塞浦路斯的超镁铁质熔岩——太古代科马提质玄武岩的类似物

塞浦路斯特罗多斯蛇绿岩套上部枕状熔岩中见有超镁铁质枕状熔岩的小型孤立体。一般可分为细粒、无斑隐晶质到含少量橄榄石斑晶的和细粒,含大量橄榄石斑晶的两种。橄榄石斑晶为自形—半自形,或空心骸晶,粒径0.1—3毫米,最大可达5毫米左右,成分为Fo_(37-91)。分布于玻璃基质中的普通辉石呈针状、束状(扇形集合体)和骸状,晶体长0.3—1.5毫米,宽仅0.04—0.06毫米,具典型的鬣刺结构。超镁铁质熔岩的MgO含量为10—30%,Mg/Mg+Fe~(2+)均在0.8左右,CaO/A1_2O_3为0.8—1.5,多在0.8左右,TiO_2平均含量为0.32%。稀土元素配分模式属轻稀土亏损,重稀土平坦型。以上特征表明把它们称为科马提质玄武岩是合适的。

Analogues of Komatiitic Basalts: Ultramafic Lavas From Cyprus

Some small isolated masses of ultramafic lavas have been found in the Upper Pillow Lava of the Troodos ophiolite complex, Cyprus. The ultramafic outcrops described here occur some 13 miles to the south-west of Nicosia, near the village of Margi. Two samples (79-4-2 and 79-4-4) were collected from this area in 1979. In this paper an account is given of their petrography, mineralogy and chemistry. We wish to emphasize some of these rocks are analogues of komatiitic basalts. Our study, although preliminary, shows that there is a remarkable similarity in texture, mineralogy, marjor element and trace element composition of the rocks for comparison with komatiitic basalts.