巫建华, 宋凯, 牛子良, 郭恒飞, 刘帅. 河北围场御道口盆地流纹岩锆石U-Pb年龄、地球化学特征及其地质意义[J]. 地质通报, 2019, 38(7): 1191-1205.
    引用本文: 巫建华, 宋凯, 牛子良, 郭恒飞, 刘帅. 河北围场御道口盆地流纹岩锆石U-Pb年龄、地球化学特征及其地质意义[J]. 地质通报, 2019, 38(7): 1191-1205.
    WU Jianhua, SONG Kai, NIU Ziliang, GUO Hengfei, LIU Shuai. ZirconU-Pb age and geochemical characteristics of the rhyolite of the Yudaokou basin in Weichang, Hebei Province, and their geological implications[J]. Geological Bulletin of China, 2019, 38(7): 1191-1205.
    Citation: WU Jianhua, SONG Kai, NIU Ziliang, GUO Hengfei, LIU Shuai. ZirconU-Pb age and geochemical characteristics of the rhyolite of the Yudaokou basin in Weichang, Hebei Province, and their geological implications[J]. Geological Bulletin of China, 2019, 38(7): 1191-1205.

    河北围场御道口盆地流纹岩锆石U-Pb年龄、地球化学特征及其地质意义

    ZirconU-Pb age and geochemical characteristics of the rhyolite of the Yudaokou basin in Weichang, Hebei Province, and their geological implications

    • 摘要: 对河北省围场县御道口盆地流纹岩进行SHRIMP锆石U-Pb定年,结果表明,盆地内流纹岩的锆石206Pb/238U年龄加权平均值为155.2±2.0Ma,属于晚侏罗世早期岩浆活动的产物,与辽源地块新民组和燕山陆內造山带髫髻山组的地质时代一致。流纹岩分为灰白色流纹岩和肉红色流纹岩2种,均具有较高的SiO2、K2O、Al2O3含量和低的CaO、MgO含量,属高钾钙碱性系列,肉红色流纹岩的K2O/Na2O和Fe2O3/FeO值略高于灰白色流纹岩。流纹岩的稀土元素总量较高,轻、重稀土元素分馏明显,负Eu异常明显,具右倾轻稀土元素富集型稀土元素配分曲线特征;富集大离子亲石元素Rb、Th、U、Ga、Y和高场强元素Zr、Hf、Nb、Ta,亏损大离子亲石元素Ba、Sr,具有A2型花岗岩和低Sr-Ba流纹岩的微量元素特征,具有较高的(87Sr/86Sr)i值(0.708606~0.711171)、较低的εNdt)值(-9.78~-7.11)、相对年轻的TDM2(1520~1737Ma)和较低的(206Pb/204Pb)t、(207Pb/204Pb)t、(208Pb/204Pb)t值,在εNdt)-(87Sr/86Sr)i图解上投影点位于下地壳和亏损地幔之间,在(207Pb/204Pb)t-(206Pb/204Pb)t和(208Pb/204Pb)t-(206Pb/204Pb)t图解上投影点位于下地壳和地幔之间,指示流纹岩可能是DMM型(亏损型)地幔岩浆、EMⅠ富集地幔岩浆和少量古老下地壳物质混合形成的年轻下地壳部分熔融的产物。御道口盆地流纹岩的锶-钕-铅同位素特征与内蒙古基底隆起带的长英质火山-侵入岩基本一致,也与燕山陆內造山带的长英质火山-侵入岩相似,但不同于辽源地块的长英质火山-侵入岩。

       

      Abstract: The SHRIMP U-Pb dating of zircon yielded a 206Pb/238U age of 155.2±2.0Ma for rhyolites in Yudaokou basin, located in Weichang County, northern Hebei Province, indicating that its geological age is early Late Jurassic, consistent with that of Xinmin Formation of Liaoyuan Block and Tiaojishan Formation of the Yanshan intracontinental orogenic belt. The rhyolites can be divided into gray and pinkish red colors, and both are characterized by typical enrichment of SiO2, K2O and Al2O3, low content of CaO and MgO, thus belonging to high-K calc-alkaline series rocks. Only the ratios of K2O/Na2O and Fe2O3/FeO of cinnamon rhyolite are slightly higher than the values of the gray one. Furthermore, the rhyolites exhibit high content of ∑REE, obvious fractionation of LREE and HREE, and strong negative Eu anomaly, possessing features of enrichment of LREE. These rocks are characterized by enrichment of LILE such as Rb, Th, U, Ga and Y, but depletion of Ba and Sr. In addition, HFSE, such as Zr, Hf, Nb and Ta are enriched as well. All of the samples show the trace element characteristics of A2-type granite and low Sr-Ba rhyolite, sharing the features of relatively high (87Sr/86Sr)i values (0.708606~0.711171), low εNd(t) values (-9.78~-7.11), and young TDM2 (1520~1737Ma), lower (206Pb/204Pb)t (16.93~17.06), (207Pb/204Pb)t (15.37~15.43) and (208Pb/204Pb)t (37.30~37.72). The projection points are located between the lower crust and the depleted mantle in the diagram of εNd(t)-(87Sr/86Sr)i, and between the lower crust and mantle in the diagram of (207Pb/204Pb)t-(206Pb/204Pb)t and (208Pb/204Pb)t-(206Pb/204Pb)t, indicating that the rhyolite in the Yudaokou basin was probably formed by partial melting of young lower crust material which originated from DMM mantle, EMI enriched mantle magma and old lower crustal material. The source material was different from felsic volcanic-intrusive rocks in Liaoyuan Block, but similar to felsic volcanic-intrusive rocks in the Yanshan intracontinental orogenic belt.

       

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