滇东南老君山地区多期岩浆作用地球化学及成岩成矿背景研究

发布时间：2018-06-21 22:35

本文选题：早古生代花岗岩 + 中生代花岗岩　；参考：《南京大学》2015年博士论文

【摘要】：作为大陆地壳重要的组成部分,花岗岩的岩石成因与大陆地壳的演化存在密切的联系。侵位于滇东南老君山地区的早古生代花岗岩和晚中生代花岗岩是该区最重要的侵入体,对于其成因,特别是源区的性质和形成的地球动力学背景尚需要深入的研究。华南早古生代造山作用一直以来都是学术研究的热点,其中一个关键问题是造山运动所引起的花岗质岩浆作用过程中是否有地幔物质的参与。针对这一科学问题,本文对华南板块西部滇东南老君山地区三期典型的早古生代花岗岩(团田单元,南捞单元,老城坡单元)进行了详细的地质年代学和地球化学研究。LA-ICP-MS锆石U-Pb年代学显示这三期花岗岩的结晶年龄分别为～436Ma,～430Ma,～427Ma。其岩浆锆石的￡Hf(t)值为-14～+3,指示这三期花岗岩的源区具有不均一性的特征。三期岩体均包含继承锆石核,其U-Pb年代和Hf模式年龄为元古代。大量的主微量元素协变组合显示老君山早古生代花岗岩具有明显的线性混合趋势。其中团田和南捞单元岩体具有强过铝质的地球化学特征(A/CNK1.1),而老城坡单元岩体具有弱过铝质特征(A/CNK=1.0～1.1)。相对于老城坡单元岩体,团田和南捞单元岩体表现为高K_2O、Rb/Sr、Rb/Ba和εNd(t)值,低 TFe_2O_3、Al_2O_3、MnO、MgO、CaO、TiO_2、Na_2O、Mg#和Nb/Ta值的特征。上述事实表明团田和南捞单元花岗岩形成于部分熔融的元古代变质沉积岩,其中基本上没有幔源物质的参与;然而,老城坡花岗岩很可能来源于壳源长英质熔体和幔源基性岩浆的混合作用。值得注意的是幔源组分相对于壳源组分具有更低的Nd同位素组成,而这与华南最近发现的幔源玄武岩具有一致的同位素特征。武夷-云开造山垮塌造成了早古生代华夏板块下地壳的部分熔融。其广泛的早古生代花岗质岩浆作用,以及伴随出现的幔源岩浆,表明了这个时期华南板块西部处于后碰撞伸展的构造环境。软流圈的上涌和玄武质岩浆的底侵很可能引起了华南板块西部大规模的长英质岩浆作用,幔源熔体在这个过程中提供了能量和物质。我们本次研究还对老君山地区与成矿有关的三类晚中生代花岗岩,包括中粗粒花岗岩、中细粒花岗岩和花岗斑岩,进行详细的地质年代学、主微量元素、矿物化学和Nd-Hf同位素研究。这三类花岗岩的锆石U-Pb定年结果分别为90.1±0.7 Ma,89.7±0.8 Ma,86.0±0.5 Ma,显示其在同一时期发生侵位。所有样品均显示强过铝质、富碱的特征,元素特征表现为高P、Li、Rb、Cs、Ta、Sn、W 和 U,低 Ti、Mg、Co、Ni、Sr、Ba、Zr、Hf、Th 及稀土元素。岩浆在运移过程中发生了明显的分异演化作用,其中斜长石和钾长石的结晶分异作用主要控制岩浆中Rb、Sr、Ba和Eu的浓度;而磷灰石、独居石等副矿物结晶分异作用则影响着稀土元素含量。地球化学特征显示老君山地区晚中生代花岗岩主要为高分异S型花岗岩。全岩εNd(t)值为-12.2～-10.8,锆石εHf(t)值为-15.5～-2.5,其Nd和Hf同位素两阶段模式年龄均为中-古元古代。研究表明,这些S型花岗岩均起源于中-古元古代陆壳中类似变质泥岩组分的部分熔融。老君山地区这三类晚中生代花岗岩的Sn含量远高于大陆上地壳和下地壳的平均值,属于含锡花岗岩。本次研究还对老君山地区-都龙超大型锡矿中的主要成矿矿物锡石进行了详细的锡石LA-MC-ICP-MS U-Pb定年,获得206Pb/207Pb-238U/207Pb等时线年龄为86.6～90.6Ma,表明都龙矿区锡成矿作用主要发生在晚白垩纪,这与本次研究所测得老君山地区晚中生代含锡花岗岩的成岩年龄相一致。紧密的时间以及空间关系显示老君山地区晚中生代岩浆热液活动是都龙矿区锡成矿作用的关键。对含锡花岗岩中主要造岩矿物的电子探针研究进一步支持了富含挥发组分(F,C1)的老君山含锡岩浆主要起源于成熟度较高的地壳源区。其中黑云母电子探针成分显示含锡花岗岩的氧逸度低于Ni-NiO(NNO)体系,表明其岩浆结晶过程处于相对还原的环境。在低氧逸度还原条件下,Sn在岩浆中主要呈二价形式存在,具有较大的离子半径,因此Sn2+不易进入到成岩矿物的晶格中,而倾向于在结晶分异晚期的残余熔体和流体中富集。因此,老君山地区晚中生代岩浆演化过程中高程度的分异结晶作用有利于Sn在花岗质岩浆中发生初次富集,而晚期岩浆还原性的条件(fO_2NNO)使Sn在运移过程中更倾向于进入到热液流体中从而导致锡的再次富集,最终在有利的构造部位发生沉淀形成锡矿化。都龙超大型锡多金属矿床位于老君山地区西南部,是中国第三大锡石硫化物矿床,其锡的储量约30万吨。而与其相邻的个旧地区还存在中国第一大锡矿床-个旧超大型锡多金属矿床。作为滇东南地区两个世界级的锡多金属矿区,老君山和个旧具有一致的晚白X 世成岩成矿时代,因而综合对比这两个地区同时期的岩浆岩有助于更好地理解整个区域在这个时期的岩浆演化历史与成矿构造背景。相比于同时期的个旧矿区花岗岩,老君山地区花岗岩具有高的 Rb、Rb/Sr、初始 87Sr/86Sr 和锆石εHf(t)值,低的 TFe_2O_3、Al_2O_3、MgO、TiO_2、P_2O_5 和稀土元素含量。地球化学结果显示强过铝质的老君山花岗岩很可能代表长英质端元组分,其起源于纯壳源的中-古元古代变质沉积岩中泥质组分的部分熔融,而个旧花岗岩则可能来源于壳源岩浆(如老君山花岗质岩浆)和幔源基性岩浆(个旧辉长岩-细粒镁铁质包体MME)的混合作用。老君山和个旧地区岩浆作用很可能反映华南板块西部在晚白垩世处于伸展的板内构造环境。上涌的软流圈地幔及底侵的玄武质岩浆引起了上覆陆壳中变质沉积岩的部分熔融,从而形成S型花岗质岩浆(如老君山花岗岩),而幔源基性岩浆注入浅部地壳,同时与壳源长英质岩浆发生混合作用形成个旧(花岗岩-MME-辉长岩)杂岩体。这种岩浆作用的差异也同时合理地反映在这两个地区细微成矿差异上。通常相对高含量的Cu赋存于地幔,而相对高含量的Sn赋存于地壳。起源于纯壳源岩浆的老君山地区主要形成以Sn-Zn矿化为主的都龙锡多金属矿床,而经历了广泛的壳幔相互反应的个旧地区则形成了以Sn-Cu矿化为主的个旧锡多金属矿床。
