【作者】 管涛；

【导师】 黄智龙；

【作者基本信息】 中国科学院研究生院（地球化学研究所） ， 地球化学， 2005， 博士

【摘要】 白马寨镍矿区煌斑岩位于哀牢山断裂带的南段,是该条带上新生代富钾火成岩的重要组成部分。通过对其进行详细的地质学、岩石学、矿物学、同位素年代学、元素和同位素地球化学研究,并和整个条带这类岩石地质地球化学进行充分对比,总结了白马寨镍矿区煌斑岩的成因信息及其与区域富钾火成岩的成因联系;初步查明白马寨镍矿区煌斑岩富集地幔交代流体的性质和交代富集事件发生的时代;定量反演了岩石的部分熔融程度、源区残留矿物相、源区REE含量、结晶分异过程;初步建立了本区煌斑岩的地球动力学成因模式。本研究主要取得以下几点认识: 1、白马寨镍矿区煌斑岩的侵位时代为32.01±0.60～32.46±0.62Ma,为哀牢山断裂带新生代早期高钾岩浆活动的产物。 2、白马寨镍矿区煌斑岩为碱性系列、钾玄质-超钾质的钙碱性煌斑岩。俯冲陆壳和洋壳析出的流体对交代富集地幔源区均有贡献,岩浆演化过程中地壳混染作用微弱,部分熔融和结晶分异对成岩过程均有影响。依REE含量可以将其分成两组,元素地球化学特征显示低REE组煌斑岩经历了单斜辉石+橄榄石+斜长石±Fe-Ti氧化物±磷灰石的结晶分异。高REE组煌斑岩经历了橄榄石+单斜辉石+斜长石的结晶分异。低REE组和高REE组煌斑岩分别是交代富集地幔约10%和4%部分熔融的产物。岩石学混合计算模拟出的低REE组煌斑岩原始岩浆熔融残留相的矿物比例分别为Ol_67.21Opx_16.99Cpx_11.82Gar_4.00。源区REE含量定量模拟计算表明白马寨镍矿区煌斑岩源于富LREE的交代富集地幔。低REE组煌斑岩结晶分异模拟计算表明,矿区低REE组煌斑岩为原始岩浆直接结晶、相对低结晶分异程度（23.74%）、相对高结晶分异程度（44.15%）的产物。造岩矿物和全岩地球化学特征与马厂箐金矿区、北衙金矿区、姚安金矿区、老王寨金矿区煌斑岩和钙碱性煌斑岩相似但又有区别,体现了哀牢山断裂带新生代富钾火成岩地幔源区和岩浆演化既相似又存在不均一性。 3、依据区域地质、岩石学、矿物学、地球化学,初步建立了白马寨镍矿区煌斑岩的成因模式:约70～50Ma开始的印度板块向亚洲板块碰撞俯冲,俯冲析出的流体（包括小规模熔体）交代了扬子地块陆下岩石圈地幔,形成白马寨镍矿更多还原

【Abstract】 Lamprophyres in the Baimazhai nickel deposit are located on the southern segment of Ailaoshan fault belt. These lamprophyres are important parts of Cenozoic potassic rocks on this belt. On the basis of detailed study on their geology, petrology, mineralogy, chronology, elemental and isotopic geochemistry, as well as comparison with other similar rocks on this belt, genetic information of the lamprophyres in Baimazhai nickel deposit has been summed up, genetic relation with regional potassic volcanic rocks has been built, character of the metasomatic fluids and time of the metasomatic enrichment have been preliminarily investigated, partial melting degree, residual mineral and trace elemental composition in the mantle source, fractional crystallization processes have been modeled, and the geodynamical model of the potassic igneous rocks on the whole belt have been preliminarily proposed. Several conclusions have been drawn from this study as followings:1 The age of lamprophyres in the Baimazhai nickel deposit is between 32.01 ±0.60Ma and 32.46 ±0.62Ma, so they are products of early pulse of Cenozoic potassic magmatism in Ailaoshan fault belt.2 All samples are alkaline series, potassic and ultrapotassic calc-alkaline lamprophyres. The fluids derived from dehydration of subducted slab, both continental crust and oceanic crust contributed to enrichment of metasomatic mantle. The lamprophyres was subtly contaminated by crustal substances. Both partial melting and crystallization fractionation play an important role in rock-forming processes. Elemental geochemistry show that low REE group lamprophyres experienced crystallization fractionation of a mineral assemblage of clinopyroxene+olivine+plagioclase±Fe-Ti oxide±apatite, high REE group lamprophyres experienced crystallization fractionation of a mineral assemblage of olivine+clinopyroxene+plagioclase. Low REE group and high REE group lamprophyres are 10% and 4% partial melting of the metasomatic enriched mantle. Petrological mixing calculation show that the ratios of meltingresidue of the primary magma of the low REE group lamprophyres is Ole7.21OpXi6.99Cpxn.s2Gar4.00. Modelling calculation of the REE of the mantle source show that the lamprophyres in Baimazhai nickel deposit are derived from LREE-enriched metasomatic enriched mantle. Modelling calculation of crystallization fractionation of the low REE group lamprophyres show that the low REE group lamprophyres in Baimazhai nickel deposit are products crystallized from primary magma, relatively low crystallization degree (23.74%) and relatively high crystallization degree (44.15%) magma. Geochemica! characteristics of the rock-forming minerals and whole rock show that there are both similarity and difference among lamprophyres in the Baimazhai nickel deposit and those in Machangqing gold deposit, Baiya gold deposit, Yaoan gold deposit and Laowangzhai gold doposit on Ailaoshan fault belt, indicating the regional mantle source being heterogeneous.3> According to regional geology, petrology, mineralogy and geochemistry, genetic model of the lamprophyres has been preliminaryly proposed: about 70~50Ma collision and subduction between India plate and Asia plate initiated, and the fluid (including small-scale melt) metasomatized the Yantze sub-continental lithospheric mantle, forming enriched mantle source of the lamprophyres in Baimazhai nickel deposit. With subduction continued, about 40Ma (the timing of initiation of Cenozoic potassic magmatism on the Ailaoshan fault belt), slab break-off took place between subducting ancient Tethyan slab and India slab, and cause asenospheric mantle upwelling. Under transtensive background, hot asenospheric mantle initiated partial melting of former enriched lithospheric mantle, which formed the lamprophyres in Baimazhai nickel deposit. Regional large-scale potassic magmatism initiated the large-scale strike-slip shear of the Ailaoshan fault belt (about 27-22Ma).更多还原