大别山南山岭石榴橄榄岩成因的岩石学研究  

Petrological study for origin of Nanshanling garnet peridotite from Dabie Mountain.

作　　者：路凤香[1] 金振民[1] 桑隆康[1] 储玲林[1] 金淑燕[1] 

机构地区：[1]中国地质大学地球科学学院,武汉430074

出　　处：《岩石学报》2007年第11期2757-2765,共9页Acta Petrologica Sinica

基　　金：国家973项目(2003CD716506)资助。

摘　　要：大别山罗田穹隆东南侧的南山岭石榴橄榄岩岩体面积小(173×133m^2),由贵橄榄石(75%)。透辉石(10%)和镁铝石榴石(15%)组成。本文通过岩石学及地球化学研究,并与大别山的碧溪岭、毛屋、饶拔寨、芝麻坊岩体以及其他地区的基性岩浆杂岩体(如红格岩体、元宝山岩体、柴北缘岩体)、残留地幔块体(五大连池、鹤壁、山旺)等不同成因的超镁铁岩进行对比后认为,该岩体属于火成成因,是镁铁-超镁铁杂岩体的一部分。表现在:橄榄岩呈块状构造,矿物分布均匀未见定向排列,镜下呈现典型的火成结构;FeO^T含量高(21.36%),Mg~#(0.77)低,Mg+Ni/Fe+Mn(3.06)<7,V(175.5×10^(-6))含量高于地幔块体成因的橄榄岩;REE总量偏低,LREE弱富集,(La/Yb)_N=3.1,低于饶拔寨、芝麻坊等残留地幔块体成因的橄榄岩。南山岭橄榄岩在微量元素蛛网图中,具有Ba、U、Pb、Zr、Eu的正异常和Nb的负异常,石榴橄榄岩全岩以及透辉石单矿物都具有高^(87)Sr/86 Sr(0.7088,0.7086)和低ε_(Nd)(t)(-6.55～-6.01)的特征,尽管南山岭与碧溪岭岩体距离很近而且都属于火成成因,但岩石的结构构造、变质变形的印记、REE配分形式和同位素特征都有区别,表明二者的源区及演化经历不同,相比之下,南山岭岩浆源区地壳组分的作用更为明显。在ε_(Nd)(t)-(^(87)Sr/^(86)Sr)_t图解中南山岭橄榄岩的投点十分靠近大别山北麓120～130Ma侵位的祝家铺辉石岩-辉长岩岩体群的投点分布范围,暗示可能有与罗田穹窿西北侧祝家铺岩体群的岩浆活动相对应。The Nansharding gamet-bearing peridotite body ( - 173 x 133 M(2)) is located in southeast slop of Luotian dome in Southern Dabie Mountain, Yuexi County, Anhui province, east central China. Based on the study of petrology and geochemistry and comparison with different types of peridotite in Dabie Mountain such as Bixiling, Maowu, Raobazhai and Zhimafang and in other places such as Yuanbaoshan and Hongge mafic-ultramafinc complex; Hebi and Wudalianchi residual mantle samples indicate that Nanshanling peridotites are a portion of mafic-ultramafic body intruding into the continental crust as basic magmas. Peridotite is composed of olivine (75%), clinopyroxe ( 10%) and garnet ( 15%) and shows massive structure, homogeneous distribution of minerals in the rock, and typical igneous texture. Garnet peridotites are high in FeO(T) (21. 36%), low in Mg(#)(0. 77), Mg + Ni/Fe + Mn (3. 06) < 7, and the abundances of V ( 177. 8 x 10(-8)) are higher than the that of residual mantle block. Nanshanling peridotites are low in total REE, (La/Yb)(N) = 3.1 which is lower than that of residual mantle block in Raobazhai and Zhimafang. Nanshanling peridotites show Ba, U, Pb,Zr,Eu enrichment and negative Nb anomaly in primitive mantle-normalized trace element plots. Rb-Sr and Sm-Nd isotopic analysis of whole-rock samples and mineral separates have been carried out and indicate high (87) Sr/(86) Sr ( 0.7088, 0. 7086) and low epsilon(Nd) (t) ( - 6.55, - 6.01) values implying that the resource of magmas contain crust components. Although both Nanshanling and Bixiling have same perogenetic genesis and nearby each others, they have different rock texture, BEE pattern, history of deformation and isotopic features indicating that they have different magma sources and experiences. In a diagram of epsilon(Nd) (t) _( (87) Sr/(86) Sr)(t), the plots of Nansharding whole rock and Cpx fall within elongation direction of mantle reservoir and close to the range of the plots from Zhujiapu pyroxenite-gabbros bodies which occurred at northwest slop of Luoti

关 键 词：石榴橄榄岩 镁铁-超镁铁杂岩体 火成成因 残留地幔块体 罗田穹隆 

分 类 号：P588.125[天文地球—岩石学]