[Abstract]:As an important part of the continental crust, the petrogenesis of the granite is closely related to the evolution of the continental crust. The early Palaeozoic granites and late Mesozoic granites, which are located in the Laojun Mountain area in southeastern Yunnan, are the most important intrusive bodies in this area, and their genesis, especially the nature of the source area and the geodynamic background of the formation, is still yet to be found. The early Paleozoic orogeny in Southern China has always been a hot spot of academic research. One of the key problems is whether the mantle material is involved in the granitic magmatism caused by the orogenic movement. In view of this scientific problem, this paper is a typical early stage of the three stage of the Laojun Mountain area in the Western Southern China, the western part of the Southern China plate. .LA-ICP-MS zircon U-Pb chronology of geological chronology and geochemistry of the Palaeozoic granites (group field unit, South fishing unit, and old city slope unit) shows that the crystallization ages of these three phases of granites are 436Ma, 430Ma and 427Ma. Hf (T) of the magma zircon is -14 to +3, indicating the source area of the three periods of granites. The characteristics of heterogeneity. The three phase of the rock mass contains the inherited zircon core, and its U-Pb age and Hf model age are Proterozoic. A large number of major and microelement covariant combinations show that the early Palaeozoic granites in Laojun Mountain have obvious linear mixing trend. The rock mass of the urban slope unit has a weak peraluminous character (A/CNK=1.0 ~ 1.1). Compared with the old city slope unit rock mass, the mass of the Tuan Tian and the Nan salvo unit shows a high K_2O, Rb/Sr, Rb/Ba and epsilon Nd (T) values, which are low TFe_2O_3, Al_2O_3, MnO, MgO, and CaO. The metamorphic sedimentary rocks of the Proterozoic are basically not involved in the mantle derived materials; however, the old city slope granites are likely to be derived from the mixture of crust source feldspar and mantle derived basic magma. It is worth noting that the mantle source composition has a lower Nd isotope composition relative to the source component of the crust, and this is with the mantle derived basalts recently discovered in Southern China. The rock has consistent isotopic characteristics. Wuyi - Yunkai orogeny resulted in the partial melting of the lower crust of the early Paleozoic Cathaysian plate. Its extensive early Palaeozoic granitic magmatism and the accompanying mantle derived magma showed the tectonic setting of the western Southern China plate in the post collision extension. The upwelling and basaltic of the asthenosphere. The undergression of the magma may lead to a large amount of felsic magmatism in the western part of the Southern China plate. The mantle derived melts provided energy and substance in this process. In this study we also studied three types of Late Mesozoic granites related to mineralization in the Laojun Mountain area, including mesogranitic granite, medium fine granites and granite porphyry. Fine geological chronology, main trace