Basalt oceanic

The redox properties of these systems are vitally important for possible abiotic chemical syntheses the main minerals present in young basalt ocean basins, at depths between 300 and 1,300 m, are pyrite (FeS2), pyrrhotite (FeS) and magnetite (Fe3C>4) (the PPM system). 

A number of models have been proposed which link crustal evolution with the mantle Nd-isotope evolution curve, the most realistic of which is probably the transport-balance model of Nagler and Kramers (1998). This model is based upon their empirically derived Nd-isotope mantle evolution curve and assumes that the upper mantle melts to form basaltic oceanic crust, which is then reprocessed to form continental crust. An important aspect of the model is that it also includes crustal recycling, such that as the volume of continental crust grows with time, proportionately some crust is recycled back into the mantle through erosion and subduction. 

Bach W., and Edwards, K.J., 2003. Iron and sulfide oxidation within the basaltic ocean crust Implications for chemolithoautotrophic microbial biomass production. Geochimica et Cosmochimica Acta, 67 3871-3887. 

Table 1.1 also contains data for average concentrations of the 25 selected elements in the oceanic crust. As a first approximation, we have assumed for this part of the compilation that the oceanic crust mainly consists of the so-called ocean ridge basalt (MORE). Large volumes of this basaltic ocean crust have undergone hydrothermal alteration connected with a gain of H2O, CO2, Na, Mg and S from heated sea water and losses of Si, Ca, Ee, Mn, etc. from the altered basalt to the ocean water reservoir. 

Oceanic-arc — dominated by tholeiltic basalts Oceanic-arc — dominated by calc-alkali basalts 5-ActivB continental margin , , ... 

The different basalt fields are subdivided according to Ti/V ratio (Figure 5.10). MORB plote between Ti/V ratios of 20 and 50, although there is considerable overlap with the fields of continental flood basalt and back-arc basin basalts. Ocean-island and alkali basalts plot between Ti/V ratios of 50 and 100. Island-arc tholeiites plot between Ti/V ratios of 10 and 20 with a small overlap onto the field of MORB, Calc-alkali lavas plot with a near-vertical trend and with Ti/V ratios between 15 and 50. 

A plot of FI and F2 separates MORE, volcanic-arc basalts, shoshonites and within-plate basalts (ocean-island basalts and continental tholeiites) from each other (Figure 5.19a). A plot of F2 and F3 separates island-arc tholeiites, cak-alkali basalts... 

Northern Hemisphere Reference Line — a line against which enrichment in Pb isotopes may be measured in the mantle source of oceanic basalts Ocean-Island Alkali Basalt, ... 

Ocean-Island Basalt Ocean-Island Tholeiite -Ocean-Ridge Granite... 

Titanomaghemites are the main magnetic constituents in the basaltic oceanic basement, but they also occur in continental igneous rocks" (Bleil and Petersen, 1982). 

Ocean Basins. Ocean basins are primarily formed from oceanic basalts and maybe interspersed with continental remnants, ridges, seamounts, or volcanic islands rising from the depths. Average water depth is around 4000 m but the most significant mineralization is generally found at 5000 m for manganese nodules, 4000 m for biogenic oozes, and 3000 m for hydrothermal metalliferous sulfides. The area is poorly explored, however. 

The flow of hydrothermal solutions iato the oceans from hydrothermal vents, ie, springs coming from the sea floor ia areas of active volcanism, and the chemical reactions occurring there by high temperature alteration of basalts ate of significance ia the mass balance of and. Eurthermore,... 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

Fig. 9-4 Photograph of landslides (soil avalanches) that occurred following earthquakes in Panama on July 17,1976, near Jaque. In the background is a bay of the Pacific Ocean. The effects of this earthquake are described by Garwood et al. (1979), who estimated that about 42 km (about 10%) of the region near the epicenter of the earthquake was devegetated. The bedrock is mostly island-arc basalts and andesites. (Photography by N. C. Garwood.)...

In Fig. 1.85 iron contents of epidote from two different geologic environments, island arc and oceanic ridge or ophiolite, are summarized. It can be seen in Fig. 1.85 that the iron content of epidote from ridge basalt and ophiolite is generally lower than... 

Humphris, S.E. and Thompson, G. (1978) Hydrothermal alteration of oceanic basalts by seawater. Geochim. Cosmochim. Acta, 42, 107-125. 

Wolery, T.J. (1978) Some chemical aspects of hydrothermal processes at midoceanic ridges — A theoretical study I, Basalt-seawater reaction and chemical cycling between the oceanic crust and the oceans. II, Calculation of chemical equilibrium between aqueous solutions and minerals. Ph.D. Thesis, Northwestern U. 

Bulk rock chemistry of hydrothermally altered midoceanic ridge basalt has been well studied and used to estimate the geochemical mass balances of oceans today (Wolery and Sleep, 1976 Humphris and Thompson, 1978 Mottl, 1983). In contrast, very few analytical data on hydrothermally altered volcanic rocks that recently erupted at back-arc basins are available. However, a large number of analytical data have been accumulated on the hydrothermally altered Miocene volcanic rocks from the Green tuff region in the Japanese Islands which are inferred to have erupted in a back-arc tectonic setting (section 1.5.3). 

Fame G (1986) Principles of Isotope Geology, Second Edition. John Wiley and Sons, New York Fleischer RL, Raabe OG (1975) Recoiling alpha-emitting nuclei. Mechanisms for uranium-series disequilibrium. Geochim Cosmochim Acta 42 973-978 Goldstein SJ, Murrell MT, Williams RW (1993) Pa and h chronology of mid-ocean ridge basalts. Earth Planet Sci Lett 115 151-159... 

Goldstein SJ, Murrell, MT, Wilhams RW (1993) Pa and h chronology of mid-ocean ridge basalts. Earth Planet Sci Lett 115 151-159... 

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