我国金伯利岩中的深源岩石包体

作者研究发现山东胜利1号、辽宁50号、51号及42号岩体中,见有纯橄岩、石榴二辉橄榄岩、尖晶二辉橄榄岩及云母橄榄岩包体;河北涉县及山东红旗2号金伯利岩中见有榴辉岩包体。包体形态为浑圆状、椭圆状,其大小为1-15cm。纯橄岩和石榴二辉橄榄岩比其寄主金伯利岩富含Cr_2O_3、NiO_3、贫CaO、CO_2、K_2O、Na_2O、TiO_2和Al_2O_3,其稀土配分模式为LREE富集型。根据深源岩石包体的温度、压力条件的估算,认为纯橄岩和石榴二辉橄榄岩来自上地幔深处,为上地幔局部熔融的残余物,而河北涉县金伯利岩中榴辉岩包体来自下地壳,云母橄榄岩类为软流圈顶部的地幔交代作用带上的岩石,尖晶二辉橄榄岩是来自上地幔较浅部位,它们为金伯利岩浆的偶然捕虏体。

DEEP SEATED XENOLITHS IN KIMBERLITES FROM CHINA

The ultramafic xenoliths in kimberlites from China have been found from Shengli-1 pipe of Shandong, and No. 50, No. 51, No. 42 pipes of Liao- ning, they are predominatly dunites, garnet Iherzolites, followed by spinel Iherzolites and mica peridotites. The eclogite xenoliths have been found in Hebei kimberlites and Hongqi-2 dike of Shandong. Most of the xenoliths are extensively altered. The form of the xenoliths range from spherical or ellipsoidal to tabular. Their size ranges from less than a centimetre to 15cm in diameter. The xenoliths larger than 15 cm are rare. Dunites and garnet lherzolites are richer in Cr2O3, NiO, and pooer in CaO, CO2, (K2O + Na2O), TiO2 and Al2O3 than those of host kimberlites, and are characterized by simple linear REE distribution pattern showing light REE enrichment.Most of the garnet Iherzolites extend from the depth of 100 - 180km. Spinel Iherzolites occur at depth of 83 - 120 km. Mica-rich peridotites apparently is restricted to the uppermost mantle zone. Eclogite nodules in Hebei kimberlites that formed at the low equilibration temperatures and pressure conditions are believed to have been derived from lower crust. Mica-rich peridotites and spinel lherzolites are accidental xenoliths, but most of garnet lherzolites and dunites are residues during partial melting of upper mantle materials.