摘要
四川盆地西北部广元地区二叠系碳酸盐岩地层被辉绿岩岩脉沿断层侵入并发育断层破碎带。为明确广元地区杨家岩剖面中二叠统辉绿岩岩脉断层破碎带中热液锆石特征,探讨与锆石形成有关的热液活动性质、来源及时限,本文利用薄片观察、扫描电镜+阴极发光分析、LA-ICP-MS锆石U-Pb同位素定年以及荧光分析等技术方法和手段开展综合研究。结果表明:热液锆石主要产出于辉绿岩脉断层泥质–角砾状充填物中,具典型热液锆石形态、结构及微量元素特征;锆石^(206)Pb/^(238)U表面年龄为110~114 Ma,加权平均年龄为112.0±0.9 Ma,说明燕山Ⅲ幕(早白垩世末期)构造运动及流体活动已影响到龙门山北段的川西北地区。携带SiO_(2)等物质、具较高温度的深部热液流体与烃类流体混合沿断层带进入二叠系,除在断层破碎带中与Zr^(4+)结合形成热液锆石外,还形成部分次生溶孔;对于封闭性较好的区域,因压力释放及温度降低,过饱和SiO_(2)迅速晶出并充填孔隙及裂缝,使岩石孔隙度急剧降低;晚期方解石的沉淀进一步降低岩石的储集空间,严重影响储层储集性能。流体充填是造成川西北部广元地区火山岩侵入体断层破碎带火山岩及围岩致密化的重要原因。
Hydrothermal zircons within fault damage zones filled with diabase veins in the Lower Permian Maokou Formation have been identified in the Guangyuan area(northwestern Sichuan,Southwestern China).This study elucidates the features,origin,and timing of the zircons in the fault damage zone through a combination of petrographic descriptions,coupled with SEM,cathodoluminescence,fluid inclusion,geochemical,LA-ICP-MS isotopic data of the zircon,and evidence from burial history.The zircons exhibit similar characteristics in terms of type,texture,and trace elements to typical hydrothermal zircons,primarily occurring in the fault gouge and fault breccia.The obtained apparent and weighted mean ^(207)Pb/^(206)Pb ages of 110 Ma to 114 Ma and 112.0±0.9 Ma suggest a significant influence of the Yanshanian EpisodeⅢtectonic movement(Late Early Cretaceous)and fluid events on the Northern Longmen Mountains(Northwestern Sichuan Basin).The study reveals that deep hydrothermal fluid,characterized by high temperature and enriched in SiO_(2),mixed with hydrocarbon fluid,was injected into the Permian strata along the fault zone.This process led to the formation of hydrothermal zircon containing Zr^(4+)in the fault damage zone,accompanied by the creation of partial secondary dissolved pores.In the sealing areas,supersaturated SiO_(2) precipitated rapidly and filled the pores and fractures due to pressure release and temperature reduction.This resulted in a substantial decrease in porosity,leading to a dramatic reduction in rock reservoir space and,consequently,a significant densification of the reservoir performance.
作者
刘小洪
陈珺朗
冯明友
卓宜茜
王委委
尚俊鑫
LIU Xiaohong;CHEN Junlang;FENG Mingyou;ZHUO Yiqian;WANG Weiwei;SHANG Junxin(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,Sichuan,China;Sichuan Provincial Key Laboratory of Natural Gas Geology,Chengdu 610500,Sichuan,China)
出处
《地球化学》
CAS
CSCD
北大核心
2023年第6期746-758,共13页
Geochimica
基金
国家科技重大专项(2016ZX05007004-001)
国家自然科学基金项目(41202109)
四川省创新创业训练项目(S202010615134)联合资助。
关键词
四川盆地
二叠系
辉绿岩
断层破碎带
热液锆石
Sichuan basin
Permian
diabase
fault damage zone
hydrothermal zircon
