Rocks mafic rock

This is divided into a western, a central and an eastern sector. The western Aeolian arc (Alicudi, Filicudi, Salina) consists of calc-alkaline rocks with typical island arc signatures. Mafic and intermediate rocks dominate the volcanic sequence, with minor silicic volcanics. The central islands (Vul-cano and Lipari) are dominated by calc-alkaline to shoshonitic mafic to silicic rocks mafic rocks from this sector show isotopic compositions and incompatible trace element ratios similar to the western islands. The eastern arc (Panarea and Stromboli) consists of calc-alkaline to potassic alkaline rocks. Stromboli shows geochemical and isotopic signatures akin to the Neapolitan volcanoes. The Island of Panarea, located between Stromboli and Lipari, has intermediate characteristics between these two volcanoes (Calanchi et al. 2002a). 

Blundy JD, Brooker RA (2003) Trace element partitioning during melting and ciystalhzation of mafic rocks in the lower crust. Contrib Mineral Petrol (submitted). 

Figure 5 presents Ni in 0-5-cm soils. There are no notable elevated concentrations of Ni in the region, with the exception of northern Maine and north-central New Brunswick. Figure 6 displays Ni in the C-horizon where there is a distinctive elevated Ni signature spatially correlative with the mafic rocks of northern New Brunswick that host mineralization at the Bathurst mining camp. 

Acidic rock Inter- mediat e rock Basic rock Ultra- mafic rock Sand- stone Shale Carbo nate Gneis s Leptit e Amphi bolite Meta- pelite Marbl e Alluvia I plain soil Soil Stream sedimen t shallow sea edimen t... 

Heinrich CA (1986) Eclogite facies regional metamorphism of hydrous mafic rocks in the Central alpine Adula nappe. J Petrol 27 123-154... 

Alteration in Allende chondmle C6 is concentrated at the margins where 5 Mg values are low (Fig. 17). Evaluation of the likelihood that low 8 Mg values could be the result of aqueous alteration will require studies of Mg isotope fractionation during low-T alteration of terrestrial mafic rocks. An alternative explanation is that low 8 Mg and alteration resulted from condensation (collision frequency of gaseous Mg is greater for the lighter isotopes). 

Hatton CJ, Sharpe MR (1989) Significance and origin of boninite-like rocks associated wifii file Bushveld Complex. In Boninite Crawford AJ (ed) Unwin Hyman, Boston, p 174-207 Helz RT (1985) Compositions of fine-grained mafic rocks from sills and dikes associated wifii the Stillwater complex. In Stillwater complex, geology and guide. Special Pub 92. Czamanske GK, Zientek ML (eds) Montana Bureau of Mines and Geology, p 97-117... 

The felsic rocks have negative Sr and Eu anomalies suggesting plagioclase fractionation. Zr/AbOs appears to be the best criteria for the discrimination of volcanic rocks and related volcaniclastic sedimentary rocks, because the rocks have been hydrothemally altered AI2O3 is the most conserved. The mafic rocks are dominantly of transitional alkaline to calc-alkaline affinity with high Cr and Ni... 

No rock samples have been collected from Mercury and Venus, and the arsenic chemistry of their crusts is unknown. Like the Moon, the crustal rocks on Mercury, Venus, and Mars are primarily basalts and other mafic rocks. If the trace element chemistry of their basalts is similar to lunar specimens, they should contain <1 mg kg-1 of arsenic. 

Basalts and gabbros are the dominant igneous rocks in oceanic crusts. In rare circumstances, the mafic rocks of the oceanic crust (e.g. at the Mid-Atlantic Ridge) contain various arsenic minerals, including... 

Felsic Describes an igneous rock, lava, or magma that is relatively enriched in silica (>66wt% as Si02) and is generally more depleted in magnesium and iron than intermediate and mafic rocks (Hyndman, 1985), 42 (Press and Siever, 2001), 74. 

Although present in small amounts, mafic rocks (here defined as those with MgO > 4 wt % ) are particularly interesting since they represent the closest relatives of primary melts generated in the upper mantle. 

A limit of MgO > 3 wt% has been chosen for provinces or volcanoes where mafic rocks are scarce. 

Fig. 1.4. Patterns of incompatible elements normalised against mantle compositions (Wood 1979 Sun and McDonough 1989) for some representative Italian Plio-Quatemary mafic rocks.

Sr, Nd and Pb isotopic ratios of mafic rocks (Fig. 1.7) show large and continuous variations. However, various regions exhibit rather restricted and distinct isotopic signatures (Conticelli et al. 2002 and references therein). Oxygen isotopic data are also variable in the volcanic rocks from central-southern Italy. Data on whole rocks have brought to the conclusion... 

Fig. 1.5. ThYb vs. Ta/Yb discriminant diagram (Pearce 1982) for representative Plio-Quatemary mafic rocks (MgO > 4 wt %) from Italy.

Fig. 1.8. Magmatic provinces in Italy, as identified from major, trace element and isotopic characteristics of mafic rocks. The Ancona-Anzio, Ortona-Roccamonfina, 41° Parallel, Tindari-Letojanni-Malta and the Sangineto tectonic lines are also indicated. Inset distribution of volcanism with orogenic (i.e. high LILE/HFSE ratios) and anorogenic (i.e. low LILE/HFSE ratios) compositions. Arrows indicates migration of orogenic magmatism from Oligocene to present. See text for explanation.

This province is characterised by the close association of KS and HKS rocks, showing diverse geochemical and isotopic signatures. Some low-potassium mafic rocks falling in the calc-alkaline compositional field have been also found. Potassic rocks display ratios of some incompatible trace elements such as Ba/La, and radiogenic isotope signatures that are close to those of the Neapolitan volcanoes (Vesuvio, Campi Flegrei, Ischia). On the contrary, ultrapotassic rocks resemble the Colle Albani and other Roman volcanoes. Therefore, the Ernici-Roccamonfina zone is characterised by the coexistence of Roman-type and Campanian-type rocks. 

The mafic rocks (MgO > 3 wt %) range from calc-alkaline and sho-shonitic to potassic and ultrapotassic (Fig. 2.2b). The Tuscan ultrapotassic... 

Fig. 2.2. A) TAS classification diagram of Tuscany magmatic rocks. Note that TAS nomenclature applies to volcanic rocks only. The dashed line divides the subalkaline and alkaline fields (Irvine and Baragar 1971). B) AQ vs. K20/Na20 diagram for mafic rocks (MgO > 3 wt%) of the Tuscany Province. For definition of AQ see Chap. 1.

Sr-Nd-Pb-Hf isotope ratios display comparable range of values in the silicic and mafic rocks and are closer to crustal than to mantle compositions (Fig. 2.4 Vollmer 1976 Hawkesworth and Vollmer 1979 Conticelli et al. 2002 Gasperini et al. 2002 author s unpublished data). These crustal-like isotopic signatures have led early authors to suggest a crustal... 

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