西准噶尔吾尔喀什尔山早泥盆世马拉苏组火山岩地球化学特征及构造意义

GEOCHEMISTRY OF VOLCANIC ROCKS FROM THE MALASU FORMATION OF EARLY DEVONIAN IN THE WEST OF UR KASHGAR MOUNTAIN,WESTERN JUNGGAR,AND ITS TECTONIC IMPLICATIONS

西准噶尔早泥盆世马拉苏组主要分布于吾尔喀什尔山西部,整体为一套火山—沉积地层。对其中火山岩进行地球化学研究表明,w（SiO2）49.51%-59.04%,w（TiO2）（0.80%-1.12%）、w（K2O＋Na2O）=3.09%-5.28%,富钠贫钾（Na2O/K2O=2.41-24.25）。高w（A12O3）（17.66%-21.19%）、w（MgO）（3.18%-7.00%,Mg#=47-56）,属于亚碱性系列。稀土元素总量高（ΣREE=30.40×10^-6-93.65×10^-6）,轻、重稀土分馏较强（（La/Yb）N=2.58-11.38）,Eu轻微负异常到正异常（Eu/Eu＊=0.71-1.35）。相对富集LILE（Rb,Ba,Th和K）,亏损HFSE（Zr,Hf）,Nb和Ta强烈亏损,Ti轻微亏损。岩石源自轻微交代的亏损地幔部分熔融,具有岛弧火山岩的地球化学特征,这为进一步认识西准噶尔博什库尔-成吉斯岩浆弧的性质及构造演化提供了证据。

The Early Devonian Malasu Formation of a suit of volcanic-sedimentary rocks,is mainly distributed in the west of Ur Kashgar Mountain,Western Junggar.Geochemical analysis reveals that the volcanic rocks of alkaline series have a low w（SiO2）（49.51%-49.51%）content,w（TiO2）=0.80% -1.02%,with total alkaline of w（K2O＋Na2O）=3.09% -5.28%,Na2O/K2O=2.41-24.25,and with high w（Al2O3）17.66% -21.19% content,w（MgO）=3.18%-7.00%,Mg#=47-56.Tested samples are rich in rare earth elements（ΣREE=30.40×10^-6-93.65×10^-6）,and LREE（（La/Yb）N=2.58-11.38）,with negative to positive Eu anomaly（Eu/Eu＊=0.71-1.35）,elative enrichment of LILE（Rb,Ba,Th and K）,depletion of HFSE（Nb,Ta,Zr and Hf）,slight depletion of Ti.It is suggested that the volcanic rocks were generated by slightly metasomatic depleted mantle partial melting,with geochemical characteristics of island arc volcanic rocks.It provides evidence for further understanding of the property and tectonic evolution of the Boshchekul-Chingiz arc in the Western Junggar.