The accretion of oceanic crust by episodic sill intrusion

Seismic refraction data from mature oceanic regions show remarkable consistency in crustal thickness between sites, yet the characteristics of different spreading centers show great variation. This leads to the paradox that the similarity in mature oceanic crust suggests that the igneous processes in crustal accretion are the same across a range of spreading rates but that the differences in the spreading centers themselves imply the opposite. We have developed a simple two dimensional model for crustal accretion at oceanic spreading centers by the episodic addition of sills at a high level within the crust, as implied by recent geophysical studies of spreading centers. Using our model, we have calculated velocity and temperature fields in the crust, including the effects of hydrothermal cooling. We show that oscillations in the temperature field due to episodicities of 200–20000 years have an effect localized to the region within 50–500 m of the intrusion. By assuming that all latent heat and excess specific heat introduced by the injection of sills is convected away by hydrothermal circulation, we estimate that the maximum heat transfer associated with hydrothermal cooling in the upper crust is of the order of 10 times greater than the conductive flux. We have calculated seismic velocities associated with the model temperature field in the crust, and we show that these are consistent with results from both seismic refraction and reflection experiments. The model may be applied to both fast and slow spreading ridges, and it accounts for the apparent increases in both the mean crustal temperature and the frequency of presence of melt with increasing spreading rate, hence resolving the paradox. We also show that the implications of this model are consistent with geological observations of layering in ophiolites.

[1]  J. Morgan,et al.  The genesis of oceanic crust: Magma injection, hydrothermal circulation, and crustal flow , 1993 .

[2]  R. White,et al.  Oceanic crustal thickness from seismic measurements and rare earth element inversions , 1992 .

[3]  J. Collier,et al.  Seismic mapping of a magma chamber beneath the Valu Fa Ridge, Lau Basin , 1992 .

[4]  M. Bickle,et al.  Strontium alteration in the Troodos ophiolite: implications for fluid fluxes and geochemical transport in mid-ocean ridge hydrothermal systems , 1992 .

[5]  J. Collier,et al.  The Valu Fa Ridge: The pattern of volcanic activity at a back-arc spreading centre , 1992 .

[6]  Deborah K. Smith,et al.  The role of seamount volcanism in crustal construction at the Mid‐Atlantic Ridge (24°–30°N) , 1992 .

[7]  S. Solomon,et al.  Microearthquake Characteristics of a Mid‐Ocean Ridge along‐axis high , 1992 .

[8]  R. Detrick,et al.  Mid-ocean ridge magma chambers , 1992 .

[9]  F. Gasse,et al.  Contemporary, Holocene, and Quaternary deformation of the Asal Rift, Djibouti: Implications for the mechanics of slow spreading ridges , 1991 .

[10]  S. Solomon,et al.  Ocean bottom seismometer facilities available , 1991 .

[11]  Richard M. Jones.  No misuse of NSF grants found , 1991 .

[12]  N. Sleep.  Hydrothermal circulation, anhydrite precipitation, and thermal structure at ridge axes , 1991 .

[13]  H. Huppert,et al.  Convection and crystallization in magma cooled from above , 1990 .

[14]  E. Parmentier,et al.  Spreading rate dependence of three-dimensional structure in oceanic spreading centres , 1990, Nature.

[15]  S. Solomon,et al.  The three-dimensional seismic velocity structure of the East Pacific Rise near latitude 9° 30′ N , 1990, Nature.

[16]  W. J. Morgan,et al.  A nonlinear rheology model for mid‐ocean ridge axis topography , 1990 .

[17]  John A. Orcutt,et al.  The structure of 0‐ to 0.2‐m.y.‐old oceanic crust at 9°N on the East Pacific Rise from expanded spread profiles , 1990 .

[18]  I. I. Kim,et al.  No evidence from multichannel reflection data for a crustal magma chamber in the MARK area on the Mid-Atlantic Ridge , 1990, Nature.

[19]  J. Collier,et al.  Seismic images of a magma chamber beneath the Lau Basin back-arc spreading centre , 1990, Nature.

[20]  J. Mutter,et al.  New seismic images of oceanic crustal structure , 1990 .

[21]  J. Mutter,et al.  A two- and three-dimensional analysis of gravity anomalies associated with the East Pacific Rise at 9°N and 13°N , 1990 .

[22]  A. Harding,et al.  Evidence for a smaller magma chamber beneath the East Pacific Rise at 9°30′ N , 1990, Nature.

