内蒙古乌兰浩特索伦镇地区中生代侵入岩特征研究

内蒙古乌兰浩特索伦镇地区位于大兴安岭中南段。该区中生代侵入岩广泛发育。开展侵入岩的年代学、地球化学特征研究能为深入探讨区域构造背景提供依据。3个样品K—Ar全岩法测年结果(93.39Ma-108.48Ma)证明侵入岩形成于早白垩世,略晚于其南侧同一构造带上的杜尔基地区侵入岩年龄(100.15Ma-120.29Ma),符合太行山-大兴安岭早白垩世侵入岩时代自南向北由老变新的演化趋势。岩石地球化学分析结果显示岩石属于碱性系列,具有高硅、高钾、富碱、过铝、贫钙、镁、铁等特征。稀土元素总量为(77.96-241.29)μg/g,平均值为158.92μg/g,与杜尔基地区早白垩世侵入岩的稀土总量平均值(146.85μg/g)及华北克拉通内碱性系列岩石的稀土总量平均值(163.32μg/g)都非常接近。稀土元素球粒陨石标准化曲线整体右倾,因Eu负异常而呈“V”型形态,与太行山一大兴安岭地区早白垩世典型岩体的稀土配分型式极为相似。侵入岩的成因类型为A-型,形成于伸展构造环境。

Study on characteristics of Mesozoic intrusive rocks in Suolunzhen area,Ulanhot, Inner Mongolia

Suolunzhen area in Ulanhot, Inner Mongolia, where Mesozoic intrusive rocks are widely developed, is located in the middle-south part of the Dahinggan Mountains. Studying on chronology and geochemical characteristics of intrusive rocks will give some references to discuss the regional tectonic settings of intru- sive rocks. Three samples from this area yield whole-rock K-Ar ages of 93.39-108.48 Ma, implying that the intrusive rocks might be formed in early Cretaceous, slightly later than the age of Duerji intrusive rocks (100. 15- 120. 29 Ma) developed in the same tectonic belt, consistent with the evolution trend of the Taihangshan-Dahinggan Mountains early Cretaceous intrusive rocks varying in ages from older to younger in the direction from south to north. The results of petrogeochemical analyses of sixteen samples show that the intrusive rocks belong to alkaline igneous series charaeterised by high Si and K, enrichment of alka-line, peraluminous and low content of Ca, Mg and Fe. The ∑REE values (77.96-241.29 μg/g; average, 158. 92/.μg/g) are very close to those of Duerji intrusive rocks (average ∑REE=146.85 μg/g) and north China craton alkaline series rocks (average .∑REE= 163.32/μg/g). Chrondrite normalized REE patterns of the intrusive rocks show decreasing trends with strongly Eu-depleted V-shaped patterns, which are similar to those of the early Cretaceous typical alkaline series rocks in Taihangshan-Dahinggan Mountains. The genetic type of the intrusive rocks belongs to Atype, suggesting their formation in the environment of ex- tensional tectonics.