Application And Validity Of Multiple Geothermobarometers On The Aishan Granite,Jiaobei Terrane

Temperature and pressure are important physical conditions for forming of various rocks.It is of great significance to study the temperature and pressure ofin the rocks rock forming processes.To identify the physical and chemical condition,one of the effective approaches is calibration of the geothermobarometers with experimental synthetic minerals.However,the natural geological process is far more complicated,leadsing to different results of temperature and pressure obtained with different geothermobarometers for the same sample.In addition,calibration by different authors could differ with each other.Therefore,the mineral geothermobarometer might give semi-quantitative temperature and pressure.Same method applied to different rock samples for comparison produces identical results.This implies that the deviation could be a systematic error in calibration.Jiaodong Peninsula is one of the most important gold in China.There are three stages of granites.Many scholars mainly studied Linglong and Guojialing intrusions which show direct contact with gold deposits on the surface.The Aishan granite is less outcropped and has not been observed showing direct contact with gold deposits on the surface,so it received much less attention.However,the age of Aishan granite is about 116±1 Ma,which is very close to that of large-scale gold mineralization in Jiaodong?120±5 Ma?.This implies a direct or indirect relationship with regional mineralization.Based on previous works,I found that under the condition of fixed pressure P or 1/T,the relationship between P and 1/T with ln X is close to linear respectly.So I fitted a new formula about Titani Q?1-4 kbar?:lnX_TiO2^quartz =??-5535.33?/T?k??+0.00612*P?kbar?-130.40162*?P?kbar?/T?k??-1.59524+ln a _TiO2,R²=0.98545,However,due to the lack of experimental data,the accuracy is still to be verified.In this thesis,the temperature and pressure conditions of each lithological units of the Aishan granites are quantitatively estimated with Al?in?hornblende geobarometer,Q-Ab-Or phase diagram method,Ti-in-quartz geothermometer and Zr-in-sphene geothermometer.We also compared the rock forming temperature and pressure of the 3 stages of Mesozoic granite in the Jiaobei terrane.The pressure of Linglong granites,guojialing granites and Aishan granites are about 2.8-3.5 kbar,2.8-4 kbar and 1.5-2.1kbar respectively,converted into crystallization and denudation depth.Linglong granites is similar to Guojialing granites,which is about 11-12km,while Aishan granites is about 5-6 km,which indicates that the denudation rate reaches 0.6 km/Ma between 130-119 Ma.This confirms that strong geological activities must have taken place in the era,and on the other hand further confirmed the abrupt uplift and denudation of the crust in the eastern China in the early Cretaceous.Our research shows that the erosion of Aishan granitic body is limited.As a composite granitic body with multiple lithofacies,there might be a huge unexposed volume underground,which should be more closely related to the regional gold mineralization.