Minerals modal composition

The modal compositions of the Oseberg Formation are typical of first-cycle lithic arenites. The detrital mineral assemblage is very uniform throughout the... 

Table 1.3. Major-element composition (%) of the minerals used to calculate the composition of a gabbro with known modal abundances.

Diffusion modeling, on the other hand, also predicts that accnrate temperatnres can be obtained from refractory accessory minerals, if they occur in a rock that is modally dominated by a readily exchangeable mineral (Valley 2001). The basis of this approach is that the accessory mineral preserves the isotope composition from crystallization becanse of slow diffnsion while the dominant mineral preserves its isotope composition by mass balance because there are no other snfficiently abnn-dant exchangeable phases. 

Table 1(b). Mineral Composition of Lac du Bonnet Granite and of Olivine Gabbro used in Sorption Studies (Modal wt%)... 

The acapulcoite-lodranite clan is the prototypical primitive achondrite group. The acapulcoites have modal mineral abundances very much like those of ordinary chondrites, relict chondrules are reported from a few, and their bulk compositions are broadly chondritic (McCoy etal.,l 996 Mittlefehldt et al., 1996, 1998). The lodranites are distinctly nonchondritic. They are generally depleted in... 

Peridotite fertilization may also result from the fractional solidihcation of exotic (deep-seated) melts inhltrated in wall rocks of translithospheric magma conduits. This process was hrst described in composite mantle xenoliths (Wilshire and Shervais, 1975 Gurney and Harte, 1980 Irving, 1980 Wilshire et al., 1980 Boivin, 1982 Harte, 1983 Harte et al, 1993 Menzies et ah, 1987), where it is referred to as modal metasomatism when new (generally hydrous) minerals are precipitated (Dawson, 1984 Kempton, 1987), or Fe-Ti metasomatism (Menzies et al., 1987) when the attention is focused on chemical enrichment. In contrast with ultramafic xenoliths, the tectonically emplaced and oceanic peridotites contain only sparse rock types attributable to mantle metasomatism by deep-seated melts. Examples of wall-rock, modal, and Fe-Ti metasomatism were nevertheless described in IP orogenic Iherzolites, notably in the Pyrenees (Fabrics et al., 1989 Bodinier et al., 1988, 1990, 2003 McPherson et al., 1996 Woodland et al., 1996). 

Detailed studies of the incompatible trace-element budget of mantle xenoliths illustrate the problems. Mass balance studies that use modal analyses and mineral compositions to calculate... 

Figure 15 Illustration of the effects of host-rock contamination on whole-rock REE geochemistry. Chondrite-normalized REE patterns of measured whole-rock peridotites compared with REE abundances calculated from modal data plus mineral compositions. Also compared are mixtures of calculated whole-rock and kimberlite for each diagram. Two specimens, (a) and (b) are high-r and low-T garnet Iherzolites from Somerset Island, Nunuvut (Canada) (after Schmidberger and Erancis, 2001).

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