The petrology and Ar-Ar Dating studies of the early Proterozoic Huang-Yuan Massif in the Central Qilian, China

• Main Authors: Po-Hsiang Chang, 張博翔
• Other Authors: Ching-Lang Tsai
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/89240314451630835948

碩士 === 國立成功大學 === 地球科學系碩博士班 === 92 === 　　Dating area is located at about 50km northwestern to Hsineng, Northwestern China. This area belong to Huang-Yuan Massif which is located in the central part between the North Qilian and central-south Qilian Mountains. For this area, we study the petrology、mineral chemistry、40Ar-39Ar dating, and hope to know the P-T Paths and metamorphism age. 　　The main rock types of studies area are metapelites and metabasites. The mineral assemblages of the metapelites are Bio+Mus+Feld+Qtz+Grt±Sill±Chl±Op±Tur±Cal±Sph ±Zir±Ap±REE. Micas define schistosity. Feldspar and quartz as the porphyroblasts or matrix. Garnet is porphyroblast. Sillimanite of the sillimanite zone and micas together from prefer-oriented, while sillimanite of contact metamorphism is of the matrix, some sillimanite of contact metamorphism with micas form schistosity due to ductile shear. The mineral assemblages of the metabasites are Amp+Plag+Qtz±Bio±Grt±Ep±Cpx±Op±Sph±Zir±Ap. Amphibole define schistosity. Garnet was produced by contact metamorphism. Epidote was produced by fluidization of ductile shear zone or saussuritization. Cpx in the meta-gabbro have irrengular grain boundary by ductile shearing. The rocks have been mylonited in the ductile shear zone. The peak metamorphism of studied area is amphibolite facies-granulite facies transition zone. The retrograde metamorphism lower to zeolite facies. 　　The result of EDS analysis:(1) The T-P of core and rim of pre-tectonic1 garnet of Timihe are 400〜430℃、7.9〜8.8kbar，630〜665℃、8.3〜9.4kbar, respectively. (2) The T-P of core and rim of inter-tectonics1-2 garnet of Sanchabeizhigou are 480〜500℃、5.4〜5.6kbar，550〜580℃、6.1〜6.5kbar, respectively. (3) The T-P of core and rim of inter-tectonic2-3〜syn-tectonic3 garnet of Gualahe are 430〜470℃、5.1〜5.7kbar，450〜520℃、8〜9kbar, respectively. (4) The T-P of core and rim of inter-tectonics1-2 garnet of Tunxiahe are 430〜480℃、6.7〜7.1kbar，540℃、7.9〜8.4kbar, respectively. (5) The T of core and rim of pre-tectonic1 garnet in the Sill zone of Baokuhe are 720〜750℃，750〜780℃, respectively. The T-P in the Grt zone of Baokuhe are 480〜500℃、4〜4.4kbar，570〜600℃、5.4〜5.8kbar,respectively.The T from core to rim of post-tectonic3 garnet is 514 to 372℃. 　　The 40Ar-39Ar datings of the muscovite and biotite extracted from the metapelites reveal that the plateau ages are 424.9±2.42Ma and 421.46±4.21Ma respectively. They show that the Argon isotope system of the Precambrian basement rocks were resetted by the Caledonian orogeny.