本文選題：鋯石U-Pb年代學(xué)　切入點：地球化學(xué)　出處：《大地構(gòu)造與成礦學(xué)》2016年04期

【摘要】：桂東北越城嶺巖體是一個由加里東期-印支期花崗巖組成的復(fù)式巖基,是目前南嶺地區(qū)鎢錫礦產(chǎn)調(diào)查評價的重點對象。本文選取該復(fù)式巖體中的加里東期不同巖性花崗巖,包括細(xì)�；◢忛W長巖、(粗)中粒斑狀二長花崗巖和(中)細(xì)粒(斑狀 含斑)二長花崗巖為研究對象,進行LA-ICP-MS鋯石U-Pb年代學(xué)、礦物學(xué)、地球化學(xué)和Nd-Hf同位素組成研究。研究結(jié)果表明,細(xì)�；◢忛W長巖和(粗)中粒斑狀二長花崗巖具有較低SiO_2(70%)含量和A/CNK值(0.99~1.05),較高CaO、TiO_2含量和FeO+MgO值,中等(La/Yb)N值以及中度虧損Ba、Sr、Eu元素等特征,副礦物以榍石為主加少量磁鐵礦,屬于I型花崗巖,形成時間為435~438 Ma;(中)細(xì)粒(斑狀-含斑)二長花崗巖具有富硅(70%)、富堿、貧鈣,高A/CNK值(1.04~1.14),低FeO+MgO值和(La/Yb)N值,中到重度虧損Ba、Sr、Eu元素等特征,副礦物含量低,以鈦鐵礦、獨居石為主,為S型花崗巖,形成時間為423~429 Ma,略晚于前者。C/MF-A/MF圖解反映I型花崗巖由變質(zhì)中基性火成巖部分熔融形成,源區(qū)具有負(fù)且穩(wěn)定的εNd(t)值( 7.1~ 7.9)和εHf(t)值( 6.4~ 7.8),平均地殼存留年齡為1.8 Ga左右。S型花崗巖的ε_(Nd)(t)值( 7.9~ 8.8)和t_(Nd2DM)值(1.81~1.88 Ga)與I型花崗巖類似,但是其CaO/Na_2O值(0.28~0.64)和相對分散的ε_(Hf)(t)值( 2.6~ 7.9)和t_(Hf2DM)值(1.57~1.90 Ga)說明源區(qū)可能存在變雜砂巖、變泥質(zhì)巖和年輕地殼組分的三元混合,且以前兩者為主。綜合分析華南加里東造山帶構(gòu)造演化序列可以得知,造山帶從褶皺縮短、逆沖加厚階段向伸展垮塌階段轉(zhuǎn)化而形成的等溫降壓過程,是形成越城嶺花崗巖的誘因。等溫降壓過程可以通過巖基旁側(cè)新寧-資源深大斷裂的松弛調(diào)整來實現(xiàn)。
[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.
【作者單位】： 中國地質(zhì)調(diào)查局武漢地質(zhì)調(diào)查中心;中國地質(zhì)調(diào)查局花崗巖成巖成礦研究中心;中國地質(zhì)大學(xué)(武漢)地質(zhì)調(diào)查研究院;
【基金】：中國地質(zhì)調(diào)查局地質(zhì)大調(diào)查項目(1212011120804、1212011120798、12120114020701) 右江成礦區(qū)桂西地區(qū)地質(zhì)礦產(chǎn)調(diào)查二級項目(DD2016034)聯(lián)合資助
【分類號】：P597.3;P588.1

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