Ultramafic Inclusions

McGibbon (1991) determined that the spinel Iherzolite inclusions record temperatures between 880°C and 1,100°C which implies that they originated from the mantle at depths of 35-70 km. The depth of origin of the clinopyroxenite and glimmerite inclusions is restricted by the stability of plagioclase to less than 30 km. 

McGibbon (1991) also reported that the Sr/ Sr and ratios of spinel Iherzolite and clinopy- 

The inclusions of crustal rocks in the lava flows of the Erebus volcanic province consist of lower-crustal granulites, upper-crustal basement rocks, and supra-crustal rocks. Berg (1991) described inclusions from 17 sites in the Erebus volcanic province, 7 of which are located in the Royal Society Range (Brandau Vent, Roaring Valley, Foster Crater, Ward Valley, The Bulwark, Lower and Upper Radian Glacier) and five on Ross Island (Cape Crozier, Cape Bame, and at three places on the Hut Point Peninsula). 

The boulders of Cenozoic rocks that occur in the Discovery subprovine and along the coast of McMurdo Sound were collected and dated by the fossils they contain (Harrington 1969 Stott et al. 1983 Stilwell etal. 1993). 

The upper-crustal inclusions described by Berg (1991) consist of granitic and metamorphic rocks of the basement complex that underlies the Transantarctic Mountains. The metamorphic rocks are primarily quartzites, calc-siUcate gneisses, and pelitic schists some of which contain sillimanite. The upper-crustal inclusions are particularly abundant at sites in the Transantarctic Mountains but also occur at other sites where inclusions are present. 

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Frey F. A. and Prinz M. (1978) Ultramafic inclusions from San Carlos, Arizona petrologic and geochemical data bearing on their petrogenesis. Earth Planet. Sci. Lett. 38, 139—176. 

Galer S. J. G. and O Nions R. K. (1989) Chemical and isotopic studies of ultramafic inclusions from the San Carlos Volcanic Field, Arizona a bearing on their petrogenesis. J. Petrol. 30, 1033-1064. 

Baldridge W. S. (1979) Mafic and ultramafic inclusion suites from the Rio Grande Rift (New Mexico) and their bearing on the composition and thermal state of the lithosphere. J. Volcanol. Geotherm. Res. 6, 319—351. 

Tanaka T. and AoM K.-I. (1981) Petrogenetic implications of REE and Ba data on mafic and ultramafic inclusions from Itinome-gata, Japan. J. Geol. 89, 369-390. 

Funkhauser JG, Naughton JJ (1968) Radiogenic hehum and argon in ultramafic inclusions from Hawau. J Geophys Res 73 4601-4608... 

The ultramafic inclusions in Fig. 16.6c have a bimodal distribution of the Sr/ Sr ratios and a low average Rb/Sr ratio of 0.030 0.038 (la). Three friable inclusions define a straight line on the Rb-Sr geo-chronometry diagram in Fig. 16.7 that corresponds to a date of 1,140 Ma (k = 1.42 x 10" year 0 and an initial Sr/ Sr ratio of 0.70345. The geological significance of this date is questionable because it relies entirely on the elevated Sr/ Sr ratio of sample CC-82 which has a low strontium concentration of only 3.01 ppm and is therefore susceptible to contamination by ground water or meltwater. 

Fig. 16.7 The ultramafic inclusions that were erupted with the Cenozoic alkali-rich lavas at Cape Crozier (CC-82) and Cape Bird (CB-64) on Ross Island and at Brandau vent (BV-5g) in the Royal Society Range define a straight line that yields a date of 1140 Ma. This date is largely based on the sample of trachyte (CC-82) which contains only 3.01 ppm of strontium and is susceptible to contanunation by radiogenic Sr. Therefore, the geological significance of the Rb-Sr date is questionable (Data from Stuckless and Ericksen (1976))...

In conclusion, Berg (1991) pointed out that ultra-mafic inclusions that contain orthopyroxene resemble the two-pyroxene granulite inclusions and, in some cases, are interbedded with them in the largest specimens. However, as noted before, the ultramafic inclusions are not genetically related to the Ferrar Dolerite or to the Cenzoic alkalic lavas of the McMurdo Volcanic Group (McGibbon 1991). 

Hamilton E. 1. The abundance and distribution of uranium in some oceanic, continental ultramafic inclusions and host basalts. Chem. Geo ., 16, 1975, 221-31. 

Clearly, there is no simple interpretation of ultramafic inclusions in lavas in terms of primitive lanthanide distributions or lanthanide distributions complementary to those found in the crust. Some peridotites do have nearly chondritic lanthanide distributions, some are strongly depleted in light lanthanides, but most nodules in lavas are enriched in light lanthanides relative to chondrites. 

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