吉林抚松四道砬子河岩组斜长角闪岩成因

Genesis of Amphibolite of Sidaolazihe Formation in Fusong Area,Jilin Province

在吉林抚松地区出露有一套太古宙角闪岩相变质岩石,其形成时代和成因机制长期存在争议。选定其中的斜长角闪岩作为研究对象,进行了岩石学、矿物学、岩石地球化学、锆石U-Pb年代学系统研究,分析了其形成过程,探讨了同时期构造岩浆演化背景。斜长角闪岩LA-ICP-MS锆石U-Pb测年取得的岩浆型锆石年龄分别为(2 555±13)Ma、(2 528±13)Ma、(2 529±9.8)Ma,表明其形成于新太古代晚期(2.55~2.50 Ga)。主量元素平均化学成分与基性火山岩中玄武岩成分相似,Si O2含量为46.22%~59.6%,平均值为51.13%;Al2O3含量11.83%~17.59%,平均值为13.42%。稀土元素总量53.74×10-6~219.07×10-6,平均值为108.17×10-6,(La/Yb)N=2.07~8.98,平均值5.19,表明轻稀土相对富集且轻重稀土分馏较明显。微量元素中较富集K、Rb、Ba等大离子亲石元素(LILE);亏损Zr、Ti、Nd、Ta等高场强元素(HFSE)。综合岩石矿物组成及地球化学成分特征,认为吉林抚松地区斜长角闪岩属正变质岩,原岩应为玄武质火山岩,岩浆主要来源于亏损地幔,同时伴有少量古老地壳的混染再造,形成于岛弧环境,该区是华北克拉通新太古代吉—辽—冀弧陆碰撞增生造山带的北延部分。

The formation age and genetic mechanism of the set of metamorphic rocks of Archean amphibolite ta- cies, outcropped in Fusong area of Jihn Province, is a long-existed and unresolved problem. This paper selected the amphibolite from the metamorphic rocks as the studying object, and analyzed the forming process and dis- cussed the evolution background of the contemporaneous tectonomagmatism by systematically studying petrology, mineralogy, petrogeochemistry and zircon U-Pb chronology characteristics. LA-ICP-MS U-Pb zircon dating of magmatic zircons yields the ages of （2,555 ± 13） Ma, （2,528 ± 13）Ma and （2,529±9. 8） Ma, which indi- cates that the formation age of the magma belongs to Late Neoarchean （2. 55-2.50 Ga）. The average contents of the major elements are similar to those of basalt; the contents of SiO2 are ranging from 46. 22% to 59.6% with the average of 51.13% ; while contents of A1203 are from 11.83% to 17.59% with the average of 13.42%. The total REE content are ranging from 53.74 × 10^-6 to 219.07 × 10^-6, and the average is 108.17 × 10^-6. The ratios of （La/Yb）N range from 2. 07 to 8.98 with the average of 5.19, which indicates that the light rare earth elements （LREE） are relative enrichment and the light-heavy REEs are obviously fractionated.The contents of trace elements in the amphibolite are characterized by relative enrichment in large ion lithophile elements （LILE）, i. e. K, Rb and Ba, and by depletion in high field-strength elements （I-IFSE）, i. e. , Zr, Ti, Nd and Ta. The primary rock of this set of metamorphic rock association is regarded as basaltic volcanic by comprehensively studying their mineral composition and geochemical component, thus the metamorphic rocks belong to orthometamorphite. The magma, formed in the island-arc environment, is mainly derived from deple- ted mantle and simultaneously accompanied by the contamination and reconstruction of a small quantity of old crust. This study area was considered to be the northern extension part of Neoarchean Jilin-Liaoning-Hebei arc- continent collisional accretion-type orogenic belt of North China Craton.