【作者】 凌锦兰；

【导师】 姜常义；

【作者基本信息】 长安大学 ， 矿产普查与勘探， 2011， 硕士

【摘要】 塔里木板块东北部包括新疆北山地区和甘肃西部的柳园地区,因其早二叠世期间的镁铁质-超镁铁质岩石非常发育而倍受地学界广泛关注。其中,坡北岩体中的坡一、坡十侵入体产出有工业矿床；罗东岩体及笔架山岩带中的红石山岩体、漩涡岭岩体发现了镍铜硫化物矿化体。目前,对罗东岩体开展了初步的矿产普查和矿点检查工作,但缺少罗东岩体岩石成因的综合研究。为此,本论文通过罗东岩体岩相学、晶体化学、稀土元素、微量元素地球化学和Nd、Sr、Pb同位素组成等方面的系统研究,科学论证其岩浆演化过程、原生岩浆和地幔源区性质。通过研究取得了以下几点认识：1、罗东镁铁质-超镁铁质岩体平面形态为眼球状,出露面积约2.1km2。由纯橄岩、单辉橄榄岩、斜长二辉橄榄岩、橄榄二辉岩、方辉辉石岩、橄长岩、橄榄辉长岩、辉长岩、苏长辉长岩和淡色辉长岩组成,堆晶结构和堆晶层理发育,属于层状岩体。主要造岩矿物有橄榄石、辉石和斜长石,副矿物有铬尖晶石、磁铁矿和钛铁矿。2、岩石化学组成总体上属于富镁的基性-超基性岩范畴,大部分样品的m/f=3.37-6.29,属铁质系列。TiO2、K2O、P2O5、微量元素和稀土元素丰度很低(∑REE=4.89×10-6～14.58×10-6)。稀土元素配分曲线大体上表现为平坦型,大部分具有不同程度的正铕异常。岩石地球化学特征表明岩体与围岩之间的同化混染较弱。3、岩相学、岩石化学和矿物晶体化学特征显示岩浆演化早期阶段的分离结晶／堆晶相主要为橄榄石和铬尖晶石,晚期阶段主要为单斜辉石和斜方辉石,整个演化过程均伴有斜长石的分离结晶作用。岩浆向铁富集方向演化,遵从于拉班玄武质岩浆的演化趋势。4、原生岩浆的MgO=14.7%,属于苦橄质岩浆。5、εNd(t) =+7.03～+7.67,εSr(t)=-7.23～-3.05, (206Pb/204Pb)i=18.068～18.414, (207Pb/204Pb)i=15.513～15.629, (208Pb/204Pb)i=38.078～38.409。岩体具有OIB型Nd、Sr同位素组成和与MORB相似的Pb同位素组成,表明岩浆源区属于亏损型地幔源区。6、OIB型Nd、Sr同位素组成和苦橄质原生岩浆证明罗东岩体的形成与地幔柱活动有关,可能是地幔柱轴部部分熔融的产物。由此表明,罗东岩体应该是塔里木大火成岩省的组成部分。更多还原

【Abstract】 The northeastern of Tarim plate includes Beishan region of Xinjiang and Liuyuan region of western Gansu. It develops a series of regional mafic-ultramafic rock during early Permian and highly concerned by geologists. No.l body and No.10 body in Pobei intrusion have magmatic sulphide deposits; Hongshishan intrusion, Xuanwoling intrusion in Bijiashan zone and Luodong intrusion develops Ni-Cu sulphide mineralization. Currently, Luodong intrusion has carried out a preliminary survey and mining inspection, lacking of comprehensive study for petrogenesis. Therefor, this paper select Luodong intrusion as research object, through systematically research on petrography, crystal chemistry, rare earth elements, trace elements and Sr, Nd, Pb isotopic geochemistry of the intrusion, scientifically demonstrates its magmatic evolution process, primary magma and mantle source nature. Based on these researches we get some understanding as follows:1. Lens shaped Luodong mafic-ultramafic intrusion covers an area of 2.1 km2. It consists of dunite, wehrlite, lherzolite, olivine websterite, peridotite pyroxenite, troctolite, olivine gabbro, gabbro, noritegabbro and leucogabbro. The Luodong intrusion is a layered intrusion with obvious cumulus textures and cumulus layering. The main rock-forming minerals are olivine, pyroxene and plagioclase, the accessoryminerals are Cr-spinel, magnetite and ilmenite.2. The rock chemical compositions in the mass belong to basic and ultrabasic rocks with rich magnesium. Most of the samples’ m/f are 3.37-6.29, which belong to iron series. All kinds of rocks are characterized with very low TiO2, K2O, P2O5, rare earth elements and trace elements (∑REE=4.89×10-6～14.58×10-6) content. The REE patterns are flat, with positive Eu anomalies to different extent. The characteristics of petrochemistry do not show strong crustal contamination.3. The study of petrography, petrochemistry and crystal chemistry of minerals suggest that the primary magma of the Luodong intrusion have undergone fractional crystallization or cumulus crystal of olivine and Cr-spinel in the early stage and clinopyxene, orthopyroxene in the later stage. Plagioclase fractionally crystallizated during magma evolution. The direction of magmatic evolution of the iron enrichment, in compliance with tholeiitic magma evolution trend.4. MgO content of Primary magma is 14.7%, it belongs to picritic magma.5.εNd(t)=+7.03～+7.67,εSr(t)=-7.23～-3.05, (206Pb/204Pb)i=18.068～18.414, (207Pb/204Pb)i=15.513～15.629, (208Pb/204Pb)i=38.078～38.409. The intrusion has OIB-like Nd, Sr isotopic compositions and MORB-like Pb isotopic compositions, indicating that magma source is a depleted mantle source.6. OIB-like Nd, Sr isotopic compositions and picritic primary magma indicate that Luodong intrusion has an affinity with mantle plume and it may be formed by partial melting of axis plume. The Luodong intrusion is thus a part of Tarim Large Igneous Province.更多还原