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Igneous and metamorphic processes associated with the formation of Chilean Ophiolites and their implication for ocean floor metamorphism, seismic layering, and magnetism

1976; American Geophysical Union; Volume: 81; Issue: 23 Linguagem: Inglês

10.1029/jb081i023p04370

2156-2202

Charles R. Stern, Maarten J. de Wit, J.R. Lawrence,

Paleontology and Stratigraphy of Fossils

Journal of Geophysical Research (1896-1977)Volume 81, Issue 23 p. 4370-4380 Metamorphism and Alteration of the Oceanic Crust Igneous and metamorphic processes associated with the formation of Chilean Ophiolites and their implication for ocean floor metamorphism, seismic layering, and magnetism Charles Stern, Charles SternSearch for more papers by this authorMaarten J. de Wit, Maarten J. de WitSearch for more papers by this authorJames R. Lawrence, James R. LawrenceSearch for more papers by this author Charles Stern, Charles SternSearch for more papers by this authorMaarten J. de Wit, Maarten J. de WitSearch for more papers by this authorJames R. Lawrence, James R. LawrenceSearch for more papers by this author First published: 10 August 1976 https://doi.org/10.1029/JB081i023p04370Citations: 70AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Abstract A metamorphic overprint on the pseudostratigraphy of ophiolite complexes in southern Chile shows an extremely steep vertical metamorphic gradient passing downward from zeolite to amphibolite facies in 2 km, followed by a transition to fresh gabbros. Burial metamorphism does not explain either the steep metamorphic gradient or the abrupt termination of this metamorphic effect. A combination of hydrothermal and contact metamorphism associated with circulation of seawater and igneous and tectonic activity at a spreading center can better explain these observations. Such a model is supported by 18O/16O isotope data. Disequilibrium textures indicate that spreading rapidly removes amphibolized metagabbros from the zone of effective metamorphism, while overlying rocks undergo greenschist metamorphism in a less restricted region in the vicinity of the spreading center. This model is consistent with metamorphic features displayed by other ophiolites and ocean floor metamorphism. The metamorphism produces a zone of metagabbros (amphibolites) underlain by fresh gabbros, which may account for the transition from seismic layer 3A to 3B. The amphibolites in the Chilean ophiolites contain abundant skeletal networks of secondary opaque minerals similar to those observed in ocean floor amphibolites from dredge hauls, which preserve higher-remnant magnetism than either fresh gabbros or the gabbros, dikes, and pillow lavas in the greenschist facies. A zone of amphibolitized metagabbros with high natural remnant magnetism could make a significant contribution to magnetic anomalies, particularly away from the ridge, where the remnant magnetism of the quenched lava of layer 2 is progressively reduced by metamorphism from below and weathering from above. References Anderson, R. N., Petrological significance of low heat flow on the flanks of the mid-ocean ridges, Geol. Soc. Amer. Bull., 83, 2974, 1972. Bonatti, E., Metallogenesis at oceanic spreading centers, Annu. Rev. Earth Planet. Sci., 3, 401–431, 1975. Bonatti, E., J. Honnorez, P. Kirst, F. 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