新疆富蕴县恰库尔特—带碱性花岗岩的基本特征及形成的大地构造背景

THE FUNDAMENTAL FEATURES AND TECTONIC SETTING OF THE ALKALI GRANITES FROM QIAKUERTE REGION, FUYUN COUNTY, XINJIANG

恰库尔特一带的碱性花岗岩按侵入顺序和岩性可分为:晶洞(霓石)钾长花岗岩、(霓石)碱长花岗斑岩、霓石花岗岩.这些岩石大都含碱性暗色矿物.发育指示浅成特点的晶洞构造及文象结构,从矿物组合看岩石具贫水特征;岩石化学方面以高硅、高碱或过碱,贫铝、镁、钙为主要特征;岩石通常具有高的∑REE,其中以过碱性的霓石花岗岩为最高;轻稀土较重稀土富集,并具有强的负Eu异常;微量元素地球化学图谱表明,岩石相当于洋脊花岗岩,具有高钾、铷、钍的含量,而钡、钽、铌的富集程度相对较低.以上特征和区域构造分析表明,恰库尔特一带的碱性花岗岩为阿尔泰造山带造山作用结束以后于中晚三叠世的非造山环境下形成的A型花岗岩.

According to the intrusive sequence and lithological characters, the alkali grantes from Qiakuerte region can be divided into miarolitic potash-feldspar granite, ( aegirine ) alkali-feldspar granite porphyry and aegirine-granite . All these rocks contain dark alkali minerals and miarolitic structure, micrographic texture or porphyritic texture indicating epimagmatic origin. The mineral assemblages icaten dthat the rocks are poorly aquiferous. The petrochemical features of the granites are rich in Si, K and Na and poor in Al, Mg and Ca. The granites possess high REE concentration an dstrong Eu negative anomalies, and their LREE are much more enriched than their HREE. The geochemical patterns of trace elements of the granites show that the relative concentrations of K, Rb and Th are much higher but Ba, Ta and Nb are lower in the granites from Qiakuerte region, than that from the oceanic-ridge granlte. All the above mentioned features of the granites and tectonic analyses demonstrate that the granites from Qiakuerte region are of A-type, which were formed in middle-late Triasslc anorogenic stage of the evolution of the Altalds.