敦化-密山断裂带的平移距离:来自松嫩-张广才岭-佳木斯-兴凯地块古生代-中生代岩浆作用的制约

敦化-密山断裂带是郯庐断裂北段的重要分支之一,其大规模左行走滑发生的时限以及平移距离一直存在较大争议。本文系统地总结了松嫩-张广才岭地块东缘、佳木斯地块以及兴凯地块之上古生代-中生代火成岩的锆石U-Pb年代学资料,结合其空间分布特征,对敦化-密山断裂带的平移时限及距离提供了制约。研究表明,松嫩-张广才岭地块东缘与兴凯地块在古生代-中生代期间具有类似的岩浆活动历史,两个地块之上该时期的岩浆作用可以划分为8个主要期次:中-晚寒武世(ca.500~516Ma)、早奥陶世(ca.480~486Ma)、晚奥陶世(ca.450~456Ma)、中志留世(ca.426~430Ma)、早二叠世(ca.285~292Ma)、晚二叠世(ca.255~260Ma)、晚三叠世(ca.202~210Ma)和早侏罗世(ca.185~186Ma)。相比之下,佳木斯地块中的古生代-中生代早期岩浆事件则集中在晚寒武世(~492Ma)、晚泥盆世(~388Ma)、早二叠世(~288Ma)、晚二叠世(~259Ma)和早侏罗世(~176Ma),而晚奥陶世-志留纪和晚三叠世的岩浆活动在佳木斯地块未见报道。早白垩世晚期(ca.105~110Ma)和晚白垩世(ca.90~94Ma)的岩浆活动在三个地块均存在。上述结果表明兴凯地块东缘与松嫩-张广才岭地块东缘在早古生代经历了共同的地质演化历史,而中生代早期,兴凯地块西缘与松嫩-张广才岭地块东缘经历了同样的岩浆作用历史。上述结果暗示,敦化-密山断裂可能经历了至少两次平移,分别发生在中-晚二叠世-早三叠世和中-晚侏罗世-早白垩世,推测其总的平移距离约400km。结合研究区中生代期间的构造演化历史,敦化-密山断裂中生代的左行平移应与中-晚侏罗世-早白垩世期间古太平洋板块(Izanagi板块)的斜向俯冲相联系。

The offset distance of the Dunhua-Mishan Fault: Constraints from Paleozoic-Mesozoic magmatism within the Songnen-Zhangguangcai Range, Jiamusi, and Khanka massifs

The Dunhua-Mishan Fault is one of important branches of the northern segment of Tan-Lu Fault, its distance and age of large-scale sinistral strike-slip faulting remains a hot debate. In this study, the geochronological data of the Paleozoic-Mesozoic igneous rocks within the Songnen-Zhangguangcai Range, Jiamusi, and Khanka massifs, together with their spatial and temporal variations, provide close constraints in this regard. Geochronological data suggest that the eastern margin of the Songnen-Zhangguangcai Range and Khanka massifs share a common magmatic history during Paleozoic to Mesozoic. The Paleozoic-Early Mesozoic magmatism within the mentioned-above two massifs can be divided into eight stages, i.e., Middle-Late Cambrian (ca.500~516Ma), Early Ordovician (ca.480~486Ma), Late Ordovician (ca.450~456Ma), Middle Silurian (ca.426~430Ma), Early Permian (ca.285~292Ma), Late Permian (ca.255~260Ma), Late Triassic (ca.202~210Ma) and Early Jurassic (ca.185~186Ma). By comparison, Paleozoic-Early Mesozoic magmatic events within the Jiamusi Massif concentrate in Late Cambrian (~492Ma), Late Devonian (~388Ma), Early Permian (~288Ma), Late Permian (~259Ma), and Early Jurassic (~176Ma ), respectively. The igneous rock with Late Ordovician-Silurian and Late Triassic ages is not yet identified in the Jiamusi Massif. In addition, the late-stage of Early Cretaceous (ca.105~110Ma) and Late Cretaceous (ca.90~94Ma) igneous rocks coexisting in mentioned-above three massifs. These results indicate that the eastern margins of the Songnen-Zhangguangcai Range and Khanka massifs experienced common geological evolution during Early Paleozoic, and the western margin of the Khanka Massif and the eastern margin of the Songnen-Zhangguangcai Range Massif experience the common magmatic history in the Early Mesozoic. These findings suggest that Dunhua-Mishan Fault have undergone at least two-stage strike slip faulting, i.e., the Middle-Late Permian to Early Triassic and Middle-Late Jurassic to Early Cretaceous; the total offset distance was approximately 400km. Combining with the Mesozoic tectonic evolution in study area, the left-lateral displacement of the Dunhua-Mishan Fault was related with the oblique subduction of the Paleo-Pacific Plate (Izanagi) during Middle-Late Jurassic to Early Cretaceous.