Late Mesozoic Tectonic Evolution of Southwestern Fujian Province, South China: Constraints from Magnetic Fabric, Zircon U-Pb Geochronology and Structural Deformation

A combined study of magnetic fabrics, zircon U-Pb geochronology and structural deformation was carried out for Late Paleozoic sedimentary and Mesozoic magmatic rocks in the southwestern Fujian rift basin, South China, aiming at deciphering the tectonic evolution during Late Mesozoic. Field observations showed that the Late Mesozoic structure deformations in southwestern Fujian were categorized into four phases: NW-SE compression, ENE-WSW extension, NNE-SSW compression and NNW-SSE extension, sequentially. Zircons picked out from Juzhou granite and WNW-trending diabase dykes showed complete crystal shapes and clear oscillatory zonings on their edges, and the U-Pb dating yielded ages of 132 and 141 Ma, respectively. The susceptibility ellipsoid magnitude parameters of the Juzhou granite are characterized by flaser type strain ellipsoid, with pole density center of K3 falling into the first and the third quadrants, these features revealed that the Juzhou granite formed in ENE-WSW compressional stress field, indicating the early stage of Early Cretaceous extrusion in southwestern Fujian. The late stage of Early Cretaceous NNE-SSW extension was limited by the widespread WNW-trending diabase dykes, which were usually regarded as important indications for a regional extensional setting. On the basic of the previous researches, structural deformation studies, and the deductions above, it can be concluded that southwestern Fujian experienced five main tectonic stages during Late Mesozoic: Early Jurassic extension, Middle–Late Jurassic thrusting, early stage of Early Cretaceous extension, late stage of Early Cretaceous compression and Late Cretaceous extension.