摘要
广泛出露于华北板块东部辽吉地区的古元古代变质杂岩,多年来一直被认为是古老的陆内裂谷作用的产物,我们通过详细的野外地质调查工作发现,该变质杂岩中以往所划定的混合岩实际是不同变质程度和变形特征的岩浆成因花岗岩岩体,其岩石类型除典型的片麻状角闪正长花岗岩(俗称“条痕状花岗岩”或“辽吉花岗岩”)外,另有片麻状石英闪长岩、巨斑状黑云母二长花岗岩、巨斑状-环斑状含石榴石花岗岩和角闪辉石正长岩等。应用SHRIMP技术,本文对片麻状石英闪长岩和巨斑状-环斑状含石榴石花岗岩进行了锆石U-Pb同位素年龄测定,结果显示它们的侵位时代为1872-1850Ma,与巨斑状黑云母二长花岗岩和角闪辉石正长杂岩侵位时代相近。岩石学-地球化学特征显示片麻状石英闪长岩是“I”型花岗岩,具有岛弧型花岗岩地球化学特征;而巨斑状-环斑状含石榴石花岗岩(局部具有球斑状结构)属“S”型花岗岩。结合区内与花岗岩形成同时发生的变质作用P-T特征,这种I-、S-和A-型花岗岩的同时产出,反映他们可能形成于造山后构造背景。结合朝鲜狼林-中国辽南和龙岗太古宙陆块的结晶基底差别,可以认定华北板块在太古宙末期并非仅由东、西部陆块组成,在东部陆块至少还存在朝鲜狼林-辽南-胶东联合陆块和龙岗-鲁西-五淮陆块两个微陆块,这两个微陆块大约在1．90Ga左右发生拼合,然后它们再于1．85 Ga左右与西部地块拼合。
The Paleoproterozoic metamorphic complex, widespread in the Liaoning-Jilin Region of northeastern North China Craton,was thought to be the result of intra-plate rifting. However, our filed observations show that the magmatites are not metamorphic rocks but granitic plutons with different degree deformation and metamorphism, consisting of gneissic hornblende syenogranite （ termed by “striated granite” or “ Liaoji granite”）, gneissic quartz diorites, porphyric biotite monzogranite, porphyric-rapakivi garnet granite and hornblende pyroxene syenite. This paper presents the new zircon SHRIMP U-Pb data of gneissic quartz diorite and porphyric-rapakivi garnet granite. The results show that they were emplaced during 1872 - 1850 Ma, similar to those of porphyrie biotite monzogranite and hornblende pyroxene syenitic complex. Petrography and geochemical features indicate that the gneissic quartz diorite belong to I-type granites with geochemistry of Arc-type granitoids, whereas, porphyric-rapakivi garnet-bearing granites with rapakivi texture have geochemistry of S-type granites. With consideration of the P-T path of the regional metamorphism coeval with the emplacement of these granites, the concurrence of I-, S- and A-type granites indicates that these granites formed in the post-orogenic setting. The difference of the basement rocks between Langlin （ Korea）-Liaonan （China） block and Longgang block indicates that the North China Craton is composed of Langlin-Liaonan-Jiaodong and I.onggang-Luxi-Wuhuai blocks in the east and west block, not of West and East blocks.These two blocks in the east North China Craton assembled at about 1.9 Ga, and then collided with the West Block at about 1.85 Ga.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2005年第3期721-736,共16页
Acta Petrologica Sinica
基金
本文由国家自然科学基金(40272045和40325006)中国科学院"百人计划"资助
关键词
东部陆块
华北板块
俯冲碰撞造山
古元古代晚期
花岗岩
East Block, North China Craton, Subduction collision and orogeny, Late Paleoproterozoic, Granites
