延边和龙地区闪长岩的年代学、地球化学特征及岩石成因研究

Chronology,Geochemical Characteristic and Petrogenesis Analysis of Diorite in Helong of Yanbian Area,NE China

吉林省东部延边和龙地区中生代闪长岩的锆石LA—ICP—MSU—Pb年龄为173～175Ma。岩石的SiO2含量为53．28％～58．02％，TiO2含为0．99％～1．08％，MgO和TFe2O3含量分别为1．96％～6．45％和6．59％～9．64％，Mg#值为37～59，Na20含量为3．37％～4．88％，K2O含量为0．94％～2．30％，Na2O／K2O为1．70～4．16，Al2O3含量为15．87％～18．93％，相对富钠高铝，并且具有钠质钙碱性系列向高钾钙碱性系列过渡的趋势，稀土元素球粒陨石标准化曲线显示其具有富含轻稀土元素（LREE）、贫重稀土元素（HREE）以及无Eu负异常的特点。岩石富集大离子亲石元素（Rb，Th，Ba），明显亏损Nh，Ta，Zr，Hf和Ti等高场强元素（HFSE）。闪长岩的原始岩浆起源于受俯冲流体交代地幔楔的部分熔融，岩浆在上升过程中未受到明显的地壳混染。该期闪长岩形成于与古太平洋板块俯冲相关联的活动大陆边缘环境。

The Mesozoic diorites are exposed in Helong area, eastern Jinlin Province. LA-ICP-MS Zircon U-Pb dating indicates that they were formed at 173-175 Ma. The contents of SiO2 are 53.28%-58.02%,Ti02=0.99%-1.08%, MgO= 1.96%-6.45%, TFe203=6.59%-9.64%, Mg#=37-59, Na2O=3.37%-4.88%, K2O=0.94%-2.30%, Na2O/K2O= 1.70-4.16 and A1203=15.87%-18.93%,characterizing high Na and A1. These diorites display characteristics transitional between the sodic calc-alkaline series and high potassium calc-alkaline series. Their chondrite-normalized REE patterns are characterized by high LREEs and low HREEs without Eu negative anomalies. Trace element compositions are characterized by enrichment in large ionic lithophile elements （LILEs; e.g., Rb, U, Th） and depletion in high field strength elements （HFSEs, e.g., Nb, Ta, Zr, Hf, Ti）. The primary magma of the diorites in Helong area were derived from partial melting of mantle wedge which had been metasomatized by subduction fluids and formed in an active continental margin setting induced by subduction of the Paleo-Pacifie plate.