小兴安岭西北部花岗质糜棱岩锆石LA-ICP-MSU-Pb年龄、岩石地球化学特征及地质意义  

Zircon U-Pb LA-ICP-MS Dating,Petrogeochemical features of Granitic Mylonite in Northwestern Lesser Hinggan Mountains,and Tectonic Significance

作　　者：赵院冬[1,2] 莫宣学[1] 李士超[2] 车继英[2] 许逢明[2] 吴大天[2] 张乾峰 赵君[2] 王奎良[2] 

机构地区：[1]中国地质大学(北京),北京100083 [2]沈阳地质调查中心,沈阳110034 [3]黑龙江省齐齐哈尔矿产勘查开发总院,黑龙江齐齐哈尔161000

出　　处：《地质论评》2015年第2期443-456,共14页Geological Review

基　　金：中国地质调查局地质调查项目(编号1212011121082;1212011405701)的成果

摘　　要：通过对位于小兴安岭西北部黑河—呼玛地区与元古宙变质岩系伴生出露的三处强变形的花岗质岩石的锆石U-Pb LA-ICP-MS测年和岩石学、岩石地球化学研究,确认样品岩性分别为花岗闪长质糜棱岩（样品Ⅰ-3-4和Ⅰ-5-1）、角砾状花岗闪长岩（样品1121和1211）和花岗质糜棱岩（样品1218）,锆石U-Pb年龄为299.6±1.0Ma、300.8±1.1na和294.3±1.0 Ma,形成于晚石炭世末至早二叠世初,而非前人确定的元古宙或早石炭世,并初步认为岩石韧性变形作用发生时间介于184～170 Ma之间.三种花岗岩分别属于富硅、高铝、贫钾的过铝质钙碱性系列（Ⅰ-3-4和Ⅰ-5-1）、贫硅偏铝、高钙铁镁的偏铝质高钾钙碱性系列（1 121和1211）和富硅钾、低钙镁铝的弱过铝质钾玄质系列（1218）,稀土元素特征相似,富集轻稀土,相对亏损重稀土,具有明显或弱的Eu负异常,微量元素富集Rb、La、Th、U等大离子亲石元素,相对亏损Sr和高场强元素Nb、Ta、Zr、Hf,具有高分异Ⅰ型花岗岩和A型花岗岩的特征,在构造环境判别图R1-R2图上分别落在同碰撞造山、晚造山和造山后环境,在Nb-Y图落入火山弧—同碰撞环境和板内环境.结合区域资料,认为上述花岗岩是兴安地块与松嫩地块晚古生代碰撞造山的产物,记录了两块体间碰撞造山到造山后伸展作用.In Northwest of Lesser Hinggan Mountains, some deformated granitoidse outcrop with Proterozoic metamorphic rocks. The writers studied these granitoids on petrology, geochronology and petrogeochemistry. Five samples are granodioritic mylonite（ sample I-3-4, I-5-1 ）, brecciated granodiorite（ sample 1121,1211 ） and granitic mylonite （sample 1218） respectively, and the corresponding primary rock formed at 299.6 ±1.0Ma, 300.8 ± 1. 1Ma and 294. 3 ± 1. 0 Ma of the Late Carboniferous and the Early Permian, not the Proterozoic or Early Carboniferous that the predecessors determined. It is deduced that the ductile deformation happened at 184 - 170Ma. Petrochemically, these rock belong to Peraluminous calc-alkaline serie with high Si, A1, low K（ sample I- 3-4, I-5-1）, and Metaluminous high K calc-alkaline series with high Ca, Fe, Mg, low Si（sample 1121,1211 ）, and Peraluminous shoshonite series with high Si, K, low Ca, Mg, AI（ sample 1218）. They enriched in LREE, depleted in HREE relatively, and have negative Eu anomalies. They enriched in Rb, La, Th, U, and depleted in Sr, Nb, Ta, Zr. All these characters show that these granite are high fractionated I-type granitoids and A-type granite. The discriminant diagram of tectonic environment show they formed in syn-collision, late-orogenic and post-orogenic environment respectively. Combined with regional geological data, writers propose that these granite are formed during the collision and orogen of the Hinggan （ Xing＇ an ） block with Songnen （ Songhua River-- Nenjiang River） block in Late Paleozoic.

关 键 词：小兴安岭西北部黑河—呼玛地区 花岗质糜棱岩 兴安地块 晚古生代 碰撞造山作用 

分 类 号：P588.332[天文地球—岩石学] P597.3[天文地球—地质学]