elements, mineral chemistry and Nd-Hf isotopes. The zircon U-Pb dating results of these three types of granites are 90.1 + 0.7 Ma, 89.7 + 0.8 Ma and 86 + 0.5 Ma, showing emplacement at the same time. All samples show strong peraluminous, alkali rich characteristics, and the elements are characterized by high P, Li, Rb, Cs, Ta, Sn, W and U, low Ti, Mg, Co, Ni, Sr, Ba, Zr, Hf, Th and rare earth elements. The magma has obvious differentiation and evolution during the migration process, in which the crystallization differentiation of plagioclase and potassium feldspar mainly controls Rb, Sr, and concentration in magma, while the crystallization of apatite and monazite influences the content of rare earth elements. Geochemistry The characteristics show that the late Mesozoic granites in the Laojun Mountain area are mainly high fractionated S type granites. The total rock epsilon Nd (T) value is -12.2 to -10.8, the zircon epsilon Hf (T) value is -15.5 to -2.5, and the two stage model age of Nd and Hf isotopes are both middle and Paleoproterozoic. The Sn content of the three types of Late Mesozoic granites in the Laojun Mountain area is far higher than the average value of the continental upper crust and lower crust, and it belongs to the tin bearing granite. This study also made a detailed stannite LA-MC-ICP-MS U-Pb dating for the major metallogenic mineral deposits in the Laojun Mountain Region - Du long super large tin deposit, and obtained 206Pb/207Pb-23 The 8U/207Pb isochronous line age is 86.6 ~ 90.6Ma, indicating that the tin mineralization in the Ditong mining area mainly occurred in the late Cretaceous period, which is in accordance with the age of diagenesis of the late Mesozoic tin bearing granite in the Laojun Mountain area. The close time and spatial relationship showed that the late Mesozoic magmatic hydrothermal activity in the Laojun Mountain area was the tin in the Dulong mining area The electron probe study of the main rock forming minerals in the tin bearing granite further supports the origin of the Laojun Mountain containing F (C1) rich in the high maturity of the crust source. The biotite electron probe composition shows that the oxygen fugacity of the tin bearing granite is lower than the Ni-NiO (NNO) system, indicating that its magma is magma The crystallization process is in a relative reduction environment. Under the condition of low oxygen fugacity, Sn exists mainly in the two valence form of the magma and has a larger ionic radius. Therefore, Sn2+ is not easy to enter the lattice of the diagenetic mineral, but tends to be enriched in the residual melt and flow body in the late crystallization differentiation. Therefore, the late Mesozoic magma in the Laojun Mountain area In the process of evolution, the high degree of differentiation crystallization is beneficial to the initial enrichment of Sn in the granitic magma, and the condition of late magma