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广西佛子冲铅锌(银)矿田岩浆岩的时代及地球化学特征 总被引:16,自引:1,他引:16
广西佛子冲铅锌(银)矿田内发育两个岩浆岩系列,即海西期弱碱质S型花岗岩系和燕山期钙碱质Ⅰ型花岗质火山岩系,两者的地球化学特征差异十分显著。钙碱质岩系由早期至晚期,其岩石特征参数、微量元素及稀土元素表现出规律性变化,反映出同源火山岩浆的演化特征。铅锌(银)成矿作用与钙碱质岩系,尤其是晚期浅成侵入体(次火山岩)密切相关。 相似文献
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C. M. Hohenberg R. H. Brazzle O. V. Pravdivtseva A. P. Meshik 《Journal of Earth System Science》1998,107(4):413-423
129Xe, from the decay of the now-extinct 16.7 Ma129I, accumulates in iodine-bearing sites and since most iodine host phases are secondary, the I-Xe system is typically a chronometer for post-formational processes. The validity of the I-Xe chronometer is confirmed by comparison with Pb-Pb ages on phosphate and feldspar separates from twelve meteorites. Phosphate separates are found to be concordant with Pb-Pb for all six samples in which useful I-Xe data were obtained. Feldspar is a better iodine host than apatite in H chondrites, typically providing good I-Xe isochrons. These too are concordant with the Pb-Pb ages of the corresponding phosphates for five out of six feldspar separates. The exception is Allegan whose feldspar yields one of the oldest I-Xe ages observed, similar to those for CI and CM magnetites. We attribute this to a more primary mineralization, predating the secondary phosphate from which the comparison Pb-Pb age was obtained. Absolute I-Xe ages, found using the reported Pb-Pb age of Acapulco phosphate provide an absolute I-Xe age of 4.566 ± 0.002 Ga for both Shallowater and Bjurböle irradiation standards. This allows relative I-Xe ages to be interpreted in the context of absolute ages. 相似文献
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