吉林东南部古元古代中——晚期富钾花岗质岩石的时代、成因及其对区域构造演化的制约

Age and petrogenesis of Middle-Late Paleoproterozoic potassium-rich granitic rocks in southeastern Jilin and their constraints on regional tectonic evolution

通过对吉林东南部富钾花岗质岩石系统的锆石U-Pb年代学和地球化学研究,并结合Lu-Hf同位素结果来制约其形成时代、成因和构造环境。研究结果表明,富钾花岗质岩石形成于2.08 Ga±,而与之伴生的辉石斜长角闪岩中变质锆石形成于1.90 Ga±;富钾花岗质岩石具有富硅、富碱、富钾和贫镁等特征,主体属于高钾钙碱性系列,具有典型的壳源成因特点。Lu-Hf同位素结果显示,岩石可能来源于2.34~2.73 Ga新生地壳物质的部分熔融,并具有少量古老地壳物质的涉入。结合前人有关区域变质火山-沉积岩系和基性侵入体等研究成果,本文认为吉林东南部富钾花岗质岩石应形成于类似弧后盆地的伸展环境,并且区域上遭受了1.90 Ga±变质事件的改造。

Zircon U-Pb and whole-rock geochemistry combined with the Lu-Hf isotopes were carried out on the K-rich granitic rocks of the southeastern Jilin Province to constrain the emplacement age,petrogenesis and tectonic setting. The results show that the K-rich granitic rocks were formed at ca. 2. 08 Ga,and the coexisting amphibolites were metamorphosed at ca. 1. 90 Ga. The K-rich granitic rocks are rich in SiO_2,K_2O and depleted in MgO,belonging to high K calc-alkaline series,which are typical crustal genesis. The Lu-Hf isotopes indicate that source of the granites was 2. 34 ~ 2. 73 Ga juvenile crustal material contaminated by the old crust materials. Combined with the previous studies on the meta-supracrustal rocks and basic intrusives in this region,the authors propose that the K-rich granitic rocks in the southeastern Jilin could be formed under an extensional setting similar to the back-arc basin and subsequently metamorphosed at ca. 1. 90 Ga.