The Structural Features And Ages Of Activities Of Lianhuashan Fault And Changle-Nan’ao Fault

Lianhuashan fault and Changle-nan’ao fault are two important strike-slip faults in theSoutheast China. There is a huge controversy over the movement ages and the tectonicattribute of these two faults. The research of the faults plays an important role to studythe tectonic evolution of the South China Block.Lianhuashan fault mainly distribute in the Mesozoic granites and Mesozoic volcanicrocks. The macro-structural observation from the field geological survey of Lianhuashanfault indicates that grain size and the matrix content increased and the number ofporphyroclasts decreased in the mylonites from the ductile shear, showing a continuousprogressive deformation trends from the edge to the center of the ductile shear zone.Ductile shear zone foliations develop towards the NE, between40°-75°, and the dipangles are greater than50°, suggesting that Lianhuashan fault is a strike-slip fault. Thecharacteristics of the SC fabric and asymmetric porphyroclasts indicate that Lianhuashanfault is a sinistral strike-slip fault. The microscopic structural study with a microscopeindicates that a large number of quartz and feldspar brittle-ductile deformation featuresdeveloped in the mylonites from Lianhuashan fault. The characteristics of the SC fabrics,asymmetrical porphyroclasts and domino structures indicate that Lianhuashan fault is asinistral strike-slip fault. It is estimated that the deformation temperature is450-500°Cbased on the deformation behavior of quartz and feldspar in the mylonite samplecollected from Anliu town. A reliable plateau age of92.60±0.58Ma is obtained by biotite⁴⁰Ar/³⁹Ar dating, which is interpreted as representing cooling age. Combined with previous research, we believe that Lianhuashan fault experienced two strike-slip thermalevents respectively in middle Early Cretaceous and terminal Early Cretaceous-early LateCretaceous. The strike-slip thermal event in middle Early Cretaceous happened before129.7±0.4Ma. Different ages reflect the inhomogeneous cooling in Lianhuashan faultzone. The strike-slip thermal event in terminal Early Cretaceous-early Late Cretaceoushappened before92.6Ma. The studies of the Mafic Dikes show that the strike-slipmovement of Lianhuashan fault did not occur after90Ma, when the study area is inextensional tectonic setting. The tectonic attribute of Lianhuashan fault is a huge sinistralstrike-slip ductile shear zone, reflected by its characteristics as a ductile shear zone.The macro-structural observation from the field geological survey ofChangle-nan’ao fault indicates that the ductile shear zone foliations develop towards theNE, the dip angles are greater than50°, and the mineral stretching lineations plunge at15°-20°, suggesting that Changle-nan’ao fault is a strike-slip fault. The characteristicsof the SC fabric, porphyroclasts and asymmetric shear folds indicate that Changle-nan’aofault is a sinistral strike-slip fault. The microscopic structural study with a microscopindicates that rotational porphyroclasts, domino structures and quartz ribbons can beavailable in mylonitized granitic rocks, and quartz ribbons and augen quartz can beavailable in schists. It is estimated that the deformation temperature is420-530°C basedon the deformation behavior of quartz and feldspar in the schists sample collected fromDongshan town. A reliable plateau age of98.19±0.71Ma is obtained by muscovite⁴⁰Ar/³⁹Ar dating, which is interpreted as representing cooling age. Combined withprevious research, we believe that Changle-nan’ao fault experienced two strike-slipthermal events respectively in late Early Cretaceous and terminal Early Cretaceous. Thestrike-slip thermal event in late Early Cretaceous happened before121.5Ma. Thestrike-slip thermal event in terminal Early Cretaceous happened before109Ma. After thestrike-slip thermal event in terminal Early Cretaceous, Changle-nan’ao fault stoppedmoving. Different ages reflect the inhomogeneous cooling in Changle-nan’ao fault zone.The studies of the Mafic Dikes show that the strike-slip movement of Changle-nan’aofault did not occur after90Ma, when the study area is in extensional tectonic setting. The tectonic attribute of Changle-nan’ao fault is a huge sinistral strike-slip ductile shear zone,reflected by its characteristics as a ductile shear zone.Lianhuashan fault and Changle-nan’ao fault experienced two strike-slip thermalevents in middle-late Early Cretaceous and terminal Early Cretaceous-early LateCretaceous. Their evolutionary histories are controlled by Pacific Plate tectonics. Thetwo faults are close in location, approximately parallel in spatial trending, sinistralstrike-slip ductile shear zone, similar in ages of activities, generated in the same tectonicsetting. Therefore, the authors infer that the two faults presents sinistal strike-slip at thesame time. The strike-slip thermal event in middle-late Early Cretaceous happenedbefore130Ma. The strike-slip thermal event in terminal Early Cretaceous-early LateCretaceous happened before109Ma.