Mineralogy and chemistry of basalts and secondary minerals from DSDP Site 417, Atlantic Ocean


Autoria(s): Alt, Jeffrey C; Honnorez, Jose J
Cobertura

MEDIAN LATITUDE: 25.111250 * MEDIAN LONGITUDE: -68.045450 * SOUTH-BOUND LATITUDE: 25.111000 * WEST-BOUND LONGITUDE: -68.046800 * NORTH-BOUND LATITUDE: 25.111500 * EAST-BOUND LONGITUDE: -68.044100 * DATE/TIME START: 1976-12-02T00:00:00 * DATE/TIME END: 1976-12-30T00:00:00

Data(s)

02/11/1984

Resumo

Basalts from DSDP Site 417 (109 Ma) exhibit the effects of several stages of alteration reflecting the evolution of seawater-derived solution compositions and control by the structure and permeability of the crust. Characteristic secondary mineral assemblages occur in often superimposed alteration zones within individual basalt fragments. By combining bulk rock and single phase chemical analyses with detailed mineralogic and petrographic studies, chemical changes have been determined for most of the alteration stages identified in the basalts. 1) Minor amounts of saponite, chlorite, and pyrite formed locally in coarse grained portions of massive units, possibly at high temperatures during initial cooling of the basalts. No chemical changes could be determined for this stage. 2) Possible mixing of cooled hydrothermal fluids with seawater resulted in the formation of celadonite-nontronite and Fe-hydroxide-rich black halos around cracks and pillow rims. Gains of K, Rb, H20, increase of Fe 3 +/FeT and possibly some losses of Ca and Mg occurred during this stage. 3a) Extensive circulation of oxygenated seawater resulted in the formation of various smectites, K-feldspar, and Fe-hydroxides in brown and light grey alteration zones around formerly exposed surfaces. K, Rb, H20, and occasionally P were added to the rocks, Fe3+/FeT increased, and Ca, Mg, Si and occasionally Al and Na were lost. 3 b) Anoxic alteration occurred during reaction of basalt with seawater at low water-rock ratios, or with seawater that had previously reacted with basalt. Saponite-rich dark grey alteration zones formed which exhibit very little chemical change: generally only slight increases in Fe 3 +/FeT and H20 occurred. 4) Zeolites and calcite formed from seawater-derived fluids modified by previous reactions with basalt. Chemical changes involved increases of Ca, Na, H20 , and CO2 in the rocks. 5) A late stage of anoxic conditions resulted in the formation of minor amounts of Mn-calcites and secondary sulfides in previously oxidized rocks. No chemical changes were determined for this stage. Recognition of such alteration sequences is important in understanding the evolution of submarine hydrothermal systems and in interpreting chemical exchange due to seawater-basalt reactions.

Formato

application/zip, 8 datasets

Identificador

https://doi.pangaea.de/10.1594/PANGAEA.667336

doi:10.1594/PANGAEA.667336

Idioma(s)

en

Publicador

PANGAEA

Direitos

CC-BY: Creative Commons Attribution 3.0 Unported

Access constraints: unrestricted

Fonte

Supplement to: Alt, Jeffrey C; Honnorez, Jose J (1984): Alteration of the upper oceanic crust, DSDP site 417: mineralogy and chemistry. Contributions to Mineralogy and Petrology, 87(2), 149-169, doi:10.1007/BF00376221

Palavras-Chave #-; *; +; 060 Spacing; 51-417_Site; 52-417D; Al; Al2O3; Aluminium; Aluminium oxide; ambiguous, given as hole/core/sect./no; Ca; Calcium; Calcium oxide; CaO; Carbon dioxide; Clay min; Clay minerals; CO2; COMPCORE; Composite Core; Copper; Cu; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; Electron microprobe; Fe; Fe2+; Fe2+/Fe total; Fe2O3; Fe3+; FeO; Glomar Challenger; H2O; interlayer; Iron 2+; Iron 2+/Iron total ratio; Iron 2+ and 3+; Iron 3+; Iron oxide, Fe2O3; Iron oxide, FeO; K; K2O; Leg51; Leg52; Lithology; Lithology/composition/facies; Magnesium; Magnesium carbonate, magnesite; Magnesium oxide; Manganese; Manganese oxide; maximum; Mg; MgCO3; MgO; minumum; Mn; MnO; Na; Na2O; Ni; Nickel; No O; North Atlantic/CONT RISE; Number of oxygens; octahedral; ODP sample designation; P2O5; Phosphorus oxide; Potassium; Potassium oxide; Rb; Rubidium; Samp com; Sample code/label; Sample comment; Sample Method; Si; Silicon; Silicon dioxide; SiO2; Sodium; Sodium oxide; Sr; Strontium; tetrahedral; Ti; TiO2; Titanium; Titanium oxide; total; Water in rock; X-ray diffraction; X-ray fluorescence (XRF); Y; Yttrium; Zinc; Zirconium; Zn; Zr
Tipo

Dataset