新识别的"下二台"构造杂岩作为华北板块北缘东段分布的构造混杂岩带重要组成部分，其物质组成、形成时代和构造属性仍需进一步研究，这将为探讨华北板块北缘东段晚古生代构造演化提供重要依据。作者在"下二台"构造杂岩中识别出一套早-中二叠世变质火山-碎屑岩，其以变质碎屑岩为主，并夹变质火山岩，二者在野外产出上混杂在一起。变质火山岩原岩类型包括流纹岩、英安岩、安山岩、玄武安山岩，为一套钙碱性火山岩，属于准铝质-弱过铝质岩石。根据岩相学和地球化学特征，将其分为变质酸性火山岩和变质中-基性火山岩；二者均相对富集轻稀土元素，亏损重稀土元素，轻重稀土元素分馏明显，Eu负异常不明显，但变质酸性火山岩明显亏损P、Ti元素，结合高场强元素相关性特征，认为二者不是同一基性岩浆分异的产物。变质火山岩锆石LA-ICP-MS U-Pb同位素年龄为272~288Ma，代表其原岩结晶年龄，时代为早二叠世；变质酸性火山岩原始岩浆来源于地壳物质的部分熔融，变质中-基性火山岩原始岩浆来源于岩石圈地幔（俯冲带附近），并遭受了地壳物质的混染，二者均形成于活动大陆边缘火山弧环境。变质碎屑岩原岩恢复为泥砂质沉积岩和砂泥质沉积岩，相对亏损轻稀土元素，富集重稀土元素，轻重稀土元素分馏较明显，Eu异常不明显。两件碎屑岩样品锆石LA-ICP-MS U-Pb同位素年龄主要介于267~347Ma，推断其沉积下限为267Ma和269Ma，均为中二叠世；泥砂质沉积岩可能来源于再旋回的以长英质岩石为母岩的沉积岩，砂泥质沉积岩可能来源于再旋回的以长英质和镁铁质岩石为母岩的沉积岩，二者分别形成于活动大陆边缘大陆岛弧和大洋岛弧环境。下二台地区早-中二叠世变质火山-碎屑岩为"下二台"构造杂岩重要组成部分，它表明二叠纪时期华北板块北缘东段经历了三个构造演化阶段：早二叠世古亚洲洋加速俯冲，形成新的大陆弧阶段；中二叠世古亚洲洋持续俯冲，大陆弧和大洋弧碰撞阶段；晚二叠世陆-陆碰撞前阶段。

Northeast China occupies the majority of the eastern Central Asian Orogenic Belt, which mainly consists of continental blocks and accretionary terranes. The Devonian was a tectonic quiet period in the NE China region due to a lack of tectono-magmatism, but the tectonic background of this period has been unclear, especially for the Hegenshan-Heihe Suture between Xing’an and Songliao accretionary terranes, which represents the Paleozoic Nenjiang Ocean (a branch ocean of the eastern Paleo-Asian Ocean). Here we report granitic rocks from the Woluohe area, Northern Great Xing’an Range, NE China, to constrain the tectonic process of the transition from the Devonian quiet period to the Early Carboniferous active tectonic period. Three granitic rock samples produce zircon U-Pb ages of 389 Ma, 368 Ma, and 351 Ma, belonging to the Middle and Late Devonian and Early Carboniferous, respectively. They have high Si, Al, K, and Na contents, but with low Mg, Fe, and Ti contents, together with positive Hf isotopic features and low molar Al₂O₃/(MgO+FeO^T) ratios, we suggest that they were derived from partial melting of lower crustal igneous rocks. Meanwhile, the narrow major element variation at odd with the fractionation process and their negative Nb and Ta anomalies imply the obvious contribution of crustal. Comprehensive tectonic setting analysis shows all samples are in calc-alkali magmatic series with rightward fractionated REE and trace element patterns that are enriched in LREE and LILE and depleted in HREE and HFS, indicating a subduction-related magmatic arc setting. Considering the regional tectonic setting and the small scale of the Devonian plutons, we suggest a limited subduction tectonic setting during the quiet period of the northern Great Xing’an Range, which might indicate the beginning of an initial northwestward subduction of the Nenjiang Oceanic lithosphere beneath the Xing’an Accretionary Terrane in the Middle Devonian, accelerated subduction in the Late Devonian, and bidirectional subduction in the Early Carboniferous.