摘要
Dupal异常是迄今为止在地球表面出现并反映地幔地球化学特征的最大同位素异常域.首先是在南半球现代大洋玄武岩中发现了以南纬30°为中心近环球分布的Dupal异常域,近年又在北半球的中国东部、日本海等非大洋玄武岩中发现了Dupal异常.现在认为Dupal异常源区既可赋存于岩石层地幔,亦可源自深部软流层地幔或更深,但对Dupal异常源形成机制仍无定论,对北半球的Dupal异常其源区是否来自南半球地幔还有不同认识.Dupal异常源可能是多成因的,不能排除星外物质冲击的可能性.南半球大洋地幔大规模同位素异常的存在对模拟地幔对流提出了制约,也为探索地幔地球化学特征提供了新途径.
Dupal anomaly was firstly discovered by Dupre and Allcgre in 1983 when they studied. on Indian Oceanic basalts, then Hart (1984) named it after them. It is mantle Pb, Sr isotope geochemical anomaly, which was the biggest geochemical anomaly domain on the earth surface and reflects mantle heterogeneity. The Northern Hemisphere Reference Line (NHRL) was used as its cirtieria, and then Hart (1988) suggested two criteria for Dupal anomaly, i.e. delta 8 / 4Pb > 60 and 87Sr / 86Sr>0.705. For modern oceanic basalts, the anomaly only formed in south hemisphere and concentrated at 30 south latitute and nearly continuously distributed around the earth. Recently many other Dupal anomaly domain in northern hemisphere were found, such as Eastern China and its environs, Japan Sea.It was considered that Dupal anomaly occurred in the early history of the earth. Now, geochemiststry to discover where the Dupal anomaly origin is (in shallow continental lithosphere mantle? or deep convecting asthosphere mantle?), forming mechanisms the Dupal anomaly. Whether the primary origin of Dupal anomaly only located at southern hemisphere mantle or not, and how the Dupal anomaly drifted to north- era hemisphere. It was suggested that the origin of Dupal anomaly may be existed within continental lithosphere mantle and also within deep asthosphere mantle. There are several suggestions on the mechanism of Dupal anomaly origin, such as crust material subducted deeply into asthosphere mantle and sadded to its cycling; the evolution of intra-continental lithosphere mantle. We suggested that the ancient extraterrestrial meteorite might brought the anomaly Pb isotope component to southern hemisphere mantle.The discovery of Dupal anomaly gave a new approach to research of magmatic evolution, and a new chance to investigate the mantle geochemistry. Besides, the existence of Dupal anomaly in southern hemisphere oceanic basalts put some constrains on the research of modeling mantle convection. For further study on it, geochemists try to reveal the trace elemants and other element isotope features of Dupal anomaly.
出处
《地球物理学进展》
CSCD
1992年第4期63-71,共9页
Progress in Geophysics
