11:15 AM - 11:30 AM
[BPT05-09] Occurrence and U-Pb zircon dating of the Archean Dongshan gneiss in Anshan, the North China Craton
Keywords:Archean, zircon, Anshan
We carried out a comprehensive investigation of detailed observation of an outcrop in the Dongshan area, Anshan, U-Pb dating and Cathodoluminescence observations of zircons from the outcrop to constrain the emplacement age of protoliths of the orthogneisses. The outcrop consists mainly of two lithologies: highly altered metamorphosed mafic rock and orthogneisses with some generations. The orthogneisses are further subdivided into pale-gray gneiss, white gneiss and white granitic intrusion, respectively. The occurrence of the mafic rock and orthogneisses indicates that the mafic rock (1) was intruded by the pale-gray gneiss (2), the pale-gray gneiss (2) was further intruded by the white gneiss (3), and all of them were, finally, intruded by the white granitic intrusions (4). We studied Cathodoluminescence imaging and U-Pb dating of zircons carefully separated from each rock type. The results follow: (1) the metamorphosed mafic rock yields only metamorphic zircons with ca. 3.3 Ga ages, (2) only the pale-gray gneiss contains 3.8 Ga zircons, (4) the white gneiss has ca. 3.3 Ga zircons and (4) the white granitic intrusion contains very young, ca. 500 Ma, zircons.
We will report their protolith ages and the related granitic intrusion events based on the Cathodoluminescence images, U-Pb dating with LA-ICP-MS, Hf and O isotopes and REE patterns of the zircons and whole rock compositions of the host rocks.