胶莱盆地及其邻区白垩纪－古新世沉积构造演化历史及其区域动力学意义

基于野外和钻孔测井资料分析、火山岩同位素年代学分析 (40Ar-39Ar and SHRIMP U-Pb)、地震剖面的构造解释、断层运动学的野外分析结果，综合研究了胶莱盆地及其邻区白垩纪－古新世沉积构造演化历史。岩性地层分析表明，胶莱断陷盆地由三套地层单元所充填：早白垩世莱阳群和青山群、晚白垩世－古新世王氏群。青山群火山岩的同位素年代学测试结果给出了该火山岩的喷发时代在120～105 Ma。地震剖面的构造解译结果揭示胶莱盆地伸展构造受到深部两个拆离构造系统控制：一个发育于盆地南部地区，拆离断面位于深部8~10 km，向南缓倾于苏鲁造山带之下；另一个拆离系统由一系列北倾的犁式断层组成、分布于宽阔的胶莱盆地北部地区，主拆离面向北倾。这两个拆离系统分别形成于早白垩世莱阳群和晚白垩世-古新世王氏群沉积阶段。通过对不同地层单元断层滑动矢量的野外测量和古构造应力场反演，以及地层时代和同位素年代学测试结果的制约，建立了白垩纪－古新世构造应力场演替的年代序列。结果表明，胶莱盆地在白垩纪-古新世之间经历了伸展－挤压应力体制的交替演化。早白垩世伸展作用经历了两个不同的阶段：早期NW-SE向伸展和晚期近W-E向伸展。在早白垩世末期至晚白垩世初期，盆地遭受NW-SE向挤压，导致了胶莱盆地的缩短变形和郯庐断裂带的左旋走滑活动。晚白垩世－古新世时期，构造应力场转变为N-S向伸展，直到古新世末期，构造应力场转换为NE－SW向挤压。胶莱盆地和沂沭裂谷系白垩纪－古新世沉积构造演化历史对华北地区岩石圈减薄过程的动力学背景提供了重要的构造地质学制约。笔者推断，早白垩世两期引张应力作用是分别对华北地区增厚地壳或岩石圈的重力垮塌和岩石圈拆沉的响应，而早白垩世末期NW-SE向挤压记录了古太平洋板块与亚洲陆缘俯冲碰撞产生的远程效应。晚白垩世-古新世的引张伸展作用完全不同于早白垩世伸展构造，它指示了沿NNE向郯庐断裂带的右旋走滑活动及其拉分作用，在动力学上受到青藏地区块体的陆－陆碰撞产生的远程效应和古太平洋板块向亚洲大陆俯冲作用的联合应力场控制。

Cretaceous to Paleocene tectono-sedimentary evolution of the Jiaolai basin and in the contiguous areas of Shandong peninsular (North China) and geodynamic implications

This paper presents a synthesis of the study on tectono-sedimentary evolution of the Jiaolai basin (North China), based on outcropped and drilled well log lithostratigraphic analysis, isotopic (40Ar-39Ar and SHRIMP U-Pb) dating results of the volcanic rocks, structural interpretation of seismic profiles and field analysis of fault kinematics. Lithostratigraphic analysis shows that the Jiaolai basin is an extensional basin filled with three distinct rock units: the Early Cretaceous Laiyang and Qinshan Groups and the Late Cretaceous to Paleocene Wangshi Group. Isotopic dating of the volcanic rocks from the Qingshan Group yielded ages in 120 ~100 Ma for this rock unit. Structural interpretation of seismic profiles revealed that extensional structural styles of the Jiaolai basin are confined by two deep detachment systems: one developing beneath the southern margin of the Jiaolai basin with detachment zone gently dipping south underneath the Sulu orogenic basement, the other one dipping north below the broad area of the Jiaolai basin. Fault slip vector data were collected from different rock units of the basin and were analyzed in terms of stress regimes. A best chronology of the Cretaceous to Paleocene tectonic regimes has been established with the age constrained by stratigraphy and isotopic dating data. The results show that the Cretaceous to Paleocene tectonic extension and compression alternated. The Early Cretaceous extension proceeded through two phases: the early one in NW-SE and the late one in W-E. This was followed by a NW-SE compression occurring near the end of Early Cretaceous to the earliest Late Cretaceous (about 90±5 Ma). This compression resulted in contractional deformation of the Jiaolai basin and left-slip motion of the Tan-Lu fault zone. Tectonic regime changed to N-S extensional one during Late Cretaceous to Paleocene, which was ended by a NE-SW compressional phase probably occurring near the end of Paleocene. This Cretaceous to Paleocene tectono-sedimentary evolution history of the Jiaolai basin and the Yi-Shu rift zone provides constraint on geodynamic settings of the lithosphere thinning processes underneath North China. We interpreted that the two extensional phases in Early Cretaceous were dynamically associated with either gravity collapse or lithospheric delamination of the thickened crust or lithosphere in North China and the NW-SE compression was the consequence of far-field effect produced by NW-ward subduction of the Pacific plate underneath the Asian continent. The Late Cretaceous to Paleocene extensional basins are pull-apart origin related to dextral strike slip along the NNE-striking Tan-Lu fault system developed along the eastern margin of the Asian continent and dynamically associated with far-field effect of block collision occurring in the Tibetan region.