花岗质岩浆的变压结晶作用及其动力学意义:以北京房山岩体为例  

Polybaric Crystallization of Granitic Magmas and Its Dynamic Significance:A Case from the Fangshan Pluton of Beijing

作　　者：刘小丽[1] 程素华[1] 张宏远[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《现代地质》2015年第3期514-528,共15页Geoscience

基　　金：国家自然科学基金项目(41102122;40972125);中央高校基本科研业务费专项基金项目(2652013022)

摘　　要：北京房山岩体是华北克拉通东部典型的燕山期中酸性钙碱性侵入岩之一。为了更好地理解房山岩体的侵位机制和隆升-剥蚀历史,选取恰当的角闪石全铝压力计和角闪石-斜长石温度计计算其侵位压力和温度。结果表明,房山岩体的结晶压力为（（0.39~0.28）±0.06）GPa,温度为655.9~733.7℃。基于该结果,认为房山岩体在侵位过程中经历了变压结晶作用。结合房山岩体各岩石单元的侵位温度、压力、岩石结构特征以及锆石U-Pb年龄,可知其在早期经历了缓慢的隆升剥蚀过程,而晚期的巨斑状中细粒花岗闪长岩单元遭受了快速的隆升剥蚀。根据本研究估算的侵位温度和压力,房山岩体在持续侵位过程中抬升了7~8 km,平均抬升速率为2.33~2.67 km/Ma。The Fangshan pluton exposed in Beijing is one of the typical Yanshanian intermediate-acidic calcalkaline intrusions occurred in the eastern part of North China Craton. For better understanding of the emplacement mechanism and the uplift-erosion history of the Fangshan pluton,we use the suitable Al-in-hornblende geobarometer to estimate the pluton’s emplacement pressure,and the hornblende-plagioclase geothermometer to calculate the temperature of crystallization. The results show that the Fangshan pluton crystallized at the temperature of 655. 9- 733. 7 ℃ and the pressure of（ 0. 39- 0. 28） ± 0. 06 GPa. Based on the p-t conditions of the pluton crystallization,it is proposed that the Fangshan pluton experienced polybaric crystallization during the emplacement. The p-t estimations for emplacement,integrating with the characteristics of rock structure and the zircon U-Pb ages of the lithological units of the Fangshan pluton,suggest that the Fangshan pluton has experienced slow-rate erosion / uplift during the early epoch of emplacement,followed by a rapid erosion / uplift epoch related to the emplacement of the lithologically dominated granodiorite unit. Overall,the p-t conditions estimated by this study suggest that the uplift distance of the Fangshan pluton during the emplacement is 7- 8 km,and the average erosion / uplift rate for the pluton is in range of 2. 33- 2. 67 km / Ma.

关 键 词：房山岩体 变压结晶作用 角闪石全铝压力计 隆升剥蚀 

分 类 号：P588.1[天文地球—岩石学]