[23]  R. Clowes,et al.  Shallow crustal structure beneath the Juan de Fuca Ridge from 2-D seismic refraction tomography , 1990 .

[24]  J. Mutter,et al.  Structure of young oceanic crust at 13°N on the East Pacific Rise from expanding spread profiles , 1989 .

[25]  T. Murase,et al.  The use of laboratory velocity data for estimating temperature and partial melt fraction in the low‐velocity zone: Comparison with heat flow and electrical conductivity studies , 1989 .

[26]  D. Caress,et al.  Tomographic image of the magma chamber at 12°50' N on the East Pacific Rise , 1989, Nature.

[27]  D. Pollard,et al.  Surface Deformation and Shallow Dike Intrusion Processes at Inyo Craters, Long Valley, California , 1988 .

[28]  D. Clague,et al.  Implications of magma convection for the size and temperature of magma chambers at fast spreading ridges , 1988 .

[29]  P. Nehlig,et al.  Flow porosities, permeabilities and preliminary data on fluid inclusions and fossil thermal gradients in the crustal sequence of the Sumail ophiolite (Oman) , 1988 .

[30]  A. Nicolas,et al.  A new magma chamber model based on structural studies in the Oman ophiolite , 1988 .

[31]  M. Lilley,et al.  Estimation of heat and chemical fluxes from a seafloor hydrothermal vent field using radon measurements , 1988, Nature.

[32]  M. Bickle,et al.  The Volume and Composition of Melt Generated by Extension of the Lithosphere , 1988 .

[33]  C. Yorath,et al.  Asymmetric deep crustal structure across the Juan de Fuca Ridge , 1988 .

[34]  Jian Lin,et al.  Mechanisms for the origin of mid‐ocean ridge axial topography: Implications for the thermal and mechanical structure of accreting plate boundaries , 1987 .

[35]  N. Sleep,et al.  Structure of the southern Juan de Fuca Ridge from seismic reflection records , 1987 .

[36]  H. C. Heard,et al.  Thermal diffusivity of igneous rocks at elevated pressure and temperature , 1987 .

[37]  E. Baker,et al.  Characteristics of hydrothermal plumes from two vent fields on the Juan de Fuca Ridge, northeast Pacific Ocean , 1987 .

[38]  J. Mutter,et al.  Multi-channel seismic imaging of a crustal magma chamber along the East Pacific Rise , 1987, Nature.

[39]  E. Takahashi.  Melting of a dry peridotite KLB‐1 up to 14 GPa: Implications on the Origin of peridotitic upper mantle , 1986 .

[40]  G. Purdy,et al.  Crustal structure of the Mid-Atlantic Ridge at 23°N from seismic refraction studies , 1986 .

[41]  N. Sleep,et al.  A Mid‐Ocean Ridge Thermal Model: Constraints on the volume of axial hydrothermal heat flux , 1985 .

[42]  J. McClain,et al.  The East Pacific Rise in cross section: A seismic model , 1985 .

[43]  S. Solomon,et al.  Microearthquakes beneath the Median Valley of the Mid‐Atlantic Ridge near 23°N: Hypocenters and focal mechanisms , 1985 .

[44]  G. D. Harper.  Tectonics of slow spreading mid‐ocean ridges and consequences of a variable depth to the brittle/ductile transition , 1985 .

[45]  S. Solomon,et al.  Source mechanisms of earthquakes near mid-ocean ridges from body waveform inversion - Implications for the early evolution of oceanic lithosphere , 1984 .

[46]  S. Solomon,et al.  Compressional and shear wave structure of the East Pacific Rise at 11°20′N: Constraints from three‐component ocean bottom seismometer data , 1984 .

[47]  S. Stein,et al.  Age dependence of oceanic intraplate seismicity and implications for lithospheric evolution , 1983 .

[48]  C. Lister,et al.  On the intermittency and crystallization mechanisms of sub-seafloor magma chambers , 1983 .

[49]  M. Rutherford,et al.  The Origin of Rhyolite and Plagiogranite in Oceanic Crust: An Experimental Study , 1983 .

[50]  Mark A. Riedesel,et al.  Microearthquakes in the Black Smoker Hydrothermal Field, East Pacific Rise at 21°N , 1982 .

[51]  J. Garmany,et al.  Constraints on the structure of the East Pacific Rise from seismic refraction data , 1982 .

[52]  B. Lewis,et al.  Geophysical evidence for the absence of a crustal magma chamber under the northern Juan de Fuca Ridge: A contrast with ROSE results , 1982 .

