Olivine Gabbro

Table 5.4 Olivine major element compositions (in weight %). Samples occur in different types of rocks (1) = forsterite from a metamorphosed limestone (2) = hortonolite from an olivine gabbro (3) = fayalite from a pantelleritic obsidian (4) = fayalite from an Fe-gabbro (5) = forsterite from a cumulitic peridotite (6) = forsterite from a tectonitic peridotite. Samples (1) to (4) from Deer et al. (1983) sample (5) from Ottonello et al. (1979) sample (6) from Piccardo and Ottonello (1978). ...

Geological Materials. Granite was obtained from a quarry located on the Lac du Bonnet batholith near the Whiteshell Nuclear Research Establishment. An olivine gabbro sample was obtained... 

Table 1(a). Chemical Composition of Lac du Bonnet Granite and of Olivine Gabbro used in Sorption Studies Concentration in wt%... 

HjeUe and Winsnes (1972) reported chemical analyses of basalt from several nunataks in VestfjeUa including one sample of olivine gabbro from Utpostane (Fig. 14.9). In addition, Juckes (1968, 1969) pnblished a chemical analysis of basalt from the VA Nunatak which may be Nunatak A in Fig. 14.10 according to Fig. 1 of Fumes and Mitchell (1978). Later workers (e.g., Fumes and Mitchell 1978 Fumes et al. 1987 Luttinen et al. 1998) published a large number of additional major-element and trace-elanent analyses from the nunataks of Vest ella, including Plogen and Basen (Peters et al. 1989 Luttinen and Siivola 1997 Luttinen etal. 1994,1998). 

Olivine crystallizes from magmas that are rich in magnesia and low in silica and which form such rocks as gabbros, norites, peridotites and basalts. The metamorphism of impure dolomites or other sediments in which the magnesia content is high and silica low seems to produce olivine. 

It is a coarse-grained igneous rock related to gabbro, which consists of olivine and pyroxene in varying proportions. Certain pendotites contain spinel, chromite, or mica as accessories. 

The autoradiographs of the rock and mineral thin sections (Figures 4 to 6) also confirm the importance of iron oxides although biotite.(K(Mg,Fe Si AlCLQ(0H) ) and hornblende ((Na,Ca2)(Mg,Fe )(Al,Fe )(Si AlO OH ) contain ferrous iron, sorption appears to take place solely on the small opaque (iron-oxide) inclusions. In the case of biotite, these oxides are located between the basal planes, and are randomly distributed in the hornblende. Similar distributions are observed for olivine, pyroxene, and epidote. The results for pyroxene further confirm the low sorption results obtained with gabbro, where it is one of the major minerals. 

O Hara, M.J., 1963. Distribution of iron between coexisting olivines and calcium-poor pyroxenes in peridotites, gabbros, and other magnesian environments. Am. J. Sci., 261 32-46. 

The silicates consist of mineral and lithic clasts set in a fine-grained fragmental to impact-melt matrix. The most common lithic clasts are basalts, gabbros, and orthopyroxenites, while dunites are minor and anorthosites are rare. The most common mineral clasts are centimeter-sized orthopyroxene and olivine fragments, while millimeter-sized plagioclase fragments are less common. 

This can be illustrated by a natural example. In the coarse-grained Allanin magnesium-gabbro, infiltration of fluid caused the formation of reaction rims around olivine (Chinner and Dixon, 1973). The succession is olivine anthophyllite (2 wt.% H2O) — talc (4wt.% H2O + kyanite — chloritoid (8wt.% H20- -talc + kyanite. This reaction rim is H2O undersaturated, and the succession of mineral assemblages corresponds to an increase of H2O content towards the rim and can only be modeled by an increase in the availability of water towards the rim. The H20-undersamrated character of the inner rim zones does not necessitate (or justify) a CO2 component in the fluid, but rather reflects limited availability of an H2O fluid. 

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