| 桂中昆仑关A型花岗岩锆石U-Pb年代学与地球化学特征 |
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| 引用本文： | 刘飞,李堃,黄圭成,邱啸飞,严乐佳,陆世才.桂中昆仑关A型花岗岩锆石U-Pb年代学与地球化学特征[J].地球科学,2018,43(7):2313-2329. |
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| 作者姓名： | 刘飞 李堃 黄圭成 邱啸飞 严乐佳 陆世才 |
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| 作者单位： | 1.中国地质调查局武汉地质调查中心, 湖北武汉 430205 |
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| 基金项目： | 中国地质调查局地质矿产调查项目121201009000150012 |
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| 摘 要： | 华南腹地燕山期岩浆活动、成因及其构造意义存在争议.本文选取桂中地区昆仑关花岗岩为研究对象，进行了系统的年代学、地球化学和Sm-Nd同位素研究.锆石LA-ICP-MS U-Pb定年结果为97.7±1.3 Ma（MSWD=1.6），表明昆仑关花岗岩是燕山晚期岩浆活动产物.地球化学分析显示，岩体富硅（SiO2=69.42%~72.52%），富碱（全碱=7.43%~8.43%），富钾（K2O=4.00%~5.02%，K2O/Na2O比值=1.17~1.62），富铝（Al2O3=13.65%~14.25%），低钙（CaO=1.20%~2.78%）；富集Rb、Th、U、K、Pb，亏损Ba、Nb、Sr、P、Ti；轻稀土富集，重稀土亏损，具明显Eu负异常（δEu=0.45~0.61），稀土元素分配图呈典型的"右倾"型；里德曼指数（δ）为2.06~2.41，属高钾钙碱性系列，铝饱和指数（A/CNK）为0.93~1.16，属准铝质-过铝质岩石.岩体的εNd（t）介于-7.68~-10.31，二阶段Nd模式年龄（TDM2）为1.52~1.73 Ga，均值1.58 Ga.岩石学、地球化学和Sm-Nd同位素特征表明昆仑关花岗岩为A型花岗岩，是在伸展构造环境中及低压、高温条件下由古元古代华夏基底部分熔融形成，并伴有幔源岩浆的混合.结合邻区同期次的岩浆活动和成矿作用，表明100~90 Ma华南腹地经历了一次重要的岩石圈拉张事件.
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| 关 键 词： | 昆仑关岩体 A型花岗岩 华南 燕山晚期 岩石圈拉张 地球化学 |
| 收稿时间： | 2018-03-14 |
Zircon U-Pb Geochronology and Geochemical Characteristics of the Kunlunguan A-Type Granite in Central Guangxi |
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| Abstract: | For studying the Late Yanshan magmatism in South China hinterland, and analyzing its petrogenesis and tectonic significance, this paper carries out systematical geochronological, geochemical and Sm-Nd isotopic investigations on the Kunlunguan granitic pluton in central Guangxi. LA-ICP-MS zircon U-Pb dating yields a weighted mean 206Pb/238U age of 97.7±1.3 Ma (MSWD=1.6), implying its Late Yanshan intrusion time. Geochemical compositions show that it is enriched in Si (SiO2=69.42%-72.52%), alkali (total alkali=7.43%-8.43%), K(K2O=4.00%-5.02%, K2O/Na2O=1.17-1.62), Al(Al2O3=13.65%-14.25%), but depleted in Ca(CaO=1.20%-2.78%). Rb, Th, U, K, Pb elements are enriched in the intrusion while Ba, Nb, Sr, P, Ti elements are depleted. REE is characterized by obvious negative Eu anomalies (δEu=0.45-0.61), and exhibits right-dipping patterns with LREE enrichment. Its aluminum saturation index value (A/CNK) ranges from 0.93 to 1.16, while redman index value (δ) ranges from 2.06 to 2.41, indicating the intrusion belongs to high-K calc-alkaline series and metaluminous to peraluminous rocks. Its εNd(t) value varies between -7.68 to -10.31, and the correspondent two-stage Nd isotopic modal ages range from 1.52 to 1.73 Ga (average value is 1.58 Ga). Mineralogy and geochemical characteristics indicate that Kunlunguan pluton is A-type granite. It has formed by partial melting of the Cathaysia paleoproterozoic felsic crustal material, being mixed with some mantle drived mafic malts, under a low-pressure, high-temperature condition at an extensional tectonic setting. Taking the igneous and metallogenic events in central Guangxi and adjacent areas into consideration, this study suggests that the lithosphere of South China hinterland thinned in 100-90 Ma. |
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