渤海湾盆地济阳坳陷碎屑锆石裂变径迹年龄记录的构造抬升事件

摘要

The dating of clastic rocks collected from the Jiyang depression in the southeast Bohai Bay Basin (BBB) is to reveal the provenance and its uplift/exhumation and tectonic thermal events based on the detrital zircon fission track ages.The study can provide new geothermological constraints for the tectonic evolution of the North China Craton (NCC),especially the Proterozoic tectonic evolution.The 14 sandstone/siltstone samples are gathered from the core drilling in Late Cretaceous-the Pliocene of Jiyang depression.The annealing age of the zircon fission track (ZFT) is in range from 308 ± 35Ma to 145 ± 19Ma,with all of their single ZFTa is older than their depositional age.So these zircons are detrital zircons.The P(x2) of single grain age in 13 samples is less than 5％,which can be used to indicate their sediment provenance and their tectonic history.The best fit peak ages of these mixed grain form 9 groups which are of P1 (1187Ma),P2 (720～548Ma),P3 (526Ma),P4 (330～319Ma),P5 (296 ～274Ma),P6 (213～201Ma),P7 (195 ～ 177Ma),P8 (134 ～ 102Ma) and P9 (94Ma).They and the DZFTa of 230Ma which past the x2 test indicate 9 period tectonic exhumation/magmatism of the NCC from the Mesoproterozoic to the Late Cretaceous.They are the Mesoproterozoic Qinyu uplifting movement,the Neoproterozoic uplifting in ca.720 ～575Ma,the Jixian uplifting movement in ca.548Ma,the ca.526Ma uplifting in late of the Early Cambrian,the Hercynian uplifting movement,the Late Triassic Indosinian Movement,the Early Jurassic compression movement (Late Indosinian Movement),the Early Cretaceous Yanshanian magmatism and the Late Cretaceous Yanshanian uplifting.The northern margin of NCC,the ancient continental land and NCC interior (Jiyang depression) are three major provenances of Upper Cretaceous-Pliocene detrital zircon of clastic rocks in Jiyang depression.The exhumation rate gradually increased since the Paleozoic with value of the Paleozoic,Triassic,Early-Middle Jurassic and Cretaceous were of 0.020 ～0.033 mm/y,033 ～ 0.042mm/y,0.034 ～ 0.049mm/y,and 0.041 ～ 0.097mrn/y,respectively,reflecting the Cretaceous tectonic/magmatic activity in the provenance is the most intense.The Mesoproterozoic-Late Cretaceous tectonic movement recorded by detrital zircon fission track records provides chronological evidence to explore the tectonic evolution of the North China Craton,especially the evolution of the Proterozoic.The comprehensive analysis inferred that NCC may be involved in the assemblage and rifting of the Rodinia supercontinent.%对采自渤海湾盆地东南部济阳坳陷的碎屑岩进行测年研究,目的是通过碎屑锆石裂变径迹年龄揭示源区及其抬升剥露史和构造热事件,为华北克拉通构造演化特别是元古宙构造演化提供新的热年代学约束.14件上白垩统-上新统砂岩/粉砂岩岩心样品测年结果显示,锆石裂变径迹年龄分布在308±35Ma ～ 145±19Ma之间,且所有单颗粒锆石径迹年龄均大于其沉积年龄,表明这些锆石为碎屑锆石.除1件样品外,其余13件样品的单颗粒年龄的P(x2)＜5％,可以用来识别源区及其构造抬升.未通过x2检验的锆石二项式最佳拟合峰值年龄集中分为9组:P1 (1187Ma)、P2(720～548Ma)、P3 (526Ma)、P4(330 ～319Ma)、P5(296～ 274Ma)、P6(213～201Ma)、P7(195～ 177Ma、162Ma)、P8(134～102Ma)和P9(94Ma),加上通过x2检验的三叠纪(230Ma),指示源区中元古代-晚白垩世经历的9期构造抬升/岩浆活动.它们分别是发生在中元古代的芹峪运动、新元古代的构造抬升(约720 ～575Ma)、～548Ma的蓟县运动;古生代～526Ma早寒武世末构造运动、海西期构造抬升;晚三叠世印支期挤压构造抬升、早-中侏罗世印支期弱挤压抬升、早白垩世燕山期强烈岩浆活动及晚白垩世燕山晚期的抬升.华北克拉通北缘、克拉通内部古陆和盆地内部是渤海湾盆地上白垩统-上新统的主要物源区,古生代以来剥露速率逐渐增大,古生代、三叠纪、早-中侏罗世和白垩纪分别为0.020～0.033mm/y,0.033～0.042mm/y,0.034～0.049mm/y和0.041～0.097mm/y,反映源区白垩纪构造/岩浆活动最强烈.锆石裂变径迹年龄记录的中元古代-晚白垩世构造运动对探讨华北克拉通的构造演化特别是元古宙的演化提供了年代学证据,综合分析推断华北克拉通可能参与了Rodinia超大陆的形成与裂解.