摘要
沿大型断裂带出露的深成岩体记录并保存了形成时的大地构造活动及后期演化和变形的重要信息。为了更好地理解羌塘西部花岗岩的成因机制和演化历史,本文选取了龙木错断裂南部的泽错岩体进行地球化学、SHRIMP锆石U-Pb年代学及云母和钾长石40Ar/39热年代学分析。全岩地球化学判别图显示花岗岩样品为高钾钙碱性系列至钙碱性系列和过铝质。矿物组合表明无角闪石且含白云母。以上特征均显示出明显的S型花岗岩趋势。锆石U-Pb年龄为123±1. 7Ma至107±1. 4Ma,表明岩浆侵位的时代为早白垩世,此时班公-怒江洋仍在向北俯冲。云母和钾长石40Ar/39年龄及前人低温热年代学数据显示,侵位后岩体至少有四个阶段的冷却,包括120~90Ma、90~38Ma、38~26Ma和26~0Ma。第一阶段在侵位后10Myr内快速冷却至低于~320℃,而随后以相对较慢的速率冷却至~220℃。从90Ma到38Ma期间经历了较长时期极为缓慢的冷却,该阶段构造活动趋于静止,表明羌塘地体-拉萨地体碰撞应发生在90Ma之前。中新世受控于龙木错断裂左旋走滑的影响,最后一期的构造变形以东西向伸展为主,深成岩逐渐剥露至地表。龙木错断裂可能作为中新世以来高原物质向东运移西部边界的一条新的应力释放途径。
Batholites exhumated from depth along large-scale fault zone can record and preserve important information for original tectonic activity and postdated evolution process.To better understand the genesis and evolution history of the granitoid intrusion in western Qiangtang,we select Chem Co pluton occurring to the south of Longmu Co fault and applied SHRIMP zircon U-Pb,geochemistry,mica and K-feldspar 40Ar/39 Ar analysis.Major element geochemistry distinguishes that the Chem Co granite rocks are high-K alkaline to calc-alkaline series and peraluminous.Mineral modal shows that absent of amphibole but containing muscovite.All these characters suggest the distinctive evolution trend of S-type granite.Zircon U-Pb ages ranging from 123±1.7 Ma to 107±1.4 Ma show that the emplacement occurred in Early Cretaceous and suggest that the Bangong-Nujiang Ocean was still subducting northward during this period.Mica and K-feldspar 40Ar/39 Ar ages together with previous low-temperature thermochronology data show that after the magmatic emplacement,this batholite has experienced at least four episodes of cooling,including 120~90 Ma,90~38 Ma,38~26 Ma and 26~0 Ma.The first stage was a fast cooling below^320℃occurred within 10 Myr after emplacement,with a subsequent relatively slower rate till^220℃.Then from 90 Ma to 38 Ma,this region underwent a relatively long period of slow cooling,during this stage tectonic activity tends to be stationary,which reveals that the Qiangtang and Lhasa terranes should collide predated 90 Ma.During the Miocene,controlled by the Longmu Co fault left-lateral strike-slip,the last stage of regional deformation is dominated by E-W extension,with batholites gradually exhumated to the surface.The active Longmu Co fault may serve as a new pathway for stress relief during Miocene in response to plateau material escaping eastwards on its western boundary.
作者
韩帅
李海兵
潘家伟
卢海建
郑勇
刘栋梁
白明坤
张进江
HAN Shuai;LI HaiBing;PAN JiaWei,LU HaiJian,ZHENG Yong,LIU DongLiang;BAI MingKun;ZHANG JinJiang(MNR Key Laboratory of Deep-Earth Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第6期1647-1672,共26页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41672211)
中国地质科学院基本科研业务费项目(JYYWF201810)
中国地质调查局项目(DD20160022)联合资助
关键词
泽错
S型花岗岩
地球化学
热年代学
演化历史
龙木错断裂
Chem Co
S-type granite
Geochemistry
Thermochronology
Evolution history
Longmu Co fault
