FAULT DISTRIBUTION PATTERNS OF THE LUXI BLOCK,SHANDONG,AND MESOZOIC SEDIMENTARY-MAGMATIC-STRUCTURAL EVOLUTION SEQUENCE

Faults in the Luxi block have two different distribution patterns: one is the radiate distribution pattern,and the other is the concentric circular distribution pattern,with faults encircling the core of the block basement.The former is composed of NW-striking,steep-dipping,basement dextral ductile shear zones and faults of complex mechanical nature in the cover sediments,and the latter consists of three major cover extensional detachment zones,with the main detachment surfaces lying at the unconformities between the Paleozoic cover and Precambrian basement,disconformities between the Carboniferous and Ordovician and faults between the Meso-Cenozoic downfaulting-sedimentary series and Cenozoic volcanic-sedimentary rocks.Mesozoic structural styles include three levels: Indosinian overthrusts and folds,middle Yanshanian NNE-oriented box folds and late Yanshanian conjugate(NW and NNE),normal to strike-slip faults.Accordingly,the Luxi block experienced three stages of basin formation,i.e.: the Early to Middle Jurassic,Early Cretaceous and Late Cretaceous.The superimposition of these Mesozoic basins in space gave rise to a complex basin-mountain coupling relation inside the block.There were two periods of magmatic activity,i.e.the Early Jurassic(190—180Ma) and Early Cretaceous(132—110Ma).By integrating the sedimentary records,magmatism and structural deformation,the Mesozoic structural history of the Luxi block may be divided into six stages: Late Triassic compression,Early to Middle Jurassic weak extension,Middle to Late Jurassic compression and crustal thickening,Early Cretaceous continental rifting and crustal extension,terminal Early Cretaceous compression and basin inversion event,and Late Cretaceous uplift.These structural evolution stages and events have great significance for the study and understanding of the Mesozoic structural regime transition and dynamic transformation in the deep interior of the lithosphere in eastern China.