新疆博格达中段木垒地区基性侵入岩岩石地球化学、锆石U-Pb年代学及其构造意义

博格达造山带大量分布基性岩,其成因研究对区域构造演化具有重要意义。本次对博格达造山带中段木垒地区的基性岩进行了系列研究工作,初步对岩石成因和构造环境进行了探讨,为博格达造山带研究提供了新的依据。岩石地球化学特征显示,辉绿岩的SiO₂含量为47.71%~53.7%,K₂O含量为0.61%~1.87%,Na₂O含量为2.97%~5.14%,显示富钠贫钾特征,属准铝质中-高钾钙碱性岩石系列。Mg#值为29.80~47.89,远低于原始玄武质岩浆的参考数值65,表明区内基性岩可能是原始岩浆经历较强程度分异作用后的产物;分异指数(DI)均大于35.00,固结指数均远小于30,均显示辉绿岩分异程度较高。稀土元素特征显示较高稀土总量、轻稀土强烈富集的右倾模式,相对富集Rb、Ba、K、Th等大离子亲石元素,相对亏损Nb、Ti、Hf、Zr等高场强元素。辉绿岩锆石U-Pb年龄为(305.9±3.1)Ma;辉绿岩岩浆可能源于亏损尖晶石橄榄岩相至原始尖晶石橄榄岩相之间,为较低程度部分熔融及分异演化综合作用形成的产物,为晚石炭世博格达弧后裂陷盆地晚期局限性伸展作用的产物。

Geochemistry,Zircon U-Pb Dating and Tectonic Significance of Basitein the Middle Section of Bogda Orogenic Belt,Xinjiang

Basic rock is widly distributed in Bogda orogenic belt.Studies on its genesis is of great significance to the regional tectonic evolution.Geochemical characteristics of rocks show that the SiO 2 in Diabases is 47.71%~53.7%,the K2O is 0.61%~1.87%,and Na2O is 2.97%~5.14%.are metaluminous,and show transitional characteristics from the calc-alkaline to high-potassic calc-alkaline series,belonging to quasi-aluminous medium-high calc-alkaline series.The Mg#values range from 29.80 to 47.89,which is much lower than the reference value of the original basaltic magma 65,indicating that the basic rocks in this area may be the product of strong differentiation from the primitive magma.The differentiation index(DI)is higher than 35.00,while the consolidation index is lower than 30,implying that the diabase suffered strong differentiation.The charateristics of rare earth element(REE)show a right-dipping mode with high total contents and intense enrichment of light REEs.Large-ionic lithophilic elements such as Rb,Ba,K,and Th,are relatively enriched and high-field elements such as Nb,Ti,Hf,and Zr are relatively depleted.The diabase zircon U-Pb dating is(305.9±3.1)Ma.Diabase magma may derive from the transitional phase of Depleted spinel peridotite facies and Primitive spinel peridotite facies and is a moderate partial melting of the lithospheric mantle and the evolution of magma differentiation,which is the product of limited extension of Bogda post-arc rift basin in Late Carboniferous.