Basalt continental

The La-Y-Nb Using a comparatively small number of samples, Cabanis and Lecolle (1989) diagram of constructed a triangular diagram based upon La-Y—Nb concentrations which Cabanis and discriminates between volcanic-arc basalts, continental basalts and oceanic basalts. 

LIP (Large Igneous Province) is a large basaltic continental or oceanic igneous province, generally composed at the surface of flood basalts (e.g., Deccan Traps, Iceland). 

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. 

Positive Eu anomaly is observed for hydrothermal solution issuing from the hydrothermal vent on the seawater at East Pacific Rise (Bence, 1983 Michard et al., 1983 Michard and AlbarMe, 1986). Guichard et al. (1979) have shown that the continental hydrothermal barites have a positive Eu anomaly, indicating a relatively reduced environment. Graf (1977) has shown that massive sulfide deposits and associated rocks from the Bathurst-Newcastle district. New Brunswick have positive Eu anomalies. These data are compatible with positive Eu anomaly of altered basaltic rocks, ferruginous chert and Kuroko ores in Kuroko mine area having positive Eu anomaly and strongly support that Eu is present as divalent state in hydrothermal solution responsible for the hydrothermal alteration and Kuroko mineralization. 

Figure 7. (a) vs. Sr/ Sr diagram for mid-ocean ridge, ocean island and continental basalts... 

Asmerom Y(1999) Th-U fractionation and mantle stmctnre. Earth Planet Sci Lett 166 163-175 Asmerom Y, Edwards R L (1995) U-series isotope evidence for the origin of continental basalts. Earth Planet Sci Lett 134 1-7... 

Figure 22. U-Th equiline diagram showing U-Th isotopes may be sensitive to the effects of assimilation of pre-existing (>350 kyr) arc basalts or continental crast. This is much more complicated using long-lived isotopic systems (e.g., Sr/ Sr or " Nd/ " " Nd) because in these systems pre-existing arc basalts will be indistinguishable from new magmas and crastal assimilation will be hard to distinguish from subducted sediment addition unless assimilation is coupled to differentiation.

The Morensky-type deposits can be found in very large bodies of basaltic magma, which were intruded into stable continental rock. An example includes the Busheld Complex in South Africa and the Great Dyke of Zimbabwe. Mineralization similar to the above is also found in the Stillwater Complex in Montana, USA. 

Figure 5.9 Least-square fit of the 206Pb/204Pb ratios listed in Table 5.9 on basalts from different oceanic islands with spherical harmonics to the degree 4. The results are reported as lines of constant values. Results in continental areas are not shown. 

The early Earth was probably much more geothermaUy active than the Earth is today. [122] The continents of early Earth were most likely small with vertical profiles at, or near, sea-level. [125,181] Subaerial (in addition to submarine) tectonic rift zones and hydrothermal vent fields were probably ubiquitous and vigorous. [182] Extensive continental hydrothermal zones enriched in reducing inorganic and organic vent products and subject to wet/dry cycles were probably common. The low-profile shield continents of the early Earth must have been extensively surfaced with basalt and rhyolite, [183] some of which could have been porphyritic. 

Figure 14. Plot of Li isotopic composition vs. concentration of thermal waters from the continents and the oceans (see text for references). Differences between the isotopic range of marine versus non-marine fluids emphasizes the variability in 5 Li of continental rocks compared to oceanic basalt. The dilution of the continental fluids goes along with their lower temperatures vent fluids are the only truly geothermal samples here, with temperatures in excess of 300°C.

Support for this conclusion comes from laser ablation analyses of mantle olivines recently reported by Norman et al. (2004). The loess and continental basalt samples suggest that evolved crustal materials may be on average approximately 0.4-0.6%o lower in 5 Mg than the primitive Cl/mantle reservoir (Fig. 1). 

Figure 5. A plot of A Mg vs. 5 Mg for terrestrial Mg materials. Within best estimates of uncertainties (cross) all of the data lie in the region bounded by equilibrium and kinetic mass fractionation laws. Waters, carbonates, and organic Mg (chlorophyll) have higher A Mg values than mantle and crustal Mg reservoirs represented by mantle pyroxene, loess, and continental basalts. The difference in A Mg values is attributable to episodes of kinetic mass fractionation.

For a simple model of Ca cycling, where the Ca sources for the ocean are weathering of continental rocks, pore fluids in the marine environment, and ocean floor basalt (Gieskes and Lawrence 1981 Berner etal. 1983 Elderheld etal. 1999), and the primary sink is the biological fixation of Ca into sediments, the rate of change of 5 Ca (= 5sw ) of the oceans is given by ... 

Richter FM, Davis AM, Ehel DS, Hashimoto A (2002) Elemental and isotopic fractionation of Type B calcium-, aluminum-rich inclusions Experiments, theoretical considerations, and constraints on their thermal evolution. Geochim Cosmochim Acta 66 521-540 Richter FM, Davis AM, DePaolo DJ, Watson EB (2003) Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochim Cosmochim Acta 67 3905-3923 Rudnick RL, Fountain DM (1995) Nature and composition of the continental crust—a lower crustal perspective. Rev Geophys 33 267-309... 

The Pinguino veins, occupy more than 30 fault controlled structures. They have a NW and ENE strike and are hosted in Triassic continental sedimentary rocks and lower Jurassic epiclastic and volcaniclastic rocks, and are spatially related to lower Jurassic subvolcanic dioritic intrusions, basaltic sills and andesitic porphyries (Jovic etal. 2005). 

Mantle-derived basalts, on the other hand, have a relatively uniform composition with 8 Li values of 4 2%o (Tomaszak 2004 Elliott et al. 2004). The continental crust generally has a lighter Ei isotope composition than the upper mantle from which it was derived (Teng et al. 2004). Considering the small Li isotope fractionation at high temperature igneous differentiation processes (Tomaszak 2004), pristine... 

Fig. 3.8 Plot of 8 0 values vs Mg numbers for oceanic basalts filled circles) and continental basalts open circles). The shaded field denotes the 20 range of a MORE mean value of +S.l%o, the clear vertical field denotes the range for primary basaltic partial melts in equilibrium with a peridotitic source (Harmon and Hoefs, 1995)...

Continental basalts tend to be enriched in relative to oceanic basalts and exhibit considerably more variability in O-isotope composition, a feature attributed to interaction with 0-enriched continental crust during magma ascent (Harmon and Hoefs 1995 Baker et al. 2000). 

In order to trace the migration of basalt-derived REE in the salt, REE distribution patterns (Fig. 7) and Nd isotopic compositions (Fig. 8) have been determined in a salt horizon adjacent to a basalt dyke (Fig. 2). The flat REE distribution patterns and the almost basaltic Nd isotopic composition of the salt samples collected at the basalt-salt contact point to a basaltic origin of the REE for this sample. With increasing distance from the contact, the patterns are more and more depleted in Ce, Pr, Nd, Sm, and Eu and the Nd isotopic compositions are slightly shifted towards lower eNd values, which, however, still remain above values typical for continental crust or Permian seawater (Stille et al. 1996, and citations therein). This evolution of the REE distribution patterns and the Nd isotopic compositions could basically be due to mixing between a basalt and a salt end member or, alternatively, it could have been fractionation of the REE during migration in the salt that modified the REE patterns. 

Fig. 8. The evolution of the Nd isotopic compositions with distance in the salt profile together with the compositions of average basalt and average continental crust. The error bars represent 2 sigma mean values of the individual measurements.

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