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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 in West Junggar is mainly distributed in the western part of Wuer Kashgar Mountain. It is a set of volcano-sedimentary formations. The geochemical study of volcanic rocks shows that the contents of w (SiO2) 49.51% -59.04%, w (TiO2) 0.80% -1.12%, w (K2O + Na2O) = 3.09% -5.28% /K2O=2.41~24.25). High w (A12O3) (17.66% ~ 21.19%), w (MgO) (3.18% ~ 7.00%, Mg # = 47 ~ 56) belong to the subalkaline series. The content of rare earth elements is high (ΣREE = 30.40 × 10-6 ~ 93.65 × 10-6), the fraction of light and heavy REEs is strong (La / Yb) N = 2.58-11.38) /Eu*=0.71~1.35). Relative enrichment of LILE (Rb, Ba, Th and K), loss of HFSE (Zr, Hf), intensive depletion of Nb and Ta, and slight loss of Ti. The partial melting of the depleted mantle originating from minor metasomatism, with the geochemical characteristics of island arc volcanic rocks, provides evidence for further understanding of the nature and tectonic evolution of the Boschur-Chenggish magmatic arc in western Junggar.