丹东花岗岩的地球化学特征及其成因

Geochemical features and origin of Dandong granite.

新的SHRIMP定年结果表明,原先划归于古元古代的丹东花岗杂岩现在被确定为中生代岩体.其岩浆型环锆石带的年龄代表结晶年龄,为167～157 Ma;但是这些锆石的核部年龄主体为古元古代.本文侧重探讨丹东花岗岩体的岩石学和地球化学特征,论证其起源和产生的构造背景.研究结果表明,丹东花岗岩体具铕异常(Eu/Eu*=0.59～1.41),轻重稀土分异明显,其微量元素特征与安第斯型构造背景下的花岗岩特征一致,其tDM和εNd(t)变化范围分别为1.93～2.30 Ga和-17.95～-21.32.εNd(t)-t图解显示丹东花岗岩的源岩以古元古代中酸性壳源岩石为主.构造环境环境判别结果表明其形成于大陆边缘岩浆弧.结合中生代丹东地区所处的大地构造背景,本文认为丹东花岗岩体的起源和侵位与古太平洋板块向欧亚板块的俯冲有关.

New SHRIMP dating reveals that the previously-known Paleoproterozoic Dandong granitic complex is Mesozoic. SHRIMP dating to zircon oscillation rims yielded a crystallization age of 167 similar to 157 Ma of mica monzogranite, however the weighted mean age of inherited zircon in the zircon core is Paleoproterozoic. This paper mainly describes petrological and geochemical characters of Dandong Granite in order to discuss its origin and tectonic setting. The REE pattern of Dandong Granite shows negative Eu anomalies, Eu/Eu* = 0.59 similar to 1.41. There is distinct differentiation between light rare earth elements and heavy rare earth element. The granite shares all the features of trace elements common to the granite in the Andes-type continental margin. It shows that t(DM) of the pluton ranges from 2.30 Ga to 1.93 Ga, epsilon(Nd) (t) of the pluton has a range from - 17.95 to - 21.32. In the epsilon(Nd) (t) - t diagram, the source rock of Dandong Granite was mainly derived from Paleoproterozoic and medium to acid crustal rocks. Tectonic discrimination shows that it was formed in the continental marginal arc. In conjunction to Mesozoic tectonic setting of Dandong area, it is deduced that origin and emplacement of Dandong Granite are related to subduction of the Paleo-Pacific Plate to the Eurasia Plate.