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dc.contributor.authorSanfilippo, Alessio  Concept link
dc.contributor.authorDick, Henry JB  Concept link
dc.contributor.authorMarschall, Horst R.  Concept link
dc.contributor.authorLissenberg, C. Johan  Concept link
dc.contributor.authorUrann, Ben  Concept link
dc.date.accessioned2019-03-13T13:20:08Z
dc.date.available2019-06-05T07:53:16Z
dc.date.issued2018-12-05
dc.identifier.citationSanfilippo, A., Dick, H. J. B., Marschall, H. R., Lissenberg, C. J., & Urann, B. (2019). Emplacement and high-temperature evolution of gabbros of the 16.5 degrees N oceanic core complexes (Mid-Atlantic Ridge): Insights into the compositional variability of the lower oceanic crust. Geochemistry Geophysics Geosystems, 20(1), 46-66.en_US
dc.identifier.urihttps://hdl.handle.net/1912/23793
dc.descriptionAuthor Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 20(1), (2019): 46-66, doi: 10.1029/2018GC007512.en_US
dc.description.abstractThis study reports the composition of the oceanic crust from the 16.5°N region of the Mid‐Atlantic Ridge, a spreading ridge segment characterized by a complex detachment fault system and three main oceanic core complexes (southern, central, and northern OCCs). Lithologies recovered from the core complexes include both greenschist facies and weathered pillow basalt, diabase, peridotite, and gabbro, while only weathered and fresh pillow basalt was dredged from the rift valley floor. The gabbros are compositionally bimodal, with the magmatic crust in the region formed by scattered intrusions of chemically primitive plutonic rocks (i.e., dunites and troctolites), associated with evolved oxide‐bearing gabbros. We use thermodynamic models to infer that this distribution is expected in regions where small gabbroic bodies are intruded into mantle peridotites. The occurrence of ephemeral magma chambers located in the lithospheric mantle enables large proportions of the melt to be erupted after relatively low degrees of fractionation. A large proportion of the dredged gabbros reveal evidence for deformation at high‐temperature conditions. In particular, chemical changes in response to deformation and the occurrence of very high‐temperature ultramylonites (>1000 °C) suggest that the deformation related to the oceanic detachment commenced at near‐solidus conditions. This event was likely associated with the expulsion of interstitial, evolved magmas from the crystal mush, a mechanism that enhanced the formation of disconnected oxide‐gabbro seams or layers often associated with crystal‐plastic fabrics in the host gabbros. This granulite‐grade event was soon followed by hydrothermal alteration revealed by the formation of amphibole‐rich veins at high‐temperature conditions (~900 °C).en_US
dc.description.sponsorshipThe geochemical data used in this study and the parameters of the model are included as Tables in the supporting information. The data published will be contributed to the Petrological Database (www.earthchem.org/petdb). We thank the captain and crew of the R/V Knorr for their help and enthusiasm during our cruise to the 16.5° core complexes. Deborah Smith served as best chief scientist ever. Hans Schouten and Joe Cann kept H. J. B. D. in line and together with Vincent Salters, Ross Parnell‐Turner, Fuwu Ji, Dana Yoerger, Camilla Palmiotto, A. Zheleznov, H. L. Bai, and Will Junkin interpreted the geophysical data and described the rock samples on which this paper is based. A. S. was financially supported with an InterRidge fellowship and by the Societa' Italiana di Minerlogia e Petrografia. H. R. M. acknowledges support from the Wilhelm und Else Heraeus Stiftung. H. J. B. D. acknowledges support from the National Science Foundation grants MG&G 1155650 and MG&G 1434452, and discussions and assistance in the laboratory from Ma Qiang. Fuwu Ji, Joe Cann, Deborah Smith, Hans Schouten, and Ross Parnell‐Turner assisted in dredging, sample description, and provide the authors with considerable insight into the geologic and geophysical data collected during the Knorr cruise 210 Leg 5. Comments by E. Rampone, G Ceuleneer, and an anonymous reviewer improved the quality of the manuscript.en_US
dc.publisherAmerican Geophysical Unionen_US
dc.relation.urihttps://doi.org/10.1029/2018GC007512
dc.subjectgabbroen_US
dc.subjectdetachmenten_US
dc.subjectoceanic core complexen_US
dc.subjectmelt‐rock reactionsen_US
dc.subjectlower oceanic crusten_US
dc.titleEmplacement and high-temperature evolution of gabbros of the 16.5 degrees N oceanic core complexes (Mid-Atlantic Ridge): Insights into the compositional variability of the lower oceanic crust.en_US
dc.typeArticleen_US
dc.description.embargo2019-06-05en_US
dc.identifier.doi10.1029/2018GC007512


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