首页|西天山早寒武世夏特辉长岩:南天山洋早期俯冲的岩浆记录

西天山早寒武世夏特辉长岩:南天山洋早期俯冲的岩浆记录

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相对于西天山晚古生代—中生代广泛存在的岩浆事件,其天山早古生代初期地质记录保存较少,此在很大程度上制约了学界对于亚洲洋早期演化的认识.此次选取的夏特辉长岩位于中天山南缘构造混杂岩带北侧,LA-ICPMS锆石U-Pb测年结果为(523±5)Ma,属早寒武世,其与中天山早古生代岩浆活动构成有"西早-东晚"的时空分布特征,从而在一定程度上奠定了西天山"西早-东晚"的剪刀差式闭合事件.夏特辉长岩为钠质的钙碱性系列,岩石地球化学特征反映其形成过程中经历有橄榄石、尖晶石等矿物的分离结晶以及斜长石的堆晶作用.该辉长岩富集大离子亲石元素、亏损高场强元素,构造岩浆环境判别图解也进一步指示其为弧岩浆作用的产物.锆石Hf同位素特征具有正的εHf(t)值(+1.47～+11.91),显示出亏损地幔的物质源区.此外,较高的Th/Nb原始地幔标准化比值和较低的Nb/La值,暗示了岩浆形成过程中存有俯冲物质的卷入.夏特辉长岩的形成表明南天山洋在早寒武世已经开始向中天山地块之下俯冲,伴随着中天山地块的俯冲、消减,沿中天山地块周缘于早寒武世已经形成有陆缘弧岩浆体系.
Early Cambrian Xiate Gabbro in Western Tianshan:Magmatic Records of Initial Subduction of the South Tianshan Ocean
Compared with the widespread magmatic events between the late Paleozoic and the early Mesozoic in Western Tianshan,the intrusive magmatic record of the early Paleozoic are preserved less,which conatrained our understanding on the early evolution of the Asian Ocean.Xiate gabbro is exposed in the north of the South-em Margin of the Central Tianshan,and zircon LA-ICPMS U-Pb dating shows that the formation age is 523±5 Ma,suggesting the Early Cambrian emplacement.Combined with the research on the regional igneous rocks,we believe that the Paleozoic subduction of the Paleo-Asian Ocean initiated in the west and then gradually expand-ed to the east,which may lay the foundation for the scissors closure(earlier in the west and later in the east)of the Tianshan Ocean.The geochemical characteristics of the Sodium and calcium alkaline rocks studied show that they have experienced the fractional crystallization of olivine,spinels,and the cumulation of plagioclase during their formation.The gabbro is a sodic and calc-alkaline series rocks,rich in large ion lithophile elements(LILE)and depleted in high field strength elements(HFSE).Discrimination diagrams of tectonic magmatic en-vironment indicate that it is a product of arc magmatism.The ε Hf(t)values range from+1.47 to+11.91,indi-cating a distinct mantle material source;the higher(Th/Nb)PM and lower Nb/La ratios imply the involvement of subduction materials during magmatic evolution.The formation age and petrogenetic characteristics of the Xi-ate gabbro indicate that the South Tianshan Ocean began to subduct towards the Central Tianshan Block in the Early Cambrian,and the initial arc magmatism was formed during the tectonic event.

south margin of central Tianshanthe petrogenesis of gabbroarc magmatic activity in Early Cambrian

李平、朱涛、吕鹏瑞、王洪亮、陈隽璐

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中国地质调查局西安地质调查中心/西北地质科技创新中心,陕西西安 710119

中国地质调查局造山带地质研究中心,陕西西安 710119

陕西紫阳中志留统底界层型剖面野外科学观测研究站,陕西西安 710119

中天山南缘 辉长岩岩石成因 早寒武世弧岩浆活动

中国地质调查局项目中国地质调查局项目中国地质调查局项目中国地质调查局项目陕西省自然科学基础研究计划陕西省自然科学基础研究计划陕西省自然科学基础研究计划国家自然科学基金国家自然科学基金

DD20243439DD20240073DD20230228121201140205012023-JC-YB-2682023-JC-ZD-152022JM-1494087206141502061

2024

10.12401/j.nwg.2023146

西北地质
中国地质学会 西安地质矿产研究所

西北地质

CSTPCD北大核心
影响因子：0.759
ISSN：1009-6248
年,卷(期)：2024.57(3)