摘要
利用锆石U-Pb年代学、矿物化学、全岩元素和同位素地球化学等方法,结合前人的研究成果,探讨了华夏地块西部煌斑岩类岩石成因和构造意义。回龙圩云煌岩形成时代为172Ma,斑晶为金云母,全岩主要化学成分SiO247.84%~48.91%、Al2O311.42%~12.35%、CaO10.91%~13.14%、K2O2.34%~3.65%,Mg#为64~71,为钾玄质碱性基性岩。云煌岩稀土元素总量较低(∑REE=171~187),轻稀土元素富集重稀土元素亏损(LREE/HREE=10~11),δEu=0.85~0.87,类似洋岛玄武岩的稀土元素分配模式;微量元素Rb、Ba、K等大离子亲石元素富集,Nb、Ta、Ti等高场强元素亏损。云煌岩(87Sr/86Sr)i为0.705930~0.706170,(143Nd/144Nd)i为0.512334~0.512379,εNd(t)值为-0.74^-1.61;全岩δ18OV-SMOW值为9.7‰。全岩主量元素、微量元素和Sr-Nd-O同位素地球化学特征表明,回龙圩云煌岩为受富集组分交代的岩石圈地幔发生部分熔融的产物,富集组分为来自软流圈的含上地壳或俯冲洋壳沉积物的流体。华夏地块西部沿祁东至罗城一带分布的晚三叠世、中侏罗世和早白垩世的煌斑岩类和碱性玄武岩表明,区域上在这3个阶段有深大断裂活动,意味着华夏地块西部地区从晚三叠世以来就转换为岩石圈伸展的构造背景,该背景激活了长期存在的薄弱地带,华夏地块西部有煌斑岩类和碱性玄武岩分布的祁东至罗城一线可能是华夏地块西缘与扬子地块的分界线。
Petrogenesis and tectonic significance of lamprophyres in western Cathaysia Block are discussed using zircon U-Pb geochronological, mineral chemical, bulk-rock elemental and isotopic methods, combined with previous studies. Our study shows that emplacement age of minette in Huilongxu is 172 Ma, phenocryst of the minette is phlogopite, the major elements contents of minette include SiO 2(47.84%-48.91%), Al 2O 3(11.42%-12.35%), CaO(10.91%-13.14%), K2O(2.34%-3.65%), Mg^#=64-71, which belong to shoshonitic alkaline basic rock. The minette has lower total REE content(ΣREE=171-187). Chondrite-normalised rare-earth elements (REE) patterns show light rare-earth element enrichment and heavy rare-earth element depletion(LREE/HREE=10-11),δEu=0.85-0.87, like OIB rare-earth elements patterns. Primitive mantle normalised trace-element patterns show that the minette is enriched with large ion lithophile elements(such as Rb, Ba, K) and depleted in high field strength elements (such as Nb, Ta, Ti). The minette has initial ( 87 Sr/ 86 Sr) i values of 0.705 930 to 0.706 170, initial ( 143 Nd/ 144 Nd) i values of 0.512 334 to 0.512 379, and ε Nd ( t ) ranges from -0.74 to-1.61, with oxygen isotopic value (δ^18 O V-SMOW ) of 9.7‰. Bulk-rock major, trace elemental and Sr-Nd-O isotopic geochemical characteristics indicate that the minette is the melting product from lithosphere mantle which was metasomatized by fluids enriched with upper crustal materials or marine sediments from asthenosphere. Lamprophyres and alkaline basalts from Qidong-Luocheng belt in western Cathaysia Block prove that Late Triassic, Middle Jurassic and early Cretaceous deep-faults were moved, implying tectonic setting of the western Cathaysia Block transformed into lithospheric extension since the Late Triassic. The extension setting reactivated long-lived lithospheric zones of weakness, indicating that Qidong-Luocheng belt with lamprophyres and alkaline basalts could be the suture between Yangtze Block and Cathaysia Block.
作者
杨金豹
赵志丹
时毓
盛丹
方贵聪
吴祥珂
YANG Jin-bao;ZHAO Zhi-dan;SHI Yu;SHENG Dan;FANG Gui-cong;WU Xiang-ke(Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi,,Guilin University of Technology,Guilin 541006,China;Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541006,China;College of Earth Sciences,Guilin University of Technology,Guilin 541006,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;Hunan Key Lab of Land & Resource Evaluation & Utilization,Hunan Planning Institute of Land and Resources,Changsha 410007,China;Guangxi Institute of Geological Survey,Nanning 530023,China)
出处
《桂林理工大学学报》
CAS
北大核心
2019年第1期1-12,共12页
Journal of Guilin University of Technology
基金
国家自然科学基金项目(41562005)
中国地质调查局地质大调查项目(DD20160346)
广西自然科学基金项目(2016GXNSFBA380070)
广西隐伏金属矿产勘查重点实验室自主研究课题(15-140-27-13)
关键词
煌斑岩
年代学
地球化学
构造意义
华夏地块
chronology
geochemistry
tectonic significance
lamprophyre
Cathaysia Block
