A new magma chamber model based on structural studies in the Oman ophiolite

Abstract Structural mapping in the mafic-ultramafic transition zone and in the overlying crustal section of the Oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros, and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites. The crustal section near the spreading axis, and in particular the magma chamber are fed by two independent melts: a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone. Layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow. Whatever its origin, the layering orientation in the newly created crust does not necessarily reflect its original attitude. The final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen. A new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges.

[1]  A. Nicolas,et al.  Crystalline plasticity and solid state flow in metamorphic rocks , 1976 .

[2]  F. Boudier,et al.  Structural mapping in the Oman ophiolites: Mantle diapirism along an oceanic ridge , 1988 .

[3]  P. Browning.  Cryptic variation within the Cumulate Sequence of the Oman ophiolite: magma chamber depth and petrological implications , 1984, Geological Society, London, Special Publications.

[4]  C. Jaupart,et al.  The kinetics of nucleation and crystal growth and scaling laws for magmatic crystallization , 1987 .

[5]  A. Nicolas,et al.  Mantle—crust transition zone and origin of wehrlitic magmas: Evidence from the Oman ophiolite , 1988 .

[6]  A. Nicolas,et al.  Cumulative or Residual Origin for the Transition Zone in Ophiolites: Structural Evidence , 1983 .

[7]  N. Kusznir.  Thermal evolution of the oceanic crust; its dependence on spreading rate and effect on crustal structure , 1980 .

[8]  A. Nicolas,et al.  The structures of two ophiolite massifs, Bay-of-Islands, Newfoundland: A model for the oceanic crust and upper mantle , 1981 .

[9]  M. Leblanc,et al.  Structural classification of chromite pods in southern New Caledonia , 1981 .

[10]  T. Juteau,et al.  Duality of magmatism in the plutonic sequence of the Sumail Nappe, Oman , 1988 .

[11]  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 .

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

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

[14]  M. Rabinowicz,et al.  A rolling mill effect in asthenosphere beneath oceanic spreading centers , 1984 .

[15]  A. Nicolas,et al.  Structures in podiform chromite from the Maqsad district (Sumail ophiolite, Oman) , 1985 .

[16]  H. Whitechurch,et al.  Les intrusions ultrabasiques de la séquence crustale de l'ophiolite d'Oman: un événement témoin de l'extinction d'une zone d'accrétion océanique? , 1986 .

[17]  P. Blumenfeld.  Le "tuilage des megracristaux", un critere d'ecoulement rotationnel pour les fluidalites des roches magmatiques; Application au granite de Barbey-Seroux (Vosges, France) , 1983 .

[18]  John F. Casey,et al.  Magma chamber profiles from the Bay of Islands ophiolite complex , 1981 .

[19]  I. Campbell.  Some problems with the cumulus theory , 1978 .

[20]  A. Nicolas,et al.  Mantle flow at oceanic spreading centers: Models derived from ophiolites , 1982 .

[21]  J. Pallister.  Structure of the sheeted dike complex of the Samail Ophiolite near Ibra, Oman , 1981 .

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

[23]  A. Nicolas,et al.  Principles of Rock Deformation , 1987 .

[24]  T. Irvine,et al.  The J-M platinum-palladium reef of the Stillwater Complex, Montana; II, Origin by double-diffusive convective magma mixing and implications for the Bushveld Complex , 1983 .

[25]  F. Boudier,et al.  Shear zones, thrusts and related magmatism in the Oman ophiolite: Initiation of thrusting on an oceanic ridge , 1988 .

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

[27]  R. M. Noyes,et al.  Crystallization and Layering of the Skaergaard Intrusion , 1979 .

[28]  N. Sleep,et al.  Topography and tectonics of Mid‐Oceanic Ridge axes , 1979 .

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

[30]  W. Bryan,et al.  Compositional variations of young basalts in the Mid-Atlantic Ridge rift valley near lat 36°49′N , 1977 .

[31]  J. Cann,et al.  Chilling statistics indicate an ocean-floor spreading origin for the Troodos complex, Cyprus , 1974 .

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

[33]  E. Tex.  Origin of ultramafic rocks, their tectonic setting and history: A contribution to the discussion of the paper “the origin of ultramafic and ultrabasic rocks” by P.J. Wyllie , 1969 .

[34]  J. Wilson,et al.  Discordant layering relations in the Fongen–Hyllingen basic intrusion , 1982, Nature.

[35]  I. Reuber.  Complexity of the crustal sequence in the northern Oman ophiolite (Fizh and southern Aswad blocks): the effect of early slicing? , 1988 .

[36]  M. Rabinowicz,et al.  Melt segregation and flow in mantle diapirs below spreading centers: Evidence from the Oman Ophiolite , 1987 .

[37]  A. Nicolas.  A Melt Extraction Model Based on Structural Studies in Mantle Peridotites , 1986 .

[38]  D. Greenbaum.  Magmatic Processes at Ocean Ridges: Evidence from the Troodos Massif, Cyprus , 1972 .

[39]  T. Usselman,et al.  Thermal control of low-pressure fractionation processes , 1978 .

[40]  P. Browning.  The petrology, geochemistry and structure of the plutonic rocks of the Oman ophiolite , 1982 .

[41]  D. Walker,et al.  Abyssal tholeiites from the Oceanographer Fracture Zone , 1979 .

[42]  N. Sleep,et al.  Reinterpretation of seismic reflection data over the East Pacific Rise , 1982 .

[43]  G. Ceuleneer.  Structures des ophiolites d'Oman : flux mantellaire sous un centre d'expansion d'expansion oceanique et charriage a la dorsale , 1986 .

[44]  B. Lewis.  The Process of Formation of Ocean Crust , 1983, Science.