吉辽边界梅河口-开原地段晚海西—早印支期岩浆旋回及构造意义

LATE HERCYNIAN-EARLY INDOSINIAN MAGMATIC CYCLES IN MEIHEKOU-KAIYUAN BETWEEN JILIN AND LIAONING PROVINCES: Tectonic Implication

本区已获晚海西—早印支期花岗岩类6件锆石高精度测年数据和两件继承锆石年龄,确定了其活动时限305～242 Ma,主体分属早中三叠世岩石序列、晚二叠世岩石序列、中二叠世岩石序列相应的岩石单元.小四平岩体的年龄及其被晚三叠世地层不整合覆盖,指明古亚洲洋构造域完成在242～228 Ma间.基于上述岩石年龄及形成构造环境和邻近地区磨拉石相发育的层位,揭示古吉黑造山带晚海西—早印支期构造运动或构造-岩浆旋回具有多幕式的递进演化模式,并受显生宙泛大陆旋回所制约.

Six high precision zircon dating data and two inherited zircon ages for the Late Hercynian-Early Indosinian granitoid in this area are obtained.Its formation ages are confirmed as 305-242 Ma,which can be assigned into the Early-Middle Triassic rock unit,Late Permian rock unit and Middle Permian rock unit,respectively.The age of Xiaosiping pluton and the fact that this pluton is covered unconformably by the Late Triassic strata indicate that the Paleo-Asian oceanic tectonic domain was completed between 242 and 228 Ma.Based on the above rock ages,as well as its tectonic settings and the occurrence of the adjacent molasse facies layer,it is revealed that the Late Hercynian-Early Indosinian tectonic movement or tectonomagmatic cycle of the Paleo-Jihei orogenic belt experienced a multi-episode progressive evolution,and was constrained by the Phanerozoic Pangea cycle.