give values also ranging from a few tens of meters up to a few hundred meters [44][45][46], while at DSDP Hole 504B the extrusive-dike transition is -150m thick [16]. These estimates are comparable to the thickness 129 of the layer 2Aj2B transition estimated seismically.…”

Section: £££ Hooft Et Al J Earth and Planetary Science Lerrers 14mentioning

confidence: 99%

“…When the effect of cooling against the Blanco Fracrure Zone is removed from the MBA, the RMBA signarure is almost flat along the Cleft and Vance Segments. The RMBA on the Gorda Ridge is elevated by [10][11][12][13][14][15][16][17][18][19][20] The predicted variation in crustal thickness is shown assuming that both mantle density and crustal thickness variations are controlled by mantle temperature [l eo . Crustal thickness variations account for 70%-75% of the RMBA signal; the remainder is due to temperature-related mantle density variations.…”

Section: Modeling Of Residual Mantle Bouguer Anomaliesmentioning

confidence: 99%

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The influence of magma supply and eruptive processes on axial morphology, crustal construction and magma chambers

Hooft¹

1996

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The influence of porosity and crack morphology on seismic velocity and permeability in the upper oceanic crust

Carlson

2014

Geochem Geophys Geosyst

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[1] The purpose of this study is to explore the relationships between porosity, crack morphology, seismic velocity, and permeability in the upper oceanic crust. In a theoretical model, velocity is a quadratic function of porosity U, and the coefficients are functions of the fractional area of asperity contact A f across the cracks, a measure of crack morphology; thus, v 5 v(A f , U). Fits to data sets from the lava and dike sections in Holes 504B and 1256D yield A f 5 0.096(8) and 0.045(3), with rms errors of 1.7 and 0.3%, respectively. Lower values of A f account for the high porosities and low velocities observed in Layer 2A. After 0.2 Ma, the porosities of both Layer 2A and the deeper part of the lava pile remain in the range 8 6 4%. The observed increase of Layer 2A velocities after 0.2 Ma is caused largely by changing crack morphology as opposed to decreasing porosity; at 8% porosity, an increase of A f from 0.003 to 0.1 accounts for an increase of velocity from 3 to >5 km/s. An empirical log-linear relationship between permeability j and v suggests a relationship between j and A f as well. This relationship between j and v can be explained if the permeability coefficient j o is a closely constrained quadratic function of the area of asperity contact A f . A f is thus the primary variable affecting both seismic velocities and the permeability of the uppermost oceanic crust.

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DSDP Hole 504B, the first reference section over 1 km through Layer 2 of the oceanic crust

Cited by 203 publications

References 19 publications

Stable and Strontium Isotopic Profiles through Hydrothermally Altered Upper Oceanic Crust, Hole 504B

Stable and Strontium Isotopic Profiles through Hydrothermally Altered Upper Oceanic Crust, Hole 504B

The influence of magma supply and eruptive processes on axial morphology, crustal construction and magma chambers

The influence of porosity and crack morphology on seismic velocity and permeability in the upper oceanic crust

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