华北陆块北缘印支期S型花岗岩带特征及其构造环境

Characteristics and tectonic setting of Indosinian S-type granites in the northern margin of North China landmass

华北陆块北缘内蒙古中部地区分布着大量近东西向展布的印支期花岗岩 ,形成一条规模巨大的复式花岗岩带。岩石类型主要为斑状黑云二长花岗岩、钾长花岗岩 ,1∶5万区调同位素测年获得 2 0 7～ 2 2 7Ma的一系列锆石U-Pb表面年龄 ,岩相学和岩石地球化学研究显示其具有S型花岗岩特征 ,表明其形成于碰撞后构造环境 ,并不是华北板块与西伯利亚板块碰撞造山作用的产物。

Indosinian S_type granites are widely distributed in central Inner Mongolia on the northern margin of North China landmass. Spread in nearly EW direction, the granites have formed a gigantic compound granite belt, with porphyritic biotite_admellite and moyite being the two main types. SiO 2 is abundant, Al 2O 3 is 12.38% ～15.34%. A/NKC (molecule ratio)>1.1, K 2O/Na 2O=1.1～3.1, δ=1.9～2.6, ΣREE is 45.778×10 -6 ～486.501×10 -6 , and δEu=0.1～0.8. A series of zircon U_Pb surface ages (207～227 Ma) for the granites have been recently obtained from 1/50?000 regional geological survey. As the lithofacies and geochemical characteristics of the granites are similar to those of S_type granites, the authors conclude that the Indosinian granite in this area was formed in a post_collision setting instead of in the setting of syn_collision between North China plate and Siberia plate.