华南晚中生代构造体制转折结束时限研究——兼与华北燕山地区对比

中国东部中生代构造体制转折过程及其相应的岩浆作用是当前研究热点。福建是华南中生代多期次火山活动发育最齐全的地区之一，锆石SHRIMP UPb法测年表明：福建分布最广的晚中生代“南园组”火山岩形成时代可明显分为两期，分别为中侏罗世末—晚侏罗世（162.3～149.8Ma）和早白垩世（142.3～130.1Ma）。区域地质构造和地层对比表明，该两期火山岩形成于不同的火山活动旋回和构造背景，不能归入同一地层组中。与华北燕山地区相比较，前者层位相当于髫髻山组，后者层位相当于张家口组，推断它们分别形成于华南构造体制转折最终结束前后。据此提出华南中生代构造体制转折结束于晚侏罗世（149.8～142.3Ma），也即华南与华北的构造体制转折基本同时结束。

Study on the Ending Time of Late Mesozoic Tectonic Regime Transition in South China——Comparing to the Yanshan Area in North China

Current studies are focusing on the process and related magmatism of Mesozoic tectonic regime transition in eastern China.Fujian is one of the areas where multiple volcanic activities took place in South China during Mesozoic.Zircon SHRIMP U-Pb dating indicates that formation time of widespread volcanic rock of Late Paleozoic Nanyuan Formation in Fujian can be divided into two periods:middle Jurassic to late Jurassic(162.3-149.8Ma)and early Cretaceous(142.3-130.1Ma).Based on regional structure and stratigraphy,the two periods of volcanic rocks in Fujian belong to different volcanic cycles and different tectonic settings,so they can not be assigned into the same Formation.Compared with the Yanshanian sequences in North China,the former is equivalent to the Tiaojishan Formation and the latter the Zhangjiakou Formation,implying that both of them formed before or after the end of late Mesozoic tectonic regime transition in South China respectively.It was proposed that Mesozoic tectonic regime transition in South China ended in late Jurassic(149.8-142.3Ma),i.e.,the transitions ended at almost same time in both South China and North China.