岩石矿物学杂志2025，Vol.44Issue(5)：1157-1192,36.DOI:10.20086/j.cnki.yskw.2025.4205
陇山杂岩麻粒岩相变质作用p-T轨迹及构造意义
p-T path of granulite facies metamorphism of Longshan Complex and its tectonic significance
摘要
Abstract
The Longshan Complex,distributed in Baoji of Shaanxi Province and Tianshui of Gansu Province,is lo-cated at the junction of the Qinling orogenic belt and the Qilian orogenic belt,and is the material basis for under-standing the tectonic evolution and attribution of the region.In this paper,detailed petrography,mineral chemis-try,phase equilibrium modeling and titanite U-Pb geochronology studies were carried out on garnet-bearing amphib-olites samples collected from the Longshan Complex.Based on detailed petrographicobservations and mineral chem-ical analyses,it was determined that the garnet-bearing amphibolites recorded three stages of metamorphic mineral assemblages.The mineral assemblage in the prograde metamorphic stage(M1)is represented by fine-grained plagioclase,amphibole and quartz in garnet;the mineral assemblage in the peak metamorphic stage(M2)is represented by plagioclase+amphibole+quartz+garnet+ilmenite+titanite+melt;and the mineral assemblage in the retrograde metamorphic stage(M3)is represented by plagioclase+amphibole+quartz+ilmenite+melt,forming a sym-plectite texture.According to the geothermobarometers,the temperature and pressure conditions in the prograde meta-morphic stage(M1)are 563℃ and 0.82 GPa.The results of phase equilibrium modeling for the peak metamorphic stage(M2)show that the temperature and pressure conditions are 800～818℃,1.28～1.32 GPa and 740～770 ℃,1.17～1.20 GPa.For the retrograde metamorphic stage(M3),the temperature and pressure conditions of one sample cal-culated by phase equilibrium modeling are 691～703 ℃,1.03～1.06 GPa,and the temperature and pressure condi-tions of another sample obtained by the geothermobarometer are 683℃ and 0.8 GPa.The amphibolites have experi-enced the prograde metamorphic stage to the peak metamorphic stage and then to the retrograde metamorphic stage,and recorded a clockwise metamorphic p-T path.The peak metamorphic temperature and pressure conditions are close to or similar to those in many areas of the Qinling Complex.The results of laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)titanite U-Pb geochronology show that the intersection ages of titanite in the garnet-bearing amphibolites are 380.5±4.8 Ma,430.8±6.7 Ma,431.6±6.1 Ma and 433.4±4.0 Ma.In sum-mary,by comparing the metamorphic temperature and pressure conditions and metamorphic ages of the Longshan Complex with those of the Qinling Complex,it was found that the metamorphic age of the Longshan Complex in this region is close to the last retrograde metamorphic age of the Qinling Complex in the eastern section of the North Qin-ling,and the peak metamorphic temperature and pressure conditions are similar to the granulite facies metamor-phism of the Qinling Complex in the western section of the North Qinling.It is speculated that the Longshan Com-plex may be the western extension of the North Qinling orogenic belt.关键词
秦-祁结合部位/陇山杂岩/相平衡模拟/榍石U-Pb定年/变质作用Key words
Qinling-Qilian connection zone/Longshan complex/phase-equilibrium simulation/titanite U-Pb dat-ing/metamorphism分类
天文与地球科学引用本文复制引用
段增印,卢俊生..陇山杂岩麻粒岩相变质作用p-T轨迹及构造意义[J].岩石矿物学杂志,2025,44(5):1157-1192,36.基金项目
国家自然科学基金项目(41872195) （41872195）
西北大学大陆演化与早期生命全国重点实验室项目 National Natural Science Foundation of China(41872195) （41872195）
Project of the State Key Laboratory of Continental Dynamics at Northwest University （）