reducibility (fO_2NNO) makes Sn more inclined to enter the hydrothermal fluid in the process of migration, which leads to the re enrichment of tin, and eventually precipitates in the favorable tectonic site to form tin mineralization. The tin polymetallic deposit is located in the southwest of Laojun Mountain area. It is the third largest cassiterite sulfide deposit in China. Its tin reserves are about 300 thousand tons. There are also the first largest tin deposits in the adjacent areas, the old super large tin polymetallic deposit. As two world-class tin polymetallic ore deposits in southeastern Yunnan, the Laojun Mountain and the old are of the old. Unanimous late white X
In the age of diagenesis and mineralization, the comprehensive comparison of the two regions of the same period of magmatism helps to better understand the whole region's magmatic evolution history and metallogenic tectonic setting in this period. Compared with the granite in the same old mining area, the granite in the Laojun Mountain area has high Rb, Rb/Sr, initial 87Sr/86Sr and zircon epsilon Hf (T) values. TFe_2O_3, Al_2O_3, MgO, TiO_2, P_2O_5 and rare earth elements. The geochemical results show that the strong peraluminous Laojun Mountain granite is likely to represent the felsic end tuple, which originated from the partial melting of the argillaceous components in the Mesoproterozoic metamorphic sedimentary rocks of the pure crustal source, and the old granite may be derived from the crust source magma (such as the old gentleman. The mixture of mantle derived granitic magma and mantle derived basic magma (the old gabbro - fine mafic inclusion MME). The magmatism in Laojun Mountain and the old area may reflect the extensional tectonic environment of the western Southern China plate in the late Cretaceous. The upwelling of the asthenosphere mantle and the basaltic magma from the bottom of the basaltic magma caused the metamorphism in the overlying continental crust. The partial melting of sedimentary rocks formed S granitic magma (such as the Laojun Mountain granite), and the mantle derived basic magma injected into the shallow crust and mixed with the crust source felsic magma to form an old (granite -MME- gabbro) complex. The difference of this magmatism is also reasonably reflected in the subtle mineralization in the two regions. Generally, the relatively high content of Cu occurs in the mantle, while the relatively high content of Sn exists in the crust. The Laojun Mountain area, which originated from the pure crust source magma, mainly formed the Dulong tin polymetallic deposit, mainly with Sn-Zn mineralization, and the old area, which has experienced a wide range of crust and mantle interaction, formed an old tin polymetallic deposit dominated by Sn-Cu mineralization. Deposit.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P588.11;P611

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