周口店地区接触变质岩的演化:来自碳质拉曼光谱温度计的证据

Evolution of contactolite in the Zhoukoudian area:evidence from the carbon Raman spectrum thermometer

燕山板内构造带是华北克拉通中部遭受长期造山演化作用的活动区,详细的岩浆活动和变质作用研究对于恢复其造山热演化过程具有重要意义。构造带内周口店地区的房山岩体是中生代燕山运动晚期的产物,但关于房山岩体周缘受到接触热变质作用的古老地体变质演化历史却缺乏详细的研究。本研究在房山岩体红柱石-黑云母接触变质带内采集了岩石样品,通过岩相学的详细观察和碳质物拉曼光谱温度计的计算,得到了以下认识:岩石中红柱石斑晶核部的碳质包体记录下了早期区域变质过程的变质温度(约550℃),红柱石斑晶及边部中的碳质包体共同记录了峰期变质温度条件(约598℃),岩石基质中碳质包体可能记录了岩石接触热变质的峰后期变质温度(598~574℃)。研究结果表明,接触热变质带的岩石受到房山侵入岩释放的热量而迅速加热,在达到峰期变质温度后又随岩体的冷却而降温,导致了近等压的p-T-t轨迹。

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.