[53]  K. Macdonald.  Mid-Ocean Ridges: Fine Scale Tectonic, Volcanic and Hydrothermal Processes Within the Plate Boundary Zone , 1982 .

[54]  H. Jackson,et al.  Oceanic spreading rate and crustal thickness , 1981, Marine Geophysical Researches.

[55]  J. Pallister,et al.  Samail Ophiolite plutonic suite: Field relations, phase variation, cryptic variation and layering, and a model of a spreading ridge magma chamber , 1981 .

[56]  H. Taylor,et al.  An oxygen isotope profile in a section of Cretaceous oceanic crust, Samail Ophiolite, Oman: Evidence for δ18O buffering of the oceans by deep (>5 km) seawater-hydrothermal circulation at mid-ocean ridges , 1981 .

[57]  J. Smewing.  Mixing characteristics and compositional differences in mantle‐derived melts beneath spreading axes: Evidence from cyclically layered rocks in the ophiolite of North Oman , 1981 .

[58]  G. Wasserburg,et al.  Sm‐Nd, Rb‐Sr, and 18O/16O isotopic systematics in an oceanic crustal section: Evidence from the Samail Ophiolite , 1981 .

[59]  P. Stoffa,et al.  Magma chamber and mantle reflections – East Pacific Rise , 1980 .

[60]  Gerald M. Mavko,et al.  Velocity and attenuation in partially molten rocks , 1980 .

[61]  Robert D. Ballard,et al.  Hydrothermal heat flux of the “black smoker” vents on the East Pacific Rise , 1980 .

[62]  C R B Lister,et al.  Heat Flow and Hydrothermal Circulation , 1980 .

[63]  G. Pálmason.  A continuum model of crustal generation in Iceland - kinematic aspects , 1980 .

[64]  L. Cathles,et al.  Hydrothermal convection at slow-spreading mid-ocean ridges , 1979 .

[65]  C. Fowler.  The Mid-Atlantic Ridge: structure at 45" N , 1978 .

[66]  N. Sleep.  Thermal structure and kinematics of mid-oceanic ridge axis, some implications to basaltic volcanism , 1978 .

[67]  Roger N. Anderson,et al.  The mechanisms of heat transfer through the floor of the Indian Ocean , 1977 .

[68]  R. Whitmarsh,et al.  Upper mantle structure beneath the Mid-Atlantic Ridge north of the Azores based on observations of compressional waves , 1977 .

[69]  J. Dewey,et al.  Geometry of plate accretion , 1977 .

[70]  B. Parsons,et al.  An analysis of the variation of ocean floor bathymetry and heat flow with age , 1977 .

[71]  C. Fowler.  Crustal structure of the Mid-Atlantic ridge crest at 37"N , 1976 .

[72]  G. Sutton,et al.  Evolution of oceanic crust: 1. A physical model of the East Pacific Rise crest derived from seismic refraction data , 1976 .

[73]  B. Kennett,et al.  Structure of the East Pacific Rise from an Ocean Bottom Seismometer Survey , 1976 .

[74]  N. Sleep.  Formation of oceanic crust: Some thermal constraints , 1975 .

[75]  David L. Williams,et al.  The Galapagos Spreading Centre: Lithospheric Cooling and Hydrothermal Circulation , 1974 .

[76]  A. McBirney,et al.  Properties of some common igneous rocks and their melts at high temperatures , 1973 .

[77]  G. Pálmason.  Kinematics and Heat Flow in a Volcanic Rift Zone, with Application to Iceland , 1973 .

[78]  D. Oldenburg,et al.  Thermal Model of Ocean Ridges , 1973 .

[79]  D. McKenzie.  Some remarks on heat flow and gravity anomalies , 1967 .

[80]  Jian Lin,et al.  Mechanisms of lithospheric extension at mid-ocean ridges , 1989 .

[81]  Denis Norton,et al.  Theory of Hydrothermal Systems , 1984 .

[82]  H. Taylor.  Oxygen and Hydrogen Isotope Studies of Hydrothermal Interactions at Submarine and Subaerial Spreading Centers , 1983 .

[83]  K. Macdonald.  A Geophysical Comparison between Fast and Slow Spreading Centers: Constraints on Magma Chamber Formation and Hydrothermal Activity , 1983 .

[84]  C. Lister.  The Basic Physics of Water Penetration into Hot Rock , 1983 .

[85]  C. Fowler,et al.  Oceanic crustal structure—Mid-Atlantic Ridge at 45° N , 1979 .