西伯利亚克拉通东南缘1.84Ga构造热事件——俄罗斯斯塔诺夫南带南缘混合岩化黑云斜长片麻岩锆石U-Pb年龄和Hf同位素记录

Recognition of the 1.84 Ga tectono-thermal event in the southeastern margin of the Siberian craton: record from zircon U-Pb dates and Hf isotopes of migmatitic biotite plagioclase gneiss from the southern edge of southern Stanov belt,Tydna,Far East,Russia

对俄罗斯远东腾达(Tydna)斯塔诺夫南带南缘混合岩化黑云斜长片麻岩中锆石进行了U-Pb年龄测定和Hf同位素测试,获得其锆石核部年龄主要为≥2.57、~2.39、~2.33和~2.20 Ga,锆石增生边年龄为1.84 Ga,可靠的最年轻碎屑锆石年龄为~2.20 Ga,表明其原岩沉积时代为古元古代,而不是以往认为的太古宙,混合岩化事件年龄为1.84 Ga。锆石核部εHf(t)值为2.7^-16.2,Hf同位素地壳模式年龄为3.7~2.8 Ga;锆石增生边的εHf(t)值为-7.5^-18.6,峰值为-15,Hf同位素地壳模式年龄为3.6~2.9 Ga。锆石的εHf(t)值基本为负值说明这些岩石主要来自于地壳岩石的部分熔融;Hf同位素两阶段模式年龄的峰值在~3.4 Ga,表明它们可能主要来源于阿尔丹地盾下地壳物质的部分熔融。这些年龄资料将为西伯利亚克拉通东南缘地质构造演化提供重要的年代学制约。

The formation of the Columbian supercontinent at 1.9~1.8 Ga has been a topic of wide interest in recent years.The assemblage of the supercontinent has been recorded in the Siberian craton by the 1.9~1.8 Ga high grade metamorphic belt.The U-Pb zircon geochronological study has gained a new insight into the geological evolution of the southeastern margin of the Siberian craton.Zircons from migmatitic biotite plagioclase gneiss show core-rim textures in cathodoluminescence（CL） image.Core features indicate detrital deposits of magmatic origin zircons.Structureless overgrowths are metamorphic in origin.The four age groups of detrital cores are ≥2.57,~2.39,~2.33 and ~2.20 Ga.The age of migmatitic overgrowths is 1.84 Ga.It is therefore suggested that the sediments were deposited at^2.20 Ga and derived from Archean and Paleoproterozoic source rocks.These data indicate that the metamorphic rocks were formed in Paleoproterozoic instead of Archaean as conventionally thought.Hafnium analysis shows that the cores of zircons from migmatitic felsic gneiss have negative or positive as well as variable εHf（t） values（-16.2 to＋2.7） and Archean（3.7 to 2.8 Ga） depleted-mantle model ages,the overgrowths of zircon have negative variable εHf（t） values（-18.6 to-7.5） and Archean（3.6 to 2.9 Ga） depleted-mantle model ages.The εHf（t） values of most zircon cores are negative,indicative of a recycled continental crust.The source region of these magmas might have been related to Archean material of the Aldan Craton,suggesting derivation from an isotopically heterogeneous old crust source.U-Pb in situ zircon dating shows a 1.84 Ga overgrowth of zircons in migmatitic gneiss,implying Paleoproterozoic migmatization.The 1.84 Ga age of the migmatization event is correlated with the 1.9~1.8 Ga high grade metamorphism recorded in other regions of the world such as North America craton,Greenland,Baltica,and North China Craton,and was probably related to the formation of the Columbia.