冀东分水岭岩体锆石U-Pb年代学、地球化学特征及地质意义

Geochronology,Geochemical Characteristics in the Fenshuiling Complex in the East Hebei Province and Its Significance

冀东分水岭岩体位于马兰峪隆起西段,为复式岩体,其岩性为花岗闪长岩和黑云母二长花岗岩,花岗闪长岩呈带状环绕黑云母二长花岗岩分布,锆石U-Pb定年揭示其年龄分别为157.4±2.7Ma和162.0±4.0Ma。花岗闪长岩的SiO_264.50%~65.56%,K_2O+Na_2O 7.24%~7.70%,K_2O/Na_2O 0.58~0.67,A/CNK0.91~0.97,呈高硅富钾,属准铝质高钾钙碱性系列,为I型花岗岩;而黑云母二长花岗岩SiO_273.25%~74.56%,K_2O+Na_2O 7.22%~8.58%,K_2O/Na_2O 0.86~1.04,A/CNK 1.09~1.24,较花岗闪长岩更富硅、钾,为过铝质高钾钙碱性系列,属成熟度不高的A型花岗岩。两者稀土配分曲线呈右倾型式,具稀土总量较低,轻重稀土分馏明显,微量元素均亏损Nb-Ta、Zr-Hf,显示以壳源成分为主,具幔源混染特征。花岗闪长岩具弱Eu正异常,且富集Sr,源区深度较大;而黑云母二长花岗岩具Eu负异常,亏损Sr,源区有少量斜长石残留。岩体形成与太平洋板块俯冲构造背景密切相关,为中生代构造转换体制的产物。

The Fenshuiling Complex is situated in the west of the Malanyu uplift,that is the west of the intrusive rock belt of the central east Hebei Province. U-Pb Zircon Geochronology shows that granodiorite：157.4±2.7 Ma,biotite adamellite162.0±4.0 Ma,later granodiorite distributed around the early biotite adamellite in a ring belt.It is a typcial complex massif.The granodiorite belongs to the metaluminous high potassium calc-alkaline series,I type granite,SiO264.50%65.56%,（K2O＋Na2O）7.24%7.70 %,（K2O/Na2O）0.580.67,A/CNK 0.910.97}.In contrast,the biotite adamellite has a higher content about SiO2 and K2O,belongs to peraluminous high potassium calc-alkaline series,I-A type granite{SiO273.25%74.56%,（K2O＋Na2O）7.22%8.58 %,（K2O/Na2O）0.861.04;A/CNK1.091.24}.From REE and trace element,the granodiorite is relatively low in the total REE,and enrichmet in LREE and depieton in HREE,loss of Nb-Ta,Zr-Hf.All this show more crustal genesis,and less mantle genesis.The granodiorite positive Eu,Sr anomaly.While the biotite adamellite negative Eu,Sr anomaly,show that granodiorite source region is deeper than biotite adamellite.About tectonic setting,the formation of the rock mass is closely related with the subduction of Pacific plate,form from（syn-collision）-（aftert clllosion）,producted by transformation of teconic.Now,the research on Fenshuiling complex has a great significance in summaring the laws of magmation and tectonic activity.