【摘要】 锆石LA-ICP-MSU-Pb年龄(220.6±2.0Ma)表明研究区超基性岩属于印支晚期岩浆活动的产物。主微量元素研究显示超基性岩具有相对较低的SiO2(43.22%～44.48%)、K2O(0.10%～0.17%)和Na2O(0.15%～2.13%)以及较高的MgO含量(29.23%～30.38%)和Mg#值(83～84)、轻稀土(LREE)相对富集((La/Yb)N=1.95-2.61)、缺少明显的Eu异常(δEu=0.90～1.08)、富集大离子亲石元素(Rb和Sr)和Pb、以及亏损高场强元素Nb、Ta、Zr和Ti;Sr、Nd、Hf同位素研究表明,超基性岩具有低的(87Sr/86Sr)i(0.70394～0.70408)、正的εNd(t)(3.5～4.0)和εHf(t)(9.6～14.4)。综合研究表明:红旗岭超基性岩来自亏损的岩石圈地幔源区,且源区部分熔融前受到了来自俯冲大洋(古亚洲洋)沉积物析出流体的交代作用影响。原始岩浆在上升侵位过程中经历了明显的矿物(橄榄石、斜方辉石等)分离结晶作用,但在上升过程没有受到地壳物质的明显混染。构造和动力学背景分析研究表明,研究区超基性岩为佳木斯地块和华北克拉通碰撞造山后伸展拉张阶段的产物。更多还原

【Abstract】 Zircon LA-ICP-MS U-Pb analysis yields an age of 220.6±2.0Ma for the ultramafic rocks from Hongqiling,Jilin Province,NE China,indicating that these rocks were formed during Late Indochina stage.The rocks are characterized by low SiO2 (43.22%~44.48%),K2O (0.10%~0.17%) and Na2O (0.15%~2.13%) contents,high MgO( 29.23%~30.38%) and Mg# values (83~84),enrichment in LREE ((La/Yb)N=1.95~2.61),large ion lithophile elements (LILEs,Rb and Sr) and Pb,depletion in the high field strength elements (HFSEs),such as Nb,Ta,Zr and Ti,without significant Eu anomalies.In addition,the ultramafic rocks have low initial 87Sr/86Sr ratios (0.70394~0.70408),positive εNd(t) (7.2~8.1) and εHf(t) values (9.6~14.4).Based on the above discussions,we proposed that the studied ultramafic rocks were derived from a depleted lithospheric mantle (garnet-lherzolite) source which was metasomatized by the fluid from the dehydration of the subducted oceanic (Paleo-Asian Ocean) sediments.When the primary magma ascent,obvious fractionation of olivine and clinopyroxene took place,significant crustal contamination,however,did not occur.Otherwise,tectonic and geodynamic investigation indicate that the studied ultramafic rocks were formed in a post-orogenic extensional setting after the collision between the Jiamusi block and North China Craton (NNC).更多还原