华夏地块生长与演化：来自赣江河流沉积物碎屑锆石Lu-Hf同位素的制约

The Ctustal Growth and Evolution of Cathaysia Block: Constraints from Detrital Zircon Lu-Hf Isotopes of the Ganjiang River Sediments

为研究赣江河流沉积物的物质来源及源区地壳生长和演化规律,对已报道年龄的123个赣江河流沉积物碎屑锆石中的80个代表性锆石开展Lu-Hf同位素组成分析。研究表明:赣江碎屑锆石年龄分布特征与华夏地块的年龄分布非常一致,表明赣江沉积物主要来源于华夏地块;结合Hf同位素分析结果,能够反映源区华夏地块的形成与演化历史。新太古代锆石的εHf(t)值近似为0,表明该时期发生了强烈的壳幔混合作用;中-新元古代锆石εHf(t)值既有正值也有负值,说明源区物质既有古老地壳物质的再循环,也有新生地壳物质的加入;显生宙以来,εHf(t)值绝大多数为负值,且对应的两阶段模式年龄以古元古代-中元古代的年龄为主,说明显生宙以来的岩浆活动主要来源于古元古代-中元古代新生地壳的再造,直接来源于亏损地幔的物质很少。2.1~1.1 Ga是华夏地块地壳生长的主要阶段,此阶段形成的物质构成现今华夏地块全部地壳物质的80%以上。

In order to study the source of sediments from the Ganjiang River and the crustal growth history of source region,representative 80 zircons was measured for Hf isotopic composition of 123 the Ganjiang River＇ s detrital zircon which has been reported. The detrital zircon U-Pb age distribution of sediments from the Ganjiang River is consistent with those of the Cathaysia Block,which indicates dominant contribution of material from the Cathaysia Block to the Ganjiang River. The detrital zircon U-Pb ages and Hf isotopic composition of the Ganjiang River＇s sediments can reflect the formation and evolution history of the Cathaysia Block. The εHf（ t） values of the Neoarchean detrital zircons approximately 0,it shows that the strong crust mantle mixing occurred in this period; εHf（ t） values of the Mesoproterozoic and Neoproterozoic detrital zircons have both positive and negative values,indicated that the material of the source region is not only the recycling of ancient crustal materials,but also the addition of new crustal material; most of the εHf（ t） is negative since Phanerozoic and the age of two stage mode corresponding to the Paleoproterozoic to Mesoproterozoic,indicated that the magmations after phanerozoic eon are most derived from the juvenile crust formed in paleoproterozoic- Mesoproterozoic,and little of them derived from depleted mantle. Meanwhile 2. 1-1. 1 Ga is the main stage that Cathaysia Block continental growth evolved from depleted mantle to the crust,and material that formed in this stage constitute 80% of the Cathaysia Block crust material.