伊犁地块北缘早石炭世阿拉斯坦闪长岩成因及其对北天山洋俯冲过程的启示

伊犁地块北缘存在大量石炭纪岩浆岩，但对早石炭世中晚期(340~320 Ma)的岩浆岩鲜有报道，在一定程度上影响对该阶段区域构造演化的认识。为探讨伊伊犁地块北缘早石炭世的大地构造背景，对伊犁地块北缘阿拉斯坦河流域新发现的早石炭世中期闪长岩体开展了详细的岩石学、地球化学、锆石U-Pb年代学和Lu-Hf同位素研究。阿拉斯坦闪长岩岩体中发育微粒闪长质包体，两者在多组主量和微量元素的双变量图解中均表现出不同的演化趋势，表明其不同的成因和起源。两种岩石均具有富集大离子亲石元素，而亏损Nb、Ta、Ti等高场强元素的特征，具有俯冲带岩石的地球化学信息。结合区域资料，认为伊犁地块北缘在早石炭世中晚期之后整体处于伸展背景，可能与北天山洋的俯冲板片回转或后撤相关。

Petrogenesis of the Early Carboniferous Alasitan diorites from the northern margin of Yili Block and implication for subduction process of the North Tianshan Ocean

There are massive Carboniferous magmatic rocks in the northern Yili Block.However, rare middle-late Early Carboniferous (340~320 Ma) magmatic rocks were reported, which limited our understanding for the tectonic evolution of the northern Chinese West Tianshan of this period.In order to constrain the tectonic setting of the northern Yili Block, we conducted detailed petrology, geochemistry, zircon U-Pb dating and Lu-Hf isotope analyses on a newly identified middle Early Carboniferous dioritic pluton along the Alasitan river in the northern Yili Block.Microgranular dioritic enclaves are widely developed within the diorites.The two types of rocks display different evolutionary trends in multiple bivariate diagrams of major and trace elements, indicating different petrogenesis and magma sources.Both types of rocks are enriched in LILEs, depleted in HFSEs (Nb, Ta, Ti), which are characteristics of magmatic arc rocks.Combined with regional geology, we suggested that the northern Yili Block experienced regional extension since the middle-late Early Carboniferous, which might be related to the slab roll back or retreat of the North Tianshan oceanic crust.