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Observation of manganese deposits on the East Pacific Rise during the CYAMEX-RITA expedition (1981)

Cyamex Scientific Team ; Francheteau, Jean ; Needham, H D ; [et al.]

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In: Supplement to: Cyamex Scientific Team; Francheteau, Jean; Needham, H D; Choukroune, P; Juteau, Thierry; Séguret, Marie J M; Ballard, R D; Fox, P J; Normark, William R; Carranza, A; Cordoba, D; Guerrero, Gerardo; Rangin, Claude (1981): First manned submersible dives on the East Pacific Rise at 21�N (project RITA): General results. Marine Geophysical Research, 4(4), 345-379, https://doi.org/10.1007/BF00286034

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Publication Date: 2023-08-28

Description: A submersible study has been conducted in February - March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera - Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of giant size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.

Keywords: CY78-16DF; CY78-17V; CY78-18V; CYAMEX; Cyana (Submersible); Deposit type; DEPTH, sediment/rock; Description; East Pacific Rise; Event label; Identification; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; OBSE; Observation; Position; Quantity of deposit; Sediment sample; Sediment type; SES; Substrate type; Visual description

Type: Dataset

Format: text/tab-separated-values, 21 data points

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Chemical analyses of hydrothermal deposits and associated material from Transform fault 'A' on the Mid-Atlantic Ridge, FAMOUS area (2023)

Hoffert, Michel ; Perseil, E A ; Hekinian, Roger ; [et al.]

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Publication Date: 2023-09-26

Description: Sampled hydrothermal deposits from Transform fault 'A' on the Mid-Atlantic Ridge have been classified into two main categories according to the relative proportion of the black Fe-Mn concretions with respect to the clay-rich fraction: clay-rich hydrothermal material and black Fe-Mn concretions (nodules). These materials have been analysed for their chemical composition by arc spectrometry using an ARL quantometer were made at the University of Strasbourg. This method consists of melting the sample in a mixture of lithium tetraborate and then introducing the melt into in a glycolated solvent prior analysis. Trace elements were determined using graphite discs . Na and K were determined by emission spectrometry (precision of +- 2.0%).

Keywords: Aluminium oxide; Arc spectrometry; Barium; Boron; Calcium oxide; Chromium; Cobalt; Copper; CY-74-23-12; CY-74-26-14; CY-74-26-15; CY-74-26-16; Description; Elevation of event; Event label; FAMOUS 06-74; FAMOUS74; Gallium; Geochemistry; GRAB_subCyana; Grab, on Cyana [Submersible]; Identification; Iron oxide, Fe2O3; Latitude of event; Le Noroit; Longitude of event; Loss on ignition; Magnesium oxide; manganese micronodule; manganese nodule; Manganous manganic oxide; Mid Atlantic Ridge; Mid-Atlantic Ridge; Nickel; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; ocean; Optical emission spectrography; Potassium oxide; Sample type; sediment; Silicon dioxide; Sodium oxide; Strontium; Titanium(II) oxide; Vanadium; Wet chemistry; Zinc

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Format: text/tab-separated-values, 270 data points

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Chemical analyses of Fe-Mn coatings separated from the margins of basaltic rocks from Transform Fault 'A' and from the the Rift Valley near 36°50'N in the Mid-Atlantic Ridge (2023)

Hoffert, Michel ; Perseil, E A ; Hekinian, Roger ; [et al.]

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Publication Date: 2023-09-26

Description: In order to evaluate the possible influence of hydrothermal activity on Fe-Mn coatings found on the surfaces of basaltic rocks in the median part of Transform Fault "A", a few samples collected in different structural settings less than 2 km away from the hydrothermal fields. They were analysed along with samples further West in the Transform Valley (sample ARP 74-13-23) and from the top of the deepestescarpment of the inner West wall of the Rift Valley near 36'50'N (sample cyp 74-31-40). Chemical analyses were done by arc spectrometry using an ARL quantometer were made at the University of Strasbourg. This method consists of melting the sample in a mixture of lithium tetraborate and then introducing the melt into in a glycolated solvent prior analysis. Trace elements were determined using graphite discs . Na and K were determined by emission spectrometry (precision of +- 2.0%).

Keywords: Aluminium oxide; Archimède (Submersible); Arc spectrometry; ARP-74-13-23; Barium; Boron; Calcium oxide; Chromium; Cobalt; Copper; CY-74-19-7; CY-74-22-10; CY-74-22-9; CY-74-23-11; CY-74-31-40; Deposit type; Elevation of event; Emission spectrography; Event label; FAMOUS 06-74; FAMOUS 07-74; FAMOUS74; Gallium; Geochemistry; Grab; GRAB; GRAB_subCyana; Grab, on Cyana [Submersible]; Identification; Iron oxide, Fe2O3; Latitude of event; Le Noroit; Longitude of event; Loss on ignition; Magnesium oxide; manganese micronodule; manganese nodule; Manganous manganic oxide; Mid-Atlantic Ridge; Nickel; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; ocean; Optical emission spectrography; Potassium oxide; sediment; Silicon dioxide; Sodium oxide; Strontium; Titanium(II) oxide; Vanadium; Wet chemistry; Zinc

Type: Dataset

Format: text/tab-separated-values, 132 data points

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4

Electronic Resource

Geochemical and mineralogical evidence for the occurrence of at least three distinct magma types in the ‘famous’ region (1981)

Roex, Anton P. ; Erlank, A. J. ; Needham, H. D.

