东北地区新开岭-科洛杂岩变形规律与成因

Deformation Characteristics and Genesis of the Xinkailing-Keluo Complex in NE China

新开岭-科洛杂岩位于中国东北地区的嫩江-黑河构造带中,其变形规律与成因一直是制约东北地区乃至邻区构造演化的关键问题之一.据详尽的野外调查,系统分析了岩石宏观糜棱面理、矿物拉伸线理、"A"型褶皱、不对称褶皱、眼球状旋转构造和显微书斜式、眼球状旋转等构造样式.构造解析及运动学分析反映杂岩带两侧整体分别向NW及SE向的伸展滑脱特征;杂岩带内黑云斜长片麻岩及侵入糜棱岩中的闪长玢岩锆石U-Pb(LA-ICP-MS)定年及区域对比研究结果显示,其韧性变形变质作用时代为中侏罗世(167 Ma),变质峰期时限为170~163 Ma,中侏罗世晚期(163 Ma)暴露于地表.新开岭-科洛杂岩具上盘盖层、拆离韧性剪切带及下盘核杂岩3层式结构特征.核内为大面积分布的花岗岩类,地层时代远比核外地层偏新,并无"古老"的变质岩;拆离韧性剪切带变形温度约400~500℃,其变质强度达绿片岩相,后期发生明显退变质作用.新开岭-科洛岩浆核杂岩主要是在岩浆底侵、花岗岩岩体强力侵位引起地壳隆升的伸展构造背景下形成.

Xinkailing-Keluo complex, located in Nenjiang-Heihe tectonic belt, NE China, has fully undergone regional tectonic movement and therefore recorded plentiful evolution information. Its residual deformation signatures and genetic mechanisms could provide key clues about regional tectonic evolution history of not only the adjacent region but also the whole north-east area of China. Based on detailed field survey, this paper conducted systematic studies on different types of structure units, foliation of mylonite rock, stretching lineation of minerals, A-type fold, asymmetrical fold, augen-shaped rotational structure and microscopic book skew structure. The results revealed a significant fact two wings of the complex have the extension of NW and SE respectively, The mineral of zircon have been identified from internal biotite-plagioclase gneiss and intrusive dioritic-porphyrite body in mylonite country rock.Its U-Pb dating of zircon and regional study both indicated these deformation mainly occurred during Middle-Jurasic(167 Ma), and reached metamorphic peak during 170-163 Ma. Then it was uplifted by tectonic movement and exposed to the ground in late Middle-Jurasic. Xinkailing-Keluo complex was composed of three layers architecture,the upper cap rock, middle zone and lower complex.The internal part is mainly composed by granite,which are much younger than its outer part.The metamorphic temperature ranged from 400 to 500 degree, reaching extent of greenschist facies and was followed by retrograde metamorphism. Later, the regional uplift happened due to the granite magma underplating and the Xinkailing-Keluo magmatic core complex formed under regional stretch tectonic background.