黑龙江东部海音山花岗闪长岩年龄、岩石成因及构造背景

Age,petrogenesis and tectonic implication of granodiorites in Haiyinshan area,eastern Heilongjiang

对黑龙江东部海音山林场地区花岗闪长岩开展锆石U-Pb年代学和岩石地球化学研究,以确定其形成时代,源区性质和构造背景。花岗闪长岩锆石年代学研究表明其形成于早白垩世(128±1 Ma和126±1 Ma)。岩石地球化学研究显示,花岗闪长岩富SiO_2(67.31%~70.19%)、Al_2O_3(13.72%~15.52%)、K_2O(3.01%~4.06%)、Na_2O(2.92%~3.81%),贫CaO(2.03%~3.04%)、FeO和MgO,属于高钾钙碱性岩系列。富集大离子亲石元素(如Rb、Ba、K)、轻稀土元素(LREE),相对亏损高场强元素(如Nb、Ta、Ti、P)。岩浆源区为镁铁质下地壳的部分熔融所形成。结合区域同时代岩浆岩的研究成果,认为海音山花岗闪长岩形成于古太平洋板块向欧亚大陆俯冲下的火山弧环境。

The authors undertake zircon U-Pb dating and geochemical studies of granodiorites at Haiyinshan tree farm area in eastern Heilongjiang,NE China,with the aim of constraining the formation time,magma source and tectonic setting of the granodiorites. Zircon U-Pb dating results indicate that the granodiorites were formed in Early Cretaceous( 128 ± 1 and 126 ± 1 Ma). Geochemically,the granodiorites are rich in SiO_2( 67. 31% ~70. 19%),Al_2O_3( 13. 72% ~ 15. 52%),K_2O( 3. 01% ~ 4. 06%),Na_2O( 2. 92% ~ 3. 81%),and depleted in Ca( 2. 03% ~ 3. 04%),Mg,and Fe,belonging to high-K calc-alkaline series. Trace element analysis shows that large ion lithophile elements( LILEs),e. g. Rb,Ba and K and light rare earth element( LREE) are enriched,and high field strength elements( e. g. Nb,Ta,Ti,P) are depleted. It is concluded that the primary magma of granodiorites is likely derived from partial melting of mafic lower crustal materials. Combined with the results of regional contemporary magmatic rocks,it is suggested that the Haiyinshan granodiorites formed in volcanic arc setting related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.