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    河北省撒岱沟门斑岩型钼矿床二长花岗岩的锆石U-Pb年龄及其意义

    Zircon U-Pb dating of adamellite from the Sadaigoumen porphyry molybdenum deposit in Fengning, Hebei Province, and its significance

    • 摘要: 提要:河北省丰宁县撒岱沟门斑岩型钼矿床位于华北地台板块的燕辽成矿带,其含矿岩体撒岱沟门二长花岗岩体缺乏精确定年以厘定其形成时代,本文采用LA-MC-ICP-MS方法对其年龄进行了精确测定,并在总结前人资料的基础上,探讨了该地区的成矿构造背景。结果表明,撒岱沟门二长花岗岩体成岩年龄为257.4~247.7 Ma。由于侵位冷却作用,岩体下部的年龄为(247.7±1.2)Ma,较岩体上部的年龄(257.4±1.1) Ma和(256.9±0.9)Ma晚。同时,继承锆石(年龄为(1826±14)Ma)的存在,指示在成岩过程中发生了同化混染作用。该地区的成矿构造背景表明,250 Ma左右的华北板块北缘处于由强烈挤压背景向后造山转换的阶段,这种构造体制的转化有利于岩体的形成。

       

      Abstract: Abstract: The Sadaigoumen molybdenum deposit lies in the Yan-Liao metallogenic belt, which is located on the north margin of North China platform. For the purpose of accurate determination of the age of ore-bearing adamellite, the authors employed the zircon LA-MC-ICP-MS dating, which yielded a concordant age of (257.4±1.1) Ma and two weighted average ages of (256.9±0.9) Ma and (247.7±1.2) Ma. Because of the cooling of the intrusion, the age of the lower part of the rock (247.7±1.2) Ma is younger than the ages of the upper part (257.4±1.1) Ma and (256.9±0.9) Ma. The inherited zircon age implies assimilation in the process of mineralization, which is consistent with the previous study result of I-type granite. Combined with the previous study, the authors investigated the metallogenic geodynamics background of the study area. North China platform was transformed from the strong squeezing stage to the post-orogenic stage around 250 Ma, which was favorable for the formation of adamellite.

       

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