桂东北越城岭岩体加里东期成岩作用:锆石U-Pb年代学、地球化学和Nd-Hf同位素制约

发布时间：2018-03-29 15:51

本文选题：锆石U-Pb年代学　切入点：地球化学　出处：《大地构造与成矿学》2016年04期

【摘要】：桂东北越城岭岩体是一个由加里东期-印支期花岗岩组成的复式岩基,是目前南岭地区钨锡矿产调查评价的重点对象。本文选取该复式岩体中的加里东期不同岩性花岗岩,包括细粒花岗闪长岩、(粗)中粒斑状二长花岗岩和(中)细粒(斑状含斑)二长花岗岩为研究对象,进行LA-ICP-MS锆石U-Pb年代学、矿物学、地球化学和Nd-Hf同位素组成研究。研究结果表明,细粒花岗闪长岩和(粗)中粒斑状二长花岗岩具有较低SiO_2(70%)含量和A/CNK值(0.99~1.05),较高CaO、TiO_2含量和FeO+MgO值,中等(La/Yb)N值以及中度亏损Ba、Sr、Eu元素等特征,副矿物以榍石为主加少量磁铁矿,属于I型花岗岩,形成时间为435~438 Ma;(中)细粒(斑状-含斑)二长花岗岩具有富硅(70%)、富碱、贫钙,高A/CNK值(1.04~1.14),低FeO+MgO值和(La/Yb)N值,中到重度亏损Ba、Sr、Eu元素等特征,副矿物含量低,以钛铁矿、独居石为主,为S型花岗岩,形成时间为423~429 Ma,略晚于前者。C/MF-A/MF图解反映I型花岗岩由变质中基性火成岩部分熔融形成,源区具有负且稳定的εNd(t)值( 7.1~ 7.9)和εHf(t)值( 6.4~ 7.8),平均地壳存留年龄为1.8 Ga左右。S型花岗岩的ε_(Nd)(t)值( 7.9~ 8.8)和t_(Nd2DM)值(1.81~1.88 Ga)与I型花岗岩类似,但是其CaO/Na_2O值(0.28~0.64)和相对分散的ε_(Hf)(t)值( 2.6~ 7.9)和t_(Hf2DM)值(1.57~1.90 Ga)说明源区可能存在变杂砂岩、变泥质岩和年轻地壳组分的三元混合,且以前两者为主。综合分析华南加里东造山带构造演化序列可以得知,造山带从褶皱缩短、逆冲加厚阶段向伸展垮塌阶段转化而形成的等温降压过程,是形成越城岭花岗岩的诱因。等温降压过程可以通过岩基旁侧新宁-资源深大断裂的松弛调整来实现。
[Abstract]:The Yuechengling rock body in northeast Guangxi is a complex rock base composed of Caledonian and Indosinian granites, which is the key object of the investigation and evaluation of tungsten and tin deposits in Nanling area. In this paper, the Caledonian lithologic granites in the complex rock mass are selected. The LA-ICP-MS zircon U-Pb chronology and mineralogy were studied including fine granodiorite granodiorite (coarse) porphyry monzonitic granites and (middle) fine-grained (porphyry porphyry) monzonitic granitic granitic granodiorite granodiorite. Geochemistry and Nd-Hf isotopic composition. The results show that the fine-grained granodiorite and (coarse) medium-grain porphyry monzomorphic granodiorite have lower Sio _ 2 ~ (70) content and A/CNK value of 0.99O _ (1.05), higher CaOTiO _ 2 content and FeO MgO value. The secondary minerals are sphene with a small amount of magnetite, which belongs to I-type granite, and formed at a time of 435 ~ 438 Majiao (porphyry porphyry) monzonitic granites with rich silicon, alkali and poor calcium, and the secondary minerals are mainly sphene and a small amount of magnetite. It is characterized by high A/CNK value of 1.04 ~ 1.14%, low FeO MgO value and La- / Yb ~ (2 +) N value, moderate to severe depletion of Bao-Sr-EU element, low secondary mineral content, mainly ilmenite, monazite, and S-type granite. The formation time is 423429Ma, which is slightly later than that of the former. C / MF-A / MF diagram shows that the I-type granite is formed by partial melting of metamorphic basic igneous rocks. The source region has negative and stable values of 蔚 NdT (7. 1 ~ 7. 9) and 蔚 Hft (6. 4 ~ 7. 8) (mean crustal survival age is about 1. 8 Ga.) for the S type granites, the values of 蔚 ndt0. 8 and T-d-2DM are similar to those of the I type granites, and the mean crustal survival age is about 1. 8 Ga. The average crustal age is about 1. 8 Ga. The values of 蔚-Ndt0. 8) and TD2DM) are similar to those of the I type granites, and are similar to those of the I type granites. However, the CaO/Na_2O value of 0.28 ~ 0.64) and the relatively dispersed values of 蔚 ~ (2. 6 ~ ~ (7. 9)) and T _ (T) ~ (Hf2DM) of 1.571.90Ga) indicate that there may be a ternary mixture of mixed sandstone, argillaceous rocks and young crustal components in the source area. By analyzing the tectonic evolution sequence of the Caledonian orogenic belt in South China, it can be concluded that the isothermal pressure reduction process of the orogenic belt changed from fold shortening, thicken thrust stage to extensional collapse stage. The isothermal depressurization process can be realized by the relaxation adjustment of Xinning deep fault on the side of rock base.
【作者单位】：中国地质调查局武汉地质调查中心;中国地质调查局花岗岩成岩成矿研究中心;中国地质大学(武汉)地质调查研究院;
【基金】：中国地质调查局地质大调查项目(1212011120804、1212011120798、12120114020701) 右江成矿区桂西地区地质矿产调查二级项目(DD2016034)联合资助
【分类号】：P597.3;P588.1

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