YAN Jun1, CUI Ying1*, ZHANG Cong2

(1. The Key Laboratory of Orogenic Belts and Crustal Evolution. Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;
2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)

Abstract: The Yanshan intraplate tectonic belt is an active area in the central part of the North China Craton that has been suffered from the long-term orogenic evolution. The detailed study of magmatism and metamorphism is of great significance to restore the orogenic thermal evolution process of the Yanshan intraplate tectonic belt. The Fangshan pluton in the Zhoukoudian area within the Yanshan intraplate tectonic belt is the product of the late Mesozoic Yanshan orogeny. However, there is lack of detailed researches on the metamorphic evolution history of the ancient terrane around the Fangshan pluton subjected to the contact thermal metamorphism. In this study, rock samples were collected from the andalusite-biotite contact metamorphic zone of the Fangshan pluton. Through the detailed of petrographic observation and the calculation of Raman spectrum thermometer of carbonaceous materials, the following understandings have been obtained. The carbonaceous inclusions in the core of andalusite phenocryst in the rock had recorded the metamorphic temperature of early regional metamorphic process (~550 ℃). Those in both core and rim of the andalusite phenocryst had jointly recorded the peak metamorphic temperature (~598 ℃). Those in the rock matrix could have recorded metamorphic temperatures of the post-peak contact thermal metamorphism (598－574 ℃). The results show that the contactolite in the contacting thermal metamorphic zone had experienced the rapid heating by the heat released from intruded magma of the Fangshan intrusion, and then cooling with the cooling of magma of the Fangshan intrusion after the peak metamorphic temperature. This resulted in a nearly isobaric p-T-t trajectory for the contactolite.

Keywords: carbonaceous material; Raman spectrum; thermometer; the Zhoukoudian area; the andalusite-biotite contact metamorphic zone; the p-T-t trajectory

ACTA MINERALOGICA SINICA Vol. 43, No. 4, 2023, Page 490