胶北地体荆山群禄格庄组沉积时代与物源——来自山东沐浴店地区长石石英岩碎屑锆石U-Pb年龄与稀土元素的新证据

Depositional timing and provenance of the Lugezhuang Formation in the Jingshan Group in the Jiaobei terrane: New evidence from detrital zircon U-Pb ages and rare earth elements of arkose-quartzite in Mayudian,Shandong Province

荆山群禄格庄组是胶北地体古元古代变沉积岩系最重要的组成部分之一,准确测定其原岩沉积时代与物质源区,对进一步探讨荆山群与粉子山群之间的成因关系具有重要的地质意义。以山东莱阳沐浴店地区出露的禄格庄组长石石英岩为研究对象,通过对长石石英岩中碎屑锆石内部矿物包体、阴极发光图像、LA-ICP-MSU-Pb定年与稀土元素组成的综合研究发现,沐浴店地区禄格庄组长石石英岩的碎屑锆石207Pb/206Pb年龄介于2502~1970 Ma之间,其中最小一组碎屑锆石上交点年龄为2079 Ma,结合沐浴店地区禄格庄组记录了1934 Ma变质年龄,初步限定沐浴店地区荆山群禄格庄组的原岩沉积时代为2079~1934 Ma。综合以上研究及相关数据表明,荆山群禄格庄组、南辽河群里尔峪组和集安群蚂蚁河组的碎屑锆石都具有2200~2100 Ma的单峰年龄;而粉子山群小宋组-祝家夼组、北辽河群浪子山组与老岭群达台山组都以出现大于2500 M a的峰值年龄为特征。结合胶-辽-吉带的其他地质数据,推测粉子山群小宋组与祝家夼组沉积时可能靠近被动大陆边缘的一侧,而荆山群禄格庄组可能更靠近岩浆岛弧的一侧,二者可能属于同时异相沉积的产物。

As the Lugezhuang Formation of Jingshan Group is one of the most important parts of the Paleoproterozoic meta-sedimentary rocks in the Jiaobei terrane, accurate determination of its depositional timing and provenance is of great geological significance for further exploring the genetic relationship between the Jingshan Group and the Fenzishan Group. A comprehensive study on mineral inclusions,cathodoluminescence( CL) images,LA-ICP-MS U-Pb dates,and in-situ rare earth element( REE) compositions of detrital zircons indicates that the age of detrital zircons of the arkose-quartzite of the Lugezhuang Formation in the Muyudian area ranges from 2502 Ma to 1970 Ma,of which the youngest group age of detrital zircons is circa 2079 Ma.Combined with its metamorphic age of circa 1934 Ma of the Lugezhuang Formation,it is preliminary determined that the depositional timing of the Lugezhuang Formation ranges from 2079 Ma to 1934 Ma.On the basis of above and published data,detrital zircons from the Lugezhuang Formation of Jingshan Group,Lieryu Formation of South Liaohe Group and Mayinghe Formation of the Ji’ an Group all have a single peak of 2200 ~ 2100 Ma. The Xiaosong Formation and Zhujiakuang Formation of Fenzishan Group, Liangzishan Formatin of North Liaohe Group and Dataishan Formation of Laoling Group are all characterized by peak ages greater than 2500 Ma.Combining with geology of the Jiao-Liao-Ji belt,it is speculated that the Xiaosong Formation and Zhujiakuang Formation of the Fenzishan Group might be deposited close to the passive continental margin, while the Lugezhuang Formation of the Jingshan Group might be deposited closer to the magmatic island arc.Therefore,the rocks of Fenzishan Group and Jingshan Group might be simultaneously deposited in different sedimentary facies.