中国东南部余江基性岩体的SHRIMP锆石U-Pb年龄及其地质意义  

SHRIMP ZIRCON U-Pb AGE OF LATE MESOZOIC BASALTIC MAGMATISM IN THE YUJIANG REGION,SOUTHEASTERN CHINA AND ITS IMPLICATION

作　　者：李瑞玲[1] 李真真[1] 

机构地区：[1]中国地质调查局发展研究中心,北京100037

出　　处：《矿物岩石》2010年第2期45-49,共5页Mineralogy and Petrology

基　　金：国家自然科学基金项目(批准号:40402011)

摘　　要：中国东南部是我国重要的中生代花岗质岩石和钨锡多金属矿床集中发育的地区,该区基性侵入岩体或岩墙是研究岩石圈伸展的时限和机制的理想对象之一。研究以赣东北地区余江基性岩体为对象,利用SHRIMP锆石U-Pb法对该岩体进行精确的测年结果表明:余江基性岩体侵入白垩纪红色砂岩,岩性为橄榄辉绿辉长岩,主要由橄榄石、普通辉石、斜长石(An=31~60,为中拉长石)组成,锆石的形态和阴极发光特征暗示它们为深部地幔来源温度较高的条件下快速侵位的基性岩浆所形成的锆石,少量具有明显环带的锆石可能为捕获的锆石;对16个代表性锆石进行SHRIMP锆石U-Pb年龄的测试,各测点的U和Th质量分数较低,分别为77×10-6~934×10-6和67×10-6~923×10-6,Th/U比值为0.3~1.9,除了2个点为捕获锆石,其余14个锆石的SHRIMP年龄相对集中,为106 Ma±10 Ma^86.0 Ma±1.8 Ma,14个锆石的SHRIMP谐和年龄为91 Ma±3 Ma(MSWD=3.9),代表了余江基性岩体的侵位年龄,综合分析认为中国东南部晚白垩世整体处于岩石圈伸展构造背景。Late Mesozoic granitoid and W-Sn polymetallic deposits widely occurred in southeastern China.Although Late Mesozoic lithosphere extension has been generally accepted by most researchers,its time limitation and mechanism remained controversial.The basic intrusive rock or dyke is an ideal object to study the timing and mechanism of lithosphere extension,but accurate dating of the rock is poorly understood.In this paper,SHRIMP zircon U-Pb age of representative basic magmatic rocks in the Yujiang region,southeastern China is studied.The Yujiang rock body intruded Late Cretaceous red layers,and are mainly composed of olive,augite and plagioclase（An= 31~60）.Zircon morphology and cathodoluminescence image indicate that zircons were probably formed by rapid emplacement of basic magma derived from mantle at higher temperature,and a few zircons with oscillatory zoning are probably relict of the crust.Zircons from the Yujiang basic intrusive rocks have lower U and Th contents of 77×10-6~ 934×10-6 and 67×10-6~ 923×10-6,and Th/U ratios of 0.3~1.9.16 zircon grains were analyzed,of which 14 analyses form a concentration group with a weighted mean 206Pb/238U age of 91 Ma± 3 Ma（MSWD=3.9）,representing the emplacement age of the Yujing rock.Therefore,it is considered that the southeastern China was subjected to lithospheric extension during Late Cretaceous.

关 键 词：锆石SHRIMP U-PB年龄 余江基性岩 岩石圈伸展 中国东南部 

分 类 号：P597[天文地球—地球化学]