Homogeneous basalts from the East Pacific Rise at 21N: steady state magma reservoirs at moderately fast spreading centers
Juteau, T.; Eissen, J.P.; Francheteau, J.; Needham, D.; Choukroune, P.; Rangin, C.; Séguret, M.; Ballard, R.D.; Fox, P.J.; Normark, W.R.; Carranza, A.; Cordoba, D.; Guerrero, J. (1980). Homogeneous basalts from the East Pacific Rise at 21N: steady state magma reservoirs at moderately fast spreading centers. Oceanol. Acta 3(4): 487-503
In: Oceanologica Acta. Elsevier/Gauthier-Villars: Montreuil. ISSN 0399-1784; e-ISSN 1878-4143, more
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| Keywords |
Chemical compounds > Sulphur compounds > Sulphides
Earth sciences > Geology > Petrology
Magma
Rocks > Igneous rocks > Volcanic rocks > Basalts
Rocks > Igneous rocks > Volcanic rocks > Lava > Pillow lava
Topographic features > Submarine features > Ridges > Submarine ridges > Mid-ocean ridges
ISE, East Pacific Rise [Marine Regions]
Marine/Coastal |
| Authors | | Top |
- Juteau, T.
- Eissen, J.P.
- Francheteau, J.
- Needham, D.
- Choukroune, P.
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- Rangin, C.
- Séguret, M.
- Ballard, R.D.
- Fox, P.J.
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- Normark, W.R.
- Carranza, A.
- Cordoba, D.
- Guerrero, J.
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| Abstract |
Forty basaltic rocks collected by submersible during the 'Cyamex' expedition (1978) on the East Pacific Rise at 21N, a moderately fast spreading segment (6 cm/year opening rate) of the mid-ocean ridge, consist of angular pillow fragments and glass buds, sheet-flow slabs and samples of columnar pillars standing in collapsed fossil lava pools. The collection shows petrographic homogeneity when compared with basalts on other segments of mid-ocean ridges: olivine-phyric, or highly plagioclase-phyric rocks, so common in the slow-spreading 'Famous' area in the Atlantic, are absent. All samples are typical low-potassium oceanic tholeiites with a limited fractionation trend. Pillow-lavas, thin and thick sheet-flows cannot be distinguished by their major element compositions, as in the Galapagos rift which has the same spreading rate as the EPR at 21N. Further, ferrobasalts have been described from the Galapagos rift, but do not appear in the Cyamex rocks. In the pillows and sheet-flow samples, four generations of olivine and plagioclase crystals are distinguished. Samples from the fossil lava pools are aphyric. The corresponding magma batches are presumed to have migrated rapidly through the magma chamber, and to have been extruded in large volumes, possibly during episodes of high instantaneous opening rate. Fe-Ni and Fe-Cu-rich sulphide phases are common in all lava types as massive globules scattered through the glass, or as microglobules decorating the walls of empty vesicles. Palagonite and Fe-Mn oxide thicknesses across the strike of the Rise indicate relative ages compatible with successive extrusions at the Rise axis. |
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