| The formation age and genetic mechanism of the set of metamorphic rocks of Archean amphibolite facies,outcropped in Fusong area of Jilin Province,is a long-existed and unresolved problem.This paper selects the amphibolite from the metamorphic rocks as the studying object,and analyzes its forming process and discusses the evolution background of the contemporaneous tectonomagmatism by systematicallystudying its petrology,mineralogy,petrogeochemistry and Zircon U-Pb chronology characteristics.LA-ICP-MS U-Pb zircon dating of magmatic zirconsyieldsthe ages of?2555±13?Ma,?2528±13?Ma and?2529±9.8?Ma,which indicates that the formation age of the magma belongs to late Neoarchean?2.552.50Ga?.The average content of the major elements is similar to that of basalt,the content of SiO2 is ranging from 46.22%to 59.6%with the average of 51.13%;While that of Al2O3 is from 11.83%to 17.59%with the average of13.42%.The total REE content is ranging from 53.74×10-6 to 219.07×10-6,and the average is 108.17×10-6;The ratio of LaN/YbN is ranging from 2.07 to 8.98 with the average of5.19,which indicates that the light rare earth elements?LREE?are relatively enriched and the light-heavy REE are obviously fractionated.The contents of trace elements in the amphibolite are characterized by relatively enriched in large ion lithophile elements?LILE?,i.e.,K,Rb and Ba,and depletes high field-strength elements?HFSE?,i.e.,Zr,Ti,Nd and Ta.The primary rock of this set of metamorphic rock association is thought to be basaltic volcanic by comprehensively studying their mineral composition and geochemical component,thus the metamorphic rocks belongs to orthometamorphite.The magma,formed in the island-arc environment,was mainly derived from depleted mantle and simultaneously accompanied by the contamination and reconstruction of a small quantity of old crust.This area is thought to be the northern extension part of Neoarchean Jilin-Liaoning-Hebei arc-continent collisional accretion-type orogenic belt of North China Craton. |
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