Mineral Chemistry and Geochemistry of the Xiaojiang-Liangnong Complexes and their Enclaves in Zhejiang

• Main Authors: Chiung-Mei Yen, 顏琼美
• Other Authors: Cheng-Hong Chen
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/15134581662679457724

碩士 === 國立臺灣大學 === 地質科學研究所 === 93 === Late Yanshanian magmatism in South China caused vast granitic intrusions including large amounts of I-type granitoids and small amounts of A-type granites from late Jurassic to early Cretaceous, distributed mainly in the Southeast Coast Magmatic Belt (SCMB). The Xiaojiang-Liangnong Complexes and their enclaves in Zhejiang is the target of this study, samples from Longwangtang, Taohua Island, Qingtian in Zhejiang and Fuzhou, Zhangzhou, Kuiqi, Bijiashan in Fujian are concerned. Xiaojiang Complexes include three types of enclaves and two types of hosts. The analyses of mineral chemistry and geochemistry indicate that characters of the first type of enclaves are similar to their hosts, which could have resulted from differentiation of the enclaves representing fragments of early, chilled margins, disrupted during the ascent of magmas. The third type of enclaves are characterized by high-Mg, low-Ca compositions, and they represent the basic products of early differentiation from magmas of the first type. The second type of enclaves belonging to medium-K series are characterized by high-Al,Na compositions. The Sr isotope and geochemical data indicate they could differentiate from the underplating basic magmas of post-orogenic stage of Late Yanshanian magmatism. Liangnong Complexes include one type of enclaves and two types of hosts. All samples from Liangnong Complexes belong to products of differentiation. Using the Al-in-amphibole geobarometer, the samples of this study were estimated to have been emplaced at shallow depths (3-8 km). The analyses results of Xiaojiang-Liangnong Complexes are close to the emplacement ages, depths, geochemical characters of the Late Yanshanian granitoids in Zhejiang and Fujian in this study. They all belong to the intrusions of I- and A-type granitoids of post-orogenic stage of Late Yanshanian magmatism reflecting tectonism from compressional to extensional environment.