Abstract
The mode of occurrence, fabric, mineralogical and chemical features of ultrabasic inclusions in basalts of the South Far East are discussed in detail and compared with similar inclusions from various parts of the world. The inclusions occur mostly in alkalic varieties of basalt and commonly have cataclastic fabrics exhibiting preferred orientation of grains. They consist principally of olivine, enstatite or bronzite, chrome-diopside and spinel. Except for spinel, the compositions of the minerals are remarkably similar on a world-wide basis, whereas the enclosing rocks are represented by a variety of alkalic basalts. Chromium content of the inclusions is usually high compared to very low values for enclosing basalt. It is concluded that such inclusions are xenoliths of ultrabasic rocks rather than indigenous crystal differentiates. Their most plausible derivation is from the peridotite layer. This hypothesis explains their consistent composition, their association with deep rifts, the undifferentiated natu...
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