G gabbros

During the formation of the magma by partial melting of a mechanical mixture of mantle-derived rocks and crustal rocks (e.g., gabbro dikes that intruded the deep continental crust)... 

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... 

Most of the other pristine nonmare rocks are Mg-suite rocks troctolitic, noritic, and gabbro-noritic rocks that, based on evidence from a few texturally pristine samples (e.g., Dymek et al., 1975 Marvin and Warren, 1980), probably all formed as cumulates. The highest-mg cumulates include several with ultramafic modes, but only one of these, dunite 72415 (Dymek et al., 1975), has a mass >1 g (Figure 14), so many of them may actually be grossly unrepresentative samples of troctolites. High-Ca pyroxene apparently... 

The ophiolite consists of several large massifs. Each of them exposes a more or less complete ophiolitic sequence, comprising a thick mantle section (up to 12 km), a gabbro sequence (0.5-6 km), a sheeted dike complex (1-1.5 km), a thick extrusive sequence (0.5-2 km), and interbedded oceanic sediments (e.g., Lippard et al., 1986). 

Bezzi A. and Piccardo G. B. (1971) Structural featrrres of the Ligurian ophiolites petrologic evidence for the oceanic floor of the Northern Apennines geosyncline a contribution to the problem of the alpinetype gabbro-peridotite associations. Mem. Soc. Geol. Italiana 10, 53-63. 

Bonatti E., Honnorez J., and Eerrara G. (1971) Peridotite-gabbro-basalt complex from the equatorial mid-Atlantic ridge. Phil. Trans. Roy. Soc. London A268, 385 -402. 

Zhang R. Y. and Liou J. G. (1997) Partial transformation of gabbro to coesite-bearing eclogite from Yangkou, the Su-Lu terrane, eastern China. J. Metamorph. Geol. 15,183—202. 

A third approach that is commonly used to constrain chemical fluxes compares differently altered materials, such as altered pillow margins and less altered pillow interiors, or samples with or without alteration haloes around veins (e.g., Alt et al., 1986), mineralized and unmineralized zones or differently altered gabbros (e.g., Bach et al., 2001) in order to constrain chemical changes associated with alteration. However, least altered samples only rarely reflect the original composition reliably. A second problem in this approach is the relatively small sample sizes typically analyzed from ocean drilling materials. Typical sample sizes are about 15 cm, which is small when compared with local variability in modal mineralogy. Indeed, individual phenocryst phases can be several millimeters in size. Local variability in modal mineralogy is particularly common in pillow lavas where phenocryst abundances can vary as a function of radial distance from the center or vertically within the center... 

Fresh MORE Units Bulk rock gains (+) and losses ( —) for extrusives Dikes Gabbros Average crustal gainsAosses Units Total flux from crust Units Hydrothermal fluxes from submarine vents (gyr ) River fluxes (g yr )... 

Chinner G. A. and Dixon J. E. (1973) Some high-pressure paragenesis of the allalin gabbro, Valais, Switzerland. J. Petrol. 14, 185-202. 

Aherns, T. J. Schubert, G. 1975. Gabbro-eclogite reaction rate and its geophysical significance. Reviews of Geophysics and Space Physics, 13, 383-400. 

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