新疆特克斯东南大哈拉军山组玄武安山岩地球化学特征:岩石成因和构造背景探讨

特克斯东南大哈拉军山组玄武安山岩具有钙碱性火山岩的地球化学特征,Nb、Ta等高场强元素强烈亏损,强不相容元素比值明显不同于原始地幔、亏损地幔和富集地幔而倾向于地壳,具有岛弧火山岩的特点,与新源县南及其东部大哈拉军山组火山岩一起指示了西天山在早石炭世-晚石炭世处于汇聚而不是伸展的大地构造背景。与岛弧作用有关的俯冲沉积物的交代作用是其源区受改造的最主要方式,岩浆演化以包括橄榄石、单斜辉石在内的分离结晶作用为主。

GEOCHEMICAL CHARACTERISTICS OF BASALTIC ANDESITES FROM DAHALAJUNSHAN FORMATION, SOUTHESTERN TEKESI (XINJIANG): PETROGENESIS AND ITS TECTONIC SIGNIFICANCE

The basaltic andesites from Dahalajunshan Formation in southeastern Tekesi County, Xinjiang, are of calc-alkaline composition, and show depletion in HFSEs (e.g., Nb, Ta) and enrichment in LILEs. Moreover, the ratios of strongly incompatible elements are distinct from those for the primitive, depleted and enriched mantle, indicating involvement of crustal components in the mantle source. Based on field geological observation of the contemporaneous volcanics from Xinyuan and its surrounding areas, it is proposed in the paper that western Tianshan was in a convergent rather than an extensional setting during early-late Carboniferous. The mantle source region might have undergone metasomatism related to subducted sediments and the derived magma may have experienced significant fractional crystallization of olivine and clinopyroxene during the magmatic process.