- journal_title：Geology
- Contributor：Enrico Bonatti ; Daniele Brunelli ; Paola Fabretti ; Marco Ligi ; Rosana Asunta Portaro ; Monique Seyler
- Publisher：Geological Society of America
- Date：2001-
- Format：text/html
- Language：en
- Identifier：10.1130/0091-7613(2001)029<0979:SSCOCF>2.0.CO;2
- journal_abbrev：Geology
- issn：0091-7613
- volume：29
- issue：11
- firstpage：979
Mid-ocean ridges create oceanic lithosphere consisting normally of basaltic crust a few kilometers thick overlying a peridotitic mantle. However, lithosphere free of basaltic crust formed during the past ∼30 m.y. at an ∼50-km-long stretch of Mid-Atlantic Ridge south of the Romanche Fracture Zone, giving rise to a >500-km-long strip of ocean floor exposing mostly mantle peridotites that have undergone an unusually low (≤5%) degree of melting, mixed with peridotites that reacted with a small fraction of basaltic melt. This lithosphere contains <10% of scattered gabbroic pockets, representing melt frozen above 25 km depth within a relatively cold subaxial lithosphere. Numerical modeling excludes dry melting below this crust-free lithosphere, because of the cooling effect of the long- offset Romanche transform combined with a regional mantle thermal minimum; however, modeling allows a limited extent of hydrous melting. This unusual lithosphere, unable to expel the melt fraction, characterizes cold spots along mid-ocean ridges.