华北地块东段和龙超镁铁质科马提岩的发现及特征

和龙岩体赋存于新太古代夹皮沟—金城洞花岗绿岩带中,与围岩发生同变形变质。岩体具有典型的科马提岩冷凝结构分层和鬣刺结构、冷凝多面体节理。上述特征是作者1990年发现确认的。该科马提岩的矿物学特征:玻璃质脱玻形成铁皂石等矿物;斜方辉石和橄榄石鬣刺呈中空骸晶状,大部被滑石、铁白云石、绿泥石、磁铁矿等取代,但仍保留完好的长柱状假像;堆积带中橄榄石呈微细粒、新鲜,仅发生网状蛇纹石化。岩石化学特征富MgO,CaO/Al_2O_3=1.04,用科马提岩分类图判别为超镁铁质科马提岩。

Discovery and Identification of Helong Ultramafic Komatiite in the Eastern Part of North China Block

The Helong rockbody occurs in the Jiapigou - Jinchengdong granitic greenstone belt in the late Archaean, which were deformed and metamorphosed simultaneously with the wall rocks, charactered by typical chilled ko-matiite textural stratification, spinifex texture and chilled polyhedric joint. The characteristics as mentioned above are discovered and determined by the authors in 1990. The komatiite has the following mineralogical characteristics: the devitrification of rock forms such minerals as cathkinite; orthopyroxene and olivine spinifex shows intermediate hollow skeletal crystal, most of which are replaced by talc, ankerite, chlorite and magnetite , but still keeps undamaged columnar pseudomorphism; olivine in the accumulation zone shows fine, fresh and net -like serpentinization. Its petrochemical characteristics show that it is rich in MgO and CaO/Al2O3 = 1. 04. It is classified as ultramafic komatiite based on the komatiite classification map.