朝鲜半岛古元古代摩天岭群的碎屑锆石U-Pb年龄及其地质意义

Detrital zircon U-Pb ages of the Machollyong Group in Korean Peninsula: Regional correlation and tectonic implications

克拉通内部活动带变质沉积建造蕴藏了早期超大陆形成中地体聚-散动力学过程的重要信息,碎屑锆石年代学则是揭示这种信息的最佳工具之一。针对华北（中-朝）克拉通最具代表性的古元古代活动带（辽-吉-朝活动带）中巨量沉积建造精细表征方面的空白区域,本文开展了朝鲜半岛检德地区摩天岭群的碎屑锆石年代学研究。SIMS U-Pb定年结果显示,北大川组变火山碎屑岩样品的锆石年龄谱记录了约2.53Ga的主要年龄峰值和约2.19Ga的最年轻峰值,说明北大川组开始沉积的时代应该晚于2.2Ga。南大川组变沉积岩样品碎屑锆石记录的最年轻峰值年龄为约2.02Ga,说明南大川组的沉积时代应该不早于2.02Ga;其锆石年龄谱记录了一个主要年龄峰值区域（2.02～2.18Ga）、一个次要年龄峰值（约2.46Ga）和一些2.78～3.30 Ga的古老年龄,指示其物质源区主要为同区古元古代地质体和邻近地体上的太古宙变质基底。区域对比表明,摩天岭群与中国境内辽吉活动带中的辽河群及集安群/老岭群具有基本一致的碎屑锆石年龄谱,说明它们不仅是同一时代的产物,而且分享类似的物质源区。这些时代一致、物源相近的沉积建造可以为甄别古元古代辽-吉-朝活动带的大地构造属性提供重要参考。与沉积年龄相近的碎屑锆石占据主导的碎屑锆石年龄谱反映了汇聚板块边缘各类盆地的典型特征,而相悖于大部分碎屑锆石年龄远大于地层沉积年龄的裂谷型盆地。

The meta-sedimentary successions in the intra-cratonic mobile belts encapsulate essential information for deciphering the convergent and divergent geodynamic processes of constituent terranes during the construction of early supercontinents.The detrital zircon geochronology presents a key to probing it.With a view to bridging the gap in the characterization of massive meta-sedimentary successions in the most representative Paleoproterozoic mobile belts（ i.e.,the Liao-Ji-Korea mobile belt） in the North China Craton,this study carried out a detrital zircon SIMS U-Pb dating on the Machollyong Group at Komdok,Korean Peninsula.Zircons from one meta-pyroclastic sample of the Puktaechon formation yielded a dominant peak age of ca.2.53 Ga and a youngest peak age of ca.2.19 Ga,constraining their formation time to later than 2.2 Ga.Detrital zircons from one meta-sedimentary sample of the Namdaechon formation yielded a dominant peak age span from 2.02 to 2.18 Ga,a subordinate peak age of ca.2.46 Ga and a few older ages from2.78 to 3.30 Ga, reflecting dual provenances of the Paleoproterozoic plutons in the Rangnim Massif and the Neoarchean and Mesoarchean crusts in the neighboring terranes.The youngest detrital age constrains the maximum deposition time of the Namdaechon formation at ca.2.02 Ga.Regional comparison suggests that the Machollyong Group shows consistent detrital zircon age spectra with the Liaohe Group and Ji＇an/Laoling groups in the Liao-Ji mobile belt.Such consistency indicates their synchronization in deposition and similarity in provenance.These coeval and consanguineous litho-stratigraphic sequences can provide insightful reference for calibrating the tectonic affinity in the Liao-Ji and Korea mobile belt during the Paleoproterozoic.The dominance of detrital zircons with ages close to the depositional age is characteristic of various basins on convergent plate margins,but inconsistent with rift basins commonly featuring much older detrital zircons than the depositional age.