摘要
乳山海阳所地区超镁铁岩多以包体状赋存于新元古代片麻状二长花岗岩中，成群出现、分段集中；主要岩石类型有蛇纹石化橄辉岩、辉橄岩、透闪石化单斜辉石岩、角闪石岩和少量斜长角闪岩（变辉长岩），偶见纯橄岩；化学成分上贫镁、铝，富铁、钙，m／f比值为0．92～5．44；稀土总量为9．44×10－6～88．56×10－6，∑LREE／∑HREE=215～5．93；所含微量元素与上地幔丰度比较，其中相容元素Ni，Co均亏损，不相容元素Rb，Cs，Ta，Th，Hf则均富集。从超基性岩到基性岩的微量元素变化特点可以看出，形成超镁铁岩的构造环境曾由活动陆缘向火山岛弧发生过迁移。海阳所地区超镁铁岩的宏观特征和化学成分特点与蛇绿岩中超镁铁岩差异较大，属非蛇绿岩型的超镁铁岩，为胶南造山带形成初期的深成侵入岩。
A set of ultramafic rocks with an outcropping area of 4. 5km2 spread in Haiyangsuoarea,Rushan city of Shandong Province. They occur largely as inclusions in Neoproterozoicslightly gneissic adamellite. The individual inclusions vary in size from 1m2 for small ones to1. 7km2 for the largest one. They are elongated and as lens in shape. The direction of longaxes ranges between 60°~80°. The magnetic survey and drilling data have shown that theultramafic rocks are all rootless blocks. Serpentinized olivine pyroxenite, pyrolite,tremolitized clinopyroxenite, hornblendite and a small amount of dunite and amphibolite(metagabbro)are its major rock types. They have experienced high greenschist -facies-low amphibolite facies metamorphism and deformation. The SiO, content of the ultramaficrocks varies from 34. 04%~49. 80%, belonging to ultrabasic-basic rocks. m/f ratios arebetween 0. 92~5. 44. According to the ultrarnafic rock classification proposed by Wu Liren(1963), they belong to the ferruginous ultramafic rocks. The total rare earth element are9. 44 × 10-6~88. 56 ×10-6 with ∑LREE/∑HREE being 2. 15~7. 08 and δEu equal to 0.76~1. 37 (δEu values of the ultrabasic rocks are less than 1, while those of the basic rocksgreater than 1). On the REE distribution plot, amphibolites have flat curves, while otherrocks are of light-rare earth enrichment type with the normalized REE patterns declinedslightly to the right. In terms of the trace element contents relative to their abundances inthe upper mantle, the compatible elements, such as Ni and Co are depleted, while theincompatible elements such as Rb, Cs, Ta, Th and Hf are enriched. Compared with theMORB - amphibolite, Sr, K, Rb, Ba, Th, Ta, Nb and Ce are enriched , while Y and Yb aredepleted. As to the Serpentinized pyrolite, Rb , Cs, Ta, Th, Y and Yb are depleted; and thevariations of trace elements from ultrabasic to basic rocks reflect the migration of the tectonicenvironment from the active continental margin towards volcanic arc. The macroscopicfeatrues and chemical compositions of the ultramafic rocks all suggest that the ultramaficrocks in this region are of non-ophiolite type.The arguments are as follows: cumulatetexture are absent and no associated deep-sea sediments and pillow lavas have ever beenfound; the ultramafic rocks have intruded into the Jinshan group; and clinopyroxeniteintruded into tyrolite; and chemically, the m/f ratios are low, as contrast to the ultramaficrocks in ophiolites, for which the m/f ratios are greater than 6. 5 in general-
出处
《山东地质》
1997年第2期1-9,共9页
Geology of Shandong
