【摘要】 本文首次报道了侵位于狮泉河蛇绿岩（蛇纹石化超基性岩）中的具有OIB性质的辉绿岩以及赞岐岩型的高镁闪长岩。其中闪长岩具有较高的TiO₂、Y及Yb含量,较低的Sr/Y比值和La/Yb比值,与日本Setouchi火山岩带的赞岐岩以及前人报道的同期洋内初始俯冲成因相关的高镁安山岩性质一致。辉绿岩富LREE,高Zr/Y、TiO₂/Yb和Nb/Yb比值,Nb、Ti负异常,Pb正异常,表现出了俯冲带相关的OIB性质;采用LA-ICP-MS锆石U-Pb定年方法,测得辉绿岩脉的成岩年龄为163. 7±0. 54Ma（MSWD=3. 8）,且该年龄与前人报道的160. 8±2. 3Ma的高镁安山岩年龄较为接近。综合分析本文及前人年代学与岩石地球化学相关数据,认为狮泉河辉绿岩和闪长岩同时形成于洋内俯冲的初始阶段。这种岩石组合与太平洋IBM岛链初始俯冲的岩石组合相似,但该OIB成因机制中俯冲作用与地幔柱之间的相互关系仍需进一步讨论。更多还原

【Abstract】 This paper for the first time reports OIB-type diabase intruding into the Shiquanhe ophiolite,as well as diorite with high magnesium andesite（ HMA） properties. The diorites have high TiO₂,Y and Yb contents,lower Sr/Y and La/Yb ratios,which is consistent with the high-magnesia andesite associated with the sanukite rock in the Setouchi volcanic rock belt in Japan and the initial inner-oceanic subduction reported by the predecessors. Based on LA-ICP-MS zircon U-Pb isotope dating,the OIB-type diabase yields a zircon U-Pb weighted mean age of 163. 7 ± 0. 54 Ma（ MSWD = 3. 8）. The measured samples have SiO₂ of 40. 93% ～ 49. 88% and Mg^# of 46. 3 ～ 60. 4,with the following geochemical characteristics: rich in LREE,with high Zr/YTiO₂/Yb and Nb/Yb ratios,Nb and Ti negative anomalies,and Pb positive anomalies,indicating OIB properties associated with a subduction zone. Putting the OIB-type diabase and associated HMA-type diorite back to the Shiquanhe ophiolite background,it is inferred that the Shiquanhe diabase and diorite are simultaneously formed in the initial stage of oceanic crust subduction. Besides,the timing of initial subduction associated with the Shiquanhe ophiolite is much later than that of the Bangong-Nujiang suture zone,suggesting that ophiolites from the two belts represent remnants of separate oceanic crusts. The rock assemblage of the studied samples is similar with the synchronous HMA-type diorite,while the OIB-type diabase from the Shiquanhe ophiolite is similar to the rock assemblage in the Izu-Bonin-Mariana island arc（ Southwest Pacific） formed during the initial stage of oceanic subduction,suggesting the presence of an early stage oceanic subduction zone in the late Mid-Jurassic time,but the relationship between the subduction and the OIB genesis remains uncertainty and needs further studying.更多还原