四川阿布郎当超镁铁质侵入体成岩机制的地球化学约束  

Geochemical constraints on the petrogenesis of the Abulangdang ultramafic intrusion, Sichuan Province, China

作　　者：马言胜[1,2] 陶琰[1] 钟宏[1] 朱飞霖[1,2] 王兴阵[3] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵阳550002 [2]中国科学院研究生院,北京100049 [3]安徽理工大学资源与环境工程系,淮南232001

出　　处：《岩石学报》2009年第5期1146-1158,共13页Acta Petrologica Sinica

基　　金：中国科学院重要方向项目(KZCX2-YW-QO4-06);国家自然科学基金项目(40773033;40873028;40730420)资助

摘　　要：阿布郎当超镁铁质侵入体位于扬子地台西缘,康滇地轴中段,安宁河深大断裂之西侧。该岩体呈似同心环状相带分布,基性程度很高,岩体的中心为含长橄榄岩,向外依次过渡为含长辉橄岩、辉橄岩及斜长辉橄岩,边缘带斜长橄辉岩。在岩体的边缘带附近存在明显的Cu-Ni-PGE矿化。随着近年来矿产价格的走高和国家对地质普查工作的力度加大,阿布郎当岩体又重新引起人们的关注。该岩体在地质勘探方面已经积累了丰富的资料,但在地球化学方面的研究还很薄弱。本文对阿布郎当超镁铁岩体进行了系统的主要造岩矿物成分、主量元素、微量元素及铂族元素含量的分析,讨论了该岩体的原始岩浆和地幔部分熔融程度,并对成岩过程进行了探讨。研究认为,阿布郎当超镁铁质岩属拉斑玄武岩系列,是峨眉山大火成岩省构造-岩浆活动产物,成岩原始岩浆为苦橄质岩浆,由类似于洋岛玄武岩岩浆源区成分的地幔经18%左右的部分熔融形成。在岩浆上升过程中,最先结晶的镁铁矿物由于岩浆的流动而集中于岩浆管道的中央,于是形成各种岩石的环带分布。当岩浆上升侵入阿布郎当岩浆房以后,发生了以橄榄石为代表的铁铁矿物的堆积,与此同时,岩浆在岩浆房内继续进行着结晶分异并且还可能与围岩发生了混染,导致岩体边缘相附近出现了硫化物的熔离。在后期的地壳运动中,阿布朗当岩浆房露出地表,即今天所见到的阿不朗当超镁铁质岩体。The Abulangdang ultramafic intrusion lies in the west margin of the Yangtze Block, the middle of Kang-Dian axis of earth and the west side of the An-Ning River deep fault. The zoned-like rocks of Abulangdang are, from the core to the outside, composed of plagioclase-bearing peridotite, pyroxene peridotite, plagioclase pyroxene peridotite, and plagioclase olivine pyroxenite. The significant Cu-Ni-PGE mineralization occurs along the marginal facies. Recently, as the increasing strength of geological survey of the nation and the increasing prices of metal, especially the noble metals, the Abulangdang intrusion attracted attention once again. However, it is still poor on the aspect of geochemistry though abundant data of geological survey for the intrusion has been accumulated. This paper provided a basic study on major elements, trace elements and platinum-group elements for the Abulangdang ultramafic rocks as well as the compositions of the rock-forming minerals. We discussed the primary magma of the intrusion, the degree of partial melting of the mantle, and the process of rock-forming. The results show that Abulangdang ultramafic rocks are products of tectonic-magmatic activity in the Emeishan Large Igneous Province (ELIP) and belong to tholeiitic evolution trend. The Abulangdang ultramafic rocks were formed from picritic-like magmas generated by relatively high degrees (18%) of partial melting of an OIB-type mantle source. During ascent of the magma, the mafic minerals which crystallized in the early stage concentrated in the middle of the magma conduit and formed the zoned-like pattern of the rocks. The accumulation of mafic minerals which represented as olivine occurred after the magma intruded Abulangdang magma chamber. At the same time, the crystallization differentiation of magma would continue in the magma chamber and assimilation between magma and country rocks probably caused the liquation of sulfide which occurred near the marginal facies of the intrusion. In the course of late crustal movement, the Abu

关 键 词：峨眉山大火成岩省 超镁铁岩 部分熔融 阿布郎当 四川 

分 类 号：P588.125[天文地球—岩石学]