Springer

Contributions to mineralogy and petrology 77 (1981), S. 24-37

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Bulk rock major and trace element variations in selected basalts from the Famous area, in conjunction with a detailed study of the chemical compositions of phenocryst minerals and associated melt inclusions are used to place constraints on the genetic relationship among the various lava types. The distribution of NiO in olivine and Cr-spinel phenocrysts distinguishes the picritic basalts, plagioclase phyric basalts and plagioclase-pyroxene basalts from the olivine basalts. For a given Mg/Mg+Fe2+ atomic ratio of the mineral, the NiO content of these phenocrysts in the former three basalt types is low relative to that in the phenocrysts in the olivine basalts. The Zr/Nb ratio of the lavas similarly distinguishes the olivine basalts from the plagioclase phyric and plagioclase pyroxene basalts and, in addition, distinguishes the picritic basalts from the other basalt types. These differences indicate that the different magma groups could not have been processed through the same magma chamber, and preclude any direct inter-relationship via open or closed system fractional crystallization. The Fe-Mg partitioning between olivine and host rock suggests that the picritic basalts represent olivine (±Cr-spinel) enriched magmas, derived from a less MgO rich parental magma. The partitioning of Fe and Mg between olivine, Cr-spinel and coexisting liquid is used to predict a primary magma composition parental to the picritic basalts. This magma is characterized by relatively high MgO (12.3%) and CaO (12.6%) and low FeO* (7.96%) and TiO2 (0.63%). Least squares calculations indicate that the plagioclase phyric basalts are related to the plagioclase-pyroxene basalts by plagioclase and minor clinopyroxene and olivine accumulation. The compositional variations within the olivine basalts can be accounted for by fractionation of plagioclase, clinopyroxene and olivine in an open system, steady state, magma chamber in the average proportions 45∶32∶23. It is suggested that the most primitive olivine basalts can be derived from a pristine mantle composition by approximately 17% equilibrium partial melting. Although distinguished by its higher Zr/Nb ratio and lower NiO content of phenocryst phases, the magma parental to the picritic basalts can be derived from a similar source composition by approximately 27% equilibrium partial melting. It is suggested that the parental magma to the plagioclase-pyroxene and plagioclase phyric basalts might have been derived from greater depth resulting in the fractionation of the Zr/Nb ratio by equilibration with residual garnet.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01161499

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5

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Pattern of opening rates along the axis of the Mid-Atlantic Ridge (1982)

Douaran, S. Le ; Needham, H. D. ; Francheteau, J.

[s.l.] : Nature Publishing Group

Nature 300 (1982), S. 254-257

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Six R/V Jean Charcot magnetic profiles approximately normal to the strike of the Mid-Atlantic Ridge were acquired during the 1977 Vema cruise in conjunction with multi narrow-beam bathymetry obtained with the Seabeam system8'9. The Seabeam bathymetry demonstrates that each profile is within one ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/300254a0

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6

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Inner floor of the Rift Valley: first submersible study (1974)

BELLAICHE, G. ; CHEMINEE, J. L. ; FRANCHETEAU, J. ; [et al.]

[s.l.] : Nature Publishing Group

Nature 250 (1974), S. 558-560

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Fig. 1 Topographic cross section of the Rift Valley near 36° 50'N, based on surface-ship data2, showing the setting of the Inner Floor in the area of the Archimede dives (Fig. 2). Needham and Francheteau2 showed that, in the area visited by Archimsde, steep, inward facing slopes of the deepest ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/250558a0

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7

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Massive deep-sea sulphide ore deposits discovered on the East Pacific Rise (1979)

Francheteau, J. ; Needham, H. D. ; Choukroune, P. ; [et al.]

[s.l.] : Nature Publishing Group

Nature 277 (1979), S. 523-528

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Massive ore-grade zinc, copper and iron sulphide deposits have been found at the axis of the East Pacific Rise. Although their presence on the deep ocean-floor had been predicted there was no supporting observational evidence. The East Pacific Rise deposits represent a modern analogue of ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/277523a0

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8

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First manned submersible dives on the East Pacific Rise at 21°N (project RITA): General results (1981)

Francheteau, J. ; Needham, H. D. ; Choukroune, P. ; [et al.]

Springer

Marine geophysical researches 4 (1981), S. 345-379

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ISSN: 1573-0581

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract A submersible study has been conducted in February–March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera-Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of gian size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00286034

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